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Sample records for crack growth behaviors

  1. Anomalous mechanical behavior and crack growth of oxide glasses

    Science.gov (United States)

    Seaman, Jared Hilliard

    This thesis is concerned with analytically describing anomalous mechanical behaviors of glass. A new slow crack growth model is presented that considers a semi-elliptical crack in a cylindrical glass rod subjected to 4-point bending that is both loaded statically and under a time-dependent load. This model is used to explain a suppression of the loading-rate dependency of ion-exchanged strengthened glass. The stress relaxation behavior of an ion-exchanged strengthened glass is then analyzed in view of a newly observed water-assisted surface stress relaxation mechanism. By making refinements to a time-dependent Maxwell material model for stress buildup and relaxation, the anomalous subsurface compressive stress peak in ion-exchanged strengthened glass is explained. The notion of water-assisted stress relaxation is extended to the crack tip, where high tensile stresses exist. A toughening effect has historically been observed for cracks aged at subcritical stress intensity factors, where crack tip stress relaxation is hypothesized. A simple fracture mechanics model is developed that estimates a shielding stress intensity factor that is then superimposed with the far-field stress intensity factor. The model is used to estimate anomalous "restart" times for aged cracks. The same model predicts a non-linear crack growth rate for cracks loaded near the static fatigue limit. Double cantilever beam slow crack growth experiments were performed and new slow crack growth data for soda-lime silicate glass was collected. Interpretation of this new experimental slow crack growth data suggests that the origin of the static fatigue limit in glass is due to water-assisted stress relaxation. This thesis combines a number of studies that offer a new unified understanding of historical anomalous mechanical behaviors of glass. These anomalies are interpreted as simply the consequence of slow crack growth and water-assisted surface stress relaxation.

  2. Numerical investigation of ductile crack growth behavior in a dissimilar metal welded joint

    Energy Technology Data Exchange (ETDEWEB)

    Wang, H.T. [MOE Key Laboratory of Pressurized System and Safety, School of Mechanical and Power Engineering, East China University of Science and Technology, Shanghai 200237 (China); Wang, G.Z., E-mail: gzwang@ecust.edu.cn [MOE Key Laboratory of Pressurized System and Safety, School of Mechanical and Power Engineering, East China University of Science and Technology, Shanghai 200237 (China); Xuan, F.Z.; Tu, S.T. [MOE Key Laboratory of Pressurized System and Safety, School of Mechanical and Power Engineering, East China University of Science and Technology, Shanghai 200237 (China)

    2011-08-15

    Highlights: > Ductile crack growth behavior in a dissimilar metal welded joint was simulated. > Interface crack growth tends to deviate into material with lower yield stress. > Crack locations and mismatches affect local stress-strain distribution. > Local stress-strain leads to different crack growth resistances and paths. - Abstract: In this paper, the finite element method (FEM) based on GTN model is used to investigate the ductile crack growth behavior in single edge-notched bend (SENB) specimens of a dissimilar metal welded joint (DMWJ) composed of four materials in the primary systems of nuclear power plants. The J-{Delta}a resistance curves, crack growth paths and local stress-strain distributions in front of crack tips are calculated for eight initial cracks with different locations in the DMWJ and four cracks in the four homogenous materials. The results show that the initial cracks with different locations in the DMWJ have different crack growth resistances and growth paths. When the initial crack lies in the centers of the weld Alloy182 and buttering Alloy82, the crack-tip plastic and damage zones are symmetrical, and the crack grow path is nearly straight along the initial crack plane. But for the interface cracks between materials and near interface cracks, the crack-tip plastic and damage zones are asymmetric, and the crack growth path has significant deviation phenomenon. The crack growth tends to deviate into the material whose yield stress is lower between the two materials on both sides of the interface. The different initial crack locations and mismatches in yield stress and work hardening between different materials in the DMWJ affect the local stress triaxiality and plastic strain distributions in front of crack tips, and lead to different ductile crack growth resistances and growth paths. For the accurate integrity assessment for the DMWJ, the fracture toughness data and resistance curves for the initial cracks with different locations in the

  3. Crack initiation and crack growth behavior of carbon and low-alloy steels

    Energy Technology Data Exchange (ETDEWEB)

    Gavenda, D.J.; Luebbers, P.R.; Chopra, O.K. [Argonne National Lab., IL (United States). Energy Technology Div.

    1997-01-01

    Section III of the ASME Boiler and Pressure Vessel Code specifies fatigue design curves for structural materials. These curves were based on tests of smooth polished specimens at room temperature in air. The effects of reactor coolant environments are not explicitly addressed by the Code design curves, but recent test data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of carbon and low-alloy steels. Under certain loading and environmental conditions, fatigue lives of test specimens may be a factor of {approx}70 shorter than in air. Results of fatigue tests that examine the influence of reactor environment on crack imitation and crack growth of carbon and low-alloy steels are presented. Crack lengths as a function of fatigue cycles were determined in air by a surface replication technique, and in water by block loading that leaves marks on the fracture surface. Decreases in fatigue life of low-alloy steels in high-dissolved-oxygen (DO) water are primarily caused by the effects of environment during early stages of fatigue damage, i.e., growth of short cracks <100 {micro}m in depth. For crack sizes of >100 {micro}m, crack growth rates in high-DO water are higher than in air by one order of magnitude. The effects of LWR environments on growth of short cracks are discussed.

  4. Crack-growth behavior in thick welded plates of Inconel 718 at room and cryogenic temperatures

    Science.gov (United States)

    Forman, R. G.

    1974-01-01

    Results of mechanical-properties and axial-load fatigue and fracture tests performed on thick welded plates of Inconel 718 superalloy are presented. The test objectives were to determine the tensile strength properties and the crack-growth behavior in electron-beam, plasma-arc, and gas tungsten are welds for plates 1.90 cm (0.75 in) thick. Base-metal specimens were also tested to determine the flaw-growth behavior. The tests were performed in room-temperature-air and liquid nitrogen environments. The experimental crack-growth-rate data are correlated with theoretical crack-growth-rate predictions for semielliptical surface flaws.

  5. STOCHASTIC CRACKING AND HEALING BEHAVIORS OF THIN FILMS DURING REACTION-DIFFUSION GROWTH

    Institute of Scientific and Technical Information of China (English)

    S.L. Zhu; S.L. Yang; Y.M. Xiong; M.S. Li; S.J. Geng; C.S. Hu; Fuhui Wang; W. T. Wu

    2001-01-01

    The stochastic cracking and healing behaviors of reaction-diffusion growth of thin filmswere studied by means of Markov processes analysis. We chose the thermal growth ofoxide scales on metals as an example of reaction-diffusion growth. The thermal growthof oxide films follows power law when no cracking occurs. Our results showed that thegrowth kinetics under stochastic cracking and healing conditions was different fromthat without cracking. It might be altered to either pseudo-linear or pseudo-power lawsdependent upon the intensity and frequency of the cracking of the films. When thehoping items dominated, the growth followed pseudo-linear law; when the diffusionalitems dominated, it followed pseudo-power law with the exponentials lower than theintrinsical values. The numerical results were in good agreement with the meassuredkinetics of isothermal and cyclic oxidation of NiAl-0.1 Y (at. %) alloys in air at 1273K.

  6. Corrosion Fatigue Crack Growth Behavior at Notched Hole in 7075-T6 Under Biaxial and Uniaxial Fatigue with Different Phases

    Science.gov (United States)

    2015-09-17

    CORROSION FATIGUE CRACK GROWTH BEHAVIOR AT NOTCHED HOLE IN 7075-T6 UNDER BIAXIAL AND UNIAXIAL FATIGUE WITH DIFFERENT PHASES... CORROSION FATIGUE CRACK GROWTH BEHAVIOR AT NOTCHED HOLE IN 7075-T6 UNDER BIAXIAL AND UNIAXIAL FATIGUE WITH DIFFERENT PHASES THESIS...UNLIMITED AFIT-ENY-MS-15-S-065 CORROSION FATIGUE CRACK GROWTH BEHAVIOR AT NOTCHED HOLE IN 7075-T6 UNDER BIAXIAL AND UNIAXIAL FATIGUE WITH

  7. Fatigue crack growth behaviors of a new burn-resistant highly-stabilized beta titanium alloy

    Institute of Scientific and Technical Information of China (English)

    WU Huan; ZHAO Yongqing; ZENG Weidong; QIAN Li

    2009-01-01

    This article presents the fatigue crack growth (FCG) behaviors of a new burn-resistant highly-stabilized beta Ti40 alloy. The FCG rotes were analyzed. The fracture surfaces and the side surfaces of the test samples were explored. The results show that frequency affects the cracking behaviors of Ti40 alloy. Temperature also plays an important role in Ti40 alloy cracking. At room temperature (25℃), when the frequency increases, the cracking rate changes a little in the range of low stress intensity factor (ΔK), while it changes significantly when ΔK is high. At 500℃, the cracking rate of Ti40 alloy changes significantly during all the course of clacking. The frequency also affects the microstructure patterns of Ti40 alloy. A number of secondary cracks appear in the area more than 200 μm from the main crack at a high ΔK when the fre-quency is 1 Hz, but only a few secondary cracks exist when the frequency is 10 Hz. Facet image is the main image of the fracture surfaces when the frequency is 1 Hz. While, ductile striation occupies most of the area of fracture surfaces when the frequency is 10 Hz.

  8. Effect of Microstructure on Creep Crack Growth Behavior of a Near- α Titanium Alloy IMI-834

    Science.gov (United States)

    Satyanarayana, D. V. V.; Omprakash, C. M.; Sridhar, T.; Kumar, Vikas

    2009-01-01

    In the present study, the effect of microstructure ( i.e., α + β and transformed β) on creep crack growth (CCG) behavior of a near-alpha (IMI 834) titanium alloy has been explored at temperatures 550 °C and 600 °C. For characterizing the CCG behavior of the alloy, both stress intensity factor ( K) and energy integral parameter ( C t ) were used in the present investigation. The use of stress intensity factor ( K) as crack-tip parameter is not appropriate in the present study as no unique correlation between crack growth rate and K could be obtained from the observed trend due to transients in the creep crack rate data. On the other hand, C t parameter for both microstructural conditions consolidates CCG data into a single trend. The alloy with fully transformed β microstructure exhibits better CCG resistance as compared to bimodal ( α + β) microstructure. This is consistent with the fact that the transformed β structure offers superior creep resistance as compared to α + β microstructure. Microstructural examination has revealed that CCG for both microstructural conditions is accompanied by formation of damage zone in the form of numerous environmental-assisted secondary surface cracks (perpendicular to the stress axis) ahead of the main crack tip. For α + β microstructure of the alloy, the surface creep cracks were formed by growth and coalescence of microcracks nucleated by fracture of primary α particles. While in the interior of the specimens, CCG occurred by growth and coalescence of microvoids nucleated at primary α/transformed β (matrix) interfaces. For β microstructure of the alloy, while the surface creep cracks formed by growth and coalescence of microvoids nucleated at titanium enriched surface oxide particles, in the interior CCG occurred by nucleation of intergranular cavities.

  9. 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

  10. 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

  11. Effects of microstructure on fatigue crack growth behavior in cold-rolled dual phase steels

    Energy Technology Data Exchange (ETDEWEB)

    Li, Shengci [School of Materials Science and Engineering, State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Kang, Yonglin, E-mail: kangylin@ustb.edu.cn [School of Materials Science and Engineering, State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Kuang, Shuang [Technical Research Institute, Shougang Corporation, Ltd., Beijing 100043 (China)

    2014-08-26

    Fatigue crack growth behaviors of cold-rolled dual phase steels with different microstructures were investigated at room temperature. The ferrite–martensite dual-phase microstructure was obtained by intercritical annealing. Fatigue crack growth (FCG) behaviors were described by both the Paris model and a new exponential model; fatigue fractography and surface morphology near the fracture were arrested by scanning electron microscopy (SEM); the relationship between macroscopic and microcosmic FCG rate was analyzed quantificationally. The results showed that both the models can be used to describe the fatigue crack growth rate of the samples rather well; fatigue striations and secondary cracks were observed in the fracture surface at stable expanding region (II), while the fracture at rapid expanding region (III) combined dimple and quasi-cleavage morphology; the roughness of fracture surface and the degree of secondary cracking increased with an increase in martensite content, leading to a higher threshold value. Moreover, the changes of microcosmic FCG rate were smoother than that of the macroscopic FCG rate.

  12. Time-dependent Creep Crack Growth Behavior of Alloy 617 at 800 .deg. C

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Woogon; Kim, Minhwan; Kim, Yongwan [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Park, Jaeyoung; Ekaputra, I. M. W. [Pukyong National Univ., Busan (Korea, Republic of)

    2014-05-15

    The VHTR components are designed to be used for a 60 year lifetime at a high temperature, the creep crack growth (CCG) behavior as well as creep behavior is very important for the design application due to creep damage during the long service life at elevated temperatures. Alloy 617 is a major candidate material for the IHX component. The design of the component, which will operate well into the creep range, will require a good understanding of creep crack growth deformation. Efforts are now being undertaken in the Generation IV program to provide data needed for the design and licensing of the nuclear plants, and with this goal in mind, to meet the needs of the conceptual designers of the VHTR system, 'Gen-IV Materials Handbook DB' is being established through an international collaboration program of several GIF (Gen-IV Forum) countries. CCG experimental data should be prepared to 'the Gen-IV Materials Handbook DB' website, because the CCG data for Alloy 617 are not available in the ASME design code. In this paper, experimental creep crack growth data were obtained through a series of CCG tests performed under different applied loads at 800 .deg. C. The CCG behavior was characterized in terms of the C{sup *} fracture mechanics parameter, and the CCGR equation for Alloy 617 was presented. Experimental CCG data of Alloy 617 were obtained from a series of creep crack growth tests under different applied loads at 800 .deg. C.

  13. STUDY ON THE SURFACE CRACK GROWTH BEHAVIOR IN 14MnNbq BRIDGE STEEL

    Institute of Scientific and Technical Information of China (English)

    Yanping Liu; Chuanyao Chen; Guoqing Li

    2010-01-01

    Three-dimensional crack closure correction methods are investigated in this paper.The fatigue crack growth tests of surface cracks in 14MnNbq steel for bridge plate subjected to tensile and bending loadings are systematically conducted.The experimentally measured fatigue crack growth rates of surface cracks are compared with those of through-thickness cracks in detail.It is found that the crack growth rates of surface cracks are lower than those of through-thickness cracks.In order to correct their differences in fatigue crack growth rates,a dimensionless crack closure correction model is proposed.Although this correction model is determined only by the experimental data of surface cracks under tensile loading with a constant ratio R=0.05,it can correlate the surface crack growth rates with reasonable accuracy under tensile and bending loadings with various stress ratios ranging from 0 to 0.5.Furthermore,predictions of fatigue life and crack aspect ratio for surface cracks are discussed,and the predicted results are also compared with those obtained from other prediction approaches.Comparison results show that the proposed crack closure correction model gives better prediction of fatigue life than other models.

  14. Stress Corrosion Crack Growth Behavior of Titanium Alloy/Bioactive Glasses Sandwiches in Simulated Human Physiological Environment

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Based on a series of newly developed bioactive glasses having suitable thermo-mechanical properties to allow application as fixation agents between bone and titanium alloy biomedical implants, the stress corrosion crack growth(SCCG) behavior of their interfaces with Ti6Al4V was investigated in simulated body fluid (SBF) with the objectiveof discerning the salient mechanisms of crack advance and to assess the reliability of the bonds. Results indicatedthat crack growth rates in Ti6Al4V/glass/Ti6Al4V sandwich specimens were nearly the same as or slightly lowerthan those in the bulk glasses at comparable stress intensities; indeed, cracks would prefer to propagate off theinterface, suggesting that the Ti6Al4V/glass interface has relatively good crack-growth resistance. Mechanistically,interfacial crack growth appears to be controlled by the classic stress corrosion mechanisms for silicate glasses, withno discernible effect of bioactivity on the SCCG behavior being observed.

  15. Effect of Specimen Orientation on Fatigue Crack Growth Behavior in Friction Stir Welded Al7075-T651 Joints

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, Yeui Han; Kim, Seon Jin [Pukyoung National University, Busan (Korea, Republic of)

    2014-12-15

    The aim of this paper is to investigate the effects of crack orientation on fatigue crack growth behavior in friction stir welded (FSWed) Al 7075-T651. Fatigue crack growth testing was conducted on compact tension (CT) specimens machined from the friction stir welds and the base metal under constant stress intensity factor range control. Tests were performed with the crack propagating nominally perpendicular to the weld line (termed the TL specimen) and the crack propagating in a parallel direction of the weld line (termed the LT specimen), and with three different constant stress intensity factor ranges. Both these specimen orientations were found to have a considerable effect on the fatigue crack growth behavior. Paris’s law was adopted for the analysis of experimental results; the exponent m of the WM-LT specimen was determined to be 3.56, which was the largest value in this experimental conditions.

  16. 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.

  17. Geometry and Material Constraint Effects on Creep Crack Growth Behavior in Welded Joints

    Science.gov (United States)

    Li, Y.; Wang, G. Z.; Xuan, F. Z.; Tu, S. T.

    2017-02-01

    In this work, the geometry and material constraint effects on creep crack growth (CCG) and behavior in welded joints were investigated. The CCG paths and rates of two kinds of specimen geometry (C(T) and M(T)) with initial cracks located at soft HAZ (heat-affected zone with lower creep strength) and different material mismatches were simulated. The effect of constraint on creep crack initiation (CCI) time was discussed. The results show that there exists interaction between geometry and material constraints in terms of their effects on CCG rate and CCI time of welded joints. Under the condition of low geometry constraint, the effect of material constraint on CCG rate and CCI time becomes more obvious. Higher material constraint can promote CCG due to the formation of higher stress triaxiality around crack tip. Higher geometry constraint can increase CCG rate and reduce CCI time of welded joints. Both geometry and material constraints should be considered in creep life assessment and design for high-temperature welded components.

  18. Subcritical Crack-Growth and Lifetime Behavior of Glass and SiC under Static Load

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Crack initiation and subcritical crack growth in glass sheet and SiC bar specimen under static loading were investigated to study the failure process. It has been demonstrated that the lifetime process of brittle materials involves three possible forms of crack growth: subcritical crack growth,partly subcritical crack growth and instantaneous fracture without subcritical crack growth.Curves of v-K obtained in step-by-step static fatigue tests and in constant loading rate tests showed different trends for borosilicate glass sheet. α-SiC that is generally considered immune to mechanical fatigue effect and environmental attack was also tested under static loading and the lifetime was measured. The results showed that the threshold load to damage effect was over 80% of the initial strength for the SiC.

  19. Accelerated Near-Threshold Fatigue Crack Growth Behavior of an Aluminum Powder Metallurgy Alloy

    Science.gov (United States)

    Piascik, Robert S.; Newman, John A.

    2002-01-01

    Fatigue crack growth (FCG) research conducted in the near threshold regime has identified a room temperature creep crack growth damage mechanism for a fine grain powder metallurgy (PM) aluminum alloy (8009). At very low DK, an abrupt acceleration in room temperature FCG rate occurs at high stress ratio (R = Kmin/Kmax). The near threshold accelerated FCG rates are exacerbated by increased levels of Kmax (Kmax less than 0.4 KIC). Detailed fractographic analysis correlates accelerated FCG with the formation of crack-tip process zone micro-void damage. Experimental results show that the near threshold and Kmax influenced accelerated crack growth is time and temperature dependent.

  20. Creep and Creep Crack Growth Behaviors for SMAW Weldments of Gr. 91 Steel

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Woo Gon; Yin, Song Nan; Park, Ji Yeon; Hong, Sung Deok; Kim, Yong Wan [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Park, Jae Young [Pukyong National University, Busan (Korea, Republic of)

    2010-05-15

    High Cr ferritic resistance steels with tempered martensite microstructures posses enhanced creep strength at the elevated temperatures. Those steels as represented by a modified 9Cr-1Mo steel (ASME Grade 91, hereafter Gr.91) are regarded as main structural materials of sodium-cooled fast reactors (SFR) and reactor pressure vessel materials of very high temperature reactors (VHTR). The SFR and VHTR systems are designed during long-term duration reaching 60 years at elevated temperatures and often subjected to non-uniform stress and temperature distribution during service. These conditions may generate localized creep damage and propagate the cracks and ultimately may cause a fracture. A significant portion of its life is spent in crack propagation. Therefore, a creep crack growth rate (CCGR) due to creep damage should be assessed for both the base metal (BM) and welded metal (WM). Enough CCGR data for them should be provided for assessing their structural integrities. However, their CCGR data for the Gr. 91 steels is still insufficient. In this study, the CCGR for the BM and the WM of the Gr. 91 steel was comparatively investigated. A series of the CCG tests were conducted under different applied loads for the BM and the WM at 600 .deg. C. The CCGR was characterized in terms of the C parameter, and their CCG behavior were compared, respectively

  1. Fatigue crack growth behavior of the simulated HAZ of 800 MPa grade high-performance steel

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Sanghoon [Division of Materials Science and Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791 (Korea, Republic of); Kang, Donghwan; Kim, Tae-Won [School of Mechanical Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791 (Korea, Republic of); Lee, Jongkwan [Research Institute of Industrial Science and Technology, 75-9, Youngcheon, Dongtan, Hwaseong, Gyeonggi-do 445-813 (Korea, Republic of); Lee, Changhee, E-mail: chlee@hanyang.ac.kr [Division of Materials Science and Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791 (Korea, Republic of)

    2011-03-15

    Research highlights: {yields} Fatigue crack resistances of HSB800 base steel and HAZs: Base steel > FGHAZ > CGHAZ > ICCGHAZ. {yields} In the case of ICCGHAZ, fatigue cracks are rapidly initiated and propagated through massive M-A constituents. {yields} Fatigue crack growth rate of CGHAZ was faster than that of FGHAZ, mainly due to the coarsened prior austenite grain and martensite packet. - Abstract: The present study focuses on the fatigue properties in the weld heat-affected zone (HAZ) of 800 MPa grade high-performance steel, which is commonly used in bridges and buildings. Single- and multi-pass HAZs were simulated by the Gleeble system. Fatigue properties were estimated using a crack propagation test under a 0.3 stress ratio and 0.1 load frequencies. The microstructures and fracture surfaces were analyzed by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results of the crack propagation test showed that the fatigue crack growth rate of coarse-grained HAZ (CGHAZ) was faster than fine-grained HAZ (FGHAZ), although both regions have identical fully martensite microstructures, because FGHAZ has smaller prior austenite grain and martensite packet sizes, which can act as effective barriers to crack propagation. The fatigue crack growth rate of intercritically reheated CGHAZ (ICCGHAZ) was the fastest among local zones in the HAZ, due to rapid crack initiation and propagation via the massive martensite-austenite (M-A) constituent.

  2. An investigation of fracture and fatigue crack growth behavior of cast niobium aluminide intermetallics

    Energy Technology Data Exchange (ETDEWEB)

    Ye, F.; Soboyejo, W.O. [Ohio State Univ., Columbus, OH (United States). Dept. of Materials Science and Engineering; Farkas, D. [Department of Materials Science and Engineering, Virginia Polytechnic Institute and State University, 213 Holden Hall, Blacksburg, VA 24061-0237 (United States)

    1999-05-31

    This paper presents the results of a combined experimental and theoretical study of fracture toughness and fatigue crack growth in cast Nb-15Al-xTi (x=10, 25 and 40 at%) niobium aluminide-based intermetallics. Fracture toughness and fatigue crack growth resistance are shown to improve significantly in the cast alloy containing 40 at% Ti. The improvements in the fracture toughness of the 40Ti alloy are shown to be due to the combined effects of ligament toughening, crack-tip plasticity and crack-tip blunting. The atomistic simulations show that the increased plasticity in these alloys is associated with their higher Ti content. The micromechanisms of fatigue crack growth are also elucidated. The implications of the results are discussed for potential structural application of niobium aluminide intermetallics. (orig.) 19 refs.

  3. Mechanical properties and crack growth behavior of polycrystalline copper using molecular dynamics simulation

    Science.gov (United States)

    Qiu, Ren-Zheng; Li, Chi-Chen; Fang, Te-Hua

    2017-08-01

    This study investigated the mechanical properties and crack propagation behavior of polycrystalline copper using a molecular dynamics simulation. The effects of temperature, grain size, and crack length were evaluated in terms of atomic trajectories, slip vectors, common neighbor analysis, the material’s stress-strain diagram and Young’s modulus. The simulation results show that the grain boundary of the material is more easily damaged at high temperatures and that grain boundaries will combine at the crack tip. From the stress-strain diagram, it was observed that the maximum stress increased as the temperature decreased. In contrast, the maximum stress was reduced by increasing the temperature. With regard to the effect of the grain size, when the grain size was too small, the structure of the sample deformed due to the effect of atomic interactions, which caused the grain boundary structure to be disordered in general. However, when the grain size was larger, dislocations appeared and began to move from the tip of the crack, which led to a new dislocation phenomenon. With regards to the effect of the crack length, the tip of the crack did not affect the sample’s material when the crack length was less than 5 nm. However, when the crack length was above 7.5 nm, the grain boundary was damaged, and twinning structures and dislocations appeared on both sides of the crack tip. This is because the tip of the crack was blunt at first before sharpening due to the dislocation effect.

  4. CREEP CRACK GROWTH BEHAVIOR OF ALLOY 718 DURING HIGH TEMPERATURE EXPOSURE

    Institute of Scientific and Technical Information of China (English)

    J.X. Dong; M.C. Zhang; Y.P. Zeng; X.S. Xie

    2005-01-01

    Alloy 718 is a precipitation strengthened nickel-based superalloy based on the precipitation ofγ"-Ni3Nb (DO22 structure) and γ-Ni3(Al, Ti) (Ll2 structure) phases. Creep crack growth rate(CCGR) was investigated after high temperature exposure at 593, 650 and 677℃ for 2000h inAlloy 718. In addition to the coalescence of γ'/ γ" and the amount increasing of δ phase, theexistence of a bcc chromium enriched α-Cr phase was observed by SEM, and the weight fraction of α-Cr and other phases were determined by chemical phase analysis methods. The CCGR behavior and regulation have been analyzed by means of strength and structure analysis approaches. The experimental results show higher the exposure temperature and longer the ex posure time, lower the CCGR. This is probably attributed to the interaction of material softening and brittling due to complex structure changes during high temperature exposure. Therefore,despite α-Cr phase formation and amount enhancement were run in this test range. It seems to us a srnall amount of α-Cr will be not harmful for creep crack propagation resistance, which is critical for disk application in aircraft and land-based gas turbine.

  5. The Growth of Small Corrosion Fatigue Cracks in Alloy 7075

    Science.gov (United States)

    Piascik, Robert S.

    2015-01-01

    The corrosion fatigue crack growth characteristics of small (greater than 35 micrometers) surface and corner cracks in aluminum alloy 7075 is established. The early stage of crack growth is studied by performing in situ long focal length microscope (500×) crack length measurements in laboratory air and 1% sodium chloride (NaCl) environments. To quantify the "small crack effect" in the corrosive environment, the corrosion fatigue crack propagation behavior of small cracks is compared to long through-the-thickness cracks grown under identical experimental conditions. In salt water, long crack constant K(sub max) growth rates are similar to small crack da/dN.

  6. Creep Crack Growth Behavior of Alloys 617 and 800H in Air and Impure Helium Environments at High Temperatures

    Science.gov (United States)

    Grierson, D. S.; Cao, G.; Brooks, P.; Pezzi, P.; Glaudell, A.; Kuettel, D.; Fischer, G.; Allen, T.; Sridharan, K.; Crone, W. C.

    2016-11-01

    The environmental degradation of intermediate heat exchanger (IHX) materials in impure helium has been identified as an area with major ramifications on the design of very high-temperature reactors (VHTR). It has been reported that in some helium environments, non-ductile failure is a significant failure mode for Alloy 617 with long-term elevated-temperature service. Non-ductile failure of intermediate exchangers can result in catastrophic consequences; unfortunately, the knowledge of creep crack initiation and creep crack growth (CCG) in candidate alloys is limited. Current codes and code cases for the candidate alloys do not provide specific guidelines for effects of impure helium on the high-temperature behavior. The work reported here explores creep crack growth characterization of Alloy 617 and Alloy 800H at elevated temperatures in air and in impure helium environments, providing information on the reliability of these alloys in VHTR for long-term service. Alloy 617 was found to exhibit superior CCG resistance compared to Alloy 800H. For Alloy 617 tested at 973 K (700 °C), a notable increase in the resistance to crack growth was measured in air compared to that measured in the helium environment; CCG results for Alloy 800H suggest that air and helium environments produce similar behavior. Testing of grain boundary-engineered (GBE) Alloy 617 samples revealed that, although the technique produces superior mechanical properties in many respects, the GBE samples exhibited inferior resistance to creep crack growth compared to the other Alloy 617 samples tested under similar conditions. Grain size is noted as a confounding factor in creep crack growth resistance.

  7. Creep Crack Growth Behavior of Alloys 617 and 800H in Air and Impure Helium Environments at High Temperatures

    Science.gov (United States)

    Grierson, D. S.; Cao, G.; Brooks, P.; Pezzi, P.; Glaudell, A.; Kuettel, D.; Fischer, G.; Allen, T.; Sridharan, K.; Crone, W. C.

    2017-03-01

    The environmental degradation of intermediate heat exchanger (IHX) materials in impure helium has been identified as an area with major ramifications on the design of very high-temperature reactors (VHTR). It has been reported that in some helium environments, non-ductile failure is a significant failure mode for Alloy 617 with long-term elevated-temperature service. Non-ductile failure of intermediate exchangers can result in catastrophic consequences; unfortunately, the knowledge of creep crack initiation and creep crack growth (CCG) in candidate alloys is limited. Current codes and code cases for the candidate alloys do not provide specific guidelines for effects of impure helium on the high-temperature behavior. The work reported here explores creep crack growth characterization of Alloy 617 and Alloy 800H at elevated temperatures in air and in impure helium environments, providing information on the reliability of these alloys in VHTR for long-term service. Alloy 617 was found to exhibit superior CCG resistance compared to Alloy 800H. For Alloy 617 tested at 973 K (700 °C), a notable increase in the resistance to crack growth was measured in air compared to that measured in the helium environment; CCG results for Alloy 800H suggest that air and helium environments produce similar behavior. Testing of grain boundary-engineered (GBE) Alloy 617 samples revealed that, although the technique produces superior mechanical properties in many respects, the GBE samples exhibited inferior resistance to creep crack growth compared to the other Alloy 617 samples tested under similar conditions. Grain size is noted as a confounding factor in creep crack growth resistance.

  8. INVESTIGATION OF THE LOW-CYCLE FATIGUE AND FATIGUE CRACK GROWTH BEHAVIORS OF P91 BASE METAL AND WELD JOINTS

    Institute of Scientific and Technical Information of China (English)

    H.C. Yang; Y. Tu; M.M. Yu; J. Zhao

    2004-01-01

    Low cycle fatigue tests and crack growth propagations tests on P91 pipe base metal and its weld joints were conducted at three different temperatures: room temperature,550℃ and 575℃. The strain-life was analyzed, and the changes in fatigue life behavior and fatigue growth rates with increasing temperature were discussed. The different properties of the base metal and its weld joint have been analyzed.

  9. Three-dimensional fatigue crack growth behavior in an aluminum alloy investigated with in situ high-resolution synchrotron X-ray microtomography

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, H., E-mail: huizhang@sp-mac4.pse.tut.ac.jp [Department of Production Systems Engineering, Toyohashi University of Technology, 1-1, Hibarigaoka, Tempaku, Toyohashi, Aichi 441-8580 (Japan); Toda, H.; Qu, P.C.; Sakaguchi, Y.; Kobayashi, M. [Department of Production Systems Engineering, Toyohashi University of Technology, 1-1, Hibarigaoka, Tempaku, Toyohashi, Aichi 441-8580 (Japan); Uesugi, K.; Suzuki, Y. [Japan Synchrotron Radiation Research Institute, 1-1-1, Kouto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198 (Japan)

    2009-06-15

    The fatigue crack propagation process in an Al-Mg-Si alloy was investigated using in situ high-resolution synchrotron radiation X-ray microtomography. Tomography datasets were obtained at periodic intervals throughout the 120,000 fatigue cycles. Three-dimensional rendering of the through-thickness crack shape indicates that in a number of regions the adjacent sides of two branched cracks tend to overlap with fatigue cycling and form a crack overlapping region. Measured crack growth rates in each tomographic slice show that crack growth retardation generally occurs in these crack overlapping regions. The through-thickness variation in crack tip opening displacement was also measured and was used to account for the observed crack propagation behavior. Crack morphologies were observed at different load levels in a fatigue cycle. The crack closure level varied for two selected regions comprising different overlapping cracks. The correlation of the crack growth rate with both crack opening and closure levels was discussed and interpreted.

  10. Fatigue-crack growth behavior of Type 347 stainless steels under simulated PWR water conditions

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Seokmin; Min, Ki-Deuk; Yoon, Ji-Hyun; Kim, Min-Chul; Lee, Bong-Sang [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-10-15

    Fatigue crack growth rate (FCGR) curve of stainless steel exists in ASME code section XI, but it is still not considering the environmental effects. The longer time nuclear power plant is operated, the more the environmental degradation issues of materials pop up. There are some researches on fatigue crack growth rate of S304 and S316, but researches of FCGR of S347 used in Korea nuclear power plant are insufficient. In this study, the FCGR of S347 stainless steel was evaluated in the PWR high temperature water conditions. The FCGRs of S347 stainless steel under pressurized-water conditions were measured by using compact-tension (CT) specimens at different levels of dissolved oxygen (DO) and frequency. 1. FCGRs of SS347 were slower than that in ASME XI and environmental effect did not occur when frequency was higher than 1Hz. 2. Fatigue crack growth is accelerated by corrosion fatigue and it is more severe when frequency is slower than 0.1Hz. 3. Increase of crack tip opening time increased corrosion fatigue and it deteriorated environmental fatigue properties.

  11. Crack growth behavior under creep-fatigue conditions using compact and double edge notch tension-compression specimens

    Science.gov (United States)

    Narasimha Chary, Santosh Balaji

    inspection of fatigue surfaces, it has been found that that better alignment control procedures are needed to ensure symmetric crack fronts for the DEN(T-C) specimen. Creep-fatigue crack growth tests were conducted on 9Cr-1Mo (P91) steels at 625°C with various hold times. These tests were conducted using C(T) specimens under constant load amplitude conditions (tension-tension) and DEN(T-C) specimens under displacement like conditions (tension-compression). Crack growth data generated under creep-fatigue conditions using standard C(T) specimens correlated well with crack growth data generated using DEN(T-C) specimens. The crack growth rates per cycle increased significantly with increase in hold time when crack growth data were plotted with the cyclic stress intensity parameter, Delta-K. A transient behavior in the initial portion of da/dN versus Delta-K plots were observed for the hold time tests, as reported previously by several other researchers. It is shown for the C(T) specimens that the creep-fatigue interactions during crack growth for various hold times are represented better by the (Ct)avg parameter implying that the P91 steel behaves in a creep-ductile manner. Significant differences (factors of 2 to 5) were observed between the calculated values of (Ct)avg and those based on measured values of force-line deflection. It is also shown that there is a high risk of obtaining invalid data in longer hold time tests under force-control conditions. The usefulness of DEN(T-C) specimens for crack growth studies under displacement controlled conditions to combat ratcheting problems in tests conducted under load conditions is established. The tests conditions for the round-robin program on creep-fatigue crack growth testing in support of ASTM E-2760 are finalized. Further developments needed in creep-fatigue crack growth testing are also presented.

  12. Fatigue crack growth rate (FCGR) behavior of nicalon/SiC composites

    Energy Technology Data Exchange (ETDEWEB)

    Miriyala, N.; Liaw, P.K.; Yu, N. [Univ. of Tennessee, Knoxville, TN (United States)] [and others

    1995-04-01

    The objective is to develop a fundamental understanding of fatigue crack growth phenomenon in Nicalon/SiC composites. Ultrasonic measurements were continued on the Nicalon/SiC composite specimens to correlate elastic moduli with percentage porosity in the in-plane as well as through-thickness directions. A micromechanics model based on periodic microstructure was developed to predict the elastic stiffness constants of the Nicalon/SiC composites. The predicted values were in good agreement with the experimental results.

  13. Crack growth behavior of warm-rolled 316L austenitic stainless steel in high-temperature hydrogenated water

    Science.gov (United States)

    Choi, Kyoung Joon; Yoo, Seung Chang; Jin, Hyung-Ha; Kwon, Junhyun; Choi, Min-Jae; Hwang, Seong Sik; Kim, Ji Hyun

    2016-08-01

    To investigate the effects of warm rolling on the crack growth of 316L austenitic stainless steel, the crack growth rate was measured and the oxide structure was characterized in high-temperature hydrogenated water. The warm-rolled specimens showed a higher crack growth rate compared to the as-received specimens because the slip bands and dislocations produced during warm rolling served as paths for corrosion and cracking. The crack growth rate increased with the dissolved hydrogen concentration. This may be attributed to the decrease in performance and stability of the protective oxide layer formed on the surface of stainless steel in high-temperature water.

  14. Crack Initiation and Growth Behavior of Cold-Sprayed Ni Particles on IN718 Alloy

    Science.gov (United States)

    Cavaliere, P.; Silvello, A.

    2017-03-01

    Cold spray processing parameters, governing particle velocity and impact energy, are analyzed in the present paper for pure Ni sprayed on IN718 substrates. Finite element modeling (FEM) was used to calculate the particle impact velocity and temperature as a function of gas temperature and pressure and particle density and dimensions. Experimental evidence underlines the possibility of performing repairing through cold spray thanks to the good level of adhesion achievable by employing optimal combinations of materials and spray processing parameters. In the present paper, the potential repairing of cracked superalloys sheets, by employing cold spray technology, is presented. 30° surface V-notched IN718 panels have been repaired by using pure Ni cold-sprayed powders. The bending behavior of the repaired sheets was analyzed by FEM and mechanical testing in order to compare the properties with those belonging to the unrepaired panels. Simulations and mechanical results showed a reduction in the stress intensity factor, a modification of the crack initiation site and a crack retardation in the repaired structures if compared with the unrepaired ones. The K factor was quantified; the resistance of repaired panels was increased of more than eight times in the case of repairing with Ni cold spray particles. Geometrical and mechanical properties of the coating-substrate interfaces, such as adhesion strength and residual stresses influencing the coatings behavior, were largely analyzed.

  15. Fatigue Crack Growth Behavior of Nickel-base Superalloy Haynes 282 at 550-750 °C

    Science.gov (United States)

    Rozman, K. A.; Kruzic, J. J.; Hawk, J. A.

    2015-08-01

    The fatigue crack growth rates for nickel-based superalloy Haynes 282 were measured at temperatures of 550, 650, and 750 °C using compact tension specimens with a load ratio of 0.1 and cyclic loading frequencies of 25 Hz and 0.25 Hz. Increasing the temperature from 550 to 750 °C caused the fatigue crack growth rates to increase from ~20 to 60% depending upon the applied stress intensity level. The effect of reducing the applied loading frequency increased the fatigue crack growth rates from ~20 to 70%, also depending upon the applied stress intensity range. The crack path was observed to be transgranular for the temperatures and frequencies used during fatigue crack growth rate testing. At 750 °C, there were some indications of limited intergranular cracking excursions at both loading frequencies; however, the extent of intergranular crack growth was limited and the cause is not understood at this time.

  16. Acoustic emission studies for characterization of fatigue crack growth behavior in HSLA steel

    Science.gov (United States)

    Kumar, Jalaj; Ahmad, S.; Mukhopadhyay, C. K.; Jayakumar, T.; Kumar, Vikas

    2016-01-01

    High strength low alloy (HSLA) steels are a group of low carbon steels and used in oil and gas pipelines, automotive components, offshore structures and shipbuilding. Fatigue crack growth (FCG) characteristics of a HSLA steel have been studied at two different stress ratios (R = 0.3 and 0.5). Acoustic emission (AE) signals generated during the FCG tests have been used to understand the FCG processes. The AE signals were captured by mounting two piezoelectric sensors on compact tension specimens in liner location configuration. The AE generated in stage II of the linear Paris region of FCG has been attributed to the presence of two sub-stages with two different slopes. The AE generated at higher values of stress intensity factor is found to be useful to identify the transition from stage II to stage III of the FCG. AE location analysis has provided support for increased damage at the crack tip for higher stress ratio. The peak stress intensity (Kmax) values at the crack tip have shown good correlation with the transitions from stage IIa to stage IIb and stage II to stage III of the FCG for the two stress ratios.

  17. Environmental crack-growth behavior of high strength pressure vessel alloys

    Science.gov (United States)

    Forman, R. G.

    1975-01-01

    Results of sustained-load environmental crack growth threshold tests performed on six spacecraft pressure vessel alloys are presented. The alloys were Inconel 718, 6Al-4V titanium, A-286 steel, AM-350 stainless steel, cryoformed AISI 301 stainless steel; and cryoformed AISI 304L steel. The test environments for the program were air, pressurized gases of hydrogen, oxygen, nitrogen, and carbon dioxide, and liquid environments of distilled water, sea water, nitrogen tetroxide, hydrazine, aerozine 50, monomethyl hydrazine, and hydrogen peroxide. Surface flaw type specimens were used with flaws located in both base metal and weld metal.

  18. Fatigue Crack Growth Rate Behavior of Type 347 Stainless Steel in Simulated PWR Water Environment

    Energy Technology Data Exchange (ETDEWEB)

    Min, Ki Deuk; Kim, Seon Jin [Hanyang University, Seoul (Korea, Republic of); Kim, Dae Whan; Lee, Bong Sang [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2012-05-15

    The pressurizer surge line of a Korean standard nuclear power plane uses Nb stabilized type 347 stainless steel. The pressurizer surge line is the pipe connecting the pressurizer and the hot leg line, and the path controlling the pressure and temperature of the cooling system of the nuclear reactor, operated at 316 .deg. C and in a 150atm. The pressurizer surge line operated at high temperature and high pressure receives thermal stress by a temperature change and mechanical stress by a pressure change at the same time, and by being exposed to the high temperature and high pressure cooling water environment of a nuclear power plant, environmental fatigue by stress and corrosion is the main damage instrument. As the effect of environmental fatigue has been reported, through low cycle fatigue, fatigue life evaluations of austenite stainless steel have been conducted, but evaluations of fatigue crack growth rate to evaluate the soundness are very poor. In this study, evaluated characteristics of fatigue crack growth rate base on a change of dissolved oxygen in a PWR environment

  19. Influences of post weld heat treatment on fatigue crack growth behavior of TIG welding of 6013 T4 aluminum alloy joint (Part 1. Fatigue crack growth across the weld metal)

    Energy Technology Data Exchange (ETDEWEB)

    Haryadi, Gunawan Dwi; Kim, Seon Jin [Pukyong National University, Busan (Korea, Republic of)

    2011-09-15

    The present study evaluates the influences of PWHT on FCG behavior and tensile properties of TIG butt welded Al 6013-T4 sheets. Crack propagation tests were carried out on compact tension (CT) specimens. The T82 heat treatment was varied in three artificial aging times (soaking) of 6, 18 and 24 hours. The results of T82 heat treatment with artificial aging variations were tested for their fatigue crack growth rates at the main metal zone, the heat-affected zone (HAZ), and the welded metal zone. It has been observed that the various agings in heat treatment T82 are sensitive to the mechanical properties (fatigue crack growth rate test, tensile test). The results show that PWHT-T82 for 18 hours aging is the highest fatigue resistance, while the aging 18 hours provided the highest tensile test result.

  20. Slow crack growth in spinel in water

    Science.gov (United States)

    Schwantes, S.; Elber, W.

    1983-01-01

    Magnesium aluminate spinel was tested in a water environment at room temperature to establish its slow crack-growth behavior. Ring specimens with artificial flaws on the outside surface were loaded hydraulically on the inside surface. The time to failure was measured. Various precracking techniques were evaluated and multiple precracks were used to minimize the scatter in the static fatigue tests. Statistical analysis techniques were developed to determine the strength and crack velocities for a single flaw. Slow crack-growth rupture was observed at stress intensities as low as 70 percent of K sub c. A strengthening effect was observed in specimens that had survived long-time static fatigue tests.

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

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Penghui [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); National Engineering Research Center for Equipment and Technology of Cold Strip Rolling, Yanshan University, Qinhuangdao 066004 (China); Qian, Lihe, E-mail: dlhqian@yahoo.com [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); National Engineering Research Center for Equipment and Technology of Cold Strip Rolling, Yanshan University, Qinhuangdao 066004 (China); Meng, Jiangying [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Liu, Shuai; Zhang, Fucheng [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); National Engineering Research Center for Equipment and Technology of Cold Strip Rolling, Yanshan University, Qinhuangdao 066004 (China)

    2015-10-01

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

  2. Microstructure vs. Near-threshold Fatigue Crack Growth Behavior of an Heat-treated Ductile Iron

    Directory of Open Access Journals (Sweden)

    Radomila KONEČNÁ

    2012-03-01

    Full Text Available Perferritic isothermal ductile iron (IDI® is an intermediate grade between the low-strength grades of austempered ductile iron (ADI and pearlitic ductile iron (DI recently developed by Zanardi Fonderie Italy. IDI is produced by heat-treating an unalloyed nodular cast iron. The specific matrix microstructure is called “Perferritic” and consists predominantly of ferrite and pearlite. Compared to the pearlitic grades of nodular ductile iron, IDI combines similar strength with higher toughness as a result of the isothermal heat treatment. In this contribution the fatigue crack growth resistance and Kath of IDI are investigated and correlated to mechanical properties and microstructural features. The threshold Ka was determined using the load shedding technique as per ASTM Standard E-647 using CT specimens extracted from a cast block. Tensile specimens were extracted from the broken CT halves and used to determine the static mechanical properties. A metallographic investigation was carried out to correlate structural features and mechanical properties.DOI: http://dx.doi.org/10.5755/j01.ms.18.1.1336

  3. Fatigue Crack Growth Behavior Evaluation of Grainex Mar-M 247 for NASA's High Temperature, High Speed Turbine Seal Test Rig

    Science.gov (United States)

    Delgado, Irebert R.; Steinetz, Bruce M.; Rimnac, Clare M.; Lewandowski, John J.

    2008-01-01

    The fatigue crack growth behavior of Grainex Mar-M 247 is evaluated for NASA s Turbine Seal Test Facility. The facility is used to test air-to-air seals primarily for use in advanced jet engine applications. Because of extreme seal test conditions of temperature, pressure, and surface speeds, surface cracks may develop over time in the disk bolt holes. An inspection interval is developed to preclude catastrophic disk failure by using experimental fatigue crack growth data. By combining current fatigue crack growth results with previous fatigue strain-life experimental work, an inspection interval is determined for the test disk. The fatigue crack growth life of the NASA disk bolt holes is found to be 367 cycles at a crack depth of 0.501 mm using a factor of 2 on life at maximum operating conditions. Combining this result with previous fatigue strain-life experimental work gives a total fatigue life of 1032 cycles at a crack depth of 0.501 mm. Eddy-current inspections are suggested starting at 665 cycles since eddy current detection thresholds are currently at 0.381 mm. Inspection intervals are recommended every 50 cycles when operated at maximum operating conditions.

  4. The crack growth mechanism in asphaltic mixes

    NARCIS (Netherlands)

    Jacobs, .M.M.J.; Hopman, P.C.; Molenaar, A.A.A.

    1995-01-01

    The crack growth mechanism in asphalt concrete (Ac) mixes is studied. In cyclic tests on several asphaltic mixes crack growth is measured, both with crack foils and with cOD-gauges. It is found that crack growth in asphaltic mixes is described by three processes which are parallel in time: cohesive

  5. Effect of specimen thickness of fatigue-crack-growth behavior and fracture toughness of 7075-T6 and 7178-T6 aluminum alloys

    Science.gov (United States)

    Hudson, C. M.; Newman, J. C., Jr.

    1973-01-01

    A study was made to determine the effects of specimen thickness on fatigue crack growth and fracture behavior of 7075-T6 and 7178-T6 aluminum alloy sheet and plate. Specimen thicknesses ranged from 5.1 to 12.7 mm (0.20 to 0.50 in.) for 7075-T6 and from 1.3 to 6.4 mm (0.05 to 0.25 in.) for 7178-T6. The stress ratios R used in the crack growth experiments were 0.02 and 0.50. For 7075-T6, specimen thickness had relatively little effect on fatigue-crack growth. However, the fracture toughness of the thickness of the thickest gage of 7075-T6 was about two-thirds of the fracture toughness of the thinner gages of 7075-T6. For 7178-T6, fatigue cracks generally grew somewhat faster in the thicker gages than in the thinnest gage. The fracture toughness of the thickest gage of 7178-T6 was about two-thirds of the fracture toughness of the thinner gages of 7178-T6. Stress intensity methods were used to analyze the experimental results. For a given thickness and value of R, the rate of fatigue crack growth was essentially a single-valued function of the stress intensity range for 7075-T6 and 7178-T6. An empirical equation developed by Forman, Kearney, and Engle fit the 7075-T6 and 7178-T6 crack growth data reasonably well.

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

    Energy Technology Data Exchange (ETDEWEB)

    Guan, Mingfei [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Yu, Hao, E-mail: yhzhmr@126.com [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China)

    2013-01-01

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

  7. Crack Initiation and Growth Behavior at Corrosion Pit in 7075-T6 High Strength Aluminum Alloy

    Science.gov (United States)

    2013-06-01

    was not used to measure the transition from corrosion pit to long crack [25]. . . . . . . . . . . 22 3.1 Composition of a typical sample of 7075 -T6...lives. 24 III. Methodology 3.1 Material Research was conducted using 7075 -T6 aluminum. This alloy is commonly used in aerospace applications and as a... material properties of this alloy. It is important to note that these properties were also used in all finite element models. Table 3.1: Composition of

  8. Fatigue crack growth behaviors of SA508 Gr.3 Cl.2 base and weld material in 290 .deg. C water environment

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Pyungyeon; Kim, Jeong Hyeon; Jang, Changheui [KAIST, Daejeon (Korea, Republic of); Cho, Hyunchul [Doosan Heavy Industries and Construction Co., Ltd., Changwon (Korea, Republic of)

    2012-04-15

    The fatigue crack growth behaviors of SA508 Gr.3 Cl.2 low alloy steel in high temperature water environment were investigated. Overall, weld metal showed similar crack growth rate as that of base metal. At 0.01 Hz, fatigue crack growth rate (FCGR) was higher than that in air while the difference was smaller at 0.1 Hz. Also, FCGR showed ΔK dependency at 0.1 Hz only, indicating that the environmental effect was much greater at slower loading frequency of 0.01 Hz. FCGR of SA508 Gr.3 Cl.2 low alloy steel was compatible to or smaller than the ASME Sec. XI fatigue reference curves in high temperature water environment.

  9. Effect of Microstructures on Fatigue Crack Growth Behavior of Friction Stir Processed NiAl Bronze Alloy

    Science.gov (United States)

    Lv, Yuting; Ding, Yang; Han, Yuanfei; Wu, Laizhi; Wang, Liqiang; Lu, Weijie

    2017-01-01

    Abstract: Friction stir processed (FSPed) NAB alloy exhibits inhomogeneous microstructures that can be divided into three subregions from the top surface to the bottom according to α phase morphologies: Widmanstatten α subregion, banded α colonies, and stream-like α colonies. In this study, a constant stress intensity range (ΔK) was used for each sample to study the effect of microstructures on the fatigue crack growth rate (FCGR) of FSPed NAB alloy. The results show that α phase in banded and stream-like α colonies experiences completely dynamic recrystallization and forms equiaxed α grains during FSP. The FCGR of FSPed NAB alloy continuously decreases from the top surface to the bottom. In the subregion with stream-like α colonies, the alloy containing a higher content of equiaxed α grains and fine κ iv phase, and less retained β (β') phase exhibits the best FCG resistance. The equiaxed α grains deflect the main crack and increase crack tortuosity effect, which make a main contribution to FCG resistance of FSPed NAB alloy, while martensite β' phase produced during FSP accelerates its fatigue crack growth. Compared to matrix alloy, FSPed NAB alloy exhibits better FCG resistance only at high ΔK levels. At low ΔK levels, the crack deflection effect caused by coarser κ phase in the matrix alloy obviously improves its FCG resistance. With the increasing ΔK, the aforementioned crack deflection effect gradually diminishes and fatigue crack prefers to propagate in a flat way, resulting in higher FCGR of matrix alloy.

  10. Effects of large amounts of hydrogen on the fatigue crack growth behavior of torsional prestrained carbon steel

    Directory of Open Access Journals (Sweden)

    Yuta Matsuda

    2016-01-01

    Full Text Available The effects of large amounts of hydrogen on the fatigue crack growth properties of torsional prestrained ferritic–pearlitic low-carbon steel were investigated. Hydrogen-precharged specimens were produced by conducting cathodic charge to the virgin material and to torsional prestrained JIS-S10C and JISS25C steels (hereafter S10C and S25C steels. Rotating bending fatigue tests were conducted in air at room temperature. Hydrogen content, CH, increased with torsional prestrain for both S10C and S25C steels; the CH of the torsional prestrained S25C steel precharged with hydrogen was lower than that of S10C at the same torsional prestrain. No clear difference between the maximum CH values of the torsional fractured S10C and S25C hydrogen-precharged steel specimens. With respect to crack initiation, there was no obvious difference between the uncharged and precharged specimens in spite of the large amount of CH induced by torsional prestrain. The acceleration of fatigue crack growth by hydrogen was the main cause of the decreased fatigue life. For the virgin material, hydrogen had no obvious effect on the fatigue crack growth rate. In contrast, for the torsional prestrained materials, the acceleration ratios, {(da/dNH/(da/dNU}, increased with the torsional prestrain and CH. However, {(da/dNH/(da/dNU} did not exceed the value of about 30, even when a large amount of hydrogen was charged (10.0 ≤ CH ≤ 30.3 mass ppm. A hydrogen content threshold was found; hydrogen content above this limit enhances the growth of the non-propagated crack, even for metals with lower hardness (HV < 200.

  11. Numerical Investigation for the Microstructural Effects on the Crack Growth Behavior of Particulate Composite Materials

    Science.gov (United States)

    2006-07-26

    When the damage constitutive law is adopted in an analysis, we perform an incremental analysis, just like the case of elastoplasticity (see Okada...isotropic elastoplasticity . 2.4 Some other issues associated with the damage constitutive law-initiation of nonlinear deformation Material...ABSTRACT In present investigation, analyses for the damage evolution behavior of particulate composite materials by using the finite element method

  12. Quantity effect of radial cracks on the cracking propagation behavior and the crack morphology.

    Directory of Open Access Journals (Sweden)

    Jingjing Chen

    Full Text Available In this letter, the quantity effect of radial cracks on the cracking propagation behavior as well as the circular crack generation on the impacted glass plate within the sandwiched glass sheets are experimentally investigated via high-speed photography system. Results show that the radial crack velocity on the backing glass layer decreases with the crack number under the same impact conditions during large quantities of repeated experiments. Thus, the "energy conversion factor" is suggested to elucidate the physical relation between the cracking number and the crack propagation speed. Besides, the number of radial crack also takes the determinative effect in the crack morphology of the impacted glass plate. This study may shed lights on understanding the cracking and propagation mechanism in laminated glass structures and provide useful tool to explore the impact information on the cracking debris.

  13. A New Method of Retarding Fatigue Crack Growth on Pressure Vessels

    Institute of Scientific and Technical Information of China (English)

    Jianzhong YIN; Yanyan WANG; Xinwei DING

    2001-01-01

    An artificial wedge to retard fatigue crack growth in tension has been investigated. The results show that an artificial wedge can reduce the growth rate of fatigue crack on Surface fatigue crack and, the fatigue crack growth behavior is essentially similar in-depth and width directions. Based on a theoretical analysis, a model for the effective crack growth parameter △Keff is presented. It is shown that the relationships between the calculated △Keff value and crack speed are almost the same as those of cracked specimens without a wedge. Therefore this model can be applied to estimate retardation behavior.

  14. EFFECT OF OVERLOAD ON CRACK GROWTH IN FIBER REINFORCED METAL LAMINATES

    Institute of Scientific and Technical Information of China (English)

    1998-01-01

    This paper is concerned with fatigue behavior of glass fiber reinforced aluminium laminates (GLARE) under overload fatigue loading. The effect of single overload on the crack growth rates in GLARE was investigated, and the mechanism of the retardation of crack growth determined. Crack growth retardation by overload was observed in GLARE, but much smaller than monolithic metals. The retardation of crack growth in GLARE is only controlled by the effective stress intensity factor experienced by the constituent metals at crack tips.

  15. 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.

  16. Mechanical Behavior of 3D Crack Growth in Transparent Rock-Like Material Containing Preexisting Flaws under Compression

    Directory of Open Access Journals (Sweden)

    Hu-Dan Tang

    2015-01-01

    Full Text Available Mechanical behavior of 3D crack propagation and coalescence is investigated in rock-like material under uniaxial compression. A new transparent rock-like material is developed and a series of uniaxial compressive tests on low temperature transparent resin materials with preexisting 3D flaws are performed in laboratory, with changing values of bridge angle β (inclination between the inner tips of the two preexisting flaws of preexisting flaws in specimens. Furthermore, a theoretical peak strength prediction of 3D cracks coalescence is given. The results show that the coalescence modes of the specimens are varying according to different bridge angles. And the theoretical peak strength prediction agrees well with the experimental observation.

  17. Experimental Investigation of Fatigue Crack Growth Behavior in Friction Stir Welded 7075-T111 Aluminum Alloy Joints under Constant Stress Intensity Factor Range Control Testing (For L T Orientation Specimen)

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, Yeui Han; Kim, Seon Jin [Pukyong Nat' l Univ., Busan (Korea, Republic of)

    2013-06-15

    In this study, as a series of studies aimed at investigating the spatial randomness of fatigue crack growth for friction stir welded (FSWed) 7075-T111 aluminum alloy joints, the fatigue crack growth behavior of FSWed 7075-T111 aluminum alloy joints was investigated for L T orientation specimens. Fatigue crack growth tests were conducted under constant stress intensity factor range (SEFOR) control for 5 specimens of the FSWed 7075-T111 aluminum alloy, including base metal (B M), heat affected zone (Haz), and weld metal (W M) specimens. The mean fatigue crack growth rate of W M specimens was found to be the highest, whereas that of Haz and W M specimens was the lowest. Furthermore, the variability of fatigue crack growth rate was found to be the highest in W M specimens and lowest in B M specimens.

  18. Monitoring Growth of Closed Fatigue Crack Using Subharmonic Phased Array

    Science.gov (United States)

    Ohara, Y.; Endo, H.; Hashimoto, M.; Shintaku, Y.; Yamanaka, K.

    2010-02-01

    To ensure the safety and reliability of atomic power plants and airplanes, the technique of monitoring closed fatigue cracks is requisite. Here we monitored the distribution of the crack depths and closure behavior in the length direction after 48000 and 87000 fatigue cycles using subharmonic phased array for crack evaluation (SPACE). The crack depths in the subharmonic images were larger than those in the fundamental images. Specifically, the difference was larger at near the side surface than at the center. The percentage of the closed part varied with the crack growth in the specimen. In addition, we fabricated shoe for SPACE to facilitate mechanical scanning. Thus, it was demonstrated that SPACE is useful in monitoring closed fatigue crack growth.

  19. Fatigue crack growth detect, assess, avoid

    CERN Document Server

    Richard, Hans Albert

    2016-01-01

    This book offers a concise introduction to fatigue crack growth, based on practical examples. It discusses the essential concepts of fracture mechanics, fatigue crack growth under constant and variable amplitude loading and the determination of the fracture-mechanical material parameters. The book also introduces the analytical and numerical simulation of fatigue crack growth as well as crack initiation. It concludes with a detailed description of several practical case studies and some exercises. The target group includes graduate students, researchers at universities and practicing engineers.

  20. Uncertainty Quantification in Fatigue Crack Growth Prognosis

    Directory of Open Access Journals (Sweden)

    Shankar Sankararaman

    2011-01-01

    Full Text Available This paper presents a methodology to quantify the uncertainty in fatigue crack growth prognosis, applied to structures with complicated geometry and subjected to variable amplitude multi-axial loading. Finite element analysis is used to address the complicated geometry and calculate the stress intensity factors. Multi-modal stress intensity factors due to multi-axial loading are combined to calculate an equivalent stress intensity factor using a characteristic plane approach. Crack growth under variable amplitude loading is modeled using a modified Paris law that includes retardation effects. During cycle-by-cycle integration of the crack growth law, a Gaussian process surrogate model is used to replace the expensive finite element analysis. The effect of different types of uncertainty – physical variability, data uncertainty and modeling errors – on crack growth prediction is investigated. The various sources of uncertainty include, but not limited to, variability in loading conditions, material parameters, experimental data, model uncertainty, etc. Three different types of modeling errors – crack growth model error, discretization error and surrogate model error – are included in analysis. The different types of uncertainty are incorporated into the crack growth prediction methodology to predict the probability distribution of crack size as a function of number of load cycles. The proposed method is illustrated using an application problem, surface cracking in a cylindrical structure.

  1. Effects of crack depth and specimen size on ductile crack growth of SENT and SENB specimens for fracture mechanics evaluation of pipeline steels

    Energy Technology Data Exchange (ETDEWEB)

    Xu, J. [Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Richard Birkelands vei 1a, N-7491 Trondheim (Norway); School of Materials Science and Engineering, University of Science and Technology Beijing (USTB), 100083 Beijing (China); Zhang, Z.L., E-mail: zhiliang.zhang@ntnu.n [Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Richard Birkelands vei 1a, N-7491 Trondheim (Norway); Ostby, E.; Nyhus, B. [SINTEF, Materials and Chemistry, N-7465 Trondheim (Norway); Sun, D.B. [School of Materials Science and Engineering, University of Science and Technology Beijing (USTB), 100083 Beijing (China)

    2009-12-15

    A strong geometry dependence of ductile crack growth resistance emerges under large scale yielding. The geometry dependence is associated with different levels of crack tip constraint conditions. However, in a recent attempt to identify appropriate fracture mechanics specimens for pipeline steels, an 'independent' relationship between the crack growth resistance curves and crack depths for SENT specimens has been observed experimentally. In this paper, we use the complete Gurson model to study the effects of crack depth and specimen size on ductile crack growth behavior. Crack growth resistance curves for plane strain, mode I crack growth under large scale yielding conditions have been computed. SENB and SENT specimens with three different specimen sizes, each specimen size with three different crack depths, have been selected. It has been found that crack tip constraint (Q-parameter) has a weak dependence on the crack depth for specimens in the low constraint regime.

  2. Effect of constraint on crack propagation behavior in BGA soldered joints

    Institute of Scientific and Technical Information of China (English)

    王莉; 王国忠; 方洪渊; 钱乙余

    2001-01-01

    The effects of stress triaxiality on crack propagation behavior in the BGA soldered joint were analyzed using FEM method. The computation results verified that stress triaxiality factor has an important effect on crack growth behavior. Crack growth rate increased with increasing stress triaxiality at the near-tip region, which is caused by increasing crack lengths or decreasing solder joint heights. Solder joint deformation is subjected to constraint effect provided by its surrounding rigid ceramic substrate, the constraint can be scaled by stress triaxiality near crack tip region. Therefore, it can be concluded that crack growth rate increased when the constraint effect increases.

  3. Subcritical crack growth in two titanium alloys.

    Science.gov (United States)

    Williams, D. N.

    1973-01-01

    Measurement of subcritical crack growth during static loading of precracked titanium alloys in salt water using samples too thin for plane strain loading to predominate was examined as a method for determining the critical stress intensity for crack propagation in salt water. Significant internal crack growth followed by arrest was found at quite low stress intensities, but crack growth rates were relatively low. Assuming these techniques provided a reliable measurement of the critical stress intensity, the value for annealed Ti-4Al-1.5Mo-0.5V alloy was apparently about 35 ksi-in. to the 1/2 power, while that for annealed Ti-4Al-3Mo-1V was below 45 ksi-in. to the 1/2 power. Crack growth was also observed in tests conducted in both alloys in an air environment. At 65 ksi-in. to the 1/2 power, the extent of crack growth was greater in air than in salt water. Ti-4Al-3Mo-1V showed arrested crack growth in air at a stress intensity of 45 ksi-in. to the 1/2 power.

  4. Correlation Between Transient Regime and Steady-State Regime on Creep Crack Growth Behavior of Grade 91 Steel

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jae Young; Ekaputra, I. M. W.; Kim, Seon Jin [Pukyong National Univ., Busan (Korea, Republic of); Kim, Woo Gon; Kim, Eung Seon [KAERI, Daejeong (Korea, Republic of)

    2015-12-15

    A correlation between the transient regime and steady state regime on the creep crack growth (CCG) for Grade 91 steel, which is used as the structural material for the Gen-IV reactor systems, was investigated. A series of CCG tests were performed using 1/2' CT specimens under a constant applied load and at a constant temperature of 600 °C. The CCG rates for the transient and steady state regimes were obtained in terms of C* parameter. The transient CCG rate had a close correlation with the steady-state CCG rate, as the slope of the transient CCG data was very similar to that of the steady state data. The transient rate was slower by 5.6 times as compared to the steady state rate. It can be inferred that the steady state CCG rate, which is required for long-time tests, can be predicted from the transient CCG rate obtained from short-time tests.

  5. Characterization of crack growth under combined loading

    Science.gov (United States)

    Feldman, A.; Smith, F. W.; Holston, A., Jr.

    1977-01-01

    Room-temperature static and cyclic tests were made on 21 aluminum plates in the shape of a 91.4x91.4-cm Maltese cross with 45 deg flaws to develop crack growth and fracture toughness data under mixed-mode conditions. During cyclic testing, it was impossible to maintain a high proportion of shear-mode deformation on the crack tips. Cracks either branched or turned. Under static loading, cracks remained straight if shear stress intensity exceeded normal stress intensity. Mixed-mode crack growth rate data compared reasonably well with published single-mode data, and measured crack displacements agreed with the straight and branched crack analyses. Values of critical strain energy release rate at fracture for pure shear were approximately 50% higher than for pure normal opening, and there was a large reduction in normal stress intensity at fracture in the presence of high shear stress intensity. Net section stresses were well into the inelastic range when fracture occurred under high shear on the cracks.

  6. Scaling invariance of fatigue crack growth in gigacycle loading regime

    Science.gov (United States)

    Oborin, V.; Bannikov, M.; Naimark, O.; Palin-Luc, T.

    2010-11-01

    The role of the collective behavior of defect ensembles at the crack tip and the laws of fatigue crack propagation in R4 high-strength steel have been studied under conditions of symmetric tension-compression gigacycle loading at 20 kHz. At every stage of the fatigue crack growth, replicas from the sample side surface were taken and studied by the method of three-dimensional relief profilometry (using NewView interferometer profilometer) so as to study the scaling-invariant laws of defect-related structure evolution.

  7. Characteristics of Crack Growth in High Performance Concrete Subjected to Fire

    Institute of Scientific and Technical Information of China (English)

    Gaifei PENG; Sammy Yin Nin CHAN; Jianhua YAN; Yefeng LIU; Quanxin YI

    2005-01-01

    An experimental investigation was conducted to identify the characteristics of crack growth in high performance concrete (HPC) subjected to fire, including two parts of work, I.e. Crack growth resistance determinations and cracking observations, using concrete of three strength grades 40 Mpa, 70 Mpa, and 110 Mpa. The crack growth resistance curves (R-curves) of HPC subjected to high temperatures were determined using notched three-point bend beam specimens of 100 mm×100 mm×300 mm. The R-curve (crack growth resistance curve) flattening shows that the crack growth resistance has been significantly reduced by elevated temperature. Concrete with a higher strength grade has a steeper R-curve, with a higher fracture toughness but a shorter critical crack growth. The shorter critical crack growth means that concrete of a higher strength grade has a more brittle behavior. The concrete cracking observations reveal that the consequences of rapid heating are quite different from those of slow heating. For slow heating at a rate of 0.5℃/min, HPC suffered no obvious cracking below 600℃ even if it had a high moisture content. Explosive spalling is an extreme case of the internal cracking driven mainly by vapor pressure. All these results confirmed the vapor pressure mechanism for spalling behavior which should be more significant for denser concrete. The crack growth ranges obtained from the R-curve determination results are in good agreement with those measured in the concrete cracking observations.

  8. Crack growth monitoring at CFRP bond lines

    Science.gov (United States)

    Rahammer, M.; Adebahr, W.; Sachse, R.; Gröninger, S.; Kreutzbruck, M.

    2016-02-01

    With the growing need for lightweight technologies in aerospace and automotive industries, fibre-reinforced plastics, especially carbon-fibre (CFRP), are used with a continuously increasing annual growth rate. A promising joining technique for composites is adhesive bonding. While rivet holes destroy the fibres and cause stress concentration, adhesive bond lines distribute the load evenly. Today bonding is only used in secondary structures due to a lack of knowledge with regard to long-term predictability. In all industries, numerical simulation plays a critical part in the development process of new materials and structures, while it plays a vital role when it comes to CFRP adhesive bondings conducing the predictability of life time and damage tolerance. The critical issue with adhesive bondings is crack growth. In a dynamic tensile stress testing machine we dynamically load bonded CFRP coupon specimen and measure the growth rate of an artificially started crack in order to feed the models with the results. We also investigate the effect of mechanical crack stopping features. For observation of the bond line, we apply two non-contact NDT techniques: Air-coupled ultrasound in slanted transmission mode and active lockin-thermography evaluated at load frequencies. Both methods give promising results for detecting the current crack front location. While the ultrasonic technique provides a slightly higher accuracy, thermography has the advantage of true online monitoring, because the measurements are made while the cyclic load is being applied. The NDT methods are compared to visual inspection of the crack front at the specimen flanks and show high congruence. Furthermore, the effect of crack stopping features within the specimen on the crack growth is investigated. The results show, that not all crack fronts are perfectly horizontal, but all of them eventually come to a halt in the crack stopping feature vicinity.

  9. Thermally activated processes of fatigue crack growth in steels

    Science.gov (United States)

    Tanaka, Masaki; Fujii, Atsushi; Noguchi, Hiroshi; Higashida, Kenji

    2014-02-01

    Fatigue crack growth rates in steels at high and low temperatures have been investigated using Paris curves. The fatigue crack growth rates at high temperatures are quite different from those at low temperatures. Arrhenius plots between fatigue crack growth rate (da/dN) and test temperatures at constant stress intensity factor range (ΔKI) indicate a difference of the rate-controlling process for fatigue crack growth with temperature. Slip deformation at the crack tip governs fatigue crack growth at high temperatures, while hydrogen diffusion is associated with crack growth at low temperatures.

  10. Creep, Fatigue and Environmental Interactions and Their Effect on Crack Growth in Superalloys

    Science.gov (United States)

    Telesman, J.; Gabb, T. P.; Ghosn, L. J.; Smith, T.

    2017-01-01

    Complex interactions of creep/fatigue/environment control dwell fatigue crack growth (DFCG) in superalloys. Crack tip stress relaxation during dwells significantly changes the crack driving force and influence DFCG. Linear Elastic Fracture Mechanics, Kmax, parameter unsuitable for correlating DFCG behavior due to extensive visco-plastic deformation. Magnitude of remaining crack tip axial stresses controls DFCG resistance due to the brittle-intergranular nature of the crack growth process. Proposed a new empirical parameter, Ksrf, which incorporates visco-plastic evolution of the magnitude of remaining crack tip stresses. Previous work performed at 704C, extend the work to 760C.

  11. Fatigue Crack Propagation Behavior of Rubber-toughened Epoxy Resin

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Fatigue crack propagation (FCP) behaviors of mass fraction 15% CTBN (carboxyl-terminated butadiene-acrylonitrile), 15% Qishi toughening-agent toughened anhydride-cured epoxy resins (EP), and pure anhydride-cured EP were measured. The results showed that the two main toughening mechanisms, localized shear yielding and void plastics growth, which occurred near the threshold region because the rubber size is much less than the plastics size at the crack front, improved the near threshold FCP behavior and increased the threshold. The stable FCP behavior was obviously improved with the FCP rates decreased to less than 21%.

  12. Mesh sensitivity effects on fatigue crack growth by crack-tip blunting and re-sharpening

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2007-01-01

    Crack-tip blunting under tensile loads and re-sharpening of the crack-tip during unloading is one of the basic mechanisms for fatigue crack growth in ductile metals. Based on an elastic–perfectly plastic material model, crack growth computations have been continued up to 700 full cycles by using...

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

    NARCIS (Netherlands)

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

    2008-01-01

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

  14. A computational study of the time dependent crack growth process

    Energy Technology Data Exchange (ETDEWEB)

    Brust, F.W.; Krishnaswamy, P.

    1992-01-01

    Universal studies of creep crack growth for (1) constant load and (2) variable load cases are presented. Results of the constant load cases is compared to experiment. The behavior of displacements and integral creep for fracture parameters are discussed for both load cases. The need for using a constitutive law which can handle cyclic creep is discussed.

  15. Characterization of Cracking and Crack Growth Properties of the C5A Aircraft Tie-Box Forging

    Science.gov (United States)

    Piascik, Robert S.; Smith, Stephen W.; Newman, John A.; Willard, Scott A.

    2003-01-01

    Detailed destructive examinations were conducted to characterize the integrity and material properties of two aluminum alloy (7075-T6) horizontal stabilizer tie box forgings removed.from US. Air Force C5A and C5B transport aircraft. The C5B tie box forging was,found to contain no evidence of cracking. Thirteen cracks were found in the CSA,forging. All but one of the cracks observed in the C5A component were located along the top cap region (one crack was located in the bottom cap region). The cracks in the C5A component initiated at fastener holes and propagated along a highly tunneled intergranular crack path. The tunneled crack growth configuration is a likelv result of surface compressive stress produced during peening of the .forging suijace. The tie box forging ,fatigue crack growth, fracture and stress corrosion cracking (SCC) properties were characterized. Reported herein are the results of laboratory air ,fatigue crack growth tests and 95% relative humidity SCC tests conducted using specimens machined from the C5A ,forging. SCC test results revealed that the C5A ,forging material was susceptible to intergranular environmental assisted cracking: the C5A forging material exhibited a SCC crack-tip stress-intensity factor threshold of less than 6 MPadn. Fracture toughness tests revealed that the C5A forging material exhibited a fracture toughness that was 25% less than the C5B forging. The C5A forging exhibited rapid laboratory air fatigue crack growth rates having a threshold crack-tip stress-intensity factor range of less than 0.8 MPa sup m. Detailed fractographic examinations revealed that the ,fatigue crack intergranular growth crack path was similar to the cracking observed in the C5A tie box forging. Because both fatigue crack propagation and SCC exhibit similar intergranular crack path behavior, the damage mechanism resulting in multi-site cracking of tie box forgings cannot be determined unless local cyclic stresses can be quantified.

  16. ENDOFEM INTEGRATED METHODOLOGY FOR FATIGUE CRACK GROWTH

    Institute of Scientific and Technical Information of China (English)

    C.F.Lee; L.T.Hsiao

    2002-01-01

    In this paper, the FEM with the incremental endochronic cyclic plasticity (EndoFEM) and the rc controlled node-released strategy are employed to study the fatigue crack opened/closed load (Pop) of A1 2024-T3 CCT specimens provided by Mageed and Pandey under several crack lengths and the constant amplitude with various load ratio (R). After statisfactory results are achieved by comparisons of computed Pop values and cited experimental data, the simulations will be extended to the crack lengths with significant bending effect due to short ligaments or high peak (Pmax) or high positive or very low negative R cyclic loads. Through these simulations, the complete map of Pop/Pmax vs. Kmax and R can be constructed and thereafter its correspondant empirical formulae can be proposed. Using these formulae and selecting the traditional fatigue crack growth parameter ΔKeff, the A1 2024-T3 fatigue crack growth rate da/dN vs. ΔK and R data, provided by Hiroshi and Schijve, can be employed to proposed empirical formulae of da/dN vs. ΔKeff and R. After integration, fatigue-crack-growth length a vs. N curves computed by EndoFEM can be obtained. The results are agreed very well with the existing experimental curves. According to the above procedures of simulation and steps of comparions with experiment, this paper may provides an integrate methodology of numerical simulation in the studies of fatigue crack growth for academic and industrial researches and design analysis.

  17. Fatigue crack growth under variable amplitude loading

    Science.gov (United States)

    Sidawi, Jihad A.

    1994-01-01

    Fatigue crack growth tests were conducted on an Fe 510 E C-Mn steel and a submerged arc welded joint from the same material under constant, variable, and random loading amplitudes. Paris-Erdogan's crack growth rate law was tested for the evaluation of m and C using the stress intensity factor K, the J-integral, the effective stress intensity factor K(sub eff), and the root mean square stress intensity factor K(sub rms) fracture mechanics concepts. The effect of retardation and residual stresses resulting from welding was also considered. It was found that all concepts gave good life predictions in all cases.

  18. Fatigue cracks in Eurofer 97 steel: Part II. Comparison of small and long fatigue crack growth

    Science.gov (United States)

    Kruml, T.; Hutař, P.; Náhlík, L.; Seitl, S.; Polák, J.

    2011-05-01

    The fatigue crack growth rate in the Eurofer 97 steel at room temperature was measured by two different methodologies. Small crack growth data were obtained using cylindrical specimens with a shallow notch and no artificial crack starters. The growth of semicircular cracks of length between 10-2000 μm was followed in symmetrical cycling with constant strain amplitude ( R ɛ = -1). Long crack data were measured using standard CT specimen and ASTM methodology, i.e. R = 0.1. The growth of cracks having the length in the range of 10-30 mm was measured. It is shown that the crack growth rates of both types of cracks are in a very good agreement if J-integral representation is used and usual assumptions of the crack closure effects are taken into account.

  19. Fatigue cracks in Eurofer 97 steel: Part II. Comparison of small and long fatigue crack growth

    Energy Technology Data Exchange (ETDEWEB)

    Kruml, T., E-mail: kruml@ipm.cz [Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Zizkova 22, CZ 61662 Brno (Czech Republic); Hutar, P.; Nahlik, L.; Seitl, S.; Polak, J. [Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Zizkova 22, CZ 61662 Brno (Czech Republic)

    2011-05-01

    The fatigue crack growth rate in the Eurofer 97 steel at room temperature was measured by two different methodologies. Small crack growth data were obtained using cylindrical specimens with a shallow notch and no artificial crack starters. The growth of semicircular cracks of length between 10-2000 {mu}m was followed in symmetrical cycling with constant strain amplitude (R{sub {epsilon}} = -1). Long crack data were measured using standard CT specimen and ASTM methodology, i.e. R = 0.1. The growth of cracks having the length in the range of 10-30 mm was measured. It is shown that the crack growth rates of both types of cracks are in a very good agreement if J-integral representation is used and usual assumptions of the crack closure effects are taken into account.

  20. Fatigue crack growth simulations of 3-D linear elastic cracks under thermal load by XFEM

    Institute of Scientific and Technical Information of China (English)

    Himanshu PATHAK[1; Akhilendra SINGH[2; I.V. SINGH[3; S. K. YADAV[3

    2015-01-01

    This paper deals with the fatigue crack growth simulations of three-dimensional linear elastic cracks by XFEM under cyclic thermal load. Both temperature and displacement approximations are extrinsically enriched by Heaviside and crack front enrichment functions. Crack growth is modelled by successive linear extensions, and the end points of these linear extensions are joined by cubic spline segments to obtain a modified crack front. Different crack geometries such as planer, non-planer and arbitrary spline shape cracks are simulated under thermal shock, adiabatic and isothermal loads to reveal the sturdiness and versatility of the XFEM approach.

  1. Subcritical crack growth in fibrous materials

    CERN Document Server

    Santucci, Stéphane; Deschanel, Stéphanie; Vanel, Loic; Ciliberto, Sergio

    2006-01-01

    We present experiments on the slow growth of a single crack in a fax paper sheet submitted to a constant force $F$. We find that statistically averaged crack growth curves can be described by only two parameters : the mean rupture time $\\tau$ and a characteristic growth length $\\zeta$. We propose a model based on a thermally activated rupture process that takes into account the microstructure of cellulose fibers. The model is able to reproduce the shape of the growth curve, the dependence of $\\zeta$ on $F$ as well as the effect of temperature on the rupture time $\\tau$. We find that the length scale at which rupture occurs in this model is consistently close to the diameter of cellulose microfibrils.

  2. Predictions for fatigue crack growth life of cracked pipes and pipe welds using RMS SIF approach and experimental validation

    Energy Technology Data Exchange (ETDEWEB)

    Arora, Punit, E-mail: punit@barc.gov.in [Bhabha Atomic Research Centre, Department of Atomic Energy, Maharashtra, Mumbai 400 085 (India); Singh, P.K.; Bhasin, Vivek; Vaze, K.K.; Ghosh, A.K. [Bhabha Atomic Research Centre, Department of Atomic Energy, Maharashtra, Mumbai 400 085 (India); Pukazhendhi, D.M.; Gandhi, P.; Raghava, G. [Structural Engineering Research Centre, Chennai 600 113 (India)

    2011-10-15

    The objective of the present study is to understand the fatigue crack growth behavior in austenitic stainless steel pipes and pipe welds by carrying out analysis/predictions and experiments. The Paris law has been used for the prediction of fatigue crack growth life. To carry out the analysis, Paris constants have been determined for pipe (base) and pipe weld materials by using Compact Tension (CT) specimens machined from the actual pipe/pipe weld. Analyses have been carried out to predict the fatigue crack growth life of the austenitic stainless steel pipes/pipes welds having part through cracks on the outer surface. In the analyses, Stress Intensity Factors (K) have been evaluated through two different schemes. The first scheme considers the 'K' evaluations at two points of the crack front i.e. maximum crack depth and crack tip at the outer surface. The second scheme accounts for the area averaged root mean square stress intensity factor (K{sub RMS}) at deepest and surface points. Crack growth and the crack shape with loading cycles have been evaluated. In order to validate the analytical procedure/results, experiments have been carried out on full scale pipe and pipe welds with part through circumferential crack. Fatigue crack growth life evaluated using both schemes have been compared with experimental results. Use of stress intensity factor (K{sub RMS}) evaluated using second scheme gives better fatigue crack growth life prediction compared to that of first scheme. Fatigue crack growth in pipe weld (Gas Tungsten Arc Welding) can be predicted well using Paris constants of base material but prediction is non-conservative for pipe weld (Shielded Metal Arc Welding). Further, predictions using fatigue crack growth rate curve of ASME produces conservative results for pipe and GTAW pipe welds and comparable results for SMAW pipe welds. - Highlights: > Predicting fatigue crack growth of Austenitic Stainless Steel pipes and pipe welds. > Use of RMS-SIF and

  3. Crack Growth along Interfaces in Porous Ceramic Layers

    DEFF Research Database (Denmark)

    Sørensen, Bent F.; Horsewell, Andy

    2001-01-01

    Crack growth along porous ceramic layers was studied experimentally. Double cantilever beam sandwich specimens were loaded with pure bending moments to obtain stable crack growth. The experiments were conducted in an environmental scanning electron microscope enabling in situ observations...

  4. Controlling fatigue crack paths for crack surface marking and growth investigations

    Directory of Open Access Journals (Sweden)

    S. Barter

    2016-01-01

    Full Text Available While it is well known that fatigue crack growth in metals that display confined slip, such as high strength aluminium alloys, develop crack paths that are responsive to the loading direction and the local microstructural orientation, it is less well known that such paths are also responsive to the loading history. In these materials, certain loading sequences can produce highly directional slip bands ahead of the crack tip and by adjusting the sequence of loads, distinct fracture surface features or progression marks, even at very small crack depths can result. Investigating the path a crack selects in fatigue testing when particular combinations of constant and variable amplitude load sequences are applied is providing insight into crack growth. Further, it is possible to design load sequences that allow very small amounts of crack growth to be measured, at very small crack sizes, well below the conventional crack growth threshold in the aluminium alloy discussed here. This paper reports on observations of the crack path phenomenon and a novel test loading method for measuring crack growth rates for very small crack depths in aluminium alloy 7050-T7451 (an important aircraft primary structural material. The aim of this work was to firstly generate short- crack constant amplitude growth data and secondly, through the careful manipulation of the applied loading, to achieve a greater understanding of the mechanisms of fatigue crack growth in the material being investigated. A particular focus of this work is the identification of the possible sources of crack growth retardation and closure in these small cracks. Interpreting these results suggests a possible mechanism for why small fatigue crack growth through this material under variable amplitude loading is faster than predicted from models based on constant amplitude data alone.

  5. Analysis of deterministic and statistical approaches to fatigue crack growth in pressure vessels

    Energy Technology Data Exchange (ETDEWEB)

    Francisco, Alexandre S.; Melo, P.F. Frutuoso e [Universidade Federal, Rio de Janeiro, RJ (Brazil). Coordenacao dos Programas de Pos-graduacao de Engenharia. Programa de Engenharia Nuclear. E-mail: frutuoso@lmn.con.ufrj.br

    2000-07-01

    This work presents three approaches to the fatigue crack growth process in steel pressure vessels as applied to failure probability calculation. In the Thomson's methodology, the crack growth is the term that represents the mechanical behavior which along the time will take the pressure vessel to a structural failure. The first result of failure probability will be obtained considering a deterministic approach, since the crack growth laws are of a deterministic nature. This approach will provide a reference value. Next, two statistical approaches will be performed based on the fact that fatigue crack growth is a random phenomenon. One of them takes into account only the variability of experimental data, proposing a distribution function to represent the failure process. The other, the stochastic approach, considers the random nature of crack growth along time, by performing the randomization of a crack growth law. The solution of this stochastic equation is a transition distribution function fitted to experimental data. (author)

  6. Brittle-tough transitions during crack growth in toughened adhesives

    Science.gov (United States)

    Thoules, Michael

    2008-03-01

    The use of structural adhesives in automotive applications relies on an effective understanding of their performance under crash conditions. In particular, there is considerable potential for mechanics-based modeling of the interaction between an adhesive layer and the adherends, to replace current empirical approaches to design. Since energy dissipation during a crash, mediated by plastic deformation of the structure, is a primary consideration for automotive applications, traditional approaches of fracture mechanics are not appropriate. Cohesive-zone models that use two fracture parameters - cohesive strength and toughness - have been shown to provide a method for quantitative mechanics analysis. Combined numerical and experimental techniques have been developed to deduce the toughness and strength parameters of adhesive layers, allowing qualitative modeling of the performance of adhesive joints. These techniques have been used to study the failure of joints, formed from a toughened adhesive and sheet metal, over a wide range of loading rates. Two fracture modes are observed: quasi-static crack growth and dynamic crack growth. The quasi-static crack growth is associated with a toughened mode of failure; the dynamic crack growth is associated with a more brittle mode of failure. The results of the experiments and analyses indicate that the fracture parameters for quasi-static crack growth in this toughened system are essentially rate independent, and that quasi-static crack growth can occur even at the highest crack velocities. Effects of rate appear to be limited to the ease with which a transition to dynamic fracture could be triggered. This transition appears to be stochastic in nature, and it does not appear to be associated with the attainment of any critical value for crack velocity or loading rate. Fracture-mechanics models exist in the literature for brittle-ductile transitions in rate-dependent polymers, which rely on rate dependent values of toughness

  7. Cracks growth behaviors of commercial pure titanium under nanosecond laser irradiation for formation of nanostructure-covered microstructures (with sub-5-μm)

    Science.gov (United States)

    Pan, A. F.; Wang, W. J.; Mei, X. S.; Zheng, B. X.; Yan, Z. X.

    2016-11-01

    This study reported on the formation of sub-5-μm microstructures covered on titanium by cracks growth under 10-ns laser radiation at the wavelength of 532 nm and its induced light modification for production of nanostructures. The electric field intensity and laser power density absorbed by commercial pure titanium were computed to investigate the self-trapping introduced by cracks and the effect of surface morphology on laser propagation characteristics. It is found that nanostructures can form at the surface with the curvature radius below 20 μm. Meanwhile, variable laser fluences were applied to explore the evolution of cracks on commercial pure titanium with or without melt as spot overlap number increased. Experimental study was first performed at the peak laser fluence of 1.063 J/cm2 to investigate the microstructures induced only by cracks growth. The results demonstrated that angular microstructures with size between 1.68 μm and 4.74 μm was obtained and no nanostructure covered. Then, at the peak laser fluence of 2.126 J/cm2, there were some nanostructures covered on the melt-induced curved microstructured surface. However, surface molten material submerged in the most of cracks at the spot overlap number of 744, where the old cracks disappeared. The results indicated that there was too much molten material and melting time at the peak laser fluence of 2.126 J/cm2, which was not suitable for obtainment of perfect micro-nano structures. On this basis, peak laser fluence was reduced down to 1.595 J/cm2 and the sharp sub-5 μm microstructures with nanostructures covered was obtained at spot overlap number of 3720.

  8. Partial discharge-induced crack growth in dielectric materials

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Partial discharge(PD) of an air-filled semi-permeable crack in a dielectric material is studied based on the streamer-type discharge mechanism to explore the effects of applied mechanical-electric fields on crack growth.Within the frame of two-dimensional deformation,the electric field inside the crack is first derived by taking the crack deformation into account.Then,the effects of electric field before PD are discussed through considering the contribution of the induced electric field inside the deformed crack space to the total energy release rate.Finally,PD and its effects on crack growth are investigated.It is found that:(1) before PD,the applied electric field always retards crack growth;(2) during PD,the applied electric field can induce crack growth in dielectric materials.

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

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2004-01-01

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

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

    DEFF Research Database (Denmark)

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

    2007-01-01

    capable of modelling variations in the discontinuous displacement field on both sides of the crack and hence also capable of modelling the case where equal stresses are present on each side of the crack. The enrichment was implemented for the 3-node constant strain triangle (CST) and a standard algorithm...... was used to solve the non-linear equations. The performance of the element is illustrated by modelling fracture mechanical benchmark tests. Investigations were carried out on the performance of the element for different crack lengths within one element. The results are compared with previously obtained...

  11. Fatigue crack growth retardation in spot heated mild steel sheet

    Indian Academy of Sciences (India)

    B B Verma; P K Ray

    2002-08-01

    A fatigue crack can be effectively retarded by heating a spot near the crack tip under nil remote stress condition. The subcritical spot heating at a proper position modifies the crack growth behaviour in a way, more or less, similar to specimen subjected to overload spike. It is observed that the extent of crack growth retardation increases with increasing level of overload as well as with increasing spot temperature. It is also observed that modification in crack growth behaviour is a function of location of heating spot and maximum retardation is observed at + 5 position.

  12. Fatigue crack growth in additive manufactured products

    Directory of Open Access Journals (Sweden)

    A. Riemer

    2015-10-01

    Full Text Available Additive Manufacturing (AM is a new innovative technique that allows the direct fabrication of complex, individual, delicate and high-strength products, based on their 3D data. Selective Laser Melting (SLM is one of the AM processes that generates metallic components layer by layer using powder-bed technique. The irradiation and consequent melting of metallic powder is realised by the laser source. Employing SLM, especially complex and individual products, such as implants or aerospace parts, are well suited for economic production in small batches. The first important issue in this work was to analyse the fatigue crack growth (FCG in titanium alloy Ti-6-4 and stainless steel 316L processed by SLM. As a first step, stress intensity range decreasing tests were performed on SLM samples in their “as-built” condition. The next step was to adopt measures for optimisation of fatigue crack growth performance of SLM parts. For this purpose various heat treatments such as stress relief annealing and hot isostatic pressing (HIP were applied to the CT specimens. Finally, the strong impact of heat treatment on the residual lifetime was demonstrated by numerical fatigue crack growth simulations. For this purpose, the hip joint implant consisting of Ti-6-4 and processed by SLM was taken into account. It was found that residual stresses have a strong influence on the crack growth in Ti-6-4, while the influence of the micro-pores on the threshold values remains low. In contrast the results for 316L show that its fracturemechanical behaviour is not affected by residual stresses, whereas the microstructural features lead to modification in the da/dN-K-data. The second fundamental aim of this work was to demonstrate the possibilities of the SLM process. For that reason, the individually tailored bicycle crank was optimised regarding its weight and local stresses and finally manufactured using the SLM system. The iterative optimisation procedure was based on

  13. Environmentally assisted crack growth rates of high-strength aluminum alloys

    Science.gov (United States)

    Connolly, Brain J.; Deffenbaugh, Kristen L.; Moran, Angela L.; Koul, Michelle G.

    2003-01-01

    The scope of this project is to evaluate the environmentally assisted long crack growth behavior of candidate high-strength aluminum alloys/tempers, specifically AA7150-T7751 and AA7040-T7651, for consideration as viable replacements/refurbishment for stress-corrosion cracking in susceptible AA7075-T6 aircraft components found in aging aircraft systems.

  14. STUDY ON FATIGUE CRACK GROWTH BEHAVIOR OF 16MnR STEEL UNDER DIFFERENT CONDITIONS%16MnR钢在不同条件下的疲劳裂纹扩展规律

    Institute of Scientific and Technical Information of China (English)

    熊缨; 陈冰冰; 郑三龙; 高增梁

    2009-01-01

    采用压力容器用16MnR热轧钢不同缺口尺寸、不同厚度的紧凑拉伸(CT)试样,进行了不同温度、不同应力比条件的一系列疲劳裂纹扩展实验,得到了相应实验条件下的疲劳裂纹扩展速率.讨论了高温环境、缺口半径,应力比及试样厚度对疲劳裂纹扩展行为的影响规律.结果表明:16MnR钢在环境温度为150和300℃时的疲劳裂纹扩展速率比25和425℃时低,300℃时疲劳裂纹扩展速率最低,300℃以上时随温度的升高裂纹扩展速率增大;缺口半径的大小对初期疲劳裂纹扩展有较大的影响;应力比对16MnR钢的疲劳裂纹扩展行为没有影响;疲劳裂纹扩展速率随试样厚度的增大而增大.%16MnR steelis a most widely used material for pressure vessels.The study on fatigue is very important for safety and fatigue life assessment of pressure vessels.Several experimental researches for fatigue of 16MnR steel were conducted and test data have been gotten,but it was short of fatigue study of the material under various conditions at present.The fatigue crack growth tests of 16MnR hot-rolling steel were carried out at different temperatures and R-ratios with compact tension(CT)specimens in this paper.Different sized circular notches at the tip of the slot ranging from very sharp to blunt were used in the CT specimens and the radii of the notches were 0.1,1 and 2 mm,and the thicknesses of CT specimens were 3.8,12.5,18 and 25 mm,respectively.The fatigue crack growth performances were obtained.The effects of temperatures,notch sizes,R-ratios and specimen thickness on fatigue crack growth behaviors were studied.It was shown that the fatigue crack growth rates at 150 and 300℃were lower than those at 25 and 425℃.the lowest one was at 300℃ and the crack growth rate increased with temperature above 300℃.The great influence of notch sizes on the fatigue crack growth rate was observed at early stage of crack growth only.The results also indicated

  15. 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...

  16. A cohesive segments method for the simulation of crack growth

    NARCIS (Netherlands)

    Remmers, J.J.C.; De Borst, R.; Needleman, A.

    2003-01-01

    A numerical method for crack growth is described in which the crack is not regarded as a single discontinuity that propagates continuously. Instead, the crack is represented by a set of overlapping cohesive segments. These cohesive segments are inserted into finite elements as discontinuities in the

  17. Characterisation of Fatigue Crack Growth in Silicone for Deap Technology

    DEFF Research Database (Denmark)

    Thorup, Thor

    2012-01-01

    In this paper, the fatigue crack growth characteristics of Elastosil R RT 625 are determined by performing fatigue crack experiments based on ISO 27727. Elastosil R RT 625 is a silicone rubber used by Danfoss PolyPower A/S as the dielectric material in their DEAP elements. Cracks were characteris...

  18. Fatigue crack growth in an aluminum alloy-fractographic study

    Science.gov (United States)

    Salam, I.; Muhammad, W.; Ejaz, N.

    2016-08-01

    A two-fold approach was adopted to understand the fatigue crack growth process in an Aluminum alloy; fatigue crack growth test of samples and analysis of fractured surfaces. Fatigue crack growth tests were conducted on middle tension M(T) samples prepared from an Aluminum alloy cylinder. The tests were conducted under constant amplitude loading at R ratio 0.1. The stress applied was from 20,30 and 40 per cent of the yield stress of the material. The fatigue crack growth data was recorded. After fatigue testing, the samples were subjected to detailed scanning electron microscopic (SEM) analysis. The resulting fracture surfaces were subjected to qualitative and quantitative fractographic examinations. Quantitative fracture analysis included an estimation of crack growth rate (CGR) in different regions. The effect of the microstructural features on fatigue crack growth was examined. It was observed that in stage II (crack growth region), the failure mode changes from intergranular to transgranular as the stress level increases. In the region of intergranular failure the localized brittle failure was observed and fatigue striations are difficult to reveal. However, in the region of transgranular failure the crack path is independent of the microstructural features. In this region, localized ductile failure mode was observed and well defined fatigue striations were present in the wake of fatigue crack. The effect of interaction of growing fatigue crack with microstructural features was not substantial. The final fracture (stage III) was ductile in all the cases.

  19. Numerical simulations of material mismatch and ductile crack growth

    Energy Technology Data Exchange (ETDEWEB)

    Oestby, Erling

    2002-07-01

    Both the global geometry and inhomogeneities in material properties will influence the fracture behaviour of structures in presence of cracks. In this thesis numerical simulations have been used to investigate how some aspects of both these issues affect the conditions at the crack-tip. The thesis is organised in an introduction chapter, summarising the major findings and conclusions, a review chapter, presenting the main aspects of the developments in the field of fracture mechanics, and three research papers. Paper I considers the effect of mismatch in hardening exponent on the local near-tip stress field for stationary interface cracks in bi-materials under small scale yielding conditions. It is demonstrated that the stress level in the weaker material increases compared to what is found in the homogeneous material for the same globally applied load level, with the effect being of increasing importance as the crack-tip is approached. Although a coupling between the radial and angular dependence of the stress fields exists, the evolving stress field can still be normalised with the applied J. The effect on the increase in stress level can closely be characterised by the difference in hardening exponent, {delta}n, termed the hardening mismatch, and is more or less independent of the absolute level of hardening in the two materials. Paper II and Ill deal with the effects of geometry, specimen size, hardening level and yield stress mismatch in relation to ductile crack growth. The ductile crack growth is simulated through use of the Gurson model. In Paper H the effect of specimen size on the crack growth resistance is investigated for deep cracked bend and shallow cracked tensile specimens. At small amounts of crack growth the effect of specimen size on the crack growth resistance is small, but a more significant effect is found for larger amounts of crack growth. The crack growth resistance decreases in smaller specimens loaded in tension, whereas the opposite is

  20. Subcritical crack growth of selected aerospace pressure vessel materials

    Science.gov (United States)

    Hall, L. R.; Bixler, W. D.

    1972-01-01

    This experimental program was undertaken to determine the effects of combined cyclic/sustained loads, stress level, and crack shape on the fatigue crack growth rate behavior of cracks subjected to plane strain conditions. Material/environment combinations tested included: 2219-T87 aluminum plate in gaseous helium, room air, and 3.5% NaCl solution at room temperature, liquid nitrogen, and liquid hydrogen; 5Al-2.5 Sn (ELI) titanium plate in liquid nitrogen and liquid hydrogen and 6AL-4V (ELI) STA titanium plate in gaseous helium and methanol at room temperature. Most testing was accomplished using surface flawed specimens instrumented with a clip gage to continuously monitor crack opening displacements at the specimen surface. Tapered double cantilever beam specimens were also tested. Static fracture and ten hour sustained load tests were conducted to determine fracture toughness and apparent threshold stress intensity values. Cyclic tests were performed using sinusoidal loading profiles at 333 MHz (20 cpm) and trapezoidal loading profiles at both 8.3 MHz (0.5 cpm) and 3.3 MHz (0.2 cpm). Data were evaluated using modified linear elastic fracture mechanics parameters.

  1. Fatigue Crack Growth Fundamentals in Shape Memory Alloys

    Science.gov (United States)

    Wu, Y.; Ojha, A.; Patriarca, L.; Sehitoglu, H.

    2015-03-01

    In this study, based on a regression of the crack tip displacements, the stress intensity range in fatigue is quantitatively determined for the shape memory alloy Ni2FeGa. The results are compared to the calculated stress intensity ranges with a micro-mechanical analysis accounting for the transformation-induced tractions. The effective stress intensity ranges obtained with both methods are in close agreement. Also, the fatigue crack closure levels were measured as 30 % of the maximum load using virtual extensometers along the crack flanks. This result is also in close agreement with the regression and micro-mechanical modeling findings. The current work pointed to the importance of elastic moduli changes and the residual transformation strains playing a role in the fatigue crack growth behavior. Additional simulations are conducted for two other important shape memory alloys, NiTi and CuZnAl, where the reductions in stress intensity range were found to be lower than Ni2FeGa.

  2. The role of grain boundary structure and crystal orientation on crack growth asymmetry in aluminum

    Energy Technology Data Exchange (ETDEWEB)

    Adlakha, I. [School for Engineering of Matter, Transport, and Energy, Arizona State University, Tempe, AZ 85287 (United States); Tschopp, M.A. [U.S. Army Research Laboratory, Aberdeen Proving Ground, MD 21005 (United States); Solanki, K.N., E-mail: kiran.solanki@asu.edu [School for Engineering of Matter, Transport, and Energy, Arizona State University, Tempe, AZ 85287 (United States)

    2014-11-17

    Atomistic simulations have shown that the grain boundary (GB) structure affects a number of physical, mechanical, thermal, and chemical properties, which can have a profound effect on macroscopic properties of polycrystalline materials. The research objective herein is to use atomistic simulations to explore the role that GB structure and the adjacent crystallographic orientations have on the directional asymmetry of an intergranular crack (i.e. cleavage behavior is favored along one direction, while ductile behavior along the other direction of the interface) for aluminum grain boundaries. Simulation results from seven 〈110〉 symmetric tilt grain boundaries (STGBs) show that the GB structure and the associated free volume directly influence the stress–strain response, crack growth rate, and crack tip plasticity mechanisms for middle-tension (M(T)) crack propagation specimens. In particular, the structural units present within the GB promote whether a dislocation or twinning-based mechanism operates at the crack tip during intergranular fracture along certain GBs (e.g., the ‘E’ structural unit promotes twinning at the crack tip in Al). Furthermore, the crystallography of the adjacent grains, and therefore the available slip planes, can significantly affect the crack growth rates in both directions of the crack – this creates a strong directional asymmetry in the crack growth rate in the Σ11 (113) and the Σ27 (552) STGBs. Upon comparing these results with the theoretical Rice criterion, it was found that certain GBs in this study (Σ9 (221), Σ11 (332) and Σ33 (441)) show an absence of directional asymmetry in the observed crack growth behavior, in conflict with the Rice criterion. The significance of the present research is that it provides a physical basis for the role of GB character and crystallographic orientation on intergranular crack tip deformation behavior.

  3. Fatigue Crack Growth Threshold Testing of Metallic Rotorcraft Materials

    Science.gov (United States)

    Newman, John A.; James, Mark A.; Johnson, William M.; Le, Dy D.

    2008-01-01

    Results are presented for a program to determine the near-threshold fatigue crack growth behavior appropriate for metallic rotorcraft alloys. Four alloys, all commonly used in the manufacture of rotorcraft, were selected for study: Aluminum alloy 7050, 4340 steel, AZ91E Magnesium, and Titanium alloy Ti-6Al-4V (beta-STOA). The Federal Aviation Administration (FAA) sponsored this research to advance efforts to incorporate damage tolerance design and analysis as requirements for rotorcraft certification. Rotorcraft components are subjected to high cycle fatigue and are typically subjected to higher stresses and more stress cycles per flight hour than fixed-wing aircraft components. Fatigue lives of rotorcraft components are generally spent initiating small fatigue cracks that propagate slowly under near-threshold cracktip loading conditions. For these components, the fatigue life is very sensitive to the near-threshold characteristics of the material.

  4. Stochastic modeling of thermal fatigue crack growth

    CERN Document Server

    Radu, Vasile

    2015-01-01

    The book describes a systematic stochastic modeling approach for assessing thermal-fatigue crack-growth in mixing tees, based on the power spectral density of temperature fluctuation at the inner pipe surface. It shows the development of a frequency-temperature response function in the framework of single-input, single-output (SISO) methodology from random noise/signal theory under sinusoidal input. The frequency response of stress intensity factor (SIF) is obtained by a polynomial fitting procedure of thermal stress profiles at various instants of time. The method, which takes into account the variability of material properties, and has been implemented in a real-world application, estimates the probabilities of failure by considering a limit state function and Monte Carlo analysis, which are based on the proposed stochastic model. Written in a comprehensive and accessible style, this book presents a new and effective method for assessing thermal fatigue crack, and it is intended as a concise and practice-or...

  5. Growth of inclined fatigue cracks using the biaxial CJP model

    Directory of Open Access Journals (Sweden)

    G. Laboviciute

    2015-07-01

    Full Text Available The CJP model of crack tip stresses is a modified version of the Williams crack tip stress field which takes account of simplified stress distributions that arise from the presence of a zone of plastic deformation associated with the crack flanks and crack tip, and that act on the elastic field responsible for driving crack growth. The elastic stress field responsible for crack growth is therefore controlled by the applied loading and by the induced boundary stresses at the interface with the plastic zone. This meso-scale model of crack tip stresses leads to a modified set of crack tip stress intensity factors that include the resultant influence of plastic wake-induced crack tip shielding, and which therefore have the potential to help resolve some longstanding controversies associated with plasticity-induced closure. A full-field approach has now been developed for stress using photoelasticity and also for displacement using digital image correlation. This paper considers the characterisation of crack growth rate data with the biaxial CJP model, using compact tension specimens that contain inclined cracks at the notch tip with initial angles of 30°, 45° and 60° to the horizontal axis. Significant experimental difficulties are experienced in growing cracks in a biaxial field under uniaxial tensile loading, as the natural tendency of the crack is to turn so that it becomes perpendicular to the maximum principal stress direction. However, crack angle is not an issue in the CJP model which calculates the stress field parallel with, and perpendicular to, the crack plane. These stress components can be rotated into directions comparable with the usual KI and KII directions and used to calculate stress intensity parameters that should be directly comparable with the standard stress intensity formulations. Another difficulty arises, however, in finding published expressions for KI and KII for CT specimens with curved or kinked cracks. The CJP model

  6. Fatigue crack growth rate test using a frequency sweep method

    Institute of Scientific and Technical Information of China (English)

    Xun ZHOU; Xiao-li YU

    2008-01-01

    Fatigue crack propagation characteristics of a diesel engine crankshaft are studied by measuring the fatigue crack growth rate using a frequency sweep method on a resonant fatigue test rig. Based on the phenomenon that the system frequency will change when the crack becomes large, this method can be directly applied to a complex component or structure. Finite element analyses (FEAs) are performed to calibrate the relation between the frequency change and the crack size, and to obtain the natural frequency of the test rig and the stress intensity factor (SIF) of growing cracks. The crack growth rate i.e. da/dN-AK of each crack size is obtained by combining the testing-time monitored data and FEA results. The results show that the crack growth rate of engine crankshaft, which is a component with complex geometry and special surface treatment, is quite different from that of a pure material. There is an apparent turning point in the Paris's crack partition. The cause of the fatigue crack growth is also dis-cussed.

  7. Thermo-Mechanical Fatigue Crack Growth of RR1000

    Directory of Open Access Journals (Sweden)

    Christopher John Pretty

    2017-01-01

    Full Text Available Non-isothermal conditions during flight cycles have long led to the requirement for thermo-mechanical fatigue (TMF evaluation of aerospace materials. However, the increased temperatures within the gas turbine engine have meant that the requirements for TMF testing now extend to disc alloys along with blade materials. As such, fatigue crack growth rates are required to be evaluated under non-isothermal conditions along with the development of a detailed understanding of related failure mechanisms. In the current work, a TMF crack growth testing method has been developed utilising induction heating and direct current potential drop techniques for polycrystalline nickel-based superalloys, such as RR1000. Results have shown that in-phase (IP testing produces accelerated crack growth rates compared with out-of-phase (OOP due to increased temperature at peak stress and therefore increased time dependent crack growth. The ordering of the crack growth rates is supported by detailed fractographic analysis which shows intergranular crack growth in IP test specimens, and transgranular crack growth in 90° OOP and 180° OOP tests. Isothermal tests have also been carried out for comparison of crack growth rates at the point of peak stress in the TMF cycles.

  8. Thermo-Mechanical Fatigue Crack Growth of RR1000

    Science.gov (United States)

    Pretty, Christopher John; Whitaker, Mark Thomas; Williams, Steve John

    2017-01-01

    Non-isothermal conditions during flight cycles have long led to the requirement for thermo-mechanical fatigue (TMF) evaluation of aerospace materials. However, the increased temperatures within the gas turbine engine have meant that the requirements for TMF testing now extend to disc alloys along with blade materials. As such, fatigue crack growth rates are required to be evaluated under non-isothermal conditions along with the development of a detailed understanding of related failure mechanisms. In the current work, a TMF crack growth testing method has been developed utilising induction heating and direct current potential drop techniques for polycrystalline nickel-based superalloys, such as RR1000. Results have shown that in-phase (IP) testing produces accelerated crack growth rates compared with out-of-phase (OOP) due to increased temperature at peak stress and therefore increased time dependent crack growth. The ordering of the crack growth rates is supported by detailed fractographic analysis which shows intergranular crack growth in IP test specimens, and transgranular crack growth in 90° OOP and 180° OOP tests. Isothermal tests have also been carried out for comparison of crack growth rates at the point of peak stress in the TMF cycles. PMID:28772394

  9. Thermo-Mechanical Fatigue Crack Growth of RR1000.

    Science.gov (United States)

    Pretty, Christopher John; Whitaker, Mark Thomas; Williams, Steve John

    2017-01-04

    Non-isothermal conditions during flight cycles have long led to the requirement for thermo-mechanical fatigue (TMF) evaluation of aerospace materials. However, the increased temperatures within the gas turbine engine have meant that the requirements for TMF testing now extend to disc alloys along with blade materials. As such, fatigue crack growth rates are required to be evaluated under non-isothermal conditions along with the development of a detailed understanding of related failure mechanisms. In the current work, a TMF crack growth testing method has been developed utilising induction heating and direct current potential drop techniques for polycrystalline nickel-based superalloys, such as RR1000. Results have shown that in-phase (IP) testing produces accelerated crack growth rates compared with out-of-phase (OOP) due to increased temperature at peak stress and therefore increased time dependent crack growth. The ordering of the crack growth rates is supported by detailed fractographic analysis which shows intergranular crack growth in IP test specimens, and transgranular crack growth in 90° OOP and 180° OOP tests. Isothermal tests have also been carried out for comparison of crack growth rates at the point of peak stress in the TMF cycles.

  10. Fatigue Reliability of Deck Structures Subjected to Correlated Crack Growth

    Institute of Scientific and Technical Information of China (English)

    G.Q. Feng; Y. Garbatov; C. Guedes Soares

    2013-01-01

    The objective of this work is to analyse fatigue reliability of deck structures subjected to correlated crack growth. The stress intensity factors of the correlated cracks are obtained by finite element analysis and based on which the geometry correction functions are derived. The Monte Carlo simulations are applied to predict the statistical descriptors of correlated cracks based on the Paris-Erdogan equation. A probabilistic model of crack growth as a function of time is used to analyse the fatigue reliability of deck structures accounting for the crack propagation correlation. A deck structure is modelled as a series system of stiffened panels, where a stiffened panel is regarded as a parallel system composed of plates and are longitudinal. It has been proven that the method developed here can be conveniently applied to perform the fatigue reliability assessment of structures subjected to correlated crack growth.

  11. Improvement of the extended finite element method for ductile crack growth

    Energy Technology Data Exchange (ETDEWEB)

    Pourmodheji, R. [Department of Mechanical Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Mashayekhi, M., E-mail: mashayekhi@cc.iut.ac.ir [Department of Mechanical Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of)

    2012-08-15

    The continuum damage mechanics (CDM) model is added to the extended finite element method (XFEM) to provide a model of ductile crack growth. In this model, the criterion for crack growth in the evaluation of ductile materials is the critical damage parameter obtained from continuum damage mechanics. Numerical implementation of the CDM-XFEM model was used to simulate crack growth modeling in comparison with experimental results, and the results are presented in this paper. The CDM-XFEM model was experimentally validated by the ductile damage evolution measured in A533B1 steel through three-point bending and compact tension tests. The identification of damage parameters was performed under various conditions. The critical load at crack growth initiation, the ductile behavior of cracks and the fracture toughness, J{sub Ic}, were also predicted with the CDM-XFEM model simulations. The results confirm the potential of the CDM-XFEM model for predicting crack growth in ductile materials. Using the proposed model, crack propagation has been simulated within two examples; center inclined crack and single edged notched beam for A533B1 steel.

  12. Corrosion fatigue behavior of fastening hole structure and virtual crack propagation tests

    Institute of Scientific and Technical Information of China (English)

    Youhong Zhang; Xinlong Chang; Guozhi Lv; Hui Wang; Zhong Li; Yueliang Cheng

    2008-01-01

    The fatigue crack propagation behavior of the LY12CZ aluminum alloy fastener involving a central hole in air or in 3.5wt% NaC1 solution was investigated. The experimental results indicated that the corrosion fatigue crack growth rate decreased with the increasing loading frequency, and in a corrosive environment, the crack growth rate was slightly larger than that in air.Based on the experimental results, the virtual corrosion fatigue crack propagation tests were investigated and the stochastic process method and the AFGROW simulation method were presented. The normal process and lognormal process were considered for the stochastic process method based on the numerically fitted Paris equation. The distribution of crack size and the corresponding prob-abilistic model of crack length distribution for a given number of cycles can be found by integrating the stochastic process over time.Using the AFGROW software, the virtual simulation was carried out to analyze the corrosion fatigue crack growth behavior and the predicted crack growth curve was in good agreement with the experimental results.

  13. Moving singularity creep crack growth analysis with the /Delta T/c and C/asterisk/ integrals. [path-independent vector and energy rate line integrals

    Science.gov (United States)

    Stonesifer, R. B.; Atluri, S. N.

    1982-01-01

    The physical meaning of (Delta T)c and its applicability to creep crack growth are reviewed. Numerical evaluation of (Delta T)c and C(asterisk) is discussed with results being given for compact specimen and strip geometries. A moving crack-tip singularity, creep crack growth simulation procedure is described and demonstrated. The results of several crack growth simulation analyses indicate that creep crack growth in 304 stainless steel occurs under essentially steady-state conditions. Based on this result, a simple methodology for predicting creep crack growth behavior is summarized.

  14. An ultrasonic method for dynamic monitoring of fatigue crack initiation and growth.

    Science.gov (United States)

    Mi, Bao; Michaels, Jennifer E; Michaels, Thomas E

    2006-01-01

    Attached ultrasonic sensors can detect changes caused by crack initiation and growth if the wave path is directed through the area of critical crack formation. Dynamics of cracks opening and closing under load cause nonlinear modulation of received ultrasonic signals, enabling small cracks to be detected by stationary sensors. A methodology is presented based upon the behavior of ultrasonic signals versus applied load to detect and monitor formation and growth of cracks originating from fastener holes. Shear wave angle beam transducers operating in through transmission mode are mounted on either side of the hole such that the transmitted wave travels through the area of expected cracking. Time shift is linear with respect to load, and is well explained by path changes due to strain combined with wave speed changes due to acoustoelasticity. During subsequent in situ monitoring with unknown loads, the measured time of flight is used to estimate the load, and behavior of the received energy as a function of load is the basis for crack detection. Results are presented from low cycle fatigue tests of several aluminum specimens and illustrate the efficacy of the method in both determining the applied load and monitoring crack initiation and growth.

  15. Fatigue crack growth study of SCS6/Ti-15-3 composite

    Science.gov (United States)

    Kantzos, P.; Telesman, J.

    1990-01-01

    A study was performed to determine the fatigue crack growth (FCG) behavior and the associated fatigue damage processes in a (0)8- and (90)8-oriented SCS6/Ti-15-3 composite. Companion testing was also done on identically processed Ti-15-3 unreinforced material. The active fatigue crack growth failure processes were very similar for both composite orientations tested. For both orientations, fatigue crack growth was along the fiber direction. It was found that the composite constituent most susceptible to fatigue damage was the interface region and, in particular, the carbon coating surrounding the fiber. The failure of the interface region led to crack initiation and also strongly influenced the FCG behavior in this composite. The failure of the interface region was apparently driven by normal stresses perpendicular to the fiber direction. The FCG rates were considerably higher for the (90)8-oriented CT specimens in comparison to the unreinforced material.

  16. Analysis of steady-state ductile crack growth

    DEFF Research Database (Denmark)

    Niordson, Christian

    1999-01-01

    the finite element mesh remains fixed relative to the tip of the growing crack. Fracture is modelled using two different local crack growth criteria. One is a crack opening displacement criterion, while the other is a model in which a cohesive zone is imposed in front of the crack tip along the fracture zone......The fracture strength under quasi-static steady-state crack growth in an elastic-plastic material joined by a laser weld is analyzed. Laser welding gives high mismatch between the yield stress within the weld and the yield stress in the base material. This is due to the fast termic cycle, which....... Both models predict that in general a thinner laser weld gives higher interface strength. Furthermore, both fracture criteria show, that the preferred path of the crack is close outside the weld material; a phenomenon also observed in experiments....

  17. Crack growth analysis due to PWSCC in dissimilar metal butt weld for reactor piping considering hydrostatic and normal operating conditions

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Hwee Sueng; Huh, Nam Su [Seoul Nat' l Univ., Seoul (Korea, Republic of); Lee, Seung Gun; Park, Heung Bae [KEPCO Engineering and Construction Company, Gyeonggi (Korea, Republic of); Lee, Sung Ho [KHNP Central Research Institute, Daejeon (Korea, Republic of)

    2013-01-15

    This study investigates the crack growth behavior due to primary water stress corrosion cracking (PWSCC) in the dissimilar metal butt weld of a reactor piping using Alloy 82/182. First, detailed finite element stress analyses were performed to predict the stress distribution of the dissimilar metal butt weld in which the hydrostatic and the normal operating loads as well as the weld residual stresses were considered to evaluate the stress redistribution due to mechanical loadings. Based on the stress distributions along the wall thickness of the dissimilar metal butt weld, the crack growth behavior of the postulated axial and circumferential cracks were predicted, from which the crack growth diagram due to PWSCC was proposed. The present results can be applied to predict the crack growth rate in the dissimilar metal butt weld of reactor piping due to PWSCC.

  18. Effect of band-overload on fatigue crack growth rate of HSLA steel

    Science.gov (United States)

    Abhinay, S. V.; Tenduwe, Om Prakash; Kumar, Ajit; Dutta, K.; Verma, B. B.; Ray, P. K.

    2015-02-01

    Fatigue crack growth behavior is important parameter of structural materials. This parameters can be used to predict their life, service reliability and operational safety in different conditions. The material used in this investigation is an HSLA steel. In this investigation effect of single overload and band-overload on fatigue crack growth of same steel are studied using compact tension (CT) specimens under mode-I condition and R=0.3. It is observed that overload and band-overload applications resulted retardation on the fatigue crack growth rate in most of the cases. It is also noticed that maximum retardation took place on application of seven successive overload cycles. Application of ten and more overload cycles caused no crack growth retardation.

  19. Fracture Mechanical Markov Chain Crack Growth Model

    DEFF Research Database (Denmark)

    Gansted, L.; Brincker, Rune; Hansen, Lars Pilegaard

    1991-01-01

    On the basis of the B-model developed in [J. L. Bogdanoff and F. Kozin, Probabilistic Models of Cumulative Damage. John Wiley, New York (1985)] a new numerical model incorporating the physical knowledge of fatigue crack propagation is developed. The model is based on the assumption that the crack...

  20. Prediction of Crack Growth in Aqueous Environments.

    Science.gov (United States)

    1986-07-01

    Impedance for the Propagation of a Crack Through HY80 Steel in 3.5Z NaCl Solution at 25*C Under Sinusoidal Loading Condi t ions...THE PROPAGATION OF A CRACK THROUGH HY80 STEEL IN 3.5% NaCI SOLUTION AT 25°C UNDER SINUSOIDAL LOADING CONDITIONS 49 and the properties of greatest...VELOCITY AS A FUNCTION OF TIME FOR A CRACK GROWN AT CONSTANT CURRENT IN HY80 STEEL Initial conditions CI in Table 5. 66 400 UJ x v> l/> L. 0

  1. Fatigue crack growth prediction in 2xxx AA with friction stir weld HAZ properties

    Directory of Open Access Journals (Sweden)

    A. Tzamtzis

    2016-02-01

    Full Text Available An analytical model is developed to predict fatigue crack propagation rate under mode I loading in 2024 aluminum alloy with FSW HAZ material characteristics. Simulation of the HAZ local properties in parent 2024 AA was performed with overaging using specific heat treatment conditions. The model considers local cyclic hardening behavior in the HAZ to analyze crack growth. For the evaluation of the model, the analytical results have been compared with experimental fatigue crack growth on overaged 2024 alloy simulating material behavior at different positions within the HAZ. The analytical results showed that cyclic hardening at the crack tip can be used successfully with the model to predict FCG in a material at overaged condition associated with a location in the FSW HAZ.

  2. Standard test method for creep-fatigue crack growth testing

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2010-01-01

    1.1 This test method covers the determination of creep-fatigue crack growth properties of nominally homogeneous materials by use of pre-cracked compact type, C(T), test specimens subjected to uniaxial cyclic forces. It concerns fatigue cycling with sufficiently long loading/unloading rates or hold-times, or both, to cause creep deformation at the crack tip and the creep deformation be responsible for enhanced crack growth per loading cycle. It is intended as a guide for creep-fatigue testing performed in support of such activities as materials research and development, mechanical design, process and quality control, product performance, and failure analysis. Therefore, this method requires testing of at least two specimens that yield overlapping crack growth rate data. The cyclic conditions responsible for creep-fatigue deformation and enhanced crack growth vary with material and with temperature for a given material. The effects of environment such as time-dependent oxidation in enhancing the crack growth ra...

  3. Simulating Fatigue Crack Growth in Spiral Bevel Gears

    Science.gov (United States)

    Spievak, Lisa E.; Wawrzynek, Paul A.; Ingraffea, Anthony R.

    2000-01-01

    The majority of helicopter transmission systems utilize spiral bevel gears to convert the horizontal power from the engine into vertical power for the rotor. Due to the cyclical loading on a gear's tooth, fatigue crack propagation can occur. In rotorcraft applications, a crack's trajectory determines whether the gear failure will be benign or catastrophic for the aircraft. As a result, the capability to predict crack growth in gears is significant. A spiral bevel gear's complex shape requires a three dimensional model of the geometry and cracks. The boundary element method in conjunction with linear elastic fracture mechanics theories is used to predict arbitrarily shaped three dimensional fatigue crack trajectories in a spiral bevel pinion under moving load conditions. The predictions are validated by comparison to experimental results. The sensitivity of the predictions to variations in loading conditions and crack growth rate model parameters is explored. Critical areas that must be understood in greater detail prior to predicting more accurate crack trajectories and crack growth rates in three dimensions are identified.

  4. Frequency dependence of fatigue and corrosion fatigue crack growth rate

    Energy Technology Data Exchange (ETDEWEB)

    Marvasti, Mohammad Hassan; Chen, Weixing [Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB (Canada); Kania, Richard; Worthingham, Robert [TransCanada Pipelines Limited, Calgary, AB (Canada); Van Boven, Gregory [Spectra Energy Transmission Limited, Vancouver, BC (Canada)

    2010-07-01

    It was in the mid-1980s that stress corrosion cracking (SCC) was first found in near-neutral pH conditions on the TransCanada pipeline system. Since then, there have been many reports of pipeline cracking in Canada in these conditions. The huge quantity of pipelines in Canada and the number of failures have brought great interest in investigation of this cracking. A study was conducted on one X52 pipeline steel. It used compact tension specimens for corrosion fatigue and fatigue tests in air. The following conclusions were drawn: 1) crack growth in near-neutral pH conditions can be explained by a factor, which reflects the combined action of the mechanical driving force and the hydrogen effects; 2) mechanical dormancy can be common when oil and gas pipelines are in operation; 3) hydrogen is a determining factor of crack growth when pipeline steels are exposed to near-neutral pH conditions.

  5. Crack growth threshold under hold time conditions in DA Inconel 718 – A transition in the crack growth mechanism

    Directory of Open Access Journals (Sweden)

    E. Fessler

    2016-01-01

    Full Text Available Aeroengine manufacturers have to demonstrate that critical components such as turbine disks, made of DA Inconel 718, meet the certification requirements in term of fatigue crack growth. In order to be more representative of the in service loading conditions, crack growth under hold time conditions is studied. Modelling crack growth under these conditions is challenging due to the combined effect of fatigue, creep and environment. Under these conditions, established models are often conservative but the degree of conservatism can be reduced by introducing the crack growth threshold in models. Here, the emphasis is laid on the characterization of crack growth rates in the low ΔK regime under hold time conditions and in particular, on the involved crack growth mechanism. Crack growth tests were carried out at high temperature (550 °C to 650 °C under hold time conditions (up to 1200 s in the low ΔK regime using a K-decreasing procedure. Scanning electron microscopy was used to identify the fracture mode involved in the low ΔK regime. EBSD analyses and BSE imaging were also carried out along the crack path for a more accurate identification of the fracture mode. A transition from intergranular to transgranular fracture was evidenced in the low ΔK regime and slip bands have also been observed at the tip of an arrested crack at low ΔK. Transgranular fracture and slip bands are usually observed under pure fatigue loading conditions. At low ΔK, hold time cycles are believed to act as equivalent pure fatigue cycles. This change in the crack growth mechanism under hold time conditions at low ΔK is discussed regarding results related to intergranular crack tip oxidation and its effect on the crack growth behaviour of Inconel 718 alloy. A concept based on an “effective oxygen partial pressure” at the crack tip is proposed to explain the transition from transgranular to intergranular fracture in the low ΔK regime.

  6. High Temperature Fatigue Crack Growth Rate of G91 Steel with Applying 30 Seconds Hold Time

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jong Bum; Park, Chang Gyu; Koo, Gyeong Hoi [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Lee, Jong Hoon [Sungkyunkwan University, Suwon (Korea, Republic of); Kim, Bum Joon [Osan Univ., Osan (Korea, Republic of)

    2015-05-15

    Subsection NH since 2004. The database of creep and creep-fatigue crack growth rate of G91 steel is necessary for the structural integrity evaluation of the SFR structures because the database of these properties of materials is insufficient through the world. Moreover, it is difficult to use the database which is gained by the research center of advanced countries because it is not to be opened. Therefore, it is necessary to make an effort to get the database of material properties. Creep-fatigue crack initiation and growth tests for a G91 tubular specimen, including a machined defect, have been performed by Kim and it attempted to assess a high temperature crack behavior of G91 side plate specimen by Lee. Creep-fatigue crack growth rate were compared in terms of different temperature range. Tests were performed at temperatures of 500, 550 and 600, respectively. Stress ratio was set to 0.1 and trapezoidal shape of stress condition was applied to the specimens to perform the creep-fatigue crack growth rate tests. Each specimen's surface was polished and fatigue pre-crack was manufactured by fatigue test before the high temperature test. And DCPD method was adopted to measure the crack length in the high temperature.

  7. Testing study of subcritical crack growth rate and fracture toughness in different rocks

    Institute of Scientific and Technical Information of China (English)

    CAO Ping; LI Jiang-teng; YUAN Hai-ping

    2006-01-01

    Subcritical crack growth of double torsion specimens made of ore, lherzolite, marble and granite was studied using Instron1342 type electro hydraulic servo test machine. The relations of the mode-Ⅰ stress intensity factor KI versus the subcritical crack growth velocity v and the fracture toughness KIC were obtained by the double torsion constant displacement load relaxation method. The behavior of subcritical crack growth was analyzed for different rocks. The results show that lgKI-lgv relations of four kinds of rocks measured by this method accord with linear rule, i.e. the relations between subcritical crack growth velocity and stress intensity factor have a power law, which is in good agreement with CHARLES theory. lgKI-lgv curves move to top left corner with the decrease of the elastic modulus, which implies that the subcritical crack growth velocity speeds up. The maximum subcritical crack growth velocity exhibits negative exponential increase, and mode-Ⅰ fracture toughness KIC decreases with the decrease of elastic modulus. The testing results provide a basis for time-dependence of rock engineering stability.

  8. Fatigue Crack Growth on Double Butt Weld with Toe Crack of Pipelines Steel

    OpenAIRE

    HADJOUI, Féthi; Benachour, Mustapha; Benguediab,Mohamed

    2012-01-01

    The welded structures have a broad applicability (car industry, aeronautical, marine, pipelines, etc.). The welding being an assembled process, presents both advantages and disadvantages. A simple existing defect after welding can generate a catastrophic fracture. This work studies the fatigue crack growth of double butt weld with toe crack. Two types of pipeline material are studied with knowing API 5L grades X60 and X70 where tension form of loading is applied. In order to p...

  9. Influence of hydrogen environments on crack growth in Inconel 718

    Science.gov (United States)

    Walter, R. J.; Chandler, W. T.

    1978-01-01

    The effect of hydrogen environments on sustained-load and cyclic-load crack growth in Inconel 718 was investigated using fracture-mechanics-type specimens. The sustained-load crack growth was determined to be a function of heat-treatment condition, temperature, and hydrogen pressure. The threshold stress intensity for subcritical crack growth was independent of hydrogen pressure at pressures greater than 21 MN/sq m (3000 psi). The cyclic-load crack growth rate in Inconel 718 at low and moderate stress intensity ranges increased with increasing hydrogen pressure. Decreasing the cyclic frequency from 1.0 to 0.1 Hz considerably increased the cyclic crack growth rate at 0.069 MN/sq m (10 psi) and at 68.9 MN/sq m (10,000 psi) hydrogen pressure. A series of measurements performed between 1.0 and 0.1 Hz showed that the crack growth rate increased as a complex function of the time per cycle.

  10. Anomolous Fatigue Crack Growth Phenomena in High-Strength Steel

    Science.gov (United States)

    Forth, Scott C.; James, Mark A.; Johnston, William M., Jr.; Newman, James C., Jr.

    2004-01-01

    The growth of a fatigue crack through a material is the result of a complex interaction between the applied loading, component geometry, three-dimensional constraint, load history, environment, material microstructure and several other factors. Previous studies have developed experimental and computational methods to relate the fatigue crack growth rate to many of the above conditions, with the intent of discovering some fundamental material response, i.e. crack growth rate as a function of something. Currently, the technical community uses the stress intensity factor solution as a simplistic means to relate fatigue crack growth rate to loading, geometry and all other variables. The stress intensity factor solution is a very simple linear-elastic representation of the continuum mechanics portion of crack growth. In this paper, the authors present fatigue crack growth rate data for two different high strength steel alloys generated using standard methods. The steels exhibit behaviour that appears unexplainable, compared to an aluminium alloy presented as a baseline for comparison, using the stress intensity factor solution.

  11. Influence of chemical liquids on the fatigue crack growth of the AZ31 magnesium alloy

    Science.gov (United States)

    Wang, Zhang-Zhong; He, Xian-Cong; Bai, Yun-Qiang; Ba, Zhi-Xin; Dai, Yu-Ming; Zhou, Heng-Zhi

    2012-03-01

    The fatigue crack growth behavior of an AZ31 magnesium alloy was investigated by comparing the effect of zirconate and phosphate chemical liquids. The morphology, components, and phase compositions of the chemical depositions at the fatigue crack tip were analyzed by employing scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), respectively. For samples with and without the chemical liquids, their stress-intensity factor values at the fatigue crack tip were compared by using a stress-strain gauge. The results demonstrated that a zirconate film (Zr x O y ·Zn x O y ) and a phosphate film (Zn3(PO4)2·4H2O and MgZnP2O7) could be formed on the fatigue crack-surface at the fatigue crack tip. The stress distribution was changed because of the chemical depositions and the causticity of the chemical liquids. This could decrease the stress-intensity factor value and thus effectively cause fatigue crack closure, which reduces the fatigue crack growth rate. Moreover, it was found that the fatigue crack closure effect of zirconates was more positive than that of phosphates.

  12. 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.

  13. 疲劳裂纹扩展行为的跨尺度分析方法%MULTISCALING ANALYSIS APPROACH OF FATIGUE CRACK GROWTH BEHAVIOR

    Institute of Scientific and Technical Information of China (English)

    唐雪松; 赵小鹏

    2012-01-01

    By taking the dual-scale strain energy density factor as controlling quantity,a multiscaling fatigue crack growth model is developed in this work.Hence,the whole fatigue failure process can be depicted in a consistent way by applying the proposed model.It no longer needs dividing a fatigue process into two different stages of fatigue crack initiation and propagation described by different approaches as usual.Then,the experimental S-N curves for different cyclic stress ratios are exactly re-produced by the proposed model.When the effects of material micro-structure are taken into account,the discrete fatigue test data can be re-produced.The results indicate that the size of initial micro-defects as well as the different evolution modes of material micro-structure have a pronounced influence on the fatigue life of specimens.The microscopic effect is a main reason of the scatter of fatigue test data.%该文以跨尺度应变能密度因子作为裂纹扩展的控制参量,建立了跨尺度疲劳裂纹扩展模型。疲劳破坏全过程可用该模型进行统一描述,而不必划分成疲劳裂纹形成与扩展两个不同阶段,采用不同的理论分别进行分析。以LY12铝合金板为例,采用上述模型,精确拟合出不同循环特征下的S-N试验曲线。当考虑材料微结构的影响时,疲劳试验数据的发散性也可拟合出来。研究表明:材料初始缺陷及微结构在疲劳过程中的演化特性,对于构件的疲劳寿命有显著影响,是疲劳试验数据发散的主要原因。

  14. Thermomechanical fatigue crack growth in a cast polycrystalline superalloy

    Directory of Open Access Journals (Sweden)

    Moverare Johan J.

    2014-01-01

    Full Text Available Thermomechanical fatigue (TMF crack growth testing has been performed on the polycrystalline superalloy IN792. All tests were conducted in mechanical strain control in the temperature range between 100 and 750 °C. The influence of in-phase (IP and out-of-phase (OP TMF cycles was investigated as well as the influence of applying extended dwell times (up to 6 hours at the maximum temperature. The crack growth rates were also evaluated based on linear elastic fracture mechanics and described as a function of the stress intensity factor KI. Without dwell time at the maximum temperature, the crack growth rates are generally higher for the OP-TMF cycle compared to the IP-TMF cycle, when equivalent nominal strain ranges are compared. However, due to the fact that the tests were conducted in mechanical strain control, the stress response is very different for the IP and OP cycles. Also the crack closure level differs significantly between the cycle types. By taking the stress response into account and comparing the crack growth rates for equivalent effective stress intensity factor rages ΔKeff defined as Kmax − Kclosure, very similar crack growth rates were actually noticed independent of whether an IP or OP cycle were used. While the introduction of a 6 hour dwell time significantly increased the crack growth rates for the IP-TMF cycle, a decrease in crack growth rates versus ΔKeff were actually seen for the OP-TMF cycle. The fracture behaviour during the different test conditions has been investigated using scanning electron microscopy.

  15. Dynamic crack growth in a nonlocal progressively cavitating solid

    DEFF Research Database (Denmark)

    Needleman, A.; Tvergaard, Viggo

    1998-01-01

    Dynamic crack growth is analyzed numerically using a nonlocal constitutive formulation for a porous ductile material. The delocalization relates to the void growth and coalescence mechanism and is incorporated in terms of an integral condition on the rate of increase of the void volume fraction....... The material is modeled as elastic-viscoplastic with the thermal softening due to adiabatic heating accounted for. Finite element computations are carried our for edge cracked specimens subject to tensile impact loading. Two values of the material characteristic length and two finite-element discretizations...... to increase and the crack speed to decrease with increasing values of the material characteristic length. The crack growth predictions using the nonlocal constitutive model exhibit less mesh sensitivity than the corresponding ones based on the local constitutive relation. However, for the largest value...

  16. Thermographic characterization of stress during crack growth

    Science.gov (United States)

    Cramer, K. E.; Dawicke, David S.; Welch, Christopher S.

    1992-01-01

    A full-field-thermographic technique for imaging stress patterns in dynamically loaded structures using general purpose IR imaging and image processing hardware is described. The inspection technique is based on the thermoelastic effect. A simple geometry is examined, and the experimentally determined values for the stress invariant are shown to be consistent with theoretical and numerical calculations. The application of full-field-thermographic measurement would ensure that the observed stress field has a common sampling period, thus allowing the observation of rapidly occurring stress anomalies such as the propagation of a fatigue crack. Fatigue crack propagation in two consecutive thermoelastic stress images from an aluminum sample is shown.

  17. Microstructural mechanisms of cyclic deformation, fatigue crack initiation and early crack growth.

    Science.gov (United States)

    Mughrabi, Haël

    2015-03-28

    In this survey, the origin of fatigue crack initiation and damage evolution in different metallic materials is discussed with emphasis on the responsible microstructural mechanisms. After a historical introduction, the stages of cyclic deformation which precede the onset of fatigue damage are reviewed. Different types of cyclic slip irreversibilities in the bulk that eventually lead to the initiation of fatigue cracks are discussed. Examples of trans- and intercrystalline fatigue damage evolution in the low cycle, high cycle and ultrahigh cycle fatigue regimes in mono- and polycrystalline face-centred cubic and body-centred cubic metals and alloys and in different engineering materials are presented, and some microstructural models of fatigue crack initiation and early crack growth are discussed. The basic difficulties in defining the transition from the initiation to the growth of fatigue cracks are emphasized. In ultrahigh cycle fatigue at very low loading amplitudes, the initiation of fatigue cracks generally occupies a major fraction of fatigue life and is hence life controlling.

  18. Fatigue crack growth in Aluminium Alloys

    NARCIS (Netherlands)

    Van Kranenburg, C.

    2010-01-01

    Fatigue is a gradual process of local strength reduction. It is a phenomenon of damage accumulation at stress concentrations caused by fluctuating stresses and/or strains. In metals this results in microscopic cracks. These will start to grow under continued cyclic loading until final failure occurs

  19. Estimating crack growth in temperature damaged concrete

    Science.gov (United States)

    Recalde, Juan Jose

    2009-12-01

    Evaluation of the structural condition of deteriorated concrete infrastructure and evaluation of new sustainable cementitious materials require an understanding of how the material will respond to applied loads and environmental exposures. A fundamental understanding of how microstructural changes in these materials relate to changes in mechanical properties and changes in fluid penetrability is needed. The ability to provide rapid, inexpensive assessment of material characteristics and relevant engineering properties is valuable for decision making and asset management purposes. In this investigation, the effects of changes in dynamic elastic properties with water content and fluid penetrability properties before and after a 300°C exposure were investigated based on estimates of the crack density parameter from dry and saturated cracked media. The experimental and analytical techniques described in this dissertation allow calculation of a value for the crack density parameter using nondestructive determination of wet and dry dynamic shear modulus of relatively thin disks. The techniques were used to compare a conventional concrete mixture to several mixtures with enhanced sustainability characteristics. The three enhanced sustainable materials investigated were a very high fly ash mixture, a magnesium phosphate cement based mortar, and a magnesium phosphate cement based concrete, and were compared to a conventional concrete mixture. The analysis provided both quantitative assessment of changes with high temperature damage and autogenous healing, and estimates of changes in mean crack trace lengths. The results showed that water interaction, deterioration due to damage, and autogenous healing recovery were different for the magnesium phosphate cement based mixtures than the portland cement based concrete mixtures. A strong correlation was found between log-transformed Air Permeability Index, dynamic shear modulus, and crack density parameter. The findings imply

  20. The effect of fatigue cracks on fastener flexibility, load distribution, and fatigue crack growth

    Science.gov (United States)

    Whitman, Zachary Layne

    Fatigue cracks typically occur at stress risers such as geometry changes and holes. This type of failure has serious safety and economic repercussions affecting structures such as aircraft. The need to prevent catastrophic failure due to fatigue cracks and other discontinuities has led to durability and damage tolerant methodologies influencing the design of aircraft structures. Holes in a plate or sheet filled with a fastener are common fatigue critical locations in aircraft structure requiring damage tolerance analysis (DTA). Often, the fastener is transferring load which leads to a loading condition involving both far-field stresses such as tension and bending, and localized bearing at the hole. The difference between the bearing stress and the tensile field at the hole is known as load transfer. The ratio of load transfer as well as the magnitude of the stresses plays a significant part in how quickly a crack will progress to failure. Unfortunately, the determination of load transfer in a complex joint is far from trivial. Many methods exist in the open literature regarding the analysis of splices, doublers and attachment joints to determine individual fastener loads. These methods work well for static analyses but greater refinement is needed for crack growth analysis. The first fastener in a splice or joint is typically the most critical but different fastener flexibility equations will all give different results. The constraint of the fastener head and shop end, along with the type of fastener, affects the stiffness or flexibility of the fastener. This in turn will determine the load that the fastener will transfer within a given fastener pattern. However, current methods do not account for the change in flexibility at a fastener as the crack develops. It is put forth that a crack does indeed reduce the stiffness of a fastener by changing its constraint, thus lessening the load transfer. A crack growth analysis utilizing reduced load transfer will result in

  1. Phase-field study of grain boundary tracking behavior in crack-seal microstructures

    CERN Document Server

    Ankit, Kumar; Selzer, Michael; Reichardt, Mathias

    2012-01-01

    In order to address the vein-growth problem in geology, a multi-phase-field model is used to capture the dynamics of crystals precipitating from a super-saturated solution. To gain a complete understanding, we investigate the influence of various boundary conditions on crystal growth (free-growth and crack-sealing) that result in formation of vein microstructures. To begin with, we consider the anisotropy in surface energy to simulate crystals (with flat facets and sharp corners) possessing different orientations and study the resulting growth competition to deduce a consistent orientation selection rule in the free-growth regime. Next, from crack-sealing simulations, we co-relate the grain boundary tracking behavior and the relative rates of crack opening and trajectory, initial grain size and wall roughness. Further, we illustrate how these parameters induce the microstructural transition between blocky (crystals growing anisotropically) to fibrous morphology (isotropic) and formation of grain boundaries. T...

  2. Crack growth rate in core shroud horizontal welds using two models for a BWR

    Energy Technology Data Exchange (ETDEWEB)

    Arganis Juárez, C.R., E-mail: carlos.arganis@inin.gob.mx; Hernández Callejas, R.; Medina Almazán, A.L.

    2015-05-15

    Highlights: • Two models were used to predict SCC growth rate in a core shroud of a BWR. • A weld residual stress distribution with 30% stress relaxation by neutron was used. • Agreement is shown between the measurements of SCC growth rate and the predictions. • Slip–oxidation model is better at low fluences and empirical model at high fluences. - Abstract: An empirical crack growth rate correlation model and a predictive model based on the slip–oxidation mechanism for Stress Corrosion Cracking (SCC) were used to calculate the crack growth rate in a BWR core shroud. In this study, the crack growth rate was calculated by accounting for the environmental factors related to aqueous environment, neutron irradiation to high fluence and the complex residual stress conditions resulting from welding. In estimating the SCC behavior the crack growth measurements data from a Boiling Water Reactor (BWR) plant are referred to, and the stress intensity factor vs crack depth throughout thickness is calculated using a generic weld residual stress distribution for a core shroud, with a 30% stress relaxation induced by neutron irradiation. Quantitative agreement is shown between the measurements of SCC growth rate and the predictions of the slip–oxidation mechanism model for relatively low fluences (5 × 10{sup 24} n/m{sup 2}), and the empirical model predicted better the SCC growth rate than the slip–oxidation model for high fluences (>1 × 10{sup 25} n/m{sup 2}). The relevance of the models predictions for SCC growth rate behavior depends on knowing the model parameters.

  3. Fatigue crack growth behaviour of Al-Li alloys

    Science.gov (United States)

    Saravanakumar, R.; Ramakrishna, K. S.; Kanna, B. Avinash

    2013-06-01

    Al-Li alloys are being used in aircraft structures due to its low density and inherent mechanical properties. Fatigue Crack Growth (FCG) resistance is usually high compared to conventional Al-alloys attributed to increased modulus and crack closure. Extensive investigations concern about the FCG resistance and crack closure in Al-Li alloys. The present work reviews the FCG resistance in Al-Li alloys and the mechanisms associated with it. The alloy 8090 is taken for the consideration and sometimes compared with 2024.

  4. SEM in-situ investigation on fatigue cracking behavior of P/M Rene95 alloy with surface inclusions

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The low-cycle fatigue behavior of powder metallurgy Rene95 alloy containing surface inclusions was investigated by in-situ observation with scanning electron microscopy (SEM). The process of fatigue crack initiation and early stage of propagation behavior indicates that fatigue crack mainly occurs at the interface between the inclusion and the matrix. The effect of inclusion on the fatigue crack initiation and the early stage of crack growth was very obvious. The fatigue crack growth path in the matrix is similar to the shape of inclusion made on the basis of fatigue fracture image analysis. The empiric relation between the surface and inside crack growth length, near a surface inclusion, can be expressed. Therefore, the fatigue crack growth rate or life of P/M Rene95 alloy including the inclusions can be evaluated on the basis of the measurable surface crack length parameter. In addition, the effect of two inclusions on the fatigue crack initiation behavior was investigated by the in-situ observation with SEM.

  5. Small-crack test methods

    Science.gov (United States)

    Larsen, James M.; Allison, John E.

    This book contains chapters on fracture mechanics parameters for small fatigue cracks, monitoring small-crack growth by the replication method, measurement of small cracks by photomicroscopy (experiments and analysis), and experimental mechanics of microcracks. Other topics discussed are the real-time measurement of small-crack-opening behavior using an interferometric strain/displacement gage; direct current electrical potential measurement of the growth of small cracks; an ultrasonic method for the measurement of the size and opening behavior of small fatigue cracks; and the simulation of short crack and other low closure loading conditions, utilizing constant K(max) Delta-K-decreasing fatigue crack growth procedures.

  6. Monitoring of fatigue crack growth using guided ultrasonic waves

    Science.gov (United States)

    Masserey, B.; Kostson, E.; Fromme, P.

    2010-04-01

    Varying loading conditions of aircraft structures result in stress concentration at fastener holes, where multi layer components are connected, possibly leading to the development of fatigue cracks. Guided ultrasonic waves propagating along a structure allow in principle for the efficient non-destructive testing of large plate-like structures, such as aircraft wings. This contribution presents a study of the detection and monitoring of fatigue crack growth using both low frequency and higher frequency guided ultrasonic wave modes. Two types of structures were used, single layer aluminum tensile specimens, and multi layer structures consisting of two adhesively bonded aluminum plate-strips. Fatigue experiments were carried out and it was shown that fatigue crack detection and growth monitoring at a fastener hole during cyclic loading using both guided wave types is possible. The sensitivity and repeatability of the measurements were ascertained, having the potential for fatigue crack detection at critical and difficult to access fastener locations. Good agreement was observed between the experimental results and predictions from full three-dimensional numerical simulations of the scattering of the low frequency guided ultrasonic wave at the fastener hole and crack. The robustness of the methodology for practical in-situ ultrasonic monitoring of fatigue crack growth is discussed.

  7. Methodology to evaluate the crack growth rate by stress corrosion cracking in dissimilar metals weld in simulated environment of PWR nuclear reactor

    Energy Technology Data Exchange (ETDEWEB)

    Paula, Raphael G.; Figueiredo, Celia A.; Rabelo, Emerson G., E-mail: raphaelmecanica@gmail.com, E-mail: caf@cdtn.br, E-mail: egr@cdtn.br [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)

    2013-07-01

    Inconel alloys weld metal is widely used to join dissimilar metals in nuclear reactors applications. It was recently observed failures of weld components in plants, which have triggered an international effort to determine reliable data on the stress corrosion cracking behavior of this material in reactor environment. The objective of this work is to develop a methodology to determine the crack growth rate caused by stress corrosion in Inconel alloy 182, using the specimen (Compact Tensile) in simulated PWR environment. (author)

  8. Fatigue crack growth from narrow-band Gaussian spectrum loading in 6063 aluminum alloy

    Energy Technology Data Exchange (ETDEWEB)

    Veers, P.S.; Van Den Avyle, J.A.

    1990-01-01

    Constant amplitude and narrow-band Gaussian loadings are applied to extruded 6063 aluminum crack-growth specimens in an effort to characterize the effective stress intensity levels during random loading. Crack-growth rates are determined for constant amplitude loadings at stress ratios (R) of 0.09, 0.3 and 0.5, and for a variable amplitude loading simulated to match a narrow-band Gaussian spectrum. Crack-opening stress levels measured by the compliance method during the constant amplitude loading are found to differ substantially for -T5 and -T6 heat treatments due to a change from intergranular to transgranular crack growth. Crack-opening load ratios correlate well with the maximum applied stress intensity factor, K{sub max}, for the -T5 material. The K{sub max} dependence leads to an effective halving of the crack-growth exponent. Calculated variable amplitude lives are much shorter when this correlation is taken into account (an acceleration effect) and show a greater difference between loading blocks condensed by racetrack filtering at threshold levels of two and four standard deviations, similar to what was observed in the tests. Crack-opening-load measurements in one specimen with the narrow-band Gaussian (variable amplitude) loading failed to detect any closure. A substantial difference in the closure behavior of nominally identical R = .3 tests indicates that closure may occur irregularly in the extruded aluminum. Calculated crack-growth lives, assuming no closure in the variable amplitude tests, are much shorter than the test results. Including closure in the variable amplitude loadings greatly improves the predictions. 14 refs., 16 figs.

  9. Effects of microscale inertia on dynamic ductile crack growth

    Science.gov (United States)

    Jacques, N.; Mercier, S.; Molinari, A.

    2012-04-01

    The aim of this paper is to investigate the role of microscale inertia in dynamic ductile crack growth. A constitutive model for porous solids that accounts for dynamic effects due to void growth is proposed. The model has been implemented in a finite element code and simulations of crack growth in a notched bar and in an edge cracked specimen have been performed. Results are compared to predictions obtained via the Gurson-Tvergaard-Needleman (GTN) model where micro-inertia effects are not accounted for. It is found that microscale inertia has a significant influence on the crack growth. In particular, it is shown that micro-inertia plays an important role during the strain localisation process by impeding void growth. Therefore, the resulting damage accumulation occurs in a more progressive manner. For this reason, simulations based on the proposed modelling exhibit much less mesh sensitivity than those based on the viscoplastic GTN model. Microscale inertia is also found to lead to lower crack speeds. Effects of micro-inertia on fracture toughness are evaluated.

  10. Crack growth time dependence analysis of granite under compressive-shear stresses state

    Institute of Scientific and Technical Information of China (English)

    LI Jiang-teng; CAO Ping; Gu De-sheng; Wu Chao

    2008-01-01

    The curves of crack relative length //b and crack growth time t of granite were gained under compressive stresses state according to subcritical crack growth parameters and crack stability growth equation by double-torsion constant displacement load relaxa-tion method. The relations between crack relative length and the crack growth time were discussed under different stresses and different crack lengths. The results show that there is a turning point on curve of crack relative length //b and crack growth time of granite. The slope of curve is small when crack relative length is less than the vertical coordinate of the point, and crack grows stably in this case. Cracks grow, encounter and integrate catastro-phically when crack relative length is more than the vertical coordinate of the point, and there is not a gradual stage from crack stability growth to crack instability growth, i.e. rock mass instability is sudden. The curves of crack relative length //b and crack growth time t of granite move to right with decrease of stress σ1 or crack length a, which implies that limit time increases consequently. The results correspond to practicality.

  11. On the Effects of Temperature and Loading Frequency on the Fatigue Crack Growth Rate of G91 Steel

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jongbum; Park, Changgyu [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Lee, Jonghoon; Lim, Byeongsoo [Sungkyunkwan Univ., Suwon (Korea, Republic of); Kim, Bumjoon [Osan Univ., Osan (Korea, Republic of)

    2014-05-15

    The material data of fatigue crack growth and creep crack growth for robust structural integrity evaluations lacks in Subsection NH while it provides material properties of G91 steel for design purposes at high temperature conditions. Creep-fatigue crack initiation and growth tests for a G91 tubular specimen, including a machined defect, have been performed by Kim and it attempted to assess a high temperature crack behavior of G91 side plate specimen by Lee. The fatigue crack growth tests of a G91 compact tension (CT) specimen were performed by Kim at three different temperatures (500 .deg. C, 550 .deg. C, and 600 .deg. C), three loading frequencies (0.1Hz, 1Hz, and 20Hz), and two loading ratio values of 0.1 and 0.3, respectively; thus total 18 test conditions were applied. In this study, complementary tests were performed for selected 8 test conditions among total 18 test conditions to assess the effects of temperature and loading frequency on the fatigue crack growth rate of G91 steel and the test results were discussed. It is known that the fatigue crack growth rate increases as loading frequency decreases, as temperature increases, and load ratio (R) increases, it depends on the test conditions and relative sensitivity. In this study, the fatigue crack growth tests for a G91 compact tension specimen were performed for a various loading frequencies, loading ratios, and temperatures. As shown in Fig. 5 ∼ Fig. 10, it was confirmed that the fatigue crack growth rate increases apparently as temperature increases. The effects of loading frequency and load ratio were assessed by comparing above results and it was found that the fatigue crack growth increases as loading frequency decreases from 20Hz to 0.1Hz and load ratio increases from 0.1 to 0.3. Collected data for high temperature fatigue crack growth of G91 steel would be utilized for the structural integrity assessment of SFR components.

  12. Characterization of Fatigue Crack Growth Behavior in LENS Fabricated Ti-6Al-4V Using High-Energy Synchrotron X-Ray Microtomography (Postprint)

    Science.gov (United States)

    2016-03-30

    the likelihood of crack initiation from the ompeting spot welds or pores instead of the initial flaw yields ow success rate during experimentation...Deposited Ti-6Al-4V and Inconel 718, ICAF, Bridg. Gap Between Theory Oper. Pract., Springer, The Netherlands, 2009, pp. 1261–1274. [9] L. Bian, S.M

  13. Environmental stress cracking of PVC and PVC-CPE - Part III Crack growth

    NARCIS (Netherlands)

    Breen, J.

    1995-01-01

    The fracture toughness of Polyvinylchloride (PVC) and PVC modified with 10% chlorinated polyethylene (PVC-CPE) was studied in vapour and in liquid environments by crack growth measurements on single-edge notch specimens under three-point bending at 23°C. In addition, some results obtained in air at

  14. Constitutive Mixed Mode Behavior of Cracks in Concrete

    DEFF Research Database (Denmark)

    Jacobsen, Jonas Sejersbøl

    interpretation of the crack behavior. A stiff biaxial test set-up is applied to the mixed mode measurements. The relative opening and sliding of the crack is used as the control signals in a new enhanced closed control loop. The opening and the sliding of the crack are measured by clip gauges using a pair...... may open in mixed mode, i.e. a combination of opening and sliding. To get a thorough description of the structural consequences it is important to include the stress transferring effects related to the mixed mode opening. The existing constitutive mixed mode models either have a rather extensive model...... in a double notch specimen, the crack is exposed to mixed mode opening. The experiments may be used in a direct interpretation of the mixed mode behavior. The elliptic yield surface in the associated elasto-plastic material model is controlled by two hardening parameters, which represent the actual...

  15. The Effects of Load Ratio on Threshold Fatigue Crack Growth of Aluminum Alloys

    OpenAIRE

    Newman, John Andrew

    2000-01-01

    The integrity of nearly all engineering structures are threatened by the presence of cracks. Structural failure occurs if a crack larger than a critical size exists. Although most well designed structures initially contain no critical cracks, subcritical cracks can grow to failure under fatigue loading, called fatigue crack growth (FCG). Because it is impossible or impractical to prevent subcritical crack growth in most applications, a damage tolerant design philosophy was developed for cr...

  16. Deformation and crack growth response under cyclic creep conditions

    Energy Technology Data Exchange (ETDEWEB)

    Brust, F.W. Jr. [Battelle Memorial Institute, Columbus, OH (United States)

    1995-12-31

    To increase energy efficiency, new plants must operate at higher and higher temperatures. Moreover, power generation equipment continues to age and is being used far beyond its intended original design life. Some recent failures which unfortunately occurred with serious consequences have clearly illustrated that current methods for insuring safety and reliability of high temperature equipment is inadequate. Because of these concerns, an understanding of the high-temperature crack growth process is very important and has led to the following studies of the high temperature failure process. This effort summarizes the results of some recent studies which investigate the phenomenon of high temperature creep fatigue crack growth. Experimental results which detail the process of creep fatigue, analytical studies which investigate why current methods are ineffective, and finally, a new approach which is based on the T{sup *}-integral and its ability to characterize the creep-fatigue crack growth process are discussed. The potential validity of this new predictive methodology is illustrated.

  17. Elevated temperature crack growth in advanced powder metallurgy aluminum alloys

    Science.gov (United States)

    Porr, William C., Jr.; Gangloff, Richard P.

    1990-01-01

    Rapidly solidified Al-Fe-V-Si powder metallurgy alloy FVS0812 is among the most promising of the elevated temperature aluminum alloys developed in recent years. The ultra fine grain size and high volume fraction of thermally stable dispersoids enable the alloy to maintain tensile properties at elevated temperatures. In contrast, this alloy displays complex and potentially deleterious damage tolerant and time dependent fracture behavior that varies with temperature. J-Integral fracture mechanics were used to determine fracture toughness (K sub IC) and crack growth resistance (tearing modulus, T) of extruded FVS0812 as a function of temperature. The alloy exhibits high fracture properties at room temperature when tested in the LT orientation, due to extensive delamination of prior ribbon particle boundaries perpendicular to the crack front. Delamination results in a loss of through thickness constraint along the crack front, raising the critical stress intensity necessary for precrack initiation. The fracture toughness and tensile ductility of this alloy decrease with increasing temperature, with minima observed at 200 C. This behavior results from minima in the intrinsic toughness of the material, due to dynamic strain aging, and in the extent of prior particle boundary delaminations. At 200 C FVS0812 fails at K levels that are insufficient to cause through thickness delamination. As temperature increases beyond the minimum, strain aging is reduced and delamination returns. For the TL orientation, K (sub IC) decreased and T increased slightly with increasing temperature from 25 to 316 C. Fracture in the TL orientation is governed by prior particle boundary toughness; increased strain localization at these boundaries may result in lower toughness with increasing temperature. Preliminary results demonstrate a complex effect of loading rate on K (sub IC) and T at 175 C, and indicate that the combined effects of time dependent deformation, environment, and strain aging

  18. Behavior of Transversal Crack on Slab Corner During V-H Rolling Process

    Institute of Scientific and Technical Information of China (English)

    YU Hai-liang; LIU Xiang-hua; LI Chang-sheng; Y. Kusaba

    2006-01-01

    The behavior of transversal cracks on the surface of the slab corner during vertical and horizontal (V-H) rolling process with flat vertical roll and groove vertical roll was simulated by explicit dynamic finite element method. The closure and growth of crack and the contact pressure on surfaces of the crack in contacting zone between slab and roll during rolling process were analyzed. The results showed that during vertical rolling process, when the groove vertical roll is used, the maximum contact pressure on surfaces of the crack is 115 MPa, and the closure of crack is stable; when the flat vertical roll is used, the maximum contact pressure on surfaces of the crack is 70 MPa, and it fluctuates greatly. During horizontal rolling process, when groove vertical roll is used, the contact pressure becomes zero which may accelerate the growth of crack; when flat vertical roll is used, there is still contact pressure. The calculated results are in good agreement with the results of test.

  19. Cracking behavior of tungsten armor under ELM-like thermal shock loads: A computational study

    Directory of Open Access Journals (Sweden)

    Muyuan Li

    2015-03-01

    Full Text Available In this work, the cracking behavior of tungsten under edge-localized mode (ELM-like thermal shock loads was investigated on the basis of a rigorous computational fracture mechanical analysis combined with the finite element method. Typical transient thermal shock loads of ELM conditions were considered with a relevant range of power density and base temperature for a loading duration of 1 ms. Crack initiation and progressive growth were predicted using the extended finite element method and the J-integral was calculated for the assumed precrack by means of the virtual crack extension method. For a power density of 1 GW/m2 and higher, a crack is preferably initiated near the edge of the loading area and is then followed by a gradual horizontal kinking, parallel to the loading surface. The crack formation is predicted for the power density of 0.6 GW/m2 and above, and when the base temperature is higher than 600 °C, almost no cracks is predicted. The numerically predicted cracking behavior agrees in general with the experimental observations.

  20. EFFECT OF CARBODIIMIDE ON THE FATIGUE CRACK GROWTH RESISTANCE OF RESIN-DENTIN BONDS

    Science.gov (United States)

    Zhang, Zihou; Beitzel, Dylan; Majd, Hessam; Mutluay, Mustafa; Tezvergil-Mutluay, Arzu; Tay, Franklin R.; Pashley, David H.; Arola, Dwayne

    2015-01-01

    Recent studies have shown that ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) inactivates endogenous dentin proteases, thereby preventing collagen degradation and improving the durability of adhesive bonds to dentin. Bond durability is routinely assessed by monotonic microtensile testing, which does not consider the cyclic nature of mastication. Objective to characterize the effect of an EDC pretreatment on the fatigue crack growth behavior of resin-dentin bonds. Methods Bonded interface Compact Tension (CT) specimens were prepared using a three-step etch-and-rinse adhesive and hybrid resin-composite. Adhesive bonding of the treated groups included a 1 min application of an experimental EDC conditioner to the acid-etched dentin. The control groups did not receive EDC treatment. The fatigue crack growth resistance was examined after storage in artificial saliva for 0, 3 and 6 months. Results There was no significant difference in the immediate fatigue crack growth resistance of the EDC-treated and control groups at 0 months. However, after the 3 and 6 months storage periods the EDC-treated groups exhibited significantly greater (p≤0.05) fatigue crack growth resistance than the control specimens. Significance Although the EDC treatment maintained the fatigue crack growth resistance of the dentin bonds through 6 months of storage, additional studies are needed to assess its effectiveness over longer periods and in relation to other cross-linking agents. PMID:26739775

  1. Slow Crack Growth of Brittle Materials With Exponential Crack-Velocity Formulation. Part 1; Analysis

    Science.gov (United States)

    Choi, Sung R.; Nemeth, Noel N.; Gyekenyesi, John P.

    2002-01-01

    Extensive slow-crack-growth (SCG) analysis was made using a primary exponential crack-velocity formulation under three widely used load configurations: constant stress rate, constant stress, and cyclic stress. Although the use of the exponential formulation in determining SCG parameters of a material requires somewhat inconvenient numerical procedures, the resulting solutions presented gave almost the same degree of simplicity in both data analysis and experiments as did the power-law formulation. However, the fact that the inert strength of a material should be known in advance to determine the corresponding SCG parameters was a major drawback of the exponential formulation as compared with the power-law formulation.

  2. Three Dimensional Numerical Simulation and Characterization of Crack Growth in the Weld Region of a Friction Stir Welded Structure

    Science.gov (United States)

    Seshadri, Banavara R.; Smith, Stephen W.; Newman, John A.

    2013-01-01

    Friction stir welding (FSW) fabrication technology is being adopted in aerospace applications. The use of this technology can reduce production cost, lead-times, reduce structural weight and need for fasteners and lap joints, which are typically the primary locations of crack initiation and multi-site fatigue damage in aerospace structures. FSW is a solid state welding process that is well-suited for joining aluminum alloy components; however, the process introduces residual stresses (both tensile and compressive) in joined components. The propagation of fatigue cracks in a residual stress field and the resulting redistribution of the residual stress field and its effect on crack closure have to be estimated. To insure the safe insertion of complex integral structures, an accurate understanding of the fatigue crack growth behavior and the complex crack path process must be understood. A life prediction methodology for fatigue crack growth through the weld under the influence of residual stresses in aluminum alloy structures fabricated using FSW will be detailed. The effects and significance of the magnitude of residual stress at a crack tip on the estimated crack tip driving force are highlighted. The location of the crack tip relative to the FSW and the effect of microstructure on fatigue crack growth are considered. A damage tolerant life prediction methodology accounting for microstructural variation in the weld zone and residual stress field will lead to the design of lighter and more reliable aerospace structures

  3. Crack growth of 10M Ni-Mn-Ga material in cyclic mechanical loading

    Science.gov (United States)

    Aaltio, I.; Ge, Y.; Pulkkinen, H.; Sjöberg, A.; Söderberg, O.; Liu, X. W.; Hannula, S.-P.

    The 10M martensitic Ni-Mn-Ga single crystal materials are usually applied in the magneto-mechanical actuators. Therefore, it is important to know the possible effect of the long-term cyclic shape changes on their structure and behavior. This can be evaluated with the mechanical fatigue testing. In the present study, the single crystal 10M Ni-Mn-Ga samples of different compositions were applied to strain-controlled uniaxial mechanical cycling in the multivariant state at ambient temperature. The experiments revealed distinctive changes of the twin variant structure, especially in the mobile twin area, density of twin boundaries, and in the tendency for fatigue crack growth. Characterization of the crack surface showed that the cracks in the microscale grow in a step-wise manner on specific crystallographic planes, i.e, twin boundary planes, but that the macroscopic crack does not occur only along crystallographic directions.

  4. An Experimental Investigation of the Effects of Vacuum Environment on the Fatigue Life, Fatigue-Crack-Growth Behavior, and Fracture Toughness of 7075-T6 Aluminum Alloy. Ph.D. Thesis - North Carolina State Univ.

    Science.gov (United States)

    Hudson, C. M.

    1972-01-01

    Axial load fatigue life, fatigue-crack propagation, and fracture toughness tests were conducted on 0.090-inch thick specimens made of 7075-T6 aluminum alloy. The fatigue life and fatigue-crack propagation experiments were conducted at a stress ratio of 0.02. Maximum stresses ranged from 33 to 60 ksi in the fatigue life experiments, and from 10 to 40 ksi in the fatigue-crack propagation experiments, and fatigue life experiments were conducted at gas pressures of 760, 0.5, 0.05, and 0.00000005 torr. Fatigue-crack-growth and fracture toughness experiments were conducted at gas pressures of 760 and 5 x 10 to the minus 8th power torr. Residual stress measurements were made on selected fatigue life specimens to determine the effect of such stresses on fatigue life. Analysis of the results from the fatigue life experiments indicated that fatigue life progressively increased as the gas pressure decreased. Analysis of the results from the fatigue-crack-growth experiments indicates that at low values of stress-intensity range, the fatigue crack growth rates were approximately twice as high in air as in vacuum. Fracture toughness data showed there was essentially no difference in the fracture toughness of 7075-T6 in vacuum and in air.

  5. Stress Corrosion Cracking Behavior of X80 Pipeline Steel in Acid Soil Environment with SRB

    Science.gov (United States)

    Wang, Dan; Xie, Fei; Wu, Ming; Liu, Guangxin; Zong, Yue; Li, Xue

    2017-06-01

    Self-designed experimental device was adopted to ensure the normal growth of sulphate-reducing bacteria (SRB) in sterile simulated Yingtan soil solution. Stress corrosion cracking (SCC) behavior of X80 pipeline steel in simulated acid soil environment was investigated by electrochemical impedance spectroscopy, slow strain rate test, and scanning electron microscope. Results show that the presence of SRB could promote stress corrosion cracking susceptibility. In a growth cycle, polarization resistance first presents a decrease and subsequently an increase, which is inversely proportional to the quantities of SRB. At 8 days of growth, SRB reach their largest quantity of 1.42 × 103 cells/g. The corrosion behavior is most serious at this time point, and the SCC mechanism is hydrogen embrittlement. In other SRB growth stages, the SCC mechanism of X80 steel is anodic dissolution. With the increasing SRB quantities, X80 steel is largely prone to SCC behavior, and the effect of hydrogen is considerably obvious.

  6. Fatigue crack growth rates of rotor steel at elevated temperatures

    Institute of Scientific and Technical Information of China (English)

    LIU Chang-hai; MA Li-juan; TANG Li-qiang

    2008-01-01

    Low fatigue samples were obtained from the outer edges of rotor steel (30CrlMolV) which had operated under different temperatures conditions.Based on this data,the effects of temperature on fatigue crack growth rates were investigated.This paper presents a derivation of the superposition expression of two natural logarithms governing crack growth rates and also discusses the relationship between a material's constants and temperature.These results can provide experimental and theoretical references for fatigue life design of root steel in steam turbines.

  7. Dynamic crack growth in a fiber-reinforced composite plate

    Institute of Scientific and Technical Information of China (English)

    LIU Kaixin; LIU Weifu; Zhang Jinxiang; LI Rong; ZHANG Guohua; FU Bin

    2005-01-01

    This paper reports an experiment on the failure of a precracked plate made of unidirectional glass-epoxy fiber-reinforced composites subjected to three-point bending impact load. In the experiment, the whole process of crack growth was recorded by using high-speed photographic technique, in which a transmitted light path was adopted. Moreover, a new phenomenon of dynamic fracture has been observed. Based on the results, some preliminary studies have been carried out on the rate and path of the crack growth, as well as the failure mode.

  8. Accelerated crack growth, residual stress, and a cracked zinc coated pressure shell

    Science.gov (United States)

    Dittman, Daniel L.; Hampton, Roy W.; Nelson, Howard G.

    1987-01-01

    During a partial inspection of a 42 year old, operating, pressurized wind tunnel at NASA-Ames Research Center, a surface connected defect 114 in. long having an indicated depth of a 0.7 in. was detected. The pressure shell, constructed of a medium carbon steel, contains approximately 10 miles of welds and is cooled by flowing water over its zinc coated external surface. Metallurgical and fractographic analysis showed that the actual detect was 1.7 in. deep, and originated from an area of lack of weld penetration. Crack growth studies were performed on the shell material in the laboratory under various loading rates, hold times, and R-ratios with a simulated shell environment. The combination of zinc, water with electrolyte, and steel formed an electrolytic cell which resulted in an increase in cyclic crack growth rate by as much as 500 times over that observed in air. It was concluded that slow crack growth occurred in the pressure shell by a combination of stress corrosion cracking due to the welding residual stress and corrosion fatigue due to the cyclic operating stress.

  9. Accelerated crack growth, residual stress, and a cracked zinc coated pressure shell

    Science.gov (United States)

    Dittman, Daniel L.; Hampton, Roy W.; Nelson, Howard G.

    1987-01-01

    During a partial inspection of a 42 year old, operating, pressurized wind tunnel at NASA-Ames Research Center, a surface connected defect 114 in. long having an indicated depth of a 0.7 in. was detected. The pressure shell, constructed of a medium carbon steel, contains approximately 10 miles of welds and is cooled by flowing water over its zinc coated external surface. Metallurgical and fractographic analysis showed that the actual detect was 1.7 in. deep, and originated from an area of lack of weld penetration. Crack growth studies were performed on the shell material in the laboratory under various loading rates, hold times, and R-ratios with a simulated shell environment. The combination of zinc, water with electrolyte, and steel formed an electrolytic cell which resulted in an increase in cyclic crack growth rate by as much as 500 times over that observed in air. It was concluded that slow crack growth occurred in the pressure shell by a combination of stress corrosion cracking due to the welding residual stress and corrosion fatigue due to the cyclic operating stress.

  10. Growth patterns and dynamics of mud cracks at different diagenetic stages and its geological significance

    Institute of Scientific and Technical Information of China (English)

    Zhen-yu ZHAO; Yan-ru GUO; Yan WANG; Hong LIU; Qing ZHANG

    2014-01-01

    This paper discusses the growth stages, spatial structures, quantitative fitting relationships among various parameters, growth patterns and influencing factors of mud cracks by field survey, core observation and SEM analysis. The study shows that:(1) Mud crack growth can go through three stages, i.e. the syndiagenetic stage, the burial diagenetic stage (including early diagenetic stage, middle-late diagenetic stage) and the epidiagenetic stage. (2) Quantitative fitting relationships among various parameters allow a great significance to describe the spatial structure, the regional distribution and the growth environment of mud cracks. (3) Mud crack growth has three models, such as the unilateral growth model including the linear growth pattern, the curvilinear growth pattern and the bifurcation growth pattern, the multilateral growth model including the intersectional growth pattern, the join growth pattern and the dispersed growth pattern, and the mixed growth model including the combination of any patterns listed above. (4) Modern mud crack growth usually undergoes four stages. Sand beds in sand-mud rhythmic strata can play a lubricative role on crack growth and provide enough sandy deposits for filling cracks. (5) Mud crack growth usually produces bifurcation and bifurcation angles which are mostly 120° or 90° that are related to sediment heterogeneity and released energy. (6) Factors affecting mud crack growth cover many aspects: clay content and salinity can control the number of mud cracks in different areas;terrain can control mud crack morphology;and different sedimentary cycles can control the growth patterns and filling models of mud cracks.

  11. Numerical simulation of stable fatigue crack growth rate using a cohesive zone model

    NARCIS (Netherlands)

    Silitonga, S.; Maljaars, J.; Soetens, F.; Snijder, H.H.

    2012-01-01

    Predicting the remaining fatigue life of a structure with crack(s) is generally conducted by the fracture mechanics method. This method is aimed at predicting the crack growth and final fracture due to fluctuating loads. The crack growth curve required for these calculations is constructed on the ba

  12. Analysis of Fatigue Crack Growth in Ship Structural Details

    Directory of Open Access Journals (Sweden)

    Leheta Heba W.

    2016-04-01

    Full Text Available Fatigue failure avoidance is a goal that can be achieved only if the fatigue design is an integral part of the original design program. The purpose of fatigue design is to ensure that the structure has adequate fatigue life. Calculated fatigue life can form the basis for meaningful and efficient inspection programs during fabrication and throughout the life of the ship. The main objective of this paper is to develop an add-on program for the analysis of fatigue crack growth in ship structural details. The developed program will be an add-on script in a pre-existing package. A crack propagation in a tanker side connection is analyzed by using the developed program based on linear elastic fracture mechanics (LEFM and finite element method (FEM. The basic idea of the developed application is that a finite element model of this side connection will be first analyzed by using ABAQUS and from the results of this analysis the location of the highest stresses will be revealed. At this location, an initial crack will be introduced to the finite element model and from the results of the new crack model the direction of the crack propagation and the values of the stress intensity factors, will be known. By using the calculated direction of propagation a new segment will be added to the crack and then the model is analyzed again. The last step will be repeated until the calculated stress intensity factors reach the critical value.

  13. Crack Growth Modeling and Life Prediction of Pipeline Steels Exposed to Near-Neutral pH Environments: Dissolution Crack Growth and Occurrence of Crack Dormancy in Stage I

    Science.gov (United States)

    Zhao, Jiaxi; Chen, Weixing; Yu, Mengshan; Chevil, Karina; Eadie, Reg; Van Boven, Greg; Kania, Richard; Been, Jenny; Keane, Sean

    2017-04-01

    This investigation was initiated to provide governing equations for crack initiation, crack growth, and service life prediction of pipeline steels in near-neutral pH (NNpH) environments. This investigation has focused on the crack initiation and early-stage crack growth. The investigation considered a wide range of conditions that could lead to crack initiation, crack dormancy, and crack transition from a dormant state to active growth. It is concluded that premature rupture caused by stress cracking at a service life of about 20 to 30 years previously observed during field operation could take place only when the worst conditions responsible for crack initiation and growth have been realized concurrently at the site of rupture. This also explains the reason that over 95 pct of NNpH cracks remain harmless, while about 1 pct of them become a threat to the integrity of pipeline steels.

  14. Kinetics of fatigue crack growth and crack paths in the old puddled steel after 100-years operating time

    Directory of Open Access Journals (Sweden)

    G. Lesiuk

    2015-10-01

    Full Text Available The goal of the authors’ investigations was determination of the fatigue crack growth in fragments of steel structures (of the puddled steel and its cyclic behavior. Tested steel elements coming from the turn of the 19th and 20th were gained from still operating ancient steel construction (a main hall of Railway Station, bridges etc.. This work is a part of investigations devoted to the phenomenon of microstructural degradation and its potential influence on their strength properties. The analysis of the obtained results indicated that those long operating steels subject to microstructure degradation processes consisting mainly in precipitation of carbides and nitrides inside ferrite grains, precipitation of carbides at ferrite grain boundaries and degeneration of pearlite areas [1, 2]. It is worth noticing that resistance of the puddled steel to fatigue crack propagation in the normalized state was higher. The authors proposed the new kinetic equation of fatigue crack growth rate in such a steel. Thus the relationship between the kinetics of degradation processes and the fatigue crack growth rate also have been shown. It is also confirmed by the materials research of the viaduct from 1885, which has not shown any significant changes in microstructure. The non-classical kinetic fatigue fracture diagrams (KFFD based on deformation ( or energy (W approach was also considered. In conjunction with the results of low- and high-cycle fatigue and gradual loss of ductility as a consequence (due to the microstructural degradation processes - it seems to be a promising construction of the new kinetics fatigue fracture diagrams with the energy approach.

  15. Experimental and Finite Element Modeling of Near-Threshold Fatigue Crack Growth for the K-Decreasing Test Method

    Science.gov (United States)

    Smith, Stephen W.; Seshadri, Banavara R.; Newman, John A.

    2015-01-01

    The experimental methods to determine near-threshold fatigue crack growth rate data are prescribed in ASTM standard E647. To produce near-threshold data at a constant stress ratio (R), the applied stress-intensity factor (K) is decreased as the crack grows based on a specified K-gradient. Consequently, as the fatigue crack growth rate threshold is approached and the crack tip opening displacement decreases, remote crack wake contact may occur due to the plastically deformed crack wake surfaces and shield the growing crack tip resulting in a reduced crack tip driving force and non-representative crack growth rate data. If such data are used to life a component, the evaluation could yield highly non-conservative predictions. Although this anomalous behavior has been shown to be affected by K-gradient, starting K level, residual stresses, environmental assisted cracking, specimen geometry, and material type, the specifications within the standard to avoid this effect are limited to a maximum fatigue crack growth rate and a suggestion for the K-gradient value. This paper provides parallel experimental and computational simulations for the K-decreasing method for two materials (an aluminum alloy, AA 2024-T3 and a titanium alloy, Ti 6-2-2-2-2) to aid in establishing clear understanding of appropriate testing requirements. These simulations investigate the effect of K-gradient, the maximum value of stress-intensity factor applied, and material type. A material independent term is developed to guide in the selection of appropriate test conditions for most engineering alloys. With the use of such a term, near-threshold fatigue crack growth rate tests can be performed at accelerated rates, near-threshold data can be acquired in days instead of weeks without having to establish testing criteria through trial and error, and these data can be acquired for most engineering materials, even those that are produced in relatively small product forms.

  16. Crack growth simulation in heterogeneous material by S-FEM and comparison with experiments

    Directory of Open Access Journals (Sweden)

    Masanori Kikuchi

    2015-10-01

    Full Text Available Fully automatic fatigue crack growth simulation system is developed using S-version FEM (SFEM. This system is extended to fracture in heterogeneous material. In the heterogeneous material, crack tip stress field becomes mixed mode condition, and crack growth path is affected by inhomogeneous materials and mixed mode conditions. Stress Intensity Factors (SIF in mixed mode condition are evaluated using Virtual Crack Closure Method (VCCM. Criteria for crack growth amount and crack growth path are used based on these SIFs, and growing crack configurations are obtained. Three crack growth problems are simulated. One is crack growth in bi-materila made of CFRP plate and Aluminum alloy. Initial crack is located in CFRP plate, and grows toward Aluminum alloy. Crack growing direction changes and results are compared with experimental one. Second problem is crack growth in bimaterial made of PMMA and Aluminum alloy. Initial crack is located in PMMA plate and parallel to phase boundary. By cahnging loading conditions, several cases are simulated and compared with experimental ones. In the experiment, crack grows into pahse boundary and grow along it. This case is simulated precisely, and the effect of pahse boundary is discussed. Last case is Stress Corrosion Cracking (SCC at Hot-Leg Safe-End of Pressurized Water Rreactor. This location is made of many kinds of steels by welding. In some steel, SCC does not occur and in other steel, SCC is accelerated. As a result, small surface crack grows in complicated manner.

  17. Analysis of hygral induced crack growth in multiphase materials

    NARCIS (Netherlands)

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

    1996-01-01

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

  18. Probabilistic Model for Fatigue Crack Growth in Welded Bridge Details

    DEFF Research Database (Denmark)

    Toft, Henrik Stensgaard; Sørensen, John Dalsgaard; Yalamas, Thierry

    2013-01-01

    In the present paper a probabilistic model for fatigue crack growth in welded steel details in road bridges is presented. The probabilistic model takes the influence of bending stresses in the joints into account. The bending stresses can either be introduced by e.g. misalignment or redistributio...

  19. Numerical simulation of fatigue crack growth rate and crack retardation due to an overload using a cohesive zone model

    NARCIS (Netherlands)

    Silitonga, S.; Maljaars, J.; Soetens, F.; Snijder, H.H.

    2014-01-01

    In this work, a numerical method is pursued based on a cohesive zone model (CZM). The method is aimed at simulating fatigue crack growth as well as crack growth retardation due to an overload. In this cohesive zone model, the degradation of the material strength is represented by a variation of the

  20. Environment assisted crack growth in nickel-base superalloys at elevated temperature

    Science.gov (United States)

    Evans, Jeffrey Lee

    The environmental effect on the fatigue crack growth rate of Ni-base superalloys at elevated temperature was evaluated in this study. A set of crack growth tests was performed on the turbine disk alloy ME3 at 704°C (1300°F) in vacuum and in air at 0 and 10 second hold times using two microstructures developed with two different cooling rates from the solution heat treat temperature. Fatigue crack growth tests were also conducted at 25°C (77°F) with the two microstructures. Also, a set of oxidation experiments was conducted in order to evaluate the high temperature oxidation behavior of ME3. The microstructure was analyzed and the main differences between the two cooling rates were in the amounts of minor phase particles and size of secondary gamma prime particles. The crack growth rate results suggest that there is no measurable effect of environment or microstructure at room temperature. For the tests conducted in air at elevated temperature, both hold time and microstructural effects were evident. A coupling effect was also observed between the microstructure and the environment. The samples that were slow cooled, and had larger secondary gamma prime particles, had slower crack growth rates and less intergranular fracture in air than the fast cooled samples. A possible explanation for this would be excess free chromium available along grain boundaries due to its low solubility in gamma prime, providing for greater oxidation resistance. An elevated temperature fatigue crack growth rate model for Ni-base superalloys is also proposed.

  1. Fatigue crack propagation behavior of a single crystalline superalloy

    Science.gov (United States)

    Lerch, B. A.; Antolovich, Stephen D.

    1990-01-01

    Crack propagation mechanisms occurring at various temperatures in a single crystalline Ni-base alloy, Rene N4, were investigated. The rates of crack growth at 21, 704, 927, 1038, and 1093 C were measured in specimens with 001-line and 110-line directions parallel to the load axis and the machined notch, respectively, using a pulsed dc potential drop apparatus, and the fracture surfaces at each temperature were examined using SEM. Crack growth rates (CGRs) for specimens tested at or below 927 C were similar, while at two higher temperatures, the CGRs were about an order of magnitude higher than at the lower temperatures. Results of SEM observations showed that surface morphologies depended on temperature.

  2. Separating the Influence of Environment from Stress Relaxation Effects on Dwell Fatigue Crack Growth in a Nickel-Base Disk Alloy

    Science.gov (United States)

    Telesman, J.; Gabb, T. P.; Ghosn, L. J.

    2016-01-01

    Both environmental embrittlement and crack tip visco-plastic stress relaxation play a significant role in determining the dwell fatigue crack growth (DFCG) resistance of nickel-based disk superalloys. In the current study performed on the Low Solvus High Refractory (LSHR) disk alloy, the influence of these two mechanisms were separated so that the effects of each could be quantified and modeled. Seven different microstructural variations of LSHR were produced by controlling the cooling rate and the subsequent aging and thermal exposure heat treatments. Through cyclic fatigue crack growth testing performed both in air and vacuum, it was established that four out of the seven LSHR heat treatments evaluated, possessed similar intrinsic environmental resistance to cyclic crack growth. For these four heat treatments, it was further shown that the large differences in dwell crack growth behavior which still persisted, were related to their measured stress relaxation behavior. The apparent differences in their dwell crack growth resistance were attributed to the inability of the standard linear elastic fracture mechanics (LEFM) stress intensity parameter to account for visco-plastic behavior. Crack tip stress relaxation controls the magnitude of the remaining local tensile stresses which are directly related to the measured dwell crack growth rates. It was hypothesized that the environmentally weakened grain boundary crack tip regions fail during the dwells when their strength is exceeded by the remaining local crack tip tensile stresses. It was shown that the classical creep crack growth mechanisms such as grain boundary sliding did not contribute to crack growth, but the local visco-plastic behavior still plays a very significant role by determining the crack tip tensile stress field which controls the dwell crack growth behavior. To account for the influence of the visco-plastic behavior on the crack tip stress field, an empirical modification to the LEFM stress

  3. Crack growth through low-cycle fatigue loading of material ARMOX 500T

    Directory of Open Access Journals (Sweden)

    V. Pepel

    2016-10-01

    Full Text Available This paper presents microstructure analysis of the creation and growth of cracks in uniaxial load. Analyse were done for steel Armox 500T (armour sheet. Results show that cracks are present quit early in steel lifetime. First micro cracks occur before the 200th cycles, whereby crack growth is progressive during further loading. Also it can be seen that after a certain number of cycles there are more longer cracks then shorter ones.

  4. CRACK PROPAGATION BEHAVIOR AND LIFETIME PREDICTION IN ALUMINA AND ZIRCONIA

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The lifetime prediction of ceramics is discussed on the basis of the relationship between stress intensity factor KI and crack velocity v. The effects of water environment, the cyclic loading and microstructure of material on KI-v characteristics are studied by carrying out the crack growth tests by the double torsion (DT) method under the static and cyclic loading in both environments of air and water for alumina and zirconia. KI-v characteristics determined by the double torsion method are used to predict time-to-failure under the cyclic loading of alumina and zirconia ceramics. The predictions agree qualitatively with the experimental results.

  5. Prediction of Crack Growth Aqueous Environments.

    Science.gov (United States)

    1983-06-01

    facility development was described in Section III. This section describes the results of our preliminary experiments. We selected HY8o steel and Ti-6A1...23 S.~~~ ~ ~ ~"VoS - :.SS S......... . .. S. SSUSOX 0 The HY80 and Ti-6A1-4V should have very different passivation rates, surface film properties, and...combinations other than Ti- 6A1-4V and HY80 in 3.5% NaCl solutions will be examined to obtain AC impedance data for a range of SCC behavior. (2) Under

  6. Creep-Environment Interactions in Dwell-Fatigue Crack Growth of Nickel Based Superalloys

    Science.gov (United States)

    Maciejewski, Kimberly; Dahal, Jinesh; Sun, Yaofeng; Ghonem, Hamouda

    2014-05-01

    A multi-scale, mechanistic model is developed to describe and predict the dwell-fatigue crack growth rate in the P/M disk superalloy, ME3, as a function of creep-environment interactions. In this model, the time-dependent cracking mechanisms involve grain boundary sliding and dynamic embrittlement, which are identified by the grain boundary activation energy, as well as, the slip/grain boundary interactions in both air and vacuum. Modeling of the damage events is achieved by adapting a cohesive zone (CZ) approach which considers the deformation behavior of the grain boundary element at the crack tip. The deformation response of this element is controlled by the surrounding continuum in both far field (internal state variable model) and near field (crystal plasticity model) regions and the intrinsic grain boundary viscosity which defines the mobility of the element by scaling up the motion of dislocations into a mesoscopic scale. This intergranular cracking process is characterized by the rate at which the grain boundary sliding reaches a critical displacement. A damage criterion is introduced by considering the grain boundary mobility limit in the tangential direction leading to strain incompatibility and failure. Results of simulated intergranular crack growth rate using the CZ model are generated for temperatures ranging from 923 K to 1073 K (650 °C to 800 °C), in both air and vacuum. These results are compared with those experimentally obtained and analysis of the model sensitivity to loading conditions, particularly temperature and oxygen partial pressure, are presented.

  7. Empirical formulas for description of the fatigue crack growth rate

    Energy Technology Data Exchange (ETDEWEB)

    Rozumek, D. [Opole University of Technology, Faculty of Mechanical Engineering, Opole (Poland)

    2010-02-15

    The paper presents the test results obtained for fatigue crack growth in flat specimens subjected to bending. The tests were conducted for different loading amplitudes and different load ratios using the {delta}J parameter. Accuracy of description of the fatigue crack growth rate was tested with use of different empirical formulas. One-side restrained specimens made of 10HNAP steel were tested. In each tested specimen, there was the external notch 5 mm in depth, and the notch rounding radius was {rho}=0.2 mm. The tests were carried out at the fatigue test stand MZGS-100 under loading frequency 28.8 Hz. It has been found that the obtained results depend on the applied empirical formula. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  8. Effects of hydrogen concentration on slow crack growth in stainless steels

    Science.gov (United States)

    Singh, S.; Altstetter, C.

    1982-10-01

    The behavior of four austenitic stainless steel alloys containing bulk hydrogen contents up to 50 ppm by weight (0.28 at. pct) has been determined in sustained load and in slow strain rate tensile tests. Tests of these same alloys were also made in hydrogen gas. AISI 301 and two compositions of AISI 304 of different austenite stability showed typical three stage crack propagation regimes under sustained load. AISI 310S did not. The slow crack growth vs stress intensity relation was quite sensitive to hydrogen content above a minimum value and also sensitive to austenite stability. It was shown that hydrogen contents up to 40 wt ppm had no influence on the austenite stability at tensile elongations up to 60 pct. Fractographic and phase analysis results are presented, and a model for crack propagation is discussed.

  9. Some Considerations on Short Crack Growth Behaviour in Aircraft Structures,

    Science.gov (United States)

    1983-03-01

    of publications of which this is one. Participation in AGARI) activities is by invitation only and is normally limited to citizens of the NATO...nations. The content of this publication has been reproduced directly from material soupplied by AGARI) or the athors. Published March 1)83 (opyright © A...almost universally accepted. Relatino "fatique quality" or "duratility" to the behavior of small initial cracks at the design staoe is a technique

  10. Application of cyclic J-integral to low cycle fatigue crack growth of Japanese carbon steel pipe

    Energy Technology Data Exchange (ETDEWEB)

    Miura, N.; Fujioka, T.; Kashima, K. [and others

    1997-04-01

    Piping for LWR power plants is required to satisfy the LBB concept for postulated (not actual) defects. With this in mind, research has so far been conducted on the fatigue crack growth under cyclic loading, and on the ductile crack growth under excessive loading. It is important, however, for the evaluation of the piping structural integrity under seismic loading condition, to understand the fracture behavior under dynamic and cyclic loading conditions, that accompanies large-scale yielding. CRIEPI together with Hitachi have started a collaborative research program on dynamic and/or cyclic fracture of Japanese carbon steel (STS410) pipes in 1991. Fundamental tensile property tests were conducted to examine the effect of strain rate on tensile properties. Cracked pipe fracture tests under some loading conditions were also performed to investigate the effect of dynamic and/or cyclic loading on fracture behavior. Based on the analytical considerations for the above tests, the method to evaluate the failure life for a cracked pipe under cyclic loading was developed and verified. Cyclic J-integral was introduced to predict cyclic crack growth up to failure. This report presents the results of tensile property tests, cracked pipe fracture tests, and failure life analysis. The proposed method was applied to the cracked pipe fracture tests. The effect of dynamic and/or cyclic loading on pipe fracture was also investigated.

  11. Crack growth sparse pursuit for wind turbine blade

    Science.gov (United States)

    Li, Xiang; Yang, Zhibo; Zhang, Han; Du, Zhaohui; Chen, Xuefeng

    2015-01-01

    One critical challenge to achieving reliable wind turbine blade structural health monitoring (SHM) is mainly caused by composite laminates with an anisotropy nature and a hard-to-access property. The typical pitch-catch PZTs approach generally detects structural damage with both measured and baseline signals. However, the accuracy of imaging or tomography by delay-and-sum approaches based on these signals requires improvement in practice. Via the model of Lamb wave propagation and the establishment of a dictionary that corresponds to scatters, a robust sparse reconstruction approach for structural health monitoring comes into view for its promising performance. This paper proposes a neighbor dictionary that identifies the first crack location through sparse reconstruction and then presents a growth sparse pursuit algorithm that can precisely pursue the extension of the crack. An experiment with the goal of diagnosing a composite wind turbine blade with an artificial crack is performed, and it validates the proposed approach. The results give competitively accurate crack detection with the correct locations and extension length.

  12. In situ characterization of delamination and crack growth of a CGO–LSM multi-layer ceramic sample investigated by X-ray tomographic microscopy

    DEFF Research Database (Denmark)

    Bjørk, Rasmus; Esposito, Vincenzo; Lauridsen, Erik Mejdal;

    2014-01-01

    The densification, delamination and crack growth behavior in a Ce0.9Gd0.1O1.95 (CGO) and (La0.85Sr0.15)0.9MnO3 (LSM) multi-layer ceramic sample was studied using in situ X-ray tomographic microscopy (microtomography) to investigate the critical dynamics of crack propagation and delamination...... in a multilayered sample. Naturally occurring defects, caused by the sample preparation process, are shown not to be critical in sample degradation. Instead defects are nucleated during the debinding step. Crack growth is significantly faster along the material layers than perpendicular to them, and crack growth...

  13. 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.

  14. Microstructure dependent fatigue crack growth in Al–Mg–Sc alloy

    Energy Technology Data Exchange (ETDEWEB)

    Li, Mengjia [School of Materials Science and Engineering, Central South University, Changsha 410083 (China); Pan, Qinglin, E-mail: csupql@163.com [The Key Laboratory of Nonferrous Materials Science and Engineering of Ministry of Education, Central South University, Changsha 410083 (China); Shi, Yunjia; Wang, Ying [School of Materials Science and Engineering, Central South University, Changsha 410083 (China)

    2014-08-12

    The fatigue crack growth behavior of Al–Mg–Sc alloy was investigated by tensile testing and fatigue testing. Different annealing treatments were applied to the alloy. Microstructure characterization of the alloy was carried out by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM) and optical microscopy (OM). The size of Al{sub 3}(Sc{sub 1−x}Zr{sub x}) particle was calculated by software. The fatigue crack growth (FCG) rate (da/dN) was discussed with stress intensity factor range (ΔK) in Paris's region. The Paris exponent m and constants C were used to calculate the fatigue life. The fatigue process and crack closure effects were discussed with the yield strength and tensile strength of Al–Mg–Sc alloy. Results show that the microstructure, tensile strength and fatigue crack growth rate were greatly dependent on the annealing temperature, and the high resistance of Al–Mg–Sc alloy was mainly due to the combination microstructures of sub-grains, dislocations and these Al{sub 3}(Sc{sub 1−x}Zr{sub x}) precipitates.

  15. Effect of T-stress on the cleavage crack growth resistance resulting from plastic flow

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    1998-01-01

    Crack growth is studied numerically for cases where fracture occurs by atomic separation, sc that the length scale of the fracture process is typically much smaller than the dislocation spacing. Thus, the crack growth mechanism is brittle, but due to plastic flow at some distance from the crack t...

  16. Hydrogen adsorption and diffusion, and subcritical-crack growth in high-strength steels and nickel base alloys

    Science.gov (United States)

    Wei, R. P.; Klier, K.; Simmons, G. W.

    1974-01-01

    Coordinated studies of the kinetics of crack growth and of hydrogen adsorption and diffusion were initiated to develop information that is needed for a clearer determination of the rate controlling process and possible mechanism for hydrogen enhanced crack growth, and for estimating behavior over a range of temperatures and pressures. Inconel 718 alloy and 18Ni(200) maraging steel were selected for these studies. 18Ni(250) maraging steel, 316 stainless steel, and iron single crystal of (111) orientation were also included in the chemistry studies. Crack growth data on 18Ni(250) maraging steel from another program are included for comparison. No sustained-load crack growth was observed for the Inconel 718 alloy in gaseous hydrogen. Gaseous hydrogen assisted crack growth in the 18Ni maraging steels were characterized by K-independent (Stage 2) extension over a wide range of hydrogen pressures (86 to 2000 torr or 12 kN/m2 to 266 kN/m2) and test temperatures (-60 C to +100 C). The higher strength 18Ni(250) maraging steel was more susceptible than the lower strength 200 grade. A transition temperature was observed, above which crack growth rates became diminishingly small.

  17. Standard test method for measurement of fatigue crack growth rates

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2015-01-01

    1.1 This test method covers the determination of fatigue crack growth rates from near-threshold to Kmax controlled instability. Results are expressed in terms of the crack-tip stress-intensity factor range (ΔK), defined by the theory of linear elasticity. 1.2 Several different test procedures are provided, the optimum test procedure being primarily dependent on the magnitude of the fatigue crack growth rate to be measured. 1.3 Materials that can be tested by this test method are not limited by thickness or by strength so long as specimens are of sufficient thickness to preclude buckling and of sufficient planar size to remain predominantly elastic during testing. 1.4 A range of specimen sizes with proportional planar dimensions is provided, but size is variable to be adjusted for yield strength and applied force. Specimen thickness may be varied independent of planar size. 1.5 The details of the various specimens and test configurations are shown in Annex A1-Annex A3. Specimen configurations other than t...

  18. Fatigue crack propagation behavior of ultrahigh molecular weight polyethylene.

    Science.gov (United States)

    Connelly, G M; Rimnac, C M; Wright, T M; Hertzberg, R W; Manson, J A

    1984-01-01

    The relative fatigue crack propagation resistance of plain and carbon fiber-reinforced ultrahigh molecular weight polyethylene (UHMWPE) was determined from cyclic loading tests performed on compact tension specimens machined from the tibial components of total knee prostheses. Both materials were characterized by dynamic mechanical spectroscopy, X-ray diffraction, and differential scanning calorimetry. The cyclic tests used loading in laboratory air at 5 Hz using a sinusoidal wave form. Dynamic mechanical spectroscopy showed that the reinforced UHMWPE had a higher elastic storage modulus than the plain UHMWPE, whereas X-ray diffraction and differential scanning calorimetry showed that the percent crystallinity and degree of order in the crystalline regions were similar for the two materials. Fatigue crack propagation in both materials proved to be very sensitive to small changes in the applied cyclic stress intensity range. A 10% increase in stress intensity resulted in approximately an order of magnitude increase in fatigue crack growth rate. The fatigue crack propagation resistance of the reinforced UHMWPE was found to be significantly worse than that of the plain UHMWPE. This result was attributed to poor bonding between the carbon fibers and the UHMWPE matrix and the ductile nature of the matrix itself.

  19. Anodic Dissolution Behavior of the Crack Tip of X70 Pipeline Steel in Near-Neutral pH Environment

    Science.gov (United States)

    Cui, Zhongyu; Wang, Liwei; Liu, Zhiyong; Du, Cuiwei; Li, Xiaogang; Wang, Xin

    2016-12-01

    In this work, the anodic dissolution behavior of the fresh metal surface at crack tip of X70 steel in near-neutral pH environment was investigated using galvanic corrosion simulation method. The solution environment, strain, strain rate, hydrogen enrichment, and fresh metal surface at the crack tip were considered. Corrosion current of the specimen during fast stretching increased linearly with plastic strain. The increment and increase rate of the corrosion current during plastic deformation stage were dependent on the strain rate. Combining Faraday's law and crack tip strain rate equation, the crack growth rate (CGR) induced by the anodic dissolution of the fresh metal surface was calculated. Results show that CGR caused by anodic dissolution was roughly one order lower than that measured on the compact tensile specimen under cyclic load. This finding indicated that hydrogen embrittlement may play a dominate role in stress corrosion crack propagation of pipeline steels in near-neutral pH environment.

  20. Crack Growth Monitoring in Harsh Environments by Electric Potential Measurements

    Energy Technology Data Exchange (ETDEWEB)

    Lloyd, Wilson Randolph; Reuter, Walter Graham; Weinberg, David Michael

    1999-09-01

    Electric potential measurement (EPM) technology offers an attractive alternative to conventional nondestructive evaluation (NDE) for monitoring crack growth in harsh environments. Where conventional NDE methods typically require localized human interaction, the EPM technique developed at the Idaho National Engineering and Environmental Laboratory (INEEL) can be operated remotely and automatically. Once a crack-like defect is discovered via conventional means, EPM can be applied to monitor local crack size changes. This is of particular interest in situations where an identified structural defect is not immediately rejectable from a fitness-for-service viewpoint, but due to operational and environmental conditions may grow to an unsafe size with continuing operation. If the location is in a harsh environment where periodic monitoring by normal means is either too costly or not possible, a very expensive repair may be immediately mandated. However, the proposed EPM methodology may offer a unique monitoring capability that would allow for continuing service. INEEL has developed this methodology, supporting equipment, and calibration information to apply EPM in a field environment for just this purpose. Laboratory and pilot scale tests on full-size engineering structures (pressure vessels and piping) have been successfully performed. The technique applicable is many severe environments because the sensitive equipment (electronics, operators) can be situated in a remote location, with only current and voltage probe electrical leads entering into the harsh environment. Experimental results showing the utility of the methodology are presented, and unique application concepts that have been examined by multiple experiments are discussed.

  1. Face/core debond fatigue crack growth characterization using the sandwich mixed mode bending specimen

    DEFF Research Database (Denmark)

    Manca, Marcello; Quispitupa, Amilcar; Berggreen, Christian;

    2012-01-01

    Face/core fatigue crack growth in foam-cored sandwich composites is examined using the mixed mode bending (MMB) test method. The mixed mode loading at the debond crack tip is controlled by changing the load application point in the MMB test fixture. Sandwich specimens were manufactured using H45...... critical load, at load ratios of R=0.1 and 0.2. The crack length was determined during fatigue testing using the analytical compliance expression and verified by visual measurements. Fatigue crack growth results revealed higher crack growth rates for mode I dominated loading. For specimens with H45 core...

  2. Effect of crack propagation on crack tip fields

    Directory of Open Access Journals (Sweden)

    F.V. Antunes

    2013-07-01

    Full Text Available Crack closure influences fatigue crack growth rate and must be included in the design of components. Plasticity induced crack closure is intimately linked with the crack tip plastic deformation, which becomes residual as the crack propagates. The objective here is to study numerically the effect of crack propagation on crack tip fields. The transient effect observed at the beginning of crack propagation is linked to the hardening behavior of material. The effect of mesh refinement is studied, and a singular behavior is evident, which is explained by the sharp crack associated with mesh topology, composed of a regular pattern of square elements. The plastic zone size measured perpendicularly to crack flank in the residual plastic wake is quantified and compared with literature models. Finally, the removal of material at the first node behind crack tip with load cycling was observed for plane strain state and some hardening models in plane stress state.

  3. Matrix cracking and creep behavior of monolithic zircon and zircon silicon carbide fiber composites

    Science.gov (United States)

    Anandakumar, Umashankar

    room temperature and elevated temperatures, and the validity of the various models of first matrix cracking behavior. In order to understand the creep behavior of composites, it is important to study the creep behavior of matrix, fiber, and composites under identical conditions to determine the role of various constituents. Creep studies were conducted in an inert atmosphere in four point bending and uniaxial tension modes on zircon and zircon silicon carbide fiber composites at four different temperatures of 1250°C, 1300°C, 1350°C, and 1400°C, and over the stress range of 10--200 MPa. The strain rate was measured as a function of the stress and temperature to determine the stress exponent and activation energy, and microstructural analysis was done on crept samples using scanning electron microscopy. The composites exhibited a much lower creep rate than the monolilth, indicating that the major portion of the creep load was carried by the fibers. In flexural mode, both zircon and composite samples exhibited bimodal creep behavior, with the stress exponent (n) increasing with increasing stress. For zircon, at lower-stresses n was in the range of 2.1--2.6 and increased to 7--7.9 at higher stresses. Microstructural studies showed that diffusional creep was the rate controlling mechanism at lower stresses, while the higher stress exponent observed at higher stresses, was due to linkage of cavities and damage accumulation resulting in a higher strain rate. In the case of composites, the stress exponent was ≈1 at lower stresses, and increased to 3--5 at higher stresses, indicating that diffusional creep (and grain boundary sliding) was rate controlling at lower stresses, and either creep cavitation and crack growth or dislocation creep was the rate controlling mechanism at higher stresses. Anomalous creep curves with strain jumps were observed for the first time during the creep of ceramic composites at lower temperatures and higher stresses. Microstructural studies

  4. Nonlinear Dynamic Behaviors of Rotated Blades with Small Breathing Cracks Based on Vibration Power Flow Analysis

    Directory of Open Access Journals (Sweden)

    Hailong Xu

    2016-01-01

    Full Text Available Rotated blades are key mechanical components in turbomachinery and high cycle fatigues often induce blade cracks. Accurate detection of small cracks in rotated blades is very significant for safety, reliability, and availability. In nature, a breathing crack model is fit for a small crack in a rotated blade rather than other models. However, traditional vibration displacements-based methods are less sensitive to nonlinear characteristics due to small breathing cracks. In order to solve this problem, vibration power flow analysis (VPFA is proposed to analyze nonlinear dynamic behaviors of rotated blades with small breathing cracks in this paper. Firstly, local flexibility due to a crack is derived and then time-varying dynamic model of the rotated blade with a small breathing crack is built. Based on it, the corresponding vibration power flow model is presented. Finally, VPFA-based numerical simulations are done to validate nonlinear behaviors of the cracked blade. The results demonstrate that nonlinear behaviors of a crack can be enhanced by power flow analysis and VPFA is more sensitive to a small breathing crack than displacements-based vibration analysis. Bifurcations will occur due to breathing cracks and subharmonic resonance factors can be defined to identify breathing cracks. Thus the proposed method can provide a promising way for detecting and predicting small breathing cracks in rotated blades.

  5. Evaluation of creep-fatigue crack growth for large-scale FBR reactor vessel and NDE assessment

    Energy Technology Data Exchange (ETDEWEB)

    Joo, Young Sang; Kim, Jong Bum; Kim, Seok Hun; Yoo, Bong

    2001-03-01

    Creep fatigue crack growth contributes to the failure of FRB reactor vessels in high temperature condition. In the design stage of reactor vessel, crack growth evaluation is very important to ensure the structural safety and setup the in-service inspection strategy. In this study, creep-fatigue crack growth evaluation has been performed for the semi-elliptical surface cracks subjected to thermal loading. The thermal stress analysis of a large-scale FBR reactor vessel has been carried out for the load conditions. The distributions of axial, radial, hoop, and Von Mises stresses were obtained for the loading conditions. At the maximum point of the axial and hoop stress, the longitudinal and circumferential surface cracks (i.e. PTS crack, NDE short crack and shallow long crack) were postulated. Using the maximum and minimum values of stresses, the creep-fatigue crack growth of the proposed cracks was simulated. The crack growth rate of circumferential cracks becomes greater than that of longitudinal cracks. The total crack growth of the largest PTS crack is very small after 427 cycles. The structural integrity of a large-scale reactor can be maintained for the plant life. The crack depth growth of the shallow long crack is faster than that of the NDE short crack. In the ISI of the large-scale FBR reactor vessel, the ultrasonic inspection is beneficial to detect the shallow circumferential cracks.

  6. Mechanisms of dwell fatigue crack growth in an advanced nickel disc alloy RR1000

    Directory of Open Access Journals (Sweden)

    Yu S.Y.

    2014-01-01

    Full Text Available RR1000 is one of an advanced class of nickel-based superalloys developed for disc applications. Under one hour dwell fatigue loading, complex crack growth behaviour has been observed especially in a coarse grained version of this alloy. At a temperature of 700 ∘C in air an increase of nearly two orders of magnitude in crack growth rates compared to baseline fatigue crack growth rates may be seen. However for certain microstructural conditions, cracks can also demonstrate retardation following initial acceleration. When using a direct current potential difference (d.c.p.d technique for monitoring crack growth, a damage zone of a few hundred microns is often measured ahead of a fast growing crack. Advanced characterisation techniques including SEM, ECCI and X-ray tomography have been adopted in the current study to understand the observed damage zone and retardation phenomenon. It is found that damage zones measured by d.c.p.d reflect brittle and non-uniform advance of the crack resulting from continuous dynamic or quasi-dynamic fracture of an oxide intrusion ahead of the crack tip during the dwell period. In contrast, cracking of the oxide intrusion is less frequent or even prevented during dwell periods associated with a retarded and slow growing crack. Crack tip stress relaxation plays an important role in dictating whether or not dynamic cracking of the oxide intrusion can be avoided.

  7. FATIGUE GROWTH MODELING OF MIXED-MODE CRACK IN PLANE ELASTIC MEDIA

    Institute of Scientific and Technical Information of China (English)

    Yan Xiangqiao

    2005-01-01

    This paper presents an extension of a displacement discontinuity method with cracktip elements (a boundary element method) proposed by the author for fatigue crack growth analysis in plane elastic media under mixed-mode conditions. The boundary element method consists of the non-singular displacement discontinuity elements presented by Crouch and Starfield and the crack-tip displacement discontinuity elements due to the author. In the boundary element implementation the left or right crack-tip element is placed locally at the corresponding left or right crack tip on top of the non-singular displacement discontinuity elements that cover the entire crack surface and the other boundaries. Crack growth is simulated with an incremental crack extension analysis based on the maximum circumferential stress criterion. In the numerical simulation, for each increment of crack extension, remeshing of existing boundaries is not required because of an intrinsic feature of the numerical approach. Crack growth is modeled by adding new boundary elements on the incremental crack extension to the previous crack boundaries. At the same time, the element characteristics of some related elements are adjusted according to the manner in which the boundary element method is implemented. As an example, the fatigue growth process of cracks emanating from a circular hole in a plane elastic plate is simulated using the numerical simulation approach.

  8. Fatigue Crack Growth Analysis Under Spectrum Loading in Various Environmental Conditions

    Science.gov (United States)

    Mikheevskiy, S.; Glinka, G.; Lee, E.

    2013-03-01

    The fatigue process consists, from the engineering point of view, of three stages: crack initiation, fatigue crack growth, and the final failure. It is also known that the fatigue process near notches and cracks is governed by local strains and stresses in the regions of maximum stress and strain concentrations. Therefore, the fatigue crack growth can be considered as a process of successive crack increments, and the fatigue crack initiation and subsequent growth can be modeled as one repetitive process. The assumptions mentioned above were used to derive a fatigue crack growth model based, called later as the UniGrow model, on the analysis of cyclic elastic-plastic stresses-strains near the crack tip. The fatigue crack growth rate was determined by simulating the cyclic stress-strain response in the material volume adjacent to the crack tip and calculating the accumulated fatigue damage in a manner similar to fatigue analysis of stationary notches. The fatigue crack growth driving force was derived on the basis of the stress and strain history at the crack tip and the Smith-Watson-Topper (SWT) fatigue damage parameter, D = σmaxΔɛ/2. It was subsequently found that the fatigue crack growth was controlled by a two-parameter driving force in the form of a weighted product of the stress intensity range and the maximum stress intensity factor, Δ K p K {max/1- p }. The effect of the internal (residual) stress induced by the reversed cyclic plasticity has been accounted for and therefore the two-parameter driving force made it possible to predict the effect of the mean stress including the influence of the applied compressive stress, tensile overloads, and variable amplitude spectrum loading. It allows estimating the fatigue life under variable amplitude loading without using crack closure concepts. Several experimental fatigue crack growth datasets obtained for the Al 7075 aluminum alloy were used for the verification of the proposed unified fatigue crack growth

  9. Influence of Particulate Reinforcement and Equal-Channel Angular Pressing on Fatigue Crack Growth of an Aluminum Alloy

    Directory of Open Access Journals (Sweden)

    Lisa Köhler

    2015-05-01

    Full Text Available The fatigue crack growth behavior of unreinforced and particulate reinforced Al 2017 alloy, manufactured by powder metallurgy and additional equal-channel angular pressing (ECAP, is investigated. The reinforcement was done with 5 vol % Al2O3 particles with a size fraction of 0.2–2 µm. Our study presents the characterization of these materials by electron microscopy, tensile testing, and fatigue crack growth measurements. Whereas particulate reinforcement leads to a drastic decrease of the grain size, the influence of ECAP processing on the grain size is minor. Both reinforced conditions, with and without additional ECAP processing, exhibit reduced fatigue crack growth thresholds as compared to the matrix material. These results can be ascribed to the well-known effect of the grain size on the crack growth, since crack deflection and closure are directly affected. Despite their small grain size, the thresholds of both reinforced conditions depend strongly on the load ratio: tests at high load ratios reduce the fatigue threshold significantly. It is suggested that the strength of the particle-matrix-interface becomes the critical factor here and that the particle fracture at the interfaces dominates the failure behavior.

  10. 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.

  11. Creep crack growth analysis using C{sub t}-parameter for internal circumferential and external axial surface cracks in a pressurized cylinder

    Energy Technology Data Exchange (ETDEWEB)

    Tun, Nwe Ni; Yang, Hee Seung; Yu, Jong Min; Yoon, Kee Bong [Dept. of Mechanical Engineering, Chung Ang University, Seoul (Korea, Republic of)

    2016-12-15

    Creep crack growth at elevated temperatures is a critical consideration in estimating the remaining life of high temperature structural components and in deciding their inspection interval. In this study, creep crack growth analyses for external radial-axial and internal radial-circumferential surface cracks in a pressurized cylinder were conducted by an analytical method. The effect of crack depth and crack length on the variations in Ct and remaining life predictions were investigated for surface cracks with various initial aspect ratios. It was observed that the remaining life of an internal radial-circumferential surface crack was approximately 53 times longer than that of an external radial-axial surface crack for the same crack size and loading conditions with 316 stainless steel material. It was also observed that the variations in remaining life, crack propagations, and the Ct values were considerably sensitive to the crack location and crack depth. Convergence of crack aspect ratio was not observed when the crack depth ratio was increased. Since the method is independent of material properties and location of the crack geometries, it can be extended to various material properties and various locations of the surface crack geometries.

  12. Complete Tangent Stiffness for eXtended Finite Element Method by including crack growth parameters

    DEFF Research Database (Denmark)

    Mougaard, J.F.; Poulsen, P.N.; Nielsen, L.O.

    2013-01-01

    The eXtended Finite Element Method (XFEM) is a useful tool for modeling the growth of discrete cracks in structures made of concrete and other quasi‐brittle and brittle materials. However, in a standard application of XFEM, the tangent stiffness is not complete. This is a result of not including...... the crack geometry parameters, such as the crack length and the crack direction directly in the virtual work formulation. For efficiency, it is essential to obtain a complete tangent stiffness. A new method in this work is presented to include an incremental form the crack growth parameters on equal terms...

  13. Residual stress relaxation in typical weld joints and its effect on fatigue and crack growth

    Institute of Scientific and Technical Information of China (English)

    Liangbi LI; Zhengquan WAN; Zili WANG; Chunyan JI

    2009-01-01

    Many factors influence the fatigue and crack growth behavior of welded joints. Some structures often undergo fairly large static loading before they enter service or variable amplitude cyclic loading when they are in service. The combined effect of both applied stress and high initial residual stress is expected to cause the residual stresses relaxation. Only a few papers seem to deal with appropriate procedures for fatigue analysis and crack growth by considering the combined effect of variable amplitude cyclic loading with residual stresses relaxation. In this article, some typical welded connections in ship-shaped structures are investigated with 3-D elastic-plastic finite element analysis. The effect of residual stress relaxation, initial residual stress, and the applied load after variable amplitude cyclic loading is revealed, and a formula for predicting the residual stress at hot spot quantitatively is proposed. Based on the formula, an improved fatigue procedure is introduced. Moreover, crack growth of typical weld joints considering residual stresses relaxation is studied.

  14. Thresholds of time dependent intergranular crack growth in a nickel disc alloy Alloy 720Li

    OpenAIRE

    Li Hangyue; Fisk Joe; Lim Lik-Beng; Williams Steve; Bowen Paul

    2014-01-01

    At high temperatures in air, introducing a dwell period at the peak stress of fatigue cycles promotes time dependent intergranular crack growth which can increase crack growth rates by upto a few orders of magnitude from the rates of transgranular fatigue crack growth in superalloys. It is expected that time dependent intergranular crack growth in nickel-based superalloys may not occur below a critical mechanical driving force, ΔKth−IG, analogous to a fatigue threshold (ΔKth) and a critical t...

  15. Crack Growth in Concrete Gravity Dams Based on Discrete Crack Method

    Directory of Open Access Journals (Sweden)

    A. R. Lohrasbi

    2008-01-01

    Full Text Available Seepage is the most parameter in water management safety and in stable agricultural. This seepage is passed through the cracks that are present to some degree in hydraulic structures. They may exist as basic defects in the constituent materials or may be induced in construction or during service life. To avoid such failure in concrete dams, safety would be an important factor. Over-design carries heavy penalty in terms of excess weight. So the fracture mechanics theory is a principal necessity of evaluating the stability of such crack propagation. For the process of crack propagation analysis in concrete structures, there are two general models: discrete crack and smeared crack. This study surveys the crack propagation in concrete gravity dams based on discrete crack methods. Moreover, we use a program provided specifically for this purpose.

  16. A NOVEL PARAMETER FOR EVALUATING THE FATIGUE CRACK GROWTH RATE IN CARBON STEELS

    Institute of Scientific and Technical Information of China (English)

    X.S.Wang; S.Q.Zhu; N.Kawagoishi; H.Nisitani

    2001-01-01

    A novel parameter is suggested for evaluating the fatigue crack growth rate in carbonsteels.Fatigue crack propagation tests of an annealed 0.42% carbon steel were carriedout under different conditions to investigate the relationship between this dominatingparameter and the crack opening displacement (COD).A new equation of fatiguecrack growth rate is formulated in terms of the suggested parameter.The physicalmeanings of the material parameters in this equation are explored experimentally.Considering the relation of crack growth and deformation properties,a simple andapplicable method is proposed to evaluate the fatigue crack growth rate.It is alsoobserved that the material parameters in the fatigue crack growth rate equation ofcarbon steels are related linearly to the material strength.The results are in a goodagreement with experimental results.

  17. Thresholds of time dependent intergranular crack growth in a nickel disc alloy Alloy 720Li

    Directory of Open Access Journals (Sweden)

    Li Hangyue

    2014-01-01

    Full Text Available At high temperatures in air, introducing a dwell period at the peak stress of fatigue cycles promotes time dependent intergranular crack growth which can increase crack growth rates by upto a few orders of magnitude from the rates of transgranular fatigue crack growth in superalloys. It is expected that time dependent intergranular crack growth in nickel-based superalloys may not occur below a critical mechanical driving force, ΔKth−IG, analogous to a fatigue threshold (ΔKth and a critical temperature, Tth. In this study, dwell fatigue crack growth tests have been carefully designed and conducted on Alloy 720Li to examine such thresholds. Unlike a fatigue threshold, the threshold stress intensity factor range for intergranular crack growth is observed to be highly sensitive to microstructure, dwell time and test procedure. The near threshold crack growth behaviour is made complex by the interactions between grain boundary oxidation embrittlement and crack tip stress relaxation. In general, lower ΔKth−IG values are associated with finer grain size and/or shorter dwell times. Often a load increasing procedure promotes stress relaxation and tends to lead to higher ΔKth−IG. When there is limited stress relaxation at the crack tip, similar ΔKth−IG values are measured with load increasing and load shedding procedures. They are generally higher than the fatigue threshold (ΔKth despite faster crack growth rates (da/dN in the stable crack growth regime. Time dependent intergranular crack growth cannot be activated below a temperature of 500 ∘C.

  18. Effects of the Loading and Unloading Conditions on the Stress Relaxation Behavior of Pre-cracked Granite

    Science.gov (United States)

    Yang, Haiqing; Liu, Junfeng; Zhou, Xiaoping

    2017-05-01

    The relaxation behavior plays an important role in evaluating the long-term safety of the surrounding rock mass. Normally, the characters of the stress relaxation behavior of a rock mass can be described as the time-dependent rheological crack propagation features. Based on the subcritical crack growth parameters obtained in the double-torsion experiment, the stress relaxation behavior of pre-cracked granite column specimens is presented. The results of the stress relaxation tests indicate that for a certain confining pressure level, the increase in the uniaxial strain contributes to the propagation of the rheological cracks. For stress relaxation tests conducted under different confining pressure conditions, the propagation of the rheological cracks depends mainly on the D value of the axial and confining pressures. Specifically, the rheological cracks tend to propagate more sufficiently with a higher D value. The experimental results are in good agreement with the analytical solution, in accordance with the Burgers model. Furthermore, the results of the stress relaxation tests conducted under different unloading rates show that the relaxation behavior of the studied material tends to be more obvious for a relatively lower unloading rate of the confining pressure. Finally, the failure patterns obtained under stress relaxation and traditional tests are compared. In detail, for the specimens in the traditional triaxial compression test, the fracture is caused by the abrupt coalescence of the wing cracks and the failure is tensile-shear mixed mode, whereas during the stress relaxation test, the failure is transformed into the smooth coalescence of the tensile rheological cracks. The present research can increase the understanding of the relaxation behavior of hard rock under different engineering environments.

  19. Hydrogen adsorption and diffusion, and subcritical-crack growth in high strength steels and nickel base alloys

    Science.gov (United States)

    Wei, R. P.; Klier, K.; Simmons, G. W.; Chornet, E.

    1973-01-01

    Embrittlement, or the enhancement of crack growth by gaseous hydrogen in high strength alloys, is of primary interest in selecting alloys for various components in the space shuttle. Embrittlement is known to occur at hydrogen gas pressures ranging from fractions to several hundred atmospheres, and is most severe in the case of martensitic high strength steels. Kinetic information on subcritical crack growth in gaseous hydrogen is sparse at this time. Corroborative information on hydrogen adsorption and diffusion is inadequate to permit a clear determination of the rate controlling process and possible mechanism in hydrogen enhanced crack growth, and for estimating behavior over a range of temperatures and pressures. Therefore, coordinated studies of the kinetics of crack growth, and adsorption and diffusion of hydrogen, using identical materials, have been initiated. Comparable conditions of temperature and pressure will be used in the chemical and mechanical experiments. Inconel 718 alloy and 18Ni(200) maraging steel have been selected for these studies. Results from these studies are expected to provide not only a better understanding of the gaseous hydrogen embrittlement phenomenon itself, but also fundamental information on hydrogen adsorption and diffusion, and crack growth information that can be used directly for design.

  20. Chemical and metallurgical aspects of environmentally assisted fatigue crack growth in 7075-T651 aluminum alloy

    Science.gov (United States)

    Gao, Ming; Wei, R. P.; Pao, P. S.

    1988-07-01

    A comprehensive study has been carried out on a 7075-T651 alloy to examine the influence of water vapor on fatigue crack growth. The kinetics of fatigue crack growth were determined as a function of water vapor pressure at room temperature and at 353 K. Detailed fractographic analyses and surface chemistry studies were carried out to identify the micromechanisms and to quantify the chemical interactions for corrosion fatigue crack growth in this alloy. Experiments were also carried out in ultra-high vacuum and in oxygen to provide for comparisons. Two regions of fatigue crack growth response were identified. In the low pressure region (below 67 Pa at 5 Hz), crack growth is controlled by the rate of transport of water vapor to the crack tip, and the response can be described by a model for transport controlled crack growth. At pressures above 67 Pa, additional increases in crack growth rate occurred, which are attributed to the further reactions of water vapor with segregated magnesium in this alloy. Different micromechanisms for crack growth have been identified for vacuum, oxygen, and water vapor. These micromechanisms are considered in relation to the environmental parameters through a modified superposition model for corrosion fatigue.

  1. 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.

  2. Multiple Crack Growth Prediction in AA2024-T3 Friction Stir Welded Joints, Including Manufacturing Effects

    DEFF Research Database (Denmark)

    Carlone, Pierpaolo; Citarella, Roberto; Sonne, Mads Rostgaard

    2016-01-01

    boundary element method (FEM-DBEM) procedure, coupling the welding process simulation to the subsequent crack growth assessment, is proposed and applied to simulate multiple crack propagation, with allowance for manufacturing effects. The friction stir butt welding process of the precipitation hardened AA......2024-T3 alloy was simulated using a thermo-mechanical FEM model to predict the process induced residual stress field and material softening. The computed stress field was transferred to a DBEM environment and superimposed to the stress field produced by a remote fatigue traction load applied......A great deal of attention is currently paid by several industries toward the friction stir welding process to realize lightweight structures. Within this aim, the realistic prediction of fatigue behavior of welded assemblies is a key factor. In this work an integrated finite element method - dual...

  3. Slow Crack Growth of Brittle Materials With Exponential Crack-Velocity Formulation. Part 2; Constant Stress Rate Experiments

    Science.gov (United States)

    Choi, Sung R.; Nemeth, Noel N.; Gyekenyesi, John P.

    2002-01-01

    The previously determined life prediction analysis based on an exponential crack-velocity formulation was examined using a variety of experimental data on glass and advanced structural ceramics in constant stress rate and preload testing at ambient and elevated temperatures. The data fit to the relation of strength versus the log of the stress rate was very reasonable for most of the materials. Also, the preloading technique was determined equally applicable to the case of slow-crack-growth (SCG) parameter n greater than 30 for both the power-law and exponential formulations. The major limitation in the exponential crack-velocity formulation, however, was that the inert strength of a material must be known a priori to evaluate the important SCG parameter n, a significant drawback as compared with the conventional power-law crack-velocity formulation.

  4. Slow Crack Growth of Brittle Materials With Exponential Crack-Velocity Formulation. Part 3; Constant Stress and Cyclic Stress Experiments

    Science.gov (United States)

    Choi, Sung R.; Nemeth, Noel N.; Gyekenyesi, John P.

    2002-01-01

    The previously determined life prediction analysis based on an exponential crack-velocity formulation was examined using a variety of experimental data on advanced structural ceramics tested under constant stress and cyclic stress loading at ambient and elevated temperatures. The data fit to the relation between the time to failure and applied stress (or maximum applied stress in cyclic loading) was very reasonable for most of the materials studied. It was also found that life prediction for cyclic stress loading from data of constant stress loading in the exponential formulation was in good agreement with the experimental data, resulting in a similar degree of accuracy as compared with the power-law formulation. The major limitation in the exponential crack-velocity formulation, however, was that the inert strength of a material must be known a priori to evaluate the important slow-crack-growth (SCG) parameter n, a significant drawback as compared with the conventional power-law crack-velocity formulation.

  5. A study on fatigue crack growth in dual phase martensitic steel in air environment

    Indian Academy of Sciences (India)

    K V Sudhakar; E S Dwarakadasa

    2000-06-01

    Dual phase (DP) steel was intercritically annealed at different temperatures from fully martensitic state to achieve martensite plus ferrite, microstructures with martensite contents in the range of 32 to 76%. Fatigue crack growth (FCG) and fracture toughness tests were carried out as per ASTM standards E 647 and E 399, respectively to evaluate the potential of DP steels. The crack growth rates (/) at different stress intensity ranges ( ) were determined to obtain the threshold value of stress intensity range ( th). Crack path morphology was studied to determine the influence of microstructure on crack growth characteristics. After the examination of crack tortuosity, the compact tension (CT) specimens were pulled in static mode to determine fracture toughness values. FCG rates decreased and threshold values increased with increase in vol.% martensite in the DP steel. This is attributed to the lower carbon content in the martensite formed at higher intercritical annealing (ICA) temperatures, causing retardation of crack growth rate by crack tip blunting and/or deflection. Roughness induced crack closure was also found to contribute to the improved crack growth resistance at higher levels of martensite content. Scanning electron fractography of DP steel in the near threshold region revealed transgranular cleavage fracture with secondary cracking. Results indicate the possibility that the DP steels may be treated to obtain an excellent combination of strength and fatigue properties.

  6. DETERMINISTIC EVALUATION OF DELAYED HYDRIDE CRACKING BEHAVIORS IN PHWR PRESSURE TUBES

    Directory of Open Access Journals (Sweden)

    YOUNG-JIN OH

    2013-04-01

    Full Text Available Pressure tubes made of Zr-2.5 wt% Nb alloy are important components consisting reactor coolant pressure boundary of a pressurized heavy water reactor, in which unanticipated through-wall cracks and rupture may occur due to a delayed hydride cracking (DHC. The Canadian Standards Association has provided deterministic and probabilistic structural integrity evaluation procedures to protect pressure tubes against DHC. However, intuitive understanding and subsequent assessment of flaw behaviors are still insufficient due to complex degradation mechanisms and diverse influential parameters of DHC compared with those of stress corrosion cracking and fatigue crack growth phenomena. In the present study, a deterministic flaw assessment program was developed and applied for systematic integrity assessment of the pressure tubes. Based on the examination results dealing with effects of flaw shapes, pressure tube dimensional changes, hydrogen concentrations of pressure tubes and plant operation scenarios, a simple and rough method for effective cooldown operation was proposed to minimize DHC risks. The developed deterministic assessment program for pressure tubes can be used to derive further technical bases for probabilistic damage frequency assessment.

  7. An investigation of environmental effects on fatigue crack growth in Q1N (HY80) steel

    Science.gov (United States)

    Soboyejo, W. O.; Knott, J. F.

    1990-11-01

    Fatigue threshold tests have been conducted on through-thickness and semielliptic cracks in laboratory air, vacuum, and salt water at stress ratios (R = Kmin/Kmax @#@) of 0.2 and 0.7. The effects of stress ratio are rationalized by crack closure concepts. Environmental effects are explained by considerations of the irreversibility of slip at the crack tip and the role of debris on the fracture surfaces. Differences in the fatigue crack growth rates in the three environments are attributed largely to the extent of the irreversibility of slip due to the chemisorption of water/ water vapor at the crack tip. Debris in saltwater solutions is also shown to significantly affect the near-threshold growth through its influence on crack closure and the transportation of environment to the crack tip.

  8. The effects of cold rolling orientation and water chemistry on stress corrosion cracking behavior of 316L stainless steel in simulated PWR water environments

    Science.gov (United States)

    Chen, Junjie; Lu, Zhanpeng; Xiao, Qian; Ru, Xiangkun; Han, Guangdong; Chen, Zhen; Zhou, Bangxin; Shoji, Tetsuo

    2016-04-01

    Stress corrosion cracking behaviors of one-directionally cold rolled 316L stainless steel specimens in T-L and L-T orientations were investigated in hydrogenated and deaerated PWR primary water environments at 310 °C. Transgranular cracking was observed during the in situ pre-cracking procedure and the crack growth rate was almost not affected by the specimen orientation. Locally intergranular stress corrosion cracks were found on the fracture surfaces of specimens in the hydrogenated PWR water. Extensive intergranular stress corrosion cracks were found on the fracture surfaces of specimens in deaerated PWR water. More extensive cracks were found in specimen T-L orientation with a higher crack growth rate than that in the specimen L-T orientation with a lower crack growth rate. Crack branching phenomenon found in specimen L-T orientation in deaerated PWR water was synergistically affected by the applied stress direction as well as the preferential oxidation path along the elongated grain boundaries, and the latter was dominant.

  9. Subcritical crack growth under mode I, II, and III loading for Coconino sandstone

    Science.gov (United States)

    Ko, Tae Young

    In systems subjected to long-term loading, subcritical crack growth is the principal mechanism causing the time-dependent deformation and failure of rocks. Subcritical crack growth is environmentally-assisted crack growth, which can allow cracks to grow over a long period of time at stresses far smaller than their failure strength and at tectonic strain rates. The characteristics of subcritical crack growth can be described by a relationship between the stress intensity factor and the crack velocity. This study presents the results of studies conducted to validate the constant stress-rate test for determining subcritical crack growth parameters in Coconino sandstone, compared with the conventional testing method, the double torsion test. The results of the constant stress-rate test are in good agreement with the results of double torsion test. More importantly, the stress-rate tests can determine the parameter A with a much smaller standard deviation than the double torsion test. Thus the constant stress-rate test seems to be both a valid and preferred test method for determining the subcritical crack growth parameters in rocks. We investigated statistical aspects of the constant stress-rate test. The effects of the number of tests conducted on the subcritical crack growth parameters were examined and minimum specimen numbers were determined. The mean and standard deviation of the subcritical crack growth parameters were obtained by randomly selecting subsets from the original strength data. In addition, the distribution form of the subcritical crack growth parameters and the relation between the parameter n and A were determined. We extended the constant stress-rate test technique to modes II and III subcritical crack growth in rocks. The experimental results of the modes I, II and III tests show that the values of the subcritical crack growth parameters are similar to each other. The subcritical crack growth parameter n value for Coconino sandstone has the range

  10. COMBINED DELAUNAY TRIANGULATION AND ADAPTIVE FINITE ELEMENT METHOD FOR CRACK GROWTH ANALYSIS

    Institute of Scientific and Technical Information of China (English)

    Pramote DECHAUMPHAI; Sutthisak PHONGTHANAPANICH; Thanawat SRICHAROENCHAI

    2003-01-01

    The paper presents the utilization of the adaptive Delaunay triangulation in the finite element modeling of two dimensional crack propagation problems, including detailed description of the proposed procedure which consists of the Delaunay triangulation algorithm and an adaptive remeshing technique. The adaptive remeshing technique generates small elements around crack tips and large elements in the other regions. The resulting stress intensity factors and simulated crack propagation behavior are used to evaluate the effectiveness of the procedure. Three sample problems of a center cracked plate, a single edge cracked plate and a compact tension specimen, are simulated and their results assessed.

  11. Effects of loading variables on fatigue-crack growth in liquid-metal environments

    CSIR Research Space (South Africa)

    Fernandes, PJL

    1995-10-01

    Full Text Available is examined using standard LEFM testing procedures. The effects of environment, load ratio, cyclic frequency and load waveform on the rate of crack growth are investigated. At Delta K > Delta K-th, crack growth rates are approximately an order of magnitude...

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

    DEFF Research Database (Denmark)

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

    2015-01-01

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

  13. Theoretical and numerical studies on morphological transitions in crack growth

    CERN Document Server

    Mühle, V

    1999-01-01

    This paper investigates the formation of crack patterns in stationary and transient temperature fields analytically with linear elastic fracture mechanics and numerically with the finite elements method (FEM). In particular, we consider the experimental situation of a narrow thin strip of hot glass slowly lowered into cold water, with temperature difference and velocity as variable parameters. The parameter regions of no crack, one straight crack and one oscillating crack are determined. The type of phase transition related to the borderline between straight and oscillating crack is characterized. The theoretical results are compared with those of other Similar investigations and comparisons are done for the propagation of multiple cracks. Quenching of a wide thin strip leads to a hierarchy of cracks whose scaling properties are analyzed. Without any fitting, theory and experiment agree surprisingly well.

  14. Influence of K{sub max} and r on fatigue crack growth - A 3D-model

    Energy Technology Data Exchange (ETDEWEB)

    Gudladt, Hans-Joachim [Institut fuer Werkstoffkunde, Universitaet der Bundeswehr Muenchen, Neubiberg (Germany); Steinbock, Johanna [Lehrstuhl fuer Werkstoffkunde und Werkstoffmechanik, Technische Universitaet Muenchen, Garching (Germany)

    2010-04-15

    To study the influence of the stress intensity factor and the R-ratio on the fatigue crack growth rate different kind of crack propagation experiment have been carried out on the steels X5CrNi18-10 and C45E. The experiments show that both parameters the maximum stress intensity K{sub max} and the R-ratio affect the crack growth rate. Consequently, the authors developed a 3D-model, which describes the dependence of da/dN on K{sub max} and the R-ratio. Discussing the experiments, special attention has been paid to the threshold behavior of the investigated materials. Finally, a new model to describe the influence of the R-ratio on the threshold K{sub max,th} for R-ratios from -{infinity} to 1 is presented. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  15. Numerical investigation on stress corrosion cracking behavior of dissimilar weld joints in pressurized water reactor plants

    Directory of Open Access Journals (Sweden)

    Lingyan Zhao

    2014-07-01

    Full Text Available There have been incidents recently where stress corrosion cracking (SCC observed in the dissimilar metal weld (DMW joints connecting the reactor pressure vessel (RPV nozzle with the hot leg pipe. Due to the complex microstructure and mechanical heterogeneity in the weld region, dissimilar metal weld joints are more susceptible to SCC than the bulk steels in the simulated high temperature water environment of pressurized water reactor (PWR. Tensile residual stress (RS, in addition to operating loads, has a great contribution to SCC crack growth. Limited experimental conditions, varied influence factors and diverging experimental data make it difficult to accurately predict the SCC behavior of DMW joints with complex geometry, material configuration, operating loads and crack shape. Based on the film slip/dissolution oxidation model and elastic-plastic finite element method (EPFEM, an approach is developed to quantitatively predict the SCC growth rate of a RPV outlet nozzle DMW joint. Moreover, this approach is expected to be a pre-analytical tool for SCC experiment of DMW joints in PWR primary water environment.

  16. Crack growth behaviour of low alloy steels for pressure boundary components under transient light water reactor operating conditions (CASTOC)

    Energy Technology Data Exchange (ETDEWEB)

    Foehl, J.; Weissenberg, T. [Materialpruefungsanstalt, Univ. Stuttgart (Germany); Gomez-Briceno, D.; Lapena, J. [Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas (CIEMAT) (Spain); Ernestova, M.; Zamboch, M. [Nuclear Research Inst. (NRI) (Czech Republic); Seifert, H.P.; Ritter, S. [Paul Scherrer Inst. (PSI) (Switzerland); Roth, A.; Devrient, B. [Framatome ANP GmbH (F ANP) (Germany); Ehrnsten, U. [Technical Research Centre of Finland (VTT) (Finland)

    2004-07-01

    water at stress intensity factors above the limit for linear elastic fracture mechanics. There is evidence that the prediction curves of the ASME Boiler and Pressure Vessel Code Section XI, Appendix A are not conservative for some relevant cases with regard to crack growth rates under cyclic load even in oxygenated high purity BWR water. The CASTOC results have provided an important contribution to the understanding of crack growth behavior on the one hand as a function of time and on the other hand as a consequence of the number and height of loading events. This is an important key for the evaluation of transient events, which may occur in a plant during service. (orig.)

  17. Influence of crack shielding on subcritical crack growth in zirconia ceramics; Influencia del apantallamientoen la propagacion subcritica de fisuras en materiales de circona

    Energy Technology Data Exchange (ETDEWEB)

    Casellas, D.; Feder, A.; Llanes, L.; Anglada, M.

    2001-07-01

    The increase in fatigue life under a constant applied load, due to the presence of crack shielding, was studied. Time to failure was estimated by using a mathematical function that describes the crack shielding developed during subcritical crack growth. Such results were compared with experimental fatigue lives obtained in Y-TZP/PSZ materials. From this it may be concluded that the initial slope of crack shielding curves greatly influences the rime to failure. (Author) 5 refs.

  18. Behavior of Stress Corrosion Cracking in a Magnesium Alloy

    Institute of Scientific and Technical Information of China (English)

    SONG Renguo; YANG Fanger; BLAWERT Carsten; DIETZEL Wolfgang

    2009-01-01

    Slow strain rate testing (SSRT) was employed to study the stress corrosion cracking (SCC) behavior of ZE41 magnesium alloy in 0.01 M NaCl solution. Smooth tensile specimens with different thicknesses were strained dynamically in both longitudinal and transverse direction under permanent immersions at a strain rate of 10-6 s-1. It is found that ZE41 magnesium alloy is susceptible to SCC in 0.01 M NaCl solution. The SCC susceptibility of the thinner specimen is lower than that of the thicker specimen. Also, the longitudinal specimens are slightly more susceptible to SCC than the transverse specimens. The SCC mechanism of magnesium alloy is attributed to the combination of anodic dissolution with hydrogen embrittlement.

  19. Influence of bending test configuration on cracking behavior of FRC

    DEFF Research Database (Denmark)

    Finazzi, Silvia; Paegle, Ieva; Fischer, Gregor;

    2014-01-01

    This paper describes an investigation of the influence of the testing configuration for Fiber Reinforced Concrete in bending and aims at evaluating the influence of the test configuration details on the characterization of the material. Two different types of FRC, Steel Fiber Reinforced Concrete...... (SFRC) and Engineered Cementitious Composites (ECC), were tested and are described in this study. The materials were chosen so that one of them would be strain hardening (ECC) and the other tension softening (SFRC). Notched and un-notched three- and four-point bending tests were carried out to determine...... 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...

  20. Subcritical crack growth in oxide and non-oxide ceramics using the Constant Stress Rate Test

    Directory of Open Access Journals (Sweden)

    Agnieszka Wojteczko

    2015-12-01

    Full Text Available Fracture toughness is one of the most important parameters for ceramics description. In some cases, material failure occurs at lower stresses than described by KIc parameter. In these terms, determination of fracture toughness only, proves to be insufficient. This may be due to environmental factors, such as humidity, which might cause subcritical crack propagation in a material. Therefore, it is very important to estimate crack growth velocities to predict lifetime of ceramics used under specific conditions. Constant Stress Rate Test is an indirect method of subcritical crack growth parameters estimation. Calculations are made by using strength data, thus avoiding crack measurement. The expansion of flaws causes reduction of material strength. If subcritical crack growth phenomenon occurs, critical value of crack lengths increases with decreasing stress rate due to longer time for flaw to grow before the critical crack propagation at KIc takes place. Subcritical crack growth phenomenon is particularly dangerous for oxide ceramics due to chemical interactions occurring as a result of exposure to humidity. This paper presents results of Constant Stress Rate Test performed for alumina, zirconia, silicon carbide and silicon nitride in order to demonstrate the differences in subcritical crack propagation phenomenon course.

  1. The reduction in fatigue crack growth resistance of dentin with depth.

    Science.gov (United States)

    Ivancik, J; Neerchal, N K; Romberg, E; Arola, D

    2011-08-01

    The fatigue crack growth resistance of dentin was characterized as a function of depth from the dentino-enamel junction. Compact tension (CT) specimens were prepared from the crowns of third molars in the deep, middle, and peripheral dentin. The microstructure was quantified in terms of the average tubule dimensions and density. Fatigue cracks were grown in-plane with the tubules and characterized in terms of the initiation and growth responses. Deep dentin exhibited the lowest resistance to the initiation of fatigue crack growth, as indicated by the stress intensity threshold (ΔK(th) ≈ 0.8 MPa•m(0.5)) and the highest incremental fatigue crack growth rate (over 1000 times that in peripheral dentin). Cracks in deep dentin underwent incremental extension under cyclic stresses that were 40% lower than those required in peripheral dentin. The average fatigue crack growth rates increased significantly with tubule density, indicating the importance of microstructure on the potential for tooth fracture. Molars with deep restorations are more likely to suffer from the cracked-tooth syndrome, because of the lower fatigue crack growth resistance of deep dentin.

  2. Direct assessment of tensile stress-crack opening behavior of Strain Hardening Cementitious Composites (SHCC)

    DEFF Research Database (Denmark)

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

    2012-01-01

    at the level of a single crack. The derived tensile stress-crack opening behavior is utilized to analyze and compare the influence of various composite parameters on the resulting tensile behavior. The deformations occurring during tensile loading are furthermore examined using a digital image...

  3. Interface debond crack growth in tension–tension cyclic loading of single fiber polymer composites

    DEFF Research Database (Denmark)

    Pupurs, Andrejs; Goutianos, Stergios; Brøndsted, Povl;

    2013-01-01

    Fiber/matrix interface debond crack growth from a fiber break is defined as one of the key mechanisms of fatigue damage in unidirectional composites. Considering debond as an interface crack its growth in cyclic loading is analyzed utilizing a power law, where the debond growth rate is a power...... for glass fiber/epoxy single fiber composites. Analytical method in the steady-state growth region and FEM for short debonds are combined for calculating the strain energy release rate of the growing debond crack. Interface failure parameters in fatigue are determined by fitting the modeling...

  4. Application of the cracked pipe element to creep crack growth prediction

    Energy Technology Data Exchange (ETDEWEB)

    Brochard, J.; Charras, T.

    1997-04-01

    The modification of a computer code for leak before break analysis is very briefly described. The CASTEM2000 code was developed for ductile fracture assessment of piping systems with postulated circumferential through-wall cracks under static or dynamic loading. The modification extends the capabilities of the cracked pipe element to the determination of fracture parameters under creep conditions (C*, {phi}c and {Delta}c). The model has the advantage of evaluating significant secondary effects, such as those from thermal loading.

  5. Fatigue Crack Closure Analysis Using Digital Image Correlation

    Science.gov (United States)

    Leser, William P.; Newman, John A.; Johnston, William M.

    2010-01-01

    Fatigue crack closure during crack growth testing is analyzed in order to evaluate the critieria of ASTM Standard E647 for measurement of fatigue crack growth rates. Of specific concern is remote closure, which occurs away from the crack tip and is a product of the load history during crack-driving-force-reduction fatigue crack growth testing. Crack closure behavior is characterized using relative displacements determined from a series of high-magnification digital images acquired as the crack is loaded. Changes in the relative displacements of features on opposite sides of the crack are used to generate crack closure data as a function of crack wake position. For the results presented in this paper, remote closure did not affect fatigue crack growth rate measurements when ASTM Standard E647 was strictly followed and only became a problem when testing parameters (e.g., load shed rate, initial crack driving force, etc.) greatly exceeded the guidelines of the accepted standard.

  6. Crack growth in the through-thickness direction of hydrided thin-wall Zircaloy sheet

    Science.gov (United States)

    Raynaud, Patrick A.; Koss, Donald A.; Motta, Arthur T.

    2012-01-01

    In a reactivity-initiated accident, cladding failure may occur by crack initiation within a defect such as a hydride rim or blister and subsequent crack propagation through the thickness of the thin-wall cladding. In such a circumstance, determining the cladding resistance to crack propagation in the through-thickness direction is crucial to predicting cladding failure. To address this issue, through-thickness crack propagation in hydrided Zircaloy-4 sheet was analyzed at 25 °C, 300 °C, and 375 °C. At 25 °C, the fracture toughness decreased with increasing hydrogen content and with an increasing fraction of radial hydrides. Hydride particles fractured ahead of the crack tip, creating a path for crack growth. At both 300 °C and 375 °C, the resistance to crack-growth initiation was sufficiently high that crack extension was often caused by crack-tip blunting. There was no evidence of hydride particles fracturing near the crack tip, and no significant effect of hydrogen content on fracture toughness was observed at these elevated temperatures.

  7. Effects of microstructure and crystallography on crack path and intrinsic resistance to shear-mode fatigue crack growth

    Directory of Open Access Journals (Sweden)

    J. Pokluda

    2015-10-01

    Full Text Available The paper focuses on the effective resistance and the near-threshold growth mechanisms in the ferritic-pearlitic and the pure pearlitic steel. The influence of microstructure on the shear-mode fatigue crack growth is divided here into two factors: the crystal lattice type and the presence of different phases. Experiments were done on ferritic-pearlitic steel and pearlitic steel using three different specimens, for which the effective mode II and mode III threshold values were measured and fracture surfaces were reconstructed in three dimensions using stereophotogrammetry in scanning electron microscope. The ferritic-pearlitic and pearlitic steels showed a much different behaviour of modes II and III cracks than that of the ARMCO iron. Both the deflection angle and the mode II threshold were much higher and comparable to the austenitic steel. Mechanism of shear-mode crack behaviour in the ARMCO iron, titanium and nickel were described by the model of emission of dislocations from the crack tip under a dominant mode II loading. In other tested materials the cracks propagated under a dominance of the local mode I. In the ferritic-pearlitic and pearlitic steels, the reason for such behaviour was the presence of the secondary-phase particles (cementite lamellas, unlike in the previously austenitic steel, where the fcc structure and the low stacking fault energy were the main factors. A criterion for mode I deflection from the mode II crack-tip loading, which uses values of the effective mode I and mode II thresholds, was in agreement with fractographical observations.

  8. The Shrinkage Cracking Behavior in Reinforced Reactive Powder Concrete Walls

    Directory of Open Access Journals (Sweden)

    Samir A. Al-Mashhadi

    2017-07-01

    Full Text Available In this study, the reduced scale wall models were used (they are believed to resemble as much as possible the field conditions to study the shrinkage behavior of reactive powder concrete (RPC base restrained walls. Six base restrained RPC walls were casted in different length/height ratios of two ratios of steel fiber by volume in Summer. These walls were restrained by reinforced concrete bases to provide the continuous base restraint to the walls. The mechanical properties of reactive powder concrete investigated were; compressive strength between (75.3 – 140.1 MPa, splitting tensile strength between (5.7 – 13.9 MPa, flexural tensile strength (7.7 – 24.5 MPa, and static modulus of elasticity (32.7 – 47.1GPa. Based on the observations of this work, it was found that the cracks did not develop in the reduced scale of the reactive powder concrete (RPC walls restrained from movement at their bases for different L/H ratios (2, 5, and 10 and for two ratio of steel fiber (1% & 2% during 90 days period of drying conditions. Moreover, the shrinkage values increase toward the edges. Based on the results of this work, the increase in the maximum shrinkage values of walls with 1% steel fiber were (29%, 28%, 28% of the maximum shrinkage values of walls with 2% steel fiber of length/height ratios of (2, 5, and 10 respectively. The experimental observation in beam specimens showed that the free shrinkage, tensile strain capacity and elastic tensile strain capacity (at date of cracking of beams with 1% steel fiber were higher than the beams with 2% steel fiber by about (24%, (45% and (42% respectively

  9. Fatigue crack growth monitoring of idealized gearbox spline component using acoustic emission

    Science.gov (United States)

    Zhang, Lu; Ozevin, Didem; Hardman, William; Kessler, Seth; Timmons, Alan

    2016-04-01

    The spline component of gearbox structure is a non-redundant element that requires early detection of flaws for preventing catastrophic failures. The acoustic emission (AE) method is a direct way of detecting active flaws; however, the method suffers from the influence of background noise and location/sensor based pattern recognition method. It is important to identify the source mechanism and adapt it to different test conditions and sensors. In this paper, the fatigue crack growth of a notched and flattened gearbox spline component is monitored using the AE method in a laboratory environment. The test sample has the major details of the spline component on a flattened geometry. The AE data is continuously collected together with strain gauges strategically positions on the structure. The fatigue test characteristics are 4 Hz frequency and 0.1 as the ratio of minimum to maximum loading in tensile regime. It is observed that there are significant amount of continuous emissions released from the notch tip due to the formation of plastic deformation and slow crack growth. The frequency spectra of continuous emissions and burst emissions are compared to understand the difference of sudden crack growth and gradual crack growth. The predicted crack growth rate is compared with the AE data using the cumulative AE events at the notch tip. The source mechanism of sudden crack growth is obtained solving the inverse mathematical problem from output signal to input signal. The spline component of gearbox structure is a non-redundant element that requires early detection of flaws for preventing catastrophic failures. In this paper, the fatigue crack growth of a notched and flattened gearbox spline component is monitored using the AE method The AE data is continuously collected together with strain gauges. There are significant amount of continuous emissions released from the notch tip due to the formation of plastic deformation and slow crack growth. The source mechanism of

  10. The Effects of Salt Water on the Slow Crack Growth of Soda Lime Silicate Glass

    Science.gov (United States)

    Hausmann, Bronson D.; Salem, Jonathan A.

    2016-01-01

    The slow crack growth parameters of soda-lime silicate were measured in distilled and salt water of various concentrations in order to determine if stress corrosion susceptibility is affected by the presence of salt and the contaminate formation of a weak sodium film. Past research indicates that solvents effect the rate of crack growth, however, the effects of salt have not been studied. The results indicate a small but statistically significant effect on the slow crack growth parameters A and n. However, for typical engineering purposes, the effect can be ignored.

  11. 7075-T6 and 2024-T351 Aluminum Alloy Fatigue Crack Growth Rate Data

    Science.gov (United States)

    Forth, Scott C.; Wright, Christopher W.; Johnston, William M., Jr.

    2005-01-01

    Experimental test procedures for the development of fatigue crack growth rate data has been standardized by the American Society for Testing and Materials. Over the past 30 years several gradual changes have been made to the standard without rigorous assessment of the affect these changes have on the precision or variability of the data generated. Therefore, the ASTM committee on fatigue crack growth has initiated an international round robin test program to assess the precision and variability of test results generated using the standard E647-00. Crack growth rate data presented in this report, in support of the ASTM roundrobin, shows excellent precision and repeatability.

  12. Fatigue crack growth from handling surface anomalies in a Nickel based superalloy at high temperature

    Directory of Open Access Journals (Sweden)

    Gourdin Stéphane

    2014-06-01

    Full Text Available Aircraft engine manufacturers have to demonstrate that handling surface anomalies in sensible areas of discs are not critical for in-service life of a component. Currently, the models used consider anomalies as long cracks propagating from the first cycle, which introduce a certain degree of conservatism when calculating the fatigue life of surface flaws. Preliminary studies have shown that the first stages of crack propagation from surface anomalies are responsible for the conservative results. Thus, the aim of the study is to characterize the crack propagation from typical surface anomalies and to establish a new crack growth model, which can account for the micro-propagation stage.

  13. Finite element simulation of stress intensity factors in elastic-plastic crack growth

    Institute of Scientific and Technical Information of China (English)

    ALSHOAIBI Abdulnaser M.; ARIFFIN Ahmad Kamal

    2006-01-01

    A finite element program developed elastic-plastic crack propagation simulation using Fortran language. At each propagation step, the adaptive mesh is automatically refined based on a posteriori h-type refinement using norm stress error estimator. A rosette of quarter-point elements is then constructed around the crack tip to facilitate the prediction of crack growth based on the maximum normal stress criterion and to calculate stress intensity factors under plane stress and plane strain conditions.Crack was modelled to propagate through the inter-element in the mesh. Some examples are presented to show the results of the implementation.

  14. HIGH TEMPERATURE FATIGUE CRACK GROWTH BEHAVIOR OF A NOVEL POWDER METALLURGY SUPERALLOY FGH98%新型镍基粉末高温合金FGH98的高温疲劳裂纹扩展行为研究

    Institute of Scientific and Technical Information of China (English)

    杨健; 董建新; 张麦仓; 贾建; 陶宇

    2013-01-01

    测定了新型粉末高温合金FGH98在650℃空气环境中的疲劳裂纹扩展速率,与前两代粉末高温合金FGH95和FGH96的裂纹扩展速率进行了比较分析,研究了合金显微结构以及保载时间对FGH98合金裂纹扩展速率的影响.结果表明,FGH98合金的高温疲劳裂纹扩展抗力较前两代粉末高温合金有了明显提高.控制固溶后以适当的方式冷却,使得二次和三次γ′相均匀匹配析出,可以获得具有良好疲劳裂纹扩展抗力的合金组织.粗晶组织有利于降低FGH98合金的疲劳裂纹扩展速率,尤其是在近门槛区.FGH98合金的高温疲劳裂纹扩展速率随保载时间的增加而增加,其断裂模式相应地从穿晶-沿晶混合断裂变为沿晶断裂.%Powder metallurgy superalloys are important materials for manufacturing aero engine turbine disks which are subjected to loading in the forms of fatigue and creep-fatigue in service. In order to meet the increasing demands for advanced aero engines with high thrust-weight ratios, a novel generation of Ni-based powder metallurgy superalloy FGH98 was developed, which was expected to have high strength and good damage tolerance property. For the sake of examining the fatigue crack growth resistance of FGH98, the fatigue crack growth rate of this novel superalloy was investigated at 650℃ in air and then compared with those of the first two generations of powder metallurgy superalloys FGH95 and FGH96. The effects of microstructures and hold-time on the fatigue crack growth behavior of FGH98 were studied. It was found that the fatigue crack growth resistance of FGH98 was significantly improved in comparison with those of FGH95 and FGH96. Conducting proper cooling methods after solution could make the secondary and tertiary γ' phase precipitate in a uniform order, causing that the alloy could have good fatigue crack propagation resistance. It was also found that FGH98 with coarser grains showed a lower fatigue crack

  15. 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.

  16. Effect of fracture surface roughness on shear crack growth

    Energy Technology Data Exchange (ETDEWEB)

    Gross, T.S.; Watt, D.W. (New Hampshire Univ., Durham, NH (United States). Dept. of Mechanical Engineering); Mendelsohn, D.A. (Ohio State Univ., Columbus, OH (United States). Dept. of Engineering Mechanics)

    1992-12-01

    A model of fracture surface interference for Mode I fatigue crack profiles was developed and evaluated. Force required to open the crack faces is estimated from point contact expressions for Mode I stress intensity factor. Force transfer across contacting asperities is estimated and used to calculate Mode II resistance stress intensity factor (applied factor is sum of effective and resistance factors). Electro-optic holographic interferometry was used to measure 3-D displacement field around a Mode I fatigue pre-crack in Al loaded in Mode II shear. Induced Mode I crack face displacements were greater than Mode II displacements. Plane stress shear lip caused displacement normal to surface as the crack faces are displaced. Algorithms are being developed to track the displacements associated with the original coordinate system in the camera. A 2-D boundary element method code for mixed mode I and II loading of a rough crack (sawtooth asperity model) has been completed. Addition of small-scale crack tip yielding and a wear model are completed and underway, respectively.

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

    DEFF Research Database (Denmark)

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

    2015-01-01

    This article presents a novel method to asses a crack growing/damage event in fibre reinforced plastic, or adhesive using Fibre Bragg Grating (FBG) sensors embedded in a host material. Different features of the crack mechanism that induce a change in the FBG response were identified. Double...... Cantilever Beams specimens made with glass fibre glued with structural adhesive, were instrumented with an array of FBG sensors embedded in the material and tested using an experimental fracture procedure. A digital image correlation technique was used to determine the presence of the specific phenomena...

  18. Application of the cracked pipe element to creep crack growth prediction

    Energy Technology Data Exchange (ETDEWEB)

    Brochard, J.; Charras, T. [C.E.A.-C.E.-Saclay DRN/DMT, Gif Sur Yvette (France); Ghoudi, M. [C.E.A.-C.E.-Saclay, Gif Sur Yvette (France)

    1997-04-01

    Modifications to a computer code for ductile fracture assessment of piping systems with postulated circumferential through-wall cracks under static or dynamic loading are very briefly described. The modifications extend the capabilities of the CASTEM2000 code to the determination of fracture parameters under creep conditions. The main advantage of the approach is that thermal loads can be evaluated as secondary stresses. The code is applicable to piping systems for which crack propagation predictions differ significantly depending on whether thermal stresses are considered as primary or secondary stresses.

  19. Stress-induced martensitic transformation in metastable austenitic stainless steels: Effect on fatigue crack growth rate

    Science.gov (United States)

    Khan, Z.; Ahmed, M.

    1996-04-01

    This paper addresses the influence of cyclic stress-induced martensitic transformation on fatigue crack growth rates in metastable austenitic stainless steels. At low applied stress and mean stress values in AISI type 301 stainless steel, fatigue crack growth rate is substantially retarded due to a cyclic stress-induced γ-α' and γ-ɛ martensitic transformation occurring at the crack-tip plastic zone. It is suggested that the transformation products produce a compressive residual stress at the tip of the fatigue crack, which essentially lowers the effective stress intensity and hence retards the fatigue crack growth rate. At high applied stress or mean stress values, fatigue crack growth rates in AISI type 301 steels become almost equal to those of stable AISI type 302 alloy. As the amount of transformed products increases (with an increase in applied or mean stress), the strain-hardening effect brought about by the transformed martensite phase appears to accelerate fatigue crack growth, offsetting the contribution from the compressive residual stress produced by the positive volume change of γ → α' or ɛ transformation.

  20. Fracture toughness and fatigue crack growth of oxide dispersion strengthened copper

    Energy Technology Data Exchange (ETDEWEB)

    Alexander, D.J.; Gieseke, B.G. [Oak Ridge National Laboratory, TN (United States)

    1996-04-01

    The fracture toughness and fatigue crack growth behavior of copper dispersion strengthened with aluminum oxide (0.15 wt % Al) was examined. In the unirradiated condition, the fracture toughness was about 45 kJ/m{sup 2} (73 MPa{radical}m) at room temperature, but decreased significantly to only 3 Kj/m{sup 2} (20 MPa{radical}m), at 250{degrees}C. After irradiation at approximately 250{degrees}C to about 2.5 displacements per atom (dpa), the toughness was very low, about 1 kJ/m{sup 2} (48 MOa{radical}m), and at 250{degrees}C the toughness was very low, about 1kJ/m{sup 2} (12 mPa{radical}m). The fatigue crack growth rate of unirradiated material at room temperature is similiar to other candidate structural alloys such as V-4Cr-4Ti and 316L stainless steel. The fracture properties of this material at higher temperatures and in controlled environments need further investigation, in both irradiated and unirradiated conditions.

  1. An adaptive ARX model to estimate the RUL of aluminum plates based on its crack growth

    Science.gov (United States)

    Barraza-Barraza, Diana; Tercero-Gómez, Víctor G.; Beruvides, Mario G.; Limón-Robles, Jorge

    2017-01-01

    A wide variety of Condition-Based Maintenance (CBM) techniques deal with the problem of predicting the time for an asset fault. Most statistical approaches rely on historical failure data that might not be available in several practical situations. To address this issue, practitioners might require the use of self-starting approaches that consider only the available knowledge about the current degradation process and the asset operating context to update the prognostic model. Some authors use Autoregressive (AR) models for this purpose that are adequate when the asset operating context is constant, however, if it is variable, the accuracy of the models can be affected. In this paper, three autoregressive models with exogenous variables (ARX) were constructed, and their capability to estimate the remaining useful life (RUL) of a process was evaluated following the case of the aluminum crack growth problem. An existing stochastic model of aluminum crack growth was implemented and used to assess RUL estimation performance of the proposed ARX models through extensive Monte Carlo simulations. Point and interval estimations were made based only on individual history, behavior, operating conditions and failure thresholds. Both analytic and bootstrapping techniques were used in the estimation process. Finally, by including recursive parameter estimation and a forgetting factor, the ARX methodology adapts to changing operating conditions and maintain the focus on the current degradation level of an asset.

  2. Measurement and simulation of crack growth rate and direction under non-proportional loadings

    Directory of Open Access Journals (Sweden)

    Y. Hos

    2015-10-01

    Full Text Available A series of fatigue experiments on thin-walled tubes under tension and torsion, the experimental results – crack path and crack growth life – are measured and compared. It is observed that the cracks follow a curvature from a tensile to a shear dominated growth with increasing crack length. The results are enforced by the high amplitudes applied to the specimens causing large cyclic plastic deformations and crack growth rates in the order of 10-3 mm/cycle. The non-linear nature of the cyclic deformation has been taken into account by applying a cyclic plasticity model, and plasticity-induced crack closure is captured by a contact formulation. Already for the uniaxial reference case the current limitations in modelling plasticity induced crack closure – a prerequisite for achieving realistic simulation results – have become obvious. Measurements have shown that friction and roughness induced closure processes come up, especially for non-planar crack surfaces, challenge to be met in the future.

  3. Transport and Corrosion Behavior of Cracked Reinforced Concrete

    DEFF Research Database (Denmark)

    Pease, Bradley Justin

    to enter the concrete. This is, among others, important in the corrosion of reinforcing steel. When cracks protrude to the depth of reinforcing steel, liquids containing aggressive ions (i.e. chlorides associated with salts and sea water) may rapidly access and initiate corrosion of the reinforcing...... structures. These models currently lack some of the scientific validity to fully represent actual field structures, i.e. structures containing cracks. Further understanding, therefore is needed on the effect cracks have on transport and corrosion in reinforced concrete. The fundamental mechanisms...... of transport and corrosion in cracked, reinforced concrete are not yet fully understood. The scope of this study therefore is to develop a link between concrete cracks and the relevant transport mechanism(s) under particular environmental conditions. It is envisioned that a finite element model...

  4. A test procedure for determining the influence of stress ratio on fatigue crack growth

    Science.gov (United States)

    Fitzgerald, J. H.; Wei, R. P.

    1974-01-01

    A test procedure is outlined by which the rate of fatigue crack growth over a range of stress ratios and stress intensities can be determined expeditiously using a small number of specimens. This procedure was developed to avoid or circumvent the effects of load interactions on fatigue crack growth, and was used to develop data on a mill annealed Ti-6Al-4V alloy plate. Experimental data suggest that the rates of fatigue crack growth among the various stress ratios may be correlated in terms of an effective stress intensity range at given values of K max. This procedure is not to be used, however, for determining the corrosion fatigue crack growth characteristics of alloys when nonsteady-state effects are significant.

  5. Fatigue Crack Growth Rate of Ti-6Al-4V Considering the Effects of Fracture Toughness and Crack Closure

    Institute of Scientific and Technical Information of China (English)

    ZHANG Junhong; YANG Shuo; LIN Jiewei

    2015-01-01

    Fatigue fracture is one of the main failure modes of Ti-6Al-4V alloy, fracture toughness and crack closure have strong effects on the fatigue crack growth(FCG) rate of Ti-6Al-4V alloy. The FCG rate of Ti-6Al-4V is investigated by using experimental and analytical methods. The effects of stress ratio, crack closure and fracture toughness on the FCG rate are studied and discussed. A modified prediction model of the FCG rate is proposed, and the relationship between the fracture toughness and the stress intensity factor(SIF) range is redefined by introducing a correcting coefficient. Notched plate fatigue tests (including the fracture toughness test and the FCG rate test) are conducted to investigate the influence of affecting factors on the FCG rate. Comparisons between the predicted results of the proposed model, the Paris model, the Walker model, the Sadananda model, and the experimental data show that the proposed model gives the best agreement with the test data particularly in the near–threshold region and the Paris region, and the corresponding calculated fatigue life is also accurate in the same regions. By considering the effects of fracture toughness and crack closure, the novel FCG rate prediction model not only improves the estimating accuracy, but also extends the adaptability of the FCG rate prediction model in engineering.

  6. Fatigue crack growth rate of Ti-6Al-4V considering the effects of fracture toughness and crack closure

    Science.gov (United States)

    Zhang, Junhong; Yang, Shuo; Lin, Jiewei

    2015-03-01

    Fatigue fracture is one of the main failure modes of Ti-6Al-4V alloy, fracture toughness and crack closure have strong effects on the fatigue crack growth(FCG) rate of Ti-6Al-4V alloy. The FCG rate of Ti-6Al-4V is investigated by using experimental and analytical methods. The effects of stress ratio, crack closure and fracture toughness on the FCG rate are studied and discussed. A modified prediction model of the FCG rate is proposed, and the relationship between the fracture toughness and the stress intensity factor(SIF) range is redefined by introducing a correcting coefficient. Notched plate fatigue tests (including the fracture toughness test and the FCG rate test) are conducted to investigate the influence of affecting factors on the FCG rate. Comparisons between the predicted results of the proposed model, the Paris model, the Walker model, the Sadananda model, and the experimental data show that the proposed model gives the best agreement with the test data particularly in the near-threshold region and the Paris region, and the corresponding calculated fatigue life is also accurate in the same regions. By considering the effects of fracture toughness and crack closure, the novel FCG rate prediction model not only improves the estimating accuracy, but also extends the adaptability of the FCG rate prediction model in engineering.

  7. Fatigue Crack Growth Rate of Inconel 718 Sheet at Cryogenic Temperatures

    Science.gov (United States)

    Wells, Douglas; Wright, Jonathan; Hastings, Keith

    2005-01-01

    Inconel 718 sheet material was tested to determine fatigue crack growth rate (FCGR) at cryogenic conditions representative of a liquid hydrogen (LH2) environment at -423 degree F. Tests utilized M(T) and ESE(T) specimen geometries and environments were either cold gaseous helium or submersion in LH2. The test results support a significant improvement in the fatigue crack growth threshold at -423 degree F compared to -320 degree F or 70 degree F.

  8. Simple Predicting Method for Fatigue Crack Growth Rate Based on Tensile Strength of Carbon Steel

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Three types of fatigue tests for an annealed carbon steel containing carbon of 0.42 % were carried out on smooth specimens and specimens with a small blind hole in order to investigate the fatigue crack growth law. A simple predicting method for crack growth rates has been proposed involving strength σb and the relation between cyclic stress and strain. The validity of proposed method has been confirmed by experiments on several carbon steels with different loadings.

  9. Online fatigue crack growth monitoring with clip gauge and direct current potential drop

    OpenAIRE

    De Tender, Steven; Micone, Nahuel; De Waele, Wim

    2016-01-01

    Fatigue is a well-known failure phenomenon which has been and still is extensively studied. Often structures are designed according to the safe-life principle so no crack initiation occurs. Nowadays there is a high emphasis on cost-efficiency, and one might rather opt for a fail-safe design. Therefore a certain amount of crack growth can be allowed in structures, but then a good knowledge of stresses and related crack growth rates is needed. To this end, extensive studies are done to obtain a...

  10. Growth of long fatigue cracks under non-proportional loadings – experiment and simulation

    Directory of Open Access Journals (Sweden)

    Y. Hos

    2016-07-01

    Full Text Available An experimental campaign was carried out on thin-walled tubes under tension and torsion. The results from experiments are measured and compared. It is observed that cracks follow a shear-dominated growth pattern with increasing crack length, instead of a tension-dominated one. The experiments are performed with high amplitudes applied to the specimens, resulting in large cyclic plastic deformations and crack growth rates up to 10-3 mm/cycle. Stress intensity factors were calculated for the proportional loading case.

  11. Effect of cold work on the growth rates of stress corrosion cracks in structural materials of nuclear systems

    Energy Technology Data Exchange (ETDEWEB)

    Magdowski, R.; Speidel, M.O. [Swiss Federal Inst. of Tech., Zurich (Switzerland). Inst. of Metallurgy

    1996-10-01

    The growth rates of stress corrosion cracks in austenitic stainless steels and nickel base alloy 600 exposed to simulated boiling water reactor coolant were measured by fracture mechanics testing techniques. Cold work may increase the crack growth rates up to one hundred times. In both, the annealed condition and the cold worked condition, the stress corrosion crack growth rates are independent of stress intensity over a wide K-range and crack growth rates correlate well with yield strength and hardness. In the annealed condition the fracture path is intergranular, but higher degrees of cold work introduce higher proportions of transgranular stress corrosion cracking.

  12. Fatigue Crack Growth under High Pressure of Gaseous Hydrogen in a 15-5PH Martensitic Stainless Steel: Influence of Pressure and Loading Frequency

    Science.gov (United States)

    Sun, Z.; Moriconi, C.; Benoit, G.; Halm, D.; Henaff, G.

    2013-03-01

    In this study, the effect of gaseous hydrogen pressure in relation with the loading frequency on the fatigue crack growth behavior of a precipitation-hardened martensitic stainless steel is investigated. It is found that increasing the hydrogen pressure from 0.09 to 9 MPa induces an enhancement of the fatigue crack growth rates. This enhancement is pronounced particularly at higher stress intensity factor amplitudes at 9 MPa. Meanwhile, decreasing the frequency from 20 to 0.2 Hz under 0.9 MPa of hydrogen reveals a significant increase in the crack growth rates that tends to join the curve obtained under 9 MPa at 20 Hz, but with a different cracking mode. However, it is shown that the degradation in fatigue crack growth behavior derives from a complex interaction between the fatigue damage and the amount of hydrogen enriching the crack tip, which is dependent on the hydrogen pressure, loading frequency, and stress intensity factor level. Scanning electron microscope (SEM) observations of the fracture surfaces are used to support the explanations proposed to account for the observed phenomena.

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

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Longzhou

    2012-11-30

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

  14. Environmentally assisted cracking behavior of dissimilar metal weldments in simulated BWR coolant environments

    Science.gov (United States)

    Huang, J. Y.; Chiang, M. F.; Jeng, S. L.; Huang, J. S.; Kuo, R. C.

    2013-01-01

    The environmentally assisted cracking behavior of dissimilar metal (DM) welds, including Alloy 52-A 508 and Alloy 82-A508, under simulated BWR coolant conditions was studied. Effects of postweld heat treatment and sulfur content of the base metal on the corrosion fatigue and SCC growth rates of DM welds were evaluated. The crack growth rates for the DM weld heat-treated at 621 °C for 24 h were observed to be faster than those for the as-welded. But the DM weld heat-treated at 621 °C for 8 h + 400 °C for 200 h showed better SCC resistance than the as-welded. The longer the heat treatment at 621 °C, the higher the chromium carbides density along the grain boundary was observed. Sulfur could diffuse out of the base metal and segregate along the grain boundaries of the dilution zone, leading to weakening the grain boundary strength and the SCC resistance of the Alloy 52-A508 weld.

  15. Creep crack growth in a reactor pressure vessel steel at 360 deg C

    Energy Technology Data Exchange (ETDEWEB)

    Rui Wu; Seitisleam, F.; Sandstroem, R. [Swedish Institute for Metals Research, Stockholm (Sweden)

    1998-12-31

    Plain creep (PC) and creep crack growth (CCG) tests at 360 deg C and post metallography were carried out on a low alloy reactor pressure vessel steel (ASTM A508 class 2) with different microstructures. Lives for the CCG tests were shorter than those for the PC tests and this is more pronounced for simulated heat affected zone microstructure than for the parent metal at longer lives. For the CCG tests, after initiation, the cracks grew constantly and intergranularly before they accelerated to approach rupture. The creep crack growth rate is well described by C*. The relations between reference stress, failure time and steady crack growth rate are presented for the CCG tests. It is demonstrated that the failure stress due to CCG is considerably lower than the yield stress at 360 deg C. Consequently, the CCG will control the static strength of a reactor vessel. (orig.) 17 refs.

  16. Accelerated Threshold Fatigue Crack Growth Effect-Powder Metallurgy Aluminum Alloy

    Science.gov (United States)

    Piascik, R. S.; Newman, J. A.

    2002-01-01

    Fatigue crack growth (FCG) research conducted in the near threshold regime has identified a room temperature creep crack growth damage mechanism for a fine grain powder metallurgy (PM) aluminum alloy (8009). At very low (Delta) K, an abrupt acceleration in room temperature FCG rate occurs at high stress ratio (R = K(sub min)/K(sub max)). The near threshold accelerated FCG rates are exacerbated by increased levels of K(sub max) (K(sub max) = 0.4 K(sub IC)). Detailed fractographic analysis correlates accelerated FCG with the formation of crack-tip process zone micro-void damage. Experimental results show that the near threshold and K(sub max) influenced accelerated crack growth is time and temperature dependent.

  17. Fracture resistance and fatigue crack growth characteristics of two Al-Cu-Mg-Zr alloys

    Science.gov (United States)

    Sarkar, Bhaskar; Lisagor, W. B.

    1992-01-01

    The dependence of strength, fracture resistance, and fatigue crack growth rate on the aging conditions of two alloy compositions based on Al-3.7Cu-1.85Mg-0.2Mn is investigated. Mechanical properties were evaluated in two heat treatment conditions and in two orientations (longitudinal and transverse). Compact tension specimens were used to determine fatigue crack growth characteristics and fracture resistance. The aging response was monitored on coupons using hardness measurements determined with a standard Rockwell hardness tester. Fracture resistance is found to increase with increasing yield strength during artificial aging of age-hardenable 2124-Zr alloys processed by powder metallurgy techniques. Fatigue crack growth rate increases with increasing strength. It is argued that these changes are related to deformation modes of the alloys; a homogeneous deformation mode tends to increase fracture resistance and to decrease the resistance to the fatigue crack propagation rate.

  18. An Effective Fem-Based Approach for Discrete 3D Crack Growth

    DEFF Research Database (Denmark)

    Nielsen, Morten Eggert; Lambertsen, Søren Heide; Pedersen, Erik B.

    2015-01-01

    A new geometric approach for discrete crack growth modeling is proposed and implemented in a commercial FEM software. The basic idea is to model the crack growth by removing volumes of material as the crack front advances. Thereby, adaptive meshing techniques, found in commercial software, is well......-suited for relatively fast and reasonable meshing of the updated geometry. Influence on structural stiffness is negligible, as the amount of removed material is kept insignificant. The approach is automatized in ANSYS APDL and demonstrated by means of energy-based mixed mode stress intensity factors and the crack...... growth direction criterion by Richard. The applicability of the implemented approach is validated against a previously published experimental result, which tests a mixed mode I + III fatigue loading of a modified CT specimen. The proposed approach may be used as a computational framework for modeling...

  19. Creep-Fatigue Crack Growth Interaction in Nickel Base Supper Alloy

    Directory of Open Access Journals (Sweden)

    F. Djavanroodi

    2008-01-01

    Full Text Available Most engineering components which operate at elevated temperatures are subjected to non-steady loading during service. This paper describes the current fracture mechanics concepts that are employed to predict cracking of Nickel base supper alloy materials at high temperatures under low and high frequency cyclic loading. A model for predicting creep crack growth in terms of C* and the creep uniaxial ductility is presented at low frequency and at high frequency power law relation is used to predict the crack growth rate. When dealing with creep/fatigue interaction a simple cumulative damage concept with fractography evidence is used to predict the crack growth rate. It is shown that these models give good agreement with the experimental results.

  20. Estimation of Crack Growth Properties of High Strength Metallic Materials by a Novel Technique

    Directory of Open Access Journals (Sweden)

    P R Sadananda Rao

    2010-12-01

    Full Text Available This research work proposes a novel technique based on fracture mechanics approach for the quick determination of fatigue crack growth rate and threshold stress intensity factor range (ΔKth of metallic materials using circumferentially cracked round bar (CCRBspecimen geometry. The literature survey indicates that the fatigue crack growth rate data generated using ASTM E-647 standard test specimens were strongly dependent on specimen size and its configuration. Also the standard test procedure is more cumbersome and time consuming requires costly instrumentation. Aluminum 2014T6 alloy is used as the test specimen because of its wide applicationin automobiles and aero plane industry. It is found that the test procedure is simple, reliable, less time consuming and uses simple instrumentation. The obtained fatigue crack growth rate is found to be very close to the values obtained by using standard specimens. This methodology can be widely applied in industries for rapid determination of ΔKth any metallic materials.

  1. Influence of high pressure hydrogen on cyclic load crack growth in metals

    Science.gov (United States)

    Jewett, R. P.; Walter, R. J.; Chandler, W. T.

    1978-01-01

    The effect of high pressure hydrogen on the crack growth rate of various nickel-base alloys was studied at ambient temperature. Considerable enhancement of the cyclic flaw growth rate was observed for Inconel 718, wrought and cast, and Waspaloy, a nickel-base alloy similar to Inconel 718. Only slight enhancement of the flaw growth rate for Alloy 903 was observed.

  2. Intrinsic fatigue crack growth rates for Al-Li-Cu-Mg alloys in vacuum

    Science.gov (United States)

    Slavik, D. C.; Blankenship, C. P., Jr.; Starke, E. A., Jr.; Gangloff, R. P.

    1993-01-01

    The influences of microstructure and deformation mode on inert environment intrinsic fatigue crack propagation were investigated for Al-Li-Cu-Mg alloys AA2090, AA8090, and X2095 compared to AA2024. The amount of coherent shearable delta-prime (Al3Li) precipitates and extent of localized planar slip deformation were reduced by composition (increased Cu/Li in X2095) and heat treatment (double aging of AA8090). Intrinsic growth rates, obtained at high constant K(max) to minimize crack closure and in vacuum to eliminate any environmental effect, were alloy dependent; da/dN varied up to tenfold based on applied Delta-K or Delta-K/E. When compared based on a crack tip cyclic strain or opening displacement parameter, growth rates were equivalent for all alloys except X2095-T8, which exhibited unique fatigue crack growth resistance. Tortuous fatigue crack profiles and large fracture surface facets were observed for each Al-Li alloy independent of the precipitates present, particularly delta-prime, and the localized slip deformation structure. Reduced fatigue crack propagation rates for X2095 in vacuum are not explained by either residual crack closure or slip reversibility arguments; the origin of apparent slip band facets in a homogeneous slip alloy is unclear.

  3. Cracking behavior of tungsten armor under ELM-like thermal shock loads: A computational study

    National Research Council Canada - National Science Library

    Li, Muyuan; Werner, Ewald; You, Jeong-Ha

    2015-01-01

    In this work, the cracking behavior of tungsten under edge-localized mode (ELM)-like thermal shock loads was investigated on the basis of a rigorous computational fracture mechanical analysis combined with the finite element method...

  4. Subcritical crack growth in a chemically reactive environment-implications for caprock integrity for CO2 storage

    Science.gov (United States)

    Fan, Z.; Eichhubl, P.; Callahan, O. A.; Major, J. R.; Chen, X.

    2015-12-01

    Seal integrity of cap-rock is a critical constraint on the long term performance of CO2 containment site. During fluid migration, the coupled geochemical reaction of minerals and geomechanical deformation of rock matrix may affect the seal integrity. The potential leakage of injected CO2 from cap-rock through preexisting fractures/faults represents a major concern associated with geological storage of CO2. To address the fundamental question of CO2 leakage through subcritical growth of fractures driven by chemically reactive fluid across caprocks, we build a Dugdale cohesive model. Ahead of the physical crack tip, a narrow band of cohesive zone is assumed to exist with the upper and lower cohesive surfaces held by the cohesive traction. In the vicinity of the crack tip, minerals dissolve due to the acidic environment and migrate from the physical crack tip into the cohesive zone causing damage of rock matrix in the form of a reduction of cohesive traction.Focusing on the dissolution of calcite and following the stress corrosion theory, we assume the degradation of cohesive traction is linearly proportional to the concentration of Ca2+whose evolution follows the reactive diffusion equation. Using a critical crack opening displacement criterion, the subcritical propagation behavior of crack due to stress corrosion is captured and the rate-limiting effects including the chemical reactions to produce the Ca2+ and the transport of minerals along the newly generated fracture cohesive zone are incorporated. Subcritical crack growth rate under different chemical environment conditions is examined and compared with the experimental fracture mechanics testing.

  5. BEHAVIOR OF CRACKED EGGS AT NON – DESTRUCTIVE IMPACT

    Directory of Open Access Journals (Sweden)

    Jana Strnková

    2014-02-01

    Full Text Available The influence of cracks on the dynamical frequency response of eggshells was studied. The non-destructive impact tests of the intact and cracked eggs were performed. Record of impact force time history was enabled by experimental device. Response of eggshell to the impact was described by the surface displacement of the eggshell. This response was measured by the laser interferometry. The force and response were also expressed in the frequency domain using of the fast Fourier transform. Both time and frequency response were affected by the presence of cracks. It was shown that the influence of cracks on the eggshell response was more effectively described in the frequency domain. The frequency response was relatively very sensitive to the position and orientation of cracks. The frequency response function was characterized by many peaks. Five excitation resonant frequency characteristic of signals were extracted based on the difference of frequency domain response signals. Distinction between intact and cracked eggs was enabled by these parameters. Even if some main problems were solved some of them remained unsolved. One of them was the effect of the impacting body r shape. This problem could be effectively solved namely using of numerical methods. In order to describe the response of eggshell response to the non-destructive impact using of the numerical simulation exact description of eggshell shape was performed. This numerical simulation will be subject of forthcoming paper.

  6. SCC crack growth rate of cold-worked austenitic stainless steels in PWR primary water conditions

    Energy Technology Data Exchange (ETDEWEB)

    Guerre, C.; Raquet, O.; Herms, E. [Commissariat a l' Energie Atomique (CEA), DEN/DPC/SCCME/LECA, Gif-sur-Yvette Cedex (France); Marie, S. [Commissariat a l' Energie Atomique (CEA), DEN/DM2S/SEMT/LISN, Gif-sur-Yvette Cedex (France); Le Calvar, M. [Inst. for Radiological Protection and Nuclear Safety (IRSN), DSR/SAMS, Fontenay-aux-Roses Cedex (France)

    2007-07-01

    Stress corrosion cracking (SCC) of stainless steels (SS) is a significant cause of failure in the pressurized water reactors (PWR). Most of the reported case history failures of SS in PWR can be attributed to pollutants (chloride, sulphate) and / or locally oxygenated environments, even to sensitisation of the SS. However, some failures have been attributed to heavy cold work (CW) of SS. In laboratory tests, SCC initiation of cold-worked SS has been obtained using slow strain rate tests (SSRT) in nominal PWR environment. This paper describes constant load and cyclic crack growth rate (CGR) tests on cold-worked SS, on CT specimens. 304L and 316L have been tested with a CW up to 60 %. CW 316L is more prone to cracking than 304L. Over 30 % of CW, 316L is susceptible to crack propagation under constant load. CW is the main controlling parameter for cracking. (author))

  7. Crack growth through the thickness of thin-sheet Hydrided Zircaloy-4

    Science.gov (United States)

    Raynaud, Patrick A. C.

    In recent years, the limits on fuel burnup have been increased to allow an increase in the amount of energy produced by a nuclear fuel assembly thus reducing waste volume and allowing greater capacity factors. As a result, it is paramount to ensure safety after longer reactor exposure times in the case of design-basis accidents, such as reactivity-initiated accidents (RIA). Previously proposed failure criteria do not directly address the particular cladding failure mechanism during a RIA, in which crack initiation in brittle outer-layers is immediately followed by crack growth through the thickness of the thin-wall tubing. In such a case, the fracture toughness of hydrided thin-wall cladding material must be known for the conditions of through-thickness crack growth in order to predict the failure of high-burnup cladding. The fracture toughness of hydrided Zircaloy-4 in the form of thin-sheet has been examined for the condition of through-thickness crack growth as a function of hydride content and distribution at 25°C, 300°C, and 375°C. To achieve this goal, an experimental procedure was developed in which a linear hydride blister formed across the width of a four-point bend specimen was used to inject a sharp crack that was subsequently extended by fatigue pre-cracking. The electrical potential drop method was used to monitor the crack length during fracture toughness testing, thus allowing for correlation of the load-displacement record with the crack length. Elastic-plastic fracture mechanics were used to interpret the experimental test results in terms of fracture toughness, and J-R crack growth resistance curves were generated. Finite element modeling was performed to adapt the classic theories of fracture mechanics applicable to thick-plate specimens to the case of through-thickness crack growth in thin-sheet materials, and to account for non-uniform crack fronts. Finally, the hydride microstructure was characterized in the vicinity of the crack tip by

  8. Influence of orientation and temperature on the fatigue crack growth of a nickel-based directionally solidified superalloy

    Energy Technology Data Exchange (ETDEWEB)

    He, Xiaohua [AML, School of Aerospace, Tsinghua University, Beijing 100084 (China); Zhang, Yangyang [Beijing Institute of Space Launch Technology, Beijing 100084 (China); Shi, Huiji, E-mail: shihj@mail.tsinghua.edu.cn [AML, School of Aerospace, Tsinghua University, Beijing 100084 (China); Gu, Jialin [Department of Material Science, Tsinghua University, Beijing 100084 (China); Li, Changpeng [Corporate Technology, Siemens Ltd. (China); Kadau, Kai [Siemens Energy Inc., Charlotte (United States); Luesebrink, Oliver [Siemens Power Generation, Mulheim an der Ruhr (Germany)

    2014-11-17

    Fatigue crack growth (FCG) behaviors of a widely used nickel-based directionally solidified (DS) superalloy have been investigated. Standard compact tension (CT) specimens in longitudinal, transverse and diagonal directions are cast and tested at 25 °C, 600 °C and 850 °C to reveal the orientation and temperature dependence. The post-test fractography is observed through scanning electron microscope (SEM) and optical microscope (OM) to understand the underlying mechanism responsible for the fracture modes. Results indicate that cracks in all three orientations exhibit a similar propagating behavior, while the temperature shows a significant effect on the crack propagation regardless of the influence of orientation. It has been found that a higher temperature leads to a faster propagation rate in the initial stage due to the cyclic softening response of materials. However, the FCG rates of specimens at lower temperature speed up more rapidly and exceed those at higher temperature in the following stage. This is attributed to the crack closure effect induced by the oxidation at a much higher temperature. Therefore, a new model based on thermal activation is proposed to get a better ability for the FCG rate prediction of the DS superalloy under different temperatures.

  9. Fatigue crack growth characteristics of nitrogen-alloyed type 347 stainless under operating conditions of a pressurized water reactor

    Energy Technology Data Exchange (ETDEWEB)

    Min, Ki Deuk; Hong, Seok Min; Kim, Dae Whan; Lee, Bong Sang [Korea Atomic Energy Research Institute, Nuclear Materials Safety Research Division, Daejeon (Korea, Republic of); Kim, Seon Jin [Hanyang University, Division of materials science and engineering, Seoul (Korea, Republic of)

    2017-06-15

    The fatigue crack growth behavior of Type 347 (S347) and Type 347N (S347N) stainless steel was evaluated under the operating conditions of a pressurized water reactor (PWR). These two materials showed different fatigue crack growth rates (FCGRs) according to the changes in dissolved oxygen content and frequency. Under the simulated PWR conditions for normal operation, the FCGR of S347N was lower than that of S347 and insensitive to the changes in PWR water conditions. The higher yield strength and better corrosion resistance of the nitrogen-alloyed Type 347 stainless steel might be a main cause of slower FCGR and more stable properties against changes in environmental conditions.

  10. Growth model for large branched three-dimensional hydraulic crack system in gas or oil shale.

    Science.gov (United States)

    Chau, Viet T; Bažant, Zdeněk P; Su, Yewang

    2016-10-13

    Recent analysis of gas outflow histories at wellheads shows that the hydraulic crack spacing must be of the order of 0.1 m (rather than 1 m or 10 m). Consequently, the existing models, limited to one or several cracks, are unrealistic. The reality is 10(5)-10(6) almost vertical hydraulic cracks per fracking stage. Here, we study the growth of two intersecting near-orthogonal systems of parallel hydraulic cracks spaced at 0.1 m, preferably following pre-existing rock joints. One key idea is that, to model lateral cracks branching from a primary crack wall, crack pressurization, by viscous Poiseuille-type flow, of compressible (proppant-laden) frac water must be complemented with the pressurization of a sufficient volume of micropores and microcracks by Darcy-type water diffusion into the shale, to generate tension along existing crack walls, overcoming the strength limit of the cohesive-crack or crack-band model. A second key idea is that enforcing the equilibrium of stresses in cracks, pores and water, with the generation of tension in the solid phase, requires a new three-phase medium concept, which is transitional between Biot's two-phase medium and Terzaghi's effective stress and introduces the loading of the solid by pressure gradients of diffusing pore water. A computer program, combining finite elements for deformation and fracture with volume elements for water flow, is developed to validate the new model.This article is part of the themed issue 'Energy and the subsurface'.

  11. The Effects of LCF Loadings on HCF Crack Growth

    Science.gov (United States)

    2007-11-02

    and Elastoplastic Behaviour of Materials, Berlin, 1992, 19-24. 5. Powell, B. E., Henderson, I. and Duggan, T. V. "The effect of combined major and...Powell, B. E. and Duggan, T. V. "Predicting the onset of high cycle fatigue damage : an application for long crack threshold data", Int. J. Fatigue, 8

  12. Random polycrystals of grains containing cracks: Model of quasistatic elastic behavior for fractured systems

    Science.gov (United States)

    Berryman, James G.; Grechka, Vladimir

    2006-12-01

    A model study on fractured systems was performed using a concept that treats isotropic cracked systems as ensembles of cracked grains by analogy to isotropic polycrystalline elastic media. The approach has two advantages: (a) Averaging performed is ensemble averaging, thus avoiding the criticism legitimately leveled at most effective medium theories of quasistatic elastic behavior for cracked media based on volume concentrations of inclusions. Since crack effects are largely independent of the volume they occupy in the composite, such a non-volume-based method offers an appealingly simple modeling alternative. (b) The second advantage is that both polycrystals and fractured media are stiffer than might otherwise be expected, due to natural bridging effects of the strong components. These same effects have also often been interpreted as crack-crack screening in high-crack-density fractured media, but there is no inherent conflict between these two interpretations of this phenomenon. Results of the study are somewhat mixed. The spread in elastic constants observed in a set of numerical experiments is found to be very comparable to the spread in values contained between the Reuss and Voigt bounds for the polycrystal model. Unfortunately, computed Hashin-Shtrikman bounds are much too tight to be in agreement with the numerical data, showing that polycrystals of cracked grains tend to violate some implicit assumptions of the Hashin-Shtrikman bounding approach. However, the self-consistent estimates obtained for the random polycrystal model are nevertheless very good estimators of the observed average behavior.

  13. Effect of Prestrain on Fatigue Crack Growth in Low-carbon Steel

    Directory of Open Access Journals (Sweden)

    Melnikov B.E.

    2011-05-01

    Full Text Available The current procedures of fatigue design of marine pipeline components allow for extending service life by considering a certain portion of the crack growth well before it turns into the instable phase. In structural components of transport systems material may undergo plastic pre-strain during the construction. The effect of pre-strain on the crack growth may be different depending on the material properties. Fatigue crack propagation was examined in testing symmetrically notched specimens machined from pre-strained steel plate coupons. Non-simultaneous crack initiation and propagation at the notches was reduced to symmetrical scheme by a simple coordinate transformation procedure. It was found that tensile pre-strain up to 0.01 did not substantially change the crack growth rate related to the stress intensity factor scale. Further increase of plastic pre-strain of material up to 0.15 caused almost two-times slowing down the crack growth rate compared to that of virgin material.

  14. Influence of overloads on dwell time fatigue crack growth in Inconel 718

    Energy Technology Data Exchange (ETDEWEB)

    Saarimäki, Jonas, E-mail: jonas.saarimaki@liu.se [Division of Engineering Materials, Department of Management and Engineering, Linköping University, SE-58183 Linköping (Sweden); Moverare, Johan [Division of Engineering Materials, Department of Management and Engineering, Linköping University, SE-58183 Linköping (Sweden); Siemens Industrial Turbomachinery AB, Materials Technology, SE-61283 Finspång (Sweden); Eriksson, Robert; Johansson, Sten [Division of Engineering Materials, Department of Management and Engineering, Linköping University, SE-58183 Linköping (Sweden)

    2014-08-26

    Inconel 718 is one of the most commonly used superalloys for high temperature applications in gasturbines and aeroengines and is for example used for components such as turbine discs. Turbine discs can be subjected to temperatures up to ∼700 °C towards the outer radius of the disc. During service, the discs might start to develop cracks due to fatigue and long dwell times. Additionally, temperature variations during use can lead to large thermal transients during start-up and shutdown which can lead to overload peaks in the normal dwell time cycle. In this study, tests at 550 °C with an overload prior to the start of each dwell time, have been performed. The aim of the investigation was to get a better understanding of the effects of overloads on the microstructure and crack mechanisms. The microstructure was studied using electron channelling contrast imaging (ECCI). The image analysis toolbox in Matlab was used on cross sections of the cracks to quantify: crack length, branch length, and the number of branches in each crack. It was found that the amount of crack branching increases with an increasing overload and that the branch length decreases with an increasing overload. When the higher overloads were applied, the dwell time effect was almost cancelled out. There is a strong tendency for an increased roughness of the crack path with an increasing crack growth rate.

  15. Fatigue crack growth rate does not depend on mantle thickness: an idealized cemented stem construct under torsional loading.

    Science.gov (United States)

    Hertzler, Justin; Miller, Mark A; Mann, Kenneth A

    2002-07-01

    Retrieval studies indicate that cemented stem loosening in femoral components of total hip replacement can initiate at the stem-cement interface. The etiology of the crack propagation process from the stem-cement interface is not well understood, but cracks are typically associated with thin cement mantles. In this study, a combination of experimental and computational methods was used to investigate the fatigue crack propagation process from the stem-PMMA cement interface using a novel torsional loading model. Constructs with thin (1 mm), medium (3 mm) or thick (7 mm) cement mantles were evaluated. Crack growth was stable for all cases and the rate of crack growth diminished with increasing crack length. Crack growth rate did not depend on mantle thickness (p > 0.05) over the first 1 mm of crack length, but cracks in thin mantles reached the full thickness of the mantle in the fewest number of loading cycles. The fracture mechanics-based finite element models indicated decreased stress intensity factors with increasing crack length and were consistent with the experimental findings. When combined with a fatigue crack growth Paris-law for PMMA cement, the finite element models provided reasonable predictions of the crack growth process.

  16. Modeling crack growth during Li insertion in storage particles using a fracture phase field approach

    Science.gov (United States)

    Klinsmann, Markus; Rosato, Daniele; Kamlah, Marc; McMeeking, Robert M.

    2016-07-01

    Fracture of storage particles is considered to be one of the major reasons for capacity fade and increasing power loss in many commercial lithium ion batteries. The appearance of fracture and cracks in the particles is commonly ascribed to mechanical stress, which evolves from inhomogeneous swelling and shrinkage of the material when lithium is inserted or extracted. Here, a coupled model of lithium diffusion, mechanical stress and crack growth using a phase field method is applied to investigate how the formation of cracks depends on the size of the particle and the presence or absence of an initial crack, as well as the applied flux at the boundary. The model shows great versatility in that it is free of constraints with respect to particle geometry, dimension or crack path and allows simultaneous observation of the evolution of lithium diffusion and crack growth. In this work, we focus on the insertion process. In particular, we demonstrate the presence of intricate fracture phenomena, such as, crack branching or complete breakage of storage particles within just a single half cycle of lithium insertion, a phenomenon that was only speculated about before.

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

    Energy Technology Data Exchange (ETDEWEB)

    Bahn, Chi Bum, E-mail: bahn@pusan.ac.kr [Pusan National University, 2 Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan 609-735 (Korea, Republic of); Majumdar, Saurin [Argonne National Laboratory, Lemont, IL 60439 (United States)

    2015-04-01

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

  18. High frequency guided waves for hidden fatigue crack growth monitoring in multi-layer aerospace structures

    Science.gov (United States)

    Chan, Henry; Fromme, Paul

    2015-03-01

    Varying loading conditions of aircraft structures result in stress concentration at fastener holes, where multi-layered components are connected, possibly leading to the development of fatigue cracks. High frequency guided waves propagating along the structure allow for the non-destructive testing of such components, e.g., aircraft wings. However, the sensitivity for the detection of small, potentially hidden, fatigue cracks has to be ascertained. The type of multi-layered model structure investigated consists of two adhesively bonded aluminium plate-strips. Fatigue experiments were carried out. The sensitivity of the high frequency guided wave modes to monitor fatigue crack growth at a fastener hole during cyclic loading was investigated, using both standard pulse-echo equipment and laser interferometry. The sensitivity and repeatability of the measurements were ascertained, having the potential for fatigue crack growth monitoring at critical and difficult to access fastener locations from a stand-off distance.

  19. Influence of material's cyclic deformation behaviour on fatigue crack growth threshold

    Institute of Scientific and Technical Information of China (English)

    ZHANG Rui; SUN Yi; WANG zhen-qing

    2008-01-01

    To investigate the relation between material's cyclic plastic behaviour and fatigue crack growth, a new model is proposed. The model incorporated the two intrinsic properties of material' s cyclic plastic and crack tip' s deformation dislocation to interpret fatigue crack threshold. The relation between material's cyclic hardening parameters (cyclic hardening amplitude and cyclic hardening rate) and fatigue threshold is studied. Fatigue threshold is determined based on the dislocation-free zone (DFZ) model, the theory of cohesive zone and the cyclic deformation behaviour. The results show that fatigue threshold increases with the decrease of the amplitude of cyclic hardening and is independent of cyclic hardening rate, but fatigue crack growth rate increa-ses with the increase of cyclic hardening rate.

  20. STUDY ON FATIGUE SHORT CRACK GROWTH LAW AND FATIGUE LIFE FOR MEDIUM CARBON STEELS

    Institute of Scientific and Technical Information of China (English)

    1998-01-01

    The fatigue crack initiation from notch root and the short-crack growth laws of two medium carbon alloying structural steels-35CrMo and 42CrMo are investigated under the different stress ratios R=0.1, 0.3) and three-point bending condition. The relationships between the maximum stress range at the notch root Δσmax and the number of cycles before fatigue crack initiation Ni are determined. The threshold stresses of fatigue crack initiation (Δσmax)th are got, and the smallcrack growth laws are obtained for these steels. An effective and convenient method is proposed for predicting the fatigue life of the notch specimens.

  1. Fatigue crack growth under remote and local compression – a state-of-the-art review

    Directory of Open Access Journals (Sweden)

    A. Chahardehi

    2016-01-01

    Full Text Available There is an ever increasing need for accurate understanding of the fatigue crack growth behaviour in major engineering materials and components. With the move towards more complex, probabilistic assessments, the traditional ‘safe’ or conservative approach for prediction of fatigue crack growth rate may no longer be attractive. Current codes and standards tend to be ambiguous about the treatment of compressive stress cycles: on the one hand code guidance on fatigue crack initiation may be non-conservative, while assessment of crack propagation may be inconsistently conservative. Where codes are non-conservative they could lead to dangerous assessments. The current paper provides a critical review of state-of-the-art in literature and a study of current code implications.

  2. Crack growth resistance for anisotropic plasticity with non-normality effects

    DEFF Research Database (Denmark)

    Tvergaard, Viggo; Legarth, Brian Nyvang

    2006-01-01

    For a plastically anisotropic solid a plasticity model using a plastic flow rule with non-normality is applied to predict crack growth. The fracture process is modelled in terms of a traction–separation law specified on the crack plane. A phenomenological elastic–viscoplastic material model...... is applied, using one of two different anisotropic yield criteria to account for the plastic anisotropy, and in each case the effect of the normality flow rule is compared with the effect of non-normality. Conditions of small scale yielding are assumed, with mode I loading conditions far from the crack...

  3. Small Crack Growth and Its Influence in Near Alpha-Titanium Alloys

    Science.gov (United States)

    1989-06-01

    M.N. James An Assessment of Crack Closure and the Extent of the J.F. Knott Short Crack Regime in QIN ( HY80 ) Steel . Fatigue Fract Engng Mater Struct, 8...Effects in A508 F. Mudry Steel . A. Pinneau Fatigue of Engineering Materials and Structures, 6, pp 349-358 (1983) 3 B.N. Leis Discussion of the Short...Crack Growth in Steels and A.J. McEvily Aluminium Alloys. In: Proceedings of the Int Conf on Fatigue Thresholds, Stockholm, Sweden, 2, pp 36 (1981) 21

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

    Directory of Open Access Journals (Sweden)

    Ronnie Rusli

    2011-05-01

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

  5. Computational aspects of crack growth in sandwich plates from reinforced concrete and foam

    Science.gov (United States)

    Papakaliatakis, G.; Panoskaltsis, V. P.; Liontas, A.

    2012-12-01

    In this work we study the initiation and propagation of cracks in sandwich plates made from reinforced concrete in the boundaries and from a foam polymeric material in the core. A nonlinear finite element approach is followed. Concrete is modeled as an elastoplastic material with its tensile behavior and damage taken into account. Foam is modeled as a crushable, isotropic compressible material. We analyze slabs with a pre-existing macro crack at the position of the maximum bending moment and we study the macrocrack propagation, as well as the condition under which we have crack arrest.

  6. Quantitative image analysis of WE43-T6 cracking behavior

    Science.gov (United States)

    Ahmad, A.; Yahya, Z.

    2013-06-01

    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.

  7. Near-threshold fatigue crack growth properties at elevated temperature for 1Cr-1Mo-0.25V steel and 12Cr stainless steel

    Science.gov (United States)

    Matsuoka, Saburo; Takeuchi, Etsuo; Nishijima, Satoshi; McEvily, Arthur J.

    1989-04-01

    Near-threshold fatigue crack growth properties were investigated for a low-alloy steel 1Cr-1Mo-0.25V and a stainless steel SUS403 (13Cr) in the temperature range from 25 to 550°C. Fatigue tests were conducted at frequencies of 0.5, 5, and 50 Hz, in a manner designed to avoid crack closure. The effective value of threshold stress intensity range increased with increasing temperature and with decreasing frequency for the Cr-Mo-V steel, whereas the effective threshold stress intensity range was independent of temperature and frequency in the case of the SUS403 steel. At a given Δ K value, the fatigue crack growth rates accelerated with increasing temperature and with decreasing frequency for the Cr-Mo-V steel. However, although the rate of fatigue crack growth was independent of frequency at a given temperature for the SUS403 steel, the rate did increase with temperature. The observed threshold levels and crack growth behavior were closely related to the oxidation process of the bare surface formed at the crack tip during each load cycle.

  8. A High-Sensitivity Potential-Drop Technique for Fatigue Crack Growth Measurements,

    Science.gov (United States)

    1979-08-01

    inappropriate to assume that crack growth characteristics at the surface are representative of crack behaviour in the specimen mid-thickness. 2.2 Ultrasonic...techniques has been described by several authors [23-25], and offers the advantages of high noise rejection and low current consumption . However, as the...Colonel B.C. Joshi, Military, Naval and Air Adviser, High Commission of India, Red Hill, A.C.T. Director, Defence Research Centre, Kuala Lumpur, Malaysia

  9. The Impact of Cracked Microparticles on the Mechanical and the Fracture Behavior of Particulate Composite

    Directory of Open Access Journals (Sweden)

    Waleed K. Ahmed

    2015-10-01

    Full Text Available In this investigation a metallic composite with a cracked micro has been investigated using finite element method. Particulate reinforced composite is one of the most favorite composite due to it quit isotopic properties. While being in metallic status, the micro particles may be subjected to deterioration which lead to crack embedded initiation within the micro particle. This crack lead to degradation in the mechanical as well as the fracture behavior in the composite. Mechanical characteristics through estimating the stiffness of the composite has been studied for intact and cracked particles as well as for the fractured particles. It has been found that as long as the crack propagates in the micro particle, there is reduction in the composite stiffness and increases in the stress intensity factor (SIF.

  10. Stress Corrosion Cracking and Fatigue Crack Growth Studies Pertinent to Spacecraft and Booster Pressure Vessels

    Science.gov (United States)

    Hall, L. R.; Finger, R. W.

    1972-01-01

    This experimental program was divided into two parts. The first part evaluated stress corrosion cracking in 2219-T87 aluminum and 5Al-2.5Sn (ELI) titanium alloy plate and weld metal. Both uniform height double cantilever beam and surface flawed specimens were tested in environments normally encountered during the fabrication and operation of pressure vessels in spacecraft and booster systems. The second part studied compatibility of material-environment combinations suitable for high energy upper stage propulsion systems. Surface flawed specimens having thicknesses representative of minimum gage fuel and oxidizer tanks were tested. Titanium alloys 5Al-2.5Sn (ELI), 6Al-4V annealed, and 6Al-4V STA were tested in both liquid and gaseous methane. Aluminum alloy 2219 in the T87 and T6E46 condition was tested in fluorine, a fluorine-oxygen mixture, and methane. Results were evaluated using modified linear elastic fracture mechanics parameters.

  11. Evaluation of magnetic flux leakage signals on fatigue crack growth of mild steel

    Directory of Open Access Journals (Sweden)

    M.I.M Ahmad

    2015-12-01

    Full Text Available In engineering applications, analysis of crack growth life is useful in situations where an unexpected crack has been found in a component of a machine, vehicle, or structure. The objective of this research is to investigate the correlation curve of magnetic flux leakage, Hp(y signals by evaluating their critical value point with respect to step size. Moreover, the relation of fatigue crack growth rate, da/dN toward the stress intensity range, ΔK and Hp(y in metal components is also discussed in this paper. The tension-tension fatigue test was conducted with the metal magnetic memory scanning device and crack opening displacement (COD gauges in 10 Hz (testing frequency by applying a load for 3.0-5.0 kN respectively. As a result, the correlation curve of Hp(y was built with the R-Squared values in the range of 0.99 and one mathematical model has been developed for estimation analysis. The sigmoidal shape curve was plotted on the graph of da/dN versus ΔK and also with Hp(y. Thus, for validation, the linear relation is represented between ΔK and Hp(y that present a good approach for magnetic parameter to be developed in the fatigue crack growth analysis. Therefore, the magnetic method has greater capability to analyze the fatigue crack propagation life in a real application.

  12. A Comparison Study of Machine Learning Based Algorithms for Fatigue Crack Growth Calculation.

    Science.gov (United States)

    Wang, Hongxun; Zhang, Weifang; Sun, Fuqiang; Zhang, Wei

    2017-05-18

    The relationships between the fatigue crack growth rate ( d a / d N ) and stress intensity factor range ( Δ K ) are not always linear even in the Paris region. The stress ratio effects on fatigue crack growth rate are diverse in different materials. However, most existing fatigue crack growth models cannot handle these nonlinearities appropriately. The machine learning method provides a flexible approach to the modeling of fatigue crack growth because of its excellent nonlinear approximation and multivariable learning ability. In this paper, a fatigue crack growth calculation method is proposed based on three different machine learning algorithms (MLAs): extreme learning machine (ELM), radial basis function network (RBFN) and genetic algorithms optimized back propagation network (GABP). The MLA based method is validated using testing data of different materials. The three MLAs are compared with each other as well as the classical two-parameter model ( K * approach). The results show that the predictions of MLAs are superior to those of K * approach in accuracy and effectiveness, and the ELM based algorithms show overall the best agreement with the experimental data out of the three MLAs, for its global optimization and extrapolation ability.

  13. An evaluation on fatigue crack growth in a fine-grained isotropic graphite

    Energy Technology Data Exchange (ETDEWEB)

    Wang Hongtao; Sun Libin [Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084 (China); Li Chenfeng [College of Engineering, Swansea University, Singleton Park, Swansea SA2 8PP (United Kingdom); Shi Li [Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084 (China); Wang Haitao, E-mail: wanght@tsinghua.edu.cn [Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084 (China)

    2012-09-15

    Highlights: Black-Right-Pointing-Pointer The propagation of micro- and macro-fatigue cracks in IG-11 graphite was studied. Black-Right-Pointing-Pointer The curves of the fatigue crack growth rate versus the SIF range show three stages. Black-Right-Pointing-Pointer The fatigue microcrack propagation is very sensitive to graphite's microstructures. Black-Right-Pointing-Pointer Graphite's microstructures have no significant impact on fatigue macrocrack growth. Black-Right-Pointing-Pointer The fatigue fracture surface indicates the fracture mechanism of the IG-11 graphite. - Abstract: The aim of this paper is to investigate the mechanism of fatigue crack propagation in IG-11 graphite, and determine the crack growth rate in relation to the stress level. Experimental studies were performed at both micro and macro scales. For fatigue microcrack propagation, single-edge-notch specimens were chosen for testing and the fatigue crack growth was measured in situ with a scanning electron microscope. For fatigue macrocrack propagation, CT specimens were used and the fatigue crack growth was measured with a high-accuracy optic microscope. Combining the two groups of experimental results, the following conclusions are derived: (1) The heterogeneous microstructures of the graphite material have significant impact on the fatigue microcrack growth, while their influence on fatigue macrocrack growth is very limited. (2) The relationship between the fatigue crack growth rate and the crack-tip stress intensity factor range can be expressed in the form of Paris formulae, which contains three stages: an initial rising part with a small slope, an abrupt rise with a very large acceleration, and a short final part with a small slope. (3) The fatigue fracture surface of the graphite material contains considerable sliding of leaf-shape graphite flakes combined with small cotton-shape plastic deformations. These sliding traces are approximately aligned at 45 Degree-Sign , showing the

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

    Science.gov (United States)

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

    1991-11-01

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

  15. 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.

  16. Coupled FEM-DBEM method to assess crack growth in magnet system of Wendelstein 7-X

    Directory of Open Access Journals (Sweden)

    R. Citarella

    2013-10-01

    Full Text Available The fivefold symmetric modular stellarator Wendelstein 7-X (W7-X is currently under construction in Greifswald, Germany. The superconducting coils of the magnet system are bolted onto a central support ring and interconnected with five so-called lateral support elements (LSEs per half module. After welding of the LSE hollow boxes to the coil cases, cracks were found in the vicinity of the welds that could potentially limit the allowed number N of electromagnetic (EM load cycles of the machine. In response to the appearance of first cracks during assembly, the Stress Intensity Factors (SIFs were calculated and corresponding crack growth rates of theoretical semi-circular cracks of measured sizes in potentially critical position and orientation were predicted using Paris’ law, whose parameters were calibrated in fatigue tests at cryogenic temperature. In this paper the Dual Boundary Element Method (DBEM is applied in a coupled FEM-DBEM approach to analyze the propagation of multiple cracks with different shapes. For this purpose, the crack path is assessed with the Minimum Strain Energy density criterion and SIFs are calculated by the J-integral approach. The Finite Element Method (FEM is adopted to model, using the commercial codes Ansys or Abaqus;, the overall component whereas the submodel analysis, in the volume surrounding the cracked area, is performed by FEM (“FEM-FEM approach” or alternatively by DBEM (“FEM-DBEM approach”. The “FEM-FEM approach” considers a FEM submodel, that is extracted from the FEM global model; the latter provide the boundary conditions for the submodel. Such approach is affected by some restrictions in the crack propagation phase, whereas, with the “FEM-DBEM approach”, the crack propagation simulation is straightforward. In this case the submodel is created in a DBEM environment with boundary conditions provided by the global FEM analysis; then the crack is introduced and a crack propagation analysis

  17. STRATIFIED MODEL FOR ESTIMATING FATIGUE CRACK GROWTH RATE OF METALLIC MATERIALS

    Institute of Scientific and Technical Information of China (English)

    YANG Yong-yu; LIU Xin-wei; YANG Fan

    2005-01-01

    The curve of relationship between fatigue crack growth rate and the stress strength factor amplitude represented an important fatigue property in designing of damage tolerance limits and predicting life of metallic component parts. In order to have a morereasonable use of testing data, samples from population were stratified suggested by the stratified random sample model (SRAM). The data in each stratum corresponded to the same experiment conditions. A suitable weight was assigned to each stratified sample according to the actual working states of the pressure vessel, so that the estimation of fatigue crack growth rate equation was more accurate for practice. An empirical study shows that the SRAM estimation by using fatigue crack growth rate data from different stoves is obviously better than the estimation from simple random sample model.

  18. A direct XFEM formulation for modeling of cohesive crack growth in concrete

    DEFF Research Database (Denmark)

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

    2007-01-01

    Applying a direct formulation for the enrichment of the displacement field an extended finiteelement (XFEM) scheme for modeling of cohesive crack growth is developed. Only elements cut by thecrack is enriched and the scheme fits within the framework of standard FEM code. The scheme isimplemented...... for the 3-node constant strain triangle (CST) and the 6-node linear strain triangle (LST).Modeling of standard concrete test cases such as fracture in the notched three point beam bending test(TPBT) and in the four point shear beam test (FPSB) illustrates the performance. The XFEM results showgood agreement...... with results obtained by applying standard interface elements in FEM and withexperimental results. In conjunction with criteria for crack growth local versus nonlocal computation ofthe crack growth direction is discussed....

  19. A GENERAL CONSTITUTIVE RELATION FOR FATIGUE CRACK GROWTH ANALYSIS OF METAL STRUCTURES

    Institute of Scientific and Technical Information of China (English)

    W.C. Cui; X.P. Huang

    2003-01-01

    Crack growth rate curves are the fundamental material property for metal structures under fatigue loading. Although there are many crack growth rate curves available in the literature, few of them showed the capability to explain various special phenomena observed in tests. A modified constitutive relation recently proposed by McEvily and his co-workers showed very promising capability. This modified constitutive relation is further generalized by (1) introducing an unstable fracture condition; (2) defining a virtual strength to replace the yield stress; and (3) defining an overload and underload parameter. The performances of this general constitutive relation for fatigue crack growth is extensively studied and it is found that this general constitutive relation is able to explain various phenomena observed with particular strong capability on load sequence effect.

  20. Growth of Small Cracks in Aeroengine Disc Materials.

    Science.gov (United States)

    1988-06-01

    1755-1765. 5.21 B. A. Lerch, N. Jayaraman and S. 0. Antolovich . Mater. Sci. Eng., Vol. 66, 1984, pp. 151-166. 5.22 J. E. King, "Fatigue Crack Propagation...Leverant, in STP 520, ASTM, 1973, pp. 37-67. 6.17 S. Bashir, P. Taupin and S. D. Antolovich , "Low Cycle Fatigue of AS-HIP and HIP + Forged Rene 95," Met...13A, Oct. 1982, pp. 1755-1765. 6.20 B. A. Lerch, N. Jayaramau and J. D. Antolovich , Mater. Sci. and Eng., Vol. 66, pp. 151-166. 6.21 C. W. Brown, J. E

  1. Crack Initiation and Growth in Rigid Polymeric Closed-Cell Foam Cryogenic Applications

    Science.gov (United States)

    Sayyah, Tarek; Steeve, Brian; Wells, Doug

    2006-01-01

    Cryogenic vessels, such as the Space Shuttle External Tank, are often insulated with closed-cell foam because of its low thermal conductivity. The coefficient of thermal expansion mismatch between the foam and metallic substrate places the foam under a biaxial tension gradient through the foam thickness. The total foam thickness affects the slope of the stress gradient and is considered a significant contributor to the initiation of subsurface cracks. Rigid polymeric foams are brittle in nature and any subsurface cracks tend to propagate a finite distance toward the surface. This presentation investigates the relationship between foam thickness and crack initiation and subsequent crack growth, using linear elastic fracture mechanics, in a rigid polymeric closed-cell foam through analysis and comparison with experimental results.

  2. Review of environmental effects on fatigue crack growth of austenitic stainless steels

    Energy Technology Data Exchange (ETDEWEB)

    Shack, W.J.; Kassner, T.F. [Argonne National Lab., IL (United States)

    1994-05-01

    Fatigue and environmentally assisted cracking of piping, pressure vessel cladding, and core components in light water reactors are potential concerns to the nuclear industry and regulatory agencies. The degradation processes include intergranular stress corrosion cracking of austenitic stainless steel (SS) piping in boiling water reactors (BWRs), and propagation of fatigue or stress corrosion cracks (which initiate in sensitized SS cladding) into low-alloy ferritic steels in BWR pressure vessels. Crack growth data for wrought and cast austenitic SSs in simulated BWR water, developed at Argonne National Laboratory under US Nuclear Regulatory Commission sponsorship over the past 10 years, have been compiled into a data base along with similar data obtained from the open literature. The data were analyzed to develop corrosion-fatigue curves for austenitic SSs in aqueous environments corresponding to normal BWR water chemistries, for BWRs that add hydrogen to the feedwater, and for pressurized water reactor primary-system-coolant chemistry.

  3. Power Law Versus Exponential Form of Slow Crack Growth of Advanced Structural Ceramics: Dynamic Fatigue

    Science.gov (United States)

    Choi, Sung R.; Gyekenyesi, John P.

    2002-01-01

    The life prediction analysis based on an exponential crack velocity formulation was examined using a variety of experimental data on glass and advanced structural ceramics in constant stress-rate ("dynamic fatigue") and preload testing at ambient and elevated temperatures. The data fit to the strength versus In (stress rate) relation was found to be very reasonable for most of the materials. It was also found that preloading technique was equally applicable for the case of slow crack growth (SCG) parameter n > 30. The major limitation in the exponential crack velocity formulation, however, was that an inert strength of a material must be known priori to evaluate the important SCG parameter n, a significant drawback as compared to the conventional power-law crack velocity formulation.

  4. Effects of Aqueous Solutions on the Slow Crack Growth of Soda-Lime-Silicate Glass

    Science.gov (United States)

    Hausmann, Bronson D.; Salem, Jonathan A.

    2016-01-01

    The slow crack growth (SCG) parameters of soda-lime-silicate were measured in distilled and saltwater of various concentrations in order to determine if the presence of salt and the contaminate formation of a weak sodium film affects stress corrosion susceptibility. Past research indicates that solvents affect the rate of crack growth; however, the effects of salt have not been studied. The results indicate a small but statistically significant effect on the SCG parameters A and n at high concentrations; however, for typical engineering purposes, the effect can be ignored.

  5. Crack Growth Rate Modeling of a Titanium-Aluminide Alloy Under Thermal-Mechanical Cycling

    Science.gov (United States)

    1991-12-01

    is integrated using Simpson’s rule. The integration of f(t) from t = ta to t = tb is: fIb f(t) dt ,,---- [f(t4 ) + 4f(tj) + f(tb)1 (5.68) ie 6 where... Knott , J.F. International Journal of Fracture Mechanics 1971, pp 462-467 101. Halliday M.D. and Beevers, C.J., ’The d.c. Electrical Potential Method for...Test Methods for Fracture and Fatigue Crack Growth ASTM STP 877, 1985, pp 67-85. 108. Ritchie, R.O., Garrett, G.G., and Knott , J.F., " Crack-Growth

  6. Inclined defects and their effect on the fatigue limit and small crack growth

    Directory of Open Access Journals (Sweden)

    Roiko Andrew

    2014-06-01

    Full Text Available Small FIB (Focused Ion Beam milled notches were introduced in quenched and tempered 34CrNiMo6 steel to monitor initiation and growth of cracks in situ. The effect of the defects on the fatigue limit is discussed in terms of the √area model. Notches with projected √area of 30 to 56 μm normal to the applied stress were inclined by 0, 45, and 60 degrees. The effect of size and inclination on the small crack growth as well as the fatigue limit is discussed.

  7. FACTORS AFFECTING FATIGUE CRACK GROWTH RATES OF FIBER REINFORCED METAL LAMINATES

    Institute of Scientific and Technical Information of China (English)

    1998-01-01

    Based upon an analytical model for predicting the crack growth in fiber reinforced metal laminates (FRMLs), some factors affecting the fatigue crack growth rates of FRMLs were analyzed, including the lay-up of FRMLs, the modulus of the fibers, the residual stresses in FRMLs, the bonding strength and the shear modulus of the adhesive, etc.It was shown from the present analysis that the interface number of the laminates, the modulus of the fibers and the residual stresses in FRMLs have very great effects on the fatigue lives of FRMLs, but the effects of the bonding strength and the shear modulus of the adhesive are relatively small.

  8. STUDY OF FATIGUE CRACK GROWTH IN 6063-T6 ALUMINUM ALLOY

    Directory of Open Access Journals (Sweden)

    Nirpesh Vikram

    2015-12-01

    Full Text Available The present study relates to fracture mechanics and its aim is to validate the experimental analysis with analytical analysis and find out a relationship between loading parameters and crack growth rate for 6063-T6 Aluminum Alloy. All analysis was done on Side edge notch specimen. The constant U was found to depend on stress ratio R. Variation in load range affects the crack growth rate constant m. For constant load range its variation was negligible, constant C was almost constant at variable load range. Variation of maximum load affects constant C.

  9. Fracture analysis of cracked metallic plate repaired with adhesive bonding composite patch

    Institute of Scientific and Technical Information of China (English)

    Su Weiguo; Mu Zhitao

    2014-01-01

    Fatigue crack growth test of cracked metallic plate repaired with adhesive bonding composite patch was conducted to study the fracture behavior of crack patching. The failure mode was that crack grows along with adhesive debonding. The crack length and debonding area were measured at different numbers of cycles. The nonlinear three-dimensional(3D)finite element(FE)model considering adhesive debonding and crack growth simultaneously was developed. The experimental and analytical results were in good agreement with each other.

  10. NASCRAC - A computer code for fracture mechanics analysis of crack growth

    Science.gov (United States)

    Harris, D. O.; Eason, E. D.; Thomas, J. M.; Bianca, C. J.; Salter, L. D.

    1987-01-01

    NASCRAC - a computer code for fracture mechanics analysis of crack growth - is described in this paper. The need for such a code is increasing as requirements grow for high reliability and low weight in aerospace components. The code is comprehensive and versatile, as well as user friendly. The major purpose of the code is calculation of fatigue, corrosion fatigue, or stress corrosion crack growth, and a variety of crack growth relations can be selected by the user. Additionally, crack retardation models are included. A very wide variety of stress intensity factor solutions are contained in the code, and extensive use is made of influence functions. This allows complex stress gradients in three-dimensional crack problems to be treated easily and economically. In cases where previous stress intensity factor solutions are not adequate, new influence functions can be calculated by the code. Additional features include incorporation of J-integral solutions from the literature and a capability for estimating elastic-plastic stress redistribution from the results of a corresponding elastic analysis. An example problem is presented which shows typical outputs from the code.

  11. Subcritical crack growth and mechanical weathering: a new consideration of how moisture influences rock erosion rates.

    Science.gov (United States)

    Eppes, Martha-Cary; Keanini, Russell; Hancock, Gregory S.

    2016-04-01

    The contributions of moisture to the mechanical aspects of rock weathering and regolith production are poorly quantified. In particular, geomorphologists have largely overlooked the role of subcritical crack growth processes in physical weathering and the fact that moisture strongly influences the rates of those processes. This influence is irrespective of the function that moisture plays in stress loading mechanisms like freezing or hydration. Here we present a simple numerical model that explores the efficacy of subcritical crack growth in granite rock subaerially exposed under a range of moisture conditions. Because most weathering-related stress loading for rocks found at, or near, Earth's surface (hereafter surface rocks) is cyclic, we modeled crack growth using a novel combination of Paris' Law and Charles' Law. This combination allowed us to apply existing empirically-derived data for the stress corrosion index of Charles' Law to fatigue cracking. For stress, we focused on the relatively straightforward case of intergranular stresses that arise during solar-induced thermal cycling by conductive heat transfer, making the assumption that such stresses represent a universal minimum weathering stress experienced by all surface rocks. Because all other tensile weathering-related stresses would be additive in the context of crack growth, however, our model can be adapted to include other stress loading mechanisms. We validated our calculations using recently published thermal-stress-induced cracking rates. Our results demonstrate that 1) weathering-induced stresses as modeled herein, and as published by others, are sufficient to propagate fractures subcritically over long timescales with or without the presence of water 2) fracture propagation rates increase exponentially with respect to moisture, specifically relative humidity 3) fracture propagation rates driven by thermal cycling are strongly dependent on the magnitude of diurnal temperature ranges and the

  12. Fatigue behaviour and crack growth rate of cryorolled Al 7075 alloy

    Energy Technology Data Exchange (ETDEWEB)

    Das, Prosenjit [Central Mechanical Engineering Research Institute (CSIR), Durgapur 713209 (India); Department of Metallurgical and Materials Engineering, IIT Roorkee, Roorkee 247667 (India); Jayaganthan, R., E-mail: rjayafmt@iitr.ernet.in [Department of Metallurgical and Materials Engineering, IIT Roorkee, Roorkee 247667 (India); Chowdhury, T. [School of Material Science and Engineering, Bengal Engineering and Science University, Shibpur (India); Singh, I.V. [Department of Mechanical and Industrial Engineering, IIT Roorkee, Roorkee 247667 (India)

    2011-09-15

    Highlights: {yields} High cycle fatigue of cryorolled Al 7075 alloy has been investigated. {yields} Cryorolled Al alloy showed significant enhancement in fatigue strength. {yields} FCGR resistance of the ufg Al alloy is higher at higher values of applied stress. - Abstract: The effects of cryorolling (CR) on high cycle fatigue (HCF) and fatigue crack growth rate behaviour of Al 7075 alloy have been investigated in the present work. The Al 7075 alloy was rolled for different thickness reductions (40% and 70%) at cryogenic (liquid nitrogen) temperature and its tensile strength, fatigue life, and fatigue crack growth mechanism were studied by using tensile testing, constant amplitude stress controlled fatigue testing, and fatigue crack growth rate testing using load shedding (decreasing {Delta}K) technique. The microstructural characterization of the alloy was carried out by using Field emission scanning electron microscopy (FESEM). The cryorolled Al alloy after 70% thickness reduction exhibits ultrafine grain (ufg) structure as observed from its FESEM micrographs. The cryorolled Al 7075 alloys showed improved mechanical properties (Y.S, U.T.S, Impact energy and Fracture toughness are 430 Mpa, 530 Mpa, 21 J, 24 Mpa m{sup 1/2} for 40CR alloy) as compared to the bulk 7075 Al alloy. It is due to suppression of dynamic recovery and accumulation of higher dislocations density in the cryorolled Al alloys. The cryorolled Al alloy investigated under HCF regime of intermediate to low plastic strain amplitudes has shown the significant enhancement in fatigue strength as compared to the coarse grained (CG) bulk alloy due to effective grain refinement. Fatigue crack growth (FCGR) resistance of the ufg Al alloy has been found be higher, especially at higher values of applied stress intensity factor {Delta}K The reasons behind such crack growth retardation is due to diffused crack branching mechanism, interaction between a propagating crack and the increased amount of grain

  13. DYNAMIC BEHAVIOR OF TWO COLLINEAR PERMEABLE CRACKS IN A PIEZOELECTRIC LAYER BONDED TO TWO HALF SPACES

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    The dynamic behavior of two collinear cracks in a piezoelectric layer bonded to two half spaces under harmonic anti-plane shear waves was investigated by means of Schmidt method. The cracks are vertically to the interfaces of the piezoelectric layer.The boundary conditions of the electrical field were assumed to be the permeable crack surface. By using the Fourier transform, the problem can be solved with the help of two pairs of triple integral equations. Numerical examples were presented to show the effect of the geometry of the interacting cracks, the piezoelectric constants of the materials and the frequency of the incident waves upon the stress intensity factors. The results show that the dynamic field will impede or enhance the propagation of the crack in a piezoelectric material at different stages of the frequency of the incident waves. It is found that the electric displacement intensity factors for the permeable crack surface conditions are much smaller than that for the impermeable crack surface conditions.

  14. Mechanical behavior and failure mechanism of pre-cracked specimen under uniaxial compression

    Science.gov (United States)

    Liu, Ting; Lin, Baiquan; Yang, Wei

    2017-08-01

    As a desirable permeability enhancement method, hydraulic slotting has been widely used for enhanced coal bed methane (ECBM) recovery in China. Aiming at the problem that the action mechanism of the slot on the mechanical properties of the slotted coal is still unclear, this paper investigates the effects of flaw inclination on the strength, deformation and cracking process of the pre-cracked specimens. The result shows that the stress-strain curves can be divided into three categories based on the stress behaviors, dropping step by step or dropping sharply, after the peak. With an increase of the flaw inclination, the strength and elastic modulus of the pre-cracked specimen increases gradually, which is verified by the numerical simulation and theoretical results. Analysis of the cracking processes indicates that the initiation position of the first crack in specimens with various flaw inclinations is different, which is caused by the various distributions of tensile and compressive stress concentration zones. The distribution of the stress field controls the cracking process which will in turn affect the stress field distribution. With the propagation of the cracks, the tensile stress concentration zones expand and the concentration degree lowers gradually, while the compressive stress concentration zones show the opposite variation trend. Based on the above results, an optimized slot arrangement method has been proposed for the field application of hydraulic slotting.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-07-01

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

  16. Small Crack Growth and Fatigue Life Predictions for High-Strength Aluminium Alloys. Part 1; Experimental and Fracture Mechanics Analysis

    Science.gov (United States)

    Wu, X. R.; Newman, J. C.; Zhao, W.; Swain, M. H.; Ding, C. F.; Phillips, E. P.

    1998-01-01

    The small crack effect was investigated in two high-strength aluminium alloys: 7075-T6 bare and LC9cs clad alloy. Both experimental and analytical investigations were conducted to study crack initiation and growth of small cracks. In the experimental program, fatigue tests, small crack and large crack tests A,ere conducted under constant amplitude and Mini-TWIST spectrum loading conditions. A pronounced small crack effect was observed in both materials, especially for the negative stress ratios. For all loading conditions, most of the fatigue life of the SENT specimens was shown to be crack propagation from initial material defects or from the cladding layer. In the analysis program, three-dimensional finite element and A weight function methods were used to determine stress intensity factors and to develop SIF equations for surface and corner cracks at the notch in the SENT specimens. A plastisity-induced crack-closure model was used to correlate small and large crack data, and to make fatigue life predictions, Predicted crack-growth rates and fatigue lives agreed well with experiments. A total fatigue life prediction method for the aluminum alloys was developed and demonstrated using the crack-closure model.

  17. Material size effects on crack growth along patterned wafer-level Cu–Cu bonds

    DEFF Research Database (Denmark)

    Tvergaard, Viggo; Niordson, Christian Frithiof; Hutchinson, John W.

    2013-01-01

    The role of micron-scale patterning on the interface toughness of bonded Cu-to-Cu nanometer-scale films is analyzed, motivated by experimental studies of Tadepalli, Turner and Thompson. In the experiments 400nm Cu films were deposited in various patterns on Si wafer substrates and then bonded...... together. Crack growth along the bond interface is here studied numerically using finite element analyses. The experiments have shown that plasticity in the Cu films makes a major contribution to the macroscopic interface toughness. To account for the size dependence of the plastic flow a strain gradient...... plasticity model is applied here for the metal. A cohesive zone model is applied to represent the crack growth along the bond between the two Cu films. This cohesive zone model incorporates the effect of higher order stresses in the continuum, such that the higher order tractions on the crack faces decay...

  18. Sub-surface Fatigue Crack Growth at Alumina Inclusions in AISI 52100 Roller Bearings

    DEFF Research Database (Denmark)

    Cerullo, Michele

    2014-01-01

    Sub-surface fatigue crack growth at non metallic inclusions is studied in AISI 52100 bearing steel under typical rolling contact loads. A first 2D plane strain finite element analysis is carried out to compute the stress history in the innner race at a characteristic depth, where the Dang Van...... damage factor is highest. Subsequently the stress history is imposed as boundary conditions in a periodic unit cell model, where an alumina inclusion is embedded in a AISI 52100 matrix. Cracks are assumed to grow radially from the inclusion under cyclic loading. The growth is predicted by means...... of irreversible fatigue cohesive elements. Different orientations of the cracks and different matrix-inclusion bonding conditions are analyzed and compared....

  19. Friction Stir Welding of 7075-T651 Aluminum Plates and Its Fatigue Crack Growth Property

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Chi Ok; Sohn, Hye Jeong; Kim, Seon Jin [Pukyong National University, Busan (Korea, Republic of)

    2011-10-15

    Friction stir welding (FSW) method has extensively been used in manufacturing methods because of the several advantages over conventional welding methods, such as better mechanical properties, reduced occurrence of joining defects, high material saving, and low production time, etc. The aim of this paper is to review the optimal FSW conditions using the previous experimental results and is to investigate the fatigue crack growth rate in three different zones, WM, HAZ and BM for FSWed Al7075-T651 aluminum plates. As far as our experiments are concerned, the optimal conditions are obtained as rotation speed, 800rpm and travelling speed, 0.5mm/sec. The fatigue crack growth rate showed strong dependency on three different zones WM, HAZ and BM, and crack driving force.

  20. Fatigue crack growth from handling surface anomalies in a nickel based superalloy at high temperature

    Directory of Open Access Journals (Sweden)

    Gourdin Stéphane

    2014-01-01

    Full Text Available Aircraft engine manufacturers have to demonstrate that handling surface anomalies in sensitive areas of discs are not critical for in-service life of a component. Currently, the models used consider anomalies as long cracks propagating from the first cycle, which introduces a certain degree of conservatism when calculating the fatigue life of surface flaws. Preliminary studies have shown that the first stages of crack propagation from surface anomalies are responsible for the conservative results. Thus, the aim of the study is to characterize the crack propagation from typical surface anomalies and to establish a new crack growth model, which can account for the micro-propagation stage. To separate the effects of the geometry of the anomalies and the residual stress state after introduction of the surface flaws, two V-type anomalies are studied: scratches and dents. Different studies have shown that the residual stresses beneath the anomalies seem to control the fatigue life of samples exhibiting scratches and dents. In order to monitor the crack micro-propagation, a direct current potential drop technique, coupled with heat tints is used during fatigue tests at elevated temperature. Thermal treatments releasing the residual stresses are also used to decouple the effect of crack morphology and residual stresses.

  1. Restraint of fatigue crack growth by wedge effects of fine particles

    CERN Document Server

    Takahashi, I; Kotani, N

    2000-01-01

    Presents some experimental results which demonstrate restraint of fatigue crack growth in an Al-Mg alloy by wedge effects of fine particles. Fatigue test specimens were machined from a JIS A5083P-O Al-Mg alloy plate of 5 mm thickness and an EDM starter notch was introduced to each specimen. Three kinds of fine particles were prepared as the materials to be wedged into the fatigue cracks, i.e. magnetic particles and two kinds of alumina particles having different mean particle sizes of 47.3 mu m and 15.2 mu m. Particles of each kind were suspended in an oil to form a paste, which was applied on the specimen surface covering the notch zone prior to the fatigue tests. In order to make some fracture mechanics approaches, in situ observations of fatigue cracks were performed for the two cases using a CCD microscope, with a magnification of *1000. The crack length and the crack opening displacement (COD) at the notch root, delta , were measured. The crack retardation effect continues almost through the entire lifet...

  2. Effect of laser shock processing on fatigue crack growth of duplex stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Rubio-Gonzalez, C., E-mail: crubio@cidesi.mx [Centro de Ingenieria y Desarrollo Industrial, Pie de la Cuesta, 702, Desarrollo San Pablo, Queretaro, Qro., 76130 (Mexico); Felix-Martinez, C. [Centro de Ingenieria y Desarrollo Industrial, Pie de la Cuesta, 702, Desarrollo San Pablo, Queretaro, Qro., 76130 (Mexico); Gomez-Rosas, G. [Universidad de Guadalajara, Guadalajara, Jal (Mexico); Ocana, J.L.; Morales, M.; Porro, J.A. [Departamento de Fisica Aplicada a la Ingenieria Industrial, E.T.S.I.I., Universidad Politecnica de Madrid (Spain)

    2011-01-25

    Research highlights: {yields} LSP is an effective surface treatment to improve fatigue properties of duplex stainless steel. {yields} Increasing pulse density, fatigue crack growth rate is reduced. {yields} Microstructure is not affected by LSP. {yields} Compressive residual stresses increases increasing pulse density. - Abstract: Duplex stainless steels have wide application in different fields like the ship, petrochemical and chemical industries that is due to their high strength and excellent toughness properties as well as their high corrosion resistance. In this work an investigation is performed to evaluate the effect of laser shock processing on some mechanical properties of 2205 duplex stainless steel. Laser shock processing (LSP) or laser shock peening is a new technique for strengthening metals. This process induces a compressive residual stress field which increases fatigue crack initiation life and reduces fatigue crack growth rate. A convergent lens is used to deliver 2.5 J, 8 ns laser pulses by a Q-switched Nd:YAG laser, operating at 10 Hz with infrared (1064 nm) radiation. The pulses are focused to a diameter of 1.5 mm. Effect of pulse density in the residual stress field is evaluated. Residual stress distribution as a function of depth is determined by the contour method. It is observed that the higher the pulse density the greater the compressive residual stress. Pulse densities of 900, 1600 and 2500 pul/cm{sup 2} are used. Pre-cracked compact tension specimens were subjected to LSP process and then tested under cyclic loading with R = 0.1. Fatigue crack growth rate is determined and the effect of LSP process parameters is evaluated. In addition fracture toughness is determined in specimens with and without LSP treatment. It is observed that LSP reduces fatigue crack growth and increases fracture toughness if this steel.

  3. Development of a crack growth analysis is program for reactor head penetration

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Sung Yull; Choi, Kwang Hee; Park, Jeong Il [Korea Electric Power Research Institute, Taejon (Korea, Republic of); Kang, Young Hwan; Park, Sung Ho; Kim, Il; Kim, Young Jong; Yoo, Young Joon; Yoo, Wan; Maeng, Wan Young; Choi, Suk Nam; Kim, Kee Suk; Yoon, Sung Won; Kim, Jee Ho; Park, Myung Kyu [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    1996-12-31

    Crack growth analysis program for Reactor Head Penetration is being developed for applying to plants such as, Kori 1, Kori 2, Kori 3,4 YoungKwang 1,2 and Uljin 1,2 (1) Stress Evaluation - The stress analysis is required to evaluate the structure integrity for the RVH penetration tubes. The RVH penetration tubes are geometrically non-symmetry except center one. Thus, 3D finite element analysis should be employed for the stress analysis. The magnitude and distribution of residual stress resulted from welding can be determined analytically by simulation welding procedure. (2) Flaw Evaluation - There are two objectives of the penetration tube flaw evaluation to predict the time required for a crack to propagate to the acceptance criteria. The first objective is to perform the parametric evaluation for a postulated crack. The second objective is to develop the flaw evaluation program for the crack detected during the inspection. (3) Characterization of Material Properties of Alloy 600 - These study is to provide data which similarly represent the properties of PWR power plants in Korea. The data is used for analyzing of the stress distribution around penetration tubes. And the PWSCC data will be used for the crack growth rate of the penetration tubes. (author). 92 refs., 121 figs.

  4. Fracture behavior of short circumferentially surface-cracked pipe

    Energy Technology Data Exchange (ETDEWEB)

    Krishnaswamy, P.; Scott, P.; Mohan, R. [Battelle, Columbus, OH (United States)] [and others

    1995-11-01

    This topical report summarizes the work performed for the Nuclear Regulatory Comniission`s (NRC) research program entitled ``Short Cracks in Piping and Piping Welds`` that specifically focuses on pipes with short, circumferential surface cracks. The following details are provided in this report: (i) material property deteminations, (ii) pipe fracture experiments, (iii) development, modification and validation of fracture analysis methods, and (iv) impact of this work on the ASME Section XI Flaw Evaluation Procedures. The material properties developed and used in the analysis of the experiments are included in this report and have been implemented into the NRC`s PIFRAC database. Six full-scale pipe experiments were conducted during this program. The analyses methods reported here fall into three categories (i) limit-load approaches, (ii) design criteria, and (iii) elastic-plastic fracture methods. These methods were evaluated by comparing the analytical predictions with experimental data. The results, using 44 pipe experiments from this and other programs, showed that the SC.TNP1 and DPZP analyses were the most accurate in predicting maximum load. New Z-factors were developed using these methods. These are being considered for updating the ASME Section XI criteria.

  5. Fatigue Crack Growth Prediction for generalized fiber metal laminates and hybrid materials

    NARCIS (Netherlands)

    Wilson, G.S.

    2013-01-01

    The excellent durability performance of Glare, a thin fiber metal laminate (FML) material system, is now being proven in service. This has motivated work towards the application of FMLs to thicker structures driven by damage tolerance. In order to fully characterize the crack growth life of such mat

  6. Influence of High Strength Steel Microstructure on Fatigue Crack Growth Rate

    Directory of Open Access Journals (Sweden)

    Enefola S. Ameh

    2016-07-01

    Full Text Available This study examines the effect of high strength steel microstructure morphology on fatigue crack growth rate (FCGR. To achieve this aim, three different heat treatment methods (normalizing, austempering quenching and tempering were considered and all the steel specimens were initially heated to 9500C austenization temperature for ninety minutes and then processed via the different heat treatment methods before viewing the resultant microstructures under light optical microscope (LOM. Fatigue crack growth rate tests were conducted on the resultant microstructures with compact tension specimens at room temperature as prescribed by American standard testing method E647. Results of FCGR tests showed normalized microstructure has the lowest FCGR (6.2698E-06, followed by quenched and tempered (7.9519E-06, asreceived (8.15E-06 and austempered (9.6667E-06 microstructure considering a low stress intensity factor range. The trend of results showed insignificant effect of microstructure over the Paris regime growth indicating fatigue crack growth rate is not a reliable parameter for correlating rate of crack propagation to microstructure

  7. Hydrogen Isotope Effect on the Fatigue Crack Growth Rate in Pipeline Steel

    Science.gov (United States)

    Connolly, Matthew; Slifka, Andrew; Drexler, Elizabeth; Hydrogen Pipeline Safety Team

    Hydrogen (H2) is desirable for energy storage as it is cleaner burning and can store a larger amount of energy than an equal mass of gasoline. One problem in the development of a hydrogen economy is to find or develop materials that ensure the safe, reliable, and cost-effective flow of energy from the source to the user. It is expected steels will be needed to serve this function. However, the existing network of natural gas pipeline, for example, is constructed of ferrous materials which are susceptible to embrittlement and subsequent increased fatigue crack growth rates after exposure to hydrogen. It is expected that diffusion rates play an important role on fatigue crack growth rates. We report the measurement of the fatigue crack growth rate in a high strength pipeline steel in a gaseous deuterium (D2) environment, in an effort to determine the role of diffusion rate on FCGR, because D2 is chemically identical to H2, but with twice the mass. We found that the D2 fatigue crack growth rate was not enhanced compared to air as is seen in an H2 environment; in fact our D2 rate measurement was slightly slower than in air, a result which is not expected to be due to diffusion rates alone. NIST Materials Measurement Laboratory, Applied Chemicals and Materials Division.

  8. Correlation of microstructure and fatigue crack growth resistance in Ti-6Al-4V alloy

    CSIR Research Space (South Africa)

    Masete, Stephen

    2016-10-01

    Full Text Available The effect of the microstructure on fatigue crack growth resistance of the Ti-6Al-4V alloy was investigated. Various microstructures were produced by solution treatment above the beta transus temperature followed by cooling at different rates...

  9. Mode I and Mode II Interlaminar Crack Growth Resistances of Ceramic Matrix Composites at Ambient Temperature

    Science.gov (United States)

    2007-03-02

    polymer matrix composite , used as comparison, showed R-curve behavior and typically 2-3 and 8 times greater in GI and GII, respectively, than the CMCs. Experimental error analysis concerning the effect of the off-the-center of a crack plane on GI and GII was also

  10. Influence of dissolved hydrogen on the fatigue crack growth behaviour of AISI 4140 steel

    Science.gov (United States)

    Ramasagara Nagarajan, Varun

    Many metallic structural components come into contact with hydrogen during manufacturing processes or forming operations such as hot stamping of auto body frames and while in service. This interaction of metallic parts with hydrogen can occur due to various reasons such as water molecule dissociation during plating operations, interaction with atmospheric hydrogen due to the moisture present in air during stamping operations or due to prevailing conditions in service (e.g.: acidic or marine environments). Hydrogen, being much smaller in size compared to other metallic elements such as Iron in steels, can enter the material and become dissolved in the matrix. It can lodge itself in interstitials locations of the metal atoms, at vacancies or dislocations in the metallic matrix or at grain boundaries or inclusions (impurities) in the alloy. This dissolved hydrogen can affect the functional life of these structural components leading to catastrophic failures in mission critical applications resulting in loss of lives and structural component. Therefore, it is very important to understand the influence of the dissolved hydrogen on the failure of these structural materials due to cyclic loading (fatigue). For the next generation of hydrogen based fuel cell vehicles and energy systems, it is very crucial to develop structural materials for hydrogen storage and containment which are highly resistant to hydrogen embrittlement. These materials should also be able to provide good long term life in cyclic loading, without undergoing degradation, even when exposed to hydrogen rich environments for extended periods of time. The primary focus of this investigation was to examine the influence of dissolved hydrogen on the fatigue crack growth behaviour of a commercially available high strength medium carbon low alloy (AISI 4140) steel. The secondary objective was to examine the influence of microstructure on the fatigue crack growth behaviour of this material and to determine the

  11. Assessing reliability of fatigue indicator parameters for small crack growth via a probabilistic framework

    Science.gov (United States)

    Rovinelli, Andrea; Guilhem, Yoann; Proudhon, Henry; Lebensohn, Ricardo A.; Ludwig, Wolfgang; Sangid, Michael D.

    2017-06-01

    Microstructurally small cracks exhibit large variability in their fatigue crack growth rate. It is accepted that the inherent variability in microstructural features is related to the uncertainty in the growth rate. However, due to (i) the lack of cycle-by-cycle experimental data, (ii) the complexity of the short crack growth phenomenon, and (iii) the incomplete physics of constitutive relationships, only empirical damage metrics have been postulated to describe the short crack driving force metric (SCDFM) at the mesoscale level. The identification of the SCDFM of polycrystalline engineering alloys is a critical need, in order to achieve more reliable fatigue life prediction and improve material design. In this work, the first steps in the development of a general probabilistic framework are presented, which uses experimental result as an input, retrieves missing experimental data through crystal plasticity (CP) simulations, and extracts correlations utilizing machine learning and Bayesian networks (BNs). More precisely, experimental results representing cycle-by-cycle data of a short crack growing through a beta-metastable titanium alloy, VST-55531, have been acquired via phase and diffraction contrast tomography. These results serve as an input for FFT-based CP simulations, which provide the micromechanical fields influenced by the presence of the crack, complementing the information available from the experiment. In order to assess the correlation between postulated SCDFM and experimental observations, the data is mined and analyzed utilizing BNs. Results show the ability of the framework to autonomously capture relevant correlations and the equivalence in the prediction capability of different postulated SCDFMs for the high cycle fatigue regime.

  12. Predictions of mixed mode interface crack growth using a cohesive zone model for ductile fracture

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2004-01-01

    Special interface elements that account for ductile failure by the nucleation and growth of voids to coalescence are used to analyse crack growth. In these elements the stress component tangential to the interface is accounted for, as determined by the requirement of compatibility with the surrou......Special interface elements that account for ductile failure by the nucleation and growth of voids to coalescence are used to analyse crack growth. In these elements the stress component tangential to the interface is accounted for, as determined by the requirement of compatibility...... with the surrounding material in the tangential direction. Thus, the present interface description incorporates the important effect of stress triaxiality on damage evolution, which is not part of the usual cohesive zone models. The interface elements have been used previously for mode I loading conditions...... Elsevier Ltd. All rights reserved....

  13. Fatigue crack behavior on a Cu-Zn-Al SMA

    Directory of Open Access Journals (Sweden)

    V. Di Cocco

    2014-10-01

    Optical Microscope (LOM observations. Furthermore a fatigue crack propagation and fracture surface scanning electron microscope (SEM observations have been performed in order to evaluate the crack path and the main crack micromechanisms.

  14. Effects of a Hydrogen Gas Environment on Fatigue Crack Growth of a Stable Austenitic Stainless Steel

    Science.gov (United States)

    Kawamoto, Kyohei; Oda, Yasuji; Noguchi, Hiroshi; Higashida, Kenji

    In order to clarify the effects of a hydrogen gas environment on the fatigue crack growth characteristics of stable austenitic stainless steels, bending fatigue tests were carried out in a hydrogen gas, in a nitrogen gas at 1.0 MPa and in air on a SUS316L using the Japanese Industrial Standards (type 316L). Also, in order to discuss the difference in the hydrogen sensitivity between austenitic stainless steels, the fatigue tests were also carried out on a SUS304 using the Japanese Industrial Standards (type 304) metastable austenitic stainless steel as a material for comparison. The main results obtained are as follows. Hydrogen gas accelerates the fatigue crack growth rate of type 316L. The degree of the fatigue crack growth acceleration is low compared to that in type 304. The fracture surfaces of both the materials practically consist of two parts; the faceted area seemed to be brittle and the remaining area occupying a greater part of the fracture surface and seemed to be ductile. The faceted area does not significantly contribute to the fatigue crack growth rate in both austenitic stainless steels. The slip-off mechanism seems to be valid not only in air and in nitrogen, but also in hydrogen. Also, the main cause of the fatigue crack growth acceleration of both materials occurs by variation of the slip behaviour. The difference in the degree of the acceleration, which in type 316L is lower than in type 304, seems to be caused by the difference in the stability of the γ phase.

  15. Cracking behavior in a dissimilar weld between high silicon nodular cast iron and ferritic stainless steel

    Science.gov (United States)

    Kim, Sanghoon; Lee, Sangchul; Han, Kyutae; Hong, Seunggab; Lee, Changhee

    2010-06-01

    In this work, the microstructural evolution and cracking behavior of a dissimilar weld between high silicon nodular cast iron and ferritic stainless steel was investigated. An austenitic filler metal (Y309) was employed to produce the dissimilar weld. Microstructural analysis revealed that cracking formed at the unmixed zone (UMZ) and propagated into the partially melted zone (PMZ) in the bond line between the cast iron and the Y309, with hard layers formed around the bond line. The cracking behavior was strongly related to the difference in the melting points of cast iron and the Y309 filler metal, the local liquation of the laves phase, and the constitutional liquation between the graphite and austenite phases in the PMZ.

  16. Creep and Creep-Fatigue Crack Growth at Structural Discontinuities and Welds

    Energy Technology Data Exchange (ETDEWEB)

    Dr. F. W. Brust; Dr. G. M. Wilkowski; Dr. P. Krishnaswamy; Mr. Keith Wichman

    2010-01-27

    The subsection ASME NH high temperature design procedure does not admit crack-like defects into the structural components. The US NRC identified the lack of treatment of crack growth within NH as a limitation of the code and thus this effort was undertaken. This effort is broken into two parts. Part 1, summarized here, involved examining all high temperature creep-fatigue crack growth codes being used today and from these, the task objective was to choose a methodology that is appropriate for possible implementation within NH. The second part of this task, which has just started, is to develop design rules for possible implementation within NH. This second part is a challenge since all codes require step-by-step analysis procedures to be undertaken in order to assess the crack growth and life of the component. Simple rules for design do not exist in any code at present. The codes examined in this effort included R5, RCC-MR (A16), BS 7910, API 579, and ATK (and some lesser known codes). There are several reasons that the capability for assessing cracks in high temperature nuclear components is desirable. These include: (1) Some components that are part of GEN IV reactors may have geometries that have sharp corners - which are essentially cracks. Design of these components within the traditional ASME NH procedure is quite challenging. It is natural to ensure adequate life design by modeling these features as cracks within a creep-fatigue crack growth procedure. (2) Workmanship flaws in welds sometimes occur and are accepted in some ASME code sections. It can be convenient to consider these as flaws when making a design life assessment. (3) Non-destructive Evaluation (NDE) and inspection methods after fabrication are limited in the size of the crack or flaw that can be detected. It is often convenient to perform a life assessment using a flaw of a size that represents the maximum size that can elude detection. (4) Flaws that are observed using in-service detection

  17. Finite element analysis of three dimensional crack growth by the use of a boundary element sub model

    DEFF Research Database (Denmark)

    Lucht, Tore

    2009-01-01

    A new automated method to model non-planar three dimensional crack growth is proposed which combines the advantages of both the boundary element method and the finite element method. The proposed method links the two methods by a submodelling strategy in which the solution of a global finite...... element model containing an approximation of the crack is interpolated to a much smaller boundary element model containing a fine discretization of the real crack. The method is validated through several numerical comparisons and by comparison to crack growth measured in a test specimen for an engineering...

  18. Influences of gaseous environment on low growth-rate fatigue crack propagation in steels. Annual report No. 1, January 1980. Report No. FPL/R/80/1030

    Energy Technology Data Exchange (ETDEWEB)

    Ritchie, R.O.; Suresh, S.; Toplosky, J.

    1980-01-01

    The influence of gaseous environment is examined on fatigue crack propagation behavior in steels. Specifically, a fully martensitic 300-M ultrahigh strength steel and a fully bainitic 2-1/4Cr-1Mo lower strength steel are investigated in environments of ambient temperature moist air and low pressure dehumidified hydrogen and argon gases over a wide range of growth rates from 10/sup -8/ to 10/sup -2/ mm/cycle, with particular emphasis given to behavior near the crack propagation threshold ..delta..K/sub 0/. It is found that two distinct growth rate regimes exist where hydrogen can markedly accelerate crack propagation rates compared to air, (1) at near-threshold levels below (5 x 10/sup -6/ mm/cycle) and (2) at higher growth rates, typically around 10/sup -5/ mm/cycle above a critical maximum stress intensity K/sub max//sup T/. Hydrogen-assisted crack propagation at higher growth rates is attributed to a hydrogen embrittlement mechanism, with K/sub max//sup T/ nominally equal to K/sub Iscc/ (the sustained load stress corrosion threshold) in high strength steels, and far below K/sub Iscc/ in the strain-rate sensitive lower strength steels. Hydrogen-assisted crack propagation at near-threshold levels is attributed to a new mechanism involving fretting-oxide-induced crack closure generated in moist (or oxygenated) environments. The absence of hydrogen embrittlement mechanisms at near-threshold levels is supported by tests showing that ..delta..K/sub 0/ values in dry gaseous argon are similar to ..delta..K/sub 0/ values in hydrogen. The potential ramifications of these results are examined in detail.

  19. Thermal Stresses and Cracks During the Growth of Large-sized Sapphire with SAPMAC Method

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The finite-element method has been used to study the thermal stress distribution in large-sized sapphire crystals grown with the sapphire growth technique with micro-pulling and shoulder-expanding at cooled center (SAPMAC) method. A critical defect model has been established to explain the growth and propagation of cracks during the sapphire growing process. It is demonstrated that the stress field depends on the growth rate, the ambient temperature and the crystallizing direction. High stresses always exist near the growth interfaces, at the shoulder-expanding locations, the tailing locations and the sites where the diameters undergo sharp changes. The maximum stresses always occur at the interface of seeds and crystals. Cracks often form in the critical defect region and spread in the m-planes and a-planes under applied tensile stresses during crystal growth. The experimental results have verified that with the improved system of crystal growth and well-controlled techniques, the large-sized sapphire crystals of high quality can be grown due to absence of cracks.

  20. Fatigue crack growth due to overloads in plain concrete using scaling laws

    Indian Academy of Sciences (India)

    Sonalisa Ray; J M Chandra Kishen

    2012-02-01

    Scaling laws are represented in power law form and can be utilized to extract the characteristic properties of a new phenomenon with the help of self-similar solutions. In this work, an attempt has been made to propose a scaling law analytically, for plain concrete when subjected to variable amplitude loading. Due to the application of overload on concrete structures, acceleration in the crack growth process takes place. A closed form expression has been developed to capture the acceleration in crack growth rate in conjunction with the principles of dimensional analysis and self-similarity. The proposed model accounts for parameters such as, the tensile strength, fracture toughness, overload effect and the structural size. Knowing the governed and the governing parameters of the physical problem and by using the concepts of self-similarity, a relationship is obtained between the different parameters involved. The predicted results are compared with experimental crack growth data for variable amplitude loading and are found to capture the overload effect with sufficient accuracy. Through a sensitivity analysis, fracture toughness is found to be the most dominant parameter in accelerating the crack length due to application of overload.

  1. Effect of cold work and processing orientation on stress corrosion cracking behavior of alloy 600

    Energy Technology Data Exchange (ETDEWEB)

    Moshier, W.C.; Brown, C.M.

    2000-03-01

    Cold work accelerates stress corrosion cracking (SCC) growth rates in Alloy 600 (UNS N06600). However, the variation in crack growth rates generated from cold-worked material has been significant, and the effect has been difficult to quantify. A study was performed in hydrogenated water adjusted to pH 10.2 to evaluate systematically the effect of cold work on Alloy 600 as a function of temperature, amount of cold work, stress intensity factor, and processing orientation. Cold work was introduced into the material by tensile prestraining or cold-rolling plate product. Crack growth rates were determined between 252 C and 360 C, stress intensity factors between 21 MPa{radical}m and 55 MPa{radical}m, and yield strengths between 201 MPa and 827 MPa. The material with the highest yield strength was cold-rolled and tested in the longitudinal-transverse (LT) and short-transverse (ST) orientations. Crack growth rates increased with increasing temperature, stress intensity factor, and yield strength. Furthermore, crack growth rates were a strong function of the processing orientation in the cold-rolled plate, with growth rates approximately an order of magnitude greater in the ST orientation compared to the LT orientation. Crack growth rates in the LT orientation were measured between 0.003 x 10{sup {minus}9} m/s and 1.95 x 10{sup {minus}9} m/s and between 0.066 x 10{sup {minus}9} m/s and 6.3 x 10{sup {minus}9} m/s in the ST orientation. Activation energies were slightly greater in the ST orientation, ranging from 154 kcal/mol to 191 kcal/mol, compared to activation energies between 126 kJ/mol and 157 kJ/mol in the LT orientation. Results of this study demonstrated that, although cold work can be used to accelerate SCC, the orientation of crack growth significantly can affect the results and must be taken into account when analyzing data from cold-worked material.

  2. Fatigue crack growth in austempered ductile and grey cast irons - stress ratio effects in air and mine water

    Energy Technology Data Exchange (ETDEWEB)

    James, M.N. [Plymouth Univ. (United Kingdom). Dept. of Mech. and Marine Eng.; Li Wenfong [Department of Mechanical Engineering, University of Sydney, Sydney, NSW 2006 (Australia)

    1999-06-15

    A study is presented of the effect of stress ratio on fatigue crack growth in grey (GI) and austempered ductile (ADI) cast irons in laboratory air and, for the ADI, in synthetic mine water. Fatigue crack closure was measured by compliance techniques and factored out of the applied {Delta}K values ({Delta}K=K{sub max}-K{sub min}) to give effective stress intensity values. Crack growth rate modelling was then attempted for the laboratory air data using a two-parameter approach ({Delta}K and K{sub max}). This worked well for the ADI, but not for the GI, probably due to the much larger scatter inherent in the fatigue crack growth rates in the latter alloy. Trends in the observed growth rate and closure data for the two alloys are explained in terms of mechanism changes arising from microstructural/crack tip plastic zone interactions, and K{sub max} effects. (orig.) 9 refs.

  3. Crack Growth Mechanisms under Anti-Plane Shear in Composite Laminates

    Science.gov (United States)

    Horner, Allison Lynne

    The research conducted for this dissertation focuses on determining the mechanisms associated with crack growth in polymer matrix composite laminates subjected to anti-plane shear (mode III) loading. For mode III split-beam test methods were proposed, and initial evaluations were conducted. A single test method was selected for further evaluation. Using this test method, it was determined that the apparent mode III delamination toughness, GIIIc , depended on geometry, which indicated a true material property was not being measured. Transverse sectioning and optical microscopy revealed an array of transverse matrix cracks, or echelon cracks, oriented at approximately 45° and intersecting the plane of the delamination. Subsequent investigations found the echelon array formed prior to the onset of planar delamination advance and that growth of the planar delamination is always coupled to echelon array formation in these specimens. The evolution of the fracture surfaces formed by the echelon array and planar delamination were studied, and it was found that the development was similar to crack growth in homogenous materials subjected to mode III or mixed mode I-III loading, although the composite laminate architecture constrained the fracture surface development differently than homogenous materials. It was also found that, for split-beam specimens such as those used herein, applying an anti-plane shear load results in twisting of the specimen's uncracked region which gives rise to a mixed-mode I-III load condition. This twisting has been related to the apparent mode III toughness as well as the orientation of the transverse matrix cracks. A finite element model was then developed to study the mechanisms of initial echelon array formation. From this, it is shown that an echelon array will develop, but will become self-limiting prior to the onset of planar delamination growth.

  4. Initiation and growth kinetics of solidification cracking during welding of steel

    Science.gov (United States)

    Aucott, L.; Huang, D.; Dong, H. B.; Wen, S. W.; Marsden, J. A.; Rack, A.; Cocks, A. C. F.

    2017-01-01

    Solidification cracking is a key phenomenon associated with defect formation during welding. To elucidate the failure mechanisms, solidification cracking during arc welding of steel are investigated in situ with high-speed, high-energy synchrotron X-ray radiography. Damage initiates at relatively low true strain of about 3.1% in the form of micro-cavities at the weld subsurface where peak volumetric strain and triaxiality are localised. The initial micro-cavities, with sizes from 10 × 10−6 m to 27 × 10−6 m, are mostly formed in isolation as revealed by synchrotron X-ray micro-tomography. The growth of micro-cavities is driven by increasing strain induced to the solidifying steel. Cavities grow through coalescence of micro-cavities to form micro-cracks first and then through the propagation of micro-cracks. Cracks propagate from the core of the weld towards the free surface along the solidifying grain boundaries at a speed of 2–3 × 10−3 m s−1. PMID:28074852

  5. Initiation and growth kinetics of solidification cracking during welding of steel

    Science.gov (United States)

    Aucott, L.; Huang, D.; Dong, H. B.; Wen, S. W.; Marsden, J. A.; Rack, A.; Cocks, A. C. F.

    2017-01-01

    Solidification cracking is a key phenomenon associated with defect formation during welding. To elucidate the failure mechanisms, solidification cracking during arc welding of steel are investigated in situ with high-speed, high-energy synchrotron X-ray radiography. Damage initiates at relatively low true strain of about 3.1% in the form of micro-cavities at the weld subsurface where peak volumetric strain and triaxiality are localised. The initial micro-cavities, with sizes from 10 × 10‑6 m to 27 × 10‑6 m, are mostly formed in isolation as revealed by synchrotron X-ray micro-tomography. The growth of micro-cavities is driven by increasing strain induced to the solidifying steel. Cavities grow through coalescence of micro-cavities to form micro-cracks first and then through the propagation of micro-cracks. Cracks propagate from the core of the weld towards the free surface along the solidifying grain boundaries at a speed of 2–3 × 10‑3 m s‑1.

  6. Multiscale approach to micro/macro fatigue crack growth in 2024-T3 aluminum panel

    Science.gov (United States)

    Sih, G. C.

    2014-01-01

    When two contacting solid surfaces are tightly closed and invisible to the naked eye, the discontinuity is said to be microscopic regardless of whether its length is short or long. By this definition, it is not sufficient to distinguish the difference between a micro- and macro-crack by using the length parameter. Microcracks in high strength metal alloys have been known to be several centimeters or longer. Considered in this work is a dual scale fatigue crack growth model where the main crack can be micro or macro but there prevails an inherent microscopic tip region that is damaged depending on the irregularities of the microstructure. This region is referred to as the "micro-tip" and can be simulated by a sharp wedge with different angles in addition to mixed boundary conditions. The combination is sufficient to model microscopic entities in the form of voids, inclusions, precipitations, interfaces, in addition to subgrain imperfections, or cluster of dislocations. This is accomplished by using the method of "singularity representation" such that closed form asymptotic solutions can be obtained for the development of fatigue crack growth rate relations with three parameters. They include: (1) the crack surface tightness σ* represented by σ o/ σ ∞ = 0.3-0.5 for short cracks in region I, and 0.1-0.2 for long cracks in region II, (2) the micro/macro material properties reflected by the shear modulus ratio µ* (=µmicro/µmacro varying between 2 and 5) and (3) the most sensitive parameter d* being the micro-tip characteristic length d* (= d/ d o) whose magnitude decreases in the direction of region I→II. The existing fatigue crack growth data for 2024-T3 and 7075-T6 aluminum sheets are used to reinterpret the two-parameter d a/d N= C(Δ K) n relation where Δ K has now been re-derived for a microcrack with surfaces tightly in contact. The contact force will depend on the mean stress σm or mean stress ratio R as the primary parameter and on the stress

  7. Dynamic behavior of anchors in cracked and uncracked concrete: A progress report

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez, M.; Yong-gang Zhang; Lotze, D. [Univ. of Texas, Austin, TX (United States)] [and others

    1995-04-01

    In early 1993, the US Nuclear Regulatory Commission began a research program at The University of Texas at Austin, dealing with the dynamic behavior of anchors in cracked and uncracked concrete. In this paper, the progress of that research program is reviewed. The test program is summarized, the work performed to date is reviewed, with emphasis on the dynamic and static behavior of single tensile anchors in uncracked concrete. General conclusions from that work are discussed, and future plans are presented.

  8. Creep and Creep-Fatigue Crack Growth at Structural Discontinuities and Welds

    Energy Technology Data Exchange (ETDEWEB)

    Dr. F. W. Brust; Dr. G. M. Wilkowski; Dr. P. Krishnaswamy; Mr. Keith Wichman

    2010-01-27

    The subsection ASME NH high temperature design procedure does not admit crack-like defects into the structural components. The US NRC identified the lack of treatment of crack growth within NH as a limitation of the code and thus this effort was undertaken. This effort is broken into two parts. Part 1, summarized here, involved examining all high temperature creep-fatigue crack growth codes being used today and from these, the task objective was to choose a methodology that is appropriate for possible implementation within NH. The second part of this task, which has just started, is to develop design rules for possible implementation within NH. This second part is a challenge since all codes require step-by-step analysis procedures to be undertaken in order to assess the crack growth and life of the component. Simple rules for design do not exist in any code at present. The codes examined in this effort included R5, RCC-MR (A16), BS 7910, API 579, and ATK (and some lesser known codes). There are several reasons that the capability for assessing cracks in high temperature nuclear components is desirable. These include: (1) Some components that are part of GEN IV reactors may have geometries that have sharp corners - which are essentially cracks. Design of these components within the traditional ASME NH procedure is quite challenging. It is natural to ensure adequate life design by modeling these features as cracks within a creep-fatigue crack growth procedure. (2) Workmanship flaws in welds sometimes occur and are accepted in some ASME code sections. It can be convenient to consider these as flaws when making a design life assessment. (3) Non-destructive Evaluation (NDE) and inspection methods after fabrication are limited in the size of the crack or flaw that can be detected. It is often convenient to perform a life assessment using a flaw of a size that represents the maximum size that can elude detection. (4) Flaws that are observed using in-service detection

  9. Thermal behavior in the cracking reaction zone of scramjet cooling channels at different channel aspect ratios

    Science.gov (United States)

    Zhang, Silong; Feng, Yu; Jiang, Yuguang; Qin, Jiang; Bao, Wen; Han, Jiecai; Haidn, Oskar J.

    2016-10-01

    To study the thermal behavior in the cracking reaction zone of regeneratively cooled scramjet cooling channels at different aspect ratios, 3-D model of fuel flow in terms of the fuel's real properties and cracking reaction is built and validated through experiments. The whole cooling channel is divided into non-cracking and cracking reaction zones. Only the cracking reaction zone is studied in this article. The simulation results indicate that the fuel conversion presents a similar distribution with temperature because the fuel conversion in scramjet cooling channels is co-decided by the temperature and velocity but the temperature plays the dominate role. For the cases given in this paper, increasing the channel aspect ratio will increase the pressure drop and it is not beneficial for reducing the wall temperature because of the much severer thermal stratification, larger conversion non-uniformity, the corresponding M-shape velocity profile which will cause local heat transfer deterioration and the decreased chemical heat absorption. And the decreased chemical heat absorption caused by stronger temperature and conversion non-uniformities is bad for the utilization of chemical heat sink, chemical recuperation process and the ignition performance.

  10. Influence of temperature and exploitation period on fatigue crack growth parameters in different regions of welded joints

    Directory of Open Access Journals (Sweden)

    Ivica Camagic

    2016-03-01

    Full Text Available The influence of exploitation period and temperature on the fatigue crack growth parameters indifferent regions of a welded joint is analysed for new and exploited low-alloyed Cr-Mo steel A-387 Gr. B. The parent metal is a part of a reactor mantle which was exploited for over 40 years, and recently replaced with new material. Fatigue crack growth parameters, threshold value Kth, coefficient C and exponent m, have been determined, both at room and exploitation temperature. Based on testing results, fatigue crack growth resistance in different regions of welded joint is analysed in order to justify the selected welding procedure specification.

  11. The Effects of Shot and Laser Peening on Fatigue Life and Crack Growth in 2024 Aluminum Alloy and 4340 Steel

    Science.gov (United States)

    Everett, R. A., Jr.; Matthews, W. T.; Prabhakaran, R.; Newman, J. C., Jr.; Dubberly, M. J.

    2001-01-01

    Fatigue and crack growth tests have been conducted on 4340 steel and 2024-T3 aluminum alloy, respectively, to assess the effects of shot peening on fatigue life and the effects of shot and laser peening on crack growth. Two current programs involving fixed and rotary-wing aircraft will not be using shot peened structures. Since the shot peening compressive residual stress depth is usually less than the 0.05-inch initial damage tolerance crack size, it is believed by some that shot peening should have no beneficial effects toward retarding crack growth. In this study cracks were initiated from an electronic-discharged machining flaw which was cycled to produce a fatigue crack of approximately 0.05-inches in length and then the specimens were peened. Test results showed that after peening the crack growth rates were noticeably slower when the cracks were fairly short for both the shot and laser peened specimens resulting in a crack growth life that was a factor of 2 to 4 times greater than the results of the average unpeened test. Once the cracks reached a length of approximately 0.1-inches the growth rates were about the same for the peened and unpeened specimens. Fatigue tests on 4340 steel showed that the endurance limit of a test specimen with a 0.002-inch-deep machining-like scratch was reduced by approximately 40 percent. However, if the "scratched" specimen was shot peened after inserting the scratch, the fatigue life returned to almost 100 percent of the unflawed specimens original fatigue life.

  12. Experimental approach for mixed-mode fatigue delamination crack growth with large-scale bridging in polymer composites

    DEFF Research Database (Denmark)

    Holmes, John W.; Liu, Liu; Sørensen, Bent F.

    2014-01-01

    of delaminations in a typical fibre-reinforced polymer composite was investigated under a constant cyclic loading amplitude. Pure mode I, mode II and mixed-mode crack growth conditions were examined. The results, analysed using a J-integral approach, show that the double cantilever beam loaded with uneven bending......An experimental apparatus utilizing double cantilever beam specimens loaded with uneven bending moments was developed to study the mixed-mode fatigue crack growth in composites. The approach is suitable when large-scale bridging of cracks is present. To illustrate the testing method, cyclic growth...... crack growth rate observed. In addition to details concerning the equipment, a general discussion of the development of cyclic bridging laws for delamination growth in the presence of large-scale bridging is provided....

  13. Fatigue Crack Growth Rate of Type 347 Stainless Steel at the PWR Environment

    Energy Technology Data Exchange (ETDEWEB)

    Min, Ki Deuk; Kim, Seon Jin [Hanyang University, Seoul (Korea, Republic of); Kim, Dae Whan; Lee, Bong Sang [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2010-10-15

    Materials used in nuclear power plants are low alloy steel, stainless steel, and superalloy steel. Understanding the characteristics of these materials is important in the development of nuclear power plant related technology. Nb-stabilized Type 347 stainless steel is used for the coolant pressurizer surge line of Korea Standard Nuclear Power Plant (KSNPP). Surge line of PWR nuclear reactor are damaged by thermal fatigue due to thermal gradient during heat-up and cool-down, mechanical fatigue due to mechanical stress, and corrosion fatigue due to nuclear reactor water environment. Fatigue is an important factor which limits the life of structure. Fatigue crack growth rate curves in nuclear reactor environment are needed to evaluate the integrity of nuclear reactor structure but that result is not sufficient. In this study, fatigue crack growth rates at nuclear reactor environment are produced to evaluate integrity of nuclear power plant section 5

  14. PROBABILISTIC MODELS FOR LONG FATIGUE CRACK GROWTH RATES OF LZ50 AXLE STEEL

    Institute of Scientific and Technical Information of China (English)

    ZHAO Yong-xiang; HE Chao-ming; YANG Bing; HUANG Yu-zhong; GAO Qing; WU Ping-bo

    2005-01-01

    Experimental study is performed on the probabilistic models for the long fatigue crack growth rates (da/dN) of LZ50 axle steel. An equation for crack growth rate was derived to consider the trend of stress intensity factor range going down to the threshold and the average stress effect. The probabilistic models were presented on the equation. They consist of the probabilistic da/dN-△K relations, the confidence-based da/dN-△K relations, and the probabilistic- and confidence-based da/dN-△K relations.Efforts were made respectively to characterize the effects of probabilistic assessments due to the scattering regularity of test data, the number of sampling, and both of them.These relations can provide wide selections for practice. Analysis on the test data of LZ50 steel indicates that the present models are available and feasible.

  15. Effect of Hot Deformation on Formation and Growth of Thermal Fatigue Crack in Chromium Wear Resistant Cast Iron

    Institute of Scientific and Technical Information of China (English)

    CHANG Li-min; LIU Jian-hua

    2006-01-01

    The formation and growth of thermal fatigue crack in chromium wear resistant cast iron was investigated, and the effect of hot deformation on the crack was analyzed by means of optical microscope and scanning electron microscope and high frequency induction thermal fatigue tester. The results show that eutectic carbide is the main location and passage for initiation and extension of thermal fatigue cracks, hot deformation can improve the eutectic carbide′s morphology and distribution, inhibit the generation and propagation of thermal fatigue cracks. In the experiment, the propagation rate of thermal fatigue crack reduces with the quantity of hot deformation increasing, which was analyzed in the point view of the activation energy of crack propagation.

  16. SEM in-situ Fatigue Observation on Crack Initiation and Growth from Inclusion in P/M Rene95 Superalloy

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A special designed experiment was conducted for observing cr ack initiation and growth in P/M Rene95 superalloy under tension-tensi on loading by self-made SEM in-situ fatigue loading stag. Several alum ina inclusion particles exposed at the specimen surface were observed carefully. During fatigue test inclusions led to cracks initiation. Th e cracks can be formed by two mechanisms. Generally, the cracks nuclea ted at the interface between inclusion and matrix. Sometimes, cracks w ere also formed inside the inclusion. As the increase of cycles, some cracks at the interface between inclusion and matrix broadened and pro pagated along the direction about 45€?to the loading axis. On the oth er hand, the cracks inside the inclusion propagated in the inclusion a nd towards matrix.

  17. Sensitivity Analysis of Fatigue Crack Growth Model for API Steels in Gaseous Hydrogen

    Science.gov (United States)

    Amaro, Robert L; Rustagi, Neha; Drexler, Elizabeth S; Slifka, Andrew J

    2014-01-01

    A model to predict fatigue crack growth of API pipeline steels in high pressure gaseous hydrogen has been developed and is presented elsewhere. The model currently has several parameters that must be calibrated for each pipeline steel of interest. This work provides a sensitivity analysis of the model parameters in order to provide (a) insight to the underlying mathematical and mechanistic aspects of the model, and (b) guidance for model calibration of other API steels. PMID:26601024

  18. Sensitivity Analysis of Fatigue Crack Growth Model for API Steels in Gaseous Hydrogen.

    Science.gov (United States)

    Amaro, Robert L; Rustagi, Neha; Drexler, Elizabeth S; Slifka, Andrew J

    2014-01-01

    A model to predict fatigue crack growth of API pipeline steels in high pressure gaseous hydrogen has been developed and is presented elsewhere. The model currently has several parameters that must be calibrated for each pipeline steel of interest. This work provides a sensitivity analysis of the model parameters in order to provide (a) insight to the underlying mathematical and mechanistic aspects of the model, and (b) guidance for model calibration of other API steels.

  19. Crack Growth Testing of an Aluminum Oxynitride (AlON) for International Space Station Kick Panes

    Science.gov (United States)

    Salem, Jonathan A.

    2017-01-01

    The mechanical properties of an aluminum oxynitride supplied as ground beams and disks were measured using ASTM International (formerly American Society for Testing and Materials) standard test methods. The slow crack growth tests were complicated by a "short" finish that increased strength scatter. Refining of the finish by more material removal in the second stage of grinding or the use of uniaxial grinding as specified in ASTM C1499 might have avoided the issue. The structural design parameters are an elastic modulus of E = 319 GPa, Poisson's ratio of v = 0.26, a fracture toughness of KIvb(A) = 2.18 MPa/m, slow crack growth (SCG) parameter n = 36, and SCG parameter A = 1.96 x 10-11 m/s.(MPa/m)n. For a ground finish, the Weibull parameters are a mean modulus of m = 14.0 and characteristic strength of ?sigma theta = 250.2 MPa. The 2015 vintage material exhibits similar mechanical properties to a 2010 vintage billet. Indentation flaws were not sensitive to the inherent crack growth mechanisms of this material and produced misleading results.

  20. Influences on the thermomechanical fatigue crack growth of the nickel alloy 617

    Energy Technology Data Exchange (ETDEWEB)

    Schlesinger, Michael; Schweizer, Christoph; Brontfeyn, Yakiv [Fraunhofer-Institut fuer Werkstoffmechanik (IWM), Freiburg im Breisgau (Germany)

    2015-02-01

    The following contribution deals with the experimental investigation and theoretical evaluation of fatigue crack growth under isothermal and non-isothermal conditions at the nickel alloy 617. The microstructure and mechanical properties of alloy 617 are influenced significantly by the thermal heat treatment and the following thermal exposure in service. Hence, a solution annealed and a long-time service exposed material condition is studied. The crack growth measurement is carried out by using an alternate current potential drop system, which is integrated into a thermomechanical fatigue (TMF) test facility. The measured fatigue crack growth rates results in a function of material condition, temperature and load waveform. Furthermore, the results of the non-isothermal tests depend on the phase between thermal and mechanical load (in-phase, out-of-phase). A fracture mechanic based, time dependent model is upgraded by an approach to consider environmental effects, where almost all model parameters represent directly measurable values. A consistent of all results and a good correlation with the experimental data can be achieved.

  1. Characterization of Residual Stress Effects on Fatigue Crack Growth of a Friction Stir Welded Aluminum Alloy

    Science.gov (United States)

    Newman, John A.; Smith, Stephen W.; Seshadri, Banavara R.; James, Mark A.; Brazill, Richard L.; Schultz, Robert W.; Donald, J. Keith; Blair, Amy

    2015-01-01

    An on-line compliance-based method to account for residual stress effects in stress-intensity factor and fatigue crack growth property determinations has been evaluated. Residual stress intensity factor results determined from specimens containing friction stir weld induced residual stresses are presented, and the on-line method results were found to be in excellent agreement with residual stress-intensity factor data obtained using the cut compliance method. Variable stress-intensity factor tests were designed to demonstrate that a simple superposition model, summing the applied stress-intensity factor with the residual stress-intensity factor, can be used to determine the total crack-tip stress-intensity factor. Finite element, VCCT (virtual crack closure technique), and J-integral analysis methods have been used to characterize weld-induced residual stress using thermal expansion/contraction in the form of an equivalent delta T (change in local temperature during welding) to simulate the welding process. This equivalent delta T was established and applied to analyze different specimen configurations to predict residual stress distributions and associated residual stress-intensity factor values. The predictions were found to agree well with experimental results obtained using the crack- and cut-compliance methods.

  2. Review of environmental effects on fatigue crack growth of austenitic stainless steels.

    Energy Technology Data Exchange (ETDEWEB)

    Shack, W. J.; Kassner, T. F.; Energy Technology

    1994-07-11

    Fatigue and environmentally assisted cracking of piping, pressure vessel cladding, and core components in light water reactors are potential concerns to the nuclear industry and regulatory agencies. The degradation processes include intergranular stress corrosion cracking of austenitic stainless steel (SS) piping in boiling water reactors (BWRs), and propagation of fatigue or stress corrosion cracks (which initiate in sensitized SS cladding) into low-alloy ferritic steels in BWR pressure vessels. Crack growth data for wrought and cast austenitic SSs in simulated BWR water, developed at Argonne National Laboratory under US Nuclear Regulatory Commission sponsorship over the past 10 years, have been compiled into a data base along with similar data obtained from the open literature. The data were analyzed to develop corrosion-fatigue curves for austenitic SSs in aqueous environments corresponding to normal BWR water chemistries, for BWRs that add hydrogen to the feedwater, and for pressurized water reactor primary-system-coolant chemistry. The corrosion-fatigue data and curves in water were compared with the air line in Section XI of the ASME Code.

  3. Cracks path growth in turbine blades with TBC under thermo – mechanical cyclic loadings

    Directory of Open Access Journals (Sweden)

    T. Sadowski

    2016-02-01

    Full Text Available Blades of combustion turbines are extremely loaded turbojet elements, which transmit operative energy onto a rotor. Experiences of many years indicate, that cracks initiation and propagation in the blades during the operation time can cause destruction not only of the engine, but sometimes an airplane. In high temperature one of the most often occuring interactions in the turbine engine are time variable force fields, caused by non-stationary flowing of an exhaust gas and aerodynamical interaction of the engine elements. The extremal thermo-mechanical loadings initiate gradual degradation process of the blades as a result of fatigue and material creep. More often Thermal Barrier Coatings (TBCs are applied on the turbine blade surface to provide protection not only against the high temperature but also against aggressive environment. The paper presents the advantages of applying of the TBC layers for increase of the cracks resistance to gradual degradation of the turbine blades. The level of save values of thermo-mechanical loading was estimated. Analysis of critical values of loading leading to crack initiation, further growth and the final blade fragmentation was performed. The most efforted places of the turbine blades were selected and crack paths due to thermo-mechanical cyclic loading were determined.

  4. An experimental study on the effects of compressive stress on the fatigue crack growth of low-alloy steel

    Energy Technology Data Exchange (ETDEWEB)

    Jones, D.P.; Hoppe, R.G. [Westinghouse Electric Corp., West Mifflin, PA (United States). Bettis Atomic Power Lab.; Hechmer, J.L. [Babcock and Wilcox Co., Barberton, OH (United States); James, B.A. [Colorado School of Mines, Golden, CO (United States). Dept. of Metallurgy

    1993-12-01

    A series of fatigue crack growth rate tests was conducted in order to study effects of negative stress ratio on fatigue crack growth rate of low-alloy steel in air. Four-point bend specimens were used to simulate linear stress distributions typical of pressure vessel applications. This type of testing adds to knowledge on negative stress ratio effects for low-alloy steels obtained in the past from uniform tension-compression tests. Applied bending stress range was varied over twice the yield strength. Load control was used for tests for which the stress range was less than twice the yield strength and deflection control was used for the higher stress range tests. Crack geometries were both short and long fatigue cracks started at notches and tight fatigue cracks for which crack closure could occur over the full crack face. Results are presented in terms of the stress intensity factor ratio R = K{sub MIN}/K{sub MAX}. The negative R-ratio test results were correlated to an equation of the form da/dN = C[{Delta}K/(A-R)]{sup n}, where A, C, and n are curve fitting parameters. It was found that effects of negative R-ratio on fatigue crack growth rates for even the high stress range tests could be bounded by correlating the above equation to only positive R-ratio test results and extending the resulting equation into the negative R-ratio regime.

  5. Three-dimensional effects of microstructures on short fatigue crack growth in an Al-Li 8090 alloy

    Science.gov (United States)

    Wen, Wei; Zhai, Tongguang

    2011-09-01

    Al-Li 8090 alloy specimens were fatigued using a self-aligning four-point bend rig at R = 0.1 and room temperature, in air, under constant maximum stress control. The crystallographic characteristics of fatigue crack initiation and early growth were studied using EBSD. It was found that the growth behaviour of a short crack were controlled by the twist (α) and tilt (β) components of crack plane deflection across each of the first 20 grain boundaries along the crack path, and that the α angle at the first grain boundary encountered by a micro-crack was critical in determining whether the crack could become propagating or non-propagating. In addition to the orientations of the two neighbouring grains, the tilt of their boundary could also affect α across the boundary. A minimum α-map for a vertical micro-crack was calculated to evaluate the resistance to crack growth into a neighbouring grain with a random orientation. Such an α-map is of value in alloy design against fatigue damage by optimising texture components in the alloys.

  6. Time-Dependent Fatigue Crack Propagation Behavior of Two Solid-Solution-Strengthened Ni-Based Superalloys—INCONEL 617 and HAYNES 230

    Science.gov (United States)

    Ma, Longzhou; Roy, Shawoon K.; Hasan, Muhammad H.; Pal, Joydeep; Chatterjee, Sudin

    2012-02-01

    The fatigue crack propagation (FCP) as well as the sustained loading crack growth (SLCG) behavior of two solid-solution-strengthened Ni-based superalloys, INCONEL 617 (Special Metals Corporation Family of Companies) and HAYNES 230 (Haynes International, Inc., Kokomo, IN), were studied at increased temperatures in laboratory air under a constant stress-intensity-factor ( K) condition. The crack propagation tests were conducted using a baseline cyclic triangular waveform with a frequency of 1/3 Hz. Various hold times were imposed at the maximum load of a fatigue cycle to study the hold time effect. The results show that a linear elastic fracture mechanics (LEFM) parameter, stress intensity factor ( K), is sufficient to describe the FCP and SLCG behavior at the testing temperatures ranging from 873 K to 1073 K (600 °C to 800 °C). As observed in the precipitation-strengthened superalloys, both INCONEL 617 and HAYNES 230 exhibited the time-dependent FCP, steady SLCG behavior, and existence of a damage zone ahead of crack tip. A thermodynamic equation was adapted to correlate the SLCG rates to determine thermal activation energy. The fracture modes associated with crack propagation behavior were discussed, and the mechanism of time-dependent FCP as well as SLCG was identified. Compared with INCONEL 617, the lower crack propagation rates of HAYNES 230 under the time-dependent condition were ascribed to the different fracture mode and the presence of numerous W-rich M6C-type and Cr-rich M23C6-type carbides. Toward the end, a phenomenological model was employed to correlate the FCP rates at cycle/time-dependent FCP domain. All the results suggest that an environmental factor, the stress assisted grain boundary oxygen embrittlement (SAGBOE) mechanism, is mainly responsible for the accelerated time-dependent FCP rates of INCONEL 617 and HAYNES 230.

  7. Crack Growth Modeling and Life Prediction of Pipeline Steels Exposed to Near-Neutral pH Environments: Stage II Crack Growth and Overall Life Prediction

    Science.gov (United States)

    Zhao, Jiaxi; Chen, Weixing; Yu, Mengshan; Chevil, Karina; Eadie, Reg; Been, Jenny; Van Boven, Greg; Kania, Richard; Keane, Sean

    2017-04-01

    This investigation was initiated to provide governing equations for crack initiation, crack growth, and service life prediction of pipeline steels in near-neutral pH (NNpH) environments. This investigation develops a predictive model considering loading interactions occurring during oil and gas pipeline operation with underload-type variable pressure fluctuations. This method has predicted lifetimes comparable to the actual service lives found in the field. This is in sharp contrast with the predictions made by existing methods that are either conservative or inconsistent with the field observations. It has been demonstrated that large slash loads ( R-ratio is 0.05), often seen during gas pipeline operation, are a major life-limiting factor and should be avoided where possible. Oil pipelines have shorter lifetime because of their more frequent pressure fluctuations and larger amplitude load cycles. The accuracy of prediction can be improved if pressure data with appropriate sampling intervals are used. The sampling interval error is much larger in the prediction of oil pipelines than gas pipelines because of their different compressibility but is minimized if the pressure sampling rate for the data is at or less than one minute.

  8. Secondary Crystal Growth on a Cracked Hydrotalcite-Based Film Synthesized by the Sol-Gel Method.

    Science.gov (United States)

    Lee, Wooyoung; Lee, Chan Hyun; Lee, Ki Bong

    2016-05-02

    The sol-gel synthesis method is an attractive technology for the fabrication of ceramic films due to its preparation simplicity and ease of varying the metal composition. However, this technique presents some limitations in relation to the film thickness. Notably, when the film thickness exceeds the critical limit, large tensile stresses occur, resulting in a cracked morphology. In this study, a secondary crystal growth method was introduced as a post-treatment process for Mg/Al hydrotalcite-based films synthesized by the sol-gel method, which typically present a cracked morphology. The cracked hydrotalcite-based film was hydrothermally treated for the secondary growth of hydrotalcite crystals. In the resulting film, hydrotalcite grew with a vertical orientation, and the gaps formed during the sol-gel synthesis were filled with hydrotalcite after the crystal growth. The secondary crystal growth method provides a new solution for cracked ceramic films synthesized by the sol-gel method.

  9. ADAPTATION OF CRACK GROWTH DETECTION TECHNIQUES TO US MATERIAL TEST REACTORS

    Energy Technology Data Exchange (ETDEWEB)

    A. Joseph Palmer; Sebastien P. Teysseyre; Kurt L. Davis; Gordon Kohse; Yakov Ostrovsky; David M. Carpenter; Joy L. Rempe

    2015-04-01

    A key component in evaluating the ability of Light Water Reactors to operate beyond 60 years is characterizing the degradation of materials exposed to radiation and various water chemistries. Of particular concern is the response of reactor materials to Irradiation Assisted Stress Corrosion Cracking (IASCC). Some test reactors outside the United States, such as the Halden Boiling Water Reactor (HBWR), have developed techniques to measure crack growth propagation during irradiation. The basic approach is to use a custom-designed compact loading mechanism to stress the specimen during irradiation, while the crack in the specimen is monitored in-situ using the Direct Current Potential Drop (DCPD) method. In 2012 the US Department of Energy commissioned the Idaho National Laboratory and the MIT Nuclear Reactor Laboratory (MIT NRL) to take the basic concepts developed at the HBWR and adapt them to a test rig capable of conducting in-pile IASCC tests in US Material Test Reactors. The first two and half years of the project consisted of designing and testing the loader mechanism, testing individual components of the in-pile rig and electronic support equipment, and autoclave testing of the rig design prior to insertion in the MIT Reactor. The load was applied to the specimen by means of a scissor like mechanism, actuated by a miniature metal bellows driven by pneumatic pressure and sized to fit within the small in-core irradiation volume. In addition to the loader design, technical challenges included developing robust connections to the specimen for the applied current and voltage measurements, appropriate ceramic insulating materials that can endure the LWR environment, dealing with the high electromagnetic noise environment of a reactor core at full power, and accommodating material property changes in the specimen, due primarily to fast neutron damage, which change the specimen resistance without additional crack growth. The project culminated with an in

  10. The dynamic behavior of two collinear cracks in magneto-electro-elastic composites under harmonic anti-plane shear waves

    Institute of Scientific and Technical Information of China (English)

    SUN Yu-guo; WU Lin-zhi

    2005-01-01

    The dynamic behavior of two collinear cracks in magneto-electro-elastic composites under harmonic anti-plane shear waves is studied using the Schmidt method for the permeable crack surface conditions. By using the Fourier transform, the problem can be solved with a set of triple integral equations in which the unknown variable is the jump of the displacements across the crack surfaces. In solving the triple integral equations, the jump of the displacements across the crack surface is expanded in a series of Jacobi polynomials. It can be obtained that the stress field is independent of the electric field and the magnetic flux.

  11. Crack Propagation Behaviors of Multi-Layered SiC Composite Tubes

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Daejong; Lee, Donghee; Lee, Hyeon-Geun; Park, Ji Yeon; Kim, Weon-Ju [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-10-15

    SiC composite cladding has various advantages compared to current Zr alloy cladding in terms of accident resistance and neutron economy. However, its brittle properties and corresponding low reliability make it difficult for a use of SiC ceramics as cladding materials. In this study, fracture behaviors of several SiC composite cladding tubes, particularly crack propagation behavior were evaluated using an acoustic emission method. AE analysis is a useful tool for examination of the multi-layered SiC composite with complex structure which provides information of crack propagation. Failure of an inner monolith SiC in the triplex SiC composite tube will cause significant problems such as hermeticity, degradation of SiC{sub f}/SiC. Duplex SiC composite might be the alternative.

  12. Behavior of two parallel symmetry permeable cracks in functionally graded piezoelectric materials subjected to an anti-plane shear loading

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The behavior of two parallel symmetry permeable cracks in functionally graded piezoelectric materials subjected to an anti-plane shear loading was investigated. To make the analysis tractable, it was assumed that the material properties varied exponentially with coordinate vertical to the crack. By using the Fourier transform, the problem could be solved with the help of two pairs of dual integral equations, in which the unknown variables were the jumps of the displacements across the crack surfaces. To solve the dual integral equations, the displacement on the crack surfaces expanded in a series of Jacobi polynomials. The normalized stress and electrical displacement intensity factors were determined for different geometric and property parameters for permeable electric boundary conditions. Numerical examples were provided to show the effect of the geometry of the interacting cracks and the functionally graded material parameter upon the stress intensity factors of cracks.

  13. Monitoring of hidden fatigue crack growth in multi-layer aircraft structures using high frequency guided waves

    Science.gov (United States)

    Chan, H.; Masserey, B.; Fromme, P.

    2015-03-01

    Varying loading conditions of aircraft structures result in stress concentration at fastener holes, where multi-layered components are connected, potentially leading to the development of hidden fatigue cracks in inaccessible layers. High frequency guided waves propagating along the structure allow for the structural health monitoring (SHM) of such components, e.g., aircraft wings. Experimentally the required guided wave modes can be easily excited using standard ultrasonic wedge transducers. However, the sensitivity for the detection of small, potentially hidden, fatigue cracks has to be ascertained. The type of multi-layered model structure investigated consists of two adhesively bonded aluminum plate-strips with a sealant layer. Fatigue experiments were carried out and the growth of fatigue cracks at the fastener hole in one of the metallic layers was monitored optically during cyclic loading. The influence of the fatigue cracks of increasing size on the scattered guided wave field was evaluated. The sensitivity and repeatability of the high frequency guided wave modes to detect and monitor the fatigue crack growth was investigated, using both standard pulse-echo equipment and a laser interferometer. The potential for hidden fatigue crack growth monitoring at critical and difficult to access fastener locations from a stand-off distance was ascertained. The robustness of the methodology for practical in situ ultrasonic monitoring of fatigue crack growth is discussed.

  14. On the Fracture Toughness and Crack Growth Resistance of Bio-Inspired Thermal Spray Hybrid Composites

    Science.gov (United States)

    Resnick, Michael Murray

    the values of a real nacre. Although, the fracture toughness was primary property of this study and the values were well matched, the fracture behavior found to be somewhat different between the hybrid composite and nacre. In particular, the hybrid composite was unable to exhibit any significant toughness under slow crack growth conditions, which is the most attractive feature of nacre. This thesis focuses on first investigating the toughness in the sprayed hybrid composites by using standard resistance curve (R-curve) measurements. The study then focused on developing thermal spray modified hybrid composites with improved toughness, as well as with higher application temperatures, beyond the limitation of epoxy.

  15. 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

    on the definition of measured and derived parameters, including toughness, elastic properties and strength. This paper discusses a number of test procedures for selected material properties including tension and flexure. A comparative experimental study was carried out using two distinct fiber reinforced...... 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...

  16. A method to generate conformal finite-element meshes from 3D measurements of microstructurally small fatigue-crack propagation: 3D Meshes of Microstructurally Small Crack Growth

    Energy Technology Data Exchange (ETDEWEB)

    Spear, A. D. [Department of Mechanical Engineering, University of Utah, Salt Lake City UT USA; Hochhalter, J. D. [NASA Langley Research Center, Hampton VA USA; Cerrone, A. R. [GE Global Research Center, Niskayuna NY USA; Li, S. F. [Lawrence Livermore National Laboratory, Livermore CA USA; Lind, J. F. [Lawrence Livermore National Laboratory, Livermore CA USA; Suter, R. M. [Department of Physics, Carnegie Mellon University, Pittsburgh PA USA; Ingraffea, A. R. [School of Civil & Environmental Engineering, Cornell University, Ithaca NY USA

    2016-04-27

    In an effort to reproduce computationally the observed evolution of microstructurally small fatigue cracks (MSFCs), a method is presented for generating conformal, finite-element (FE), volume meshes from 3D measurements of MSFC propagation. The resulting volume meshes contain traction-free surfaces that conform to incrementally measured 3D crack shapes. Grain morphologies measured using near-field high-energy X-ray diffraction microscopy are also represented within the FE volume meshes. Proof-of-concept simulations are performed to demonstrate the utility of the mesh-generation method. The proof-of-concept simulations employ a crystal-plasticity constitutive model and are performed using the conformal FE meshes corresponding to successive crack-growth increments. Although the simulations for each crack increment are currently independent of one another, they need not be, and transfer of material-state information among successive crack-increment meshes is discussed. The mesh-generation method was developed using post-mortem measurements, yet it is general enough that it can be applied to in-situ measurements of 3D MSFC propagation.

  17. 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.

  18. Behavior of a crack within a Dissimilar Metal Weld Part by using an Overlay Weld

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Kang Soo; Lee, Ho Jin; Lee, Bong Sang [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2009-05-15

    In recent years, the dissimilar metal welds, Alloy 82/182 welds, used to connect the stainless steel piping and low alloy steel or carbon steel components in a nuclear reactor piping system have experienced a cracking due to a primary water stress corrosion (PWSCC).It is well known that one reason for the cracking is the residual stress by the weld. But, it is difficult to estimate the weld residual stress exactly due to the many parameters for the welding process. In this paper, a Butt model weld specimen was manufactured and the residual stresses of the weld specimen were measured by the X-Ray method and a Hole Drilling Technique. These results were compared with the results of the Butt FEM Model to confirm the confidence of the FEM input. Also, an analysis of the Crack FEM models made by the ABAQUS Code was performed to estimate the behavior of a crack within a Dissimilar Metal Weld Part (DMWP) when an overlay weld on the DMWP was done.

  19. Fatigue behaviour and crack growth of ferritic steel under environmental conditions

    Energy Technology Data Exchange (ETDEWEB)

    Herter, K.H.; Schuler, X.; Weissenberg, T. [Stuttgart Univ. (Germany). MPA

    2012-07-01

    The assessment of fatigue and cyclic crack growth behaviour of safety relevant components is of importance for the ageing management with regard to safety and reliability. For cyclic stress evaluation different codes and standards provide fatigue analysis procedures to be performed considering the various mechanical and thermal loading histories and geometric complexities of the components. For the fatigue design curves used as a limiting criteria the influence of different factors like e.g. environment, surface finish and temperature must be taken into consideration in an appropriate way. Fatigue tests were performed in the low cycle fatigue (LCF) und high cycle fatigue (HCF) regime with low alloy steels as well as with Nb- and Ti-stabilized German austenitic stainless steels in air and high temperature (HT) boiling water reactor environment to extend the state of knowledge of environmentally assisted fatigue (EAF) as it can occur in boiling water reactor (BWR) plants. Using the reactor pressure vessel (RPV) steel 22NiMoCr3-7 experimental data were developed to verify the influence of BWR coolant environment (high purity water as well as sulphate containing water with 90 ppb SO{sub 4} at a test temperature of 240 C and an oxygen content of 400 ppb) on the fatigue life and to extend the basis for a reliable estimation of the remaining service life of reactor components. Corresponding experiments in air were performed to establish reference data to determine the environmental correction factor F{sub en} accounting for the environment. The experimental results are compared with international available mean data curves, the new design curves and on the basis of the environmental factor F{sub en}. Furthermore the behaviour of steel 22NiMoCr3-7 in oxygenated high temperature water under transient loading conditions was investigated with respect to crack initiation and cyclic crack growth. In this process the stress state of the specimen and the chemical composition of

  20. Cracking behavior of tungsten armor under ELM-like thermal shockloads II: A revised prediction for crack appearance map

    Directory of Open Access Journals (Sweden)

    Muyuan Li

    2016-12-01

    Full Text Available In this work, the surface cracking features of tungsten armor under thermal shock loads by edge-localized mode (ELM were investigated by means of computational fracture mechanics analysis. For the simulation it was assumed that a small crack was initiated at low temperature after the shut-off of thermal load in contrast to the previous studies where the presence of a crack before thermal loading was assumed. The threshold power density for surface cracking was predicted to range between 0.3 and 0.6GW/m2 while the threshold of base temperature lay between 200 and 400°C. The theoretically predicted damage map agreed well with the experimental data from electron beam irradiation tests. The current simulation model turned out to match better to the real experimental observation than the previous predictions where the threshold base temperature lies roughly between 400 and 600°C.

  1. Glass fabrics self-cracking catalytic growth of boron nitride nanotubes

    Science.gov (United States)

    Wang, Jilin; Peng, Daijang; Long, Fei; Wang, Weimin; Gu, Yunle; Mo, Shuyi; Zou, Zhengguang; Fu, Zhengyi

    2017-02-01

    Glass fabrics were used to fabricate boron nitride nanotubes (BNNTs) with a broad diameter range through a combined chemical vapor deposition and self-propagation high-temperature synthesis (CVD-SHS) method at different holding times (0min, 30min, 90min, 180min and 360min). SEM characterization has been employed to investigate the macro and micro structure/morphology changes of the glass fabrics and BNNTs in detail. SEM image analysis has provided direct experimental evidences for the rationality of the optimized self-cracking catalyst VLS growth mechanism, including the transformation situations of the glass fabrics and the BNNTs growth processes respectively. This paper was the further research and compensation for the theory and experiment deficiencies in the new preparation method of BNNTs reported in our previous work. In addition, it is likely that the distinctive self-cracking catalyst VLS growth mechanism could provide a new idea to preparation of other inorganic functional nano-materials using similar one-dimensional raw materials as growth templates and catalysts.

  2. Comparison of Crack Initiation, Propagation and Coalescence Behavior of Concrete and Rock Materials

    Science.gov (United States)

    Zengin, Enes; Abiddin Erguler, Zeynal

    2017-04-01

    There are many previously studies carried out to identify crack initiation, propagation and coalescence behavior of different type of rocks. Most of these studies aimed to understand and predict the probable instabilities on different engineering structures such as mining galleries or tunnels. For this purpose, in these studies relatively smaller natural rock and synthetic rock-like models were prepared and then the required laboratory tests were performed to obtain their strength parameters. By using results provided from these models, researchers predicted the rock mass behavior under different conditions. However, in the most of these studies, rock materials and models were considered as contains none or very few discontinuities and structural flaws. It is well known that rock masses naturally are extremely complex with respect to their discontinuities conditions and thus it is sometimes very difficult to understand and model their physical and mechanical behavior. In addition, some vuggy rock materials such as basalts and limestones also contain voids and gaps having various geometric properties. Providing that the failure behavior of these type of rocks controlled by the crack initiation, propagation and coalescence formed from their natural voids and gaps, the effect of these voids and gaps over failure behavior of rocks should be investigated. Intact rocks are generally preferred due to relatively easy side of their homogeneous characteristics in numerical modelling phases. However, it is very hard to extract intact samples from vuggy rocks because of their complex pore sizes and distributions. In this study, the feasibility of concrete samples to model and mimic the failure behavior vuggy rocks was investigated. For this purpose, concrete samples were prepared at a mixture of %65 cement dust and %35 water and their physical and mechanical properties were determined by laboratory experiments. The obtained physical and mechanical properties were used to

  3. The influences of precrack orientations in welded joint of Ti-6Al-4V on fatigue crack growth

    Energy Technology Data Exchange (ETDEWEB)

    Wang Xuedong, E-mail: wxue2004@yeah.net [Key Laboratory for Advanced Materials Processing Technology of Ministry of Education, Department of Mechanical Engineering, Tsinghua University, Beijing 100084 (China); Shi Qingyu; Wang Xin; Zhang Zenglei [Key Laboratory for Advanced Materials Processing Technology of Ministry of Education, Department of Mechanical Engineering, Tsinghua University, Beijing 100084 (China)

    2010-02-15

    Ti-6Al-4V lamella microstructure obtained by {beta} annealing, which had slow fatigue crack propagation rate and high propagation resistance, was used as base metal and welded by tungsten-inert-gas welding (TIG). Three kinds of orientations were designed to study the influences of precrack orientations and locations on fatigue crack growth rate in as-weld welded joints. In comparison, the classical total-life fatigue performances of the joints were also studied. The results showed that, no matter the precrack was initiated in the center of the weld, near the fusion-line or in HAZ, the fatigue crack propagation rates in the initial stage were all slower than that of the base metal. The fatigue crack in the central region of the weld seam propagated by striation mechanism in the initial propagation stage, and the weld metal exhibited lower fatigue crack propagation rate and higher threshold stress intensity than the base metal and the other joint specimens.

  4. Stress corrosion cracking behavior of Alloy 600 in high temperature water

    Energy Technology Data Exchange (ETDEWEB)

    Webb, G.L.; Burke, M.G.

    1995-07-01

    SCC susceptibility of Alloy 600 in deaerated water at 360 C (statically loaded U-bend specimens) is dependent on microstructure and whether the material was cold-worked and annealed (CWA) or hot-worked and annealed (HWA). All cracking was intergranular, and materials lacking grain boundary carbides were most susceptible to SCC initiation. CWA tubing materials are more susceptible to SCC initiation than HWA ring-rolled forging materials with similar microstructures (optical metallography). In CWA tubing materials, one crack dominated and grew to a visible size. HWA materials with a low hot-working finishing temperature (<925 C) and final anneals at 1010-1065 C developed both large cracks (similar to those in CWA materials) and small intergranular microcracks detectable only by destructive metallography. HWA materials with a high hot-working finishing temperature (>980 C) and a high-temperature final anneal (>1040 C), with grain boundaries that are fully decorated, developed only microcracks in all specimens. These materials did not develop large, visually detectable cracks, even after more than 300 weeks exposure. A low-temperature thermal treatment (610 C for 7h), which reduces or eliminates SCC in Alloy 600, did not eliminate microcrack formation in high temperature processed HWA materials. Conventional metallographic and analytical electron microscopy (AEM) were done on selected materials to identify the factors responsible for the observed differences in cracking behavior. Major difference between high-temperature HWA and low-temperature HWA and CWA materials was that the high temperature processing and final annealing produced predominantly ``semi-continuous`` dendritic M{sub 7}C{sub 3} carbides along grain boundaries with a minimal amount of intragranular carbides. Lower temperature processing produced intragranular M7C3 carbides, with less intergranular carbides.

  5. Adaptation of Crack Growth Detection Techniques to US Material Test Reactors

    Energy Technology Data Exchange (ETDEWEB)

    A. Joseph Palmer; Sebastien P. Teysseyre; Kurt L. Davis; Joy L. Rempe; Gordon Kohse; Yakov Ostrovsky; David M. Carpenter

    2014-04-01

    A key component in evaluating the ability of Light Water Reactors to operate beyond 60 years is characterizing the degradation of materials exposed to radiation and various water chemistries. Of particular concern is the response of reactor materials to Irradiation Assisted Stress Corrosion Cracking (IASCC). Some materials testing reactors (MTRs) outside the U.S., such as the Halden Boiling Water Reactor (HBWR), have deployed a technique to measure crack growth propagation during irradiation. This technique incorporates a compact loading mechanism to stress the specimen during irradiation. A crack in the specimen is monitored using the Direct Current Potential Drop (DCPD) method. A project is underway to develop and demonstrate the performance of a similar type of test rig for use in U.S. MTRs. The first year of this three year project was devoted to designing, analyzing, fabricating, and bench top testing a mechanism capable of applying a controlled stress to specimens while they are irradiated in a pressurized water loop (simulating PWR reactor conditions). During the second year, the mechanism will be tested in autoclaves containing high pressure, high temperature water with representative water chemistries. In addition, necessary documentation and safety reviews for testing in a reactor environment will be completed. In the third year, the assembly will be tested in the Massachusetts Institute of Technology Reactor (MITR) and Post Irradiation Examinations (PIE) will be performed.

  6. INFLUENCE OF TEMPERATURE ON BEHAVIOR OF THE INTERFACIAL CRACK BETWEEN THE TWO LAYERS

    Directory of Open Access Journals (Sweden)

    Jelena M Djoković

    2010-01-01

    Full Text Available In this paper is considered a problem of the semi-infinite crack at the interface between the two elastic isotropic layers in conditions of the environmental temperature change. The energy release rate needed for the crack growth along the interface was determined, for the case when the two-layered sample is cooled from the temperature of the layers joining down to the room temperature. It was noticed that the energy release rate increases with the temperature difference increase. In the paper is also presented the distribution of stresses in layers as a function of the temperature and the layers' thickness variations. Analysis is limited to the case when the bimaterial sample is exposed to uniform temperature.

  7. Cyclic Deformation Behavior and Fatigue Crack Propagation of Low Carbon Steel Prestrained in Tension

    Directory of Open Access Journals (Sweden)

    J. G. Wang

    2009-01-01

    Full Text Available The tests were performed on low carbon steel plate. In the tension fatigue tests, two angle values (ϕ=0° and ϕ=45°, ϕ is the angle between the loading and the rolling direction have been chosen. The influence of strain path change on the subsequent initial work softening rate and the saturation stress has been investigated. Dislocation microstructure was observed by transmission electron microscopy. It was found that the strain amount of preloading in tension has obviously affected the cyclic softening phenomenon and the initial cyclic softening rate. It was observed that the reloading axial stress for ϕ=45° case increased more than that of ϕ=0° case, due to the anisotropism of Q235. In the fatigue crack propagation tests, the experimental results show that with increasing the pretension deformation degree, the fatigue crack growth rate increases, especially at the near threshold section.

  8. ROLE OF GRAIN BOUNDARY CARBIDES IN CRACKING BEHAVIOR OF Ni BASE ALLOYS

    Directory of Open Access Journals (Sweden)

    SEONG SIK HWANG

    2013-02-01

    Full Text Available The primary water stress corrosion cracking (PWSCC of Alloy 600 in a PWR has been reported in the control rod drive mechanism (CRDM, pressurizer instrumentation, and the pressurizer heater sleeves. Recently, two cases of boric acid precipitation that indicated leaking of the primary cooling water were reported on the bottom head surface of steam generators (SG in Korea. The PWSCC resistance of Ni base alloys which have intergranular carbides is higher than those which have intragranular carbides. Conversely, in oxidized acidic solutions like sodium sulfate or sodium tetrathionate solutions, the Ni base alloys with a lot of carbides at the grain boundaries and shows less stress corrosion cracking (SCC resistance. The role of grain boundary carbides in SCC behavior of Ni base alloys was evaluated and effect of intergranular carbides on the SCC susceptibility were reviewed from the literature.

  9. Crack propagation in fracture mechanical graded structures

    Directory of Open Access Journals (Sweden)

    B. Schramm

    2015-10-01

    Full Text Available The focus of manufacturing is more and more on innovative and application-oriented products considering lightweight construction. Hence, especially functional graded materials come to the fore. Due to the application-matched functional material gradation different local demands such as absorbability, abrasion and fatigue of structures are met. However, the material gradation can also have a remarkable influence on the crack propagation behavior. Therefore, this paper examines how the crack propagation behavior changes when a crack grows through regions which are characterized by different fracture mechanical material properties (e.g. different threshold values KI,th, different fracture toughness KIC. In particular, the emphasis of this paper is on the beginning of stable crack propagation, the crack velocity, the crack propagation direction as well as on the occurrence of unstable crack growth under static as well as cyclic loading. In this context, the developed TSSR-concept is presented which allows the prediction of crack propagation in fracture mechanical graded structures considering the loading situation (Mode I, Mode II and plane Mixed Mode and the material gradation. In addition, results of experimental investigations for a mode I loading situation and numerical simulations of crack growth in such graded structures confirm the theoretical findings and clarify the influence of the material gradation on the crack propagation behavior.

  10. Effect of laser shock processing on fatigue crack growth and fracture toughness of 6061-T6 aluminum alloy

    Energy Technology Data Exchange (ETDEWEB)

    Rubio-Gonzalez, C. [Centro de Ingenieria y Desarrollo Industrial, Pie de la cuesta No. 702, Desarrollo San Pablo, Queretaro, Qro. 76130 (Mexico)]. E-mail: crubio@cidesi.mix; Ocana, J.L. [Departamento de Fisica Aplicada a la Ingenieria Industrial, E.T.S.I.I. Universidad Politecnica de Madrid (Spain); Gomez-Rosas, G. [Centro de Ingenieria y Desarrollo Industrial, Pie de la cuesta No. 702, Desarrollo San Pablo, Queretaro, Qro. 76130 (Mexico); Molpeceres, C. [Departamento de Fisica Aplicada a la Ingenieria Industrial, E.T.S.I.I. Universidad Politecnica de Madrid (Spain); Paredes, M. [Centro de Ingenieria y Desarrollo Industrial, Pie de la cuesta No. 702, Desarrollo San Pablo, Queretaro, Qro. 76130, Mexico (Mexico); Banderas, A. [Centro de Ingenieria y Desarrollo Industrial, Pie de la cuesta No. 702, Desarrollo San Pablo, Queretaro, Qro. 76130, Mexico (Mexico); Porro, J. [Departamento de Fisica Aplicada a la Ingenieria Industrial, E.T.S.I.I. Universidad Politecnica de Madrid (Spain); Morales, M. [Departamento de Fisica Aplicada a la Ingenieria Industrial, E.T.S.I.I. Universidad Politecnica de Madrid (Spain)

    2004-11-25

    Laser shock processing (LSP) or laser shock peening is a new technique for strengthening metals. This process induces a compressive residual stress field which increases fatigue crack initiation life and reduces fatigue crack growth rate. Specimens of 6061-T6 aluminum alloy are used in this investigation. A convergent lens is used to deliver 1.2 J, 8 ns laser pulses by a Q-switch Nd:YAG laser, operating at 10 Hz. The pulses are focused to a diameter of 1.5 mm onto a water-immersed type aluminum samples. Effect of pulse density in the residual stress field is evaluated. Residual stress distribution as a function of depth is assessed by the hole drilling method. It is observed that the higher the pulse density the larger the zone size with compressive residual stress. Densities of 900, 1350 and 2500 pulses/cm{sup 2} with infrared (1064 nm) radiation are used. Pre-cracked compact tension specimens were subjected to LSP process and then tested under cyclic loading with R = 0.1. Fatigue crack growth rate is determined and the effect of LSP process parameters is evaluated. Fatigue crack growth rate is compared in specimens with and without LSP process. In addition fracture toughness is determined in specimens with and without LSP treatment. It is observed that LSP reduces fatigue crack growth and increases fracture toughness in the 6061-T6 aluminum alloy.

  11. Comparison of Fatigue Properties and Fatigue Crack Growth Rates of Various Implantable Metals

    Directory of Open Access Journals (Sweden)

    Yoshimitsu Okazaki

    2012-12-01

    Full Text Available The fatigue strength, effects of a notch on the fatigue strength, and fatigue crack growth rate of Ti-15Zr-4Nb-4Ta alloy were compared with those of other implantable metals. Zr, Nb, and Ta are important alloying elements for Ti alloys for attaining superior long-term corrosion resistance and biocompatibility. The highly biocompatible Ti-15Zr-4Nb-4Ta alloy exhibited an excellent balance between strength and ductility. Its notched tensile strength was much higher than that of a smooth specimen. The strength of 20% cold-worked commercially pure (C.P. grade 4 Ti was close to that of Ti alloy. The tension-to-tension fatigue strength of an annealed Ti-15Zr-4Nb-4Ta rod at 107 cycles was approximately 740 MPa. The fatigue strength of this alloy was much improved by aging treatment after solution treatment. The fatigue strengths of C.P. grade 4 Ti and stainless steel were markedly improved by 20% cold working. The fatigue strength of Co-Cr-Mo alloy was markedly increased by hot forging. The notch fatigue strengths of 20% cold-worked C.P. grade 4 Ti, and annealed and aged Ti-15Zr-4Nb-4Ta, and annealed Ti-6Al-4V alloys were less than those of the smooth specimens. The fatigue crack growth rate of Ti-15Zr-4Nb-4Ta was the same as that of Ti-6Al-4V. The fatigue crack growth rate in 0.9% NaCl was the same as that in air. Stainless steel and Co-Cr-Mo-Ni-Fe alloy had a larger stress-intensity factor range (ΔK than Ti alloy.

  12. Post-cracking behavior of blocks, prisms, and small concrete walls reinforced with plant fiber

    Directory of Open Access Journals (Sweden)

    I. I. Soto

    Full Text Available Structural masonry using concrete blocks promotes the rationalization of construction projects, lowering the final cost of a building through the elimination of forms and the reduction of the consumption of reinforcement bars. Moreover, production of a block containing a combination of concrete and vegetable fiber sisal results in a unit with properties such as mechanical strength, stiffness, flexibility, ability to absorb energy, and post-cracking behavior that are comparable to those of a block produced with plain concrete. Herein are reported the results of a study on the post-cracking behavior of blocks, prisms, and small walls reinforced with sisal fibers (lengths of 20 mm and 40 mm added at volume fractions of 0.5% and 1%. Tests were performed to characterize the fibers and blocks and to determine the compressive strength of the units, prisms, and small walls. The deformation modulus of the elements was calculated and the stress-strain curves were plotted to gain a better understanding of the values obtained. The compression test results for the small walls reinforced with fibers were similar to those of the reference walls and better than the blocks and prisms with added fibers, which had resistances lower than those of the corresponding conventional materials. All elements prepared with the addition of sisal exhibited an increase in the deformation capacity (conferred by the fibers, which was observed in the stress-strain curves. The failure mode of the reference elements was characterized by an abrupt fracture, whereas the reinforced elements underwent ductile breakage. This result was because of the presence of the fibers, which remained attached to the faces of the cracks via adhesion to the cement matrix, thus preventing loss of continuity in the material. Therefore, the cement/plant fiber composites are advantageous in terms of their ductility and ability to resist further damage after cracking.

  13. Quantitative observations of hydrogen-induced, slow crack growth in a low alloy steel

    Science.gov (United States)

    Nelson, H. G.; Williams, D. P.

    1973-01-01

    Hydrogen-induced slow crack growth, da/dt, was studied in AISI-SAE 4130 low alloy steel in gaseous hydrogen and distilled water environments as a function of applied stress intensity, K, at various temperatures, hydrogen pressures, and alloy strength levels. At low values of K, da/dt was found to exhibit a strong exponential K dependence (Stage 1 growth) in both hydrogen and water. At intermediate values of K, da/dt exhibited a small but finite K dependence (Stage 2), with the Stage 2 slope being greater in hydrogen than in water. In hydrogen, at a constant K, (da/dt) sub 2 varied inversely with alloy strength level and varied essentially in the same complex manner with temperature and hydrogen pressure as noted previously. The results of this study provide support for most of the qualitative predictions of the lattice decohesion theory as recently modified by Oriani. The lack of quantitative agreement between data and theory and the inability of theory to explain the observed pressure dependence of slow crack growth are mentioned and possible rationalizations to account for these differences are presented.

  14. Characterization of Interlaminar Crack Growth in Composites with the Double Cantilever Beam Specimen

    Science.gov (United States)

    Hunston, D. L.

    1984-01-01

    A project to examine the double cantilever beam specimen as a quantitative test method to assess the resistance of various composite materials to interlaminar crack growth is discussed. A second objective is to investigate the micromechanics of failure for composites with tough matrix resins from certain generic types of polymeric systems: brittle thermosets, toughened thermosets, and thermoplastics. Emphasis is given to a discussion of preliminary results in two areas: the effects of temperature and loading rate for woven composites, and the effects of matrix toughening in woven and unidirectional composites.

  15. Interface crack growth for anisotropic plasticity with non-normality effects

    DEFF Research Database (Denmark)

    Tvergaard, Viggo; Legarth, Brian Nyvang

    2007-01-01

    elastic–viscoplastic material model is applied, using an anisotropic yield criterion, and in each case analyzed the effect of non-normality is compared with results for the standard normality flow rule. Due to the mismatch of elastic properties across the interface the corresponding elastic solution has...... an oscillating stress singularity, and with conditions of small scale yielding this solution is applied as boundary conditions on the outer edge of the region analyzed. Crack growth resistance curves are calculated numerically, and the effect of the near-tip mode mixity on the steady-state fracture toughness...

  16. Evaluation of Orientation Dependence of Fracture Toughness and Fatigue Crack Propagation Behavior of As-Deposited ARCAM EBM Ti-6Al-4V

    Science.gov (United States)

    Seifi, Mohsen; Dahar, Matthew; Aman, Ron; Harrysson, Ola; Beuth, Jack; Lewandowski, John J.

    2015-03-01

    This preliminary work documents the effects of test orientation with respect to build and beam raster directions on the fracture toughness and fatigue crack growth behavior of as-deposited EBM Ti-6Al-4V. Although ASTM/ISO standards exist for determining the orientation dependence of various mechanical properties in both cast and wrought materials, these standards are evolving for materials produced via additive manufacturing (AM) techniques. The current work was conducted as part of a larger America Makes funded project to begin to examine the effects of process variables on the microstructure and fracture and fatigue behavior of AM Ti-6Al-4V. In the fatigue crack growth tests, the fatigue threshold, Paris law slope, and overload toughness were determined at different load ratios, R, whereas fatigue precracked samples were tested to determine the fracture toughness. The as-deposited material exhibited a fine-scale basket-weave microstructure throughout the build, and although fracture surface examination revealed the presence of unmelted powders, disbonded regions, and isolated porosity, the resulting mechanical properties were in the range of those reported for cast and wrought Ti-6Al-4V. Remote access and control of testing was also developed at Case Western Reserve University to improve efficiency of fatigue crack growth testing.

  17. Mode I and mixed I/III crack initiation and propagation behavior of V-4Cr-4Ti alloy at 25{degrees}C

    Energy Technology Data Exchange (ETDEWEB)

    Li, H.X.; Kurtz, R.J.; Jones, R.H. [Pacific Northwest National Lab., Richland, WA (United States)

    1997-04-01

    The mode I and mixed-mode I/III fracture behavior of the production-scale heat (No. 832665) of V-4Cr-4Ti has been investigated at 25{degrees}C using compact tension (CT) specimens for a mode I crack and modified CT specimens for a mixed-mode I/III crack. The mode III to mode I load ratio was 0.47. Test specimens were vacuum annealed at 1000{degrees}C for 1 h after final machining. Both mode I and mixed-mode I/III specimens were fatigue cracked prior to J-integral testing. It was noticed that the mixed-mode I/III crack angle decreased from an initial 25 degrees to approximately 23 degrees due to crack plane rotation during fatigue cracking. No crack plane rotation occurred in the mode I specimen. The crack initiation and propagation behavior was evaluated by generating J-R curves. Due to the high ductility of this alloy and the limited specimen thickness (6.35 mm), plane strain requirements were not met so valid critical J-integral values were not obtained. However, it was found that the crack initiation and propagation behavior was significantly different between the mode I and the mixed-mode I/III specimens. In the mode I specimen crack initiation did not occur, only extensive crack tip blunting due to plastic deformation. During J-integral testing the mixed-mode crack rotated to an increased crack angle (in contrast to fatigue precracking) by crack blunting. When the crack initiated, the crack angle was about 30 degrees. After crack initiation the crack plane remained at 30 degrees until the test was completed. Mixed-mode crack initiation was difficult, but propagation was easy. The fracture surface of the mixed-mode specimen was characterized by microvoid coalescence.

  18. DYNAMIC BEHAVIOR OF TWO UNEQUAL PARALLEL PERMEABLE INTERFACE CRACKS IN A PIEZOELECTRIC LAYER BONDED TO TWO HALF PIEZOELECTRIC MATERIALS PLANES

    Institute of Scientific and Technical Information of China (English)

    SUN Jian-liang; ZHOU Zhen-gong; WANG Biao

    2005-01-01

    The dynamic behavior of two unequal parallel permeable interface cracks in a piezoelectric layer bonded to two half-piezoelectric material planes subjected to harmonic anti-plane shear waves is investigated. By using the Fourier transform, the problem can be solved with the help of two pairs of dual integral equations in which the unknown variables were the jumps of the displacements across the crack surfaces. Numerical results are presented graphically to show the effects of the geometric parameters, the frequency of the incident wave on the dynamic stress intensity factors and the electric displacement intensity factors. Especially, the present problem can be returned to static problem of two parallel permeable interface cracks. Compared with the solutions of impermeable crack surface condition, it is found that the electric displacement intensity factors for the permeable crack surface conditions are much smaller.

  19. Acoustic emission analysis of crack resistance and fracture behavior of 20GL steel having the gradient microstructure and strength

    Science.gov (United States)

    Nikulin, S.; Nikitin, A.; Belov, V.; Rozhnov, A.; Turilina, V.; Anikeenko, V.; Khatkevich, V.

    2017-07-01

    The crack resistances as well as fracture behavior of 20GL steel quenched with a fast-moving water stream and having gradient microstructure and strength are analyzed. Crack resistance tests with quenched and normalized flat rectangular specimens having different cut lengths loaded by three-point bending with acoustic emission measurements have been performed. The critical J-integral has been used as the crack resistance parameter of the material. Quenching with a fast moving water stream leads to gradient (along a specimen wall thickness) strengthening of steel due to highly refined gradient microstructure formation of the troostomartensite type. Quenching with a fast-moving water stream increases crack resistance Jc , of 20GL steel by a factor of ∼ 1.5. The fracture accrues gradually with the load in the normalized specimens while the initiated crack is hindered in the variable ductility layer and further arrested in the more ductile core in the quenched specimens.

  20. Investigation of the dwell period's influence on the fatigue crack growth of a titanium alloy

    Energy Technology Data Exchange (ETDEWEB)

    Lefranc, P. [LMPM, UMR CNRS 6617, ENSMA, 86961 Futuroscope Chasseneuil Cedex (France); LMS, UMR CNRS 7649, Ecole Polytechnique, 91128 Palaiseau Cedex (France); SNECMA Groupe SAFRAN, 77550 Moissy Cramayel (France); Sarrazin-Baudoux, C. [LMPM, UMR CNRS 6617, ENSMA, 86961 Futuroscope Chasseneuil Cedex (France)], E-mail: baudoux@lmpm.ensma.fr; Doquet, V. [LMS, UMR CNRS 7649, Ecole Polytechnique, 91128 Palaiseau Cedex (France); Petit, J. [LMPM, UMR CNRS 6617, ENSMA, 86961 Futuroscope Chasseneuil Cedex (France)

    2009-03-15

    The dwell effect, which is known to induce a reduction in the fatigue life of titanium alloys at room temperature, is related to early crack initiation. The present results support faster crack growth rates. The governing mechanisms are identified by mean of scanning electron microfractographic observations. The potential role of the atmosphere is examined through comparative testing performed in air and in high vacuum in order to distinguish the specific contributions of cold creep and environment assistance.

  1. 铸造奥氏体不锈钢的疲劳裂纹扩展%Fatigue crack growth of cast austenitic stainless steels

    Institute of Scientific and Technical Information of China (English)

    吕绪明; 李时磊; 王西涛; 王艳丽

    2015-01-01

    用紧凑拉伸试样研究了载荷比、单峰过载和两步高-低幅加载对Z3CN20-09M铸造奥氏体不锈钢疲劳裂纹扩展速率的影响。当应力强度因子范围相同时,疲劳裂纹扩展速率随载荷比的增大而增大。单峰过载使裂纹扩展速率先有短暂的增加后长距离的减速扩展,出现裂纹扩展迟滞现象。两步高-低幅加载时,若两步的最大载荷不同,第二步裂纹扩展也会出现迟滞现象。用两参数模型和Wheeler模型能够预测恒幅载荷和变幅载荷下的疲劳裂纹扩展行为。%The influences of stress ratio, single overload and high-low loading sequence on the fatigue crack growth of Z3CN20-09M cast austenitic stainless steels were studied with compact tension specimens. When the stress intensity factor range is identical, the fatigue crack growth rate increases with the increase of stress ratio. During single overload, the fatigue crack growth rate shows a short period of acceleration followed by a significant decrease, leading to subsequent crack growth retardation. Similarly, high-low loading sequence with the maximum load in the second step lower than that in the first loading step results in significant crack growth retardation in the second loading step. A two-parameter model and Wheeler’ s model are found to predict well the crack growth behav-ior under constant-amplitude loading and variable-amplitude loading, respectively.

  2. 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.

  3. Bayesian Model on Fatigue Crack Growth Rate of Type 304 Stainless Steel

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Sanhae; Yoon, Jae Young; Hwang, Il Soon [Nuclear Materials Laboratory, Seoul National University, Seoul (Korea, Republic of)

    2015-10-15

    The fatigue crack growth rate curve is typically estimated by deterministic methods in accordance with the ASME Boiler and Pressure Vessel Code Sec. XI. The reliability of nuclear materials must also consider the environmental effect. This can be overcome by probabilistic methods that estimate the degradation of materials. In this study, fatigue tests were carried out on Type 304 stainless steel (STS 304) to obtain a fatigue crack growth rate curve and Paris' law constants. Tests were conducted on a constant load and a constant delta K, respectively. The unknown constants of Paris' law were updated probabilistically by Bayesian inference and the method can be used for the probabilistic structural integrity assessment of other nuclear materials. In this paper, Paris' law constants including C and m for Type 304 stainless steel were determined by probabilistic approach with Bayesian Inference. The Bayesian update process is limited in accuracy, because this method should assume initial data distribution. If we select an appropriate distribution, this updating method is powerful enough to get data results considering the environment and materials. Until now, remaining lives of NPPs are estimated by deterministic methods using a priori model to finally assess structural integrity. Bayesian approach can utilize in-service inspection data derived from aged properties.

  4. Stress corrosion cracking behavior of annealed and cold worked 316L stainless steel in supercritical water

    Energy Technology Data Exchange (ETDEWEB)

    Sáez-Maderuelo, A., E-mail: alberto.saez@ciemat.es; Gómez-Briceño, D.

    2016-10-15

    Highlights: • The alloy 316L is susceptible to stress corrosion cracking in supercritical water. • The susceptibility of alloy 316L increases with temperature and plastic deformation. • Dynamic strain ageing processes may be active in the material. - Abstract: The supercritical water reactor (SCWR) is one of the more promising designs considered by the Generation IV International Forum due to its high thermal efficiency and improving security. To build this reactor, standardized structural materials used in light water reactors (LWR), like austenitic stainless steels, have been proposed. These kind of materials have shown an optimum behavior to stress corrosion cracking (SCC) under LWR conditions except when they are cold worked. It is known that physicochemical properties of water change sharply with pressure and temperature inside of the supercritical region. Owing to this situation, there are several doubts about the behavior of candidate materials like austenitic stainless steel 316L to SCC in the SCWR conditions. In this work, alloy 316L was studied in deaerated SCW at two different temperatures (400 °C and 500 °C) and at 25 MPa in order to determine how changes in this variable influence the resistance of this material to SCC. The influence of plastic deformation in the behavior of alloy 316L to SCC in SCW was also studied at both temperatures. Results obtained from these tests have shown that alloy 316L is susceptible to SCC in supercritical water reactor conditions where the susceptibility of this alloy increases with temperature. Moreover, prior plastic deformation of 316L SS increased its susceptibility to environmental cracking in SCW.

  5. Effect of Microstructure on Low Temperature Cracking Behavior of EN82H Welds

    Energy Technology Data Exchange (ETDEWEB)

    W. J. Mills; C. M. Brown; M. G. Burke

    2001-04-30

    As-fabricated EN82H welds are susceptible to low temperature embrittlements in 54 degree C hydrogenated water. Values of J[sub]IC in water are typically 90% to 98% lower than those in air due to a fracture mechanism transition from microvoid coalescence to hydrogen-included intergranular fracture. Environmental J[sub]IC testing demonstrated that a high temperature (1093 degree C) anneal and furnace-cool alleviates the material's susceptibility to hydrogen-induced intergranular cracking. To identify metallurgical and compositional features that are responsible for the material's environment-sensitive behavior, detailed characterization of the microstructure and grain boundary chemistry for the as-fabricated and as-annealed materials was performed. Results from light optical microscopy, analytical electron microscopy, electron probe microanalysis, Auger electron spectroscopy and mechanical property characterization are used to provide insight into the observed low temperature embrittlement phenomenon. The key microstructural feature responsible for low temperature cracking in as-fabricated welds appears to be fine niobium and titanium-rich carbonitrides that cover most grain boundaries. These precipitates are effective hydrogen traps that promote hydrogen-induced intergranular cracking. Dissolution the fine carbonitrides during the 1093 degree C anneal reduces grain boundary trapping sites, which accounts for the improved fracture resistance displayed by the annealed weld. The role of strength level in promoting low temperature embrittlement is evaluated by cold-rolling the annealed weld to increase its yield strength from 280 to 640 MPa. The annealed and cold-rolled weld exhibits high toughness in 54 degree C water and shows no evidence of hydrogen-induced intergranular cracking, thereby demonstrating that strength is not a primary cause of low temperature embrittlement.

  6. An experimental study on the effects of compressive stress on the fatigue crack growth of low-alloy steel

    Energy Technology Data Exchange (ETDEWEB)

    Jones, D.P.; Hoppe, R.G. (Westinghouse Electric Corp., West Mifflin, PA (United States). Bettis Atomic Power Lab.); Hechmer, J.L. (Babcock Wilcox Co., Barberton, OH (United States)); James, B.A. (Colorado School of Mines, Golden, CO (United States). Metallurgy Dept.)

    1994-08-01

    A series of fatigue crack growth rate tests was conducted in order to study the effects of negative stress ratio upon the fatigue crack growth rate of low-alloy steel in air environment. The tests used four-point bend specimens in order to simulate linear stress distributions typical of many pressure vessel applications. This type of testing adds to the knowledge on negative stress ratio effects for low-alloy steels that in the past have been obtained from uniform tension-compression tests. Additionally, the applied bending stress range was varied from low values of applied stress to high values of applied stress over twice the yield strength. Load control was used for tests for which the stress range was less than twice the yield strength and deflection control was used for the higher stress range tests. The crack geometries involved were both short and long fatigue cracks started at notches and tight fatigue cracks for which crack closure could occur over the full crack face. The results are presented in terms of the stress intensity factor ratio R = K[sub MIN]/K[sub MAX]. The negative R-ratio test results were correlated to an equation of the form da/dN = C[[delta]K/(A-R)][sup n] where A, C and n are curve-fitting parameters. It was found that the effects of negative R-ratio on the fatigue crack growth rates for even the high stress range tests could be bounded by correlating the foregoing equation to only positive R-ratio test results and extending the resulting equation into the negative R-ratio regime.

  7. Effect of Stress Ratio on Fatigue Crack Growth Rate at Notched Hole in 7075-T6 Aluminum Alloy Under Biaxial Fatigue

    Science.gov (United States)

    2016-08-18

    crack tips. The crack growth rate was observed using optical microscopy. In addition, the test generates more accurate definition of the Walker...48 xvi List of Symbols Symbol Definition a crack length (mm) α angle between the y-axis and the...of loads and moments in different directions. And that not in an ideal environment, corrosive environment while enhance and accelerate the crack

  8. 用直流电压降法研究316LN 不锈钢的疲劳裂纹扩展行为%Research on Fatigue Crack Growth Behavior of 316LN Stainless Steel by Direct Current Potential Drop Method

    Institute of Scientific and Technical Information of China (English)

    陈凯; 杜东海; 陆辉; 张乐福; 徐雪莲; 石秀强; 孟凡江; 鲍一晨; 刘晓强

    2016-01-01

    采用直流电压降(DCPD)方法测试了316LN 不锈钢在室温和350℃的疲劳裂纹扩展速率,得到室温和350℃下该材料疲劳裂纹扩展门槛值ΔK th ,并分析了试样断口形貌.结果表明:采用 DCPD 方法测得室温和350℃下ΔK th分别为11.9,8.1 MPam 1/2,与文献值相符,350℃下的疲劳裂纹扩展速率比室温下的要高2~20倍;在裂纹亚临界扩展区,疲劳裂纹扩展速率与应力强度因子范围服从 Paris 公式,其参数 n 与温度无关,参数 D 与温度成线性正比关系;试样疲劳破坏形式为穿晶断裂.%Fatigue crack growth rates of 31 6LN stainless steel at room temperature and 350 ℃ were measured by the direct current potential drop (DCPD)method,and then the fatigue-crack growth threshold (ΔK th ) at room temperature and 350 ℃ was obtained.The fatigue fracture morphology was also analyzed.The results show that the ΔK th obtained by the DCPD method at room temperature and 350 ℃ was 1 1.9,8.1 MPa�m1/2 respectively, coinciding well with the values from references.The fatigue crack growth rates at 350 ℃ were about 2-20 times as high as those at room temperature.In the subcritical propagation zone,the relationship between fatigue crack growth rate and stress intensity factor range accorded with Paris equation.The parameter m in the equation was temperature-independent while parameter D showed a linearly positive correlation with temperature.The failure mode of the specimen was transgranular fracture.

  9. High-voltage electron-microscopic observation of cyclic slip behavior around a fatigue crack tip in an iron alloy

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, Yoshimasa [National Institute of Advanced Industrial Science and Technology (AIST), 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan)], E-mail: yoshim.takahashi@aist.go.jp; Tanaka, Masaki; Higashida, Kenji [Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Noguchi, Hiroshi [Department of Mechanical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan)

    2009-04-15

    The cyclic slip behavior around a fatigue crack tip originally located inside a bulk Fe-Si alloy was successfully observed by a high-voltage electron microscope in combination with a novel specimen preparation method. The method, by taking advantages of ion milling and focused ion beam techniques, ensures that the original shape of the crack tip is preserved without introducing additional slips. The observation confirms that the slip bands emitted from the fatigue crack tip are bounded by a labyrinth-like wall structure.

  10. The Effects of Test Temperature, Temper, and Alloyed Copper on the Hydrogen-Controlled Crack Growth Rate of an Al-Zn-Mg-(Cu) Alloy

    Energy Technology Data Exchange (ETDEWEB)

    G.A. Young, Jr.; J.R. Scully

    2000-09-17

    The hydrogen embrittlement controlled stage II crack growth rate of AA 7050 (6.09 wt.% Zn, 2.14 wt% Mg, 2.19 wt.% Cu) was investigated as a function of temper and alloyed copper level in a humid air environment at various temperatures. Three tempers representing the underaged, peak aged, and overaged conditions were tested in 90% relative humidity (RH) air at temperatures between 25 and 90 C. At all test temperatures, an increased degree of aging (from underaged to overaged) produced slower stage II crack growth rates. The stage II crack growth rate of each alloy and temper displayed Arrhenius-type temperature dependence with activation energies between 58 and 99 kJ/mol. For both the normal copper and low copper alloys, the fracture path was predominantly intergranular at all test temperatures (25-90 C) in each temper investigated. Comparison of the stage II crack growth rates for normal (2.19 wt.%) and low (0.06 wt.%) copper alloys in the peak aged and overaged tempers showed the beneficial effect of copper additions on stage II crack growth rate in humid air. In the 2.19 wt.% copper alloy, the significant decrease ({approx} 10 times at 25 C) in stage II crack growth rate upon overaging is attributed to an increase in the apparent activation energy for crack growth. IN the 0.06 wt.% copper alloy, overaging did not increase the activation energy for crack growth but did lower the pre-exponential factor, {nu}{sub 0}, resulting in a modest ({approx} 2.5 times at 25 C) decrease in crack growth rate. These results indicate that alloyed copper and thermal aging affect the kinetic factors that govern stage II crack growth rate. Overaged, copper bearing alloys are not intrinsically immune to hydrogen environment assisted cracking but are more resistant due to an increased apparent activation energy for stage II crack growth.

  11. A comprehensive flow-induced vibration model to predict crack growth and leakage potential in steam generator tubes

    Energy Technology Data Exchange (ETDEWEB)

    El Bouzidi, Salim [School of Engineering, University of Guelph, Guelph, Ontario N1G 2W1 (Canada); Hassan, Marwan, E-mail: mahassan@uoguelph.ca [School of Engineering, University of Guelph, Guelph, Ontario N1G 2W1 (Canada); Riznic, Jovica [Operational Engineering Assessment Division, Canadian Nuclear Safety Commission, Ottawa, Ontario K1P 5S9 (Canada)

    2015-10-15

    Highlights: • Comprehensive flow induced vibrations time domain model was developed. • Simulations of fluidelastic instability and turbulence were conducted. • Nonlinear effect due to the clearances at the supports was studied. • Prediction of stresses due to fluid excitation was obtained. • Deterministic and stochastic analyses for crack and leakage rate were conducted. - Abstract: Flow-induced vibrations (FIVs) are a major threat to the operation of nuclear steam generators. Turbulence and fluidelastic instability are the two main excitation mechanisms leading to tube vibrations. The consequences to the operation of steam generators are premature wear of the tubes, as well as development of cracks that may leak hazardous fluids. This paper investigates the effect of tube support clearance on the integrity of tube bundles within steam generators. Special emphasis will be placed on crack propagation and leakage rates. A crack growth model is used to simulate the growth of surface flaws and through-wall cracks of various initial sizes due to a wide range of support clearances. Leakage rates are predicted using a two-phase flow leakage model. Nonlinear finite element analysis is used to simulate a full U-bend subjected to fluidelastic and turbulence forces. Monte Carlo simulations are then used to conduct a probabilistic assessment of steam generator life due to crack development.

  12. Crack initiation and propagation behavior of WC particles reinforced Fe-based metal matrix composite produced by laser melting deposition

    Science.gov (United States)

    Wang, Jiandong; Li, Liqun; Tao, Wang

    2016-08-01

    It is generally believed that cracks in metal matrix composites (MMC) parts manufacturing are crucial to the reliable material properties, especially for the reinforcement particles with high volume fraction. In this paper, WC particles (WCp) reinforced Fe-based metal matrix composites (WCp/Fe) were manufactured by laser melting deposition (LMD) technology to investigate the characteristics of cracks formation. The section morphology of composites were analyzed by optical microscope (OM), and microstructure of WCp, matrix and interface were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), in order to study the crack initiation and propagation behavior under different laser process conditions. The temperature of materials during the laser melting deposition was detected by the infrared thermometer. The results showed that the cracks often appeared after five layers laser deposition in this experiment. The cracks crossed through WC particles rather than the interface, so the strength of interface obtained by the LMD was relatively large. When the thermal stress induced by high temperature gradient during LMD and the coefficient of thermal expansion mismatch between WC and matrix was larger than yield strength of WC, the cracks would initiate inside WC particle. Cracks mostly propagated along the eutectic phases whose brittleness was very large. The obtained thin interface was beneficial to transmitting the stress from particle to matrix. The influence of volume fraction of particles, laser power and scanning speed on cracks were investigated. This paper investigated the influence of WC particles size on cracks systematically, and the smallest size of cracked WC in different laser processing parameters was also researched.

  13. Slow crack growth resistance and bridging stress determination in alumina-rich magnesium aluminate spinel/tungsten composites

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez-Suarez, T.; Lopez-Esteban, S.; Pecharroman, C. [Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones Cientificas (CSIC), C/ Sor Juana Ines de la Cruz, 3, 28049 Cantoblanco, Madrid (Spain); Moya, J.S. [Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones Cientificas (CSIC), C/ Sor Juana Ines de la Cruz, 3, 28049 Cantoblanco, Madrid (Spain)], E-mail: jsmoya@icmm.csic.es; El Attaoui, H.; Benaqqa, C.; Chevalier, J. [Universite de Lyon, INSA-Lyon, MATEIS, UMR CNRS 5510, 20 avenue Albert Einstein, Villeurbanne F-69621 (France)

    2009-04-15

    The slow crack growth (SCG) resistance (V-K{sub I} diagrams) of magnesium aluminate spinel and its tungsten composites with different metallic content (7, 10, 14 and 22 vol.%) is reported. It is found that tungsten plays a crucial role in the composite by increasing crack resistance: the higher the W content, the higher the stress intensity factor needed for crack extension at a given rate. The reinforcement is due to the bridging mechanism performed by metal particles, as it strongly affects the compliance of cracked specimens. Its magnitude is estimated by a compliance function {phi}(a) from a double torsion test. From the compliance function, R-curve behaviour is predicted for the composite with highest tungsten content. It explains the effect of metal particles on SCG curves. The W-MgAl{sub 2}O{sub 4} interface is believed to influence the reinforcement mechanism.

  14. In Search of a Time Efficient Approach to Crack and Delamination Growth Predictions in Composites

    Science.gov (United States)

    Krueger, Ronald; Carvalho, Nelson

    2016-01-01

    Analysis benchmarking was used to assess the accuracy and time efficiency of algorithms suitable for automated delamination growth analysis. First, the Floating Node Method (FNM) was introduced and its combination with a simple exponential growth law (Paris Law) and Virtual Crack Closure technique (VCCT) was discussed. Implementation of the method into a user element (UEL) in Abaqus/Standard(Registered TradeMark) was also presented. For the assessment of growth prediction capabilities, an existing benchmark case based on the Double Cantilever Beam (DCB) specimen was briefly summarized. Additionally, the development of new benchmark cases based on the Mixed-Mode Bending (MMB) specimen to assess the growth prediction capabilities under mixed-mode I/II conditions was discussed in detail. A comparison was presented, in which the benchmark cases were used to assess the existing low-cycle fatigue analysis tool in Abaqus/Standard(Registered TradeMark) in comparison to the FNM-VCCT fatigue growth analysis implementation. The low-cycle fatigue analysis tool in Abaqus/Standard(Registered TradeMark) was able to yield results that were in good agreement with the DCB benchmark example. Results for the MMB benchmark cases, however, only captured the trend correctly. The user element (FNM-VCCT) always yielded results that were in excellent agreement with all benchmark cases, at a fraction of the analysis time. The ability to assess the implementation of two methods in one finite element code illustrated the value of establishing benchmark solutions.

  15. Acceleration and localization of subcritical crack growth in a natural composite material.

    Science.gov (United States)

    Lennartz-Sassinek, S; Main, I G; Zaiser, M; Graham, C C

    2014-11-01

    Catastrophic failure of natural and engineered materials is often preceded by an acceleration and localization of damage that can be observed indirectly from acoustic emissions (AE) generated by the nucleation and growth of microcracks. In this paper we present a detailed investigation of the statistical properties and spatiotemporal characteristics of AE signals generated during triaxial compression of a sandstone sample. We demonstrate that the AE event amplitudes and interevent times are characterized by scaling distributions with shapes that remain invariant during most of the loading sequence. Localization of the AE activity on an incipient fault plane is associated with growth in AE rate in the form of a time-reversed Omori law with an exponent near 1. The experimental findings are interpreted using a model that assumes scale-invariant growth of the dominating crack or fault zone, consistent with the Dugdale-Barenblatt "process zone" model. We determine formal relationships between fault size, fault growth rate, and AE event rate, which are found to be consistent with the experimental observations. From these relations, we conclude that relatively slow growth of a subcritical fault may be associated with a significantly more rapid increase of the AE rate and that monitoring AE rate may therefore provide more reliable predictors of incipient failure than direct monitoring of the growing fault.

  16. Analysis Of Ductile Crack Growth In Pipe Test In STYLE Project

    Energy Technology Data Exchange (ETDEWEB)

    Yin, Shengjun [ORNL; Williams, Paul T [ORNL; Klasky, Hilda B [ORNL; Bass, Bennett Richard [ORNL

    2012-01-01

    The Oak Ridge National Laboratory (ORNL) is conducting structural analyses, both deterministic and probabilistic, to simulate a large scale mock-up experiment planned within the European Network for Structural Integrity for Lifetime Management non-RPV Components (STYLE). The paper summarizes current ORNL analyses of STYLE s Mock-up3 experiment to simulate/evaluate ductile crack growth in a cladded ferritic pipe. Deterministic analyses of the large-scale bending test of ferritic surge pipe, with an internal circumferential crack, are simulated with a number of local micromechanical approaches, such as Gurson-Tvergaard-Needleman (GTN) model and cohesive-zone model. Both WARP 3D and ABAQUS general purpose finite element programs are being used to predict the failure load and the failure mode, i.e. ductile tearing or net-section collapse, as part of the pre-test phase of the project. Companion probabilistic analyses of the experiment are utilizing the ORNL developed open-source Structural Integrity Assessment Modular - Probabilistic Fracture Mechanics (SIAM-PFM) framework. SIAM-PFM contains engineering assessment methodology such as the tearing instability (J-T analysis) module developed for inner surface cracks under bending load. The driving force J-integral estimations are based on the SC.ENG1 or SC.ENG2 models. The J-A2 methodology is used to transfer (constraint-adjust) J-R curve material data from standard test specimens to the Mock-up3 experiment configuration. The probabilistic results of the Mock-Up3 experiment obtained from SIAM-PFM will be compared to those generated using the deterministic finite element modeling approach. The objective of the probabilistic analysis is to provide uncertainty bounds that will assist in assessing the more detailed 3D finite-element solutions and to also assess the level of confidence that can be placed in the best-estimate finite-element solutions.

  17. Unified nano-mechanics based probabilistic theory of quasibrittle and brittle structures: I. Strength, static crack growth, lifetime and scaling

    Science.gov (United States)

    Le, Jia-Liang; Bažant, Zdeněk P.; Bazant, Martin Z.

    2011-07-01

    strength and tests of the power law for the crack growth rate. The theory is shown to match closely numerous test data on strength and static lifetime of ceramics and concrete, and explains why their histograms deviate systematically from the straight line in Weibull scale. Although the present unified theory is built on several previous advances, new contributions are here made to address: (i) a crack in a disordered nano-structure (such as that of hydrated Portland cement), (ii) tail probability of a fiber bundle (or parallel coupling) model with softening elements, (iii) convergence of this model to the Gaussian distribution, (iv) the stress-life curve under constant load, and (v) a detailed random walk analysis of crack front jumps in an atomic lattice. The nonlocal behavior is captured in the present theory through the finiteness of the number of links in the weakest-link model, which explains why the mean size effect coincides with that of the previously formulated nonlocal Weibull theory. Brittle structures correspond to the large-size limit of the present theory. An important practical conclusion is that the safety factors for strength and tolerable minimum lifetime for large quasibrittle structures (e.g., concrete structures and composite airframes or ship hulls, as well as various micro-devices) should be calculated as a function of structure size and geometry.

  18. Crack growth tests on a ferritic reactor pressure vessel steel under the simultaneous influence of simulated BWR coolant and irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Hoffmann, H. [VGB PowerTech e.V., Essen (Germany); Huettner, F. [Hamburgische Electricitaets-Werke AG, Hamburg (Germany); Ilg, U. [EnBW Kraftwerke AG, Philippsburg (Germany); Wachter, O. [E.ON Kernkraft GmbH, Hannover(Germany); Widera, M. [RWE Power AG, Essen (Germany); Brozova, A.; Ernestova, M.; Kysela, J.; Vsolak, R. [Nuclear Research Institute Rez plc (Czech Republic)

    2004-07-01

    Crack growth tests under constant load with initial in-situ cycling were performed on the low alloy reactor pressure vessel (RPV) steel 22 NiMoCr 3 7 (A 508 Cl. 2) with the goal to determine crack growth rates of irradiated and non-irradiated steel under the simultaneous influence of simulated BWR coolant and irradiation. The tests were performed under conditions as near as possible to operational conditions in a commercial BWR reactor. The research results are summarized and are compared with international data. (orig.)

  19. Evaluation of HAZ liquation cracking susceptibility and HAZ softening behavior in modified 800H

    Energy Technology Data Exchange (ETDEWEB)

    Lundin, C.D.; Qiao, C.Y.P. (Tennessee Univ., Knoxville, TN (United States). Dept. of Materials Science and Engineering)

    1992-11-20

    A modified 800H alloy, developed at Oak Ridge National Laboratory (ORNL), is one of the candidate materials designed for high temperature applications. Extensive mechanical and corrosion investigations have been completed and it has been proven that modified 800 has excellent high temperature mechanical and metallurgical behavior. Weldability studies of modified 800H are being carried out at the University of Tennessee, Knoxville. A series of modified 800H alloys and two similar commercial high temperature materials (310Ta and HR3C) were used to conduct this investigation. A preliminary weldability evaluation has been accomplished and the major part of the results (HAZ liquation cracking resistance and HAZ softening behavior in modified 800H) is addressed in this report. The basic conclusion of this investigation is that modified 800H material possesses good resistance to HAZ liquation cracking especially with a grain size control (thermo-mechanical treatment). The information from this study is important to the further modification of the material in order to extend its applications.

  20. Sub-critical crack growth in silicate glasses: Role of network topology

    Energy Technology Data Exchange (ETDEWEB)

    Smedskjaer, Morten M., E-mail: mos@bio.aau.dk [Department of Chemistry and Bioscience, Aalborg University, 9220 Aalborg (Denmark); Bauchy, Mathieu [Department of Civil and Environmental Engineering, University of California, Los Angeles, California 90095 (United States)

    2015-10-05

    The presence of water in the surrounding atmosphere can cause sub-critical crack growth (SCCG) in glasses, a phenomenon known as fatigue or stress corrosion. Here, to facilitate the compositional design of more fatigue-resistant glasses, we investigate the composition dependence of SCCG by studying fourteen silicate glasses. The fatigue curves (V-K{sub I}) have been obtained by indentation experiments through measurements of the crack length as a function of post-indentation fatigue duration. Interestingly, we find that the fatigue resistance parameter N is generally improved by increasing the alumina content and is thereby found to exhibit a fairly linear dependence on the measured Vickers hardness H{sub V} for a wide range of N and H{sub V} values. This finding highlights the important role of network topology in governing the SCCG in silicate glasses, since hardness has been shown to scale linearly with the number of atomic constraints. Our results therefore suggest that glasses showing under-constrained flexible networks, which feature floppy internal modes of deformation, are more readily attacked by water molecules, thus promoting stress corrosion and reducing the fatigue resistance.

  1. Crack growth rates and fracture toughness of irradiated austenitic stainless steels in BWR environments.

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-01-21

    In light water reactors, austenitic stainless steels (SSs) are used extensively as structural alloys in reactor core internal components because of their high strength, ductility, and fracture toughness. However, exposure to high levels of neutron irradiation for extended periods degrades the fracture properties of these steels by changing the material microstructure (e.g., radiation hardening) and microchemistry (e.g., radiation-induced segregation). Experimental data are presented on the fracture toughness and crack growth rates (CGRs) of wrought and cast austenitic SSs, including weld heat-affected-zone materials, that were irradiated to fluence levels as high as {approx} 2x 10{sup 21} n/cm{sup 2} (E > 1 MeV) ({approx} 3 dpa) in a light water reactor at 288-300 C. The results are compared with the data available in the literature. The effects of material composition, irradiation dose, and water chemistry on CGRs under cyclic and stress corrosion cracking conditions were determined. A superposition model was used to represent the cyclic CGRs of austenitic SSs. The effects of neutron irradiation on the fracture toughness of these steels, as well as the effects of material and irradiation conditions and test temperature, have been evaluated. A fracture toughness trend curve that bounds the existing data has been defined. The synergistic effects of thermal and radiation embrittlement of cast austenitic SS internal components have also been evaluated.

  2. Improvement of Cracking-resistance and Flexural Behavior of Cement-based Materials by Addition of Rubber,Particles

    Institute of Scientific and Technical Information of China (English)

    KANG Jingfu; JIANG Yongqi

    2008-01-01

    By ring test and bend test,the improvement of waste tire rubber particles on the crack-resistance and flexural behaviors of cement-based materials were investigated.Test results show that the cracking time of the ring specimens can be retarded by the incorporation of rubber particles in the cement paste and mortar.The improvement in the crack-resistance depended on the rubber fraction.When the rubber fraction was 20%in volume,the cracking time was retarded about 15 h for the paste and 24 d for the mortar respectively.Flexural properties were evaluated based on the bend test results for both mortar and concrete containing different amount of rubber particles.Test results show that rubberized mortar and concrete specimens exhibit ductile failure and significant deformation before fracture.The ultimate deformations of both mortar and concrete specimen increase more than 2-4 times than control specimens.

  3. Carbon nanotube-based sensor and method for detection of crack growth in a structure

    Science.gov (United States)

    Smits, Jan M. (Inventor); Kite, Marlen T. (Inventor); Moore, Thomas C. (Inventor); Wincheski, Russell A. (Inventor); Ingram, JoAnne L. (Inventor); Watkins, Anthony N. (Inventor); Williams, Phillip A. (Inventor)

    2007-01-01

    A sensor has a plurality of carbon nanotube (CNT)-based conductors operatively positioned on a substrate. The conductors are arranged side-by-side, such as in a substantially parallel relationship to one another. At least one pair of spaced-apart electrodes is coupled to opposing ends of the conductors. A portion of each of the conductors spanning between each pair of electrodes comprises a plurality of carbon nanotubes arranged end-to-end and substantially aligned along an axis. Because a direct correlation exists between the resistance of a carbon nanotube and its strain, changes experienced by the portion of the structure to which the sensor is coupled induce a corresponding change in the electrical properties of the conductors, thereby enabling detection of crack growth in the structure.

  4. Evaluation of Fatigue Crack Growth and Fracture Properties of Cryogenic Model Materials

    Science.gov (United States)

    Newman, John A.; Forth, Scott C.; Everett, Richard A., Jr.; Newman, James C., Jr.; Kimmel, William M.

    2002-01-01

    The criteria used to prevent failure of wind-tunnel models and support hardware were revised as part of a project to enhance the capabilities of cryogenic wind tunnel testing at NASA Langley Research Center. Specifically, damage-tolerance fatigue life prediction methods are now required for critical components, and material selection criteria are more general and based on laboratory test data. The suitability of two candidate model alloys (AerMet 100 and C-250 steel) was investigated by obtaining the fatigue crack growth and fracture data required for a damage-tolerance fatigue life analysis. Finally, an example is presented to illustrate the newly implemented damage tolerance analyses required of wind-tunnel model system components.

  5. The radiation swelling effect on fracture properties and fracture mechanisms of irradiated austenitic steels. Part II. Fatigue crack growth rate

    Science.gov (United States)

    Margolin, B.; Minkin, A.; Smirnov, V.; Sorokin, A.; Shvetsova, V.; Potapova, V.

    2016-11-01

    The experimental data on the fatigue crack growth rate (FCGR) have been obtained for austenitic steel of 18Cr-10Ni-Ti grade (Russian analog of AISI 321 steel) irradiated up to neutron dose of 150 dpa with various radiation swelling. The performed study of the fracture mechanisms for cracked specimens under cyclic loading has explained why radiation swelling affects weakly FCGR unlike its effect on fracture toughness. Mechanical modeling of fatigue crack growth has been carried out and the dependencies for prediction of FCGR in irradiated austenitic steel with and with no swelling are proposed and verified with the obtained experimental results. As input data for these dependencies, FCGR for unirradiated steel and the tensile mechanical properties for unirradiated and irradiated steels are used.

  6. Fracture Resistance Measurement Method for in situ Observation of Crack Mechanisms

    DEFF Research Database (Denmark)

    Sørensen, Bent F.; Horsewell, A.; Jørgensen, O.

    1998-01-01

    observation and acoustic emission, As an example, crack growth in a cubic-phase yttria-stabilized zirconia is detected easily by in situ observation of the crack-tip region, Many fracture toughness measurements are obtained for each specimen, giving high confidence in the measured fracture toughness value......, In situ observation is useful for the study of toughening mechanisms and subcritical crack-growth behavior and to sort out erroneous measurements (e.g., due to crack branching)....

  7. Numerical Simulation Procedure for Modeling TGO Crack Propagation and TGO Growth in Thermal Barrier Coatings upon Thermal-Mechanical Cycling

    Directory of Open Access Journals (Sweden)

    Ding Jun

    2014-01-01

    Full Text Available This paper reports a numerical simulation procedure to model crack propagation in TGO layer and TGO growth near a surface groove in metal substrate upon multiple thermal-mechanical cycles. The material property change method is employed to model TGO formation cycle by cycle, and the creep properties for constituent materials are also incorporated. Two columns of repeated nodes are placed along the interface of the potential crack, and these nodes are bonded together as one node at a geometrical location. In terms of critical crack opening displacement criterion, onset of crack propagation in TGO layer has been determined by finite element analyses in comparison with that without predefined crack. Then, according to the results from the previous analyses, the input values for the critical failure parameters for the subsequent analyses can be decided. The robust capabilities of restart analysis in ABAQUS help to implement the overall simulation for TGO crack propagation. The comparison of the TGO final deformation profile between numerical and experimental observation shows a good agreement indicating the correctness and effectiveness of the present procedure, which can guide the prediction of the failure in TGO for the future design and optimization for TBC system.

  8. A novel technique for measuring stress-corrosion crack-growth rates in single-crystal experiments

    Energy Technology Data Exchange (ETDEWEB)

    Lichter, B.D. [Vanderbilt Univ., Nashville, TN (United States)]|[Delft Univ. of Technology (Netherlands); Flanagan, W.F. [Vanderbilt Univ., Nashville, TN (United States)

    1994-12-31

    Crack-growth occurs discontinuously in oriented copper-gold single-crystals during slow-strain rate experiments performed under anodic polarization in aqueous NaCl solutions. Crack advance between major crack arrests is accompanied by load-drops and current-transients which can be quantitatively related to the length of the advance as well as yielding the average instantaneous rate of advance. Two independent but self-consistent methods are used: (1) mechanical analysis of the load-drops, taking into account the elastic displacement of the load-train and of the specimen, due to both the load and the crack advance, and (2) analysis of the current-transients in which it is argued that the current is proportional to the rate of new surface production. Results show that the crack velocity is on the order of 50--400{mu}/s, depending on the environment and potential, too slow to be explained by a running brittle crack, and too fast to be explained by Faradaic dissolution.

  9. Slow Crack Growth and Fatigue Life Prediction of Ceramic Components Subjected to Variable Load History

    Science.gov (United States)

    Jadaan, Osama

    2001-01-01

    Present capabilities of the NASA CARES/Life (Ceramic Analysis and Reliability Evaluation of Structures/Life) code include probabilistic life prediction of ceramic components subjected to fast fracture, slow crack growth (stress corrosion), and cyclic fatigue failure modes. Currently, this code has the capability to compute the time-dependent reliability of ceramic structures subjected to simple time-dependent loading. For example, in slow crack growth (SCG) type failure conditions CARES/Life can handle the cases of sustained and linearly increasing time-dependent loads, while for cyclic fatigue applications various types of repetitive constant amplitude loads can be accounted for. In real applications applied loads are rarely that simple, but rather vary with time in more complex ways such as, for example, engine start up, shut down, and dynamic and vibrational loads. In addition, when a given component is subjected to transient environmental and or thermal conditions, the material properties also vary with time. The objective of this paper is to demonstrate a methodology capable of predicting the time-dependent reliability of components subjected to transient thermomechanical loads that takes into account the change in material response with time. In this paper, the dominant delayed failure mechanism is assumed to be SCG. This capability has been added to the NASA CARES/Life (Ceramic Analysis and Reliability Evaluation of Structures/Life) code, which has also been modified to have the ability of interfacing with commercially available FEA codes executed for transient load histories. An example involving a ceramic exhaust valve subjected to combustion cycle loads is presented to demonstrate the viability of this methodology and the CARES/Life program.

  10. The relationship between community structural characteristics, the context of crack use, and HIV risk behaviors in San Salvador, El Salvador.

    Science.gov (United States)

    Dickson-Gomez, Julia; McAuliffe, Timothy; Rivas de Mendoza, Lorena; Glasman, Laura; Gaborit, Mauricio

    2012-02-01

    This paper explores community structural factors in different low-income communities in the San Salvador, El Salvador, that account for differences in the social context in which crack is used and HIV risk behaviors among crack users. Results suggest that both more distal (type of low-income community, level of violent crime, and poverty) and proximate structural factors (type of site where drugs are used, and whether drugs are used within or outside of community of residence) influence HIV risk behaviors among drug users. Additionally, our results suggest that community structural factors influence the historical and geographic variation in drug use sites.

  11. Irradiation-assisted stress corrosion cracking behavior of austenitic stainless steels applicable to LWR core internals.

    Energy Technology Data Exchange (ETDEWEB)

    Chung, H. M.; Shack, W. J.; Energy Technology

    2006-01-31

    This report summarizes work performed at Argonne National Laboratory on irradiation-assisted stress corrosion cracking (IASCC) of austenitic stainless steels that were irradiated in the Halden reactor in simulation of irradiation-induced degradation of boiling water reactor (BWR) core internal components. Slow-strain-rate tensile tests in BWR-like oxidizing water were conducted on 27 austenitic stainless steel alloys that were irradiated at 288 C in helium to 0.4, 1.3, and 3.0 dpa. Fractographic analysis was conducted to determine the fracture surface morphology. Microchemical analysis by Auger electron spectroscopy was performed on BWR neutron absorber tubes to characterize grain-boundary segregation of important elements under BWR conditions. At 0.4 and 1.4 dpa, transgranular fracture was mixed with intergranular fracture. At 3 dpa, transgranular cracking was negligible, and fracture surface was either dominantly intergranular, as in field-cracked core internals, or dominantly ductile or mixed. This behavior indicates that percent intergranular stress corrosion cracking determined at {approx}3 dpa is a good measure of IASCC susceptibility. At {approx}1.4 dpa, a beneficial effect of a high concentration of Si (0.8-1.5 wt.%) was observed. At {approx}3 dpa, however, such effect was obscured by a deleterious effect of S. Excellent resistance to IASCC was observed up to {approx}3 dpa for eight heats of Types 304, 316, and 348 steel that contain very low concentrations of S. Susceptibility of Types 304 and 316 steels that contain >0.003 wt.% S increased drastically. This indicates that a sulfur related critical phenomenon plays an important role in IASCC. A sulfur content of <0.002 wt.% is the primary material factor necessary to ensure good resistance to IASCC. However, for Types 304L and 316L steel and their high-purity counterparts, a sulfur content of <0.002 wt.% alone is not a sufficient condition to ensure good resistance to IASCC. This is in distinct contrast to

  12. Irradiation-assisted stress corrosion cracking behavior of austenitic stainless steels applicable to LWR core internals.

    Energy Technology Data Exchange (ETDEWEB)

    Chung, H. M.; Shack, W. J.; Energy Technology

    2006-01-31

    This report summarizes work performed at Argonne National Laboratory on irradiation-assisted stress corrosion cracking (IASCC) of austenitic stainless steels that were irradiated in the Halden reactor in simulation of irradiation-induced degradation of boiling water reactor (BWR) core internal components. Slow-strain-rate tensile tests in BWR-like oxidizing water were conducted on 27 austenitic stainless steel alloys that were irradiated at 288 C in helium to 0.4, 1.3, and 3.0 dpa. Fractographic analysis was conducted to determine the fracture surface morphology. Microchemical analysis by Auger electron spectroscopy was performed on BWR neutron absorber tubes to characterize grain-boundary segregation of important elements under BWR conditions. At 0.4 and 1.4 dpa, transgranular fracture was mixed with intergranular fracture. At 3 dpa, transgranular cracking was negligible, and fracture surface was either dominantly intergranular, as in field-cracked core internals, or dominantly ductile or mixed. This behavior indicates that percent intergranular stress corrosion cracking determined at {approx}3 dpa is a good measure of IASCC susceptibility. At {approx}1.4 dpa, a beneficial effect of a high concentration of Si (0.8-1.5 wt.%) was observed. At {approx}3 dpa, however, such effect was obscured by a deleterious effect of S. Excellent resistance to IASCC was observed up to {approx}3 dpa for eight heats of Types 304, 316, and 348 steel that contain very low concentrations of S. Susceptibility of Types 304 and 316 steels that contain >0.003 wt.% S increased drastically. This indicates that a sulfur related critical phenomenon plays an important role in IASCC. A sulfur content of <0.002 wt.% is the primary material factor necessary to ensure good resistance to IASCC. However, for Types 304L and 316L steel and their high-purity counterparts, a sulfur content of <0.002 wt.% alone is not a sufficient condition to ensure good resistance to IASCC. This is in distinct contrast to

  13. On the relative role of processes whose sequence results in crack growth in the cladding of LMFBR fuel pins

    Science.gov (United States)

    Mikhlin, E. Ya.

    1991-08-01

    Processes are discussed the joint effect of which results in crack development in austenitic steel-clad oxide fuel pins. Such processes include generation of Te which is considered as the main embrittling agent, its transport and accumulation at the cladding inner surface, where together with Cs it forms a liquid surface-acting medium, and finally, development of intergranular cracks in the cladding caused by the contact with this medium. As the process of crack growth in itself proceeds faster than accumulation of liquid surfactants at the cladding, the cracks will be able to reach the critical length only after the necessary amount of Te has been accumulated. Its accumulation is determined and therefore, controlled by the process of Te transport in the fuel grains. It is shown that the main contribution to the accumulation of Te at the cladding surface is provided by the hottest internal zones of the fuel pellet. On the basis of the analysis given, means are discussed, for inhibiting or blocking the crack growth.

  14. Application of an interface failure model to predict fatigue crack growth in an implanted metallic femoral stem.

    Science.gov (United States)

    Chen, J; Browne, M; Taylor, M; Gregson, P J

    2004-03-01

    A novel computational modelling technique has been developed for the prediction of crack growth in load bearing orthopaedic alloys subjected to fatigue loading. Elastic-plastic fracture mechanics has been used to define a three-dimensional fracture model, which explicitly models the opening, sliding and tearing process. This model consists of 3D nonlinear spring elements implemented in conjunction with a brittle material failure function, which is defined by the fracture energy for each nonlinear spring element. Thus, the fracture energy criterion is implicit in the brittle material failure function to search for crack initiation and crack development automatically. A degradation function is employed to reduce interfacial fracture properties corresponding to the number of cycles; thus fatigue lifetime can be predicted. Unlike other failure modelling methods, this model predicts the failure load, crack path and residual stiffness directly without assuming any pre-flaw condition. As an example, fatigue of a cobalt based alloy (CoCrMo) femoral stem is simulated. Experimental fatigue data was obtained from four point bending tests. The finite element model simulated a fully embedded implant with a constant point load. Comparison between the model and mechanical test results showed good agreement in fatigue crack growth rate.

  15. 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

  16. Review of Environmentally Assisted Cracking

    Science.gov (United States)

    Sadananda, K.; Vasudevan, A. K.

    2011-02-01

    Many efforts have been made in the past by several researchers to arrive at some unifying principles governing the embrittlement phenomena. An inescapable conclusion reached by all these efforts was that the behavior is very complex. Hence, recognizing the complexity of material/environment behavior, we focus our attention here only in extracting some similarities in the experimental trends to arrive at some generic principles of behavior. Crack nucleation and growth are examined under static load in the presence of internal and external environments. Stress concentration, either pre-existing or in-situ generated, appears to be a requirement for embrittlement. A chemical stress concentration factor is defined for a given material/environment system as the ratio of failure stress with and without the damaging chemical environment. All factors that affect the buildup of the required stress concentration, such as planarity of slip, stacking fault energy, etc., also affect the stress-corrosion behavior. The chemical stress concentration factor is coupled with the mechanical stress concentration factor. In addition, generic features for all systems appear to be (a) an existence of a threshold stress as a function of concentration of the damaging environment and flow properties of the material, and (b) an existence of a limiting threshold as a function of concentration, indicative of a damage saturation for that environment. Kinetics of crack growth also depends on concentration and the mode of crack growth. In general, environment appears to enhance crack tip ductility on one side by the reduction of energy for dislocation nucleation and glide, and to reduce cohesive energy for cleavage, on the other. These two opposing factors are coupled to provide environmentally induced crack nucleation and growth. The relative ratio of these two opposing factors depends on concentration and flow properties, thereby affecting limiting thresholds. The limiting concentration or

  17. Development of a numerical procedure for mixed mode K-solutions and fatigue crack growth in FCC single crystal superalloys

    Science.gov (United States)

    Ranjan, Srikant

    2005-11-01

    Fatigue-induced failures in aircraft gas turbine and rocket engine turbopump blades and vanes are a pervasive problem. Turbine blades and vanes represent perhaps the most demanding structural applications due to the combination of high operating temperature, corrosive environment, high monotonic and cyclic stresses, long expected component lifetimes and the enormous consequence of structural failure. Single crystal nickel-base superalloy turbine blades are being utilized in rocket engine turbopumps and jet engines because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. These materials have orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. Computation of stress intensity factors (SIFs) and the ability to model fatigue crack growth rate at single crystal cracks subject to mixed-mode loading conditions are important parts of developing a mechanistically based life prediction for these complex alloys. A general numerical procedure has been developed to calculate SIFs for a crack in a general anisotropic linear elastic material subject to mixed-mode loading conditions, using three-dimensional finite element analysis (FEA). The procedure does not require an a priori assumption of plane stress or plane strain conditions. The SIFs KI, KII, and KIII are shown to be a complex function of the coupled 3D crack tip displacement field. A comprehensive study of variation of SIFs as a function of crystallographic orientation, crack length, and mode-mixity ratios is presented, based on the 3D elastic orthotropic finite element modeling of tensile and Brazilian Disc (BD) specimens in specific crystal orientations. Variation of SIF through the thickness of the specimens is also analyzed. The resolved shear stress intensity coefficient or effective SIF, Krss, can be computed as a function of crack tip SIFs and the

  18. Spatial Randomness of Fatigue Crack Growth Rate in Friction Stir Welded 7075-T111 Aluminum Alloy Welded Joints (Case of L T Orientation Specimen)

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, Yeui Han; Kim, Seon Jin [Pukyong Nat' l Univ., Busan (Korea, Republic of)

    2013-09-15

    This study aims to investigate the spatial randomness of fatigue crack growth rate for the friction stir welded (FSWed) 7075-T111 aluminum alloy joints. Our previous fatigue crack growth test data are adopted in this investigation. To clearly understand the spatial randomness of fatigue crack growth rate, fatigue crack growth tests were conducted under constant stress intensity factor range (SEFOR) control testing. The experimental data were analyzed for two different materials-base metal (BM) and weld metal (WM)-to investigate the effects of spatial randomness of fatigue crack growth rate and material properties, the friction stir welded (FSWed) 7075-T111 aluminum alloy joints, namely weld metal (WM) and base metal (BM). The results showed that the variability, as evaluated by Wobble statistical analysis, of the WM is higher than that of the BM.

  19. A fracture mechanics analysis of bonded repaired skin/stiffener structures with inclined central crack

    Energy Technology Data Exchange (ETDEWEB)

    Chung, Ki Hyun; Yang, Won Ho; Kim, Cheol; Heo, Sung Pil [Sungkyunkwan Univ., Seoul (Korea, Republic of); Ko, Myung Hoon [Daelim College, Anyang (Korea, Republic of)

    2001-07-01

    Composite patch repair of cracked aircraft structures has been accepted as one of improving fatigue life and attaining better structural integrity. Analysis for the stress intensity factor at the skin/stiffener structure with inclined central crack repaired by composite stiffened panels are developed. A numerical investigation was conducted to characterize the fracture behavior and crack growth behavior. In order to investigate the crack growth direction, Maximum Tangential Stress(MTS) criteria is used. The main objective of this research is the validation of the inclined crack patching design. In this paper, the reduction of stresses intensity factors at the crack-tip and prediction of crack growth direction are determined to evaluate the effects of various non-dimensional design parameter including; composite patch thickness and stiffener distance. The research on cracked structure subjected to mixed mode loading is accomplished and it is evident that more work using different approaches is necessary.

  20. Theoretical analysis on bending behavior of functionally graded composite beam crack-controlled by ultrahigh toughness cementitious composites

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Ultrahigh toughness cementitious composites (UHTCC) obviously show strain hardening property under tensile or bending loading. The failure pattern of the UHTCC components exhibits multiple fine cracks under uniaxial tensile loading with prominent tensile strain capacity in excess of 3%, with merely 60 μm average crack width even corresponding to the ultimate tensile strain state. The approach adopted is based on the concept of functionally-graded concrete, where part of the concrete, which surrounds the main longitudinal reinforcement in a RC (reinforced concrete) member, is strategically replaced with UHTCC with excellent crack-controlling ability. Investigations on bending behavior of functionally-graded composite beam crack controlled by UHTCC has been carried out, including theo- retical analysis, experimental research on long composite beams without web reinforcement, validation and comparison between experimental and theoretical results, and analysis on crack control. In addition to improving bearing capacity, the results indicate that functionally-graded composite beams using UHTCC has been found to be very effective in preventing corrosion-induced damage compared with RC beams. Therefore, durability and service life of the structure could be enhanced. This paper discusses the development of internal force and crack propagation during loading process, and presents analysis of the internal force in different stages, moment-curvature relationship from loading to damage and calculation of mid-span deflection and ductility index. In the end, the theoretical formulae have been validated by experimental results.

  1. In-situ scanning electron microscope studies of crack growth in an aluminum metal-matrix composite

    Science.gov (United States)

    Manoharan, M.; Lewandowski, J. J.

    1990-01-01

    Edge-notched specimens of a cast and extruded Al alloy-based, alumina particulate-reinforced composite in the annealed condition were tested in situ in a SEM apparatus equipped with a deformation stage permitting the direct observation of crack growth phenomena. Fracture in this composite is seen to proceed by initiation of microcracks ahead of the macrocrack; as deformation proceeds, the microcracks lengthen, and crack propagation occurs when the region of intense plastic straining becomes comparable to the macrocrack-microcrack distance. The sequence is then repeated.

  2. Overlapping Spreading Centers: Implications from Crack Growth Simulation by the Displacement Discontinuity Method

    Science.gov (United States)

    Sempere, Jean-Christophe; MacDonald, Ken C.

    1986-02-01

    Overlapping spreading centers (OSC's) are a fundamental aspect of accretionary processes at intermediate and fast-spreading centers and typically occur at deep points along the axial depth profile. They have a characteristic geometry consisting of two en echelon overlapping, curving ridges separated by an elongated depression. The length to width ratio of this overlap basin is typically 3∶1. We have been successful in reproducing the overlapping spreading center geometry by modelling the growth of two initially parallel elastic cracks of given length and offset in a tensile stress field at infinity. A boundary element displacement discontinuity method was used to solve this problem. Our calculated results are compared with seafloor observations in terms of the size and shape of the overlap region. For small OSC's, there is a very good agreement between calculations and observations but, for large ones, the overlap basin tends to be longer than our predicted results indicate. This suggests that the assumptions made in the model (i.e., perfectly elastic, isotropic and homogeneous medium) are perhaps valid for the brittle lid above the magma chamber that underlies OSC's with small offsets (OSC's with large offsets. Our modelling shows that the initial interaction of closely spaced surface ruptures along spreading centers is to deflect away from one another as they approach. The deflection will be the greatest for small misalignments of the fracture systems, thus even minor misalignments of the spreading centers may result in the development of OSC's. Where the misalignment is less than the width of the cracking front, the fracture systems may meet head-on creating a saddle point along the axial depth profile. Our results support the hypothesis suggested by Macdonald et al. [1984] in which overlapping spreading centers develop where two magmatic pulses migrate toward each other along the strike of the spreading center following fracture systems and magmatic conduits

  3. Effect of welding processes and consumables on fatigue crack growth behaviour of armour grade quenched and tempered steel joints

    Directory of Open Access Journals (Sweden)

    G. Magudeeswaran

    2014-03-01

    Full Text Available Quenched and Tempered (Q&T steels are widely used in the construction of military vehicles due to its high strength to weight ratio and high hardness. These steels are prone to hydrogen induced cracking (HIC in the heat affected zone (HAZ after welding. The use of austenitic stainless steel (ASS consumables to weld the above steel was the only available remedy because of higher solubility for hydrogen in austenitic phase. The use of stainless steel consumables for a non-stainless steel base metal is not economical. Hence, alternate consumables for welding Q&T steels and their vulnerability to HIC need to be explored. Recent studies proved that low hydrogen ferritic steel (LHF consumables can be used to weld Q&T steels, which can give very low hydrogen levels in the weld deposits. The use of ASS and LHF consumables will lead to distinct microstructures in their respective welds. This microstructural heterogeneity will have a drastic influence in the fatigue crack growth resistance of armour grade Q&T steel welds. Hence, in this investigation an attempt has been made to study the influence of welding consumables and welding processes on fatigue crack growth behaviour of armour grade Q&T Steel joints. Shielded metal arc welding (SMAW and Flux cored arc welding (FCAW were used for fabrication of joints using ASS and LHF consumables. The joints fabricated by SMAW process using LHF consumable exhibited superior fatigue crack growth resistance than all other joints.

  4. Effects of Low Temperature on Hydrogen-Assisted Crack Growth in Forged 304L Austenitic Stainless Steel

    Science.gov (United States)

    Jackson, Heather; San Marchi, Chris; Balch, Dorian; Somerday, Brian; Michael, Joseph

    2016-08-01

    The objective of this study was to evaluate effects of low temperature on hydrogen-assisted crack propagation in forged 304L austenitic stainless steel. Fracture initiation toughness and crack-growth resistance curves were measured using fracture mechanics specimens that were thermally precharged with 140 wppm hydrogen and tested at 293 K or 223 K (20 °C or -50 °C). Fracture initiation toughness for hydrogen-precharged forgings decreased by at least 50 to 80 pct relative to non-charged forgings. With hydrogen, low-temperature fracture initiation toughness decreased by 35 to 50 pct relative to room-temperature toughness. Crack growth without hydrogen at both temperatures was microstructure-independent and indistinguishable from blunting, while with hydrogen microcracks formed by growth and coalescence of microvoids. Initiation of microvoids in the presence of hydrogen occurred where localized deformation bands intersected grain boundaries and other deformation bands. Low temperature additionally promoted fracture initiation at annealing twin boundaries in the presence of hydrogen, which competed with deformation band intersections and grain boundaries as sites of microvoid formation and fracture initiation. A common ingredient for fracture initiation was stress concentration that arose from the intersection of deformation bands with these microstructural obstacles. The localized deformation responsible for producing stress concentrations at obstacles was intensified by low temperature and hydrogen. Crack orientation and forging strength were found to have a minor effect on fracture initiation toughness of hydrogen-supersaturated 304L forgings.

  5. Characterization of the Q parameter for evaluating creep crack growth rate for type 316LN stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Ekaputra, I. M. W.; Park, Jae Young; Kim, Seon Jin [Pukyong National University, Busan (Korea, Republic of); Kim, Woo Gon; Kim, Eung Seon [KAERI, Daejeon (Korea, Republic of)

    2016-07-15

    In this study, the Q parameter was characterized to evaluate the Creep crack growth rate (CCGR) of type 316LN stainless steel. Creep crack growth (CCG) data were obtained by CCG tests under different applied loads at 600 .deg. C. An additional CCG test was conducted at 550 .deg. C to investigate the possible temperature dependence of the stress intensity factor. An equation using the Q parameter for evaluating CCGR was proposed, and this parameter was characterized and compared with the typical C fracture parameter, which is commonly used. The Q parameter exhibited good linearity of the data, exhibiting no nonlinearity-induced dual value at the early stage. The Q parameter was suitable for characterizing the CCGR regardless of different applied loads and types of steels. In addition, fracture microstructures near the crack revealed a typical intergranular fracture mode, and this fracture was dominantly propagated along the grain boundary. The cracks were developed by the growth and interlinking of cavities, which were attributed to the precipitates forming along the grain boundary.

  6. Effect of welding processes and consumables on fatigue crack growth behaviour of armour grade quenched and tempered steel joints

    Institute of Scientific and Technical Information of China (English)

    G. MAGUDEESWARAN; V. BALASUBRAMANIAN; G. MADHUSUDHAN REDDY

    2014-01-01

    Quenched and Tempered (Q&T) steels are widely used in the construction of military vehicles due to its high strength to weight ratio and high hardness. These steels are prone to hydrogen induced cracking (HIC) in the heat affected zone (HAZ) after welding. The use of austenitic stainless steel (ASS) consumables to weld the above steel was the only available remedy because of higher solubility for hydrogen in austenitic phase. The use of stainless steel consumables for a non-stainless steel base metal is not economical. Hence, alternate consumables for welding Q&T steels and their vulnerability to HIC need to be explored. Recent studies proved that low hydrogen ferritic steel (LHF) consumables can be used to weld Q&T steels, which can give very low hydrogen levels in the weld deposits. The use of ASS and LHF consumables will lead to distinct microstructures in their respective welds. This microstructural heterogeneity will have a drastic influence in the fatigue crack growth resistance of armour grade Q&T steel welds. Hence, in this investigation an attempt has been made to study the influence of welding con-sumables and welding processes on fatigue crack growth behaviour of armour grade Q&T Steel joints. Shielded metal arc welding (SMAW) and Flux cored arc welding (FCAW) were used for fabrication of joints using ASS and LHF consumables. The joints fabricated by SMAW process using LHF consumable exhibited superior fatigue crack growth resistance than all other joints.

  7. Effect of stress ratio and frequency on fatigue crack growth rate of 2618 aluminium alloy silicon carbide metal matrix composite

    Indian Academy of Sciences (India)

    Nirbhay Singh; Ram Khelawan; G N Mathur

    2001-04-01

    Effect of stress ratio and frequency on the fatigue crack propagation of 2618 aluminium alloy–silicon carbide composite were investigated at ambient temperature. With the first set of specimens, the fatigue crack growth rates were studied at three frequencies of 1 Hz, 5 Hz and 10 Hz at a stress ratio of 0.1 whereas the effects of stress ratios of 0.1, 0.25 and 0.50 were studied with the second set of specimens. The study showed that the fatigue crack propagation behaviour of this metal matrix composite was influenced to an appreciable extent by the stress ratio, but not by the fatigue frequencies used in this investigation.

  8. Comparison of creep crack growth rates on the base and welded metals of modified 9Cr-1Mo steel

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Woo Gon; Yun, Song Nam; Kim, Yong Wan; Kim, Sung Ho [KAERI, Daejeon (Korea, Republic of); Park, Jae Young; Kim, Seon Jin [Pukyong National Univ., Busan (Korea, Republic of)

    2009-07-01

    This paper is to compare Creep Crack Growth Rates (CCGR) on the Base Metal (BM) and Welded Metal (WM) of modified 9Cr-1Mo steel for Gen-IV reactors. Welded specimens were prepared by Shielded Metal Arc Weld (SMAW) method. To obtain material properties for the BM and welded metal, a series of creep and tensile tests was conducted at 600 .deg. C, and CCG tests was also performed using 1/2'' compact tension specimens under different applied loads at 600 .deg. C. Their CCGR behaviors were analyzed by using the empirical equation of the da/dt vs. C{sup *} parameter and compared, respectively. It appeared that, for a given value of C{sup *}, the rate of creep propagation was about 2.0 times faster than in the WM than the BM. This reason is that a creep rate in the WM was largely attributed when compared with that in the BM. From this result, it can be utilized for assessing the rate of creep propagation on the BM and WM of the G91 steel.

  9. Cohesive zone model for intergranular slow crack growth in ceramics: influence of the process and the microstructure

    Science.gov (United States)

    Romero de la Osa, M.; Estevez, R.; Olagnon, C.; Chevalier, J.; Tallaron, C.

    2011-10-01

    Ceramic polycrystals are prone to slow crack growth (SCG) which is stress and environmentally assisted, similarly to observations reported for silica glasses. The kinetics of fracture are known to be dependent on the load level, the temperature and the relative humidity. In addition, evidence is available on the influence of the microstructure on the SCG rate with an increase in the crack velocity with decreasing the grain size. Crack propagation takes place beyond a load threshold, which is grain size dependent. We present a cohesive zone model for the intergranular failure process. The methodology accounts for an intrinsic opening that governs the length of the cohesive zone and allows the investigation of grain size effects. A rate and temperature-dependent cohesive model is proposed (Romero de la Osa M, Estevez R et al 2009 J. Mech. Adv. Mater. Struct. 16 623-31) to mimic the reaction-rupture mechanism. The formulation is inspired by Michalske and Freiman's picture (Michalske and Freiman 1983 J. Am. Ceram. Soc. 66 284-8) together with a recent study by Zhu et al (2005 J. Mech. Phys. Solids 53 1597-623) of the reaction-rupture mechanism. The present investigation extends a previous work (Romero de la Osa et al 2009 Int. J. Fracture 158 157-67) in which the problem is formulated. Here, we explore the influence of the microstructure in terms of grain size, their elastic properties and residual thermal stresses originating from the cooling from the sintering temperature down to ambient conditions. Their influence on SCG for static loadings is reported and the predictions compared with experimental trends. We show that the initial stress state is responsible for the grain size dependence reported experimentally for SCG. Furthermore, the account for the initial stresses enables the prediction of a load threshold below which no crack growth is observed: a crack arrest takes place when the crack path meets a region in compression.

  10. Embedded Shape Memory Alloy Particles for the Self-Sensing of Fatigue Crack Growth in an Aluminum Alloy

    Science.gov (United States)

    Leser, William Paul

    Future aerospace vehicles will be built using novel materials for mission conditions that are difficult to replicate in a laboratory. Structural health monitoring and condition-based maintenance will be critical to ensure the reliability of such vehicles. A multi-functional aluminum alloy containing embedded shape memory alloy (SMA) particles to detect fatigue crack growth is proposed. The regions of intensified strain near the tip of a growing fatigue crack cause the SMA particles to undergo a solid-to-solid phase transformation from austenite to martensite, releasing a detectable and identifiable acoustic emission (AE) signal that can be used to locate the crack in the affected component. This study investigates the AE response of two SMA systems, Ni-Ti, and Co-Ni-Al. Tensile (Ni-Ti) and compressive (Co-Ni-Al) tests were conducted to study the strain-induced transformation response in both of the alloy systems. It was found that the critical stress for transformation in both SMA systems was easily identified by a burst of AE activity during both transformation and reverse transformation. AE signals from these experiments were collected for use as training data for a Bayesian classifier to be used to identify transformation signals in a Al7050 matrix with embedded SMA particles. The Al/SMA composite was made by vacuum hot pressing SMA powder between aluminum plates. The effect of hot pressing temperature and subsequent heat treatments (solutionizing and peak aging) on the SMA particles was studied. It was found that, at the temperatures required, Co-Ni-Al developed a second phase that restricted the transformation from austenite to martensite, thus rendering it ineffective as a candidate for the embedded particles. Conversely, Ni-Ti did survive the embedding process and it was found that the solutionizing heat treatment applied after hot pressing was the main driver in determining the final transformation temperatures for the Ni-Ti particles. The effect of hot

  11. THE BEHAVIOR OF TWO COLLINEAR CRACKS IN MAGNETO-ELECTRO-ELASTIC COMPOSITES UNDER ANTI-PLANE SHEAR STRESS LOADING

    Institute of Scientific and Technical Information of China (English)

    Sun Yuguo; Zhou Zhengong

    2005-01-01

    In this paper, the behavior of two collinear cracks in magneto-electro-elastic composite material under anti-plane shear stress loading is studied by the Schmidt method for permeable electric boundary conditions. By using the Fourier transform, the problem can be solved with a set of triple integral equations in which the unknown variable is the jump of displacements across the crack surfaces. In solving the triple integral equations, the unknown variable is expanded in a series of Jacobi polynomials. Numerical solutions are obtained. It is shown that the stress field is independent of the electric field and the magnetic flux.

  12. Electrochemical investigation on the hydrogen permeation behavior of 7075-T6 Al alloy and its influence on stress corrosion cracking

    Science.gov (United States)

    Zheng, Chuan-bo; Yan, Bing-hao; Zhang, Ke; Yi, Guo

    2015-07-01

    The hydrogen permeation behavior and stress corrosion cracking (SCC) susceptibility of precharged 7075-T6 Al alloy were investigated in this paper. Devanthan-Stachurski (D-S) cell tests were used to measure the apparent hydrogen diffusivity and hydrogen permeation current density of specimens immersed in 3.5wt% NaCl solution. Electrochemical experiment results show that the SCC susceptibility is low during anodic polarization. Both corrosion pits and hydrogen-induced cracking are evident in scanning electron microscope images after the specimens have been charging for 24 h.

  13. Effect of Organophilic Montmorillonite on Ther-mal-oxidative Aging Behavior of SBS Modified Bitumen Crack Filling Material

    Institute of Scientific and Technical Information of China (English)

    YU Jianying; WANG Xilin; KUANG Dongliang; ZHANG Henglong

    2009-01-01

    Styrene-butadiene-styrene(SBS)modified bitumen crack filling material with or-ganophilic montmorillonite(OCFM)was prepared by melt blending.X-ray diffraction analysis shows that the interlayer spacing of organophilic montmorillonite(OMMT)in OCFM is widened and an exfoliated structure may be formed.Thermal-oxidative aging behavior of OCFM and SBS modified bitumen crack filling material(SCFM)was investigated.The experimental results indicate that the rate of thermal-oxidative aging of OCFM is much slower than that of SCFM,which can be attributed to barrier of exfoliated structure of OCFM to oxygen.

  14. ON ANTI-PLANE SHEAR BEHAVIOR OF A GRIFFITH PERMEABLE CRACK IN PIEZOELECTRIC MATERIALS BY USE OF THE NON-LOCAL THEORY

    Institute of Scientific and Technical Information of China (English)

    周振功; 杜善义; 王彪

    2003-01-01

    In this paper, the non-local theory of elasticity is applied to obtain the behavior of a Griffith crack in the piezoelectric materials under anti-plane shear loading for permeable crack surface conditions. By means of the Fourier transform, the problem can be solved with the help of a pair of dual integral equations with the unknown variable being the jump of the displacement across the crack surfaces. These equations are solved by the Schmidt method. Numerical examples are provided.Unlike the classical elasticity solutions, it is found that no stress and electric displacement singularity is present at the crack tip. The non-local elastic solutions yield a finite hoop stress at the crack tip,thus allowing for a fracture criterion based on the maximum stress hypothesis. The finite hoop stress at the crack tip depends on the crack length and the lattice parameter of the materials, respectively.

  15. 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

    bottles a second time in order to avoid explosion of bottles of precious Seltzer water. Since then, many theories and experimental results have been...R.C. Pohanka, S.W. Freiman, and B.A. Bender , "Effect of the Phase Transformation on the Fracture Behavior 202 of BaTiO3," Jour. Am. Ceram. Soc., 61

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

    DEFF Research Database (Denmark)

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

    2015-01-01

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

  17. Assessment of the Efficiency of HWCon IASCC Crack Growth Rate for High Fluence BWRMaterials

    Energy Technology Data Exchange (ETDEWEB)

    Teysseyre, Sebastien Paul [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2016-09-01

    This report describes the experimental study performed to assess the efficiency of hydrogen water chemistry on the propagation rate of cracks generated by irradiation assisted stress corrosion cracking in high fluence material. The selection of the material and the test procedures followed for this study are presented. The test results obtained with 8.6 dpa specimen are discussed.

  18. Crack initiation behavior of notched specimens on heat resistant steel under service type loading at high temperature

    Directory of Open Access Journals (Sweden)

    Lu Cui

    2016-10-01

    Full Text Available Cracks at notches deserve special consideration in the design of steam turbine components. This work is addressed to investigate the crack initiation behavior a 10%Cr rotor steel with the help of notched specimens under service-type loading. A significant drifting down of the peak-values of axial deformation under constant amplitude load was observed. Crack initiation was evaluated with the help of the relationship between irreversible deformation energy and cycle number. Further, metallographic examinations were employed to characterize the superposition of creep and fatigue damage mechanisms. Both Neuber-hypothesis and von Mises equivalent strain at notch root were applied for lifetime prediction. Finally, the effectiveness of both methods is validated by comparing with experimental results

  19. Gear Crack Propagation Investigation

    Science.gov (United States)

    1995-01-01

    Reduced weight is a major design goal in aircraft power transmissions. Some gear designs incorporate thin rims to help meet this goal. Thin rims, however, may lead to bending fatigue cracks. These cracks may propagate through a gear tooth or into the gear rim. A crack that propagates through a tooth would probably not be catastrophic, and ample warning of a failure could be possible. On the other hand, a crack that propagates through the rim would be catastrophic. Such cracks could lead to disengagement of a rotor or propeller from an engine, loss of an aircraft, and fatalities. To help create and validate tools for the gear designer, the NASA Lewis Research Center performed in-house analytical and experimental studies to investigate the effect of rim thickness on gear-tooth crack propagation. Our goal was to determine whether cracks grew through gear teeth (benign failure mode) or through gear rims (catastrophic failure mode) for various rim thicknesses. In addition, we investigated the effect of rim thickness on crack propagation life. A finite-element-based computer program simulated gear-tooth crack propagation. The analysis used principles of linear elastic fracture mechanics, and quarter-point, triangular elements were used at the crack tip to represent the stress singularity. The program had an automated crack propagation option in which cracks were grown numerically via an automated remeshing scheme. Crack-tip stress-intensity factors were estimated to determine crack-propagation direction. Also, various fatigue crack growth models were used to estimate crack-propagation life. Experiments were performed in Lewis' Spur Gear Fatigue Rig to validate predicted crack propagation results. Gears with various backup ratios were tested to validate crack-path predictions. Also, test gears were installed with special crack-propagation gages in the tooth fillet region to measure bending-fatigue crack growth. From both predictions and tests, gears with backup ratios

  20. 不同片层组织对TC4-DT钛合金裂纹扩展行为的影响%Influence of Lamellar Microstructure on Fatigue Crack Propagation Behavior of TC4-DT of Damage Tolerance

    Institute of Scientific and Technical Information of China (English)

    祝力伟; 朱知寿; 王新南; 曹春晓

    2011-01-01

    The effects of lamellar microstructure on fatigue crack propagation behavior of damage tolerance for TC4-DT alloy plate were studied. Lamellar microstructure of TC4-DT alloy plate was obtained using different β heat treatment. Fatigue crack growth rate with fine and coarse lamellar structure were characterized. The experimental results show that in near threshold and low growth region of Paris region, microstructure with coarse lamellar has tremendous influence to the fatigue crack growth rate; Microstructure with fine lamellar structure had a lower fatigue crack growth rate and flexuous crack propagating route in the lamellar microstructure compared with the coarse lamellar structure. With the increasing of lamellar thickness, fatigue crack growth rate accelerated. In order to achieve an excellent damage tolerance, it is necessary to obtain fine lamellar structure with near β heat treatment by controlling the parameter strictly.%采用三种β热处理制度对TC4-DT钛合金板材进行热处理,调整合金的显微组织和损伤容限性能.利用金相显微镜对不同热处理制度下合金的片层组织特征参数进行观察,分析了不同片层组织对合金疲劳裂纹扩展速率的影响.结果表明,粗片层组织的疲劳裂纹扩展速率在近门槛区对组织比较敏感;在Paris区,细片层组织具有较低的疲劳裂纹扩展速率,随着片层厚度的增加,裂纹扩展速率加快;合金在β区短时保温具有更好的综合性能.

  1. STABLE OR UNSTABLE CRACK GROWTHS IN THIN ROCK PLATE UNDER COMPRESSION FOR PREDICTING BUCKLING ROCKBURST%岩爆的屈曲失稳机制

    Institute of Scientific and Technical Information of China (English)

    刘小明

    2003-01-01

    Underground cavern opening can cause the surrounding rock tangential compressive stress to raise rapidly. Such high compressive stress increase can result in some original pre-existing cracks growing parallelly to the free surface of the remaining rock. This paper presents a model of crack stable or unstable propagation under compressive stress in thin layers that are separated from the main rock mass due to crack growth. Based on this analysis of flat plate buckling,a rock burst mechanism is presented. Immediate and delayed rock burst mechanism are proposed to explain time dependency in brittle rock sub-critical crack growth under compression. Influence of free surface on the surface-parallel crack growth is also discussed.

  2. Hybrid use of steel and carbon-fiber reinforced concrete for monitoring of crack behavior

    OpenAIRE

    Ding, Yining; Han, Z; Zhang, Y; Azevedo, Cecília Maria

    2012-01-01

    In order to study the damage after concrete cracking, the influence of the combined use of steel fiber and carbon fiber on the conductivity and crack resistance of concrete beam under flexural loading were investigated. Carbon fiber and steel fiber were added as diphasic conductive materials to produce the electric conductive and ductile concrete. This paper reports the experimental and analytical work associated with establishing the crack width in relation to the fractional c...

  3. Use of ultrasonic back-reflection intensity for predicting the onset of crack growth due to low-cycle fatigue in stainless steel under block loading.

    Science.gov (United States)

    Islam, Md Nurul; Arai, Yoshio; Araki, Wakako

    2015-02-01

    The present study proposes the use of ultrasonic back-reflected waves for evaluating low cycle fatigue crack growth from persistent slip bands (PSBs) of stainless steel under block loading. Fatigue under high-low block loading changes the back-reflected intensity of the ultrasonic wave that emanates from the surface. Measuring the change in ultrasonic intensity can predict the start of crack growth with reasonable accuracy. The present study also proposes a modified constant cumulative plastic strain method and a PSB damage evolution model to predict the onset of crack growth under block loads.

  4. Apparent activation energy of subcritical crack growth of SiC/SiC composites at elevated temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Chou, Y.S.; Stackpoole, M.M.; Bordia, R. [Univ. of Washington, Seattle, WA (United States)] [and others

    1995-04-01

    The purpose of this study is to investigate the environmental effect of oxygen-containing gases on the subcritical crack growth of continuous fiber (Nicalon {open_quotes}SiC{close_quotes}) reinforced ceramic matrix (SiC) composites at elevated temperatures. This is a continuing project and the primary goal for this time period is to obtain an apparent activation energy for SiC/SiC materials with two different interfaces: carbon and boron nitride coatings. In the past six months, the authors have conducted studies of subcritical crack growth on SiC/SiC composite materials in a corrosive (O{sub 2}) as well as an inert (Ar) atmosphere for temperatures ranging from 800 to 1100{degree}C.

  5. Cyclic-load crack growth in ASME SA-105 grade II steel in high-pressure hydrogen at ambient temperature

    Science.gov (United States)

    Walter, R. J.; Chandler, W. T.

    1976-01-01

    ASME SA-105 Grade II steel, which is used in high-pressure hydrogen compressor systems, is similar to steels used or considered for use in high-pressure hydrogen storage vessels and pipelines. This paper summarizes the results of a program conducted to provide cyclic-load crack growth rate (da/dN) data for a fracture mechanics analysis of a 15,000 psi hydrogen compressor facility which contains pulse quieter and after-cooler separator vessels constructed of the ASME SA-105 Grade II steel. Included in the program were tests performed to assist in establishing operating procedures that could minimize the effect of hydrogen on crack growth rates during operation.

  6. A review of irradiation effects on LWR core internal materials - IASCC susceptibility and crack growth rates of austenitic stainless steels

    Science.gov (United States)

    Chopra, O. K.; Rao, A. S.

    2011-02-01

    Austenitic stainless steels (SSs) are used extensively as structural alloys in the internal components of light water reactor (LWR) pressure vessels because of their relatively high strength, ductility, and fracture toughness. However, exposure to neutron irradiation for extended periods changes the microstructure (radiation hardening) and microchemistry (radiation-induced segregation) of these steels, and degrades their fracture properties. Irradiation-assisted stress corrosion cracking (IASCC) is another degradation process that affects LWR internal components exposed to neutron radiation. The existing data on irradiated austenitic SSs were reviewed to evaluate the effects of key parameters such as material composition, irradiation dose, and water chemistry on IASCC susceptibility and crack growth rates of these materials in LWR environments. The significance of microstructural and microchemistry changes in the material on IASCC susceptibility is also discussed. The results are used to determine (a) the threshold fluence for IASCC and (b) the disposition curves for cyclic and IASCC growth rates for irradiated SSs in LWR environments.

  7. Influence of vacuum carburizing treatment on fatigue crack growth characteristic in DSG2

    Directory of Open Access Journals (Sweden)

    K. Nambu

    2015-10-01

    Full Text Available The aim of this research is to clarify the influence of vacuum carburizing on the fatigue-crack progress characteristics of DSG2 steel. The test specimen tempering material (QT material and vacuum carburizing material (VC material has been used. The fatigue-crack progress was examined by subjecting the samples to four-point bending. The loading-capacity fixed experiment was done using a maximum load of Pmax = 4000– 7000 N. The ΔK fixed experiment was done using a load of ΔK = 18–36 MPa√m. The crack progress speed of VC material fell, after the high crack progress speed was shown, and after it showed the minimum, it showed the tendency to go up again. This is considered to be what is depended on the compressive residual stress given to the carburizing layer. From this, it is thinkable that there is a crack progress depression effect in a carburizing layer. In VC material, a carburizing layer has a crack progress depression effect from a plunger-helix bottom to about 2.6 mm, and it turned out that it is larger than an effective carburizing layer. Moreover, in each ΔK, it was shown that depression effect revelation differs and the crack progress process accompanying it was able to be shown typically.

  8. 渗注锆酸盐对AZ31镁合金疲劳裂纹扩展速率的影响%Effects of the Zirconate Deposition on Fatigue Crack Growth Rate in AZ31 Magnesium Alloy

    Institute of Scientific and Technical Information of China (English)

    贺显聪; 王章忠; 白允强; 巴志新; 周衡志; 沈鸿烈

    2011-01-01

    The zirconate deposition behavior and effects of the zirconate on fatigue crack growth rate at the fatigue crack tip of AZ31 magnesium alloy under alternate loads were investigated. The morphology and components of the zirconate deposition at the fatigue crack tip were characterized by means of scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), and X-ray diffractometry (XRD), respectively. The stress intensity factors at the fatigue crack tips with and without zirconate deposition were measured by taking advantage of strain gauge. The results show that the zirconate (ZrxOy ZnxOy) films can be formed at the fatigue crack tips of AZ31 magnesium alloy. The stress intensity factor value is decreased about 40%, which effectively yields fatigue crack closure, reduce or even vanishes the fatigue crack growth rate.%研究交变载荷作用下,在AZ31镁合金疲劳裂纹尖端渗注锆酸盐的沉积行为及其对疲劳裂纹扩展速率的影响.用扫描电镜(SEM)、能谱仪(EDS)及X射线衍射仪(XRD)观察分析裂纹尖端的形貌和物相成分,采取贴应变片方法确定渗注锆酸盐前后应力强度因子的变化.结果表明:锆酸盐转化液能在AZ31镁合金疲劳裂纹尖端形成锆酸盐ZrxOyZnxOy覆层;渗注锆酸盐后裂纹尖端应力强度因子降低约40%,能有效增强疲劳裂纹闭合效应,降低或延滞其疲劳裂纹扩展速率.

  9. Indentation studies on Y[sub 2]O[sub 3]-stabilized ZrO[sub 2]; 2: Toughness determination from stable growth of indentation-induced cracks

    Energy Technology Data Exchange (ETDEWEB)

    Dransmann, G.W.; Steinbrech, R.W. (Inst. fuer Reaktorwerkstoffe, Juelich (Germany)); Pajares, A.; Guiberteau, F. (Univ. de Extremadura, Badajoz (Spain). Facultad de Ciencias); Dominguez-Rodriguez, A. (Univ. de Sevilla (Spain). Dept. de Fisic Materia Condensada); Heuer, A.H. (Case Western Reserve Univ., Cleveland, OH (United States). Dept. of Materials Science and Engineering)

    1994-05-01

    Stable indentation cracks were grown in four-point bend tests to study the fracture toughness of two Y[sub 2]O[sub 3]-stabilized ZrO[sub 2] ceramics containing 3 and 4 mol% Y[sub 2]O[sub 3]. By combining microscopic in situ stable crack growth observations at discrete stresses with crack profile measurements, the dependence of toughness on crack extension was determined from crack extension plots, which graphically separate the crack driving residual stress intensity and applied stress intensity factors. Both materials exhibit steeply rising R-curves, with a plateau toughness of 4.5 and 3.1 MPa[center dot]m[sup 1/2] for the 3- and 4-mol% materials, respectively. The magnitude of the plateau toughness reflects the fraction of tetragonal grain contributing to transformation toughening.

  10. Influence of the Peak Tensile Overload Cycles on the Fatigue Crack Growth o