Detection and closure measurement of short fatigue crack initiated at notch root

International Nuclear Information System (INIS)

Lee, Jong-Hyung; Kobayashi, Hideo

1985-01-01

Short fatigue cracks initiated at the notch root were successfully detected at a fairly high accuracy by the ultrasonic amplitude calibration method for the notched compact specimens of an A508-3 steel. Crack closure measurements by the ultrasonic and back-face strain compliance methods were also performed. Crack growth characteristics at the notch root are similar to those of delyed retardation caused by a single peak overload. Also, transitional behavior from short cracks to long cracks was interpreted in terms of effective stress intensity ΔKsub(eff). The relation between crack growth rate da/dN and ΔKsub(eff) for short cracks shows a fairly good agreement with those for long cracks. (author)

Crack initiation under generalized plane strain conditions

International Nuclear Information System (INIS)

Shum, D.K.M.; Merkle, J.G.

1991-01-01

A method for estimating the decrease in crack-initiation toughness, from a reference plane strain value, due to positive straining along the crack front of a circumferential flaw in a reactor pressure vessel is presented in this study. This method relates crack initiation under generalized plane strain conditions with material failure at points within a distance of a few crack-tip-opening displacements ahead of a crack front, and involves the formulation of a micromechanical crack-initiation model. While this study is intended to address concerns regarding the effects of positive out-of- plane straining on ductile crack initiation, the approach adopted in this work can be extended in a straightforward fashion to examine conditions of macroscopic cleavage crack initiation. Provided single- parameter dominance of near-tip fields exists in the flawed structure, results from this study could be used to examine the appropriateness of applying plane strain fracture toughness to the evaluation of circumferential flaws, in particular to those in ring-forged vessels which have no longitudinal welds. In addition, results from this study could also be applied toward the analysis of the effects of thermal streaming on the fracture resistance of circumferentially oriented flaws in a pressure vessel. 37 refs., 8 figs., 1 tab

Crack Initiation and Growth Behavior at Corrosion Pit in 2024-T3 Aluminum Alloy

Science.gov (United States)

2014-09-01

concepts of fracture mechanics. Corrosion crack initiation or growth can develop when exposed to continuous or intermittent humid environment during...act as nucleation sites. For many materials of the structure such as Al, steel the growth of fatigue cracks from corrosion pit stands legitimate...critical or rather threshold values below which the nucleation of fatigue crack is not possible [6]. Under certain conditions that prevail on

Fatigue crack initiation in hybrid boron/glass/aluminum fiber metal laminates

International Nuclear Information System (INIS)

Chang, P.-Y.; Yeh, P.-C.; Yang, J.-M.

2008-01-01

The fatigue crack initiation behavior of a high modulus and hybrid boron/glass/aluminum fiber/metal laminate (FML) was investigated experimentally and analytically. Two types of hybrid boron/glass/aluminum FMLs were fabricated and studied, which consisted of aluminum alloy sheets as the metal layers and a mixture of boron fibers and glass fibers as the composite layers. For the first type, the boron fiber/prepreg and the glass fiber/prepreg were used separately in the composite layers, and for the second type, the boron fibers and the glass fibers were mingled together to form a hybrid boron/glass/prepreg composite layer. These hybrid FMLs were consolidated using an autoclave curing process. The incorporation of the boron fibers improved the Young's modulus of the composite layer in FMLs, which in turn, would improve the fatigue crack initiation life of the Al sheet. The experimental results clearly showed that the fatigue crack initiation lives for both types of hybrid boron/glass/aluminum FMLs were superior to the monolithic aluminum alloy under the same loading condition. An analytical approach was proposed to calculate the fatigue crack initiation lives of hybrid boron/glass/aluminum FMLs based on the classical laminate theory and the small-crack theory. A good correlation was obtained between the predictions and the experimental results

Evaluation of initial degradation in stress corrosion cracking by magnetic methods

International Nuclear Information System (INIS)

Takaya, Shigeru; Suzuki, Takayuki; Matsumoto, Yoshihiro; Demachi, Kazuyuki; Uesaka, Mitsuru

2003-01-01

Two magnetic methods are proposed for the evaluation of initial degradations of type 304 stainless steel in stress corrosion cracking (SCC). The first one is the measurement of the distribution of chromium depletion by means of a magnetic force microscope (MFM). MFM observations are performed for some samples sensitized in various conditions, and the obtained results coincide with the expected ones from the chromium behavior. Moreover, the phase distributions in the solution-annealed and sensitized states are observed by electron backscatter pattern technique. The observation results show that the phase transformation from the austenite phase to the martensite phase occurred along grain boundaries where the chromium was depleted. The second one is the detection of initial SCC cracks by measurement of magnetic flux densities. In-situ measurement of magnetic flux density during the SCC test and MFM observation reveal the relation of initial SCC cracks and magnetic properties. (author)

Dynamic Initiation and Propagation of Multiple Cracks in Brittle Materials

Directory of Open Access Journals (Sweden)

Xiaodan Ren

2013-07-01

Full Text Available Brittle materials such as rock and ceramic usually exhibit apparent increases of strength and toughness when subjected to dynamic loading. The reasons for this phenomenon are not yet well understood, although a number of hypotheses have been proposed. Based on dynamic fracture mechanics, the present work offers an alternate insight into the dynamic behaviors of brittle materials. Firstly, a single crack subjected to stress wave excitations is investigated to obtain the dynamic crack-tip stress field and the dynamic stress intensity factor. Second, based on the analysis of dynamic stress intensity factor, the fracture initiation sizes and crack size distribution under different loading rates are obtained, and the power law with the exponent of −2/3 is derived to describe the fracture initiation size. Third, with the help of the energy balance concept, the dynamic increase of material strength is directly derived based on the proposed multiple crack evolving criterion. Finally, the model prediction is compared with the dynamic impact experiments, and the model results agree well with the experimentally measured dynamic increasing factor (DIF.

Ductile crack initiation in the Charpy V-notch test

International Nuclear Information System (INIS)

Server, W.L.; Norris, D.M. Jr.; Prado, M.E.

1978-01-01

Initiation and growth of a crack in the Charpy V-notch test was investigated by performing both static and impact controlled deflection tests. Test specimens were deformed to various deflections, heat-tinted to mark crack extension and broken apart at low temperature to allow extension measurements. Measurement of the crack extension provided an estimate of crack initiation as defined by different criteria. Crack initiation starts well before maximum load, and is dependent on the definition of ''initiation''. Using a definition of first micro-initiation away from the ductile blunting, computer model predictions agreed favorably with the experimental results

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

Three-Dimensional Analysis of Enamel Crack Behavior Using Optical Coherence Tomography.

Science.gov (United States)

Segarra, M S; Shimada, Y; Sadr, A; Sumi, Y; Tagami, J

2017-03-01

The aim of this study was to nondestructively analyze enamel crack behavior on different areas of teeth using 3D swept source-optical coherence tomography (SS-OCT). Ten freshly extracted human teeth of each type on each arch ( n = 80 teeth) were inspected for enamel crack patterns on functional, contact and nonfunctional, or noncontact areas using 3D SS-OCT. The predominant crack pattern for each location on each specimen was noted and analyzed. The OCT observations were validated by direct observations of sectioned specimens under confocal laser scanning microscopy (CLSM). Cracks appeared as bright lines with SS-OCT, with 3 crack patterns identified: Type I - superficial horizontal cracks; Type II - vertically (occluso-gingival) oriented cracks; and Type III - hybrid or complicated cracks, a combination of a Type I and Type III cracks, which may or may not be confluent with each other. Type II cracks were predominant on noncontacting surfaces of incisors and canines and nonfunctional cusps of posterior teeth. Type I and III cracks were predominant on the contacting surfaces of incisors, cusps of canines, and functional cusps of posterior teeth. Cracks originating from the dental-enamel junction and enamel tufts, crack deflections, and the initiation of new cracks within the enamel (internal cracks) were observed as bright areas. CLSM observations corroborated the SS-OCT findings. We found that crack pattern, tooth type, and the location of the crack on the tooth exhibited a strong correlation. We show that the use of 3D SS-OCT permits for the nondestructive 3D imaging and analysis of enamel crack behavior in whole human teeth in vitro. 3D SS-OCT possesses potential for use in clinical studies for the analysis of enamel crack behavior.

On crack initiation in notched, cross-plied polymer matrix composites

Science.gov (United States)

Yang, Q. D.; Schesser, D.; Niess, M.; Wright, P.; Mavrogordato, M. N.; Sinclair, I.; Spearing, S. M.; Cox, B. N.

2015-05-01

The physics of crack initiation in a polymer matrix composite are investigated by varying the modeling choices made in simulations and comparing the resulting predictions with high-resolution in situ images of cracks. Experimental data were acquired using synchrotron-radiation computed tomography (SRCT) at a resolution on the order of 1 μm, which provides detailed measurement of the location, shape, and size of small cracks, as well as the crack opening and shear displacements. These data prove sufficient to discriminate among competing physical descriptions of crack initiation. Simulations are executed with a high-fidelity formulation, the augmented finite element method (A-FEM), which permits consideration of coupled damage mechanisms, including both discrete cracks and fine-scale continuum damage. The discrete cracks are assumed to be nonlinear fracture events, governed by reasonably general mixed-mode cohesive laws. Crack initiation is described in terms of strength parameters within the cohesive laws, so that the cohesive law provides a unified model for crack initiation and growth. Whereas the cracks investigated are typically 1 mm or less in length, the fine-scale continuum damage refers to irreversible matrix deformation occurring over gauge lengths extending down to the fiber diameter (0.007 mm). We find that the location and far-field stress for crack initiation are predicted accurately only if the variations of local stress within plies and in the presence of stress concentrators (notches, etc.) are explicitly computed and used in initiation criteria; stress redistribution due to matrix nonlinearity that occurs prior to crack initiation is accounted for; and a mixed-mode criterion is used for crack initiation. If these factors are not all considered, which is the case for commonly used failure criteria, predictions of the location and far-field stress for initiation are not accurate.

Study of crack initiation in low-cycle fatigue of an austenitic stainless steel

International Nuclear Information System (INIS)

Mu, P.

2011-03-01

The material studied is an austenitic stainless steel, that is widely used in nuclear equipment for its very high corrosion resistance combined to good mechanical properties. Although crack initiation is proved to play an important role in fatigue, its mechanisms have not been fully understood. Some crack initiation criteria based on physical mechanisms of plastic deformation have been defined. However, these criteria are not easy to use and valid, as they need local variables at the grain scale. The present study aims at establishing a crack initiation criterion in low-cycle fatigue, which should be usable under variable amplitude loading conditions. Tension-compression fatigue tests were first carried out to characterize the mechanical behavior of the stainless steel AISI 316L. The mechanical behavior was simulated using a self-consistent model using a crystalline plastic law based on dislocation densities. The evolution of surface damage was observed during a fatigue test using an in situ optical microscopic device. Cracks were analyzed after 2000 cycles and their crystallographic characteristics calculated. As surface grains exhibit larger strain because they are less constraint by neighbor grains, a specific numerical frame is necessary to determine stress state in surface grains. A localization law specific to surface grains under cyclic loading was identified from finite element simulations. The proposed form needs an intergranular accommodation variable, on the pattern of the localization law of Cailletaud-Pilvin. Stress-strain state in surface grains was simulated. Potential indicators for crack initiation were then compared on a same experimental data base. Indicators based on the equivalent plastic strain were found to be suitable indicators of fatigue damage. (author)

Probability of crack-initiation and application to NDE

Energy Technology Data Exchange (ETDEWEB)

Prantl, G [Nuclear Safety Inspectorate HSK, (Switzerland)

1988-12-31

Fracture toughness is a property with a certain variability. When a statistical distribution is assumed, the probability of crack initiation may be calculated for a given problem defined by its geometry and the applied stress. Experiments have shown, that cracks which experience a certain small amount of ductile growth can reliably be detected by acoustic emission measurements. The probability of crack detection by AE-techniques may be estimated using this experimental finding and the calculated probability of crack initiation. (author).

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.

Probabilistic and microstructural aspects of fatigue cracks initiation in Inconel 718

International Nuclear Information System (INIS)

Alexandre, F.

2004-03-01

Thermomechanical treatments have been recently developed to produce Inconel 718DA (Direct Aged). This alloy optimisation leads to an increase of the fatigue life but also the scatter. The aim of this study is on the one hand the understanding of the fatigue crack initiation mechanisms and on the other hand the modelling of the fatigue life and the scatter. An experimental study showed that the fatigue cracks were initiated from carbide particles in fine grain alloy. Interrupted tensile tests show that the particles cracking occurred at the first quarter of the fatigue cycle. Fatigue behaviour tests were also performed on various grain size 718 alloys. The last experimental part was devoted to measurements of the low cycle fatigue crack growth rates using a high focal distance microscope. For these tests, EDM micro-defects were used for the fatigue crack initiation sites. This method was also used to observe the small fatigue crack coalescence. A fatigue life model is proposed. It is based on the three fatigue crack initiation mechanisms competition: particle crack initiation on the surface, internal particle crack initiation and Stade I crack initiation. The particle fatigue crack initiation is supposed instantaneous at a critical stress level. The Tanaka and Mura model is used for analysing the Stage I crack initiation number of cycles. The fatigue crack growth rate was analysed using the Tomkins model identified on the small fatigue crack growth rate measurements. The proposed fatigue life model decomposed in three levels: a deterministic one and two probabilistic with and without crack coalescence. (author)

Initiation of delayed hydride cracking in zirconium-2.5 wt% niobium

International Nuclear Information System (INIS)

Shalabi, A.F.; Meneley, D.A.

1990-01-01

Delayed hydride cracking in zirconium alloys is caused by the repeated precipitation and cracking of brittle hydrides. The growth kinetic of the hydrides have been measured to evaluate the critical hydride length for crack initiation. Hydride growth leading to crack initiation follows an approximate (time) 1/3 law on the average; crack propagation proceeds in a stepwise fashion. The critical length of hydride for crack initiation increases with stress and temperature. The fracture criterion for crack initiation predicts the critical hydride length at a give stress level and temperature. The fracture initiation mechanism of the hydride confirms the temperature effects for heating and cooling cycles under services loads. (orig.)

Comparison of fatigue crack initiation behavior in different microstructures of TC21 titanium alloy

Directory of Open Access Journals (Sweden)

Tan Changsheng

2018-01-01

Full Text Available Cyclic heterogeneous deformation, slip characteristics and crack nucleation with different microstructures, such as bimodal microstructure (BM and fine lamellar microstructure (FLM in TC21 alloy (Ti-6Al-2Sn-2Zr-3Mo-1Cr-2Nb-0.1Si, were systematically investigated and analyzed during high cycle fatigue at room temperature. The results demonstrated that the FLM microstructure possesses higher high-cycle fatigue strength than those of the BM one. For BM, the heterogeneous plastic deformation existed within the different large primary α phase, such as equiaxed primary α and primary α lath. The cracks at interfaces and slip bands easily coalesce with each other to form large cracks in BM. However, the α laths with similar morphology and size (nanosize distributed uniformly in FLM and could relatively deform homogeneously in micro-region, which delayed the initiation of the fatigue crack. Based on the electron-backscattered diffraction (EBSD analysis, it found that the strain was nonuniformly distributed in BM, however, it is relatively homogeneous in FLM. Moreover, lots of straight cracks are parallel and along single intrusions within the β grain which delays the coalescence of cracks.

High temperature crack initiation in an austenitic stainless steel

International Nuclear Information System (INIS)

Laiarinandrasana, Lucien

1994-01-01

The study deals with crack initiation at 600 deg. C and 650 deg. C, on an austenitic stainless steel referenced by Z2 CND 17 12. The behaviour laws of the studied plate were updated in comparison with existing data. Forty tests were carried out on CT specimens, with continuous fatigue with load or displacement controlled, pure creep, pure relaxation, creep-fatigue and creep-relaxation loadings. The practical initiation definition corresponds to a small crack growth of about the grain size, monitored by electrical potential drop technique. The time necessary for the crack to initiate is predicted with fracture mechanics global and local approaches, with the help of microstructural observations and finite element results. An identification of a 'Paris' law' for continuous cyclic loading and of a unique correlation between the initiation time and C h * for creep tests was established. For the local approach, crack initiation by creep can be interpreted as the reaching of a critical damage level, by using a damage incremental rule. For creep-fatigue tests, crack growth rates at initiation are greater than those of Paris' law for continuous fatigue. A calculation of a transition time between elastic-plastic and creep domains shows that crack initiation can be interpreted whether by providing Paris' law with an acceleration term when the dwell period is less than the transition time, or by calculating a creep contribution which relies on C h * parameter when the dwell period and/or the initiation times are greater than the transition time. Creep relaxation tests present crack growth rates at initiation which are less than those for 'equivalent' creep-fatigue tests. These crack growth rates decrease when increasing hold time, but also when temperature decreases. Though, for hold times which are important enough and at lower temperature, there is no effect of the dwell period insofar as crack growth rate is equal to continuous fatigue

Crack initiation modeling of a directionally-solidified nickel-base superalloy

Science.gov (United States)

Gordon, Ali Page

crystal plasticity model was used to simulate the material behavior in the L and T orientations. The constitutive model was implemented in ABAQUS and a parameter estimation scheme was developed to obtain the material constants. A physically-based model was developed for correlating crack initiation life based on the experimental life data and predictions are made using the crack initiation model. Assuming a unique relationship between the damage fraction and cycle fraction with respect to cycles to crack initiation for each damage mode, the total crack initiation life has been represented in terms of the individual damage components (fatigue, creep-fatigue, creep, and oxidation-fatigue) observed at the end state of crack initiation.

Analysis of crack initiation and growth in the high level vibration test at Tadotsu

International Nuclear Information System (INIS)

Kassir, M.K.; Park, Y.J.; Hofmayer, C.H.; Bandyopadhyay, K.K.; Shteyngart, S.

1993-08-01

The High Level Vibration Test data are used to assess the accuracy and usefulness of current engineering methodologies for predicting crack initiation and growth in a cast stainless steel pipe elbow under complex, large amplitude loading. The data were obtained by testing at room temperature a large scale modified model of one loop of a PWR primary coolant system at the Tadotsu Engineering Laboratory in Japan. Fatigue crack initiation time is reasonably predicted by applying a modified local strain approach (Coffin-Mason-Goodman equation) in conjunction with Miner's rule of cumulative damage. Three fracture mechanics methodologies are applied to investigate the crack growth behavior observed in the hot leg of the model. These are: the ΔK methodology (Paris law), ΔJ concepts and a recently developed limit load stress-range criterion. The report includes a discussion on the pros and cons of the analysis involved in each of the methods, the role played by the key parameters influencing the formulation and a comparison of the results with the actual crack growth behavior observed in the vibration test program. Some conclusions and recommendations for improvement of the methodologies are also provided

Crack propagation behavior of TiN coatings by laser thermal shock experiments

International Nuclear Information System (INIS)

Choi, Youngkue; Jeon, Seol; Jeon, Min-seok; Shin, Hyun-Gyoo; Chun, Ho Hwan; Lee, Youn-seoung; Lee, Heesoo

2012-01-01

Highlights: ► The crack propagation behavior of TiN coating after laser thermal shock experiment was observed by using FIB and TEM. ► Intercolumnar cracks between TiN columnar grains were predominant cracking mode after laser thermal shock. ► Cracks were propagated from the coating surface to the substrate at low laser pulse energy and cracks were originated at coating-substrate interface at high laser pulse energy. ► The cracks from the interface spread out transversely through the weak region of the columnar grains by repetitive laser shock. - Abstract: The crack propagation behavior of TiN coatings, deposited onto 304 stainless steel substrates by arc ion plating technique, related to a laser thermal shock experiment has been investigated using focused ion beam (FIB) and transmission electron microscopy (TEM). The ablated regions of TiN coatings by laser ablation system have been investigated under various conditions of pulse energies and number of laser pulses. The intercolumnar cracks were predominant cracking mode following laser thermal shock tests and the cracks initiated at coating surface and propagated in a direction perpendicular to the substrate under low loads conditions. Over and above those cracks, the cracks originated from coating-substrate interface began to appear with increasing laser pulse energy. The cracks from the interface also spread out transversely through the weak region of the columnar grains by repetitive laser shock.

Stress corrosion cracks initiation of recrystallized Zircaloy-4 in iodine-methanol solutions

International Nuclear Information System (INIS)

Mozzani, N.

2013-01-01

During the pellet-cladding interaction, Zirconium-alloy fuel claddings might fail when subjected to incidental power transient in nuclear Pressurized Water Reactors, by Iodine-induced Stress Corrosion Cracking (I-SCC). This study deals with the intergranular initiation of I-SCC cracks in fully recrystallized Zircaloy-4, in methyl alcohol solution of iodine at room temperature, with the focus on critical mechanical parameters and iodine concentration. It was carried out with an approach mixing experiments and numerical simulations. An anisotropic and viscoplastic mechanical behavior model was established and validated over a wide range of loadings. With numerous constant elongation rate tensile tests and four points bending creep tests, the existence of a threshold iodine concentration I0 close to 10 -6 g.g -1 was highlighted, necessary to the occurrence of I-SCC damage, along with a transition concentration I1 close to 2.10 -4 g.g -1 . Above I1 the mechanism changes, leading to a sped up crack initiation and a loss of sensitivity towards mechanical parameters. The importance of concentration on parameters such as crack density, crack average length and intergranular and transgranular crack velocities was evidenced. Experimental results show that plastic strain is not required for I-SCC crack initiation, if the test time is long enough in the presence of stress. Its main influence is to rush the occurrence of cracking by creating initiation sites, by way of breaking the oxide layer and building up intergranular stress. Below I1, the critical strains at initiation show a substantial strain rate sensitivity. In this domain, a threshold stress of 100 MPa was found, well below the yield stress. Thanks to the combined use of notched specimens and numerical simulations, a strong protective effect of an increasing stress bi-axiality ratio was found, both in the elastic and plastic domains. Proton-irradiated samples, up to a dose of 2 dpa, were tested in the same conditions

Analysis of crack initiation and growth in the high level vibration test at Tadotsu

International Nuclear Information System (INIS)

Kassir, M.K.; Hofmayer, C.H.; Bandyopadhyay, K.K.

1991-01-01

A High Level Vibration Test (HLVT) Program was carried out recently on the seismic table at the Tadotsu Engineering Laboratory of Nuclear Power Engineering Center (NUPEC) in Japan. The objective of the study being performed at Brookhaven National Laboratory is to use the HLVT data to assess the accuracy and usefulness of existing methods for predicting crack initiation and growth under complex, large amplitude loading. The work to be performed as part of this effort involves: (1) analysis of the stress/strain distribution in the vicinity of the crack, including the potential for residual stresses due to the weld repair; (2) analysis of the number of load cycles required for crack initiation, including estimates of the impact of the weld repair on the crack initiation behavior; (3) analysis of crack advance as a function of applied loading (classic fatigue versus cyclic tearing) taking into account the variable amplitude loading and the possible influence of the repair; and (4) material property testing to supplement the work performed as part of the HLVT, providing the materials data necessary to perform the analysis efforts. A summary of research progress for FY 1990 is presented. 2 refs

Subsurface crack initiation and propagation mechanisms in gigacycle fatigue

International Nuclear Information System (INIS)

Huang Zhiyong; Wagner, Daniele; Bathias, Claude; Paris, Paul C.

2010-01-01

In the very high cycle regime (N f > 10 7 cycles) cracks can nucleate on inclusions, 'supergrains' and pores, which leads to fish-eye propagation around the defect. The initiation from an inclusion or other defect is almost equal to the total crack growth lifetime, perhaps much more than 99% of this lifetime in many cases. Integration of the Paris law allows one to predict the number of cycles to crack initiation. A cyclic plastic zone around the crack exists, and recording the surface temperature of the sample during the test may allow one to follow crack propagation and determine the number of cycles to crack initiation. A thermo-mechanical model has been developed. In this study several fish-eyes from various materials have been observed by scanning electron microscopy, and the fractographic results analyzed as they related to the mechanical and thermo-mechanical models.

Analysis of SCC initiation/propagation behavior of stainless steels in LWR environments

International Nuclear Information System (INIS)

Saito, Koichi; Kuniya, Jiro

1999-01-01

This paper presents a method to analyze initiation and propagation behavior of stress corrosion cracking (SCC) of stainless steels on the basis of a new prediction algorithm in which the initiation period and propagation period of SCC under irradiation conditions are considered from a practical viewpoint. The prediction algorithm is based on three ideas: (1) threshold neutron fluence of radiation-enhanced SCC (RESCC), (2) equivalent critical crack depth, and (3) threshold stress intensity factor for SCC (K ISCC ). SCC initiation/propagation behavior in light water reactor (LWR) environments is analyzed by incorporating model equations on irradiation hardening, irradiation-enhanced electrochemical potentiokinetic reactivation (EPR) and irradiation stress relaxation that are phenomena peculiar to neutron irradiation. The analytical method is applied to predict crack growth behavior of a semi-elliptical surface crack in a flat plane that has an arbitrary residual stress profile; specimens are sensitized type 304 stainless steels which had been subjected to neutron irradiation in high temperature water. SCC growth behavior of a semi-elliptical surface crack was greatly dependent on the distribution of residual stress in a flat plane. When residual stress at the surface of the flat plane was relatively small, the method predicted SCC propagation did not take place. (author)

Crack initiation life analysis in notched pipe under cyclic bending loads

International Nuclear Information System (INIS)

Lee, Joon Seong; Kwak, Sang Log; Kim, Young Jin; Park, Youn Won

2001-01-01

In order to improve leak-before-break methodology, more precisely the crack growth evaluation, a round robin analysis was proposed by the CEA Saclay. The aim of this analysis was to evaluate the crack initiation life, penetration life and shape of through wall crack under cyclic bending loads. The proposed round robin analysis is composed of three main topic; fatigue crack initiation, crack propagation and crack penetration. This paper deals with the first topic, crack initiation in a notched pipe under four point bending. Both elastic-plastic finite element analysis and Neuber's rule were used to estimate the crack initiation life and the finite element models were verified by mesh-refinement, stress distribution and global deflection. In elastic-plastic finite element analysis, crack initiation life was determined by strain amplitude at the notch tip and strain-life curve of the material. In the analytical method, Neuber's rule with the consideration of load history and mean stress effect, was used for the life estimation. The effect of notch tip radius, strain range, cyclic hardening rule were examined in this study. When these results were compared with the experimental ones, the global deformation was a good agreement but crack initiation cycle was higher than the experimental result

Crack initiation and growth in welded structures

International Nuclear Information System (INIS)

Assire, A.

2000-01-01

This work concerns the remaining life assessment of a structure containing initial defects of manufacturing. High temperature crack initiation and growth are studied for austenitic stainless steels, and defect assessment methods are improved in order to take into account welded structures. For these one, the probability to have a defect is significant. Two kinds of approaches are commonly used for defect assessment analysis. Fracture mechanics global approach with an energetic criterion, and local approach with a model taking into account the physical damage mechanism. For both approaches mechanical fields (stress and strain) have to be computed everywhere within the structure. Then, Finite Element computation is needed. The first part of the thesis concerns the identification of non linear kinematic and isotropic constitutive models. A pseudo-analytical method is proposed for a 'Two Inelastic Strain' model. This method provides a strategy of identification with a mechanical meaning, and this enables to associate each parameter to a physical phenomenon. Existing identifications are improved for cyclic plasticity and creep on a large range of stress levels. The second part concerns high temperature crack initiation and growth in welded structures. Finite Element analysis on plate and tube experimental configuration enable to understand the phenomenons of interaction between base metal and weld metal under mechanical and thermal loading. Concerning global approach, criteria based on C* parameter (Rice integral for visco-plasticity) are used. Finite Element computations underline the fact that for a defect located in the weld metal, C* values strongly depend on the base metal creep strain rate, because widespread visco-plasticity is located in both metals. A simplified method, based on the reference stress approach, is proposed and validated with Finite Element results. Creep crack growth simplified assessment is a quite good validation of the experimental results

Very High Cycle Fatigue Crack Initiation Mechanism in Nugget Zone of AA 7075 Friction Stir Welded Joint

Directory of Open Access Journals (Sweden)

Chao He

2017-01-01

Full Text Available Very high cycle fatigue behavior of nugget zone in AA 7075 friction stir welded joint was experimentally investigated using ultrasonic fatigue testing system (20 kHz to clarify the crack initiation mechanism. It was found that the fatigue strength of nugget zone decreased continuously even beyond 107 cycles with no traditional fatigue limits. Fatigue cracks initiated from the welding defects located at the bottom side of the friction stir weld. Moreover, a special semicircular zone could be characterized around the crack initiation site, of which the stress intensity factor approximately equaled the threshold of fatigue crack propagation rate. Finally, a simplified model was proposed to estimate the fatigue life by correlating the welding defect size and applied stress. The predicted results are in good agreement with the experimental results.

Workshop on initiation of stress corrosion cracking under LWR conditions: Proceedings

International Nuclear Information System (INIS)

Nelson, J.L.; Cubicciotti, D.; Licina, G.J.

1988-05-01

A workshop titled ''Initiation of Stress Corrosion Cracking under LWR Conditions'' was held in Palo Alto, California on November 13, 1986, hosted by the Electric Power Research Institute. Participants were experts on the topic from nuclear steam supply and component manufacturers, public and private research laboratories, and university environments. Presentations included discussions on the definition of crack initiation, the effects of environmental and electrochemical variables on cracking susceptibility, and detection methods for the determination of crack initiation events and measurement of critical environmental and stress parameters. Examination of the questions related to crack initiation and its relative importance to the overall question of cracking of LWR materials from these perspectives provided inputs to EPRI project managers on the future direction of research efforts designed to prevent and control cracking. Thirteen reports have been cataloged separately

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)

A study on the fracture strength of steel fiber reinforced concrete structures with initial cracks

International Nuclear Information System (INIS)

Chang, Dong Il; Chai, Won Kyu; Lee, Myeong Gu

1991-01-01

Fracture tests were carried out in order to investigate the fracture behavior of SFRC(Steel Fiber Reinforced Concrete) structures with initial cracks. Sixty three SFRC beams were used in the tests. And the fracture mode, and relations between loading and mid-span deflection of the beams were observed. On the base of test results, fracture behavior of SFRC beams resulted from steel fiber content and initial crack length to beam depth ratio were found out, and the stress intensity factors, the modulus of rupture and the fracture energy of SFRC beams may then be calculated. According to the results of regression analysis, prediction formulas for the modulus of rupture and the fracture energy of SFRC beams are also suggested. (Author)

Crack initiation at high temperature on an austenitic stainless steel

International Nuclear Information System (INIS)

Laiarinandrasana, L.

1994-01-01

The study deals with crack initiation at 600 degrees Celsius and 650 degrees Celsius, on an austenitic stainless steel referenced by Z2 CND 17 12. The behaviour laws of the studied plate were update in comparison with existing data. Forty tests were carried out on CT specimens, with continuous fatigue with load or displacement controlled, pure creep, pure relaxation, creep-fatigue and creep-relaxation loadings. The practical initiation definition corresponds to a small crack growth of about the grain size, monitored by electrical potential drop technique. The time necessary for the crack to initiate is predicted with fracture mechanics global and local approaches, with the helps of microstructural observations and finite elements results. An identification of a 'Paris'law' for continuous cyclic loading and of a unique correlation between the initiation time and C * k for creep tests was established. For the local approach, crack initiation by creep can be interpreted as the reaching of a critical damage level, by using a damage incremental rule. For creep-fatigue tests, crack growth rates at initiation are greater than those of Paris'law for continuous fatigue. A calculation of a transition time between elastic-plastic and creep domains shows that crack initiation can be interpreted whether by providing Paris'law with an acceleration term when the dwell period is less than the transition time, or by calculating a creep contribution which relies on C * k parameter when the dwell period and/or the initiation times are greater than the transition time. Creep relaxation tests present crack growth rates at initiation which are less than those for 'equivalent' creep-fatigue tests. These crack growth rates when increasing hold time, but also when temperature decreases. Though, for hold times which are important enough and at lower temperature, there is no effect of the dwell period insofar as crack growth rate is equal to continuous fatigue Paris law predicted ones

Fatigue crack propagation behavior of stainless steel welds

Science.gov (United States)

Kusko, Chad S.

The fatigue crack propagation behavior of austenitic and duplex stainless steel base and weld metals has been investigated using various fatigue crack growth test procedures, ferrite measurement techniques, light optical microscopy, stereomicroscopy, scanning electron microscopy, and optical profilometry. The compliance offset method has been incorporated to measure crack closure during testing in order to determine a stress ratio at which such closure is overcome. Based on this method, an empirically determined stress ratio of 0.60 has been shown to be very successful in overcoming crack closure for all da/dN for gas metal arc and laser welds. This empirically-determined stress ratio of 0.60 has been applied to testing of stainless steel base metal and weld metal to understand the influence of microstructure. Regarding the base metal investigation, for 316L and AL6XN base metals, grain size and grain plus twin size have been shown to influence resulting crack growth behavior. The cyclic plastic zone size model has been applied to accurately model crack growth behavior for austenitic stainless steels when the average grain plus twin size is considered. Additionally, the effect of the tortuous crack paths observed for the larger grain size base metals can be explained by a literature model for crack deflection. Constant Delta K testing has been used to characterize the crack growth behavior across various regions of the gas metal arc and laser welds at the empirically determined stress ratio of 0.60. Despite an extensive range of stainless steel weld metal FN and delta-ferrite morphologies, neither delta-ferrite morphology significantly influence the room temperature crack growth behavior. However, variations in weld metal da/dN can be explained by local surface roughness resulting from large columnar grains and tortuous crack paths in the weld metal.

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.

Crack initiation life analysis in notched pipe under cyclic bending loads

International Nuclear Information System (INIS)

Goak, S. R.; Kim, Y. J.; Lee, J. S.; Park, Y. W.

2000-01-01

In order to improve LBB(Leak-Before-Break) methodology, more precisely the crack growth evaluation, a benchmark problem was proposed by the CEA Saclay. The aim of this benchmark analysis was to evaluate the crack growth in a notched pipe under cyclic bending loads. The proposed benchmark analysis is composed of three main topic; fatigue crack initiation, crack propagation and crack penetration. This paper deals with the first topic, crack initiation in a notched pipe under four point bending. Both elastic-plastic finite element analysis and Neuber's rule were used to estimate the crack initiation life and the finite element models were verified by mesh-refinement, stress distribution and global deflection. In elastic-plastic finite element analysis, crack initiation life was determined by strain amplitude at the notch tip and strain-life curve of the material. In the analytical method, Neuber's rule with the consideration of load history and mean stress effect, was used for the life estimation. The effect of notch tip radius, strain range, cyclic hardening rule were examined in this study. When these results were compared with the experimental ones, the global deformation was a good agreement but the crack initiation cycle was higher than the experimental result

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

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.

Investigation on the Crack Initiation of V-Shaped Notch Tip in Precision Cropping

Directory of Open Access Journals (Sweden)

Lijun Zhang

2014-01-01

Full Text Available The crack initiation of V-shaped notch tip has a very important influence on the cross-section quality and the cropping time for every segment of metal bar in course of low stress precision cropping. By the finite element method, the influence of machining precision of V-shaped notch bottom corner on the crack initiation location is analyzed and it is pointed out that the crack initiation point locates in the place at the maximal equivalent stress change rate on V-shaped notch surface. The judgment criterion of the crack initiation direction is presented and the corresponding crack initiation angle can be calculated by means of the displacement extrapolation method. The factual crack initiation angle of the metal bar has been measured by using the microscopic measurement system. The formula of the crack initiation life of V-shaped notch tip is built, which mainly includes the stress concentration factor of V-shaped notch, the tensile properties of metal material, and the cyclic loading conditions. The experimental results show that the obtained theoretical analyses about the crack initiation location, the crack initiation direction, and the crack initiation time in this paper are correct. It is also shown that the crack initiation time accounts for about 80% of the cropping time for every segment of the metal bar.

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)

Dynamic crack initiation toughness : experiments and peridynamic modeling.

Energy Technology Data Exchange (ETDEWEB)

Foster, John T.

2009-10-01

This is a dissertation on research conducted studying the dynamic crack initiation toughness of a 4340 steel. Researchers have been conducting experimental testing of dynamic crack initiation toughness, K{sub Ic}, for many years, using many experimental techniques with vastly different trends in the results when reporting K{sub Ic} as a function of loading rate. The dissertation describes a novel experimental technique for measuring K{sub Ic} in metals using the Kolsky bar. The method borrows from improvements made in recent years in traditional Kolsky bar testing by using pulse shaping techniques to ensure a constant loading rate applied to the sample before crack initiation. Dynamic crack initiation measurements were reported on a 4340 steel at two different loading rates. The steel was shown to exhibit a rate dependence, with the recorded values of K{sub Ic} being much higher at the higher loading rate. Using the knowledge of this rate dependence as a motivation in attempting to model the fracture events, a viscoplastic constitutive model was implemented into a peridynamic computational mechanics code. Peridynamics is a newly developed theory in solid mechanics that replaces the classical partial differential equations of motion with integral-differential equations which do not require the existence of spatial derivatives in the displacement field. This allows for the straightforward modeling of unguided crack initiation and growth. To date, peridynamic implementations have used severely restricted constitutive models. This research represents the first implementation of a complex material model and its validation. After showing results comparing deformations to experimental Taylor anvil impact for the viscoplastic material model, a novel failure criterion is introduced to model the dynamic crack initiation toughness experiments. The failure model is based on an energy criterion and uses the K{sub Ic} values recorded experimentally as an input. The failure model

Cross-validated detection of crack initiation in aerospace materials

Science.gov (United States)

Vanniamparambil, Prashanth A.; Cuadra, Jefferson; Guclu, Utku; Bartoli, Ivan; Kontsos, Antonios

2014-03-01

A cross-validated nondestructive evaluation approach was employed to in situ detect the onset of damage in an Aluminum alloy compact tension specimen. The approach consisted of the coordinated use primarily the acoustic emission, combined with the infrared thermography and digital image correlation methods. Both tensile loads were applied and the specimen was continuously monitored using the nondestructive approach. Crack initiation was witnessed visually and was confirmed by the characteristic load drop accompanying the ductile fracture process. The full field deformation map provided by the nondestructive approach validated the formation of a pronounced plasticity zone near the crack tip. At the time of crack initiation, a burst in the temperature field ahead of the crack tip as well as a sudden increase of the acoustic recordings were observed. Although such experiments have been attempted and reported before in the literature, the presented approach provides for the first time a cross-validated nondestructive dataset that can be used for quantitative analyses of the crack initiation information content. It further allows future development of automated procedures for real-time identification of damage precursors including the rarely explored crack incubation stage in fatigue conditions.

Effect of temperature on crack initiation in gas formed structures

Energy Technology Data Exchange (ETDEWEB)

Gohari, S.; Vrcelj, Z.; Sharifi, S.; Sharifishourabi, G.; Abadi, R. [Universiti Teknlogi Malaysia, Skudai (Malaysia)

2013-12-15

In the gas forming process, the work piece is formed by applying gas pressure. However, the gas pressure and the accompanying gas temperature can result in crack initiation and unstable crack growth. Thus, it is vital to determine the critical values of applied gas pressure and temperature to avoid crack and fracture failure. We studied the mechanism of fracture using an experimental approach and finite element simulations of a perfect aluminum sheet containing no inclusions and voids. The definition of crack was based on ductile damage mechanics. For inspection of initiation of crack and rupture in gas-metal forming, the ABAQUS/EXPLICIT simulation was used. In gas forming, the applied load is the pressure applied rather than the punching force. The results obtained from both the experimental approach and finite element simulations were compared. The effects of various parameters, such as temperature and gas pressure value on crack initiation, were taken into account.

The characteristics of ultra-high performance concrete and cracking behavior of reinforced concrete tensile specimens

Directory of Open Access Journals (Sweden)

H.A. Rahdar

2016-09-01

Full Text Available The tensile behavior of concrete depends on some factors such as member dimensions, reinforcement ratio, diameter of rebar, strength and elasticity modulus of material. In this research the experimental method is used to examine the characteristics and the behavior of ultra-high performance concrete on the tensile behavior of concrete members reinforced by steel rebar. The results show that increasing the rebar cover on diameter rebar ratio (C/d increases the initial stiffening before the cracking stage in concrete. Also, by increasing of reinforcement ratio the cracking space decreased.

Study of stress corrosion cracking initiation of high alloy materials

Energy Technology Data Exchange (ETDEWEB)

Blahetova, Marie; Cihal, Vladimir; Lasek, Stanislav [Department of Materials Engineering, VSB - Technical University of Ostrava, tr. 17. listopadu 15, 708 33 Ostrava - Poruba (Czech Republic)

2004-07-01

The stainless steels and related alloys with sufficient resistance to a general corrosion can be susceptible to a localized corrosion (pitting, cracking, intergranular corrosion) in certain environment under specific conditions. The Drop Evaporation Test (DET) was developed for study of stainless materials resistance to stress corrosion cracking (SCC) at elevated temperatures 100 - 300 deg. C under constant external load using a chloride containing water solution. In the contribution the initiation and propagation of short cracks as well as pits were observed during the test. The crack initiation and/or propagation can be influenced by the cyclic thermal stresses, when the diluted water solution drops cool down the hot sample. The coordinates measurement of microscopic pits and sharp corrosion crack tips by the travelling microscope method allowed to derive the crack growth lengths and rates of short cracks. (authors)

Study of stress corrosion cracking initiation of high alloy materials

International Nuclear Information System (INIS)

Blahetova, Marie; Cihal, Vladimir; Lasek, Stanislav

2004-01-01

The stainless steels and related alloys with sufficient resistance to a general corrosion can be susceptible to a localized corrosion (pitting, cracking, intergranular corrosion) in certain environment under specific conditions. The Drop Evaporation Test (DET) was developed for study of stainless materials resistance to stress corrosion cracking (SCC) at elevated temperatures 100 - 300 deg. C under constant external load using a chloride containing water solution. In the contribution the initiation and propagation of short cracks as well as pits were observed during the test. The crack initiation and/or propagation can be influenced by the cyclic thermal stresses, when the diluted water solution drops cool down the hot sample. The coordinates measurement of microscopic pits and sharp corrosion crack tips by the travelling microscope method allowed to derive the crack growth lengths and rates of short cracks. (authors)

Development of crack growth and crack initiation test units for stress corrosion cracking examinations in high-temperature water environments under neutron irradiation (1) (Contract research)

International Nuclear Information System (INIS)

Izumo, Hironobu; Ishida, Takuya; Kawamata, Kazuo; Inoue, Shuichi; Ide, Hiroshi; Saito, Takashi; Ishitsuka, Etsuo; Chimi, Yasuhiro; Ise, Hideo; Miwa, Yukio; Ugachi, Hirokazu; Nakano, Junichi; Kaji, Yoshiyuki; Tsukada, Takashi

2009-04-01

To evaluate integrity of irradiation-assisted stress corrosion cracking (IASCC) on in-core structural materials used in light water reactors (LWRs), useful knowledge regarding IASCC has been obtained mainly by post-irradiation examinations (PIEs). In the core of commercial LWRs, however, the actual IASCC occurs under the effects of irradiation on both materials and high-temperature water environment. Therefore, it is necessary to confirm the suitability of the knowledge by PIE with comparison to IASCC behaviors during in-core SCC tests. Fundamental techniques for in-core crack growth and crack initiation tests have been developed already at the Japan Materials Testing Reactor (JMTR) of the Japan Atomic Energy Agency (JAEA). For the in-core crack growth test technique, to evaluate the effects of neutron irradiation on stainless steels irradiated to low neutron fluences, it is indispensable to develop new loading technique which is applicable to compact tension (CT) specimens with thickness of 0.5 inch (0.5T), from the viewpoint of validity based on the fracture mechanics. Based on the present technical investigation for the in-core loading technique, it is expected that a target load of 7.6 kN approximately can apply to a 0.5T-CT specimen by adopting a loading unit of a lever type instead of the previous uni-axial tension type. For the in-core crack initiation test technique, moreover, construction of a loading unit adopting linear variable differential transformers (LVDTs) has been investigated and technical issues have examined. (author)

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)

Evaluation of strength and failure of brittle rock containing initial cracks under lithospheric conditions

Science.gov (United States)

Li, Xiaozhao; Qi, Chengzhi; Shao, Zhushan; Ma, Chao

2018-02-01

Natural brittle rock contains numerous randomly distributed microcracks. Crack initiation, growth, and coalescence play a predominant role in evaluation for the strength and failure of brittle rocks. A new analytical method is proposed to predict the strength and failure of brittle rocks containing initial microcracks. The formulation of this method is based on an improved wing crack model and a suggested micro-macro relation. In this improved wing crack model, the parameter of crack angle is especially introduced as a variable, and the analytical stress-crack relation considering crack angle effect is obtained. Coupling the proposed stress-crack relation and the suggested micro-macro relation describing the relation between crack growth and axial strain, the stress-strain constitutive relation is obtained to predict the rock strength and failure. Considering different initial microcrack sizes, friction coefficients and confining pressures, effects of crack angle on tensile wedge force acting on initial crack interface are studied, and effects of crack angle on stress-strain constitutive relation of rocks are also analyzed. The strength and crack initiation stress under different crack angles are discussed, and the value of most disadvantaged angle triggering crack initiation and rock failure is founded. The analytical results are similar to the published study results. Rationality of this proposed analytical method is verified.

Fatigue crack growth behavior under cyclic thermal transient stress

International Nuclear Information System (INIS)

Ueda, Masahiro; Kano, Takashi; Yoshitoshi, Atsushi.

1986-01-01

Thermal fatigue tests were performed using straight pipe specimens subjected to cyclic thermal shocks of liquid sodium, and crack growth behaviors were estimated using striation patterns observed clearly on any crack surface. Crack growth rate under cyclic thermal strain reaches the maximum at one depth, and after that it decreases gradually with crack depth. The peak location of crack growth rate becomes deeper by superposition of constant primary stress. Parallel cracks co-existing in the neighborhood move the peak to shallower location and decrease the maximum crack growth rate. The equivalent stress intensity factor range calculated by Walker's formula is successfully applied to the case of negative stress ratio. Fatigue crack growth rate under cyclic thermal strain agreed well with that under the constant temperature equal to the maximum value in the thermal cycle. Simplified methods for calculating the stress intensity factor and the crack interference factor have been developed. Crack growth behavior under thermal fatigue could be well predicted using numerical analysis results. (author)

Fatigue crack growth behavior under cyclic transient thermal stress

International Nuclear Information System (INIS)

Ueda, Masahiro; Kano, Takashi; Yoshitoshi, Atsushi.

1987-01-01

Thermal fatigue tests were performed using straight pipe specimens subjected to cyclic thermal shocks of liquid sodium, and crack growth behaviors were estimated using striation patterns observed clearly on any crack surface. Crack growth rate under cyclic thermal strain reaches the maximum at one depth, and after that it decreases gradually with crack depth. The peak location of crack growth rate becomes deeper by superposition of constant primary stress. Parallel cracks co-existing in the neighborhood move the peak to shallower location and decrease the maximum crack growth rate. The equivalent stress intensity factor range calculated by Walker's formula is successfully applied to the case of negative stress ratio. Fatigue crack growth rate under cyclic thermal strain agreed well with that under the constant temperature equal to the maximum value in the thermal cycle. Simplified methods for calculating the stress intensity factor and the crack interference factor have been developed. Crack growth behavior under thermal fatigue could be well predicted using numerical analysis results. (author)

A new technique for detection of dynamic crack initiation

International Nuclear Information System (INIS)

Miya, K.; Yanagi, H.; Someya, K.

1986-01-01

A new test device was constructed to measure dynamic fracture toughness using electromagnetic force as a dynamic load and a laser system for the detection of load-line deflection. This method provides several advantages with respect to load control, high strain rate and easy instrumentation of the test device. Using the device, experiments on the dynamic fracture were performed with use of edge-cracked three point bending specimens which were made from the nuclear pressure vessel material A508cl.3. The present paper reports on the characteristic feature of dynamic fracture, the measuring technique of dynamic loading and deflection, the detection of dynamic crack initiation and fractographic observation. The detection of the dynamic crack initiation was made possible by the application of an AC electrical potential method that employs a lock-in amplifier driven by a demodulation mode of signal averager and guarantees a fast response to the crack initiation. It was found that the fracture was initiated after unloading of the electromagnetic force is finished, in other words, the fracture was caused by an inertia force and the dynamic fracture toughness Jsub(Id) of the test material was elevated with the increasing loading rate. (orig.)

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

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

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.)

Transient subcritical crack-growth behavior in transformation-toughened ceramics

International Nuclear Information System (INIS)

Dauskardt, R.H.; Ritchie, R.O.; Carter, W.C.; Veirs, D.K.

1990-01-01

Transient subcritical crack-growth behavior following abrupt changes in the applied load are studied in transformation-toughened ceramics. A mechanics analysis is developed to model the transient nature of transformation shielding of the crack tip, K s , with subcritical crack extension following the applied load change. conditions for continued crack growth, crack growth followed by arrest, and no crack growth after the load change, are considered and related to the magnitude and sign of the applied load change and to materials properties such as the critical transformation stress. The analysis is found to provide similar trends in K s compared to values calculated from experimentally measured transformation zones in a transformation-toughened Mg-PSZ. In addition, accurate prediction of the post load-change transient crack-growth behavior is obtained using experimentally derived steady-state subcritical crack-growth relationships for cyclic fatigue in the same material

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%

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%.

Effect of amorphous lamella on the crack propagation behavior of crystalline Mg/amorphous Mg-Al nanocomposites

Science.gov (United States)

Hai-Yang, Song; Yu-Long, Li

2016-02-01

The effects of amorphous lamella on the crack propagation behavior in crystalline/amorphous (C/A) Mg/Mg-Al nanocomposites under tensile loading are investigated using the molecular dynamics simulation method. The sample with an initial crack of orientation [0001] is considered here. For the nano-monocrystal Mg, the crack growth exhibits brittle cleavage. However, for the C/A Mg/Mg-Al nanocomposites, the ‘double hump’ behavior can be observed in all the stress-strain curves regardless of the amorphous lamella thickness. The results indicate that the amorphous lamella plays a critical role in the crack deformation, and it can effectively resist the crack propagation. The above mentioned crack deformation behaviors are also disclosed and analyzed in the present work. The results here provide a strategy for designing the high-performance hexagonal-close-packed metal and alloy materials. Project supported by the National Natural Science Foundation of China (Grant Nos. 11372256 and 11572259), the 111 Project (Grant No. B07050), the Program for New Century Excellent Talents in University of Ministry of Education of China (Grant No. NCET-12-1046), and the Program for New Scientific and Technological Star of Shaanxi Province, China (Grant No. 2012KJXX-39).

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.

Initiation model for intergranular stress corrosion cracking in BWR pipes

International Nuclear Information System (INIS)

Hishida, Mamoru; Kawakubo, Takashi; Nakagawa, Yuji; Arii, Mitsuru.

1981-01-01

Discussions were made on the keys of intergranular stress corrosion cracking of austenitic stainless steel in high-temperature water in laboratories and stress corrosion cracking incidents in operating plants. Based on these discussions, a model was set up of intergranular stress corrosion cracking initiation in BWR pipes. Regarding the model, it was presumed that the intergranular stress corrosion cracking initiates during start up periods whenever heat-affected zones in welded pipes are highly sensitized and suffer dynamic strain in transient water containing dissolved oxygen. A series of BWR start up simulation tests were made by using a flowing autoclave system with slow strain rate test equipment. Validity of the model was confirmed through the test results. (author)

An energy analysis of crack-initiation and arrest in epoxy

Science.gov (United States)

Chudnovsky, A.; Kim, A.; Bosnyak, C. P.

1992-01-01

The objective of this work is to study fracture processes such as crack initiation and arrest in epoxy. A compact tension specimen with displacement-controlled loading is employed to observe multiple crack initiations and arrests. The energy release rate at crack initiation is significantly higher than that at crack arrest, as has been observed elsewhere. In this study, the difference between these energy release rates is found to depend on specimen size (scale effect), and is quantitatively related to the fracture surface morphology. The scale effect, similar to that in strength theory, is conventionally attributed to the statistics of defects which control the fracture process. Triangular shaped ripples, deltoids, are formed on the fracture surface of the epoxy during the slow sub-critical crack growth, prior to the smooth mirrorlike surface characteristic of fast cracks. The deltoids are complimentary on the two crack faces which excludes any inelastic deformation from consideration. The deltoids are analogous to the ripples created on a river surface downstream from a small obstacle. However, in spite of the expectation based on this analogy and the observed scale effect, there are no 'defects' at the apex of the deltoids detectable down to the 0.1 micron level. This suggests that the formation of deltoids during the slow process of subcritical crack growth is an intrinsic feature of the fracture process itself, triggered by inhomogeneity of material on a submicron scale. This inhomogeneity may be related to a fluctuation in the cross-link density of the epoxy.

An initial investigation of the sub-microsecond features of dynamic crack propagation in PMMA and the RDX-based explosive PBX 9205

Science.gov (United States)

Washabaugh, Peter; Hill, Larry

2007-06-01

A dynamic crack propagating in a brittle material releases enough thermal energy to produce visible light. The dynamic fracture of even macroscopically amorphous materials becomes unsteady as the crack propagation velocity approaches the material wave-speeds. The heat generated at a crack-tip, especially as it jumps, may be a mechanism to initiate a self-sustaining reaction in an energetic material. Experiments were conducted in specimens to simulate an infinite plate for 20 μs. The initial specimens were 152 mm square by 6 mm thick acrylic sheets, and were fabricated to study non-steady near-wave-speed crack propagation. A variant of this specimen embedded a 25 mm x 3 mm PBX 9205 pellet to explore the influence of dynamic Mode-I cracks in these materials. The crack was initiated by up to 0.2 g of Detasheet placed along a precursor 50 mm long notch, with a shield to contain the reaction products and prevent propagation along the fractured surfaces. The crack was studied by means of a streak camera and a Fourier-filter of the light reflecting off the newly minted surfaces. The sub-microsecond behavior of holes initiating, preceding and coalescing with the main crack were observed in the PMMA samples. The embedding and mechanical loading of explosives by this technique did not initiate a self-sustaining reaction in preliminary testing.

Nonparametric Change Point Diagnosis Method of Concrete Dam Crack Behavior Abnormality

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Zhanchao Li

2013-01-01

Full Text Available The study on diagnosis method of concrete crack behavior abnormality has always been a hot spot and difficulty in the safety monitoring field of hydraulic structure. Based on the performance of concrete dam crack behavior abnormality in parametric statistical model and nonparametric statistical model, the internal relation between concrete dam crack behavior abnormality and statistical change point theory is deeply analyzed from the model structure instability of parametric statistical model and change of sequence distribution law of nonparametric statistical model. On this basis, through the reduction of change point problem, the establishment of basic nonparametric change point model, and asymptotic analysis on test method of basic change point problem, the nonparametric change point diagnosis method of concrete dam crack behavior abnormality is created in consideration of the situation that in practice concrete dam crack behavior may have more abnormality points. And the nonparametric change point diagnosis method of concrete dam crack behavior abnormality is used in the actual project, demonstrating the effectiveness and scientific reasonableness of the method established. Meanwhile, the nonparametric change point diagnosis method of concrete dam crack behavior abnormality has a complete theoretical basis and strong practicality with a broad application prospect in actual project.

Study of initiation and growth of stress corrosion cracks. Quantitative characterization and modeling

International Nuclear Information System (INIS)

Peyrat, Christine

1997-01-01

A phenomenological study of Stress Corrosion Cracking (SCC) cracks initiation and growth was carried out on a Z 2 CN 18.10 stainless steel in a boiling aqueous magnesium chloride solution at 153 deg. C. The characterization method exploits the morphological information (cracks shape and size distribution) available on a specimen after SCC test. This method, independent of any mechanistic hypothesis, led to the analytical representation of the growth rate of a given crack as a function of its depth and of the density of deeper cracks. The presence of this last parameter could be the expression of a 'shielding effect' of mechanical origin, exerted by the cracks of large size. A 'true initiation' rate was calculated by an extrapolation based on the analytical expression of the growth rate. This analytical representation of cracks initiation and growth accounts for the saturation observed in the experimental determination of the 'apparent initiation'. As time goes, the number of cracks deeper than a given threshold depth tends towards a limit which depends very strongly on the chosen threshold. This saturation effect can be interpreted as exclusively due to the way the small cracks propagate, as the 'true initiation' rate can be expressed versus time by a simple power law. In the case of slow strain rate tests, it is shown that the kinetic parameters characteristic of initiation and growth depend on the applied elongation rate. In particular, the initial crack growth rate increases with elongation rate. The validity domains of the proposed expressions have been specified by means of SCC tests carried out under different types of mechanical loading. (author) [fr

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.

The assessment of creep-fatigue initiation and crack growth

International Nuclear Information System (INIS)

Priest, R.H.; Miller, D.A.

1991-01-01

An outline of Nuclear Electric's Assessment Procedure for the High Temperature Response of Structures ('R5') for creep-fatigue initiation and crack growth is given. A unified approach is adopted for both regimes. For initiation, total damage is described in terms of separate creep and fatigue components. Ductility exhaustion is used for estimating creep damage whilst continuous cycling endurance data are used to evaluate the fatigue damage term. Evidence supporting this approach is given through the successful prediction of creep-fatigue endurances for a range of materials, cycle types, dwell period times, etc. Creep-fatigue crack growth is similarly described in terms of separated creep and fatigue components. Crack growth rates for each component are characterised in terms of fracture mechanics parameters. It is shown that creep crack growth rates can be rationalised on a ductility basis. Creep-fatigue interactions are accommodated in the cyclic growth component through the use of materials coefficients which depend on dwell time. (orig.)

Ductile Crack Initiation Criterion with Mismatched Weld Joints Under Dynamic Loading Conditions.

Science.gov (United States)

An, Gyubaek; Jeong, Se-Min; Park, Jeongung

2018-03-01

Brittle failure of high toughness steel structures tends to occur after ductile crack initiation/propagation. Damages to steel structures were reported in the Hanshin Great Earthquake. Several brittle failures were observed in beam-to-column connection zones with geometrical discontinuity. It is widely known that triaxial stresses accelerate the ductile fracture of steels. The study examined the effects of geometrical heterogeneity and strength mismatches (both of which elevate plastic constraints due to heterogeneous plastic straining) and loading rate on critical conditions initiating ductile fracture. This involved applying the two-parameter criterion (involving equivalent plastic strain and stress triaxiality) to estimate ductile cracking for strength mismatched specimens under static and dynamic tensile loading conditions. Ductile crack initiation testing was conducted under static and dynamic loading conditions using circumferentially notched specimens (Charpy type) with/without strength mismatches. The results indicated that the condition for ductile crack initiation using the two parameter criterion was a transferable criterion to evaluate ductile crack initiation independent of the existence of strength mismatches and loading rates.

Crack Tip Creep Deformation Behavior in Transversely Isotropic Materials

International Nuclear Information System (INIS)

Ma, Young Wha; Yoon, Kee Bong

2009-01-01

Theoretical mechanics analysis and finite element simulation were performed to investigate creep deformation behavior at the crack tip of transversely isotropic materials under small scale creep (SCC) conditions. Mechanical behavior of material was assumed as an elastic-2 nd creep, which elastic modulus ( E ), Poisson's ratio (v ) and creep stress exponent ( n ) were isotropic and creep coefficient was only transversely isotropic. Based on the mechanics analysis for material behavior, a constitutive equation for transversely isotropic creep behavior was formulated and an equivalent creep coefficient was proposed under plain strain conditions. Creep deformation behavior at the crack tip was investigated through the finite element analysis. The results of the finite element analysis showed that creep deformation in transversely isotropic materials is dominant at the rear of the crack-tip. This result was more obvious when a load was applied to principal axis of anisotropy. Based on the results of the mechanics analysis and the finite element simulation, a corrected estimation scheme of the creep zone size was proposed in order to evaluate the creep deformation behavior at the crack tip of transversely isotropic creeping materials

Role of cavity formation in SCC of cold worked carbon steel in high-temperature water. Part 2. Study of crack initiation behavior

International Nuclear Information System (INIS)

Yamada, Takuyo; Aoki, Masanori; Miyamoto, Tomoki; Arioka, Koji

2013-01-01

To consider the role of cavity formation in stress corrosion cracking (SCC) of cold worked (CW) carbon steel in high-temperature water, SCC and creep growth (part 1) and initiation (part 2) tests were performed. The part 2 crack initiation tests used blunt notched compact tension (CT) type specimens of CW carbon steel exposed under the static load condition in hydrogenated pure water and in air in the range of temperatures between 360 and 450°C. Inter-granular (IG) crack initiation was observed both in water and in air even in static load condition when steel specimens had been cold worked. 1/T type temperature dependencies of initiation times were observed for CW carbon steel, and the crack initiation times in an operating pressurized heavy water reactor, PHWR (Pt Lepreau) seemed to lie on the extrapolated line of the experimental results. Cavities were identified at the grain boundaries near the bottom of a notch (highly stressed location) before cracks initiated both in water and air. The cavities were probably formed by the condensation of vacancies and they affected the bond strength of the grain boundaries. To assess the mechanism of IGSCC initiation in high temperature water, the diffusion of vacancies driven by stress gradients was studied using a specially designed CT specimen. As a model for IGSCC in CW carbon steel in high temperature water, it was concluded that the formation of cavities from the collapse of vacancies offers the best interpretation of the present data. (author)

On the transition of short cracks into long fatigue cracks in reactor pressure vessel steels

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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

Flexural Cracking Behavior Of Steel Fiber Reinforced Concrete Beams

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Ashraf Abdalkader

2017-08-01

Full Text Available Steel fibers are added to concrete due to its ability to improve the tensile strength and control propagation of cracks in reinforced concrete members. Steel fiber reinforced concrete is made of cement fine water and coarse aggregate in addition to steel fibers. In this experimental work flexural cracking behavior of reinforced concrete beams contains different percentage of hooked-end steel fibers with length of 50 mm and equivalent diameter of 0.5 mm was studied. The beams were tested under third-point loading test at 28 days. First cracking load maximum crack width cracks number and load-deflection relations were investigated to evaluate the flexural cracking behavior of concrete beams with 34 MPa target mean strength. Workability wet density compressive and splitting tensile strength were also investigated. The results showed that the flexural crack width is significantly reduced with the addition of steel fibers. Fiber contents of 1.0 resulted in 81 reduction in maximum crack width compared to control concrete without fiber. The results also showed that the first cracking load and maximum load are increased with the addition of steel fibers.

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)

Stable crack growth behaviors in welded CT specimens -- finite element analyses and simplified assessments

International Nuclear Information System (INIS)

Yagawa, Genki; Yoshimura, Shinobu; Aoki, Shigeru; Kikuchi, Masanori; Arai, Yoshio; Kashima, Koichi; Watanabe, Takayuki; Shimakawa, Takashi

1993-01-01

The paper describes stable crack growth behaviors in welded CT specimens made of nuclear pressure vessel A533B class 1 steel, in which initial cracks are placed to be normal to fusion line. At first, using the relations between the load-line displacement (δ) and the crack extension amount (Δa) measured in experiments, the generation phase finite element crack growth analyses are performed, calculating the applied load (P) and various kinds of J-integrals. Next, the simplified crack growth analyses based on the GE/EPRI method and the reference stress method are performed using the same experimental results. Some modification procedures of the two simplified assessment schemes are discussed to make them applicable to inhomogeneous materials. Finally, a neural network approach is proposed to optimize the above modification procedures. 20 refs., 13 figs., 1 tab

Specific energy of cold crack initiation in welding low alloy high-strength steels

International Nuclear Information System (INIS)

Brednev, V.I.; Kasatkin, B.S.

1988-01-01

Methods for determination of energy spent on cold crack initiation, when testing welded joint samples by the Implant method, are described. Data on the effect of the steel alloying system, cooling rate of welded joints, content of diffusion hydrogen on the critical specific energy spent on the development of local plastic deformation upto cold crack initiation are presented. The value of specific energy spent on cold crack initiation is shown to be by two-three orders lower than the value of impact strength minimum accessible. The possibility to estimate welded joint resistance to cold crack initiation according to the critical specific energy is established

Fatigue life assessment based on crack growth behavior in reduced activation ferritic/martensitic steel

International Nuclear Information System (INIS)

Nogami, Shuhei; Sato, Yuki; Hasegawa, Akira

2010-01-01

Crack growth behavior under low cycle fatigue in reduced activation ferritic/martensitic steel, F82H IEA-heat (Fe-8Cr-2W-0.2V-0.02Ta), was investigated to improve the fatigue life assessment method of fusion reactor structural material. Low cycle fatigue test was carried out at room temperature in air at a total strain range of 0.4-1.5% using an hourglass-type miniature fatigue specimen. The relationship between the surface crack length and life fraction was described using one equation independent of the total strain range. Therefore, the fatigue life and residual life could be estimated using the surface crack length. Moreover, the microcrack initiation life could be estimated using the total strain range if there was a one-to-one correspondence between the total strain range and number of cycles to failure. The crack growth rate could be estimated using the total strain range and surface crack length by introducing the concept of the normalized crack growth rate. (author)

Nonparametric Change Point Diagnosis Method of Concrete Dam Crack Behavior Abnormality

OpenAIRE

Li, Zhanchao; Gu, Chongshi; Wu, Zhongru

2013-01-01

The study on diagnosis method of concrete crack behavior abnormality has always been a hot spot and difficulty in the safety monitoring field of hydraulic structure. Based on the performance of concrete dam crack behavior abnormality in parametric statistical model and nonparametric statistical model, the internal relation between concrete dam crack behavior abnormality and statistical change point theory is deeply analyzed from the model structure instability of parametric statistical model ...

On the calculation of crack propagation behavior in disks and plates using a mixed finite method

International Nuclear Information System (INIS)

Fischer, W.

1991-01-01

According to the linear theory of elasticity, infinitely high stresses occur in the crack tips of cracked components. Plastic flow initiation or previous damage, however, will limit these stress singularities to an upper maximum stress for all real materials. To permit acquisition of this highly localized material behavior, while avoiding a very high physical nonlinear calculation effort for the evaluation of crack propagation behavior in disks and plates, models essentially based on Dugdale and Barenblatt are used. This involves determining the stress and displacement conditions required for the simulation of crack propagation by means of a mixed finite method introducing the disk cutting forces and plate curvatures or moments as unknown quantities. In addition to pure disk and plate problems, also coupled disk-plate problems are covered, where the coupling, on one hand, is due to the consideration of high deformations. (orig.) With 66 figs., 8 tabs [de

Fatigue-crack propagation behavior of Inconel 718

International Nuclear Information System (INIS)

James, L.A.

1975-09-01

The techniques of linear-elastic fracture mechanics were used to characterize the effect of several variables (temperature, environment, cyclic frequency, stress ratio, and heat-treatment variations) upon the fatigue-crack growth behavior of Inconel 718 base metal and weldments. Relevant crack growth data on this alloy from other laboratories is also presented. (33 fig, 39 references)

Fatigue crack growth resistance and crack closure behavior in two aluminum alloys for aeronautical applications

Directory of Open Access Journals (Sweden)

Elenice Maria Rodrigues

2005-09-01

Full Text Available Aluminum-lithium alloys are candidate materials for many aerospace applications because of their high specific strength and elastic modulus. These alloys have several unique characteristics such as excellent fatigue crack growth resistance when compared with that of the conventional 2000 and 7000 series alloys. In this study, fatigue crack propagation behavior has been examined in a commercial thin plate of Al-Li-Cu-Mg alloy (8090, with specific emphasis at the fatigue threshold. The results are compared with those of the traditional Al-Cu-Mg alloy (2024. Fatigue crack closure is used to explain the different behavior of the compared alloys.

Mathematical modeling of vibration processes in reinforced concrete structures for setting up crack initiation monitoring

Science.gov (United States)

Bykov, A. A.; Matveenko, B. P.; Serovaev, G. S.; Shardakov, I. N.; Shestakov, A. P.

2015-03-01

The contemporary construction industry is based on the use of reinforced concrete structures, but emergency situations resulting in fracture can arise in their exploitation. In a majority of cases, reinforced concrete fracture is realized as the process of crack formation and development. As a rule, the appearance of the first cracks does not lead to the complete loss of the carrying capacity but is a fracture precursor. One method for ensuring the safe operation of building structures is based on crack initiation monitoring. A vibration method for the monitoring of reinforced concrete structures is justified in this paper. An example of a reinforced concrete beam is used to consider all stages related to the analysis of the behavior of natural frequencies in the development of a crack-shaped defect and the use of the obtained numerical results for the vibration test method. The efficiency of the method is illustrated by the results of modeling of the physical part of the method related to the analysis of the natural frequency evolution as a response to the impact action in the crack development process.

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

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.

The PACE-1450 experiment - Crack and leakage behavior of a pre-stressed concrete containment wall considering ageing

International Nuclear Information System (INIS)

Hermann, N.; Mueller, H.S.; Niklasch, C.; Michel-Ponnelle, S.; Bento, C.; Masson, B.

2015-01-01

As an intermediate sized experiment the PACE-1450 experiment aims to investigate the behavior of a curved specimen (length: 3.5 m, width: 1.8 m, height: 1.2 m) which is representative for a 1450 MWe nuclear power plant containment under accidental loading conditions. One focus of this experimental test campaign is the consideration of the ageing of the structure which among other effects leads to a pre-stressing loss. The crack behavior of the realistically reinforced specimen is of as much interest as it is the leakage behavior when an inner pressure occurs within the containment. The reinforcement layout of the specimen is very similar to the original geometry and consists mainly of reinforcement meshes of bars near the inner and outer surface and four pre-stressing cables in the circumferential direction. During the tests the specimen is loaded by pressure which simulates the internal accidental containment pressure of up to 6 bars (absolute pressure). The resulting ring tensile stress in the cylindrical part of the containment is externally applied by hydraulic jacks. An initial pre-stressing of the specimen of 12 MPa is realized in such a way that decreasing the pre-stressing force for the purpose of simulating the ageing of the structure is possible. The facility allows for the cracking of the pre-stressed specimen and for leakage measurements at different controlled crack widths. The specimen is equipped with embedded optical fiber strain and temperature sensors and a sound detection system to record the initiation of cracks. The paper explains the test set-up and presents results of the ongoing test series regarding the cracking and leakage behavior of the specimen

Influence of bending test configuration on cracking behavior of FRC

DEFF Research Database (Denmark)

Finazzi, Silvia; Paegle, Ieva; Fischer, Gregor

2014-01-01

the flexural load-deformation response of FRC. This research focuses particularly on the influence of the appearance and depth of the notch on the cracking behavior of FRC. For this purpose, several specimens, both un-notched and notched with different depths of the notch (25 mm and 45 mm), were tested....... The results obtained in the various tests are compared to determine to what extent the notch can affect cracking behavior and the resulting evaluation of the material according to the method described in the standard. Formation of cracking and the crack development has been documented by means of a digital...

Cracking Behavior of a Concrete Arch Dam with Weak Upper Abutment

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Lei Xu

2017-01-01

Full Text Available The cracking behavior and failure mode of a 78 m high concrete double-curvature arch dam with weak upper abutment are investigated through performing cracking analysis. The mechanical behavior of concrete is simulated using a smeared crack model, in which a combination of the compression yield surface and the crack detection surface with a damaged elasticity concept is employed to describe the failure of concrete. The arch dam with practical mechanical properties of the upper and lower abutments is firstly studied with emphasis on its cracking behavior during overloading. Then, a comprehensive sensitivity analysis is carried out to investigate the influence of the ratio of the mechanical properties of upper abutment to those of lower abutment on dam failure with prime attention placed on the failure mode. Simulation results indicate the adopted smeared crack model is well-suited to the crack analysis of concrete arch dam. It is shown that cracking is localized around the interface between upper and lower abutments, which leads to a fast crack growth in the through-thickness direction of dam and finally causes the dam failure. Furthermore, the sensitivity analysis presents three types of failure modes corresponding to different ratio value, wherein Modes II and III should be avoided since the weak upper abutment plays a predominant role in the cracking and failure of concrete arch dam.

Comparative Study on Crack Initiation and Propagation of Glass under Thermal Loading

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Yu Wang

2016-09-01

Full Text Available This paper explores the fracture process based on finite element simulation. Both probabilistic and deterministic methods are employed to model crack initiation, and several commonly used criteria are utilized to predict crack growth. It is concluded that the criteria of maximum tensile stress, maximum normal stress, and maximum Mises stress, as well as the Coulomb-Mohr criterion are able to predict the initiation of the first crack. The mixed-mode criteria based on the stress intensity factor (SIF, energy release rate, and the maximum principal stress, as well as the SIF-based maximum circumferential stress criterion are suitable to predict the crack propagation.

Study on the fatigue crack initiation life under spherical contact

Energy Technology Data Exchange (ETDEWEB)

Cho, Yong Joo; Kim, Tae Wan [Busan National Univ., Busan (Korea, Republic of); Lee, Mun Ju [Samsung Electronics Co., Ltd., Suwon (Korea, Republic of)

2001-08-01

In case of contact fatigue, the accurate calculation of surface tractions and subsurface stress is essential to the prediction of crack initiation life. Surface tractions influencing shear stress amplitude have been obtained by contact analysis based on influence function. Subsurface stress has been obtained by using rectangular patch solutions. In this study, to simulate asperity contact under sliding condition, the tip of asperity was simulated by sphere and to calculate crack initiation life in the substrate, dislocation pileup theory was used.

Study on the fatigue crack initiation life under spherical contact

International Nuclear Information System (INIS)

Cho, Yong Joo; Kim, Tae Wan; Lee, Mun Ju

2001-01-01

In case of contact fatigue, the accurate calculation of surface tractions and subsurface stress is essential to the prediction of crack initiation life. Surface tractions influencing shear stress amplitude have been obtained by contact analysis based on influence function. Subsurface stress has been obtained by using rectangular patch solutions. In this study, to simulate asperity contact under sliding condition, the tip of asperity was simulated by sphere and to calculate crack initiation life in the substrate, dislocation pileup theory was used

Oxidization and stress corrosion cracking initiation of austenitic alloys in supercritical water

International Nuclear Information System (INIS)

Behnamian, Y.; Li, M.; Luo, J.L.; Chen, W.X.; Zheng, W.; Guzonas, D.A.

2012-01-01

This study determined the stress corrosion cracking behaviour of austenitic alloys in pure supercritical water. Austenitic stainless steels 310S, 316L, and Inconel 625 were tested as static capsule samples at 500 o C for up to 5000 h. After that period, crack initiations were readily observed in all samples, signifying susceptibility to stress corrosion cracking. The microcracks in 316L stainless steel and Inconel 625 were almost intergranular, whereas transgranular microcrack initiation was observed in 310S stainless steel. (author)

Oxidization and stress corrosion cracking initiation of austenitic alloys in supercritical water

Energy Technology Data Exchange (ETDEWEB)

Behnamian, Y.; Li, M.; Luo, J.L.; Chen, W.X. [Univ. of Alberta, Dept. of Chemical and Materials Engineering, Edmonton, Alberta (Canada); Zheng, W. [Materials Technology Laboratory, NRCan, Ottawa, Ontario (Canada); Guzonas, D.A. [Atomic Energy of Canada Limited, Chalk River, Ontario (Canada)

2012-07-01

This study determined the stress corrosion cracking behaviour of austenitic alloys in pure supercritical water. Austenitic stainless steels 310S, 316L, and Inconel 625 were tested as static capsule samples at 500{sup o}C for up to 5000 h. After that period, crack initiations were readily observed in all samples, signifying susceptibility to stress corrosion cracking. The microcracks in 316L stainless steel and Inconel 625 were almost intergranular, whereas transgranular microcrack initiation was observed in 310S stainless steel. (author)

Delayed hydride cracking behavior for zircaloy-2 plate

International Nuclear Information System (INIS)

Mills, J.W.; Huang, F.H.

1991-01-01

The delayed hydride cracking (DHC) behaviour for Zircaloy-2 plate was characterized at temperatures ranging from 300 to 550 o F. Specimens with a longitudinal (T-L) orientation exhibited a classic two-stage DHC response. At K values slightly above the threshold level (K th ), crack-growth rates increased dramatically with increasing K values (stage I). The K th value was found to be 11 and 14 ksi√ in at 400 and 500 o F. At high K values (stage II), cracking rates were relatively insensitive to applied K levels. Stage II crack growth was a thermally activated process described by an Arrhenius-type relationship with an activation energy of 65 kJ/mol. This energy level agreed with the theoretical activation energy for hydrogen diffusion into the triaxial stress field ahead of a crack. Above a critical temperature (300 o F), an overtemperature cycle was required to initiate DHC. The magnitude of the thermal excursion required to initiate cracking was found to increase at higher test temperatures. Specimens with a transverse(L-T) orientation showed a very low sensitivity to DHC because of an unfavorable crystallographic orientation for hydride reorientation. Metallographic and fractographic examinations were performed to understand the DHC mechanism. (author)

Hole Defects Affect the Dynamic Fracture Behavior of Nearby Running Cracks

Directory of Open Access Journals (Sweden)

R. S. Yang

2018-01-01

Full Text Available Effects of defects on the dynamic fracture behavior of engineering materials cannot be neglected. Using the experimental system of digital laser dynamic caustics, the effects of defects on the dynamic fracture behavior of nearby running cracks are studied. When running cracks propagate near to defects, the crack path deflects toward the defect; the degree of deflection is greater for larger defect diameters. When the running crack propagates away from the defect, the degree of deflection gradually reduces and the original crack path is restored. The intersection between the caustic spot and the defect is the direct cause of the running crack deflection; the intersection area determines the degree of deflection. In addition, the defect locally inhibits the dynamic stress intensity factor of running cracks when they propagate toward the defect and locally promotes the dynamic stress intensity factor of running cracks when they propagate away from the defect.

Determination and demarcation of fatigue crack initiation phase in rotating bending condition

International Nuclear Information System (INIS)

Pasha, R.A.; Rehman, K.; Shah, M.

2012-01-01

In engineering applications, components often experience cyclic loading and therefore, have crack initiation propagation phase. In this research work experimental demarcation of fatigue crack initiation has been investigated. Initiation phase of fatigue life of Aluminium was determined by using single and two step fatigue loading test on four point rotating bending fatigue testing machine. Experimental data is used to determine the distinction between the initiation and propagation phase. Initiation phase is determined at different stress levels. The obtained results demonstrate the effect of stress level on initiation phase and propagation phase. (author)

Constitutive Mixed Mode Behavior of Cracks in Concrete

DEFF Research Database (Denmark)

Jacobsen, Jonas Sejersbøl

of custom made orthogonal gauge rails mounted on the specimen. The precise orthogonal gauge rails entail a direct interpretation of the mixed mode crack opening process, ensuring that the achieved response over the ligament is equal to the prescribed mixed mode displacement. After a crack is initiated...

The influence of microstructure on fatigue crack initiation in spheroidal graphite cast irons

International Nuclear Information System (INIS)

Starkey, M.S.; Irving, P.E.

1979-01-01

This paper reports the first stage of this work which concentrates on fatigue crack initiation with particular emphasis on the influence of microstructure. The fatigue lives of three fully ferritic and two fully pearlitic irons, each with different graphite nodule size distributions, have been determined at two strain amplitudes, 0.005 and 0.00018. The tests were carried out in fully reversed strain control on smooth cylindrical specimens in a servohydraulic testing machine. The effects of matrix structure and strength were clearly seen in that the pearlitic irons were superior at both strain levels. Nodule size on the other hand appeared to have no significant effect. The crack initiation sites in the specimens were located by interrupting the tests on detection of a 5% tensile load drop and heat tinting, before continuing. After failure, which was defined as complete separation, the fracture faces were examined on the scanning electron microscope. In the majority of the specimens the major crack origin was found to be a surface micropore with depths ranging from 50 to 250 μm. It is suggested that these micropores and not the graphite modules strongly influence the crack initiation behaviour in SG iron. These findings were confirmed by monitoring the initiation and growth of surface cracks from micropores using surface replica techniques. The influence of microstructure on the percentage of life spent in initiating and propagating a crack was thus determined. Hence the factors contributing to the fatigue behaviour of SG irons can be quantified. Their influence on predictions of cycles to crack initiation using the local approach is discussed. (orig.) 891 RW/orig. 892 RKD [de

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)

Crack growth behavior of low-alloy bainitic 51CrV4 steel

OpenAIRE

Canadinç, Demircan; Lambers, H. G.; Gorny B.; Tschumak, S.; Maier, H.J.

2010-01-01

The crack growth behavior of low-alloy bainitic 51CrV4 steel was investigated. The current results indicate that the stress state present during the isothermal bainitic transformation has a strong influence on the crack propagation behavior in the near threshold regime, when the crack growth direction is perpendicular to the loading axis of the original sample undergoing phase transformation. However, the influence of stresses superimposed during the bainitic transformation on the crack growt...

High temperature initiation and propagation of cracks in 12%Cr-steel turbine disks

Directory of Open Access Journals (Sweden)

S. Foletti

2013-10-01

Full Text Available This work aims to study the crack propagation in 12%Cr steel for turbine disks. Creep Crack Growth (CCG tests on CT specimens have been performed to define the proper fracture mechanics which describes the initiation of the crack propagation and the crack growth behaviour for the material at high temperature. Results have been used to study the occurrence of crack initiation on a turbine disk at the extreme working temperature and stress level experienced during service, and validate the use of C* integral in correlating creep growth rate on the disk component, in case C* is numerically calculated through FEM analysis or calculated by the use of reference stress concept.

The crystallography of fatigue crack initiation in Incoloy-908 and A-286 steel

International Nuclear Information System (INIS)

Krenn, C.R.

1996-12-01

Fatigue crack initiation in the austenitic Fe-Ni superalloys Incoloy-908 and A-286 is examined using local crystallographic orientation measurements. Results are consistent with sharp transgranular initiation and propagation occurring almost exclusively on {111} planes in Incoloy-908 but on a variety of low index planes in A-286. This difference is attributed to the influence of the semicoherent grain boundary η phase in A-286. Initiation in each alloy occurred both intergranularly and transgranularly and was often associated with blocky surface oxide and carbide inclusions. Taylor factor and resolved shear stress and strain crack initiation hypotheses were tested, but despite an inconclusive suggestion of a minimum required {111} shear stress, none of the hypotheses were found to convincingly describe preferred initiation sites, even within the subsets of transgranular cracks apparently free from the influence of surface inclusions. Subsurface inclusions are thought to play a significant role in crack initiation. These materials have applications for use in structural conduit for high field superconducting magnets designed for fusion energy use

Diffraction-based study of fatigue crack initiation and propagation in aerospace aluminum alloys

Science.gov (United States)

Gupta, Vipul K.

The crack initiation sites and microstructure-sensitive growth of small fatigue cracks are experimentally characterized in two precipitation-hardened aluminum alloys, 7075-T651 and 7050-T7451, stressed in ambient temperature moist-air (warm-humid) and -50°C dry N2 (cold-dry) environmental conditions. Backscattered electron imaging (BSE) and energy dispersive spectroscopy (EDS) of the fracture surfaces showed that Fe-Cu rich constituent particle clusters are the most common initiation sites within both alloys stressed in either environment. The crack growth within each alloy, on average, was observed to be slowed in the cold-dry environment than in the warm-humid environment, but only at longer crack lengths. Although no overwhelming effects of grain boundaries and grain orientations on small-crack growth were observed, crack growth data showed local fluctuations within individual grains. These observations are understood as crack propagation through the underlying substructure at the crack surface and frequent interaction with low/high-angle grain and subgrain boundaries, during cyclic loading, and, are further attributed to periodic changes in crack propagation path and multiple occurrences of crack-branching observed in the current study. SEM-based stereology in combination with electron backscattered diffraction (EBSD) established fatigue crack surface crystallography within the region from ˜1 to 50 mum of crack initiating particle clusters. Fatigue crack facets were parallel to a wide variety of crystallographic planes, with pole orientations distributed broadly across the irreducible stereographic triangle between the {001} and {101}-poles within both warm-humid and cold-dry environments. The results indicate environmentally affected fatigue cracking in both cases, given the similarity between the observed morphology and crystallography with that of a variety of aerospace aluminum alloys cracked in the presence of moist-air. There was no evidence of

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

radiation-induced hardening is observed. The microstructural deformation mode of proton irradiated Zircaloy-4 strained in the transverse direction is basal channeling, and deformation is localized in macroscopic deformation bands. The critical resolved shear stresses of the basal and prismatic gliding systems are reversed by proton-irradiation. The dislocation loops microstructure, the hardening, and the deformation modes of neutron-irradiated Zircaloy-4 are fairly well simulated by proton-irradiation. Proton-irradiation induces a significant increase of the I-SCC crack initiation susceptibility, after transverse tensile testing. At low iodine concentrations, cracks initiate on the macroscopic deformation bands, and when there is an increase in the iodine concentration, the level of local deformation necessary to crack initiation decreases. (author)

Analysis on the Initial Cracking Parameters of Cross-Measure Hydraulic Fracture in Underground Coal Mines

Directory of Open Access Journals (Sweden)

Yiyu Lu

2015-07-01

Full Text Available Initial cracking pressure and locations are important parameters in conducting cross-measure hydraulic fracturing to enhance coal seam permeability in underground coalmines, which are significantly influenced by in-situ stress and occurrence of coal seam. In this study, stress state around cross-measure fracturing boreholes was analyzed using in-situ stress coordinate transformation, then a mathematical model was developed to evaluate initial cracking parameters of borehole assuming the maximum tensile stress criterion. Subsequently, the influences of in-situ stress and occurrence of coal seams on initial cracking pressure and locations in underground coalmines were analyzed using the proposed model. Finally, the proposed model was verified with field test data. The results suggest that the initial cracking pressure increases with the depth cover and coal seam dip angle. However, it decreases with the increase in azimuth of major principle stress. The results also indicate that the initial cracking locations concentrated in the second and fourth quadrant in polar coordinate, and shifted direction to the strike of coal seam as coal seam dip angle and azimuth of maximum principle stress increase. Field investigation revealed consistent rule with the developed model that the initial cracking pressure increases with the coal seam dip angle. Therefore, the proposed mathematical model provides theoretical insight to analyze the initial cracking parameters during cross-measure hydraulic fracturing for underground coalmines.

Stress corrosion cracking behavior of zircaloy-2 in iodine environment

International Nuclear Information System (INIS)

Ikeda, Seiichi

1983-01-01

The effects of strain rates, iodine partial pressure and testing temperature on SCC behavior of zircaloy-2 in iodine environment were studied by means of slow strain rate technique (SSRT). SCC behavior of recrystallized specimens in iodine environment was remarkably influenced by the testing temperatures, and the susceptibility to SCC of specimens tested at 623 K was higher than that at 573 K. The susceptibility to SCC of recrystallized specimens increased with increasing iodine partial pressure at the lower strain rates of 4.2 x 10 -6 s -1 and 8.3 x 10 -7 s -1 . Cold worked specimens indicate no SCC failure in iodine environment regardless of strain rates, although those were tested only at 573 K. Fractographic observation revealed that SCC features of recrystallized specimens can be classified into two groups. One group, mostly specimens tested at 573 K, are characterized by the fact that cracks are initiated from corrosion pits. The other group are characterized by transgranuler SCC in the absence of pitting. This type of crack is found on specimens tested in environments containing more than 570 Pa iodine and seems to be produced by iodine embrittlement. (author)

Fatigue-crack growth behavior in dissimilar metal weldments

International Nuclear Information System (INIS)

James, L.A.

1977-03-01

The techniques of linear-elastic fracture mechanics were used to characterize fatigue-crack propagation behavior in three dissimilar metal weldments at test temperatures of 800 0 F (427 0 C) and 1000 0 F (538 0 C). The weldments studied included Inconel 718/Type 316, all using Inconel 82 as the filler metal. In general, fatigue-crack growth rates in the weldments were equal to, or less than, those observed in the base metals. Crack deviation from the expected path perpendicular to the loading axis was noted in some cases, and is discussed

Plastic collapse behavior for thin tube with two parallel cracks

International Nuclear Information System (INIS)

Moon, Seong In; Chang, Yoon Suk; Kim, Young Jin; Lee, Jin Ho; Song, Myung Ho; Choi, Young Hwan; Kim, Joung Soo

2004-01-01

The current plugging criterion is known to be too conservative for some locations and types of defects. Many defects detected during in-service inspection take on the form of multiple cracks at the top of tube sheet but there is no reliable plugging criterion for the steam generator tubes with multiple cracks. Most of the previous studies on multiple cracks are confined to elastic analyses and only few studies have been done on the steam generator tubes failed by plastic collapse. Therefore, it is necessary to develop models which can be used to estimate the failure behavior of steam generator tubes with multiple cracks. The objective of this study is to verify the applicability of the optimum local failure prediction models proposed in the previous study. For this, plastic collapse tests are performed with the tube specimens containing two parallel through-wall cracks. The plastic collapse load of the steam generator tubes containing two parallel through-wall cracks are also estimated by using the proposed optimum global failure model and the applicability is investigated by comparing the estimated results with the experimental results. Also, the interaction effect between two cracks was evaluated to explain the plastic collapse behavior

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.

Fatigue crack closure behavior at high stress ratios

Science.gov (United States)

Turner, C. Christopher; Carman, C. Davis; Hillberry, Ben M.

1988-01-01

Fatigue crack delay behavior at high stress ratio caused by single peak overloads was investigated in two thicknesses of 7475-T731 aluminum alloy. Closure measurements indicated no closure occurred before or throughout the overload plastic zones following the overload. This was further substantiated by comparing the specimen compliance following the overload with the compliance of a low R ratio test when the crack was fully open. Scanning electron microscope studies revealed that crack tunneling and possibly reinitiation of the crack occurred, most likely a result of crack-tip blunting. The number of delay cycles was greater for the thinner mixed mode stress state specimen than for the thicker plane strain stress state specimen, which is similar to low R ratio test results and may be due to a larger plastic zone for the mixed mode cased.

Behavior of Fatigue Crack Tip Opening in Air and Corrosive Atmosphere

Science.gov (United States)

Hayashi, Morihito; Toeda, Kazunori

In the study, a formula for predicting fatigue crack tip opening displacement is deduced firstly. And then, due to comparing actual crack growth rate with the deduced formula, the crack tip configuration factor is defined to figure out the crack tip opening configuration that is useful to clarify the behavior of fatigue crack tip formation apparently. Applying the concept, the crack growth of 7/3 brass and 6/4 brass is predicted from the formula, by replacing material properties such as plastic flow resistance, Young modulus, the Poisson ratio, and fatigue toughness, and fatigue test conditions such as the stress intensity factor range, the load ratio, and cycle frequency. Furthermore, the theoretically expected results are verified with the fatigue tests which were carried out on CT specimens under different load conditions of load ratio, cycle frequency, and cyclic peak load, in different environments of air or corrosive ammonia atmosphere, for various brasses. And by comparing and discussing the calculated crack growth rate with attained experimental results, the apparent configuration factor at the crack tip is determined. And through the attained factor which changes along with crack growth, the behaviors of fatigue crack tip formation under different test conditions have been found out.

Heat affected zone and fatigue crack propagation behavior of high performance steel

International Nuclear Information System (INIS)

Choi, Sung Won; Kang, Dong Hwan; Kim, Tae Won; Lee, Jong Kwan

2009-01-01

The effect of heat affected zone in high performance steel on fatigue crack propagation behavior, which is related to the subsequent microstructure, was investigated. A modified Paris-Erdogan equation was presented for the analysis of fatigue crack propagation behavior corresponding to the heat affected zone conditions. Fatigue crack propagation tests under 0.3 stress ratio and 0.1 load frequency were conducted for both finegrained and coarse-grained heat affected zones, respectively. As shown in the results, much higher crack growth rate occurred in a relatively larger mean grain size material under the same stress intensity range of fatigue crack propagation process for the material.

Description of the initiation and progress of cracks for hot cracks in temperature resistant 1% CrMoV castings under creep or fatigue stress

International Nuclear Information System (INIS)

Bareiss, J.; Maile, K.; Berger, C.; Mayer, K.H.; Weiss, M.

1994-01-01

The results available so far have shown that under vibration stress at room temperature and at 530 C, the simplified equations of fracture mechanics are sufficient (in spite of the complicated fault geometries), in order to conservatively describe the behaviour of fault positions (open or partly-healed hot cracks) with regard to their crack initiation behaviour if combined with the findings US test technique. Here the sample castings which in the initial state showed fault indications of US type EET near the surface, tend to earlier initiation of a crack compared to lower fault positions of the samples. Internal fault positions (partially healed hot cracks) often only showed local cracks (trans-crystalline deformation cracks) within the fault area with an order of magnitude of about 10-50 μm, in spite of exceeding the threshold value Δ Ko. The comparison of the crack propagation behaviour of the sample castings, determined via the potential sensor method on medium lengths of fault with the results of crack growth of fracture mechanics samples in the da/dN- Δ K diagram showed for the evaluated sample castings with a relatively great initial depth or length of fault that the upper scatter band limit of the Paris Law determined for the material can be used to estimate the fault position behaviour. (orig./RHM) [de

Detection of ductile crack initiation by acoustic emission testing

International Nuclear Information System (INIS)

Richter, H.; Boehmert, J.; Viehrig, H.W.

1998-08-01

A Charpy impact test equipment is described permitting simultaneous measurement of impact force, crack tip opening, acoustic emissions and magnetic emissions. The core of the equipment is an inverted pendulum ram impact testing machine and the tests have been performed with laterally notched, pre-fatigue ISO-V specimens made of steels of various strength and toughness properties. The tests are intended to ascertain whether the acoustic emission method is suitable for detecting steady crack initiation in highly ductile steels. (orig./CB) [de

The effect of chloride on general corrosion and crack initiation of low-alloy steels in oxygenated high-temperature water

International Nuclear Information System (INIS)

Herbst, Matthias; Roth, Armin; Widera, Martin; Kuester, Karin; Huettner, Frank; Nowak, Erika

2012-01-01

The effect of chloride on the general corrosion and its potential impact on EAC crack initiation of low-alloy steel (German reactor pressure vessel steel 22 NiMoCr 3 7) in oxygenated high-temperature water were investigated. The general corrosion behavior was analyzed by exposure tests with either permanently increased chloride concentration levels or temporary chloride transients. The potential effect on EAC crack initiation was analyzed with pre-strained C-ring specimens and in SSRT (CERT) tests with slowly rising strain. Both kinds of tests were performed under simulated BWR conditions and with different chloride levels. The chloride concentrations of 5 to 50 ppb were chosen according to the action levels of the German water chemistry guideline for the reactor coolant of BWRs (VGB R401J, 2006). In all exposure tests, none of the pre-strained C-ring specimens showed crack initiation during up to 1000 hours of exposure time with up to 50 ppb chloride. Investigations of the oxide layer thickness after immersion testing revealed a decrease with increasing chloride concentration. As shown by post-test chemical analysis of the oxide layer composition by TOF-SIMS, this effect is most likely primarily due to adsorption of chloride on the oxide layer surface, since only very limited penetration of chloride into the oxide was detected. In contrast to the tests with C-ring specimens, where no crack initiation occurred, slightly accelerated crack initiation at lower elongation levels was observed at increasing chloride concentrations in SSRT tests under simulated BWR conditions using actively loaded specimens. In addition, SSRT specimens that were cyclically loaded at the oxide fracture elongation level were used to generate a continuous, exposure of bare metal to the environment by repeated fracture of the oxide. This loading pattern did not cause crack initiation at all chloride concentrations applied (up to 50 ppb). From these results, it may be concluded that at least

On the behavior of crack surface ligaments

International Nuclear Information System (INIS)

Nilsson, P.; Staahle, P.; Sundin, K.G.

1998-01-01

Small ligaments connecting the fracture surfaces just behind a moving crack front are assumed to exist under certain conditions. The ligaments are rapidly torn as the crack advances. Inelastic straining of such ligaments influences the energy balance in the fracture process. The rapid tearing of a single ligament is studied both numerically and experimentally. An elastic visco-plastic material model is adopted for finite-element calculations. The results show that relatively large amounts of energy are dissipated during the tearing process. Further, the energy needed to tear a ligament increases rapidly with increasing tearing rate. The computed behavior is partly verified in a few preliminary experiments. The implications for slow stable crack tip speeds during dynamic fracture are discussed. (orig.)

Risk estimation for LCF crack initiation

OpenAIRE

Schmitz, Sebastian; Rollmann, Georg; Gottschalk, Hanno; Krause, Rolf

2013-01-01

An accurate risk assessment for fatigue damage is of vital importance for the design and service of today's turbomachinery components. We present an approach for quantifying the probability of crack initiation due to surface driven low-cycle fatigue (LCF). This approach is based on the theory of failure-time processes and takes inhomogeneous stress fields and size effects into account. The method has been implemented as a finite-element postprocessor which uses quadrature formulae of higher o...

On short cracks that depart from elastoplastic notch tips

Directory of Open Access Journals (Sweden)

Verônica Miquelin Machado

2017-07-01

Full Text Available The behavior of short cracks that depart from elastoplastic notch tips is modeled to estimate the stresses required to initiate and to propagate cracks in notched structural components, and to evaluate the size of tolerable crack-like defects under general loading conditions. This analysis can model both fatigue and environmentally assisted cracking problems; can evaluate notch sensitivity in both cases; and can as well be used to establish design or acceptance criteria for tolerable non-propagating crack-like defects in such cases. The growth of short cracks is assumed driven by the applied stresses and by the stress gradient ahead the notch tip, and supported by the material resistances to crack initiation and to long crack propagation by fatigue or EAC. In the elastoplastic case, the stress gradient ahead of the notch tip is quantified by a J-field to consider the short crack behavior. The tolerable short crack predictions made by this model are evaluated by suitable fatigue and EAC tests of notched specimens specially designed to start nonpropagating cracks from the notch tips, both under elastic and elastoplastic conditions.

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

Characterization of mixed mode crack opening in concrete

DEFF Research Database (Denmark)

Jacobsen, Jonas Sejersbøl; Poulsen, Peter Noe; Olesen, John Forbes

2012-01-01

components of the mixed mode displacement are measured using a custom made orthogonal gauge, and the measurements are used directly as the closed loop control signals. A double notch, concrete specimen is used for the crack investigation. The tests are divided into two steps, a pure Mode I opening step......In real concrete structures cracks often open in mixed mode after their initiation. To capture the direct material behavior of a mixed mode crack opening a stiff biaxial testing machine, capable of imposing both normal and shear loads on a given crack area, has been applied. The opening and sliding......, where a macro crack is initiated in the specimen followed by the mixed mode opening step. The high stiffness of the set-up together with the closed control loop ensures a stable crack initiation followed by a controllable mixed mode opening. The deep notches result in a plane crack, only influenced...

Master curve based correlation between static initiation toughness KIC and crack arrest toughness KIa

International Nuclear Information System (INIS)

Wallin, K.; Rintamaa, R.

1999-01-01

Historically the ASME reference curve concept assumes a constant relation between static fracture toughness initiation toughness and crack arrest toughness. In reality, this is not the case. Experimental results show that the difference between K IC and K Ia is material specific. For some materials there is a big difference while for others they nearly coincide. So far, however, no systematic study regarding a possible correlation between the two parameters has been performed. The recent Master curve method, developed for brittle fracture initiation estimation, has enabled a consistent analysis of fracture initiation toughness data. The Master curve method has been modified to be able to describe also crack arrest toughness. Here, this modified 'crack arrest master curve' is further validated and used to develop a simple, but yet (for safety assessment purpose) adequately accurate correlation between the two fracture toughness parameters. The correlation enables the estimation of crack arrest toughness from small Charpy-sized static fracture toughness tests. The correlation is valid for low Nickel steels ≤ (1.2% Ni). If a more accurate description of the crack arrest toughness is required, it can either be measured experimentally or estimated from instrumented Charpy-V crack arrest load information. (orig.)

A study on the fracture energy of Steel Fiber Reinforced Concrete structures with initial cracks

International Nuclear Information System (INIS)

Chang, Dong-Il; Sim Jongsung; Chai, Won-Kyu; Lee, Myeong-Gu

1991-01-01

Fracture test is performed in order to investigate the fracture behavior of SFRC (Steel Fiber Reinforced Concrete) structures. Thirty six SFRC beams are used in this test. The relationships between loading, strain, and mid-span deflection of the beams are observed under the three point loading system. From the test results, the effects of the fiber content, the fiber aspect ratio and the initial crack ratio on the concrete fracture behavior were studied, and the flexural strength and the fracture energy of SFRC beams were also calculated. According to the regression technique, some empirical formulae for predicting the flexural strength and the fracture energy of SFRC beams are also suggested. (author)

Fatigue crack initiation and growth life prediction with statistical consideration

International Nuclear Information System (INIS)

Kwon, J.D.; Choi, S.H.; Kwak, S.G.; Chun, K.O.

1991-01-01

Life prediction or residual life prediction of structures or machines is one of the most strongly world wide needed problems as requirement in the stage of slowly developing economy which comes after rapidly and highly developing stage. For the purpose of statistical life prediction, fatigue test was conducted under the 3 stress levels, and for each stress level, 20 specimens are used. The statistical properties of the crack growth parameter m and C in the fatigue crack growth law of da/dN = C(ΔK) m , and the relationship between m and C, and the statistical distribution pattern of fatigue crack initiation, growth and fracture lives can be obtained by experimental results

Numerical modelling of crack initiation and propagation in concrete structure under hydro-mechanical loading

International Nuclear Information System (INIS)

Bian, H.B.; Jia, Y.; Shao, J.F.

2012-01-01

Document available in extended abstract form only. This subject is devoted to numerical analysis of crack initiation and propagation in concrete structures due to hydro-mechanical coupling processes. When the structures subjected to the variation in hydraulic conditions, fractures occur as a consequence of coalescence of diffuse damage. Consequently, the mechanical behaviour of concrete is described by an isotropic damage model. Once the damage reaches a critical value, a macroscopic crack is initiated. In the framework of extended Finite Element Method (XFEM), the propagation of localized crack is studied in this paper. Each crack is then considered as a discontinuity surface of displacement. According to the determination of crack propagation orientations, a tensile stress-based criterion is used. Furthermore, spatial variations of mechanical properties of concrete are also taken into account using the Weibull distribution function. Finally, the proposed model is applied to numerical analysis of a concrete liner in the context of feasibility studies for geological storage of radioactive wastes. The numerical results show that the proposed approach is capable to reproduce correctly the initiation and propagation crack process until the complete failure of concrete structures during hydro-mechanical loading. The concrete is most widely used construction material in many engineering applications. It is generally submitted to various environmental loading: such as the mechanical loading, the variation of relative humidity and the exposure to chemical risk, etc. In order to evaluate the safety and durability of concrete structures, it is necessary to get a good knowledge on the influence of loading path on the concrete behaviour. The objective of this paper is to study numerically the crack propagation in concrete structure under hydro-mechanical loading,.i.e. the mechanical behaviour of concrete subjected to drying process. The drying process leads to desiccation

Effect of variable load on crack initiation microalloyed steel S 690-QL

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M. Burzić

2015-01-01

Full Text Available The accumulation of damage in the form of initiation and growth of micro-cracks is the first stage of destruction that ends when the merger microcracks form macro cracks. Cracks formed in the cycle number N =104 - 105 are the result of low cycle fatigue. From the need to evaluate low cycle fatigue life was carried out to investigate the low cycle fatigue microalloyed high-strength steel S690QL in the heat-treated.

Mechanism of fatigue crack initiation in austenitic stainless steels in light water reactor environments

International Nuclear Information System (INIS)

Chopra, O.K.; Shack, W.J.; Muscara, J.

2003-01-01

This paper examines the mechanism of fatigue crack initiation in austenitic stainless steels (SSs) in light water reactor (LWR) coolant environments. The effects of key material and loading variables on the fatigue lives of wrought and cast austenitic SSs in air and LWR environments have been evaluated. The influence of reactor coolant environments on the formation and growth of fatigue cracks in polished smooth SS specimens is discussed. The results indicate that the fatigue lives of these steels are decreased primarily by the effects of the environment on the growth of cracks <200 μm and, to a lesser extent, on enhanced growth rates of longer cracks. The fracture morphology in the specimens has been characterized. Exploratory fatigue tests were conducted to study the effects of surface micropits or minor differences in the surface oxide on fatigue crack initiation. (author)

Finite element analysis of the influence of elastic anisotropy on stress intensification at stress corrosion cracking initiation sites in fcc alloys

Science.gov (United States)

Meric de Bellefon, G.; van Duysen, J. C.

2018-05-01

A recent finite-element method (FEM)-based study from the present authors quantified the effect of elastic anisotropy of grains on stress intensification at potential intergranular stress corrosion cracking (IGSCC) initiation sites in austenitic stainless steels. In particular, it showed that the auxetic behavior of grains (negative Poisson's ratio) in some directions plays a very important role in IGSCC initiation, since it can induce local stress intensification factors of about 1.6. A similar effect is expected for other fcc alloys such as Ni-based alloys. The present article confirms those results and paves the way to the definition of an IGSCC susceptibility index by identifying grain configurations that are the most favorable for crack initiation. The index will rely on the probability to get those configurations on surface of specimens.

Initiation of stress corrosion cracking in pre-stained austenitic stainless steels exposed to primary water

International Nuclear Information System (INIS)

Huguenin, P.

2012-01-01

Austenitic stainless steels are widely used in primary circuits of Pressurized Water Reactors (PWR) plants. However, a limited number of cases of Intergranular Stress Corrosion Cracking (IGSCC) has been detected in cold-worked (CW) areas of non-sensitized austenitic stainless steel components in French PWRs. A previous program launched in the early 2000's identified the required conditions for SCC of cold-worked stainless steels. It was found that a high strain hardening coupled with a cyclic loading favoured SCC. The present study aims at better understanding the role of pre-straining on crack initiation and at developing an engineering model for IGSCC initiation of 304L and 316L stainless steels in primary water. Such model will be based on SCC initiation tests on notched (not pre-cracked) specimens under 'trapezoidal' cyclic loading. The effects of pre-straining (tensile versus cold rolling), cold-work level and strain path on the SCC mechanisms are investigated. Experimental results demonstrate the dominating effect of strain path on SCC susceptibility for all pre-straining levels. Initiation can be understood as crack density and crack depth. A global criterion has been proposed to integrate both aspects of initiation. Maps of SCC initiation susceptibility have been proposed. A critical crack depth between 10 and 20 μm has been demonstrated to define transition between slow propagation and fast propagation for rolled materials. For tensile pre-straining, the critical crack depth is in the range 20 - 50 μm. Experimental evidences support the notion of a KISCC threshold, whose value depends on materials, pre-straining ant load applied. The initiation time has been found to depend on the applied loading as a function of (σ max max/YV) 11,5 . The effect of both strain path and surface hardening is indirectly taken into account via the yield stress. In this study, material differences rely on strain path effect on mechanical properties. As a result, a stress

Study of Hot Salt Stress Corrosion Crack Initiation of Alloy IMI 834 by using DC Potential Drop Method

Energy Technology Data Exchange (ETDEWEB)

Pustode, Mangesh D. [Bharat Forge Ltd., Pune (India); Dewangan, Bhupendra [Tata Steel, Jamshedpur (India); Raja, V. S. [Indian Institute of Technology Bombay, Mumbai (India); Paulose, Neeta; Babu, Narendra [Gas Turbine Research Establishment (GTRE), Bangalore (India)

2016-10-15

DC potential drop technique was employed during the slow strain rate tests to study the hot salt stress corrosion crack (HSSCC) initiation at 300 and 400 ℃. Threshold stresses for HSSCC initiation were found to about 88 % of the yield strength at both temperatures, but the time from crack initiation to final failure (Δtscc) decreased significantly with temperature, which reflects larger tendency for brittle fracture and secondary cracking. The brittle fracture features consisted of transgranular cracking through the primary α grain and discontinuous faceted cracking through the transformed β grains.

Influence of intermetallic particles on short fatigue crack initiation in AA2050-T8 and AA7050-T7451

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Nizery Erembert

2014-06-01

Full Text Available Fatigue crack initiation at particles is studied in hot rolled 2050-T8 and 7050-T7451 material, using 1 to 4 mm cross section specimens. Both size and aspect ratio of particles are observed to affect their probability of being damaged. In 2050-T8 material, the probability that a matrix crack initiate at a cracked particle increases with its size, and no effect of aspect ratio is observed. In 2050-T8 specimens, matrix cracks initiate at both precracked (Al, Cu, Fe, Mn particles and particles cracked during cycling. Initiation in 7050-T74 specimens occur on Mg2Si particles which may be cracked or debonded, and Al7Cu2Fe particles that are cracked during cyclic loading.

Crack propagation behavior of Ti-5Ta alloy in boiling nitric acid solution

International Nuclear Information System (INIS)

Motooka, Takafumi; Kiuchi, Kiyoshi

1999-05-01

The crack propagation behavior of Ti-5Ta alloy both in boiling nitric acid solution and in air at room temperature has been investigated. The crack growth rate of Ti-5Ta alloy was measured as a function of the stress intensity factor range. After the tests, the fracture surface morphology was observed by a scanning electron microscope and the crystallographic orientation was examined by X-ray diffraction analysis. Difference in the crack growth behavior was not observed in both environments. The crack growth rate in boiling nitric acid solution was similar to that in air at room temperature. Moreover, the crystallographic orientation of Ti-5Ta alloy had little effect on the fatigue behavior, because this alloy does not have the susceptibility to SCC in nitric acid solution. (author)

Molecular dynamics simulation of effect of hydrogen atoms on crack propagation behavior of α-Fe

Energy Technology Data Exchange (ETDEWEB)

Song, H.Y., E-mail: gsfshy@sohu.com; Zhang, L.; Xiao, M.X.

2016-12-16

The effect of the hydrogen concentration and hydrogen distribution on the mechanical properties of α-Fe with a pre-existing unilateral crack under tensile loading is investigated by molecular dynamics simulation. The results reveal that the models present good ductility when the front region of crack tip has high local hydrogen concentration. The peak stress of α-Fe decreases with increasing hydrogen concentration. The studies also indicate that for the samples with hydrogen atoms, the crack propagation behavior is independent of the model size and boundaries. In addition, the crack propagation behavior is significantly influenced by the distribution of hydrogen atoms. - Highlights: • The distribution of hydrogen plays a critical role in the crack propagation. • The peak stress decrease with the hydrogen concentration increasing. • The crack deformation behavior is disclosed and analyzed.

Fatigue-crack propagation behavior of Inconel 600

International Nuclear Information System (INIS)

James, L.A.

1976-05-01

The techniques of linear-elastic fracture mechanics were employed to characterize the effects of several parameters upon the fatigue-crack propagation behavior of Inconel 600. The parameters studied included temperature, cyclic frequency, stress ratio, thermal aging, and a limited amount of testing in a liquid sodium environment

Artificial-Crack-Behavior Test Evaluation of the Water-Leakage Repair Materials Used for the Repair of Water-Leakage Cracks in Concrete Structures

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Soo-Yeon Kim

2016-09-01

Full Text Available There are no existing standard test methods at home and abroad that can verify the performance of water leakage repair materials, and it is thus very difficult to perform quality control checks in the field of water leakage repair. This study determined that the key factors that have the greatest impact on the water leakage repair materials are the micro-behaviors of cracks, and proposed an artificial-crack-behavior test method for the performance verification of the repair materials. The performance of the 15 kinds of repair materials that are currently being used in the field of water leakage repair was evaluated by applying the proposed test method. The main aim of such a test method is to determine if there is water leakage by injecting water leakage repair materials into a crack behavior test specimen with an artificial 5-mm crack width, applying a 2.5 mm vertical behavior load at 100 cycles, and applying 0.3 N/mm2 constant water pressure. The test results showed that of the 15 kinds of repair materials, only two effectively sealed the crack and thus stopped the water leakage. The findings of this study confirmed the effectiveness of the proposed artificial-crack-behavior test method and suggest that it can be used as a performance verification method for checking the responsiveness of the repair materials being used in the field of water leakage repair to the repetitive water leakage behaviors that occur in concrete structures. The study findings further suggest that the use of the proposed test method makes it possible to quantify the water leakage repair quality control in the field.

A method for probing the effects of conformal nanoscale coatings on fatigue crack initiation in electroplated Ni films

International Nuclear Information System (INIS)

Straub, T.; Baumert, E.K.; Eberl, C.; Pierron, O.N.

2012-01-01

This paper describes an experimental technique to identify robust nanoscale coatings for improving the long-term reliability of metallic microelectromechanical systems. More specifically, the influence of nanoscale alumina coatings on the fatigue crack initiation process in 20 μm thick electrodeposited Ni films was investigated in a mild (30 °C, 50% RH) and harsh (80 °C, 90% RH) environment. Atomic-layer-deposited alumina layers, with thicknesses of 5 and 25 nm, were coated on Ni fatigue micro-resonators, and the fatigue degradation behavior in the very high cycle fatigue regime was compared to that of uncoated structures. Evidence based on post-test scanning electron microscopy and resonant frequency evolution plots shows that the coatings do not prevent the formation of fatigue extrusions and micro-cracks. However, their formation is likely delayed for the 25 nm thick alumina-coated Ni films. - Highlights: ► Effect of alumina coatings (5 and 25 nm thick) on fatigue initiation in nickel films ► Fatigue tests were performed at 30 °C, 50% relative humidity (RH) and 80 °C, 90% RH. ► Coatings did not prevent fatigue extrusions and micro-cracks. ► 25 nm coatings likely delayed the formation of fatigue extrusions and micro-cracks. ► The technique can be used to identify reliable nanoscale coatings.

Contribution to the determination of priority constructive influences on the hot crack initiation of welded components

International Nuclear Information System (INIS)

Gollnow, Christian

2015-01-01

load conditions from production process the specimens were treated with various tensile and bending load partly before and during TIG-welding. With regard to the respective load cases the local and two-dimensional analyses of solidification crack critical parameters were carried out close to the weld, time and spatial resolved. Additionally, case analyses on components in the production process were done in order to evaluate the primary design-specific influence to solidification cracking. The general influence of the design to the process parameters was evaluated. Furthermore, the transferability of the laboratory test results on components was examined. The performed investigations yield significant knowledge to prevent solidification cracks, especially for component manufacturing. The design-specific influence on the solidification behavior and the weld microstructure was detected which was proved as a solidification crack criterion. This work describes feasible mechanisms of different stress conditions with respect to the initiation of solidification cracks. In addition, the results show substantial solidification specific differences between pre-load and load during the welding process. It was described the mutual influence of design and welding process, material-specific based on in-situ detected displacement values. The data obtained are of importance for further numerical simulations, especially for the validation of numerical models that represent the solidification crack-critical component deformations.

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

Localized deformation as a key precursor to initiation of intergranular stress corrosion cracking of austenitic stainless steels employed in nuclear power plants

International Nuclear Information System (INIS)

Karlsen, Wade; Diego, Gonzalo; Devrient, Bastian

2010-01-01

Cold-work has been associated with the occurrence of intergranular cracking of stainless steels employed in light water reactors. This study examined the deformation behavior of AISI 304, AISI 347 and a higher stacking fault energy model alloy subjected to bulk cold-work and (for 347) surface deformation. Deformation microstructures of the materials were examined and correlated with their particular mechanical response under different conditions of temperature, strain rate and degree of prior cold-work. Select slow-strain rate tensile tests in autoclaves enabled the role of local strain heterogeneity in crack initiation in pressurized water reactor environments to be considered. The high stacking fault energy material exhibited uniform strain hardening, even at sub-zero temperatures, while the commercial stainless steels showed significant heterogeneity in their strain response. Surface treatments introduced local cold-work, which had a clear effect on the surface roughness and hardness, and on near-surface residual stress profiles. Autoclave tests led to transgranular surface cracking for a circumferentially ground surface, and intergranular crack initiation for a polished surface.

Crack Growth Behavior in the Threshold Region for High Cycle Fatigue Loading

Science.gov (United States)

Forman, R. G.; Zanganeh, M.

2014-01-01

This paper describes the results of a research program conducted to improve the understanding of fatigue crack growth rate behavior in the threshold growth rate region and to answer a question on the validity of threshold region test data. The validity question relates to the view held by some experimentalists that using the ASTM load shedding test method does not produce valid threshold test results and material properties. The question involves the fanning behavior observed in threshold region of da/dN plots for some materials in which the low R-ratio data fans out from the high R-ratio data. This fanning behavior or elevation of threshold values in the low R-ratio tests is generally assumed to be caused by an increase in crack closure in the low R-ratio tests. Also, the increase in crack closure is assumed by some experimentalists to result from using the ASTM load shedding test procedure. The belief is that this procedure induces load history effects which cause remote closure from plasticity and/or roughness changes in the surface morphology. However, experimental studies performed by the authors have shown that the increase in crack closure is a result of extensive crack tip bifurcations that can occur in some materials, particularly in aluminum alloys, when the crack tip cyclic yield zone size becomes less than the grain size of the alloy. This behavior is related to the high stacking fault energy (SFE) property of aluminum alloys which results in easier slip characteristics. Therefore, the fanning behavior which occurs in aluminum alloys is a function of intrinsic dislocation property of the alloy, and therefore, the fanned data does represent the true threshold properties of the material. However, for the corrosion sensitive steel alloys tested in laboratory air, the occurrence of fanning results from fretting corrosion at the crack tips, and these results should not be considered to be representative of valid threshold properties because the fanning is

Effect of Microstructure on Time Dependent Fatigue Crack Growth Behavior In a P/M Turbine Disk Alloy

Science.gov (United States)

Telesman, Ignacy J.; Gabb, T. P.; Bonacuse, P.; Gayda, J.

2008-01-01

A study was conducted to determine the processes which govern hold time crack growth behavior in the LSHR disk P/M superalloy. Nineteen different heat treatments of this alloy were evaluated by systematically controlling the cooling rate from the supersolvus solutioning step and applying various single and double step aging treatments. The resulting hold time crack growth rates varied by more than two orders of magnitude. It was shown that the associated stress relaxation behavior for these heat treatments was closely correlated with the crack growth behavior. As stress relaxation increased, the hold time crack growth resistance was also increased. The size of the tertiary gamma' in the general microstructure was found to be the key microstructural variable controlling both the hold time crack growth behavior and stress relaxation. No relationship between the presence of grain boundary M23C6 carbides and hold time crack growth was identified which further brings into question the importance of the grain boundary phases in determining hold time crack growth behavior. The linear elastic fracture mechanics parameter, Kmax, is unable to account for visco-plastic redistribution of the crack tip stress field during hold times and thus is inadequate for correlating time dependent crack growth data. A novel methodology was developed which captures the intrinsic crack driving force and was able to collapse hold time crack growth data onto a single curve.

Heavy-Section Steel Technology Program: Recent developments in crack initiation and arrest research

International Nuclear Information System (INIS)

Pennell, W.E.

1991-01-01

Technology for the analysis of crack initiation and arrest is central to the reactor pressure vessel fracture-margin-assessment process. Regulatory procedures for nuclear plants utilize this technology to assure the retention of adequate fracture-prevention margins throughout the plant operating license period. As nuclear plants age and regulatory procedures dictate that fracture-margin assessments be performed, interest in the fracture-mechanics technology incorporated into those procedures has heightened. This has led to proposals from a number of sources for development and refinement of the underlying crack-initiation and arrest-analysis technology. An important element of the Heavy-Section Steel Technology (HSST) Program is devoted to the investigation and evaluation of these proposals. This paper presents the technological bases and fracture-margin assessment objectives for some of the recently proposed crack-initiation and arrest-technology developments. The HSST Program approach to the evaluation of the proposals is described and the results and conclusions obtained to date are presented

Effects of thermal cracking on the dynamic behavior of reinforced concrete containment structures

International Nuclear Information System (INIS)

Castellani, A.; Fontana, A.

1977-01-01

Thick concrete cylinders acted on by horizontal dynamic forces are analyzed. According to the dimensions they may simulate a containment structure or a reactor core support. In particular, the effects of thermal cracking on their dynamic behavior are investigated; up to now the tests are confined to vertical cracking which is likely to appear under a thermal gradient of approximately 35 to 45 0 C on the wall. At higher temperatures, the number and extension of these cracks increase, till a stabilized crack pattern is reached. This is the main subject of the present investigation. The horizontal forces call for a shear transmission along the crack. According to the literature, shear stresses can be transmitted by aggregate interlock, by shear friction, and by the dowel action provided by horizontal reinforcement. These effects may accomodate the shear transmission along the crack required to resist a given distribution of horizontal forces. On the other hand, the shear rigidity of the structure may be negatively affected by the cracking, depending on the crack width and distribution and on the amplitude of the applied forces. In this case a dynamic behavior of the structure is to be analyzed with proper consideration to the existing cracking

Effect of temperature upon the fatigue-crack propagation behavior of Hastelloy X-280

International Nuclear Information System (INIS)

James, L.A.

1976-05-01

The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of Hastelloy X-280 in an air environment. Also included in this study are survey tests to determine the effects of thermal aging and stress ratio upon crack growth behavior in this alloy

Comparison of the microstructure, deformation and crack initiation behavior of austenitic stainless steel irradiated in-reactor or with protons

Science.gov (United States)

Stephenson, Kale J.; Was, Gary S.

2015-01-01

The objective of this study was to compare the microstructures, microchemistry, hardening, susceptibility to IASCC initiation, and deformation behavior resulting from proton or reactor irradiation. Two commercial purity and six high purity austenitic stainless steels with various solute element additions were compared. Samples of each alloy were irradiated in the BOR-60 fast reactor at 320 °C to doses between approximately 4 and 12 dpa or by a 3.2 MeV proton beam at 360 °C to a dose of 5.5 dpa. Irradiated microstructures consisted mainly of dislocation loops, which were similar in size but lower in density after proton irradiation. Both irradiation types resulted in the formation of Ni-Si rich precipitates in a high purity alloy with added Si, but several other high purity neutron irradiated alloys showed precipitation that was not observed after proton irradiation, likely due to their higher irradiation dose. Low densities of small voids were observed in several high purity proton irradiated alloys, and even lower densities in neutron irradiated alloys, implying void nucleation was in process. Elemental segregation at grain boundaries was very similar after each irradiation type. Constant extension rate tensile experiments on the alloys in simulated light water reactor environments showed excellent agreement in terms of the relative amounts of intergranular cracking, and an analysis of localized deformation after straining showed a similar response of cracking to surface step height after both irradiation types. Overall, excellent agreement was observed after proton and reactor irradiation, providing additional evidence that proton irradiation is a useful tool for accelerated testing of irradiation effects in austenitic stainless steel.

A numerical study of crack initiation in a bcc iron system based on dynamic bifurcation theory

International Nuclear Information System (INIS)

Li, Xiantao

2014-01-01

Crack initiation under dynamic loading conditions is studied under the framework of dynamic bifurcation theory. An atomistic model for BCC iron is considered to explicitly take into account the detailed molecular interactions. To understand the strain-rate dependence of the crack initiation process, we first obtain the bifurcation diagram from a computational procedure using continuation methods. The stability transition associated with a crack initiation, as well as the connection to the bifurcation diagram, is studied by comparing direct numerical results to the dynamic bifurcation theory [R. Haberman, SIAM J. Appl. Math. 37, 69–106 (1979)].

Effect of Layering on Cracking Initiation and Propagation under Uniaxial Compression

Science.gov (United States)

Modiriasari, A.; Jiang, L.; Yoon, H.; Bobet, A.; Pyrak-Nolte, L. J.

2017-12-01

Rock anisotropy can arise from textural and structural causes both of which contribute to anisotropic strength and moduli. Rock variability makes it difficult to determine which properties dominate failure. Here, laboratory experiments were performed on 3D printed samples to examine the effect of layering on crack formation. Samples with two pre-existing coplanar flaws were fabricated using an additive 3D printing process (Projet CJP 360). Layers of gypsum (0.2 mm thick) were printed in either a horizontal (H) or a vertical (V) orientation to create prismatic samples (152.4 mm x 76.2 mm x 25.1 mm) with two 12.7 mm long coplanar flaws (19.05 mm apart) oriented at 450 with the load. Cracks were induced under uniaxial loading conditions. Digital image correlation (DIC) and acoustic emission (AE) (18 AE sensors with a frequency range of 100-450 kHz) were used to monitor crack evolution. DIC imaging of the V specimen during uniaxial compression showed that smooth cracks were initiated and propagated from the tips of the flaws parallel to the layering. Unlike the strongly bonded samples, no cracks were formed between the pre-existing flaws. The failure mechanism between the flaws was controlled by the weak bonding between the layers, and not by the coalescence of the new cracks. However, for the H specimen, failure was caused by crack coalescence between the two flaws. The new cracks exhibited a step-like roughness that was influenced by the layering in the sample. AE events were only detected when a synchronized mode was used. 3D printed samples can be effectively used to study the effect of anisotropic layering on crack initiation and propagation in a repeatable and controlled manner. Acknowledgements: Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security

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.

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.

Small fatigue cracks; Proceedings of the Second International Conference/Workshop, Santa Barbara, CA, Jan. 5-10, 1986

Energy Technology Data Exchange (ETDEWEB)

Ritchie, R.O.; Lankford, J.

1986-01-01

Topics discussed in this volume include crack initiation and stage I growth, microstructure effects, crack closure, environment effects, the role of notches, analytical modeling, fracture mechanics characterization, experimental techniques, and engineering applications. Papers are presented on fatigue crack initiation along slip bands, the effect of microplastic surface deformation on the growth of small cracks, short fatigue crack behavior in relation to three-dimensional aspects and the crack closure effect, the influence of crack depth on crack electrochemistry and fatigue crack growth, and nondamaging notches in fatigue. Consideration is also given to models of small fatigue cracks, short crack theory, assessment of the growth of small flaws from residual strength data, the relevance of short crack behavior to the integrity of major rotating aero engine components, and the relevance of short fatigue crack growth data to the durability and damage tolerance analyses of aircraft.

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)

Indentation Damage and Crack Repair in Human Enamel*

Science.gov (United States)

Rivera, C.; Arola, D.; Ossa, A.

2013-01-01

Tooth enamel is the hardest and most highly mineralized tissue in the human body. While there have been a number of studies aimed at understanding the hardness and crack growth resistance behavior of this tissue, no study has evaluated if cracks in this tissue undergo repair. In this investigation the crack repair characteristics of young human enamel were evaluated as a function of patient gender and as a function of the distance from the Dentin Enamel Junction (DEJ). Cracks were introduced via microindentation along the prism direction and evaluated as a function of time after the indentation. Microscopic observations indicated that the repair of cracks began immediately after crack initiation and reaches saturation after approximately 48 hours. During this process he crack length decreased up to 10% of the initial length, and the largest degree of reduction occurred in the deep enamel, nearest the DEJ. In addition, it was found that the degree of repair was significantly greater in the enamel of female patients. PMID:23541701

Surface crack behavior in socket weld of nuclear piping under fatigue loading condition

International Nuclear Information System (INIS)

Choi, Y.H.; Kim, J.S.; Choi, S.Y.

2005-01-01

The ASME B and PV Code Sec. III allows the socket weld for the nuclear piping in spite of the weakness on the weld integrity. Recently, the integrity of the socket weld is regarded as a safety concern in nuclear power plants because many failures and leaks have been reported in the socket weld. OPDE (OECD Piping Failure Data Exchange) database lists 108 socket weld failures among 2,399 nuclear piping failure cases during 1970 to 2001. Eleven failures in the socket weld were also reported in Korean NPPs. Many failure cases showed that the root cause of the failure is the fatigue and the gap requirement for the socket weld given in ASME Code was not satisfied. The purpose of this paper is to evaluate the fatigue crack behavior of a surface crack in the socket weld under fatigue loading condition considering the gap effect. Three-dimensional finite element analysis was performed to estimate the fatigue crack behavior of the surface crack. Three types of loading conditions such as the deflection due to vibration, the pressure transient ranging from P=0 to 15.51 MPa, and the thermal transient ranging from T=25 C to 288 C were considered. The results are as follows; 1) The socket weld is susceptible to the vibration where the vibration levels exceed the requirement in the ASME operation and maintenance (OM) Code. 2) The effect of pressure or temperature transient load on the socket weld integrity is not significant. 3) No-gap condition gives very high possibility of the crack initiation at the socket weld under vibration loading condition. 4) For the specific systems having the vibration condition to exceed the requirement in the ASME Code OM and/or the transient loading condition from P=0 and T=25 C to P=15.51 MPa and T=288 C, radiographic examination to examine the gap during the construction stage is recommended. (orig.)

Quantitative characterization of initiation and propagation in stress corrosion cracking. An approach of a phenomenological model

International Nuclear Information System (INIS)

Raquet, O.

1994-01-01

A purely phenomenological study of stress corrosion cracking was performed using the couple Z2CN 18.10 (304L) austenitic stainless steel/boiling MgCl 2 aqueous solution. The exploitation of the morphological information (shape of the cracks and size distribution) available after constant elongation rate tests led to the proposal of an analytical expression of the crack initiation and growth rates. This representation allowed to quantitatively characterize the influence of the applied strain rate as well as the effect of corrosion inhibitors on the crack initiation and propagation phases. It can be used in the search for the stress corrosion cracking mechanisms as a 'riddle' for the determination of the rate controlling steps. As a matter of fact, no mechanistic hypothesis has been used for its development. (author)

Estimating the Initial Crack Size in a Particulate Composite Material: An Analytical and Experimental Approach

National Research Council Canada - National Science Library

Liu, C

2001-01-01

The objectives in this report are to: determine the inherent critical initial crack size in a particulate composite material, determine the statistical distribution function of the inherent critical crack size, normal distribution, two...

Multi-scale analysis of deformation behavior at SCC crack tip (2). (Contract research)

International Nuclear Information System (INIS)

Kaji, Yoshiyuki; Miwa, Yukio; Tsukada, Takashi; Hayakawa, Masao; Nagashima, Nobuo

2007-03-01

This report describes a result of the research conducted by the Japan Atomic Energy Agency and the National Institute for Materials Science under contract with Japan Nuclear Energy Safety Organization (JNES) that was concerned with a multi-scale analysis of plastic deformation behavior at the crack tip of stress corrosion cracking (SCC). The research was carried out to evaluate the validity of the SCC growth data acquired in the intergranular SCC (IGSCC) project based on a mechanistic understanding of SCC. For the purpose, in this research, analyses of the plastic deformation behavior and microstructure around the crack tip were performed in a nano-order scale. The hardness measured in nano, meso and macro scales was employed as a common index of the strength, and the essential data necessary to understand the SCC propagation behavior were acquired and analyzed that are mainly a size of plastic deformation region and a microstructural information in the region, e.g. data of crystallografy, microscopic deformation and dislocations at the inside of grains and grain boundaries. In this year, we analyzed the state of plastic deformation region at the crack tip of IGSCC under various conditions and investigated relationship between crack growth behavior and stress intensity factor. Especially, we investigated in detail about two different hardened specimens used in the SCC growth tests in the IGSCC project. (J.P.N.)

Stress corrosion cracking of Alloy 82 in hydrogenated steam at 400 C: influence of microstructural and mechanical parameters on initiation of SCC cracks

International Nuclear Information System (INIS)

Chaumun, Elizabeth

2016-01-01

In Pressurize Water Reactors (PWR), Stress Corrosion Cracking (SCC) is the mean degradation mode of components pieced together by welding. Nickel based alloys are, among others, used in dissimilar metal welding (DMW). International report showed only 3 cracking cases in Alloy 82 out of 300 cracking cases concerned on nickel based alloys DMW in primary water circuit. The aim of this study is to identify which microstructural and local mechanism parameters at microstructure scale provide the initiation of SCC cracks. Characterizations performed on specimen surface to identify those parameters are composed of chemical composition analysis and EBSD analysis (Electron Back-Scattered Diffraction) to know the morphology and the crystallography of grains for microstructure features on one hand, and experimental strain fields measured by Digital Imaging Correlation (DIC) of gold micro-grids deposed by electronic lithography on U-bend specimen surface and stress fields calculated along grains boundaries by finite element for local mechanical features on the other hand. The correlation between those characterizations and localization of initiation sites of SCC cracks, obtained on U-bend specimens tested in autoclave in hydrogen steam water at 400 C and 188 bar for 3500 hours, confirmed the susceptibility of the Alloy 82 in SCC conditions with intergranular SCC cracks. The perpendicular position to the loading direction (mode I) is the worst conditions for grains boundary in SCC. The others points concern the chemical composition (precipitation, impurities) around grain boundary and the grain boundary type which is more susceptible when it is a High Angle Grain Boundary. It is following by the mechanical characterization (stress and strain gradient) along grain boundary. This methodology can be used to other material and helped to define which microstructural and mechanical parameter can be define the initiation of SCC cracks. (author) [fr

Fatigue crack initiation – The role of point defects

Czech Academy of Sciences Publication Activity Database

Polák, Jaroslav; Man, Jiří

2014-01-01

Roč. 65, AUG (2014), s. 18-27 ISSN 0142-1123 R&D Projects: GA ČR(CZ) GAP108/10/2371; GA ČR(CZ) GA13-23652S Institutional support: RVO:68081723 Keywords : Fatigue crack initiation * Point defects * Persistent slip band * Intrusion * Extrusion Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.275, year: 2014

Fracture behavior of filament in Nb_3Sn strands with crack-bridging model

International Nuclear Information System (INIS)

Yong, Huadong; Yang, Penglei; Xue, Cun; Zhou, Youhe

2016-01-01

Highlights: • The crack-bridging model is used to study the fracture behavior of filaments. • Two different fracture modes are characterized by the number of bridging bronzes. • Short twist pitch has better mechanical stability for the tensile loadings. • The widths of bridging bronze and filament have different effects for the central crack and two collinear cracks. - Abstract: The Nb_3Sn strands which have high critical field are used in cable-in-conduit conductors (CICCs). The superconducting strands are twisted multistage and experience complex thermal and electromagnetic loadings. Due to their brittleness, the cracking of the Nb_3Sn filaments will occur under mechanical loading. In this paper, based on the linear elastic fracture theory, we study the effects of tension loading on the fracture behavior of central crack firstly. The strain energy release rates for different twist pitches and cabling stages are presented. As the triplet is subjected to the uniaxial strain, the cracking probability will increase with the twist pitch. The crack number increases with the applied strain, and wider filament or bronze can lead to smaller crack number under the same applied strain. In addition, multistage cabling has better mechanical stability. Next, the two collinear crack problem is considered. The variations of microcrack number show that the wider bronze can provide more resistance for the propagating of the large cracks. We can conclude that the bronze plays an important role in improving the stability and strength.

Fatigue crack growth behavior of RAFM steel in Paris and threshold regimes at different temperatures

Energy Technology Data Exchange (ETDEWEB)

Babu, M. Nani; Sasikala, G., E-mail: gsasi@igcar.gov.in; Dutt, B. Shashank; Venugopal, S.; Bhaduri, A.K.; Jayakumar, T.

2014-04-01

Fatigue crack growth (FCG) behavior of a reduced activation ferritic martensitic (indigenous RAFM) steel has been evaluated at 300, 653 and 823 K in Paris and threshold regimes. The effect of temperature on threshold stress intensity factor range and associated crack closure mechanisms is highlighted. The FCG results were compared with those for EUROFER 97. Further, crack tip effective stress intensity factor ranges (ΔK{sub tip,eff}) have been evaluated by taking crack tip shielding into account in order to examine the effect of temperature on true intrinsic FCG behavior.

Affection mechanism research of initiation crack pressure of perforation parameters of horizontal well

Directory of Open Access Journals (Sweden)

Hua Tong

2016-09-01

Full Text Available Horizontal wells show better affect and higher success rate in low water ratio cement, complex fracture zone, crevice and heavy oil blocks, it is the main measures to expand control area of a single well. Hydraulic fracturing technology is the most financial way to improve the penetration of the reservoir to increase the production. However, compare with the vertical wells, the fracture of Horizontal wells are more complex, and lead to the initiation crack pressure is much higher than vertical wells. In this paper, defined the crack judging basis, and established the finite element model which could compute the initial crack pressure, to research the affection mechanism of perforation azimuth angle, density, diameter and depth, to provide references of perforation project's design and optimize. The research of this paper has significances on further understanding the affection mechanism of perforation parameters.

Fracture and subcritical crack-growth behavior of Y-Si-Al-O-N glasses and Si3N4 ceramics

International Nuclear Information System (INIS)

Bhatnagar, A.; Hoffman, M.J.; Dauskardt, R.H.

2000-01-01

Fracture and environmentally assisted subcritical crack-growth processes are examined in bulk Y-Si-Al-O-N oxynitride glasses with compositions typical of the grain boundary phase of silicon nitride ceramics. Both long-crack (in compact tension specimens) as well as short-crack behavior (using indentation techniques) were investigated to establish a reliable fracture toughness and to elucidate the anomalous densification behavior of the oxynitride glass. Environmentally assisted subcritical crack-growth processes were studied in inert, moist, and wet environments under both cyclic and static loading conditions. Behavior is discussed in terms of the interaction of the environment with the crack tip. Likely mechanisms for environmentally assisted crack growth are discussed and related to the subcritical crack-growth behavior of silicon nitride ceramics

Studies on the disbonding initiation of interfacial cracks.

Energy Technology Data Exchange (ETDEWEB)

McAdams, Brian J. (Lehigh University, Bethlehem, PA); Pearson, Raymond A. (Lehigh University, Bethlehem, PA)

2005-08-01

With the continuing trend of decreasing feature sizes in flip-chip assemblies, the reliability tolerance to interfacial flaws is also decreasing. Small-scale disbonds will become more of a concern, pointing to the need for a better understanding of the initiation stage of interfacial delamination. With most accepted adhesion metric methodologies tailored to predict failure under the prior existence of a disbond, the study of the initiation phenomenon is open to development and standardization of new testing procedures. Traditional fracture mechanics approaches are not suitable, as the mathematics assume failure to originate at a disbond or crack tip. Disbond initiation is believed to first occur at free edges and corners, which act as high stress concentration sites and exhibit singular stresses similar to a crack tip, though less severe in intensity. As such, a 'fracture mechanics-like' approach may be employed which defines a material parameter--a critical stress intensity factor (K{sub c})--that can be used to predict when initiation of a disbond at an interface will occur. The factors affecting the adhesion of underfill/polyimide interfaces relevant to flip-chip assemblies were investigated in this study. The study consisted of two distinct parts: a comparison of the initiation and propagation phenomena and a comparison of the relationship between sub-critical and critical initiation of interfacial failure. The initiation of underfill interfacial failure was studied by characterizing failure at a free-edge with a critical stress intensity factor. In comparison with the interfacial fracture toughness testing, it was shown that a good correlation exists between the initiation and propagation of interfacial failures. Such a correlation justifies the continuing use of fracture mechanics to predict the reliability of flip-chip packages. The second aspect of the research involved fatigue testing of tensile butt joint specimens to determine lifetimes at sub

Models for ductile crack initiation and tearing resistance under mode 1 loading in pressure vessel steels

International Nuclear Information System (INIS)

Jones, M.R.

1988-06-01

Micromechanistic models are presented which aim to predict plane strain ductile initiation toughness, tearing resistance and notched bar fracture strains in pressure vessel steels under monotonically increasing tensile (mode 1) loading. The models for initiation toughness and tearing resistance recognize that ductile fracture proceeds by the growth and linkage of voids with the crack-tip. The models are shown to predict the trend of initiation toughness with inclusion spacing/size ratio and can bound the available experimental data. The model for crack growth can reproduce the tearing resistance of a pressure vessel steel up to and just beyond crack growth initiation. The fracture strains of notched bars pulled in tension are shown to correspond to the achievement of a critical volume fraction of voids. This criterion is combined with the true stress - true strain history of a material point ahead of a blunting crack-tip to predict the initiation toughness. An attempt was made to predict the fracture strains of notched tensile bars by adopting a model which predicts the onset of a shear localization phenomenon. Fracture strains of the correct order are computed only if a ''secondary'' void nucleation event at carbide precipitates is taken into account. (author)

Effect of membrane and through-wall bending stresses on fatigue crack growth behavior and coolant leakage velocity

International Nuclear Information System (INIS)

Yoo, Yeon-Sik

2003-11-01

This study clarified the effect of a membrane and a through-wall bending stresses on fatigue crack growth behavior and coolant leakage velocity due to irregularity of crack surface. Each stress component relates to fatigue crack growth behavior directly in general and thus the wild-used K I solutions are anticipated to give good evaluation results on it. Meanwhile, it is necessary to notify that surface irregularity for coolant leakage assessment is made by stress history in nature. Surface irregularity is known to be largely classified into the following two aspects: surface roughness due to continuous crack opening and closure behavior and surface turnover due to cyclic bending stress dominance. Therefore, the deterministic parameters on resistance of coolant leakage by surface irregularity are considered to be not only stress history but crack opening behavior. (author)

Effect of a new specimen size on fatigue crack growth behavior in thick-walled pressure vessels

International Nuclear Information System (INIS)

Shariati, Mahmoud; Mohammadi, Ehsan; Masoudi Nejad, Reza

2017-01-01

Fatigue crack growth in thick-walled pressure vessels is an important factor affecting their fracture. Predicting the path of fatigue crack growth in a pressure vessel is the main issue discussed in fracture mechanics. The objective of this paper is to design a new geometrical specimen in fatigue to define the behavior of semi-elliptical crack growth in thick-walled pressure vessels. In the present work, the importance of the behavior of fatigue crack in test specimen and real conditions in thick-walled pressure vessels is investigated. The results of fatigue loading on the new specimen are compared with the results of fatigue loading in a cylindrical pressure vessel and a standard specimen. Numerical and experimental methods are used to investigate the behavior of fatigue crack growth in the new specimen. For this purpose, a three-dimensional boundary element method is used for fatigue crack growth under stress field. The modified Paris model is used to estimate fatigue crack growth rates. In order to verify the numerical results, fatigue test is carried out on a couple of specimens with a new geometry made of ck45. A comparison between experimental and numerical results has shown good agreement. - Highlights: • This paper provides a new specimen to define the behavior of fatigue crack growth. • We estimate the behavior of fatigue crack growth in specimen and pressure vessel. • A 3D finite element model has been applied to estimate the fatigue life. • We compare the results of fatigue loading for cylindrical vessel and specimens. • Comparison between experimental and numerical results has shown a good agreement.

Effect of temperature upon the fatigue-crack propagation behavior of Inconel 625

International Nuclear Information System (INIS)

James, L.A.

1977-03-01

The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of mill-annealed Inconel 625 in an air environment over the range 75 0 - 1200 0 F (24 0 - 649 0 C). In general, fatigue-crack growth rates increased with increasing test temperature. Two different specimen sizes were employed at each test temperature, and no effects of specimen size upon crack growth were noted

Comparison of delayed hydride cracking behavior of two zirconium alloys

Energy Technology Data Exchange (ETDEWEB)

Ponzoni, L.M.E. [CNEA – Centro Atómico Constituyentes, Hidrógeno en Materiales, Av. Gral. Paz 1499, San Martín (B1650KNA), Bs. As. (Argentina); Mieza, J.I. [CNEA – Centro Atómico Constituyentes, Hidrógeno en Materiales, Av. Gral. Paz 1499, San Martín (B1650KNA), Bs. As. (Argentina); Instituto Sabato, UNSAM–CNEA, Av. Gral. Paz 1499, San Martín (B1650KNA), Bs. As. (Argentina); De Las Heras, E. [CNEA – Centro Atómico Constituyentes, Hidrógeno en Materiales, Av. Gral. Paz 1499, San Martín (B1650KNA), Bs. As. (Argentina); Domizzi, G., E-mail: domizzi@cnea.gov.ar [CNEA – Centro Atómico Constituyentes, Hidrógeno en Materiales, Av. Gral. Paz 1499, San Martín (B1650KNA), Bs. As. (Argentina); Instituto Sabato, UNSAM–CNEA, Av. Gral. Paz 1499, San Martín (B1650KNA), Bs. As. (Argentina)

2013-08-15

Delayed hydride cracking (DHC) is an important failure mechanism that may occur in Zr alloys during service in water-cooled reactors. Two conditions must be attained to initiate DHC from a crack: the stress intensity factor must be higher than a threshold value called K{sub IH} and, hydrogen concentration must exceed a critical value. Currently the pressure tubes for CANDU reactor are fabricated from Zr–2.5Nb. In this paper the critical hydrogen concentration for DHC and the crack velocity of a developmental pressure tube, Excel, was evaluated and compared with that of Zr–2.5Nb. The DHC velocity values measured in Excel were higher than usually reported in Zr–2.5Nb. Due to the higher hydrogen solubility limits in Excel, its critical hydrogen concentration for DHC initiation is 10–50 wppm over that of Zr–2.5Nb in the range of 150–300 °C.

Case Study of Crack Initiation from Bi-material Notches

Czech Academy of Sciences Publication Activity Database

Klusák, Jan; Knésl, Zdeněk

2011-01-01

Roč. 452-453, - (2011), s. 449-452 ISSN 1013-9826. [Fracture and Damage Mechanics /9./. Nagasaki, 20.09.2010-22.09.2010] R&D Projects: GA ČR GAP108/10/2049; GA ČR GA101/08/0994 Institutional research plan: CEZ:AV0Z20410507 Keywords : Crack initiation * bi-material notch * fracture mechanics Subject RIV: JL - Materials Fatigue, Friction Mechanics

Stress corrosion cracking of titanium alloys

Science.gov (United States)

May, R. C.; Beck, F. H.; Fontana, M. G.

1971-01-01

Experiments were conducted to study (1) the basic electrochemical behavior of titanium in acid chloride solutions and (2) the response of the metal to dynamic straining in the same evironment. The aim of this group of experiments was to simulate, as nearly as possible, the actual conditions which exist at the tip of a crack. One of the foremost theories proposed to explain the propagation of stress corrosion cracks is a hydrogen embrittlement theory involving the precipitation of embrittling titanium hydrides inside the metal near the crack tip. An initial survey of the basic electrochemical literature indicated that surface hydrides play a critical role in the electrochemistry of titanium in acid solutions. A comprehensive analysis of the effect of surface films, particularly hydrides, on the electrochemical behavior of titanium in these solution is presented.

Combined Effect of Initial Curing Temperature and Crack Width on Chloride Penetration in Reinforced Concrete Beams

Directory of Open Access Journals (Sweden)

Elkedrouci Lotfi

2018-01-01

Full Text Available Reinforced concrete (RC structures are gradually being degraded all over the world, largely due to corrosion of the embedded steel bars caused by an attack of chloride penetration. Initial curing would be regarded as one factor influencing chloride diffusion in concrete in combination with cover cracking that is also of great attention for reinforced structures. In this study, a non-steady state diffusion test of chloride ion involving RC beam specimens with a water-to-cement ratio of 0.5, initial curing temperatures of 5°C or 20°C and three types of crack widths ranging from 0 to 0.2mm was performed. Chloride content at 5°C or was determined. The results show that the higher chloride content was obtained in condition of crack width large than 0.1mm with low initial curing temperature and there are no obvious differences in chloride content when the crack width was not larger than 0.1mm.

Finite element analysis of fatigue crack closure under plane strain state

International Nuclear Information System (INIS)

Lee, Hak Joo; Kang, Jae Youn; Song, Ji Ho

2004-01-01

An elastic-plastic finite element analysis of fatigue crack closure is performed for plane strain conditions. The stabilization behavior of crack opening level and the effect of mesh size on the crack opening stress are investigated. In order to obtain a stabilized crack opening level for plane strain conditions, the crack must be advanced through approximately four times the initial monotonic plastic zone. The crack opening load tends to increase with the decrease of mesh size. The mesh size nearly equal to the theoretical plane strain cyclic plastic zone size may provide reasonable numerical results comparable with experimental crack opening data. The crack opening behavior is influenced by the crack growth increment and discontinuous opening behavior is observed. A procedure to predict the most appropriate mesh size for different stress ratio is suggested. Crack opening loads predicted by the FE analysis based on the procedure suggested resulted in good agreement with experimental ones within the error of 5 %. Effect of the distance behind the crack tip on the crack opening load determined by the ASTM compliance offset method based on the load-displacement relation and by the rotational offset method based on the load-differential displacement relation is investigated. Optimal gage location and method to determine the crack opening load is suggested

Stress corrosion crack initiation of alloy 182 weld metal in primary coolant - Influence of chemical composition

Energy Technology Data Exchange (ETDEWEB)

Calonne, O.; Foucault, M.; Steltzlen, F. [AREVA (France); Amzallag, C. [EDF SEPTEN (France)

2011-07-01

Nickel-base alloys 182 and 82 have been used extensively for dissimilar metal welds. Typical applications are the J-groove welds of alloy 600 vessel head penetrations, pressurizer penetrations, heater sleeves and bottom mounted instrumented nozzles as well as some safe end butt welds. While the overall performance of these weld metals has been good, during the last decade, an increasing number of cases of stress corrosion cracking of Alloy 182 weld metal have been reported in PWRs. In this context, the role of weld defects has to be examined. Their contribution in the crack initiation mechanism requires laboratory investigations with small scale characterizations. In this study, the influence of both alloy composition and weld defects on PWSCC (Stress Corrosion Cracking in Primary Water) initiation was investigated using U-bend specimens in simulated primary water at 320 C. The main results are the following: -) the chemical compositions of the weld deposits leading to a large propensity to hot cracking are not the most susceptible to PWSCC initiation, -) macroscopically, superficial defects did not evolve during successive exposures. They can be included in large corrosion cracks but their role as 'precursors' is not yet established. (authors)

Effects of surface cracks and strain rate on the tensile behavior of Balmoral Red granite

Directory of Open Access Journals (Sweden)

Mardoukhi Ahmad

2015-01-01

Full Text Available This paper presents an experimental procedure for studying the effects of surface cracks on the mechanical behavior of Balmoral Red granite under dynamic and quasi-static loading. Three different thermal shocks were applied on the surface of the Brazilian Disc test samples by keeping a flame torch at a fixed distance from the sample surface for 10, 30, and 60 seconds. Microscopy clearly shows that the number of the surface cracks increases with the duration of the thermal shock. After the thermal shock, the Brazilian Disc tests were performed using a servohydraulic materials testing machine and a compression Split Hopkinson Pressure Bar (SHPB device. The results show that the tensile strength of the rock decreases and the rate sensitivity of the rock increases as more cracks are introduced to the structure. The DIC analysis of the Brazilian disc tests shows that the fracture of the sample initiates at the center of the samples or slightly closer to the incident bar contact point. This is followed by crushing of the samples at both contact points with the stress bars.

Indentation damage and crack repair in human enamel.

Science.gov (United States)

Rivera, C; Arola, D; Ossa, A

2013-05-01

Tooth enamel is the hardest and most highly mineralized tissue in the human body. While there have been a number of studies aimed at understanding the hardness and crack growth resistance behavior of this tissue, no study has evaluated if cracks in this tissue undergo repair. In this investigation the crack repair characteristics of young human enamel were evaluated as a function of patient gender and as a function of the distance from the Dentin Enamel Junction (DEJ). Cracks were introduced via microindentation along the prism direction and evaluated as a function of time after the indentation. Microscopic observations indicated that the repair of cracks began immediately after crack initiation and reaches saturation after approximately 48 h. During this process he crack length decreased up to 10% of the initial length, and the largest degree of reduction occurred in the deep enamel, nearest the DEJ. In addition, it was found that the degree of repair was significantly greater in the enamel of female patients. Copyright © 2013 Elsevier Ltd. All rights reserved.

Fatigue Crack Growth Behavior of and Recognition of AE Signals from Composite Patch-Repaired Aluminum Panel

International Nuclear Information System (INIS)

Kim, Sung Jin; Kwon, Oh Yang; Jang, Yong Joon

2007-01-01

The fatigue crack growth behavior of a cracked and patch-repaired Ah2024-T3 panel has been monitored by acoustic emission(AE). The overall crack growth rate was reduced The crack propagation into the adjacent hole was also retarded by introducing the patch repair. AE signals due to crack growth after the patch repair and those due to debonding of the plate-patch interface were discriminated by using the principal component analysis. The former showed high center frequency and low amplitude, whereas the latter showed long rise tine, low frequency and high amplitude. This type of AE signal recognition method could be effective for the prediction of fatigue crack growth behavior in the patch-repaired structures with the aid of AE source location

Experimental evidence and physical models of fatigue crack initiation

Czech Academy of Sciences Publication Activity Database

Polák, Jaroslav; Man, Jiří

2016-01-01

Roč. 91, OCT (2016), s. 294-303 ISSN 0142-1123 R&D Projects: GA ČR(CZ) GA13-23652S; GA ČR GA13-32665S; GA MŠk(CZ) ED1.1.00/02.0068 Institutional support: RVO:68081723 Keywords : Crack initiation * Persistent slip band * Point defects * Extrusions * Intrusions Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.899, year: 2016

Probabilistic modeling of material resistance to crack initiation due to hydrided region overloads in CANDU Zr-2.5%Nb pressure tubes

International Nuclear Information System (INIS)

Gutkin, L.; Scarth, D.A.

2014-01-01

Zr-2.5%Nb pressure tubes in CANDU nuclear reactors are susceptible to hydride-assisted cracking at the locations of stress concentration, such as in-service flaws. Probabilistic methodology is being developed to evaluate such flaws for crack initiation due to hydrided region overloads, which occur when the applied stress acting on a flaw with an existing hydrided region at its tip exceeds the stress at which the hydrided region is formed. As part of this development, probabilistic modeling of pressure tube material resistance to overload crack initiation has been performed on the basis of a set of test data specifically designed to study the effects of non-ratcheting hydride formation conditions and load reduction prior to hydride formation. In the modeling framework, the overload resistance is represented as a power-law function of the material resistance to initiation of delayed hydride cracking under constant loading, where both the overload crack initiation coefficient and the overload crack initiation exponent vary with the flaw geometry. In addition, the overload crack initiation coefficient varies with the extent of load reduction prior to hydride formation as well as the number of non-ratcheting hydride formation thermal cycles. (author)

Probabilistic modeling of material resistance to crack initiation due to hydrided region overloads in CANDU Zr-2.5%Nb pressure tubes

Energy Technology Data Exchange (ETDEWEB)

Gutkin, L.; Scarth, D.A. [Kinectrics Inc., Toronto, ON (Canada)

2014-07-01

Zr-2.5%Nb pressure tubes in CANDU nuclear reactors are susceptible to hydride-assisted cracking at the locations of stress concentration, such as in-service flaws. Probabilistic methodology is being developed to evaluate such flaws for crack initiation due to hydrided region overloads, which occur when the applied stress acting on a flaw with an existing hydrided region at its tip exceeds the stress at which the hydrided region is formed. As part of this development, probabilistic modeling of pressure tube material resistance to overload crack initiation has been performed on the basis of a set of test data specifically designed to study the effects of non-ratcheting hydride formation conditions and load reduction prior to hydride formation. In the modeling framework, the overload resistance is represented as a power-law function of the material resistance to initiation of delayed hydride cracking under constant loading, where both the overload crack initiation coefficient and the overload crack initiation exponent vary with the flaw geometry. In addition, the overload crack initiation coefficient varies with the extent of load reduction prior to hydride formation as well as the number of non-ratcheting hydride formation thermal cycles. (author)

Study of creep crack growth behavior of 316LN welds

International Nuclear Information System (INIS)

Venugopal, S.; Kumar, Yatindra; Sasikala, G.

2016-01-01

Creep crack growth (CCG) behavior plays an important role in the assessment of structural integrity of components operating at elevated temperature under load/stress condition. Integrity of the welded components is decided primarily by that of the weld. Creep crack growth behavior of 316LN welds prepared using consumables developed indigenously for welding the 316L(N) SS components for the Prototype Fast Breeder Reactor has been studied. The composition of the consumable is tailored to ensure about 5 FN (ferrite number) of δ ferrite in the weld deposit. Constant load CCG tests were carried out as per ASTM E1457 at different applied loads at temperatures in the range 823-923 K on CT specimens fabricated from 'V-type' weld joints with notch in the weld centre. The creep crack growth rate (α) is commonly correlated to a time dependent fracture mechanics parameter known as C*. The α3-C* correlations (α=D(C*) φ ) were established in the temperature range 823-923 K. The crack growth rates at different temperature have been compared with that given in RCC-MR. Extensive microstructural and fractographic studies using optical and scanning electron microscopy were carried out on the CCG tested specimens to understand the effect of transformation of delta ferrite on the creep damage and fracture mechanisms associated with CCG in the weld metal at different test conditions. (author)

Precursor Evolution and Stress Corrosion Cracking Initiation of Cold-Worked Alloy 690 in Simulated Pressurized Water Reactor Primary Water

Energy Technology Data Exchange (ETDEWEB)

Zhai, Ziqing [Pacific Northwest National Laboratory, 622 Horn Rapids Road, P.O. Box 999, Richland, Washington 99352.; Toloczko, Mychailo [Pacific Northwest National Laboratory, 622 Horn Rapids Road, P.O. Box 999, Richland, Washington 99352.; Kruska, Karen [Pacific Northwest National Laboratory, 622 Horn Rapids Road, P.O. Box 999, Richland, Washington 99352.; Bruemmer, Stephen [Pacific Northwest National Laboratory, 622 Horn Rapids Road, P.O. Box 999, Richland, Washington 99352.

2017-05-22

Stress corrosion crack initiation of two thermally-treated, cold-worked (CW) alloy 690 (UNS N06690) materials was investigated in 360oC simulated PWR primary water using constant load tensile (CLT) tests and blunt notch compact tension (BNCT) tests equipped with direct current potential drop (DCPD) for in-situ detection of cracking. SCC initiation was not detected by DCPD for either the 21% or 31%CW CLT specimens loaded at their yield stress after ~9,220 hours, however intergranular (IG) precursor damage and isolated surface cracks were observed on the specimens. The two 31%CW BNCT specimens loaded at moderate stress intensity after several cyclic loading ramps showed DCPD-indicated crack initiation after 10,400 hours of exposure at constant stress intensity, which was resulted from significant growth of IG cracks. The 21%CW BNCT specimens only exhibited isolated small IG surface cracks and showed no apparent DCPD change throughout the test. Post-test cross-section examinations revealed many grain boundary (GB) nano-cavities in the bulk of all the CLT and BNCT specimens particularly for the 31%CW materials. Cavities were also found along GBs extending to the surface suggesting an important role in crack nucleation. This paper provides an overview of the evolution of GB cavities and discusses their effects on crack initiation in CW alloy 690.

Effect of Local Strain Distribution of Cold-Rolled Alloy 690 on Primary Water Stress Corrosion Crack Growth Behavior

Directory of Open Access Journals (Sweden)

Kim S.-W.

2017-06-01

Full Text Available This work aims to study the stress corrosion crack growth behavior of cold-rolled Alloy 690 in the primary water of a pressurized water reactor. Compared with Alloy 600, which shows typical intergranular cracking along high angle grain boundaries, the cold-rolled Alloy 690, with its heterogeneous microstructure, revealed an abnormal crack growth behavior in mixed mode, that is, in transgranular cracking near a banded region, and in intergranular cracking in a matrix region. From local strain distribution analysis based on local mis-orientation, measured along the crack path using the electron back scattered diffraction method, it was suggested that the abnormal behavior was attributable to a heterogeneity of local strain distribution. In the cold-rolled Alloy 690, the stress corrosion crack grew through a highly strained area formed by a prior cold-rolling process in a direction perpendicular to the maximum principal stress applied during a subsequent stress corrosion cracking test.

Fracture behavior of filament in Nb{sub 3}Sn strands with crack-bridging model

Energy Technology Data Exchange (ETDEWEB)

Yong, Huadong, E-mail: yonghd@lzu.edu.cn; Yang, Penglei; Xue, Cun; Zhou, Youhe

2016-01-15

Highlights: • The crack-bridging model is used to study the fracture behavior of filaments. • Two different fracture modes are characterized by the number of bridging bronzes. • Short twist pitch has better mechanical stability for the tensile loadings. • The widths of bridging bronze and filament have different effects for the central crack and two collinear cracks. - Abstract: The Nb{sub 3}Sn strands which have high critical field are used in cable-in-conduit conductors (CICCs). The superconducting strands are twisted multistage and experience complex thermal and electromagnetic loadings. Due to their brittleness, the cracking of the Nb{sub 3}Sn filaments will occur under mechanical loading. In this paper, based on the linear elastic fracture theory, we study the effects of tension loading on the fracture behavior of central crack firstly. The strain energy release rates for different twist pitches and cabling stages are presented. As the triplet is subjected to the uniaxial strain, the cracking probability will increase with the twist pitch. The crack number increases with the applied strain, and wider filament or bronze can lead to smaller crack number under the same applied strain. In addition, multistage cabling has better mechanical stability. Next, the two collinear crack problem is considered. The variations of microcrack number show that the wider bronze can provide more resistance for the propagating of the large cracks. We can conclude that the bronze plays an important role in improving the stability and strength.

Fatigue Behavior of Long and Short Cracks in Wrought and Powder Aluminum Alloys.

Science.gov (United States)

1984-05-01

The effects of cyclic frequency, electrochemical potential and bulk solution composition on the kinetics of small corrosion fatigue cracks have not...threshold behavior between cast iron (co = 113 MPa) and maraging steel (co = 1906 MPa), as a function of surface roughness (to simulate crack size) (after...4130 steel the crack size effect on corrosion fatigue, Fig. 2, is predicted in part based on linear superposition of stress corrosion growth rates for

Metal magnetic memory technique used to predict the fatigue crack propagation behavior of 0.45%C steel

Energy Technology Data Exchange (ETDEWEB)

Chongchong, Li [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China); Lihong, Dong, E-mail: lihong.dong@126.com [National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China); Haidou, Wang [National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China); Guolu, Li [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Binshi, Xu [National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China)

2016-05-01

Monitoring fatigue crack propagation behavior of ferromagnetic components is very important. In this paper, the tension–tension fatigue tests of center cracked tension (CCT) specimens were carried out; the variation regularity of both tangential and normal components of magnetic signals during fatigue process were investigated. The results showed that the initial abnormal signals which appeared at the notch were reversed after cyclic loading. The abnormal magnetic signals became more significant with the increase of fatigue cycles and reversed again after failure. The characteristic parameters, i.e., the peak value of tangential component, B{sub tp}, and maximum gradient value of normal component, K{sub m}, showed similar variation trends during the fatigue process, which can be divided into three different stages. An approximate linear relationship was found between the characteristic parameters and fatigue crack length 2a. The feasibility of predicting the fatigue crack propagation using the abnormal magnetic signals was discussed. What's more, the variation and distribution of the magnetic signals were also analyzed based on the theory of magnetic charge. - Highlights: • A novel and passive NDT method, i.e. MMMT method, is proposed. • Both tangential and normal components of magnetic signals were investigated. • The prediction of crack propagation by abnormal magnetic signals was discussed. • A linear relationship was found between the parameters and fatigue crack length 2a. • The parameters can be potentially used to evaluate the crack propagation state.

Observations of the severity of notch-root radius in initiation of subcritical crack growth

International Nuclear Information System (INIS)

Reuter, W.G.; Eiholzer, C.R.; Tupper, M.A.

1981-01-01

Slow bend tests were conducted on Charpy specimens containing precracks or machined notches of 0.10 or 0.25 mm radius. The test specimens were fabricated from three heats of annealed Type 304 stainless steel. The purpose of these tests was to examine the effects of notch root radius, in very ductile materials, on initiation of subcritical crack growth. In addition, it was intended to establish the critical values of J, COD, etc. for the single-edge notch specimen for comparison with results obtained from specimens containing surface flaws. This paper will briefly describe only those results of the calculation for J. The tests were monitored by acoustic emission to identify the load corresponding to initiation of subcritical crack growth, by a crack-opening displacement gage (COD), by cross-head displacement, and by stop-action photography

Artificial-Crack-Behavior Test Evaluation of the Water-Leakage Repair Materials Used for the Repair of Water-Leakage Cracks in Concrete Structures

OpenAIRE

Soo-Yeon Kim; Sang-Keun Oh; Byoungil Kim

2016-01-01

There are no existing standard test methods at home and abroad that can verify the performance of water leakage repair materials, and it is thus very difficult to perform quality control checks in the field of water leakage repair. This study determined that the key factors that have the greatest impact on the water leakage repair materials are the micro-behaviors of cracks, and proposed an artificial-crack-behavior test method for the performance verification of the repair materials. The per...

Studies on the behavior of part-through circumferential crack at intrados in elbows under in-plane bending moment

International Nuclear Information System (INIS)

Srivastava, A.; Prabhakaran, K.M.; Ghosh, A.K.

2011-01-01

Highlights: → Behavior of cracked elbows with part-through crack at intrados under bending moment is studied. → Some part of crack always opens and some part gets closed irrespective of mode of applied moment. → Fraction of the crack that opens basically decides the weakening effect of the cracked elbow. → Results will be useful for fracture studies and limit load estimation especially for LBB. - Abstract: This paper presents the behavior of part-through circumferential crack at intrados in elbows under in-plane bending moment. This is based on detailed non-linear (both material and geometric) finite element analysis performed on various sizes of elbows (generally used in piping industry), having different crack sizes. It is observed that some part of the crack always opens and some part gets closed irrespective of the mode of applied bending moment (opening/closing). The fraction of the crack that opens basically decides the weakening effect of the cracked elbow. It is observed that there is a threshold value of crack length and crack depth, before which no crack opening is observed under opening mode. Also as elbow becomes thinner, the threshold value of above two parameters increases. Quite interestingly, the part of crack which closes in opening mode opens under closing mode. The above mentioned study on the behavior of crack will be useful for fracture studies and limit load estimation especially when leak before break concept is to be employed.

Evaluation of local stress for stress corrosion crack initiation by three-dimensional polycrystal model

International Nuclear Information System (INIS)

Kamaya, Masayuki; Kitamura, Takayuki

2006-01-01

In order to understand the initiation behavior of microstructurally small cracks in a stress corrosion cracking condition, it is important to know the tensile normal stress acting on the grain boundary (normal G.B. stress). The local stress in a polycrystalline body is greatly influenced by deformation constraint which is caused by anisotropic and/or inhomogeneous property of each grain. In present study, the local normal G.B. stress on bi- and tri-crystal bodies and a three-dimensional polycrystalline body consisting of 100 grains were evaluated by the finite element method under a remote uniform tensile stress condition. The polycrystalline body was generated by using a Monte Carlo procedure and random orientations were assigned to each grain. It was revealed that the local normal G.B. stress on the polycrystalline body is inhomogeneous under uniform applied stress. The stress tends to be large near the triple points due to the deformation constraint caused by adjacent grains, even though the grain boundary inclination to the load axis has large influence. It was also shown that particular high stress was not observed at corners of the polycrystalline body. (author)

Creep and creep fatigue crack behavior of 1Cr- and 9Cr-steels

International Nuclear Information System (INIS)

Maile, K.; Klenk, A.; Schellenberg, G.; Granacher, J.; Tramer, M.

2000-01-01

A large database for creep crack initiation and propagation under constant load conditions is available on conventional power plant steels of types 1%Cr and 12%Cr. Modern plants are often used in the medium and peak load regime, thus the dominant loading situation in high temperature components is creep fatigue. For life assessment data about crack initiation and growth under creep fatigue loading are required. These characteristics can not be substituted by pure fatigue or creep crack data. Therefore, a comprehensive test programme was started to investigate the creep fatigue crack behaviour of a 1%CrMoNiV turbine rotor steel (30CrMoNiV 4 11) at 550 C and a new 9%CrMoVNb pipe steel (type P 9 1) at 600 C. DENT-specimen with 15 and 60 mm thickness as well as side grooved CT-specimen with 25 and 50 mm thickness have been tested to determine possible influences of geometry and thus to check the transferability of the data to components. The creep fatigue crack growth results of tests with dwell times between t H = 0,32h and 10 h lie in the scatterbands given by creep crack growth results. Nevertheless a higher crack growth rate under creep fatigue conditions can be stated. An increase in crack growth rate due to creep fatigue is clearly visible. Loading situations with frequencies higher than 1.10 -4 Hz should be not assessed with pure creep crack results or sufficient safety margins have to be applied. (orig.)

Fatigue Crack Growth Behavior of Gas Metal Arc Welded AISI 409 Grade Ferritic Stainless Steel Joints

Science.gov (United States)

Lakshminarayanan, A. K.; Shanmugam, K.; Balasubramanian, V.

2009-10-01

The effect of filler metals such as austenitic stainless steel, ferritic stainless steel, and duplex stainless steel on fatigue crack growth behavior of the gas metal arc welded ferritic stainless steel joints was investigated. Rolled plates of 4 mm thickness were used as the base material for preparing single ‘V’ butt welded joints. Center cracked tensile specimens were prepared to evaluate fatigue crack growth behavior. Servo hydraulic controlled fatigue testing machine with a capacity of 100 kN was used to evaluate the fatigue crack growth behavior of the welded joints. From this investigation, it was found that the joints fabricated by duplex stainless steel filler metal showed superior fatigue crack growth resistance compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Higher yield strength and relatively higher toughness may be the reasons for superior fatigue performance of the joints fabricated by duplex stainless steel filler metal.

Crack initiation through vibration fatigue of small-diameter pipes

International Nuclear Information System (INIS)

Comby, R.; Thebault, Y.; Papaconstantinou, T.

2002-01-01

Socket welds are used extensively for small bore piping connections in nuclear power plant systems. Numerous fatigue-related failures occurred in the past ten years mainly on safeguard systems and continue to occur frequently, showing that corrective actions did not take into account all aspects of the problem. Destructive examination of cracked small bore piping connections allowed a better understanding of failure mechanisms and a prediction of crack initiation site depending on nozzle fittings such as run pipe and small bore pipe thickness. A three-dimensional finite element model confirmed the conclusions of the lab examinations. For thick run pipes, it was shown that the failure tend to initiate predominantly at the socket weld toe or at the root, depending on the respective thickness of coupling and small bore pipe. Some additional studies, based on RSE-M code, are in progress in order to determine the maximum stresses location. Lessons learned through these investigations led to optimise the in-service inspection scope and to define solutions to be carried out to prevent failure of ''susceptible'' small bore pipe connections. Since July 2000, a large program is in progress to select all ''susceptible'' small bore pipes in safety-related systems and to apply corrective measures such as piping modifications or system operational modifications. (authors)

Effect of pre-deformation on the fatigue crack initiation life of X60 pipeline steel

International Nuclear Information System (INIS)

Zheng, M.; Luo, J.H.; Zhao, X.W.; Bai, Z.Q.; Wang, R.

2005-01-01

It is impossible to keep petroleum and natural gas transmission pipelines free from defects in the manufacturing, installation and servicing processes. The damage might endanger the safety of pipelines and even shorten their service life; gas or petroleum release due to defects may jeopardise the surrounding ecological environments with associated economic and life costs. Pre-tensile deformation of X60 steel is employed to experimentally simulate the influence of dents on the fatigue crack initiation life. The investigation indicates that the fatigue crack initiation life of pre-deformed X60 pipeline steel can be assessed by a previously proposed energetic approach. The threshold for crack initiation increases with the pre-deformation due to a strain hardening effect, while the fatigue resistant factor exhibits a maximum with pre-deformation owing to its special dependence on fracture strain and fracture strength. The result is expected to be beneficial to the understanding of the effect of damage on the safety of pipelines and fatigue life prediction

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

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

Theoretical and numerical studies of crack initiation and propagation in rock masses under freezing pressure and far-field stress

Directory of Open Access Journals (Sweden)

Yongshui Kang

2014-10-01

Full Text Available Water-bearing rocks exposed to freezing temperature can be subjected to freeze–thaw cycles leading to crack initiation and propagation, which are the main causes of frost damage to rocks. Based on the Griffith theory of brittle fracture mechanics, the crack initiation criterion, propagation direction, and crack length under freezing pressure and far-field stress are analyzed. Furthermore, a calculation method is proposed for the stress intensity factor (SIF of the crack tip under non-uniformly distributed freezing pressure. The formulae for the crack/fracture propagation direction and length of the wing crack under freezing pressure are obtained, and the mechanism for coalescence of adjacent cracks is investigated. In addition, the necessary conditions for different coalescence modes of cracks are studied. Using the topology theory, a new algorithm for frost crack propagation is proposed, which has the capability to define the crack growth path and identify and update the cracked elements. A model that incorporates multiple cracks is built by ANSYS and then imported into FLAC3D. The SIFs are then calculated using a FISH procedure, and the growth path of the freezing cracks after several calculation steps is demonstrated using the new algorithm. The proposed method can be applied to rocks containing fillings such as detritus and slurry.

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

Numerical analysis for fatigue life prediction on railroad RCF crack initiation

NARCIS (Netherlands)

Ma, Y.; Markine, V.L.

2015-01-01

In the present paper, a numerical procedure for surface crack initiation analysis based on the critical plane approach is proposed. The complex stress/strain state of wheel and rail (W/R) contact is analysed by means of submodelling approach together with the transient contact nodal loads obtained

In situ observation of rolling contact fatigue cracks by laminography using ultrabright synchrotron radiation

Directory of Open Access Journals (Sweden)

Y. Nakai

2015-10-01

Full Text Available In rolling contact fatigue (RCF, cracks usually initiate from inclusions beneath the surface and propagate to the contact surface. In the present study, synchrotron radiation computed laminography (SRCL imaging was performed to observe flaking defects during the RCF of a high-strength steel. Specially fabricated inclusion-rich steel plate specimens were employed in the experiments. For the in situ observation of crack propagation, a compact RCF testing machine was developed, and a 4D analysis scheme was applied to the data obtained by SRCL. RCF tests were carried out near the measurement hatch of the beam line used SRCL to enable the successive observation of crack initiation and growth behaviors. Specimens before and after the occurrence of flaking were observed by SRCL, and flaking defects and cracks under the surface were successfully detected. As a result, details of the crack initiation and flaking process in RCF could be discussed. Shear-type horizontal cracks were found to initiate after the initiation and propagation of tensile-type vertical cracks along inclusions, where the face of the vertical cracks was perpendicular to the rolling direction and rolling surface. Therefore, the formation of vertical cracks is considered to affect shear-type crack formation and flaking, where the shape and length of inclusions also affect the initiation and propagation of vertical cracks.

Effect of direction of approach to temperature on the delayed hydrogen cracking behavior of cold-worked Zr-2.5Nb

International Nuclear Information System (INIS)

Ambler, J.F.R.

1984-01-01

The delayed hydrogen cracking behavior of cold-worked Zr-2.5Nb at temperatures above about 423 K depends upon the direction of approach to test temperature. Cooling to the test temperatures results in an increase in crack growth rate, da/dt, with increase in temperature, given by the following Arrhenius relationship da/dt = 6.86 X 10 -1 exp(--71500/RT) Heating from room temperature to the test temperature results in the same increase in da/dt with temperature, but only up to a certain temperature, T /SUB DAT/ . The temperature, T /SUB DAT/ , increases with the amount of hydride precipitated during cooling to room temperature, prior to heating, and with cooling rate. The results obtained can be explained in terms of the Simpson and Puls model of delayed hydrogen cracking, if the hydride precipitated at the crack tip is initially fully constrained and the matrix hydride loses constraint during heating

Crack initiation at high temperature on an austenitic stainless steel; Amorcage de fissure a haute temperature dans un acier inoxydable austenitique

Energy Technology Data Exchange (ETDEWEB)

Laiarinandrasana, L

1994-11-25

The study deals with crack initiation at 600 and 650 degrees Celsius, on an austenitic stainless steel referenced by Z2 CND 17 12. The behaviour laws of the studied plate were update in comparison with existing data. Forty tests were carried out on CT specimens, with continuous fatigue with load or displacement controlled, pure creep, pure relaxation, creep-fatigue and creep-relaxation loadings. The practical initiation definition corresponds to a small crack growth of about the grain size. The time necessary for the crack to initiate is predicted with fracture mechanics global and local approaches, with the helps of microstructural observations and finite elements results. An identification of a `Paris`law` for continuous cyclic loading and of a unique correlation between the initiation time and C{sup *}{sub k} for creep tests was established. For the local approach, crack initiation by creep can be interpreted as the reaching of a critical damage level, by using a damage incremental rule. For creep-fatigue tests, crack growth rates at initiation are greater than those of Paris`law for continuous fatigue. A calculation of a transition time between elastic-plastic and creep domains shows that crack initiation can be interpreted whether by providing Paris`law with an acceleration term when the dwell period is less than the transition time, or by calculating a creep contribution which relies on C{sup *}{sub k} parameter when the dwell period and/or the initiation times are greater than the transition time. Creep relaxation tests present crack growth rates at initiation which are less than those for `equivalent` creep-fatigue tests. These crack growth rates when increasing hold time, but also when temperature decreases. Though, for hold times which are important enough and at lower temperature, there is no effect of the dwell period insofar as crack growth rate is equal to continuous fatigue Paris law predicted ones. (Abstract Truncated)

Crack-arrest behavior in SEN wide plates of low-upper-shelf base metal tested under nonisothermal conditions: WP-2 series

International Nuclear Information System (INIS)

Naus, D.J.; Keeney-Walker, J.; Bass, B.R.; Robinson, G.C. Jr.; Iskander, S.K.; Alexander, D.J.; Fields, R.J.; deWit, R.; Low, S.R.; Schwartz, C.W.

1990-08-01

The Heavy-Section Steel Technology (HSST) Program at the Oak Ridge National Laboratory under the sponsorship of the Nuclear Regulatory Commission is conducting analytical and experimental studies aimed at understanding the circumstances that would initiate the growth of an existing crack in a reactor pressure vessel (RPV) and the conditions leading to arrest of a propagating crack. Objectives of these studies are to determine (1) if the material will exhibit crack-arrest behavior when the driving force on a crack exceeds the ASME limit, (2) the relationship between K Ia and temperature, and (3) the interaction of fracture modes (arrest, stable crack growth, unstable crack growth, and tensile instability) when arrest occurs at high temperatures. In meeting these objectives, crack-arrest data are being developed over an expanded temperature range through tests involving large thermally shocked cylinders, pressurized thermally shocked vessels, and wide-plate specimens. The wide-plate specimens provide the opportunity for a significant number of data points to be obtained at relatively affordable costs. These tests are designed to provide fracture-toughness measurements approaching or above the onset of the Charpy upper-shelf regime in a rising toughness region and with an increasing driving force. This document discusses test methodology and results. 23 refs., 92 figs., 25 tabs

Effect of temperature upon the fatigue-crack propagation behavior of Inconel X-750

International Nuclear Information System (INIS)

James, L.A.

1976-05-01

The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of precipitation heat-treated Inconel X-750 in an air environment over the range 75-1200 0 F. In general, fatigue-crack growth rates increased with increasing test temperature

On the Crack Initiated From the Bi-material Notch Tip

Czech Academy of Sciences Publication Activity Database

Profant, T.; Klusák, Jan; Kotoul, M.

452-453, - (2011), s. 441-444 ISSN 1013-9826. [Fracture and Damage Mechanics. Nagasaki, 20.09.2010-22.09.2010] R&D Projects: GA ČR GAP108/10/2049; GA ČR GA101/08/0994 Institutional research plan: CEZ:AV0Z20410507 Keywords : orthotropic bi-material notch * crack initiation * Matched asymptotic procedure Subject RIV: JL - Materials Fatigue, Friction Mechanics

Comparison of the microstructure, deformation and crack initiation behavior of austenitic stainless steel irradiated in-reactor or with protons

Energy Technology Data Exchange (ETDEWEB)

Stephenson, Kale J., E-mail: kalejs@umich.edu; Was, Gary S.

2015-01-15

Highlights: • Dislocation loops were the prominent defect, but neutron irradiation caused higher loop density. • Grain boundaries had similar amounts of radiation-induced segregation. • The increment in hardness and yield stress due to irradiation were very similar. • Relative IASCC susceptibility was nearly identical. • The effect of dislocation channel step height on IASCC was similar. - Abstract: The objective of this study was to compare the microstructures, microchemistry, hardening, susceptibility to IASCC initiation, and deformation behavior resulting from proton or reactor irradiation. Two commercial purity and six high purity austenitic stainless steels with various solute element additions were compared. Samples of each alloy were irradiated in the BOR-60 fast reactor at 320 °C to doses between approximately 4 and 12 dpa or by a 3.2 MeV proton beam at 360 °C to a dose of 5.5 dpa. Irradiated microstructures consisted mainly of dislocation loops, which were similar in size but lower in density after proton irradiation. Both irradiation types resulted in the formation of Ni–Si rich precipitates in a high purity alloy with added Si, but several other high purity neutron irradiated alloys showed precipitation that was not observed after proton irradiation, likely due to their higher irradiation dose. Low densities of small voids were observed in several high purity proton irradiated alloys, and even lower densities in neutron irradiated alloys, implying void nucleation was in process. Elemental segregation at grain boundaries was very similar after each irradiation type. Constant extension rate tensile experiments on the alloys in simulated light water reactor environments showed excellent agreement in terms of the relative amounts of intergranular cracking, and an analysis of localized deformation after straining showed a similar response of cracking to surface step height after both irradiation types. Overall, excellent agreement was observed

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)

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 ...

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.

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

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

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

Ductile crack initiation and propagation assessed via in situ synchrotron radiation-computed laminography

International Nuclear Information System (INIS)

Morgeneyer, T.F.; Helfen, L.; Sinclair, I.; Proudhon, H.; Xu, F.; Baumbach, T.

2011-01-01

Ductile crack initiation and propagation within a naturally aged aluminium alloy sheet has been observed in situ via synchrotron radiation-computed laminography, a technique specifically adapted to three-dimensional imaging of thin objects that are laterally extended. Voids and intermetallic particles, and their subsequent evolution during ductile crack extension at different associated levels of stress triaxiality, were clearly observed within fracture coupons of a reasonable engineering length-scale, overcoming the conventional sample size limitation of computed tomography at high resolutions.

Influence of surface defects on the fatigue crack initiation in pearlitic steel

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Toribio Jesús

2014-06-01

Full Text Available Tensile fatigue tests were performed under load control, with constant stress range Δσ on pearlitic steel wires, from the hot rolled bar to the commercial prestressing steel wire (which has undergone seven cold drawing steps. Results show that fatigue cracks in pearlitic steels initiate at the wire surface starting from small defects, whose size decreases with the drawing process. Fatigue cracks created from defects (initiation phase exhibit a fractographic appearance consisting of ductile microtearing events which can be classified as tearing topography surface or TTS, and exhibit a remarkably lower spacing in the prestressing steel wire than in the hot rolled bar. In addition, some S-N tests were performed in both material forms under a stress range of about half the yield strength. In these tests, the main part of the fatigue life corresponds to the propagation stage in the hot rolled bar whereas such a main part of the life is associated with the initiation stage in the case of the prestressing steel wire.

Role of hydrogen on the incipient crack tip deformation behavior in α-Fe: An atomistic perspective

Science.gov (United States)

Adlakha, I.; Solanki, K. N.

2018-01-01

A crack tip in α-Fe presents a preferential trap site for hydrogen, and sufficient concentration of hydrogen can change the incipient crack tip deformation response, causing a transition from a ductile to a brittle failure mechanism for inherently ductile alloys. In this work, the effect of hydrogen segregation around the crack tip on deformation in α-Fe was examined using atomistic simulations and the continuum based Rice-Thompson criterion for various modes of fracture (I, II, and III). The presence of a hydrogen rich region ahead of the crack tip was found to cause a decrease in the critical stress intensity factor required for incipient deformation for various crack orientations and modes of fracture examined here. Furthermore, the triaxial stress state ahead of the crack tip was found to play a crucial role in determining the effect of hydrogen on the deformation behavior. Overall, the segregation of hydrogen atoms around the crack tip enhanced both dislocation emission and cleavage behavior suggesting that hydrogen has a dual role during the deformation in α-Fe.

Corrosion fatigue initiation and short crack growth behaviour of austenitic stainless steels under light water reactor conditions

International Nuclear Information System (INIS)

Seifert, H.P.; Ritter, S.; Leber, H.J.

2012-01-01

Highlights: ► Corrosion fatigue in austenitic stainless steels under light water reactor conditions. ► Identification of major parameters of influence on initiation and short crack growth. ► Critical system conditions for environmental reduction of fatigue initiation life. ► Comparison with the environmental factor (F env ) approach. - Abstract: The corrosion fatigue initiation and short crack growth behaviour of different wrought low-carbon and stabilised austenitic stainless steels was characterised under simulated boiling water reactor and pressurised water reactor primary water conditions by cyclic fatigue tests with sharply notched fracture mechanics specimens. The special emphasis was placed to the behaviour at low corrosion potentials and, in particular, to hydrogen water chemistry conditions. The major parameter effects and critical conjoint threshold conditions, which result in relevant environmental reduction and acceleration of fatigue initiation life and subsequent short crack growth, respectively, are discussed and summarised. The observed corrosion fatigue behaviour is compared with the fatigue evaluation procedures in codes and regulatory guidelines.

Heavy-Section Steel Technology Program: Recent developments in crack initiation and arrest research

International Nuclear Information System (INIS)

Pennell, W.E.

1991-01-01

Technology for the analysis of crack initiation and arrest is central to the reactor pressure vessel fracture-margin-assessment process. Regulatory procedures for nuclear plants utilize this technology to assure the retention of adequate fracture-prevention margins throughout the plant operating license period. As nuclear plants age and regulatory procedures dictate that fracture-margin assessments be performed, interest in the fracture-mechanics technology incorporated into those procedures has heightened. This has led to proposals from a number of sources for development and refinement of the underlying crack-initiation and arrest-analysis technology. This paper presents an overview of ongoing Heavy-Section Steel Technology (HSST) Program research aimed at refining the fracture toughness data used in the analysis of fracture margins under pressurized-thermal-shock loading conditions. 33 refs., 13 figs

Investigation on effect of laser shock processing on fatigue crack initiation and its growth in aluminum alloy plate

International Nuclear Information System (INIS)

Zhang, X.Q.; Li, H.; Yu, X.L.; Zhou, Y.; Duan, S.W.; Li, S.Z.; Huang, Z.L.; Zuo, L.S.

2015-01-01

Highlights: • LSP can greatly delay crack formation. • The micro-crack growing processes and its fracture are showed clearly. • Surface topographies and crack initiation locations are displayed. - Abstract: A series of contrasting experiments were carried out to examine the effects of laser shock processing (LSP) on fatigue properties of slot in 7075-T6 aluminum alloy plate. Both side surfaces of slot were subjected to LSP. The surface topographies were observed and the residual stresses were tested. The treated and the un-treated specimens were pulled by the fatigue cyclic loading respectively. The fatigue crack propagating processes were recorded, and the fatigue fracture microscopic morphologies were analyzed by scanning electron microscope (SEM). Experimental results and analyses show that LSP induces micro-dent on surface and squeezes the compressive residual stresses into surface layer of specimen. It can remarkably delay the micro-crack formation, and transfer the location of fatigue crack initiation from top surface to sub-surface. The spacing of fatigue striations on the treated specimen fatigue fracture obviously decreases. Therefore, the fatigue life of specimen after LSP treatment significantly increases

Evaluation of stress corrosion crack growth in BWR piping systems

International Nuclear Information System (INIS)

Kassir, M.; Sharma, S.; Reich, M.; Chang, M.T.

1985-05-01

This report presents the results of a study conducted to evaluate the effects of stress intensity factor and environment on the growth behavior of intergranular stress corrosion cracks in type 304 stainless steel piping systems. Most of the detected cracks are known to be circumferential in shape, and initially started at the inside surface in the heat affected zone near girth welds. These cracks grow both radially in-depth and circumferentially in length and, in extreme cases, may cause leakage in the installation. The propagation of the crack is essentially due to the influence of the following simultaneous factors: (1) the action of applied and residual stress; (2) sensitization of the base metal in the heat affected zone adjacent to girth weld; and (3) the continuous exposure of the material to an aggressive environment of high temperature water containing dissolved oxygen and some levels of impurities. Each of these factors and their effects on the piping systems is discussed in detail in the report. The report also evaluates the time required for hypothetical cracks in BWR pipes to propagate to their critical size. The pertinent times are computed and displayed graphically. Finally, parametric study is performed in order to assess the relative influence and sensitivity of the various input parameters (residual stress, crack growth law, diameter of pipe, initial size of defect, etc.) which have bearing on the growth behavior of the intergranular stress corrosion cracks in type 304 stainless steel. Cracks in large-diameter as well as in small-diameter pipes are considered and analyzed. 27 refs., 25 figs., 10 tabs

Fractal and probability analysis of creep crack growth behavior in 2.25Cr–1.6W steel incorporating residual stresses

Energy Technology Data Exchange (ETDEWEB)

Xu, Mengjia; Xu, Jijin, E-mail: xujijin_1979@sjtu.edu.cn; Lu, Hao; Chen, Jieshi; Chen, Junmei; Wei, Xiao

2015-12-30

Graphical abstract: - Highlights: • Statistical and fractal analysis is applied to study the creep fracture surface. • The tensile residual stresses promote the initiation of creep crack. • The fractal dimension of a mixed mode fracture surface shows a wavy variation. • The fractal dimension increases with increasing intergranular fracture percentage. • Height coordinates of intergranular fracture surface fit Gaussian distribution. - Abstract: In order to clarify creep crack growth behavior in 2.25Cr–1.6W steel incorporating residual stresses, creep crack tests were carried out on the tension creep specimens, in which the residual stresses were generated by local remelting and cooling. Residual stresses in the specimens were measured using Synchrotron X-ray diffraction techniques. The fracture surface of the creep specimen was analyzed using statistical methods and fractal analysis. The relation between fractal dimension of the fracture surface and fracture mode of the creep specimen was discussed. Due to different fracture mechanisms, the probability density functions of the height coordinates vary with the intergranular crack percentage. Good fitting was found between Gaussian distribution and the probability function of height coordinates of the high percentage intergranular crack surface.

Fractal and probability analysis of creep crack growth behavior in 2.25Cr–1.6W steel incorporating residual stresses

International Nuclear Information System (INIS)

Xu, Mengjia; Xu, Jijin; Lu, Hao; Chen, Jieshi; Chen, Junmei; Wei, Xiao

2015-01-01

Graphical abstract: - Highlights: • Statistical and fractal analysis is applied to study the creep fracture surface. • The tensile residual stresses promote the initiation of creep crack. • The fractal dimension of a mixed mode fracture surface shows a wavy variation. • The fractal dimension increases with increasing intergranular fracture percentage. • Height coordinates of intergranular fracture surface fit Gaussian distribution. - Abstract: In order to clarify creep crack growth behavior in 2.25Cr–1.6W steel incorporating residual stresses, creep crack tests were carried out on the tension creep specimens, in which the residual stresses were generated by local remelting and cooling. Residual stresses in the specimens were measured using Synchrotron X-ray diffraction techniques. The fracture surface of the creep specimen was analyzed using statistical methods and fractal analysis. The relation between fractal dimension of the fracture surface and fracture mode of the creep specimen was discussed. Due to different fracture mechanisms, the probability density functions of the height coordinates vary with the intergranular crack percentage. Good fitting was found between Gaussian distribution and the probability function of height coordinates of the high percentage intergranular crack surface.

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.

Numerical analysis of macro-crack formation behavior within the lump coke; Cokes sonai kiretsu shinten kiko no kaiseki

Energy Technology Data Exchange (ETDEWEB)

Aoki, H; Sato, H; Miura, T [Tohoku University, Sendai (Japan). Faculty of Engineering

1995-03-15

The thermal stress analysis within lump coke was studied in order to investigate macro-crack formation and deformation behavior which strongly influence heat and mass transfer in a coke oven chamber. The dilatation of plastic layer, heating rate dependence of thermophysical and mechanical properties of coal/coke, creep in the plastic and semi-coke layers, macro-crack propagation and radiative heat transfer within the macro-crack were considered in an analytical model. The macro-crack propagation was determined from the estimated crack tip stress intensity factor, K{sub I}, at the macro-crack tip compared with the plane strain fracture toughness, K{sub IC}, through the unsteady-state calculation. Calculated results on crack formation and deformation behavior of lump coke were in good agreement with experimental observations in a laboratory-scale oven chamber. The analytical model could predict micro-crack formation within the lump coke normal to the heated wall and the coke surface close to the heated wall. 12 refs., 13 figs.

Crack initiation and growth in welded structures; Amorcage et propagation de la fissuration dans les jonctions soudees

Energy Technology Data Exchange (ETDEWEB)

Assire, A

2000-10-13

This work concerns the remaining life assessment of a structure containing initial defects of manufacturing. High temperature crack initiation and growth are studied for austenitic stainless steels, and defect assessment methods are improved in order to take into account welded structures. For these one, the probability to have a defect is significant. Two kinds of approaches are commonly used for defect assessment analysis. Fracture mechanics global approach with an energetic criterion, and local approach with a model taking into account the physical damage mechanism. For both approaches mechanical fields (stress and strain) have to be computed everywhere within the structure. Then, Finite Element computation is needed. The first part of the thesis concerns the identification of non linear kinematic and isotropic constitutive models. A pseudo-analytical method is proposed for a 'Two Inelastic Strain' model. This method provides a strategy of identification with a mechanical meaning, and this enables to associate each parameter to a physical phenomenon. Existing identifications are improved for cyclic plasticity and creep on a large range of stress levels. The second part concerns high temperature crack initiation and growth in welded structures. Finite Element analysis on plate and tube experimental configuration enable to understand the phenomenons of interaction between base metal and weld metal under mechanical and thermal loading. Concerning global approach, criteria based on C* parameter (Rice integral for visco-plasticity) are used. Finite Element computations underline the fact that for a defect located in the weld metal, C* values strongly depend on the base metal creep strain rate, because widespread visco-plasticity is located in both metals. A simplified method, based on the reference stress approach, is proposed and validated with Finite Element results. Creep crack growth simplified assessment is a quite good validation of the experimental results

Statistical analysis of fatigue crack growth behavior for grade B cast steel

International Nuclear Information System (INIS)

Li, W.; Sakai, T.; Li, Q.; Wang, P.

2011-01-01

Tests for fatigue crack growth rate (FCGR) and crack-tip opening displacement (CTOD) were performed to clarify the fatigue crack growth behavior of a railway grade B cast steel. The threshold values of this steel with specific survival probabilities are evaluated, in which the mean value is 8.3516 MPa m 1/2 , very similar to the experimental value, about 8.7279 MPa m 1/2 . Under the conditions of plane strain and small-scale yielding, the values of fracture toughness for this steel with specific survival probabilities are converted from the corresponding critical CTOD values, in which the mean value is about 138.4256 MPa m 1/2 . In consideration of the inherent variability of crack growth rates, six statistical models are proposed to represent the probabilistic FCGR curves of this steel in entire crack propagation region from the viewpoints of statistical evaluation on the number of cycles at a given crack size and the crack growth rate at a given stress intensity factor range, stochastic characteristic of crack growth as well as statistical analysis of coefficient and exponent in FCGR power law equation. Based on the model adequacy checking, result shows that all models are basically in good agreement with test data. Although the probabilistic damage-tolerant design based on some models may involve a certain amount of risk in stable crack propagation region, they just accord with the fact that the dispersion degree of test data in this region is relatively smaller.

Risk behaviors for sexually transmitted diseases among crack users

Directory of Open Access Journals (Sweden)

Rafael Alves Guimarães

2015-08-01

Full Text Available AbstractObjectives: to investigate the prevalence and risk behaviors by means of reporting of sexually transmitted diseases among crack users.Method: cross-sectional study carried out with 588 crack users in a referral care unit for the treatment of chemical dependency. Data were collected by means of face-to-face interview and analyzed using Stata statistical software, version 8.0.Results: of the total participants, 154 (26.2%; 95% CI: 22.8-29.9 reported antecedents of sexually transmitted diseases. Ages between 25 and 30 years (RP: 2.1; 95% CI: 1.0-4.0 and over 30 years (RP: 3.8; 95% CI: 2.1-6.8, alcohol consumption (RP: 1.9; 95% CI: 1.1-3.3, antecedents of prostitution (RP: 1.9; 95% CI: 1.3-2.9 and sexual intercourse with person living with human immunodeficiency virus/AIDS (RP: 2.7; 95% CI: 1.8-4.2 were independently associated with reporting of sexually transmitted diseases.Conclusion: the results of this study suggest high risk and vulnerability of crack users for sexually transmitted diseases.

FATIGUE CRACK PROPAGATION THROUGH AUSTEMPERED DUCTILE IRON MICROSTRUCTURE

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Lukáš Bubenko

2010-10-01

Full Text Available Austempered ductile iron (ADI has a wide range of application, particularly for castings used in automotive and earth moving machinery industries. These components are usually subjected to variable dynamic loading that may promote initiation and propagation of fatigue cracks up to final fracture. Thus, it is important to determine the fatigue crack propagation behavior of ADI. Since fatigue crack growth rate (da/dN vs. stress intensity factor K data describe fatigue crack propagation resistance and fatigue durability of structural materials, da/dN vs. Ka curves of ADI 1050 are reported here. The threshold amplitude of stress intensity factor Kath is also determined. Finally, the influence of stress intensity factor amplitude to the character of fatigue crack propagation through the ADI microstructure is described.

Evolution of dislocation structure and fatigue crack behavior in Fe-Si alloys during cyclic bending test

International Nuclear Information System (INIS)

Ushioda, Kohsaku; Takebayashi, Shigeto; Goto, Shoji; Komatsu, Yoshinari; Hoshino, Akinori

2010-01-01

The evolution of dislocation structures was investigated by means of TEM in Fe-Si alloys with 0, 0.5 and 1.0 mass% Si during a cyclic bending test in conjunction with fatigue crack behavior. The addition of Si increased the fatigue strength. In steel without Si the cell structure develops, whereas in steel with 1%Si the vein structure evolves, which is considered to lead to the increased fatigue strength. The cell structure in 0%Si steel is postulated to be caused by the easy cross slip of dislocations, whereas the vein structure in the steels with Si is inferred to be caused by the difficulty in cross slip presumably due to the decrease in stacking fault energy. Furthermore, the steel containing Si shows a dislocation free zone (DFZ) along grain boundaries. A transgranular fracture takes place in 0%Si steel, while in 1%Si steel many intergranular cracks were observed just beneath the top surface, which was thought to be caused by the fact that a) strains are dispersed within grains owing to the vein structure and b) micro cracks are initiated and propagated along a DFZ.

Influence of hydride microstructure on through-thickness crack growth in zircaloy-4 sheet

International Nuclear Information System (INIS)

Raynaud, P.A.; Meholic, M.J.; Koss, D.A.; Motta, A.T.; Chan, K.S.

2007-01-01

The fracture toughness of cold-worked and stress-relieved Zircaloy-4 sheet subject to through-thickness crack growth within a 'sunburst' hydride microstructure was determined at 25 o C. The results were obtained utilizing a novel testing procedure in which a narrow linear strip of hydride blister was fractured at small loads under bending to create a well-defined sharp pre-crack that arrested at the blister-substrate interface. The hydriding procedure also forms 'sunburst' hydrides emanating from the blister that were aligned both in the plane of the crack and in the crack growth direction. Subsequent tensile loading caused crack growth initiation into the field of 'sunburst' hydrides. Specimen failure occurred under near-linear elastic behavior, and the fracture toughness for crack growth initiation into sunburst hydrides was in the range K Q ∼10-15 MPa√m. These results, when combined with those of a previous study, indicate that the through-thickness crack growth initiation toughness at 25 o C is very sensitive to the hydride microstructure. (author)

The crack propagating behavior of composite coatings prepared by PEO on aluminized steel during in situ tensile processing

International Nuclear Information System (INIS)

Chen Zhitong; Li Guang; Wu Zhenqiang; Xia Yuan

2011-01-01

Research highlights: → Composite coatings on the aluminized steel were prepared by the plasma electrolytic oxidation (PEO) technique, which comprised of Fe-Al layer, Al layer and Al 2 O 3 layer. → The evaluation method of the crack critical opening displacement δ c was introduced to describe quantitatively the resistance of Al layer to the propagation behavior of cracks and evaluate the fracture behavior of composite coatings. → The crack propagating model was established. - Abstract: This paper investigates the in situ tensile cracks propagating behavior of composite coatings on the aluminized steel generated using the plasma electrolytic oxidation (PEO) technique. Cross-sectional micrographs and elemental compositions were investigated by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). The composite coatings were shown to consist of Fe-Al, Al and Al 2 O 3 layers. The cracks propagating behavior was observed in real-time in situ SEM tensile test. In tensile process, the cracks were temporarily stopped when cracks propagated from Fe-Al layer to Al layer. The critical crack opening displacement δ c was introduced to quantitatively describe the resistance of the Al layer. There was a functional relation among the thickness ratio t Al /t Al 2 O 3 , the δ c of composite coatings and tensile cracks' spacing. The δ c increased with the increasing of the thickness ratio (t Al /t Al 2 O 3 ). The high δ c value means high fracture resistance. Therefore, a control of the thickness ratio t Al /t Al 2 O 3 was concerned as a key to improve the toughness and strength of the aluminized steel.

Extended timescale atomistic modeling of crack tip behavior in aluminum

International Nuclear Information System (INIS)

Baker, K L; Warner, D H

2012-01-01

Traditional molecular dynamics (MD) simulations are limited not only by their spatial domain, but also by the time domain that they can examine. Considering that many of the events associated with plasticity are thermally activated, and thus rare at atomic timescales, the limited time domain of traditional MD simulations can present a significant challenge when trying to realistically model the mechanical behavior of materials. A wide variety of approaches have been developed to address the timescale challenge, each having their own strengths and weaknesses dependent upon the specific application. Here, we have simultaneously applied three distinct approaches to model crack tip behavior in aluminum at timescales well beyond those accessible to traditional MD simulation. Specifically, we combine concurrent multiscale modeling (to reduce the degrees of freedom in the system), parallel replica dynamics (to parallelize the simulations in time) and hyperdynamics (to accelerate the exploration of phase space). Overall, the simulations (1) provide new insight into atomic-scale crack tip behavior at more typical timescales and (2) illuminate the potential of common extended timescale techniques to enable atomic-scale modeling of fracture processes at typical experimental timescales. (paper)

Fatigue crack growth behavior and AE signal recognition from a composite patch repaired Ai thein plate

International Nuclear Information System (INIS)

Kim, Sung Jin; Kwon, Oh Yang

2004-01-01

The fatigue crack growth behavior of a fatigue-cracked and patch-repaired AA2024-T3 plate has been monitored. It was found that the overall crack growth rate was reduced and the crack propagation into the adjacent hole was also retarded. Signals due to crack growth after patch-repair and those due to debonding of the plate-patch interface were discriminated each other by using principal component analysis. The former showed higher center frequency and lower amplitude, whereas the latter showed longer rise time, lower frequency and higher amplitude.

Crack behavior of oxidation resistant coating layer on Zircaloy-4 for accident tolerant fuel claddings

International Nuclear Information System (INIS)

Park, Jung Hwan; Kim, Eui Jung; Jung, Yang Il; Park, Dong Jun; Kim, Hyun Gil; Park, Jeong Yong; Yang, Jae Ho

2016-01-01

Terrani et al. reported the oxidation resistance of Fe-based alloys for protecting zirconium alloys from the rapid oxidation in a high-temperature steam environment. Kim and co-workers also reported the corrosion behavior of Cr coated zirconium alloy using a plasma spray and laser beam scanning. Cracks are developed by tensile stress, and this significantly deteriorates the oxidation resistance. This tensile stress is possibly generated by the thermal cycle or bending or the irradiation growth of zirconium. In this study, Cr was deposited by AIP on to Zircaloy-4 plate, and the crack behavior of Cr coated Zircaloy-4 under uni-axial tensile strain was observed. In addition, the strain of the as-deposited state was calculated by iso-inclination method. Coating began to crack at 8% of applied strain. It is assumed that a well-densified structure by AIP tends to be resistant to cracking under tensile strain.

Crack behavior of oxidation resistant coating layer on Zircaloy-4 for accident tolerant fuel claddings

Energy Technology Data Exchange (ETDEWEB)

Park, Jung Hwan; Kim, Eui Jung; Jung, Yang Il; Park, Dong Jun; Kim, Hyun Gil; Park, Jeong Yong; Yang, Jae Ho [KAERI, Daejeon (Korea, Republic of)

2016-05-15

Terrani et al. reported the oxidation resistance of Fe-based alloys for protecting zirconium alloys from the rapid oxidation in a high-temperature steam environment. Kim and co-workers also reported the corrosion behavior of Cr coated zirconium alloy using a plasma spray and laser beam scanning. Cracks are developed by tensile stress, and this significantly deteriorates the oxidation resistance. This tensile stress is possibly generated by the thermal cycle or bending or the irradiation growth of zirconium. In this study, Cr was deposited by AIP on to Zircaloy-4 plate, and the crack behavior of Cr coated Zircaloy-4 under uni-axial tensile strain was observed. In addition, the strain of the as-deposited state was calculated by iso-inclination method. Coating began to crack at 8% of applied strain. It is assumed that a well-densified structure by AIP tends to be resistant to cracking under tensile strain.

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

Fatigue Crack Growth Behavior of Austempered AISI 4140 Steel with Dissolved Hydrogen

Directory of Open Access Journals (Sweden)

Varun Ramasagara Nagarajan

2017-11-01

Full Text Available The focus of this investigation was to examine the influence of dissolved hydrogen on the fatigue crack growth behavior of an austempered low-alloy AISI 4140 steel. The investigation also examined the influence of dissolved hydrogen on the fatigue threshold in this material. The material was tested in two conditions, as-received (cold rolled and annealed and austempered (austenitized at 882 °C for 1 h and austempered at 332 °C for 1 h. The microstructure of the annealed specimens consisted of a mix of ferrite and fine pearlite; the microstructure of the austempered specimens was lower bainite. Tensile and Compact Tension specimens were prepared. To examine the influence of dissolved hydrogen, two subsets of the CT specimens were charged with hydrogen for three different time periods between 150 and 250 h. All of the CT samples were then subjected to fatigue crack growth tests in the threshold and linear regions at room temperature. The test results indicate that austempering resulted in significant improvement in the yield and tensile strength as well as the fracture toughness of the material. The test results also show that, in the absence of dissolved hydrogen, the crack growth rate in the threshold and linear regions was lower in austempered samples compared to the as-received (annealed samples. The fatigue threshold was also slightly greater in the austempered samples. In presence of dissolved hydrogen, the crack growth rate was dependent upon the ∆K value. In the low ∆K region (<30 MPa√m, the presence of dissolved hydrogen caused the crack growth rate to be higher in the austempered samples as compared to annealed samples. Above this value, the crack growth rate was increasingly greater in the annealed specimens when compared to the austempered specimens in presence of dissolved hydrogen. It is concluded that austempering of 4140 steel appears to provide a processing route by which the strength, hardness, and fracture toughness of

An analysis method for fatigue crack initiation on geometrical singularities

International Nuclear Information System (INIS)

Amzallag, C.; Bernard, J.L.; Pellissier-Tanon, A.; Vassal, J.M.

1982-05-01

For studying the significance of defects a promising point of view is to separate fatigue crack initiation and propagation. Comparing the works done on these two stages it appears that relatively few has been done on the first one. This presentation shows how this stage can be evaluated by using appropriate criteria. The validation of a criterion through experimental data obtained on actual and simulated singularities for different specimen geometries is presented

The role of extrusions and intrusions in fatigue crack initiation

Czech Academy of Sciences Publication Activity Database

Polák, Jaroslav; Mazánová, Veronika; Heczko, Milan; Petráš, Roman; Kuběna, Ivo; Casalena, L.; Man, Jiří

2017-01-01

Roč. 185, NOV (2017), s. 46-60 ISSN 0013-7944 R&D Projects: GA MŠk(CZ) LQ1601; GA MŠk LM2015069; GA ČR(CZ) GA13-23652S; GA ČR GA15-08826S Institutional support: RVO:68081723 Keywords : Extrusion * Fatigue crack initiation * Intrusion * Persistent slip marking * Stainless steel Subject RIV: JL - Materials Fatigue, Friction Mechanics OBOR OECD: Audio engineering, reliability analysis Impact factor: 2.151, year: 2016

The effect of texture variation on delayed hydride cracking behavior of Zr-2.5%Nb plate

International Nuclear Information System (INIS)

Kim, S.-S.; Kim, Y.S.; Kuk, I.-H.

1999-01-01

In order to investigate the effect of texture variation on the delayed hydride cracking behavior in Zr-2.5%Nb plates, crack growth rate and K IH tests have been carried out at temperature ranges varying from 415 to 506 K after texture modification by rolling. The texture variation of plates was achieved by direct-rolling and cross-rolling. Texture was measured through the determination of inverse pole figures, from which the basal pole components were calculated. The results have shown that the texture of a plate in which the basal poles are concentrated in the transverse direction can be changed significantly by cross-rolling. The crack growth rate increases exponentially with the basal pole component in the direction normal to the cracking plane. The increase in stress relieving temperature on cold worked material reduces crack growth rate. K IH decreases linearly with the basal pole component, and a behavior of which could be explained by the uniformly dispersed aggregate composite theory. (orig.)

A model for crack initiation in the Li-ion battery electrodes

Energy Technology Data Exchange (ETDEWEB)

Panat, Rahul, E-mail: rahul.panat@wsu.edu

2015-12-01

The development of high energy density Lithium-ion batteries is of intense interest due to their application in the electric car and consumer electronics industry. The primary limiter in using high energy density battery electrodes is the cracking of the electrode material due to the severe strain caused by the charging–discharging cycles. In this paper, a linear perturbation model is used to describe the evolution of the electrode surface under stress. The driving force for the surface undulation formation is the reduction in the electrode strain energy. The kinetics of mass transport is described by the surface and volume diffusion. The model predicts that the Si electrode will develop surface undulations of the order of sub-1 μm length scale on the electrode surface, showing a reasonable agreement with experimental results reported in literature. Such surface undulations roughen the anode surface and can form notches that can act as crack initiation sites. It is also shown that this model is applicable when the temperature of the system is not constant and the system is not isolated. The limitations of the model are also discussed. - Highlights: • This work presents a theoretical formulation that predicts crack formation at an electrode surface under a lithiation cycle. • The research provides the critical parameters required to improve the life of the Li-ion batteries. • These research findings can be used to modify the surface structure to minimize crack formation. • The predictions from the model show a reasonable agreement with the experiments. • None of the theoretical literature so far has addressed the crack formation problem addressed in this paper.

Towards the prediction of the growth of crack networks: influence of microstructural parameters on scattering at initiation

International Nuclear Information System (INIS)

Osterstock, St.

2008-10-01

This research thesis aims at understanding the importance of microstructure in the scattering of mechanical fields and of its potential influence on fatigue crack initiation, at studying the grains in which equi-biaxial fatigue cracks are appearing, and at proposing a coalescence model based on the discrete dislocation dynamics (DDD). After an overview of fatigue, the author describes the tests developed by EDF or the CEA to study thermal fatigue. Then, he presents the equi-biaxial fatigue test which allows the first stages of initiation of thermal fatigue cracks to be studied. Maps of cracked areas are obtained by Electron Back Scattered Diffraction, and results are discussed with respect to results obtained in dislocation dynamics. Polycrystalline computations are implemented. They allow a better understanding of the importance of the material microstructure for the scattering of the surface grain mechanical fields. Finally, a coalescence model is presented, based on experimental results obtained during the equi-biaxial fatigue testing. Coalescence criteria are proposed

Crack initiation and propagation on the polymeric material ABS (Acrylonitrile Butadiene Styrene, under ultrasonic fatigue testing

Directory of Open Access Journals (Sweden)

G. M. Domínguez Almaraz

2015-10-01

Full Text Available Crack initiation and propagation have been investigated on the polymeric material ABS (Acrylonitrile Butadiene Styrene, under ultrasonic fatigue testing. Three controlled actions were implemented in order to carry out fatigue tests at very high frequency on this material of low thermal conductivity, they are: a The applying load was low to limit heat dissipation at the specimen neck section, b The dimensions of testing specimen were small (but fitting the resonance condition, in order to restraint the temperature gradient at the specimen narrow section, c Temperature at the specimen neck section was restrained by immersion in water or oil during ultrasonic fatigue testing. Experimental results are discussed on the basis of thermo-mechanical behaviour: the tail phenomenon at the initial stage of fatigue, initial shear yielding deformation, crazed development on the later stage, plastic strain on the fracture surface and the transition from low to high crack growth rate. In addition, a numerical analysis is developed to evaluate the J integral of energy dissipation and the stress intensity factor K, with the crack length

Crack initiation and propagation paths in small diameter FSW 6082-T6 aluminium tubes under fatigue loading

Directory of Open Access Journals (Sweden)

Roberto Tovo

2016-03-01

Full Text Available This paper reports results of fatigue tests of friction stir welded (FSW aluminium tubes. Relatively small 38 mm diameter tubes were used and hence an automated FSW process using a retracting tool was designed for this project, as the wall thickness of the aluminium tube was similar to the diameter of the FSW tool. This is a more complex joint geometry to weld than the more usual larger diameter tube reported in the literature. S-N fatigue testing was performed using load ratios of R = 0.1 and R = -1. Crack path analysis was performed using both low magnification stereo microscopy and scanning electron microscopy, in order to identify crack initiation sites and to determine the direction of crack propagation. Work is still in progress to follow the crack path through the various microstructural zones associated with the weld. A simple statistical analysis was used to characterize the most typical crack initiation site. This work forms part of a wider project directed at determining multiaxial fatigue design rules for small diameter 6082-T6 aluminium tubes that could be of use in the ground vehicle industry.

Probabilistic and microstructural aspects of fatigue cracks initiation in Inconel 718; Aspects probabilistes et microstructuraux de l'amorcage des fissures de fatigue dans l'alliage INCO 718

Energy Technology Data Exchange (ETDEWEB)

Alexandre, F

2004-03-15

Thermomechanical treatments have been recently developed to produce Inconel 718DA (Direct Aged). This alloy optimisation leads to an increase of the fatigue life but also the scatter. The aim of this study is on the one hand the understanding of the fatigue crack initiation mechanisms and on the other hand the modelling of the fatigue life and the scatter. An experimental study showed that the fatigue cracks were initiated from carbide particles in fine grain alloy. Interrupted tensile tests show that the particles cracking occurred at the first quarter of the fatigue cycle. Fatigue behaviour tests were also performed on various grain size 718 alloys. The last experimental part was devoted to measurements of the low cycle fatigue crack growth rates using a high focal distance microscope. For these tests, EDM micro-defects were used for the fatigue crack initiation sites. This method was also used to observe the small fatigue crack coalescence. A fatigue life model is proposed. It is based on the three fatigue crack initiation mechanisms competition: particle crack initiation on the surface, internal particle crack initiation and Stade I crack initiation. The particle fatigue crack initiation is supposed instantaneous at a critical stress level. The Tanaka and Mura model is used for analysing the Stage I crack initiation number of cycles. The fatigue crack growth rate was analysed using the Tomkins model identified on the small fatigue crack growth rate measurements. The proposed fatigue life model decomposed in three levels: a deterministic one and two probabilistic with and without crack coalescence. (author)

Analysis of Crack Propagation Path on the Anisotropic Bi-Material Rock

Directory of Open Access Journals (Sweden)

Chao-Shi Chen

2010-01-01

Full Text Available This paper presents a single-domain boundary element method (SDBEM for linear elastic fracture mechanics analysis in the 2D anisotropic bimaterial. In this formulation, the displacement integral equation is collocated on the uncracked boundary only, and the traction integral equation is collocated on one side of the crack surface only. The complete fundamental solution (Green's function for anisotropic bi-materials was also derived and implemented into the boundary integral formulation so the discretization along the interface can be avoided except for the interfacial crack part. A special crack-tip element was introduced to capture exactly the crack-tip behavior. A computer program with the FORTRAN code has been developed to effectively calculate the stress intensity factors, crack initiation angle, and propagation path of an anisotropic bi-material. This SDBEM program has been verified having a good accuracy with the previous researches. In addition, a rock of type (1/(2 disk specimen with a central crack was made to conduct the Brazilian test under diametrical loading. The result shows that the numerical analysis can predict relatively well the direction of crack initiation and the path of crack propagation.

Crack initiation and growth in welded structures; Amorcage et propagation de la fissuration dans les jonctions soudees

Energy Technology Data Exchange (ETDEWEB)

Assire, A

2000-10-13

This work concerns the remaining life assessment of a structure containing initial defects of manufacturing. High temperature crack initiation and growth are studied for austenitic stainless steels, and defect assessment methods are improved in order to take into account welded structures. For these one, the probability to have a defect is significant. Two kinds of approaches are commonly used for defect assessment analysis. Fracture mechanics global approach with an energetic criterion, and local approach with a model taking into account the physical damage mechanism. For both approaches mechanical fields (stress and strain) have to be computed everywhere within the structure. Then, Finite Element computation is needed. The first part of the thesis concerns the identification of non linear kinematic and isotropic constitutive models. A pseudo-analytical method is proposed for a 'Two Inelastic Strain' model. This method provides a strategy of identification with a mechanical meaning, and this enables to associate each parameter to a physical phenomenon. Existing identifications are improved for cyclic plasticity and creep on a large range of stress levels. The second part concerns high temperature crack initiation and growth in welded structures. Finite Element analysis on plate and tube experimental configuration enable to understand the phenomenons of interaction between base metal and weld metal under mechanical and thermal loading. Concerning global approach, criteria based on C* parameter (Rice integral for visco-plasticity) are used. Finite Element computations underline the fact that for a defect located in the weld metal, C* values strongly depend on the base metal creep strain rate, because widespread visco-plasticity is located in both metals. A simplified method, based on the reference stress approach, is proposed and validated with Finite Element results. Creep crack growth simplified assessment is a quite good validation of the experimental

Study of cyclic strain localization and fatigue crack initiation using FIB technique

Czech Academy of Sciences Publication Activity Database

Man, Jiří; Vystavěl, T.; Weidner, A.; Kuběna, Ivo; Petrenec, Martin; Kruml, Tomáš; Polák, Jaroslav

2012-01-01

Roč. 39, JUN (2012), s. 44-53 ISSN 0142-1123 R&D Projects: GA ČR GAP108/10/2371 Institutional research plan: CEZ:AV0Z20410507 Keywords : fatigue crack initiation * persistent slip band * focused ion beam (FIB) Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.976, year: 2012

On fatigue crack growth mechanisms of MMC: Reflection on analysis of 'multi surface initiations'

International Nuclear Information System (INIS)

Mkaddem, A.; El Mansori, M.

2009-01-01

This work attempts to examine the mechanisms of fatigue when cracks synergetically initiate in more than one site at the specimen surface. The metal matrix composites (MMC) i.e. silicon carbide particles reinforced aluminium matrix composites (Al/SiC p -MMC), seem to be good candidates to accelerate fatigue failures following multi surface initiations (MSI). Closure effects of MSI mechanisms on the variation of fatigue behaviour are explored for various stress states. Experiments were carried out using non pre-treated and pre-treated specimens. Using an Equivalent Ellipse Method (EEM), it is shown that the aspect of surface finish of specimen plays an important role on crack growth. Scanning Electron Microscope (SEM) inspections have lead to distinguishing the initiation regions from propagation regions and final separation regions. It is also revealed that the total lifetime of specimens is sensitive to heat treatment. Moreover, it is found that the appearance of MSI in cycled materials is more probable at high level of fatigue loads.

Averaged strain energy density-based synthesis of crack initiation life in notched steel bars under torsional fatigue

Directory of Open Access Journals (Sweden)

Filippo Berto

2016-10-01

Full Text Available The torsional fatigue behaviour of circumferentially notched specimens made of austenitic stainless steel, SUS316L, and carbon steel, SGV410, characterized by different notch root radii has been recently investigated by Tanaka. In that contribution, it was observed that the total fatigue life of the austenitic stainless steel increases with increasing stress concentration factor for a given applied nominal shear stress amplitude. By using the electrical potential drop method, Tanaka observed that the crack nucleation life was reduced with increasing stress concentration, on the other hand the crack propagation life increased. The experimental fatigue results, originally expressed in terms of nominal shear stress amplitude, have been reanalysed by means of the local strain energy density (SED averaged over a control volume having radius R0 surrounding the notch tip. To exclude all extrinsic effects acting during the fatigue crack propagation phase, such as sliding contact and/or friction between fracture surfaces, crack initiation life has been considered in the present work. In the original paper, initiation life was defined in correspondence of a 0.1÷0.4-mm-deep crack. The control radius R0 for fatigue strength assessment of notched components, thought of as a material property, has been estimated by imposing the constancy of the averaged SED for both smooth and cracked specimens at NA = 2 million loading cycles

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.

Microstructure-based approach for predicting crack initiation and early growth in metals.

Energy Technology Data Exchange (ETDEWEB)

Cox, James V.; Emery, John M.; Brewer, Luke N.; Reedy, Earl David, Jr.; Puskar, Joseph David; Bartel, Timothy James; Dingreville, Remi P. M.; Foulk, James W., III; Battaile, Corbett Chandler; Boyce, Brad Lee

2009-09-01

Fatigue cracking in metals has been and is an area of great importance to the science and technology of structural materials for quite some time. The earliest stages of fatigue crack nucleation and growth are dominated by the microstructure and yet few models are able to predict the fatigue behavior during these stages because of a lack of microstructural physics in the models. This program has developed several new simulation tools to increase the microstructural physics available for fatigue prediction. In addition, this program has extended and developed microscale experimental methods to allow the validation of new microstructural models for deformation in metals. We have applied these developments to fatigue experiments in metals where the microstructure has been intentionally varied.

Relationship Between Unusual High-Temperature Fatigue Crack Growth Threshold Behavior in Superalloys and Sudden Failure Mode Transitions

Science.gov (United States)

Telesman, J.; Smith, T. M.; Gabb, T. P.; Ring, A. J.

2017-01-01

An investigation of high temperature cyclic fatigue crack growth (FCG) threshold behavior of two advanced nickel disk alloys was conducted. The focus of the study was the unusual crossover effect in the near-threshold region of these type of alloys where conditions which produce higher crack growth rates in the Paris regime, produce higher resistance to crack growth in the near threshold regime. It was shown that this crossover effect is associated with a sudden change in the fatigue failure mode from a predominant transgranular mode in the Paris regime to fully intergranular mode in the threshold fatigue crack growth region. This type of a sudden change in the fracture mechanisms has not been previously reported and is surprising considering that intergranular failure is typically associated with faster crack growth rates and not the slow FCG rates of the near-threshold regime. By characterizing this behavior as a function of test temperature, environment and cyclic frequency, it was determined that both the crossover effect and the onset of intergranular failure are caused by environmentally driven mechanisms which have not as yet been fully identified. A plausible explanation for the observed behavior is proposed.

Experimental investigation of crack initiation in face-centered cubic materials in the high and very high cycle fatigue regime

Energy Technology Data Exchange (ETDEWEB)

Straub, Thomas

2016-07-01

Materials in many modern small-scale applications are under complex cyclic stress states and undergo up to 10{sup 9} cycles. Fatigue mechanisms limit their lifetime and lead to failure. Therefore, the Very High Cycle Fatigue (VHCF) regime needs to be studied. This thesis investigates the fatigue mechanisms and crack initiation of nickel, aluminum and copper on a small-scale in the VHCF regime by means of innovative fatigue experimentation. Firstly, the development and implementation of a novel custom-built resonant fatigue setup showed that the resonant frequency of bending micro-samples changes with increasing cycle number due to the accumulating fatigue damage. Then, additional insights on early damage formation have been explored. Mechanisms, prior to crack initiation, such as slip band formation at a state where it appears in only a few grains, have been observed. Cyclic hardening, vacancy formation and oxidation formation may be considered as possible explanations for early fatigue mechanisms. In addition, the new experimental setup can be used to define parameters needed for crack initiation models. Finally, these crack initiation processes have been experimentally examined for pure aluminum and pure copper.

An Experimental and Numerical Study on Cracking Behavior of Brittle Sandstone Containing Two Non-coplanar Fissures Under Uniaxial Compression

Science.gov (United States)

Yang, Sheng-Qi; Tian, Wen-Ling; Huang, Yan-Hua; Ranjith, P. G.; Ju, Yang

2016-04-01

To understand the fracture mechanism in all kinds of rock engineering, it is important to investigate the fracture evolution behavior of pre-fissured rock. In this research, we conducted uniaxial compression experiments to evaluate the influence of ligament angle on the strength, deformability, and fracture coalescence behavior of rectangular prismatic specimens (80 × 160 × 30 mm) of brittle sandstone containing two non-coplanar fissures. The experimental results show that the peak strength of sandstone containing two non-coplanar fissures depends on the ligament angle, but the elastic modulus is not closely related to the ligament angle. With the increase of ligament angle, the peak strength decreased at a ligament angle of 60°, before increasing up to our maximum ligament angle of 120°. Crack initiation, propagation, and coalescence were all observed and characterized from the inner and outer tips of pre-existing non-coplanar fissures using photographic monitoring. Based on the results, the sequence of crack evolution in sandstone containing two non-coplanar fissures was analyzed in detail. In order to fully understand the crack evolution mechanism of brittle sandstone, numerical simulations using PFC2D were performed for specimens containing two non-coplanar fissures under uniaxial compression. The results are in good agreement with the experimental results. By analyzing the stress field, the crack evolution mechanism in brittle sandstone containing two non-coplanar fissures under uniaxial compression is revealed. These experimental and numerical results are expected to improve the understanding of the unstable fracture mechanism of fissured rock engineering structures.

Multi-scale analysis of deformation behavior at SCC crack tip (3) (Contract research)

International Nuclear Information System (INIS)

Kaji, Yoshiyuki; Miwa, Yukio; Tsukada, Takashi; Hayakawa, Masao; Nagashima, Nobuo

2008-08-01

In recent years, incidents of the stress corrosion cracking (SCC) were frequently reported that occurred to the various components of domestic boiling water reactors (BWR), and the cause investigation and measure become the present important issue. By the Japan nuclear energy safety organization (JNES), a research project on the intergranular SCC (IGSCC) in nuclear grade stainless steels (henceforth, IGSCC project) is under enforcement from a point of view to secure safety and reliability of BWR, and SCC growth data of low carbon stainless steels are being accumulated for the weld part or the work-hardened region adjacent to the weld metal. In the project, it has been an important subject to guarantee the validity of accumulated SCC data. At a crack tip of SCC in compact tension (CT) type specimen used for the SCC propagation test, a macroscopic plastic region is formed where heterogeneity of microstructure developed by microscopic sliding and dislocations is observed. However, there is little quantitative information on the plastic region, and therefore, to assess the data of macroscopic SCC growth rate and the validity of propagation test method, it is essentially required to investigate the plastic region at the crack tip in detail from a microscopic viewpoint. This report describes a result of the research conducted by the Japan Atomic Energy Agency and the National Institute for Materials Science under contract with JNES that was concerned with a multi-scale analysis of plastic deformation behavior at the crack tip of SCC. The research was carried out to evaluate the validity of the SCC growth data acquired in the IGSCC project based on a mechanistic understanding of SCC. For the purpose, in this research, analyses of the plastic deformation behavior and microstructure around the crack tip were performed in a nano-order scale. The hardness measured in nano, meso and macro scales was employed as a common index of the strength, and the essential data necessary

Stress corrosion cracking for 316 stainless steel clips in a condensate stabilizer

Energy Technology Data Exchange (ETDEWEB)

Al-Awar, A.; Aldajah, S.; Harhara, A. [Department of Mechanical Engineering, United Arab Emirates University, P. O. Box 17555 Al-AIn 17555 (United Arab Emirates)

2011-09-15

In one of the gas processing facilities in Abu Dhabi, UAE; a case of 316L stainless steel material failure occurred in the fractionating column due to stress cracking corrosion twice in a cycle of less than 2 years. This paper studies the stress corrosion cracking behavior of the 316L stainless steel in an accelerated corrosion environment and compares it with a higher corrosion resistant nickel alloy (Inconel 625). The experimental work was designed according to ASTM G36 standard, the samples were immersed in a boiling magnesium chloride medium which provided the accelerated corrosion environment and the tested samples were shaped into U-bend specimens as they underwent both plastic and elastic stresses. The specimens were then tested to determine the time required for cracks to initiate. The results of the experimental work showed that the main mode of failure was stress corrosion cracking initiated by the proven presence of chlorides, hydrogen sulfide, and water at elevated temperatures. Inconel 625 samples placed in the controlled environment showed better corrosion resistance as it took them an average of 56 days to initiate cracks, whereas it took an average of 24 days to initiate cracks in the stainless steel 316L samples. The scanning electron microscopy (SEM) micrographs showed that the cracks in the stainless steel 316L samples were longer, wider, and deeper compared to the cracks of Inconel 625. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Characterization of cracking in Strain-Hardening Cementitious Composites using the compact tension test

DEFF Research Database (Denmark)

Pereira, Eduardo B.; Fischer, Gregor; Barros, Joaquim A. O.

The characterization of the tensile behavior of strain hardening cementitious composites (SHCC) is of significant importance to the material design. In a previous work the tensile stress-crack opening response of different types of SHCC was characterized using notched specimens tested in direct...... tension, where a single crack was obtained and mechanically characterized by performing Single Crack Tension Test (SCTT). In this study the tensile behavior of SHCC materials is characterized under eccentric tensile load using the Compact Tension Test (CTT). The long edge notch placed in the rectangular...... plate specimens and the eccentrically applied tensile load create the local conditions necessary to the initiation of a single crack at the tip of the notch. Further propagation and opening of the crack in Mode I allow the assessment of the tensile load-displacement relationship. The experimental...

Corrosion fatigue cracking behavior of Inconel 690 (TT) in secondary water of pressurized water reactors

International Nuclear Information System (INIS)

Xiao Jun; Chen Luyao; Qiu Shaoyu; Chen Yong; Lin Zhenxia; Fu Zhenghong

2015-01-01

Inconel 690 (TT) is one of the key materials for tubes of steam generators for pressurized water reactors, where it is susceptible to corrosion fatigue cracking. In this paper, the corrosion fatigue cracking behavior of Inconel 690 (TT) was investigated under small scale yielding conditions, in the simulated secondary water of pressurized water reactor. It was observed that the fatigue crack growth rate was accelerated by a maximum factor up to 3 in the simulated secondary water, comparing to that in room temperature air. In addition, it was found that the accelerating effect was influenced by out-of-plane cracking of corrosion fatigue cracks and also correlated with stress intensity factor range, maximum stress intensity factor and stress ratio. (authors)

Short fatigue cracks growth and closure behavior in an austenitic stainless steel at 600 C and 650 C

International Nuclear Information System (INIS)

Polvora, J.P.; Laiarinandrasana, L.; Drubay, B.; Piques, R.; Martelet, B.

1995-01-01

In this work, following fatigue crack growth tests carried out at the CEN-SACLAY (AMORFIS program) by Laiarinandrasana (1994) on 316 L(N) CT specimens at 650 0 C and 600 0 C, short crack behavior of cracks emanating from machined notches is investigated. Experimental results are presented and discussions are directed to notch plasticity effect in relation with variations in crack opening stress intensity factor, K op , with crack lenght (author). 12 refs., 5 figs., 2 tab

Effect of heat-treatment on elevated temperature fatigue-crack growth behavior of two heats of Alloy 718

International Nuclear Information System (INIS)

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

1978-05-01

The room temperature and elevated temperature fatigue-crack growth behavior of two heats of Alloy 718 was characterized within a linear-elastic fracture mechanics framework. Two different heat-treatments were used: the ''conventional'' (ASTM A637) treatment, and a ''modified'' heat-treatment designed to improve the toughness of Alloy 718 base metal and weldments. Heat-to-heat variations in the fatigue-crack propagation behavior were observed in the conventionally-treated material. On the other hand, no heat-to-heat variations were observed in the modified condition. Furthermore, both heats of Alloy 718 exhibited superior fatigue-crack growth resistance when given the modified heat-treatment. Electron fractographic examination of Alloy 718 fatigue fracture surfaces revealed that the operative crack growth mechanisms were dependent on heat-treatment, temperature, and ΔK level

Stress and strain field singularities, micro-cracks, and their role in failure initiation at the composite laminate free-edge

Science.gov (United States)

Dustin, Joshua S.

A state-of-the-art multi-scale analysis was performed to predict failure initiation at the free-edge of an angle-ply laminate using the Strain Invariant Failure Theory (SIFT), and multiple improvements to this analysis methodology were proposed and implemented. Application of this analysis and theory led to the conclusion that point-wise failure criteria which ignore the singular stress and strain fields from a homogenized analysis and the presence of free-edge damage in the form of micro-cracking, may do so at the expense of failure prediction capability. The main contributions of this work then are made in the study of the laminate free-edge singularity and in the effects of micro-cracking at the composite laminate free-edge. Study of both classical elasticity and finite element solutions of the laminate free-edge stress field based upon the assumption of homogenized lamina properties reveal that the order of the free-edge singularity is sufficiently small such that the domain of dominance of this term away from the laminate free-edge is much smaller than the relevant dimensions of the microstructure. In comparison to a crack-tip field, these free-edge singularities generate stress and strain fields which are half as intense as those at the crack-tip, leading to the conclusion that existing flaws at the free-edge in the form of micro-cracks would be more prone to the initiation of free-edge failure than the existence of a singularity in the free-edge elasticity solutions. A methodical experiment was performed on a family of [±25°/90°] s laminates made of IM7/8552 carbon/epoxy composite, to both characterize micro-cracks present at the laminate free-edge and to study their behavior under the application of a uniform extensional load. The majority of these micro-cracks were of length on the order of a few fiber diameters, though larger micro-cracks as long as 100 fiber diameters were observed in thicker laminates. A strong correlation between the application of

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.

In situ observations of crack arrest and bridging by nanoscale twins in copper thin films

International Nuclear Information System (INIS)

Kim, Seong-Woong; Li Xiaoyan; Gao Huajian; Kumar, Sharvan

2012-01-01

In situ tensile experiments in a transmission electron microscope revealed that micro-cracks in ultrafine grained, free-standing, thin copper foils containing nanoscale twins initiated in matrix domains separated by the twins and then arrested at twin boundaries as twin boundary sliding proceeded. The adjacent microcracks eventually coalesced through shear failure of the bridging twins. To investigate the atomic mechanism of this rarely seen nanoscale crack bridging behavior, molecular dynamics simulations were performed to show that during crack propagation twin boundaries are impinged upon by numerous dislocations from the plastically deforming matrix. These dislocations react at the interface and evolve into substantially impenetrable dislocation walls that strongly confine crack nucleation and resist crack propagation, leading to the experimentally observed crack bridging behavior. The present results raise an approach to significantly toughening polycrystalline thin films by incorporating nanoscale twin structures into individual grains that serve as crack bridging ligaments.

Short fatigue cracks growth and closure behavior in an austenitic stainless steel at 600 C and 650 C

Energy Technology Data Exchange (ETDEWEB)

Polvora, J.P.; Laiarinandrasana, L.; Drubay, B.; Piques, R.; Martelet, B. [Instituto de Pesquisas Energeticas e Nucleares (IPEN), Sao Paulo, SP (Brazil)

1995-12-31

In this work, following fatigue crack growth tests carried out at the CEN-SACLAY (AMORFIS program) by Laiarinandrasana (1994) on 316 L(N) CT specimens at 650{sup 0}C and 600{sup 0}C, short crack behavior of cracks emanating from machined notches is investigated. Experimental results are presented and discussions are directed to notch plasticity effect in relation with variations in crack opening stress intensity factor, K{sub op}, with crack lenght (author). 12 refs., 5 figs., 2 tab.

Investigating the process of white etching crack initiation in bearing steel

Energy Technology Data Exchange (ETDEWEB)

Gould, Benjamin; Greco, Aaron

2016-04-01

White etching cracks (WECs) have been identified as a dominant mode of premature failure within wind turbine gearbox bearings. Though WECs have been reported in the field for over a decade, the conditions leading to WECs, and the process by which this failure culminates, are both highly debated. In previously published work, the generation of WECs on a benchtop scale was linked to sliding at the surface of the test sample, it was also postulated that the generation of WECs was dependent on the cumulative energy that had been applied to the sample over the entirety of the test. In this paper, a three ring on roller bench top test rig is used to systematically alter the cumulative energy that a sample experiences through changes in normal load, sliding, and run time, in an attempt to correlate cumulative energy with the formation of WECs. It was determined that, in the current test setup, the presence of WECs can be predicted by this energy criterion. The authors then used this information to study the process by which WECs initiate. Lastly, it was found that, under the current testing conditions, the formation of a dark etching microstructure precedes the formation of a crack, and a crack precedes the formation of white etching microstructure.

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

The Crack Initiation and Propagation in threshold regime and S-N curves of High Strength Spring Steels

International Nuclear Information System (INIS)

Gubeljak, N; Predan, J; Senčič, B; Chapetti, M D

2016-01-01

An integrated fracture mechanics approach is proposed to account for the estimation of the fatigue resistance of component. Applications, estimations and results showed very good agreements with experimental results. The model is simple to apply, accounts for the main geometrical, mechanical and material parameters that define the fatigue resistance, and allows accurate predictions. It offers a change in design philosophy: It could be used for design, while simultaneously dealing with crack propagation thresholds. Furthermore, it allows quantification of the material defect sensitivity. In the case of the set of fatigue tests carried out by rotational bending of specimens without residual stresses, the estimated results showed good agreement and that an initial crack length of 0.5 mm can conservatively explain experimental data. In the case of fatigue tests carried out on the springs at their final condition with bending at R = 0.1 our data shows the influence of compressive residual stresses on fatigue strength. Results also showed that the procedures allow us to analyze the different combinations of initial crack length and residual stress levels, and how much the fatigue resistance can change by changing that configuration. For this set of tests, the fatigue resistance estimated for an initial crack length equal to 0.35 mm, can explain all testing data observed for the springs. (paper)

Near-surface modifications for improved crack tolerant behavior of high strength alloys: trends and prospects

International Nuclear Information System (INIS)

Hettche, L.R.; Rath, B.B.

1982-01-01

The purpose of this chapter is to examine the potential of surface modifications in improving the crack tolerant behavior of high strength alloys. Provides a critique of two of the most promising and versatile techniques: ion implantation and laser beam surface processing. Discusses crack tolerant properties; engineering characterization; publication trends and Department of Defense interests; and emergent surface modification techniques. Finds that the efficiency with which high strength alloys can be incorporated into a structure or component is dependent on the following crack tolerant properties: fracture toughness, fatigue resistance, sustained loading cracking resistance, fretting fatigue resistance, and hydrogen embrittlement resistance. Concludes that ion implantation and laser surface processing coupled with other advanced metallurgical procedures and fracture mechanic analyses provide the means to optimize both the bulk and surface controlled crack tolerant properties

Initiation and propagation of fatigue cracks in cast IN713LC superalloy

Czech Academy of Sciences Publication Activity Database

Kunz, Ludvík; Lukáš, Petr; Konečná, R.

2010-01-01

Roč. 77, č. 11 (2010), s. 2008-2015 ISSN 0013-7944 R&D Projects: GA MPO FT-TA4/023; GA AV ČR 1QS200410502 Institutional research plan: CEZ:AV0Z20410507 Keywords : IN 713LC * high temperature fatigue * crystallographic fatigue crack initiation * mean stress effect Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.571, year: 2010

Effect of main inclusions on crack initiation in bearing steel in the very high cycle fatigue regime

Science.gov (United States)

Gu, Chao; Bao, Yan-ping; Gan, Peng; Wang, Min; He, Jin-shan

2018-06-01

This work aims to investigate the effect of main inclusions on crack initiation in bearing steel in the very high cycle fatigue (VHCF) regime. The size and type of inclusions in the steel were quantitatively analyzed, and VHCF tests were performed. Some fatigue cracks were found to be initiated in the gaps between inclusions (Al2O3, MgO-Al2O3) and the matrix, while other cracks originated from the interior of inclusions (TiN, MnS). To explain the related mechanism, the tessellated stresses between inclusions and the matrix were calculated and compared with the yield stress of the matrix. Results revealed that the inclusions could be classified into two types under VHCF; of these two, only one type could be regarded as holes. Findings in this research provide a better understanding of how inclusions affect the high cycle fatigue properties of bearing steel.

Fatigue crack growth behavior in equine cortical bone

Science.gov (United States)

Shelton, Debbie Renee

2001-07-01

Objectives for this research were to experimentally determine crack growth rates, da/dN, as a function of alternating stress intensity factor, DeltaK, for specimens from lateral and dorsal regions of equine third metacarpal cortical bone tissue, and to determine if the results were described by the Paris law. In one set of experiments, specimens were oriented for crack propagation in the circumferential direction with the crack plane transverse to the long axis of the bone. In the second set of experiments, specimens were oriented for radial crack growth with the crack plane parallel to the long axis of the bone. Results of fatigue tests from the latter specimens were used to evaluate the hypothesis that crack growth rates differ regionally. The final experiments were designed to determine if crack resistance was dependent on region, proportion of hooped osteons (those with circumferentially oriented collagen fibers in the outer lamellae) or number of osteons penetrated by the crack, and to address the hypothesis that hooped osteons resist invasion by cracks better than other osteonal types. The transverse crack growth data for dorsal specimens were described by the Paris law with an exponent of 10.4 and suggested a threshold stress intensity factor, DeltaKth, of 2.0 MPa·m1/2 and fracture toughness of 4.38 MPa·m 1/2. Similar results were not obtained for lateral specimens because the crack always deviated from the intended path and ran parallel to the loading direction. Crack growth for the dorsal and lateral specimens in the radial orientation was described by the Paris law with exponents of 8.7 and 10.2, respectively, and there were no regional differences in the apparent DeltaK th (0.5 MPa·m1/2) or fracture toughness (1.2 MPa·m 1/2). Crack resistance was not associated with cortical region, proportion of hooped osteons or the number of osteons penetrated by the crack. The extent to which cracks penetrate osteons was influenced by whether the collagen fiber

Stress Corrosion Cracking Behavior of LD10 Aluminum Alloy in UDMH and N2O4 propellant

Science.gov (United States)

Zhang, Youhong; Chang, Xinlong; Liu, Wanlei

2018-03-01

The LD10 aluminum alloy double cantilever beam specimens were corroded under the conditions of Unsymmetric Uimethyl Hydrazine (UDMH), Dinitrogen Tetroxide (N2O4), and 3.5% NaCl environment. The crack propagation behavior of the aluminum alloy in different corrosion environment was analyzed. The stress corrosion cracking behavior of aluminum alloy in N2O4 is relatively slight and there are not evident stress corrosion phenomenons founded in UDMH.

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.

Fatigue Crack Behavior of Stainless Steel 304 by the Addition of Carbon Nanotubes

Directory of Open Access Journals (Sweden)

Rizwanulhaque Syed

2014-01-01

Full Text Available Fatigue is the main source of almost half of whole mechanical failures. This research investigated the effect on cyclic fatigue behavior of stainless steel 304 (SS304 when including carbon nanotubes (CNTs at the crack tip. The cyclic fatigue tests were conducted on compact tension (CT specimens to establish the relationship between crack growth and the number of cycles (a-N. It is found that the incorporation of a small amount of CNTs increased the fatigue life of the SS304/metal. Micrographs showed that the enhancement in fatigue life is caused by CNTs dense arrangement around the crack tip, entangled with each other, and finer grain size. Smooth bonding at the interface of the CNTs and SS304 grains is also observed.

Evaluation of Fatigue Crack Initiation for Volumetric Flaw in Pressure Tube

International Nuclear Information System (INIS)

Choi, Sung Nam; Yoo, Hyun Joo

2005-01-01

CAN/CSA.N285.4-94 requires the periodic inservice inspection and surveillance of pressure tubes in operating CANDU nuclear power reactors. If the inspection results reveal a flaw exceeding the acceptance criteria of the Code, the flaw must be evaluated to determine if the pressure is acceptable for continued service. Currently, the flaw evaluation methodology and acceptance criteria specified in CSA-N285.05-2005, 'Technical requirements for in-service evaluation of zirconium alloy pressure tubes in CANDU reactors'. The Code is applicable to zirconium alloy pressure tubes. The evaluation methodology for a crack-like flaw is similar to that of ASME B and PV Sec. XI, 'Inservice Inspection of Nuclear Power Plant Components'. However, the evaluation methodology for a blunt volumetric flaw is described in CSA-N285.05-2005 code. The object of this paper is to address the fatigue crack initiation evaluation for the blunt volumetric flaw as it applies to the pressure tube at Wolsong NPP

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

An evaluation on the effect of reversed plastic zone on the fatigue crack opening behavior under 2-D plane stress

International Nuclear Information System (INIS)

Choi, Hyeon Chang

2005-01-01

The relationship between fatigue crack opening behavior and the reversed plastic zone sizes is studied. An elastic-plastic Finite Element Analysis (FEA) is performed to examine the opening behavior of fatigue crack, where the contact elements are used in the mesh of the crack tip area. The smaller element size than reversed plastic zone size is used for evaluating the distribution of reversed plastic zone. In the author's previous results the FEA could predict the crack opening level, which crack tip elements were in proportion to the theoretical reversed plastic zone size. It is found that the calculated reversed plastic zone size is related to the theoretical reversed plastic zone size and crack opening level. The calculated reversed plastic zone sizes are almost equal to the reversed plastic zone considering crack opening level obtained by experimental results. It can be possible to predict the crack opening level from the reversed plastic zone size calculated by finite element method. We find that the experimental crack opening levels correspond with the opening values of contact nodes on the calculated reversed plastic zone of finite element simulation

Growth behavior of fatigue cracks in ultrafine grained Cu smooth specimens with a small hole

Directory of Open Access Journals (Sweden)

Masahiro Goto

2015-10-01

Full Text Available In order to study the growth mechanism of fatigue cracks in ultrafine grained copper, stresscontrolled fatigue tests of round-bar specimens with a small blind hole as a crack starter were conducted. The hole was drilled on the surface where an intersection between the shear plane of the final ECAP processing and the specimen surface makes an angle of 45° or 90° with respect to the loading axis. At a low stress (  a = 90 MPa, the direction of crack paths was nearly perpendicular to the loading direction regardless of the location of the hole. Profile of crack face was examined, showing the aspect ratio (b/a of b/a = 0.82. At a high stress (  a = 240 MPa, although the growth directions inclined 45° and 90° to the loading-axis were observed depending on the location of the drilling hole, crack faces in these cracks were extended along one set of maximum shear stress planes, corresponding to the final ECAP shear plane. The value of aspect ratios was b/a = 0.38 and 1.10 for the cracks with 45° and 90° inclined path directions, respectively. The role of deformation mode at the crack tip areas on crack growth behavior were discussed in terms of the mixed-mode stress intensity factor. The crack path formation at high stress amplitudes was affected by the in-plane shear-mode deformation at the crack tip.

Subcritical crack growth behavior of AI2O3-Glass dental composites

NARCIS (Netherlands)

Zhu, Q.; With, G. de; Dortmans, L.J.M.G.; Feenstra, F.

2003-01-01

The purpose of this study is to investigate the subcritical crack growth (SCG) behavior of alumina-glass dental composites. Alumina-glass composites were fabricated by infiltrating molten glass to porous alumina preforms. Rectangular bars of the composite were subject to dynamic loading in air, with

Unstable propagation behavior of a ductile crack in SUS-304 stainless steel under high compliance tensile loading

International Nuclear Information System (INIS)

Tomoda, Yoshio

1981-01-01

In relation to the safe maintenance of nuclear power plants, it is necessary to prevent reactor coolant pipings from burst type failure caused by the unstable propagation of defects and cracks, such as stress corrosion cracking and fatigue cracks. In ductile materials, crack propagation is stable in tensile loading under fixed grip condition, when a specimen is controlled to deform in proportion to the increase of tensile load. However, it has been known that the instability of ductile cracks occurs after tensile load reached the maximum, especially under constant loading condition arising in the loading devices with high compliance or low tensile rigidity. In order to confirm the reliability of SUS 304 stainless pipes subjected to SCC, the crack propagation behavior was examined with the specimens having center cracks, using both testing machines with high compliance and low compliance. The instability of ductile cracks and the propagation velocity of unstable cracks were analyzed, and the calculated results were compated with the experimental results. Not only the compliance of testing machines but also the conditions of specimens affected the propagation of cracks. (Kako, I.)

Exceptional cracking behavior in H-implanted Si/B-doped Si0.70Ge0.30/Si heterostructures

Science.gov (United States)

Chen, Da; Wang, Dadi; Chang, Yongwei; Li, Ya; Ding, Rui; Li, Jiurong; Chen, Xiao; Wang, Gang; Guo, Qinglei

2018-01-01

The cracking behavior in H-implanted Si/B-doped Si0.70Ge0.30/Si structures after thermal annealing was investigated. The crack formation position is found to closely correlate with the thickness of the buried Si0.70Ge0.30 layer. For H-implanted Si containing a buried 3-nm-thick B-doped Si0.70Ge0.30 layer, localized continuous cracking occurs at the interfaces on both sides of the Si0.70Ge0.30 interlayer. Once the thickness of the buried Si0.70Ge0.30 layer increases to 15 and 70 nm, however, a continuous sharp crack is individually observed along the interface between the Si substrate and the B-doped Si0.70Ge0.30 interlayer. We attribute this exceptional cracking behavior to the existence of shear stress on both sides of the buried Si0.70Ge0.30 layer and the subsequent trapping of hydrogen, which leads to a crack in a well-controlled manner. This work may pave the way for high-quality Si or SiGe membrane transfer in a feasible manner, thus expediting its potential applications to ultrathin silicon-on-insulator (SOI) or silicon-germanium-on-insulator (SGOI) production.

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

Creep Behavior and Durability of Cracked CMC

Science.gov (United States)

Bhatt, R. T.; Fox, Dennis; Smith, Craig

2015-01-01

To understand failure mechanisms and durability of cracked Ceramic matrix composites (CMCs), Melt Infiltration (MI) SiCSiC composites with Sylramic-iBN fibers and full Chemical vapour infiltration SiCSiC composites with Sylramic-ion bombarded BN (iBN) and Hi-Nicalon -S fibers were pre-cracked between 150 to 200 megapascal and then creep and Sustained Peak Low Cycle Fatigue (SPLCF) tested at 13150 C at stress levels from 35 to 103 megapascal for up to 200 hours under furnace and burner rig conditions. In addition creep testing was also conducted on pre-cracked full Chemical vapour infiltration SiCSiC composites at 14500 C between 35 and 103 megapascal for up to 200 hours under furnace conditions. If the specimens survived the 200 hour durability tests, then they were tensile tested at room temperature to determine their residual tensile properties. The failed specimens were examined by Scanning electron microscope (SEM) to determine the failure modes and mechanisms. The influence of crack healing matrix, fiber types, crack density, testing modes and interface oxidation on durability of cracked Ceramic matrix composites (CMCs) will be discussed.

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.

The shape of extrusions and intrusions and initiation of stage I fatigue cracks

Czech Academy of Sciences Publication Activity Database

Polák, Jaroslav; Man, Jiří; Vystavěl, T.; Petrenec, Martin

2009-01-01

Roč. 517, 1-2 (2009), s. 204-211 ISSN 0921-5093 R&D Projects: GA ČR GA106/06/1096; GA ČR GA101/07/1500 Institutional research plan: CEZ:AV0Z20410507 Keywords : Extrusion * Intrusion * Fatigue crack initiation * Stainless steel Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.901, year: 2009

Probabilistic modeling of crack networks in thermal fatigue

International Nuclear Information System (INIS)

Malesys, N.

2007-11-01

Thermal superficial crack networks have been detected in mixing zone of cooling system in nuclear power plants. Numerous experimental works have already been led to characterize initiation and propagation of these cracks. The random aspect of initiation led to propose a probabilistic model for the formation and propagation of crack networks in thermal fatigue. In a first part, uniaxial mechanical test were performed on smooth and slightly notched specimens in order to characterize the initiation of multiple cracks, their arrest due to obscuration and the coalescence phenomenon by recovery of amplification stress zones. In a second time, the probabilistic model was established under two assumptions: the continuous cracks initiation on surface, described by a Poisson point process law with threshold, and the shielding phenomenon which prohibits the initiation or the propagation of a crack if this one is in the relaxation stress zone of another existing crack. The crack propagation is assumed to follow a Paris' law based on the computation of stress intensity factors at the top and the bottom of crack. The evolution of multiaxial cracks on the surface can be followed thanks to three quantities: the shielding probability, comparable to a damage variable of the structure, the initiated crack density, representing the total number of cracks per unit surface which can be compared to experimental observations, and the propagating crack density, representing the number per unit surface of active cracks in the network. The crack sizes distribution is also computed by the model allowing an easier comparison with experimental results. (author)

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.

Effect of Residual Strain on PWSCC Initiation of Alloy 690 in Primary Water of PWR

International Nuclear Information System (INIS)

Lee, Eun-Hee; Kim, Sung-Woo; Eom, Ki-Hyeon; Hwang, Seong-Sik

2016-01-01

The object of this study is to attempt to correlate the susceptibility to crack initiation of Alloy 690 with the levels of cold work in simulated primary water. Experiments were conducted in high-temperature water to accelerate the cracking behavior and to determine the severity of crack initiation as a function of level of cold work for Alloy 690. Cracking susceptibility was determined by measuring the crack length per unit area and crack density. SCC initiation susceptibility of Alloy 690 increased with increase of the residual strain induced by the prior cold-rolling process. The 20% cold-rolled specimen exhibited mostly IG cracks, while the 30% and 40% cold-rolled specimens revealed significant amounts of IG and TG cracks. Most cracks were observed near the smallest cross-section area of the tapered specimen, where the maximum stress was applied, indicating that the SCC initiation susceptibility was strongly dependent on the applied stress. In order to find the correlation between SCC initiation susceptibility and residual strain induced by cold work, more analyses need to be performed in terms of the crack length per unit area and the crack density, as a strong indicative for SCC initiation susceptibility

Damage Mechanisms and Controlled Crack Propagation in a Hot Pressed Silicon Nitride Ceramic. Ph.D. Thesis - Northwestern Univ., 1993

Science.gov (United States)

Calomino, Anthony Martin

1994-01-01

The subcritical growth of cracks from pre-existing flaws in ceramics can severely affect the structural reliability of a material. The ability to directly observe subcritical crack growth and rigorously analyze its influence on fracture behavior is important for an accurate assessment of material performance. A Mode I fracture specimen and loading method has been developed which permits the observation of stable, subcritical crack extension in monolithic and toughened ceramics. The test specimen and procedure has demonstrated its ability to generate and stably propagate sharp, through-thickness cracks in brittle high modulus materials. Crack growth for an aluminum oxide ceramic was observed to be continuously stable throughout testing. Conversely, the fracture behavior of a silicon nitride ceramic exhibited crack growth as a series of subcritical extensions which are interrupted by dynamic propagation. Dynamic initiation and arrest fracture resistance measurements for the silicon nitride averaged 67 and 48 J/sq m, respectively. The dynamic initiation event was observed to be sudden and explosive. Increments of subcritical crack growth contributed to a 40 percent increase in fracture resistance before dynamic initiation. Subcritical crack growth visibly marked the fracture surface with an increase in surface roughness. Increments of subcritical crack growth loosen ceramic material near the fracture surface and the fracture debris is easily removed by a replication technique. Fracture debris is viewed as evidence that both crack bridging and subsurface microcracking may be some of the mechanisms contributing to the increase in fracture resistance. A Statistical Fracture Mechanics model specifically developed to address subcritical crack growth and fracture reliability is used together with a damaged zone of material at the crack tip to model experimental results. A Monte Carlo simulation of the actual experiments was used to establish a set of modeling input

40 CFR Table 12 to Subpart Uuu of... - Initial Compliance With Organic HAP Emission Limits for Catalytic Cracking Units

Science.gov (United States)

2010-07-01

... 40 Protection of Environment 12 2010-07-01 2010-07-01 true Initial Compliance With Organic HAP Emission Limits for Catalytic Cracking Units 12 Table 12 to Subpart UUU of Part 63 Protection of... HAP Emission Limits for Catalytic Cracking Units As stated in § 63.1565(b)(4), you shall meet each...

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.

Experimental investigations of the influence of thickness and mixed-mode loading on the crack initial angle in LC4-CS aluminum

Science.gov (United States)

Dong, Huiru; Guo, Wanlin; Yu, Liang

2002-05-01

The influence of thickness and mixed mode I/II loading on the crack initial angle of aluminum LC4-CS plates of 2, 4, 8 and 14 mm thickness was investigated experimentally from tensile-tearing testing of the compact-tension-shear type specimens. Experimental results of the crack initial angle for various thickness plates and load mode mixity were presented, and compared with theoretical predictions form the maximum tangential stress criterion and the maximum triaxial stress criterion. The crack initial angle is found to vary not only with load mode mixity but also with specimen thickness. The experimental result show a god agreement with theoretical predictions in 2, 14 mm- thickness specimens but a great deal difference in 8 mm-thickness specimens. The results are discussed in the viewpoint of 3D failure theory.

Fatigue crack growth behaviour of semi-elliptical surface cracks for an API 5L X65 gas pipeline under tension

Science.gov (United States)

Shaari, M. S.; Akramin, M. R. M.; Ariffin, A. K.; Abdullah, S.; Kikuchi, M.

2018-02-01

The paper is presenting the fatigue crack growth (FCG) behavior of semi-elliptical surface cracks for API X65 gas pipeline using S-version FEM. A method known as global-local overlay technique was used in this study to predict the fatigue behavior that involve of two separate meshes each specifically for global (geometry) and local (crack). The pre-post program was used to model the global geometry (coarser mesh) known as FAST including the material and boundary conditions. Hence, the local crack (finer mesh) will be defined the exact location and the mesh control accordingly. The local mesh was overlaid along with the global before the numerical computation taken place to solve the engineering problem. The stress intensity factors were computed using the virtual crack closure-integral method (VCCM). The most important results is the behavior of the fatigue crack growth, which contains the crack depth (a), crack length (c) and stress intensity factors (SIF). The correlation between the fatigue crack growth and the SIF shows a good growth for the crack depth (a) and dissimilar for the crack length (c) where stunned behavior was resulted. The S-version FEM will benefiting the user due to the overlay technique where it will shorten the computation process.

Transient thermal-mechanical behavior of cracked glass-cloth-reinforced epoxy laminates at low temperatures

International Nuclear Information System (INIS)

Shindo, Y.; Ueda, S.

1997-01-01

We consider the transient thermal-mechanical response of cracked G-10CR glass-cloth-reinforced epoxy laminates with temperature-dependent properties. The glass-cloth-reinforced epoxy laminates are suddenly cooled on the surfaces. A generalized plane strain finite element model is used to study the influence of warp angle and crack formation on the thermal shock behavior of two-layer woven laminates at low temperatures. Numerical calculations are carried out, and the transient temperature distribution and the thermal-mechanical stresses are shown graphically

A case study of environmental assisted cracking in a low alloy steel under simulated environment of pressurized water reactor

International Nuclear Information System (INIS)

Shahzad, M.; Qureshi, A.H.; Waqas, H.; Hussain, N.

2011-01-01

Highlights: → We study environmental assisted cracking (EAC) in simulated PWR environment. → The corrosion rate in simulated coolant is low but increases with B conc. → A516 steel shows EAC in simulated coolant particularly at high oxygen levels. → Fracture occurs when the surface cracks join the subsurface cracks. → Corrosion of MnS inclusions and ferrite provide crack nucleation sites. -- Abstract: The electromechanical behavior of a pressure vessel grade steel A516 has been investigated using potentiodynamic polarization curves and slow strain rate test (SSRT) in simulated environment of pressurized water reactor. The anodic polarization behavior shows that the steel remains active in the solution till localized attack (pitting) starts. The cracks initiated at the surface propagate in a trans-granular mode. These cracks are initiated at the inclusion (MnS) sites and at the interfaces between local anode (ferrite) and local cathode (pearlite). It seems that the ultimate fracture occurs when the propagating surface cracks join the subsurface hydrogen induced cracks. The addition of oxygen in the testing chamber to supersaturation levels shifts the corrosion potential to anodic side and significantly lowers the strength and ductility. Compared to the room temperature properties, the UTS and tensile elongation in various simulated conditions are reduced by 10-25% and 25-75%, respectively.

Identification of Flaws Responsible for Crack Initiation and Micromechanisms of Slow Crack Growth in the Delayed Fracture of Alumina.

Science.gov (United States)

1982-02-01

A-"AIS012 CALIFORNIA UNdIV LOS ANSELES DEPT OF MATERIALS SCIEN--ETC F/S 11/6 IDENTIFICATION OF FLAWS RESPONSIBLE FOR CRACK INITIATION AM %I--ETC(U...Sines and Adams . 71 It might be thought that other compressive loading devices could serve the same purpoee. For example, a spherical joint instead of the...compressive strength can be 18 times the tensile strength as reported by Adams . 92 This is because the established criteria are damage criter- ia, not

Cracking and load-deformation behavior of fiber reinforced concrete: Influence of testing method

DEFF Research Database (Denmark)

Paegle, Ieva; Minelli, Fausto; Fischer, Gregor

2016-01-01

cementitious composites with strain hardening and strain softening behavior. Digital Image Correlation was utilized in the experimental program to detect and quantify the formation of cracks. Results show that the different test methodologies valuate specific aspects of material performance. The outcome...

Numerical evaluation of cracked pipes under dynamic loading

International Nuclear Information System (INIS)

Petit, M.; Jamet, P.

1989-01-01

In order to apply the leak-before-break concept to piping systems, the behavior of cracked pipes under dynamic, and especially seismic, loadings must be studied. A simple finite element model of a cracked pipe has been developed and implemented in the general purpose computer code CASTEM 2000. The model is a generalization of the approach proposed by Paris and Tada (1). Considered loads are bending moment and axial force (representing thermal expansion and internal pressure.) The elastic characteristics of the model are determined using the Zahoor formulae for the geometry-dependent factors. Owing to the material behabior plasticity must be taken into account. To represent the crack growth, the material is defined by two characteristic values: J 1c which is the level of energy corresponding to crack initiation and the tearing modulus, T, which governs the length of propagation of the crack. For dynamic loads, unilateral conditions are imposed to represent crack closure. The model has been used for the design of dynamic tests to be conducted on shaking tables. Test principle is briefly described and numerical results are presented. Finally evaluation of margin, due to plasticity, in comparison with the standard design procedure is made

Evaluation of micro fatigue crack growth under equi-biaxial stress by membranous pressure fatigue test

International Nuclear Information System (INIS)

Iida, Satoshi; Abe, Shigeki; Nakamura, Takao; Kamaya, Masayuki

2014-01-01

For preventing nuclear power plant (NPP) accidents, NPPs are required to ensure system safety in long term safe operation under aging degradation. Now, fatigue accumulation is one of major ageing phenomena and are evaluated to ensure safety by design fatigue curve that are based on the results of uniaxial fatigue tests. On the other hand, thermal stress that occurs in piping of actual components is not uniaxial but equi-biaxial. For accurate evaluation, it is required to conform real circumstance. In this study, membranous pressure fatigue test was conducted to simulated equi-biaxial stress. Crack initiation and crack growth were examined by replica investigation. Calculation result of equivalent stress intensity factor shows crack growth under equi-biaxial stress is faster than under uniaxial stress. It is concluded that equi-biaxial fatigue behavior should be considered in the evaluation of fatigue crack initiation and crack growth. (author)

Fatigue crack growth behavior of a new single crystal nickel-based superalloy (CMSX-4) at 650 C

International Nuclear Information System (INIS)

Sengupta, A.; Putatunda, S.K.

1994-01-01

CMSX-4 is a recently developed rhenium containing single crystal nickel-based superalloy. This alloy has potential applications in many critical high-temperature applications such as turbine blades, rotors, nuclear reactors, etc. The fatigue crack growth rate and the fatigue threshold data of this material is extremely important for accurate life prediction, as well as failure safe design, at elevated temperatures. In this paper, the fatigue crack growth behavior of CMSX-4 has been studied at 650 C. The investigation also examined the influence of γ' precipitates (size and distribution) on the near-threshold fatigue crack growth rate and the fatigue threshold. The influence of load ratio on the fatigue crack growth rate and the fatigue threshold was also examined. Detailed fractographic studies were carried out to determine the crack growth mechanism in fatigue in the threshold region. Compact tension specimens were prepared from the single crystal nickel-based superalloy CMSX-4 with [001] orientation as the tensile loading axis direction. These specimens were given three different heat treatments to produce three different γ' precipitate sizes and distributions. Fatigue crack growth behavior of these specimens was studied at 650 C in air. The results of the present investigation indicate that the near-threshold fatigue crack growth rate decreases and that the fatigue threshold increases with an increase in the γ' precipitate size at 650 C. The fatigue threshold decreased linearly with an increase in load ratio. Fractographs at 650 C show a stage 2 type of crack growth along {100} type of crystal planes in the threshold region, and along {111} type of crystal planes in the high ΔK region

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.

Modeling of crack in concrete structures subjected to severe loadings

International Nuclear Information System (INIS)

Nguyen, T.G.

2012-01-01

Concrete is a construction materials are prevalent in the world. However, in many industries, it is becoming more common to study the safety margins of a structure with respect to solicitations. It becomes important to predict the failure mode of the structure. Much work has already been made in the world on this subject, leading to operational models in computer codes using finite elements. Nevertheless, difficulties remain, mainly related to concrete cracking. These difficulties lead to open problems concerning the location, initiation and crack propagation. The thesis explores two ways of improving methods of numerical simulation of crack propagation. The first possibility of improvement is the use of the extended finite element method, XFEM. A modeling of mechanical behavior of crack is introduced and leads to a description of crack propagation from one element to another. The second possibility is based on damage mechanics. As part of the modeling of damage generalized standard type, the localization phenomenon has been studied numerically for various behaviors: viscous or damage fragile. These behaviors are described in the same spirit that the laws of the visco-elastic or visco-plasticity or plasticity classics, from a general thermodynamic interpretation. In particular, the laws gradient of damage are also considered in conjunction with recent results from the literature. It is well known that a gradient model for interpreting the effects of scale structures under mechanical loading. It also plays an interesting role in the effects of strain localization. (author)

Fatigue crack initiation and propagation in steels exposed to inert and corrosive environments. Final report, May 1, 1977--December 31, 1977

Energy Technology Data Exchange (ETDEWEB)

Youseffi, K.; Finnie, I.

1978-02-01

The fatigue crack initiation life of AISI 1018 steel was investigated using compact tension specimens having sharp notch root radii. The data were analyzed using two methods for predicting initiation in strain cycling experiments. Also, another approach in which initiation is related to the stress intensity factor was developed. The next phase, that of propagation, was studied using AISI 1018 steel and a new high strength steel HY-180. The crack propagation data obtained for both steels tested in air can be described accurately by the power law first suggested by Paris, da/dN = C(..delta..K)/sup n/, where a is the crack length, N the number of cycles, and C and n are material constants. However, the exponent n was found to be two times larger for AISI 1018 steel than HY-180 steel.

Fatigue crack initiation and propagation in steels exposed to inert and corrosive environments. Final report, May 1, 1977--December 31, 1977

International Nuclear Information System (INIS)

Youseffi, K.; Finnie, I.

1978-02-01

The fatigue crack initiation life of AISI 1018 steel was investigated using compact tension specimens having sharp notch root radii. The data were analyzed using two methods for predicting initiation in strain cycling experiments. Also, another approach in which initiation is related to the stress intensity factor was developed. The next phase, that of propagation, was studied using AISI 1018 steel and a new high strength steel HY-180. The crack propagation data obtained for both steels tested in air can be described accurately by the power law first suggested by Paris, da/dN = C(ΔK)/sup n/, where a is the crack length, N the number of cycles, and C and n are material constants. However, the exponent n was found to be two times larger for AISI 1018 steel than HY-180 steel

Modeling the initiation of Primary Water Stress Corrosion Cracking in nickel base alloys 182 and 82 of Pressurized Water Reactors

International Nuclear Information System (INIS)

Wehbi, Mickael

2014-01-01

Nickel base welds are widely used to assemble components of the primary circuit of Pressurized Water Reactors (PWR) plants. International experience shows an increasing number of Stress Corrosion Cracks (SCC) in nickel base welds 182 and 82 which motivates the development of models predicting the time to SCC initiation for these materials. SCC involves several parameters such as materials, mechanics or environment interacting together. The goal of this study is to have a better understanding of the physical mechanisms occurring at grains boundaries involved in SCC. In-situ tensile test carried out on oxidized alloy 182 evidenced dispersion in the susceptibility to corrosion of grain boundaries. Moreover, the correlation between oxidation and cracking coupled with micro-mechanical simulations on synthetic polycrystalline aggregate, allowed to propose a cracking criterion of oxidized grain boundaries which is defined by both critical oxidation depth and local stress level. Due to the key role of intergranular oxidation in SCC and since significant dispersion is observed between grain boundaries, oxidation tests were performed on alloys 182 and 82 in order to model the intergranular oxidation kinetics as a function of chromium carbides precipitation, temperature and dissolved hydrogen content. The model allows statistical analyses and is embedded in a local initiation model. In this model, SCC initiation is defined by the cracking of the intergranular oxide and is followed by slow and fast crack growth until the crack depth reaches a given value. Simplifying assumptions were necessary to identify laws used in the SCC model. However, these laws will be useful to determine experimental conditions of future investigations carried out to improve the calibration used parameters. (author)

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.)

Crack path in aeronautical titanium alloy under ultrasonic torsion loading

Directory of Open Access Journals (Sweden)

A. Nikitin

2016-01-01

Full Text Available This paper discusses features of fatigue crack initiation and growth in aeronautical VT3-1 titanium alloy under pure torsion loading in gigacycle regime. Two materials: extruded and forged VT3-1 titanium alloys were studied. Torsion fatigue tests were performed up to fatigue life of 109 cycles. The results of the torsion tests were compared with previously obtained results under fully reversed axial loading on the same alloys. It has been shown that independently on production process as surface as well subsurface crack initiation may appear under ultrasonic torsion loading despite the maximum stress amplitude located at the specimen surface. In the case of surface crack initiation, a scenario of crack initiation and growth is similar to HCF regime except an additional possibility for internal crack branching. In the case of subsurface crack, the initiation site is located below the specimen surface (about 200 μm and is not clearly related to any material flaw. Internal crack initiation is produced by shear stress in maximum shear plane and early crack growth is in Mode II. Crack branching is limited in the case of internal crack initiation compared to surface one. A typical ‘fish-eye’ crack can be observed at the torsion fracture surface, but mechanism of crack initiation seems not to be the same than under axial fatigue loading.

Stress corrosion cracking behavior of Nd:YAG laser-treated aluminum alloy 7075

International Nuclear Information System (INIS)

Yue, T.M.; Yan, L.J.; Chan, C.P.

2006-01-01

Nd-YAG laser surface treatment was conducted on 7075-T651 aluminum alloy with the aim of improving the stress corrosion cracking resistance of the alloy. Laser surface treatment was performed under two different gas environments, air and nitrogen. After the laser treatment, coarse constituent particles were removed and fine cellular/dendritic structures had formed. In addition, for the N 2 -treated specimen, an AlN phase was detected. The results of the stress corrosion test showed that after 30 days of immersion, the untreated specimen had been severely attacked by corrosion, with intergranular cracks having formed along the planar grain boundaries of the specimen. For the air-treated specimen, some relatively long stress corrosion cracks and a small number of relatively large corrosion pits were found. The cracks mainly followed the interdendritic boundaries; the fusion boundary was found to be acting as an arrestor to corrosion attacks. In contrast, only few short stress corrosion cracks appeared in the N 2 -treated specimen, indicating an improvement in corrosion initiation resistance. The superior corrosion resistance was attributed to the formation of the AlN phase in the surface of the laser-melted layer, which is an electrical insulator. The electrochemical impedance measurements taken during the stress corrosion test showed that the film resistance of the laser-treated specimens was always higher than that of the untreated specimen, with the N 2 -treated specimen showing the highest resistance

Study on fracture and stress corrosion cracking behavior of casing sour service materials

International Nuclear Information System (INIS)

Sequera, C.; Gordon, H.

2003-01-01

Present work describes sulphide stress corrosion cracking and fracture toughness tests performed to high strength sour service materials of T-95, C-100 and C-110 oil well tubular grades. P-110 was considered as a reference case, since it is one of the high strength materials included in specification 5CT of American Petroleum Institute, API. Sulphide stress corrosion cracking, impact and fracture toughness values obtained in the tests show that there is a correspondence among them. A decreasing classification order was established, namely C-100, T-95, C-110 and P-110. Special grades steels studied demonstrated a better behavior in the evaluated properties than the reference case material grade: P-110. Results obtained indicate that a higher sulphide stress corrosion cracking resistance is related to a higher toughness. The fracture toughness results evidence the hydrogen influence on reducing the toughness values. (author)

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.

Development of a Physically-Based Methodology for Predicting Material Variability in Fatigue Crack Initiation and Growth Response

National Research Council Canada - National Science Library

Chan, Kwai

2004-01-01

... of aerospace structural alloys. In this three-year program, physics-based fatigue crack initiation and growth models were developed and integrated into a probabilistic micromechanical code for treating fatigue life variability...

Effect of dynamic strain ageing on the environmentally assisted cracking of low-alloy steels oxygenated high-temperature water

International Nuclear Information System (INIS)

Devrient, B.; Roth, A.; Kuester, K.; Ilg, U.; Widera, M.

2007-01-01

The plastic deformation behavior of low-alloy steels (LAS) is significantly influenced by their individual susceptibility to dynamic strain ageing (DSA). Interstitial atoms of nitrogen (N) or carbon (C) in the steel matrix can change the mechanical properties like ductility and strength by interaction with moving dislocations during plastic deformation. The degree of DSA is depending on temperature and strain rate during plastic deformation. Under critical parameter combinations strength increases while ductility decreases. Furthermore, the interaction of dislocations and interstitial atoms can lead to a localization of plastic deformation, which results in planar gliding processes. Shear bands in LAS types with a high susceptibility to DSA show significantly higher slip steps during plastic deformation as compared to heats with low susceptibility to DSA. Since the basic mechanism of environmentally-assisted cracking (EAC) of LAS in high-temperature water (HTW) environment is slip-step-dissolution, slip behavior is of crucial nature for the kinetics of crack initiation and crack growth. Therefore, a program concerning deformation behavior, slip characterization regarding distribution and size, and behavior in oxygenated HTW environment was performed. Analysis of slip steps by advanced techniques for surface morphology investigation showed that the maximum height of slip steps is in the range of freshly formed magnetite layers on LAS in oxygenated HTW environment. This supports the active effect of localized deformation on EAC in LAS types of high susceptibility to DSA. The exposure to oxygenated HTW environment with additional mechanical loading under critical combinations of temperature and strain rate of different LAS types with high, intermediate and low susceptibility to DSA in Slow Strain Rate Tensile-tests (SSRT) showed preferential crack initiation in the areas of coarse shear bands due to localized deformation. Furthermore, a continuous transition of the

Ductile fracture of circumferentially cracked pipes subjected to bending loads

International Nuclear Information System (INIS)

Zahoor, A.; Kanninen, M.F.

1981-01-01

A plastic fracture mechanics methodology is presented for part-through cracks in pipes under bending. A previous analysis result on the behavior of part-through cracks in pipes is reviewed. Example quantitative results for the initiation and instability of radial growth of part-through cracks are presented and compared with the experimental data to demonstrate the applicability of the method. The analyses in our previous work are further developed to include the instability of circumferential growth of part-through cracks. Numerical results are then presented for a compliant piping system, under displacement controlled bending, which focus on (1) instability of radial growth (unstable wall breakthrough) and (2) instability of circumferential growth of the resulting throughthe-thickness crack. The combined results of the above two types of analyses are presented on a safety assessment diagram. This diagram defines a curve of critical combination of length and depth of part-through cracks which delineates leak from fracture. The effect of piping compliance on the leak-before-break assessment is discussed

Ductile fracture of circumferentially cracked pipes subjected to bending loads

Energy Technology Data Exchange (ETDEWEB)

Zahoor, A.; Kanninen, M.F.

1981-10-01

A plastic fracture mechanics methodology is presented for part-through cracks in pipes under bending. A previous analysis result on the behavior of part-through cracks in pipes is reviewed. Example quantitative results for the initiation and instability of radial growth of part-through cracks are presented and compared with the experimental data to demonstrate the applicability of the method. The analyses in our previous work are further developed to include the instability of circumferential growth of part-through cracks. Numerical results are then presented for a compliant piping system, under displacement controlled bending, which focus on (1) instability of radial growth (unstable wall breakthrough) and (2) instability of circumferential growth of the resulting throughthe-thickness crack. The combined results of the above two types of analyses are presented on a safety assessment diagram. This diagram defines a curve of critical combination of length and depth of part-through cracks which delineates leak from fracture. The effect of piping compliance on the leak-before-break assessment is discussed.

Fracture behavior of circumferentially surface-cracked elbows. Technical report, October 1993--March 1996

International Nuclear Information System (INIS)

Kilinski, T.; Mohan, R.; Rudland, D.; Fleming, M.

1996-12-01

This report presents the results from Task 2 of the Second International Piping Integrity Research Group (IPIRG-2) program. The focus of the Task 2 work was directed towards furthering the understanding of the fracture behavior of long-radius elbows. This was accomplished through a combined analytical and experimental program. J-estimation schemes were developed for both axial and circumferential surface cracks in elbows. Large-scale, quasi-static and dynamic, pipe-system, elbow fracture experiments under combined pressure and bending loads were performed on elbows containing an internal surface crack at the extrados. In conjunction with the elbow experiments, material property data were developed for the A106-90 carbon steel and WP304L stainless steel elbow materials investigated. A comparison of the experimental data with the maximum stress predictions using existing straight pipe fracture prediction analysis methods, and elbow fracture prediction methods developed in this program was performed. This analysis was directed at addressing the concerns regarding the validity of using analysis predictions developed for straight pipe to predict the fracture stresses of cracked elbows. Finally, a simplified fitting flaw acceptance criteria incorporating ASME B2 stress indices and straight pipe, circumferential-crack analysis was developed

Fracture behavior of circumferentially surface-cracked elbows. Technical report, October 1993--March 1996

Energy Technology Data Exchange (ETDEWEB)

Kilinski, T.; Mohan, R.; Rudland, D.; Fleming, M. [and others

1996-12-01

This report presents the results from Task 2 of the Second International Piping Integrity Research Group (IPIRG-2) program. The focus of the Task 2 work was directed towards furthering the understanding of the fracture behavior of long-radius elbows. This was accomplished through a combined analytical and experimental program. J-estimation schemes were developed for both axial and circumferential surface cracks in elbows. Large-scale, quasi-static and dynamic, pipe-system, elbow fracture experiments under combined pressure and bending loads were performed on elbows containing an internal surface crack at the extrados. In conjunction with the elbow experiments, material property data were developed for the A106-90 carbon steel and WP304L stainless steel elbow materials investigated. A comparison of the experimental data with the maximum stress predictions using existing straight pipe fracture prediction analysis methods, and elbow fracture prediction methods developed in this program was performed. This analysis was directed at addressing the concerns regarding the validity of using analysis predictions developed for straight pipe to predict the fracture stresses of cracked elbows. Finally, a simplified fitting flaw acceptance criteria incorporating ASME B2 stress indices and straight pipe, circumferential-crack analysis was developed.

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

Fracture Toughness and Fatigue Crack Growth Behavior of As-Cast High-Entropy Alloys

Science.gov (United States)

Seifi, Mohsen; Li, Dongyue; Yong, Zhang; Liaw, Peter K.; Lewandowski, John J.

2015-08-01

The fracture toughness and fatigue crack growth behavior of two as-vacuum arc cast high-entropy alloys (HEAs) (Al0.2CrFeNiTi0.2 and AlCrFeNi2Cu) were determined. A microstructure examination of both HEA alloys revealed a two-phase structure consisting of body-centered cubic (bcc) and face-centered cubic (fcc) phases. The notched and fatigue precracked toughness values were in the range of those reported in the literature for two-phase alloys but significantly less than recent reports on a single phase fcc-HEA that was deformation processed. Fatigue crack growth experiments revealed high fatigue thresholds that decreased significantly with an increase in load ratio, while Paris law slopes exhibited metallic-like behavior at low R with significant increases at high R. Fracture surface examinations revealed combinations of brittle and ductile/dimpled regions at overload, with some evidence of fatigue striations in the Paris law regime.

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)

AFM and SEM-FEG study on fundamental mechanisms leading to fatigue crack initiation

Czech Academy of Sciences Publication Activity Database

Man, Jiří; Valtr, M.; Petrenec, Martin; Dluhoš, J.; Kuběna, Ivo; Obrtlík, Karel; Polák, Jaroslav

2015-01-01

Roč. 76, JUL (2015), s. 11-18 ISSN 0142-1123 R&D Projects: GA ČR(CZ) GAP108/10/2371; GA MŠk(CZ) ED1.1.00/02.0068; GA ČR(CZ) GA13-23652S Institutional support: RVO:68081723 Keywords : fatigue crack initiation * 316L austenitic steel * atomic force microscopy * extrusion * intrusion Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.162, year: 2015

Reasons for the treatment of users of crack in a therapeutic community

Directory of Open Access Journals (Sweden)

Maycon Rogério Seleghim

2015-07-01

Full Text Available Objective: Knowing the motivation of crack users for treatment in hospital environments. Method: Descriptive and qualitative search, using the design of some cases. Twenty male crack users, aged over 18 years old, hospitalized in a Therapeutic Community in Southern Brazil, were interviewed. A semi-structured interview was used and the data were analyzed by their thematic content. Results: Were found three categories that reflect the treatment motivations: perception of the crack harmful consequences; the compulsive use of drugs as the treatment initiation; and, the family participation looking for a treatment. Conclusion: Significant events (turning points favored the interruption of the crack use and the family assumed a very important place to the users behavior in relation to the use of the drug, exclusively. Descriptors: Street drugs, Crack Cocaine, Substance Abuse Treatment Centers, Family.

Initiation of Stress Corrosion Cracking of 26Cr-1Mo Ferritic Stainless Steels in Hot Chloride Solution

International Nuclear Information System (INIS)

Kwon, H. S.; Hehemann, R. F.

1987-01-01

Elongation measurements of 26Cr-1Mo ferritic stainless steels undergoing stress corrosion in boiling LiCl solution allow the induction period to be distinguished from the propagation period of cracks by the deviation of elongation from the logarithmic creep law. Localised corrosion cells are activated exclusively at slip steps by loading and developed into corrosion trenches. No cracks have developed from the corrosion trenches until the induction period is exceeded. The induction period is regarded as a time for localised corrosion cells to achieve a critical degree of occlusion for crack initiation. The repassivation rate of exposed metal by creep or emergence of slip steps decreases as the load increases and is very sensitive to the microstructural changes that affect slip tep height. The greater susceptibility to stress corrosion cracking of either prestrained or grain coarsened 26Cr-1Mo alloy compared with that of mill annealed material results from a significant reduction of repassivation rate associated with the increased slip step height. The angular titanium carbonitrides particles dispersed in Ti-stabilized 26Cr-1Mo alloy have a detrimental effect on the resistance to stress corrosion cracking

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

An Investigation of the Sub-Microsecond Features of Dynamic Crack Propagation in PMMA and the Rdx-Based Explosive PBX 9205

Science.gov (United States)

Washabaugh, P. D.; Hill, L. G.

2007-12-01

A dynamic crack propagating in a brittle material releases enough thermal energy to produce visible light. The dynamic fracture of even macroscopically amorphous materials becomes unsteady as the crack propagation velocity approaches the material wave-speeds. The heat generated at a crack-tip, especially as it jumps, may be a mechanism to initiate a self-sustaining reaction in an energetic material. Experiments were conducted in specimens to simulate an infinite plate for ˜10 μs. The initial specimens were 152 mm square by 6 mm thick acrylic sheets, and were fabricated to study non-steady near-wave-speed crack propagation. A variant of this specimen embedded a 25 mm×3 mm PBX 9205 pellet to explore the influence of dynamic Mode-I cracks in these materials. The crack was initiated by up to 0.24 g of Detasheet placed along a precursor 50 mm long notch, with a shield to contain the reaction products and prevent propagation along the fractured surfaces. The crack was studied by means of a streak camera and a Fourier-filter of the light reflecting off the newly minted surfaces. The sub-microsecond behavior of holes initiating, preceding and coalescing with the main crack were observed in the PMMA samples. The embedding and mechanical loading of explosives by this technique did not initiate a self-sustaining reaction in preliminary testing.

Stress Corrosion Cracking Behavior of Multipass TIG-Welded AA2219 Aluminum Alloy in 3.5 wt pct NaCl Solution

Science.gov (United States)

Venugopal, A.; Sreekumar, K.; Raja, V. S.

2012-09-01

The stress corrosion cracking (SCC) behavior of the AA2219 aluminum alloy in the single-pass (SP) and multipass (MP) welded conditions was examined and compared with that of the base metal (BM) in 3.5 wt pct NaCl solution using a slow-strain-rate technique (SSRT). The reduction in ductility was used as a parameter to evaluate the SCC susceptibility of both the BM and welded joints. The results showed that the ductility ratio ( ɛ NaCl/( ɛ air) was 0.97 and 0.96, respectively, for the BM and MP welded joint, and the same was marginally reduced to 0.9 for the SP welded joint. The fractographic examination of the failed samples revealed a typical ductile cracking morphology for all the base and welded joints, indicating the good environmental cracking resistance of this alloy under all welded conditions. To understand the decrease in the ductility of the SP welded joint, preexposure SSRT followed by microstructural observations were made, which showed that the decrease in ductility ratio of the SP welded joint was caused by the electrochemical pitting that assisted the nucleation of cracks in the form of corrosion induced mechanical cracking rather than true SCC failure of the alloy. The microstructural examination and polarization tests demonstrated a clear grain boundary (GB) sensitization of the PMZ, resulting in severe galvanic corrosion of the SP weld joint, which initiated the necessary conditions for the localized corrosion and cracking along the PMZ. The absence of PMZ and a refined fusion zone (FZ) structure because of the lesser heat input and postweld heating effect improved the galvanic corrosion resistance of the MP welded joint greatly, and thus, failure occurred along the FZ.

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)

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.

The effect of heat treatment and test parameters on the aqueous stress corrosion cracking of D6AC steel

Science.gov (United States)

Gilbreath, W. P.; Adamson, M. J.

1974-01-01

The crack growth behavior of D6AC steel as a function of stress intensity, stress and corrosion history and test technique, under sustained load in natural seawater, 3.3 percent NaCl solution, distilled water, and high humidity air was investigated. Reported investigations of D6AC were considered with emphasis on thermal treatment, specimen configuration, fracture toughness, crack-growth rates, initiation period, threshold, and the extension of corrosion fatigue data to sustained load conditions. Stress history effects were found to be most important in that they controlled incubation period, initial crack growth rates, and apparent threshold.

Refined Analysis of Fatigue Crack Initiation Life of Beam-to-Column Welded Connections of Steel Frame under Strong Earthquake

Directory of Open Access Journals (Sweden)

Weilian Qu

2017-01-01

Full Text Available This paper presents a refined analysis for evaluating low-cycle fatigue crack initiation life of welded beam-to-column connections of steel frame structures under strong earthquake excitation. To consider different length scales between typical beam and column components as well as a few crucial beam-to-column welded connections, a multiscale finite element (FE model having three different length scales is formulated. The model can accurately analyze the inelastic seismic response of a steel frame and then obtain in detail elastoplastic stress and strain field near the welded zone of the connections. It is found that the welded zone is subjected to multiaxial nonproportional loading during strong ground motion and the elastoplastic stress-strain field of the welded zone is three-dimensional. Then, using the correlation of the Fatemi-Socie (FS parameter versus fatigue life obtained by the experimental crack initiation fatigue data of the structural steel weldment subjected to multiaxial loading, the refined evaluation approach of fatigue crack initiation life is developed based on the equivalent plastic strain at fatigue critical position of beam end seams of crucial welded connections when the steel frame is subjected to the strong earthquake excitation.

Microstructure and mechanical properties of internal crack healing in a low carbon steel

Energy Technology Data Exchange (ETDEWEB)

Xin, Ruishan [Department of Mechanical Engineering, Tsinghua University, Beijing 100084 (China); Key Laboratory for Advanced Materials Processing Technology of Ministry of Education, Tsinghua University, Beijing 100084 (China); Ma, Qingxian, E-mail: maqxdme@mail.tsinghua.edu.cn [Department of Mechanical Engineering, Tsinghua University, Beijing 100084 (China); Key Laboratory for Advanced Materials Processing Technology of Ministry of Education, Tsinghua University, Beijing 100084 (China); Li, Weiqi [Department of Mechanical Engineering, Tsinghua University, Beijing 100084 (China); Key Laboratory for Advanced Materials Processing Technology of Ministry of Education, Tsinghua University, Beijing 100084 (China)

2016-04-26

The behavior of internal crack healing in a low carbon steel at elevated temperatures was investigated. The internal cracks were introduced into low carbon steel samples via the drilling and compression method. The microstructure of crack healing zone was observed using optical microscopy and scanning electron microscopy. The mechanical properties of crack healing zone at room temperature were tested. The results show that there are two mechanisms of crack healing in the low carbon steel. Crack healing is caused by atomic diffusion at lower temperatures, and mainly depends on recrystallization and grain growth at higher temperatures. The microstructural evolution of crack healing zone can be divided into four stages, and the fracture morphology of crack healing zone can be classified into five stages. At the initial healing stage, the fracture exhibits brittle or low ductile dimple fracture. The ultimate fracture mode is dimple and quasi-cleavage mixed fracture. Fine grain microstructures improve the ultimate tensile strength of crack healing zone, which is even higher than that of the matrix. The strength recovery rate is higher than that of the plasticity.

An application of the J-integral to an incremental analysis of blunting crack behavior

International Nuclear Information System (INIS)

Merkle, J.G.

1989-01-01

This paper describes an analytical approach to estimating the elastic-plastic stresses and strains near the tip of a blunting crack with a finite root radius. Rice's original derivation of the path independent J-integral considered the possibility of a finite crack tip root radius. For this problem Creager's elastic analysis gives the relation between the stress intensity factor K I and the near tip stresses. It can be shown that the relation K I 2 = E'J holds when the root radius is finite. Recognizing that elastic-plastic behavior is incrementally linear then allows a derivation to be performed for a bielastic specimen having a crack tip region of reduced modulus, and the result differentiated to estimate elastic-plastic behavior. The result is the incremental form of Neuber's equation. This result does not require the assumption of any particular stress-strain relation. However by assuming a pure power law stress-strain relation and using Ilyushin's principle, the ordinary deformation theory form of Neuber's equation, K σ K var epsilon = K t 2 , is obtained. Applications of the incremental form of Neuber's equation have already been made to fatigue and fracture analysis. This paper helps to provide a theoretical basis for these methods previously considered semiempirical. 26 refs., 4 figs

Elastic-plastic dynamic behavior of guard pipes due to sudden opening of longitudinal cracks in the inner pipe and crash to the guard pipe wall

International Nuclear Information System (INIS)

Theuer, E.; Heller, M.

1979-01-01

Integrity of guard pipes is an important parameter in the design of nuclear steam supply systems. A guard pipe shall withstand all kinds of postulated inner pipe breaks without failure. Sudden opening of a crack in the inner pipe and crash of crack borders to the guard pipe wall represent a shock problem where complex phenomena of dynamic plastification as well as dynamic behavior of the entire system have to be taken in consideration. The problem was analyzed by means of Finite Element computation using the general purpose program MARC. Equation of motion was resolved by direct integration using the Newmark β-operator. Analysis shows that after 1,2 m sec crack borders touch the guard pipe wall for the first time. At this moment a considerable amount of local plastification appears in the inner pipe wall, while the guard pipe is nearly unstressed. After initial touching, the crack borders begin to slip along the guard pipe wall. Subsequently, a short withdrawal of the crack borders and a new crash occur, while the inner pipe rolls along the guard pipe wall. The analysis procedure described is suitable for designing numerous guard pipe geometries as well as U-Bolt restraint systems which have to withstand high-energy pipe rupture impact. (orig.)

Environmentally-assisted cracking behavior of a high level nuclear waste container alloy

International Nuclear Information System (INIS)

James, L.A.; Duncan, D.R.

1987-06-01

The environmentally assisted cracking behavior of cast American Society for Testing and Materials A27 steel in a simulated groundwater environment was studied using both statically loaded and cyclically loaded specimens. Compared to other aqueous environments, the groundwater environment is relatively nonaggressive, probably because of its high pH and low level of dissolved oxygen. 18 refs., 5 figs., 1 tab

Determination of the bonding strength in solid oxide fuel cells' interfaces by Schwickerath crack initiation test

DEFF Research Database (Denmark)

Boccaccini, D. N.; Sevecek, O.; Frandsen, Henrik Lund

2017-01-01

An adaptation of the Schwickerath crack initiation test (ISO 9693) was used to determine the bonding strength between an anode support and three different cathodes with a solid oxide fuel cell interconnect. Interfacial elemental characterization of the interfaces was carried out by SEM/EDS analys...

Numerical Analysis of Rolling Contact Fatigue Crack Initiation and Fatigue Life Prediction of the Railway Crossing

NARCIS (Netherlands)

Xin, L.; Markine, V.L.; Shevtsov, I.

2015-01-01

The procedure for analysing rolling contact fatigue crack initiation and fatigue life prediction of the railway turnout crossing is developed. A three-dimensional finite element (FE) model is used to obtain stress and strain results, considering the dynamic effects of wheel-crossing rolling contact.

Standard test method for measurement of creep crack growth times in metals

CERN Document Server

American Society for Testing and Materials. Philadelphia

2007-01-01

1.1 This test method covers the determination of creep crack growth (CCG) in metals at elevated temperatures using pre-cracked specimens subjected to static or quasi-static loading conditions. The time (CCI), t0.2 to an initial crack extension δai = 0.2 mm from the onset of first applied force and creep crack growth rate, ˙a or da/dt is expressed in terms of the magnitude of creep crack growth relating parameters, C* or K. With C* defined as the steady state determination of the crack tip stresses derived in principal from C*(t) and Ct (1-14). The crack growth derived in this manner is identified as a material property which can be used in modeling and life assessment methods (15-25). 1.1.1 The choice of the crack growth correlating parameter C*, C*(t), Ct, or K depends on the material creep properties, geometry and size of the specimen. Two types of material behavior are generally observed during creep crack growth tests; creep-ductile (1-14) and creep-brittle (26-37). In creep ductile materials, where cr...

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.

Time-dependent crack growth in steam generator tube leakage

International Nuclear Information System (INIS)

Chung, H.D.; Lee, J.H.; Park, Y.W.; Choi, Y.H.

2006-01-01

In general, cracks found in steam generator tubes have semi-elliptical shapes and it is assumed to be rectangular shape for conservatism after crack penetration. Hence, the leak and crack growth behavior has not been clearly understood after the elliptical crack penetrates the tube wall. Several experimental results performed by Argonne Nation Laboratory exhibited time-dependent crack growth behavior of rectangular flaws as well as trapezoidal flaws under constant pressure. The crack growth faster than expected was observed in both cases, which is likely attributed to time-dependent crack growth accompanied by fatigue sources such as the interaction between active jet and crack. The stress intensity factor, K 1 , is necessary for the prediction of the observed fatigue crack growth behavior. However, no K 1 solution is available for a trapezoidal flaw. The objective of this study is to develop the stress intensity factor which can be used for the fatigue analysis of a trapezoidal crack. To simplify the analysis, the crack is assumed to be a symmetric trapezoidal shape. A new K 1 formula for axial trapezoidal through-wall cracks was proposed based on the FEM results. (author)

Short fatigue cracks nucleation and growth in lean duplex stainless steel LDX 2101

Energy Technology Data Exchange (ETDEWEB)

Strubbia, R., E-mail: strubbia@ifir-conicet.gov.ar [Instituto de Física Rosario – CONICET, Universidad Nacional de Rosario (Argentina); Hereñú, S.; Alvarez-Armas, I. [Instituto de Física Rosario – CONICET, Universidad Nacional de Rosario (Argentina); Krupp, U. [Faculty of Engineering and Computer Science, University of Applied Sciences Osnabrück (Germany)

2014-10-06

This work is focused on the fatigue damage of lean duplex stainless steels (LDSSs) LDX 2101. Special interest is placed on analyzing short fatigue crack behavior. In this sense, short crack initiation and growth during low cycle fatigue (LCF) and short crack nucleation during high cycle fatigue (HCF) of this LDSS have been studied. The active slip systems and their associated Schmid factors (SF) are determined using electron backscattered diffraction (EBSD). Additionally, the dislocation structure developed during cycling is observed by transmission electron microscopy (TEM). Regardless of the fatigue regime, LCF and HCF, short cracks nucleate along intrusion/extrusions in ferritic grains. Moreover, during the LCF phase boundaries decelerate short crack propagation. These results are rationalized by the hardness of the constitutive phases and the dependence of screw dislocation mobility in the ferrite phase on strain rate and stress amplitude.

Influence of tip mass on dynamic behavior of cracked cantilever pipe conveying fluid with moving mass

International Nuclear Information System (INIS)

Yoon, Han Ik; Son, In Soo

2005-01-01

In this paper, we studied about the effect of the open crack and a tip mass on the dynamic behavior of a cantilever pipe conveying fluid with a moving mass. The equation of motion is derived by using Lagrange's equation and analyzed by numerical method. The cantilever pipe is modelled by the Euler-Bernoulli beam theory. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments. The influences of the crack, the moving mass, the tip mass and its moment of inertia, the velocity of fluid, and the coupling of these factors on the vibration mode, the frequency, and the tip-displacement of the cantilever pipe are analytically clarified

Effect of temperature on the rate of fatigue crack propagation in some steels during low cycle fatigue

International Nuclear Information System (INIS)

Taira, S.; Fujino, M.; Maruyama, S.

Temperature dependence of the rate of fatigue crack propagation in steels was examined, and compared with the temperature dependence of tensile ductility. Microcracks initiate and affect the propagation behavior of the main crack at elevated temperatures. Factors found to be elucidated include initiation rate of microcracks, reduction of ductility of the material in the vicinity of the main crack tip, and relaxation of concentrated strain by multi-cracks. It was found that during a strain controlled low cycle fatigue test at 1 cpm, the rate of crack propagation is largest at the blue-brittleness temperature range (200 to 300 0 C) in a low carbon steel. On the other hand, it is largest at above 700 0 C in austenite stainless steels. The temperature dependence of the rate of fatigue crack propagation is opposite to that of tensile ductility. Microcracks formed in the vicinity of the main crack tip were calculated, by considering the strain concentration and strain cycles imposed. Then, the local fracture strain was evaluated. Good correlation was found between the rate of crack propagation and the local fracture strain. (U.S.)

Cracking behavior of reinforced concrete beams: experiment and simulations on the numerical influence of the steel-concrete bond

International Nuclear Information System (INIS)

Jason, L.; Torre-Casanova, A.; Pinelli, X.; Davenne, L.

2013-01-01

Experimental and numerical results are provided in this contribution to study the global and cracking behaviors of two reinforced concrete beams subjected to four point bending. Experimentally, the use of image correlation technique enables to obtain precise information concerning the cracking properties (spacing, cumulated, maximum and mean values of the opening). Numerically, two simulations are compared taking into account a bond model between steel and concrete or supposing a perfect relation between the two materials. In both cases, a good agreement is achieved between numerical and experimental results even if the introduction of the bond effects has a direct influence during the development of the cracks (better agreement during the 'active' cracking phase). (authors)

Behavioral Initiatives in Broad Perspective.

Science.gov (United States)

California Univ., Los Angeles. Center for Mental Health in Schools.

This booklet is a technical assistance sampler addressing the issues of student misbehavior, discipline problems, and behavioral initiatives. The term behavioral initiative is defined, disciplining children with disabilities is discussed, and a cautionary note concerning ignoring students' reasons for misbehavior is presented. A brief entitled…

EPRI research program NDE techniques for crack initiation of steam turbine rotor

International Nuclear Information System (INIS)

Goto, T.; Kimura, J.; Kawamoto, K.; Kadoya, Y.; Viswanathan, R.

1990-01-01

EPRI RP 2481-8 aims at the development of nondestructive methods for the life assessment of steam turbine rotor for its crack initiation caused by creep and/or fatigue. As a part of the research project, the demonstration of the state of the art NDE techniques was conducted during June to August of 1988 at EPRI NDE Center, Charlotte, N.C. by Mitsubishi Heavy Industries, Ltd. using four rotors retired after long term service (16-22x10 4 hr). This paper introduces the results of the demonstration

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)

The crack-initiation threshold in ceramic materials subject to elastic/plastic indentation

International Nuclear Information System (INIS)

Lankford, J.; Davidson, D.L.

1979-01-01

The threshold for indentation cracking is established for a range of ceramic materials, using the techniques of scanning electron microscopy and acoustic emission. It is found that by taking into account indentation plasticity, current theories may be successfully combined to predict threshold indentation loads and crack sizes. Threshold cracking is seen to relate to radial rather than median cracking. (author)

Crack initiation and crack growth in high temperature materials under cyclic thermal stresses; Rissinitiierung und Risswachstum in Hochtemperaturwerkstoffen unter zyklisch thermischer Beanspruchung

Energy Technology Data Exchange (ETDEWEB)

Gruen, C.

1996-12-01

The high temperatures of use in drive units, such as the combustion chamber or the hot gas turbine, for example, usually cause high temperature changes. Great temperature differences occur for short periods in the components, and thermal shock is produced. In this work, theoretical and experimental investigations are introduced on crack initiation and crack growth in high temperature materials under cyclic thermal stresses. The experiments were carried out with the inter-metallic phase Ni{sub 3}Al, the nickel-based alloy Nimonic 80A and the iron-based alloy PM 2000 strengthened by oxide dispersion (ODS). A characteristic crack appearance picture was found for each material, which was examined more closely. The stresses occurring in the sample during one cycle were calculated with the aid of the finite element program ABAQUS, knowing the specific material parameters. Based on the linear-elastic fracture mechanics, stress intensity factors were calculated on the superimposition principle. Using the material data from isothermal crack propagation experiments, the prediction of fatigue crack spread with cyclic thermal stresses is compared with the experimental findings. (orig./AKF) [Deutsch] Die hohen Einsatztemperaturen in Antriebsaggregaten wie z.B. der Brennkammer oder der Heissgasturbine bedingen in der Regel hohe Temperaturwechsel. Dabei treten kurzzeitig grosse Temperaturunterschiede in den Bauteilen auf, ein Thermoschock wird erzeugt. In der vorliegenden Arbeit werden theoretische und experimentelle Untersuchungen zur Rissinitiierung und zum Risswachstum in Hochtemperaturwerkstoffen unter zyklisch thermischer Belastung vorgestellt. Die Experimente wurden mit der intermetallischen Phase Ni{sub 3}Al, der Nickelbasislegierung Nimonic 80A und der oxid-dispersionsverfestigten (ODS) Eisenbasislegierung PM2000 durchgefuehrt. Fuer jeden Werkstoff stellte sich ein charakteristisches Risserscheinungsbild dar, das naeher untersucht wurde. Die in der Probe auftretenden

Weibull modeling of particle cracking in metal matrix composites

International Nuclear Information System (INIS)

Lewis, C.A.; Withers, P.J.

1995-01-01

An investigation into the occurrence of reinforcement cracking within a particulate ZrO 2 /2618 Al alloy metal matrix composite under tensile plastic straining has been carried out, special attention being paid to the dependence of fracture on particle size and shape. The probability of particle cracking has been modeled using a Weibull approach, giving good agreement with the experimental data. Values for the Weibull modulus and the stress required to crack the particles were found to be within the range expected for the cracking of ceramic particles. Additional information regarding the fracture behavior of the particles was provided by in-situ neutron diffraction monitoring of the internal strains, measurement of the variation in the composite Young's modulus with straining and by direct observation of the cracked particles. The values of the particle stress required for the initiation of particle cracking deduced from these supplementary experiments were found to be in good agreement with each other and with the results from the Weibull analysis. Further, it is shown that while both the current experiments, as well as the previous work of others, can be well described by the Weibull approach, the exact values of the Weibull parameters do deduced are very sensitive to the approximations and the assumptions made in constructing the model

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)