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Sample records for intermediate crack induced

  1. Hydrogen-Induced Cracking of the Drip Shield

    International Nuclear Information System (INIS)

    F. Hua

    2004-01-01

    Hydrogen-induced cracking is characterized by the decreased ductility and fracture toughness of a material due to the absorption of atomic hydrogen in the metal crystal lattice. Corrosion is the source of hydrogen generation. For the current design of the engineered barrier without backfill, hydrogen-induced cracking may be a concern because the titanium drip shield can be galvanically coupled to rock bolts (or wire mesh), which may fall onto the drip shield, thereby creating conditions for hydrogen production by electrochemical reaction. The purpose of this report is to analyze whether the drip shield will fail by hydrogen-induced cracking under repository conditions within 10,000 years after emplacement. Hydrogen-induced cracking is a scenario of premature failure of the drip shield. This report develops a realistic model to assess the form of hydrogen-induced cracking degradation of the drip shield under the hydrogen-induced cracking. The scope of this work covers the evaluation of hydrogen absorbed due to general corrosion and galvanic coupling to less noble metals (e.g., Stainless Steel Type 316 and carbon steels) under the repository conditions during the 10,000-year regulatory period after emplacement and whether the absorbed hydrogen content will exceed the critical hydrogen concentration value, above which the hydrogen-induced cracking is assumed to occur. This report also provides the basis for excluding the features, events, and processes (FEPs) related to hydrogen-induced cracking of the drip shield with particular emphasis on FEP 2.1.03.04.OB, hydride cracking of drip shields (DTN: M00407SEPFEPLA.000 [DIRS 170760]). This report is prepared according to ''Technical Work Plan (TWP) for: Regulatory Integration Modeling and Analysis of the Waste Form and Waste Package'' (BSC 2004 [DIRS 169944])

  2. Microstructural characterization of hydrogen induced cracking in TRIP-assisted steel by EBSD

    Energy Technology Data Exchange (ETDEWEB)

    Laureys, A., E-mail: Aurelie.Laureys@UGent.be [Department of Materials Science and Engineering, Ghent University (UGent), Technologiepark 903, B-9052 Ghent (Belgium); Depover, T. [Department of Materials Science and Engineering, Ghent University (UGent), Technologiepark 903, B-9052 Ghent (Belgium); Petrov, R. [Department of Materials Science and Engineering, Ghent University (UGent), Technologiepark 903, B-9052 Ghent (Belgium); Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft (Netherlands); Verbeken, K. [Department of Materials Science and Engineering, Ghent University (UGent), Technologiepark 903, B-9052 Ghent (Belgium)

    2016-02-15

    The present work evaluates hydrogen induced cracking by performing an elaborate EBSD (Electron BackScatter Diffraction) study in a steel with transformation induced plasticity (TRIP-assisted steel). This type of steel exhibits a multiphase microstructure which undergoes a deformation induced phase transformation. Additionally, each microstructural constituent displays a different behavior in the presence of hydrogen. The aim of this study is to obtain a better understanding on the mechanisms governing hydrogen induced crack initiation and propagation in the hydrogen saturated multiphase structure. Tensile tests on notched samples combined with in-situ electrochemical hydrogen charging were conducted. The tests were interrupted at stresses just after reaching the tensile strength, i.e. before macroscopic failure of the material. This allowed to study hydrogen induced crack initiation and propagation by SEM (Scanning Electron Microscopy) and EBSD. A correlation was found between the presence of martensite, which is known to be very susceptible to hydrogen embrittlement, and the initiation of hydrogen induced cracks. Initiation seems to occur mostly by martensite decohesion. High strain regions surrounding the hydrogen induced crack tips indicate that further crack propagation may have occurred by the HELP (hydrogen-enhanced localized plasticity) mechanism. Small hydrogen induced cracks located nearby the notch are typically S-shaped and crack propagation was dominantly transgranularly. The second stage of crack propagation consists of stepwise cracking by coalescence of small hydrogen induced cracks. - Highlights: • Hydrogen induced cracking in TRIP-assisted steel is evaluated by EBSD. • Tensile tests were conducted on notched hydrogen saturated samples. • Crack initiation occurs by a H-Enhanced Interface DEcohesion (HEIDE) mechanism. • Crack propagation involves growth and coalescence of small cracks. • Propagation is governed by the characteristics of

  3. Microstructural characterization of hydrogen induced cracking in TRIP-assisted steel by EBSD

    International Nuclear Information System (INIS)

    Laureys, A.; Depover, T.; Petrov, R.; Verbeken, K.

    2016-01-01

    The present work evaluates hydrogen induced cracking by performing an elaborate EBSD (Electron BackScatter Diffraction) study in a steel with transformation induced plasticity (TRIP-assisted steel). This type of steel exhibits a multiphase microstructure which undergoes a deformation induced phase transformation. Additionally, each microstructural constituent displays a different behavior in the presence of hydrogen. The aim of this study is to obtain a better understanding on the mechanisms governing hydrogen induced crack initiation and propagation in the hydrogen saturated multiphase structure. Tensile tests on notched samples combined with in-situ electrochemical hydrogen charging were conducted. The tests were interrupted at stresses just after reaching the tensile strength, i.e. before macroscopic failure of the material. This allowed to study hydrogen induced crack initiation and propagation by SEM (Scanning Electron Microscopy) and EBSD. A correlation was found between the presence of martensite, which is known to be very susceptible to hydrogen embrittlement, and the initiation of hydrogen induced cracks. Initiation seems to occur mostly by martensite decohesion. High strain regions surrounding the hydrogen induced crack tips indicate that further crack propagation may have occurred by the HELP (hydrogen-enhanced localized plasticity) mechanism. Small hydrogen induced cracks located nearby the notch are typically S-shaped and crack propagation was dominantly transgranularly. The second stage of crack propagation consists of stepwise cracking by coalescence of small hydrogen induced cracks. - Highlights: • Hydrogen induced cracking in TRIP-assisted steel is evaluated by EBSD. • Tensile tests were conducted on notched hydrogen saturated samples. • Crack initiation occurs by a H-Enhanced Interface DEcohesion (HEIDE) mechanism. • Crack propagation involves growth and coalescence of small cracks. • Propagation is governed by the characteristics of

  4. Environmentally-induced cracking of zirconium alloys - a review

    International Nuclear Information System (INIS)

    Cox, B.

    1990-01-01

    The general field of environmentally-induced cracking of zirconium alloys has been reviewed and the phenomena that are observed and the progress in understanding the mechanisms are summarized. The details of the industrially important pellet-clad interaction failures of nuclear reactor fuel have been left for a companion review, and only observations on the mechanism are summarized briefly here. It is concluded that in the zirconium alloy system, by virtue of the physical peculiarities of the system, it is easier to reach unambiguous conclusions about the environmental cracking mechanisms that are operating than with other systems. Thus, chemical dissolution in either liquid or vapour phase is thought to be the principal mechanism for intergranular cracking, while adsorption-induced embrittlement is thought to be the most common transgranular quasi-cleavage process. Hydrogen embrittlement in this system can be identified because it requires precipitated hydride that gives characteristic fractography when cracked. Only in a few instances does stress-corrosion cracking appear to proceed by a hydride cracking mechanism. (orig.)

  5. Role of plasticity-induced crack closure in fatigue crack growth

    Directory of Open Access Journals (Sweden)

    Jesús Toribio

    2013-07-01

    Full Text Available The premature contact of crack surfaces attributable to the near-tip plastic deformations under cyclic loading, which is commonly referred to as plasticity induced crack closure (PICC, has long been focused as supposedly controlling factor of fatigue crack growth (FCG. Nevertheless, when the plane-strain near-tip constraint is approached, PICC lacks of straightforward evidence, so that its significance in FCG, and even the very existence, remain debatable. To add insights into this matter, large-deformation elastoplastic simulations of plane-strain crack under constant amplitude load cycling at different load ranges and ratios, as well as with an overload, have been performed. Modeling visualizes the Laird-Smith conceptual mechanism of FCG by plastic blunting and re-sharpening. Simulation reproduces the experimental trends of FCG concerning the roles of stress intensity factor range and overload, but PICC has never been detected. Near-tip deformation patterns discard the filling-in a crack with material stretched out of the crack plane in the wake behind the tip as supposed PICC origin. Despite the absence of closure, load-deformation curves appear bent, which raises doubts about the trustworthiness of closure assessment from the compliance variation. This demonstrates ambiguities of PICC as a supposedly intrinsic factor of FCG and, by implication, favors the stresses and strains in front of the crack tip as genuine fatigue drivers.

  6. Study on Corrosion-induced Crack Initiation and Propagation of Sustaining Loaded RCbeams

    Science.gov (United States)

    Zhong, X. P.; Li, Y.; Yuan, C. B.; Yang, Z.; Chen, Y.

    2018-05-01

    For 13 pieces of reinforced concrete beams with HRB500 steel bars under long-term sustained loads, at time of corrosion-induced initial crack of concrete, and corrosion-induced crack widths of 0.3mm and 1mm, corrosion of steel bars and time-varying behavior of corrosion-induced crack width were studied by the ECWD (Electro-osmosis - constant Current – Wet and Dry cycles) accelerated corrosion method. The results show that when cover thickness was between 30 and 50mm,corrosion rates of steel bars were between 0.8% and 1.7% at time of corrosion-induced crack, and decreased with increasing concrete cover thickness; when corrosion-induced crack width was 0.3mm, the corrosion rate decreased with increasing steel bar diameter, and increased with increasing cover thickness; its corrosion rate varied between 0.98% and 4.54%; when corrosion-induced crack width reached 1mm, corrosion rate of steel bars was between 4% and 4.5%; when corrosion rate of steel bars was within 5%, the maximum and average corrosion-induced crack and corrosion rate of steel bars had a good linear relationship. The calculation model predicting the maximum and average width of corrosion-induced crack is given in this paper.

  7. Effects of off-centered cracks and restraint of induced bending caused by pressure on the crack-opening-area analysis of pipes

    International Nuclear Information System (INIS)

    Rahman, S.; Wilkowski, G.M.; Bonora, N.

    1996-01-01

    Current models for the crack-opening-area analysis of pipes with circumferential through-wall cracks are based on various idealizations or assumptions which are often necessary to simplify the mathematical formulation and numerical calculation. This paper focuses on the validity of two such assumptions that involve off-centered cracks and the restraint of induced bending caused by pressure, and quantifies their effects on the crack-opening area analysis of pipes. Finite element and/or simple estimation methods were employed to compute the center-crack-opening displacement and crack-opening shape for a through-wall-cracked pipe, considering off-centered cracks and the restraint of induced bending caused by pressure. The results of the analyses show that, for both cases, the crack-opening area can be reduced significantly. For pipes with off-centered cracks, the crack-opening area can be evaluated from analyses of symmetrically centered cracks and assuming elliptical profile. For pipes with complete restraint of the induced bending caused by pressure, the reduction in crack-opening area depends on the crack size. When the crack size is small, the restraint effects can be ignored. However, when the crack size is large, the restrained crack opening can be significantly smaller than the unrestrained crack opening, depending on the length of pipe involved; hence, it may be important for the crack-opening-area and leak-rate analyses. (orig.)

  8. Effects of off-centered crack and restraint of induced bending due to pressure on the crack-opening-area analysis of pipes

    International Nuclear Information System (INIS)

    Rahman, S.; Ghadiali, N.; Wilkowski, G.; Bonora, N.

    1995-01-01

    Estimation of leak rate is an important element in developing leak-before-break (LBB) methodology for piping integrity and safety analysis of nuclear power plants. Here, current models for the crack-opening-area analysis of pipes with circumferential through-wall cracks are based on various idealizations or assumption which are often necessary to simplify the mathematical formulation and numerical calculation. This paper focuses on the validity of two such assumptions involving off-centered cracks and restraint of induced bending due to pressure and quantifies their effects on the crack-opening analysis of pipes. Both finite element and/or simple estimation methods were employed to compute the center-crack-opening displacement and crack-opening shape for a through-wall-cracked pipe considering off-centered cracks and restrain of induced bending due to pressure. The results of analyses show that for both cases the crack-opening area can be reduced significantly. For pipes with off-centered cracks, the crack-opening area can be evaluated from analyses of symmetrically centered cracks and assuming elliptical profile. For pipes with complete restraint of induced bending due to pressure, the reduction of crack-opening area depends on the crack size. When the crack size is small, the restraint effects can be ignored. However, when the crack size is larger, the restrained crack-opening can be significantly smaller than the unrestrained crack-opening depending on the length of pipe involved, and hence, may be important for the crack-opening-area and leak-rate analyses

  9. Influence of sample geometry and microstructure on the hydrogen induced cracking characteristics under uniaxial load

    Energy Technology Data Exchange (ETDEWEB)

    Laureys, A., E-mail: aurelie.laureys@ugent.be [Department of Materials, Textiles and Chemical Engineering, Ghent University (UGent), Tech Lane Ghent Science Park - Campus A, Technologie park 903, B-9052 Gent (Belgium); Depover, T., E-mail: tom.depover@ugent.be [Department of Materials, Textiles and Chemical Engineering, Ghent University (UGent), Tech Lane Ghent Science Park - Campus A, Technologie park 903, B-9052 Gent (Belgium); Petrov, R., E-mail: roumen.petrov@ugent.be [Department of Materials, Textiles and Chemical Engineering, Ghent University (UGent), Tech Lane Ghent Science Park - Campus A, Technologie park 903, B-9052 Gent (Belgium); Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft (Netherlands); Verbeken, K., E-mail: kim.verbeken@ugent.be [Department of Materials, Textiles and Chemical Engineering, Ghent University (UGent), Tech Lane Ghent Science Park - Campus A, Technologie park 903, B-9052 Gent (Belgium)

    2017-04-06

    The present work evaluates hydrogen induced cracking in a TRIP (transformation induced plasticity) assisted steel and pure iron. The goal of this work is to understand the effect of the macroscopic stress distribution in the material on the hydrogen induced cracking phenomenon. Additionally, the effect of a complex multiphase microstructure on the characteristics of hydrogen induced cracking was investigated by comparing results for TRIP-assisted steel and pure iron as reference material. Tensile tests on notched and unnotched samples combined with in-situ electrochemical hydrogen charging were conducted. Tests were performed until the tensile strength was reached and until fracture. The resulting hydrogen induced cracks were studied by optical microscopy and scanning electron microscopy (SEM). Hydrogen induced cracks showed a typical S-shape and crack propagation was mainly transgranular, independently of the presence of a notch or the material's microstructure. This was also the case for the V-shaped secondary crack network and resulting stepped crack morphology characteristic for hydrogen induced damage. These observations indicate that the stress state surrounding the crack tip has a very large impact on the hydrogen induced cracking characteristics. The use of a notch or the presence of a different microstructure did not influence the overall hydrogen induced cracking features, but did change the kinetics of the hydrogen induced cracking process.

  10. Influence of sample geometry and microstructure on the hydrogen induced cracking characteristics under uniaxial load

    International Nuclear Information System (INIS)

    Laureys, A.; Depover, T.; Petrov, R.; Verbeken, K.

    2017-01-01

    The present work evaluates hydrogen induced cracking in a TRIP (transformation induced plasticity) assisted steel and pure iron. The goal of this work is to understand the effect of the macroscopic stress distribution in the material on the hydrogen induced cracking phenomenon. Additionally, the effect of a complex multiphase microstructure on the characteristics of hydrogen induced cracking was investigated by comparing results for TRIP-assisted steel and pure iron as reference material. Tensile tests on notched and unnotched samples combined with in-situ electrochemical hydrogen charging were conducted. Tests were performed until the tensile strength was reached and until fracture. The resulting hydrogen induced cracks were studied by optical microscopy and scanning electron microscopy (SEM). Hydrogen induced cracks showed a typical S-shape and crack propagation was mainly transgranular, independently of the presence of a notch or the material's microstructure. This was also the case for the V-shaped secondary crack network and resulting stepped crack morphology characteristic for hydrogen induced damage. These observations indicate that the stress state surrounding the crack tip has a very large impact on the hydrogen induced cracking characteristics. The use of a notch or the presence of a different microstructure did not influence the overall hydrogen induced cracking features, but did change the kinetics of the hydrogen induced cracking process.

  11. Hydrogen-Induced Delayed Cracking in TRIP-Aided Lean-Alloyed Ferritic-Austenitic Stainless Steels

    Directory of Open Access Journals (Sweden)

    Suvi Papula

    2017-06-01

    Full Text Available Susceptibility of three lean-alloyed ferritic-austenitic stainless steels to hydrogen-induced delayed cracking was examined, concentrating on internal hydrogen contained in the materials after production operations. The aim was to study the role of strain-induced austenite to martensite transformation in the delayed cracking susceptibility. According to the conducted deep drawing tests and constant load tensile testing, the studied materials seem not to be particularly susceptible to delayed cracking. Delayed cracks were only occasionally initiated in two of the materials at high local stress levels. However, if a delayed crack initiated in a highly stressed location, strain-induced martensite transformation decreased the crack arrest tendency of the austenite phase in a duplex microstructure. According to electron microscopy examination and electron backscattering diffraction analysis, the fracture mode was predominantly cleavage, and cracks propagated along the body-centered cubic (BCC phases ferrite and α’-martensite. The BCC crystal structure enables fast diffusion of hydrogen to the crack tip area. No delayed cracking was observed in the stainless steel that had high austenite stability. Thus, it can be concluded that the presence of α’-martensite increases the hydrogen-induced cracking susceptibility.

  12. Laser-induced cracks in ice due to temperature gradient and thermal stress

    Science.gov (United States)

    Yang, Song; Yang, Ying-Ying; Zhang, Jing-Yuan; Zhang, Zhi-Yan; Zhang, Ling; Lin, Xue-Chun

    2018-06-01

    This work presents the experimental and theoretical investigations on the mechanism of laser-induce cracks in ice. The laser-induced thermal gradient would generate significant thermal stress and lead to the cracking without thermal melting in the ice. The crack density induced by a pulsed laser in the ice critically depends on the laser scanning speed and the size of the laser spot on the surface, which determines the laser power density on the surface. A maximum of 16 cracks within an area of 17 cm × 10 cm can be generated when the laser scanning speed is at 10 mm/s and the focal point of the laser is right on the surface of the ice with a laser intensity of ∼4.6 × 107 W/cm2. By comparing the infrared images of the ice generated at various experimental conditions, it was found that a larger temperature gradient would result in more laser-induced cracks, while there is no visible melting of the ice by the laser beam. The data confirm that the laser-induced thermal stress is the main cause of the cracks created in the ice.

  13. Hydrogen Induced Cracking of Drip Shield

    Energy Technology Data Exchange (ETDEWEB)

    G. De

    2003-02-24

    One potential failure mechanism for titanium and its alloys under repository conditions is via the absorption of atomic hydrogen in the metal crystal lattice. The resulting decreased ductility and fracture toughness may lead to brittle mechanical fracture called hydrogen-induced cracking (HIC) or hydrogen embrittlement. For the current design of the engineered barrier without backfill, HIC may be a problem since the titanium drip shield can be galvanically coupled to rock bolts (or wire mesh), which may fall onto the drip shield, thereby creating conditions for hydrogen production by electrochemical reaction. The purpose of this scientific analysis and modeling activity is to evaluate whether the drip shield will fail by HIC or not under repository conditions within 10,000 years of emplacement. This Analysis and Model Report (AMR) addresses features, events, and processes related to hydrogen induced cracking of the drip shield. REV 00 of this AMR served as a feed to ''Waste Package Degradation Process Model Report'' and was developed in accordance with the activity section ''Hydrogen Induced Cracking of Drip Shield'' of the development plan entitled ''Analysis and Model Reports to Support Waste Package PMR'' (CRWMS M&O 1999a). This AMR, prepared according to ''Technical Work Plan for: Waste Package Materials Data Analyses and Modeling'' (BSC 2002), is to feed the License Application.

  14. Hydrogen-induced cracking: 2

    International Nuclear Information System (INIS)

    Puls, M.P.

    1984-12-01

    There is a strong motivation for understanding the factors controlling zirconium hydride reorientation under stress because of the important role this plays in hydrogen-induced crack growth and/or crack initiation in zirconium and its alloys, particularly under thermal cycling conditions. Following an approach developed by Sauthoff, an analysis of the orienting effect of external stress on the nucleation, growth and coarsening of γ- and delta-zirconium hydride precipitates in zirconium and its alloys is presented. The analysis is based on a previous theoretical study of some of the factors affecting hydride solubility in stressed and unstressed solids. Expressions are derived for the effect of stress on nucleation, growth and coarsening. We conclude, on the basis of these that the preferential orientation of hydride precipitates under stress is most efficient during the nucleation stage. The reason for this is that the overall driving force for nucleation, for the chosen parameters and the usual experimental conditions, is fairly small. Therefore, the driving force for orientating under stress can be a substantial fraction of the overall driving force. The analysis shows that hydride growth is unlikely to play a role in preferential orientation, but coarsening could be important under carefully chosen experimental conditions, which may be relevant to the hydride-cracking process

  15. The pipeline fracture behavior and pressure assessment under HIC (Hydrogen induced cracking) environment

    Energy Technology Data Exchange (ETDEWEB)

    Shaohua, Dong [China National Petroleum Corporation (CNPC), Beijing (China); Lianwei, Wang [University of Science and Technology Beijing (USTB), Beijing (China)

    2009-07-01

    As Hydrogen's transmit and diffuse, after gestating for a while, the density of hydrogen around crack tip of pipeline will get to the critical density, and the pipeline material will descend, make critical stress factor, the reason of pipeline Hydrogen Induced Cracking is Hydrogen's transmit and diffuse. The stress factor of Hydrogen Induced Cracking under surroundings-condition of stress is the key that estimate material's rupture behavior. The paper study the relationship among hydrogen concentrate, crack tip stress, stain field, hydrogen diffusion and inner pressure for crack tip process zone, then determined the length of HIC (hydrogen induced cracking) process zone. Based on the theory of propagation which reason micro-crack making core, dislocation model is produced for fracture criteria of HIC, the influence between material and environments under the HIC is analyzed, step by step pipeline maximum load pressure and threshold of J-integrity ( J{sub ISCC} ) is calculated, which is very significant for pipeline safety operation. (author)

  16. Hydrogen induced crack growth in Grade-12 titanium

    International Nuclear Information System (INIS)

    Ahn, T.M.; Lee, K.S.

    1984-01-01

    Internal hydrogen induced crack growth rates were measured in Grade-12 titanium which is a candidate material for high-level nuclear waste containers. As-received and hydrogen charged samples (5 ppM to 330 ppM hydrogen) were used for slow crack growth measurements at constant loads using a Krak Gauge. The testing temperature ranged from room temperature to 148 0 C. The crack growth kinetics under low to moderate loads are linear, but this linear rate is interrupted by discrete fast crack jump segments with parabolic or cubic type kinetics. These fast jump segments are thought to be associated with the passage of the crack front through the alpha-beta interface phase or with the initial loading sequence. By measuring striation spacings on the fracture surface, most crack growth rates observed are found to be in stage II. The striations are considered to be associated with hydride fracture. The crack path is either transgranular in the alpha phase or interfacial in the alpha phase adjacent to the beta phase. For transgranular growth, crack growth rates are constant and slower than those for interfacial growth which is associated with fast crack growth through a high hydrogen concentration region. Most stage II crack growth rates depend slightly on the stress intensity suggesting the contribution of plastic tearing process to stage II kinetics. The activation energies for crack growth are much lower than the activation energy of hydrogen diffusion through the alpha phase, implying that hydrogen is transported along dislocations, grain boundaries or interfaces. When the temperature is increased, the crack velocity first reaches a maximum and then decreases at higher temperatures. These temperature effects come from lower hydrogen concentration trapped at dislocations or from slower hydride nucleation kinetics, both at higher temperatures

  17. Chloride ingress in cracked concrete : A laser induced breakdown spectroscopy (LIBS) study

    NARCIS (Netherlands)

    Savija, B.; Schlangen, E.; Pacheco Farias, J.; Millar, S.; Eichler, T.; Wilsch, G.

    2014-01-01

    racks are always present in reinforced concrete structures. In the presented research, influence of mechanical cracks on chloride ingress is studied. A compact reinforced concrete specimen was designed, mimicking the cracking behaviour of beam elements. Cracks of different widths were induced by

  18. Desiccation-crack-induced salinization in deep clay sediment

    Directory of Open Access Journals (Sweden)

    S. Baram

    2013-04-01

    Full Text Available A study on water infiltration and solute transport in a clayey vadose zone underlying a dairy farm waste source was conducted to assess the impact of desiccation cracks on subsurface evaporation and salinization. The study is based on five years of continuous measurements of the temporal variation in the vadose zone water content and on the chemical and isotopic composition of the sediment and pore water in it. The isotopic composition of water stable isotopes (δ18O and δ2H in water and sediment samples, from the area where desiccation crack networks prevail, indicated subsurface evaporation down to ~ 3.5 m below land surface, and vertical and lateral preferential transport of water, following erratic preferential infiltration events. Chloride (Cl− concentrations in the vadose zone pore water substantially increased with depth, evidence of deep subsurface evaporation and down flushing of concentrated solutions from the evaporation zones during preferential infiltration events. These observations led to development of a desiccation-crack-induced salinization (DCIS conceptual model. DCIS suggests that thermally driven convective air flow in the desiccation cracks induces evaporation and salinization in relatively deep sections of the subsurface. This conceptual model supports previous conceptual models on vadose zone and groundwater salinization in fractured rock in arid environments and extends its validity to clayey soils in semi-arid environments.

  19. The effects of strain induced martensite on stress corrosion cracking in AISI 304 stainless steel

    International Nuclear Information System (INIS)

    Lee, W. S.; Kwon, S. I.

    1989-01-01

    The effects of strain induced martensite on stress corrosion cracking behavior in AISI 304 stainless steel in boiling 42 wt% MgCl 2 solution were investigated using monotonic SSRT and cyclic SSRT with R=0.1 stress ratio. As the amount of pre-strain increased, the failure time of the specimens in monotonic SSRT test decreased independent of the existence of strain induced martensite. The strain induced martensite seems to promote the crack initiation but to retard the crack propagation during stress corrosion cracking

  20. Intermediate Crack Induced Debonding in Concrete Beams Strengthened with CFRP Plates - An Experimental Study

    DEFF Research Database (Denmark)

    Rusinowski, Piotr Michal; Täljsten, Björn

    2009-01-01

    , ductility and even durability. Design of structural strengthening applications using externally bonded FRP composites is usually based on conventional design approaches with improvement to account for the presence and characteristics of the FRP material. Non-conventional design issues that are specific...... of the strengthening method. End-peeling has governed a large interest and several debonding models have been presented. However, interfacial peeling at flexural cracks has not attained the same focus – even though this debonding failure is most likely more common. This paper presents laboratory tests of concrete...... beams strengthened in flexure with CFRP epoxy bonded plates. Wrapping with CFRP sheets was applied in order to try to localize the failure initiation. Concrete cracking as well as debonding initiation and propagation was possible to observe with help of advanced optical measuring system and high speed...

  1. Modeling Restrained Shrinkage Induced Cracking in Concrete Rings Using the Thick Level Set Approach

    Directory of Open Access Journals (Sweden)

    Rebecca Nakhoul

    2018-03-01

    Full Text Available Modeling restrained shrinkage-induced damage and cracking in concrete is addressed herein. The novel Thick Level Set (TLS damage growth and crack propagation model is used and adapted by introducing shrinkage contribution into the formulation. The TLS capacity to predict damage evolution, crack initiation and growth triggered by restrained shrinkage in absence of external loads is evaluated. A study dealing with shrinkage-induced cracking in elliptical concrete rings is presented herein. Key results such as the effect of rings oblateness on stress distribution and critical shrinkage strain needed to initiate damage are highlighted. In addition, crack positions are compared to those observed in experiments and are found satisfactory.

  2. Pump, sodium, inducer, intermediate size (ISIP) (impeller/inducer/diffuser retrofit)

    International Nuclear Information System (INIS)

    Paradise, D.R.

    1978-01-01

    This specification defines the requirements for the Intermediate-Size Inducer Pump (ISIP), which is to be made by replacing the impeller of the FFTF Prototype Pump with a new inducer, impeller, diffuser, seal, and necessary adapter hardware. Subsequent testing requirements of the complete pump assembly are included

  3. Strain-induced corrosion cracking in ferritic components of BWR primary circuits

    International Nuclear Information System (INIS)

    Seifert, H.-P.; Ritter, S.; Ineichen, U.; Tschanz, U.; Gerodetti, B.

    2003-04-01

    The present final report of the RIKORR project is a summary of a literature survey and of the experimental work performed by PSI on the environmentally-assisted cracking (EAC) and dynamic strain ageing (DSA) susceptibility of low-alloy steels (LAS) in high-temperature (HT) water. Within this project, the EAC crack growth behaviour of different low-alloy RPV steels, weld filler and weld heat-affected zone materials has been investigated under simulated transient and steady-state BWR/NWC power operation conditions. The strain-induced corrosion cracking (SICC) / low-frequency corrosion fatigue (CF) and stress corrosion cracking (SCC) crack growth behaviour of different low-alloy RPV steels under simulated transient and stationary BWR/NWC conditions was characterized by slow rising load / low-frequency corrosion fatigue and constant load / periodical partial unloading / ripple load tests with pre-cracked fracture mechanics specimens in oxygenated HT water at temperatures of either 288, 250, 200 or 150 o C. Modern high-temperature water loops, on-line crack growth monitoring and fractographic analysis by scanning electron microscopy (SEM) were used to quantify the cracking response. (author)

  4. Stress corrosion cracking mitigation by ultrasound induced cavitation technique

    Energy Technology Data Exchange (ETDEWEB)

    Fong, C.; Lee, Y.C. [Industrial Technology Research Inst., Taiwan (China); Yeh, T.K. [National Tsing Hua Univ., Taiwan (China)

    2014-07-01

    Cavitation is usually considered as a damaging mechanism under erosion corrosion condition. However, if used appropriately, cavitation can be applied as a peening technique for surface stress modification process. The aim of surface stress modification is to alter the stress state of processed surface through direct or indirect thermo-mechanical treatments to reduce cracking problems initiated from surface. Ultrasonic devices are used to generate cavitation bubbles which when collapse will produce high intensity shock waves and high velocity micro-jet streams. The cavitation impact when properly controlled will create plastically deformed compressive layers in nearby surfaces and minimize cracking susceptibility in corrosive environments. This study is to investigate the effectiveness of Ultrasound Induced Cavitation (UIC) technique in surface stress improvement. Ultrasonic cavitation treatment of SS304 stainless steel under pure water is carried out with different controlling parameters. The cavitation impact on SS304 surface is measured in terms of surface roughness, surface strain, hardness, and microstructural characteristics. The in-depth residual stress distribution and crack mitigation effect are also evaluated. Test result indicates ultrasound induced cavitation treatment only has minor effect on surface physical characteristics. The extent of compressive stress produced on top surface exceeds the yield strength and can reach a depth above 150 μm. The maximum surface strain measured is generally below 20%, which is not considered detrimental to accelerate crack initiation. Stress corrosion verification tests show UIC treatment is capable in preventing environmental assisted cracking of stainless steels in severely corrosive conditions. In view of the test results, UIC technique has demonstrated to be a low cost, low contaminating, and effective surface stress improvement technology. (author)

  5. Stress corrosion cracking mitigation by ultrasound induced cavitation technique

    International Nuclear Information System (INIS)

    Fong, C.; Lee, Y.C.; Yeh, T.K.

    2014-01-01

    Cavitation is usually considered as a damaging mechanism under erosion corrosion condition. However, if used appropriately, cavitation can be applied as a peening technique for surface stress modification process. The aim of surface stress modification is to alter the stress state of processed surface through direct or indirect thermo-mechanical treatments to reduce cracking problems initiated from surface. Ultrasonic devices are used to generate cavitation bubbles which when collapse will produce high intensity shock waves and high velocity micro-jet streams. The cavitation impact when properly controlled will create plastically deformed compressive layers in nearby surfaces and minimize cracking susceptibility in corrosive environments. This study is to investigate the effectiveness of Ultrasound Induced Cavitation (UIC) technique in surface stress improvement. Ultrasonic cavitation treatment of SS304 stainless steel under pure water is carried out with different controlling parameters. The cavitation impact on SS304 surface is measured in terms of surface roughness, surface strain, hardness, and microstructural characteristics. The in-depth residual stress distribution and crack mitigation effect are also evaluated. Test result indicates ultrasound induced cavitation treatment only has minor effect on surface physical characteristics. The extent of compressive stress produced on top surface exceeds the yield strength and can reach a depth above 150 μm. The maximum surface strain measured is generally below 20%, which is not considered detrimental to accelerate crack initiation. Stress corrosion verification tests show UIC treatment is capable in preventing environmental assisted cracking of stainless steels in severely corrosive conditions. In view of the test results, UIC technique has demonstrated to be a low cost, low contaminating, and effective surface stress improvement technology. (author)

  6. Modelling of liquid sodium induced crack propagation in T91 martensitic steel: Competition with ductile fracture

    Energy Technology Data Exchange (ETDEWEB)

    Hemery, Samuel [Institut PPRIME, CNRS, Université de Poitiers, ISAE ENSMA, UPR 3346, Téléport 2, 1 Avenue Clément Ader, BP 40109, 86961 Futuroscope Chasseneuil Cedex (France); Berdin, Clotilde, E-mail: clotilde.berdin@u-psud.fr [Univ Paris-Sud, SP2M-ICMMO, CNRS UMR 8182, F-91405 Orsay Cedex (France); Auger, Thierry; Bourhi, Mariem [Ecole Centrale-Supelec, MSSMat CNRS UMR 8579, F-92295 Chatenay Malabry Cedex (France)

    2016-12-01

    Liquid metal embrittlement (LME) of T91 steel is numerically modeled by the finite element method to analyse experimental results in an axisymmetric notched geometry. The behavior of the material is identified from tensile tests then a crack with a constant crack velocity is introduced using the node release technique in order to simulate the brittle crack induced by LME. A good agreement between the simulated and the experimental macroscopic behavior is found: this suggests that the assumption of a constant crack velocity is correct. Mechanical fields during the embrittlement process are then extracted from the results of the finite element model. An analysis of the crack initiation and propagation stages: the ductile fracture probably breaks off the LME induced brittle fracture. - Highlights: • T91 martensitic steel is embrittled by liquid sodium depending on the loading rate at 573 K. • The mechanical behavior is modeled by a von Mises elastic-plastic law. • The LME induced crack propagates at a constant velocity. • The mechanical state at the crack tip does not explain a brittle crack arrest. • The occurrence of the ductile fracture breaks off the brittle fracture.

  7. Computer assisted tomography for the non-destructive evaluation of hydrogen-induced cracking in steel

    International Nuclear Information System (INIS)

    Tapping, R.L.; Sawicka, B.D.

    1986-06-01

    Computer assisted tomography (CAT) was used to assess hydrogen-induced cracking in steel exposed to an H 2 S-saturated ('sour') environment. In this case the environment was the NACE TM-02-84 test for susceptibility to hydrogen-induced cracking. The feasibility of using CAT in this application was shown in a previous paper. This study extends the application of CAT to a quantitative assessment of the cracking. Optimal parameters for CAT imaging in such an application are determined and the advantages of using CAT in comparison to traditional inspection methods are discussed

  8. Evaluation Model for Restraint Effect of Pressure Induced Bending on the Plastic Crack Opening of Circumferential Through-Wall-Crack

    International Nuclear Information System (INIS)

    Kim, Jin-Weon

    2006-01-01

    Most of the pipe crack evaluation procedures, including leak-before-break (LBB) analysis, assume that the cracked pipe subjected to remote bending or internal pressure is free to rotate. In this case, the pressure induced bending (PIB) enhances crack opening of a through-wall-crack (TWC) in a pipe. In a real piping system, however, the PIB will be restrained because the ends of the pipe are constrained by the rest of the piping system. Hence, the amount of restraint affects the crack opening of a TWC in a pipe, and the restraint effect on crack opening directly affects the results of LBB evaluation. Therefore, it is necessary to investigate the restraint effect of PIB on crack opening displacement (COD) to quantify the uncertainties in current analysis procedures and to ensure the application of LBB concepts to nuclear piping systems. Recently, several researches were conducted to investigate the restraint effect of PIB on COD, and they proposed a simplified model to evaluate COD under restrained conditions. However, these results are quite limited because the restraint effect was evaluated only in terms of linear-elastic crack opening. In practice, the TWC in a pipe behaves plastically under normal operating loads, and the current LBB analysis methodologies require elastic-plastic crack opening evaluation. Therefore, this study evaluates the restraint effect of PIB on the plastic crack opening of a TWC in a pipe using finite element analysis under various influencing parameters. Based on these results, a closed-from model to be able to estimate the restraint effect of PIB on plastic crack opening is proposed

  9. Modeling of hydrogen induced cold cracking in a ferritic steel

    International Nuclear Information System (INIS)

    Chen, Qianqiang

    2015-01-01

    This thesis is aimed at studying the hydrogen induced cold cracking (HICC) in the heated affected zone (HAZ) of weldments and at proposing a criterion to predict this phenomenon. HICC is attributable to three factors: i) a susceptible microstructure; ii) hydrogen concentration; and iii) a critical stress. To this end, first tensile tests on smooth specimens charged with hydrogen were performed to investigate hydrogen embrittlement of martensite. According to these results, a ductile-brittle damage model is proposed in order to establish a HICC criterion. In order to validate this criterion, we performed the modified Tekken tests. The Tekken test was chosen because one can control the welding parameters in order to induce cold cracking. The modified Tekken tests have then been modeled using a fully coupled thermo-metallo-mechanical-diffusion model using the finite element method. This model allows to compute martensite's portion, residual stress level and hydrogen concentration in the HAZ. By applying the HICC criterion to these tests, cold cracking phenomenon has been correctly predicted. (author)

  10. Technique to eliminate helium induced weld cracking in stainless steels

    International Nuclear Information System (INIS)

    Chin-An Wang; Chin, B.A.

    1992-01-01

    Experiments have shown that Type 316 stainless steel is susceptible to heat-affected-zone (HAZ) cracking upon cooling when welded using the gas tungsten arc (GTA) process under lateral constraint. The cracking has been hypothesized to be caused by stress-assisted helium bubble growth and rupture at grain boundaries. This study utilized an experimental welding setup which enabled different compressive stresses to be applied to the plates during welding. Autogenous GTA welds were produced in Type 316 stainless steel doped with 256 appm helium. The application of a compressive stress, 55 Mpa, during welding suppressed the previously observed catastrophic cracking. Detailed examinations conducted after welding showed a dramatic change in helium bubble morphology. Grain boundary bubble growth along directions parallel to the weld was suppressed. Results suggest that stress-modified welding techniques may be used to suppress or eliminate helium-induced cracking during joining of irradiated materials

  11. Iodine induced stress corrosion cracking of zircaloy cladding tubes

    International Nuclear Information System (INIS)

    Brunisholz, L.; Lemaignan, C.

    1984-01-01

    Iodine is considered as one of the major fission products responsible for PCI failure of Zry cladding by stress corrosion cracking (SCC). Usual analysis of SCC involves both initiation and growth as sequential processes. In order to analyse initiation and growth independently and to be able to apply the procedures of fracture mechanics to the design of cladding, with respect to SCC, stress corrosion tests of Zry cladding tubes were undertaken with a small fatigue crack (approx. 200 μm) induced in the inner wall of each tube before pressurization. Details are given on the techniques used to induce the fatigue crack, the pressurization test procedure and the results obtained on stress releaved or recrystallized Zry 4 tubings. It is shown that the Ksub(ISCC) values obtained during these experiments are in good agreement with those obtained from large DCB fracture mechanics samples. Conclusions will be drawn on the applicability of linear elastic fracture mechanics (LEFM) to cladding design and related safety analysis. The work now underway is aimed at obtaining better understanding of the initiation step. It includes the irradiation of Zry samples with heavy ions to simulate the effect of recoil fragments implanted in the inner surface of the cladding, that could create a brittle layer of about 10 μm

  12. Crack propagation in teeth: a comparison of perimortem and postmortem behavior of dental materials and cracks.

    Science.gov (United States)

    Hughes, Cris E; White, Crystal A

    2009-03-01

    This study presents a new method for understanding postmortem heat-induced crack propagation patterns in teeth. The results demonstrate that patterns of postmortem heat-induced crack propagation differ from perimortem and antemortem trauma-induced crack propagation patterns. Dental material of the postmortem tooth undergoes dehydration leading to a shrinking and more brittle dentin material and a weaker dentin-enamel junction. Dentin intertubule tensile stresses are amplified by the presence of the pulp cavity, and initiates crack propagation from the internal dentin, through the dentin-enamel junction and lastly the enamel. In contrast, in vivo perimortem and antemortem trauma-induced crack propagation initiates cracking from the external surface of the enamel toward the dentin-enamel junction where the majority of the energy of the crack is dissipated, eliminating the crack's progress into the dentin. These unique patterns of crack propagation can be used to differentiate postmortem taphonomy-induced damage from antemortem and perimortem trauma in teeth.

  13. Prediction of Cracking Induced by Indirect Actions in RC Structures

    Science.gov (United States)

    Anerdi, Costanza; Bertagnoli, Gabriele; Gino, Diego; Malavisi, Marzia; Mancini, Giuseppe

    2017-10-01

    Cracking of concrete plays a key role in reinforced concrete (RC) structures design, especially in serviceability conditions. A variety of reasons contribute to develop cracking and its presence in concrete structures is to be considered as almost unavoidable. Therefore, a good control of the phenomenon in order to provide durability is required. Cracking development is due to tensile stresses that arise in concrete structures as a result of the action of direct external loads or restrained endogenous deformations. This paper focuses on cracking induced by indirect actions. In fact, there is very limited literature regarding this particular phenomenon if compared to its high incidence in the construction practice. As a consequence, the correct prediction of the crack opening, width and position when structures are subjected to imposed deformations, such as massive castings or other highly restrained structures, becomes a compelling task, not so much for the structural capacity, as for their durability. However, this is only partially addressed by commonly used design methods, which are usually intended for direct actions. A set of non-linear analysis on simple tie models is performed using the Finite Element Method in order to study the cracking process under imposed deformations. Different concrete grades have been considered and analysed. The results of this study have been compared with the provisions of the most common codes.

  14. High temperature salt corrosion cracking of intermediate products of titanium alloys

    International Nuclear Information System (INIS)

    Sinyavskij, V.S.; Usova, V.V.; Lunina, S.I.; Kushakevich, S.A.; Makhmutova, E.A.; Khanina, Z.K.

    1982-01-01

    The high temperature salt corrosion cracking (HTSCC) of intermediate products from titanium base alloys in the form of hot rolled plates and rods has been studied. The investigated materials are as follows: VT20 pseudo-α-alloy, VT6 and VT14 α+β alloys; the comparison has been carried out with commercial titanium and low-alloyed OT4-1 α-alloy. The experiments have been held at 400 and 500 deg C, defining different stress levels: 0.4; 0.5; 0.75 and 0.9 tausub(0.2). The test basis - not less than 100 h. Standard tensile samples of circular cross section with NaCl (approximately 0.2-0.3 mg/cm 2 ) salt coatings, cut off from hot-rolled rods along the direction of rolling and hot-rolled plates along and across the direction of rolling have been tested. It has been extablished before hand that the notch doesn't affect the resistance of titanium alloys to HTSCC. The sensitivity of titanium alloy subproducts to HTSCC is estimated as to the time until the failure of the sample with salt coatings and without them. It is shown that salt coating practically doesn't affect the behaviour of titanium, that allows to consider it to be resistant to HTSCC. Titanium alloys alloying with β-isomorphous stabilizing additions increases it's HTSCC resistance. Vanadium alloying of the alloy (VT6 alloy of Ti-Al-V system) produces a favourable effect; intermediate products of VT14 (α+β) alloy (Ti-Al-V-Mo system), containing two β-stabilizing additions-vanadium and molybdenum, have satisfactory HTSCC resistance. It is shown that by changes is mechanical properties of alloys during HTSCC one can indirectly judge about their HTSCC sensitivity

  15. Role of microtexture in the interaction and coalescence of hydrogen-induced cracks

    Energy Technology Data Exchange (ETDEWEB)

    Venegas, V. [Departamento de Ingenieria Metalurgica, IPN-ESIQIE, UPALM Edif. 7, Zacatenco, Mexico D.F. 07738 (Mexico); Caleyo, F. [Departamento de Ingenieria Metalurgica, IPN-ESIQIE, UPALM Edif. 7, Zacatenco, Mexico D.F. 07738 (Mexico)], E-mail: fcaleyo@gmail.com; Baudin, T. [Laboratoire de Physico-Chimie de l' Etat Solide, ICMMO, UMR CNRS 8182, Batiment 410, Universite de Paris Sud, 91405, Orsay, Cedex (France); Hallen, J.M. [Departamento de Ingenieria Metalurgica, IPN-ESIQIE, UPALM Edif. 7, Zacatenco, Mexico D.F. 07738 (Mexico); Penelle, R. [Laboratoire de Physico-Chimie de l' Etat Solide, ICMMO, UMR CNRS 8182, Batiment 410, Universite de Paris Sud, 91405, Orsay, Cedex (France)

    2009-05-15

    The role of microtexture in hydrogen-induced crack interaction and coalescence is investigated in line pipe steels using electron backscatter diffraction. Experimental evidence shows that, depending on the local grain orientation, crack interaction and coalescence can depart from the conditions predicted by the mixed-mode fracture mechanics of isotropic linear elastic materials. Stress simulation and microtexture analysis are used to explain the experimental observations.

  16. Role of microtexture in the interaction and coalescence of hydrogen-induced cracks

    International Nuclear Information System (INIS)

    Venegas, V.; Caleyo, F.; Baudin, T.; Hallen, J.M.; Penelle, R.

    2009-01-01

    The role of microtexture in hydrogen-induced crack interaction and coalescence is investigated in line pipe steels using electron backscatter diffraction. Experimental evidence shows that, depending on the local grain orientation, crack interaction and coalescence can depart from the conditions predicted by the mixed-mode fracture mechanics of isotropic linear elastic materials. Stress simulation and microtexture analysis are used to explain the experimental observations.

  17. Smeared crack modelling approach for corrosion-induced concrete damage

    DEFF Research Database (Denmark)

    Thybo, Anna Emilie Anusha; Michel, Alexander; Stang, Henrik

    2017-01-01

    In this paper a smeared crack modelling approach is used to simulate corrosion-induced damage in reinforced concrete. The presented modelling approach utilizes a thermal analogy to mimic the expansive nature of solid corrosion products, while taking into account the penetration of corrosion...... products into the surrounding concrete, non-uniform precipitation of corrosion products, and creep. To demonstrate the applicability of the presented modelling approach, numerical predictions in terms of corrosion-induced deformations as well as formation and propagation of micro- and macrocracks were......-induced damage phenomena in reinforced concrete. Moreover, good agreements were also found between experimental and numerical data for corrosion-induced deformations along the circumference of the reinforcement....

  18. Corrosion cracking

    International Nuclear Information System (INIS)

    Goel, V.S.

    1985-01-01

    This book presents the papers given at a conference on alloy corrosion cracking. Topics considered at the conference included the effect of niobium addition on intergranular stress corrosion cracking, corrosion-fatigue cracking in fossil-fueled-boilers, fracture toughness, fracture modes, hydrogen-induced thresholds, electrochemical and hydrogen permeation studies, the effect of seawater on fatigue crack propagation of wells for offshore structures, the corrosion fatigue of carbon steels in seawater, and stress corrosion cracking and the mechanical strength of alloy 600

  19. Internal hydrogen-induced subcritical crack growth in austenitic stainless steels

    Science.gov (United States)

    Huang, J. H.; Altstetter, C. J.

    1991-11-01

    The effects of small amounts of dissolved hydrogen on crack propagation were determined for two austenitic stainless steel alloys, AISI 301 and 310S. In order to have a uniform distribution of hydrogen in the alloys, they were cathodically charged at high temperature in a molten salt electrolyte. Sustained load tests were performed on fatigue precracked specimens in air at 0 ‡C, 25 ‡C, and 50 ‡C with hydrogen contents up to 41 wt ppm. The electrical potential drop method with optical calibration was used to continuously monitor the crack position. Log crack velocity vs stress intensity curves had definite thresholds for subcritical crack growth (SCG), but stage II was not always clearly delineated. In the unstable austenitic steel, AISI 301, the threshold stress intensity decreased with increasing hydrogen content or increasing temperature, but beyond about 10 wt ppm, it became insensitive to hydrogen concentration. At higher concentrations, stage II became less distinct. In the stable stainless steel, subcritical crack growth was observed only for a specimen containing 41 wt ppm hydrogen. Fractographic features were correlated with stress intensity, hydrogen content, and temperature. The fracture mode changed with temperature and hydrogen content. For unstable austenitic steel, low temperature and high hydrogen content favored intergranular fracture while microvoid coalescence dominated at a low hydrogen content. The interpretation of these phenomena is based on the tendency for stress-induced phase transformation, the different hydrogen diffusivity and solubility in ferrite and austenite, and outgassing from the crack tip. After comparing the embrittlement due to internal hydrogen with that in external hydrogen, it is concluded that the critical hydrogen distribution for the onset of subcritical crack growth is reached at a location that is very near the crack tip.

  20. Hydrogen-induced crack interaction and coalescence: the role of local crystallographic texture

    Energy Technology Data Exchange (ETDEWEB)

    Caleyo, F.; Hallen, J. M.; Venegas, V. [ESIQIE, Instituto Politecnico Nacional, Mexico, (Mexico); Baudin, T. [Universite de Paris Sud, Orsay, (France)

    2010-07-01

    Hydrogen induced cracking (HIC) is a big concern in pipeline industry specialized in sour service. The strategies to improve HIC resistance of pipeline steel have not been completely efficient. This study investigated the role of grain orientation in the interaction and coalescence of non-coplanar HIC cracks through experimental analysis. HIC samples of pipeline steels (API 5L X46 and ASME-A106) were studied using automated electron backscatter diffraction (EBSD) and orientation imaging microscopy (OIM). The results showed that the microtexture can play a significant role in the coalescence of closely spaced non-coplanar HIC cracks. It was also found that the presence of cleavage planes and slip systems correctly oriented to the mixed-mode stresses can activate low-resistance transgranular paths along in which cracks can merge. It is demonstrated that crystallographic texture must be considered in developing predictive models for the study of the stepwise propagation of HIC cracking in pipeline steels.

  1. The Effect of Crack Width on Chloride-Induced Corrosion of Steel in Concrete

    Directory of Open Access Journals (Sweden)

    Weiwei Li

    2017-01-01

    Full Text Available When subjected to loading or thermal shrinkage, reinforced concrete structures usually behave in a cracking state, which raises the risk of bar corrosion from the working environment. The influence of cover cracking on chloride-induced corrosion was experimentally investigated through a 654-day laboratory test on cracked reinforced concrete specimens exposed to chloride solution. The concrete specimens have a dimension of 100 mm × 100 mm × 400 mm and a single prefabricated crack at the midspan. When the percentage concentration of chloride ion (0.6%, 1.2%, 2.1%, 3.0%, and 6.0% and crack width (uncracked, 0.2, 0.3, 0.4, and 0.5 mm are taken as variables, the experimental results showed that the corrosion rates for cracked specimens increased with increasing percentage concentration of chloride and increasing crack width. This study also showed the interrelationship between crack width and percentage concentration of chloride on the corrosion rate. In addition, an empirical model, incorporating the influence of the cover cracking and chloride concentration, was developed to predict the corrosion rate. This model allows the prediction of the maximum allowable wcr based on the given percentage concentration of chloride in the exposure condition.

  2. Detection and Analysis of Enamel Cracks by Quantitative Light-induced Fluorescence Technology.

    Science.gov (United States)

    Jun, Mi-Kyoung; Ku, Hye-Min; Kim, Euiseong; Kim, Hee-Eun; Kwon, Ho-Keun; Kim, Baek-Il

    2016-03-01

    The ability to accurately detect tooth cracks and quantify their depth would allow the prediction of crack progression and treatment success. The aim of this in vitro study was to determine the capabilities of quantitative light-induced fluorescence (QLF) technology in the detection of enamel cracks. Ninety-six extracted human teeth were selected for examining naturally existing or suspected cracked teeth surfaces using a photocuring unit. QLF performed with a digital camera (QLF-D) images were used to assess the ability to detect enamel cracks based on the maximum fluorescence loss value (ΔFmax, %), which was then analyzed using the QLF-D software. A histologic evaluation was then performed in which the samples were sectioned and observed with the aid of a polarized light microscope. The relationship between ΔFmax and the histology findings was assessed based on the Spearman rank correlation. The sensitivity and specificity were calculated to evaluate the validity of using QLF-D to analyze enamel inner-half cracks and cracks extending to the dentin-enamel junction. There was a strong correlation between the results of histologic evaluations of enamel cracks and the ΔFmax value, with a correlation coefficient of 0.84. The diagnostic accuracy of QLF-D had a sensitivity of 0.87 and a specificity of 0.98 for enamel inner-half cracks and a sensitivity of 0.90 and a specificity of 1.0 for cracks extending to the dentin-enamel junction. These results indicate that QLF technology would be a useful clinical tool for diagnosing enamel cracks, especially given that this is a nondestructive method. Copyright © 2016 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  3. Oxidation induced crack healing of Cr2(Al,Si)C max phase ceramic

    NARCIS (Netherlands)

    Shen, L.; Li, S.B.; Van der Zwaag, S.; Sloof, W.G.

    2013-01-01

    The oxidation crack healing of Cr2AlC and Cr2(Al,Si)C was studied and compared with known healing of Ti2AlC. The oxidation induced crack healing of Ti2AlC is relatively fast and leads to full strength recovery, but the oxidation product contains besides ?-Al2O3 also undesired TiO2. However, when

  4. Investigation of Non-Uniform Rust Distribution and Its Effects on Corrosion Induced Cracking in Reinforced Concrete

    Directory of Open Access Journals (Sweden)

    Sutrisno Wahyuniarsih

    2017-01-01

    Full Text Available Uniform corrosion still widely used by a lot of researchers and engineers to analyze the corrosion induced cracking. However, in practice, corrosion process occurred non-uniformly. The part nearest to the exposed surface is more likely to have faster corrosion initiation compared with other regions. This research is mainly focused on investigating the effect of non-uniform rust distribution to cover cracking in reinforced concrete. An experimental test performed using accelerated corrosion test by using 5% NaCl solution and applied a constant electric current to the concrete samples. The rust distribution and measurement were observed by using a digital microscope. Based on the experimental result, it was found that the rust was distributed in a non-uniform pattern. As a result, the cracks also formed non-uniformly along the perimeter of steel bar. At the last part of this paper, a simulation result of concrete cracking induced by non-uniform corrosion is presented. The result compared with a simulation using uniform corrosion assumption to investigate the damage pattern of each model. The simulation result reveals stress evolution due to rust expansion which leads to concrete cracking. Furthermore, a comparison of stresses induced by non-uniform corrosion and uniform corrosion indicates that non-uniform corrosion could lead to earlier damage to the structure which is specified by the formation and propagation of the crack.

  5. EBSD study of hydrogen-induced cracking in API-5 L-X46 pipeline steel

    International Nuclear Information System (INIS)

    Venegas, V.; Caleyo, F.; Gonzalez, J.L.; Baudin, T.; Hallen, J.M.; Penelle, R.

    2005-01-01

    The spatial distribution of plastic deformation and grain orientation surrounding hydrogen-induced cracks (HIC) is investigated in samples of API-5L-X46 pipeline steel using scanning electron microscopy and electron backscattering diffraction (EBSD). This work shows direct experimental evidence of the influence of microstructure, microtexture and mesotexture on HIC crack path

  6. Cracking of GaN on sapphire from etch-process-induced nonuniformity in residual thermal stress

    International Nuclear Information System (INIS)

    Lacroix, Yves; Chung, Sung-Hoon; Sakai, Shiro

    2001-01-01

    An experiment was performed to explain the appearance of cracks along mesa structures during the processing of GaN device layers grown on sapphire substrates. Micro-Raman spectroscopy was used to measure the position-dependent stress in the GaN layer. We show evidence that the stress at the interface with the substrate may be larger along the mesa structures than that of the as-grown layer, and that this increase in stress can be enough to induce cracks along mesa structures during processing. We report on the formation of cracks that propagate guided by the nonuniformity of the stress induced by the formation of mesa structures in the GaN layer, independent of crystal direction. The understanding of cracking mechanisms has implications in GaN-based device structures that require heteroepitaxial growth of layers with different lattice size and thermal expansion coefficients. [copyright] 2001 American Institute of Physics

  7. Influence of fatigue crack wake length and state of stress on crack closure

    Science.gov (United States)

    Telesman, Jack; Fisher, Douglas M.

    1988-01-01

    The location of crack closure with respect to crack wake and specimen thickness under different loading conditions was determined. The rate of increase of K sub CL in the crack wake was found to be significantly higher for plasticity induced closure in comparison to roughness induced closure. Roughness induced closure was uniform throughout the thickness of the specimen while plasticity induced closure levels were 50 percent higher in the near surface region than in the midthickness. The influence of state of stress on low-high load interaction effects was also examined. Load interaction effects differed depending upon the state of stress and were explained in terms of delta K sub eff.

  8. Helium-induced weld cracking in austenitic and martensitic steels

    International Nuclear Information System (INIS)

    Lin, H.T.; Chin, B.A.

    1991-01-01

    Helium was uniformly implanted into type 316 stainless steel and Sandvik HT-9 (12Cr-1MoVW) to levels of 0.18 to 256 and 0.3 to 1 a.p.p.m., respectively, using the ''tritium trick'' technique. Autogenous bead-on-plate, full penetration, welds were then produced under fully constrained conditions using the gas tungsten arc welding (GTAW) process. The control and hydrogen-charged plates of both alloys were sound and free of any weld defects. For the 316 stainless steel, catastrophic intergranular fracture occurred in the heat-affected zone (HAZ) of welds with helium levels ≥ 2.5 a.p.p.m. In addition to the HAZ cracking, brittle fracture along the centreline of the fusion zone was also observed for the welds containing greater than 100 a.p.p.m. He. For HT-9, intergranular cracking occurred in the HAZ along prior-austenite grain boundaries of welds containing 1 a.p.p.m. He. Electron microscopy observations showed that the cracking in the HAZ originated from the growth and coalescence of grain-boundary helium bubbles and that the fusion-zone cracking resulted from the growth of helium bubbles at dendrite boundaries. The bubble growth kinetics in the HAZ is dominated by stress-induced diffusion of vacancies into bubbles. Results of this study indicate that the use of conventional GTAW techniques to repair irradiation-degraded materials containing even small amounts of helium may be difficult. (author)

  9. Crack propagation under thermal cycling loading inducing a thermal gradient in the specimen thickness

    International Nuclear Information System (INIS)

    Le, H.N.

    2009-05-01

    This study aims to figure out the crack growth phenomenon by thermal fatigue induced by thermal gradient through thickness of specimen. Firstly, an experimental facility has been developed: a rectangular parallelepiped specimen is subjected to thermal cycling between 350 C and 100 C; the specimen is freed to expand and contract. Two semi-circular notches (0,1 mm depth and 4 mm length) have been machined on the surface of the specimen. A series of interrupted tests has been carried out to characterize and quantify the crack growth in depth and surface of the pre-existing crack. Next, a three-dimensional crack growth simulation has been implemented in ABAQUS. Automation using Python was used to simulate the propagation of a crack under thermal cycling, with re-meshing at crack front after each calculation step. No assumption has been taken on the crack front during the crack propagation. A comparison with test results showed very good agreement on the evolution of crack front shape and on the kinetics of propagation on the edge and the heart of pre-existing crack. An analytical approach was also developed based on the calculation of stress intensity factors (SIC). A two-dimensional approach was first introduced enabling us to better understand the influence of various thermal and geometric parameters. Finally, a three dimensional approach, with an elliptical assumption crack shape during the propagation, leading to a prediction of crack growth on the surface and in depth which is very similar to that obtained numerically, but with computational time much lower. (author)

  10. Impacts of bedding directions of shale gas reservoirs on hydraulically induced crack propagation

    Directory of Open Access Journals (Sweden)

    Keming Sun

    2016-03-01

    Full Text Available Shale gas reservoirs are different from conventional ones in terms of their bedding architectures, so their hydraulic fracturing rules are somewhat different. In this paper, shale hydraulic fracturing tests were carried out by using the triaxial hydraulic fracturing test system to identify the effects of natural bedding directions on the crack propagation in the process of hydraulic fracturing. Then, the fracture initiation criterion of hydraulic fracturing was prepared using the extended finite element method. On this basis, a 3D hydraulic fracturing computation model was established for shale gas reservoirs. And finally, a series of studies were performed about the effects of bedding directions on the crack propagation created by hydraulic fracturing in shale reservoirs. It is shown that the propagation rules of hydraulically induced fractures in shale gas reservoirs are jointly controlled by the in-situ stress and the bedding plane architecture and strength, with the bedding direction as the main factor controlling the crack propagation directions. If the normal tensile stress of bedding surface reaches its tensile strength after the fracturing, cracks will propagate along the bedding direction, and otherwise vertical to the minimum in-situ stress direction. With the propagating of cracks along bedding surfaces, the included angle between the bedding normal direction and the minimum in-situ stress direction increases, the fracture initiation and propagation pressures increase and the crack areas decrease. Generally, cracks propagate in the form of non-plane ellipsoids. With the injection of fracturing fluids, crack areas and total formation filtration increase and crack propagation velocity decreases. The test results agree well with the calculated crack propagation rules, which demonstrate the validity of the above-mentioned model.

  11. Study of scratch-induced stress corrosion cracking for steam generator tubes and scratch control

    International Nuclear Information System (INIS)

    Meng, F.; Xu, X.; Liu, X.; Wang, J.

    2014-01-01

    This paper introduces field cases for scratch-induced stress corrosion cracking (SISCC) of steam generator tubes in PWR and current studies in laboratories. According to analysis result of broke tubes, scratches caused intergranular stress corrosion cracking (IGSCC) with outburst. The effect of microstructure for nickel-base alloys, residual stresses caused by scratching process and water chemistry on SISCC and possible mechanism of SISCC are discussed. The result shows that scratch-induced microstructure evolution contributes to SISCC significantly. The causes of scratches during steam generator tubing manufacturing and installation process are stated and improved reliability with scratch control is highlighted for steam generator tubes in newly built nuclear power plants. (author)

  12. Study of scratch-induced stress corrosion cracking for steam generator tubes and scratch control

    Energy Technology Data Exchange (ETDEWEB)

    Meng, F.; Xu, X.; Liu, X. [Shanghai Nuclear Engineering Research and Design Institute, Shanghai (China); Wang, J. [Chinese Academy of Sciences, Institute of Metal Research, Shenyang (China)

    2014-07-01

    This paper introduces field cases for scratch-induced stress corrosion cracking (SISCC) of steam generator tubes in PWR and current studies in laboratories. According to analysis result of broke tubes, scratches caused intergranular stress corrosion cracking (IGSCC) with outburst. The effect of microstructure for nickel-base alloys, residual stresses caused by scratching process and water chemistry on SISCC and possible mechanism of SISCC are discussed. The result shows that scratch-induced microstructure evolution contributes to SISCC significantly. The causes of scratches during steam generator tubing manufacturing and installation process are stated and improved reliability with scratch control is highlighted for steam generator tubes in newly built nuclear power plants. (author)

  13. Model of parameters controlling resistance of pipeline steels to hydrogen-induced cracking

    KAUST Repository

    Traidia, Abderrazak; El-Sherik, A. M.; Duval, Sé bastien; Lubineau, Gilles; El Yagoubi, Jalal

    2014-01-01

    NACE MR0175/ISO 15156-2 standard provides test conditions and acceptance criteria to evaluate the resistance of carbon and low-alloy steels to hydrogen-induced cracking (HIC). The second option proposed by this standard offers a large flexibility

  14. Tungsten recrystallization and cracking under ITER-relevant heat loads

    Energy Technology Data Exchange (ETDEWEB)

    Budaev, V.P., E-mail: Budaev@mail.ru [NRC «Kurchatov Institute», Akademika Kurchatova pl., Moscow (Russian Federation); Martynenko, Yu.V. [NRC «Kurchatov Institute», Akademika Kurchatova pl., Moscow (Russian Federation); National Research Nuclear University MEPhI, Kashirskoe sh. 31, Moscow (Russian Federation); Karpov, A.V.; Belova, N.E. [NRC «Kurchatov Institute», Akademika Kurchatova pl., Moscow (Russian Federation); Zhitlukhin, A.M. [SRC RF TRINITI, Moscow Region (Russian Federation); Klimov, N.S., E-mail: klimov@triniti.ru [SRC RF TRINITI, Moscow Region (Russian Federation); National Research Nuclear University MEPhI, Kashirskoe sh. 31, Moscow (Russian Federation); Podkovyrov, V.L.; Barsuk, V.A.; Putrik, A.B.; Yaroshevskaya, A.D. [SRC RF TRINITI, Moscow Region (Russian Federation); Giniyatulin, R.N. [Efremov Institute, St. Petersburg (Russian Federation); Safronov, V.M. [Institution «Project Center ITER», Moscow (Russian Federation); SRC RF TRINITI, Moscow Region (Russian Federation); Khimchenko, L.N. [Institution «Project Center ITER», Moscow (Russian Federation)

    2015-08-15

    The tungsten surface structure was analyzed after the test in the QSPA-T under heat loads relevant to those expected in the ITER during disruptions. Repeated pulses lead to the melting and the resolidification of the tungsten surface layer of ∼50 μm thickness. There is ∼50 μm thickness intermediate layer between the original structure and the resolidified layer. The intermediate layer is recrystallized and has a random grains’ orientation whereas the resolidified layer and basic structure have texture with preferable orientation 〈1 0 0〉 normal to the surface. The cracks which were normal to the surface were observed in the resolidified layer as well as the cracks which were parallel to the surface at the depth up to 300 μm. Such cracks can result in the brittle destruction which is a hazard for the full tungsten divertor of the ITER. The theoretical analysis of the crack formation reasons and a possible consequence for the ITER are given.

  15. Rock-Salt Growth-Induced (003) Cracking in a Layered Positive Electrode for Li-Ion Batteries

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Hanlei [Materials; amp, Department; NorthEast; Omenya, Fredrick [NorthEast; Yan, Pengfei [Environmental; Luo, Langli [Environmental; Whittingham, M. Stanley [NorthEast; Wang, Chongmin [Environmental; Zhou, Guangwen [Materials; amp, Department; NorthEast

    2017-10-20

    For the first time, the (003) cracking is observed and determined to be the major cracking mechanism for the primary particles of Ni-rich layered dioxides as the positive electrode for Li-ion batteries. Using transmission electron microscopy techniques, here we show that the propagation and fracturing of platelet-like rock-salt phase along the (003) plane of the layered oxide are the leading cause for the cracking of primary particles. The fracturing of the rock-salt platelet is induced by the stress discontinuity between the parent layered oxide and the rock-salt phase. The high nickel content is considered to be the key factor for the formation of the rock-salt platelet and thus the (003) cracking. The (003)-type cracking can be a major factor for the structural degradation and associated capacity fade of the layered positive electrode.

  16. Effects of δ-hydride precipitation at a crack tip on crack propagation in delayed hydride cracking of Zircaloy-2

    Energy Technology Data Exchange (ETDEWEB)

    Kubo, T., E-mail: kubo@nfd.co.jp [Nippon Nuclear Fuel Development Co., Ltd., 2163 Narita-cho, Oarai-machi, Ibaraki 311-1313 (Japan); Kobayashi, Y. [M.O.X. Co., Ltd., 1828-520 Hirasu-cho, Mito, Ibaraki 311-0853 (Japan)

    2013-08-15

    Highlights: • Steady state crack velocity of delayed hydride cracking in Zircaloy-2 was analyzed. • A large stress peak is induced at an end of hydride by volume expansion of hydride. • Hydrogen diffuses to the stress peak, thereby accelerating steady hydride growth. • Crack velocity was estimated from the calculated hydrogen flux into the stress peak. • There was good agreement between calculation results and experimental data. -- Abstract: Delayed hydride cracking (DHC) of Zircaloy-2 is one possible mechanism for the failure of boiling water reactor fuel rods in ramp tests at high burnup. Analyses were made for hydrogen diffusion around a crack tip to estimate the crack velocity of DHC in zirconium alloys, placing importance on effects of precipitation of δ-hydride. The stress distribution around the crack tip is significantly altered by precipitation of hydride, which was strictly analyzed using a finite element computer code. Then, stress-driven hydrogen diffusion under the altered stress distribution was analyzed by a differential method. Overlapping of external stress and hydride precipitation at a crack tip induces two stress peaks; one at a crack tip and the other at the front end of the hydride precipitate. Since the latter is larger than the former, more hydrogen diffuses to the front end of the hydride precipitate, thereby accelerating hydride growth compared with that in the absence of the hydride. These results indicated that, after hydride was formed in front of the crack tip, it grew almost steadily accompanying the interaction of hydrogen diffusion, hydride growth and the stress alteration by hydride precipitation. Finally, crack velocity was estimated from the calculated hydrogen flux into the crack tip as a function of temperature, stress intensity factor and material strength. There was qualitatively good agreement between calculation results and experimental data.

  17. A study on fatigue crack growth behavior subjected to a single tensile overload: Part II. Transfer of stress concentration and its role in overload-induced transient crack growth

    International Nuclear Information System (INIS)

    Lee, S.Y.; Choo, H.; Liaw, P.K.; An, K.; Hubbard, C.R.

    2011-01-01

    The combined effects of overload-induced enlarged compressive residual stresses and crack tip blunting with secondary cracks are suggested to be responsible for the observed changes in the crack opening load and resultant post-overload transient crack growth behavior [Lee SY, Liaw PK, Choo H, Rogge RB, Acta Mater 2010;59:485-94]. In this article, in situ neutron diffraction experiments were performed to quantify the influence of the combined effects by investigating the internal-stress evolution at various locations away from the crack tip. In the overload-retardation period, stress concentration occurs in the crack blunting region (an overload point) until a maximum crack arrest load is reached. The stress concentration is then transferred from the blunting region to the propagating crack tip (following the overload), requiring a higher applied load, as the closed crack is gradually opened. The transfer phenomena of the stress concentration associated with a crack opening process account for the nonlinearity of strain response in the vicinity of the crack tip. The delaying action of stress concentration at the crack tip is understood in conjunction with the concept of a critical stress (i.e. the stress required to open the closed crack behind the crack tip). A linear relationship between Δε eff and ΔK eff provides experimental support for the hypothesis that ΔK eff can be considered as the fatigue crack tip driving force.

  18. Stress induced martensite at the crack tip in NiTi alloys during fatigue loading

    Directory of Open Access Journals (Sweden)

    E. Sgambitterra

    2014-10-01

    Full Text Available Crack tip stress-induced phase transformation mechanisms in nickel-titanium alloys (NiTi were analyzed by Digital Image Correlation (DIC, under fatigue loads. In particular, Single Edge Crack (SEC specimens, obtained from a commercial pseudoelastic NiTi sheet, and an ad-hoc experimental setup were used, for direct measurements of the near crack tip displacement field by the DIC technique. Furthermore, a fitting procedure was developed to calculate the mode I Stress Intensity Factor (SIF, starting from the measured displacement field. Finally, cyclic tensile tests were performed at different operating temperature, in the range 298-338 K, and the evolution of the SIF was studied, which revealed a marked temperature dependence.

  19. Transient cracks and triple junctions induced by Cocos-Nazca propagating rift

    Science.gov (United States)

    Schouten, H.; Smith, D. K.; Zhu, W.; Montesi, L. G.; Mitchell, G. A.; Cann, J. R.

    2009-12-01

    The Galapagos triple junction is a ridge-ridge-ridge triple junction where the Cocos, Nazca, and Pacific plates meet around the Galapagos microplate (GMP). On the Cocos plate, north of the large gore that marks the propagating Cocos-Nazca (C-N) Rift, a 250-km-long and 50-km-wide band of NW-SE-trending cracks crosscuts the N-S-trending abyssal hills of the East Pacific Rise (EPR). These appear as a succession of minor rifts, accommodating some NE-SW extension of EPR-generated seafloor. The rifts successively intersected the EPR in triple junctions at distances of 50-100 km north of the tip of the C-N Rift. We proposed a simple crack interaction model to explain the location of the transient rifts and their junction with the EPR. The model predicts that crack locations are controlled by the stress perturbation along the EPR, induced by the dominant C-N Rift, and scaled by the distance of its tip to the EPR (Schouten et al., 2008). The model also predicts that tensile stresses are symmetric about the C-N Rift and thus, similar cracks should have occurred south of the C-N Rift prior to formation of the GMP about 1 Ma. There were no data at the time to test this prediction. In early 2009 (AT 15-41), we mapped an area on the Nazca plate south of the C-N rift out to 4 Ma. The new bathymetric data confirm the existence of a distinctive pattern of cracks south of the southern C-N gore that mirrors the pattern on the Cocos plate until about 1 Ma, and lends support to the crack interaction model. The envelope of the symmetric cracking pattern indicates that the distance between the C-N Rift tip and the EPR varied between 40 and 65 km during this time (1-4 Ma). The breakdown of the symmetry at 1 Ma accurately dates the onset of a southern plate boundary of the GMP, now Dietz Deep Rift. At present, the southern rift boundary of the GMP joins the EPR with a steep-sided, 80 km long ridge. This ridge releases the stress perturbation otherwise induced along the EPR by elastic

  20. Intermediate-Size Inducer Pump design report. [LMFBR

    Energy Technology Data Exchange (ETDEWEB)

    Boardman, T.J.

    1979-06-15

    This report summarizes the mechanical, structural, and hydrodynamic design of the Intermediate-Size Inducer Pump (ISIP). The design was performed under Atomics International's DOE Base Technology Program by the Atomics International and Rocketdyne Divisions of Rockwell International. The pump was designed to utilize the FFTF prototype pump frame as a test vehicle to test the inducer, impeller, and diffuser plus necessary adapter hardware under simulated Large Scale Liquid Metal Fast Breeder Reactor service conditions. The report describes the design requirements including the purpose and objectives, and discusses those design efforts and considerations made to meet the requirements. Included in the report are appendices showing calculative methods and results. Also included are overall assembly and layout drawings plus some details used as illustrations for discussion of the design results and the results of water tests performed on a model of the inducer.

  1. Interfacial Crack Arrest in Sandwich Panels with Embedded Crack Stoppers Subjected to Fatigue Loading

    DEFF Research Database (Denmark)

    Martakos, G.; Andreasen, J. H.; Berggreen, Christian

    2017-01-01

    A novel crack arresting device has been implemented in sandwich panels and tested using a special rig to apply out-of-plane loading on the sandwich panel face-sheets. Fatigue crack propagation was induced in the face-core interface of the sandwich panels which met the crack arrester. The effect o...

  2. Iodine-induced stress corrosion cracking of fixed deflection stressed slotted rings of Zircaloy fuel cladding

    International Nuclear Information System (INIS)

    Sejnoha, R.; Wood, J.C.

    1978-01-01

    Stress corrosion cracking of Zircaloy fuel cladding by fission products is thought to be an important mechanism influencing power ramping defects of water-reactor fuels. We have used the fixed-deflection stressed slotted-ring technique to demonstrate cracking. The results show both the sensitivity and limitations of the stressed slotted-ring method in determining the responses of tubing to stress corrosion cracking. They are interpreted in terms of stress relaxation behavior, both on a microscopic scale for hydrogen-induced stress-relief and on a macroscopic scale for stress-time characteristics. Analysis also takes account of nonuniform plastic deformation during loading and residual stress buildup on unloading. 27 refs

  3. An effective finite element model for the prediction of hydrogen induced cracking in steel pipelines

    KAUST Repository

    Traidia, Abderrazak

    2012-11-01

    This paper presents a comprehensive finite element model for the numerical simulation of Hydrogen Induced Cracking (HIC) in steel pipelines exposed to sulphurous compounds, such as hydrogen sulphide (H2S). The model is able to mimic the pressure build-up mechanism related to the recombination of atomic hydrogen into hydrogen gas within the crack cavity. In addition, the strong couplings between non-Fickian hydrogen diffusion, pressure build-up and crack extension are accounted for. In order to enhance the predictive capabilities of the proposed model, problem boundary conditions are based on actual in-field operating parameters, such as pH and partial pressure of H 2S. The computational results reported herein show that, during the extension phase, the propagating crack behaves like a trap attracting more hydrogen, and that the hydrostatic stress field at the crack tip speed-up HIC related crack initiation and growth. In addition, HIC is reduced when the pH increases and the partial pressure of H2S decreases. Furthermore, the relation between the crack growth rate and (i) the initial crack radius and position, (ii) the pipe wall thickness and (iii) the fracture toughness, is also evaluated. Numerical results agree well with experimental data retrieved from the literature. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

  4. CAT scanning of hydrogen-induced cracks in steel

    International Nuclear Information System (INIS)

    Sawicka, B.D.; Tapping, R.L.

    1987-01-01

    Computer assisted tomography (CAT) was applied to detect small cracks caused by hydrogen ingress into carbon steel samples. The incipient cracks in the samples resulted from a quality control procedure used to test the susceptibility of carbon steel to hydrogen blistering/cracking. The method used until now to assess the extent of the cracking resulting from this test has been mechanical sectioning, polishing and microscopic examination of the sections. The CAT results are compared with the reference method and the feasibility of using CAT in the proposed application is demonstrated. (orig.)

  5. Main factors causing intergranular and quasi-cleavage fractures at hydrogen-induced cracking in tempered martensitic steels

    Science.gov (United States)

    Kurokawa, Ami; Doshida, Tomoki; Hagihara, Yukito; Suzuki, Hiroshi; Takai, Kenichi

    2018-05-01

    Though intergranular (IG) and quasi-cleavage (QC) fractures have been widely recognized as typical fracture modes of the hydrogen-induced cracking in high-strength steels, the main factor has been unclarified yet. In the present study, the hydrogen content dependence on the main factor causing hydrogen-induced cracking has been examined through the fracture mode transition from QC to IG at the crack initiation site in the tempered martensitic steels. Two kinds of tempered martensitic steels were prepared to change the cohesive force due to the different precipitation states of Fe3C on the prior γ grain boundaries. A high amount of Si (H-Si) steel has a small amount of Fe3C on the prior austenite grain boundaries. Whereas, a low amount of Si (L-Si) steel has a large amount of Fe3C sheets on the grain boundaries. The fracture modes and initiations were observed using FE-SEM (Field Emission-Scanning Electron Microscope). The crack initiation sites of the H-Si steel were QC fracture at the notch tip under various hydrogen contents. While the crack initiation of the L-Si steel change from QC fracture at the notch tip to QC and IG fractures from approximately 10 µm ahead of the notch tip as increasing in hydrogen content. For L-Si steels, two possibilities are considered that the QC or IG fracture occurred firstly, or the QC and IG fractures occurred simultaneously. Furthermore, the principal stress and equivalent plastic strain distributions near the notch tip were calculated with FEM (Finite Element Method) analysis. The plastic strain was the maximum at the notch tip and the principle stress was the maximum at approximately 10 µm from the notch tip. The position of the initiation of QC and IG fracture observed using FE-SEM corresponds to the position of maximum strain and stress obtained with FEM, respectively. These findings indicate that the main factors causing hydrogen-induced cracking are different between QC and IG fractures.

  6. Reactor vessel nozzle cracks: a photoelastic study

    International Nuclear Information System (INIS)

    Smith, C.W.

    1979-01-01

    A method consisting of a marriage between the ''frozen stress'' photoelastic approach and the local stress field equations of linear elastic fracture mechanics for estimating stress intensity factor distributions in three dimensional, finite cracked body problems is reviewed and extensions of the method are indicated. The method is then applied to the nuclear reactor vessel nozzle corner crack problem for both Intermediate Test Vessel and Boiling Water Reactor geometries. Results are compared with those of other investigators. 35 refs

  7. HYDROGEN INDUCED CRACKING IN MICROALLOYED STEELS

    Directory of Open Access Journals (Sweden)

    Duberney Hincapie-Ladino

    2015-03-01

    Full Text Available The need for microalloyed steels resistant to harsh environments in oil and gas fields, such as pre-salt which contain considerable amounts of hydrogen sulfide (H2 S and carbon dioxide (CO2 , requires that all sectors involved in petroleum industry know the factors that influence the processes of corrosion and failures by hydrogen in pipelines and components fabricated with microalloyed steels. This text was prepared from a collection of selected publications and research done at the Electrochemical Processes Laboratory of Metallurgical and Materials Engineering Department, Polytechnic School, São Paulo University. This document does not intend to be a complete or exhaustive review of the literature, but rather to address the main scientific and technological factors associated with failures by hydrogen in the presence of wet hydrogen sulfide (H2 S, particularly, when related to the Hydrogen Induced Cracking (HIC phenomenon. This complex phenomenon that involves several successive stages, HIC phenomena were discussed in terms of environmental and metallurgical variables. The HIC starts with the process of corrosion of steel, therefore must be considered the corrosive media (H2 S presence effect. Moreover, it is necessary to know the interactions of compounds present in the electrolyte with the metal surface, and how they affect the hydrogen adsorption and absorption into steel. The following stages are hydrogen diffusion, trapping and metal cracking, directly related to the chemical composition and the microstructure, factors that depend strongly on the manufacture of steel. The purpose of this paper is to provide the scientific information about the failures caused by hydrogen and challenge for the Oil and Gas Pipeline Industry.

  8. Crack cocaine inhalation induces schizophrenia-like symptoms and molecular alterations in mice prefrontal cortex.

    Science.gov (United States)

    Areal, Lorena Bianchine; Herlinger, Alice Laschuk; Pelição, Fabrício Souza; Martins-Silva, Cristina; Pires, Rita Gomes Wanderley

    2017-08-01

    Crack cocaine (crack) addiction represents a major social and health burden, especially seeing as users are more prone to engage in criminal and violent acts. Crack users show a higher prevalence of psychiatric comorbidities - particularly antisocial personality disorders - when compared to powder cocaine users. They also develop cognitive deficits related mainly to executive functions, including working memory. It is noteworthy that stimulant drugs can induce psychotic states, which appear to mimic some symptoms of schizophrenia among users. Social withdraw and executive function deficits are, respectively, negative and cognitive symptoms of schizophrenia mediated by reduced dopamine (DA) tone in the prefrontal cortex (PFC) of patients. That could be explained by an increased expression of D2R short isoform (D2S) in the PFC of such patients and/or by hypofunctioning NMDA receptors in this region. Reduced DA tone has already been described in the PFC of mice exposed to crack smoke. Therefore, it is possible that behavioral alterations presented by crack users result from molecular and biochemical neuronal alterations akin to schizophrenia. Accordingly, we found that upon crack inhalation mice have shown decreased social interaction and working memory deficits analogous to schizophrenia's symptoms, along with increased D2S/D2L expression ratio and decreased expression of NR1, NR2A and NR2B NMDA receptor subunits in the PFC. Herein we propose two possible mechanisms to explain the reduced DA tone in the PFC elicited by crack consumption in mice, bringing also the first direct evidence that crack use may result in schizophrenia-like neurochemical, molecular and behavioral alterations. Copyright © 2017 Elsevier Ltd. All rights reserved.

  9. Parameters of straining-induced corrosion cracking in low-alloy steels in high temperature water

    International Nuclear Information System (INIS)

    Lenz, E.; Liebert, A.; Stellwag, B.; Wieling, N.

    Tensile tests with slow deformation speed determine parameters of corrosion cracking at low strain rates of low-alloy steels in high-temperature water. Besides the strain rate the temperature and oxygen content of the water prove to be important for the deformation behaviour of the investigated steels 17MnMoV64, 20 MnMoNi55 and 15NiCuMoNb 5. Temperatures about 240 0 C, increased oxygen contents in the water and low strain rates cause a decrease of the material ductility as against the behaviour in air. Tests on the number of stress cycles until incipient cracking show that the parameters important for corrosion cracking at low strain velocities apply also to low-frequency cyclic loads with high strain amplitude. In knowledge of these influencing parameters the strain-induced corrosion cracking is counteracted by concerted measures taken in design, construction and operation of nuclear power stations. Essential aims in this matter are to avoid as far as possible inelastic strains and to fix and control suitable media conditions. (orig.) [de

  10. Effect of Thermomechanical Treatment on the Environmentally Induced Cracking Behavior of AA7075 Alloy

    Science.gov (United States)

    Ghosh, Rahul; Venugopal, A.; Sankaravelayudham, P.; Panda, Rajiv; Sharma, S. C.; George, Koshy M.; Raja, V. S.

    2015-02-01

    The influence of thermomechanical treatment on the stress corrosion cracking behavior of AA7075 aluminum alloy forgings was examined in 3.5% NaCl solution by varying the extent of thermomechanical working imparted to each of the conditions. The results show that inadequate working during billet processing resulted in inferior corrosion and mechanical properties. However, more working with intermediate pre-heating stages also led to precipitation of coarse particles resulting in lowering of mechanical properties marginally and a significant reduction in the general/pitting corrosion resistance. The results obtained in the present study indicate that optimum working with controlled pre-heating levels is needed during forging to achieve the desired properties. It is also demonstrated that AA7075 in the over aged condition does not show any environmental cracking susceptibility in spite of the microstructural variations in terms of size and volume fraction of the precipitates. However, the above microstructural variations definitely affected the pitting corrosion and mechanical properties significantly and hence a strict control over the working and pre-heating stages during billet processing is suggested.

  11. Evaluation of flaws or service induced cracks in pressure vessels

    International Nuclear Information System (INIS)

    Riccardella, P.C.; Copeland, J.F.; Gilman, J.

    1987-01-01

    An overview of the ASME flaw evaluation procedures for nuclear pressure vessels is presented, with emphasis on fatigue crack growth evaluations. Environmental and load-rate effects are further considered with respect to new crack growth data and a time-dependent crack growth model. This new crack growth model is applied to evaluate feedwater nozzle cracking in boiling water reactors and is compared to current and past ASME crack growth curves. The time-dependent model bounds the observed cracking and indicates that more detailed consideration of material susceptibility, in terms of sulfur content and product form, is needed

  12. Theoretical aspects of stress corrosion cracking of Alloy 22

    Science.gov (United States)

    Lee, Sang-Kwon; Macdonald, Digby D.

    2018-05-01

    Theoretical aspects of the stress corrosion cracking of Alloy 22 in contact with saturated NaCl solution are explored in terms of the Coupled Environment Fracture Model (CEFM), which was calibrated upon available experimental crack growth rate data. Crack growth rate (CGR) was then predicted as a function of stress intensity, electrochemical potential, solution conductivity, temperature, and electrochemical crack length (ECL). From the dependence of the CGR on the ECL and the evolution of a semi-elliptical surface crack in a planar surface under constant loading conditions it is predicted that penetration through the 2.5-cm thick Alloy 22 corrosion resistant layer of the waste package (WP) could occur 32,000 years after nucleation. Accordingly, the crack must nucleate within the first 968,000 years of storage. However, we predict that the Alloy 22 corrosion resistant layer will not be penetrated by SCC within the 10,000-year Intermediate Performance Period, even if a crack nucleates immediately upon placement of the WP in the repository.

  13. Variable amplitude fatigue crack growth behavior - a short overview

    International Nuclear Information System (INIS)

    Singh, Konjengbam Darunkumar; Parry, Matthew Roger; Sinclair, Ian

    2011-01-01

    A short overview concerning variable amplitude (VA) fatigue crack growth behavior is presented in this paper. The topics covered in this review encompass important issues pertaining to both single and repeated overload transients. Reviews on transient post overload effects such as plasticity induced crack closure, crack tip blunting, residual stresses, crack deflection and branching, activation of near threshold mechanisms, strain hardening are highlighted. A brief summary on experimental trends and finite element modelling of overload induced crack closure is also presented

  14. Variable amplitude fatigue crack growth behavior - a short overview

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Konjengbam Darunkumar [Indian Institute of Technology, Guwahati (India); Parry, Matthew Roger [Airbus Operations Ltd, Bristol (United Kingdom); Sinclair, Ian [University of Southampton, Southampton (United Kingdom)

    2011-03-15

    A short overview concerning variable amplitude (VA) fatigue crack growth behavior is presented in this paper. The topics covered in this review encompass important issues pertaining to both single and repeated overload transients. Reviews on transient post overload effects such as plasticity induced crack closure, crack tip blunting, residual stresses, crack deflection and branching, activation of near threshold mechanisms, strain hardening are highlighted. A brief summary on experimental trends and finite element modelling of overload induced crack closure is also presented.

  15. Glutamate Induced Thermal Equilibrium Intermediate and Counteracting Effect on Chemical Denaturation of Proteins.

    Science.gov (United States)

    Anumalla, Bramhini; Prabhu, N Prakash

    2018-01-25

    When organisms are subjected to stress conditions, one of their adaptive responses is accumulation of small organic molecules called osmolytes. These osmolytes affect the structure and stability of the biological macromolecules including proteins. The present study examines the effect of a negatively charged amino acid osmolyte, glutamate (Glu), on two model proteins, ribonuclease A (RNase A) and α-lactalbumin (α-LA), which have positive and negative surface charges at pH 7, respectively. These proteins follow two-state unfolding transitions during both heat and chemical induced denaturation processes. The addition of Glu stabilizes the proteins against temperature and induces an early equilibrium intermediate during unfolding. The stability is found to be enthalpy-driven, and the free energy of stabilization is more for α-LA compared to RNase A. The decrease in the partial molar volume and compressibility of both of the proteins in the presence of Glu suggests that the proteins attain a more compact state through surface hydration which could provide a more stable conformation. This is also supported by molecule dynamic simulation studies which demonstrate that the water density around the proteins is increased upon the addition of Glu. Further, the intermediates could be completely destabilized by lower concentrations (∼0.5 M) of guanidinium chloride and salt. However, urea subverts the Glu-induced intermediate formed by α-LA, whereas it only slightly destabilizes in the case of RNase A which has a positive surface charge and could possess charge-charge interactions with Glu. This suggests that, apart from hydration, columbic interactions might also contribute to the stability of the intermediate. Gdm-induced denaturation of RNase A and α-LA in the absence and the presence of Glu at different temperatures was carried out. These results also show the Glu-induced stabilization of both of the proteins; however, all of the unfolding transitions followed two

  16. Crack velocity measurement by induced electromagnetic radiation

    International Nuclear Information System (INIS)

    Frid, V.; Rabinovitch, A.; Bahat, D.

    2006-01-01

    Our model of electromagnetic radiation (EMR) emanated from fracture implies that EMR amplitude is proportional to crack velocity. Soda lime glass samples were tested under uniaxial tension. Comparison of crack velocity observed by Wallner line analysis and the peak amplitude of EMR signals registered during the test, showed very good correlation, validating this proportionality

  17. Crack velocity measurement by induced electromagnetic radiation

    Energy Technology Data Exchange (ETDEWEB)

    Frid, V. [Deichmann Rock Mechanics Laboratory of the Negev, Geological and Environmental Sciences Department, Ben Gurion University of the Negev, Beer Sheva (Israel)]. E-mail: vfrid@bgu.ac.il; Rabinovitch, A. [Deichmann Rock Mechanics Laboratory of the Negev, Physics Department, Ben Gurion University of the Negev, Beer Sheva (Israel); Bahat, D. [Deichmann Rock Mechanics Laboratory of the Negev, Geological and Environmental Sciences Department, Ben Gurion University of the Negev, Beer Sheva (Israel)

    2006-07-31

    Our model of electromagnetic radiation (EMR) emanated from fracture implies that EMR amplitude is proportional to crack velocity. Soda lime glass samples were tested under uniaxial tension. Comparison of crack velocity observed by Wallner line analysis and the peak amplitude of EMR signals registered during the test, showed very good correlation, validating this proportionality.

  18. Mechanisms of hydrogen induced delayed cracking in hydride forming materials

    International Nuclear Information System (INIS)

    Dutton, R.; Nuttall, K.; Puls, M.P.; Simpson, L.A.

    1977-01-01

    Mechanisms which have been formulated to describe delayed hydrogen cracking in hydride-forming metals are reviewed and discussed. Particular emphasis is placed on the commercial alloy Zr--2.5% Nb (Cb) which is extensively used in nuclear reactor core components. A quantitative model for hydrogen cracking in this material is presented and compared with available experimental data. The kinetics of crack propagation are controlled by the growth of hydrides at the stressed crack tip by the diffusive ingress of hydrogen into this region. The driving force for the diffusion flux is provided by the local stress gradient which interacts with both hydrogen atoms in solution and hydrogen atoms being dissolved and reprecipitated at the crack tip. The model is developed using concepts of elastoplastic fracture mechanics. Stage I crack growth is controlled by hydrides growing in the elastic stress gradient, while Stage II is controlled by hydride growth in the plastic zone at the crack tip. Recent experimental observations are presented which indicate that the process occurs in an intermittent fashion; hydride clusters accumulate at the crack tip followed by unstable crack advance and subsequent crack arrest in repeated cycles

  19. Mechanisms of hydrogen induced delayed cracking in hydride forming materials

    International Nuclear Information System (INIS)

    Dutton, R.; Nuttall, K.; Puls, M.P.; Simpson, L.A.

    1977-01-01

    Mechanisms which have been formulated to describe delayed hydrogen cracking in hydride-forming metals are reviewed and discussed. Particular emphasis is placed on the commercial alloy Zr-2.5 pct Nb which is extensively used in nuclear reactor core components. A quantitative model for hydrogen cracking in this material is presented and compared with available experimental data. The kinetics of crack propagation are controlled by the growth of hydrides at the stressed crack tip by the diffusive ingress of hydrogen into this region. The driving force for the diffusion flux is provided by the local stress gradient which interacts with both hydrogen atoms in solution and hydrogen atoms being dissolved and reprecipitated at the crack tip. The model is developed using concepts of elastoplastic fracture mechanics. Stage I crack growth is controlled by hydrides growing in the elastic stress gradient, while Stage II is controlled by hydride growth in the plastic zone at the crack tip. Recent experimental observations are presented which indicate that the process occurs in an intermittent fashion; hydride clusters accumulate at the crack tip followed by unstable crack advance and subsequent crack arrest in repeated cycles. 55 refs., 6 figs

  20. Remote detection of stress corrosion cracking: Surface composition and crack detection

    Science.gov (United States)

    Lissenden, Cliff J.; Jovanovic, Igor; Motta, Arthur T.; Xiao, Xuan; Le Berre, Samuel; Fobar, David; Cho, Hwanjeong; Choi, Sungho

    2018-04-01

    Chloride induced stress corrosion cracking (SCC) of austenitic stainless steel is a potential issue in long term dry storage of spent nuclear fuel canisters. In order for SCC to occur there must be a corrosive environment, a susceptible material, and a driving force. Because it is likely that the material in the heat affected zone (HAZ) of welded stainless steel structures has been sensitized as a result of chromium depletion at the grain boundaries and a thermal residual stress driving force is likely present if solution annealing is not performed, two issues are critical. Is the environment corrosive, i.e., are chlorides present in solution on the surface? And then, are there cracks that could propagate? Remote detection of chlorides on the surface can be accomplished by laser induced breakdown spectroscopy (LIBS), while cracks can be detected by shear horizontal guided waves generated by electromagnetic acoustic transducers (EMATs). Both are noncontact methods that are amenable to robotic delivery systems and harsh environments. The sensitivity to chlorine on stainless steel of a LIBS system that employs optical fiber for pulse delivery is demonstrated. Likewise, the ability of the EMAT system to detect cracks of a prescribed size and orientation is shown. These results show the potential for remote detection of Cl and cracks in dry storage spent fuel canisters.

  1. Laser cutting sandwich structure glass-silicon-glass wafer with laser induced thermal-crack propagation

    Science.gov (United States)

    Cai, Yecheng; Wang, Maolu; Zhang, Hongzhi; Yang, Lijun; Fu, Xihong; Wang, Yang

    2017-08-01

    Silicon-glass devices are widely used in IC industry, MEMS and solar energy system because of their reliability and simplicity of the manufacturing process. With the trend toward the wafer level chip scale package (WLCSP) technology, the suitable dicing method of silicon-glass bonded structure wafer has become necessary. In this paper, a combined experimental and computational approach is undertaken to investigate the feasibility of cutting the sandwich structure glass-silicon-glass (SGS) wafer with laser induced thermal-crack propagation (LITP) method. A 1064 nm semiconductor laser cutting system with double laser beams which could simultaneously irradiate on the top and bottom of the sandwich structure wafer has been designed. A mathematical model for describing the physical process of the interaction between laser and SGS wafer, which consists of two surface heating sources and two volumetric heating sources, has been established. The temperature stress distribution are simulated by using finite element method (FEM) analysis software ABAQUS. The crack propagation process is analyzed by using the J-integral method. In the FEM model, a stationary planar crack is embedded in the wafer and the J-integral values around the crack front edge are determined using the FEM. A verification experiment under typical parameters is conducted and the crack propagation profile on the fracture surface is examined by the optical microscope and explained from the stress distribution and J-integral value.

  2. An effective finite element model for the prediction of hydrogen induced cracking in steel pipelines

    KAUST Repository

    Traidia, Abderrazak; Alfano, Marco; Lubineau, Gilles; Duval, Sé bastien; Sherik, Abdelmounam M.

    2012-01-01

    This paper presents a comprehensive finite element model for the numerical simulation of Hydrogen Induced Cracking (HIC) in steel pipelines exposed to sulphurous compounds, such as hydrogen sulphide (H2S). The model is able to mimic the pressure

  3. Application of the potential-drop method to measurements of hydrogen-induced sub-critical crack growth in zirconium-2.5 wt% niobium

    International Nuclear Information System (INIS)

    Simpson, L.A.; Clarke, C.F.

    1977-10-01

    Adaptation of the potential-drop method of crack-following to the problem of hydrogen-induced sub-critical crack growth in Zr-2.5% Nb is described. Reasons for non-linearity in the calibration of crack extension against potential drop in compact tension specimens are discussed. It is shown that despite non-linearities, careful comparison of fractographic features with the potential-drop record can lead to a continuous plot of crack velocity against time or stress intensity factor. Procedures for correcting data through temperature and load changes are also described. The application of the technique to studies of the mechanism of hydrogen crack growth is illustrated with several examples. (author)

  4. Development of an Improved Crack Propagation Model for Corrosion-Induced Cover Cracking in RC Structures

    Science.gov (United States)

    Hilyati, S.; Nizam, Z. M.; Zurisman, M. A. A.; Azhar, A. T. S.

    2017-06-01

    During the last two decades, reinforced concrete (RC) has been extensively used in most of the world as one of the common construction material due to its advantages and durability. However, RC structures exposed to marine environments are subjected to chloride attack. Chlorides from seawater penetrate into RC structures are not only causing severe corrosion problems but also affect the durability and serviceability of such structures. This paper investigates the influence of transverse reinforcement and spacing of reinforcing bars on concrete cover cracking of two-way RC slab specimens using accelerated corrosion tests. The experimental program involved the testing of four RC slab specimens and was generally designed to observe the crack width and the time of crack to propagate. An improved model for predicting the timing of crack propagation based on the experimental data was then developed.

  5. Evaluation of hydrogen-Induced cracking resistance of the In625 laser coating system on a C-Mn steel substrate

    Directory of Open Access Journals (Sweden)

    Vicente Braz Trindade

    Full Text Available Abstract The corrosion of C-Mn steels in the presence of hydrogen sulfide (H2S represents a significant challenge to oil production and natural gas treatment facilities. The failure mechanism induced by hydrogen-induced cracking (HIC in a Inconel 625 coating / C-Mn steel has not been extensively investigated in the past. In the present work, an API 5CT steel was coated with In625 alloy using laser cladding and the HIC resistance of different regions, such as the coating surface, the substrate and HAZ, were evaluated. SEM observations illustrated that all HIC cracks were formed at the hard HAZ after 96h of exposure. No HIC cracks were observed in the substrate and the In625 coating after the same exposure duration. Pitting was recorded in the substrate caused by non-metallic inclusion dissolving.

  6. The effects of strain-induced martensitic transformation and temperature on impact fatigue crack propagation behavior of SUS 304 at low temperature

    International Nuclear Information System (INIS)

    Murakami, Ri-ichi; Akizono, Koichi; Kusukawa, Kazuhiro.

    1988-01-01

    The fatigue crack propagation behavior in fatigue impact at room temperature and 103 K was investigated by means of fracture mechanics, X-ray diffraction analysis and fractography for an austenitic stainless steel, SUS 304. The crack growth rate in fatigue impact decreased with decreasing temperature. The crack growth rate at room temperature was scarcely influenced by the microstructure, while at low temperature it was markedly influenced by the microstructure. The effects of microstructure and temperature on the crack growth rate were closely related to the strain-induced martensitic transformation. The martensitic transformation was influenced by the microstructure, the temperature, the fracture morphology and the stress intensity level and resulted in a decrease in crack growth rate with increasing crack opening level. (author)

  7. Influence of strain-induced martensitic transformation on fatigue short crack behaviour in an austenitic stainless steel

    International Nuclear Information System (INIS)

    Baffie, N.; Stolarz, J.; Magnin, Th.

    2000-01-01

    The influence of martensitic transformation induced by cyclic straining on the mechanisms of low cycle fatigue damage in a metastable austenitic stainless steel with different grain sizes has been investigated using macroscopic measurements and microscopic observations of short crack evolutions. The amount of martensite formed during cyclic straining increases with increasing plastic strain amplitude and cumulative plastic strain but the dominant parameter is the grain size of austenite. The fine microstructure (D = 10 μm) with maximum martensite fraction of about 20% is characterised by a better fatigue resistance than the coarse one (D 40μm and only 2% of martensite) for the same plastic strain amplitude. Martensitic transformation is found to radically modify the cyclic response of the alloy and consequently the damage mechanisms. Indeed, both short crack nucleation and growth take place exclusively in the transformed regions. A mechanism of short crack propagation based on the γ→ α' transformation assisted by stress concentration at the crack tip is proposed. The indirect influence of grain boundaries in the austenite on crack propagation in the martensite is demonstrated. The better fatigue resistance of metastable alloys with fine granular structure can thus be understood. (authors)

  8. Determination of crack morphology parameters from service failures for leak-rate analyses

    Energy Technology Data Exchange (ETDEWEB)

    Wilkowski, G.; Ghadiali, N.; Paul, D. [Battelle Memorial Institute, Columbus, OH (United States)] [and others

    1997-04-01

    In leak-rate analyses described in the literature, the crack morphology parameters are typically not well agreed upon by different investigators. This paper presents results on a review of crack morphology parameters determined from examination of service induced cracks. Service induced cracks were found to have a much more tortuous flow path than laboratory induced cracks due to crack branching associated with the service induced cracks. Several new parameters such as local and global surface roughnesses, as well as local and global number of turns were identified. The effect of each of these parameters are dependent on the crack-opening displacement. Additionally, the crack path is typically assumed to be straight through the pipe thickness, but the service data show that the flow path can be longer due to the crack following a fusion line, and/or the number of turns, where the number of turns in the past were included as a pressure drop term due to the turns, but not the longer flow path length. These parameters were statistically evaluated for fatigue cracks in air, corrosion-fatigue, IGSCC, and thermal fatigue cracks. A refined version of the SQUIRT leak-rate code was developed to account for these variables. Sample calculations are provided in this paper that show how the crack size can vary for a given leak rate and the statistical variation of the crack morphology parameters.

  9. Zircaloy-4 stress corrosion by iodine: crack kinetics and influence of irradiation on the crack initiation

    International Nuclear Information System (INIS)

    Serres, A.

    2008-01-01

    During the PWR power transients, iodine-induced stress corrosion cracking (I-SCC) is one of the potential failure modes of Zircaloy-4 fuel claddings under Pellet-Cladding Interaction conditions. The primary objective of this study is to distinguish the parameters that contribute to the I-SCC phenomenon in iodized methanol solutions at ambient temperature, on notched tensile specimens, using crack growth rate measurements provided by Direct Current Potential Drop. The results show that for a KI lower than 20 MPa.m 1/2 , the IG and mixed IG/TG velocity of propagation is a linear function of KI, regardless of the propagation mode. Between 20 and 25 MPa.m 1/2 , the TG crack growth rate also depends linearly on KI, but increases at a faster rate with respect to KI than during the IG and mixed IG/TG propagation steps. The crack propagation direction and plane (LT and TL) have an impact on the propagation modes, but no impact on the kinetics. The increase of iodine content induces an increase of the crack growth rate for a given KI, and a decrease of the KI, threshold, allowing the crack propagation. This work enables us to quantify the effect of iodine content and of KI on the crack propagation step, propose a propagation law taking into accounts these parameters, and improve the I-SCC description for models. During operation, a zirconium cladding is neutron-irradiated, modifying its microstructure and deformation modes. The second objective of the study is therefore to investigate the impact of these modifications on I-SCC. For that purpose, smooth specimens in recrystallized Zircaloy-4 are proton-irradiated to 2 dpa at 305 C, the microstructure and deformation modes of unirradiated and irradiated Zircaloy-4 are characterized by TEM and SEM, and the influence of these radiation-induced modifications on the I-SCC susceptibility is studied. The Laves phases precipitates are slightly modified by irradiation. The formation of P -type dislocation loops correlated with

  10. Strain-induced corrosion cracking in ferritic components of BWR primary circuits; Risskorrosion in druckfuehrenden ferritischen Komponenten des Primaerkreislaufes von Siedewasserreaktoren

    Energy Technology Data Exchange (ETDEWEB)

    Seifert, H.-P.; Ritter, S.; Ineichen, U.; Tschanz, U.; Gerodetti, B

    2003-04-01

    The present final report of the RIKORR project is a summary of a literature survey and of the experimental work performed by PSI on the environmentally-assisted cracking (EAC) and dynamic strain ageing (DSA) susceptibility of low-alloy steels (LAS) in high-temperature (HT) water. Within this project, the EAC crack growth behaviour of different low-alloy RPV steels, weld filler and weld heat-affected zone materials has been investigated under simulated transient and steady-state BWR/NWC power operation conditions. The strain-induced corrosion cracking (SICC) / low-frequency corrosion fatigue (CF) and stress corrosion cracking (SCC) crack growth behaviour of different low-alloy RPV steels under simulated transient and stationary BWR/NWC conditions was characterized by slow rising load / low-frequency corrosion fatigue and constant load / periodical partial unloading / ripple load tests with pre-cracked fracture mechanics specimens in oxygenated HT water at temperatures of either 288, 250, 200 or 150 {sup o}C. Modern high-temperature water loops, on-line crack growth monitoring and fractographic analysis by scanning electron microscopy (SEM) were used to quantify the cracking response. (author)

  11. Penetration of corrosion products and corrosion-induced cracking in reinforced cementitious materials

    DEFF Research Database (Denmark)

    Michel, Alexander; Pease, Brad J.; Peterova, Adela

    2014-01-01

    This paper describes experimental investigations on corrosion-induced deterioration in reinforced cementitious materials and the subsequent development and implementation of a novel conceptual model. Rejnforced mortar specimens of varying water-to-cement ratios were subjected to current-induced c......This paper describes experimental investigations on corrosion-induced deterioration in reinforced cementitious materials and the subsequent development and implementation of a novel conceptual model. Rejnforced mortar specimens of varying water-to-cement ratios were subjected to current......-dependent concentrations of corrosion products averaged through the specimen thickness. Digital image correlation (DIC) was used to measure corrosion-induced deformations including deformations between steel and cementitious matrix as well as formation and propagation of corrosion-induced cracks. Based on experimental...... observations, a conceptual model was developed to describe the penetration of solid corrosion products into capillary pores of the cementitious matrix. Only capillary pores within a corrosion accommodating region (CAR), i.e. in close proximity of the steel reinforcement, were considered accessible...

  12. Fragment mass distribution of proton-induced spallation reaction with intermediate energy

    International Nuclear Information System (INIS)

    Fan Sheng; Ye Yanlin; Xu Chuncheng; Chen Tao; Sobolevsky, N.M.

    2000-01-01

    The test of part benchmark of SHIELD code is finished. The fragment cross section and mass distribution and excitation function of the residual nuclei from proton-induced spallation reaction on thin Pb target with intermediate energy have been calculated by SHIELD code. And the results are in good agreement with measured data. The fragment mass distribution of the residual nuclei from proton-induced spallation reaction on thick Pb target with incident energy 1.6 GeV have been simulated

  13. A Continuum-Atomistic Analysis of Transgranular Crack Propagation in Aluminum

    Science.gov (United States)

    Yamakov, V.; Saether, E.; Glaessgen, E.

    2009-01-01

    A concurrent multiscale modeling methodology that embeds a molecular dynamics (MD) region within a finite element (FEM) domain is used to study plastic processes at a crack tip in a single crystal of aluminum. The case of mode I loading is studied. A transition from deformation twinning to full dislocation emission from the crack tip is found when the crack plane is rotated around the [111] crystallographic axis. When the crack plane normal coincides with the [112] twinning direction, the crack propagates through a twinning mechanism. When the crack plane normal coincides with the [011] slip direction, the crack propagates through the emission of full dislocations. In intermediate orientations, a transition from full dislocation emission to twinning is found to occur with an increase in the stress intensity at the crack tip. This finding confirms the suggestion that the very high strain rates, inherently present in MD simulations, which produce higher stress intensities at the crack tip, over-predict the tendency for deformation twinning compared to experiments. The present study, therefore, aims to develop a more realistic and accurate predictive modeling of fracture processes.

  14. Susceptibility to hydrogen-induced cracking in H2S corrosion environment of API 5L-X80 weld metal

    International Nuclear Information System (INIS)

    Hilton, J.; Fals, H. C.; Trevisan, R. E.

    2009-01-01

    The susceptibility to hydrogen-induced cracking in H 2 S environment of welded API X80 steel was studied. The flux cored arc welding (FCAW) process was employed with E71-T1 and E71-T8K6 wires. The welding parameters were kept constant, but the samples were welded using different preheat temperatures (room temperature and 100 degree centigrade). The gapped bead-on-plate (G-BOP) test was used. The specimens of modified G-BOP tests were exposed to an environment saturated in H 2 S, as recommended by the NACE TM0284 standard. The weld beads were characterized by optical microscopy and the level of residual hydrogen in the samples was measured. The fracture surface areas of hydrogen-induced cracking were calculated and the fracture mode was discussed. It was found that the preheating temperature of 100 degree centigrade was enough to avoid cracking, even in the presence of H 2 S. It was also found that the E71- T8K6 wire was more susceptible to cracking, and the typical mixed-mode fracture was predominant in all samples. (Author) 15 refs

  15. Crack embryo formation before crack initiation and growth in high temperature water

    International Nuclear Information System (INIS)

    Arioka, Koji; Yamada, Takuyo; Terachi, Takumi; Miyamoto, Tomoki

    2008-01-01

    Crack growth measurements were performed in high temperature water and in air to examine the role of creep on IGSCC growth using cold rolled non-sensitized Type316(UNS S31600), TT690 alloy, MA600 alloy, and Carbon steel (STPT42). In addition, crack initiation tests were performed also in high temperature water and in air using specially designed CT specimen. The obtained major results are as follows: (1) TT690 did crack in intergranularly in hydrogenated high temperature water if material is cold worked in heavily. (2) Cold worked carbon steel also cracked in intergranularly in dearated high temperature water. (3) Intergranular crack growth was recognized on cold worked 316, TT690, MA600, and carbon steel even in air which might be crack embryo of IGSCC. (4) Simple Arrhenius type temperature dependence was observed on IGSCC in high temperature water and creep crack growth in air. This suggested that intergranular crack growth rate was determined by some thermal activated reaction. (5) Vacancy condensation was recognized at just ahead of the crack tips of IGSCC and creep crack of cold worked steel. This showed that IGSCC and creep crack growth was controlled by same mechanism. (6) Clear evidence of vacancies condensation was recognized at just beneath the surface before crack initiation. This proved that crack did initiate as the result of diffusion of vacancies in the solid. And the incubation time seems to be controlled by the required time for the condensation of vacancies to the stress concentrated zone. (7) Diffusion of subsituational atoms was also driven by stress gradient. This is the important knowledge to evaluate the SCC initiation after long term operation in LWR's. Based on the observed results, IGSCC initiation and growth mechanism were proposed considering the diffusion process of cold worked induced vacancies. (author)

  16. Stress corrosion cracking of copper canisters

    Energy Technology Data Exchange (ETDEWEB)

    King, Fraser (Integrity Corrosion Consulting Limited (Canada)); Newman, Roger (Univ. of Toronto (Canada))

    2010-12-15

    A critical review is presented of the possibility of stress corrosion cracking (SCC) of copper canisters in a deep geological repository in the Fennoscandian Shield. Each of the four main mechanisms proposed for the SCC of pure copper are reviewed and the required conditions for cracking compared with the expected environmental and mechanical loading conditions within the repository. Other possible mechanisms are also considered, as are recent studies specifically directed towards the SCC of copper canisters. The aim of the review is to determine if and when during the evolution of the repository environment copper canisters might be susceptible to SCC. Mechanisms that require a degree of oxidation or dissolution are only possible whilst oxidant is present in the repository and then only if other environmental and mechanical loading conditions are satisfied. These constraints are found to limit the period during which the canisters could be susceptible to cracking via film rupture (slip dissolution) or tarnish rupture mechanisms to the first few years after deposition of the canisters, at which time there will be insufficient SCC agent (ammonia, acetate, or nitrite) to support cracking. During the anaerobic phase, the supply of sulphide ions to the free surface will be transport limited by diffusion through the highly compacted bentonite. Therefore, no HS. will enter the crack and cracking by either of these mechanisms during the long term anaerobic phase is not feasible. Cracking via the film-induced cleavage mechanism requires a surface film of specific properties, most often associated with a nano porous structure. Slow rates of dissolution characteristic of processes in the repository will tend to coarsen any nano porous layer. Under some circumstances, a cuprous oxide film could support film-induced cleavage, but there is no evidence that this mechanism would operate in the presence of sulphide during the long-term anaerobic period because copper sulphide

  17. Stress corrosion cracking of copper canisters

    International Nuclear Information System (INIS)

    King, Fraser; Newman, Roger

    2010-12-01

    A critical review is presented of the possibility of stress corrosion cracking (SCC) of copper canisters in a deep geological repository in the Fennoscandian Shield. Each of the four main mechanisms proposed for the SCC of pure copper are reviewed and the required conditions for cracking compared with the expected environmental and mechanical loading conditions within the repository. Other possible mechanisms are also considered, as are recent studies specifically directed towards the SCC of copper canisters. The aim of the review is to determine if and when during the evolution of the repository environment copper canisters might be susceptible to SCC. Mechanisms that require a degree of oxidation or dissolution are only possible whilst oxidant is present in the repository and then only if other environmental and mechanical loading conditions are satisfied. These constraints are found to limit the period during which the canisters could be susceptible to cracking via film rupture (slip dissolution) or tarnish rupture mechanisms to the first few years after deposition of the canisters, at which time there will be insufficient SCC agent (ammonia, acetate, or nitrite) to support cracking. During the anaerobic phase, the supply of sulphide ions to the free surface will be transport limited by diffusion through the highly compacted bentonite. Therefore, no HS. will enter the crack and cracking by either of these mechanisms during the long term anaerobic phase is not feasible. Cracking via the film-induced cleavage mechanism requires a surface film of specific properties, most often associated with a nano porous structure. Slow rates of dissolution characteristic of processes in the repository will tend to coarsen any nano porous layer. Under some circumstances, a cuprous oxide film could support film-induced cleavage, but there is no evidence that this mechanism would operate in the presence of sulphide during the long-term anaerobic period because copper sulphide

  18. Mechanism of crack initiation and crack growth under thermal and mechanical fatigue loading

    Energy Technology Data Exchange (ETDEWEB)

    Utz, S.; Soppa, E.; Silcher, H.; Kohler, C. [Stuttgart Univ. (Germany). Materials Testing Inst.

    2013-07-01

    The present contribution is focused on the experimental investigations and numerical simulations of the deformation behaviour and crack development in the austenitic stainless steel X6CrNiNb18-10 under thermal and mechanical cyclic loading in HCF and LCF regimes. The main objective of this research is the understanding of the basic mechanisms of fatigue damage and the development of simulation methods, which can be applied further in safety evaluations of nuclear power plant components. In this context the modelling of crack initiation and crack growth inside the material structure induced by varying thermal or mechanical loads are of particular interest. The mechanisms of crack initiation depend among other things on the type of loading, microstructure, material properties and temperature. The Nb-stabilized austenitic stainless steel in the solution-annealed condition was chosen for the investigations. Experiments with two kinds of cyclic loading - pure thermal and pure mechanical - were carried out and simulated. The fatigue behaviour of the steel X6CrNiNb18-10 under thermal loading was studied within the framework of the joint research project [4]. Interrupted thermal cyclic tests in the temperature range of 150 C to 300 C combined with non-destructive residual stress measurements (XRD) and various microscopic investigations, e.g. in SEM (Scanning Electron Microscope), were used to study the effects of thermal cyclic loading on the material. This thermal cyclic loading leads to thermal induced stresses and strains. As a result intrusions and extrusions appear inside the grains (at the surface), at which microcracks arise and evolve to a dominant crack. Finally, these microcracks cause a continuous and significant decrease of residual stresses. The fatigue behaviour of the steel X6CrNiNb18-10 under mechanical loading at room temperature was studied within the framework of the research project [5], [8]. With a combination of interrupted LCF tests and EBSD

  19. Mechanism of crack initiation and crack growth under thermal and mechanical fatigue loading

    International Nuclear Information System (INIS)

    Utz, S.; Soppa, E.; Silcher, H.; Kohler, C.

    2013-01-01

    The present contribution is focused on the experimental investigations and numerical simulations of the deformation behaviour and crack development in the austenitic stainless steel X6CrNiNb18-10 under thermal and mechanical cyclic loading in HCF and LCF regimes. The main objective of this research is the understanding of the basic mechanisms of fatigue damage and the development of simulation methods, which can be applied further in safety evaluations of nuclear power plant components. In this context the modelling of crack initiation and crack growth inside the material structure induced by varying thermal or mechanical loads are of particular interest. The mechanisms of crack initiation depend among other things on the type of loading, microstructure, material properties and temperature. The Nb-stabilized austenitic stainless steel in the solution-annealed condition was chosen for the investigations. Experiments with two kinds of cyclic loading - pure thermal and pure mechanical - were carried out and simulated. The fatigue behaviour of the steel X6CrNiNb18-10 under thermal loading was studied within the framework of the joint research project [4]. Interrupted thermal cyclic tests in the temperature range of 150 C to 300 C combined with non-destructive residual stress measurements (XRD) and various microscopic investigations, e.g. in SEM (Scanning Electron Microscope), were used to study the effects of thermal cyclic loading on the material. This thermal cyclic loading leads to thermal induced stresses and strains. As a result intrusions and extrusions appear inside the grains (at the surface), at which microcracks arise and evolve to a dominant crack. Finally, these microcracks cause a continuous and significant decrease of residual stresses. The fatigue behaviour of the steel X6CrNiNb18-10 under mechanical loading at room temperature was studied within the framework of the research project [5], [8]. With a combination of interrupted LCF tests and EBSD

  20. Refinement and evaluation of crack-opening-area analyses for circumferential through-wall cracks in pipes

    International Nuclear Information System (INIS)

    Rahman, S.; Brust, F.; Ghadiali, N.; Krishnaswamy, P.; Wilkowski, G.; Choi, Y.H.; Moberg, F.; Brickstad, B.

    1995-04-01

    Leak-before-break (LBB) analyses for circumferentially cracked pipes are currently being conducted in the nuclear industry to justify elimination of pipe whip restraints and jet impingement shields which are present because of the expected dynamic effects from pipe rupture. The application of the LBB methodology frequently requires calculation of leak rates. These leak rates depend on the crack-opening area of a through-wall crack in the pipe. In addition to LBB analyses, which assume a hypothetical flaw size, there is also interest in the integrity of actual leaking cracks corresponding to current leakage detection requirements in NRC Regulatory Guide 1.45, or for assessing temporary repair of Class 2 and 3 pipes that have leaks as are being evaluated in ASME Section 11. This study was requested by the NRC to review, evaluate, and refine current analytical models for crack-opening-area analyses of pipes with circumferential through-wall cracks. Twenty-five pipe experiments were analyzed to determine the accuracy of the predictive models. Several practical aspects of crack-opening such as; crack-face pressure, off-center cracks, restraint of pressure-induced bending, cracks in thickness transition regions, weld residual stresses, crack-morphology models, and thermal-hydraulic analysis, were also investigated. 140 refs., 105 figs., 41 tabs

  1. Noncontact fatigue crack evaluation using thermoelastic

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ji Min; An, Yun Kyu; Sohn, Hoon [KAIST, Daejeon (Korea, Republic of)

    2012-12-15

    This paper proposes a noncontact thermography technique for fatigue crack evaluation under a cyclic tensile loading. The proposed technique identifies and localizes an invisible fatigue crack without scanning, thus making it possible to instantaneously evaluate an incipient fatigue crack. Based on a thermoelastic theory, a new fatigue crack evaluation algorithm is proposed for the fatigue crack tip localization. The performance of the proposed algorithm is experimentally validated. To achieve this, the cyclic tensile loading is applied to a dog bone shape aluminum specimen using a universal testing machine, and the corresponding thermal responses induced by thermoelastic effects are captured by an infrared camera. The test results confirm that the fatigue crack is well identified and localized by comparing with its microscopic images.

  2. Predicting crack instability behavior of burst tests from small specimens for irradiated Zr-2.5Nb pressure tubes

    International Nuclear Information System (INIS)

    Davies, P.H.

    1997-01-01

    A scaling approach, based on the deformation J-integral at maximum load obtained from small specimens, is proposed for predicting the crack instability behavior of burst tests on irradiated Zr-2.5Nb pressure tubes. An assessment of this approach is carried out by comparison with other toughness criteria such as the modified J-integral and the plastic work dissipation rate approach. The largest discrepancy between the different parameters occurs for materials of intermediate toughness which exhibit the most stable crack growth and tunnelling up to maximum load. A study of one material of intermediate toughness suggests crack-front tunnelling has a significant influence on the results obtained from the 17-mm-wide specimens. It is shown that for a tube of intermediate toughness the different approaches can significantly underpredict the extent of stable crack growth before instability in a burst test even after correcting for tunnelling. The usefulness of a scaling approach in reducing the discrepancy between the small- and large-scale specimen results for this material is demonstrated

  3. Observations on Hydride Structures at the Tip of Arrested Cracks Grown under Conditions of Delayed Hydride Cracking

    International Nuclear Information System (INIS)

    Pettersson, Kjell; Oskarsson, Magnus; Bergqvist, Hans

    2003-04-01

    One sample of Zr2.5%Nb and one sample of cold worked and stress relieved Zircaloy-4 which have been tested for hydrogen induced crack growth have been examined in the crack tip region with the aim of determining the mechanism behind the growth of cracks. The proposed mechanisms are brittle failure of a crack tip hydride and hydrogen enhanced localized shear. The examinations were done by TEM and SEM. However attempts to produce a TEM specimen with a thinned region at the tip of the crack were unsuccessful in both samples. One feature observed in the Zr2.5%Nb material may however be an indication of intense shear deformation at the tip of the crack. On the other hand all observations on the Zircaloy-4 sample indicate precipitation of hydrides ahead of the crack tip and the presence of hydrides on the crack flanks

  4. Induction and comparison of craving for tobacco, marijuana and crack

    Directory of Open Access Journals (Sweden)

    Renata Brasil Araujo

    2015-10-01

    Full Text Available Abstract Background The literature findings report that use of multiple substances can produce adverse clinical and behavioral effects, which may affect craving and the results of drug treatment. Also, the understanding of craving construct and its interaction in the use of smoked substances is underexplored. Objectives To induce and compare craving for tobacco, marijuana and crack-cocaine on hospitalized dependents whose drug of choice is crack-cocaine. Methods Quasi-experimental study with a convenience sample consisting of 210 males divided into 3 equal groups (Group-1: craving induced by crack; Group-2: craving induced by tobacco; and Group-3: craving induced by marijuana. All participants met ICD-10 dependence criteria for cocaine/crack, marijuana and tobacco, were aged between 18 and 65 and had used these substances for at least one year. Photos were used to induce craving and self-report instruments to evaluate possible alterations. Results This study showed that craving for tobacco was more intense than for marijuana and crack, when the groups were compared by VAS. Using specific scales, both craving for tobacco and craving for marijuana were more intense than craving for crack. Discussion These results would imply interventions at the initial stages of abstinence with cognitive-behavioural techniques and pharmacotherapy in order to reduce craving.

  5. Oxidation-induced crack healing in Ti3AlC2 ceramics

    NARCIS (Netherlands)

    Song, G.M.; Pei, Y.T.; Sloof, W.G.; Li, S.B.; Hosson, J.Th.M. De; Zwaag, S. van der

    Crack healing of Ti3AlC2 was investigated by oxidizing a partially pre-cracked sample. A crack near a notch was introduced into the sample by tensile deformation. After oxidation at 1100 degrees C in air for 2 h, the crack was completely healed, with oxidation products consisting primarily of

  6. Effect of residual stress induced by cold expansion on fatigue crack ...

    African Journals Online (AJOL)

    Fatigue life and fatigue crack growth rate are controlled by stress ratio, stress level, orientation of crack, temper-ature, residual stress, corrosion, etc. The effects of residual stress on fatigue crack growth in aluminium (Al) alloy 2024-T351 by Mode I crack were investigated by applying constant amplitude cycles based on ...

  7. Crack Growth Monitoring by Embedded Optical Fibre Bragg Grating Sensors: Fibre Reinforced Plastic Crack Growing Detection

    DEFF Research Database (Denmark)

    Pereira, Gilmar Ferreira; Mikkelsen, Lars Pilgaard; McGugan, Malcolm

    2015-01-01

    This article presents a novel method to asses a crack growing/damage event in fibre reinforced plastic, or adhesive using Fibre Bragg Grating (FBG) sensors embedded in a host material. Different features of the crack mechanism that induce a change in the FBG response were identified. Double Canti...

  8. Thermally-Induced Crack Evaluation in H13 Tool Steel

    Directory of Open Access Journals (Sweden)

    Hassan Abdulrssoul Abdulhadi

    2017-11-01

    Full Text Available This study reported the effect of thermal wear on cylindrical tool steel (AISI H13 under aluminum die-casting conditions. The AISIH13 steels were immersed in the molten aluminum alloy at 700 °C before water-quenching at room temperature. The process involved an alternating heating and cooling of each sample for a period of 24 s. The design of the immersion test apparatus stylistically simulated aluminum alloy dies casting conditions. The testing phase was performed at 1850, 3000, and 5000 cycles. The samples were subjected to visual inspection after each phase of testing, before being examined for metallographic studies, surface crack measurement, and hardness characteristics. Furthermore, the samples were segmented and examined under optical and Scanning Electron Microscopy (SEM. The areas around the crack zones were additionally examined under Energy Dispersive X-ray Spectroscopy (EDXS. The crack’s maximum length and Vickers hardness profiles were obtained; and from the metallographic study, an increase in the number of cycles during the testing phase resulted in an increase in the surface crack formation; suggesting an increase in the thermal stress at higher cycle numbers. The crack length of Region I (spherically shaped was about 47 to 127 µm, with a high oxygen content that was analyzed within 140 µm from the surface of the sample. At 700 °C, there is a formation of aluminum oxides, which was in contact with the surface of the H13 sample. These stresses propagate the thermal wear crack length into the tool material of spherically shaped Region I and cylindrically shape Region II, while hardness parameters presented a different observation. The crack length of Region I was about 32% higher than the crack length of Region II.

  9. Intermediate size inducer pump - structural analysis and transient deformation studies

    International Nuclear Information System (INIS)

    Cheng, T.K.; Nishizaka, J.N.

    1979-05-01

    This report summarizes the structural and thermal transient deformation analysis of the Intermediate Size Inducer Pump. The analyses were performed in accordance to the requirements of N266ST310001, the specification for the ISIP. Results of stress analysis indicate that the thermal transient stress and strain are within the stress strain limits of RDT standard F9-4 which was used as a guide

  10. Effect of heat treatment upon the fatigue-crack growth behavior of Alloy 718 weldments

    International Nuclear Information System (INIS)

    Mills, W.J.; James, L.A.

    1981-05-01

    The microstructural features that influenced the room and elevated temperature fatigue-crack growth behavior of as-welded, conventional heat-treated, and modified heat-treated Alloy 718 GTA weldments were studied. Electron fractographic examination of fatigue fracture surfaces revealed that operative fatigue mechanisms were dependent on microstructure, temperatures and stress intensity factor. All specimens exhibited three basic fracture surface appearances at temperatures up to 538 degrees C: crystallographic faceting at low stress intensity range (ΔK) levels, striation, formation at intermediate values, and dimples coupled with striations in the highest (ΔK) regime. At 649 degrees C, the heat-treated welds exhibited extensive intergranular cracking. Laves and δ particles in the conventional heat-treated material nucleated microvoids ahead of the advancing crack front and caused on overall acceleration in crack growth rates at intermediate and high ΔK levels. The modified heat treatment removed many of these particles from the weld zone, thereby improving its fatigue resistance. The dramatically improved fatigue properties exhibited by the as-welded material was attributed to compressive residual stresses introduced by the welding process. 19 refs., 16 figs

  11. Chloride Penetration through Cracks in High-Performance Concrete and Surface Treatment System for Crack Healing

    Directory of Open Access Journals (Sweden)

    In-Seok Yoon

    2012-01-01

    Full Text Available For enhancing the service life of concrete structures, it is very important to minimize crack at surface. Even if these cracks are very small, the problem is to which extend these cracks may jeopardize the durability of these decks. It was proposed that crack depth corresponding with critical crack width from the surface is a crucial factor in view of durability design of concrete structures. It was necessary to deal with chloride penetration through microcracks characterized with the mixing features of concrete. This study is devoted to examine the effect of high strength concrete and reinforcement of steel fiber on chloride penetration through cracks. High strength concrete is regarded as an excellent barrier to resist chloride penetration. However, durability performance of cracked high strength concrete was reduced seriously up to that of ordinary cracked concrete. Steel fiber reinforcement is effective to reduce chloride penetration through cracks because steel fiber reinforcement can lead to reduce crack depth significantly. Meanwhile, surface treatment systems are put on the surface of the concrete in order to seal the concrete. The key-issue is to which extend a sealing is able to ensure that chloride-induced corrosion can be prevented. As a result, penetrant cannot cure cracks, however, coating and combined treatment can prevent chloride from flowing in concrete with maximum crack width of 0.06 mm and 0.08 mm, respectively.

  12. Role of hydrogen in stress corrosion cracking

    International Nuclear Information System (INIS)

    Mehta, M.L.

    1981-01-01

    Electrochemical basis for differentiation between hydrogen embrittlement and active path corrosion or anodic dissolution crack growth mechanisms is examined. The consequences of recently demonstrated acidification in crack tip region irrespective of electrochemical conditions at the bulk surface of the sample are that the hydrogen can evolve within the crack and may be involved in the cracking process. There are basically three aspects of hydrogen involvement in stress corrosion cracking. In dissolution models crack propagation is assumed to be caused by anodic dissolution on the crack tip sustained by cathodic reduction of hydrogen from electrolyte within the crack. In hydrogen induced structural transformation models it is postulated that hydrogen is absorbed locally at the crack tip producing structural changes which facilitate crack propagation. In hydrogen embrittlement models hydrogen is absorbed by stressed metal from proton reduction from the electrolyte within the crack and there is interaction between lattice and hydrogen resulting in embrittlement of material at crack tip facilitating crack propagation. In the present paper, the role of hydrogen in stress corrosion crack growth in high strength steels, austenitic stainless steels, titanium alloys and high strength aluminium alloys is discussed. (author)

  13. Capillary-induced crack healing between surfaces of nanoscale roughness.

    Science.gov (United States)

    Soylemez, Emrecan; de Boer, Maarten P

    2014-10-07

    Capillary forces are important in nature (granular materials, insect locomotion) and in technology (disk drives, adhesion). Although well studied in equilibrium state, the dynamics of capillary formation merit further investigation. Here, we show that microcantilever crack healing experiments are a viable experimental technique for investigating the influence of capillary nucleation on crack healing between rough surfaces. The average crack healing velocity, v̅, between clean hydrophilic polycrystalline silicon surfaces of nanoscale roughness is measured. A plot of v̅ versus energy release rate, G, reveals log-linear behavior, while the slope |d[log(v̅)]/dG| decreases with increasing relative humidity. A simplified interface model that accounts for the nucleation time of water bridges by an activated process is developed to gain insight into the crack healing trends. This methodology enables us to gain insight into capillary bridge dynamics, with a goal of attaining a predictive capability for this important microelectromechanical systems (MEMS) reliability failure mechanism.

  14. Electromigration-induced cracks in Cu/Sn3.5Ag/Cu solder reaction couple at room temperature

    International Nuclear Information System (INIS)

    He Hongwen; Xu Guangchen; Guo Fu

    2009-01-01

    Electromigration (EM) behavior of Cu/Sn 3.5 Ag/Cu solder reaction couple was investigated with a high current density of 5 x 10 3 A/cm 2 at room temperature. One dimensional structure, copper wire/solder ball/copper wire SRC was designed and fabricated to dissipate the Joule heating induced by the current flow. In addition, thermomigration effect was excluded due to the symmetrical structure of the SRC. The experimental results indicated that micro-cracks initially appeared near the cathode interface between solder matrix and copper substrate after 474 h current stressing. With current stressing time increased, the cracks propagated and extended along the cathode interface. It should be noted that the continuous Cu 6 Sn 5 intermetallic compounds (IMCs) layer both at the anode and at the cathode remained their sizes. Interestingly, tiny cracks appeared at the root of some long column-type Cu 6 Sn 5 at the cathode interface due to the thermal stress.

  15. A non-destructive test method to monitor corrosion products and corrosion-induced cracking in reinforced cement based materials

    DEFF Research Database (Denmark)

    Michel, Alexander; Pease, Bradley Justin; Peterova, Adela

    2011-01-01

    ) was conducted to describe the impact of water-to-cement ratio and corrosion current density (i.e., corrosion rate) on the reinforcement corrosion process. Focus was placed, in particular on the determination of the corrosion accommodating region (CAR) and time to corrosion-induced cracking. Experimental results...... showed that x-ray attenuation measurements allow determination of the actual concentrations of corrosion products averaged through the specimen thickness. The total mass loss of steel measured by x-ray attenuation was found to be in very good agreement with the calculated mass loss obtained by Faraday......’s law. Furthermore, experimental results demonstrated that the depth of penetration of corrosion products as well as time to corrosion-induced cracking is varying for the different water-to-cement ratios and applied corrosion current densities....

  16. Catastrophic failures due to environment-assisted cracking of metals: Case histories

    International Nuclear Information System (INIS)

    Shipilov, S.A.

    1999-01-01

    One of the most serious problems in development of reliable equipment and structures in numerous major industries, namely a problem of the environment-assisted cracking of engineering materials, has been reviewed. This problem is directly related to the problems of maintenance of the safety and reliability of potentially dangerous engineering systems, such as nuclear power plants, fossil fuel power plants, oil and gas pipelines, field equipment, oil production platforms, aircraft and aerospace technologies, chemical plants, etc. At present, environment-assisted cracking, including stress corrosion cracking, corrosion fatigue, hydrogen-induced cracking, hydrogen embrittlement, sulfide stress cracking, irradiation-assisted stress corrosion cracking, and metal-induced embrittlement, has been a major cause of the premature failures of various components and equipment in these systems. (author)

  17. Development of a novel non-contact inspection technique to detect micro cracks under the surface of a glass substrate by thermal stress-induced light scattering method

    Science.gov (United States)

    Sakata, Yoshitaro; Terasaki, Nao; Nonaka, Kazuhiro

    2017-05-01

    Fine polishing techniques, such as a chemical mechanical polishing treatment, are important techniques in glass substrate manufacturing. However, these techniques may cause micro cracks under the surface of glass substrates because they used mechanical friction. A stress-induced light scattering method (SILSM), which was combined with light scattering method and mechanical stress effects, was proposed for inspecting surfaces to detect polishing-induced micro cracks. However, in the conventional SILSM, samples need to be loaded with physical contact, and the loading point is invisible in transparent materials. Here, we introduced a novel non-contact SILSM using a heating device. A glass substrate was heated first, and then the light scattering intensity of micro cracks was detected by a cooled charge-couple device camera during the natural cooling process. Results clearly showed during the decreasing surface temperature of a glass substrate, appropriate thermal stress is generated for detecting micro cracks by using the SILSM and light scattering intensity from micro cracks changes. We confirmed that non-contact thermal SILSM (T-SILSM) can detect micro cracks under the surface of transparent materials.

  18. Multifragmentation in intermediate energy 129Xe-induced heavy-ion reactions

    International Nuclear Information System (INIS)

    Tso, Kin.

    1996-05-01

    The 129 Xe-induced reactions on nat Cu, 89 Y, 165 Ho, and 197 Au at bombarding energies of E/A = 40 ampersand 60 MeV have been studied theoretically and experimentally in order to establish the underlying mechanism of multifragmentation at intermediate energy heavy-Ion collisions. Nuclear disks formed in central heavy-ion collisions, as simulated by means of Boltzmann-like kinetic equations, break up into several fragments due to a new kind of Rayleigh-like surface instability. A sheet of liquid, stable in the limit of non-interacting surfaces, is shown to become unstable due to surface-surface interactions. The onset of this instability is determined analytically. A thin bubble behaves like a sheet and is susceptible to the surface instability through the crispation mode. The Coulomb effects associated with the depletion of charges in the central cavity of nuclear bubbles are investigated. The onset of Coulomb instability is demonstrated for perturbations of the radial mode. Experimental intermediate-mass-fragment multiplicity distributions for the 129 Xe-induced reactions are shown to be binomial at each transverse energy. From these distributions, independent of the specific target, an elementary binary decay probability p can be extracted that has a thermal dependence. Thus it is inferred that multifragmentation is reducible to a combination of nearly independent emission processes. If sequential decay is assumed, the increase of p with transverse energy implies a contraction of the emission time scale. The sensitivity of p to the lower Z threshold in the definition of intermediate-mass-fragments points to a physical Poisson simulations of the particle multiplicities show that the weak auto-correlation between the fragment multiplicity and the transverse energy does not distort a Poisson distribution into a binomial distribution. The effect of device efficiency on the experimental results has also been studied

  19. A study on fatigue crack growth behavior subjected to a single tensile overload

    International Nuclear Information System (INIS)

    Lee, S.Y.; Liaw, P.K.; Choo, H.; Rogge, R.B.

    2011-01-01

    Neutron diffraction and electric potential experiments were carried out to investigate the growth behavior of a fatigue crack subjected to a single tensile overload. The specific objectives were to (i) probe the crack tip deformation and fracture behaviors under applied loads; (ii) examine the overload-induced transient crack growth micromechanism; (iii) validate the effective stress intensity factor range based on the crack closure approach as the fatigue crack tip driving force; and (iv) establish a quantitative relationship between the crack tip driving force and crack growth behavior. Immediately after a single tensile overload was introduced and then unloaded, the crack tip became blunt and enlarged compressive residual stresses in both magnitude and zone size were observed around the crack tip. The results show that the combined contributions of the overload-induced enlarged compressive residual stresses and crack tip blunting with secondary cracks are responsible for the observed changes in the crack opening load and the resultant post-overload transient crack growth behavior.

  20. Small-angle X-ray scattering studies of metastable intermediates of beta-lactoglobulin isolated after heat-induced aggregation

    DEFF Research Database (Denmark)

    Carrotta, R.; Arleth, L.; Pedersen, J.S.

    2003-01-01

    Small-angle x-ray scattering was used for studying intermediate species, isolated after heat-induced aggregation of the A variant of bovine P-lactoglobulin. The intermediates were separated in two fractions, the heated metastable dimer and heated metastable oligomers larger than the dimer. The pa...

  1. Near-IR imaging of cracks in teeth

    Science.gov (United States)

    Fried, William A.; Simon, Jacob C.; Lucas, Seth; Chan, Kenneth H.; Darling, Cynthia L.; Staninec, Michal; Fried, Daniel

    2014-02-01

    Dental enamel is highly transparent at near-IR wavelengths and several studies have shown that these wavelengths are well suited for optical transillumination for the detection and imaging of tooth decay. We hypothesize that these wavelengths are also well suited for imaging cracks in teeth. Extracted teeth with suspected cracks were imaged at several wavelengths in the near-IR from 1300-1700-nm. Extracted teeth were also examined with optical coherence tomography to confirm the existence of suspected cracks. Several teeth of volunteers were also imaged in vivo at 1300-nm to demonstrate clinical potential. In addition we induced cracks in teeth using a carbon dioxide laser and imaged crack formation and propagation in real time using near-IR transillumination. Cracks were clearly visible using near-IR imaging at 1300-nm in both in vitro and in vivo images. Cracks and fractures also interfered with light propagation in the tooth aiding in crack identification and assessment of depth and severity.

  2. Sub-10-micrometer toughening and crack tip toughness of dental enamel

    OpenAIRE

    Ang, Siang Fung; Schulz, Anja; Pacher Fernandes, Rodrigo; Schneider, Gerold A.

    2011-01-01

    In previous studies, enamel showed indications to occlude small cracks in-vivo and exhibited R-curve behaviors for bigger cracks ex-vivo. This study quantifies the crack tip toughness (KI0, KIII0), the crack closure stress and the cohesive zone size at the crack tip of enamel and investigates the toughening mechanisms near the crack tip down to the length scale of a single enamel crystallite. The crack-opening-displacement (COD) profile of cracks induced by Vickers indents on mature bovine en...

  3. Evaluation on effects of chloride-induced deterioration on mechanical properties of RC beams with cracking damage

    International Nuclear Information System (INIS)

    Matsuo, Toyofumi; Matsumura, Takuro; Otsuka, Taku

    2015-01-01

    This paper discusses the influence of chloride-induced deterioration on mechanical properties of aging reinforced concrete (RC) structures and the applicability of the material degradation model that takes reinforcing steel corrosion into consideration for finite element analysis. We conducted the corrosion tests under the simulated tidal environment and the flexural loading tests for the RC beams with cracking damage and initial defects. Then, the experimental results were numerically correlated to validate the devised modeling. The obtained results were summarized as follows: (a) The cracking damage in specimens caused a minor effect on the reinforcing steel corrosion in the case where the thickness of cover concrete was 40 mm and main rebars did not yield before chloride attack. On the other hand the maximum corrosion ratio of the deteriorated part became considerably larger than that of the non-cracking part in the specimens where the cover concrete were removed partially to simulate spalling by the severe corrosion. (b) Based on the test results, we derived the corrosion velocity of reinforcing steel corresponding to cracking damage degrees. (c) In FEM analyses, we showed that the above modeling can estimate the flexural strength of RC beams in consideration of the degradation in elongation performance of reinforcing steel due to corrosion. (author)

  4. GdnHCl-induced unfolding intermediate in the mitochondrial carbonic anhydrase VA.

    Science.gov (United States)

    Idrees, Danish; Prakash, Amresh; Haque, Md Anzarul; Islam, Asimul; Hassan, Md Imtaiyaz; Ahmad, Faizan

    2016-10-01

    Carbonic anhydrase VA (CAVA) is a mitochondrial enzyme belonging to the α-family of CAs, which is involved in several physiological processes including ureagenesis, lipogenesis, gluconeogenesis and neuronal transmission. Here, we have tried to understand the folding mechanism of CAVA using guanidine hydrochloride (GdnHCl)-induced denaturation at pH 8.0 and 25°C. The conformational stability was measured from the GdnHCl-induced denaturation study of CAVA monitored by circular dichroism (CD) and fluorescence measurements. On increasing the concentration of GdnHCl up to 5.0, a stable intermediate was observed between the concentrations 3.25M to 3.40M of the denaturant. However, CAVA gets completely denatured at 4.0M GdnHCl. The existence of a stable intermediate state was validated by 1-anilinonaphthalene-8-sulfonic acid (ANS binding) fluorescence and near-UV CD measurements. In silico studies were also performed to analyse the effect of GdnHCl on the structure and stability of CAVA under explicit conditions. Molecular dynamics simulations for 40ns were carried out and a well-defined correlation was established for both in vitro and in silico studies. Copyright © 2016 Elsevier B.V. All rights reserved.

  5. Effect of plastic prestrain on the crack tip constraint of pipeline steels

    International Nuclear Information System (INIS)

    Eikrem, P.A.; Zhang, Z.L.; Nyhus, B.

    2007-01-01

    Before and during operation, pipelines may suffer from plastic pre-deformation due to accidental loading, cold bending and ground movement. Plastic prestrain not only modifies steel's yield and flow properties but also influences its fracture performance. This paper focuses on the effect of prestrain history on crack driving force and crack tip constraint. A single-edge notched tension specimen has been selected for the study and the crack is assumed to exist before a prestrain history was applied. The results show that prestrain history has a strong effect on the crack tip stress field. A new parameter has been proposed to characterize the prestrain-induced crack tip constraint. For the same crack tip opening displacement level, prestrain history will elevate the crack tip stress field. The prestrain-induced constraint decreases with the increase of loading

  6. The influence of cracks on chloride-induced corrosion of reinforced concrete structures - development of the experimental set-up

    NARCIS (Netherlands)

    Blagojevic, A.; Koleva, D.A.; Walraven, J.C.

    2014-01-01

    Chloride-induced corrosion of steel reinforcement is one of the major threats to durability of reinforced concrete structures in aggressive environmental conditions. When the steel reinforcement starts to corrode, structures gradually lose integrity and service life is shortened. Cracks are

  7. Hydrogen induced cold cracking studies on armour grade high strength, quenched and tempered steel weldments

    Energy Technology Data Exchange (ETDEWEB)

    Magudeeswaran, G.; Balasubramanian, V. [Centre for Materials Joining Research (CEMAJOR), Department of Manufacturing Engineering, Annamalai University, Annamalai Nagar 608 002, Tamil Nadu (India); Madhusudhan Reddy, G. [Metal Joining Section, Defence Metallurgical Research Laboratory (DMRL), Kanchanbagh (P.O.) Hyderabad 560 058 Andhra Pradesh (India)

    2008-04-15

    Quenched and tempered (Q and T) steels are prone to hydrogen induced cracking (HIC) in the heat affected zone after welding. The use of austenitic stainless steel (ASS) consumables to weld the above steel was the only available remedy because of higher solubility for hydrogen in austenitic phase. The use of stainless steel consumables for a non-stainless steel base metal is not economical. Hence, alternate consumables for welding Q and T steels and their vulnerability to HIC need to be explored. Recent studies proved that low hydrogen ferritic (LHF) steel consumables can be used to weld Q and T steels, which can give very low hydrogen levels in the weld deposits. In this investigation an attempt has been made to study the influence of welding consumables and welding processes on hydrogen induced cold cracking of armour grade Q and T steel welds by implant testing. Shielded metal arc welding (SMAW) and flux cored arc welding (FCAW) processes were used for making welds using ASS and LHF welding consumables. ASS welds made using FCAW process offered a higher resistance to HIC than all other welds considered in this investigation. (author)

  8. Thermal hydraulic conditions inducing incipient cracking in the 900 MWe unit 93 D reactor coolant pump shafts

    International Nuclear Information System (INIS)

    Bore, C.

    1995-01-01

    From 1987, 900 MWe plant operating feedback revealed cracking in the lower part of the reactor coolant pump shafts, beneath the thermal ring. Metallurgical examinations established that this was due to a thermal fatigue phenomenon known as thermal crazing, occurring after a large number of cycles. Analysis of thermal hydraulic conditions initiating the cracks does not allow exact quantification of the thermal load inducing cracking. Only qualitative analyses are thus possible, the first of which, undertaken by the pump manufacturer, Jeumont Industrie, showed that the cracks could not be due to the major transients (stop-start, injection cut-off), which were too few in number. Another explanation was then put forward: the thermal ring, shrunk onto the shaft it is required to protect against thermal shocks, loosens to allow an alternating downflow of cold water from the shaft seals and an upflow of hot water from the primary system. However, approximate calculations showed that the flow involved would be too slight to initiate the cracking observed. A more stringent analysis undertaken with the 2D flow analysis code MELODIE subsequently refuted the possibility of alternating flows beneath the ring establishing that only a hot water upflow occurred due to a 'viscosity pump' phenomenon. Crack initiation was finally considered to be due to flowrate variations beneath the ring, with the associated temperature fluctuations. This flowrate fluctuation could be due to an unidentified transient phenomenon or to a variation in pump operating conditions. This analysis of the hydraulic conditions initiating the cracks disregards shaft surface residual stresses. These are tensile stresses and show that loads less penalizing than those initially retained could cause incipient cracking. Thermal ring modifications to reduce these risks were proposed and implemented. In addition, final metallurgical treatment of the shafts was altered and implemented. In addition, final metallurgical

  9. On light cluster production in nucleon induced reactions at intermediate energy

    Energy Technology Data Exchange (ETDEWEB)

    Lacroix, D.; Blideanu, V.; Durand, D

    2004-09-01

    A dynamical model dedicated to nucleon induced reaction between 30-150 MeV is presented. It considers different stages of the reaction: the approaching phase, the in-medium nucleon-nucleon collisions, the cluster formation and the secondary de-excitation process. The notions of influence area and phase-space exploration during the reaction are introduced. The importance of the geometry of the reaction and of the conservation laws are underlined. The model is able to globally reproduce the absolute cross sections for the emission of neutron and light charged particles for proton and neutron induced reactions on heavy and intermediate mass targets ({sup 56}Fe and {sup 208}Pb). (authors)

  10. On light cluster production in nucleon induced reactions at intermediate energy

    International Nuclear Information System (INIS)

    Lacroix, D.; Blideanu, V.; Durand, D.

    2004-09-01

    A dynamical model dedicated to nucleon induced reaction between 30-150 MeV is presented. It considers different stages of the reaction: the approaching phase, the in-medium nucleon-nucleon collisions, the cluster formation and the secondary de-excitation process. The notions of influence area and phase-space exploration during the reaction are introduced. The importance of the geometry of the reaction and of the conservation laws are underlined. The model is able to globally reproduce the absolute cross sections for the emission of neutron and light charged particles for proton and neutron induced reactions on heavy and intermediate mass targets ( 56 Fe and 208 Pb). (authors)

  11. High chromium nickel base alloys hot cracking susceptibility

    International Nuclear Information System (INIS)

    Tirand, G.; Primault, C.; Robin, V.

    2014-01-01

    High Chromium nickel based alloys (FM52) have a higher ductility dip cracking sensitivity. New filler material with higher niobium and molybdenum content are developed to decrease the hot crack formation. The behavior of these materials is studied by coupling microstructural analyses and hot cracking test, PVR test. The metallurgical analyses illustrate an Nb and Mo enrichment of the inter-dendritic spaces of the new materials. A niobium high content (FM52MSS) induces the formation of primary carbide at the end of solidification. The PVR test reveal a solidification crack sensitivity of the new materials, and a lowest ductility dip cracking sensitivity for the filler material 52MSS. (authors)

  12. Effect of Grain Orientation and Boundary Distributions on Hydrogen-Induced Cracking in Low-Carbon-Content Steels

    Science.gov (United States)

    Masoumi, Mohammad; Coelho, Hana Livia Frota; Tavares, Sérgio Souto Maior; Silva, Cleiton Carvalho; de Abreu, Hamilton Ferreira Gomes

    2017-08-01

    Hydrogen-induced cracking (HIC) causes considerable economic losses in a wide range of steels exposed to corrosive environments. The effect of crystallographic texture and grain boundary distributions tailored by rolling at 850 °C in three different steels with a body-centered cube structure was investigated on HIC resistance. The x-ray and electron backscattered diffraction techniques were used to characterize texture evolutions during the rolling process. The findings revealed a significant improvement against HIC based on texture engineering. In addition, increasing the number of {111} and {110} grains, associated with minimizing the number of {001} grains in warm-rolled samples, reduced HIC susceptibility. Moreover, the results showed that boundaries associated with low {hkl} indexing and denser packing planes had more resistance against crack propagation.

  13. Hydrogen Induced Crack and Phase Transformation in Hydrogen Pressured Tensile Test of 316L Stainless Steel

    Energy Technology Data Exchange (ETDEWEB)

    Baek, Un Bong; Nam, Sung Hoon [Korea Research Institute of Standards and Science, Daejeon (Korea, Republic of); Choe, Byung Hak; Shim, Jong Hun [Gangneung-Wonju National University, Gangneung (Korea, Republic of); Kim, Young Uk [Hanyang University, Ansan (Korea, Republic of); Kim, Young Suk; Kim, Sung Soo [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Hong, Keyyong [Korea Research Institute of Ship and Ocean Engineering, Deajeon (Korea, Republic of)

    2015-02-15

    The aim of this investigation is to prove the mechanism of hydrogen induced crack (HIC) of 316L stainless steels in hydrogen pressured tensile test. Microstructures like twin, planar slip, and abnormal phase transformation around the HIC were analyzed by transmission electron microscopy. Deformation twin accompanied by planar slip could be related to the main cause of HIC in the hydrogen pressured tensile condition, because intragranular HICs were mainly observed along the boundaries of twins and planar slip lines. An abnormal forbidden diffraction was also accompanied by HIC in the hydrogen attacked area. Examination of the HIC mechanism in austenitic stainless steel can be applied to the fitness of use for alloys with the possibility of various susceptible cracks in a hydrogen and stress atmosphere.

  14. Hydrogen induced crack propagation in metal under plain-strain deformation

    International Nuclear Information System (INIS)

    Fishgojt, A.V.; Kolachev, B.A.

    1981-01-01

    A model of subcritical crack propagation conditioned by the effect of dissolved hydrogen in the case of plane-strain deformation of high-strength materials, is suggested. It is supposed that diffusion takes place in the isotropic material and hydrogen diffuses in the region of tensile stress maximum before crack tip under the effect of the stress gradient. When hydrogen achieves the critical concentration, microcrack growth takes place. Values of crack growth rates experimentally obtained agree with values calculated according to the suggested formula. Calculation and experimental data on the Ti-6Al-4V alloy, are presented [ru

  15. Modelling of iodine-induced stress corrosion cracking in CANDU fuel

    International Nuclear Information System (INIS)

    Lewis, B.J.; Thompson, W.T.; Kleczek, M.R.; Shaheen, K.; Juhas, M.; Iglesias, F.C.

    2011-01-01

    Iodine-induced stress corrosion cracking (I-SCC) is a recognized factor for fuel-element failure in the operation of nuclear reactors requiring the implementation of mitigation measures. I-SCC is believed to depend on certain factors such as iodine concentration, oxide layer type and thickness on the fuel sheath, irradiation history, metallurgical parameters related to sheath like texture and microstructure, and the mechanical properties of zirconium alloys. This work details the development of a thermodynamics and mechanistic treatment accounting for the iodine chemistry and kinetics in the fuel-to-sheath gap and its influence on I-SCC phenomena. The governing transport equations for the model are solved with a finite-element technique using the COMSOL Multiphysics (registered) commercial software platform. Based on this analysis, this study also proposes potential remedies for I-SCC.

  16. Photogrammetric Assessment of Flexure Induced Cracking of Reinforced Concrete Beams under Service Loads

    DEFF Research Database (Denmark)

    Pease, Bradley Justin; Geiker, Mette Rica; Stang, Henrik

    2006-01-01

    Reinforced concrete structures are known to crack due to restrained shrinkage, temperature gradients, application of load, and expansive reactions. Cracks provide paths for rapid ingress of moisture, chlorides, and other aggressive substances, which may affect the long-term durability...... of the structure. For example, concrete cracks located at the reinforcing steel may contribute to a rapid corrosion initiation and propagation. Previous research has shown that cracked reinforced concrete under static flexural loading may have an increased ingress of chloride ions along the reinforcement....../concrete interface. The aim of this paper is to provide a detailed description of the development of cracks in reinforced concrete under flexural load. Cracking at both realistic service load levels (1.0-1.8 times estimated cracking load) and unrealistically high service load levels (> 0.5 times beam capacity) has...

  17. Modified Dugdale cracks and Fictitious cracks

    DEFF Research Database (Denmark)

    Nielsen, Lauge Fuglsang

    1998-01-01

    A number of theories are presented in the literature on crack mechanics by which the strength of damaged materials can be predicted. Among these are theories based on the well-known Dugdale model of a crack prevented from spreading by self-created constant cohesive flow stressed acting in local...... areas, so-called fictitious cracks, in front of the crack.The Modified Dugdale theory presented in this paper is also based on the concept of Dugdale cracks. Any cohesive stress distribution, however, can be considered in front of the crack. Formally the strength of a material weakened by a modified...... Dugdale crack is the same as if it has been weakened by the well-known Griffith crack, namely sigma_CR = (EG_CR/phi)^1/2 where E and 1 are Young's modulus and crack half-length respectively, and G_CR is the so-called critical energy release rate. The physical significance of G_CR, however, is different...

  18. Manufacturing method for intragranular stress corrosion cracking-induced test specimen for stainless steel pipeline

    International Nuclear Information System (INIS)

    Futagawa, Kiyoshi.

    1994-01-01

    In a manufacturing step for intragranular stress corrosion cracking-induced for stainless steel pipelines, pipe are abutted against with each other and welded, and a heat affected portion is applied with a sensitizing heat treatment. Further, a crevice jig is attached near the heat affected portion at the inner surface of the pipe and kept in a chlorine ion added water under high temperature and high pressure at a predetermined period of time. If tap water is used instead of purified water for C.P.T. test in a step of forming sample of IGSCC (intergranular stress corrosion cracking), since the chlorine ion concentration in the tap water is relatively high, TGSCC (intragranular stress corrosion crackings caused in all of the samples. A heat input and an interlayer temperature are determined for the material of stainless pipe having a carbon content of more than 0.05% so that the welding residual stress on the inner surface is applied as tension. The condition for the heat treatment is determined as, for example, 500degC x 24hr, and the samples are kept under water at high temperature and high pressure applied with chlorine ions for 500 to 200hours. As a result, since samples of TGSCC can be formed by utilizing the manufacturing step for IGSCC, there is no requirement for providing devices for applying environmental factors separately. (N.H.)

  19. Correlation between oxidation and stress corrosion cracking of U-4.5 wt.% Nb

    International Nuclear Information System (INIS)

    Magnani, N.J.; Holloway, P.H.

    1976-01-01

    To investigate the mechanisms causing stress corrosion cracking on uranium alloys, the kinetics of crack propagation and oxide film growth for U-4.5 percent Nb were investigated at temperatures between 0 0 C and 200 0 C in oxygen, water vapor and oxygen-water vapor mixtures. Three regions of crack velocity rate versus stress intensity were observed in laboratory air. At low stress intensities (but above an effective K/sub ISCC/ of 22 MN/m/sup 3 / 2 /) crack velocity varied approximately as K 70 . In an intermediate stress intensity region (region II) the crack velocity was dependent upon K 4 . In the high stress intensity region, mechanical overloading was observed and crack velocities varied approximately as K 12 . Both cracking (region II) and oxidation rates were characterized by an activation energy of 7 kcal/mole. For stress corrosion cracking it was shown that oxygen was the primary stress corrodent, but a synergistic effect upon crack propagation rates was observed for oxygen-water vapor mixtures. Crack velocities were dependent upon the pressure of oxygen (P/sub O 2 //sup 1 / 3 /) and water vapor, while the oxidation rate was essentially independent of the pressure of these species. Stress sorption and oxide film formation stress corrosion cracking mechanisms were considered and reconciled with the stress corrosion and oxidation data

  20. Effect of plastic strain on fracture strength of cracked components

    International Nuclear Information System (INIS)

    Kamaya, Masayuki

    2009-01-01

    Nuclear power plant components are occasionally subjected to large load by earthquake and may suffer plastic strain. Although the plastic strain induced in materials increases the strength, it may reduce the fracture toughness due to a crack in the components. In this study, the effect of the plastic strain on strength of cracked components was investigated. Firstly, the change in the tensile properties and fracture toughness due to plastic strain were examined for Type 316 stainless steel and carbon steel (SM490). The degree of nominal plastic strain was 5%, 10%, 20% and 40% (only for stainless steel). Secondly, the J-integral values of surface crack on a pipe were evaluated by finite element analyses. Finally, the critical load for fracture of the cracked pipe was evaluated for various pipe and crack geometries using the J-integral values and the fracture toughness obtained. It was concluded that the plastic strain enhances the fracture strength of the cracked components when the induced plastic strain is less than 10%, although the extremely large plastic strain could reduce the strength. (author)

  1. Mechanistic dissimilarities between environmentally-influenced fatigue-crack propagation at near-threshold and higher growth rates in lower-strength steels

    Energy Technology Data Exchange (ETDEWEB)

    Suresh, S.; Ritchie, R. O.

    1981-11-01

    The role of hydrogen gas in influencing fatigue crack propagation is examined for several classes of lower strength pressure vessel and piping steels. Based on measurements over a wide range of growth rates from 10/sup -8/ to 10/sup -2/ mm/cycle, crack propagation rates are found to be significantly higher in dehumidified gaseous hydrogen compared to moist air in two distinct regimes of crack growth, namely (i) at the intermediate range of growth typically above approx. 10/sup -5/ mm/cycle, and (ii) at the near-threshold region below approx. 10/sup -6/ mm/cycle approaching lattice dimensions per cycle. Both effects are seen at maximum stress intensities (K/sub max/) far below the sustained-load threshold stress intensity for hydrogen-assisted cracking (K/sub Iscc/). Characteristics of environmentally influenced fatigue crack growth in each regime are shown to be markedly different with regard to fractography and the effect of such variables as load ratio and frequency. It is concluded that the primary mechanisms responsible for the influence of the environment in each regime are distinctly different. Whereas corrosion fatigue behavior at intermediate growth rates can be attributed to hydrogen embrittlement processes, the primary role of moist environments at near-threshold levels is shown to involve a contribution from enhanced crack closure due to the formation of crack surface corrosion deposits at low load ratios.

  2. Cracking and delamination of vapor-deposited tantalum films

    International Nuclear Information System (INIS)

    Fisher, R.M.; Duan, J.Z.; Liu, J.B.

    1990-01-01

    This paper reports on tantalum films which begin to crack and spall during vapor deposition on glass at a thickness of 180 nm. Islands and ribbons, 10 - 30 μm in size, delaminate by crack growth along the Ta/glass interface for several μm after which the crack penetrates into the glass to a depth of 0.5 - 1 μm and complete spalling occurs. X-ray diffraction showed that about 50% of the original bct, β-tantalum, phase had transformed to the bcc α-Ta phase. When Ta was deposited on glass that was first covered with 52 nm of copper, spalling was observed to begin at a thickness of 105 nm. In this case, the film first cracks and then peels along the Cu/glass interface and curls into scrolls indicating the presence of a small stress gradient. X-ray diffraction of the as-deposited film, and electron diffraction of ion-milled flakes, showed that the Ta films deposited on Cu-coated glass almost completely transform to bcc α-Ta. The critical thickness for delamination along the Cu/glass interface is about 1/2 that for cracking in the glass substrate when an intermediate layer of Cu is not present. All of the above findings are in good agreement with previous observations on Cr films

  3. Lamb Wave Line Sensing for Crack Detection in a Welded Stiffener

    Directory of Open Access Journals (Sweden)

    Yun-Kyu An

    2014-07-01

    Full Text Available This paper proposes a novel Lamb wave line sensing technique for crack detection in a welded stiffener. The proposed technique overcomes one of the biggest technical challenges of Lamb wave crack detection for real structure applications: crack-induced Lamb waves are often mixed with multiple reflections from complex waveguides. In particular, crack detection in a welded joint, one of the structural hot spots due to stress concentration, is accompanied by reflections from the welded joint as well as a crack. Extracting and highlighting crack-induced Lamb wave modes from Lamb wave responses measured at multi-spatial points along a single line can be accomplished through a frequency-wavenumber domain analysis. The advantages of the proposed technique enable us not only to enhance the crack detectability in the welded joint but also to minimize false alarms caused by environmental and operational variations by avoiding the direct comparison with the baseline data previously accumulated from the pristine condition of a target structure. The proposed technique is experimentally and numerically validated in vertically stiffened metallic structures, revealing that it successfully identifies and localizes subsurface cracks, regardless of the coexistence with the vertical stiffener.

  4. Corrosion and stress corrosion cracking in supercritical water

    Science.gov (United States)

    Was, G. S.; Ampornrat, P.; Gupta, G.; Teysseyre, S.; West, E. A.; Allen, T. R.; Sridharan, K.; Tan, L.; Chen, Y.; Ren, X.; Pister, C.

    2007-09-01

    Supercritical water (SCW) has attracted increasing attention since SCW boiler power plants were implemented to increase the efficiency of fossil-based power plants. The SCW reactor (SCWR) design has been selected as one of the Generation IV reactor concepts because of its higher thermal efficiency and plant simplification as compared to current light water reactors (LWRs). Reactor operating conditions call for a core coolant temperature between 280 °C and 620 °C at a pressure of 25 MPa and maximum expected neutron damage levels to any replaceable or permanent core component of 15 dpa (thermal reactor design) and 100 dpa (fast reactor design). Irradiation-induced changes in microstructure (swelling, radiation-induced segregation (RIS), hardening, phase stability) and mechanical properties (strength, thermal and irradiation-induced creep, fatigue) are also major concerns. Throughout the core, corrosion, stress corrosion cracking, and the effect of irradiation on these degradation modes are critical issues. This paper reviews the current understanding of the response of candidate materials for SCWR systems, focusing on the corrosion and stress corrosion cracking response, and highlights the design trade-offs associated with certain alloy systems. Ferritic-martensitic steels generally have the best resistance to stress corrosion cracking, but suffer from the worst oxidation. Austenitic stainless steels and Ni-base alloys have better oxidation resistance but are more susceptible to stress corrosion cracking. The promise of grain boundary engineering and surface modification in addressing corrosion and stress corrosion cracking performance is discussed.

  5. Use of the gapped bead-on-plate test to investigate hydrogen induced cracking of flux cored arc welds of a quenched and tempered steel

    International Nuclear Information System (INIS)

    Chen, Liang; Dunne, Druce; Davidson, Len

    2014-01-01

    Gapped bead-on-plate (G-BOP) testing of flux cored arc welds was conducted to assess the susceptibility to hydrogen induced cold cracking (HICC) of weld metal deposited on a high strength quenched and tempered steel. For preheat temperatures higher than 40°C, no weld metal cracking was observed using a shielding gas consisting of argon with 20% carbon dioxide. In contrast, the no-crack condition was not achieved for a shielding gas consisting of argon-5% carbon dioxide for preheat temperatures lower than 100°C. This extraordinary difference in weld metal HICC resistance indicates that, in general, the shielding gas mixture can exert a major influence on weld metal transverse cold cracking behaviour

  6. Development of chloride-induced corrosion in pre-cracked RC beams under sustained loading: Effect of load-induced cracks, concrete cover, and exposure conditions

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Linwen [Université de Toulouse, UPS, INSA, LMDC, Toulouse (France); Université de Sherbrooke, Quebec (Canada); François, Raoul, E-mail: raoul.francois@insa-toulouse.fr [Université de Toulouse, UPS, INSA, LMDC, Toulouse (France); Dang, Vu Hiep [Hanoi Architectural University, Faculty of Civil Engineering, Hanoi (Viet Nam); L' Hostis, Valérie [CEA Saclay, CEA, DEN, DPC, SECR, Laboratoire d' Etude du Comportement des Bétons et des Argiles, Gif-sur-Yvette (France); Gagné, Richard [Université de Sherbrooke, Quebec (Canada)

    2015-01-15

    This paper deals with corrosion initiation and propagation in pre-cracked reinforced concrete beams under sustained loading during exposure to a chloride environment. Specimen beams that were cast in 2010 were compared to specimens cast in 1984. The only differences between the two sets of beams were the casting direction in relation to tensile reinforcement and the exposure conditions in the salt-fog chamber. The cracking maps, corrosion maps, chloride profiles, and cross-sectional loss of one group of two beams cast in 2010 were studied and their calculated corrosion rates were compared to that of beams cast in 1984 in order to investigate the factors influencing the natural corrosion process. Experimental results show that, after rapid initiation of corrosion at the crack tip, the corrosion process practically halted and the time elapsing before corrosion resumed depended on the exposure conditions and cover depth.

  7. Compliance characteristics of cracked UO2 pellets

    International Nuclear Information System (INIS)

    Williford, R.E.; Mohr, C.L.; Lanning, D.D.

    1981-01-01

    The thermally induced cracking of UO 2 fuel pellets causes simultaneous reductions of the bulk (extrinsic) fuel thermal conductivity and elastic moduli to values significantly less than those for solid pellets. The magnitude of these bulk properly reductions was found to be primarily dependent on the amount of crack area in the transverse plane of the fuel. The model described herein uses a simple description of the crack geometry to couple the fuel rod thermal and mechanical behaviors by relating in-reactor data to Hooke's Law and a crack compliance model. Data from the NRC/PNL Halden experiment IFA-432 show that for a typical helium-filled BWR-design rod at 30 kW/m, the effective thermal conductivity and elastic moduli of the cracked fuel are 4/5 and 1/40 of that for solid pellets, respectively

  8. Experimental study of the crack depth ratio threshold to analyze the slow crack growth by creep of high density polyethylene pipes

    International Nuclear Information System (INIS)

    Laiarinandrasana, Lucien; Devilliers, Clémence; Lucatelli, Jean Marc; Gaudichet-Maurin, Emmanuelle; Brossard, Jean Michel

    2014-01-01

    To assess the durability of drinking water connection pipes subjected to oxidation and slow crack growth, a comprehensive database was constructed on a novel specimen geometry: the pre-cracked NOL ring. 135 tests were carried out consisting of initial crack depth ratio ranging from 0.08 to 0.6; single or double longitudinal cracks: tensile with steady strain rate and creep loading. A threshold value of the crack depth ratio of 0.2, induced by the oxidation was determined by analyzing several mechanical parameters. This threshold value was shown to be independent on the strain rate effects, single or double crack configuration and the kind of loading: tensile or creep. Creep test results with crack depth ratio larger than 0.2 were then utilized to establish a failure assessment diagram. A methodology allowing the prediction of residual lifetime of in-service pipes was proposed, using this diagram. - Highlights: • Experimental data on pre-cracked rings featuring a longitudinally cracked HDPE pipe. • Crack depth ratio threshold for slow crack growth study consecutive to oxidation. • Investigation of the effects of the single/double notch(es) and of the strain rate. • Original results obtained from tests performed with tensile and creep loadings. • Correlation between creep initiation time and C* with DENT and ring specimens

  9. On the driving force for crack growth during thermal actuation of shape memory alloys

    Science.gov (United States)

    Baxevanis, T.; Parrinello, A. F.; Lagoudas, D. C.

    2016-04-01

    The effect of thermomechanically induced phase transformation on the driving force for crack growth in polycrystalline shape memory alloys is analyzed in an infinite center-cracked plate subjected to a thermal actuation cycle under mechanical load in plain strain. Finite element calculations are carried out to determine the mechanical fields near the static crack and the crack-tip energy release rate using the virtual crack closure technique. A substantial increase of the energy release rate - an order of magnitude for some material systems - is observed during the thermal cycle due to the stress redistribution induced by large scale phase transformation. Thus, phase transformation occurring due to thermal variations under mechanical load may result in crack growth if the crack-tip energy release rate reaches a material specific critical value.

  10. Photon and proton induced fission on heavy nuclei at intermediate energies

    Directory of Open Access Journals (Sweden)

    Andrade-II E.

    2014-04-01

    Full Text Available We present an analysis of fission induced by intermediate energy protons or photons on actinides. The 660 MeV proton induced reactions are on 241Am, 238U, and 237Np targets and the Bremmstrahlung-photons with end-point energies at 50 MeV and 3500 MeV are on 232Th and 238U targets. The study was performed by means of the Monte Carlo simulation code CRISP. A multimodal fission extension was added to the code within an approach which accounts for the contribution of symmetric and asymmetric fission. This procedure allowed the investigation of fission cross sections, fissility, number of evaporated nucleons and fission-fragment charge distributions. The comparison with experimental data show a good agreement between calculations and experiments.

  11. Hydride effect on crack instability of Zircaloy cladding

    Energy Technology Data Exchange (ETDEWEB)

    Tseng, Che-Chung, E-mail: cctseng@iner.gov.tw [Institute of Nuclear Energy Research, No. 1000, Wunhua Road, Jiaan Village, Lungtan, Township, Taoyuan County 32546, Taiwan (China); Sun, Ming-Hung [Institute of Nuclear Energy Research, No. 1000, Wunhua Road, Jiaan Village, Lungtan, Township, Taoyuan County 32546, Taiwan (China); Chao, Ching-Kong [Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Keelung Road, Section 4, Taipei 106, Taiwan (China)

    2014-04-01

    Highlights: • Radial hydrides near the crack tip had a significant effect on crack propagation. • For radial hydrides off the crack line vertically, the effect on crack propagation was notably reduced. • The longer hydride platelet resulted in a remarkable effect on crack propagation. • A long split in the radial hydride precipitate would enhance crack propagation. • The presence of circumferential hydride among radial hydrides may play an important role in crack propagation. - Abstract: A methodology was proposed to investigate the effect of hydride on the crack propagation in fuel cladding. The analysis was modeled based on an outside-in crack with radial hydrides located near its crack tip. The finite element method was used in the calculation; both stress intensity factor K{sub I} and J integral were applied to evaluate the crack stability. The parameters employed in the analysis included the location of radial hydride, hydride dimensions, number of hydrides, and the presence of circumferential hydride, etc. According to our study, the effective distance between a radial hydride and the assumed cladding surface crack for the enhancement of crack propagation proved to be no greater than 0.06 mm. For a hydride not on the crack line, it would induce a relatively minor effect on crack propagation if the vertical distance was beyond 0.05 mm. However, a longer hydride precipitate as well as double radial hydrides could have a remarkable effect on crack propagation. A combined effect of radial and circumferential hydrides was also discussed.

  12. Intermediate neutron spectrum problems and the intermediate neutron spectrum experiment

    International Nuclear Information System (INIS)

    Jaegers, P.J.; Sanchez, R.G.

    1996-01-01

    Criticality benchmark data for intermediate energy spectrum systems does not exist. These systems are dominated by scattering and fission events induced by neutrons with energies between 1 eV and 1 MeV. Nuclear data uncertainties have been reported for such systems which can not be resolved without benchmark critical experiments. Intermediate energy spectrum systems have been proposed for the geological disposition of surplus fissile materials. Without the proper benchmarking of the nuclear data in the intermediate energy spectrum, adequate criticality safety margins can not be guaranteed. The Zeus critical experiment now under construction will provide this necessary benchmark data

  13. Creep and cracking of concrete hinges: insight from centric and eccentric compression experiments.

    Science.gov (United States)

    Schlappal, Thomas; Schweigler, Michael; Gmainer, Susanne; Peyerl, Martin; Pichler, Bernhard

    2017-01-01

    Existing design guidelines for concrete hinges consider bending-induced tensile cracking, but the structural behavior is oversimplified to be time-independent. This is the motivation to study creep and bending-induced tensile cracking of initially monolithic concrete hinges systematically. Material tests on plain concrete specimens and structural tests on marginally reinforced concrete hinges are performed. The experiments characterize material and structural creep under centric compression as well as bending-induced tensile cracking and the interaction between creep and cracking of concrete hinges. As for the latter two aims, three nominally identical concrete hinges are subjected to short-term and to longer-term eccentric compression tests. Obtained material and structural creep functions referring to centric compression are found to be very similar. The structural creep activity under eccentric compression is significantly larger because of the interaction between creep and cracking, i.e. bending-induced cracks progressively open and propagate under sustained eccentric loading. As for concrete hinges in frame-like integral bridge construction, it is concluded (i) that realistic simulation of variable loads requires consideration of the here-studied time-dependent behavior and (ii) that permanent compressive normal forces shall be limited by 45% of the ultimate load carrying capacity, in order to avoid damage of concrete hinges under sustained loading.

  14. Stress corrosion cracking and dealloying of copper-gold alloy in iodine vapor

    International Nuclear Information System (INIS)

    Galvez, M.F.; Bianchi, G.L.; Galvele, J.R.

    1993-01-01

    The susceptibility to stress corrosion cracking of copper-gold alloy in iodine vapor was studied and the results were analyzed under the scope of the surface mobility stress corrosion cracking mechanism. The copper-gold alloy undergoes stress corrosion cracking in iodine. Copper iodide was responsible of that behavior. The copper-gold alloy shows two processes in parallel: stress corrosion cracking and dealloying. As was predicted by the surface mobility stress corrosion cracking mechanism, the increase in strain rate induces an increase in the crack propagation rate. (Author)

  15. Giant electrocaloric effect in a cracked ferroelectrics

    Science.gov (United States)

    Huang, Cheng; Yang, Hai-Bing; Gao, Cun-Fa

    2018-04-01

    The electrocaloric effect (ECE) is the temperature change in a material induced by electrical field variation under adiabatic condition. Considering an external electric load applied on a cracked ferroelectric solid, a non-uniform electric field would be induced at the crack tip, and thus, incompatible strain field and local stress concentration would be generated around it. Furthermore, the enormous strain energy and the electrostatic energy would affect the polarization switching of the ferroelectric solid, important for the electrocaloric response. In this paper, the large negative and positive ECEs in a ferroelectric sheet with a conducting crack are investigated by the phase field method with the consideration of time-dependent Ginzburg-Landau equation. The numerical calculations indicated that the polarization field generates a sharp rise during the domain transition from polydomain to monodomain under a certain electric load. Large negative ECEs, about -10.21 K and -7.55 K, are obtained at 135 °C and 85 °C, respectively. The domain transition temperature is much lower than the Curie temperature, which enlarges the existence scope of the large ECE in ferroelectrics. The results also imply that the domain transition from a multi-domain state to a single domain takes place with the minimization of total free energy, which involves the courses of the electric field, stress field, temperature, and polarization interaction. Therefore, the non-uniform distributions of the stress-electric fields induced by the crack play an important role in ECE.

  16. Electromagnetic pulsed thermography for natural cracks inspection

    Science.gov (United States)

    Gao, Yunlai; Tian, Gui Yun; Wang, Ping; Wang, Haitao; Gao, Bin; Woo, Wai Lok; Li, Kongjing

    2017-01-01

    Emerging integrated sensing and monitoring of material degradation and cracks are increasingly required for characterizing the structural integrity and safety of infrastructure. However, most conventional nondestructive evaluation (NDE) methods are based on single modality sensing which is not adequate to evaluate structural integrity and natural cracks. This paper proposed electromagnetic pulsed thermography for fast and comprehensive defect characterization. It hybrids multiple physical phenomena i.e. magnetic flux leakage, induced eddy current and induction heating linking to physics as well as signal processing algorithms to provide abundant information of material properties and defects. New features are proposed using 1st derivation that reflects multiphysics spatial and temporal behaviors to enhance the detection of cracks with different orientations. Promising results that robust to lift-off changes and invariant features for artificial and natural cracks detection have been demonstrated that the proposed method significantly improves defect detectability. It opens up multiphysics sensing and integrated NDE with potential impact for natural understanding and better quantitative evaluation of natural cracks including stress corrosion crack (SCC) and rolling contact fatigue (RCF). PMID:28169361

  17. Contribution to the study of the mechanism of crack in amorphous silica: study by the molecular dynamics of crack in amorphous silica

    International Nuclear Information System (INIS)

    Van Brutzel, L.

    2000-01-01

    The aim of this thesis was to understand the mechanism which occurs during the crack at the atomic scale in amorphous silica. The difficulties of the experimental observations at this length scale lead us to use numerical studies by molecular dynamics to access to the dynamical and the thermodynamical informations. We have carried out large simulations with 500000 atoms and studied the structure of the amorphous silica before to studying their behaviours under an imposed strain. The structure of this simulated amorphous silica settled in three length scales. In small length scale between 0 and 5 angstrom glass is composed of tetrahedra, this is close to the crystalline structure. In intermediate length scale between 3 and 10 angstrom tetrahedra are connected together and build rings of different sizes composed in majority between 5 and 7 tetrahedra. In bigger length scale between 15 and 60 angstrom, areas with high density of rings are surrounded by areas with low density of rings. These structural considerations play an important role in initiation and propagation of a crack. Indeed. in this length scale. crack propagates by growth and coalescence of some small cavities which appear in area with low density of rings behind the crack tip. The cavities dissipate the stress with carries away a delay to propagation of the crack. This phenomenons seems ductile and leads to non linear elastic behaviour near the crack tip. We have also shown that the addition of alkali in the amorphous silica changes the structure by creation of nano-porosities and leads to enhance the ductility during the crack propagation. (author)

  18. Crack induced slip processes in 3D

    Czech Academy of Sciences Publication Activity Database

    Hora, Petr; Pelikán, Vladimír; Machová, Anna; Spielmannová, Alena; Prahl, Jakub; Landa, Michal; Červená, Olga

    2008-01-01

    Roč. 75, - (2008), s. 3612-3623 ISSN 0013-7944 R&D Projects: GA AV ČR IAA2076201; GA ČR(CZ) GA101/07/0789 Institutional research plan: CEZ:AV0Z20760514 Keywords : bcc iron * cracks * dislocation emission Subject RIV: JG - Metallurgy Impact factor: 1.713, year: 2008

  19. A crack growth evaluation method for interacting multiple cracks

    International Nuclear Information System (INIS)

    Kamaya, Masayuki

    2003-01-01

    When stress corrosion cracking or corrosion fatigue occurs, multiple cracks are frequently initiated in the same area. According to section XI of the ASME Boiler and Pressure Vessel Code, multiple cracks are considered as a single combined crack in crack growth analysis, if the specified conditions are satisfied. In crack growth processes, however, no prescription for the interference between multiple cracks is given in this code. The JSME Post-Construction Code, issued in May 2000, prescribes the conditions of crack coalescence in the crack growth process. This study aimed to extend this prescription to more general cases. A simulation model was applied, to simulate the crack growth process, taking into account the interference between two cracks. This model made it possible to analyze multiple crack growth behaviors for many cases (e.g. different relative position and length) that could not be studied by experiment only. Based on these analyses, a new crack growth analysis method was suggested for taking into account the interference between multiple cracks. (author)

  20. Effects of External Hydrogen on Hydrogen Transportation and Distribution Around the Fatigue Crack Tip in Type 304 Stainless Steel

    Science.gov (United States)

    Chen, Xingyang; Zhou, Chengshuang; Cai, Xiao; Zheng, Jinyang; Zhang, Lin

    2017-10-01

    The effects of external hydrogen on hydrogen transportation and distribution around the fatigue crack tip in type 304 stainless steel were investigated by using hydrogen microprint technique (HMT) and thermal desorption spectrometry. HMT results show that some silver particles induced by hydrogen release are located near the fatigue crack and more silver particles are concentrated around the crack tip, which indicates that hydrogen accumulates in the vicinity of the crack tip during the crack growth in hydrogen gas environment. Along with the crack propagation, strain-induced α' martensite forms around the crack tip and promotes hydrogen invasion into the matrix, which will cause the crack initiation and propagation at the austenite/ α' martensite interface. In addition, the hydrogen content in the vicinity of the crack tip is higher than that at the crack edge far away from the crack tip, which is related to the stress state and strain-induced α' martensite.

  1. Environmentally assisted cracking mechanisms in repository environments

    International Nuclear Information System (INIS)

    Mills, W.J.

    1987-02-01

    This paper assesses how environmentally assisted cracking (EAC) mechanisms in candidate container materials can be identified to enhance the accuracy of long-term projections of performance in the repository. In low and intermediate strength steels, the role of the two principal mechanisms, slip dissolution/film rupture (SD/FR) and hydrogen embrittlement (HE), is a very complex and controversial issue. No unanimity exists concerning the operative cracking mechanisms, and there is no unique or rigorous approach that would be persuasive in selecting an appropriate model. Both of the proposed mechanisms have common rate controlling processes such as surface adsorption rate, passivation rate, and oxidation rupture rate, which makes it difficult to identify the operative mechanism. Development of a quantitative model for predicting environmental effects for low-carbon steels in repository environments would provide a theoretical basis for assuring the long-term structural integrity of waste-package containment. To date, only one quantitative model has been developed. The agreement between predicted and observed behavior suggests that SD/FR processes control the environmental acceleration in crack growth rates for this class of materials. Deviations from predicted behavior due to HE effects should be uncovered experimentally. 59 refs., 4 figs., 4 tabs

  2. Intermediate heat exchanger tube vibration induced by cross and parallel mixed flow

    International Nuclear Information System (INIS)

    Kawamura, Koji

    1986-01-01

    The characteristics of pool type LMFBR intermediate heat exchanger (IHX) tube vibrations induced by cross and parallel mixed flow were basically investigated. Secondary coolant in IHX tube bundle is mixed flow of parallel jit flow along the tube axis through flow holes in baffle plates and cross flow. By changing these two flow rate, flow distributions vary in the tube bundle. Mixed flow also induces vibrations which cause fretting wear and fatigue of tube. It is therefore very important to evaluate the tube vibration characteristics for estimating the tube integrity. The results show that the relationships between tube vibrations and flow distributions in the tube bundle were cleared, and mixed flow induced tube vibration could be evaluated on the base of the characteristics of both parallel and cross flow induced vibration. From these investigations it could be concluded that the characteristics of tube vibration for various flow distributions can be systematically evaluated. (author)

  3. Mechanisms of fatigue crack retardation following single tensile overloads in powder metallurgy aluminum alloys

    Science.gov (United States)

    Bray, G. H.; Reynolds, A. P.; Starke, E. A., Jr.

    1992-01-01

    In ingot metallurgy (IM) alloys, the number of delay cycles following a single tensile overload typically increases from a minimum at an intermediate baseline stress intensity range, Delta-K(B), with decreasing Delta-K(B) approaching threshold and increasing Delta-K(B) approaching unstable fracture to produce a characteristic 'U' shaped curve. Two models have been proposed to explain this behavior. One model is based on the interaction between roughness and plasticity-induced closure, while the other model only utilizes plasticity-induced closure. This article examines these models, using experimental results from constant amplitude and single overload fatigue tests performed on two powder metallurgy (PM) aluminum alloys, AL-905XL and AA 8009. The results indicate that the 'U'-shaped curve is primarily due to plasticity-induced closure, and that the plasticity-induced retardation effect is through-thickness in nature, occurring in both the surface and interior regions. However, the retardation effect is greater at the surface, because the increase in plastic strain at the crack tip and overload plastic zone size are larger in the plane-stress surface regions than in the plane-strain interior regions. These results are not entirely consistent with either of the proposed models.

  4. Cracking at nozzle corners in the nuclear pressure vessel industry

    International Nuclear Information System (INIS)

    Smith, C.W.

    1986-01-01

    Cracks in nozzle corners at the pressure boundary of nuclear reactors have been frequently observed in service. These cracks tend to form with radial orientations with respect to the nozzle central axis and are believed to be initiated by thermal shock. However, their growth is believed to be primarily due to a steady plus a fluctuating internal pressure. Due to the impracticality of fracture testing of full-scale models, the Oak Ridge National Laboratory instituted the use of an intermediate test vessel (ITV) for use in fracture testing which had the same wall thickness and nozzle size as the prototype but significantly reduced overall length and diameter. In order to determine whether or not these ITVs could provide realistic data for full-scale reactor vessels, laboratory models of full-scale boiling water reactors and ITVs were constructed and tested. After briefly reviewing the laboratory testing and correlating results with service experience, results obtained will be used to draw some general conclusions regarding the stable growth of nonplanar cracks with curved crack fronts which are the most common precursors to fracture of pressure vessel components near junctures. Use of linear elastic fracture mechanics is made in determining stress-intensity distribution along the crack fronts

  5. Microbial healing of cracks in concrete: a review.

    Science.gov (United States)

    Joshi, Sumit; Goyal, Shweta; Mukherjee, Abhijit; Reddy, M Sudhakara

    2017-11-01

    Concrete is the most widely used construction material of the world and maintaining concrete structures from premature deterioration is proving to be a great challenge. Early age formation of micro-cracking in concrete structure severely affects the serviceability leading to high cost of maintenance. Apart from conventional methods of repairing cracks with sealants or treating the concrete with adhesive chemicals to prevent the cracks from widening, a microbial crack-healing approach has shown promising results. The unique feature of the microbial system is that it enables self-healing of concrete. The effectiveness of microbially induced calcium carbonate precipitation (MICCP) in improving durability of cementitious building materials, restoration of stone monuments and soil bioclogging is discussed. Main emphasis has been laid on the potential of bacteria-based crack repair in concrete structure and the applications of different bacterial treatments to self-healing cracks. Furthermore, recommendations to employ the MICCP technology at commercial scale and reduction in the cost of application are provided in this review.

  6. Photon and proton induced fission on heavy nuclei at intermediate energies

    Energy Technology Data Exchange (ETDEWEB)

    Andrade-II, E.; Karapetyan, G.S.; Deppman, A.; Guimaraes, V. [Universidade de Sao Paulo (USP), Sao Paulo, SP (Brazil). Instituto de Fisica; Balabekyan, A.R. [Yerevan State University, Alex Manoogian 1, Yerevan (Armenia); Demekhina, N.A. [Yerevan Physics Institute, Alikhanyan Brothers 2, Yerevan (Armenia); Joint Institute for Nuclear Research (JINR), Flerov Laboratory of Nuclear Reactions (LNR), Moscow (Russian Federation)

    2014-07-01

    We present an analysis of fission induced by intermediate energy protons or photons on actinides. The 660 MeV proton induced reactions are on {sup 241}Am, {sup 238}U, and {sup 237}Np targets and the Bremsstrahlung-photons with end-point energies at 50 MeV and 3500 MeV are on {sup 232}Th and {sup 238}U targets. The study was performed by means of the Monte Carlo simulation code CRISP. A multimodal fission extension was added to the code within an approach which accounts for the contribution of symmetric and asymmetric fission. This procedure allowed the investigation of fission cross sections, fissility, number of evaporated nucleons and fission-fragment charge distributions. The comparison with experimental data show a good agreement between calculations and experiments. (author)

  7. Identifying and Understanding Environment-Induced Crack propagation Behavior in Ni-based Superalloy INCONEL 617

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Longzhou

    2012-11-30

    The nickel-based superalloy INCONEL 617 is a candidate material for heat exchanger applications in the next-generation nuclear plant (NGNP) system. This project will study the crack propagation process of alloy 617 at temperatures of 650°C-950°C in air under static/cyclic loading conditions. The goal is to identify the environmental and mechanical damage components and to understand in-depth the failure mechanism. Researchers will measure the fatigue crack propagation (FCP) rate (da/dn) under cyclic and hold-time fatigue conditions, and sustained crack growth rates (da/dt) at elevated temperatures. The independent FCP process will be identified and the rate-controlled sustained loading crack process will be correlated with the thermal activation equation to estimate the oxygen thermal activation energy. The FCP-dependent model indicates that if the sustained loading crack growth rate, da/dt, can be correlated with the FCP rate, da/dn, at the full time dependent stage, researchers can confirm stress-accelerated grain-boundary oxygen embrittlement (SAGBOE) as a predominate effect. Following the crack propagation tests, the research team will examine the fracture surface of materials in various cracking stages using a scanning electron microscope (SEM) and an optical microscope. In particular, the microstructure of the crack tip region will be analyzed in depth using high resolution transmission electron microscopy (TEM) and electron energy loss spectrum (EELS) mapping techniques to identify oxygen penetration along the grain boundary and to examine the diffused oxygen distribution profile around the crack tip. The cracked sample will be prepared by focused ion beam nanofabrication technology, allowing researchers to accurately fabricate the TEM samples from the crack tip while minimizing artifacts. Researchers will use these microscopic and spectroscopic results to interpret the crack propagation process, as well as distinguish and understand the environment or

  8. Biaxial fatigue crack propagation behavior of perfluorosulfonic-acid membranes

    Science.gov (United States)

    Lin, Qiang; Shi, Shouwen; Wang, Lei; Chen, Xu; Chen, Gang

    2018-04-01

    Perfluorosulfonic-acid membranes have long been used as the typical electrolyte for polymer-electrolyte fuel cells, which not only transport proton and water but also serve as barriers to prevent reactants mixing. However, too often the structural integrity of perfluorosulfonic-acid membranes is impaired by membrane thinning or cracks/pinholes formation induced by mechanical and chemical degradations. Despite the increasing number of studies that report crack formation, such as crack size and shape, the underlying mechanism and driving forces have not been well explored. In this paper, the fatigue crack propagation behaviors of Nafion membranes subjected to biaxial loading conditions have been investigated. In particular, the fatigue crack growth rates of flat cracks in responses to different loading conditions are compared, and the impact of transverse stress on fatigue crack growth rate is clarified. In addition, the crack paths for slant cracks under both uniaxial and biaxial loading conditions are discussed, which are similar in geometry to those found after accelerated stress testing of fuel cells. The directions of initial crack propagation are calculated theoretically and compared with experimental observations, which are in good agreement. The findings reported here lays the foundation for understanding of mechanical failure of membranes.

  9. Comparing the floquet stability of open and breathing fatigue cracks in an overhung rotordynamic system

    Science.gov (United States)

    Varney, Philip; Green, Itzhak

    2017-11-01

    Rotor cracks represent an uncommon but serious threat to rotating machines and must be detected early to avoid catastrophic machine failure. An important aspect of analyzing rotor cracks is understanding their influence on the rotor stability. It is well-known that the extent of rotor instability versus shaft speed is exacerbated by deeper cracks. Consequently, crack propagation can eventually result in an unstable response even if the shaft speed remains constant. Most previous investigations of crack-induced rotor instability concern simple Jeffcott rotors. This work advances the state-of-the-art by (a) providing a novel inertial-frame model of an overhung rotor, and (b) assessing the stability of the cracked overhung rotor using Floquet stability analysis. The rotor Floquet stability analysis is performed for both an open crack and a breathing crack, and conclusions are drawn regarding the importance of appropriately selecting the crack model. The rotor stability is analyzed versus crack depth, external viscous damping ratio, and rotor inertia. In general, this work concludes that the onset of instability occurs at lower shaft speeds for thick rotors, lower viscous damping ratios, and deeper cracks. In addition, when comparing commensurate cracks, the breathing crack is shown to induce more regions of instability than the open crack, though the open crack generally predicts an unstable response for shallower cracks than the breathing crack. Keywords: rotordynamics, stability, rotor cracks.

  10. A study on the fractures of iodine induced stress corrosion cracking of new zirconium alloys

    International Nuclear Information System (INIS)

    Peng Qian; Zhao Wenjin; Li Weijun; Tang Zhenghua; Heng Xuemei

    2005-10-01

    The morphology and chemical compositions of I-SCC fractures of new zirconium alloys were investigated by SEM and EDXA. The feature on fracture surface for I-SCC samples, such as corrosion products, the secondary cracking, intergranular cracking and pseudo-cleavage transgranular cracking, have been observed. And the fluting, the typical characteristic of I-SCC also has been found. Intergranular cracking is visible at crack initiation stage and transgranular cracking is distinguished at crack propagation stage. The corrosion products are mainly composed of Zr and O; and I can be detected on the local pseudocleavage zone. The most of grooves on the fractures of relieved-stress annealing samples are parallel with the roll plane. The intergranular cracking in relieved-stress annealing samples is not obvious. When the test temperature increases, the activity of iodine increases and the stress on crack tip is easier to be released, thus the corrosion products on fracture also increase and intergranular cracking is visible. The partial pressure of iodine influents the thickness of corrosion products, and intergranular cracking is easier to be found when iodine partial pressure is high enough. (authors)

  11. Multifragmentation in intermediate energy 129Xe-induced heavy-ion reactions

    Energy Technology Data Exchange (ETDEWEB)

    Tso, Kin [Univ. of California, Berkeley, CA (United States)

    1996-05-01

    The 129Xe-induced reactions on natCu, 89Y, 165Ho, and 197Au at bombarding energies of E/A = 40 & 60 MeV have been studied theoretically and experimentally in order to establish the underlying mechanism of multifragmentation at intermediate energy heavy-Ion collisions. Nuclear disks formed in central heavy-ion collisions, as simulated by means of Boltzmann-like kinetic equations, break up into several fragments due to a new kind of Rayleigh-like surface instability. A sheet of liquid, stable in the limit of non-interacting surfaces, is shown to become unstable due to surface-surface interactions. The onset of this instability is determined analytically. A thin bubble behaves like a sheet and is susceptible to the surface instability through the crispation mode. The Coulomb effects associated with the depletion of charges in the central cavity of nuclear bubbles are investigated. The onset of Coulomb instability is demonstrated for perturbations of the radial mode. Experimental intermediate-mass-fragment multiplicity distributions for the 129Xe-induced reactions are shown to be binomial at each transverse energy. From these distributions, independent of the specific target, an elementary binary decay probability p can be extracted that has a thermal dependence. Thus it is inferred that multifragmentation is reducible to a combination of nearly independent emission processes. If sequential decay is assumed, the increase of p with transverse energy implies a contraction of the emission time scale. The sensitivity of p to the lower Z threshold in the definition of intermediate-mass-fragments points to a physical Poisson simulations of the particle multiplicities show that the weak auto-correlation between the fragment multiplicity and the transverse energy does not distort a Poisson distribution into a binomial distribution. The effect of device efficiency on the experimental results has also been studied.

  12. Gearbox Instrumentation for the Investigation of Bearing Axial Cracking

    Energy Technology Data Exchange (ETDEWEB)

    Keller, Jonathan A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Lambert, Scott R [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

    2018-03-27

    Failures in gearbox bearings have been the primary source of reliability issues for wind turbine drivetrains, leading to costly downtime and unplanned maintenance. The most common failure mode is attributed to so-called axial cracks or white-etching cracks, which primarily affect the intermediate and high-speed-stage bearings. The high-speed-shaft and bearing loads and sliding will be measured with a specially instrumented gearbox installed in a 1.5-megawatt turbine at the National Wind Technology Center in an upcoming test campaign. Additional instrumentation will also measure the tribological environment of these bearings, including bearing temperatures, lubricant temperature and water content, air temperature and humidity, and stray electrical current across the bearings. This paper fully describes the instrumentation package and summarizes initial results.

  13. Concrete Cracking Prediction Including the Filling Proportion of Strand Corrosion Products

    Science.gov (United States)

    Wang, Lei; Dai, Lizhao; Zhang, Xuhui; Zhang, Jianren

    2016-01-01

    The filling of strand corrosion products during concrete crack propagation is investigated experimentally in the present paper. The effects of stirrups on the filling of corrosion products and concrete cracking are clarified. A prediction model of crack width is developed incorporating the filling proportion of corrosion products and the twisting shape of the strand. Experimental data on cracking angle, crack width, and corrosion loss obtained from accelerated corrosion tests of concrete beams are presented. The proposed model is verified by experimental data. Results show that the filling extent of corrosion products varies with crack propagation. The rust filling extent increases with the propagating crack until a critical width. Beyond the critical width, the rust-filling extent remains stable. Using stirrups can decrease the critical crack width. Stirrups can restrict crack propagation and reduce the rust filling. The tangent of the cracking angle increases with increasing corrosion loss. The prediction of corrosion-induced crack is sensitive to the rust-filling extent. PMID:28772367

  14. Stress corrosion crack growth in unirradiated zircaloy

    International Nuclear Information System (INIS)

    Pettersson, K.

    1978-10-01

    Experimental techniques suitable for the determination of stress corrosion crack growth rates in irradiated Zircaloy tube have been developed. The techniques have been tested on unirradiated. Zircaloy and it was found that the results were in good agreement with the results of other investigations. Some of the results were obtained at very low stress intensities and the crack growth rates observed, gave no indication of the existance of a K sub(ISCC) for iodine induced stress corrosion cracking in Zircaloy. This is of importance both for fuel rod behavior after a power ramp and for long term storage of spent Zircaloy-clad fuel. (author)

  15. Radiation-induced instability of MnS precipitates and its possible consequences on irradiation-induced stress corrosion cracking of austenitic stainless steels

    International Nuclear Information System (INIS)

    Chung, H.M.; Sanecki, J.E.; Garner, F.A.

    1996-12-01

    Irradiation-assisted stress corrosion cracking (IASCC) is a significant materials issue for the light water reactor (LWR) industry and may also pose a problem for fusion power reactors that will use water as coolant. A new metallurgical process is proposed that involves the radiation-induced release into solution of minor impurity elements not usually thought to participate in IASCC. MnS-type precipitates, which contain most of the sulfur in stainless steels, are thought to be unstable under irradiation. First, Mn transmutes strongly to Fe in thermalized neutron spectra. Second, cascade-induced disordering and the inverse Kirkendall effect operating at the incoherent interfaces of MnS precipitates are thought to act as a pump to export Mn from the precipitate into the alloy matrix. Both of these processes will most likely allow sulfur, which is known to exert a deleterious influence on intergranular cracking, to re-enter the matrix. To test this hypothesis, compositions of MnS-type precipitates contained in several unirradiated and irradiated heats of Type 304, 316, and 348 stainless steels (SSs) were analyzed by Auger electron spectroscopy. Evidence is presented that shows a progressive compositional modification of MnS precipitates as exposure to neutrons increases in boiling water reactors. As the fluence increases, the Mn level in MnS decreases, whereas the Fe level increases. The S level also decreases relative to the combined level of Mn and Fe. MnS precipitates were also found to be a reservoir of other deleterious impurities such as F and O which could be also released due to radiation-induced instability of the precipitates

  16. Delayed hydride cracking: alternative pre-cracking method

    International Nuclear Information System (INIS)

    Mieza, Juan I.; Ponzoni, Lucio M.E.; Vigna, Gustavo L.; Domizzi, Gladys

    2009-01-01

    The internal components of nuclear reactors built-in Zr alloys are prone to a failure mechanism known as Delayed Hydride Cracking (DHC). This situation has triggered numerous scientific studies in order to measure the crack propagation velocity and the threshold stress intensity factor associated to DHC. Tests are carried out on fatigued pre-crack samples to ensure similar test conditions and comparable results. Due to difficulties in implementing the fatigue pre-crack method it would be desirable to replace it with a pre-crack produced by the same process of DHC, for which is necessary to demonstrate equivalence of this two methods. In this work tests on samples extracted from two Zr-2.5 Nb tubes were conducted. Some of the samples were heat treated to obtain a range in their metallurgical properties as well as different DHC velocities. A comparison between velocities measured in test samples pre-cracked by fatigue and RDIH is done, demonstrating that the pre-cracking method does not affect the measured velocity value. In addition, the incubation (t inc ), which is the time between the application of the load and the first signal of crack propagation, in samples pre-cracked by RDIH, was measured. It was found that these times are sufficiently short, even in the worst cases (lower speed) and similar to the ones of fatigued pre-cracked samples. (author)

  17. Predominantly elastic crack growth under combined creep-fatigue cycling

    International Nuclear Information System (INIS)

    Lloyd, G.J.

    1979-01-01

    A rationalization of the various observed effects of combined creep-fatigue cycling upon predominantly elastic fatigue-crack propagation in austenitic steel is presented. Existing and new evidence is used to show two main groups of behaviour: (i) material and cycling conditions which lead to modest increases (6-8 times) in the rate of crack growth are associated with relaxation-induced changes in the material deformation characteristics, and (ii) material and cycling conditions severe enough to generate internal fracture damage lead to significant (up to a factor of 30) increases in crack growth rate when compared with fast-cycling crack propagation rates at the same temperature. A working hypothesis is presented to show that the boundary between the two groups occurs when the scale of the nucleated creep damage is of the same magnitude as the crack tip opening displacement. This leads to the possibility of unstable crack advance. Creep crack growth rates are shown to provide an upper bound to creep-fatigue crack growth rates when crack advance is unstable. If the deformation properties only are affected by the creep-fatigue cycling then creep crack growth rates provide a lower bound. The role of intergranular oxygen corrosion in very low frequency crack growth tests is also briefly discussed. (author)

  18. Isolating the effect of radiation-induced segregation in irradiation-assisted stress corrosion cracking of austenitic stainless steels

    International Nuclear Information System (INIS)

    Busby, J.T.; Was, G.S.; Kenik, E.A.

    2002-01-01

    Post-irradiation annealing was used to help identify the role of radiation-induced segregation (RIS) in irradiation-assisted stress corrosion cracking (IASCC) by preferentially removing dislocation loop damage from proton-irradiated austenitic stainless steels while leaving the RIS of major and minor alloying elements largely unchanged. The goal of this study is to better understand the underlying mechanisms of IASCC. Simulations of post-irradiation annealing of RIS and dislocation loop microstructure predicted that dislocation loops would be removed preferentially over RIS due to both thermodynamic and kinetic considerations. To verify the simulation predictions, a series of post-irradiation annealing experiments were performed. Both a high purity 304L (HP-304L) and a commercial purity 304 (CP-304) stainless steel alloy were irradiated with 3.2 MeV protons at 360 deg. C to doses of 1.0 and 2.5 dpa. Following irradiation, post-irradiation anneals were performed at temperatures ranging from 400 to 650 deg. C for times between 45 and 90 min. Grain boundary composition was measured using scanning transmission electron microscopy with energy-dispersive spectrometry in both as-irradiated and annealed samples. The dislocation loop population and radiation-induced hardness were also measured in as-irradiated and annealed specimens. At all annealing temperatures above 500 deg. C, the hardness and dislocation densities decreased with increasing annealing time or temperature much faster than RIS. Annealing at 600 deg. C for 90 min removed virtually all dislocation loops while leaving RIS virtually unchanged. Cracking susceptibility in the CP-304 alloy was mitigated rapidly during post-irradiation annealing, faster than RIS, dislocation loop density or hardening. That the cracking susceptibility changed while the grain boundary chromium composition remained essentially unchanged indicates that Cr depletion is not the primary determinator for IASCC susceptibility. For the same

  19. Prediction of reinforcement corrosion using corrosion induced cracks width in corroded reinforced concrete beams

    International Nuclear Information System (INIS)

    Khan, Inamullah; François, Raoul; Castel, Arnaud

    2014-01-01

    This paper studies the evolution of reinforcement corrosion in comparison to corrosion crack width in a highly corroded reinforced concrete beam. Cracking and corrosion maps of the beam were drawn and steel reinforcement was recovered from the beam to observe the corrosion pattern and to measure the loss of mass of steel reinforcement. Maximum steel cross-section loss of the main reinforcement and average steel cross-section loss between stirrups were plotted against the crack width. The experimental results were compared with existing models proposed by Rodriguez et al., Vidal et al. and Zhang et al. Time prediction models for a given opening threshold are also compared to experimental results. Steel cross-section loss for stirrups was also measured and was plotted against the crack width. It was observed that steel cross-section loss in the stirrups had no relationship with the crack width of longitudinal corrosion cracks. -- Highlights: •Relationship between crack and corrosion of reinforcement was investigated. •Corrosion results of natural process and then corresponds to in-situ conditions. •Comparison with time predicting model is provided. •Prediction of load-bearing capacity from crack pattern was studied

  20. Review of current research and understanding of irradiation-assisted stress corrosion cracking

    International Nuclear Information System (INIS)

    Nelson, J.L.; Andresen, P.L.

    1992-01-01

    Concerns for irradiation-assisted stress corrosion cracking (IASCC) of reactor internals are increasing, especially for components that are not readily replaceable. Both laboratory and field data show that intergranular stress corrosion cracking of stainless steels and nickel-base alloys can result from long term exposure to the high energy neutron and gamma radiation that exists in the core of light water reactors (LWR's). Radiation affects cracking susceptibility via changes in material micro-chemistry (radiation induced segregation, or RIS), water chemistry (radiolysis) and material properties/stress (e.g., radiation induced creep and hardening). Based on many common dependencies, e.g., to solution purity, corrosion potential, crevicing and stress, IASCC falls within the continuum of environmental cracking phenomenon in high temperature water

  1. Numerical analysis for prediction of fatigue crack opening level

    International Nuclear Information System (INIS)

    Choi, Hyeon Chang

    2004-01-01

    Finite Element Analysis (FEA) is the most popular numerical method to simulate plasticity-induced fatigue crack closure and can predict fatigue crack closure behavior. Finite element analysis under plane stress state using 4-node isoparametric elements is performed to investigate the detailed closure behavior of fatigue cracks and the numerical results are compared with experimental results. The mesh of constant size elements on the crack surface can not correctly predict the opening level for fatigue crack as shown in the previous works. The crack opening behavior for the size mesh with a linear change shows almost flat stress level after a crack tip has passed by the monotonic plastic zone. The prediction of crack opening level presents a good agreement with published experimental data regardless of stress ratios, which are using the mesh of the elements that are in proportion to the reversed plastic zone size considering the opening stress intensity factors. Numerical interpolation results of finite element analysis can precisely predict the crack opening level. This method shows a good agreement with the experimental data regardless of the stress ratios and kinds of materials

  2. Elastic-plastic FEM-analysis of a nozzle corner crack and discussion of the results by some fracture mechanics concepts

    International Nuclear Information System (INIS)

    Aurich, D.; Brocks, W.; Noack, D.; Veith, H.

    1981-01-01

    From a three-dimensional elastic-plastic stress-distortion analysis according to the finite element method (FEM) for a straight inner edge crack at room temperature in a nozzle of the intermediate vessel ZB 2 made of 22 NiMoCr 37 steel, the results obtained for stresses and strains in the ligament before the crack front, the crack opening profile, and the propagation of the plastic zone as a function of internal pressure until through-plastifying of the ligament are shown and explained. (orig.) [de

  3. Microwave based method of monitoring crack formation

    International Nuclear Information System (INIS)

    Aman, Sergej; Aman, Alexander; Majcherek, Soeren; Hirsch, Soeren; Schmidt, Bertram

    2014-01-01

    The formation of cracks in glass particles was monitored by application of linearly polarized microwaves. The breakage behavior of glass spheres coated with a thin gold layer of about 50 nm, i.e. a thickness that is lower than the microwave penetration depth, was tested. In this way the investigation of fracture behavior of electronic circuits was simulated. A shielding current was induced in the gold layer by the application of microwaves. During the crack formation the distribution of this current changed abruptly and a scattered microwave signal appeared at the frequency of the incident microwaves. The time behavior of the scattered signal reflects the microscopic processes occurring during the fracture of the specimen. The duration of the increasing signal corresponds to the crack formation time in the tested specimen. This time was estimated as particle size divided by crack development speed in glass. An intense emission of electrons occurs during the formation of cracks. Due to this, coherent Thomson scattering of microwaves by emitted electrons becomes significant with a delay of a few microseconds after the initial phase of crack formation. In this time the intensity of the microwave signal increases. (paper)

  4. On the controlling parameters for fatigue-crack threshold at low homologous temperatures

    International Nuclear Information System (INIS)

    Yu, W.; Gerberich, W.W.

    1983-01-01

    Fatigue crack propagation phenomena near the threshold stress intensity level ΔK /SUB TH/ , has been a vigorously studied topic in recent years. Near threshold the crack propagates rather slowly, thus giving enough time for various physical and chemical reactions to take place. Room air, which is the most commonly encountered environment, can still supply various ingredients such as oxygen, water vapor (and thus hydrogen) to support these reactions. Much effort had been directed toward the environmental aspects of near threshold fatigue crack growth. By conducting tests under vacuum, Suresh and coworkers found that the crack propagation rate in a 2-1/4 Cr-1Mo steel was higher in vacuum than in air. An oxide induced closure, which served to reduce the effective stress intensity at the crack tip, seems to furnish a good explanation. Neumann and coworkers proposed that during the fatigue process, extrusion-intrusion pairs can develop as a consequence of reversed slip around the crack tip when the crack was propagated near threshold stress intensity. Beevers demonstrated that fatigue fracture surfaces contact each other during unloading even under tension-tension cycling. Kanninen and Atkinson also reached the conclusion that the compressive stress acting at the crack tip due to residual plasticity can induce closure. Microstructural effects have also been cited as important factors in near threshold crack growth. It is generally accepted that coarser grains have a beneficial effect on the resistance to the near threshold crack propagation

  5. Prediction of crack paths in WC-Co alloys

    International Nuclear Information System (INIS)

    Spiegler, R.; Fischmeister, H.F.

    1992-01-01

    This paper reports on a crack propagating through the WC-o microstructure which has to choose between paths along the binder/carbide interface and paths across binder regions. The latter paths are selected when the crack enters a binder region at a large angle from the nearest carbide interface, while the interface paths are preferred by cracks entering at a small angle. A critical angle can be defined for the switch from one type of crack path to the other. Empirical data for the area fractions of the two crack paths in widely different WC-Co alloys can be accounted for by a single critical angle, var-phi c = 25 degrees. Finite element analysis of the stress field in a region of binder enclosed between carbide grains shows that the preferred site for the growth of stress-induced microvoids will move from the carbide grain flanks to the interior of the binder region when the entry angle of the crack exceeds 24 degrees. Thus the observation of a critical angle deciding the crack path is verified by the stress field analysis and given a physical explanation in terms of the most likely site for microvoid formation

  6. Plasticity around an Axial Surface Crack in a Cylindrical Shell

    DEFF Research Database (Denmark)

    Krenk, Steen

    1979-01-01

    of the yield zone. The model is used to analyse published test data on surface cracked pressurised pipes. The analysis consists in COD evaluation and estimate of failure as a consequence of plastic instability. A method is proposed which deals with the problem by simultaneous analysis of a number of cracks......This paper presents a plasticity model for deep axial surface cracks in pressurised pipes. The model is used in an investigation of the relative merits of fracture criteria based on COD and plastic instability. Recent investigations have shown that the inconsistency of the singular bending stress...... on the bending stresses is considerable. In the case of surface cracks moments are induced due to the eccentricity of the crack and transverse shear effects should therefore be included. A plasticity model for a rectangular axial surface crack is developed. Like a previous surface crack model by Erdogen...

  7. Mechanical factors affecting reliability of pressure components (fatigue, cracking)

    International Nuclear Information System (INIS)

    Lebey, J.; Garnier, C.; Roche, R.; Barrachin, B.

    1978-01-01

    The reliability of a pressure component can be seriously affected by the formation and development of cracks. The experimental studies presented in this paper are devoted to three different aspects of crack propagation phenomena which have been relatively little described. In close connection with safety analyses of PWR, the authors study the influence of the environment by carrying out fatigue tests with samples bathed in hot pressurized water. Ferritic, austenitic and Incolloy 800 steels were used and the results are presented in the form of fatigue curves in the oligocyclic region. The second part of the paper relates to crack initiation cirteria in ductile steels weakened by notches. The CT samples used make it possible to study almost all types of fracture (ductile, intermediate and brittle). The use of two criteria based on the load limit and on the toughness of the material constitutes a practical way of evaluating crack propagation conditions. A series of tests carried out on notched spherical vessels of different size shows that large vessels are relatively brittle; fast unstable fracture is observed as size increases. Crack growth rate in PWR primary circuits (3/6 steel) is studied on piping elements (0.25 scale) subjected to cyclic stress variations (285 0 C and with pressure varying between 1 and 160 bar in each cycle). By calculating the stress intensity factor, correlation with results obtained in the laboratory on CT samples is possible. (author)

  8. Influence of MSD crack pattern on the residual strength of flat stiffened sheets

    Science.gov (United States)

    Nilsson, K.-F.

    A parameter study of the residual strength for a multiple site damaged (MSD) stiffened sheet is presented. The analysis is based on an elastic-plastic fracture analysis using the yield-strip model for interaction between a lead crack and the smaller MSD cracks. Two crack growth criteria, one with a pronounced crack growth resistance and one with no crack growth resistance and five different MSD crack patterns, are analysed for different sizes of the lead crack and the smaller MSD cracks. The analysis indicates that the residual strength reduction depends on all these parameters and that MSD may totally erode the crack arrest capability of a tear strap. Another important outcome is that for certain combinations also very small MSD cracks may induce a significant residual strength reduction.

  9. Micro-crack detection in high-performance cementitious materials

    DEFF Research Database (Denmark)

    Lura, Pietro; Guang, Ye; Tanaka, Kyoji

    2005-01-01

    of high-performance cement pastes in silicone moulds that exert minimal external restraint. Cast-in steel rods with varying diameter internally restrain the autogenous shrinkage and lead to crack formation. Dimensions of the steel rods are chosen so that the size of this restraining inclusion resembles......-ray tomography, do not allow sufficient resolution of microcracks. A new technique presented in this paper allows detection of microcracks in cement paste while avoiding artefacts induced by unwanted restraint, drying or temperature variations. The technique consists in casting small circular cylindrical samples...... aggregate size. Gallium intrusion of the cracks and subsequent examination by electron probe micro analysis, EPMA, are used to identify the cracks. The gallium intrusion technique allows controllable impregnation of cracks in the cement paste. A distinct contrast between gallium and the surrounding material...

  10. A reliability model for interlayer dielectric cracking during fast thermal cycling

    NARCIS (Netherlands)

    Nguyen, Van Hieu; Salm, Cora; Krabbenborg, B.H.; Krabbenborg, B.H.; Bisschop, J.; Mouthaan, A.J.; Kuper, F.G.; Ray, Gary W.; Smy, Tom; Ohta, Tomohiro; Tsujimura, Manabu

    2003-01-01

    Interlayer dielectric (ILD) cracking can result in short circuits of multilevel interconnects. This paper presents a reliability model for ILD cracking induced by fast thermal cycling (FTC) stress. FTC tests have been performed under different temperature ranges (∆T) and minimum temperatures (Tmin).

  11. The Cracking Mechanism of Ferritic-Austenitic Cast Steel

    Directory of Open Access Journals (Sweden)

    Stradomski G.

    2016-12-01

    Full Text Available In the high-alloy, ferritic - austenitic (duplex stainless steels high tendency to cracking, mainly hot-is induced by micro segregation processes and change of crystallization mechanism in its final stage. The article is a continuation of the problems presented in earlier papers [1 - 4]. In the range of high temperature cracking appear one mechanism a decohesion - intergranular however, depending on the chemical composition of the steel, various structural factors decide of the occurrence of hot cracking. The low-carbon and low-alloy cast steel casting hot cracking cause are type II sulphide, in high carbon tool cast steel secondary cementite mesh and / or ledeburite segregated at the grain solidified grains boundaries, in the case of Hadfield steel phosphorus - carbide eutectic, which carrier is iron-manganese and low solubility of phosphorus in high manganese matrix. In duplex cast steel the additional factor increasing the risk of cracking it is very “rich” chemical composition and related with it processes of precipitation of many secondary phases.

  12. Toughness determination of zirconia toughened alumina ceramics from growth of indentation-induced cracks

    International Nuclear Information System (INIS)

    Basu, D.; Sarkar, B.K.

    1996-01-01

    Short surface cracks were generated by Vickers indentation on the polished surface of alumina and different zirconia toughened alumina (ZTA) specimens, and their morphology was studied by serial sectioning. These cracks were grown in three-point bend tests under stepwise loading, and variation of toughness with crack extension was plotted to graphically separate the contributions from residual stress intensity and applied stress intensity factors. The plateau toughness determined from the intercept height of the crack extension plots exhibited an upward trend with zirconia content up to 15 vol% ZrO 2 addition in the composition, which was proportional to the fraction of transformable tetragonal grains contributing to transformation toughening. copyright 1996 Materials Research Society

  13. Experimental study on the crack detection with optimized spatial wavelet analysis and windowing

    Science.gov (United States)

    Ghanbari Mardasi, Amir; Wu, Nan; Wu, Christine

    2018-05-01

    In this paper, a high sensitive crack detection is experimentally realized and presented on a beam under certain deflection by optimizing spatial wavelet analysis. Due to the crack existence in the beam structure, a perturbation/slop singularity is induced in the deflection profile. Spatial wavelet transformation works as a magnifier to amplify the small perturbation signal at the crack location to detect and localize the damage. The profile of a deflected aluminum cantilever beam is obtained for both intact and cracked beams by a high resolution laser profile sensor. Gabor wavelet transformation is applied on the subtraction of intact and cracked data sets. To improve detection sensitivity, scale factor in spatial wavelet transformation and the transformation repeat times are optimized. Furthermore, to detect the possible crack close to the measurement boundaries, wavelet transformation edge effect, which induces large values of wavelet coefficient around the measurement boundaries, is efficiently reduced by introducing different windowing functions. The result shows that a small crack with depth of less than 10% of the beam height can be localized with a clear perturbation. Moreover, the perturbation caused by a crack at 0.85 mm away from one end of the measurement range, which is covered by wavelet transform edge effect, emerges by applying proper window functions.

  14. The manufacturing of Stress Corrosion Crack (SCC) on Inconel 600 tube

    International Nuclear Information System (INIS)

    Bae, Seunggi; Bak, Jaewoong; Kim, Seongcheol; Lee, Sangyul; Lee, Boyoung

    2014-01-01

    The Stress Corrosion Crack (SCC), taken a center stage in recently accidents about nuclear power plants, is one of the environmentally induced cracking occurred when a metallic structure under tensile stress is exposed to corrosive environment. In this study, the SCC was manufactured in the simulated corrosive environmental conditions on Inconel 600 tube that widely applied in the nuclear power plants. The tensile stress which is one of the main factors to induce SCC was given by GTAW welding in the inner surface of the specimen. The corrosive environment was simulated by using the sodium hydroxide (NaOH) and sodium sulfide (Na 2 S). In this study, SCC was manufactured in the simulated corrosive environmental conditions with Inconel 600 tube that widely applied in the nuclear power plants. 1) The SCC was manufactured on Inconel 600 tube in simulated operational environments of nuclear power plants. In the experiment, the welding heat input which is enough to induce the cracking generated the SCC near the welding bead. So, in order to prevent the SCC, the residual stress on structure should be relaxed. 2) The branch-type cracking was detected

  15. Modified Dugdale crack models - some easy crack relations

    DEFF Research Database (Denmark)

    Nielsen, Lauge Fuglsang

    1997-01-01

    the same strength as a plain Dugdale model. The critical energy release rates Gamma_CR, however, become different. Expressions (with easy computer algorithms) are presented in the paper which relate critical energy release rates and crack geometry to arbitrary cohesive stress distributions.For future...... lifetime analysis of viscoelastic materials strain energy release rates, crack geometries, and cohesive stress distributions are considered as related to sub-critical loads sigma stress-deformation tests......The Dugdale crack model is widely used in materials science to predict strength of defective (cracked) materials. A stable Dugdale crack in an elasto-plastic material is prevented from spreading by uniformly distributed cohesive stresses acting in narrow areas at the crack tips. These stresses...

  16. Concrete cover cracking with reinforcement corrosion of RC beam during chloride-induced corrosion process

    International Nuclear Information System (INIS)

    Zhang Ruijin; Castel, Arnaud; Francois, Raoul

    2010-01-01

    This paper deals with the evolution of the corrosion pattern based on two beams corroded by 14 years (beam B1CL1) and 23 years (beam B2CL1) of conservation in a chloride environment. The experimental results indicate that, at the cracking initiation stage and the first stage of cracking propagation, localized corrosion due to chloride ingress is the predominant corrosion pattern and pitting corrosion is the main factor that influences the cracking process. As corrosion cracking increases, general corrosion develops rapidly and gradually becomes predominant in the second stage of cracking propagation. A comparison between existing models and experimental results illustrates that, although Vidal et al.'s model can better predict the reinforcement corrosion of beam B1CL1 under localized corrosion, it cannot predict the corrosion of beam B2CL1 under general corrosion. Also, Rodriguez's model, derived from the general corrosion due to electrically accelerated corrosion experiments, cannot match natural chloride corrosion irrespective of whether corrosion is localized or general. Thus, for natural general corrosion in the second stage of cracking propagation, a new model based on the parameter of average steel cross-section loss is put forward to predict steel corrosion from corrosion cracking.

  17. The influence of loading frequency on near-threshold fatigue crack growth

    International Nuclear Information System (INIS)

    Ogawa, Takeshi; Tokaji, Keiro; Ochi, Satoshi

    1986-01-01

    Fatigue crack growth and crack closure in the near-threshold region were investigated under different loading frequencies for three types of steel. The results show that the loading frequency influences the near-threshold characteristics in fatigue crack growth, through the different contributions of the fretting oxide induced crack closure. This behaviour is attributed to condensation of moisture between crack faces, which is influenced by the loading frequency. The formation of the fretting oxide debris promoted by the condensation of moisture becomes marked at a higher frequency. However, it is an unstable and complicating phenomenon, since the condensation is also influenced by relative humidity, test temperature and sheet thickness. Therefore, it is concluded that non-oxide controlled crack growth characteristics should be used for the life prediction of structures. (author)

  18. Stress intensity factors of three parallel edge cracks under bending moments

    International Nuclear Information System (INIS)

    Ismail, A E

    2013-01-01

    This paper reports the study of stress intensity factors (SIF) of three edge cracks in a finite plate under bending moments. The goal of this paper was to analyze the three edge crack interactions under such loading. Several studies can be found in literature discussing on mode I SIF. However, most of these studies obtained the SIFs using tensile force. Lack of SIF reported discussing on the SIFs obtained under bending moments. ANSYS finite element program was used to develop the finite element model where singular elements were used to model the cracks. Different crack geometries and parameters were utilized in order to characterize the SIFs. According to the present results, crack geometries played a significant role in determining the SIFs and consequently induced the crack interaction mechanisms

  19. Strain-induced cracking corrosion in pipelines of conventional power plants; Dehnungsinduzierte Risskorrosion in Rohrsystemen von konventionellen Kraftwerksanlagen

    Energy Technology Data Exchange (ETDEWEB)

    Adamsky, F.J.; Kempkes, B. [PreussenElektra Engineering GmbH, Gelsenkirchen (Germany); Ernst, J. [RWE Energie AG, Essen (Germany)

    2000-07-01

    Since the mid-sixties, stress corrosion cracking has been reported in highly loaded components of conventional power plants. Damage investigations were followed by extensive fundamental studies on crack initiation and propagation mechanisms, with particular regard to the water quality. The contribution presents causes, patterns, preferred sites and operating conditions of strain-induced corrosion. [German] Seit Anfang der 60er-Jahre wird ueber Risskorrosionsschaeden im wasserberuehrten Teil konventioneller Kraftwerksanlagen berichtet, die stets an hochbeanspruchten Bereichen festzustellen sind - vorwiegend in unrunden Rohrbogen oder Fallrohrbohrungen von Kesseltrommeln. Den Schadensuntersuchungen schlossen sich umfangreiche Grundsatzuntersuchungen an, um den Mechanismus von Rissbildung und Rissfortschritt kennenzulernen und daraus dann Abhilfemassnahmen abzuleiten. Bei schadhaften Rohrboegen stellte man in den Rissbereichen meist hoehere Unrundheiten fest und bei Kesseltrommeln Spannungsspitzen an den Lochraendern. Der Wasserqualitaet, vornehmlich dem O{sub 2}-Gehalt, der Art der Konservierung bei Stillstaenden und insbesondere haeufigeren Anfahrten bei kleineren und aelteren Anlagen wurde besondere Bedeutung beigemessen. Im Beitrag werden Ursachen, Erscheinungsformen, bevorzugte Bereiche und Betriebszustaende der dehnungsinduzierten Korrosion dargestellt. (orig.)

  20. Exposure to reactive intermediate-inducing drugs during pregnancy and the incident use of psychotropic medications among children

    NARCIS (Netherlands)

    Tran, Yen-Hao; Groen, Henk; Bergman, Jorieke E H; Hak, Eelko; Wilffert, Bob

    Purpose Our study aimed to investigate the association between prenatal exposure to reactive intermediate (RI)-inducing drugs and the initiation of psychotropic medications among children. Methods We designed a cohort study using a pharmacy prescription database. Pregnant women were considered

  1. Crack modeling of rotating blades with cracked hexahedral finite element method

    Science.gov (United States)

    Liu, Chao; Jiang, Dongxiang

    2014-06-01

    Dynamic analysis is the basis in investigating vibration features of cracked blades, where the features can be applied to monitor health state of blades, detect cracks in an early stage and prevent failures. This work presents a cracked hexahedral finite element method for dynamic analysis of cracked blades, with the purpose of addressing the contradiction between accuracy and efficiency in crack modeling of blades in rotor system. The cracked hexahedral element is first derived with strain energy release rate method, where correction of stress intensity factors of crack front and formulation of load distribution of crack surface are carried out to improve the modeling accuracy. To consider nonlinear characteristics of time-varying opening and closure effects caused by alternating loads, breathing function is proposed for the cracked hexahedral element. Second, finite element method with contact element is analyzed and used for comparison. Finally, validation of the cracked hexahedral element is carried out in terms of breathing effects of cracked blades and natural frequency in different crack depths. Good consistency is acquired between the results with developed cracked hexahedral element and contact element, while the computation time is significantly reduced in the previous one. Therefore, the developed cracked hexahedral element achieves good accuracy and high efficiency in crack modeling of rotating blades.

  2. Evaluation of cracking in steam generator feedwater piping in pressurized water reactor plants

    International Nuclear Information System (INIS)

    Goldberg, A.; Streit, R.D.

    1981-05-01

    Cracking in feedwater piping was detected near the inlet to steam generators in 15 pressurized water reactor plants. Sections with cracks from nine plants are examined with the objective of identifying the cracking mechanism and assessing various factors that might contribute to this cracking. Using transmission electron microscopy, fatigue striations are observed on replicas of cleaned crack surfaces. Calculations based on the observed striation spacings gave a cyclic stress value of 150 MPa (22 ksi) for one of the major cracks. The direction of crack propagation was invariably related to the piping surface and not to the piping axis. These two factors are consistent with the proposed concept of thermally induced, cyclic, tensile surface stresses and it is concluded that the overriding factor in the cracking problem was the presence of such undocumented cyclic loads

  3. Stress-corrosion cracking in BWR and PWR piping

    International Nuclear Information System (INIS)

    Weeks, R.W.

    1983-07-01

    Intergranular stress-corrosion cracking of weld-sensitized wrought stainless steel piping has been an increasingly ubiquitous and expensive problem in boiling-water reactors over the last decade. In recent months, numerous cracks have been found, even in large-diameter lines. A number of potential remedies have been developed. These are directed at providing more resistant materials, reducing weld-induced stresses, or improving the water chemistry. The potential remedies are discussed, along with the capabilities of ultrasonic testing to find and size the cracks and related safety issues. The problem has been much less severe to date in pressurized-water reactors, reflecting the use of different materials and much lower coolant oxygen levels

  4. Crack closure and growth behavior of short fatigue cracks under random loading (part I : details of crack closure behavior)

    International Nuclear Information System (INIS)

    Lee, Shin Young; Song, Ji Ho

    2000-01-01

    Crack closure and growth behavior of physically short fatigue cracks under random loading are investigated by performing narrow-and wide-band random loading tests for various stress ratios. Artificially prepared two-dimensional, short through-thickness cracks are used. The closure behavior of short cracks under random loading is discussed, comparing with that of short cracks under constant-amplitude loading and also that of long cracks under random loading. Irrespective of random loading spectrum or block length, the crack opening load of short cracks is much lower under random loading than under constant-amplitude loading corresponding to the largest load cycle in a random load history, contrary to the behavior of long cracks that the crack opening load under random loading is nearly the same as or slightly higher than constant-amplitude results. This result indicates that the largest load cycle in a random load history has an effect to enhance crack opening of short cracks

  5. Analysis of crack opening stresses for center- and edge-crack tension specimens

    Directory of Open Access Journals (Sweden)

    Tong Di-Hua

    2014-04-01

    Full Text Available Accurate determination of crack opening stress is of central importance to fatigue crack growth analysis and life prediction based on the crack-closure model. This paper studies the crack opening behavior for center- and edge-crack tension specimens. It is found that the crack opening stress is affected by the crack tip element. By taking the crack tip element into account, a modified crack opening stress equation is given for the center-crack tension specimen. Crack surface displacement equations for an edge crack in a semi-infinite plate under remote uniform tension and partially distributed pressure are derived by using the weight function method. Based on these displacements, a crack opening stress equation for an edge crack in a semi-infinite plate under uniform tension has been developed. The study shows that the crack opening stress is geometry-dependent, and the weight function method provides an effective and reliable tool to deal with such geometry dependence.

  6. A consistent partly cracked XFEM element for cohesive crack growth

    DEFF Research Database (Denmark)

    Asferg, Jesper L.; Poulsen, Peter Noe; Nielsen, Leif Otto

    2007-01-01

    Present extended finite element method (XFEM) elements for cohesive crack growth may often not be able to model equal stresses on both sides of the discontinuity when acting as a crack-tip element. The authors have developed a new partly cracked XFEM element for cohesive crack growth with extra...... enrichments to the cracked elements. The extra enrichments are element side local and were developed by superposition of the standard nodal shape functions for the element and standard nodal shape functions for a sub-triangle of the cracked element. With the extra enrichments, the crack-tip element becomes...... capable of modelling variations in the discontinuous displacement field on both sides of the crack and hence also capable of modelling the case where equal stresses are present on each side of the crack. The enrichment was implemented for the 3-node constant strain triangle (CST) and a standard algorithm...

  7. Mechanism of crack healing at room temperature revealed by atomistic simulations

    International Nuclear Information System (INIS)

    Li, J.; Fang, Q.H.; Liu, B.; Liu, Y.; Liu, Y.W.; Wen, P.H.

    2015-01-01

    Three dimensional molecular dynamics (MD) simulations are systematically carried out to reveal the mechanism of the crack healing at room temperature, in terms of the dislocation shielding and the atomic diffusion to control the crack closure, in a copper (Cu) plate suffering from a shear loading. The results show that the process of the crack healing is actualized through the dislocation emission at a crack tip accompanied with intrinsic stacking faults ribbon forming in the crack tip wake, the dislocation slipping in the matrix and the dislocation annihilation in the free surface. Dislocation included stress compressing the crack tip is examined from the MD simulations and the analytical models, and then the crack closes rapidly due to the assistance of the atomic diffusion induced by the thermal activation when the crack opening displacement is less than a threshold value. This phenomenon is very different from the previous results for the crack propagation under the external load applied because of the crack healing (advancing) largely dependent on the crystallographic orientations of crack and the directions of external loading. Furthermore, based on the energy characteristic and considering the crack size effect, a theoretical model is established to predict the relationships between the crack size and the shear stress which qualitatively agree well with that obtained in the MD simulations

  8. Automatic crack detection method for loaded coal in vibration failure process.

    Directory of Open Access Journals (Sweden)

    Chengwu Li

    Full Text Available In the coal mining process, the destabilization of loaded coal mass is a prerequisite for coal and rock dynamic disaster, and surface cracks of the coal and rock mass are important indicators, reflecting the current state of the coal body. The detection of surface cracks in the coal body plays an important role in coal mine safety monitoring. In this paper, a method for detecting the surface cracks of loaded coal by a vibration failure process is proposed based on the characteristics of the surface cracks of coal and support vector machine (SVM. A large number of cracked images are obtained by establishing a vibration-induced failure test system and industrial camera. Histogram equalization and a hysteresis threshold algorithm were used to reduce the noise and emphasize the crack; then, 600 images and regions, including cracks and non-cracks, were manually labelled. In the crack feature extraction stage, eight features of the cracks are extracted to distinguish cracks from other objects. Finally, a crack identification model with an accuracy over 95% was trained by inputting the labelled sample images into the SVM classifier. The experimental results show that the proposed algorithm has a higher accuracy than the conventional algorithm and can effectively identify cracks on the surface of the coal and rock mass automatically.

  9. Unsaturated Seepage Analysis of Cracked Soil including Development Process of Cracks

    Directory of Open Access Journals (Sweden)

    Ling Cao

    2016-01-01

    Full Text Available Cracks in soil provide preferential pathways for water flow and their morphological parameters significantly affect the hydraulic conductivity of the soil. To study the hydraulic properties of cracks, the dynamic development of cracks in the expansive soil during drying and wetting has been measured in the laboratory. The test results enable the development of the relationships between the cracks morphological parameters and the water content. In this study, the fractal model has been used to predict the soil-water characteristic curve (SWCC of the cracked soil, including the developmental process of the cracks. The cracked expansive soil has been considered as a crack-pore medium. A dual media flow model has been developed to simulate the seepage characteristics of the cracked expansive soil. The variations in pore water pressure at different part of the model are quite different due to the impact of the cracks. This study proves that seepage characteristics can be better predicted if the impact of cracks is taken into account.

  10. Corrosion characteristics of a 4-year naturally corroded reinforced concrete beam with load-induced transverse cracks

    International Nuclear Information System (INIS)

    Fu, Chuanqing; Jin, Nanguo; Ye, Hailong; Jin, Xianyu; Dai, Wei

    2017-01-01

    Highlights: • A comprehensive study of corrosion characteristics of a naturally corroded RC beam. • New insights on the role of cracks in corrosion propagation of steel in concrete. • EMPA and 3D laser scanning provide quantitative analysis of corroded rebar. - Abstract: This work studies the corrosion characteristics of reinforcement in a 4-year naturally corroded concrete beam after accelerated chloride penetration. The results show that the presence of transverse cracks in the tension surface of reinforced concrete beam can globally exacerbate the loss of cross-sectional area of rebar. However, there is no strong correlation between the width of transverse cracks, with the width of longitudinal cracks and loss of cross-sectional area of corroded rebar at a specific location. The self-healing of cracks and sacrificing roles of stirrups at crack tips seem to reduce the impacts of cracks on the corrosion propagation.

  11. Unified description of neutron-, proton- and photon-induced fission cross sections in intermediate energy region

    International Nuclear Information System (INIS)

    Fukahori, Tokio; Iwamoto, Osamu; Chiba, Satoshi

    2003-01-01

    For an accelerator-driven nuclear waste transmutation system, it is very important to estimate sub-criticality of core system for feasibility and design study of the system. The fission cross section in the intermediate energy range has an important role. A program FISCAL has been developed to calculate neutron-, proton- and photon-induced fission cross sections in the energy region from several tens of MeV to 3 GeV. FISCAL adopts the systematics considering experimental data for Ag- 243 Am. It is found that unified description of neutron-, proton- and photon-induced fission cross sections is available. (author)

  12. Rate-dependent mode I interlaminar crack growth mechanisms in graphite/epoxy and graphite/PEEK

    Science.gov (United States)

    Gillespie, J. W., Jr.; Carlsson, L. A.; Smiley, A. J.

    1987-01-01

    In this paper the mode I fracture behavior of graphite/epoxy and graphite/PEEK composites is examined over four decades of crosshead rates (0.25-250 mm/min). Straight-sided double-cantilever-beam specimens consisting of unidirectional laminates were tested at room temperature. For graphite/epoxy the load-deflection response was linear to fracture, and stable slow crack growth initiating at the highest load level was observed for all rates tested. In contrast, mode I crack growth in the graphite/PEEK material was often unstable and showed stick-slip behavior. Subcritical crack growth occurring prior to the onset of fracture was observed at intermediate displacement rates. A mechanism for the fracture behavior of the graphite/PEEK material (based on viscoelastic, plastic, and microcrack coalescence in the process zone) is proposed and related to the observed rate-dependent phenomena.

  13. Underclad cracks growth under fatigue loading in stainless steel cladding

    International Nuclear Information System (INIS)

    Bernard, J.L.; Bodson, F.; Doule, A.; Slama, G.; Bramat, M.; Doucet, J.P.; Maltrud, F.

    1981-01-01

    Hydrogen induced cracks have been found in HAZ of PWR vessel nozzles under stainless steel cladding. Fatigue tests were performed to collect a large amount of data on the possible propagation of this type of flaws. Tests were conducted in two steps. The aim of the first step was to set up the experimental equipment and to device an adequate method for following cracks during fatigue loading. Clad plates with electroerosion machined slots were used for this purpose. The second step was then undertaken with material taken out of an actual nozzle containing hydrogen induced cracks in the HAZ under stainless steel cladding or flaws simulated by electroerosion machined slots. The test loadings were comparable to in service loadings of the nozzles. Special attention was taken to get representative R ratios. Again for the sake of representativity, the tests were performed at 300 0 C (In service temperature) and the hydrotest was simulated. The main results are: It was possible to follow the whole failure process by combining non-destructive examinations during fatigue testing and fractographic observations of broken specimens. Different striation patterns, before and after air has penetrated the actual embedded cracks were observed. Numerical simulation of fatigue crack growth of actual or simulated defects were consistent with experimental data, provided mainly that defect shape, effect of R ratio and of environment were taken into account. (orig.)

  14. Simulation of surface crack initiation induced by slip localization and point defects kinetics

    International Nuclear Information System (INIS)

    Sauzay, Maxime; Liu, Jia; Rachdi, Fatima

    2014-01-01

    Crack initiation along surface persistent slip bands (PSBs) has been widely observed and modelled. Nevertheless, from our knowledge, no physically-based fracture modelling has been proposed and validated with respect to the numerous recent experimental data showing the strong relationship between extrusion and microcrack initiation. The whole FE modelling accounts for: - localized plastic slip in PSBs; - production and annihilation of vacancies induced by cyclic slip. If temperature is high enough, point defects may diffuse in the surrounding matrix due to large concentration gradients, allowing continuous extrusion growth in agreement with Polak's model. At each cycle, the additional atoms diffusing from the matrix are taken into account by imposing an incremental free dilatation; - brittle fracture at the interfaces between PSBs and their surrounding matrix which is simulated using cohesive zone modelling. Any inverse fitting of parameter is avoided. Only experimental single crystal data are used such as hysteresis loops and resistivity values. Two fracture parameters are required: the {111} surface energy which depends on environment and the cleavage stress which is predicted by the universal binding energy relationship. The predicted extrusion growth curves agree rather well with the experimental data published for copper and the 316L steel. A linear dependence with respect to PSB length, thickness and slip plane angle is predicted in agreement with recent AFM measurement results. Crack initiation simulations predict fairly well the effects of PSB length and environment for copper single and poly-crystals. (authors)

  15. Initiation and propagation of rebar corrosion in carbonated and cracked concrete

    International Nuclear Information System (INIS)

    Ghantous, Rita-Maria

    2016-01-01

    This thesis aims to study the carbonation-induced corrosion initiation and propagation in cracked concrete under different conditions. It is performed in the framework of concrete ageing management of cooling towers of Electricity of France (EDF) nuclear power plants. Indeed some of them can be affected by cracks which may promote the carbonation of the concrete surrounding the cracks and induce a rapid reinforcement corrosion initiation in the carbonated area. Firstly, cracks representative of those encountered in the cooling towers concrete are reproduced on laboratory specimens using the three point bending test. Three crack openings are obtained (100 μm, 300 μm and 500 μm). Cracked specimens are thereafter exposed to accelerated carbonation for two aims. First for the acceleration of the concrete neutralization phase which ensure the suitable thermodynamic conditions for active corrosion initiation. Second, for the estimation of the length of the mechanically damaged steel/binder interface supposed to be comparable to the carbonated length along the rebar on both sides of the crack. It is found that carbonation at 50% CO_2 is not suitable here because it overestimated the damaged zone length, maybe due to enhanced carbonation shrinkage. The second part aims to investigate the corrosion initiation and propagation phases while varying several parameters. For this purpose, cracked and carbonated specimens are subjected to corrosion under different exposure conditions. Specimens showing different crack widths and different types of binder are corroded in a reference test in which 30 minutes of rain occurs each 3 days at 20 C. Additionally, some corrosion tests are realized under raining/drying cycles for 3 minutes rain, other at 40 C and other in natural environmental conditions. Moreover, some cracked specimens are exposed in different orientations with respect to rain. Furthermore, specimens with different bars locations are prepared in order to investigate

  16. Innovative Approach to Establish Root Causes for Cracking in Aggressive Reactor Environments

    International Nuclear Information System (INIS)

    Bruemmer, Stephen M.; Thomas, Larry E.; Vetrano, John S.; Simonen, Edward P.

    2003-01-01

    The research focuses on the high-resolution characterization of degradation microstructures and microchemistries in specimens tested under controlled conditions for the environment and for the material where in-service complexities can be minimized. Thermodynamic and kinetic modeling of crack-tip processes is employed to analyze corrosion-induced structures and gain insights into degradation mechanisms. Novel mechanistic ''fingerprinting'' of crack-tip structures is used to isolate causes of environmental cracking in tandem with quantitative measurements of crack growth. Sample preparation methods and advanced analytical techniques are used to characterize corrosion/oxidation reactions and crack-tip structures at near atomic dimensions in order to gain insight into fundamental environmental cracking mechanisms. Reactions at buried interfaces, not accessible by conventional approaches, are being systematically interrogated. Crack-growth experiments in high-temperature water environments are evaluating and isolating the effects of material condition (matrix strength, grain boundary composition and precipitation) on stress corrosion cracking (SCC). The fundamental understanding of crack advance mechanisms will establish the basis to design new corrosion-resistant alloys for current light-water reactors and advanced reactor systems

  17. Coincidence measurements of intermediate mass fragments produced in /sup 32/S-induced reactions on Ag at E/A = 22.5 MeV

    International Nuclear Information System (INIS)

    Fields, D.J.; Lynch, W.G.; Nayak, T.K.

    1986-01-01

    Single- and two-particle inclusive cross sections for the production of light nuclei and intermediate mass fragments, 3< or =Z< or =24, were measured at angles well beyond the grazing angle for /sup 32/S-induced reactions on Ag at 720 MeV. Information about fragment multiplicities and reaction dynamics was extracted from measurements of light particles, intermediate mass fragments, and targetlike residues in coincidence with intermediate mass fragments. Incomplete linear momentum transfer and non-compound-particle emission are important features of collisions producing intermediate mass fragments. About half of the incident kinetic energy in these collisions is converted into internal excitation. The mean multiplicity of intermediate mass fragments is of the order of 1. Particle correlations are strongly enhanced in the plane which contains the intermediate mass fragment and the beam axis

  18. Sub-10-micrometer toughening and crack tip toughness of dental enamel.

    Science.gov (United States)

    Ang, Siang Fung; Schulz, Anja; Pacher Fernandes, Rodrigo; Schneider, Gerold A

    2011-04-01

    In previous studies, enamel showed indications to occlude small cracks in-vivo and exhibited R-curve behaviors for bigger cracks ex-vivo. This study quantifies the crack tip's toughness (K(I0),K(III0)), the crack's closure stress and the cohesive zone size at the crack tip of enamel and investigates the toughening mechanisms near the crack tip down to the length scale of a single enamel crystallite. The crack-opening-displacement (COD) profile of cracks induced by Vickers indents on mature bovine enamel was studied using atomic force microscopy (AFM). The mode I crack tip toughness K(I0) of cracks along enamel rod boundaries and across enamel rods exhibit a similar range of values: K(I0,Ir)=0.5-1.6MPa m(0.5) (based on Irwin's 'near-field' solution) and K(I0,cz)=0.8-1.5MPa m(0.5) (based on the cohesive zone solution of the Dugdale-Muskhelishvili (DM) crack model). The mode III crack tip toughness K(III0,Ir) was computed as 0.02-0.15MPa m(0.5). The crack-closure stress at the crack tip was computed as 163-770 MPa with a cohesive zone length and width 1.6-10.1μm and 24-44 nm utilizing the cohesive zone solution. Toughening elements were observed under AFM and SEM: crack bridging due to protein ligament and hydroxyapatite fibres (micro- and nanometer scale) as well as microcracks were identified. Crown Copyright © 2010. Published by Elsevier Ltd. All rights reserved.

  19. Nonlinear ultrasonic fatigue crack detection using a single piezoelectric transducer

    Science.gov (United States)

    An, Yun-Kyu; Lee, Dong Jun

    2016-04-01

    This paper proposes a new nonlinear ultrasonic technique for fatigue crack detection using a single piezoelectric transducer (PZT). The proposed technique identifies a fatigue crack using linear (α) and nonlinear (β) parameters obtained from only a single PZT mounted on a target structure. Based on the different physical characteristics of α and β, a fatigue crack-induced feature is able to be effectively isolated from the inherent nonlinearity of a target structure and data acquisition system. The proposed technique requires much simpler test setup and less processing costs than the existing nonlinear ultrasonic techniques, but fast and powerful. To validate the proposed technique, a real fatigue crack is created in an aluminum plate, and then false positive and negative tests are carried out under varying temperature conditions. The experimental results reveal that the fatigue crack is successfully detected, and no positive false alarm is indicated.

  20. Crack detecting method

    International Nuclear Information System (INIS)

    Narita, Michiko; Aida, Shigekazu

    1998-01-01

    A penetration liquid or a slow drying penetration liquid prepared by mixing a penetration liquid and a slow drying liquid is filled to the inside of an artificial crack formed to a member to be detected such as of boiler power generation facilities and nuclear power facilities. A developing liquid is applied to the periphery of the artificial crack on the surface of a member to be detected. As the slow-drying liquid, an oil having a viscosity of 56 is preferably used. Loads are applied repeatedly to the member to be detected, and when a crack is caused to the artificial crack, the permeation liquid penetrates into the crack. The penetration liquid penetrated into the crack is developed by the developing liquid previously coated to the periphery of the artificial crack of the surface of the member to be detected. When a crack is caused, since the crack is developed clearly even if it is a small opening, the crack can be recognized visually reliably. (I.N.)

  1. Environment-assisted cracking of cast WE43-T6 magnesium

    International Nuclear Information System (INIS)

    Marrow, T.J.; Bin Ahmad, A.; Khan, I.N.; Sim, S.M.A.; Torkamani, S.

    2004-01-01

    Environment-assisted cracking of WE43 cast magnesium (4.2 wt.% Yt, 2.3 wt.% Nd, 0.7% Zr, 0.8% HRE) in the T6 peak-aged condition was induced in ambient air in notched specimens. The mechanism of fracture was studied using electron backscatter diffraction, serial sectioning and in situ observations of crack propagation. Cracks initiated at the intergranular brittle intermetallic, and propagated by transgranular cleavage. These observations imply that a microstructural model for the static fatigue limit in cast magnesium alloys may be developed which includes the effects of notch-like defects such as porosity

  2. Calculation of hydrogen diffusion toward a crack in a stressed solid

    International Nuclear Information System (INIS)

    1976-10-01

    A set of eigensolutions is derived for use in expanding the steady-state concentration of hydrogen diffusing through a region bounded by two cylinders centred on an infinite crack in a stressed solid. Comparison is made with some experimental values of the hydrogen-induced crack-propagation velocity within the framework of the theory of Dutton and Puls. (author)

  3. Analysis of hygral induced crack growth in multiphase materials

    NARCIS (Netherlands)

    Sadouki, H.; Van Mier, J.G.M.

    1996-01-01

    In this paper a numerical model for simulating crack growth processes caused by moisture movement in a porous multiphase material like concrete is proposed. In the model, the material is schematized as a regular triangular network of beam elements. The meso-material structure of the material is

  4. Microbial network of the carbonate precipitation process induced by microbial consortia and the potential application to crack healing in concrete.

    Science.gov (United States)

    Zhang, Jiaguang; Zhou, Aijuan; Liu, Yuanzhen; Zhao, Bowei; Luan, Yunbo; Wang, Sufang; Yue, Xiuping; Li, Zhu

    2017-11-06

    Current studies have employed various pure-cultures for improving concrete durability based on microbially induced carbonate precipitation (MICP). However, there have been very few reports concerned with microbial consortia, which could perform more complex tasks and be more robust in their resistance to environmental fluctuations. In this study, we constructed three microbial consortia that are capable of MICP under aerobic (AE), anaerobic (AN) and facultative anaerobic (FA) conditions. The results showed that AE consortia showed more positive effects on inorganic carbon conversion than AN and FA consortia. Pyrosequencing analysis showed that clear distinctions appeared in the community structure between different microbial consortia systems. Further investigation on microbial community networks revealed that the species in the three microbial consortia built thorough energetic and metabolic interaction networks regarding MICP, nitrate-reduction, bacterial endospores and fermentation communities. Crack-healing experiments showed that the selected cracks of the three consortia-based concrete specimens were almost completely healed in 28 days, which was consistent with the studies using pure cultures. Although the economic advantage might not be clear yet, this study highlights the potential implementation of microbial consortia on crack healing in concrete.

  5. Iodine stress corrosion cracking in Zircaloy

    International Nuclear Information System (INIS)

    Andrade, A.H.P. de; Pelloux, R.M.N.

    1983-01-01

    The subcritical growth of iodine-induced cracks in unirradiated Zircaloy plates is investigated as a function of the stress intensity factor K. The testing variables are: crystallographic texture (f-Number), microstructure (grain directionaly), heat treatment (stress relieved vs recrystallized plate), and temperature. The iodine partial pressure is 40Pa. (author) [pt

  6. Fatigue crack growth behavior in niobium-hydrogen alloys

    International Nuclear Information System (INIS)

    Lin, M.C.C.; Salama, K.

    1997-01-01

    Near-threshold fatigue crack growth behavior has been investigated in niobium-hydrogen alloys. Compact tension specimens (CTS) with three hydrogen conditions are used: hydrogen-free, hydrogen in solid solution, and hydride alloy. The specimens are fatigued at a temperature of 296 K and load ratios of 0.05, 0.4, and 0.75. The results at load ratios of 0.05 and 0.4 show that the threshold stress intensity range (ΔK th ) decreases as hydrogen is added to niobium. It reaches a minimum at the critical hydrogen concentration (C cr ), where maximum embrittlement occurs. The critical hydrogen concentration is approximately equal to the solubility limit of hydrogen in niobium. As the hydrogen concentration exceeds C cr , ΔK th increases slowly as more hydrogen is added to the specimen. At load ratio 0.75, ΔK th decreases continuously as the hydrogen concentration is increased. The results provide evidence that two mechanisms are responsible for fatigue crack growth behavior in niobium-hydrogen alloys. First, embrittlement is retarded by hydride transformation--induced and plasticity-induced crack closures. Second, embrittlement is enhanced by the presence of hydrogen and hydride

  7. Crack

    Science.gov (United States)

    ... spending time in a rehab facility or getting cognitive-behavioral therapy or other treatments. Right now, there are no medicines to treat a crack addiction. If you smoke crack, talking with a counselor ...

  8. Nonlinear ultrasonic wave modulation for online fatigue crack detection

    Science.gov (United States)

    Sohn, Hoon; Lim, Hyung Jin; DeSimio, Martin P.; Brown, Kevin; Derriso, Mark

    2014-02-01

    This study presents a fatigue crack detection technique using nonlinear ultrasonic wave modulation. Ultrasonic waves at two distinctive driving frequencies are generated and corresponding ultrasonic responses are measured using permanently installed lead zirconate titanate (PZT) transducers with a potential for continuous monitoring. Here, the input signal at the lower driving frequency is often referred to as a 'pumping' signal, and the higher frequency input is referred to as a 'probing' signal. The presence of a system nonlinearity, such as a crack formation, can provide a mechanism for nonlinear wave modulation, and create spectral sidebands around the frequency of the probing signal. A signal processing technique combining linear response subtraction (LRS) and synchronous demodulation (SD) is developed specifically to extract the crack-induced spectral sidebands. The proposed crack detection method is successfully applied to identify actual fatigue cracks grown in metallic plate and complex fitting-lug specimens. Finally, the effect of pumping and probing frequencies on the amplitude of the first spectral sideband is investigated using the first sideband spectrogram (FSS) obtained by sweeping both pumping and probing signals over specified frequency ranges.

  9. Acoustic and electromagnetic emission as a tool for crack localization

    International Nuclear Information System (INIS)

    Sedlak, P; Sikula, J; Lokajicek, T; Mori, Y

    2008-01-01

    The creation of cracks is accompanied by electric charge redistribution due to loosened chemical bounds. Electric charge on a crack wall creates dipole moments. Vibrations of crack walls produce time-dependent dipole moments and, consequently, electric and magnetic fields are generated. An electric signal is induced on metal electrodes. Simultaneously with the electromagnetic emission (EME) signal, an acoustic emission (AE) signal is generated, but due to the different velocities of propagation of both waves, the detection of the AE signal is delayed. This time delay presents the time of the wave propagation from the individual acoustic emission sensor to the crack. The defect can be located by means of these time intervals. This paper describes the localization using acoustic and electromagnetic emission signals for the two-dimensional case

  10. Confocal examination of subsurface cracking in ceramic materials.

    Science.gov (United States)

    Etman, Maged K

    2009-10-01

    The original ceramic surface finish and its microstructure may have an effect on crack propagation. The purpose of this study was to investigate the relation between crack propagation and ceramic microstructure following cyclic fatigue loading, and to qualitatively evaluate and quantitatively measure the surface and subsurface crack depths of three types of ceramic restorations with different microstructures using a Confocal Laser Scanning Microscope (CLSM) and Scanning Electron Microscope (SEM). Twenty (8 x 4 x 2 mm(3)) blocks of AllCeram (AC), experimental ceramic (EC, IPS e.max Press), and Sensation SL (SSL) were prepared, ten glazed and ten polished of each material. Sixty antagonist enamel specimens were made from the labial surfaces of permanent incisors. The ceramic abraders were attached to a wear machine, so that each enamel specimen presented at 45 degrees to the vertical movement of the abraders, and immersed in artificial saliva. Wear was induced for 80K cycles at 60 cycles/min with a load of 40 N and 2-mm horizontal deflection. The specimens were examined for cracks at baseline, 5K, 10K, 20K, 40K, and 80K cycles. Twenty- to 30-microm deep subsurface cracking appeared in SSL, with 8 to 10 microm in AC, and 7 microm close to the margin of the wear facets in glazed EC after 5K cycles. The EC showed no cracks with increasing wear cycles. Seventy-microm deep subsurface cracks were detected in SSL and 45 microm in AC after 80K cycles. Statistically, there was significant difference among the three materials (p 0.05) in crack depth within the same ceramic material with different surface finishes. The ceramic materials with different microstructures showed different patterns of subsurface cracking.

  11. Experimental Investigation on Centrifugal Compressor Blade Crack Classification Using the Squared Envelope Spectrum

    Directory of Open Access Journals (Sweden)

    Xuefeng Zhang

    2013-09-01

    Full Text Available Centrifugal compressors are a key piece of equipment for modern production. Among the components of the centrifugal compressor, the impeller is a pivotal part as it is used to transform kinetic energy into pressure energy. Blade crack condition monitoring and classification has been broadly investigated in the industrial and academic area. In this research, a pressure pulsation (PP sensor arranged in close vicinity to the crack area and the corresponding casing vibration signals are used to monitor blade crack information. As these signals cannot directly demonstrate the blade crack, the method employed in this research is based on the extraction of weak signal characteristics that are induced by blade cracking. A method for blade crack classification based on the signals monitored by using a squared envelope spectrum (SES is presented. Experimental investigations on blade crack classification are carried out to verify the effectiveness of this method. The results show that it is an effective tool for blade crack classification in centrifugal compressors.

  12. Experimental investigation on centrifugal compressor blade crack classification using the squared envelope spectrum.

    Science.gov (United States)

    Li, Hongkun; Zhang, Xuefeng; Xu, Fujian

    2013-09-18

    Centrifugal compressors are a key piece of equipment for modern production. Among the components of the centrifugal compressor, the impeller is a pivotal part as it is used to transform kinetic energy into pressure energy. Blade crack condition monitoring and classification has been broadly investigated in the industrial and academic area. In this research, a pressure pulsation (PP) sensor arranged in close vicinity to the crack area and the corresponding casing vibration signals are used to monitor blade crack information. As these signals cannot directly demonstrate the blade crack, the method employed in this research is based on the extraction of weak signal characteristics that are induced by blade cracking. A method for blade crack classification based on the signals monitored by using a squared envelope spectrum (SES) is presented. Experimental investigations on blade crack classification are carried out to verify the effectiveness of this method. The results show that it is an effective tool for blade crack classification in centrifugal compressors.

  13. Heavy-Section Steel Technology Program intermediate-scale pressure vessel tests

    International Nuclear Information System (INIS)

    Bryan, R.H.; Merkle, J.G.; Smith, G.C.; Whitman, G.D.

    1977-01-01

    The tests of intermediate-size vessels with sharp flaws permitted the comparison of experimentally observed behavior with analytical predictions of the behavior of flawed pressure vessels. Fracture strains estimated by linear elastic fracture mechanics (LEFM) were accurate in the cases in which the flaws resided in regions of high transverse restraint and the fracture toughness was sufficiently low for unstable fracture to occur prior to yielding through the vessel wall. When both of these conditions were not present, unstable fracture did occur, always preceded by stable crack growth; and the cylinders with flaws initially less than halfway through the wall attained gross yield prior to burst. Predictions of failure pressure of the vessels with flawed nozzles, based upon LEFM estimates of failure strain, were very conservative. LEFM calculations of critical load were based upon small-specimen fracture toughness test data. Whenever gross yielding preceded failure, the actual strains achieved were considerably greater than the estimated strains at failure based on LEFM. In such cases the strength of the vessel may be no longer dependent upon plane-strain fracture toughness but upon the capacity of the cracked section to carry the imposed load stably in the plastic range. Stable crack growth, which has not been predictable quantitatively, is an important factor in elastic-plastic analysis of strength. The ability of the flawed vessels to attain gross yield in unflawed sections has important qualitative implications on pressure vessel safety margins. The gross yield condition occurs in light-water-reactor pressure vessels at about 2 x design pressure. The intermediate vessel tests that demonstrated a capacity for exceeding this load confirm that the presumed margin of safety is not diminished by the presence of flaws of substantial size, provided that material properties are adequate

  14. Crack shape developments and leak rates for circumferential complex-cracked pipes

    Energy Technology Data Exchange (ETDEWEB)

    Brickstad, B.; Bergman, M. [SAQ Inspection Ltd., Stockholm (Sweden)

    1997-04-01

    A computerized procedure has been developed that predicts the growth of an initial circumferential surface crack through a pipe and further on to failure. The crack growth mechanism can either be fatigue or stress corrosion. Consideration is taken to complex crack shapes and for the through-wall cracks, crack opening areas and leak rates are also calculated. The procedure is based on a large number of three-dimensional finite element calculations of cracked pipes. The results from these calculations are stored in a database from which the PC-program, denoted LBBPIPE, reads all necessary information. In this paper, a sensitivity analysis is presented for cracked pipes subjected to both stress corrosion and vibration fatigue.

  15. Advances in crack-arrest technology for reactor pressure vessels

    International Nuclear Information System (INIS)

    Bass, B.R.; Pugh, C.E.

    1988-01-01

    The Heavy-Section Steel Technology (HSST) Program at the Oak Ridge National Laboratory (ORNL) under the sponsorship of the US Nuclear Regulatory Commission is continuing to improve the understanding of conditions that govern the initiation, rapid propagation, arrest, and ductile tearing of cracks in reactor pressure vessel (RPV) steels. This paper describes recent advances in a coordinated effort being conducted under the HSST Program by ORNL and several subcontracting groups to develop the crack-arrest data base and the analytical tools required to construct inelastic dynamic fracture models for RPV steels. Large-scale tests are being carried out to generate crack-arrest toughness data at temperatures approaching and above the onset of Charpy upper-shelf behavior. Small- and intermediate-size specimens subjected to static and dynamic loading are being developed and tested to provide additional fracture data for RPV steels. Viscoplastic effects are being included in dynamic fracture models and computer programs and their utility validated through analyses of data from carefully controlled experiments. Recent studies are described that examine convergence problems associated with energy-based fracture parameters in viscoplastic-dynamic fracture applications. Alternative techniques that have potential for achieving convergent solutions for fracture parameters in the context of viscoplastic-dynamic models are discussed. 46 refs., 15 figs., 3 tabs

  16. Experimental Study on Wing Crack Behaviours in Dynamic-Static Superimposed Stress Field Using Caustics and High-Speed Photography

    Directory of Open Access Journals (Sweden)

    L.Y. Yang

    2014-07-01

    Full Text Available During the drill-and-blast progress in rock tunnel excavation of great deep mine, rock fracture is evaluated by both blasting load and pre-exiting earth stress (pre-compression. Many pre-existing flaws in the rock mass, like micro-crack, also seriously affect the rock fracture pattern. Under blasting load with pre-compression, micro-cracks initiate, propagate and grow to be wing cracks. With an autonomous design of static-dynamic loading system, dynamic and static loads were applied on some PMMA plate specimen with pre-existing crack, and the behaviour of the wing crack was tested by caustics corroding with a high-speed photography. Four programs with different static loading modes that generate different pre-compression fields were executed, and the length, velocity of the blasting wing crack and dynamic stress intensity factor (SIF at the wing crack tip were analyzed and discussed. It is found that the behaviour of blasting-induced wing crack is affected obviously by blasting and pre-compression. And pre-compression, which is vertical to the direction of the wing crack propagation, hinders the crack propagation. Furthermore, the boundary constraint condition plays an important role on the behaviour of blasting induced crack during the experiment.

  17. Surface crack formation on rails at grinding induced martensite white etching layers

    DEFF Research Database (Denmark)

    Rasmussen, Carsten Jørn; Fæster, Søren; Dhar, Somrita

    2017-01-01

    The connection between profile grinding of rails, martensite surface layers and crack initiation has been investigated using visual inspection, optical microscopy and 3D X-ray computerized tomography. Newly grinded rails were extracted and found to be covered by a continuous surface layer...... of martensite with varying thickness formed by the grinding process. Worn R350HT and R200 rails were extracted from the Danish rail network as they had transverse bands resembling grinding marks on the running surface. The transverse bands were shown to consist of martensite which had extensive crack formation...... at the martensite/pearlite interface. The cracks in R350HT propagated down into the rail while those in the soft R200 returned to the surface causing only very small shallow spallation. The transverse bands had the same shape, size, orientation, location and periodicity which would be expected from grinding marks...

  18. Cladding failure model III (CFM III). A simple model for iodine induced stress corrosion cracking of zirconium-lined barrier and standard zircaloy cladding

    International Nuclear Information System (INIS)

    Tasooji, A.; Miller, A.K.

    1984-01-01

    A previously developed unified model (SCCIG*) for predicting iodine induced SCC in standard Zircaloy cladding was modified recently into the ''SCCIG-B'' model which predicts the stress corrosion cracking behaviour of zirconium lined barrier cladding. Several published papers have presented the capability of these models for predicting various observed behaviours related to SCC. A closed form equation, called Cladding Failure Model III (CMFIII), has been derived from the SCCIG-B model. CFMIII takes the form of an explicit equation for the radial crack growth rate dc/dt as a function of hoop strain, crack depth, temperature, and surface iodine concentration in irradiated cladding (both barrier and standard Zircaloy). CMFIII has approximately the same predictive capabilities as the physically based SCCIG and/or SCCIG-B models but is computationally faster and more convenient and can be easily utilized in fuel performance codes for predicting the behaviour of barrier and standard claddings in reactor operations. (author)

  19. Photo-induced bleaching of sensory rhodopsin II (phoborhodopsin) from Halobacterium salinarum by hydroxylamine: identification of the responsible intermediates.

    Science.gov (United States)

    Tamogami, Jun; Kikukawa, Takashi; Ikeda, Yoichi; Demura, Makoto; Nara, Toshifumi; Kamo, Naoki

    2012-01-05

    Sensory rhodopsin II from Halobacterium salinarum (HsSRII) is a retinal protein in which retinal binds to a specific lysine residue through a Schiff base. Here, we investigated the photobleaching of HsSRII in the presence of hydroxylamine. For identification of intermediate(s) attacked by hydroxylamine, we employed the flash-induced bleaching method. In order to change the concentration of intermediates, such as M- and O-intermediates, experiments were performed under varying flashlight intensities and concentrations of azide that accelerated only the M-decay. We found the proportional relationship between the bleaching rate and area under the concentration-time curve of M, indicating a preferential attack of hydroxylamine on M. Since hydroxylamine is a water-soluble reagent, we hypothesize that for M, hydrophilicity or water-accessibility increases specifically in the moiety of Schiff base. Thus, hydroxylamine bleaching rates may be an indication of conformational changes near the Schiff base. We also considered the possibility that azide may induce a small conformational change around the Schiff base. We compared the hydroxylamine susceptibility between HsSRII and NpSRII (SRII from Natronomonas pharaonis) and found that the M of HsSRII is about three times more susceptible than that of the stable NpSRII. In addition, long illumination to HsSRII easily produced M-like photoproduct, P370. We thus infer that the instability of HsSRII under illumination may be related to this increase of hydrophilicity at M and P370. Copyright © 2011 Elsevier B.V. All rights reserved.

  20. Texture, local misorientation, grain boundary and recrystallization fraction in pipeline steels related to hydrogen induced cracking

    Energy Technology Data Exchange (ETDEWEB)

    Mohtadi-Bonab, M.A., E-mail: m.mohtadi@usask.ca; Eskandari, M.; Szpunar, J.A.

    2015-01-03

    In the present study, API X60 and X60SS pipeline steels were cathodically charged by hydrogen for 8 h using 0.2 M sulfuric acid and 3 g/l ammonium thiocyanate. After charging, SEM observations showed that the hydrogen induced cracking (HIC) appeared at the center of cross section in the X60 specimen. However, HIC did not appear in the X60SS steel. Therefore, electron backscatter diffraction (EBSD) technique was used to analyze the center of cross section of as-received X60SS, X60 and HIC tested X60 specimens. The results showed that the HIC crack not only can propagate through 〈100〉||ND oriented grains but also its growth may happen in various orientations. In HIC tested X60 specimen, an accumulation of low angle grain boundaries around the crack path documented that full recrystallization was not achieved during hot rolling. Kernel Average Misorientaion (KAM) histogram illustrated that the deformation is more concentrated in as-received and HIC tested X60 specimens rather than in as-received X60SS specimen. Moreover, the concentration of coincidence site lattice (CSL) boundary in HIC tested X60 specimen was very low compared with other samples. The recrystallization area fraction in X60SS steel was very high. This high amount of recrystallization fraction with no stored energy is one of the main reasons for high HIC resistance of this steel to HIC. The orientation distribution function (ODF) of the recrystallized, substructured and deformed fractions in as-received X60SS and X60 steel showed relative close orientations in both as-received specimens.

  1. Ductile crack growth simulation from near crack tip dissipated energy

    International Nuclear Information System (INIS)

    Marie, S.; Chapuliot, S.

    2000-01-01

    A method to calculate ductile tearing in both small scale fracture mechanics specimens and cracked components is presented. This method is based on an estimation of the dissipated energy calculated near the crack tip. Firstly, the method is presented. It is shown that a characteristic parameter G fr can be obtained, relevant to the dissipated energy in the fracture process. The application of the method to the calculation of side grooved crack tip (CT) specimens of different sizes is examined. The value of G fr is identified by comparing the calculated and experimental load line displacement versus crack extension curve for the smallest CT specimen. With this identified value, it is possible to calculate the global behaviour of the largest specimen. The method is then applied to the calculation of a pipe containing a through-wall thickness crack subjected to a bending moment. This pipe is made of the same material as the CT specimens. It is shown that it is possible to simulate the global behaviour of the structure including the prediction of up to 90-mm crack extension. Local terms such as the equivalent stress or the crack tip opening angle are found to be constant during the crack extension process. This supports the view that G fr controls the fields in the vicinity near the crack tip. (orig.)

  2. The tensile effect on crack formation in single crystal silicon irradiated by intense pulsed ion beam

    Science.gov (United States)

    Liang, Guoying; Shen, Jie; Zhang, Jie; Zhong, Haowen; Cui, Xiaojun; Yan, Sha; Zhang, Xiaofu; Yu, Xiao; Le, Xiaoyun

    2017-10-01

    Improving antifatigue performance of silicon substrate is very important for the development of semiconductor industry. The cracking behavior of silicon under intense pulsed ion beam irradiation was studied by numerical simulation in order to understand the mechanism of induced surface peeling observed by experimental means. Using molecular dynamics simulation based on Stillinger Weber potential, tensile effect on crack growth and propagation in single crystal silicon was investigated. Simulation results reveal that stress-strain curves of single crystal silicon at a constant strain rate can be divided into three stages, which are not similar to metal stress-strain curves; different tensile load velocities induce difference of single silicon crack formation speed; the layered stress results in crack formation in single crystal silicon. It is concluded that the crack growth and propagation is more sensitive to strain rate, tensile load velocity, stress distribution in single crystal silicon.

  3. Crack growth monitoring in composite materials using embedded optical Fiber Bragg Grating sensor

    DEFF Research Database (Denmark)

    Pereira, Gilmar Ferreira; Mikkelsen, Lars Pilgaard; McGugan, Malcolm

    2015-01-01

    In this paper a novel method to assess a crack growing/damage event in fiber reinforced plastic, or adhesive using Fiber Bragg Grating (FBG) sensors embedded in a host material is shown. Different features of the crack mechanism that induce a change in the FBG response were identified. Double...

  4. Stress corrosion cracking tests on electron beam welded carbon steel specimens in carbonate-bicarbonate solution

    International Nuclear Information System (INIS)

    Parkins, R.N.

    1985-04-01

    Stress corrosion cracking tests have been performed on tapered carbon steel test pieces containing electron beam welds with a view to defining susceptibility to such cracking in a carbonate-bicarbonate solution at 90 C and an appropriate electrode potential. The tests involved applying cyclic loads to the specimens and it is shown that the threshold stress for cracking reduces linearly with increase in the magnitude of the cyclic load component. Extrapolation of these trends to zero fluctuating stress indicates static load threshold stresses in the vicinity of the yield stress (i.e. about 300 N/mm 2 for parent plate without a weld, 400 N/mm 2 for specimens with welds on one side only and 600 N/mm 2 for specimens having welds penetrating through the thickness of the specimen). The averages of the maximum crack velocities observed were least for parent plate material and greatest for weld metal, the former being essentially intergranular in morphology and the latter mostly transgranular, with heat affected zone material being intermediate between these extremes. (author)

  5. Heat-affected zone liquation crack on resistance spot welded TWIP steels

    Energy Technology Data Exchange (ETDEWEB)

    Saha, Dulal Chandra [Department of Advanced Materials Engineering, Dong-Eui University, 995 Eomgwangno, Busanjin-gu, Busan 614-714 (Korea, Republic of); Chang, InSung [Automotive Production Development Division, Hyundai Motor Company (Korea, Republic of); Park, Yeong-Do, E-mail: ypark@deu.ac.kr [Department of Advanced Materials Engineering, Dong-Eui University, 995 Eomgwangno, Busanjin-gu, Busan 614-714 (Korea, Republic of)

    2014-07-01

    In this study, the heat affected zone (HAZ) liquation crack and segregation behavior of the resistance spot welded twinning induced plasticity (TWIP) steel have been reported. Cracks appeared in the post-welded joints that originated at the partially melted zone (PMZ) and propagated from the PMZ through the heat affected zone (HAZ) to the base metal (BM). The crack length and crack opening widths were observed increasing with heat input; and the welding current was identified to be the most influencing parameter for crack formation. Cracks appeared at the PMZ when nugget diameter reached at 4.50 mm or above; and the liquation cracks were found to occur along two sides of the notch tip in the sheet direction rather than in the electrode direction. Cracks were backfilled with the liquid films which has lamellar structure and supposed to be the eutectic constituent. Co-segregation of alloy elements such as, C and Mn were detected on the liquid films by electron-probe microanalysis (EPMA) line scanning and element map which suggests that the liquid film was enrich of Mn and C. The eutectic constituent was identified by analyzing the calculated phase diagram along with thermal temperature history of finite element simulation. Preliminary experimental results showed that cracks have less/no significant effect on the static cross-tensile strength (CTS) and the tensile-shear strength (TSS). In addition, possible ways to avoid cracking were discussed. - Highlights: • The HAZ liquation crack during resistance spot welding of TWIP steel was examined. • Cracks were completely backfilled and healed with divorced eutectic secondary phase. • Co-segregation of C and Mn was detected in the cracked zone. • Heat input was the most influencing factor to initiate liquation crack. • Cracks have less/no significant effect on static tensile properties.

  6. Heat-affected zone liquation crack on resistance spot welded TWIP steels

    International Nuclear Information System (INIS)

    Saha, Dulal Chandra; Chang, InSung; Park, Yeong-Do

    2014-01-01

    In this study, the heat affected zone (HAZ) liquation crack and segregation behavior of the resistance spot welded twinning induced plasticity (TWIP) steel have been reported. Cracks appeared in the post-welded joints that originated at the partially melted zone (PMZ) and propagated from the PMZ through the heat affected zone (HAZ) to the base metal (BM). The crack length and crack opening widths were observed increasing with heat input; and the welding current was identified to be the most influencing parameter for crack formation. Cracks appeared at the PMZ when nugget diameter reached at 4.50 mm or above; and the liquation cracks were found to occur along two sides of the notch tip in the sheet direction rather than in the electrode direction. Cracks were backfilled with the liquid films which has lamellar structure and supposed to be the eutectic constituent. Co-segregation of alloy elements such as, C and Mn were detected on the liquid films by electron-probe microanalysis (EPMA) line scanning and element map which suggests that the liquid film was enrich of Mn and C. The eutectic constituent was identified by analyzing the calculated phase diagram along with thermal temperature history of finite element simulation. Preliminary experimental results showed that cracks have less/no significant effect on the static cross-tensile strength (CTS) and the tensile-shear strength (TSS). In addition, possible ways to avoid cracking were discussed. - Highlights: • The HAZ liquation crack during resistance spot welding of TWIP steel was examined. • Cracks were completely backfilled and healed with divorced eutectic secondary phase. • Co-segregation of C and Mn was detected in the cracked zone. • Heat input was the most influencing factor to initiate liquation crack. • Cracks have less/no significant effect on static tensile properties

  7. On applicability of crack shape characterization rules for multiple in-plane surface cracks

    International Nuclear Information System (INIS)

    Kim, Jong Min; Choi, Suhn; Park, Keun Bae; Choi, Jae Boong; Huh, Nam Su

    2009-01-01

    The fracture mechanics assessment parameters, such as the elastic stress intensity factor and the elastic-plastic J-integral, for a surface crack can be significantly affected by adjacent cracks. Regarding such an interaction effect, the relative distance between adjacent cracks, crack aspect ratio and loading condition were known to be important factors for multiple cracks, which affects the fracture mechanics assessment parameters. Although several guidance (ASME Sec. XI, BS7910, British Energy R6 and API RP579) on a crack interaction effect (crack combination rule) have been proposed and used for assessing the interaction effect, each guidance provides different rules for combining multiple surface cracks into a single surface crack. Based on the systematic elastic and elastic-plastic finite element analyses, the present study investigated the acceptability of the crack combination rules provided in the existing guidance, and the relevant recommendations on a crack interaction for in-plane surface cracks in a plate were discussed. To quantify the interaction effect, the elastic stress intensity factor and elastic-plastic J-integral along the crack front were used. As for the loading condition, only axial tension was considered. As a result, BS7910 seems to provide the most relevant crack combination rule for in-plane dual surface cracks, whereas API RP579 provides the most conservative results. In particular, ASME Sec. XI still seems to have some room for a revision to shorten the critical distance between two adjacent cracks for a crack combination. The overall tendency of the elastic-plastic analyses results is identical to that of the elastic analyses results.

  8. The interaction of fatigue cracks with a residual stress field using thermoelastic stress analysis and synchrotron X-ray diffraction experiments

    Science.gov (United States)

    Amjad, Khurram; Asquith, David; Sebastian, Christopher M.; Wang, Wei-Chung

    2017-01-01

    This article presents an experimental study on the fatigue behaviour of cracks emanating from cold-expanded holes utilizing thermoelastic stress analysis (TSA) and synchrotron X-ray diffraction (SXRD) techniques with the aim of resolving the long-standing ambiguity in the literature regarding potential relaxation, or modification, of beneficial compressive residual stresses as a result of fatigue crack propagation. The crack growth rates are found to be substantially lower as the crack tip moved through the residual stress zone induced by cold expansion. The TSA results demonstrated that the crack tip plastic zones were reduced in size by the presence of the residual compressive stresses induced by cold expansion. The crack tip plastic zones were found to be insignificant in size in comparison to the residual stress zone resulting from cold expansion, which implied that they were unlikely to have had a notable impact on the surrounding residual stresses induced by cold expansion. The residual stress distributions measured along the direction of crack growth, using SXRD, showed no signs of any significant stress relaxation or redistribution, which validates the conclusions drawn from the TSA data. Fractographic analysis qualitatively confirmed the influence on crack initiation of the residual stresses induced by the cold expansion. It was found that the application of single compressive overload caused a relaxation, or reduction in the residual stresses, which has wider implications for improving the fatigue life. PMID:29291095

  9. Shield gas induced cracks during nanosecond-pulsed laser irradiation of Zr-based metallic glass

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Hu; Noguchi, Jun; Yan, Jiwang [Keio University, Department of Mechanical Engineering, Faculty of Science and Technology, Yokohama (Japan)

    2016-10-15

    Laser processing techniques have been given increasing attentions in the field of metallic glasses (MGs). In this work, effects of two kinds of shield gases, nitrogen and argon, on nanosecond-pulsed laser irradiation of Zr-based MG were comparatively investigated. Results showed that compared to argon gas, nitrogen gas remarkably promoted the formation of cracks during laser irradiation. Furthermore, crack formation in nitrogen gas was enhanced by increasing the peak laser power intensity or decreasing the laser scanning speed. X-ray diffraction and micro-Raman spectroscopy indicated that the reason for enhanced cracks in nitrogen gas was the formation of ZrN. (orig.)

  10. Shield gas induced cracks during nanosecond-pulsed laser irradiation of Zr-based metallic glass

    Science.gov (United States)

    Huang, Hu; Noguchi, Jun; Yan, Jiwang

    2016-10-01

    Laser processing techniques have been given increasing attentions in the field of metallic glasses (MGs). In this work, effects of two kinds of shield gases, nitrogen and argon, on nanosecond-pulsed laser irradiation of Zr-based MG were comparatively investigated. Results showed that compared to argon gas, nitrogen gas remarkably promoted the formation of cracks during laser irradiation. Furthermore, crack formation in nitrogen gas was enhanced by increasing the peak laser power intensity or decreasing the laser scanning speed. X-ray diffraction and micro-Raman spectroscopy indicated that the reason for enhanced cracks in nitrogen gas was the formation of ZrN.

  11. Investigation of Bearing Axial Cracking: Benchtop and Full-Scale Test Results

    Energy Technology Data Exchange (ETDEWEB)

    Keller, Jonathan A. [National Renewable Energy Lab. (NREL), Golden, CO (United States); Gould, Benjamin [Argonne National Lab. (ANL), Argonne, IL (United States); Greco, Aaron [Argonne National Lab. (ANL), Argonne, IL (United States)

    2017-08-16

    The most common failure mode in wind turbine gearboxes is axial cracking in intermediate and high-speed-stage bearings, also commonly called white-etching cracks (WECs). Although these types of cracks have been reported for over a decade, the conditions leading to WECs, the process by which this failure culminates, and the reasons for their apparent prevalence in wind turbine gearboxes are all highly debated. This paper summarizes the state of a multipronged research effort to examine the causes of WECs in wind turbine gearbox bearings. Recent efforts have recreated WECs on a benchtop test rig in highly loaded sliding conditions, wherein it was found that the formation of a dark etching microstructure precedes the formation of a crack, and a crack precedes the formation of white-etching microstructure. A cumulative frictional sliding energy criterion has been postulated to predict the presence of WECs. Bearing loads have also been measured and predicted in steady state and transient drivetrain operations in dynamometer testing. In addition, both loads and sliding at full scale will be measured in planned uptower drivetrain testing. If the cumulative frictional sliding energy is the dominant mechanism that causes WECs, understanding the amount of frictional sliding energy that wind turbine bearings are subjected to in typical operations is the next step in the investigation. If highly loaded sliding conditions are found uptower, similar to the examined benchtop levels, appropriate mitigation solutions can be examined, ranging from new bearing coatings and improved lubricants to changes in gearbox designs and turbine operations.

  12. Investigation of irradiation induced inter-granular stress corrosion cracking susceptibility on austenitic stainless steels for PWR by simulated radiation induced segregation materials

    Energy Technology Data Exchange (ETDEWEB)

    Yonezawa, Toshio; Fujimoto, Koji; Kanasaki, Hiroshi; Iwamura, Toshihiko [Mitsubishi Heavy Industries Ltd., Takasago R and D Center, Takasago, Hyogo (Japan); Nakada, Shizuo; Ajiki, Kazuhide [Mitsubishi Heavy Industries Ltd., Kobe Shipyard and Machinery Works, Kobe, Hyogo (Japan); Urata, Sigeru [General Office of Nuclear and Fossil Power Production, Kansai Electric Power Co., Inc., Osaka (Japan)

    2000-07-01

    An Irradiation Assisted Stress Corrosion Cracking (IASCC) has not been found in Pressurized Water Reactors (PWRs). However, the authors have investigated on the possibility of IASCC so as to be able to estimate the degradation of PWR plants up to the end of their lifetime. In this study, the authors melted the test alloys whose bulk compositions simulated the grain boundary compositions of irradiated Type 304 and Type 316 CW stainless steels. Low chromium, high nickel and silicon (12%Cr-28%Ni-3%Si) steel showed high susceptibility to PWSCC (Primary Water Stress Corrosion Cracking) by SSRT (Slow Strain Rate Tensile) test in simulated PWR primary water. PWSCC susceptibility of the test steels increases with a decrease of chromium content and a increase of nickel and silicon contents. The aged test steel included coherent M{sub 23}C{sub 6} carbides with matrices at the grain boundaries showed low PWSCC susceptibility. This tendency is in very good agreement with that of the PWSCC susceptibility of nickel based alloys X-750 and 690. From these results, if there is the possibility of IASCC for austenitic stainless steels in PWRs, in the future, the IASCC shall be caused by the PWSCC as a result of irradiation induced grain boundary segregation. (author)

  13. Subsurface metals fatigue cracking without and with crack tip

    Directory of Open Access Journals (Sweden)

    Andrey Shanyavskiy

    2013-07-01

    Full Text Available Very-High-Cycle-Fatigue regime for metals was considered and mechanisms of the subsurface crack origination were introduced. In many metals first step of crack origination takes place with specific area formation because of material pressing and rotation that directed to transition in any volume to material ultra-high-plasticity with nano-structure appearing. Then by the border of the nano-structure takes place volume rotation and fracture surface creates with spherical particles which usually named Fine-Granular-Area. In another case there takes place First-Smooth-Facet occurring in area of origin due to whirls appearing by the one of the slip systems under discussed the same stress-state conditions. Around Fine-Granular-Area or First-Smooth-Facet there plastic zone appeared and, then, subsurface cracking develops by the same manner as for through cracks. In was discussed quantum-mechanical nature of fatigue crack growth in accordance with Yang’s modulus quantization for low level of deformations. New simply equation was considered for describing subsurface cracking in metals out of Fine-Granular-Area or Fist-Smooth-Facet.

  14. On the anomalous temperature dependency of fatigue crack growth of SS 316(N) weld

    Energy Technology Data Exchange (ETDEWEB)

    Babu, M. Nani; Dutt, B. Shashank; Venugopal, S. [Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India); Sasikala, G., E-mail: gsasi@igcar.gov.in [Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India); Bhaduri, A.K.; Jayakumar, T.; Raj, Baldev [Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India)

    2010-07-25

    Fatigue crack growth behaviour of a nuclear grade SS 316(N) weld metal was examined in the Paris and threshold regimes in the as-welded condition, at 300, 573 and 823 K. The {Delta}K{sub th} values were 11.2, 7.5, and 9.5 MPa {radical}m, respectively. These values were corrected for closure effects and the corresponding {Delta}K{sub th,eff} were found to be 7.7, 5.8 and 3.5 MPa {radical}m, respectively. The anomalous behaviour, i.e., the high value of {Delta}K{sub th} at 823 K has been explained based on crack closure effect which is roughness induced at 300 K and oxide induced at 823 K, with both these insignificant at 573 K. The effect of temperature on crack growth mechanism and the associated closure mechanisms are discussed. The stress shielding at the crack tip due to closure is accounted for and the effective stress intensity factor experienced by the crack tip, {Delta}K{sub eff,tip} is determined. It is demonstrated that {Delta}K{sub eff,tip} qualifies as a more appropriate parameter as the driving force for the temperature-dependent crack growth in the near-threshold and Paris regimes.

  15. An investigation of penetrant techniques for detection of machining-induced surface-breaking cracks on monolithic ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Forster, G.A.; Ellingson, W.A.

    1996-02-01

    The purpose of this effort was to evaluate penetrant methods for their ability to detect surface-breaking cracks in monolithic ceramic materials with an emphasis on detection of cracks generated by machining. There are two basic penetrant types, visible and fluorescent. The visible penetrant method is usually augmented by powder developers and cracks detected can be seen in visible light. Cracks detected by fluorescent penetrant are visible only under ultraviolet light used with or without a developer. The developer is basically a powder that wicks up penetrant from a crack to make it more observable. Although fluorescent penetrants were recommended in the literature survey conducted early in this effort, visible penetrants and two non-standard techniques, a capillary gaseous diffusion method under development at the institute of Chemical Physics in Moscow, and the {open_quotes}statiflux{close_quotes} method which involves use of electrically charged particles, were also investigated. SiAlON ring specimens (1 in. diameter, 3/4 in. wide) which had been subjected to different thermal-shock cycles were used for these tests. The capillary gaseous diffusion method is based on ammonia; the detector is a specially impregnated paper much like litmus paper. As expected, visible dye penetrants offered no detection sensitivity for tight, surface-breaking cracks in ceramics. Although the non-standard statiflux method showed promise on high-crack-density specimens, it was ineffective on limited-crack-density specimens. The fluorescent penetrant method was superior for surface-breaking crack detection, but successful application of this procedure depends greatly on the skill of the user. Two presently available high-sensitivity fluorescent penetrants were then evaluated for detection of microcracks on Si{sub 3}N{sub 4} and SiC from different suppliers. Although 50X optical magnification may be sufficient for many applications, 200X magnification provides excellent delectability.

  16. Top predators induce the evolutionary diversification of intermediate predator species.

    Science.gov (United States)

    Zu, Jian; Yuan, Bo; Du, Jianqiang

    2015-12-21

    We analyze the evolutionary branching phenomenon of intermediate predator species in a tritrophic food chain model by using adaptive dynamics theory. Specifically, we consider the adaptive diversification of an intermediate predator species that feeds on a prey species and is fed upon by a top predator species. We assume that the intermediate predator׳s ability to forage on the prey can adaptively improve, but this comes at the cost of decreased defense ability against the top predator. First, we identify the general properties of trade-off relationships that lead to a continuously stable strategy or to evolutionary branching in the intermediate predator species. We find that if there is an accelerating cost near the singular strategy, then that strategy is continuously stable. In contrast, if there is a mildly decelerating cost near the singular strategy, then that strategy may be an evolutionary branching point. Second, we find that after branching has occurred, depending on the specific shape and strength of the trade-off relationship, the intermediate predator species may reach an evolutionarily stable dimorphism or one of the two resultant predator lineages goes extinct. Crown Copyright © 2015. Published by Elsevier Ltd. All rights reserved.

  17. The significance of cladding material on the integrity of nuclear pressure vessels with cracks

    International Nuclear Information System (INIS)

    Sattari-Far, Iradj.

    1989-05-01

    The significance of the austenitic cladding layer is reviewed in this literature study. The cladding induced stresses are generally not considered when evaluating the severity of flaws in reactor pressure vessels. It has been shown that this emission may be misleading. The necessity to consider the cladding induced stresses is also emphasized in the latest edition of ASME XI. Contrary to what is commonly assumed, the austenitic cladding displays a charpy V transition region with a low ductility. The interface material (HAZ) is the most influenced region by irradiation, and a transition shift of over 100 degree C may be expected. Because of the significant difference in the thermal expansion coefficients of the cladding and the base metal, cladding induced stresses can be set up. Even after PWHT, residual stresses of yield magnitude remain in the cladding and the HAZ at ambient temperature. The cladding induced stresses are temperature dependent and decrease as the temperature increases. The cladding induced stresses have a significant influence on small defects near the inside surface of a pressure vessel. For semielliptical surface cracks, the maximum CTOD-value along the crack front is not found at the deepest point, but in the cladding/base metal interface, having a magnitude three times higher than the value in the deepest point. It implies that this type of crack would propagate along the clad/base material interface. At some point in time, the crack will reach a geometry which may cause such a severe condition at the deepest point that it will start to grow in the depth direction as well. The initiation and growth behaviour of such cracks need to be investigated to be able to assess the significance of cladding on the integrity of nuclear pressure vessels. (author) (50 figs., 33 refs.)

  18. Crack retardation by load reduction during fatigue crack propagation

    International Nuclear Information System (INIS)

    Kim, Hyun Soo; Nam, Ki Woo; Ahn, Seok Hwan; Do, Jae Yoon

    2003-01-01

    Fracture life and crack retardation behavior were examined experimentally using CT specimens of aluminum alloy 5083. Crack retardation life and fracture life were a wide difference between 0.8 and 0.6 in proportion to ratio of load reduction. The wheeler model retardation parameter was used successfully to predict crack growth behavior. By using a crack propagation rule, prediction of fracture life can be evaluated quantitatively. A statistical approach based on Weibull distribution was applied to the test data to evaluate the dispersion in the retardation life and fracture life by the change of load reduction

  19. Induction Thermography for Surface Crack Detection and Depth Determination

    Directory of Open Access Journals (Sweden)

    Beate Oswald-Tranta

    2018-02-01

    Full Text Available In the last few years, induction thermography has been established as a non-destructive testing method for localizing surface cracks in metals. The sample to be inspected is heated with a short induced electrical current pulse, and the infrared camera records—during and after the heating pulse—the temperature distribution at the surface. Transforming the temporal temperature development for each pixel to phase information makes not only highly reliable detection of the cracks possible but also allows an estimation of its depth. Finite element simulations were carried out to investigate how the phase contrast depends on parameters such as excitation frequency, pulse duration, material parameters, crack depth, and inclination angle of the crack. From these results, generalized functions for the dependency of the phase difference on all these parameters were derived. These functions can be used as an excellent guideline as to how measurement parameters should be optimized for a given material to be able to detect cracks and estimate their depth. Several experiments on different samples were also carried out, and the results compared with the simulations showed very good agreement.

  20. Investigation of Helicopter Longeron Cracks

    Science.gov (United States)

    Newman, John A.; Baughman, James; Wallace, Terryl A.

    2009-01-01

    Four cracked longerons, containing a total of eight cracks, were provided for study. Cracked regions were cut from the longerons. Load was applied to open the cracks, enabling crack surface examination. Examination revealed that crack propagation was driven by fatigue loading in all eight cases. Fatigue crack initiation appears to have occurred on the top edge of the longerons near geometric changes that affect component bending stiffness. Additionally, metallurgical analysis has revealed a local depletion in alloying elements in the crack initiation regions that may be a contributing factor. Fatigue crack propagation appeared to be initially driven by opening-mode loading, but at a crack length of approximately 0.5 inches (12.7 mm), there is evidence of mixed-mode crack loading. For the longest cracks studied, shear-mode displacements destroyed crack-surface features of interest over significant portions of the crack surfaces.

  1. Crack growth prediction method considering interaction between multiple cracks. Growth of surface cracks of dissimilar size under cyclic tensile and bending load

    International Nuclear Information System (INIS)

    Kamaya, Masayuki; Miyokawa, Eiichi; Kikuchi, Masanori

    2011-01-01

    When multiple cracks approach one another, the stress intensity factor is likely to change due to the interaction of the stress field. This causes change in growth rate and shape of cracks. In particular, when cracks are in parallel position to the loading direction, the shape of cracks becomes non-planar. In this study, the complex growth of interacting cracks is evaluated by using the S-Version finite element method, in which local detailed finite element mesh (local mesh) is superposed on coarse finite element model (global mesh) representing the global structure. In order to investigate the effect of interaction on the growth behavior, two parallel surface cracks are subjected to cyclic tensile or bending load. It is shown that the smaller crack is shielded by larger crack due to the interaction and stops growing when the difference in size of two cracks is significant. Based on simulations of various conditions, a procedure and criteria for evaluating crack growth for fitness-for-service assessment is proposed. According to the procedure, the interaction is not necessary to be considered in the crack growth prediction when the difference in size of two cracks exceeds the criterion. (author)

  2. Estimation of Fatigue Crack Growth Behavior of Cracked Specimen Under Mixed-mode Loads

    International Nuclear Information System (INIS)

    Han, Jeong Woo; Woo, Eun Taek; Han, Seung Ho

    2015-01-01

    To estimate the fatigue crack propagation behavior of compact tension shear (CTS) specimen under mixed-mode loads, crack path prediction theories and Tanaka’s equation were applied. The stress intensity factor at a newly created crack tip was calculated using a finite element method via ANSYS, and the crack path and crack increment were then obtained from the crack path prediction theories, Tanaka’s equation, and the Paris’ equation, which were preprogrammed in Microsoft Excel. A new method called the finite element crack tip updating method (FECTUM) was developed. In this method, the finite element method and Microsoft Excel are used to calculate the stress intensity factors and the crack path, respectively, at the crack tip per each crack increment. The developed FECTUM was applied to simulate the fatigue crack propagation of a single-edge notched bending (SENB) specimen under eccentric three-point bending loads. The results showed that the number of cycles to failure of the specimen obtained experimentally and numerically were in good agreement within an error range of less than 3%

  3. Estimation of Fatigue Crack Growth Behavior of Cracked Specimen Under Mixed-mode Loads

    Energy Technology Data Exchange (ETDEWEB)

    Han, Jeong Woo [KIMM, Daejeon (Korea, Republic of); Woo, Eun Taek; Han, Seung Ho [Dong-A University, Busan (Korea, Republic of)

    2015-07-15

    To estimate the fatigue crack propagation behavior of compact tension shear (CTS) specimen under mixed-mode loads, crack path prediction theories and Tanaka’s equation were applied. The stress intensity factor at a newly created crack tip was calculated using a finite element method via ANSYS, and the crack path and crack increment were then obtained from the crack path prediction theories, Tanaka’s equation, and the Paris’ equation, which were preprogrammed in Microsoft Excel. A new method called the finite element crack tip updating method (FECTUM) was developed. In this method, the finite element method and Microsoft Excel are used to calculate the stress intensity factors and the crack path, respectively, at the crack tip per each crack increment. The developed FECTUM was applied to simulate the fatigue crack propagation of a single-edge notched bending (SENB) specimen under eccentric three-point bending loads. The results showed that the number of cycles to failure of the specimen obtained experimentally and numerically were in good agreement within an error range of less than 3%.

  4. Effect of plastic strain on fracture strength of cracked components

    International Nuclear Information System (INIS)

    Kamaya, Masayuki

    2010-01-01

    Nuclear power plant components are occasionally subjected to excessive load by earthquake and may suffer plastic strain. Although the plastic strain introduced in materials increases the strength, it may reduce the fracture toughness. In this study, the effect of the plastic strain on strength of cracked components was investigated. Firstly, the change in the tensile properties and fracture toughness due to plastic strain were examined for Type 316 stainless steel and carbon steel (SM 490). The degree of nominal plastic strain was 5%, 10%, 20% and 40% (only for stainless steel). Secondly, the J-integral values of surface crack on a pipe were evaluated by finite element analyses. Finally, the critical load for fracture of the cracked pipe was evaluated for various pipe and crack geometries using the J-integral values and the fracture toughness obtained. It was concluded that the plastic strain enhances the fracture strength of the cracked components when the induced plastic strain is less than 10%, although the extremely large plastic strain could reduce the strength. (author)

  5. Computed Tomographic Imaging of Subchondral Fatigue Cracks in the Distal End of the Third Metacarpal Bone in the Thoroughbred Racehorse Can Predict Crack Micromotion in an Ex-Vivo Model

    Science.gov (United States)

    Dubois, Marie-Soleil; Morello, Samantha; Rayment, Kelsey; Markel, Mark D.; Vanderby, Ray; Kalscheur, Vicki L.; Hao, Zhengling; McCabe, Ronald P.; Marquis, Patricia; Muir, Peter

    2014-01-01

    Articular stress fracture arising from the distal end of the third metacarpal bone (MC3) is a common serious injury in Thoroughbred racehorses. Currently, there is no method for predicting fracture risk clinically. We describe an ex-vivo biomechanical model in which we measured subchondral crack micromotion under compressive loading that modeled high speed running. Using this model, we determined the relationship between subchondral crack dimensions measured using computed tomography (CT) and crack micromotion. Thoracic limbs from 40 Thoroughbred racehorses that had sustained a catastrophic injury were studied. Limbs were radiographed and examined using CT. Parasagittal subchondral fatigue crack dimensions were measured on CT images using image analysis software. MC3 bones with fatigue cracks were tested using five cycles of compressive loading at -7,500N (38 condyles, 18 horses). Crack motion was recorded using an extensometer. Mechanical testing was validated using bones with 3 mm and 5 mm deep parasagittal subchondral slots that modeled naturally occurring fatigue cracks. After testing, subchondral crack density was determined histologically. Creation of parasagittal subchondral slots induced significant micromotion during loading (pThoroughbred horses in-vivo to assess risk of condylar fracture. Horses with parasagittal crack arrays that exceed 30 mm2 may have a high risk for development of condylar fracture. PMID:25077477

  6. Evaluation of crack interaction effect for in-plane surface cracks using elastic finite element analyses

    International Nuclear Information System (INIS)

    Huh, Nam Su; Choi, Suhn; Park, Keun Bae; Kim, Jong Min; Choi, Jae Boong; Kim, Young Jin

    2008-01-01

    The crack-tip stress fields and fracture mechanics assessment parameters, such as the elastic stress intensity factor and the elastic-plastic J-integral, for a surface crack can be significantly affected by adjacent cracks. Such a crack interaction effect due to multiple cracks can magnify the fracture mechanics assessment parameters. There are many factors to be considered, for instance the relative distance between adjacent cracks, crack shape and loading condition, to quantify a crack interaction effect on the fracture mechanics assessment parameters. Thus, the current guidance on a crack interaction effect (crack combination rule), including ASME Sec. XI, BS7910, British Energy R6 and API RP579, provide different rules for combining multiple surface cracks into a single surface crack. The present paper investigates a crack interaction effect by evaluating the elastic stress intensity factor of adjacent surface cracks in a plate along the crack front through detailed 3-dimensional elastic finite element analyses. The effects of the geometric parameters, the relative distance between cracks and the crack shape, on the stress intensity factor are systematically investigated. As for the loading condition, only axial tension is considered. Based on the elastic finite element results, the acceptability of the crack combination rules provided in the existing guidance was investigated, and the relevant recommendations on a crack interaction for in-plane surface cracks in a plate were discussed

  7. The effect of aqueous environments upon the initiation and propagation of fatigue cracks in low-alloy steels

    International Nuclear Information System (INIS)

    James, L.A.

    1996-01-01

    The effect of elevated temperature aqueous environments upon the initiation and propagation of fatigue cracks in low-alloy steels is discussed in terms of the several parameters which influence such behavior. These parameters include water chemistry, impurities within the steels themselves, as well as factors such as the water flow rate, loading waveform and loading rates. Some of these parameters have similar effects upon both crack initiation and propagation, while others exhibit different effects in the two stages of cracking. In the case of environmentally-assisted crack (EAC) growth, the most important impurities within the steel are metallurgical sulfide inclusions which dissolve upon contact with the water. A ''critical'' concentration of sulfide ions at the crack tip can then induce environmentally-assisted cracking which proceeds at significantly increased crack growth rates over those observed in air. The occurrence, or non-occurrence, of EAC is governed by the mass-transport of sulfide ions to and from the crack-tip region, and the mass-transport is discussed in terms of diffusion, ion migration, and convection induced within the crack enclave. Examples are given of convective mass-transport within the crack enclave resulting from external free stream flow. The initiation of fatigue cracks in elevated temperature aqueous environments, as measured by the S-N fatigue lifetimes, is also strongly influenced by the parameters identified above. The influence of sulfide inclusions does not appear to be as strong on the crack initiation process as it is on crack propagation. The oxygen content of the environment appears to be the dominant factor, although loading frequency (strain rate) and temperature are also important factors

  8. Computed tomographic imaging of subchondral fatigue cracks in the distal end of the third metacarpal bone in the thoroughbred racehorse can predict crack micromotion in an ex-vivo model.

    Science.gov (United States)

    Dubois, Marie-Soleil; Morello, Samantha; Rayment, Kelsey; Markel, Mark D; Vanderby, Ray; Kalscheur, Vicki L; Hao, Zhengling; McCabe, Ronald P; Marquis, Patricia; Muir, Peter

    2014-01-01

    Articular stress fracture arising from the distal end of the third metacarpal bone (MC3) is a common serious injury in Thoroughbred racehorses. Currently, there is no method for predicting fracture risk clinically. We describe an ex-vivo biomechanical model in which we measured subchondral crack micromotion under compressive loading that modeled high speed running. Using this model, we determined the relationship between subchondral crack dimensions measured using computed tomography (CT) and crack micromotion. Thoracic limbs from 40 Thoroughbred racehorses that had sustained a catastrophic injury were studied. Limbs were radiographed and examined using CT. Parasagittal subchondral fatigue crack dimensions were measured on CT images using image analysis software. MC3 bones with fatigue cracks were tested using five cycles of compressive loading at -7,500N (38 condyles, 18 horses). Crack motion was recorded using an extensometer. Mechanical testing was validated using bones with 3 mm and 5 mm deep parasagittal subchondral slots that modeled naturally occurring fatigue cracks. After testing, subchondral crack density was determined histologically. Creation of parasagittal subchondral slots induced significant micromotion during loading (pBones with parasagittal crack area measurements above 30 mm2 may have a high risk of crack propagation and condylar fracture in vivo because of crack micromotion. In conclusion, our results suggest that CT could be used to quantify subchondral fatigue crack dimensions in racing Thoroughbred horses in-vivo to assess risk of condylar fracture. Horses with parasagittal crack arrays that exceed 30 mm2 may have a high risk for development of condylar fracture.

  9. Understanding and coming through PVC-tape-induced stress corrosion cracking in PWR piping system

    International Nuclear Information System (INIS)

    Shibayama, Motoaki; Shigemoto, Naoya; Noguchi, Shinji; Hirano, Shin-ichi; Takagi, Toshimitsu

    2003-01-01

    In October 2000, the 24 years old Ikata-1 PWR-type nuclear power plant suffered cracking in pipes of special two lines, where poly vinyl chloride (PVC) tape had been placed and had become baked over time. The existence of residual stress over 100 MPa in the pipes, a bit of chlorine and a feather like-pattern on the crack faces suggested the event was one of stress corrosion cracking. Residual chlorine on the pipes of special two lines was estimated to be 1100 mg/m 2 . A four points bending stress test was performed on the steel plates with the baked on PVC tape in humid air at 80degC. Taking the actual temperature, stress and chlorine on the pipes of the special two lines into consideration, cracking times were estimated to be 12 years and 15 years respectively, which were close to the actual cracking time of 24 years. The authors calculated damage to pipes with fluids of various temperature and duration, and graphed damage contour with a fluid temperature ordinate and a flow duration abscissa. The fluid conditions of major pipes at the Ikata-1 nuclear power plant, which had not received the full inspection, were positioned on so low area on the damage contour that the plant was estimated to be safe for the coming forty years. (author)

  10. Test of 6-in.-thick pressure vessels. Series 4: intermediate test vessels V-5 and V-9 with inside nozzle corner cracks

    International Nuclear Information System (INIS)

    Merkle, J.G.; Robinson, G.C.; Holz, P.P.; Smith, J.E.

    1977-01-01

    Failure testing is described for two 99-cm-diam (39-in.), 15.2-cm-thick (6-in.) steel pressure vessels, each containing one flawed nozzle. Vessel V-5 was tested at 88 0 C (190 0 F) and failed by leaking without fracturing after extensive stable crack growth. Vessel V-9 was tested at 25 0 C (75 0 F) and failed by fracturing. Material properties measured before the tests were used for pretest and posttest fracture analyses. Test results supported by analysis indicate that inside nozzle corner cracks are not subject to plane strain under pressure loading. The preparation of inside nozzle corner cracks is described in detail. Extensive experimental data are tabulated and plotted

  11. Premature failure of dissimilar metal weld joint at intermediate temperature superheater tube

    OpenAIRE

    Al Hajri, Mohammed; Malik, Anees U.; Meroufel, Abdelkader; Al-Muaili, Fahd

    2015-01-01

    Dissimilar metal weld (DMW) joint between alloyed steel (AS) and stainless steel (SS) failed at one of intermediate temperature superheater (ITSH) tube in steam/power generation plant boiler. The premature failure was detected after a relatively short time of operation (8 years) where the crack propagated circumferentially from AS side through the ITSH tube. Apart from physical examination, microstructural studies based on optical microscopy, SEM and EDX analysis were performed. The results o...

  12. Crack-opening area calculations for circumferential through-wall pipe cracks

    Energy Technology Data Exchange (ETDEWEB)

    Kishida, K.; Zahoor, A.

    1988-08-01

    This report describes the estimation schemes for crack opening displacement (COD) of a circumferential through-wall crack, then compares the COD predictions with pipe experimental data. Accurate predictions for COD are required to reliably predict the leak rate through a crack in leak-before-break applications.

  13. Crack-opening area calculations for circumferential through-wall pipe cracks

    International Nuclear Information System (INIS)

    Kishida, K.; Zahoor, A.

    1988-08-01

    This report describes the estimation schemes for crack opening displacement (COD) of a circumferential through-wall crack, then compares the COD predictions with pipe experimental data. Accurate predictions for COD are required to reliably predict the leak rate through a crack in leak-before-break applications

  14. Angular distribution of fragments from neutron-induced fission of 238U in the intermediate energy region

    International Nuclear Information System (INIS)

    Carlsson, Magnus

    2004-06-01

    Areas ranging from nuclear structure models to accelerator-driven systems benefit from improved neutron-induced fission data in the intermediate energy region. In this Master's degree thesis, the fragment angular distribution from fission of 238 U, induced by 21-MeV neutrons, has been analysed from an experiment performed with the Medley/DIFFICILE setup at the The Svedberg Laboratory in Uppsala. The data have been corrected for low energy neutrons in the beam. The results agree with other experiments, as well as with model calculations. The data should be a starting point for further analysis with a goal to deduce the fission cross-section of 238 U

  15. Process of cracking in reinforced concrete beams (simulation and experiment

    Directory of Open Access Journals (Sweden)

    I. N. Shardakov

    2016-10-01

    Full Text Available The paper presents the results of experimental and theoretical investigations of the mechanisms of crack formation in reinforced concrete beams subjected to quasi-static bending. The boundary-value problem has been formulated in the framework of brittle fracture mechanics and solved using the finite-element method. Numerical simulation of the vibrations of an uncracked beam and a beam with cracks of different size serves to determine the pattern of changes in the spectrum of eigenfrequencies observed during crack evolution. A series of sequential quasi-static 4-point bend tests leading to the formation of cracks in a reinforced concrete beam were performed. At each loading step, the beam was subjected to an impulse load to induce vibrations. Two stages of cracking were detected. During the first stage the nonconservative process of deformation begins to develope, but has not visible signs. The second stage is an active cracking, which is marked by a sharp change in eingenfrequencies. The boundary of a transition from one stage to another is well registered. The vibration behavior was examined for the ordinary concrete beams and the beams strengthened with a carbon-fiber polymer. The obtained results show that the vibrodiagnostic approach is an effective tool for monitoring crack formation and assessing the quality of measures aimed at strengthening concrete structures

  16. Examination of influencing factors on cyclic crack growth behaviour of cracked components. Final report; Untersuchung von Einflussfaktoren auf das zyklische Risswachstum angerissener Bauteile. Abschlussbericht

    Energy Technology Data Exchange (ETDEWEB)

    Soppa, Ewa Anna; Silcher, Horst

    2015-01-31

    Fatigue crack growth of short and long cracks was investigated for both materials: the Nb-stabilized austenitic stainless steel X6 CrNiNb 18-10 and the ferritic-bainitic steel 22 NiMoCr 3-7. These both steels belong to the materials in the primary circuit of german power plants. For a reliable estimation of the lifetime of components subject to cyclic fatigue a detailed knowledge of the phenomena accompanying fatigue processes and which cause both - initiation and growth of fatigue cracks is essential. The deformation induced transformation of austenite into α'-martensite at room temperature is thus very important in the initiation and growth of fatigue cracks. Because these processes are manifest at first at the microlevel, the use of methods which reveal information at high resolution is of significant importance. In order to study the initiation and growth of short cracks, cylindrical smooth specimens, compact tension C(T)- and modified C(T)-specimens have been used. Cyclic crack propagation of long cracks was investigated on compact tension C(T)-specimens with W=50 mm and B=10 mm. The SEM, TEM and EBSD technique are powerful methods for determining crystallographic orientation, for the identification of individual phases and for recealing plastic deformation. They were used for analyses of microcracks in combination with interrupted cyclic tests. The impact of crack closure on the threshold parameter ΔK{sub th} and the crack growth rate da/dN was investigated experimentally for the growth of long cracks under cyclic loading for different R-values at room temperature. Additional tests were performed at T=288 C in order to investigate the role of temperature on crack growth rates. The effect of overloads in tension and compression as another factor influencing the crack growth was also studied. Measured crack growth curves were fitted using Paris and Erdogan-Ratwani law as well as the NASGRO-equation. Fracture surfaces of selected specimens for both steels

  17. Prevention of crack initiation in valve bodies under thermal shock

    Energy Technology Data Exchange (ETDEWEB)

    Delmas, J.; Coppolani, P.

    1996-12-01

    On site and testing experience has shown that cracking in valves affects mainly the stellite hardfacing on seats and discs but may also be a concern for valve bodies. Metallurgical investigations conducted by EDF laboratories on many damaged valves have shown that most of the damage had either a chemical, manufacturing, or operating origin with a strong correlation between the origins and the type of damage. The chemical defects were either excess ferritic dilution of stellite or excess carburizing. Excess carburizing leads to a too brittle hardfacing which cracks under excessive stresses induced on the seating surfaces, via the stem, by too high operating thrusts. The same conditions can also induce cracks of the seats in the presence, in the hardfacing, of hidden defects generated during the welding process. Reduction of the number of defects results first from controls during manufacturing, mainly in the thickness of stellite. On the other hand, maintenance must be fitted to the type of defect. In-situ lapping may lead to release of cobalt, resulting in contamination of the circuit. Furthermore, it is ineffectual in the case of a crack through the seating surface, as is often found on globe valves. The use of new technologies of valves with removable seats and cobalt-free alloys solves permanently this kind of problem.

  18. Microstructural modelling of creep crack growth from a blunted crack

    NARCIS (Netherlands)

    Onck, P.R.; Giessen, E. van der

    1998-01-01

    The effect of crack tip blunting on the initial stages of creep crack growth is investigated by means of a planar microstructural model in which grains are represented discretely. The actual linking-up process of discrete microcracks with the macroscopic crack is simulated, with full account of the

  19. Crack-tip chemistry modeling of stage I stress corrosion cracking

    International Nuclear Information System (INIS)

    Jones, R.H.; Simonen, E.P.

    1991-10-01

    Stage I stress corrosion cracking usually exhibits a very strong K dependence with Paris law exponents of up to 30. 2 Model calculations indicate that the crack velocity in this regime is controlled by transport through a salt film and that the K dependence results from crack opening controlled salt film dissolution. An ionic transport model that accounts for both electromigration through the resistive salt film and Fickian diffusion through the aqueous solution was used for these predictions. Predicted crack growth rates are in excellent agreement with measured values for Ni with P segregated to the grain boundaries and tested in IN H 2 SO 4 at +900 mV. This salt film dissolution may be applicable to stage I cracking of other materials

  20. Fatigue crack growth behaviors in hot-rolled low carbon steels: A comparison between ferrite–pearlite and ferrite–bainite microstructures

    International Nuclear Information System (INIS)

    Guan, Mingfei; Yu, Hao

    2013-01-01

    The roles of microstructure types in fatigue crack growth behaviors in ferrite–pearlite steel and ferrite–bainite steel were investigated. The ferrite–bainite dual-phase microstructure was obtained by intermediate heat treatment, conducted on ferrite–pearlite hot-rolled low carbon steel. This paper presents the results from investigation using constant stress-controlled fatigue tests with in-situ scanning electron microscopy (SEM), fatigue crack growth (FCG) rate tests, and fatigue fractography analysis. Microscopy images arrested by in-situ SEM showed that the fatigue crack propagation in F–P steel could become unstable more ealier compared with that in F–B steel. The fatigue cracks in ferrite–pearlite were more tortuous and could propagate more freely than that in ferrite–bainite microstructures. However, frequent crack branching were observed in ferrite–bainite steel and it indicated that the second hard bainite phase effectively retarded the crack propagation. The variation of FCG rate (da/dN) with stress intensity factor range (ΔK) for F–P and F–B steels was discussed within the Paris region. It was shown that FCG rate of F–P steel was higher than that of F–B steel. Moreover, the fatigue fracture surface analysis proved that grain boundaries could also play a role in the resistance of crack propagation.

  1. Key intermediates in nitrogen transformation during microwave pyrolysis of sewage sludge: a protein model compound study.

    Science.gov (United States)

    Zhang, Jun; Tian, Yu; Cui, Yanni; Zuo, Wei; Tan, Tao

    2013-03-01

    The nitrogen transformations with attention to NH3 and HCN were investigated at temperatures of 300-800°C during microwave pyrolysis of a protein model compound. The evolution of nitrogenated compounds in the char, tar and gas products were conducted. The amine-N, heterocyclic-N and nitrile-N compounds were identified as three important intermediates during the pyrolysis. NH3 and HCN were formed with comparable activation energies competed to consume the same reactive substances at temperatures of 300-800°C. The deamination and dehydrogenation of amine-N compounds from protein cracking contributed to the formation of NH3 (about 8.9% of Soy-N) and HCN (6.6%) from 300 to 500°C. The cracking of nitrile-N and heterocyclic-N compounds from the dehydrogenation and polymerization of amine-N generated HCN (13.4%) and NH3 (31.3%) between 500 and 800°C. It might be able to reduce the HCN and NH3 emissions through controlling the intermediates production at temperatures of 500-800°C. Copyright © 2013 Elsevier Ltd. All rights reserved.

  2. Air-steam leakage through cracks in concrete

    International Nuclear Information System (INIS)

    Georges Nahas; Helene Simon

    2005-01-01

    axial load is applied on the reinforcement bars for cracking. In this experiment, about five almost plane vertical traversing cracks are induced. Air-steam pressure is applied in a chamber at the top of the slab. Water leakage is collected at the bottom and measured. A scenario lasting 40 hours is produced with a 4 hour temperature stage at 210 Celsius degrees followed by a 4 hour temperature stage at 160 Celsius degrees. During the experiment, the average crack opening is kept constant at the bottom of the slab by changing the applied axial load. At the top, the concrete slab is heated by heat exchange with the steam in the pressure chamber and thermal expansion of the concrete causes the cracks to close during the first stage and reopen during the following stage. A mechanical calculation with the code CAST3M aims to reproduce the mechanical behavior of the slab during the test, namely closing and reopening of the cracks at the top of the slab, where openings are measured. The model represents the five idealized cracks in bidimensional analysis with real test conditions (pressure and thermal load). The mechanical calculation furnishes data needed by the leakage calculation and unreachable to the experiment that are the internal crack profiles ( variation of the opening with the curvilinear coordinate of the crack inside the concrete slab). Various leakage calculations have been performed: linear internal crack profile with inlet crack opening varying with time, complex internal crack profile given by mechanical calculation, and finally mechanics and thermal hydraulics coupling. (authors)

  3. Analysis of short and long crack behavior and single overload effect by crack opening stress

    International Nuclear Information System (INIS)

    Song, Sam Hong; Lee, Kyeong Ro

    1999-01-01

    The study analyzed the behaviors of short and long crack as well as the effect of single tensile overload on the crack behaviors by using fatigue crack opening behavior. Crack opening stress is measured by an elastic compliance method which may precisely and continuously provide many data using strain gages during experiment. The unusual growth behaviors of short crack and crack after the single tensile overload applied, was explained by the variations of crack opening stress. In addition, fatigue crack growth rate was expressed as a linear form for short crack as for long crack by using effective stress intensity factor range as fracture mechanical parameter, which is based on crack closure concept. And investigation is performed with respect to the relation between plastic zone size formed at the crack tip and crack retardation, crack length and the number of cycles promoted or retarded, and the overload effect on the fatigue life

  4. Fatigue crack growth from a cracked elastic particle into a ductile matrix

    NARCIS (Netherlands)

    Groh, S.; Olarnrithinun, S.; Curtin, W. A.; Needleman, A.; Deshpande, V. S.; Van der Giessen, E.

    2008-01-01

    The monotonic and cyclic crack growth rate of cracks is strongly influenced by the microstructure. Here, the growth of cracks emanating from pre-cracked micron-scale elastic particles and growing into single crystals is investigated, with a focus on the effects of (i) plastic confinement due to the

  5. Recent evaluations of crack-opening-area in circumferentially cracked pipes

    Energy Technology Data Exchange (ETDEWEB)

    Rahman, S.; Brust, F.; Ghadiali, N.; Wilkowski, G.; Miura, N.

    1997-04-01

    Leak-before-break (LBB) analyses for circumferentially cracked pipes are currently being conducted in the nuclear industry to justify elimination of pipe whip restraints and jet shields which are present because of the expected dynamic effects from pipe rupture. The application of the LBB methodology frequently requires calculation of leak rates. The leak rates depend on the crack-opening area of the through-wall crack in the pipe. In addition to LBB analyses which assume a hypothetical flaw size, there is also interest in the integrity of actual leaking cracks corresponding to current leakage detection requirements in NRC Regulatory Guide 1.45, or for assessing temporary repair of Class 2 and 3 pipes that have leaks as are being evaluated in ASME Section XI. The objectives of this study were to review, evaluate, and refine current predictive models for performing crack-opening-area analyses of circumferentially cracked pipes. The results from twenty-five full-scale pipe fracture experiments, conducted in the Degraded Piping Program, the International Piping Integrity Research Group Program, and the Short Cracks in Piping and Piping Welds Program, were used to verify the analytical models. Standard statistical analyses were performed to assess used to verify the analytical models. Standard statistical analyses were performed to assess quantitatively the accuracy of the predictive models. The evaluation also involved finite element analyses for determining the crack-opening profile often needed to perform leak-rate calculations.

  6. An experimental study on the factors that affect fatigue crack growth retardation behavior in SM45C steel

    International Nuclear Information System (INIS)

    Kim, Seon Jin; Kim, Jong Hoon; Ahn, Seok Hwan

    2000-01-01

    Constant ΔK fatigue crack growth tests were performed applying an intermediate multiple overload for SM45C steel. The purpose of the present study is to investigate the effects of specimen thickness at various baseline stress intensity levels(ΔK b ), overload application position(a/W) and overload application frequency(OL Hz ) on fatigue crack growth retardation behavior. The principal results are summarized as follows. The amount of retardation for a given ΔK b level is increased with increasing the baseline stress intensity level in all specimen thickness. The normalized minimum crack growth rate is increased with increasing the specimen thickness, except for ΔK=45MPa√m. The retardation cycle is decreased with increasing the overload application position and increased with the overload application frequency

  7. Hydrogen Absorption Induced Slow Crack Growth in Austenitic Stainless Steels for Petrochemical Pressure Vessel Industries

    Directory of Open Access Journals (Sweden)

    Ronnie Rusli

    2011-05-01

    Full Text Available Type 304Land type 309 austenitic stainless steels were tested either by exposed to gaseous hydrogen or undergoing polarized cathodic charging. Slow crack growth by straining was observed in type 304L, and the formation of α‘ martensite was indicated to be precursor for such cracking. Gross plastic deformation was observed at the tip of the notch, and a single crack grew slowly from this region in a direction approximately perpendicular to the tensile axis. Martensite formation is not a necessary condition for hydrogen embrittlement in the austenitic phase.

  8. Role of prism decussation on fatigue crack growth and fracture of human enamel.

    Science.gov (United States)

    Bajaj, Devendra; Arola, Dwayne

    2009-10-01

    The role of prism decussation on the crack growth resistance of human enamel is evaluated. Miniature inset compact tension (CT) specimens embodying a section of cuspal enamel were subjected to Mode I cyclic or monotonic loads. Cracks were grown in either the forward (from outer enamel inwards) or reverse (from inner enamel outwards) direction and the responses were compared quantitatively. Results showed that the outer enamel exhibits lower resistance to the inception and growth of cracks. Regardless of the growth direction, the near-threshold region of cyclic extension was typical of "short crack" behavior (i.e. deceleration of growth with an increase in crack length). Cyclic crack growth was more stable in the forward direction and occurred over twice the spatial distance achieved in the reverse direction. In response to the monotonic loads, a rising R-curve response was exhibited by growth in the forward direction only. The total energy absorbed in fracture for the forward direction was more than three times that in the reverse. The rise in crack growth resistance was largely attributed to a combination of mechanisms that included crack bridging, crack bifurcation and crack curving, which were induced by decussation in the inner enamel. An analysis of the responses distinguished that the microstructure of enamel appears optimized for resisting crack growth initiating from damage at the tooth's surface.

  9. Improvement of elastic-plastic fatigue crack growth evaluation method. 2. Crack opening behavior

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, Yukio [Central Research Inst. of Electric Power Industry, Tokyo (Japan)

    2001-05-01

    Evaluation of crack growth behavior under cyclic loading is often required in the structural integrity assessment of cracked components. Closing and re-opening of the crack give large influence on crack growth rate through the change of fracture mechanics parameters. Based on the finite element analysis for a center-cracked plate, dependency of crack opening ratio on applied stress range and mean stress was examined. Simple formulae for representing the results were derived for plane stress and plane strain conditions. (author)

  10. Identification of cracks in thick beams with a cracked beam element model

    Science.gov (United States)

    Hou, Chuanchuan; Lu, Yong

    2016-12-01

    The effect of a crack on the vibration of a beam is a classical problem, and various models have been proposed, ranging from the basic stiffness reduction method to the more sophisticated model involving formulation based on the additional flexibility due to a crack. However, in the damage identification or finite element model updating applications, it is still common practice to employ a simple stiffness reduction factor to represent a crack in the identification process, whereas the use of a more realistic crack model is rather limited. In this paper, the issues with the simple stiffness reduction method, particularly concerning thick beams, are highlighted along with a review of several other crack models. A robust finite element model updating procedure is then presented for the detection of cracks in beams. The description of the crack parameters is based on the cracked beam flexibility formulated by means of the fracture mechanics, and it takes into consideration of shear deformation and coupling between translational and longitudinal vibrations, and thus is particularly suitable for thick beams. The identification procedure employs a global searching technique using Genetic Algorithms, and there is no restriction on the location, severity and the number of cracks to be identified. The procedure is verified to yield satisfactory identification for practically any configurations of cracks in a beam.

  11. Crack Tip Parameters for Growing Cracks in Linear Viscoelastic Materials

    DEFF Research Database (Denmark)

    Brincker, Rune

    In this paper the problem of describing the asymptotic fields around a slowly growing crack in a linearly viscoelastic material is considered. It is shown that for plane mixed mode problems the asymptotic fields must be described by 6 parameters: 2 stress intensity factors and 4 deformation...... intensity factors. In the special case of a constant Poisson ratio only 2 deformation intensity factors are needed. Closed form solutions are given both for a slowly growing crack and for a crack that is suddenly arrested at a point at the crack extension path. Two examples are studied; a stress boundary...... value problem, and a displacement boundary value problem. The results show that the stress intensity factors and the displacement intensity factors do not depend explicitly upon the velocity of the crack tip....

  12. Production of steam cracking feedstocks by mild cracking of plastic wastes

    Energy Technology Data Exchange (ETDEWEB)

    Angyal, Andras; Miskolczi, Norbert; Bartha, Laszlo; Tungler, Antal; Nagy, Lajos; Vida, Laszlo; Nagy, Gabor

    2010-11-15

    In this work the utility of new possible petrochemical feedstocks obtained by plastic waste cracking has been studied. The cracking process of polyethylene (PE), polyethylene-polypropylene (PEPP) and polyethylene-polystyrene (PEPS) has been carried out in a pilot scale tubular reactor. In this process mild reaction parameters has been applied, with the temperature of 530 C and the residence time of 15 min. The produced hydrocarbon fractions as light- and middle distillates were tested by using a laboratory steam cracking unit. It was concluded that the products of the mild cracking of plastic wastes could be applied as petrochemical feedstocks. Based on the analytical data it was determined that these liquid products contained in significant concentration (25-50 wt.%) of olefin hydrocarbons. Moreover the cracking of polystyrene containing raw material resulted in liquid products with significant amounts of aromatic hydrocarbons too. The steam cracking experiments proved that the products obtained by PE and PEPP cracking resulted in similar or better ethylene and propylene yields than the reference samples, however the aromatic content of PEPS products reduced the ethylene and propylene yields. (author)

  13. Hydride precipitation crack propagation in zircaloy cladding during a decreasing temperature history

    International Nuclear Information System (INIS)

    Stout, R.B.

    2001-01-01

    An assessment of safety, design, and cost tradeoff issues for short (ten to fifty years) and longer (fifty to hundreds of years) interim dry storage of spent nuclear fuel in Zircaloy rods shall address potential failures of the Zircaloy cladding caused by the precipitation response of zirconium hydride platelets. To perform such assessment analyses rigorously and conservatively will be necessarily complex and difficult. For Zircaloy cladding, a model for zirconium hydride induced crack propagation velocity was developed for a decreasing temperature field and for hydrogen, temperature, and stress dependent diffusive transport of hydrogen to a generic hydride platelet at a crack tip. The development of the quasi-steady model is based on extensions of existing models for hydride precipitation kinetics for an isolated hydride platelet at a crack tip. An instability analysis model of hydride-crack growth was developed using existing concepts in a kinematic equation for crack propagation at a constant thermodynamic crack potential subject to brittle fracture conditions. At the time an instability is initiated, the crack propagation is no longer limited by hydride growth rate kinetics, but is then limited by stress rates. The model for slow hydride-crack growth will be further evaluated using existing available data. (authors)

  14. Hydride precipitation crack propagation in zircaloy cladding during a decreasing temperature history

    Energy Technology Data Exchange (ETDEWEB)

    Stout, R.B. [California Univ., Livermore, CA (United States). Lawrence Livermore National Lab

    2001-07-01

    An assessment of safety, design, and cost tradeoff issues for short (ten to fifty years) and longer (fifty to hundreds of years) interim dry storage of spent nuclear fuel in Zircaloy rods shall address potential failures of the Zircaloy cladding caused by the precipitation response of zirconium hydride platelets. To perform such assessment analyses rigorously and conservatively will be necessarily complex and difficult. For Zircaloy cladding, a model for zirconium hydride induced crack propagation velocity was developed for a decreasing temperature field and for hydrogen, temperature, and stress dependent diffusive transport of hydrogen to a generic hydride platelet at a crack tip. The development of the quasi-steady model is based on extensions of existing models for hydride precipitation kinetics for an isolated hydride platelet at a crack tip. An instability analysis model of hydride-crack growth was developed using existing concepts in a kinematic equation for crack propagation at a constant thermodynamic crack potential subject to brittle fracture conditions. At the time an instability is initiated, the crack propagation is no longer limited by hydride growth rate kinetics, but is then limited by stress rates. The model for slow hydride-crack growth will be further evaluated using existing available data. (authors)

  15. Intermediate temperature embrittlement of one new Ni-26W-6Cr based superalloy for molten salt reactors

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Li [Thorium Molten Salts Reactor Center, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); University of Chinese Academy of Science, Beijing 100049 (China); Ye, Xiangxi [University of Chinese Academy of Science, Beijing 100049 (China); Cui, Chuanyong [Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Huang, Hefei; Leng, Bin [Thorium Molten Salts Reactor Center, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Li, Zhijun, E-mail: lizhijun@sinap.ac.cn [Thorium Molten Salts Reactor Center, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Zhou, Xingtai [Thorium Molten Salts Reactor Center, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China)

    2016-06-21

    Ni-26W-6Cr based superalloy is considered a potential structure material for the molten salt reactors due to its high strength and good compatibility with the fluoride salt. In the present work, the temperature dependence of the tensile behavior of the alloy was studied by tensile tests in the temperature range of 25–850 °C. This alloy exhibited a good ductility at RT and 450 °C, a ductility minimum from 650 to 750 °C and an intermediate ductility at 850 °C. TEM and EBSD characterization was performed on specimens tested at three typical temperature points (RT, 650 °C and 850 °C) to determine the deformation and fracture mechanisms accounting for the intermediate temperature embrittlement. At RT, the grain boundaries can accommodate enough dislocations to provide compatibility of the sliding between adjacent grains, then M{sub 6}C carbides act as crack origins and cause the fracture. In case of 650 °C, the grain boundaries cannot withstand the local stress even if only a small number of dislocation pile-ups exist. The premature cracks at grain boundaries impede the development of plastic deformation from single slips to multiple ones and cause the low ductility. If tested at 850 °C, the fracture process is retarded by the dynamic recovery and local dynamic recrystallization at crack tips.

  16. Correlation between passive film-induced stress and stress corrosion cracking of α-Ti in a methanol solution at various potentials

    International Nuclear Information System (INIS)

    Guo, X.Z.; Gao, K.W.; Chu, W.Y.; Qiao, L.J.

    2003-01-01

    The flow stress of a specimen of α-Ti before unloading is different with the yield stress of the same specimen after unloading and forming a passive film through immersing in a methanol solution at various constant potentials. The difference is the passive film-induced stress. The film-induced stress and susceptibility to stress corrosion cracking (SCC) in the methanol solution at various potentials were measured. At the stable open-circuit potential and under anodic polarization, both film-induced tensile stress σ p and susceptibility to SCC had a maximum value. The film-induced stress and SCC susceptibility, however, decreased steeply with a decrease in potential under cathodic polarization. When the potential V≤-280 mV SCE , the film-induced stress became compressive; correspondingly, susceptibility to SCC was zero. Therefore, the variation of film-induced stress with potential was consistent with that of susceptibility to SCC. A large film-induced tensile stress is the necessary condition for SCC of α-Ti in the methanol solution. The symbol and amount of the film-induced stress were related to the compositions of the passive film, which have been analyzed using the X-ray photoelectron spectrum (XPS)

  17. The initiation of environmentally-assisted cracking in semi-elliptical surface cracks

    International Nuclear Information System (INIS)

    James, L.A.

    1997-01-01

    A criterion to predict under what conditions EAC would Initiate In cracks In a high-sulfur steel in contact with low-oxygen water was recently proposed by Wire and U. This EAC Initiation Criterion was developed using transient analyses for the diffusion of sulfides plus experimental test results. The experiments were conducted mainly on compact tension-type specimens with initial crack depths of about 2.54 mm. The present paper expands upon the work of Wire and U by presenting results for significantly deeper initial semi-elliptical surface cracks. In addition, in one specimen, the surface crack penetrated weld-deposited cladding into the high-sulfur steel. The results for the semi-elliptical surface cracks agreed quite well with the EAC Initiation Criterion, and provide confirmation of the applicability of the criterion to crack configurations with more restricted access to water

  18. Crack growth of throughwall flaw in Alloy 600 tube during leak testing

    International Nuclear Information System (INIS)

    Bahn, Chi Bum; Majumdar, Saurin

    2015-01-01

    Graphical abstract: - Highlights: • A series of leak testing was conducted at a constant pressure and room temperature. • The time-dependent increase in the leak rate was observed. • The fractography revealed slip offsets and crystallographic facets. • Time-dependent plasticity at the crack tip caused the slip offsets. • Fatigue by jet/structure interaction caused the crystallographic facets. - Abstract: We examined the issue of whether crack growth in a full thickness material can occur in a leaking crack. A series of leak tests was conducted at a room temperature and constant pressure (17.3 MPa) with Alloy 600 tube specimens containing a tight rectangular throughwall axial fatigue crack. To exclude a potential pulsation effect by a high pressure pump, the test water was pressurized by using high pressure nitrogen gas. Fractography showed that crack growth in the full thickness material can occur in the leaking crack by two mechanisms: time-dependent plasticity at the crack tip and fatigue induced by jet/structure interaction. The threshold leak rate at which the jet/structure interaction was triggered was between 1.3 and 3.3 L/min for the specific heat of the Alloy 600 tube tested

  19. The effects of loading history on fatigue crack growth threshold

    International Nuclear Information System (INIS)

    Ogawa, Takeshi; Tokaji, Keiro; Ochi, Satoshi; Kobayashi, Hideo.

    1987-01-01

    The effects of loading history on threshold stress intensity range (ΔK th ) were investigated in a low alloy steel SFVQ1A (A508 - 3) and a low carbon steel S10C. A single overload and multiple overloads were chosen as loading history. Crack growth and crack closure following the loading histories were measured at load ratios of 0.05 and 0.70. Threshold values were determined as a fatigue limit of preloaded specimens. The ΔK th values increased with increasing overload stress intensity factor (K h ). For a given K h value, multiple overloads produced much larger increase in ΔK th than a single overload and threshold values expressed by maximum stress intensity factor (K max,th ) were almost constant, independent of stress ratio. The results obtained were discussed in terms of crack closure behaviour, and a method was proposed to evaluate the threshold value based on plasticity-induced crack closure. (author)

  20. Threshold intensity factors as lower boundaries for crack propagation in ceramics

    Directory of Open Access Journals (Sweden)

    Walter Per-Ole

    2004-11-01

    Full Text Available Abstract Background Slow crack growth can be described in a v (crack velocity versus KI (stress intensity factor diagram. Slow crack growth in ceramics is attributed to corrosion assisted stress at the crack tip or at any pre-existing defect in the ceramic. The combined effect of high stresses at the crack tip and the presence of water or body fluid molecules (reducing surface energy at the crack tip induces crack propagation, which eventually may result in fatigue. The presence of a threshold in the stress intensity factor, below which no crack propagation occurs, has been the subject of important research in the last years. The higher this threshold, the higher the reliability of the ceramic, and consequently the longer its lifetime. Methods We utilize the Irwin K-field displacement relation to deduce crack tip stress intensity factors from the near crack tip profile. Cracks are initiated by indentation impressions. The threshold stress intensity factor is determined as the time limit of the tip stress intensity when the residual stresses have (nearly disappeared. Results We determined the threshold stress intensity factors for most of the all ceramic materials presently important for dental restorations in Europe. Of special significance is the finding that alumina ceramic has a threshold limit nearly identical with that of zirconia. Conclusion The intention of the present paper is to stress the point that the threshold stress intensity factor represents a more intrinsic property for a given ceramic material than the widely used toughness (bend strength or fracture toughness, which refers only to fast crack growth. Considering two ceramics with identical threshold limits, although with different critical stress intensity limits, means that both ceramics have identical starting points for slow crack growth. Fast catastrophic crack growth leading to spontaneous fatigue, however, is different. This growth starts later in those ceramic materials

  1. The influence of specimen size on creep crack growth rate in cross-weld CT specimens cut out from a welded component

    International Nuclear Information System (INIS)

    Andersson, Peder; Segle, Peter; Samuelson, Lars Aa.

    1999-04-01

    A 3D finite element study of creep crack growth in cross-weld CT specimens with material properties of 2.25Cr1Mo at 550 deg C is carried out, where large strain and displacement theory is used. The creep crack growth rate is calculated using a creep ductility based damage model, in which the creep strain rate perpendicular to the crack plane ahead of the crack tip is integrated, considering the multiaxial stress state. The influence of specimen size on creep crack growth rate under constant load is given special attention, but the possibility to transfer results from cross-weld CT specimens to welded high temperature components is also investigated. The creep crack growth rate of a crack in a circumferentially welded pipe is compared with the creep crack growth rate of cross-weld CT specimens of three different sizes, cut out from the pipe. Although the constraint ahead of the crack tip is higher for a larger CT specimen, the creep crack growth rate is higher for a smaller specimen than for a larger one if they are loaded to attain the same stress intensity factor. If the specimens are loaded to the same C* value, however, a more complicated pattern occurs; depending on the material properties of the weldment constituents, the CT specimen with the intermediate size will either yield the highest or the lowest creep crack growth rate

  2. Cracked gas generator

    Energy Technology Data Exchange (ETDEWEB)

    Abthoff, J; Schuster, H D; Gabler, R

    1976-11-17

    A small cracked-gas generator in a vehicle driven, in particular, by an air combustion engine has been proposed for the economic production of the gases necessary for low toxicity combustion from diesel fuel. This proceeds via catalytic crack-gasification and exploitation of residual heat from exhaust gases. This patent application foresees the insertion of one of the catalysts supporting the cracked-gas reaction in a container through which the reacting mixture for cracked-gas production flows in longitudinal direction. Further, air ducts are embedded in the catalyst through which exhaust gases and fresh air flow in counter direction to the cracked gas flow in the catalyst. The air vents are connected through heat conduction to the catalyst. A cracked gas constituting H/sub 2//CO/CO/sub 2//CH/sub 4/ and H/sub 2/O can be produced from the air-fuel mixture using appropriate catalysts. By the addition of 5 to 25% of cracked gas to the volume of air drawn in by the combustion engine, a more favourable combustion can be achieved compared to that obtained under normal combustion conditions.

  3. Quarter elliptical crack growth using three dimensional finite element method and crack closure technique

    Energy Technology Data Exchange (ETDEWEB)

    Gozin, Mohammad-Hosein; Aghaie-Khafri, Mehrdad [K. N. Toosi University of Technology, Tehran (Korea, Republic of)

    2014-06-15

    Shape evolution of a quarter-elliptical crack emanating from a hole is studied. Three dimensional elastic-plastic finite element analysis of the fatigue crack closure was considered and the stress intensity factor was calculated based on the duplicated elastic model at each crack tip node. The crack front node was advanced proportional to the imposed effective stress intensity factor. Remeshing was applied at each step of the crack growth and solution mapping algorithm was considered. Crack growth retardation at free surfaces was successfully observed. A MATLAB-ABAQUS interference code was developed for the first time to perform crack growth on the basis of crack closure. Simulation results indicated that crack shape is sensitive to the remeshing strategy. Predictions based on the proposed models were in good agreement with Carlson's experiments results.

  4. Alleviation of process-induced cracking of the antireflection TiN coating (ARC-TiN) in Al-Cu and Al-Cu-Si films

    CERN Document Server

    Peng, Y C; Yang, Y R; Hsieh, W Y; Hsieh, Y F

    1999-01-01

    The alleviation of cracking of the TiN-ARC layer on Al-Cu and Al-Cu-Si films after the development process has been achieved. For the TiN-ARC/Al-Cu system, the stress-induced defects decreased with increasing TiN-ARC layer thickness. In contrast, for the TiN-ARC/Al-Cu-Si system, Si nodules formed during cooling, thereby inducing poor coverage with high aspect-ratio holes. As a result, the photoresist developer penetrated through the films. Chemical vapor deposition of TiN-ARC or predeposition of a Ti Interposing layer was used to eliminate the formation of Si nodules.

  5. Influence of alkali-silica reaction and crack orientation on the uniaxial compressive strength of concrete cores from slab bridges

    DEFF Research Database (Denmark)

    Antonio Barbosa, Ricardo; Gustenhoff Hansen, Søren; Hansen, Kurt Kielsgaard

    2018-01-01

    ASR-damaged flat slab bridges in service. Furthermore, the influence of the ASR-induced crack orientation on the compressive strength and the Young’s modulus is investigated. Uniaxial compression tests, visual observations, and thin section examinations were performed on more than 100 cores drilled...... from the three severely ASR-damaged flat slab bridges. It was found that the orientation of ASR-induced cracks has a significant influence on the uniaxial compressive strength and the stress-strain relationship of the tested cores. The compressive strength in a direction parallel to ASR cracks can...

  6. The Numerical Simulation of the Crack Elastoplastic Extension Based on the Extended Finite Element Method

    Directory of Open Access Journals (Sweden)

    Xia Xiaozhou

    2013-01-01

    Full Text Available In the frame of the extended finite element method, the exponent disconnected function is introduced to reflect the discontinuous characteristic of crack and the crack tip enrichment function which is made of triangular basis function, and the linear polar radius function is adopted to describe the displacement field distribution of elastoplastic crack tip. Where, the linear polar radius function form is chosen to decrease the singularity characteristic induced by the plastic yield zone of crack tip, and the triangle basis function form is adopted to describe the displacement distribution character with the polar angle of crack tip. Based on the displacement model containing the above enrichment displacement function, the increment iterative form of elastoplastic extended finite element method is deduced by virtual work principle. For nonuniform hardening material such as concrete, in order to avoid the nonsymmetry characteristic of stiffness matrix induced by the non-associate flowing of plastic strain, the plastic flowing rule containing cross item based on the least energy dissipation principle is adopted. Finally, some numerical examples show that the elastoplastic X-FEM constructed in this paper is of validity.

  7. Nondestructive estimation of depth of surface opening cracks in concrete beams

    International Nuclear Information System (INIS)

    Arne, Kevin; In, Chiwon; Kurtis, Kimberly; Kim, Jin-Yeon; Jacobs, Laurence J.

    2014-01-01

    Concrete is one of the most widely used construction materials and thus assessment of damage in concrete structures is of the utmost importance from both a safety point of view and a financial point of view. Of particular interest are surface opening cracks that extend through the concrete cover, as this can expose the steel reinforcement bars underneath and induce corrosion in them. This corrosion can lead to significant subsequent damage in concrete such as cracking and delamination of the cover concrete as well as rust staining on the surface of concrete. Concrete beams are designed and constructed in such a way to provide crack depths up to around 13 cm. Two different types of measurements are made in-situ to estimate depths of real surface cracks (as opposed to saw-cut notches) after unloading: one based on the impact-echo method and the other one based on the diffuse ultrasonic method. These measurements are compared to the crack depth visually observed on the sides of the beams. Discussions are given as to the advantages and disadvantages of each method

  8. The fatigue life and fatigue-crack-through-thickness behavior of a surface-cracked plate, 3

    International Nuclear Information System (INIS)

    Nam, Ki-Woo; Matsui, Kentaro; Ando, Kotoji; Ogura, Nobukazu

    1989-01-01

    The LBB (leak-before-break) design is one of the most important subjects for the evaluation and the assurance of safety in pressure vessels, piping systems, LNG carriers and various other structures. In the LBB design, it is necessary to evaluate precisely the lifetime of steel plate. Furthermore, the change in crack shape that occurs during the propagation after through thickness is of paramount importance. For this reason, in a previous report, the authors proposed a simplified evaluation model for the stress intensity factor after cracking through thickness. Using this model, the crack propagation behavior, crack-opening displacement and crack shape change of surface-cracked smooth specimens and surface-cracked specimens with a stress concentration were evaluated quantitatively. The present study was also done to investigate the fatigue crack propagation behavior of surface cracks subjected to combined tensile and bending stress. Estimation of fatigue crack growth was done using the Newman-Raju formula before through thickness, and using formula (7) and (8) after through thickness. Crack length a r at just through thickness increases with increasing a bending stress. Calculated fatigue crack shape showed very good agreement with experimental one. It was also found that particular crack growth behavior and change in crack shape after cracking through thickness can be explained quantitatively using the K value based on Eqs. (7) and (8). (author)

  9. FASTRAN II - FATIGUE CRACK GROWTH STRUCTURAL ANALYSIS (UNIX VERSION)

    Science.gov (United States)

    Newman, J. C.

    1994-01-01

    Predictions of fatigue crack growth behavior can be made with the Fatigue Crack Growth Structural Analysis (FASTRAN II) computer program. As cyclic loads are applied to a selected crack configuration with an initial crack size, FASTRAN II predicts crack growth as a function of cyclic load history until either a desired crack size is reached or failure occurs. FASTRAN II is based on plasticity-induced crack-closure behavior of cracks in metallic materials and accounts for load-interaction effects, such as retardation and acceleration, under variable-amplitude loading. The closure model is based on the Dugdale model with modifications to allow plastically deformed material to be left along the crack surfaces as the crack grows. Plane stress and plane strain conditions, as well as conditions between these two, can be simulated in FASTRAN II by using a constraint factor on tensile yielding at the crack front to approximately account for three-dimensional stress states. FASTRAN II contains seventeen predefined crack configurations (standard laboratory fatigue crack growth rate specimens and many common crack configurations found in structures); and the user can define one additional crack configuration. The baseline crack growth rate properties (effective stress-intensity factor against crack growth rate) may be given in either equation or tabular form. For three-dimensional crack configurations, such as surface cracks or corner cracks at holes or notches, the fatigue crack growth rate properties may be different in the crack depth and crack length directions. Final failure of the cracked structure can be modelled with fracture toughness properties using either linear-elastic fracture mechanics (brittle materials), a two-parameter fracture criterion (brittle to ductile materials), or plastic collapse (extremely ductile materials). The crack configurations in FASTRAN II can be subjected to either constant-amplitude, variable-amplitude or spectrum loading. The applied

  10. Computed tomographic imaging of subchondral fatigue cracks in the distal end of the third metacarpal bone in the thoroughbred racehorse can predict crack micromotion in an ex-vivo model.

    Directory of Open Access Journals (Sweden)

    Marie-Soleil Dubois

    Full Text Available Articular stress fracture arising from the distal end of the third metacarpal bone (MC3 is a common serious injury in Thoroughbred racehorses. Currently, there is no method for predicting fracture risk clinically. We describe an ex-vivo biomechanical model in which we measured subchondral crack micromotion under compressive loading that modeled high speed running. Using this model, we determined the relationship between subchondral crack dimensions measured using computed tomography (CT and crack micromotion. Thoracic limbs from 40 Thoroughbred racehorses that had sustained a catastrophic injury were studied. Limbs were radiographed and examined using CT. Parasagittal subchondral fatigue crack dimensions were measured on CT images using image analysis software. MC3 bones with fatigue cracks were tested using five cycles of compressive loading at -7,500N (38 condyles, 18 horses. Crack motion was recorded using an extensometer. Mechanical testing was validated using bones with 3 mm and 5 mm deep parasagittal subchondral slots that modeled naturally occurring fatigue cracks. After testing, subchondral crack density was determined histologically. Creation of parasagittal subchondral slots induced significant micromotion during loading (p<0.001. In our biomechanical model, we found a significant positive correlation between extensometer micromotion and parasagittal crack area derived from reconstructed CT images (SR = 0.32, p<0.05. Correlations with transverse and frontal plane crack lengths were not significant. Histologic fatigue damage was not significantly correlated with crack dimensions determined by CT or extensometer micromotion. Bones with parasagittal crack area measurements above 30 mm2 may have a high risk of crack propagation and condylar fracture in vivo because of crack micromotion. In conclusion, our results suggest that CT could be used to quantify subchondral fatigue crack dimensions in racing Thoroughbred horses in-vivo to

  11. On fatigue crack growth in ductile materials by crack-tip blunting

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2004-01-01

    One of the basic mechanisms for fatigue crack growth in ductile metals is that depending on crack-tip blunting under tensile loads and re-sharpening of the crack-tip during unloading. In a standard numerical analysis accounting for finite strains it is not possible to follow this process during...

  12. Hydrogen embrittlement and hydrogen induced stress corrosion cracking of high alloyed austenitic materials; Wasserstoffversproedung und wasserstoffinduzierte Spannungsrisskorrosion hochlegierter austenitischer Werkstoffe

    Energy Technology Data Exchange (ETDEWEB)

    Mummert, K; Uhlemann, M; Engelmann, H J [Institut fuer Festkoerper- und Werkstofforschung Dresden e.V. (Germany)

    1998-11-01

    The susceptiblity of high alloyed austenitic steels and nickel base alloys to hydrogen-induced cracking is particularly determined by 1. the distribution of hydrogen in the material, and 2. the microstructural deformation behaviour, which last process is determined by the effects of hydrogen with respect to the formation of dislocations and the stacking fault energy. The hydrogen has an influence on the process of slip localization in slip bands, which in turn affects the microstructural deformation behaviour. Slip localization increases with growing Ni contents of the alloys and clearly reduces the ductility of the Ni-base alloy. Although there is a local hydrogen source involved in stress corrosion cracking, emanating from the corrosion process at the cathode, crack growth is observed only in those cases when the hydrogen concentration in a small zone ahead of the crack tip reaches a critical value with respect to the stress conditions. Probability of onset of this process gets lower with growing Ni content of the alloy, due to increasing diffusion velocity of the hydrogen in the austenitic lattice. This is why particularly austenitic steels with low Ni contents are susceptible to transcrystalline stress corrosion cracking. In this case, the microstructural deformation process at the crack tip is also influenced by analogous processes, as could be observed in hydrogen-loaded specimens. (orig./CB) [Deutsch] Die Empfindlichkeit von hochlegierten austentischen Staehlen und Nickelbasislegierungen gegen wasserstoffinduziertes Risswachstum wird im wesentlichen bestimmt durch 1. die Verteilung von Wasserstoff im Werkstoff und 2. das mikrostrukturelle Verformungsverhalten. Das mikrostrukturelle Deformationsverhalten ist wiederum durch den Einfluss von Wasserstoff auf die Versetzungsbildung und die Stapelfehlerenergie charakterisiert. Das mikrostrukturelle Verformungsverhalten wird durch wasserstoffbeeinflusste Gleitlokalisierung in Gleitbaendern bestimmt. Diese nimmt mit

  13. Crack layer theory

    Science.gov (United States)

    Chudnovsky, A.

    1987-01-01

    A damage parameter is introduced in addition to conventional parameters of continuum mechanics and consider a crack surrounded by an array of microdefects within the continuum mechanics framework. A system consisting of the main crack and surrounding damage is called crack layer (CL). Crack layer propagation is an irreversible process. The general framework of the thermodynamics of irreversible processes are employed to identify the driving forces (causes) and to derive the constitutive equation of CL propagation, that is, the relationship between the rates of the crack growth and damage dissemination from one side and the conjugated thermodynamic forces from another. The proposed law of CL propagation is in good agreement with the experimental data on fatigue CL propagation in various materials. The theory also elaborates material toughness characterization.

  14. Curvilinear crack layer propagation

    Science.gov (United States)

    Chudnovsky, Alexander; Chaoui, Kamel; Moet, Abdelsamie

    1987-01-01

    An account is given of an experiment designed to allow observation of the effect of damage orientation on the direction of crack growth in the case of crack layer propagation, using polystyrene as the model material. The direction of crack advance under a given loading condition is noted to be determined by a competition between the tendency of the crack to maintain its current direction and the tendency to follow the orientation of the crazes at its tip. The orientation of the crazes is, on the other hand, determined by the stress field due to the interaction of the crack, the crazes, and the hole. The changes in craze rotation relative to the crack define the active zone rotation.

  15. Angular distribution of fragments from neutron-induced fission of {sup 238}U in the intermediate energy region

    Energy Technology Data Exchange (ETDEWEB)

    Carlsson, Magnus

    2004-06-01

    Areas ranging from nuclear structure models to accelerator-driven systems benefit from improved neutron-induced fission data in the intermediate energy region. In this Master's degree thesis, the fragment angular distribution from fission of {sup 238}U, induced by 21-MeV neutrons, has been analysed from an experiment performed with the Medley/DIFFICILE setup at the The Svedberg Laboratory in Uppsala. The data have been corrected for low energy neutrons in the beam. The results agree with other experiments, as well as with model calculations. The data should be a starting point for further analysis with a goal to deduce the fission cross-section of {sup 238}U.

  16. Primary water stress corrosion cracking resistance of alloy 690 heat affected zones of butt welds

    International Nuclear Information System (INIS)

    Fournier, L.; Calonne, O.; Toloczko, M.B.; Bruemmer, S.M.; Massoud, J.P.; Lemaire, E.; Gerard, R.; Somville, F.; Richnau, A.; Lagerstrom, J.

    2015-01-01

    A wide V-groove butt weld was fabricated from Alloy 690 plates using Alloy 152 filler material, maximum allowable heat input, and very stiff strong-backs. Alloy 690 heat affected zones (HAZ) was characterized in terms of microstructure and plastic strains induced by weld shrinkage. Crack initiation tests were carried out in pure hydrogenated steam at 400 C. degrees for 4000 h. Crack growth rate tests were performed in simulated PWR primary water at a temperature of 360 C. degrees. A maximum plastic strain around 5% was measured in the vicinity of the fusion line, which decreased almost linearly with the distance from the fusion line. Crack initiation tests on Alloy 690 HAZ specimens as well as on 30% cold-rolled Alloy 690 specimens were performed in pure hydrogenated steam at 400 C. degrees (partial pressure of hydrogen = 0.7 bar) for a total of 4000 h using cylindrical notched tensile specimens, reverse U-bends and flat micro-tensile specimens. No crack initiation was detected. Stress corrosion propagation rates revealed extremely low SCC (Stress Corrosion Cracking) growth rates both in the base metal and in the HAZ region whose magnitudes are of no engineering significance. Overall, the results indicated limited plastic strain induced by weld shrinkage in butt weld HAZ, and to no particular susceptibility of primary water stress corrosion cracking. (authors)

  17. An experimental investigation of the effect of shear-induced diffuse damage on transverse cracking in carbon-fiber reinforced laminates

    KAUST Repository

    Nouri, Hedi

    2013-12-01

    When subjected to in-plane loading, carbon-fiber laminates experience diffuse damage and transverse cracking, two major mechanisms of degradation. Here, we investigate the effect of pre-existing diffuse damage on the evolution of transverse cracking. We shear-loaded carbon fiber-epoxy pre-preg samples at various load levels to generate controlled configurations of diffuse damage. We then transversely loaded these samples while monitoring the multiplication of cracking by X-ray radiography. We found that diffuse damage has a great effect on the transverse cracking process. We derived a modified effective transverse cracking toughness measure, which enabled a better definition of coupled transverse cracking/diffuse damage in advanced computational models for damage prediction. © 2013 Elsevier Ltd.

  18. Techniques for intergranular crack formation and assessment in alloy 600 base and alloy 182 weld metals

    International Nuclear Information System (INIS)

    Lee, Tae Hyun; Hwang, Il Soon; Kim, Hong Deok; Kim, Ji Hyun

    2015-01-01

    A technique developed to produce artificial intergranular stress corrosion cracks in structural components was applied to thick, forged alloy 600 base and alloy 182 weld metals for use in the qualification of nondestructive examination techniques for welded components in nuclear power plants. An externally controlled procedure was demonstrated to produce intergranular stress corrosion cracks that are comparable to service-induced cracks in both the base and weld metals. During the process of crack generation, an online direct current potential drop method using array probes was used to measure and monitor the sizes and shapes of the cracks. A microstructural characterization of the produced cracks revealed realistic conformation of the crack faces unlike those in machined notches produced by an electrodischarge machine or simple fatigue loading using a universal testing machine. A comparison with a destructive metallographic examination showed that the characteristics, orientations, and sizes of the intergranular cracks produced in this study are highly reproducible.

  19. The design of an instrumented rebar for assessment of corrosion in cracked reinforced concrete

    DEFF Research Database (Denmark)

    Pease, Bradley Justin; Geiker, Mette Rica; Stang, Henrik

    2011-01-01

    rebar with 17 electronically isolated corrosion sensors. Instrumented and standard rebars were cast into concrete beams and bending cracks were induced and held open using steel frames. Epoxy impregnation was used to assess and compare cracks in the concrete around the instrumented and standard rebar...... between the steel and concrete. Cracked beams with cast-in instrumented and standard rebars were ponded with a 10\\% chloride solution and the open circuit corrosion potential (OCP) of the 17 sensors was measured for up to 62 days. Measurements from the individual sensors indicate when and where active...

  20. Reinforcement against crack propagation of PWR absorbers by development of boron-carbon-hafnium composites

    International Nuclear Information System (INIS)

    Provot, B.; Herter, P.

    2000-01-01

    In order to improve the mechanical behaviour of materials used as neutron absorbers in nuclear reactors, we have developed CERCER or CERMET composites with boron and hafnium. Thus a new composite B 4 C/HfB 2 has been especially studied. We have identified three kinds of degradation under irradiation (thermal gradient, swelling due to fission products and accidental corrosion) that induce imposed deformations cracking phenomena. Mechanical behaviour and crack propagation resistance have been studied by ball-on-three-balls and double torsion tests. A special device was developed to enable crack propagation and associated stress intensity factor measurements. Effects of structure and of a second phase are underline. First results show that these materials present crack initiation and propagation resistance much higher than pure boron carbide or hafnium diboride. We observe R-Curves effects, crack bridging or branching, crack arrests, and toughness increases that we can relate respectively to the composite structures. (author)

  1. Interaction between corrosion crack width and steel loss in RC beams corroded under load

    International Nuclear Information System (INIS)

    Malumbela, Goitseone; Alexander, Mark; Moyo, Pilate

    2010-01-01

    This paper presents results and discussions on an experimental study conducted to relate the rate of widening of corrosion cracks with the pattern of corrosion cracks as well as the level of steel corrosion for RC beams (153 x 254 x 3000 mm) that were corroded whilst subjected to varying levels of sustained loads. Steel corrosion was limited to the tensile reinforcement and to a length of 700 mm at the centre of the beams. The rate of widening of corrosion cracks as well as strains on uncracked faces of RC beams was constantly monitored during the corrosion process, along the corrosion region and along other potential cracking faces of beams using a demec gauge. The distribution of the gravimetric mass loss of steel along the corrosion region was measured at the end of the corrosion process. The results obtained showed that: the rate of widening of each corrosion crack is dependent on the overall pattern of the cracks whilst the rate of corrosion is independent of the pattern of corrosion cracks. A mass loss of steel of 1% was found to induce a corrosion crack width of about 0.04 mm.

  2. Combined effect of electric field and residual stress on propagation of indentation cracks in a PZT-5H ferroelectric ceramic

    International Nuclear Information System (INIS)

    Huang, H.Y.; Chu, W.Y.; Su, Y.J.; Qiao, L.J.; Gao, K.W.

    2005-01-01

    The combined effect of electric field and residual stress on propagation of unloaded indentation cracks in a PZT-5 ceramic has been studied. The results show that residual stress itself is too small to induce delayed propagation of the indentation cracks in silicon oil. If applied constant electric field is larger than 0.2 kV/cm, the combined effect of electric field and residual stress can cause delayed propagation of the indentation crack after passing an incubation time in silicon oil, but the crack will arrest after propagating for 10-30 μm because of decrease of the resultant stress intensity factor induced by the field and residual stress with increasing the crack length. The threshold electric field for delayed propagation of the indentation crack in silicon oil is E DP = 0.2 kV/cm. If the applied electric field is larger than 5.25 kV/cm, combined effect of the electric field and residual stress can cause instant propagation of the indentation crack, and under sustained electric field, the crack which has propagated instantly can propagate continuously, until arrest at last. The critical electric field for instant propagation of the indentation crack is E P = 5.25 kV/cm. If the applied electric field is larger than 12.6 kV/cm, the microcracks induced by the electric field initiate everywhere, grow and connect in a smooth specimen, resulting in delayed failure, even without residual stress. The threshold electric field for delayed failure of a smooth specimen in silicon oil is E DF = 12.6 kV/cm and the critical electric field for instant failure is E F = 19.1 kV/cm

  3. Thermal-mechanical properties of cracked UO2 pellets

    International Nuclear Information System (INIS)

    Williford, R.E.; Mohr, C.L.; Lanning, D.D.

    1980-11-01

    A series of experiments (IFA-431, 432, 513, and 527) sponsored by the Fuel Behavior Research Branch of the USNRC are being irradiated in the Halden Boiling Water Reactor to better define LWR fuel behavior over the normal operating range of power reactor fuel rods. One fuel behavior variable of interest is the thermally induced cracking of UO 2 fuel pellets. The effects of pellet cracking on the effective thermal conductivity and elastic moduli for the fragmented fuel were found to be primarily dependent on the free area in the r, theta plane of the fuel rod. The free area is defined as the area within the cladding inner surface that is not occupied by the fuel fragments themselves

  4. Intergranular cracking mechanism in baffle former bolt materials for PWR core internals

    Energy Technology Data Exchange (ETDEWEB)

    Yonezawa, Toshio; Arioka, Koji; Kanasaki, Hiroshi; Fujimoto, Koji [Takasago R and D Center, Mitsubishi Heavy Industries Ltd., Takasago, Hyogo (Japan); Ajiki, Kazuhide [Kobe Shipyard and Machinery, Mitsubishi Heavy Industries Ltd., Kobe, Hyogo (Japan); Matsuoka, Takanori [Nuclear Development Corp., Tokai, Ibaraki (Japan); Urata, Sigeru; Mizuta, Hitoshi [Kansai Electric Power Co., Inc., Osaka (Japan)

    2000-03-01

    In this study, the cause of intergranular cracking in baffle former bolts(BFBs) was estimated from metallurgical and chemical viewpoints based upon the experimental data and information published by EdF. At first, five kinds of possibilities were estimated as the cause of intergranular cracking in BFBs. Five possibilities estimated were (1) mechanical cracking caused by high strain in irradiation hardened austenitic stainless steels, (2) O{sub 2} SCC due to residual oxygen in the bolt stagnant region, (3) caustic SCC due to dry and wet phenomenon, (4) low pH SCC due to oxygen concentration cell, and (5) PWSCC due to radiation induced segregation. In this study each possibility was evaluated by the calculation and some out of pile tests. And also, the cause of the intergranular cracking in BFBs was estimated by the data of the post-irradiation examinations and basic out of pile tests for Type 316CW and Type 347 stainless steels in the authors' previous study. From these evaluation, the intergranular cracking in BFBs seems to be caused by the PWSCC, but not caused by mechanical cracking O{sub 2} SCC, caustic SCC or low pH SCC. (author)

  5. Fully plastic crack opening analyses of complex-cracked pipes for Ramberg-Osgood materials

    International Nuclear Information System (INIS)

    Jeong, Jae Uk; Choi, Jae Boong; Huh, Nam Su; Kim, Yun Jae

    2016-01-01

    The plastic influence functions for calculating fully plastic Crack opening displacement (COD) of complex-cracked pipes were newly proposed based on systematic 3-dimensional (3-D) elastic-plastic Finite element (FE) analyses using Ramberg-Osgood (R-O) relation, where global bending moment, axial tension and internal pressure are considered separately as a loading condition. Then, crack opening analyses were performed based on GE/EPRI concept by using the new plastic influence functions for complex-cracked pipes made of SA376 TP304 stainless steel, and the predicted CODs were compared with FE results based on deformation plasticity theory of tensile material behavior. From the comparison, the confidence of the proposed fully plastic crack opening solutions for complex-cracked pipes was gained. Therefore, the proposed engineering scheme for COD estimation using the new plastic influence functions can be utilized to estimate leak rate of a complex-cracked pipe for R-O material.

  6. Influence of Al on the fatigue crack growth behavior of Fe–22Mn–(3Al)–0.6C TWIP steels

    International Nuclear Information System (INIS)

    Ma, Penghui; Qian, Lihe; Meng, Jiangying; Liu, Shuai; Zhang, Fucheng

    2015-01-01

    The influence of Al on fatigue crack growth (FCG) behavior of the high-Mn austenitic twinning-induced plasticity (TWIP) steel was investigated by conducting FCG tests on Fe–22Mn–0Al–0.6C and Fe–22Mn–3Al–0.6C TWIP steels (hereafter, referred to as 0Al and 3Al TWIP steel, respectively). The FCG tests were performed at stress ratio of 0.1 under the control of stress intensity factor range using three-point bending specimens. Excepting that the traditional two-dimensional (2D) observation methods (optical, scanning and transmission electron microscopes) were used to observe the crack paths, fracture surfaces and microstructure features, a high-resolution synchrotron X-ray computed tomography was also applied to observe the three-dimensional (3-D) crack morphology. The results indicate that the FCG resistance of the 0Al TWIP steel is superior to that of 3Al TWIP steel in the near threshold regime. Observed from the 2D crack paths and 3D crack morphologies, it can be found that the crack surface roughness and crack deflection of the 0Al steel are greater than those of 3Al steel. It is suggested that the degree of roughness-induced crack closure decreases with the addition of Al. And the 0Al steel shows much larger plastic zone sizes ahead of the crack tip than the 3Al steel, suggesting that plasticity-induced crack closure may also play an important role in decreasing the FCG rate in the 0Al steel. By excluding the crack closure effects, the 0Al steel still exhibits a higher effective crack growth threshold value than the 3Al steel; this is considered to be due to the higher planarity of slip in the 0Al steel than in the 3Al steel, and the mechanical twins generated in the 0Al steel reduce the stress concentration at crack tip

  7. The fatigue life and fatigue crack through thickness behavior of a surface cracked plate, 2

    International Nuclear Information System (INIS)

    Nam, Ki-Woo; Fujibayashi, Shinpei; Ando, Kotoji; Ogura, Nobukazu.

    1987-01-01

    Most structures have a region where stresses concentrate, and the probability of fatigue crack initiation may be higher than in other parts. Therefore, to improve the reliability of an LBB design, it is necessary to evaluate the growth and through thickness behavior of fatigue cracks in the stress concentration part. In this paper, a fatigue crack growth test at a stress concentration region has been made on 3 % NiCrMo and HT 80 steel. Stress concentration is caused by a fillet on the plate. The main results obtained are as follows : (1) Before cracking through the plate thickness, stress concentration has a remarkable effect on the fatigue crack growth behavior and it flatens the shape of a surface crack. The crack growth behavior can be explained quantatively by using the Newman-Raju equation and the stress resolving method proposed by ASME B and P Code SecXI. (2) The da/dN-ΔK relation obtained in a stress concentration specimen shows good agreement with that obtained in a surface cracked smooth specimen. (3) It is shown that stress concentration caused by a fillet has little effect on the crack growth rate after cracking through the plate thickness. (4) By using the K value based on eq. (1), (2), particular crack growth behavior and the change in crack shape after cracking through thickness can be explained quantatively. (author)

  8. Detection of cracks on concrete surfaces by hyperspectral image processing

    Science.gov (United States)

    Santos, Bruno O.; Valença, Jonatas; Júlio, Eduardo

    2017-06-01

    All large infrastructures worldwide must have a suitable monitoring and maintenance plan, aiming to evaluate their behaviour and predict timely interventions. In the particular case of concrete infrastructures, the detection and characterization of crack patterns is a major indicator of their structural response. In this scope, methods based on image processing have been applied and presented. Usually, methods focus on image binarization followed by applications of mathematical morphology to identify cracks on concrete surface. In most cases, publications are focused on restricted areas of concrete surfaces and in a single crack. On-site, the methods and algorithms have to deal with several factors that interfere with the results, namely dirt and biological colonization. Thus, the automation of a procedure for on-site characterization of crack patterns is of great interest. This advance may result in an effective tool to support maintenance strategies and interventions planning. This paper presents a research based on the analysis and processing of hyper-spectral images for detection and classification of cracks on concrete structures. The objective of the study is to evaluate the applicability of several wavelengths of the electromagnetic spectrum for classification of cracks in concrete surfaces. An image survey considering highly discretized wavelengths between 425 nm and 950 nm was performed on concrete specimens, with bandwidths of 25 nm. The concrete specimens were produced with a crack pattern induced by applying a load with displacement control. The tests were conducted to simulate usual on-site drawbacks. In this context, the surface of the specimen was subjected to biological colonization (leaves and moss). To evaluate the results and enhance crack patterns a clustering method, namely k-means algorithm, is being applied. The research conducted allows to define the suitability of using clustering k-means algorithm combined with hyper-spectral images highly

  9. Terahertz non-destructive imaging of cracks and cracking in structures of cement-based materials

    Directory of Open Access Journals (Sweden)

    Shujie Fan

    2017-11-01

    Full Text Available Cracks and crack propagation in cement-based materials are key factors leading to failure of structures, affecting safety in construction engineering. This work investigated the application of terahertz (THz non-destructive imaging to inspections on structures of cement-based materials, so as to explore the potential of THz imaging in crack detection. Two kinds of disk specimens made of plain cement mortar and UHMWPE fiber concrete were prepared respectively. A mechanical expansion load device was deployed to generate cracks and control the whole process of cracking. Experimental tests were carried out on cracked specimens by using a commercial THz time domain spectroscopy (THz-TDS during loading. The results show that crack opening and propagation could be examined by THz clearly and the material factors influence the ability of crack resistance significantly. It was found that the THz imaging of crack initiation and propagation agrees with the practical phenomenon and supplies more information about damage of samples. It is demonstrated that the damage behavior of structures of cement-based materials can be successfully detected by THz imaging.

  10. Terahertz non-destructive imaging of cracks and cracking in structures of cement-based materials

    Science.gov (United States)

    Fan, Shujie; Li, Tongchun; Zhou, Jun; Liu, Xiaoqing; Liu, Xiaoming; Qi, Huijun; Mu, Zhiyong

    2017-11-01

    Cracks and crack propagation in cement-based materials are key factors leading to failure of structures, affecting safety in construction engineering. This work investigated the application of terahertz (THz) non-destructive imaging to inspections on structures of cement-based materials, so as to explore the potential of THz imaging in crack detection. Two kinds of disk specimens made of plain cement mortar and UHMWPE fiber concrete were prepared respectively. A mechanical expansion load device was deployed to generate cracks and control the whole process of cracking. Experimental tests were carried out on cracked specimens by using a commercial THz time domain spectroscopy (THz-TDS) during loading. The results show that crack opening and propagation could be examined by THz clearly and the material factors influence the ability of crack resistance significantly. It was found that the THz imaging of crack initiation and propagation agrees with the practical phenomenon and supplies more information about damage of samples. It is demonstrated that the damage behavior of structures of cement-based materials can be successfully detected by THz imaging.

  11. Effects of laser peening treatment on high cycle fatigue and crack propagation behaviors in austenitic stainless steel

    International Nuclear Information System (INIS)

    Masaki, Kiyotaka; Ochi, Yasuo; Matsumura, Takashi; Ikarashi, Takaaki; Sano, Yuji

    2010-01-01

    Laser peening without protective coating (LPwC) treatment is one of surface enhancement techniques using an impact wave of high pressure plasma induced by laser pulse irradiation. High compressive residual stress was induced by the LPwC treatment on the surface of low-carbon type austenitic stainless steel SUS316L. The affected depth reached about 1mm from the surface. High cycle fatigue tests with four-points rotating bending loading were carried out to confirm the effects of the LPwC treatment on fatigue strength and surface fatigue crack propagation behaviors. The fatigue strength was remarkably improved by the LPwC treatment over the whole regime of fatigue life up to 10 8 cycles. Specimens with a pre-crack from a small artificial hole due to fatigue loading were used for the quantitative study on the effect of the LPwC treatment. The fracture mechanics investigation on the pre-cracked specimens showed that the LPwC treatment restrained the further propagation of the pre-crack if the stress intensity factor range ΔK on the crack tip was less than 7.6 MPa√m. Surface cracks preferentially propagated into the depth direction as predicted through ΔK analysis on the crack by taking account of the compressive residual stresses due to the LPwC treatment. (author)

  12. VALIDATION OF CRACK INTERACTION LIMIT MODEL FOR PARALLEL EDGE CRACKS USING TWO-DIMENSIONAL FINITE ELEMENT ANALYSIS

    Directory of Open Access Journals (Sweden)

    R. Daud

    2013-06-01

    Full Text Available Shielding interaction effects of two parallel edge cracks in finite thickness plates subjected to remote tension load is analyzed using a developed finite element analysis program. In the present study, the crack interaction limit is evaluated based on the fitness of service (FFS code, and focus is given to the weak crack interaction region as the crack interval exceeds the length of cracks (b > a. Crack interaction factors are evaluated based on stress intensity factors (SIFs for Mode I SIFs using a displacement extrapolation technique. Parametric studies involved a wide range of crack-to-width (0.05 ≤ a/W ≤ 0.5 and crack interval ratios (b/a > 1. For validation, crack interaction factors are compared with single edge crack SIFs as a state of zero interaction. Within the considered range of parameters, the proposed numerical evaluation used to predict the crack interaction factor reduces the error of existing analytical solution from 1.92% to 0.97% at higher a/W. In reference to FFS codes, the small discrepancy in the prediction of the crack interaction factor validates the reliability of the numerical model to predict crack interaction limits under shielding interaction effects. In conclusion, the numerical model gave a successful prediction in estimating the crack interaction limit, which can be used as a reference for the shielding orientation of other cracks.

  13. On crack interaction effects of in-plane surface cracks using elastic and elastic-plastic finite element analyses

    International Nuclear Information System (INIS)

    Kim, Jong Min; Huh, Nam Su

    2010-01-01

    The crack-tip stress fields and fracture mechanics assessment parameters for a surface crack, such as the elastic stress intensity factor or the elastic-plastic J-integral, can be affected significantly by the adjacent cracks. Such a crack interaction effect due to multiple cracks can alter the fracture mechanics assessment parameters significantly. There are many factors to be considered, for instance the relative distance between adjacent cracks, the crack shape, and the loading condition, to quantify the crack interaction effect on the fracture mechanics assessment parameters. Thus, the current assessment codes on crack interaction effects (crack combination rules), including ASME Sec. XI, BS7910, British Energy R6 and API 579-1/ASME FFS-1, provide different rules for combining multiple surface cracks into a single surface crack. The present paper investigates crack interaction effects by evaluating the elastic stress intensity factor and the elastic-plastic J-integral of adjacent in-plane surface cracks in a plate through detailed 3-dimensional elastic and elastic-plastic finite element analyses. The effects on the fracture mechanics assessment parameters of the geometric parameters, the relative distance between two cracks, and the crack shape are investigated systematically. As for the loading condition, an axial tension is considered. Based on the finite element results, the acceptability of the crack combination rules provided in the existing guidance was investigated, and the relevant recommendations on a crack interaction for in-plane surface cracks are discussed. The present results can be used to develop more concrete guidance on crack interaction effects for crack shape characterization to evaluate the integrity of defective components

  14. The Reflective Cracking in Flexible Pavements

    Directory of Open Access Journals (Sweden)

    Pais Jorge

    2013-07-01

    Full Text Available Reflective cracking is a major concern for engineers facing the problem of road maintenance and rehabilitation. The problem appears due to the presence of cracks in the old pavement layers that propagate into the pavement overlay layer when traffic load passes over the cracks and due to the temperature variation. The stress concentration in the overlay just above the existing cracks is responsible for the appearance and crack propagation throughout the overlay. The analysis of the reflective cracking phenomenon is usually made by numerical modeling simulating the presence of cracks in the existing pavement and the stress concentration in the crack tip is assessed to predict either the cracking propagation rate or the expected fatigue life of the overlay. Numerical modeling to study reflective cracking is made by simulating one crack in the existing pavement and the loading is usually applied considering the shear mode of crack opening. Sometimes the simulation considers the mode I of crack opening, mainly when temperature effects are predominant.

  15. Singlet channel coupling in deuteron elastic scattering at intermediate energies

    International Nuclear Information System (INIS)

    Al-Khalili, J.S.; Tostevin, J.A.; Johnson, R.C.

    1990-01-01

    Intermediate energy deuteron elastic scattering is investigated in a three-body model incorporating relativistic kinematics. The effects of deuteron breakup to singlet spin intermediate states, on the elastic scattering observables for the 58 Ni(d vector, d) 58 Ni reaction at 400 and 700 MeV, are studied quantitatively. The singlet-breakup contributions to the elastic amplitude are estimated within an approximate two-step calculation. The calculation makes an adiabatic approximation in the intermediate states propagator which allows the use of closure over the np intermediate states continuum. The singlet channel coupling is found to produce large effects on the calculated reaction tensor analysing power A yy , characteristic of a dynamically induced second-rank tensor interaction. By inspection of the calculated breakup amplitudes we show this induced interaction to be of the T L tensor type. (orig.)

  16. Effect of Crack Tip Stresses on Delayed Hydride Cracking in Zr-2.5Nb Tubes

    International Nuclear Information System (INIS)

    Kim, Young Suk; Cheong, Yong Moo

    2007-01-01

    Delayed hydride cracking (DHC) tests have shown that the DHC velocity becomes faster in zirconium alloys with a higher yield stress. To account for this yield stress effect on the DHC velocity, they suggested a simple hypothesis that increased crack tip stresses due to a higher yield stress would raise the difference in hydrogen concentration between the crack tip and the bulk region and accordingly the DHC velocity. This hypothesis is also applied to account for a big leap in the DHC velocity of zirconium alloys after neutron irradiation. It should be noted that this is based on the old DHC models that the driving force for DHC is the stress gradient. Puls predicted that an increase in the yield stress of a cold worked Zr-2.5Nb tube due to neutron irradiation by about 300 MPa causes an increase of its DHC velocity by an order of magnitude or 2 to 3 times depending on the accommodation energy values. Recently, we proposed a new DHC model that a driving force for DHC is not the stress gradient but the concentration gradient arising from the stress-induced precipitation of hydrides at the crack tip. Our new DHC model and the supporting experimental results have demonstrated that the DHC velocity is governed primarily by hydrogen diffusion at below 300 .deg. C. Since hydrogen diffusion in Zr-2.5Nb tubes is dictated primarily by the distribution of the β-phase, the DHC velocity of the irradiated Zr-2.5Nb tube must be determined mainly by the distribution of the β-phase, not by the increased yield stress, which is in contrast with the hypothesis of the previous DHC models. In short, a controversy exists as to the effect on the DHC velocity of zirconium alloys of a change in the crack tip stresses by irradiation hardening or cold working or annealing. The aim of this study is to resolve this controversy and furthermore to prove the validity of our DHC model. To this end, we cited Pan et al.'s experiment where the delayed hydride cracking velocity, the tensile strengths

  17. Vibration based algorithm for crack detection in cantilever beam containing two different types of cracks

    Science.gov (United States)

    Behzad, Mehdi; Ghadami, Amin; Maghsoodi, Ameneh; Michael Hale, Jack

    2013-11-01

    In this paper, a simple method for detection of multiple edge cracks in Euler-Bernoulli beams having two different types of cracks is presented based on energy equations. Each crack is modeled as a massless rotational spring using Linear Elastic Fracture Mechanics (LEFM) theory, and a relationship among natural frequencies, crack locations and stiffness of equivalent springs is demonstrated. In the procedure, for detection of m cracks in a beam, 3m equations and natural frequencies of healthy and cracked beam in two different directions are needed as input to the algorithm. The main accomplishment of the presented algorithm is the capability to detect the location, severity and type of each crack in a multi-cracked beam. Concise and simple calculations along with accuracy are other advantages of this method. A number of numerical examples for cantilever beams including one and two cracks are presented to validate the method.

  18. Fatigue-crack propagation in gamma-based titanium aluminide alloys at large and small crack sizes

    International Nuclear Information System (INIS)

    Kruzic, J.J.; Campbell, J.P.; Ritchie, R.O.

    1999-01-01

    Most evaluations of the fracture and fatigue-crack propagation properties of γ+α 2 titanium aluminide alloys to date have been performed using standard large-crack samples, e.g., compact-tension specimens containing crack sizes which are on the order of tens of millimeters, i.e., large compared to microstructural dimensions. However, these alloys have been targeted for applications, such as blades in gas-turbine engines, where relevant crack sizes are much smaller ( 5 mm) and (c ≅ 25--300 microm) cracks in a γ-TiAl based alloy, of composition Ti-47Al-2Nb-2Cr-0.2B (at.%), specifically for duplex (average grain size approximately17 microm) and refined lamellar (average colony size ≅150 microm) microstructures. It is found that, whereas the lamellar microstructure displays far superior fracture toughness and fatigue-crack growth resistance in the presence of large cracks, in small-crack testing the duplex microstructure exhibits a better combination of properties. The reasons for such contrasting behavior are examined in terms of the intrinsic and extrinsic (i.e., crack bridging) contributions to cyclic crack advance

  19. Noncontact measurement of guided ultrasonic wave scattering for fatigue crack characterization

    Science.gov (United States)

    Fromme, P.

    2013-04-01

    Fatigue cracks can develop in aerospace structures at locations of stress concentration such as fasteners. For the safe operation of the aircraft fatigue cracks need to be detected before reaching a critical length. Guided ultrasonic waves offer an efficient method for the detection and characterization of fatigue cracks in large aerospace structures. Noncontact excitation of guided waves was achieved using electromagnetic acoustic transducers (EMAT). The transducers were developed for the specific excitation of the A0 Lamb mode. Based on the induced eddy currents in the plate a simple theoretical model was developed and reasonably good agreement with the measurements was achieved. However, the detection sensitivity for fatigue cracks depends on the location and orientation of the crack relative to the measurement locations. Crack-like defects have a directionality pattern of the scattered field depending on the angle of the incident wave relative to the defect orientation and on the ratio of the characteristic defect size to wavelength. The detailed angular dependency of the guided wave field scattered at crack-like defects in plate structures has been measured using a noncontact laser interferometer. Good agreement with 3D Finite Element simulation predictions was achieved for machined part-through and through-thickness notches. The amplitude of the scattered wave was quantified for a variation of angle of the incident wave relative to the defect orientation and the defect depth. These results provide the basis for the defect characterization in aerospace structures using guided wave sensors.

  20. Correction to the crack extension direction in numerical modelling of mixed mode crack paths

    DEFF Research Database (Denmark)

    Lucht, Tore; Aliabadi, M.H.

    2007-01-01

    In order to avoid introduction of an error when a local crack-growth criterion is used in an incremental crack growth formulation, each straight crack extension would have to be infinitesimal or have its direction corrected. In this paper a new procedure to correct the crack extension direction...

  1. Cracking behavior of thermally aged and irradiated CF-8 cast austenitic stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Y., E-mail: Yiren_Chen@anl.gov [Argonne National Laboratory, 9700 S. Cass Ave, Argonne, IL 60439 (United States); Alexandreanu, B.; Chen, W.-Y.; Natesan, K. [Argonne National Laboratory, 9700 S. Cass Ave, Argonne, IL 60439 (United States); Li, Z.; Yang, Y. [University of Florida, Gainesville, FL 32611 (United States); Rao, A.S. [US Nuclear Regulatory Commission, 11545 Rockville Pike, Rockville, MD 20852 (United States)

    2015-11-15

    To assess the combined effect of thermal aging and neutron irradiation on the cracking behavior of CF-8 cast austenitic stainless steel, crack growth rate (CGR) and fracture toughness J-R curve tests were carried out on compact-tension specimens in high-purity water with low dissolved oxygen. Both unaged and thermally aged specimens were irradiated at ∼320 °C to 0.08 dpa. Thermal aging at 400 °C for 10,000 h apparently had no effect on the corrosion fatigue and stress corrosion cracking behavior in the test environment. The cracking susceptibility of CF-8 was not elevated significantly by neutron irradiation at 0.08 dpa. Transgranular cleavage-like cracking was the main fracture mode during the CGR tests, and a brittle morphology of delta ferrite was often seen on the fracture surfaces at the end of CGR tests. The fracture toughness J-R curve tests showed that both thermal aging and neutron irradiation can induce significant embrittlement. The loss of fracture toughness due to neutron irradiation was more pronounced in the unaged than aged specimens. After neutron irradiation, the fracture toughness values of the unaged and aged specimens were reduced to a similar level. G-phase precipitates were observed in the aged and irradiated specimens with or without prior aging. The similar microstructural changes resulting from thermal aging and irradiation suggest a common microstructural mechanism of inducing embrittlement in CF-8.

  2. Quantitative image analysis of WE43-T6 cracking behavior

    International Nuclear Information System (INIS)

    Ahmad, A; Yahya, Z

    2013-01-01

    Environment-assisted cracking of WE43 cast magnesium (4.2 wt.% Yt, 2.3 wt.% Nd, 0.7% Zr, 0.8% HRE) in the T6 peak-aged condition was induced in ambient air in notched specimens. The mechanism of fracture was studied using electron backscatter diffraction, serial sectioning and in situ observations of crack propagation. The intermetallic (rare earthed-enriched divorced intermetallic retained at grain boundaries and predominantly at triple points) material was found to play a significant role in initiating cracks which leads to failure of this material. Quantitative measurements were required for this project. The populations of the intermetallic and clusters of intermetallic particles were analyzed using image analysis of metallographic images. This is part of the work to generate a theoretical model of the effect of notch geometry on the static fatigue strength of this material.

  3. On the transition of short cracks into long fatigue cracks in reactor pressure vessel steels

    Directory of Open Access Journals (Sweden)

    Singh Rajwinder

    2018-01-01

    Full Text Available Short fatigue cracks, having dimension less than 1 mm, propagate at much faster rates (da/dN even at lower stress intensity factor range (da/dN as compared to the threshold stress intensity factor range obtained from long fatigue crack growth studies. These short cracks originate at the sub-grain level and some of them ultimately transit into critical long cracks over time. Therefore, designing the components subjected to fatigue loading merely on the long crack growth data and neglecting the short crack growth behavior can overestimate the component’s life. This aspect of short fatigue cracks become even more critical for materials used for safety critical applications such as reactor pressure vessel (RPV steel in nuclear plants. In this work, the transition behaviour of short fatigue crack gowth into long fatigue crack is studied in SA508 Grade 3 Class I low alloy steel used in RPVs. In-situ characterization of initiation, propagation and transition of short fatigue cracks is performed using fatigue stage for Scanning Electron Microscope (SEM in addition to digital microscopes fitted over a servo-hydraulic fatigue machine and correlated with the microtructural information obtained using electron backscatter diffraction (EBSD. SA508 steel having an upper bainitic microstructure have several microstructural interfaces such as phase and grain boundaries that play a significant role in controlling the short fatigue crack propagation. Specially designed and prepared short fatigue specimens (eletro-polished with varying initial crack lengths of the order of tens of microns are used in this study. The transition of such short initial cracks into long cracks is then tracked to give detailed insight into the role of each phase and phase/grain boundary with an objective of establishing Kitagawa-Takahashi diagram for the given RPV steel. The behavior of the transited long cracks is then compared with the crack propagation behavior obtained using

  4. 3D dynamic simulation of crack propagation in extracorporeal shock wave lithotripsy

    Science.gov (United States)

    Wijerathne, M. L. L.; Hori, Muneo; Sakaguchi, Hide; Oguni, Kenji

    2010-06-01

    Some experimental observations of Shock Wave Lithotripsy(SWL), which include 3D dynamic crack propagation, are simulated with the aim of reproducing fragmentation of kidney stones with SWL. Extracorporeal shock wave lithotripsy (ESWL) is the fragmentation of kidney stones by focusing an ultrasonic pressure pulse onto the stones. 3D models with fine discretization are used to accurately capture the high amplitude shear shock waves. For solving the resulting large scale dynamic crack propagation problem, PDS-FEM is used; it provides numerically efficient failure treatments. With a distributed memory parallel code of PDS-FEM, experimentally observed 3D photoelastic images of transient stress waves and crack patterns in cylindrical samples are successfully reproduced. The numerical crack patterns are in good agreement with the experimental ones, quantitatively. The results shows that the high amplitude shear waves induced in solid, by the lithotriptor generated shock wave, play a dominant role in stone fragmentation.

  5. Environmentally-Assisted Cracking of Low-Alloy Reactor Pressure Vessel Steels under Boiling Water Reactor Conditions

    Energy Technology Data Exchange (ETDEWEB)

    Seifert, H.P.; Ritter, S

    2002-02-01

    The present report summarizes the experimental work performed by PSI on the environmentally-assisted cracking (EAC) of low-alloy steels (LAS) in the frame of the RIKORR-project during the period from January 2000 to August 2001. Within this project, the EAC crack growth behaviour of different low-alloy reactor pressure vessel (RPV) steels, weld filler and weld heat-affected zone materials is investigated under simulated transient and steady-state BWR/NWC power operation conditions. The EAC crack growth behaviour of different low-alloy RPV steels was characterized by slow rising load (SRL) / low-frequency corrosion fatigue (LFCF) and constant load tests with pre-cracked fracture mechanics specimens in oxygenated high-temperature water at temperatures of either 288, 250, 200 or 150 C. These tests revealed the following important interim results: Under low-flow and highly oxidizing (ECP >= 100 mV SHE) conditions, the ASME XI 'wet' reference fatigue crack growth curve could be significantly exceeded by cyclic fatigue loading at low frequencies (<0.001 Hz), at high and low load-ratios R, and by ripple loading near to DKth fatigue thresholds. The BWR VIP 60 SCC disposition lines may be significantly or slightly exceeded (even in steels with a low sulphur content) in the case of small load fluctuations at high load ratios (ripple loading) or at intermediate temperatures (200 -250 C) in RPV materials, which show a distinct susceptibility to dynamic strain ageing (DSA). (author)

  6. Towards crack-free ablation cutting of thin glass sheets with picosecond pulsed lasers

    Science.gov (United States)

    Sun, Mingying; Eppelt, Urs; Hartmann, Claudia; Schulz, Wolfgang; Zhu, Jianqiang; Lin, Zunqi

    2017-08-01

    We investigated the morphology and mechanism of laser-induced damage in the ablation cutting of thin glass sheets with picosecond laser. Two kinds of damage morphologies observed on the cross-section of the cut channel, are caused by high-density free-electrons and the temperature accumulation, respectively. Notches and micro-cracks can be observed on the top surface of the sample near the cut edge. The surface micro-cracks were related to high energy free-electrons and also the heat-affected zone. Heat-affected-zone and visible-cracks free conditions of glass cutting were achieved by controlling the repetition rate and spatial overlap of laser pulses.

  7. Inspecting cracks in foam insulation

    Science.gov (United States)

    Cambell, L. W.; Jung, G. K.

    1979-01-01

    Dye solution indicates extent of cracking by penetrating crack and showing original crack depth clearly. Solution comprised of methylene blue in denatured ethyl alcohol penetrates cracks completely and evaporates quickly and is suitable technique for usage in environmental or structural tests.

  8. FASTRAN II - FATIGUE CRACK GROWTH STRUCTURAL ANALYSIS (IBM PC VERSION)

    Science.gov (United States)

    Newman, J. C.

    1994-01-01

    Predictions of fatigue crack growth behavior can be made with the Fatigue Crack Growth Structural Analysis (FASTRAN II) computer program. As cyclic loads are applied to a selected crack configuration with an initial crack size, FASTRAN II predicts crack growth as a function of cyclic load history until either a desired crack size is reached or failure occurs. FASTRAN II is based on plasticity-induced crack-closure behavior of cracks in metallic materials and accounts for load-interaction effects, such as retardation and acceleration, under variable-amplitude loading. The closure model is based on the Dugdale model with modifications to allow plastically deformed material to be left along the crack surfaces as the crack grows. Plane stress and plane strain conditions, as well as conditions between these two, can be simulated in FASTRAN II by using a constraint factor on tensile yielding at the crack front to approximately account for three-dimensional stress states. FASTRAN II contains seventeen predefined crack configurations (standard laboratory fatigue crack growth rate specimens and many common crack configurations found in structures); and the user can define one additional crack configuration. The baseline crack growth rate properties (effective stress-intensity factor against crack growth rate) may be given in either equation or tabular form. For three-dimensional crack configurations, such as surface cracks or corner cracks at holes or notches, the fatigue crack growth rate properties may be different in the crack depth and crack length directions. Final failure of the cracked structure can be modelled with fracture toughness properties using either linear-elastic fracture mechanics (brittle materials), a two-parameter fracture criterion (brittle to ductile materials), or plastic collapse (extremely ductile materials). The crack configurations in FASTRAN II can be subjected to either constant-amplitude, variable-amplitude or spectrum loading. The applied

  9. Fatigue crack threshold relevant to stress ratio, crack wake and loading histories

    International Nuclear Information System (INIS)

    Okazaki, Masakazu; Iwasaki, Akira; Kasahara, Naoto

    2013-01-01

    Fatigue crack propagation behavior was investigated in a low alloy steel which experienced several kind of loading histories. Both the effects of stress ratio, test temperature on the fatigue crack threshold, and the change in the threshold depending on the thermo-mechanical loading histories, were experimentally investigated. It was shown that the thermo-mechanical loading history left its effect along the prior fatigue crack wake resulting in the change of fatigue crack threshold. Some discussions are made on how this type of loading history effect should be treated from engineering point of view. (author)

  10. Crack wave propagation along fracture with an induced low-velocity layer; Teisokudo no chika kiretsu zone wo denpasuru kiretsuha no bunsan tokusei

    Energy Technology Data Exchange (ETDEWEB)

    Nagano, K [Muroran Institute of Technology, Hokkaido (Japan)

    1997-10-22

    A study has been performed on underground cracks working as a geothermy reservoir layer, with respect to characteristics of elastic waves propagating with their energy concentrated on a boundary between rocks around the cracks and fluid in the underground cracks, or `crack waves`. The study has modeled a multi-crack reservoir layer according to the three-layer structure of the fluid layer and low-velocity solid layers around the former layer, whereas crack waves propagating therein were discussed for their dispersion characteristics. As a result of discussions, a guideline to the crack wave measurement at actual fields was put together as follows: because the low-velocity layer affects the dispersion characteristics of the crack waves, the structure and characteristics of the multi-crack reservoir layer may possibly be evaluated by measuring the velocity of the crack waves; evaluating the low-velocity layers requires proper selection of frequency of the crack wave to be measured; for example, at the Higashi Hachimantai field, a crack wave of several hundred hertz must be analyzed; and thickness of the low-velocity layers around main cracks, which can be estimated from the velocity of the crack wave is two meters at the greatest. 6 refs., 3 figs., 2 tabs.

  11. Hydrogen embrittlement and stress corrosion cracking in metals

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Young Suk; Cheong, Yong Mu; Im, Kyung Soo

    2004-10-15

    The objective of this report is to elucidate the mechanism for hydrogen embrittlement (HE) and stress corrosion cracking (SCC) in metals. To this end, we investigate the common features between delayed hydride cracking (DHC) in zirconium alloys and HE in metals with no precipitation of hydrides including Fe base alloys, Nickel base alloys, Cu alloys and Al alloys. Surprisingly, as with the crack growth pattern for the DHC in zirconium alloy, the metals mentioned above show a discontinuous crack growth, striation lines and a strong dependence of yield strength when exposed to hydrogen internally and externally. This study, for the first time, analyzes the driving force for the HE in metals in viewpoints of Kim's DHC model that a driving force for the DHC in zirconium alloys is a supersaturated hydrogen concentration coming from a hysteresis of the terminal solid solubility of hydrogen, not by the stress gradient, As with the crack growing only along the hydride habit plane during the DHC in zirconium alloys, the metals exposed to hydrogen seem to have the crack growing by invoking the dislocation slip along the preferential planes as a result of some interactions of the dislocations with hydrogen. Therefore, it seems that the hydrogen plays a role in inducing the slip only on the preferential planes so as to cause a strain localization at the crack tip. Sulfur in metals is detrimental in causing a intergranular cracking due to a segregation of the hydrogens at the grain boundaries. In contrast, boron in excess of 500 ppm added to the Ni3Al intermetallic compound is found to be beneficial in suppressing the HE even though further details of the mechanism for the roles of boron and sulfur are required. Carbon, carbides precipitating semi-continuously along the grain boundaries and the CSL (coherent site lattice) boundaries is found to suppress the intergranular stress corrosion cracking (IGSCC) in Alloy 600. The higher the volume fraction of twin boundaries, the

  12. Hydrogen embrittlement and stress corrosion cracking in metals

    International Nuclear Information System (INIS)

    Kim, Young Suk; Cheong, Yong Mu; Im, Kyung Soo

    2004-10-01

    The objective of this report is to elucidate the mechanism for hydrogen embrittlement (HE) and stress corrosion cracking (SCC) in metals. To this end, we investigate the common features between delayed hydride cracking (DHC) in zirconium alloys and HE in metals with no precipitation of hydrides including Fe base alloys, Nickel base alloys, Cu alloys and Al alloys. Surprisingly, as with the crack growth pattern for the DHC in zirconium alloy, the metals mentioned above show a discontinuous crack growth, striation lines and a strong dependence of yield strength when exposed to hydrogen internally and externally. This study, for the first time, analyzes the driving force for the HE in metals in viewpoints of Kim's DHC model that a driving force for the DHC in zirconium alloys is a supersaturated hydrogen concentration coming from a hysteresis of the terminal solid solubility of hydrogen, not by the stress gradient, As with the crack growing only along the hydride habit plane during the DHC in zirconium alloys, the metals exposed to hydrogen seem to have the crack growing by invoking the dislocation slip along the preferential planes as a result of some interactions of the dislocations with hydrogen. Therefore, it seems that the hydrogen plays a role in inducing the slip only on the preferential planes so as to cause a strain localization at the crack tip. Sulfur in metals is detrimental in causing a intergranular cracking due to a segregation of the hydrogens at the grain boundaries. In contrast, boron in excess of 500 ppm added to the Ni3Al intermetallic compound is found to be beneficial in suppressing the HE even though further details of the mechanism for the roles of boron and sulfur are required. Carbon, carbides precipitating semi-continuously along the grain boundaries and the CSL (coherent site lattice) boundaries is found to suppress the intergranular stress corrosion cracking (IGSCC) in Alloy 600. The higher the volume fraction of twin boundaries, the more

  13. Relation between exercise-induced ventricular arrhythmias and myocardial perfusion abnormalities in patients with intermediate pretest probability of coronary artery disease

    International Nuclear Information System (INIS)

    Elhendy, A.; Sozzi, F.B.; Van Domburg, R.T.; Bax, J.J.; Roelandt, J.R.T.C.

    2000-01-01

    We studied 302 patients (mean age 54±9 years, 152 men and 150 women) with intermediate pretest probability of CAD (range=0.25- 0.80, mean=0.43±0.20) by upright bicycle exercise stress test in conjunction with technetium-99m single-photon emission tomography (SPET) imaging. Exercise-induced VAs (frequent or complex premature ventricular contractions or ventricular tachycardia) occurred in 65 patients (22%). No significant difference was found between patients with and patient without VAs regarding the pretest probability of CAD (0.45±0.21 vs 0.43±0.20). Patients with exercise-induced VAs had a higher prevalence of perfusion abnormalities (52% vs 26%, P=0.002) and ischaemic electrocardiographic changes (31% vs 16%, P<0.05) compared to patients without VAs. A higher prevalence of perfusion abnormalities in patients with VAs was observed in both men (67% vs 35%, P<0.01) and women (38% vs 16%, P<0.05). However, the positive predictive value of exercise-induced VAs for the presence of myocardial perfusion abnormalities was higher in men than in women (67% vs 38%, P<0.05). The presence of abnormal myocardial perfusion was the only independent predictor of exercise-induced VAs (OR 2.2; 95% CI, 1.2-4.2) by multivariate analysis of clinical and stress test variables. It is concluded that in patients with intermediate pretest probability of CAD, exercise-induced VAs are predictive of a higher prevalence of myocardial perfusion abnormalities in both men and women. However, the positive predictive value of exercise-induced VAs for perfusion abnormalities is higher in men. Because of the underestimation of ischaemia by electrocardiographic changes, exercise-induced VAs should be interpreted as a marker of a higher probability of CAD. (orig./MG) (orig.)

  14. Comparing crack damage evolution in rocks deformed under conventional and true triaxial loading

    Science.gov (United States)

    Browning, J.; Meredith, P. G.; Stuart, C.; Healy, D.; Harland, S. R.; Mitchell, T. M.

    2017-12-01

    The vast majority of experimental studies investigate damage evolution using conventional triaxial stress states (σ1 > σ2 = σ3, CTA), whereas in nature the stress state is generally truly triaxial (σ1 > σ2 > σ3, TTA). We present a comparative study of crack damage evolution during CTA vs. TTA stress conditions using results from measurements made on cubic samples of sandstone deformed in three orthogonal directions with independently controlled stress paths. We have measured, simultaneously with stress and strain, changes in wave velocities in the three principal directions, together with acoustic emission (AE) output. Changes in wave velocities are associated with both elastic closure and opening of pre-existing cracks, and the inelastic formation of new cracks. By contrast, AE is associated only with the inelastic growth of new crack damage. The onset of new damage is shown to be a function of differential stress regardless of the magnitude of mean stress. Hence, we show that damage can form due to a decrease in the minimum principal stress, which reduces mean stress but increases the differential stress. We find an approximately fivefold decrease in the number of AE events in the TTA case in comparison to the CTA case. In essence, we create two end-member crack distributions; one displaying cylindrical transverse isotropy and the other planar transverse isotropy. Taken together, the AE data, the velocities and the crack densities indicate that the intermediate principal stress plays a key role in suppressing the total amount of crack growth and concentrating it in planes sub-parallel to the minimum stress. However, the size of individual cracks remains constant. Hence, the differential stress at which rocks fail (i.e. strength) will be significantly higher under TTA stress (where σ2 > σ3) than under CTA stress (where σ2 = σ3). Cyclic loading tests show that while individual stress states are important, the stress path by which these stress states are

  15. Crack propagation and the material removal mechanism of glass-ceramics by the scratch test.

    Science.gov (United States)

    Qiu, Zhongjun; Liu, Congcong; Wang, Haorong; Yang, Xue; Fang, Fengzhou; Tang, Junjie

    2016-12-01

    To eliminate the negative effects of surface flaws and subsurface damage of glass-ceramics on clinical effectiveness, crack propagation and the material removal mechanism of glass-ceramics were studied by single and double scratch experiments conducted using an ultra-precision machine. A self-manufactured pyramid shaped single-grit tool with a small tip radius was used as the scratch tool. The surface and subsurface crack propagations and interactions, surface morphology and material removal mechanism were investigated. The experimental results showed that the propagation of lateral cracks to the surface and the interaction between the lateral cracks and radial cracks are the two main types of material peeling, and the increase of the scratch depth increases the propagation angle of the radial cracks and the interaction between the cracks. In the case of a double scratch, the propagation of lateral cracks and radial cracks between paired scratches results in material peeling. The interaction between adjacent scratches depends on the scratch depth and separation distance. There is a critical separation distance where the normalized material removal volume reaches its peak. These findings can help reduce surface flaws and subsurface damage induced by the grinding process and improve the clinical effectiveness of glass-ceramics used as biological substitute and repair materials. Copyright © 2016 Elsevier Ltd. All rights reserved.

  16. Cracking in Flexural Reinforced Concrete Members

    DEFF Research Database (Denmark)

    Rasmussen, Annette Beedholm; Fisker, Jakob; Hagsten, Lars German

    2017-01-01

    The system of cracks developing in reinforced concrete is in many aspects essential when modelling structures in both serviceability- and ultimate limit state. This paper discusses the behavior concerning crack development in flexural members observed from tests and associates it with two different...... existing models. From the investigations an approach is proposed on how to predict the crack pattern in flexural members involving two different crack systems; primary flexural cracks and local secondary cracks. The results of the approach is in overall good agreement with the observed tests and captures...... the pronounced size effect associated with flexural cracking in which the crack spacing and crack widths are approximately proportional to the depth of the member....

  17. Altered dopamine levels induced by the parasite Profilicollis antarcticus on its intermediate host, the crab Hemigrapsus crenulatus

    Directory of Open Access Journals (Sweden)

    JOSÉ MIGUEL ROJAS

    2005-01-01

    Full Text Available A serotonergic pathway is apparently involved in parasite-host interactions. Previous studies conducted in our laboratory showed increased rates in oxygen consumption and alterations in body posture in the crab Hemigrapsus crenulatus parasitized by the acanthocephalan, Profilicollis antarcticus. Such changes may be related to the functions described for biogenic amines in crustaceans. During the infective stage the acanthocephalans live freely in the hemocelomic cavity, suggesting that the possible alteration induced by biogenic amines may be related to their neurohormonal function in crustaceans. To test whether the presence of P. antarcticus produced neurohormonal changes in its intermediate host, H. crenulatus, we analyzed serotonin and dopamine levels in the host using HPLC with electrochemical detection. Two groups of 11 female crabs were studied; one group was artificially inoculated with two cystacanths while the other was used as the control. Our results show a dramatic increase in hemolymph dopamine, but not serotonin in H. crenulatus parasitized by the acanthocephalan P. antarcticus. Our results, along with those reported by Maynard (1996, suggest a parasite-specific strategy involved in the behavior alteration caused by the acanthocephalans on their intermediate host. The use of a biogenic amine as a mechanism of interaction by the parasites gives them an endless number of alternative potential actions on their intermediate hosts

  18. Altered dopamine levels induced by the parasite Profilicollis antarcticus on its intermediate host, the crab Hemigrapsus crenulatus.

    Science.gov (United States)

    Rojas, José Miguel; Ojeda, F Patricio

    2005-01-01

    A serotonergic pathway is apparently involved in parasite-host interactions. Previous studies conducted in our laboratory showed increased rates in oxygen consumption and alterations in body posture in the crab Hemigrapsus crenulatus parasitized by the acanthocephalan, Profilicollis antarcticus. Such changes may be related to the functions described for biogenic amines in crustaceans. During the infective stage the acanthocephalans live freely in the hemocelomic cavity, suggesting that the possible alteration induced by biogenic amines may be related to their neurohormonal function in crustaceans. To test whether the presence of P. antarcticus produced neurohormonal changes in its intermediate host, H. crenulatus, we analyzed serotonin and dopamine levels in the host using HPLC with electrochemical detection. Two groups of 11 female crabs were studied; one group was artificially inoculated with two cystacanths while the other was used as the control. Our results show a dramatic increase in hemolymph dopamine, but not serotonin in H. crenulatus parasitized by the acanthocephalan P. antarcticus. Our results, along with those reported by Maynard (1996), suggest a parasite-specific strategy involved in the behavior alteration caused by the acanthocephalans on their intermediate host. The use of a biogenic amine as a mechanism of interaction by the parasites gives them an endless number of alternative potential actions on their intermediate hosts.

  19. Irradiation-assisted stress corrosion cracking considerations at temperatures below 288 degree C

    International Nuclear Information System (INIS)

    Simonen, E.P.; Jones, R.H.; Bruemmer, S.M.

    1995-03-01

    Irradiation-assisted stress corrosion cracking (IASCC) occurs above a critical neutron fluence in light-water reactor (LWR) water environments at 288 C, but very little information exists to indicate susceptibility as temperatures are reduced. Potential low-temperature behavior is assessed based on the temperature dependencies of intergranular (IG) SCC in the absence of irradiation, radiation-induced segregation (RIS) at grain boundaries and micromechanical deformation mechanisms. IGSCC of sensitized SS in the absence of irradiation exhibits high growth rates at temperatures down to 200 C under conditions of anodic dissolution control, while analysis of hydrogen-induced cracking suggests a peak crack growth rate near 100 C. Hence from environmental considerations, IASCC susceptibility appears to remain likely as water temperatures are decreased. Irradiation experiments and model predictions indicate that RIS also persists to low temperatures. Chromium depletion may be significant at temperatures below 100C for irradiation doses greater than 10 displacements per atom (dpa). Macromechanical effects of irradiation on strength and ductility are not strongly dependent on temperature below 288 C. However, temperature does significantly affect radiation effects on SS microstructure and micromechanical deformation mechanisms. The critical conditions for material susceptibility to IASCC at low temperatures may be controlled by radiation-induced grain boundary microchemistry, strain localization due to irradiation microstructure and irradiation creep processes. 39 refs

  20. Fuel micro-mechanics: homogenization, cracking, granular media

    International Nuclear Information System (INIS)

    Monerie, Yann

    2010-01-01

    cracked media. Cracking: The main aim of this topic is the numerical simulation of multiple cracking of strongly heterogeneous media from their sound state to their fractured state. A method called 'Non Smooth Fracture Dynamics' is proposed. It is based on a cohesive-volume finite element model and on a non-regular dynamic multi-body management (implicit scheme). The main theoretical and practical difficulties of the cohesive-volume method are discussed in detail: non-uniqueness of solutions, instabilities, dependence on the mesh system, local diversity, and experimental identification of the cohesive properties. By combining this method with analytical and numerical homogenization techniques, a two-scale volume and surface approach is developed for the cracking of media with a property gradient: the effect of the spatial distribution of weakening inclusions on the macroscopic fracture criteria and on the tortuosity of crack paths is revealed. An intermediate result of this work is the statistical characterization of the representative elementary volumes in cracking and fracture. Granular media: This more recent topic includes the numerical and stochastic analysis of discrete media in the presence or absence of a fluid phase. For the numerical analysis, the non-regular dynamic multi-body method is used. In the case of an interstitial or surrounding fluid, this method is coupled with two other classes of method according to the inertial regime and the size of the system considered: porous medium methods (homogeneous fluid equivalent) or fictitious domain type (direct numerical simulation). These methods are confirmed on fluidization and sedimentation tests. For the analysis, some results are obtained for gravity flows: blocking statistic in silo configuration, compaction effects during undersea avalanches. (author)

  1. Fatigue and environmentally assisted cracking in light water reactors

    International Nuclear Information System (INIS)

    Kassner, T.F.; Ruther, W.E.; Chung, H.M.; Hicks, P.D.; Hins, A.G.; Park, J.Y.; Shack, W.J.

    1991-12-01

    Fatigue and environmentally assisted cracking of piping, pressure vessels, and core components in light water reactors (LWRs) are important concerns as extended reactor lifetimes are envisaged. The degradation processes include intergranular stress corrosion cracking (IGSCC) of austenitic stainless steel (SS) piping in boiling water reactors (BWRs), and propagation of fatigue or SCC cracks (which initiate in sensitized SS cladding) into low-alloy ferritic steels in BWR pressure vessels. Similar cracking has also occurred in upper shell-to-transition cone girth welds in pressurized water reactor (PWR) steam generator vessels. Another concern is failure of reactor-core internal components after accumulation of relatively high fluence, which has occurred in both BWRs and PWRs. Research during the past year focused on (1) fatigue and SCC of ferritic steels used in piping and in steam generator and reactor pressure vessels, (2) role of chromate and sulfate in simulated BWR water in SCC of sensitized Type 304 SS, and (3) irradiation-assisted SCC in high- and commercial-purity Type 304 SS specimens from control-blade absorber tubes used in two operating BWRs. Failure after accumulation of relatively high fluence has been attributed to radiation-induced segregation (RIS) of elements such as Si, P, Ni, and Cr. This document provides a summary of research progress in these areas

  2. Investigation of Cracks Found in Helicopter Longerons

    Science.gov (United States)

    Newman, John A.; Baughman, James M.; Wallace, Terryl A.

    2009-01-01

    Four cracked longerons, containing a total of eight cracks, were provided for study. Cracked regions were cut from the longerons. Load was applied to open the cracks, enabling crack surface examination. Examination revealed that crack propagation was driven by fatigue loading in all eight cases. Fatigue crack initiation appears to have occurred on the top edge of the longerons near geometric changes that affect component bending stiffness. Additionally, metallurigical analysis has revealed a local depletion in alloying elements in the crack initiation regions that may be a contributing factor. Fatigue crack propagation appeared to be initially driven by opening-mode loading, but at a crack length of approximately 0.5 inches (12.7 mm), there is evidence of mixed-mode crack loading. For the longest cracks studied, shear-mode displacements destroyed crack-surface features of interest over significant portions of the crack surfaces.

  3. Crack growth retardation due to micro-roughness: a mechanism for overload effects in fatigue

    International Nuclear Information System (INIS)

    Suresh, S.

    1982-01-01

    A new mechanism for fatigue crack growth retardation following an overload is presented in this paper, based on a micro-roughness model. It is reasoned, with the aid of extensive experimental evidence available in the literature, that retardation following an overload is governed by the micromechanisms of near-threshold crack growth. This model is found to rationalize a number of hitherto unexplained experimental observations. Moreover, the present arguments, which suggest that plasticity-induced crack closure is not likely to be the primary mechanism for retardation following single overloads, do not exclude the role of residual stresses or blunting, but provide further mechanistic basis to account for the inconsistencies in the previous models. Additional sources of prolonged retardation, in terms of crack closure due to corrosion debris formed in moist environments, are suggested. It is pointed out that such environmental effects could play an important role in post-overload crack growth in certain alloy systems

  4. Statistical distribution of time to crack initiation and initial crack size using service data

    Science.gov (United States)

    Heller, R. A.; Yang, J. N.

    1977-01-01

    Crack growth inspection data gathered during the service life of the C-130 Hercules airplane were used in conjunction with a crack propagation rule to estimate the distribution of crack initiation times and of initial crack sizes. A Bayesian statistical approach was used to calculate the fraction of undetected initiation times as a function of the inspection time and the reliability of the inspection procedure used.

  5. Ultrasonic sizing of fatigue cracks

    International Nuclear Information System (INIS)

    Burns, D.J.

    1983-12-01

    Surface and buried fatigue cracks in steel plates have been sized using immersion probes as transmitters-receivers, angled to produce shear waves in the steel. Sizes have been estimated by identifying the ultrasonic waves diffracted from the crack tip and by measuring the time taken for a signal to travel to and from the crack tip. The effects of compression normal to a fatigue crack and of crack front curvature are discussed. Another diffraction technique, developed by UKAEA, Harwell, is reviewed

  6. Eddy current crack detection capability assessment approach using crack specimens with differing electrical conductivity

    Science.gov (United States)

    Koshti, Ajay M.

    2018-03-01

    Like other NDE methods, eddy current surface crack detectability is determined using probability of detection (POD) demonstration. The POD demonstration involves eddy current testing of surface crack specimens with known crack sizes. Reliably detectable flaw size, denoted by, a90/95 is determined by statistical analysis of POD test data. The surface crack specimens shall be made from a similar material with electrical conductivity close to the part conductivity. A calibration standard with electro-discharged machined (EDM) notches is typically used in eddy current testing for surface crack detection. The calibration standard conductivity shall be within +/- 15% of the part conductivity. This condition is also applicable to the POD demonstration crack set. Here, a case is considered, where conductivity of the crack specimens available for POD testing differs by more than 15% from that of the part to be inspected. Therefore, a direct POD demonstration of reliably detectable flaw size is not applicable. Additional testing is necessary to use the demonstrated POD test data. An approach to estimate the reliably detectable flaw size in eddy current testing for part made from material A using POD crack specimens made from material B with different conductivity is provided. The approach uses additional test data obtained on EDM notch specimens made from materials A and B. EDM notch test data from the two materials is used to create a transfer function between the demonstrated a90/95 size on crack specimens made of material B and the estimated a90/95 size for part made of material A. Two methods are given. For method A, a90/95 crack size for material B is given and POD data is available. Objective of method A is to determine a90/95 crack size for material A using the same relative decision threshold that was used for material B. For method B, target crack size a90/95 for material A is known. Objective is to determine decision threshold for inspecting material A.

  7. An elastic-plastic fracture mechanics based methodology to characterize cracking behavior and its application to environmental assisted processes

    International Nuclear Information System (INIS)

    Alvarez, J.A.; Gutierrez-Solana, F.

    1999-01-01

    Cracking processes suffered by new structural and piping steels when used in petroleum or other energy installations have demonstrated the need for a cracking resistance characterization methodology. This methodology, valid for both elastic and elastoplastic regimes, should be able to define crack propagation kinetics as a function of their controlling local parameters. This work summarizes an experimental and analytical methodology that has been shown to be suitable for characterizing cracking processes using compact tensile specimens, especially subcritical environmentally assisted ones, such as those induced by hydrogen in microalloyed steels. The applied and validated methodology has been shown to offer quantitative results of cracking behavior and to correlate these with the existing fracture micromechanisms. (orig.)

  8. Modelling of stress corrosion cracking in zirconium alloys

    International Nuclear Information System (INIS)

    Fandeur, O.; Rouillon, L.; Pilvin, P.; Jacques, P.; Rebeyrolle, V.

    2001-01-01

    During normal and incidental operating conditions, PWR power plants must comply with the first safety requirement, which is to ensure that the cladding wall is sound. Indeed some severe power transients potentially induce Stress Corrosion Cracking (SCC) of the zirconium alloy clad, due to strong Pellet Cladding Interaction (PCI). Since, at present, the prevention of this risk has some consequences on the French reactors manoeuvrability, a better understanding and forecast of the clad damage related to SCC/PCI is needed. With this aim, power ramp tests are performed in experimental reactors to assess the fuel rod behaviour and evaluate PCI failure risks. To study in detail SCC mechanisms, additional laboratory experiments are carried out on non-irradiated and irradiated cladding tubes. Numerical simulations of these tests have been developed aiming, on the one hand, to evaluate mechanical state variables and, on the other hand, to study consistent mechanical parameters for describing stress corrosion clad failure. The main result of this simulation is the determination of the validity ranges of the stress intensity factor, which is frequently used to model SCC. This parameter appears to be valid only at the onset of crack growth, when crack length remains short. In addition, the role of plastic strain rate and plastic strain as controlling parameters of the SCC process has been analysed in detail using the above mechanical description of the crack tip mechanical fields. Finally, the numerical determination of the first-order parameter(s) in the crack propagation rate law is completed by the development of laboratory tests focused on these parameters. These tests aim to support experimentally the results of the FE simulation. (author)

  9. Atomistics of crack propagation

    International Nuclear Information System (INIS)

    Sieradzki, K.; Dienes, G.J.; Paskin, A.; Massoumzadeh, B.

    1988-01-01

    The molecular dynamic technique is used to investigate static and dynamic aspects of crack extension. The material chosen for this study was the 2D triangular solid with atoms interacting via the Johnson potential. The 2D Johnson solid was chosen for this study since a sharp crack in this material remains stable against dislocation emission up to the critical Griffith load. This behavior allows for a meaningful comparison between the simulation results and continuum energy theorems for crack extension by appropriately defining an effective modulus which accounts for sample size effects and the non-linear elastic behavior of the Johnson solid. Simulation results are presented for the stress fields of moving cracks and these dynamic results are discussed in terms of the dynamic crack propagation theories, of Mott, Eshelby, and Freund

  10. Crack-tip constraint analyses and constraint-dependent LBB curves for circumferential through-wall cracked pipes

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Y.L.; Wang, G.Z., E-mail: gzwang@ecust.edu.cn; Xuan, F.Z.; Tu, S.T.

    2015-04-15

    Highlights: • Solution of constraint parameter τ* for through-wall cracked pipes has been obtained. • Constraint increases with increasing crack length and radius–thickness ratio of pipes. • Constraint-dependent LBB curve for through-wall cracked pipes has been constructed. • For increasing accuracy of LBB assessments, constraint effect should be considered. - Abstract: The leak-before-break (LBB) concept has been widely applied in the structural integrity assessments of pressured pipes in nuclear power plants. However, the crack-tip constraint effects in LBB analyses and designs cannot be incorporated. In this paper, by using three-dimensional finite element calculations, the modified load-independent T-stress constraint parameter τ* for circumferential through-wall cracked pipes with different geometries and crack sizes has been analyzed under different loading conditions, and the solutions of the crack-tip constraint parameter τ* have been obtained. Based on the τ* solutions and constraint-dependent J–R curves of a steel, the constraint-dependent LBB (leak-before-break) curves have been constructed. The results show that the constraint τ* increases with increasing crack length θ, mean radius R{sub m} and radius–thickness ratio R{sub m}/t of the pipes. In LBB analyses, the critical crack length calculated by the J–R curve of the standard high constraint specimen for pipes with shorter cracks is over-conservative, and the degree of conservatism increases with decreasing crack length θ, R{sub m} and R{sub m}/t. Therefore, the constraint-dependent LBB curves should be constructed to modify the over-conservatism and increase accuracy of LBB assessments.

  11. Universal Shapes formed by Interacting Cracks

    Science.gov (United States)

    Fender, Melissa; Lechenault, Frederic; Daniels, Karen

    2011-03-01

    Brittle failure through multiple cracks occurs in a wide variety of contexts, from microscopic failures in dental enamel and cleaved silicon to geological faults and planetary ice crusts. In each of these situations, with complicated curvature and stress geometries, pairwise interactions between approaching cracks nonetheless produce characteristically curved fracture paths known in the geologic literature as en passant cracks. While the fragmentation of solids via many interacting cracks has seen wide investigation, less attention has been paid to the details of individual crack-crack interactions. We investigate the origins of this widely observed crack pattern using a rectangular elastic plate which is notched on each long side and then subjected to quasistatic uniaxial strain from the short side. The two cracks propagate along approximately straight paths until the pass each other, after which they curve and release a lenticular fragment. We find that, for materials with diverse mechanical properties, the shape of this fragment has an aspect ratio of 2:1, with the length scale set by the initial cracks offset s and the time scale set by the ratio of s to the pulling velocity. The cracks have a universal square root shape, which we understand by using a simple geometric model and the crack-crack interaction.

  12. Environmentally assisted cracking in Light Water Reactors

    International Nuclear Information System (INIS)

    Chung, H.M.; Chopra, O.K.; Ruther, W.E.; Kassner, T.F.; Michaud, W.F.; Park, J.Y.; Sanecki, J.E.; Shack, W.J.

    1993-09-01

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRs) during the six months from October 1992 to March 1993. Fatigue and EAC of piping, pressure vessels, and core components in LWRs are important concerns as extended reactor lifetimes are envisaged. Topics that have been investigated include (1) fatigue of low-alloy steel used in piping, steam generators, and reactor pressure vessels. (2) EAC of cast stainless steels (SSs), (3) radiation-induced segregation and irradiation-assisted stress corrosion cracking of Type 304 SS after accumulation of relatively high fluence, and (4) EAC of low-alloy steels. Fatigue tests were conducted on medium-sulfur-content A106-Gr B piping and A533-Gr B pressure vessel steels in simulated PWR water and in air. Additional crack growth data were obtained on fracture-mechanics specimens of cast austenitic SSs in the as-received and thermally aged conditions and chromium-nickel-plated A533-Gr B steel in simulated boiling-water reactor (BWR) water at 289 degrees C. The data were compared with predictions based on crack growth correlations for ferritic steels in oxygenated water and correlations for wrought austenitic SS in oxygenated water developed at ANL and rates in air from Section XI of the ASME Code. Microchemical and microstructural changes in high- and commercial-purity Type 304 SS specimens from control-blade absorber tubes and a control-blade sheath from operating BWRs were studied by Auger electron spectroscopy and scanning electron microscopy

  13. Effects of rust in the crack face on crack detection based on Sonic-IR method

    International Nuclear Information System (INIS)

    Harai, Y.; Izumi, Y.; Tanabe, H.; Takamatsu, T.; Sakagami, T.

    2015-01-01

    Sonic-IR, which is based on the thermographic detection of the temperature rise due to frictional heating at the defect faces under ultrasonic excitation, has an advantage in the detection of closed and small defects. However, this method has a lot of nuclear factors relating to heat generation. In this study, effects of rust in the crack faces on the crack detection based on the sonic-IR method is experimentally investigated by using crack specimens. The heat generation by ultrasonic excitation was observed regularly during rust accelerated test using original device. The distribution of temperature change around the crack was changed with the progress of rust. This change in heat generation, it believed to be due to change in the contact state of the crack surface due to rust. As a result, it was found that heat generation by ultrasonic excitation is affected by rust in the crack faces. And it was also found that crack detection can be conducted by sonic-IR even if rust was generated in the crack faces. (author)

  14. Sizing of small surface-breaking tight cracks by using laser-ultrasonics

    International Nuclear Information System (INIS)

    Ochiai, M.; Miura, T.; Kuroda, H.; Yamamoto, S.; Onodera, T.

    2004-01-01

    On the nondestructive testing, not only detection but also sizing of crack is desirable because the crack depth is one of the most important parameter to evaluate the impact of the crack to the material, to estimate crack growth and ultimately to predict lifetime of the component. Moreover, accurate measurement of the crack depth optimizes countermeasures and timing of repairs, and eventually reduces total cost for plant maintenance. Laser-ultrasonic is a technique that uses two laser beams; one with a short pulse for the generation of ultrasound and another one, long pulse or continuous, coupled to an optical interferometer for detection. The technique features a large detection bandwidth, which is important for small defect inspection. Another feature of laser-ultrasonics is the remote optical scanning of generation and detection points, which enables to inspect components in narrow space and/or having complex shapes. A purpose of this paper is to describe the performance of a laser-ultrasonic testing (LUT) system on stress corrosion cracking (SCC) inspection. We have developed a new technique for sizing shallow cracks, say 0.5-1.5mm, based on the laser-induced surface wave and its frequency analysis. First, sizing capability of the system will be demonstrated by using an artificial surface-breaking slot having depth of 0-2mm in a stainless steel plate. Evaluated depths show good agreement with the machined slot depths within the accuracy of about a few hundred micrometers. Then, SCCs in a stainless steel plate are examined by using the system. Depth of SCC is evaluated every 0.2mm over the crack aperture length. The evaluated depths are compared with the depths measured by the destructive testing. (author)

  15. Concrete cover cracking due to uniform reinforcement corrosion

    DEFF Research Database (Denmark)

    Solgaard, Anders Ole Stubbe; Michel, Alexander; Geiker, Mette Rica

    2013-01-01

    and reinforcement de-passivation is a frequently used limit state. The present paper investigates an alternative limit state: corrosion-induced cover cracking. Results from numerical simulations of concrete cover cracking due to reinforcement corrosion are presented. The potential additional service life...... is calculated using literature data on corrosion rate and Faraday’s law. The parameters varied comprise reinforcement diameter, concrete cover thickness and concrete material properties, viz. concrete tensile strength and ductility (plain concrete and fibre reinforced concrete). Results obtained from......Service life design (SLD) is an important tool for civil engineers to ensure that the structural integrity and functionality of the structure is not compromised within a given time frame, i.e. the service life. In SLD of reinforced concrete structures, reinforcement corrosion is of major concern...

  16. High temperature cracking of steels: effect of geometry on creep crack growth laws

    International Nuclear Information System (INIS)

    Kabiri, M.R.

    2003-12-01

    This study was performed at Centre des Materiaux de l'Ecole des Mines de Paris. It deals with identification and transferability of high temperature creep cracking laws of steels. A global approach, based on C * and J non-linear fracture mechanics parameters has been used to characterize creep crack initiation and propagation. The studied materials are: the ferritic steels 1Cr-1Mo-1/4V (hot and cold parts working at 540 and 250 C) used in the thermal power stations and the austenitic stainless steel 316 L(N) used in the nuclear power stations. During this thesis a data base was setting up, it regroups several tests of fatigue, creep, creep-fatigue, and relaxation. Its particularity is to contain several creep tests (27 tests), achieved at various temperatures (550 to 650 C) and using three different geometries. The relevance of the C * parameter to describe the creep crack propagation was analysed by a means of systematic study of elasto-viscoplastic stress singularities under several conditions (different stress triaxiality). It has been shown that, besides the C * parameter, a second non singular term, denoted here as Q * , is necessary to describe the local variables in the vicinity of the crack tip. Values of this constraint parameter are always negative. Consequently, application of typical creep crack growth laws linking the creep crack growth rate to the C * parameter (da/dt - C * ), will be conservative for industrial applications. Furthermore, we showed that for ferritic steels, crack incubation period is important, therefore a correlation of Ti - C * type has been kept to predict crack initiation time Ti. For the austenitic stainless steel, the relevant stage is the one of the crack propagation, so that a master curve (da/dt - C * ), using a new data analysis method, was established. Finally, the propagation of cracks has been simulated numerically using the node release technique, allowing to validate analytical expressions utilised for the experimental

  17. Study of toughening mechanisms through the observations of crack propagation in nanostructured and layered metallic sheet

    International Nuclear Information System (INIS)

    Chen, A.Y.; Li, D.F.; Zhang, J.B.; Liu, F.; Liu, X.R.; Lu, J.

    2011-01-01

    Highlights: → A nanostructured and layered steel exhibits high strength and large ductility. → The excellent combination originates from a multiple interlaminar cracking. → The initiation and propagation of cracks are controlled by three aspects. → The cracks are deflected by interface and arrested by compressive residual stress. → Finally, the cracks are blunted by the graded grain size distribution. - Abstract: A layered and nanostructured (LN) 304 SS sheet was produced by combination of surface mechanical attrition treatment (SMAT) with warm co-rolling. The microstructure of LN sheet is characterized by a periodic distribution of nanocrystalline layers and micron-grained layers with a graded transition of grain size. Tensile test results show that exceptional properties of high yield strength and large elongation to fracture are achieved. A multiple interlaminar cracking was observed by scanning electron microscopy, which is induced by repeated crack initiation and propagation. The toughening mechanisms of the LN sheet are proposed to be controlling the crack propagation path by several strategies. The main cracks initiating at interface defects are arrested by large compressive residual stress, deflected by weak interface bonding and blunted by the graded grain size distribution.

  18. Crack resistance of austenitic pipes with circumferential through-wall cracks

    International Nuclear Information System (INIS)

    Foerster, K.; Grueter, L.; Setz, W.; Bhandari, S.; Debaene, J.P.; Faidy, C.; Schwalbe, K.H.

    1993-01-01

    For monotonously increasing load the correct evaluation of the crack resistance properties of a structure is essential for safety analyses. Considerable attention has been given to the through-wall case, since this is generally believed to be the controlling case with regard to complete pipe failure. The maximum load conditions for circumferential crack growth in pipes under displacement-controlled loadings has been determined. The need for crack resistance curves, measured on circumferentially through-wall cracked straight pipes of austenitic stainless steel 316L under bending, is emphasized by the limitation in the data range on small specimens and by the differences in the procedures. To answer open questions and to improve calculational methods a joint fracture mechanics program is being performed by Electricite de France, Novatome and Siemens-Interatom. The working program contains experimental and theoretical investigations on the applicability of small-specimen data to real structures. 10 refs., 10 figs., 4 tabs

  19. Cutting of metal components by intergranular cracking

    International Nuclear Information System (INIS)

    Chavand, J.; Gauthier, A.; Lopez, J.J.; Tanis, G.

    1985-01-01

    The objective of this contract was to study a new steel-sheet cutting technique for dismantling nuclear installations without in principle producing secondary waste. This technique is based on intergranular cracking of steel induced by the combined action of penetration of molten metal into the steel and application of a mechanical load. Cutting has been achieved for stainless-steel sheets with thicknesses ranging from a few mm to 50 mm and for carbon-steel plates with thicknesses between 20 and 60 mm. For carbon steel is seems possible that components as thick as 100 mm can be cut. The tests have permitted selection of the heating methods and determination of the cracking parameters for the materials and range of thickness studied. In the case of thin sheets, results were obtained for cutting in varied positions suited to the techniques of dismantling in hot cells. A temperature-measuring system using an infrared camera has been developed to determine the variation of the temperature field established in the component. In association with the three-dimensional computation code COCO developed by the CEA, this system permits prediction of the changes in stresses in the cracked zone when the cutting parameters are modified. 34 figs

  20. Effects of pulse current stimulation on the thermal fatigue crack propagation behavior of CHWD steel

    International Nuclear Information System (INIS)

    Lin, H.Q.; Zhao, Y.G.; Gao, Z.M.; Han, L.G.

    2008-01-01

    The fatigue crack propagating behaviors of cast hot working die (CHWD) steel untreated and treated by an electric current in the intermediate stage of thermal fatigue were investigated in the present study. The circle/elliptical heating affected zone (HAZ) was formed ahead of the notch tip on the fatigued specimens after pulse electric current stimulation. Both SEM observation and X-ray diffraction analysis revealed that pulse electric current stimulation refined grains/subgrains in the HAZs. With the prolonging of discharging duration, the grains/subgrains decreased in size and the dislocation density and microhardness increased gradually. The grain refinement and dislocation density increase played an important role in the material strengthening, which inevitably enhanced the propagation resistance and delayed the propagation of thermal fatigue cracks. Therefore, the pulse electric current stimulation was an effective method to improve the service lifetime of die material

  1. Evidence for a Shared Mechanism in the Formation of Urea-Induced Kinetic and Equilibrium Intermediates of Horse Apomyoglobin from Ultrarapid Mixing Experiments

    Science.gov (United States)

    Mizukami, Takuya; Abe, Yukiko; Maki, Kosuke

    2015-01-01

    In this study, the equivalence of the kinetic mechanisms of the formation of urea-induced kinetic folding intermediates and non-native equilibrium states was investigated in apomyoglobin. Despite having similar structural properties, equilibrium and kinetic intermediates accumulate under different conditions and via different mechanisms, and it remains unknown whether their formation involves shared or distinct kinetic mechanisms. To investigate the potential mechanisms of formation, the refolding and unfolding kinetics of horse apomyoglobin were measured by continuous- and stopped-flow fluorescence over a time range from approximately 100 μs to 10 s, along with equilibrium unfolding transitions, as a function of urea concentration at pH 6.0 and 8°C. The formation of a kinetic intermediate was observed over a wider range of urea concentrations (0–2.2 M) than the formation of the native state (0–1.6 M). Additionally, the kinetic intermediate remained populated as the predominant equilibrium state under conditions where the native and unfolded states were unstable (at ~0.7–2 M urea). A continuous shift from the kinetic to the equilibrium intermediate was observed as urea concentrations increased from 0 M to ~2 M, which indicates that these states share a common kinetic folding mechanism. This finding supports the conclusion that these intermediates are equivalent. Our results in turn suggest that the regions of the protein that resist denaturant perturbations form during the earlier stages of folding, which further supports the structural equivalence of transient and equilibrium intermediates. An additional folding intermediate accumulated within ~140 μs of refolding and an unfolding intermediate accumulated in <1 ms of unfolding. Finally, by using quantitative modeling, we showed that a five-state sequential scheme appropriately describes the folding mechanism of horse apomyoglobin. PMID:26244984

  2. SCC crack growth rate of cold worked 316L stainless steel in PWR environment

    Science.gov (United States)

    Du, Donghai; Chen, Kai; Yu, Lun; lu, Hui; Zhang, Lefu; Shi, Xiuqiang; Xu, Xuelian

    2015-01-01

    Many component failures in nuclear power plants were found to be caused by stress corrosion cracking (SCC) of cold worked austenitic steels. Some of the pressure boundary component materials are even cold worked up to 35% plastic deformation, leaving high residual stress and inducing high growth rate of corrosion crack. Controlling water chemistry is one of the best counter measure to mitigate this problem. In this work, the effects of temperature (200 up to 325 °C) and dissolved oxygen (0 up to 2000 μg/L) on SCC crack growth rates of cold worked austenitic stainless steel type 316L have been tested by using direct current potential drop (DCPD) method. The results showed that temperature affected SCC crack growth rates more significantly in oxygenated water than in deaerated water. In argon deaerated water, the crack growth rate exhibited a peak at about 250 °C, which needs further verification. At 325 °C, the SCC crack growth rate increased rapidly with the increase of dissolved oxygen concentration within the range from 0 up to 200 μg/L, while when dissolved oxygen was above 200 μg/L, the crack growth rate followed a shallower dependence on dissolved oxygen concentration.

  3. Small Crack Growth and Fatigue Life Predictions for High-Strength Aluminium Alloys. Part 1; Experimental and Fracture Mechanics Analysis

    Science.gov (United States)

    Wu, X. R.; Newman, J. C.; Zhao, W.; Swain, M. H.; Ding, C. F.; Phillips, E. P.

    1998-01-01

    The small crack effect was investigated in two high-strength aluminium alloys: 7075-T6 bare and LC9cs clad alloy. Both experimental and analytical investigations were conducted to study crack initiation and growth of small cracks. In the experimental program, fatigue tests, small crack and large crack tests A,ere conducted under constant amplitude and Mini-TWIST spectrum loading conditions. A pronounced small crack effect was observed in both materials, especially for the negative stress ratios. For all loading conditions, most of the fatigue life of the SENT specimens was shown to be crack propagation from initial material defects or from the cladding layer. In the analysis program, three-dimensional finite element and A weight function methods were used to determine stress intensity factors and to develop SIF equations for surface and corner cracks at the notch in the SENT specimens. A plastisity-induced crack-closure model was used to correlate small and large crack data, and to make fatigue life predictions, Predicted crack-growth rates and fatigue lives agreed well with experiments. A total fatigue life prediction method for the aluminum alloys was developed and demonstrated using the crack-closure model.

  4. Role of xanthine oxidase and reactive oxygen intermediates in LPS- and TNF-induced pulmonary edema.

    Science.gov (United States)

    Faggioni, R; Gatti, S; Demitri, M T; Delgado, R; Echtenacher, B; Gnocchi, P; Heremans, H; Ghezzi, P

    1994-03-01

    We studied the role of reactive oxygen intermediates (ROI) in lipopolysaccharide (LPS)-induced pulmonary edema. LPS treatment (600 micrograms/mouse, IP) was associated with a marked induction of the superoxide-generating enzyme xanthine oxidase (XO) in serum and lung. Pretreatment with the antioxidant N-acetylcysteine (NAC)--1 gm/kg orally, 45 minutes before LPS--or with the XO inhibitor allopurinol (AP)--50 mg/kg orally at -1 hour and +3 hours--was protective. On the other hand nonsteroidal antiinflammatory drugs (ibuprofen, indomethacin, and nordihydroguaiaretic acid) were ineffective. These data suggested that XO might be involved in the induction of pulmonary damage by LPS. However, treatment with the interferon inducer polyriboinosylic-polyribocytidylic acid, although inducing XO to the same extent as LPS, did not cause any pulmonary edema, indicating that XO is not sufficient for this toxicity of LPS. To define the possible role of cytokines, we studied the effect of direct administration of LPS (600 micrograms/mouse, IP), tumor necrosis factor (TNF, 2.5 or 50 micrograms/mouse, IV), interleukin-1 (IL-1 beta, 2.5 micrograms/mouse, IV), interferon-gamma (IFN-gamma, 2.5 micrograms/mouse, IV), or their combination at 2.5 micrograms each. In addition to LPS, only TNF at the highest dose induced pulmonary edema 24 hours later. LPS-induced pulmonary edema was partially inhibited by anti-IFN-gamma antibodies but not by anti-TNF antibodies, anti-IL-1 beta antibodies, or IL-1 receptor antagonist (IL-1Ra).

  5. The application of RBI-concept to ultrasonic measurement of fatigue cracks

    Energy Technology Data Exchange (ETDEWEB)

    Pitkaenen, J; Saerkiniemi, P; Kauppinen, P [VTT Manufacturing Technology, Espoo (Finland)

    1999-12-31

    In many power plants there are problem areas, which are not included in the official inspection programs. Flaws can be induced during service due to the service conditions in components and welded joints. These can lead to failures, which cause unforeseen shutdowns during operation and unscheduled repairs have to be earned out. The basic idea of Risk Based Inspection (RBI) methodology is to include this kind of objects in the inspection program. In this presentation two possible objects for RBI are described - thermal fatigue cracking in process piping and fatigue cracking in spinning fly wheel. (orig.) 4 refs.

  6. The application of RBI-concept to ultrasonic measurement of fatigue cracks

    Energy Technology Data Exchange (ETDEWEB)

    Pitkaenen, J.; Saerkiniemi, P.; Kauppinen, P. [VTT Manufacturing Technology, Espoo (Finland)

    1998-12-31

    In many power plants there are problem areas, which are not included in the official inspection programs. Flaws can be induced during service due to the service conditions in components and welded joints. These can lead to failures, which cause unforeseen shutdowns during operation and unscheduled repairs have to be earned out. The basic idea of Risk Based Inspection (RBI) methodology is to include this kind of objects in the inspection program. In this presentation two possible objects for RBI are described - thermal fatigue cracking in process piping and fatigue cracking in spinning fly wheel. (orig.) 4 refs.

  7. Propagation of stress-corrosion cracks in unirradiated zircaloy

    International Nuclear Information System (INIS)

    Norring, K.; Haag, Y.; Wikstroem, C.

    1982-01-01

    Propagation of iodine-induced stress-corrosion cracks in Zircaloy was studied using pre-cracked and internally pressurized cladding tubes. These were recrystallized at different temperatures, to obtain grain sizes between 4 μm and 10 μm. No statistically significant difference in propagation rate due to the difference in grain size was observed. If the obtained data, with Ksub(I) values ranging from 4 to 11 MNmsup(-3/2), were log-log plotted (da/dt = CKsub(I)sup(N)), as usual, they fell within the scatter-band of data reported earlier. But from this plot it could also be seen that the Ksub(I) interval can be divided into two separate parts having different da/dt-Ksub(I) relations. The transition takes place at a Ksub(I) value of about 8 MNmsup(-3/2). The region with lower Ksub(I) values shows a substantially lower n value than the upper region (2.4 and 9.8 respectively), and earlier reported values (n = 7 to 10). This transition is in good agreement with a transition from an intergranular to a transgranular propagation mode of the stress-corrosion crack. (orig.)

  8. Prediction of Crack Growth Aqueous Environments.

    Science.gov (United States)

    1983-06-01

    ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT. TASK AREA & WORK UNIT NUMBERS SRI International 333 Ravenswood Avenue Menlo Park, CA 94025 II...34no crack" has at least a vestigial rupture, associated with cyclic loading of the oxide film at the crack tip. The curve labeled "crack" was obtained...be an effect of crack opening. For the data set labeled "crack", the vestigial crack, although short, is very tight and the impedance is large. Under

  9. Investigation on a new inducer of pulsed eddy current thermography

    Directory of Open Access Journals (Sweden)

    Min He

    2016-09-01

    Full Text Available In this paper, a new inducer of pulsed eddy current thermography (PECT is presented. The use of the inducer can help avoid the problem of blocking the infrared (IR camera’s view in eddy current thermography technique. The inducer can also provide even heating of the test specimen. This paper is concerned with the temperature distribution law around the crack on a specimen when utilizing the new inducer. Firstly, relative mathematical models are provided. In the following section, eddy current distribution and temperature distribution around the crack are studied using the numerical simulation method. The best separation distance between the inducer and the specimen is also determined. Then, results of temperature distribution around the crack stimulated by the inducer are gained by experiments. Effect of current value on temperature rise is studied as well in the experiments. Based on temperature data, temperature features of the crack are discussed.

  10. A fracture mechanics model for iodine stress corrosion crack propagation in Zircaloy tubing

    International Nuclear Information System (INIS)

    Crescimanno, P.J.; Campbell, W.R.; Goldberg, I.

    1984-01-01

    A fracture mechanics model is presented for iodine-induced stress corrosion cracking in Zircaloy tubing. The model utilizes a power law to relate crack extension velocity to stress intensity factor, a hyperbolic tangent function for the influence of iodine concentration, and an exponential function for the influence of temperature and material strength. Comparisons of predicted to measured failure times show that predicted times are within a factor of two of the measured times for a majority of the specimens considered

  11. Residual stress and crack initiation in laser clad composite layer with Co-based alloy and WC + NiCr

    International Nuclear Information System (INIS)

    Lee, Changmin; Park, Hyungkwon; Yoo, Jaehong; Lee, Changhee; Woo, WanChuck; Park, Sunhong

    2015-01-01

    Highlights: • Major problem, clad cracking in laser cladding process, was researched. • Residual stress measurements were performed quantitatively by neutron diffraction method along the surface of specimens. • Relationship between the residual stress and crack initiation was showed clearly. • Ceramic particle effect in the metal matrix was showed from the results of residual stress measurements. • Initiation sites of generating clad cracks were specifically studied in MMC coatings. - Abstract: Although laser cladding process has been widely used to improve the wear and corrosion resistance, there are unwanted cracking issues during and/or after laser cladding. This study investigates the tendency of Co-based WC + NiCr composite layers to cracking during the laser cladding process. Residual stress distributions of the specimen are measured using neutron diffraction and elucidate the correlation between the residual stress and the cracking in three types of cylindrical specimens; (i) no cladding substrate only, (ii) cladding with 100% stellite#6, and (iii) cladding with 55% stellite#6 and 45% technolase40s. The microstructure of the clad layer was composed of Co-based dendrite and brittle eutectic phases at the dendritic boundaries. And WC particles were distributed on the matrix forming intermediate composition region by partial melting of the surface of particles. The overlaid specimen exhibited tensile residual stress, which was accumulated through the beads due to contraction of the coating layer generated by rapid solidification, while the non-clad specimen showed compressive. Also, the specimen overlaid with 55 wt% stellite#6 and 45 wt% technolase40s showed a tensile stress higher than the specimen overlaid with 100% stellite#6 possibly, due to the difference between thermal expansion coefficients of the matrix and WC particles. Such tensile stresses can be potential driving force to provide an easy crack path ways for large brittle fractures

  12. Residual stress and crack initiation in laser clad composite layer with Co-based alloy and WC + NiCr

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Changmin; Park, Hyungkwon; Yoo, Jaehong [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Lee, Changhee, E-mail: chlee@hanyang.ac.kr [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Woo, WanChuck [Neutron Science Division, Korea Atomic Energy Research Institute, Daejeon 305-353 (Korea, Republic of); Park, Sunhong [Research Institute of Industrial Science & Technology, Hyo-ja-dong, Po-Hang, Kyoung-buk, San 32 (Korea, Republic of)

    2015-08-01

    Highlights: • Major problem, clad cracking in laser cladding process, was researched. • Residual stress measurements were performed quantitatively by neutron diffraction method along the surface of specimens. • Relationship between the residual stress and crack initiation was showed clearly. • Ceramic particle effect in the metal matrix was showed from the results of residual stress measurements. • Initiation sites of generating clad cracks were specifically studied in MMC coatings. - Abstract: Although laser cladding process has been widely used to improve the wear and corrosion resistance, there are unwanted cracking issues during and/or after laser cladding. This study investigates the tendency of Co-based WC + NiCr composite layers to cracking during the laser cladding process. Residual stress distributions of the specimen are measured using neutron diffraction and elucidate the correlation between the residual stress and the cracking in three types of cylindrical specimens; (i) no cladding substrate only, (ii) cladding with 100% stellite#6, and (iii) cladding with 55% stellite#6 and 45% technolase40s. The microstructure of the clad layer was composed of Co-based dendrite and brittle eutectic phases at the dendritic boundaries. And WC particles were distributed on the matrix forming intermediate composition region by partial melting of the surface of particles. The overlaid specimen exhibited tensile residual stress, which was accumulated through the beads due to contraction of the coating layer generated by rapid solidification, while the non-clad specimen showed compressive. Also, the specimen overlaid with 55 wt% stellite#6 and 45 wt% technolase40s showed a tensile stress higher than the specimen overlaid with 100% stellite#6 possibly, due to the difference between thermal expansion coefficients of the matrix and WC particles. Such tensile stresses can be potential driving force to provide an easy crack path ways for large brittle fractures

  13. Stainless steel waste containers: an assessment of the probability of stress corrosion cracking

    International Nuclear Information System (INIS)

    Wanklyn, J.N.; Naish, C.C.

    1991-06-01

    The paper summarises information obtained from the literature and discussions held with corrosion experts from universities and industry, relevant to the possibility that stainless steel radioactive waste containers containing low level and intermediate level radioactive waste (LLW and ILW) could, when buried in concrete, suffer one or more of the forms of stress corrosion cracking (SCC). Stress corrosion cracking is caused by the simultaneous and synergistic action of a corrosive environment and stress. The initiation and propagation of SCC depend on a number of factors being present, namely a certain level of stress, an environment which will cause cracking and a susceptible metal or alloy. Generally the susceptibility of a metal or alloy to SCC increases as its strength level increases. The susceptibility in a specific environment will depend on: solution concentration, pH, temperature, and electrochemical potential of the metal/alloy. It is concluded that alkaline stress corrosion cracking is unlikely to occur under even the worst case conditions, that chloride stress corrosion cracking is a distinct possibility at the higher end of the temperature range (25-80 o C) and that stress corrosion related to sensitization of the steel will not be a problem for the majority of container material which is less than 5 mm in cross section. Thicker section material could become sensitized leading to a local problem in these areas. Contact with metals that are electrochemically more negative in corrosion potential is likely to reduce the incidence of SCC, at least locally. Measurement of repassivation potentials and rest potentials in solutions of relevant composition would provide a firmer prediction of the extent to which a high pH could reduce the likelihood of SCC caused by chlorides. (author)

  14. Cracking in fusion zone and heat affected zone of electron beam welded Inconel-713LC gas turbine blades

    Energy Technology Data Exchange (ETDEWEB)

    Chamanfar, A., E-mail: achamanfar@gmail.com [Département de Génie Mécanique, École de Technologie Supérieure, 1100 rue Notre-Dame Ouest, Montréal, Québec, Canada H3C 1K3 (Canada); Jahazi, M. [Département de Génie Mécanique, École de Technologie Supérieure, 1100 rue Notre-Dame Ouest, Montréal, Québec, Canada H3C 1K3 (Canada); Bonakdar, A.; Morin, E. [Siemens Canada Limited, 9545 Côte-de-Liesse, Dorval, Québec, Canada H9P 1A5 (Canada); Firoozrai, A. [Département de Génie Mécanique, École de Technologie Supérieure, 1100 rue Notre-Dame Ouest, Montréal, Québec, Canada H3C 1K3 (Canada)

    2015-08-26

    Electron beam welding (EBW) of shrouds in Inconel-713LC low pressure gas turbine blades was associated with cracking in fusion zone (FZ) and heat affected zone (HAZ) leading to a high scrap rate in manufacturing of gas turbine blades. In this study, in order to develop a detailed map of cracks and understand the root cause of cracking, a comprehensive microstructural and numerical analysis was performed. The elemental mapping in scanning electron microscope (SEM)-energy dispersive spectral analysis revealed segregation of alloying elements in the cracked area of FZ and HAZ. In other words, one of the cracking mechanisms in FZ and HAZ was found to be segregation induced liquation and subsequent cracking due to thermal and mechanical tensile stresses generated during EBW. Cracking in FZ also occurred because of low strength of the solidifying weld metal as well as solidification contraction. As well, γ′ dissolution and reprecipitation in HAZ leading to decreased ductility and generation of contraction stresses was another mechanism for cracking in HAZ. The numerical model was capable to predict the cracking location as well as cracking orientation with respect to the weld line.

  15. Repair welding of cracked steam turbine blades

    International Nuclear Information System (INIS)

    Bhaduri, A.K.; Gill, T.P.S.; Albert, S.K.; Shanmugam, K.; Iyer, D.R.

    1999-01-01

    The procedure for repair welding of cracked steam turbine blades made of martensitic stainless steels has been developed using the gas tungsten arc welding process. Weld repair procedures were developed using both ER316L austenitic stainless steel filler wire and ER410 martensitic stainless steel filler wire. The repair welding procedure with austenitic filler wire was developed to avoid preheating of the blade as also hydrogen induced cold cracking, and involved evaluation of three different austenitic filler wires, viz. ER309L, ER316L and ERNiCr-3. The overall development of the repair welding procedure included selection of welding consumables (for austenitic filler metal), optimisation of post weld heat treatment parameters, selection of suitable method for local pre-heating and post-weld heat treatment (PWHT) of the blades, determination of mechanical properties of weldments in as-welded and PWHT conditions, and microstructural examination. After various trials using different procedures, the procedure of local PWHT using electrical resistance heating on the top surface of the weldment and monitoring the temperature by placing a thermocouple at the bottom of the weld, was found to give the most satisfactory results. A similar procedure was used for preheating while using ER410 filler metal. Mechanical testing of weldments before and after PWHT involved tensile tests at room temperature, face and root bend tests, and microhardness measurements across the fusion line and heat affected zone. During procedure qualification, mock-ups and actual repair welding, dye penetrant testing was used at different stages and where ever possible radiography was carried out. These procedures were developed for repair welding of cracked blades in the low-pressure (LP) steam turbines of Indian nuclear power plants. The procedure with ER316 L filler wire has so far been applied for repair welding of 2 cracked blades (made of AISI 410 SS) of LP steam turbines, while the procedure

  16. Fatigue Crack Growth Rate and Stress-Intensity Factor Corrections for Out-of-Plane Crack Growth

    Science.gov (United States)

    Forth, Scott C.; Herman, Dave J.; James, Mark A.

    2003-01-01

    Fatigue crack growth rate testing is performed by automated data collection systems that assume straight crack growth in the plane of symmetry and use standard polynomial solutions to compute crack length and stress-intensity factors from compliance or potential drop measurements. Visual measurements used to correct the collected data typically include only the horizontal crack length, which for cracks that propagate out-of-plane, under-estimates the crack growth rates and over-estimates the stress-intensity factors. The authors have devised an approach for correcting both the crack growth rates and stress-intensity factors based on two-dimensional mixed mode-I/II finite element analysis (FEA). The approach is used to correct out-of-plane data for 7050-T7451 and 2025-T6 aluminum alloys. Results indicate the correction process works well for high DeltaK levels but fails to capture the mixed-mode effects at DeltaK levels approaching threshold (da/dN approximately 10(exp -10) meter/cycle).

  17. SSRI Facilitated Crack Dancing

    Directory of Open Access Journals (Sweden)

    Ravi Doobay

    2017-01-01

    Full Text Available Choreoathetoid movement secondary to cocaine use is a well-documented phenomenon better known as “crack dancing.” It consists of uncontrolled writhing movements secondary to excess dopamine from cocaine use. We present a 32-year-old male who had been using cocaine for many years and was recently started on paroxetine, a selective serotonin reuptake inhibitor (SSRI for worsening depression four weeks before presentation. He had been doing cocaine every 2 weeks for the last three years and had never “crack danced” before this episode. The authors have conducted a thorough literature review and cited studies that suggest “crack dancing” is associated with excess dopamine. There has never been a documented case report of an SSRI being linked with “crack dancing.” The authors propose that the excess dopaminergic effect of the SSRI lowered the dopamine threshold for “crack dancing.” There is a communication with the Raphe Nucleus and the Substantia Nigra, which explains how the SSRI increases dopamine levels. This is the first documented case of an SSRI facilitating the “crack dance.”

  18. Carbon emission, energy consumption and intermediate goods trade: A regional study of East Asia

    International Nuclear Information System (INIS)

    Zhang, Jingjing

    2015-01-01

    Using country level panel data from East Asia over the period 1998–2011, this paper examines the implications of international production fragmentation-induced intermediate goods trade on the link between energy consumption and carbon pollution. The paper focuses on the interaction effect between energy consumption and trade in intermediate goods on carbon emission. The empirical results presented suggest that international trade in intermediate goods decreases the positive impact on carbon emission of energy consumption. When compared with the trade in final goods, intermediate goods trade contributes to a greater decrease in carbon pollution resulting from energy consumption. These results confirm that the link between energy consumption and carbon pollution in East Asia is significantly affected by international production fragmentation-induced trade in intermediate goods. The results presented in this paper have some important policy implications. - Highlights: • This paper tests the role of intermediates trade in energy-development nexus. • Empirical study is based on data of East Asia. • International trade can reduce the carbon pollution caused by energy use. • Intermediates trade has higher moderating effect than non-intermediate trade.

  19. Environmental safety case and cement-related issues for intermediate-level waste in a co-located geological disposal facility

    International Nuclear Information System (INIS)

    Norris, Simon; Williams, Steve

    2012-01-01

    Simon Norris of the NDA described safety case and cement-related issues for a geological disposal facility for ILW. The Environmental Safety Case (ESC) needs to demonstrate a clear understanding of: - The disposal facility in its geological setting. - How the disposal system will evolve. - How the various components of system (including cementitious materials) contribute to meeting the requirement of providing a safe long-term solution for the disposed wastes. The ESC must include and support the key environmental safety arguments with underpinning lines of reasoning and detailed analysis, assessments and supporting evidence (including those relating to cementitious materials). In an ILW disposal system, cementitious materials could be used in several ways: - As in-package grouting materials and package materials. - Backfill material. - Shotcrete and other vault lining technologies that could be employed during construction and operation. - Engineered seals. - Structural materials. Given that cementitious materials will play important roles in the disposal system - and within a general strategy for managing uncertainty - the NDA is conducting, or has recently conducted, research into the following topics: - Assessment of the potential for interactions between disposal modules for low- and intermediate-level wastes and for HLW and spent fuel. - The effect of possible cementitious vault liners (e.g. composed from shotcrete) on the early post-closure evolution of waste-derived gas in a geological disposal facility for low- and intermediate-level wastes. - The evolution of cementitious backfill materials, including cracking, and related evolution of groundwater flow and chemistry in the vault environment of a geological disposal facility. - Evidence from nature and archaeology relevant to the long-term properties of cement. - Interaction of waste-derived gas (particularly carbon-14 bearing gas) with cementitious materials in the facility near-field. - The choice of in

  20. Mechanics of quasi-static crack growth

    Energy Technology Data Exchange (ETDEWEB)

    Rice, J R

    1978-10-01

    Results on the mechanics of quasi-static crack growth are reviewed. These include recent studies on the geometry and stability of crack paths in elastic-brittle solids, and on the thermodynamics of Griffith cracking, including environmental effects. The relation of crack growth criteria to non-elastic rheological models is considered and paradoxes with energy balance approaches, based on singular crack models, are discussed for visco-elastic, diffuso-elastic, and elastic-plastic materials. Also, recent approaches to prediction of stable crack growth in ductile, elastic-plastic solids are discussed.

  1. Cracks growth behaviors of commercial pure titanium under nanosecond laser irradiation for formation of nanostructure-covered microstructures (with sub-5-μm)

    Energy Technology Data Exchange (ETDEWEB)

    Pan, A.F.; Wang, W.J., E-mail: wenjunwang@mail.xjtu.edu.cn; Mei, X.S.; Zheng, B.X.; Yan, Z.X.

    2016-11-30

    Highlights: • The sub-5-μm microstructures on commercial pure titanium are creatively obtained based on cracks growth under 10 ns laser irradiation. • The distribution modification of laser energy induced by cambered microstructures was theoretically analyzed to produce nanostructures. • The sharp micro-nano structures under combined action of crack growth and hot-melt are obtained. - Abstract: This study reported on the formation of sub-5-μm microstructures covered on titanium by cracks growth under 10-ns laser radiation at the wavelength of 532 nm and its induced light modification for production of nanostructures. The electric field intensity and laser power density absorbed by commercial pure titanium were computed to investigate the self-trapping introduced by cracks and the effect of surface morphology on laser propagation characteristics. It is found that nanostructures can form at the surface with the curvature radius below 20 μm. Meanwhile, variable laser fluences were applied to explore the evolution of cracks on commercial pure titanium with or without melt as spot overlap number increased. Experimental study was first performed at the peak laser fluence of 1.063 J/cm{sup 2} to investigate the microstructures induced only by cracks growth. The results demonstrated that angular microstructures with size between 1.68 μm and 4.74 μm was obtained and no nanostructure covered. Then, at the peak laser fluence of 2.126 J/cm{sup 2}, there were some nanostructures covered on the melt-induced curved microstructured surface. However, surface molten material submerged in the most of cracks at the spot overlap number of 744, where the old cracks disappeared. The results indicated that there was too much molten material and melting time at the peak laser fluence of 2.126 J/cm{sup 2}, which was not suitable for obtainment of perfect micro-nano structures. On this basis, peak laser fluence was reduced down to 1.595 J/cm{sup 2} and the sharp sub–5

  2. Nonlinear crack mechanics

    International Nuclear Information System (INIS)

    Khoroshun, L.P.

    1995-01-01

    The characteristic features of the deformation and failure of actual materials in the vicinity of a crack tip are due to their physical nonlinearity in the stress-concentration zone, which is a result of plasticity, microfailure, or a nonlinear dependence of the interatomic forces on the distance. Therefore, adequate models of the failure mechanics must be nonlinear, in principle, although linear failure mechanics is applicable if the zone of nonlinear deformation is small in comparison with the crack length. Models of crack mechanics are based on analytical solutions of the problem of the stress-strain state in the vicinity of the crack. On account of the complexity of the problem, nonlinear models are bason on approximate schematic solutions. In the Leonov-Panasyuk-Dugdale nonlinear model, one of the best known, the actual two-dimensional plastic zone (the nonlinearity zone) is replaced by a narrow one-dimensional zone, which is then modeled by extending the crack with a specified normal load equal to the yield point. The condition of finite stress is applied here, and hence the length of the plastic zone is determined. As a result of this approximation, the displacement in the plastic zone at the abscissa is nonzero

  3. Impacts of weld residual stresses and fatigue crack growth threshold on crack arrest under high-cycle thermal fluctuations

    Energy Technology Data Exchange (ETDEWEB)

    Taheri, Said, E-mail: Said.taheri@edf.fr [EDF-LAB, IMSIA, 7 Boulevard Gaspard Monge, 91120 Palaiseau Cedex (France); Julan, Emricka [EDF-LAB, AMA, 7 Boulevard Gaspard Monge, 91120 Palaiseau Cedex (France); Tran, Xuan-Van [EDF Energy R& D UK Centre/School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester M13 9PL (United Kingdom); Robert, Nicolas [EDF-DPN, UNIE, Strategic Center, Saint Denis (France)

    2017-01-15

    Highlights: • For crack growth analysis, weld residual stress field must be considered through its SIF in presence of a crack. • Presence of cracks of same depth proves their arrest, where equal depth is because mean stress acts only on crack opening. • Not considering amplitudes under a fatigue crack growth threshold (FCGT) does not compensate the lack of FGCT in Paris law. • Propagation rates are close for axisymmetric and circumferential semi-elliptical cracks. - Abstract: High cycle thermal crazing has been observed in some residual heat removal (RHR) systems made of 304 stainless steel in PWR nuclear plants. This paper deals with two types of analyses including logical argumentation and simulation. Crack arrest in networks is demonstrated due to the presence of two cracks of the same depth in the network. This identical depth may be proved assuming that mean stress acts only on crack opening and that cracks are fully open during the load cycle before arrest. Weld residual stresses (WRS) are obtained by an axisymmetric simulation of welding on a tube with a chamfer. Axisymmetric and 3D parametric studies of crack growth on: representative sequences for variable amplitude thermal loading, fatigue crack growth threshold (FCGT), permanent mean stress, cyclic counting methods and WRS, are performed with Code-Aster software using XFEM methodology. The following results are obtained on crack depth versus time: the effect of WRS on crack growth cannot be determined by the initial WRS field in absence of crack, but by the associated stress intensity factor. Moreover the relation between crack arrest depth and WRS is analyzed. In the absence of FCGT Paris’s law may give a significant over-estimation of crack depth even if amplitudes of loading smaller than FCGT have not been considered. Appropriate depth versus time may be obtained using different values of FCGT, but axisymmetric simulations do not really show a possibility of arrest for shallow cracks in

  4. Impacts of weld residual stresses and fatigue crack growth threshold on crack arrest under high-cycle thermal fluctuations

    International Nuclear Information System (INIS)

    Taheri, Said; Julan, Emricka; Tran, Xuan-Van; Robert, Nicolas

    2017-01-01

    Highlights: • For crack growth analysis, weld residual stress field must be considered through its SIF in presence of a crack. • Presence of cracks of same depth proves their arrest, where equal depth is because mean stress acts only on crack opening. • Not considering amplitudes under a fatigue crack growth threshold (FCGT) does not compensate the lack of FGCT in Paris law. • Propagation rates are close for axisymmetric and circumferential semi-elliptical cracks. - Abstract: High cycle thermal crazing has been observed in some residual heat removal (RHR) systems made of 304 stainless steel in PWR nuclear plants. This paper deals with two types of analyses including logical argumentation and simulation. Crack arrest in networks is demonstrated due to the presence of two cracks of the same depth in the network. This identical depth may be proved assuming that mean stress acts only on crack opening and that cracks are fully open during the load cycle before arrest. Weld residual stresses (WRS) are obtained by an axisymmetric simulation of welding on a tube with a chamfer. Axisymmetric and 3D parametric studies of crack growth on: representative sequences for variable amplitude thermal loading, fatigue crack growth threshold (FCGT), permanent mean stress, cyclic counting methods and WRS, are performed with Code-Aster software using XFEM methodology. The following results are obtained on crack depth versus time: the effect of WRS on crack growth cannot be determined by the initial WRS field in absence of crack, but by the associated stress intensity factor. Moreover the relation between crack arrest depth and WRS is analyzed. In the absence of FCGT Paris’s law may give a significant over-estimation of crack depth even if amplitudes of loading smaller than FCGT have not been considered. Appropriate depth versus time may be obtained using different values of FCGT, but axisymmetric simulations do not really show a possibility of arrest for shallow cracks in

  5. Characterization of Residual Stress Effects on Fatigue Crack Growth of a Friction Stir Welded Aluminum Alloy

    Science.gov (United States)

    Newman, John A.; Smith, Stephen W.; Seshadri, Banavara R.; James, Mark A.; Brazill, Richard L.; Schultz, Robert W.; Donald, J. Keith; Blair, Amy

    2015-01-01

    An on-line compliance-based method to account for residual stress effects in stress-intensity factor and fatigue crack growth property determinations has been evaluated. Residual stress intensity factor results determined from specimens containing friction stir weld induced residual stresses are presented, and the on-line method results were found to be in excellent agreement with residual stress-intensity factor data obtained using the cut compliance method. Variable stress-intensity factor tests were designed to demonstrate that a simple superposition model, summing the applied stress-intensity factor with the residual stress-intensity factor, can be used to determine the total crack-tip stress-intensity factor. Finite element, VCCT (virtual crack closure technique), and J-integral analysis methods have been used to characterize weld-induced residual stress using thermal expansion/contraction in the form of an equivalent delta T (change in local temperature during welding) to simulate the welding process. This equivalent delta T was established and applied to analyze different specimen configurations to predict residual stress distributions and associated residual stress-intensity factor values. The predictions were found to agree well with experimental results obtained using the crack- and cut-compliance methods.

  6. Exploring How Weathering Related Stresses and Subcritical Crack Growth May Influence the Size of Sediment Produced From Different Rock Types.

    Science.gov (United States)

    Eppes, M. C.; Hallet, B.; Hancock, G. S.; Mackenzie-Helnwein, P.; Keanini, R.

    2016-12-01

    The formation and diminution of rock debris, sediment and soil at and near Earth's surface is driven in large part by in situ, non-transport related, rock cracking. Given the relatively low magnitude stresses that arise in surface and near-surface settings, this production and diminution of granular material is likely strongly influenced and/or driven by subcritical crack growth (Eppes et al., 2016), cracking that occurs under stress loading conditions much lower than a rock's strength as typically measured in the laboratory under rapid loading. Despite a relatively sound understanding of subcritical crack growth through engineering and geophysical studies, its geomorphic and sedimentologic implications have only been minimally explored. Here, based on existing studies, we formulate several hypotheses to predict how weathering-induced stresses combined with the subcritical crack growth properties of rock may influence sediment size distribution. For example, subcritical crack growth velocity (v) can be described by v = CKIn where KI is the mode I (simple opening mode) stress intensity factor, a function of tensile stress at the crack tip and crack length; C is a rock- and environment-dependent constant; and n is material constant, the subcritical crack growth index. Fracture length and spacing in rock is strongly dependent on n, where higher n values result in fewer, more distally spaced cracks (e.g. Olsen, 1993). Thus, coarser sediment might be expected from rocks with higher n values. Weathering-related stresses such as thermal stresses and mineral hydration, however, can disproportionally stress boundaries between minerals with contrasting thermal or chemical properties and orientation, resulting in granular disintegration. Thus, rocks with properties favorable to inducing these stresses might produce sediment whose size is reflective of its constituent grains. We begin to test these hypotheses through a detailed examination of crack and rock characteristics in

  7. Temperature rise and stress induced by microcracks in accelerating structures

    Directory of Open Access Journals (Sweden)

    W. Zhu

    2010-12-01

    Full Text Available The temperature rise and induced stress due to Ohmic heating in the vicinity of microcracks on the walls of high-gradient accelerating structures are considered. The temperature rise and induced stress depend on the orientation of the crack with respect to the rf magnetic field, the shape of the crack, and the power and duration of the rf pulse. Under certain conditions the presence of cracks can double the temperature rise over that of a smooth surface. Stress at the bottom of the cracks can be several times larger than that of the case when there are no cracks. We study these effects both analytically and by computer simulation. It is shown that the stress in cracks is maximal when the crack depth is on the order of the thermal penetration depth.

  8. Fatigue crack localization using laser nonliner wave modulation spectroscopy (LNWMS)

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Peipei; Sohn, Hoon [Dept. of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of); Kundu, Tribikram [Dept. of Civil Engineering and Engineering Mechanics, University of Arizona, Tucson (United States)

    2016-12-15

    Nonlinear features of ultrasonic waves are more sensitive to the presence of a fatigue crack than their linear counterparts are. For this reason, the use of nonlinear ultrasonic techniques to detect a fatigue crack at its early stage has been widely investigated. Of the different proposed techniques, laser nonlinear wave modulation spectroscopy (LNWMS) is unique because a pulse laser is used to exert a single broadband input and a noncontact measurement can be performed. Broadband excitation causes a nonlinear source to exhibit modulation at multiple spectral peaks owing to interactions among various input frequency components. A feature called maximum sideband peak count difference(MSPCD), which is extracted from the spectral plot, measures the degree of crack- induced material nonlinearity. First, the ratios of spectral peaks whose amplitudes are above a moving threshold to the total number of peaks are computed for spectral signals obtained from the pristine and the current state of a target structure. Then, the difference of these ratios are computed as a function of the moving threshold. Finally, the MSPCD is defined as the maximum difference between these ratios. The basic premise is that the MSPCD will increase as the nonlinearity of the material increases. This technique has been used successfully for localizing fatigue cracks in metallic plates.

  9. Fatigue crack localization using laser nonlinear wave modulation spectroscopy (LNWMS)

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Peipei; Sohn, Hoon [Dept. of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of); Kundu, Tribikram [Dept. of Civil Engineering and Engineering Mechanics, University of Arizona, Tucson (United States)

    2014-12-15

    Nonlinear features of ultrasonic waves are more sensitive to the presence of a fatigue crack than their linear counterparts are. For this reason, the use of nonlinear ultrasonic techniques to detect a fatigue crack at its early stage has been widely investigated. Of the different proposed techniques, laser nonlinear wave modulation spectroscopy (LNWMS) is unique because a pulse laser is used to exert a single broadband input and a noncontact measurement can be performed. Broadband excitation causes a nonlinear source to exhibit modulation at multiple spectral peaks owing to interactions among various input frequency components. A feature called maximum sideband peak count difference (MSPCD), which is extracted from the spectral plot, measures the degree of crack-induced material nonlinearity. First, the ratios of spectral peaks whose amplitudes are above a moving threshold to the total number of peaks are computed for spectral signals obtained from the pristine and the current state of a target structure. Then, the difference of these ratios are computed as a function of the moving threshold. Finally, the MSPCD is defined as the maximum difference between these ratios. The basic premise is that the MSPCD will increase as the nonlinearity of the material increases. This technique has been used successfully for localizing fatigue cracks in metallic plates.

  10. Modelling the tearing crack growth in a ductile ferritic steel using X-FEM elements

    International Nuclear Information System (INIS)

    Simatos, A.; Prabel, B.; Marie, S.; Nedelec, M.; Combescure, A.

    2012-01-01

    Extended Finite Element Method (X-FEM) is used to model a cracked structure without meshing explicitly the crack. Indeed, the crack is represented by a discontinuity of the displacement field through additional degrees of freedom using Heaviside type function or derived from the Irwin's singular fields. Initially, the stress integration in the XFEM framework supposed to divide the cut elements into sub-triangles that are conform to the crack. This was motivated in order to integrate the behaviour accurately on both sides of the crack in particular at proximity of the crack tip where singular enrichments are present. This strategy induces field projections from the usual Gauss point configuration to a variable new one that depends on the crack position in the element. For ductile fracture modelization, this approach is not applicable, because in presence of large scale yield, the projection of internal variable fields is not conservative, in particular at proximity of the crack tip. In order to circumvent this problem, a new integration strategy was proposed by B. Prabel. It consists in using 64 Gauss points that are placed without regards to the crack position. This simple integration scheme permits to take implicitly into account the crack position and the fields in the element in an accurate and consistent way. This strategy was used in problem calculation for which the plastic radius remained small. It allowed introducing the over integrated elements in the probable propagation zone, just before plastification. In the case of ductile tearing, the plasticity is not confined near the crack tip and an improvement of the proposed strategy is made. This is then used to model large ductile crack growth in a ductile ferritic steel. To validate the predictions, the modelization is compared to a second F.E. calculation using the node release technique for the crack propagation. It is then shown that the two predictions are strictly equivalents. (authors)

  11. Comparison of finite element J-integral evaluations for the blunt crack model and the sharp crack model

    International Nuclear Information System (INIS)

    Pan, Y.C.; Kennedy, J.M.

    1983-01-01

    In assessing the safety of a liquid metal fast breeder reactor (LMFBR), a major concern is that of hot sodium coming into contact with either unprotected concrete or steel-lined concrete equipment cells and containment structures. An aspect of this is the potential of concrete cracking which would significantly influence the safety assessment. Concrete cracking in finite element analysis can be modeled as a blunt crack in which the crack is assumed to be uniformly distributed throughout the area of the element. A blunt crack model based on the energy release rate and the effective strength concepts which was insensitive to the element size was presented by Bazant and Cedolin. Some difficulties were encountered in incorporating their approach into a general purpose finite element code. An approach based on the J-integral to circumvent some of the difficulties was proposed by Pan, Marchertas, and Kennedy. Alternatively, cracking can also be modeled as a sharp crack where the crack surface is treated as the boundary of the finite element mesh. The sharp crack model is adopted by most researchers and its J-integral has been well established. It is desirable to establish the correlation between the J-integrals, or the energy release rates, for the blunt crack model and the sharp crack model so that data obtained from one model can be used on the other

  12. Cracking Problems and Mechanical Characteristics of PME and BME Ceramic Capacitors

    Science.gov (United States)

    Teverovsky, Alexander

    2018-01-01

    Most failures in MLCCs are caused by cracking that create shorts between opposite electrodes of the parts. A use of manual soldering makes this problem especially serious for space industry. Experience shows that different lots of ceramic capacitors might have different susceptibility to cracking under manual soldering conditions. This simulates a search of techniques that would allow revealing capacitors that are most robust to soldering-induced stresses. Currently, base metal electrode (BME) capacitors are introduced to high-reliability applications as a replacement of precious metal electrode (PME) parts. Understanding the difference in the susceptibility to cracking between PME and BME capacitors would facilitate this process. This presentation gives a review of mechanical characteristics measured in-situ on MLCCs that includes flexural strength, Vickers hardness, indentation fracture toughness, and the board flex testing and compare characteristics of BME and PME capacitors. A history case related to cracking in PME capacitors that caused flight system malfunctions and mechanisms of failure are considered. Possible qualification tests that would allow evaluation of the resistance of MLCCs to manual soldering are suggested and perspectives related to introduction of BME capacitors discussed.

  13. Continuous monitoring of back-wall stress corrosion cracking propagation by means of potential drop techniques

    International Nuclear Information System (INIS)

    Sato, Yasumoto; Atsumi, Takeo; Shoji, Tetsuo

    2006-01-01

    In order to investigate the applicability of the potential drop techniques to the continuous monitoring of stress corrosion cracking (SCC) propagation, SCC tests were performed in a sodium thiosulfate solution at room temperature using plate specimens with weldments. The SCC propagation was monitored using the techniques of direct current potential drop (DCPD), alternating current potential drop (ACPD) and modified induced current potential drop (MICPD) on the reverse side that on which the SCC existed and effectiveness of each technique for the continuous monitoring from the reverse side of SCC was compared from the viewpoints of sensitivity to the crack propagation and measurement stability. The MICPD and DCPD techniques permit continuous monitoring of the back-wall SCC propagation, which initiates from a fatigue pre-crack at a depth of about 4 mm, from which it propagates through more than 80% of the specimen thickness. The MICPD technique can decrease the effect of the current flowing in the direction of the crack length by focusing the induced current into the local area of measurement using induction coils, so that the sensitivity of the continuous monitoring of the back wall SCC propagation is higher than that of the DCPD and ACPD techniques. (author)

  14. Crack characterization for in-service inspection planning

    International Nuclear Information System (INIS)

    Waale, J.; Ekstroem, P.

    1995-12-01

    During in-service inspection by non destructive testing the reliability is highly dependent on how the equipment is adjusted to the specific object and to the anticipated crack feature.The crack feature and morphology vary widely between different cracking mechanisms and between material types in which the cracks appear. The major objective of this study was to characterize a number of morphology parameters for common crack mechanism and structure material combinations. Critical morphology parameters are crack orientation, shape, width, surface roughness and branching. The crack parameters were evaluated from failure analyses reported from the nuclear and non-nuclear industry. In addition, a literature review was carried out on crack parameter reports and on failure analysis reports, which were further evaluated. The evaluated crack parameters were plotted and statistically processed in data groups with respect to crack mechanism and material type. The fatigue crack mechanism were classified as mechanical, thermal or corrosion fatigue and stress corrosion crack mechanism as intergranular, transgranular or inter dendritic stress corrosion cracking. Furthermore, some common weld defects were characterized for comparison. The materials were divided into three broad groups, ferritic low alloy steels, stainless steels and nickel base alloys. The results indicate significant differences between crack parameters when comparing data from different crack mechanism/material type combinations. Typical parameter values and scatter were derived for several combinations where the data was sufficient for statistical significance. 10 refs, 105 figs, 14 tabs

  15. Crack characterization for in-service inspection planning

    Energy Technology Data Exchange (ETDEWEB)

    Waale, J [SAQ Inspection Ltd, Stockholm (Sweden); Ekstroem, P [ABB Atom AB, Vaesteraas (Sweden)

    1995-12-01

    During in-service inspection by non destructive testing the reliability is highly dependent on how the equipment is adjusted to the specific object and to the anticipated crack feature.The crack feature and morphology vary widely between different cracking mechanisms and between material types in which the cracks appear. The major objective of this study was to characterize a number of morphology parameters for common crack mechanism and structure material combinations. Critical morphology parameters are crack orientation, shape, width, surface roughness and branching. The crack parameters were evaluated from failure analyses reported from the nuclear and non-nuclear industry. In addition, a literature review was carried out on crack parameter reports and on failure analysis reports, which were further evaluated. The evaluated crack parameters were plotted and statistically processed in data groups with respect to crack mechanism and material type. The fatigue crack mechanism were classified as mechanical, thermal or corrosion fatigue and stress corrosion crack mechanism as intergranular, transgranular or inter dendritic stress corrosion cracking. Furthermore, some common weld defects were characterized for comparison. The materials were divided into three broad groups, ferritic low alloy steels, stainless steels and nickel base alloys. The results indicate significant differences between crack parameters when comparing data from different crack mechanism/material type combinations. Typical parameter values and scatter were derived for several combinations where the data was sufficient for statistical significance. 10 refs, 105 figs, 14 tabs.

  16. Tensile cracks in creeping solids

    International Nuclear Information System (INIS)

    Riedel, H.; Rice, J.R.

    1979-02-01

    The loading parameter determining the stress and strain fields near a crack tip, and thereby the growth of the crack, under creep conditions is discussed. Relevant loading parameters considered are the stress intensity factor K/sub I/, the path-independent integral C*, and the net section stress sigma/sub net/. The material behavior is modelled as elastic-nonlinear viscous where the nonlinear term describes power law creep. At the time t = 0 load is applied to the cracked specimen, and in the first instant the stress distribution is elastic. Subsequently, creep deformation relaxes the initial stress concentration at the crack tip, and creep strains develop rapidly near the crack tip. These processes may be analytically described by self-similar solutions for short times t. Small scale yielding may be defined. In creep problems, this means that elastic strains dominate almost everywhere except in a small creep zone which grows around the crack tip. If crack growth ensues while the creep zone is still small compared with the crack length and the specimen size, the stress intensity factor governs crack growth behavior. If the calculated creep zone becomes larger than the specimen size, the stresses become finally time-independent and the elastic strain rates can be neglected. In this case, the stress field is the same as in the fully-plastic limit of power law hardening plasticity. The loading parameter which determines the near tip fields uniquely is then the path-independent integral C*.K/sub I/ and C* characterize opposite limiting cases. The case applied in a given situation is decided by comparing the creep zone size with the specimen size and the crack length. Besides several methods of estimating the creep zone size, a convenient expression for a characteristic time is derived, which characterizes the transition from small scale yielding to extensive creep of the whole specimen

  17. 3-D observations of short fatigue crack interaction with la2mellar and duplex microstructures in a two-phase titanium alloy

    International Nuclear Information System (INIS)

    Birosca, S.; Buffiere, J.Y.; Karadge, M.; Preuss, M.

    2011-01-01

    In situ observations of short crack growth in powder-processed Ti-6246 have been undertaken using synchrotron X-ray microtomography to investigate crack tip interaction with microstructure. Together with post-mortem analysis using electron backscatter diffraction (EBSD), it was possible to identify a number of microstructural features that affect crack propagation rates by causing crack bifurcation, crack bridging and crack deflection. Three samples with different microstructures were tested in this way: lamellar, duplex and a heterogeneous microstructure that showed regions of lamellar and duplex microstructure. The in situ fatigue experiments were carried out with a maximum stress of 410 MPa and R = 0.1. The three microstructures showed significantly different short crack propagation rates, with the lamellar microstructure displaying the fastest and the duplex microstructure the slowest rate. It was found that the lamellar microstructure develops a deeper crack than the duplex microstructure that is related to significant crack bifurcation taking place near the surface region in the lamellar but not duplex microstructure. It was also found that a columnar lamellar microstructure creates a relatively smooth crack front while a basket-weave-type microstructure forces the crack tip to undulate on the lath width scale. Crack bridging of the fine lamellar region of the duplex microstructure was observed, which seems to hinder significant crack bifurcation to occur, but still provides improved crack growth resistance that explains the low crack propagation rate. In the third microstructure the crack tended to grow slightly asymmetrically due to the heterogeneous nature of the microstructure, resulting in the intermediate growth rate. EBSD grain orientation and Schmid factor analysis of regions including the crack revealed that the crack path is strongly influenced by the crystallographic orientation of the α lamellae and grains. While in the lamellar microstructure

  18. Quenching cracks - formation and possible causes

    International Nuclear Information System (INIS)

    Macherauch, E.; Mueller, H.; Voehringer, O.

    1976-01-01

    The most important principles controlling the martensitic hardening of steels containing carbon are presented, and their effects on the cracks formed by tempering are discussed. Micro-crack formation, influenced by any increase in the carbon content, is dependent on the variations of martensitic morphology; this factor is of decisive importance. Apart from micro residual stresses, macro residual stresses become increasingly involved in the crack development. This is dependent on the given content of carbon and increase in the dimensions of the samples. Based on the empirical values gained from experience about cracks formed by tempering and using a schematic diagram, the constructive influences on the propensity to cracks formed by tempering, with regard to materials and processing, are evaluated. Also the effects of thermic, mechanical and chemical after-treatments upon the propensity to tempering cracks are discussed. In conclusion, the problem of the formation of cracks in hardened parts, i.e. the elongation of the cracks under static stress, is treated briefly. (orig.) [de

  19. Natural zeolite bitumen cracking

    Energy Technology Data Exchange (ETDEWEB)

    Kuznicki, S.M.; McCaffrey, W.C.; Bian, J.; Wangen, E.; Koenig, A. [Alberta Univ., Edmonton, AB (Canada). Dept. of Chemical and Materials Engineering

    2006-07-01

    A study was conducted to demonstrate how low cost heavy oil upgrading in the field could reduce the need for diluents while lowering the cost for pipelining. Low cost field upgrading could also contribute to lowering contaminant levels. The performance of visbreaking processes could be improved by using disposable cracking agents. In turn, the economics of field upgrading of in-situ derived bitumen would be improved. However, in order to be viable, such agents would have to be far less expensive than current commercial cracking catalysts. A platy natural zeolite was selected for modification and testing due to its unique chemical and morphological properties. A catalyst-bearing oil sand was then heat-treated for 1 hour at 400 degrees C in a sealed microreactor. Under these mild cracking conditions, the catalyst-bearing oil sand produced extractable products of much lower viscosity. The products also contained considerably more gas oil and middle distillates than raw oil sand processed under the same conditions as thermal cracking alone. According to model cracking studies using hexadecane, these modified mineral zeolites may be more active cracking agents than undiluted premium commercial FCC catalyst. These materials hold promise for partial upgrading schemes to reduce solvent requirements in the field. tabs., figs.

  20. Strain energy density-distance criterion for the initiation of stress corrosion cracking of alloy X-750

    Energy Technology Data Exchange (ETDEWEB)

    Hall, M.M. Jr.; Symons, D.M.

    1996-05-01

    A strain energy density-distance criterion was previously developed and used to correlate rising-load K{sub c} initiation data for notched and fatigue precracked specimens of hydrogen precharged Alloy X-750. This criterion, which was developed for hydrogen embrittlement (HE) cracking, is used here to correlate static-load stress corrosion cracking (SCC) initiation times obtained for smooth geometry, notched and fatigue precracked specimens. The onset of SCC crack growth is hypothesized to occur when a critical strain, which is due to environment-enhanced creep, is attained within the specimen interior. For notched and precracked specimens, initiation is shown by analysis to occur at a variable distance from notch and crack tips. The initiation site varies from very near the crack tip, for highly loaded sharp cracks, to a site that is one grain diameter from the notch, for lower loaded, blunt notches. The existence of hydrogen gradients, which are due to strain-induced hydrogen trapping in the strain fields of notch and crack tips, is argued to be controlling the site for initiation of cracking. By considering the sources of the hydrogen, these observations are shown to be consistent with those from the previous HE study, in which the characteristic distance for crack initiation was found to be one grain diameter from the notch tip, independent of notch radius, applied stress intensity factor and hydrogen level.

  1. Stress field determination in an alloy 600 stress corrosion crack specimen

    International Nuclear Information System (INIS)

    Rassineux, B.; Labbe, T.

    1995-05-01

    In the context of EDF studies on stress corrosion cracking rates in the Alloy 600 steam generators tubes, we studied the influence of strain hardened surface layers on the different stages of cracking for a tensile smooth specimen (TLT). The stress field was notably assessed to try and explain the slow/rapid-propagation change observed beyond the strain hardened layers. The main difficulty is to simulate in a finite element model the inner and outer surfaces of these strain hardened layers, produced by the final manufacturing stages of SG tubes which have not been heat treated. In the model, the strain hardening is introduced by simulating a multi-layer material. Residual stresses are simulated by an equivalent fictitious thermomechanical calculation, realigned with respect to X-ray measurements. The strain hardening introduction method was validated by an analytical calculation giving identical results. Stress field evolution induced by specimen tensile loading were studied using an elastoplastic 2D finite element calculations performed with the Aster Code. The stress profile obtained after load at 660 MPa shows no stress discontinuity at the boundary between the strain hardened layer and the rest of the tube. So we propose that a complementary calculation be performed, taking into account the multi-cracked state of the strain hardened zones by means of a damage variable. In fact, this state could induce stress redistribution in the un-cracked area, which would perhaps provide an explanation of the crack-ground rate change beyond the strain hardened zone. The calculations also evidence the harmful effects of plastic strains on a strain hardened layer due to the initial state of the tube (not heat-treated), to grit blasting or to shot peening. The initial compressive stress condition of this surface layer becomes, after plastic strain, a tensile stress condition. These results are confirmed by laboratory test. (author). 10 refs., 18 figs., 9 tabs., 2 appends

  2. Integrated FEM-DBEM simulation of crack propagation in AA2024-T3 FSW butt joints considering manufacturing effects

    DEFF Research Database (Denmark)

    Sonne, Mads Rostgaard; Carlone, P.; Citarella, R.

    2015-01-01

    This paper deals with a numerical and experimental investigation on the influence of residual stresses on fatigue crack growth in AA2024-T3 friction stir welded butt joints. An integrated FEM-DBEM procedure for the simulation of crack propagation is proposed and discussed. A numerical FEM model...... of the welding process of precipitation hardenable AA2024-T3 aluminum alloy is employed to infer the process induced residual stress field. The reliability of the FEM simulations with respect to the induced residual stresses is assessed comparing numerical outcomes with experimental data obtained by means...

  3. Environmentally assisted cracking of LWR materials

    International Nuclear Information System (INIS)

    Chopra, O.K.; Chung, H.M.; Kassner, T.F.; Shack, W.J.

    1995-12-01

    Research on environmentally assisted cracking (EAC) of light water reactor materials has focused on (a) fatigue initiation in pressure vessel and piping steels, (b) crack growth in cast duplex and austenitic stainless steels (SSs), (c) irradiation-assisted stress corrosion cracking (IASCC) of austenitic SSs, and (d) EAC in high- nickel alloys. The effect of strain rate during different portions of the loading cycle on fatigue life of carbon and low-alloy steels in 289 degree C water was determined. Crack growth studies on wrought and cast SSs have been completed. The effect of dissolved-oxygen concentration in high-purity water on IASCC of irradiated Type 304 SS was investigated and trace elements in the steel that increase susceptibility to intergranular cracking were identified. Preliminary results were obtained on crack growth rates of high-nickel alloys in water that contains a wide range of dissolved oxygen and hydrogen concentrations at 289 and 320 degree C. The program on Environmentally Assisted Cracking of Light Water Reactor Materials is currently focused on four tasks: fatigue initiation in pressure vessel and piping steels, fatigue and environmentally assisted crack growth in cast duplex and austenitic SS, irradiation-assisted stress corrosion cracking of austenitic SSs, and environmentally assisted crack growth in high-nickel alloys. Measurements of corrosion-fatigue crack growth rates (CGRs) of wrought and cast stainless steels has been essentially completed. Recent progress in these areas is outlined in the following sections

  4. In-reactor fatigue crack propagation

    International Nuclear Information System (INIS)

    Ermi, A.M.; Mervyn, D.A.; Straalsund, J.L.

    1979-08-01

    An in-reactor fatigue experiment is being designed to determine the effect of dynamic irradiation on the fatigue crack propagation (FCP) behavior of candidate fusion first wall materials. This investigation has been prompted by studies which show gross differences in crack growth characteristics of creep rupture specimens testing by postirradiation versus dynamic in-reactor methods. The experiment utilizes miniature center-cracked-tension specimens developed specifically for in-reactor studies. In the test, a chain of eight specimens, precracked to various initial crack lengths, is stressed during irradiation to determine crack growth rate as a function of stress intensity. Load levels were chosen which result in small crack growth rates encompassing a regime of the crack growth curve not previously investigated during irradiation studies of FCP. The test will be conducted on 20% cold worked 316 stainless steel at a temperature of 425 0 C, in a sodium environment, and at a frequency of 1 cycle/min. Irradiation will occur in the Oak Ridge Research Reactor, resulting in a He/dpa ratio similar to that expected at the first wall in a fusion reactor. Detailed design of the experiment is presented, along with crack growth data obtained from prototypic testing of the experimental apparatus. These results are compared to data obtained under similar conditions generated by conventional test methods

  5. The effect of crack branching on the residual lifetime of machine components containing stress corrosion cracks

    International Nuclear Information System (INIS)

    Magdowski, R.M.; Uggowitzer, P.J.; Speidel, M.O.

    1985-01-01

    A comparison is presented of theoretical, numerical and experimental investigations concerning the effect of crack branching on the reduction of stress intensity at the tip of single cracks. The results indicate that the division of a single crack into n branches reduces the stress intensity at the branch tips by a factor of about 1/√n. This permits branched cracks to grow to larger depths before becoming critical. The implication is that longer residual lifetimes and longer operating times between inspections can be calculated for machine components with growing branched stress corrosion cracks. (author)

  6. The MHD intermediate shock interaction with an intermediate wave: Are intermediate shocks physical?

    International Nuclear Information System (INIS)

    Wu, C.C.

    1988-01-01

    Contrary to the usual belief that MHD intermediate shocks are extraneous, the authors have recently shown by numerical solutions of dissipative MHD equations that intermediate shocks are admissible and can be formed through nonlinear steepening from a continuous wave. In this paper, he clarifies the differences between the conventional view and the results by studying the interaction of an MHD intermediate shock with an intermediate wave. The study reaffirms his results. In addition, the study shows that there exists a larger class of shocklike solutions in the time-dependent dissiaptive MHD equations than are given by the MHD Rankine-Hugoniot relations. it also suggests a mechanism for forming rotational discontinuities through the interaction of an intermediate shock with an intermediate wave. The results are of importance not only to the MHD shock theory but also to studies such as magnetic field reconnection models

  7. The effect of transverse crack upon parametric instability of a rotor-bearing system with an asymmetric disk

    Science.gov (United States)

    Han, Qinkai; Chu, Fulei

    2012-12-01

    It is well known that either the asymmetric disk or transverse crack brings parametric inertia (or stiffness) excitation to the rotor-bearing system. When both of them appear in a rotor system, the parametric instability behaviors have not gained sufficient attentions. Thus, the effect of transverse crack upon parametric instability of a rotor-bearing system with an asymmetric disk is studied. First, the finite element equations of motion are established for the asymmetric rotor system. Both the open and breathing transverse cracks are taken into account in the model. Then, the discrete state transition matrix (DSTM) method is introduced for numerically acquiring the instability regions. Based upon these, some computations for a practical asymmetric rotor system with open or breathing transverse crack are conducted, respectively. Variations of the primary and combination instability regions induced by the asymmetric disk with the crack depth are observed, and the effect of the orientation angle between the crack and asymmetric disk on various instability regions are discussed in detail. It is shown that for the asymmetric angle around 0, the existence of transverse (either open or breathing) crack has attenuation effect upon the instability regions. Under certain crack depth, the instability regions could be vanished by the transverse crack. When the asymmetric angle is around π/2, increasing the crack depth would enhance the instability regions.

  8. Buckling Analysis of Edge Cracked Sandwich Plate

    Directory of Open Access Journals (Sweden)

    Rasha Mohammed Hussein

    2016-07-01

    Full Text Available This work presents mainly the buckling load of sandwich plates with or without crack for different cases. The buckling loads are analyzed experimentally and numerically by using ANSYS 15. The experimental investigation was to fabricate the cracked sandwich plate from stainless steel and PVC to find mechanical properties of stainless steel and PVC such as young modulus. The buckling load for different aspect ratio, crack length, cracked location and plate without crack found. The experimental results were compared with that found from ANSYS program. Present of crack is decreased the buckling load and that depends on crack size, crack location and aspect ratio.

  9. Finite-Element Analysis of Crack Arrest Properties of Fiber Reinforced Composites Application in Semi-Elliptical Cracked Pipelines

    Science.gov (United States)

    Wang, Linyuan; Song, Shulei; Deng, Hongbo; Zhong, Kai

    2018-04-01

    In nowadays, repair method using fiber reinforced composites as the mainstream pipe repair technology, it can provide security for X100 high-grade steel energy long-distance pipelines in engineering. In this paper, analysis of cracked X100 high-grade steel pipe was conducted, simulation analysis was made on structure of pipes and crack arresters (CAs) to obtain the J-integral value in virtue of ANSYS Workbench finite element software and evaluation on crack arrest effects was done through measured elastic-plastic fracture mechanics parameter J-integral and the crack arrest coefficient K, in a bid to summarize effect laws of composite CAs and size of pipes and cracks for repairing CAs. The results indicate that the K value is correlated with laying angle λ, laying length L2/D1, laying thickness T1/T2of CAs, crack depth c/T1 and crack length a/c, and calculate recommended parameters for repairing fiber reinforced composite CAs in terms of two different crack forms.

  10. The effect of initiation feature and environment on fatigue crack formation and early propagation in aluminum zinc magnesium copper

    Science.gov (United States)

    Burns, James T.

    The current research provides insight into fatigue crack formation and progression in the poorly understood size regime that bridges safe-life and damage tolerance approaches; particular attention is given to the influences of corrosion-induced degradation and time-cycle dependent loading environment effects. Quantitative analysis of crack formation life (Ni), microstructurally small crack (database. Results show that fatigue crack formation involves a complex interaction of elastic stress concentration, due to a 3-dimensional macro-pit, coupled with local micro-feature (and constituent) induced plastic strain concentration. Such interactions cause high Ni variability, but, from an engineering perspective, a broadly corroded surface should contain an extreme group of features driving Ni to ˜0. At low-applied stresses, Ni consumes a significant portion of total life, which is well predicted by coupling elastic-plastic FEA with empirical low-cycle fatigue life models. All pristine and corroded da/dN were uniquely correlated using complex continuum stress intensity (K) and crack opening solutions which account for the stress concentrating formation feature. Multiple crack growth regimes were observed, typical of environment enhanced fatigue in Al alloys. Such behavior is not captured by prominent mechanics-based small crack models. Furthermore, neither local closure nor slip-based models captured the order of magnitude variability in da/dN attributed to microstructure. Low temperature loading produces an order of magnitude increase in Ni, and even larger reduction in da/dN, due to elimination of H-enhanced cracking by reduced external water vapor pressure, lower crack tip reaction rate (to produce atomic-H), and slower H diffusion. Engineering level modeling approaches are validated using these high fidelity experimental results, informing next generation prognosis methods for realistic airframe environments.

  11. Fatigue test results of flat plate specimens with surface cracks and evaluation of crack growth in structural components

    International Nuclear Information System (INIS)

    Shibata, Katsuyuki; Yokoyama, Norio; Ohba, Toshihiro; Kawamura, Takaichi; Miyazono, Shohachiro

    1982-12-01

    Part-through surface cracks are most frequently observed in the inspection of structural components, and it is one of the important subjects in the assessment of safety to evaluate appropriately the growth of such cracks during the service life of structural components. Due to the complexity of the stress at the front free surface, the crack growth at the surface shows a different behavior from the other part. Besides, an effect of interaction is caused in the growth of multiple surface cracks. These effects should be included in the growth analysis of surface part-through cracks. Authors have carried out a series of fatigue tests on some kinds of pipes with multiple cracks in the inner surface, and subsequently the fatigue test of flat plate specimens, made of Type 304L stainless steel, with a single or double surface cracks was carried out to study the basic characteristics in the growth of multiple surface cracks. Based on the results of the flat plate test. the correction factors for the front free surface (Cs) and interaction (Ci) of surface cracks were derived quantitatively by the following empirical expressions; Cs = 0.824. Ci = (0.227(a/b) 2 (sec(PI X/2) - 1) + 1)sup(1/m). Using these two correction factors, a procedure to predict the growth of surface cracks was developed by applying the crack growth formula to both the thickness and surface directions. Besides, the crack growth predictions based on the procedure of ASME Code Sex. XI, and the above procedure without the correction of the free surface and interactions on the crack growth behaviors were compared with the test results of flat plate specimens. The crack growth behavior predicted by the procedure described in this report showed the best agreement with the test results in respects of the crack growth life and the change in the crack shape. The criteria of the ASME Code did not agree with the test results. (author)

  12. Dynamic ductile fracture of a central crack

    Science.gov (United States)

    Tsai, Y. M.

    1976-01-01

    A central crack, symmetrically growing at a constant speed in a two dimensional ductile material subject to uniform tension at infinity, is investigated using the integral transform methods. The crack is assumed to be the Dugdale crack, and the finite stress condition at the crack tip is satisfied during the propagation of the crack. Exact expressions of solution are obtained for the finite stress condition at the crack tip, the crack shape, the crack opening displacement, and the energy release rate. All those expressions are written as the product of explicit dimensional quantities and a nondimensional dynamic correction function. The expressions reduce to the associated static results when the crack speed tends to zero, and the nondimensional dynamic correction functions were calculated for various values of the parameter involved.

  13. Fatigue crack propagation behavior under creep conditions

    International Nuclear Information System (INIS)

    Ohji, Kiyotsugu; Kubo, Shiro

    1991-01-01

    The crack propagation behavior of the SUS 304 stainless steel under creep-fatigue conditions was reviewed. Cracks propagated either in purely time-dependent mode or in purely cycle-dependent mode, depending on loading conditions. The time-dependent crack propagation rate was correlated with modified J-integral J * and the cycle-dependent crack propagation rate was correlated with J-integral range ΔJ f . Threshold was observed in the cycle-dependent crack propagation, and below this threshold the time-dependent crack propagation appeared. The crack propagation rates were uniquely characterized by taking the effective values of J * and ΔJ f , when crack closure was observed. Change in crack propagation mode occurred reversibly and was predicted by the competitive damage model. The threshold disappeared and the cycle-dependent crack propagation continued in a subthreshold region under variable amplitude conditions, where the threshold was interposed between the maximum and minimum ΔJ f . (orig.)

  14. 3D experimental and numerical study of fatigue of a slanted crack path in a thin sheet

    International Nuclear Information System (INIS)

    Esnault, Jean-Baptiste

    2014-01-01

    Propagation of fatigue cracks in 7075-T6 aluminum and S355 steel were experimentally characterized in air and in a corrosive solution in a CCP specimen. A technique of crack front marking, coupled with a 3D topographic reconstruction of the crack, allowed to characterize the three-dimensional crack path and the crack growth rate at any point of the crack front. Transverse and longitudinal profiles at different propagation stages were used to calculate the twist and tilt angle. In an elastic XFEM framework, stress intensity factors I, II and III, were calculated. While the correlation of experimental crack growth rate with ΔKI is unsatisfactory, the correlation is correct with ΔKeq emphasizing the major contribution of shear modes to the crack driving force. A finite element analysis in elasto plasticity coupled with the application of a local fatigue criterion, which depend on the equivalent plastic strain ahead of the crack front, was qualitatively able to predict the shear lips growth. A modification of the XFEM method is proposed to improve computations with cyclic plasticity. This part is based on an analytical study which suggests to replace the discontinuous 'Heaviside' enrichment by a new continuous enrichment in the elements cut by the crack. The sub-division of the elements cut by the crack, inducing a field projection of the internal variables which introduces an error in the numerical computations, is thus avoided. Convergence test cases show the potentiality of this method. (author)

  15. Cracking in Drying Colloidal Films

    Science.gov (United States)

    Singh, Karnail B.; Tirumkudulu, Mahesh S.

    2007-05-01

    It has long been known that thick films of colloidal dispersions such as wet clays, paints, and coatings crack under drying. Although capillary stresses generated during drying have been recently identified as the cause for cracking, the existence of a maximum crack-free film thickness that depends on particle size, rigidity, and packing has not been understood. Here, we identify two distinct regimes for crack-free films based on the magnitude of compressive strain at the maximum attainable capillary pressure and show remarkable agreement of measurements with our theory. We anticipate our results to not only form the basis for design of coating formulations for the paints, coatings, and ceramics industry but also assist in the production of crack-free photonic band gap crystals.

  16. Recent advances in modelling creep crack growth

    International Nuclear Information System (INIS)

    Riedel, H.

    1988-08-01

    At the time of the previous International Conference on Fracture, the C* integral had long been recognized as a promising load parameter for correlating crack growth rates in creep-ductile materials. The measured crack growth rates as a function of C* and of the temperature could be understood on the basis of micromechanical models. The distinction between C*-controlled and K I -controlled creep crack growth had been clarified and first attempts had been made to describe creep crack growth in the transient regime between elastic behavior and steady-state creep. This paper describes the progress in describing transient crack growth including the effect of primary creep. The effect of crack-tip geometry changes by blunting and by crack growth on the crack-tip fields and on the validity of C* is analyzed by idealizing the growing-crack geometry by a sharp notch and using recent solutions for the notch-tip fields. A few new three-dimensional calculations of C* are cited and important theoretical points are emphasized regarding the three-dimensional fields at crack tips. Finally, creep crack growth is described by continuum-damage models for which similarity solutions can be obtained. Crack growth under small-scale creep conditions turns out to be difficult to understand. Slightly different models yield very different crack growth rates. (orig.) With 4 figs

  17. Results of crack-arrest tests on two irradiated high-copper welds

    International Nuclear Information System (INIS)

    Iskander, S.K.; Corwin, W.R.; Nanstead, R.K.

    1990-12-01

    The objective of this study was to determine the effect of neutron irradiation on the shift and shape of the lower-bound curve to crack-arrest data. Two submerged-arc welds with copper contents of 0.23 and 0.31 wt % were commercially fabricated in 220-mm-thick plate. Crack-arrest specimens fabricated from these welds were irradiated at a nominal temperature of 288 degree C to an average fluence of 1.9 x 10 19 neutrons/cm 2 (>1 MeV). Evaluation of the results shows that the neutron-irradiation-induced crack-arrest toughness temperature shift is about the same as the Charpy V-notch impact temperature shift at the 41-J energy level. The shape of the lower-bound curves (for the range of test temperatures covered) did not seem to have been altered by irradiation compared to those of the ASME K Ia curve. 9 refs., 21 figs., 10 tabs

  18. Properties influencing cracking and separation of palm nuts in a mechanical cracker cum separator

    Directory of Open Access Journals (Sweden)

    JOSHUA OLANREWAJU OLAOYE

    2018-01-01

    Full Text Available Experimental studies of some properties influencing cracking and separation of palm kernel from the shell was conducted in a palm kernel dual processing machine. A mechanical cracking cum separating machine was developed for the study. The cracking unit consists of feed hopper, impeller shaft, cracking drum and impeller blade. The nut falls by gravity through the hopper channel into the cracking drum where the cracking process takes place through the help of impeller blades that flip the palm nut against the walls of cylindrical cracking drum. The mass of cracked nut flows through the separating unit that separates the kernel from the shell. The separation is induced by high current of air mass generated by an axial fan. A dura palm variety was selected and a total sample of eighteen thousand (18000 palm nuts were obtained and divided into two groups (feed rates, A and B, of eight thousand and ten thousand palm nuts respectively. Sample groups A and B were further divided into five sub – groups of four hundred (400 and five hundred (500 palm kernel nuts. Each sub group (feed rate was replicated four times at different shaft speeds (600, 900, 1200, 1500 and 1800 rpm. Results showed that cracking efficiencies increased with respect to speed. Un-cracked nuts percentage ranged from 1.3 to 5.3% at 7.1% moisture content, and 1.6 to 4.5% for 400 and 500 feed rates, respectively. Cracking time for both feed rates decreased with shaft speed. Throughput capacity of 11.49 kg/h was observed to be the lowest at 600 rpm and moisture content of 7.1% for both 400 feed rates and the highest throughput capacity of 37.16 kg/h was recorded at 1800 rpm at moisture contents of 9.3% and 16.1%. The results of this study shows that moisture content, engine speed and feed rate are significant parameters that influence cracking of nuts and separation of palm kernel from the shell.

  19. Combined effect of high curing temperature and crack width on chloride migration in reinforced concrete beams

    Science.gov (United States)

    Elkedrouci, L.; Diao, B.; Pang, S.; Li, Y.

    2018-03-01

    Deterioration of reinforced concrete structures is a serious concern in the construction engineering, largely due to chloride induced corrosion of reinforcement. Chloride penetration is markedly influenced by one or several major factors at the same time such as cuing in combination with different crack widths which have spectacular effect on reinforced concrete structures. This research presents the results of an experimental investigation involving reinforced concrete beams with three different crack widths ranging from 0 to 0.2mm, curing temperatures of 20°C or 40°C and water-to-cement of 0.5. Chloride content profiles were determined under non-steady state diffusion at 20°C. Based on the obtained results, higher chloride content was obtained under condition of high curing temperature in combination with large crack more than 0.1mm and there are no significant differences between narrow crack width (less than 0.1 mm) and beams without crack (0 mm).

  20. Transenamel and transdentinal penetration of hydrogen peroxide applied to cracked or microabrasioned enamel.

    Science.gov (United States)

    Briso, A L F; Lima, A P B; Gonçalves, R S; Gallinari, M O; dos Santos, P H

    2014-01-01

    The present study evaluated transenamel and transdentinal penetration of hydrogen peroxide during tooth whitening recognized in altered enamel by the presence of cracks or microabrasion. We used 72 experimental units (n=20) obtained from bovine incisors: GI-sound enamel; GII-teeth showing visible enamel cracks (4 mm to 5.7 mm in length); and GIII-microabrasioned enamel. The 12 remaining specimens were used to analyze the enamel surface morphology using scanning electron microscopy. The specimens were cylindrical and 5.7 mm in diameter and 3.5 mm thick. A product based on 35% hydrogen peroxide was used for bleaching, following the manufacturer's recommendations for use. To quantify the H2O2 penetration, the specimens were placed in artificial pulp chambers containing an acetate buffer solution. After bleaching, the solution was collected and adequately proportioned with leucocrystal violet, peroxidase enzyme, and deionized water. The resulting solution was evaluated using ultraviolet visible reflectance spectrophotometer equipment. The data were analyzed by analysis of variance (ANOVA) and Fisher's PLSD at a significance level of 0.05, and significant differences in the penetration of peroxide in different substrate conditions were observed (penamel was microabraded showed intermediate values when compared to the control group. Microabrasion and the presence of cracks in the enamel make this substrate more susceptible to penetration of hydrogen peroxide during in-office whitening.

  1. Effects of loading variables on fatigue-crack growth in liquid-metal environments

    CSIR Research Space (South Africa)

    Fernandes, PJL

    1995-10-01

    Full Text Available Liquid-metal-induced embrittlement (LMIE) refers to the loss of ductility in normally ductile metals and alloys when stressed while in contact with a liquid metal. In this study, the fatigue crack growth behaviour of brass in molten gallium...

  2. Atmospheric-Induced Stress Corrosion Cracking of Grade 2205 Duplex Stainless Steel—Effects of 475 °C Embrittlement and Process Orientation

    Directory of Open Access Journals (Sweden)

    Cem Örnek

    2016-07-01

    Full Text Available The effect of 475 °C embrittlement and microstructure process orientation on atmospheric-induced stress corrosion cracking (AISCC of grade 2205 duplex stainless steel has been investigated. AISCC tests were carried out under salt-laden, chloride-containing deposits, on U-bend samples manufactured in rolling (RD and transverse directions (TD. The occurrence of selective corrosion and stress corrosion cracking was observed, with samples in TD displaying higher propensity towards AISCC. Strains and tensile stresses were observed in both ferrite and austenite, with similar magnitudes in TD, whereas, larger strains and stresses in austenite in RD. The occurrence of 475 °C embrittlement was related to microstructural changes in the ferrite. Exposure to 475 °C heat treatment for 5 to 10 h resulted in better AISCC resistance, with spinodal decomposition believed to enhance the corrosion properties of the ferrite. The austenite was more susceptible to ageing treatments up to 50 h, with the ferrite becoming more susceptible with ageing in excess of 50 h. Increased susceptibility of the ferrite may be related to the formation of additional precipitates, such as R-phase. The implications of heat treatment at 475 °C and the effect of process orientation are discussed in light of microstructure development and propensity to AISCC.

  3. Crack growth by micropore coalescence at high temperatures

    International Nuclear Information System (INIS)

    Beere, W.

    1981-01-01

    At high temperatures in the creep regime the stress distribution around a crack is different from the low temperature elastically generated distribution. The stress distribution ahead of the crack is calculated for a crack preceded by an array of growing cavities. The cavities maintain a displacement wedge ahead of the crack. When the displacement wedge is less than one-tenth the crack length the driving force for crack growth is similar to an all elastically loaded crack. When the deforming wedge exceeds the crack length the net section stress controls crack growth. An expression is derived for a crack growing by the growth and coalescence of cavities situated in the crack plane. It is predicted that at high temperatures above a critical stress intensity, the crack propagates in a brittle fashion. (author)

  4. 21 CFR 137.190 - Cracked wheat.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 2 2010-04-01 2010-04-01 false Cracked wheat. 137.190 Section 137.190 Food and... Related Products § 137.190 Cracked wheat. Cracked wheat is the food prepared by so cracking or cutting into angular fragments cleaned wheat other than durum wheat and red durum wheat that, when tested by...

  5. Dynamic Crack Branching - A Photoelastic Evaluation,

    Science.gov (United States)

    1982-05-01

    0.41 mPai and a 0.18 MPa, and predicted a theoretical kinking angle of 84°whichagreed well with experimentally measured angle. After crack kinking...Consistent crack branching’at KIb = 2.04 MPaI -i- and r = 1.3 mm verified this crack branching criterion. The crack branching angle predicted by--.’ DD

  6. Cracking of open traffic rigid pavement

    Directory of Open Access Journals (Sweden)

    Niken Chatarina

    2017-01-01

    Full Text Available The research is done by observing the growth of real structure cracking in Natar, Lampung, Indonesia compared to C. Niken’s et al research and literature study. The rigid pavement was done with open traffic system. There are two main crack types on Natar rigid pavement: cracks cross the road, and cracks spreads on rigid pavement surface. The observation of cracks was analyzed by analyzing material, casting, curing, loading and shrinkage mechanism. The relationship between these analysis and shrinkage mechanism was studied in concrete micro structure. Open traffic make hydration process occur under vibration; therefore, fresh concrete was compressed and tensioned alternately since beginning. High temperature together with compression, cement dissociation, the growth of Ca2+ at very early age leads abnormal swelling. No prevention from outside water movement leads hydration process occur with limited water which caused spreads fine cracks. Limited water improves shrinkage and plastic phase becomes shorter; therefore, rigid pavement can’t accommodate the abnormal swelling and shrinking alternately and creates the spread of cracks. Discontinuing casting the concrete makes both mix under different condition, the first is shrink and the second is swell and creates weak line on the border; so, the cracks appear as cracks across the road.

  7. Lateral rigidity of cracked concrete structures

    International Nuclear Information System (INIS)

    Castellani, A.; Chesi, C.

    1979-01-01

    Numerical results are discussed on the lateral rigidity of reinforced concrete structures with a given crack distribution. They have been favourably checked with experimental results for cylindrical shells under the effect of a thermal gradient producing vertical cracking or vertical plus horizontal cracking. The main effects characterizing the concrete behaviour are: (1) The shear transfer across a crack; (2) The shear transfer degradation after cyclic loading; (3) The tension stiffening provided by the concrete between crack and crack, in the normal stress transfer; (4) The temperature effect on the elastic moduli of concrete, when cracks are of thermal origin. Only the 1st effect is discussed on an experimental basis. Two broad cathegories of reinforced concrete structures have been investigated in this respect: shear walls of buildings and cylindrical containment structures. The main conclusions so far reached are: (1) Vertical cracks are unlikely to decrease the lateral rigidity to less than 80% of the original one, and to less than 90% when they do not involve the entire thickness of the wall; (2) The appearence of horizontal cracks can reduce the lateral rigidity by some 30% or more; (3) A noticeable but not yet evaluated influence is shown by cyclic loading. (orig.)

  8. Semi-empirical crack tip analysis

    Science.gov (United States)

    Chudnovsky, A.; Ben Ouezdon, M.

    1988-01-01

    Experimentally observed crack opening displacements are employed as the solution of the multiple crack interaction problem. Then the near and far fields are reconstructed analytically by means of the double layer potential technqiue. Evaluation of the effective stress intensity factor resulting from the interaction of the main crack and its surrounding crazes in addition to the remotely applied load is presented as an illustrative example. It is shown that crazing (as well as microcracking) may constitute an alternative mechanism to Dugdale-Berenblatt models responsible for the cancellation of the singularity at the crack tip.

  9. Prediction of pure water stress corrosion cracking (PWSCC) in nickel base alloys using crack growth rate models

    International Nuclear Information System (INIS)

    Thompson, C.D.; Krasodomski, H.T.; Lewis, N.; Makar, G.L.

    1995-01-01

    The Ford/Andresen slip dissolution SCC model, originally developed for stainless steel components in BWR environments, has been applied to Alloy 600 and Alloy X-750 tested in deaerated pure water chemistry. A method is described whereby the crack growth rates measured in compact tension specimens can be used to estimate crack growth in a component. Good agreement was found between model prediction and measured SCC in X-750 threaded fasteners over a wide range of temperatures, stresses, and material condition. Most data support the basic assumption of this model that cracks initiate early in life. The evidence supporting a particular SCC mechanism is mixed. Electrochemical repassivation data and estimates of oxide fracture strain indicate that the slip dissolution model can account for the observed crack growth rates, provided primary rather than secondary creep rates are used. However, approximately 100 cross-sectional TEM foils of SCC cracks including crack tips reveal no evidence of enhanced plasticity or unique dislocation patterns at the crack tip or along the crack to support a classic slip dissolution mechanism. No voids, hydrides, or microcracks are found in the vicinity of the crack tips creating doubt about classic hydrogen related mechanisms. The bulk oxide films exhibit a surface oxide which is often different than the oxides found within a crack. Although bulk chromium concentration affects the rate of SCC, analytical data indicates the mechanism does not result from chromium depletion at the grain boundaries. The overall findings support a corrosion/dissolution mechanism but not one necessarily related to slip at the crack tip

  10. Computation of stress intensity factors for nozzle corner cracks by various finite element procedures

    International Nuclear Information System (INIS)

    Broekhoven, M.J.G.

    1975-01-01

    The present study aims at deriving accurate K-factors for a series of 5 elliptical nozzle corner cracks of increasing size by various finite element procedures, using a three-level recursive substructuring scheme to perform the computations in an economic way on an intermediate size computer (IBM 360/65 system). A nozzle on a flat plate has been selected for subsequent experimental verification, this configuration being considered an adequate simulation of a nozzle on a shallow shell. The computations have been performed with the ASKA finite element system using mainly HEXEC-27 (incomplete quartic) elements. The geometry has been subdivided into 5 subnets with a total of 3515 nodal points and 6250 unknowns, two main nets and one hyper net. Each crack front is described by 11 nodal points and all crack front nodes are inserted in the hyper net, which allows for the realization of the successive crack geometries by changing only a relatively small hyper net (615 to 725 unknowns). Output data have been interpreted in terms of K-factors by the global energy method, the displacement method and the stress method. Besides, a stiffness derivative procedure, recently developed at Brown University, which takes full advantage of the finite element formulation to calculate local K-factors, has been applied. Finally it has been investigated whether sufficiently accurate results can be obtained by analyzing a considerably smaller part than one half of the geometry (as strictly required by symmetry considerations), using fixed boundary conditions derived from a far cheaper analysis of the uncracked structure

  11. Fracture analysis of a central crack in a long cylindrical superconductor with exponential model

    Science.gov (United States)

    Zhao, Yu Feng; Xu, Chi

    2018-05-01

    The fracture behavior of a long cylindrical superconductor is investigated by modeling a central crack that is induced by electromagnetic force. Based on the exponential model, the stress intensity factors (SIFs) with the dimensionless parameter p and the length of the crack a/R for the zero-field cooling (ZFC) and field-cooling (FC) processes are numerically simulated using the finite element method (FEM) and assuming a persistent current flow. As the applied field Ba decreases, the dependence of p and a/R on the SIFs in the ZFC process is exactly opposite to that observed in the FC process. Numerical results indicate that the exponential model exhibits different characteristics for the trend of the SIFs from the results obtained using the Bean and Kim models. This implies that the crack length and the trapped field have significant effects on the fracture behavior of bulk superconductors. The obtained results are useful for understanding the critical-state model of high-temperature superconductors in crack problem.

  12. Propagation of stress corrosion cracks in alpha-brasses

    Energy Technology Data Exchange (ETDEWEB)

    Beggs, Dennis Vinton [Univ. of Illinois, Urbana-Champaign, IL (United States)

    1981-01-01

    Transgranular and intergranular stress corrosion cracks were investigated in alpha-brasses in a tarnishing ammoniacal solution. Surface observation indicated that the transgranular cracks propagated discontinuously by the sudden appearance of a fine crack extending several microns ahead of the previous crack tip, often associated with the detection of a discrete acoustic emission (AE). By periodically increasing the deflection, crack front markings were produced on the resulting fracture surfaces, showing that the discontinuous propagation of the crack trace was representative of the subsurface cracking. The intergranular crack trace appeared to propagate continuously at a relatively blunt crack tip and was not associated with discrete AE. Under load pulsing tests with a time between pulses, Δt greater than or equal to 3 s, the transgranular fracture surfaces always exhibited crack front markings which corresponded with the applied pulses. The spacing between crack front markings, Δx, decreased linearly with Δt. With Δt less than or equal to 1.5 s, the crack front markings were in a one-to-one correspondence with applied pulses only at relatively long crack lengths. In this case, Δx = Δx* which approached a limiting value of 1 μm. No crack front markings were observed on intergranular fracture surfaces produced during these tests. It is concluded that transgranular cracking occurs by discontinuous mechanical fracture of an embrittled region around the crack tip, while intergranular cracking results from a different mechanism with cracking occurring via the film-rupture mechanism.

  13. Contribution to the study of the mechanism of crack in amorphous silica: study by the molecular dynamics of crack in amorphous silica; Contribution a l'etude des mecanismes de rupture dans les amorphes: etude par dynamique moleculaire de la rupture de verre de silice

    Energy Technology Data Exchange (ETDEWEB)

    Van Brutzel, L

    2000-07-01

    The aim of this thesis was to understand the mechanism which occurs during the crack at the atomic scale in amorphous silica. The difficulties of the experimental observations at this length scale lead us to use numerical studies by molecular dynamics to access to the dynamical and the thermodynamical informations. We have carried out large simulations with 500000 atoms and studied the structure of the amorphous silica before to studying their behaviours under an imposed strain. The structure of this simulated amorphous silica settled in three length scales. In small length scale between 0 and 5 angstrom glass is composed of tetrahedra, this is close to the crystalline structure. In intermediate length scale between 3 and 10 angstrom tetrahedra are connected together and build rings of different sizes composed in majority between 5 and 7 tetrahedra. In bigger length scale between 15 and 60 angstrom, areas with high density of rings are surrounded by areas with low density of rings. These structural considerations play an important role in initiation and propagation of a crack. Indeed. in this length scale. crack propagates by growth and coalescence of some small cavities which appear in area with low density of rings behind the crack tip. The cavities dissipate the stress with carries away a delay to propagation of the crack. This phenomenons seems ductile and leads to non linear elastic behaviour near the crack tip. We have also shown that the addition of alkali in the amorphous silica changes the structure by creation of nano-porosities and leads to enhance the ductility during the crack propagation. (author)

  14. Crack initiation behavior of neutron irradiated model and commercial stainless steels in high temperature water

    Energy Technology Data Exchange (ETDEWEB)

    Stephenson, Kale J., E-mail: kalejs@umich.edu; Was, Gary S.

    2014-01-15

    Highlights: • Environmental constant extension rate tensile tests were performed on neutron irradiated steel. • Percentage of intergranular cracking quantified the cracking susceptibility. • Cracking susceptibility varied with test environment, solute addition, and cold work. • No singular microstructural change could explain increases in cracking susceptibility with irradiation dose. • The increment of yield strength due to irradiation correlated well with cracking susceptibility. -- Abstract: The objective of this study was to isolate key factors affecting the irradiation-assisted stress corrosion cracking (IASCC) susceptibility of eleven neutron-irradiated austenitic stainless steel alloys. Four commercial purity and seven high purity stainless steels were fabricated with specific changes in composition and microstructure, and irradiated in a fast reactor spectrum at 320 °C to doses between 4.4 and 47.5 dpa. Constant extension rate tensile (CERT) tests were performed in normal water chemistry (NWC), hydrogen water chemistry (HWC), or primary water (PW) environments to isolate the effects of environment, elemental solute addition, alloy purity, alloy heat, alloy type, cold work, and irradiation dose. The irradiated alloys showed a wide variation in IASCC susceptibility, as measured by the relative changes in mechanical properties and crack morphology. Cracking susceptibility measured by %IG was enhanced in oxidizing environments, although testing in the lowest potential environment caused an increase in surface crack density. Alloys containing solute addition of Ni or Ni + Cr exhibited no IASCC. Susceptibility was reduced in materials cold worked prior to irradiation, and increased with increasing irradiation dose. Irradiation-induced hardening was accounted for by the dislocation loop microstructure, however no relation between crack initiation and radiation hardening was found.

  15. Crack tip stress and strain

    International Nuclear Information System (INIS)

    Francois, D.

    1975-01-01

    The study of potential energy variations in a loaded elastic solid containing a crack leads to determination of the crack driving force G. Generalization of this concept to cases other than linear elasticity leads to definition of the integral J. In a linear solid, the crack tip stress field is characterized by a single parameter: the stress-intensity factor K. When the crack tip plastic zone size is confined to the elastic singularity J=G, it is possible to establish relationship between these parameters and plastic strain (and in particular the crack tip opening displacement delta). The stress increases because of the triaxiality effect. This overload rises with increasing strain hardening. When the plastic zone size expands, using certain hypotheses, delta can be calculated. The plastic strain intensity is exclusively dependent on parameter J [fr

  16. Temperature and environmentally assisted cracking in low alloy steel

    International Nuclear Information System (INIS)

    Auten, T.A.; Monter, J.V.

    1995-01-01

    Environmentally assisted cracking (EAC) can be defined as the propagation of fatigue cracks in water at rates that are anywhere from 3 to over 40 times the growth rates expected in air. In the present work, five ASTM A 508 Class 2 forgings with ladle and check analyses that ranged from 0.010 to 0.019 wt% S were tested in high purity deaerated water in the temperature range of 93 to 260 C. At 260 C these forgings did not undergo EAC, reinforcing earlier results for two similar forgings. This broad sampling indicates a strong resistance to EAC for this class of forging at 260 C. On the other hand, EAC occurred consistently in the three of these forgings that were tested below 204 C, provided the test conditions were high enough to produce a high baseline fatigue crack growth rate (FCGR), where the baseline FCGR is that expected in air. At 149 C, EAC occurred at test conditions that combined to yield a baseline FCGR greater than ∼2E-6 mm/s. At 204, 121, and 93 C, this ''critical crack growth rate'' appeared to shift to lower baseline values. The EAC that occurred at lower temperatures was a factor of 3 to 12 times higher than baseline air rates, which was not as strong as the effect for higher sulfur steels at 240 to 290 C. Also, no plateau in the growth rates occurred as it does with the higher sulfur steels. In another approach, EAC was induced at 93 and at 260 C by raising the dissolved oxygen content of the water from 15 ppb. In this case, the EAC growth rates decreased to non-EAC levels when the oxygen supply was shut off. The oxygen-related EAC occurred over a broader range of baseline growth rates than found for the EAC driven by the baseline crack tip speed. Again, this can be rationalized by the buildup of sulfur in the crack tip water, which can be associated with the higher corrosion potential of the bulk water

  17. Evaluation of the probability of crack initiation and crack instability for a pipe with a semi-elliptical crack

    International Nuclear Information System (INIS)

    Le Delliou, P.; Hornet, P.

    2001-01-01

    This paper presents some work conducted at EDF R and D Division to evaluate the probability that a semi-elliptical crack in a pipe not only initiates but also propagates when submitted to mechanical loading such as bending and pressure combined or not with a thermal shock. The first part is related to the description of the mechanical model: the simplified methods included in the French RSE-M Code used to evaluate the J-integral as well as the principle of the determination of the crack propagation. Then, the way this deterministic approach is combined to a reliability code is described. Finally, an example is shown: the initiation and the instability of a semi-elliptical crack in a pipe submitted to combined pressure and bending moment. (author)

  18. An electro-mechanical impedance model of a cracked composite beam with adhesively bonded piezoelectric patches

    Science.gov (United States)

    Yan, Wei; Cai, J. B.; Chen, W. Q.

    2011-01-01

    A model of a laminated composite beam including multiple non-propagating part-through surface cracks as well as installed PZT transducers is presented based on the method of reverberation-ray matrix (MRRM) in this paper. Toward determining the local flexibility characteristics induced by the individual cracks, the concept of the massless rotational spring is applied. A Timoshenko beam theory is then used to simulate the behavior of the composite beam with open cracks. As a result, transverse shear and rotatory inertia effects are included in the model. Only one-dimensional axial vibration of the PZT wafer is considered and the imperfect interfacial bonding between PZT patches and the host beam is further investigated based on a Kelvin-type viscoelastic model. Then, an accurate electro-mechanical impedance (EMI) model can be established for crack detection in laminated beams. In this model, the effects of various parameters such as the ply-angle, fibre volume fraction, crack depth and position on the EMI signatures are highlighted. Furthermore, comparison with existent numerical results is presented to validate the present analysis.

  19. Cocaine (Coke, Crack) Facts

    Science.gov (United States)

    ... That People Abuse » Cocaine (Coke, Crack) Facts Cocaine (Coke, Crack) Facts Listen Cocaine is a white ... 69 KB) "My life was built around getting cocaine and getting high." ©istock.com/ Marjot Stacey is ...

  20. CRACK2 - Modelling calcium carbonate deposition from bicarbonate solution in cracks in concrete

    International Nuclear Information System (INIS)

    Brodersen, K.

    2003-03-01

    The numerical CRACK2 model simulates precipitation of calcite from calcium bicarbonate solution (e.g. groundwater) passing through cracks in concrete or other cementitious materials. A summary of experimental work is followed by a detailed description of the model. Hydroxyl ions are transported by diffusion in pore systems in columns of cementitious materials. The hydroxyl is precipitating calcite from a flow of bicarbonate solution in a crack connecting the ends of a row of such columns. The cementitious material is simulated as calcium hydroxide mixed with inert material but with sodium hydroxide dissolved in the pore solution. Diffusive migration of cesium as radioactive isotope is also considered. Electrical interaction of the migrating ions is taken into account. Example calculations demonstrate effects of parameter variations on distribution of precipitated calcite in the crack and on the composition of the outflowing solution, which can be compared directly with experimental results. Leaching behavior of sodium can be used to tune the model to experimental observations. The calcite is mostly precipitated on top of the original crack surface and may under certain circumstances fill the crack. The produced thin layers of low porosity calcite act as a diffusion barrier limiting contact between cement and solution. Pore closure mechanisms in such layers are discussed. Implications for safety assessment of radioactive waste disposal are shortly mentioned. The model is also relevant for conventional uses of concrete. (au)

  1. Assessment of cracking in dissimilar metal welds

    International Nuclear Information System (INIS)

    Jenssen, Anders; Norrgaard, K.; Lagerstroem, J.; Embring, G.; Tice, D.R.

    2001-08-01

    During the refueling in 2000, indications were observed by non-destructive testing at four locations in the reactor pressure vessel (RPV) nozzle to safe end weld in Ringhals 4. All indications were confined to the outlet nozzle (hotleg) oriented at 25 deg, a nozzle with documented repair welding. Six boat samples were removed from the four locations, and the samples were subsequently subjected to a metallographic examination. The objectives were to establish the fracture morphology, and if possible the root cause for cracking. The examination revealed that cracks were present at all four boat sample locations and that they all were confined to the weld metal, alloy 182. Cracking extended in the axial direction of the safe-end. There was no evidence of any cracks extending into the RPV-steel, or the stainless steel safe-end. All cracking was interdendritic and significantly branched. Among others, these observations strongly suggested crack propagation mainly was caused by interdendritic stress corrosion cracking. In addition, crack type defects and isolated areas on the fracture surfaces suggested the presence of hot cracking, which would have been formed during fabrication. The reason for crack initiation could not be established based on the boat samples examined. However, increased stress levels due to repair welding, cold work from grinding, and defects produced during fabrication, e. g. hot cracks, may alone or in combination have contributed to crack initiation

  2. Detection of an ylide intermediate in the electrochemically-induced Stevens rearrangement of an ammonium salt by in situ UV–vis spectroelectrochemistry

    International Nuclear Information System (INIS)

    Capobianco, Amedeo; Caruso, Tonino; Palombi, Laura; Peluso, Andrea

    2013-01-01

    Highlights: ► Mechanistic insights of the electro-induced Stevens rearrangement are provided. ► The reduction of PhCOCH 2 N + (CH 3 ) 2 CH 2 Ph is ascribed to a one-electron transfer process. ► An electrogenerated ammonium ylide has been detected by UV-spectroelectrochemistry. -- Abstract: The electrochemically-induced Stevens rearrangement of 2-(benzyldimethyl)ammonium acetophenone has been investigated by in situ UV–vis spectroelectrochemistry. Voltammetric analysis and absorption spectra recorded during the potentiostatic reduction indicate that the reaction proceeds via a one-electron transfer with a Platinum cathode and generation of an ammonium ylide intermediate

  3. Seismic behaviour of un-cracked and cracked thin pipes

    International Nuclear Information System (INIS)

    Blay, N.; Brunet, G.; Gantenbein, F.; Aguilar, J.

    1995-01-01

    In order to evaluate the seismic behaviour of un-cracked and cracked thin pipes, subjected to high acceleration levels, seismic tests and calculations have been performed on straight thin pipes made of 316L stainless steel, loaded in pure bending by a permanent static and dynamic loading. The seismic tests were carried out on the AZALEE shaking table of the CEA laboratory TAMARIS. The influence of the elasto-plastic model with isotropic or kinematic hardening are studied. 5 refs., 7 figs., 2 tabs

  4. Dislocation model of a subsurface crack

    International Nuclear Information System (INIS)

    Yang, F.; Li, J.C.

    1997-01-01

    A dislocation model of a subsurface crack parallel to the surface is presented. For tensile loading, the results agree with those of previous workers except that we studied the crack very close to the surface and found that K II (mode II stress intensity factor) approaches K I (mode I stress intensity factor) to within about 22% (K II =0.78K I ). (Note that K II is zero when the crack is far away from the surface). Using bending theory for such situations, it is found that both stress intensity factors are inversely proportional to the 3/2 power of the distance between the subsurface crack and the free surface. For shear loading, the crack faces overlap each other for the free traction condition. This indicates the failure of the model. However, there was no overlap for tensile loading even though the stresses in front of the crack oscillate somewhat when the crack is very close to the surface. copyright 1997 American Institute of Physics

  5. Effect of pre-strain on creep of three AISI 316 austenitic stainless steels in relation to reheat cracking of weld-affected zones

    Science.gov (United States)

    Auzoux, Q.; Allais, L.; Caës, C.; Monnet, I.; Gourgues, A. F.; Pineau, A.

    2010-05-01

    Microstructural modifications induced by welding of 316 stainless steels and their effect on creep properties and relaxation crack propagation were examined. Cumulative strain due to multi-pass welding hardens the materials by increasing the dislocation density. Creep tests were conducted on three plates from different grades of 316 steel at 600 °C, with various carbon and nitrogen contents. These plates were tested both in the annealed condition and after warm rolling, which introduced pre-strain. It was found that the creep strain rate and ductility after warm rolling was reduced compared with the annealed condition. Moreover, all steels exhibited intergranular crack propagation during relaxation tests on Compact Tension specimens in the pre-strained state, but not in the annealed state. These results confirmed that the reheat cracking risk increases with both residual stress triaxiality and pre-strain. On the contrary, high solute content and strain-induced carbide precipitation, which are thought to increase reheat cracking risk of stabilised austenitic stainless steels did not appear as key parameters in reheat cracking of 316 stainless steels.

  6. Hydrogen assisted cracking and CO2 corrosion behaviors of low-alloy steel with high strength used for armor layer of flexible pipe

    Science.gov (United States)

    Liu, Zhenguang; Gao, Xiuhua; Du, Linxiu; Li, Jianping; Zhou, Xiaowei; Wang, Xiaonan; Wang, Yuxin; Liu, Chuan; Xu, Guoxiang; Misra, R. D. K.

    2018-05-01

    In this study, hydrogen induced cracking (HIC), sulfide stress corrosion cracking (SSCC) and hydrogen embrittlement (HE) were carried out to study hydrogen assisted cracking behavior (HIC, SSCC and HE) of high strength pipeline steel used for armor layer of flexible pipe in ocean. The CO2 corrosion behavior of designed steel with high strength was studied by using immersion experiment. The experimental results demonstrate that the corrosion resistance of designed steel with tempered martensite to HIC, SSCC and HE is excellent according to specific standards, which contributes to the low concentration of dislocation and vacancies previously formed in cold rolling process. The corrosion mechanism of hydrogen induced cracking of designed steel, which involves in producing process, microstructure and cracking behavior, is proposed. The designed steel with tempered martensite shows excellent corrosion resistance to CO2 corrosion. Cr-rich compound was first formed on the coupon surface exposed to CO2-saturated brine condition and chlorine, one of the corrosion ions in solution, was rich in the inner layer of corrosion products.

  7. Effect of pre-strain on creep of three AISI 316 austenitic stainless steels in relation to reheat cracking of weld-affected zones

    International Nuclear Information System (INIS)

    Auzoux, Q.; Allais, L.; Caes, C.; Monnet, I.; Gourgues, A.F.; Pineau, A.

    2010-01-01

    Microstructural modifications induced by welding of 316 stainless steels and their effect on creep properties and relaxation crack propagation were examined. Cumulative strain due to multi-pass welding hardens the materials by increasing the dislocation density. Creep tests were conducted on three plates from different grades of 316 steel at 600 deg. C, with various carbon and nitrogen contents. These plates were tested both in the annealed condition and after warm rolling, which introduced pre-strain. It was found that the creep strain rate and ductility after warm rolling was reduced compared with the annealed condition. Moreover, all steels exhibited intergranular crack propagation during relaxation tests on Compact Tension specimens in the pre-strained state, but not in the annealed state. These results confirmed that the reheat cracking risk increases with both residual stress triaxiality and pre-strain. On the contrary, high solute content and strain-induced carbide precipitation, which are thought to increase reheat cracking risk of stabilised austenitic stainless steels did not appear as key parameters in reheat cracking of 316 stainless steels.

  8. Steady-state propagation of interface corner crack

    DEFF Research Database (Denmark)

    Veluri, Badrinath; Jensen, Henrik Myhre

    2013-01-01

    Steady-state propagation of interface cracks close to three-dimensional corners has been analyzed. Attention was focused on modeling the shape of the interface crack front and calculating the critical stress for steady-state propagation of the crack. The crack propagation was investigated...... on the finite element method with iterative adjustment of the crack front to estimate the critical delamination stresses as a function of the fracture criterion and corner angles. The implication of the results on the delamination is discussed in terms of crack front profiles and the critical stresses...... for propagation and the angle of intersection of the crack front with the free edge....

  9. Reference-free fatigue crack detection using nonlinear ultrasonic modulation under various temperature and loading conditions

    Science.gov (United States)

    Lim, Hyung Jin; Sohn, Hoon; DeSimio, Martin P.; Brown, Kevin

    2014-04-01

    This study presents a reference-free fatigue crack detection technique using nonlinear ultrasonic modulation. When low frequency (LF) and high frequency (HF) inputs generated by two surface-mounted lead zirconate titanate (PZT) transducers are applied to a structure, the presence of a fatigue crack can provide a mechanism for nonlinear ultrasonic modulation and create spectral sidebands around the frequency of the HF signal. The crack-induced spectral sidebands are isolated using a combination of linear response subtraction (LRS), synchronous demodulation (SD) and continuous wavelet transform (CWT) filtering. Then, a sequential outlier analysis is performed on the extracted sidebands to identify the crack presence without referring any baseline data obtained from the intact condition of the structure. Finally, the robustness of the proposed technique is demonstrated using actual test data obtained from simple aluminum plate and complex aircraft fitting-lug specimens under varying temperature and loading variations.

  10. Crack Cocaine-Induced Cardiac Conduction Abnormalities Are Reversed by Sodium Bicarbonate Infusion

    Directory of Open Access Journals (Sweden)

    Carlos Henrique Miranda

    2013-01-01

    Full Text Available We report a dramatic case of a 19-year-old man with crack cocaine overdose with important clinical complications as cardiac arrest due to ventricular fibrillation and epileptics status. During this intoxication, electrocardiographic abnormalities similar to those found in tricyclic antidepressant poisoning were observed, and they were reversed by intravenous sodium bicarbonate infusion.

  11. Crack closure, a literature study

    Science.gov (United States)

    Holmgren, M.

    1993-08-01

    In this report crack closure is treated. The state of the art is reviewed. Different empirical formulas for determining the crack closure are compared with each other, and their benefits are discussed. Experimental techniques for determining the crack closure stress are discussed, and some results from fatigue tests are also reported. Experimental data from the literature are reported.

  12. Finite element simulation for creep crack growth

    International Nuclear Information System (INIS)

    Miyazaki, Noriyuki; Sasaki, Toru; Nakagaki, Michihiko; Brust, F.W.

    1992-01-01

    A finite element method was applied to a generation phase simulation of creep crack growth. Experimental data on creep crack growth in a 1Cr-1Mo-1/4V steel compact tension specimen were numerically simulated using a node-release technique and the variations of various fracture mechanics parameters such as CTOA, J, C * and T * during creep crack growth were calculated. The path-dependencies of the integral parameters J, C * and T * were also obtained to examine whether or not they could characterize the stress field near the tip of a crack propagating under creep condition. The following conclusions were obtained from the present analysis. (1) The J integral shows strong path-dependency during creep crack growth, so that it is does not characterize creep crack growth. (2) The C * integral shows path-dependency to some extent during creep crack growth even in the case of Norton type steady state creep law. Strictly speaking, we cannot use it as a fracture mechanics parameter characterizing creep crack growth. It is, however, useful from the practical viewpoint because it correlates well the rate of creep crack growth. (3) The T * integral shows good path-independency during creep crack growth. Therefore, it is a candidate for a fracture mechanics parameter characterizing creep crack growth. (author)

  13. Intermediate inflation in a generalized induced-gravity scenario

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez, Carlos [Universidad de Atacama, Departamento de Fisica, Copiapo (Chile); Herrera, Ramon [Pontificia Universidad Catolica de Valparaiso, Instituto de Fisica, Valparaiso (Chile)

    2017-09-15

    An intermediate inflationary Universe model in the context of non-minimal coupling to the scalar curvature is analyzed. We will conduct our analysis in the slow-roll approximation of the inflationary dynamics and the cosmological perturbations considering a coupling of the form F(φ) = κ + ξ{sub n}φ{sup n}. Considering the trajectories in the r-n{sub s} plane from the Planck data, we find the constraints on the parameter space in our model. (orig.)

  14. Probabilistic fracture mechanics of nuclear structural components. Consideration of transition from embedded crack to surface crack

    International Nuclear Information System (INIS)

    Yagawa, Genki; Yoshimura, Shinobu; Kanto, Yasuhiro

    1998-01-01

    This paper describes a probabilistic fracture mechanics (PFM) analysis of aged nuclear reactor pressure vessel (RPV) material. New interpolation formulas are first derived for both embedded elliptical surface cracks and semi-elliptical surface cracks. To investigate effects of transition from embedded crack to surface crack in PFM analyses, one of PFM round-robin problems set by JSME-RC111 committee, i.e. 'aged RPV under normal and upset operating conditions' is solved, employing the interpolation formulas. (author)

  15. Crack Propagation by Finite Element Method

    Directory of Open Access Journals (Sweden)

    Luiz Carlos H. Ricardo

    2018-01-01

    Full Text Available Crack propagation simulation began with the development of the finite element method; the analyses were conducted to obtain a basic understanding of the crack growth. Today structural and materials engineers develop structures and materials properties using this technique. The aim of this paper is to verify the effect of different crack propagation rates in determination of crack opening and closing stress of an ASTM specimen under a standard suspension spectrum loading from FDandE SAE Keyhole Specimen Test Load Histories by finite element analysis. To understand the crack propagation processes under variable amplitude loading, retardation effects are observed

  16. Computational uncertainties in silicon dioxide/plutonium intermediate neutron spectrum systems

    International Nuclear Information System (INIS)

    Jaegers, P.J.

    1997-01-01

    In the past several years, several proposals have been made for the long-term stabilization and storage of surplus fissile materials. Many of these proposed scenarios involve systems that have an intermediate neutron energy spectrum. Such intermediate-energy systems are dominated by scattering and fission events induced by neutrons ranging in energy from 1 eV to 100keV. To ensure adequate safety margins and cost effectiveness, it is necessary to have benchmark data for these intermediate-energy spectrum systems; however, a review of the nuclear criticality benchmarks indicates that no formal benchmarks are available. Nuclear data uncertainties have been reported for some types of intermediate-energy spectrum systems. Using a variety of Monte Carlo computer codes and cross-section sets, reported significant variations in the calculated k ∞ of intermediate-energy spectrum metal/ 235 U systems. We discuss the characteristics of intermediate neutron spectrum systems and some of the computational differences that can occur in calculating the k eff of these systems

  17. Application of acoustic emission to hydride cracking

    International Nuclear Information System (INIS)

    Sagat, S.; Ambler, J.F.R.; Coleman, C.E.

    1986-07-01

    Acoustic emission has been used for over a decade to study delayed hydride cracking (DHC) in zirconium alloys. At first acoustic emission was used primarily to detect the onset of DHC. This was possible because DHC was accompanied by very little plastic deformation of the material and furthermore the amplitudes of the acoustic pulses produced during cracking of the brittle hydride phase were much larger than those from dislocation motion and twinning. Acoustic emission was also used for measuring crack growth when it was found that for a suitable amplitude threshold, the total number of acoustic emission counts was linearly related to the cracked area. Once the proportionality constant was established, the acoustic counts could be converted to the crack length. Now the proportionality between the count rate and the crack growth rate is used to provide feedback between the crack length and the applied load, using computer technology. In such a system, the stress at the crack tip can be maintained constant during the test by adjusting the applied load as the crack progresses, or it can be changed in a predetermined manner, for example, to measure the threshold stress for cracking

  18. Fatigue-crack propagation behavior of steels in vacuum, and implications for ASME Section 11 crack growth analyses

    International Nuclear Information System (INIS)

    James, L.A.

    1985-08-01

    Section XI of the ASME Boiler and Pressure Vessel Code provides rules for the analysis of structures for which cracks or crack-like flaws have been discovered during inservice inspection. The Code provides rules for the analysis of both surface flaws as well as flaws that are embedded within the wall of the pressure vessel. In the case of surface flaws, the Code provides fatigue crack growth rate relationships for typical nuclear pressure vessel steels (e.g., ASTM A508-2 and A533-B) cycled in water environments typical of those in light-water reactors (LWR). However, for the case of embedded cracks, the Code provides crack growth relationships based on results from specimens that were cycled in an elevated temperature air environment. Although these latter relationships are often referred to as applying to ''inert'' environments, the results of this paper will show that an elevated temperature air environment is anything but inert, and that use of such relationships can result in overly pessimistic estimates of fatigue-crack growth lifetimes of embedded cracks. The reason, of course, is that embedded cracks grow in an environment that is probably much closer to a vacuum than an air environment

  19. Operation and maintenance manual addendum to Westinghouse OMM-051-00-005 for intermediate-size inducer pump (ISIP) Model 266

    International Nuclear Information System (INIS)

    1979-01-01

    This Addendum A to the Westinghouse Operation and Maintenance Manual OMM-051-00-005 contains additions, changes and deletions that modify data for the Liquid Metal Coolant Pump, Model LMP-1 to data applicable to the Rockwell International Intermediate-Size Inducer Pump (ISIP), Model 266. The major modifications on the ISIP are the new impeller/inducer assembly, diffuser vanes and new securing hardware. The paragraphs affected by Addendum A use the numbering system used in OMM-051-00-005 except each paragraph number is prefixed with an A preceding the paragraph number signifying that the paragraph is changed to conform with the ISIP configuration. Paragraphs within OMM-051-00-005 not identified in Addendum A remain unchanged with the data still valid and useable

  20. Effects of microstructure and local mechanical fields on intergranular stress corrosion cracking of a friction stir welded aluminum–copper–lithium 2050 nugget

    International Nuclear Information System (INIS)

    Dhondt, Matthieu; Aubert, Isabelle; Saintier, Nicolas; Olive, Jean Marc

    2014-01-01

    Highlights: • Applied stress changes the corrosion mode from pitting to intergranular cracking. • Residual stresses are sufficient to induce intergranular stress corrosion cracking. • Effect of crystallographic texture on the development of IGSCC evidenced by EBSD. • Cubic elasticity drives the local orientation of the intergranular cracking. • Tomography observations show the 3D nature of the corrosion development. - Abstract: The effects of the microstructure and mechanical fields on intergranular stress corrosion cracking (IGSCC) of the nugget zone of heat treated welds obtained by friction stir welding in the AA2050 aluminum alloy have been investigated at different scales. At low strain rate, in 1.0 NaCl aqueous solution, IGSCC develops in the microstructure, whereas only pitting corrosion is observed without any mechanical stress. Based on surface observations, EBSD analysis and X-ray tomography, the key role of sub-millimetric textured bands (induced by the welding process) on the IGSCC is demonstrated. Analyses at a more local scale show the grain boundary (low angle boundary, special coincident site lattice boundary or high angle boundary) do not have a significant effect on crack initiation. Crystal plasticity finite element calculations show that the threshold normal stress at grain boundaries for IGSCC development is about 80% of the macroscopic stress. It is also highlighted by crystal plasticity calculations that there is a drastic effect of the local stress field on the shape of cracks. Finally, it is shown that plasticity induced residual stresses are sufficient for the formation of IGSCC

  1. Crack tip fracture toughness of base glasses for dental restoration glass-ceramics using crack opening displacements.

    Science.gov (United States)

    Deubener, J; Höland, M; Höland, W; Janakiraman, N; Rheinberger, V M

    2011-10-01

    The critical stress intensity factor, also known as the crack tip toughness K(tip), was determined for three base glasses, which are used in the manufacture of glass-ceramics. The glasses included the base glass for a lithium disilicate glass-ceramic, the base glass for a fluoroapatite glass-ceramic and the base glass for a leucite glass-ceramic. These glass-ceramic are extensively used in the form of biomaterials in restorative dental medicine. The crack tip toughness was established by using crack opening displacement profiles under experimental conditions. The crack was produced by Vickers indentation. The crack tip toughness parameters determined for the three glass-ceramics differed quite significantly. The crack tip parameters of the lithium disilicate base glass and the leucite base glass were higher than that of the fluoroapatite base glass. This last material showed glass-in-glass phase separation. The discussion of the results clearly shows that the droplet glass phase is softer than the glass matrix. Therefore, the authors conclude that a direct relationship exists between the chemical nature of the glasses and the crack tip parameter. Copyright © 2011 Elsevier Ltd. All rights reserved.

  2. Probabilistic fracture mechanics of nuclear structural components: consideration of transition from embedded crack to surface crack

    International Nuclear Information System (INIS)

    Yagawa, G.; Yoshimura, S.

    1999-01-01

    This paper describes a probabilistic fracture mechanics (PFM) analysis of aged nuclear reactor pressure vessel (RPV) material. New interpolation formulas of three-dimensional stress intensity factors are presented for both embedded elliptical surface cracks and semi-elliptical surface cracks. To investigate effects of transition from embedded crack to surface crack in PFM analyses, one of the PFM round-robin problems set by JSME-RC111 committee (i.e. aged RPV under normal and upset operating conditions) is solved, employing the interpolation formulas. (orig.)

  3. Compressive failure with interacting cracks

    International Nuclear Information System (INIS)

    Yang Guoping; Liu Xila

    1993-01-01

    The failure processes in concrete and other brittle materials are just the results of the propagation, coalescence and interaction of many preexisting microcracks or voids. To understand the real behaviour of the brittle materials, it is necessary to bridge the gap from the relatively matured one crack behaviour to the stochastically distributed imperfections, that is, to concern the crack propagation and interaction of microscopic mechanism with macroscopic parameters of brittle materials. Brittle failure in compression has been studied theoretically by Horii and Nemat-Nasser (1986), in which a closed solution was obtained for a preexisting flaw or some special regular flaws. Zaitsev and Wittmann (1981) published a paper on crack propagation in compression, which is so-called numerical concrete, but they did not take account of the interaction among the microcracks. As for the modelling of the influence of crack interaction on fracture parameters, many studies have also been reported. Up till now, some researcher are working on crack interaction considering the ratios of SIFs with and without consideration of the interaction influences, there exist amplifying or shielding effects of crack interaction which are depending on the relative positions of these microcracks. The present paper attempts to simulate the whole failure process of brittle specimen in compression, which includes the complicated coupling effects between the interaction and propagation of randomly distributed or other typical microcrack configurations step by step. The lengths, orientations and positions of microcracks are all taken as random variables. The crack interaction among many preexisting random microcracks is evaluated with the help of a simple interaction matrix (Yang and Liu, 1991). For the subcritically stable propagation of microcracks in mixed mode fracture, fairly known maximum hoop stress criterion is adopted to compute branching lengths and directions at each tip of the crack

  4. Evaluation of Environmentally Assisted Cracking of Armour Wires in Flexible Pipes, Power Cables and Umbilicals

    Science.gov (United States)

    Zhang, Zhiying

    Environmentally assisted cracking (EAC) of armour wires in flexible pipes, power cables and umbilicals is a major concern with the development of oil and gas fields and wind farms in harsh environments. Hydrogen induced cracking (HIC) or hydrogen embrittlement (HE) of steel armour wires used in deep-water and ultra-deep-water has been evaluated. Simulated tests have been carried out in simulated sea water, under conditions where the susceptibility is the highest, i.e. at room temperature, at the maximum negative cathodic potential and at the maximum stress level expected in service for 150 hours. Examinations of the tested specimens have not revealed cracking or blistering, and measurement of hydrogen content has confirmed hydrogen charging. In addition, sulphide stress cracking (SSC) and chloride stress cracking (CSC) of nickel-based alloy armour wires used in harsh down-hole environments has been evaluated. Simulated tests have been carried out in simulated solution containing high concentration of chloride, with high hydrogen sulphide partial pressure, at high stress level and at 120 °C for 720 hours. Examinations of the tested specimens have not revealed cracking or blistering. Subsequent tensile tests of the tested specimens at ambient pressure and temperature have revealed properties similar to the as-received specimens.

  5. Monte Carlo simulation taking account of surface crack effect for stress corrosion cracking in a stainless steel SUS 304

    International Nuclear Information System (INIS)

    Tohgo, Keiichiro; Suzuki, Hiromitsu; Shimamura, Yoshinobu; Nakayama, Guen; Hirano, Takashi

    2008-01-01

    Stress corrosion cracking (SCC) in structural metal materials occurs by initiation and coalescence of micro cracks, subcritical crack propagation and multiple large crack formation or final failure under the combination of materials, stress and corrosive environment. In this paper, a Monte Carlo simulation for the process of SCC has been proposed based on the stochastic properties of micro crack initiation and fracture mechanics concept for crack coalescence and propagation. The emphasis in the model is put on the influence of semi-elliptical surface cracks. Numerical simulations are carried out based on CBB (creviced bent beam) test results of a sensitized stainless steel SUS 304 and the influence of micro crack initiation rate and coalescence condition on the simulation results is discussed. The numerical examples indicate the applicability of the present model to a prediction of the SCC behavior in real structures. (author)

  6. Normalizing effect on fatigue crack propagation at the heat-affected zone of AISI 4140 steel shielded metal arc weldings

    Directory of Open Access Journals (Sweden)

    B. Vargas-Arista

    2013-01-01

    Full Text Available The fractography and mechanical behaviour of fatigue crack propagation in the heat-affected zone (HAZ of AISI 4140 steel welded using the shielded metal arc process was analysed. Different austenitic grain size was obtained by normalizing performed at 1200 °C for 5 and 10 hours after welding. Three point bending fatigue tests on pre-cracked specimens along the HAZ revealed that coarse grains promoted an increase in fatigue crack growth rate, hence causing a reduction in both fracture toughness and critical crack length, and a transgranular brittle final fracture with an area fraction of dimple zones connecting cleavage facets. A fractographic analysis proved that as the normalizing time increased the crack length decreased. The increase in the river patterns on the fatigue crack propagation in zone II was also evidenced and final brittle fracture because of transgranular quasicleavage was observed. Larger grains induced a deterioration of the fatigue resistance of the HAZ.

  7. Mixed-mode crack tip loading and crack deflection in 1D quasicrystals

    Science.gov (United States)

    Wang, Zhibin; Scheel, Johannes; Ricoeur, Andreas

    2016-12-01

    Quasicrystals (QC) are a new class of materials besides crystals and amorphous solids and have aroused much attention of researchers since they were discovered. This paper presents a generalized fracture theory including the J-integral and crack closure integrals, relations between J1, J2 and the stress intensity factors as well as the implementation of the near-tip stress and displacement solutions of 1D QC. Different crack deflection criteria, i.e. the J-integral and maximum circumferential stress criteria, are investigated for mixed-mode loading conditions accounting for phonon-phason coupling. One focus is on the influence of phason stress intensity factors on crack deflection angles.

  8. Creep crack extension by grain-boundary cavitation

    International Nuclear Information System (INIS)

    Bassani, J.L.

    1981-01-01

    Recent work by Riedel and coworkers has led to various descriptions of stationary and moving crack tip fields under creep conditions. For stationary and growing cracks, several flow mechanisms (e.g., elastic, time-independent plastic, primary creep, and secondary creep) can dictate the analytical form of the crack tip field. In this paper, relationship between overall loading and crack velocities are modelled based upon grain-boundary cavity growth and coalescence within the zone of concentrated strain in the crack tip field. Coupled diffusion and creep growth of the cavities is considered. Overall crack extension is taken to be intermittent on a size scale equivalent to the size of a grain. Numerical results are presented for a center-cracked panel of 304 stainless steel. (author)

  9. Stress corrosion cracking of duplex stainless steels in caustic solutions

    Science.gov (United States)

    Bhattacharya, Ananya

    susceptibility. Annealed and water quenched specimens were found to be immune to SCC in caustic environment. Aging treatment at 800°C gave rise to sigma and chi precipitates in the DSS. However, these sigma and chi precipitates, known to initiate cracking in DSS in chloride environment did not cause any cracking of DSS in caustic solutions. Aging of DSS at 475°C had resulted in '475°C embrittlement' and caused cracks to initiate in the ferrite phase. This was in contrast to the cracks initiating in the austenite phase in the as-received DSS. Alloy composition and microstructure of DSS as well as solution composition (dissolved ionic species) was also found to affect the electrochemical behavior and passivation of DSS which in turn plays a major role in stress corrosion crack initiation and propagation. Corrosion rates and SCC susceptibility of DSS was found to increase with addition of sulfide to caustic solutions. Corrosion films on DSS, characterized using XRD and X-ray photoelectron spectroscopy, indicated that the metal sulfide compounds were formed along with oxides at the metal surface in the presence of sulfide containing caustic environments. These metal sulfide containing passive films are unstable and hence breaks down under mechanical straining, leading to SCC initiations. The overall results from this study helped in understanding the mechanism of SCC in caustic solutions. Favorable slip systems in the austenite phase of DSS favors slip-induced local film damage thereby initiating a stress corrosion crack. Repeated film repassivation and breaking, followed by crack tip dissolution results in crack propagation in the austenite phase of DSS alloys. Result from this study will have a significant impact in terms of identifying the alloy compositions, fabrication processes, microstructures, and environmental conditions that may be avoided to mitigate corrosion and stress corrosion cracking of DSS in caustic solutions.

  10. Evaluation of crack growth behavior and probabilistic S–N characteristics of carburized Cr–Mn–Si steel with multiple failure modes

    International Nuclear Information System (INIS)

    Li, Wei; Sun, Zhenduo; Zhang, Zhenyu; Deng, Hailong; Sakai, Tatsuo

    2014-01-01

    Highlights: • The stepwise S–N characteristics only for interior induced failure was observed. • The interior crack growth behavior with threshold conditions in different stages was clarified. • The distribution characteristics of test data in transition failure region was evaluated. • A model for evaluating the probabilistic S–N curve with multiple failure modes was developed. - Abstract: The unexpected failures of case-hardened steels in long life regime have been a critical issue in modern engineering design. In this study, the failure behavior of a carburized Cr–Mn–Si steel under very high cycle fatigue (VHCF) was investigated, and a model for evaluating the probabilistic S–N curve associated with multiple failure modes was developed. Results show that the carburized Cr–Mn–Si steel exhibits three failure modes including the surface flaw-induced failure, the interior inclusion-induced failure without the fine granular area (FGA) and the interior inclusion-induced failure with the FGA. As the predominant failure mode in the VHCF regime, the interior failure process can be divided into four stages: (i) the small crack growth around the inclusion, (ii) the stable macroscopic crack growth outside the FGA, (iii) the unstable crack growth outside the fish-eye and (iv) the momentary fracture outside the final crack growth zone. The threshold values are successively evaluated to be 2.33 MPa m 1/2 , 4.13 MPa m 1/2 , 18.51 MPa m 1/2 and 29.26 MPa m 1/2 . The distribution characteristics of the test data in transition failure region can be well characterized by the mixed two-parameter Weibull distribution function. The developed probabilistic S–N curve model is in good agreement with the test data with multiple failure modes. Although the result is somewhat conservative in the VHCF regime, it is acceptable for safety considerations

  11. Effect of yield strength on stress corrosion crack propagation under PWR and BWR environments of hardened stainless steels

    Energy Technology Data Exchange (ETDEWEB)

    Castano, M.L.; Garcia, M.S.; Diego, G. de; Gomez-Briceno, D. [CIEMAT, Nuclear Fission Department, Structural Materials Program, Avda. Complutense 22, 28040 Madrid (Spain)

    2004-07-01

    Core components of light water reactor (LWR), mainly made of austenitic stainless steels (SS), subjected to stress and exposed to relatively high fast neutron flux may suffer a cracking process termed as Irradiation Assisted Stress Corrosion Cracking (IASCC). Neutron radiation leads to critical modifications in material characteristics, which can modify their stress corrosion cracking (SCC) response. Current knowledge highlights three fundamental factors, induced by radiation, as primary contributors to IASCC of core materials: Radiation Induced Segregation (RIS) at grain boundaries, Radiation Hardening and Radiolysis. Most of the existing literature on IASCC is focussed on the influence of RIS, mainly chromium depletion, which can promote IASCC in oxidizing environments, such a Boiling Water Reactor (BWR) under normal water chemistry. However, in non-oxidizing environments, such as primary water of Pressurized Water Reactor (PWR) or BWR hydrogen water chemistry, the role played by chromium depletion at grain boundary on IASCC behaviour of highly irradiated material is irrelevant. One important issue with limited study is the effect of radiation induced hardening. The role of hardening on IASCC is became stronger considered, especially for environments where other factors, like micro-chemistry, have no significant influence. To formulate the mechanism of IASCC, a well-established method is to isolate and quantify the effect of individual parameters. The use of unirradiated material and the simulation of the irradiation effects is a procedure used with success for evaluating the influence of irradiation effects. Radiation hardening can be simulated by mechanical deformation and, although some differences exist in the types of defects produced, it is believed that the study of the SCC behaviour of unirradiated materials with different hardening levels would contribute to the understanding of IASCC mechanism. In order to evaluate the influence of hardening on the

  12. The effect of pressure loadings on the conservatism of the net-section stress criterion for the failure of cracked stainless steel piping

    International Nuclear Information System (INIS)

    Smith, E.

    1994-01-01

    The technological problem of intergranular stress corrosion cracking (IGSCC) of type 304 stainless steel piping in boiling water reactor piping systems, has provided the motivation for the considerable research interest in the integrity of cracked piping systems that are fabricated by ductile materials. IGSCC cracks are able to form at the inner surfaces of pipes. The cracks are circumferential and are able to grow slowly in service by a time dependent environmentally assisted mechanism. From a safety standpoint, it is important to know whether accident condition loadings will drive a part-through IGSCC crack unstably across the pipe thickness by a non-environmentally assisted fracture mechanism, and the resulting through-wall crack then propagate around the pipe circumference leading to a complete pipe severance. A methodology that has been developed to address this problem is a net-section stress methodology. The net-section stress approach for predicting the onset of crack extension in a piping system can give overly conservative predictions because a piping system is built-in at its end points and because crack extension requires some plastic deformation. The present paper is concerned with identifying the role of system pressure on the degree of conservatism, and two effects are important. Firstly, by inducing an axial tensile force at the cracked section, it is shown that the factor of conservatism can be increased. Secondly it is shown that the pressure induced moment at the cracked section behaves no differently to other contributions to this moment, in that all sources are associated with the same limited amount of elastic follow-up. All sources are associated with the same elastic flexibility parameter L*, which depends solely on the flexibility of the system and not on the nature of the loading

  13. Effects of irradiation on crack-arrest toughness of two high-copper welds

    International Nuclear Information System (INIS)

    Iskander, S.K.; Corwin, W.R.; Nanstad, R.K.

    1990-01-01

    The objective of this study is to determine the effect of neutron irradiation on the shift and shape of the lower-bound curve to crack-arrest data. Two submerged-arc welds with copper contents of 0.23 and 0.31 wt % were commercially fabricated in 220-mm-thick plate. Crack-arrest specimens fabricated from these welds were irradiated at a nominal temperature of 288 degree C to an average fluence of 1.9 x 10 19 neutrons/cm 2 (>1 MeV). A preliminary evaluation of the results shows that the neutron-irradiation induced crack-arrest toughness temperature shift is about the same as the Charpy V-notch impact temperature shift at the 41-J energy level. The shape of the lower-bound curves, (for the range of test temperatures covered), compared to those of the ASME K Ia -curve did not seem to have been altered by irradiation. 10 refs., 9 figs., 7 tabs

  14. Burst Pressure Prediction of Multiple Cracks in Pipelines

    International Nuclear Information System (INIS)

    Razak, N A; Alang, N A; Murad, M A

    2013-01-01

    Available industrial code such as ASME B1G, modified ASME B1G and DNV RP-F101 to assess pipeline defects appear more conservative for multiple crack like- defects than single crack-like defects. Thus, this paper presents burst pressure prediction of pipe with multiple cracks like defects. A finite element model was developed and the burst pressure prediction was compared with the available code. The model was used to investigate the effect of the distance between the cracks and the crack length. The coalescence diagram was also developed to evaluate the burst pressure of the multiple cracks. It was found as the distance between crack increases, the interaction effect comes to fade away and multiple cracks behave like two independent single cracks

  15. Fatigue crack layer propagation in silicon-iron

    Science.gov (United States)

    Birol, Y.; Welsch, G.; Chudnovsky, A.

    1986-01-01

    Fatigue crack propagation in metal is almost always accompanied by plastic deformation unless conditions strongly favor brittle fracture. The analysis of the plastic zone is crucial to the understanding of crack propagation behavior as it governs the crack growth kinetics. This research was undertaken to study the fatigue crack propagation in a silicon iron alloy. Kinetic and plasticity aspects of fatigue crack propagation in the alloy were obtained, including the characterization of damage evolution.

  16. Crack propagation and acoustic emission behavior of silver-added Dy123 bulk superconductor

    International Nuclear Information System (INIS)

    Yoneda, K.; Ye, J.

    2006-01-01

    The relationship between the crack propagation process and acoustic emission (AE) signals was investigated in 3-point bending tests in which stress loading was applied parallel to the c-axis of U-notched specimens cut from Dy123 bulk superconductors with and without the addition of silver (Ag). The average bending stress of the specimens containing 10 mass% of Ag was approximately 20% higher than that of the specimens without the addition of Ag; the total AE energy of the former specimens was approximately fourfold greater than that of the latter specimens. However, cracks initiated in all of the specimens at a bending stress level of around 25 MPa, regardless of the presence or absence of Ag. An analysis of the amplitude distribution revealed that the failure mode was matrix failure in both types of specimens. Cracks in the low-strength specimens without Ag propagated between gas holes or along cleavage planes, and the AE event count and total AE energy were low. By contrast, the high-strength Ag-added specimens had fewer gas holes and cleavage cracks on account of their improved microstructure. In these samples, crack propagation orthogonal to the cleavage planes caused Ag particles to separate from the matrix and induced cleavage cracks. The addition of Ag presumably had the effect of inhibiting crack propagation, with the result that the AE event count and AE energy increased. The results of this study indicate that failure phenomena can be interpreted by evaluating the amplitude distribution, AE event count and total AE energy. This suggests that the AE method is also applicable to evaluations of bulk superconductors

  17. Evaluation of the cracking by stress corrosion in nuclear reactor environments type BWR

    International Nuclear Information System (INIS)

    Arganis J, C. R.

    2010-01-01

    The stress corrosion cracking susceptibility was studied in sensitized, solution annealed 304 steel, and in 304-L welded with a heat treatment that simulated the radiation induced segregation, by the slow strain rate test technique, in a similar environment of a boiling water reactor (BWR), 288 C, 8 MPa, low conductivity and a electrochemical corrosion potential near 200 mV. vs. standard hydrogen electrode (She). The electrochemical noise technique was used for the detection of the initiation and propagation of the cracking. The steels were characterized by metallographic studies with optical and scanning electronic microscopy and by the electrochemical potentiodynamic reactivation of single loop and double loop. In all the cases, the steels present delta ferrite. The slow strain rate tests showed that the 304 steel in the solution annealed condition is susceptible to transgranular stress corrosion cracking (TGSCC), such as in a normalized condition showed granulated. In the sensitized condition the steel showed intergranular stress corrosion cracking, followed by a transition to TGSCC. The electrochemical noise time series showed that is possible associated different time sequences to different modes of cracking and that is possible detect sequentially cracking events, it is means, one after other, supported by the fractographic studies by scanning electron microscopy. The parameter that can distinguish between the different modes of cracking is the re passivation rate, obtained by the current decay rate -n- in the current transients. This is due that the re passivation rate is a function of the microstructure and the sensitization. Other statistic parameters like the localized index, Kurtosis, Skew, produce results that are related with mixed corrosion. (Author)

  18. Model of parameters controlling resistance of pipeline steels to hydrogen-induced cracking

    KAUST Repository

    Traidia, Abderrazak

    2014-01-01

    NACE MR0175/ISO 15156-2 standard provides test conditions and acceptance criteria to evaluate the resistance of carbon and low-alloy steels to hydrogen-induced cracking (HIC). The second option proposed by this standard offers a large flexibility on the choice of test parameters (pH, H2S partial pressure, and test duration), with zero tolerance to HIC initiation as an acceptance condition. The present modeling work is a contribution for a better understanding on how the test parameters and inclusion size can influence HIC initiation, and is therefore of potential interest for both steel makers and endusers. A model able to link the test operating parameters (pH, partial pressure of H2S, and temperature) to the maximum hydrogen pressure generated in the microstructural defects is proposed. The model results are then used to back calculate the minimum fracture toughness below which HIC extends. A minimum fracture toughness of 400 MPa√mm, at the segregation zone, prevents HIC occurrence and leads to successfully pass the HIC qualification test, even under extreme test conditions. The computed results show that the maximum generated pressure can reach up to 1,500 MPa. The results emphasize that the H2S partial pressure and test temperature can both have a strong influence on the final test results, whereas the influence of the pH of the test solution is less significant. © 2014, NACE International.

  19. Causes of Early-Age Thermal Cracking of Concrete Foundation Slabs and their Reinforcement to Control the Cracking

    Science.gov (United States)

    Bilčík, Juraj; Sonnenschein, Róbert; Gažovičová, Natália

    2017-09-01

    This paper focuses on the causes and consequences of early-age cracking of mass concrete foundation slabs due to restrained volume changes. Considering the importance of water leaking through cracks in terms of the serviceability, durability and environmental impact of watertight concrete structures, emphasis is placed on the effect of temperature loads on foundation slabs. Foundation slabs are usually restrained to some degree externally or internally. To evaluate the effect of external restraints on foundation slabs, friction and interaction models are introduced. The reinforcement of concrete cannot prevent the initiation of cracking, but when cracking has occurred, it may act to reduce the spacing and width of cracks. According to EN 1992-1-1, results of calculating crack widths with local variations included in National Annexes (NAs) vary considerably. A comparison of the required reinforcement areas according to different NAs is presented.

  20. Detection and sizing of cracks using potential drop techniques based on electromagnetic induction

    International Nuclear Information System (INIS)

    Sato, Yasumoto; Kim, Hoon

    2011-01-01

    The potential drop techniques based on electromagnetic induction are classified into induced current focused potential drop (ICFPD) technique and remotely induced current potential drop (RICPD) technique. The possibility of numerical simulation of the techniques is investigated and the applicability of these techniques to the measurement of defects in conductive materials is presented. Finite element analysis (FEA) for the RICPD measurements on the plate specimen containing back wall slits is performed and calculated results by FEA show good agreement with experimental results. Detection limit of the RICPD technique in depth of back wall slits can also be estimated by FEA. Detection and sizing of artificial defects in parent and welded materials are successfully performed by the ICFPD technique. Applicability of these techniques to detection of cracks in field components is investigated, and most of the cracks in the components investigated are successfully detected by the ICFPD and RICPD techniques. (author)