WorldWideScience

Sample records for crack tip stress

  1. ANALYSIS ON THE COHESIVE STRESS AT HALF INFINITE CRACK TIP

    Institute of Scientific and Technical Information of China (English)

    王利民; 徐世烺

    2003-01-01

    The nonlinear fracture behavior of quasi-brittle materials is closely related with the cohesive force distribution of fracture process zone at crack tip. Based on fracture character of quasi-brittle materials, a mechanical analysis model of half infinite crack with cohesive stress is presented. A pair of integral equations is established according to the superposition principle of crack opening displacement in solids, and the fictitious adhesive stress is unknown function. The properties of integral equations are analyzed, and the series function expression of cohesive stress is certified. By means of the data of actual crack opening displacement, two approaches to gain the cohesive stress distribution are proposed through resolving algebra equation. They are the integral transformation method for continuous displacement of actual crack opening, and the least square method for the discrete data of crack opening displacement. The calculation examples of two approaches and associated discussions are given.

  2. Influence of fractality of fracture surfaces on stress and displacement fields at crack tips

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    In the classic theory of fracture mechanics,expressions for calculating the stresses and displacements in the vicinity of the crack tip are deduced on the basis of the assumption that a fracture surface is a smooth surface or that a crack is a smooth crack.In fact,the surface of a crack formed during the fracture is usually very irregular.So the real asymptotic form of the stress and displacement fields at the crack tip is different from the classic one.Considering the irregularity of a real fracture surface or a real crack profile,the crack is taken as a fractal one,and then the real asymptotic form at the crack tip is developed by applying Griffith’s energy balance principle and fractal geometry.Through the developed asymptotic form,it is discovered that the fractality of the crack reduces the stress singularity at the crack tip.

  3. Analysis of Crack Tip Stress of Transversal Crack on Slab Corner During Vertical-Horizontal Rolling Process by FEM

    Institute of Scientific and Technical Information of China (English)

    YU Hai-liang; LIU Xiang-hua; WANG Guo-dong

    2008-01-01

    Behavior of transversal crack notched on slab comer during vertical-horizontal rolling process was simula-ted by FEM. The crack tip stress in the whole rolling process was obtained. Influences of the friction coefficient, the initial crack size, the edger roll profile, and the groove fillet radii of grooved edger roll on crack tip stress were ana-lyzed. For vertical rolling, the tension stress appears at crack tip near the slab top surface and the compression stress appears at crack tip near the slab side surface for the flat edger roll; however, the compression stress appears at crack tip near the slab top surface and the tension stress appears at crack tip near the slab side surface in the exit stage for the grooved edger roll. For horizontal rolling, the tension stress appears at crack tip just at the exit stage for the flat edger roll, and the tension stress appears in whole rolling stage; the tension stress value near the slab side surface is much larger than that near the slab top surface for the grooved edger roll.

  4. Stress field near interface crack tip of double dissimilar orthotropic composite materials

    Institute of Scientific and Technical Information of China (English)

    LI Jun-lin; ZHANG Shao-qin; YANG Wei-yang

    2008-01-01

    In this paper, double dissimilar orthotropic composite materials interracial crack is studied by constructing new stress functions and employing the method of com- posite material complex. When the characteristic equations' discriminants △1 >0 and △2 > 0, the theoretical formula of the stress field and the displacement field near the mode I interface crack tip are derived, indicating that there is no oscillation and inter- embedding between the interfaces of the crack.

  5. Design study of hole positions and hole shapes for crack tip stress releasing

    DEFF Research Database (Denmark)

    Pedersen, Pauli

    2004-01-01

    results for isotropic material and in general study the influence of having orthotropic material. Optimal shapes are by no means circular, and we focus on the shape of a single hole centered at (or in front of) the crack tip. It is shown that the stress field at the crack boundary can be significantly......The method of hole drilling near or at the crack tip is often used in fatigue damage repair. From a design optimization point of view, two questions are posed: Where should the hole(s) be drilled? And is there a better shape of the hole than a circular one? For the first question, we extend earlier...

  6. Evaluation of Crack-tip Stress in Titanium Oxide Film Using Piezo-spectroscopy Methods

    Institute of Scientific and Technical Information of China (English)

    WAN Keshu; ZHU Wenliang; PEZZOTTI Giuseppe; MIAO Lei; TANEMURA Sakae

    2004-01-01

    The biaxial piezo-spectroscopic coefficient of 530 nm cathodoluminescence band of polycrystalline anatase titanium oxide film was measured using a local calibration procedure. Firstly, the crack-tip stress intensity factor in titanium oxide was measured from the crack opening displacement of a Vickers indentation crack using both Irwin's formula and Fett's formula, and the validity of these two formulas was evaluated. The obtained value was about Ktip =1 MPa √m. In such a brittle material, the fracture toughness can be considered to be very close to the stress intensity factor measured in an equilibrium indentation crack (Ktip= Kc). From the Ktip value, we calculated the stress distribution ahead of the crack tip using principles of linear elastic fracture mechanics. An important finding was that the cathodoluminescence 530 nm band that originated from excitons self-trapped on TiO6 octahedra, is sensitive to stress. Using the shift of this peak and the calculated stress from linear elastic fracture mechanics, the biaxial piezo-spectroscopic coefficient of this band was determined (40 nm/GPa with a 20% error rate). Using this piezo-spectroscopic coefficient, approximate stress maps can be collected of unknown stress fields within thin films with high spatial resolution into the scanning electron microscope. The present experiments provide a vivid example of quantitative micromechanical stress analysis by piezo-spectroscopic techniques.

  7. Effect of Stress on Corrosion at Crack Tip on Pipeline Steel in a Near-Neutral pH Solution

    Science.gov (United States)

    Yang, Yao; Cheng, Y. Frank

    2016-10-01

    In this work, the local corrosion at crack tip on an API 5L X46 pipeline steel specimens was investigated under various applied loads in a near-neutral pH solution. Electrochemical measurements, including potentiodynamic polarization and electrochemical impedance spectroscopy, combined with micro-electrochemical technique and surface characterization, were conducted to investigate the effect of stress on local anodic solution of the steel at the crack tip. The stress corrosion cracking of the steel was dominated by an anodic dissolution mechanism, while the effect of hydrogen was negligible. The applied load (stress) increased the corrosion rate at the crack tip, contributing to crack propagation. The deposit of corrosion products at the crack tip could protect somewhat from further corrosion. At sufficiently large applied loads such as 740 N in the work, it was possible to generate separated cathode and anode, further accelerating the crack growth.

  8. Effect of Stress on Corrosion at Crack Tip on Pipeline Steel in a Near-Neutral pH Solution

    Science.gov (United States)

    Yang, Yao; Cheng, Y. Frank

    2016-11-01

    In this work, the local corrosion at crack tip on an API 5L X46 pipeline steel specimens was investigated under various applied loads in a near-neutral pH solution. Electrochemical measurements, including potentiodynamic polarization and electrochemical impedance spectroscopy, combined with micro-electrochemical technique and surface characterization, were conducted to investigate the effect of stress on local anodic solution of the steel at the crack tip. The stress corrosion cracking of the steel was dominated by an anodic dissolution mechanism, while the effect of hydrogen was negligible. The applied load (stress) increased the corrosion rate at the crack tip, contributing to crack propagation. The deposit of corrosion products at the crack tip could protect somewhat from further corrosion. At sufficiently large applied loads such as 740 N in the work, it was possible to generate separated cathode and anode, further accelerating the crack growth.

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

    Directory of Open Access Journals (Sweden)

    E. Sgambitterra

    2014-10-01

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

  10. ASYMPTOTIC ELASTIC STRESS FIELD NEAR A BLUNT CRACK TIP IN AN ANISOTROPIC MATERIAL

    Institute of Scientific and Technical Information of China (English)

    HUANG; Zhen-yu(

    2001-01-01

    [1]Williams M L.Oh the stress distribution at the base of a stationary crack[J].ASME J App Mech,1957,24:109~114.[2]Creager M,Paris P C,Elastic field equations for blunt cracks with reference to stress corrosion crack-ing[J].Int J Fracture,1967,3:247~251[3]Kuang Z B.The stress field near the blunt crack tip and the fracture criterion[J].Engng Fracture Mech,1982,16:19~33.[4]Ting T C T.Anisotropic Elasticity and its applica-tion[M].London:Oxford University Press,1996.[5]Ting T C T ,Hwu C.Sextic formalism in anisotropic elasticity for almost non-semisimple matrix N[J].Int J S olids Structures,1988,24:65~76.[6]Yang X X,Shen S,Kuang Z B.The degenerate so-lution for piezothermoelastic materials[J].Eur J Mech A/Solid,1997,16:779~793[7]Hwu C,Yen W J.On the anisotropic elastic inclu-sions in plane elastostatics[J].ASME J A pp Mech,1993,60:626~632.[8]Lekhnitskii S G.Theory of elasticity of an anisotrop-ic elastic body[M].Moscow:Mir Publishers,1981.[9]Hoenig A.Near-tip behavior of a crack in a plane anisotropic elastic body[J].Engng Fracture Mech,1982,16:393~403.[10]匡震邦,马法尚。裂纹端部场[M].西安:西安交通大学出版社,2001

  11. 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.

  12. Estimation of transient creep crack-tip stress fields for SE(B) specimen under elastic-plastic-creep conditions

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Han Sang; Je, Jin Ho; Kim, Dong Jun; Kim, Yun Jae [Dept. of Mechanical Engineering, Korea University, Seoul (Korea, Republic of)

    2015-10-15

    This paper estimates the time-dependent crack-tip stress fields under elastic-plastic-creep conditions. We perform Finite-Element (FE) transient creep analyses for a Single-Edge-notched-Bend (SEB) specimen. We investigate the effect of the initial plasticity on the transient creep by systematically varying the magnitude of the initial step-load. We consider both the same stress exponent and different stress exponent in the power-law creep and plasticity to determine the elastic-plastic-creep behaviour. To estimation of the crack-tip stress fields, we compare FE analysis results with those obtained numerically formulas. In addition, we propose a new equation to predict the crack-tip stress fields when the creep exponent is different from the plastic exponent.

  13. Visualizing In Situ Microstructure Dependent Crack Tip Stress Distribution in IN-617 Using Nano-mechanical Raman Spectroscopy

    Science.gov (United States)

    Zhang, Yang; Mohanty, Debapriya P.; Tomar, Vikas

    2016-11-01

    Inconel 617 (IN-617) is a solid solution alloy, which is widely used in applications that require high-temperature component operation due to its high-temperature stability and strength as well as strong resistance to oxidation and carburization. The current work focuses on in situ measurements of stress distribution under 3-point bending at elevated temperature in IN-617. A nanomechanical Raman spectroscopy measurement platform was designed and built based on a combination of a customized open Raman spectroscopy (NMRS) system incorporating a motorized scanning and imaging system with a nanomechanical loading platform. Based on the scanning of the crack tip notch area using the NMRS notch tip, stress distribution under applied load with micron-scale resolution for analyzed microstructures is predicted. A finite element method-based formulation to predict crack tip stresses is presented and validated using the presented experimental data.

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

    DEFF Research Database (Denmark)

    Brincker, Rune

    intensity factors. In the special case of a constant Poisson ratio only 2 deformation intensity factors are needed. Closed form solutions are given both for a slowly growing crack and for a crack that is suddenly arrested at a point at the crack extension path. Two examples are studied; a stress boundary...... value problem, and a displacement boundary value problem. The results show that the stress intensity factors and the displacement intensity factors do not depend explicitly upon the velocity of the crack tip....

  15. Molecular dynamics simulations of stress-induced phase transformations and grain nucleation at crack tips in Fe

    Science.gov (United States)

    Latapie, A.; Farkas, D.

    2003-09-01

    The molecular dynamics simulation technique is used to study a stress-induced new grain formation mechanism at the crack tip of a nanocrystalline alpha-iron sample at temperatures ranging from 100 to 600 K. The stress-induced formation of new bcc grains, created inside existing grains, is found to occur through a metastable bcc to fcc phase transformation at the crack tip of the sample. A Nishiyama-Wassermann orientation relationship is found between the original bcc grain and the fcc phase and a Kurdjumov-Sachs orientation relationship is found between the new bcc grain created and the fcc transition phase. The new grain nucleation is observed to increase with increasing temperature and stacking faults associated with the fcc phase are observed at the higher temperatures.

  16. Microscopic study of stress effects around micro-crack tips using a non-contact stress-induced light scattering method

    Science.gov (United States)

    Sakata, Y.; Terasaki, N.; Nonaka, K.

    2016-09-01

    Fine-polishing techniques may cause micro-cracks under glass substrate surfaces. According to highly requirement from production field, a thermal stress-induced light scattering method (T-SILSM) was successfully developed for a non-contact inspection to detect the micro-cracks through changing in the intensity of light scattering accompanied by applying thermal stress at the responding position of the micro-cracks. In this study, in order to investigate that the origin of the measuring principle in microscopic order, a newly developed microscopic T-SILSM system with a rotation stage and a numerical simulation analysis were used to investigate the following; (1) the scattering points and surface in the micro-crack, (2) the stress concentration points in the micro-crack, and (3) the relationship between these information and the point in which intensity of the light scattering changes in the micro-crack through T-SILSM. Light scattering was observed at the responding position of the micro-crack with selectivity in the direction of laser irradiation even in the microscopic order. In addition, the position of the changes in the light scattering in was at both tips in the micro-crack, and it was consistent with the stress concentration point in the micro-crack. Therefore, it can be concluded that the intentional change in light scattering though T-SILSM is originated from light scattering at micro-crack and also from stress concentration and consecutive change in refractive index at both tips in micro-crack.

  17. Microscopic study of mode I crack tip deformation

    Institute of Scientific and Technical Information of China (English)

    Deshun Fan; Caifu Qian; Zhongjun Jiang

    2005-01-01

    By simulating edge dislocation emissions from a mode I crack tip along multiple inclined slip planes, the plastic zone and dislocation-free zone around the crack tip are obtained. It is found that the shape of the mode I plastic zone consists of two leaning forward loops which is better agreement with experimental observations. Except at the crack tip there are also stress peaks in front of the crack tip. A formula of the maximum peak stress as a function of the applied stress intensity factor and the friction stress has been regressed.

  18. Effects of plastic anisotropy on crack-tip behaviour

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang; Tvergaard, Viggo; Kuroda, Mitsutoshi

    2002-01-01

    loading remote from the crack-tip. In cases where the principal axes of the anisotropy are inclined to the plane of the crack it is found that the plastic zones as well as the stress and strain fields just around the blunted tip of the crack become non-symmetric. In these cases the peak strain...... on the blunted tip occurs off the center line of the crack, thus indicating that the crack may want to grow in a different direction. When the anisotropic axes are parallel to the crack symmetry is retained, but the plastic zones and the near-tip fields still differ from those predicted by standard isotropic...

  19. H2S Stress Corrosion Tests of Welded Joint for X65 Pipeline Steel and Finite Element Numerical Analysis of Crack Tip

    Institute of Scientific and Technical Information of China (English)

    金晓军; 霍立兴; 张玉凤; 白秉仁; 李小巍; 曹军

    2003-01-01

    The microstructure of welded joint is surveyed and the mechanical properties of X65 pipeline steel are studied in this paper, which provides experimental basis of performance effect on stress corrosion. H2S stress corrosion cracking (SCC) tests on the steel are carried out in the environment based on NACE TM-01-77 solution. The threshold stress intensity factor and crack propagation velocity for base metal and HAZ are obtained. The susceptibility of welded joint for X65 pipeline steel to H2S stress corrosion cracking is investigated. The programming package ANSYS of finite element model (FEM) is used to perform the three-dimensional elastic-plastic finite element analysis of WOL specimens. Stress field and concentration of hydrogen distribution property of the crack tip are obtained.

  20. Dynamical observations on the crack tip zone and stress corrosion of two-dimensional MoS2

    Science.gov (United States)

    Ly, Thuc Hue; Zhao, Jiong; Cichocka, Magdalena Ola; Li, Lain-Jong; Lee, Young Hee

    2017-01-01

    Whether and how fracture mechanics needs to be modified for small length scales and in systems of reduced dimensionality remains an open debate. Here, employing in situ transmission electron microscopy, atomic structures and dislocation dynamics in the crack tip zone of a propagating crack in two-dimensional (2D) monolayer MoS2 membrane are observed, and atom-to-atom displacement mapping is obtained. The electron beam is used to initiate the crack; during in situ observation of crack propagation the electron beam effect is minimized. The observed high-frequency emission of dislocations is beyond previous understanding of the fracture of brittle MoS2. Strain analysis reveals dislocation emission to be closely associated with the crack propagation path in nanoscale. The critical crack tip plastic zone size of nearly perfect 2D MoS2 is between 2 and 5 nm, although it can grow to 10 nm under corrosive conditions such as ultraviolet light exposure, showing enhanced dislocation activity via defect generation.

  1. Dynamical observations on the crack tip zone and stress corrosion of two-dimensional MoS2

    KAUST Repository

    Ly, Thuc Hue

    2017-01-18

    Whether and how fracture mechanics needs to be modified for small length scales and in systems of reduced dimensionality remains an open debate. Here, employing in situ transmission electron microscopy, atomic structures and dislocation dynamics in the crack tip zone of a propagating crack in two-dimensional (2D) monolayer MoS2 membrane are observed, and atom-to-atom displacement mapping is obtained. The electron beam is used to initiate the crack; during in situ observation of crack propagation the electron beam effect is minimized. The observed high-frequency emission of dislocations is beyond previous understanding of the fracture of brittle MoS2. Strain analysis reveals dislocation emission to be closely associated with the crack propagation path in nanoscale. The critical crack tip plastic zone size of nearly perfect 2D MoS2 is between 2 and 5 nm, although it can grow to 10 nm under corrosive conditions such as ultraviolet light exposure, showing enhanced dislocation activity via defect generation.

  2. 各向异性复合材料周期性I型裂纹尖端应力分析%Analysis of stress for mode I periodic cracks near crack tip of anisotropic composite materials

    Institute of Scientific and Technical Information of China (English)

    谢秀峰; 李俊林; 杨维阳

    2011-01-01

    对各向异性复合材料板的周期性I型裂纹尖端应力场进行了力学分析.通过求解一类线性偏微分方程的边值问题,引入Westergaard应力函数,采用复变函数方法及待定系数法,给出在无穷远处受对称载荷σ作用下,周期性Ⅰ型裂纹尖端的应力强度因子,推出了各向异性复合材料板周期性Ⅰ型裂纹尖端附近应力场的理论计算公式.%Mode-I stress fields near periodic cracks tip of anisotropic composite materials were analyzed. The boundary value problem of one kind of partial differential equation was solved. By introducing Westergaard' s stress function, using complex function method and approach of undetermined coefficients, the stress intensity factors at the crack tip for mode I periodic cracks were presented under symmetrical loading a. The stress field theoretical computing formulae of mode I periodic cracks near crack tip were obtained.

  3. Calculation of the crack tip opening displacement of a crack lying in a subsurface layer

    Science.gov (United States)

    Higashida, Y.; Kamada, K.

    1985-11-01

    Crack tip opening displacement of a crack lying parallel to a free surface is calculated by counting the number of dislocations emitted into the plastic zone from a crack tip. A discrete dislocation model was used to simulate the crack, while varying the strength of dislocations so as to satisfy the boundary condition. The result coincides numerically with the predictions made in a previous paper, in which the stress intensity factor appearing in a theory of bulk materials was replaced with the one which includes the surface correction.

  4. Fracture mechanics by three-dimensional crack-tip synchrotron X-ray microscopy.

    Science.gov (United States)

    Withers, P J

    2015-03-06

    To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping. Here, we explore how this can be achieved by bringing together synchrotron X-ray diffraction and tomographic imaging. Conventionally, these are undertaken on separate synchrotron beamlines; however, instruments capable of both imaging and diffraction are beginning to emerge, such as ID15 at the European Synchrotron Radiation Facility and JEEP at the Diamond Light Source. This review explores the concept of three-dimensional crack-tip X-ray microscopy, bringing them together to probe the crack-tip behaviour under realistic environmental and loading conditions and to extract quantitative fracture mechanics information about the local crack-tip environment. X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces. Time-lapse CT, besides providing information about the three-dimensional nature of the crack and its local growth rate, can also provide information as to the activation of extrinsic toughening mechanisms such as crack deflection, crack-tip zone shielding, crack bridging and crack closure. It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement. Finally, further opportunities for synchrotron X-ray microscopy are explored.

  5. Dynamic Strain Evolution around a Crack Tip under Steady- and Overloaded-Fatigue Conditions

    Directory of Open Access Journals (Sweden)

    Soo Yeol Lee

    2015-11-01

    Full Text Available We investigated the evolution of the strain fields around a fatigued crack tip between the steady- and overloaded-fatigue conditions using a nondestructive neutron diffraction technique. The two fatigued compact-tension specimens, with a different fatigue history but an identical applied stress intensity factor range, were used for the direct comparison of the crack tip stress/strain distributions during in situ loading. While strains behind the crack tip in the steady-fatigued specimen are irrelevant to increasing applied load, the strains behind the crack tip in the overloaded-fatigued specimen evolve significantly under loading, leading to a lower driving force of fatigue crack growth. The results reveal the overload retardation mechanism and the correlation between crack tip stress distribution and fatigue crack growth rate.

  6. Assisted crack tip flipping under Mode I thin sheet tearing

    DEFF Research Database (Denmark)

    Felter, Christian Lotz; Nielsen, Kim Lau

    2017-01-01

    such as slanting, cup-cone (rooftop), or cup-cup (bathtub) the flipping crack never settles in a steady-state as the near tip stress/strain field continuously change when the flip successively initiates and develops shear-lips. A recent experimental investigation has revealed new insight by exploiting 3D X...... type loading) on the tip of a slant Mode I crack can provoke it to flip to the opposite side. Both experiments and micro-mechanics based modeling support this hypothesis....

  7. Perfect elastic-viscoplastic field at mode Ⅰ dynamic propagating crack-tip

    Institute of Scientific and Technical Information of China (English)

    WANG Zhen-qing; LIANG Wen-yan; ZHOU Bo; SU Juan

    2007-01-01

    The viscosity of material is considered at propagating crack-tip. Under the assumption that the artificial viscosity coefficient is in inverse proportion to power law of the plastic strain rate, an elastic-viscoplastic asymptotic analysis is carried out for moving crack-tip fields in power-hardening materials under plane-strain condition. A continuous solution is obtained containing no discontinuities. The variations of numerical solution are discussed for mode Ⅰ crack according to each parameter. It is shown that stress and strain both possess exponential singularity. The elasticity, plasticity and viscosity of material at crack-tip only can be matched reasonably under linear-hardening condition. And the tip field contains no elastic unloading zone for mode Ⅰ crack. It approaches the limiting case, crack-tip is under ultra-viscose situation and energy accumulates, crack-tip begins to propagate under different compression situations.

  8. Effects of crack tip geometry on dislocation emission and cleavage A possible path to enhanced ductility

    CERN Document Server

    Schiøtz, J; Carlsson, A E

    1997-01-01

    We present a systematic study of the effect of crack blunting on subsequent crack propagation and dislocation emission. We show that the stress intensity factor required to propagate the crack is increased as the crack is blunted by up to thirteen atomic layers, but only by a relatively modest amount for a crack with a sharp 60$^\\circ$ corner. The effect of the blunting is far less than would be expected from a smoothly blunted crack; the sharp corners preserve the stress concentration, reducing the effect of the blunting. However, for some material parameters blunting changes the preferred deformation mode from brittle cleavage to dislocation emission. In such materials, the absorption of preexisting dislocations by the crack tip can cause the crack tip to be locally arrested, causing a significant increase in the microscopic toughness of the crack tip. Continuum plasticity models have shown that even a moderate increase in the microscopic toughness can lead to an increase in the macroscopic fracture toughne...

  9. 正交异性复合材料板Ⅰ型三裂纹尖端场分析%Crack-Tip Stress Analysis on Three Cracks of Orthotropic Composite Materials for Mode Ⅰ

    Institute of Scientific and Technical Information of China (English)

    王丽娟; 张雪霞; 韩桂花

    2015-01-01

    研究了正交异性复合材料板三裂纹的平面问题。通过复合材料断裂中的力学模型,将此问题归结为一类偏微分方程的边值问题,构造保角映射,将均匀分布三裂纹映射为复平面上的平行周期裂纹,通过引入适当的westergaard应力函数,采用复变函数方法和待定系数法对复合材料Ⅰ型平行周期裂纹尖端的应力场进行了力学分析。最后再利用该保角映射的逆变换,将平行周期裂纹尖端的应力场变换到原均匀分布三裂纹的应力场,得到了远场受均匀分布载荷作用下的应力场和位移场的解析解。研究结果为结构和材料的强度设计提供了有意义的参考。%This paper studies the plane problems about three cracks of orthotropic composite materials. Plane frac-ture problems of composite materials can be converted into a class of boundary value problems of partial differential equation by fracture mechanics model of composite materials. It can be mapped to cracks parallel to the cycle on the complex plane by introducing the appropriate conformal mapping. The right westergaard stress function,together with the complex function method and the method of undetermined coefficients,is properly chosen to deduce the crack-tip stress on cycle of parallel cracks of orthotropic composite materials for mode Ⅰ. The parallel cycle uni-form distribution of crack-tip stress field can be transformed into the original three of stress field of crack by using the inverse transformation of conformal mapping,far field of analytical solutions of stress field and displacement field was obtained under the uniformly distributed load. The results provides a meaningful reference to the strength design of structure and material.

  10. Quasi-static crack tip fields in rate-sensitive FCC single crystals

    Indian Academy of Sciences (India)

    P Biswas; R Narasimhan

    2012-02-01

    In this work, the effects of loading rate, material rate sensitivity and constraint level on quasi-static crack tip fields in a FCC single crystal are studied. Finite element simulations are performed within a mode I, plane strain modified boundary layer framework by prescribing the two term $(K −T)$ elastic crack tip field as remote boundary conditions. The material is assumed to obey a rate-dependent crystal plasticity theory. The orientation of the single crystal is chosen so that the crack surface coincides with the crystallographic (010) plane and the crack front lies along $[10\\bar{1}]$ direction. Solutions corresponding to different stress intensity rates $\\dot{K}$, -stress values and strain rate exponents are obtained. The results show that the stress levels ahead of the crack tip increase with $\\dot{K}$ which is accompanied by gradual shrinking of the plastic zone size. However, the nature of the shear band patterns around the crack tip is not affected by the loading rate. Further, it is found that while positive -stress enhances the opening and hydrostatic stress levels ahead of crack tip, they are considerably reduced with imposition of negative -stress. Also, negative -stress promotes formation of shear bands in the forward sector ahead of the crack tip and suppresses them behind the tip.

  11. Crack-tip field on mode Ⅱ interface crack of double dissimilar orthotropic composite materials

    Institute of Scientific and Technical Information of China (English)

    Xue-xia ZHANG; Xiao-chao CUI; Wei-yang YANG; Jun-lin LI

    2009-01-01

    Two systems of non-homogeneous linear equations with 8 unknowns are obtained. This is done by introducing two stress functions containing 16 undetermined coefficients and two real stress singularity exponents with the help of boundary conditions. By solving the above systems of non-homogeneous linear equations, the two real stress singularity exponents can be determined when the double material parameters meet certain conditions. The expression of the stress function and all coefficients are obtained based on the uniqueness theorem of limit. By substituting these parameters into the corresponding mechanics equations, theoretical solutions to the stress intensity factor, the stress field and the displacement field near the crack tip of each material can be obtained when both discriminants of the characteristic equations are less than zero. Stress and displacement near the crack tip show mixed crack characteristics without stress oscillation and crack surface overlapping. As an example, when the two orthotropic materials are the same, the stress singularity exponent, the stress intensity factor, and expressions for the stress and the displacement fields of the orthotropic single materials can be derived.

  12. Crack tip shielding and anti-shielding effects of parallel cracks for a superconductor slab under an electromagnetic force

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Zhi Wen; Zhou, You He [Ministry of Education, Singapore (China); Lee, Kang Yong [Yonsei University, Seoul (Korea, Republic of)

    2012-02-15

    In this letter, the shielding or anti-shielding effect is firstly applied to obtain the behavior of two parallel cracks in a two-dimensional type-II superconducting under electromagnetic force. Fracture analysis is performed by the finite element method and the magnetic behavior of superconductor is described by the critical state Bean model. The stress intensity factors at the crack tips can be obtained and discussed for decreasing field after zero-field cooling. The shielding or anti-shielding effect at the crack tips depend on the distance between two parallel cracks and the crack length. The results indicate that the shielding effects of the two parallel cracks increase when the distance between the two parallel cracks decreases. It can be also obtained that the superconductors with shorter cracks has more remarkable shielding effect than those with longer cracks.

  13. Inhibiting Corrosion Cracking: Crack Tip Chemistry and Physics.

    Science.gov (United States)

    1986-03-14

    5 5. Swuzary 113 Rferences 114 wl NO 4L iv . List of Figuring 1. Microipette pulling machine . 29 2. Anodic polarization of 7075-T6 Al alloy in dilute...environment has a strong effect on microplastic behavior at the tip of a fatigue crack. Stolz and Pelloux suggest that nitrate ion competes with chloride...Crystalline Na2 N 20 29H20 precipitates when the filtrate is placed in a vacunm desiccator over sulfuric acid. The filtered precipitate is washed

  14. Atomistic observation of a crack tip approaching coherent twin boundaries.

    Science.gov (United States)

    Liu, L; Wang, J; Gong, S K; Mao, S X

    2014-03-18

    Coherent twin boundaries (CTBs) in nano-twinned materials could improve crack resistance. However, the role of the CTBs during crack penetration has never been explored at atomic scale. Our in situ observation on nano-twinned Ag under a high resolution transmission electron microscope (HRTEM) reveals the dynamic processes of a crack penetration across the CTBs, which involve alternated crack tip blunting, crack deflection, twinning/detwinning and slip transmission across the CTBs. The alternated blunting processes are related to the emission of different types of dislocations at the crack tip and vary with the distance of the crack tip from the CTBs.

  15. Crack tip dislocations observed by TEM-tomography in silicon single crystals

    Science.gov (United States)

    Sadamatsu, Sunao; Tanaka, Masaki; Honda, Masaki; Higashida, Kenji

    2010-07-01

    3D observations of dislocations at a crack tip were attempted by transmission electron microscopy and computed tomography in order to reveal the 3D structure of dislocations emitted around a crack tip. {011} cracks were introduced into a (001) silicon single crystal wafer by using an indentation method at room temperature. The specimens indented were heated and kept at high temperatures to introduce dislocations from the crack tip. The specimen holder was tilted ±31° by 2° step and dislocation images were taken at every step. The diffraction vector was kept nearly 220 during the tilting operation. The Burgers vectors of the dislocation segments were determined, which included the signs of Burgers vectors. The dislocations observed here were those which accommodate mode II stress intensity around the crack tip. 3D observations using electron tomography reveal these complex crucial processes around the crack tip, which should contribute to understanding the dislocation process improving fracture toughness of crystalline materials.

  16. New theory for Mode I crack-tip dislocation emission

    Science.gov (United States)

    Andric, Predrag; Curtin, W. A.

    2017-09-01

    A material is intrinsically ductile under Mode I loading when the critical stress intensity KIe for dislocation emission is lower than the critical stress intensity KIc for cleavage. KIe is usually evaluated using the approximate Rice theory, which predicts a dependence on the elastic constants and the unstable stacking fault energy γusf for slip along the plane of dislocation emission. Here, atomistic simulations across a wide range of fcc metals show that KIe is systematically larger (10-30%) than predicted. However, the critical (crack tip) shear displacement is up to 40% smaller than predicted. The discrepancy arises because Mode I emission is accompanied by the formation of a surface step that is not considered in the Rice theory. A new theory for Mode I emission is presented based on the ideas that (i) the stress resisting step formation at the crack tip creates ;lattice trapping; against dislocation emission such that (ii) emission is due to a mechanical instability at the crack tip. The new theory is formulated using a Peierls-type model, naturally includes the energy to form the step, and reduces to the Rice theory (no trapping) when the step energy is small. The new theory predicts a higher KIe at a smaller critical shear displacement, rationalizing deviations of simulations from the Rice theory. Specific predictions of KIe for the simulated materials, usually requiring use of the measured critical crack tip shear displacement due to complex material non-linearity, show very good agreement with simulations. An analytic model involving only γusf, the surface energy γs, and anisotropic elastic constants is shown to be quite accurate, serves as a replacement for the analytical Rice theory, and is used to understand differences between Rice theory and simulation in recent literature. The new theory highlights the role of surface steps created by dislocation emission in Mode I, which has implications not only for intrinsic ductility but also for crack tip

  17. 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...

  18. MODE I AND MODE II CRACK TIP ASYMPTOTIC FIELDS WITH STRAIN GRADIENT EFFECTS

    Institute of Scientific and Technical Information of China (English)

    陈少华; 王自强

    2001-01-01

    The strain gradient effect becomes significant when the size of fracture process zone around a crack tip is comparable to the intrinsic material length l,typically of the order of microns. Using the new strain gradient deformation theory given by Chen and Wang, the asymptotic fields near a crack tip in an elastic-plastic material with strain gradient effects are investigated. It is established that the dominant strain field is irrotational. For mode I plane stress crack tip asymptotic field,the stress asymptotic field and the couple stress asymptotic field can not exist simultaneously. In the stress dominated asymptotic field, the angular distributions of stresses are consistent with the classical plane stress HRR field; In the couple stress dominated asymptotic field, the angular distributions of couple stresses are consistent with that obtained by Huang et al. For mode II plane stress and plane strain crack tip asymptotic fields, only the stress-dominated asymptotic fields exist. The couple stress asymptotic field is less singular than the stress asymptotic fields. The stress asymptotic fields are the same as mode II plane stress and plane strain HRR fields,respectively. The increase in stresses is not observed in strain gradient plasticity for mode I and mode II, because the present theory is based only on the rotational gradient of deformation and the crack tip asymptotic fields are irrotational and dominated by the stretching gradient.

  19. Experimental characterization of fatigue crack tip processes

    Science.gov (United States)

    Lankford, J.; Leverant, G. R.

    1985-01-01

    Many analytical models have been proposed to describe the physical processes attendant to a fatigue crack tip, as well as the rate at which fatigue cracks grow. By applying advanced experimental methods (such as electron channeling, stereoimaging, and in-situ cyclic loading in an SEM) to a broad range of structural materials, it has been shown that it is possible to critically assess the physical assumptions incorporated into the models. Refinements in existing models and the development of new ones have resulted. New insights into materials' behavior are providing guidelines for improving the fatigue resistance of structural alloys. In the near future, even more advanced experimental methods, such as high temperature SEM stages and small angle neutron scattering, will be available to study creep/fatigue interactions in metals and ceramics.

  20. Near tip strain evolution of a growing fatigue crack

    Directory of Open Access Journals (Sweden)

    M.-L. Zhu

    2015-07-01

    Full Text Available Near tip full-field strains in a growing fatigue crack have been studied in situ using the Digital Image Correlation (DIC technique in a compact tension specimen of stainless steel 316L under tension-tension cyclic loading. An error analysis of displacements and strains has been carried out, and the results show that the precision of displacements and strains in the wake of the crack is worse than that in front of the crack. A method for the determination of crack tip location is proposed for the DIC analysis. Strain ratchetting is observed ahead of the growing fatigue crack tip and found to be dependent on the distance to the crack tip; whilst normal strains appear to stabilise behind the crack tip.

  1. Analysis of Stress for Mode Ⅱ Periodic Crack Tip of Anisotropic Composite Materials%各向异性复合材料周期性Ⅱ型裂纹尖端应力分析

    Institute of Scientific and Technical Information of China (English)

    陈云; 谢秀峰; 李俊林

    2011-01-01

    对各向异性复合材料板的周期性Ⅱ型裂纹尖端应力场进行了有关的力学分析,通过求解一类线性偏微分方程的边值问题,引入Westergaard应力函数、采用复变函数方法及待定系数法,给出在无穷远处受对称载荷τ作用下,周期性Ⅱ型裂纹尖端的应力强度因子,推出了各向异性复合材料板周期性Ⅱ型裂纹尖端附近应力场的理论计算公式。%The stress fields near Mode-Ⅱ periodic cracks tip of anisotropic composite materials were analyzed.The boundary value problem of one kind of partial differential equation was solved.The stress intensity factors at the crack tip for mode Ⅱ periodic cracks were presented under symmetric loading by introducing Westergaard's stress function and using complex function method and the approach of undetermined coefficients.The theoretical formulae for computing stress field of mode II periodic crack tips were obtained.

  2. ANALYSIS OF CRACK-TIP SINGULARITIES FOR AN INTERFACIAL PERMEABLE CRACK IN METAL/PIEZOELECTRIC BIMATERIALS

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    By modeling metal as a special piezoelectric material with extremely small piezoelectricity and extremely large permittivity, we have obtained the analytical solutions for an interfacial permeable crack in metal/piezoelectric bimaterials by means of the generalized Stroh formalism.The analysis shows that the stress fields near a permeable interfacial crack tip are usually with three types of singularities: r-1/2±iε and r-1/2. Further numerical calculation on the oscillatory index ε are given for 28 types of metal/piezoelectric bimaterials combined by seven commercial piezoelectric materials: PZT-4, BaTiO3, PZT-5H, PZT-6B, PZT-7A, P-7 and PZT-PIC 151 and four metals: copper, silver, lead and aluminum, respectively. The explicit expressions of the crack tip energy release rate (ERR) and the crack tip generalized stress intensity factors (GSIF) are obtained. It is found that both the ERR and GSIF are independent of the electric displacement loading, although they seriously depends on the mechanical loadings.

  3. Crack tip fracture toughness of base glasses for dental restoration glass-ceramics using crack opening displacements.

    Science.gov (United States)

    Deubener, J; Höland, M; Höland, W; Janakiraman, N; Rheinberger, V M

    2011-10-01

    The critical stress intensity factor, also known as the crack tip toughness K(tip), was determined for three base glasses, which are used in the manufacture of glass-ceramics. The glasses included the base glass for a lithium disilicate glass-ceramic, the base glass for a fluoroapatite glass-ceramic and the base glass for a leucite glass-ceramic. These glass-ceramic are extensively used in the form of biomaterials in restorative dental medicine. The crack tip toughness was established by using crack opening displacement profiles under experimental conditions. The crack was produced by Vickers indentation. The crack tip toughness parameters determined for the three glass-ceramics differed quite significantly. The crack tip parameters of the lithium disilicate base glass and the leucite base glass were higher than that of the fluoroapatite base glass. This last material showed glass-in-glass phase separation. The discussion of the results clearly shows that the droplet glass phase is softer than the glass matrix. Therefore, the authors conclude that a direct relationship exists between the chemical nature of the glasses and the crack tip parameter.

  4. The role of crack tip plasticity on the propagation of fracture in rocks and other brittle solids

    Science.gov (United States)

    Borja, R. I.; Rahmani, H.; Liu, F.; Aydin, A.

    2009-12-01

    Small-scale plastic yielding around a crack tip plays a key role in the propagation of fractures in brittle materials such as rocks. Linear elastic fracture mechanics (LEFM) quantifies the asymptotic strain field around a crack tip under the assumptions of linear elasticity and infinitesimal deformation. However, no material can withstand an infinite stress, and plastic yielding is expected to take place near and around a crack tip. Plastic yielding governs the extension of an existing crack, as well as determines the direction of propagation of splay cracks. Unlike in LEFM, however, no closed-form solution is available for the asymptotic strain field near and around a crack tip in the presence of inelastic deformation. In this work, we resort to finite element modeling for capturing plastic yielding and asymptotic strain field near and around a crack tip. Novel features of the modeling include an enhanced finite element around the crack tip that captures the expected asymptotic strain field, and an elastoplastic constitutive law for near-tip yielding. Through numerical simulations, we infer the likely orientation of splay cracks from the prevailing crystal orientation and overall stress field around the crack tip. We also compare the angular variation of the crack-tip enrichment function in the presence of plastic yielding with the closed-form solution derived from LEFM for different loading conditions and elastoplastic bulk constitutive laws.

  5. 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...

  6. Crack-tip constraints of through-wall cracked pipes and its similarity to curved wide plates

    Energy Technology Data Exchange (ETDEWEB)

    Jang, Youn Young; Huh, Nam Su [Dept. of Mechanical System Design Engineering, Seoul National Univ. of Science and Technology, Seoul (Korea, Republic of); Jeong, Jae Uk [Global Turbine R and D Center, Doosan Heavy Industries and Construction, Changwon (Korea, Republic of); Kim, Ki Seok; Cho, Woo Yeon [Energy Infrastructure Research Group, Steel Solution Center, POSCO, Incheon (Korea, Republic of)

    2016-10-15

    In the present study, the effects of pipe geometries, material properties and loading conditions on crack-tip constraints of pipes with circumferential Through-wall crack (TWC) were investigated via systematic 3-dimensional (3-D) Finite element (FE) analyses. The crack-tip constraints were quantified by Q-stress, and to characterize the elastic-plastic strain hardening material behavior, Ramberg-Osgood (R-O) material was employed. Based on the FE results, it was observed that crack-tip constraints of pipes with TWC were dependent on crack length and thickness of pipe, however, the effects of each variables decreased as either thickness of pipe becomes thinner or crack length becomes longer. Moreover, the effects loading modes on Q-stresses for thin-walled pipes with TWC are negligible. Finally, the present Q-stresses of pipes were compared with those of Curved wide plate (CWP) in tension to address the similarity of crack-tip constraints between pipe and CWP, which could be used to produce the CWP to measure the fracture toughness of pipes accurately.

  7. The failure criterion based on hydrogen distribution ahead of the fatigue crack tip

    Directory of Open Access Journals (Sweden)

    Yu. G. Matvienko

    2013-04-01

    Full Text Available The hydrogen effect on the fracture toughness and fatigue crack growth behaviour in the martensitic high strength steel is investigated. The secondary ion mass spectrometry method has been employed to analyse the distribution of hydrogen concentration in the zone of the crack tip and at its edges. Changes in hydrogen concentration are observed in the vicinity of the propagating crack tip and at a remote site. The hydrogen peak is reduced and moves away from the fatigue crack tip with the increase of the maximum stress intensity factor . The concept of damage evolution is used to explain fatigue crack propagation in connection with the hydrogen redistribution ahead of the crack tip. The physical failure criterion based on the hydrogen peak in the vicinity of the fatigue crack tip and the maximum stress intensity factor has been proposed. The criterion reflects changes in the hydrogen peak which resulted from the hydrogen redistribution due to the increase of the maximum stress intensity factor as the crack length increases under fatigue loading.

  8. Elastic-viscoplastic field at mixed-mode interface crack-tip under compression and shear

    Institute of Scientific and Technical Information of China (English)

    梁文彦; 王振清; 刘方; 刘晓铎

    2014-01-01

    For a compression-shear mixed mode interface crack, it is difficult to solve the stress and strain fields considering the material viscosity, the crack-tip singularity, the frictional effect, and the mixed loading level. In this paper, a mechanical model of the dynamic propagation interface crack for the compression-shear mixed mode is proposed using an elastic-viscoplastic constitutive model. The governing equations of propagation crack interface at the crack-tip are given. The numerical analysis is performed for the interface crack of the compression-shear mixed mode by introducing a displacement function and some boundary conditions. The distributed regularities of stress field of the interface crack-tip are discussed with several special parameters. The final results show that the viscosity effect and the frictional contact effect on the crack surface and the mixed-load parameter are important factors in studying the mixed mode interface crack-tip fields. These fields are controlled by the viscosity coefficient, the Mach number, and the singularity exponent.

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

    Directory of Open Access Journals (Sweden)

    Lijun Zhang

    2014-01-01

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

  10. High-voltage electron-microscopical observation of crack-tip dislocations in silicon crystals

    Energy Technology Data Exchange (ETDEWEB)

    Tanaka, Masaki [Department of Materials Science and Engineering, Kyushu University, 6-10-1 Higashi-ku Fukuoka 812-8581 (Japan)]. E-mail: masaki@dera.zaiko.kyushu-u.ac.jp; Higashida, Kenji [Department of Materials Science and Engineering, Kyushu University, 6-10-1 Higashi-ku Fukuoka 812-8581 (Japan)

    2005-07-25

    Crack-tip dislocations in silicon single crystals were observed by high-voltage electron microscopy. Cracks were introduced into silicon wafers at room temperature by a Vickers indenter. The indented specimens were annealed at 823 K in order to activate dislocation emission from the crack tip under the residual stress due to the indentation. In the specimen without annealing, no dislocations were observed around the crack. On the other hand, in the specimen after the annealing, the aspect of the early stage of dislocation emission was observed, where dislocations were emitted not as a perfect dislocation but as a partial dislocation in the hinge-type plastic zone. Prominent dislocation arrays that were emitted from a crack tip were also observed, and they were found to be of shielding type, which increases the fracture toughness of those crystals.

  11. Mode I and mixed mode crack-tip fields in strain gradient plasticity

    DEFF Research Database (Denmark)

    Goutianos, Stergios

    2011-01-01

    Strain gradients develop near the crack-tip of Mode I or mixed mode cracks. A finite strain version of the phenomenological strain gradient plasticity theory of Fleck–Hutchinson (2001) is used here to quantify the effect of the material length scales on the crack-tip stress field for a sharp...... stationary crack under Mode I and mixed mode loading. It is found that for material length scales much smaller than the scale of the deformation gradients, the predictions converge to conventional elastic–plastic solutions. For length scales sufficiently large, the predictions converge to elastic solutions....... Thus, the range of length scales over which a strain gradient plasticity model is necessary is identified. The role of each of the three material length scales, incorporated in the multiple length scale theory, in altering the near-tip stress field is systematically studied in order to quantify...

  12. Analyzing crack-tip dislocations and their shielding effect on fracture toughness

    Energy Technology Data Exchange (ETDEWEB)

    Higashida, K. [Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Fukuoka 819-0395 (Japan)], E-mail: higasida@zaiko.kyushu-u.ac.jp; Tanaka, M. [Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Fukuoka 819-0395 (Japan); Hartmaier, A. [Department of Materials Science and Engineering, University Erlangen-Nuernberg, Martensstrasse 5, 91058 Erlangen (Germany); Hoshino, Y. [Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Fukuoka 819-0395 (Japan)

    2008-06-15

    With the aim of experimental clarification of the interaction between a crack and dislocations, crack-tip dislocations in two kinds of plastic zones in silicon crystals were directly observed by high-voltage electron microscopy to analyse by their detail characterisation. Three-dimensional analysis on crack-dislocation interaction revealed that they were shielding type dislocations in both 45 deg.-shear-type and hinge-type plastic zones, which accommodate mainly mode I stress intensity at the crack tip. The crack-tip shielding fields due to dislocations also have been visualised by photoelasticity. In specimens without pre-deformation, photoelastic images due to the mode I crack-tip field were observed when an external load was applied at room temperature. In specimens pre-deformed at high temperatures, photoelastic images corresponding to the dislocation shielding were observed. The shielding field has an effect of accommodating the tensile stress concentration due to the applied load, which increases the critical stress intensity factor for crack extension.

  13. Finite deformation analysis of crack tip opening in elastic-plastic materials and implications for fracture initiation

    Energy Technology Data Exchange (ETDEWEB)

    McMeeking, R M

    1976-05-01

    Analyses of the stress and strain fields around smoothly blunting crack tips in both non-hardening and hardening elastic-plastic materials, under contained plane strain yielding and subject to mode I opening loads, have been carried out by a finite element method suitably formulated to admit large geometry changes. The results include the crack tip shape and near-tip deformation field, and the crack tip opening displacement has been related to a parameter of the applied load, the J-integral. The hydrostatic stresses near the crack tip are limited due to the lack of constraint on the blunted tip, limiting achievable stress levels except in a very small region around the crack tip in power law hardening materials. The J-integral is found to be path independent except very close to the crack tip in the region affected by the blunted tip. Models for fracture are discussed in the light of these results including one based on the growth of voids. The rate of void growth near the tip in hardening materials seems to be little different from the rate in non-hardening materials when measured in terms of crack tip opening displacement, which leads to a prediction of higher toughness in hardening materials. It is suggested that improvement of this model would follow from better understanding of void-void and void-crack coalescence and void nucleation, and some criteria and models for these are discussed. The implications of the finite element results for fracture criteria based on critical stress, strain or both are discussed with respect to transition of fracture mode and the angle of initial crack growth. Localization of flow is discussed as a possible fracture model and as a model for void-crack coalescence.

  14. Dynamic stress intensity factor KⅢ and dynamic crack propagation characteristics of anisotropic materials

    Institute of Scientific and Technical Information of China (English)

    GAO Xin; WANG Han-gong; KANG Xing-wu

    2008-01-01

    Based on the mechanics of anisotropic materials,the dynamic propagation problem of a mode Ⅲ crack in an infinite anisotropic body is investigated.Stress,strain and displacement around the crack tip are expressed as an analytical complex function,which can be represented in power series.Constant coefficients of series are determined by boundary conditions.Expressions of dynamic stress intensity factors for a mode Ⅲ crack are obtained.Components of dynamic stress,dynamic strain and dynamic displacement around the crack tip are derived.Crack propagation characteristics are represented by the mechanical properties of the anisotropic materials,i.e.,crack propagation velocity M and the parameter α.The faster the crack velocity is,the greater the maximums of stress components and dynamic displacement components around the crack tip are.In particular,the parameter α affects stress and dynamic displacement around the crack tip.

  15. Crack Tip Plasticity Associated with Corrosion Assisted Fatigue.

    Science.gov (United States)

    1982-11-15

    growing. The model presented is very similar to those previously developed by Antolovich , Saxena and I Chanani[83 and by Lanteigne and BailonE9] but...in crack tip plasticity associated with environment. The model used here is conceptually similar to those formulated by * Antolovich , et al,[ and...Lankford, J. ’Fatigue-Crack-Tip I Plastic Strains by the Stereoimaging Technique’ Exp. Mech. 1980 20, 3 134-139. 8. Antolovich , S. D., Saxena, A., and

  16. The Relationship Between Crack-Tip Strain and Subcritical Cracking Thresholds for Steels in High-Pressure Hydrogen Gas

    Science.gov (United States)

    Nibur, Kevin A.; Somerday, Brian P.; Marchi, Chris San; Foulk, James W.; Dadfarnia, Mohsen; Sofronis, Petros

    2013-01-01

    Threshold stress intensity factors were measured in high-pressure hydrogen gas for a variety of low alloy ferritic steels using both constant crack opening displacement and rising crack opening displacement procedures. Thresholds for crack extension under rising displacement, K THi, for crack extension under constant displacement, K_{{THi}}^{*} , and for crack arrest under constant displacement K THa, were identified. These values were not found to be equivalent, i.e. K THi assisted fracture mechanism was determined to be strain controlled for all of the alloys in this study, and the micromechanics of strain controlled fracture are used to explain the observed disparities between the different threshold measurements. K THa and K THi differ because the strain singularity of a stationary crack is stronger than that of a propagating crack; K THa must be larger than K THi to achieve equivalent crack tip strain at the same distance from the crack tip. Hydrogen interacts with deformation mechanisms, enhancing strain localization and consequently altering both the nucleation and growth stages of strain controlled fracture mechanisms. The timing of load application and hydrogen exposure, i.e., sequential for constant displacement tests and concurrent for rising displacement tests, leads to differences in the strain history relative to the environmental exposure history and promotes the disparity between K_{{THi}}^{*} and K THi. K THi is the only conservative measurement of fracture threshold among the methods presented here.

  17. Stress Intensity of Antiplane Conjugate Cracks in Cubic Quasicrystal

    Institute of Scientific and Technical Information of China (English)

    ZHANG Lei

    2008-01-01

    Based on the theory of Muskhelishvili, the general solutions for stress and strain of conjugate cracks in cubic quasicrystal are obtained, with which the stress intensity factors of cubic quasicrystal at crack tips and the stress distribution functions of phonon and phason fields are given. The results show that though phason field is coupled with phonon field by constitutive equations, the stress intensity factors are not coupled with any other factors.

  18. 3-D structures of crack-tip dislocations and their shielding effect revealed by electron tomography.

    Science.gov (United States)

    Tanaka, Masaki; Honda, Masaki; Sadamatsu, Sunao; Higashida, Kenji

    2010-08-01

    Three-dimensional structures of crack-tip dislocations in silicon crystals have been examined by combining scanning transmission electron microscopy and computed tomography. Cracks were introduced by a Vickers hardness tester at room temperature, and the sample was heated at 823 K for 1 h in order to introduce dislocations around the crack tips. Dislocation segments cut out from loops were observed around the crack tip, the three-dimensional structure of which was characterized by using by electron tomography. Their Burgers vectors including the sings were also determined by oscillating contrasts along dislocations. In order to investigate the effect of the dislocations on fracture behaviours, local stress intensity factor due to one dislocation was calculated, which indicates the dislocations observed were shielding type to increase fracture toughness.

  19. Stress distribution and effective stress intensity factor of a blunt crack after dislocation emission

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The stress fields induced by a dislocation and its image dislocations around a narrow elliptic void are formulated. Based on the solution, the stress distribution and effective stress intensity factor of a blunt (elliptic) crack were calculated under mode I constant loading. The results show that a dislocation-free zone (DFZ) is formed after dislocation emission. There exists a second stress peak in the DFZ except a stress peak at the blunt crack tip. With an increase in the applied stress intensity factor KIa or the friction stress τf of the material, the DFZ size and the peak stress at the crack tip decrease, but the peak stress in the DFZ and the effective stress intensity factor KIf presiding at the crack tip increase. Because of dislocation shielding effects, shielding ratio KIa/KIf increases with increasing KIa}, but it decreases with increasing τf.

  20. Stress distribution and effective stress intensity factor of a blunt crack after dislocation emission

    Institute of Scientific and Technical Information of China (English)

    钱才富; 乔利杰; 褚武扬

    2000-01-01

    The stress fields induced by a dislocation and its image dislocations around a narrow elliptic void are formulated. Based on the solution, the stress distribution and effective stress intensity factor of a blunt (elliptic) crack were calculated under mode I constant loading. The results show that a dislocation-free zone (DFZ) is formed after dislocation emission. There exists a second stress peak in the DFZ except a stress peak at the blunt crack tip. With an increase in the applied stress intensity factor Kla or the friction stress T, of the material, the DFZ size and the peak stress at the crack tip decrease, but the peak stress in the DFZ and the effective stress intensity factor Klf presiding at the crack tip increase. Because of dislocation shielding effects, shielding ratio Kla/Klf increases with increasing Kla, but it decreases with increasing Tf.

  1. Three-Dimensional Stress and Stress Intensity for Tensioned Flat Plates with Edge Cracks

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The stress in the thickness direction is an important factor influencing the fracture behavior of structural members. A stress бy tensioned flat plate with edge cracks is widely used as an analysis model. The stresses бx and бy for the plate model can be acquired from Neuber's solution. However, the solution is applicable only for a perfect plane stress or plane strain state. As a consequence of the thickness of the plate a three-dimensional (3-D) stress state will arise near the crack tip, resulting in a variation of the distribution of бx and бy stresses. A full analysis for the 3-D stress fields for a tensioned flat plate with edge cracks has been therefore carried out. The results show that the 3-D stress field near the crack tip is mainly determined by two factors: the thickness of the plate and the curvature radius at the crack tip. A further analysis has been carried out for the stress intensity near the crack tip. In this paper we give some equations matching to the 3-D stress and stress intensity, which describe precisely the stress state near the crack tip, and which can be applied effectively in engineering analysis.

  2. Characterisation of crack tip fields under non-uniform fatigue loading

    Directory of Open Access Journals (Sweden)

    D. Nowell, M.E. Kartal

    2013-07-01

    Full Text Available The paper analyses previously reported work, which uses digital image correlation to measure fatigue crack closure. As well as determining crack opening loads, the information on crack shape may be used to estimate the stress intensity factor, as well as other parameters in more complex models of crack tip fields. A number of specimens were subjected to single overload cycles, which produced a significant retardation in crack growth rate. The method previously applied to the analysis of constant amplitude loading is here used to analyse the single overload case. The stress intensity factor history is found to be very different in the two cases and the consequences of this observation for analysis of fatigue crack propagation are discussed.

  3. Crack tip dislocations observed by TEM-tomography in silicon single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Sadamatsu, Sunao; Tanaka, Masaki; Honda, Masaki; Higashida, Kenji, E-mail: sxdxmx@kyudai-mse.or [Department of Materials Science and Engineering, Kyushu University 744 Motooka, Fukuoka 819-0395 (Japan)

    2010-07-01

    3D observations of dislocations at a crack tip were attempted by transmission electron microscopy and computed tomography in order to reveal the 3D structure of dislocations emitted around a crack tip. {l_brace}011{r_brace} cracks were introduced into a (001) silicon single crystal wafer by using an indentation method at room temperature. The specimens indented were heated and kept at high temperatures to introduce dislocations from the crack tip. The specimen holder was tilted {+-}31{sup 0} by 2{sup 0} step and dislocation images were taken at every step. The diffraction vector was kept nearly 220 during the tilting operation. The Burgers vectors of the dislocation segments were determined, which included the signs of Burgers vectors. The dislocations observed here were those which accommodate mode II stress intensity around the crack tip. 3D observations using electron tomography reveal these complex crucial processes around the crack tip, which should contribute to understanding the dislocation process improving fracture toughness of crystalline materials.

  4. Propagation of stress corrosion cracks in alpha-brasses

    Energy Technology Data Exchange (ETDEWEB)

    Beggs, Dennis Vinton [Univ. of Illinois, Urbana-Champaign, IL (United States)

    1981-01-01

    Transgranular and intergranular stress corrosion cracks were investigated in alpha-brasses in a tarnishing ammoniacal solution. Surface observation indicated that the transgranular cracks propagated discontinuously by the sudden appearance of a fine crack extending several microns ahead of the previous crack tip, often associated with the detection of a discrete acoustic emission (AE). By periodically increasing the deflection, crack front markings were produced on the resulting fracture surfaces, showing that the discontinuous propagation of the crack trace was representative of the subsurface cracking. The intergranular crack trace appeared to propagate continuously at a relatively blunt crack tip and was not associated with discrete AE. Under load pulsing tests with a time between pulses, Δt greater than or equal to 3 s, the transgranular fracture surfaces always exhibited crack front markings which corresponded with the applied pulses. The spacing between crack front markings, Δx, decreased linearly with Δt. With Δt less than or equal to 1.5 s, the crack front markings were in a one-to-one correspondence with applied pulses only at relatively long crack lengths. In this case, Δx = Δx* which approached a limiting value of 1 μm. No crack front markings were observed on intergranular fracture surfaces produced during these tests. It is concluded that transgranular cracking occurs by discontinuous mechanical fracture of an embrittled region around the crack tip, while intergranular cracking results from a different mechanism with cracking occurring via the film-rupture mechanism.

  5. CRACK TIP FIELD AND J-INTEGRAL WITH STRAIN GRADIENT EFFECT

    Institute of Scientific and Technical Information of China (English)

    XIA Song; WANG Tzuchiang; CHEN Shaoha

    2004-01-01

    The mode I plane strain crack tip field with strain gradient effects is presented in this paper based on a simplified strain gradient theory within the framework proposed by Acharya and Bassani. The theory retains the essential structure of the incremental version of the conventional J2 deformation theory. No higher-order stress is introduced and no extra boundary value conditions beyond the conventional ones are required. The strain gradient effects are considered in the constitutive relation only through the instantaneous tangent modulus. The strain gradient measures are included into the tangent modulus as internal parameters. Therefore the boundary value problem is the same as that in the conventional theory. Two typical crack problems are studied: (a) the crack tip field under the small scale yielding condition induced by a linear elastic mode-I K-field and (b) the complete field for a compact tension specimen. The calculated results clearly show that the stress level near the crack tip with strain gradient effects is considerable higher than that in the classical theory. The singularity of the strain field near the crack tip is nearly equal to the square-root singularity and the singularity of the stress field is slightly greater than it. Consequently, the J-integral is no longer path independent and increases monotonically as the radius of the calculated circular contour decreases.

  6. Crack-tip strain field mapping and the toughness of metallic glasses.

    Directory of Open Access Journals (Sweden)

    Todd C Hufnagel

    Full Text Available We have used high-energy x-ray scattering to map the strain fields around crack tips in fracture specimens of a bulk metallic glass under load at room temperature and below. From the measured strain fields we can calculate the components of the stress tensor as a function of position and determine the size and shape of the plastic process zone around the crack tip. Specimens tested at room temperature develop substantial plastic zones and achieve high stress intensities ((K(If = 76 MPa m(1/2 prior to fracture. Specimens tested at cryogenic temperatures fail at reduced but still substantial stress intensities (K(If = 39 MPa m(1/2 and show only limited evidence of crack-tip plasticity. We propose that the difference in behavior is associated with changes in the flow stress and elastic constants, which influence the number density of shear bands in the plastic zone and thus the strain required to initiate fracture on an individual band. A secondary effect is a change in the triaxial state of stress around the crack tip due to the temperature dependence of Poisson's ratio. It is likely that this ability to map elastic strains on the microscale will be useful in other contexts, although interpreting shifts in the position of the scattering peaks in amorphous materials in terms of elastic strains must be done with caution.

  7. Suppressed plastic deformation at blunt crack tips due to strain gradient effects

    DEFF Research Database (Denmark)

    Mikkelsen, Lars Pilgaard; Goutianos, Stergios

    2009-01-01

    Large deformation gradients occur near a crack-tip and strain gradient dependent crack-tip deformation and stress fields are expected. Nevertheless, for material length scales much smaller than the scale of the deformation gradients, a conventional elastic-plastic solution is obtained. On the other...... hand, for significant large material length scales, a conventional elastic solution is obtained. This transition in behaviour is investigated based on a finite strain version of the Fleck-Hutchinson strain gradient plasticity model from 2001. The predictions show that for a wide range of material...

  8. Damage evolution by using the near-tip fields of a crack in gas turbine liners

    NARCIS (Netherlands)

    Altunlu, A.C.; van der Hoogt, Peter; de Boer, Andries

    2010-01-01

    A residual lifetime prediction study has been performed on a combustion liner metallic material exposed to elevated temperatures by simulating the evolution of plastic work fields at a crack tip under monotonically loading. The strain and stress distribution has been computed by finite element analy

  9. Damage evolution by using the near-tip fields of a crack in gas turbine liners

    NARCIS (Netherlands)

    Altunlu, A.C.; van der Hoogt, Peter; de Boer, Andries

    2010-01-01

    A residual lifetime prediction study has been performed on a combustion liner metallic material exposed to elevated temperatures by simulating the evolution of plastic work fields at a crack tip under monotonically loading. The strain and stress distribution has been computed by finite element

  10. Successively refined models for crack tip plasticity in polymer blends

    NARCIS (Netherlands)

    Pijnenburg, KGW; Seelig, T; van der Giessen, E

    2005-01-01

    This paper is concerned with a comparative study of different, partly complementary micromechanical models for crack tip plasticity in polymer-rubber blends. It is experimentally well established that interspersion of micron-scale rubber particles into a polymer matrix can lead to a significantly en

  11. Experimental study about nano-deformation field near quasi-cleavage crack tip

    Institute of Scientific and Technical Information of China (English)

    邢永明; 戴福隆; 杨卫FML

    2000-01-01

    Using the nano-moire method, we measure the near tip nanoscopic deformation on the {111 } plane of single crystal silicon with a loaded quasi-cleavage crack running in the [110] direction. The measured strain distribution ahead of the crack tip agrees with the linear elastic fracture mechanics prediction up to 10 nm from the crack tip. Dislocations of Peierls type are detected and they extend from the crack tip over a length of hundreds of Burgers vectors.

  12. Mechanical factors in primary water stress corrosion cracking of cold-worked stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Hammadi, Rashid Al, E-mail: rashid.alhammadi@fanr.gov.ae [Nuclear Security Division, Federal Authority for Nuclear Regulation, Abu Dhabi (United Arab Emirates); Yi, Yongsun, E-mail: yongsun.yi@kustar.ac.ae [Department of Nuclear Engineering, Khalifa University, Abu Dhabi (United Arab Emirates); Zaki, Wael, E-mail: wael.zaki@kustar.ac.ae [Department of Mechanical Engineering, Khalifa University, Abu Dhabi (United Arab Emirates); Cho, Pyungyeon, E-mail: pyungyeon.cho@kustar.ac.ae [Department of Nuclear Engineering, Khalifa University, Abu Dhabi (United Arab Emirates); Jang, Changheui, E-mail: chjang@kaist.ac.kr [Nuclear and Quantum Engineering Department, Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)

    2016-05-15

    Highlights: • PWSCC of cold-worked austenitic stainless steel was studied. • Finite element analysis was performed on a compact tension specimen. • Mechanical fields near a crack tip were evaluated using FEA. • The dependence of mechanical factors on K{sub I} and yield stress was investigated. • The crack tip normal stress was identified as a main factor controlling PWSCC. - Abstract: Finite element analysis was performed on a compact tension specimen to determine the stress and strain distributions near a crack tip. Based on the results, the crack tip stain rates by crack advance and creep rates near crack tip were estimated. By comparing the dependence of the mechanical factors on the stress intensity factor and yield stress with that of the SCC crack growth rates, it was tried to identify the main mechanical factor for the primary water stress corrosion cracking (PWSCC) of cold-worked austenitic stainless steels. The analysis results showed that the crack tip normal stress could be the main mechanical factor controlling the PWSCC, suggesting that the internal oxidation mechanism might be the most probable PWSCC mechanism of cold-worked austenitic stainless steels.

  13. Gradient plasticity crack tip characterization by means of the extended finite element method

    Science.gov (United States)

    Martínez-Pañeda, E.; Natarajan, S.; Bordas, S.

    2017-01-01

    Strain gradient plasticity theories are being widely used for fracture assessment, as they provide a richer description of crack tip fields by incorporating the influence of geometrically necessary dislocations. Characterizing the behavior at the small scales involved in crack tip deformation requires, however, the use of a very refined mesh within microns to the crack. In this work a novel and efficient gradient-enhanced numerical framework is developed by means of the extended finite element method (X-FEM). A mechanism-based gradient plasticity model is employed and the approximation of the displacement field is enriched with the stress singularity of the gradient-dominated solution. Results reveal that the proposed numerical methodology largely outperforms the standard finite element approach. The present work could have important implications on the use of microstructurally-motivated models in large scale applications. The non-linear X-FEM code developed in MATLAB can be downloaded from http://www.empaneda.com/codes.

  14. 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.

  15. Improved Stress Intensity Solutions Developed for the Multiple Site Damage Scenario: Two Unequal Through Cracks on Either Side of an Open Hole, Multiple Through Cracks, and Through Cracks Approaching an Open Hole

    Science.gov (United States)

    2014-10-01

    so the stress intensity factor at each crack tip is a function of the length of both cracks. The handbook solution by Murakami [3], was reported to...G.R., "The Stress Analysis of Cracks Handbook," Second Edition, Paris Productions, Inc., St. Louis, MO, 1985 3. Murakami , Y., et al., "Stress

  16. THERMAL STRESS FIELD WHEN CRACK ARREST IN AN AXIAL SYMMETRY METAL DIE USING ELECTROMAGNETIC HEATING

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    In order to solve the thermal stress field around crack tip in metal die when crack prevention using electromagnetic heating, a metal die with a half-embedded round crack was selected as the study object. The complex function method was used as a basis for the theoretical model of the space crack prevention in metal dies using electromagnetic heating. The crack arrest was accomplished by a pulse current discharge through the inner and outer. The theoretical analysis results show that the temperature around the crack tip rises instantly above the melting point of the metal. Small welded joints are formed at a small sphere near the crack tip inside the metal die by metal melting as a result of the heat concentration effect when the current pulse discharged. The thermal compressive stress field appears around the crack tip at the moment. The research results show that the crack prevention using electromagnetic heating can decrease the stress concentration and forms a compressive stress area around the crack tip, and also prevents the main crack from propagating further, and the goal of crack preventing can be reached.

  17. Effect of hydrogen on stress corrosion cracking of copper

    Institute of Scientific and Technical Information of China (English)

    Li-jie QIAO

    2008-01-01

    The effects of hydrogen on electrochemical behavior and susceptibility of stress corrosion cracking (SCC) of pure copper were studied. SCC susceptibility of pure copper in a 1 M NaNO2 solution was increased by pre-charged hydrogen. The effect of hydrogen on the sus-ceptibility is more obvious in the low stress region due to the longer fracture time, which resulted in a longer time for more hydrogen to diffuse toward the crack tip. Synergistic effects of hydrogen and stress on corrosion and SCC pro-cesses were discussed. The results showed that an inter-action between stress and hydrogen at the crack tip could increase the anodic dissolution rate remarkably.

  18. Microstructure of plastic zones around crack tips in silicon revealed by HVEM and AFM

    Energy Technology Data Exchange (ETDEWEB)

    Tanaka, Masaki; Higashida, Kenji; Haraguchi, Tomoko

    2004-12-15

    In order to understand the dislocation process for the sharp brittle-to-ductile transition in silicon crystals, microstructures of plastic zones around crack tips have been investigated using high-voltage electron microscopy (HVEM) and atomic force microscopy (AFM). Cracks were introduced into {l_brace}1 1 0{r_brace} silicon wafers at room temperature by Vickers indentation method. The temperature of specimens indented was raised to higher than 823 K to activate dislocation sources around a crack tip under the presence of residual stress due to the indentation. The crack observed was extending along the <1 1 0> direction from the edge of the indent. AFM study has revealed two types of fine slip bands around the crack tip: one type of slip bands is those parallel to <1 1 2>, and another type is those parallel to the <1 1 0> direction. The former is corresponding to so-called hinge-type plastic zone, and the latter is 45 deg.-shear-type. HVEM study has revealed the characteristics of dislocation structures corresponding to the both types of plastic zones. Detailed analyses of each dislocation, including the determination of the sign of Burgers vector, have been made to characterize those plastic zones.

  19. 晶体相场法研究应力状态及晶体取向对微裂纹尖端扩展行为的影响∗%Study on the effect of stress state and crystal orientation on micro-crack tip propagation b ehavior in phase field crystal metho d

    Institute of Scientific and Technical Information of China (English)

    2015-01-01

    A nanometer scale mechanism for micro crack propagation under uniaxial tension in single crystals is investigated using phase field crystal (PFC) simulation. The uniaxial tensile loading is strain controlled. And three initial typical stresses of pre-existing center crack in (111) crystal plane of face centered cubic structure are chosen to study the effects of initial stress state on micro-crack propagation. Moreover, the influences of different crystal orientations, when the crystal suffers from uniaxial tension, are also investigated. Due to the influence of time scale and length scale in the PFC method, the motion of dislocations, vacancies, shear band and twinning structure should be observed and described during the propagation process of micro cracks. In addition, the free energy curves of different processes are drawn and discussed in order to explain the different behaviors of the crystal in the propagation of cracks. Simulation results show that the propagation behavior of micro cracks can be closely associated with the initial stress state. It is found that the propagation behavior mainly occurs in the ⟨0¯11⟩(111) slip system. Besides, the crystal orientation has a significant effect on the mechanism of activation and evolution. In the pre-stretching system, slip dislocation is induced near the micro-crack tip, and then its slide in [0¯11] direction will cause the cleavage of a certain crystal plane, and promote the micro cracks to extend. However, to a certain level, the propagating direction of the micro-crack tip will turn to another slip direction [10¯1]. As a result, zigzag edge appears. By contrast, in the pre-shear system, the tip of the micro crack propagates in a cleavage mode, and results in the appearance of slip dislocation [10¯1] near the micro-crack tip. Afterwards, the motion of slip dislocation promotes the production of vacancies. And owing to the aggregation and combination of vacancies, secondary cracks form and propagate in

  20. Crack tip shielding observed with high-resolution transmission electron microscopy.

    Science.gov (United States)

    Adhika, Damar Rastri; Tanaka, Masaki; Daio, Takeshi; Higashida, Kenji

    2015-10-01

    The dislocation shielding field at a crack tip was experimentally proven at the atomic scale by measuring the local strain in front of the crack tip using high-resolution transmission electron microscopy (HRTEM) and geometric phase analysis (GPA). Single crystalline (110) silicon wafers were employed. Cracks were introduced using a Vickers indenter at room temperature. The crack tip region was observed using HRTEM followed by strain measurements using GPA. The measured strain field at the crack tip was compressive owing to dislocation shielding, which is in good agreement with the strain field calculated from elastic theory.

  1. Evaluation of Stress Intensity Factors for Multiple Cracked Circular Disks Under Crack Surface Tractions with SBFEM

    Institute of Scientific and Technical Information of China (English)

    LIU Jun-yu; LIN Gao; LI Xiao-chuan; XU Feng-lin

    2013-01-01

    Stress intensity factors (SIFs) for the cracked circular disks under different distributing surface tractions are evaluated with the scaled boundary finite element method (SBFEM).In the SBFEM,the analytical advantage of the solution in the radial direction allows SIFs to be directly determined from its definition,therefore no special crack-tip treatment is necessary.Furthermore anisotropic material behavior can be treated easily.Different distributions of surface tractions are considered for the center and double-edge-cracked disks.The benchmark examples are modeled and an excellent agreement between the results in the present study and those in published literature is found.It shows that SBFEM is effective and possesses high accuracy.The SIFs of the cracked orthotropic material circular disks subjected to different surface tractions are also evaluated.The technique of substructure is applied to handle the multiple cracks problem.

  2. Tips to Manage Anxiety and Stress

    Science.gov (United States)

    ... Corner Resources Public Tips to Manage Anxiety and Stress When you're feeling anxious or stressed, these ... that exercise feels easier. Give the Gift of Stress Relief - for Yourself or Someone You Love and ...

  3. Computational two-dimensional modeling of the stress intensity factor in a cracked metallic material

    Science.gov (United States)

    Rolón, J. E.; Cendales, E. D.; Cruz, I. M.

    2016-02-01

    Cracking of metallic engineering materials is of great importance due cost of replacing mechanical elements cracked and the danger of sudden structural failure of these elements. One of the most important parameters during consideration of the mechanical behavior of machine elements having cracking and that are subject to various stress conditions is the stress intensity factor near the crack tip called factor Kic. In this paper a computational model is developed for the direct assessment of stress concentration factor near to the crack tip and compared with the results obtained in the literature in which other models have been established, which consider continuity of the displacement of the crack tip (XBEM). Based on this numerical approximation can be establish that computational XBEM method has greater accuracy in Kic values obtained than the model implemented by the method of finite elements for the virtual nodal displacement through plateau function.

  4. Mode I stress intensity factors of slanted cracks in plates

    Science.gov (United States)

    Ismail, Al Emran; Ghazali, Mohd Zubir Mohd; Nor, Nik Hisyamudin Muhd

    2017-01-01

    This paper presents the roles of slanted cracks on the stress intensity factors (SIF) under mode I tension and bending loading. Based on the literature survey, lack of solution of SIFs of slanted cracks in plain strain plates are available. In this work, the cracks are modelled numerically using ANSYS finite element program. There are two important parameters such as slanted angles and relative crack length. SIFs at the crack tips are calculated according to domain integral method. Before the model is further used, it is validated with the existing model. It is found that the present model is well agreed with the previous model. According to finite element analysis, there are not only mode I SIFs produced but also mode II. As expected the SIFs increased as the relative crack length increased. However, when slanted angles are introduced (slightly higher than normal crack), the SIFs increased. Once the angles are further increased, the SIFs decreased gradually however they are still higher than the SIFs of normal cracks. For mode II SIFs, higher the slanted angels higher the SIFs. This is due to the fact that when the cracks are slanted, the cracked plates are not only failed due to mode I but a combination between both modes I and II.

  5. A dynamic model of a cantilever beam with a closed, embedded horizontal crack including local flexibilities at crack tips

    Science.gov (United States)

    Liu, J.; Zhu, W. D.; Charalambides, P. G.; Shao, Y. M.; Xu, Y. F.; Fang, X. M.

    2016-11-01

    As one of major failure modes of mechanical structures subjected to periodic loads, embedded cracks due to fatigue can cause catastrophic failure of machineries. Understanding the dynamic characteristics of a structure with an embedded crack is helpful for early crack detection and diagnosis. In this work, a new three-segment beam model with local flexibilities at crack tips is developed to investigate the vibration of a cantilever beam with a closed, fully embedded horizontal crack, which is assumed to be not located at its clamped or free end or distributed near its top or bottom side. The three-segment beam model is assumed to be a linear elastic system, and it does not account for the nonlinear crack closure effect; the top and bottom segments always stay in contact at their interface during the beam vibration. It can model the effects of local deformations in the vicinity of the crack tips, which cannot be captured by previous methods in the literature. The middle segment of the beam containing the crack is modeled by a mechanically consistent, reduced bending moment. Each beam segment is assumed to be an Euler-Bernoulli beam, and the compliances at the crack tips are analytically determined using a J-integral approach and verified using commercial finite element software. Using compatibility conditions at the crack tips and the transfer matrix method, the nature frequencies and mode shapes of the cracked cantilever beam are obtained. The three-segment beam model is used to investigate the effects of local flexibilities at crack tips on the first three natural frequencies and mode shapes of the cracked cantilever beam. A stationary wavelet transform (SWT) method is used to process the mode shapes of the cracked cantilever beam; jumps in single-level SWT decomposition detail coefficients can be used to identify the length and location of an embedded horizontal crack.

  6. Contribution to crack sizing by phased array ultrasonic techniques: part 2: comparison with optical, magnetic particles, fracture mechanics and metallography for last significant crack tip

    Energy Technology Data Exchange (ETDEWEB)

    Ciorau, P. [Ontario Power Generation, Inc., Pickering, Ontario (Canada)

    2007-11-15

    The paper presents phased array results for 1-D linear array probes of high frequency (7-10 MHz) in L-, and S-waves for detecting the crack shape and the last significant tip. Fatigue and stress-corrosion cracks with height ranging from 1.6 mm to 20.4 mm were detected in welded samples, piping welds and straight bars with thickness between 1.6 mm to 38 mm. The results of S-scan display are compared with different methods: optical, magnetic particles, fracture mechanics and metallography. The experimental results concluded the undersizing trend of PAUT in detecting the last crack tip or closure, in spite of using dynamic depth focusing, and/or focusing on crack tip. The average undersizing error is - 0.4 mm. This error increases for cracks with depth >12 mm. The largest errors occur when the crack is sized from outer surface coupled with initiation from the outside surface with propagation towards the inside surface. These errors were reduced by a combination of shear and longitudinal waves and by increasing the angular resolution. (author)

  7. Role of sulphur atoms on stress relaxation and crack propagation in monolayer MoS2

    Science.gov (United States)

    Wang, Baoming; Islam, Zahabul; Zhang, Kehao; Wang, Ke; Robinson, Joshua; Haque, Aman

    2017-09-01

    We present in-situ transmission electron microscopy of crack propagation in a freestanding monolayer MoS2 and molecular dynamic analysis of the underlying mechanisms. Chemical vapor deposited monolayer MoS2 was transferred from sapphire substrate using interfacial etching for defect and contamination minimization. Atomic resolution imaging shows crack tip atoms sustaining 14.5% strain before bond breaking, while the stress field decays at unprecedented rate of 2.15 GPa Å-1. Crack propagation is seen mostly in the zig-zag direction in both model and experiment, suggesting that the mechanics of fracture is not brittle. Our computational model captures the mechanics of the experimental observations on crack propagation in MoS2. While molybdenum atoms carry most of the mechanical load, we show that the sliding motion of weakly bonded sulphur atoms mediate crack tip stress relaxation, which helps the tip sustain very high, localized stress levels.

  8. Dissolution Condensation Mechanism of Stress Corrosion Cracking in Liquid Metals: Driving Force and Crack Kinetics

    Science.gov (United States)

    Glickman, Evgeny E.

    2011-02-01

    Stress corrosion cracking (SCC) in aqueous solution is driven by exothermic reactions of metal oxidation. This stimulus, as well as classical mechanisms of SCC, does not apply to SCC in liquid metals (LMs). In the framework of the dissolution-condensation mechanism (DCM), we analyzed the driving force and crack kinetics for this nonelectrochemical mode of SCC that is loosely called "liquid metal embrittlement" (LME). According to DCM, a stress-induced increase in chemical potential at the crack tip acts as the driving force for out-of-the-tip diffusion mass transfer that is fast because diffusion in LMs is very fast and surface energy at the solid-liquid interface is small. In this article, we review two versions of DCM mechanism, discuss the major physics behind them, and develop DCM further. The refined mechanism is applied then to the experimental data on crack velocity V vs stress intensity factor, the activation energy of LME, and alloying effects. It is concluded that DCM provides a good conceptual framework for analysis of a unified kinetic mechanism of LME and may also contribute to SCC in aqueous solutions.

  9. 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.

  10. Gradient plasticity crack tip characterization by means of the extended finite element method

    DEFF Research Database (Denmark)

    Martínez Pañeda, Emilio; Natarajan, S.; Bordas, S.

    2017-01-01

    Strain gradient plasticity theories are being widelyused for fracture assessment, as they provide a richerdescription of crack tip fields by incorporating the influenceof geometrically necessary dislocations. Characterizingthe behavior at the small scales involved in crack tip deformationrequires...... applications. The non-linear X-FEMcode developed in MATLAB can be downloaded fromwww.empaneda.com/codes....

  11. Thermo-elastic extended meshfree method for fracture without crack tip enrichment

    Institute of Scientific and Technical Information of China (English)

    A. ASADPOUR

    2015-01-01

    This is the first manuscript presenting an extended meshfree method for thermo- elastic fracture which does not exploit a crack tip enrichment. The crack is modeled by partition of unity enrichment of the displacement and temperature field. Only a step function is employed that facilitates the implementation. To ensure that crack tip is at the correct position, a Lagrange multiplier field ahead of the crack tip is introduced along a line. The Lagrange multiplier nodal parameters are discretised with the available meshfree functions. Two benchmark examples illustrate the efficiency of the method.

  12. Sensitivity to temperature and material properties of hydrogen concentration at a crack tip in austenitic stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Schembri, Philip E [Los Alamos National Laboratory

    2008-01-01

    It is well known that dissolved hydrogen interacts with the stress field at a crack tip, with one result being an intensification of the hydrogen concentration in the region of maximum crack tip stress. The current paper presents recent calculations in ongoing efforts to use coupled stress-diffusion finite element analyses to aid in the structural integrity assessment of pressure vessels containing tritium. The focus of the current work is quantification of the effect of material properties (structural and diffusion) and temperature on the values of maximum stress and hydrogen concentration at the tip of a crack. A one-way-coupled finite element model of a compact tension specimen is used in which the effect of stress and trapping on the hydrogen diffusion is accounted for. Results show that, within the ranges of inputs considered, maximum stress varies approximately linearly with a material's room temperature yield stress but nonlinearly with temperature. Also, peak lattice hydrogen is shown to be a strong function of solubility parameters, a moderate function of yield stress, but only a weak function of trap binding energy and density when trap density is relatively low.

  13. Crack tip dislocations revealed by electron tomography in silicon single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Tanaka, Masaki [Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan)], E-mail: masaki@zaiko.kyushu-u.ac.jp; Higashida, Kenji [Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Kaneko, Kenji [Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); JST-CREST, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Hata, Satoshi; Mitsuhara, Masatoshi [Department of Engineering Sciences for Electronics and Materials, Kyushu University, 6-1 Kasuga koen, Kasuga, Fukuoka 816-8580 (Japan)

    2008-10-15

    Crack tip dislocations in silicon single crystals have been observed by a combination of annular dark-field scanning transmission electron microscopy and computed tomography. A series of images was acquired by maintaining the diffraction vector parallel to that of crack propagation to achieve sharp images of the dislocations. The observed dislocations were reconstructed by a filtered back-projection, and exhibited three-dimensional configurations of overlaid dislocations around the crack tip.

  14. Asymptotic analysis of mode Ⅰ propagating crack-tip field in a creeping material

    Institute of Scientific and Technical Information of China (English)

    WANG Zhen-qing; ZHAO Qi-cheng; LIANG Wen-yan; FU Zhang-jian

    2003-01-01

    Adopting an elastic-viscoplastic, the asymptotic problem of mode I propagating crack-tip field is investigated. Various asymptotic solutions resulting from the analysis of crack growing programs are presented. The analysis results show that the quasi-statically growing crack solutions are the special case of the dynamic propagating solutions. Therefore these two asymptotic solutions can be unified.

  15. Thinning procedures and strains in the zones near crack tips of thin foils

    Institute of Scientific and Technical Information of China (English)

    李红旗; 陈奇志; 褚武扬

    1999-01-01

    Thinning procedures were observed by TEM in 310 stainless steel and pure aluminum. Foils thinned through shearing of mode Ⅲ crack or through tearing of mode I crack. Using micro-beam electron diffraction, the strains in the areas right ahead of crack tips of pure aluminum and TiAI alloy were measured to be 0.05 or more.

  16. Environmental fatigue of an Al-Li-Cu alloy. Part 3: Modeling of crack tip hydrogen damage

    Science.gov (United States)

    Piascik, Robert S.; Gangloff, Richard P.

    1992-01-01

    Environmental fatigue crack propagation rates and microscopic damage modes in Al-Li-Cu alloy 2090 (Parts 1 and 2) are described by a crack tip process zone model based on hydrogen embrittlement. Da/dN sub ENV equates to discontinuous crack advance over a distance, delta a, determined by dislocation transport of dissolved hydrogen at plastic strains above a critical value; and to the number of load cycles, delta N, required to hydrogenate process zone trap sites that fracture according to a local hydrogen concentration-tensile stress criterion. Transgranular (100) cracking occurs for process zones smaller than the subgrain size, and due to lattice decohesion or hydride formation. Intersubgranular cracking dominates when the process zone encompasses one or more subgrains so that dislocation transport provides hydrogen to strong boundary trapping sites. Multi-sloped log da/dN-log delta K behavior is produced by process zone plastic strain-hydrogen-microstructure interactions, and is determined by the DK dependent rates and proportions of each parallel cracking mode. Absolute values of the exponents and the preexponential coefficients are not predictable; however, fractographic measurements theta sub i coupled with fatigue crack propagation data for alloy 2090 established that the process zone model correctly describes fatigue crack propagation kinetics. Crack surface films hinder hydrogen uptake and reduce da/dN and alter the proportions of each fatigue crack propagation mode.

  17. Strain rate effects in stress corrosion cracking

    Energy Technology Data Exchange (ETDEWEB)

    Parkins, R.N. (Newcastle upon Tyne Univ. (UK). Dept. of Metallurgy and Engineering Materials)

    1990-03-01

    Slow strain rate testing (SSRT) was initially developed as a rapid, ad hoc laboratory method for assessing the propensity for metals an environments to promote stress corrosion cracking. It is now clear, however, that there are good theoretical reasons why strain rate, as opposed to stress per se, will often be the controlling parameter in determining whether or not cracks are nucleated and, if so, are propagated. The synergistic effects of the time dependence of corrosion-related reactions and microplastic strain provide the basis for mechanistic understanding of stress corrosion cracking in high-pressure pipelines and other structures. However, while this may be readily comprehended in the context of laboratory slow strain tests, its extension to service situations may be less apparent. Laboratory work involving realistic stressing conditions, including low-frequency cyclic loading, shows that strain or creep rates give good correlation with thresholds for cracking and with crack growth kinetics.

  18. Investigation on Crack Tip Transformation in NiTi Alloys: Effect of the Temperature

    Science.gov (United States)

    Sgambitterra, Emanuele; Maletta, Carmine; Furgiuele, Franco

    2015-06-01

    The effect of the temperature on crack tip transformation in Nickel-Titanium (NiTi) shape memory alloys was analyzed in this work by means of experimental and analytical approaches. In particular, single edge crack specimens were analyzed for two different values of the testing temperature in the pseudoelastic regime of the alloy, i.e., T = 298 K and T = 338 K. The thermal-dependent phase transition mechanisms occurring at the crack tip region were studied by analyzing data obtained from digital image correlation as well as by nanoindentation experiments performed near the crack tip. Finally, experimental results were compared with predictions of a recent analytical model. Results revealed that an increase in temperature causes a decrease of the phase transformation zone and that both the techniques are well suitable in capturing the thermal effect on the phase transformation mechanisms near the crack tip.

  19. 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.

  20. A Fracture Probability Competition Mechanism of Stress Corrosion Cracking

    Institute of Scientific and Technical Information of China (English)

    Yanliang HUANG

    2001-01-01

    The stress corrosion cracking (SCC) of austenitic stainless steel was studied via polarization,slow strain rate and scanning electron microscope (SEM) techniques. Many SCC mechanisms have been proposed in which hydrogen embrittlement and passive film rupture-repassivation theories are generally accepted, but they can hardly explain the SCC mechanism of austenitic stainless steel in acidic chloride solution adequately, because the steel is in active dissolution state and cathodic polarization can prevent it from occurring. Our experiment shows that the anodic current increases the creep rate and decreases the plastic strength of the material on single smooth specimen as well as at the SCC crack tip. The fractured surface was characterized as brittle cleavage, while the surface crack of smooth specimen was almost vertical to the tensile strength, which can confirm that the cracks were caused by tensile stresses. A fracture probability competition mechanism of SCC was proposed on the basis of the experimental results combined with the viewpoint of ductile-brittle fracture competition. When the anodic dissolution current is increased to a certain degree, the probability of fracture by tensile stress will exceed that by shear stress, and the brittle fracture will occur. The proposed SCC mechanism can not only explain the propagation of SCC cracks but can explain the crack initiation as well. The strain on the surface distributes unevenly when a smooth specimen is deformed, so does the anodic current distribution. The crack will initiate at a point where the anodic current density is large enough to cause the material at a specific point to fracture in brittle manner.

  1. 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.

  2. The stress field near the notch tip of an incompressible rubber-like specimen under the condition of plane strain

    Institute of Scientific and Technical Information of China (English)

    刘波; 高玉臣

    1995-01-01

    Using Gao’s constitutive relation, the stress fieid has been analyzed near the notch tip and the crack tip of an incompressible rubber-like specimen under the condition of plane strain. The asymptotic equation of the notch tip field is solved numerically; the stress and strain singularities are calculated for various notch angles and different material constant values; the stress variation with the angle coordinate is also analyzed.

  3. 3D finite element analysis on crack-tip plastic zone

    African Journals Online (AJOL)

    user

    International Journal of Engineering, Science and Technology ... 1* Research Centre, Department of Mechanical Engineering, SDM College of ... studies related to crack-tip plastic zones are of fundamental importance for assessing fracture ...

  4. Simulation Research on Stress Intensity Factors of Different Crack Aspect Ratios on Hollow Axles

    Institute of Scientific and Technical Information of China (English)

    ZHOU Suxia; XIE Jilong

    2009-01-01

    Because of the wicked service environment of the high speed train, it is possible that the hollow axle of the train may encounter the foreign object damage and form a sharp notch. Under the fatigue loading a crack can initiate from the notch and propagate to failure. It is noted that the stress intensity factor is the control parameter of the crack propagating, for the purpose of getting the more exact propagation characteristics, the stress intensity factor is studied mainly. The service loads of hollow axles are defined, and the stress distribution of hollow axles is obtained according to the load spectrum. The semi-ellipse crack configuration is defined with three parameters:the aspect ratio, the relative depth and the relative location along the crack front. Quarter point 20-node isoparametric degenerate singular elements are used for the region near the crack tip. The finite element model of crack extension of hollow axle is created, and the crack front is dispersed which can realize orthogonal extension. Based on this the stress intensity factors of crack front were calculated, and the distribution rules of the stress intensity factors of different initial crack shapes are obtained. The conclusions are compared with that of the analytic method and they agree with each other very well, and the calculating results show that there is a close relationship between the stress intensity factor and the initial crack shape. For a round crack the stress intensity factor at the surface point increases faster than the one at the center point with the crack propagation. However, for a narrow crack, the results are in contrast with that of a round one. So, all the cracks with different shapes propagate toward to a similar shape, and they grow at this shape to end. The study may contribute to the crack propagate characteristics research.

  5. Computational modeling of the mechanism of hydrogen embrittlement (HE) and stress corrosion cracking (SCC) in metals

    Science.gov (United States)

    Cendales, E. D.; Orjuela, F. A.; Chamarraví, O.

    2016-02-01

    In this article theoretical models and some existing data sets were examined in order to model the two main causes (hydrogen embrittlement and corrosion-cracking under stress) of the called environmentally assisted cracking phenomenon (EAC). Additionally, a computer simulation of flat metal plate subject to mechanical stress and cracking due both to hydrogen embrittlement and corrosion was developed. The computational simulation was oriented to evaluate the effect on the stress-strain behavior, elongation percent and the crack growth rate of AISI SAE 1040 steel due to three corrosive enviroments (H2 @ 0.06MPa; HCl, pH=1.0; HCl, pH=2.5). From the computer simulation we conclude that cracking due to internal corrosion of the material near to the crack tip limits affects more the residual strength of the flat plate than hydrogen embrittlement and generates a failure condition almost imminent of the mechanical structural element.

  6. Towards a quantification of stress corrosion mechanisms: numerical simulations of hydrogen-dislocations at the very crack tip; Vers une quantification des mecanismes de corrosion sous contrainte: simulations numeriques des interactions hydrogene-dislocations en pointe de fissure

    Energy Technology Data Exchange (ETDEWEB)

    Chateau, J.P

    1999-01-05

    We discuss the respective roles played by anodic dissolution and hydrogen in SCC mechanisms of f.c.c. materials, by studying the fracture of copper in nitrite for which we compare the results with that previously obtained in 316L steel in hot chloride. It is surprising to note that even the crystallographies at the scale of the micron are different, the macroscopic inclination of the fracture surfaces are the same. In the case of 316L steel, the formation of strong pile-ups in the presence of hydrogen leads to a zigzag fracture along alternated slip planes in the most general case. In the absence of hydrogen, as in copper, this mechanism effectively disappears. Furthermore, numerical simulations of crack shielding by dislocations emitted on one plane predict the macroscopic inclination. It shows that it is due to the mere dissolution which confines slip activity at the very crack tip in f.c.c. materials. In order to quantify the mechanism involved in 316L steel, we developed simulations which numerically solve the coupled diffusion and elasticity equations for hydrogen in the presence of a crack and shielding dislocations. They reproduce the mechanisms of hydrogen segregation on edge dislocations and of a localised softening effect by decreasing pair interactions. These mechanisms lead to i) a localisation of hydrogen embrittlement along the activated slip planes, ii) an increase of the dislocation density in pile-ups, and iii) a decrease of the cross slip probability. These three factors enhance micro-fracture at the head of a pile-up, which is responsible of thezigzag fracture. Introducing the free surface effects for hydrogen, we point out a new mechanism: the inhibition of dislocation sources at the crack tip, which is relevant with the brittle fracture surfaces observed in some cases in 316L steel. The quantification of these different mechanisms allows to give a relation between the local fracture possibility and the macroscopic parameters. A general law for

  7. Applied Stress Affecting the Environmentally Assisted Cracking

    Science.gov (United States)

    Vasudevan, A. K.

    2013-03-01

    Stress corrosion cracking (SCC) is affected by the mode of applied stress, i.e., tension, compression, or torsion. The cracking is measured in terms of initiation time to nucleate a crack or time to failure. In a simple uniaxial loading under tension or compression, it is observed that the initiation time can vary in orders of magnitude depending on the alloy and the environment. Fracture can be intergranular or transgranular or mixed mode. Factors that affect SCC are solubility of the metal into surrounding chemical solution, and diffusion rate (like hydrogen into a tensile region) of an aggressive element into the metal and liquid metallic elements in the grain boundaries. Strain hardening exponent that affects the local internal stresses and their gradients can affect the diffusion kinetics. We examine two environments (Ga and 3.5 pct NaCl) for the same alloy 7075-T651, under constant uniaxial tension and compression load. These two cases provide us application to two different governing mechanisms namely liquid metal embrittlement (7075-Ga) and hydrogen-assisted cracking (7075-NaCl). We note that, in spite of the differences in their mechanisms, both systems show similar behavior in the applied K vs crack initiation time plots. One common theme among them is the transport mechanism of a solute element to a tensile-stress region to initiate fracture.

  8. Hydrogen embrittlement and stress corrosion cracking in metals

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Young Suk; Cheong, Yong Mu; Im, Kyung Soo

    2004-10-15

    The objective of this report is to elucidate the mechanism for hydrogen embrittlement (HE) and stress corrosion cracking (SCC) in metals. To this end, we investigate the common features between delayed hydride cracking (DHC) in zirconium alloys and HE in metals with no precipitation of hydrides including Fe base alloys, Nickel base alloys, Cu alloys and Al alloys. Surprisingly, as with the crack growth pattern for the DHC in zirconium alloy, the metals mentioned above show a discontinuous crack growth, striation lines and a strong dependence of yield strength when exposed to hydrogen internally and externally. This study, for the first time, analyzes the driving force for the HE in metals in viewpoints of Kim's DHC model that a driving force for the DHC in zirconium alloys is a supersaturated hydrogen concentration coming from a hysteresis of the terminal solid solubility of hydrogen, not by the stress gradient, As with the crack growing only along the hydride habit plane during the DHC in zirconium alloys, the metals exposed to hydrogen seem to have the crack growing by invoking the dislocation slip along the preferential planes as a result of some interactions of the dislocations with hydrogen. Therefore, it seems that the hydrogen plays a role in inducing the slip only on the preferential planes so as to cause a strain localization at the crack tip. Sulfur in metals is detrimental in causing a intergranular cracking due to a segregation of the hydrogens at the grain boundaries. In contrast, boron in excess of 500 ppm added to the Ni3Al intermetallic compound is found to be beneficial in suppressing the HE even though further details of the mechanism for the roles of boron and sulfur are required. Carbon, carbides precipitating semi-continuously along the grain boundaries and the CSL (coherent site lattice) boundaries is found to suppress the intergranular stress corrosion cracking (IGSCC) in Alloy 600. The higher the volume fraction of twin boundaries, the

  9. Hydrogen embrittlement and stress corrosion cracking in metals

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Young Suk; Cheong, Yong Mu; Im, Kyung Soo

    2004-10-15

    The objective of this report is to elucidate the mechanism for hydrogen embrittlement (HE) and stress corrosion cracking (SCC) in metals. To this end, we investigate the common features between delayed hydride cracking (DHC) in zirconium alloys and HE in metals with no precipitation of hydrides including Fe base alloys, Nickel base alloys, Cu alloys and Al alloys. Surprisingly, as with the crack growth pattern for the DHC in zirconium alloy, the metals mentioned above show a discontinuous crack growth, striation lines and a strong dependence of yield strength when exposed to hydrogen internally and externally. This study, for the first time, analyzes the driving force for the HE in metals in viewpoints of Kim's DHC model that a driving force for the DHC in zirconium alloys is a supersaturated hydrogen concentration coming from a hysteresis of the terminal solid solubility of hydrogen, not by the stress gradient, As with the crack growing only along the hydride habit plane during the DHC in zirconium alloys, the metals exposed to hydrogen seem to have the crack growing by invoking the dislocation slip along the preferential planes as a result of some interactions of the dislocations with hydrogen. Therefore, it seems that the hydrogen plays a role in inducing the slip only on the preferential planes so as to cause a strain localization at the crack tip. Sulfur in metals is detrimental in causing a intergranular cracking due to a segregation of the hydrogens at the grain boundaries. In contrast, boron in excess of 500 ppm added to the Ni3Al intermetallic compound is found to be beneficial in suppressing the HE even though further details of the mechanism for the roles of boron and sulfur are required. Carbon, carbides precipitating semi-continuously along the grain boundaries and the CSL (coherent site lattice) boundaries is found to suppress the intergranular stress corrosion cracking (IGSCC) in Alloy 600. The higher the volume fraction of twin boundaries, the

  10. Fingertip and nasal tip thermal burn in crack cocaine user*

    Science.gov (United States)

    Bernardes, Fred; da Silva, Ystannyslau Bernardes; Martins, Luiz Gustavo; Sasso, Letícia Soares; de Abreu, Marilda Aparecida Milanez Morgado

    2013-01-01

    Crack cocaine addiction is a public health problem in Brazil. It is an endemic disease that affects rural and urban areas. The Ministry of Health has launched emergency programs for the treatment of dependents and to combat drug trafficking. Recognition of dermatological signs of this disease is important because through them the diagnosis can be suspected and early treatment of patients with crack cocaine addiction be provided. PMID:24173204

  11. Separating plasticity-induced closure and residual stress contributions to fatigue crack retardation following an overload

    Science.gov (United States)

    Salvati, Enrico; Zhang, Hongjia; Fong, Kai Soon; Song, Xu; Korsunsky, Alexander M.

    2017-01-01

    The introduction of an overload or underload within a constant amplitude loading fatigue test leads to a retardation or acceleration of the Fatigue Crack Growth Rate (FCGR). The understanding of the causes of these effects is essential in the context of variable amplitude fatigue loading, since in principle any loading history can be represented as a sequence of overloads and underloads. In the case of overload, along with some other minor causes, the residual stress changes at the crack tip and crack closure behind the tip can be thought of as the main factors that affect the fatigue crack growth rate. Whilst this has been recognised and accepted for many decades, controversy persists regarding the relative significance and presence of these two effects, and consensus is yet to emerge. The effect of crack closure, when the baseline loading ratio is high enough, can be inhibited so that the main cause of retardation becomes doubtless the residual stress present ahead the crack tip. In the present paper we report our attempt to deconvolve the contributions of crack closure and residual stress on crack retardation following an overload. To accomplish this task we analyse the results of fatigue tests run at two baseline load ratios, namely R=0.1 and R=0.7. At the load ratio of R=0.7 the crack closure effect is not operative, as confirmed by Digital Image Correlation analysis of the crack flanks close to the tip, and post mortem fractographic analysis of crack surfaces. Therefore, for R=0.7 the compressive residual stress region created by the overload ahead of the crack tip is the sole mechanism causing crack retardation. Therefore, for R=0.7 the focus must be placed entirely on the strain field around the crack tip. To this end, line profiles along the crack bisector of elastic strain in the crack opening direction were collected at several stages of crack propagation past the overload using in situ Synchrotron X-ray Powder Diffraction (SXRPD) technique. By

  12. Stress Corrosion Cracking of Pipeline Steels

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    This paper provides a review of the differences between high pH and near-neutral pH stress corrosion cracking ofpipeline steels, influencing factors, and mechanisms. The characteristics and historical information on both forms ofSCC are discussed. The prospect for research in the future is also presented.

  13. Film-induced stress enhancing stress corrosion cracking of austenitic stainless steel

    Institute of Scientific and Technical Information of China (English)

    李金许; 陈浩; 王燕斌; 乔利杰; 褚武扬

    2001-01-01

    A constant deflection device designed for use within a transmission electron microscopy (TEM) was used to investigate the change in dislocation configuration ahead of a crack tip during stress corrosion cracking (SCC) of type 310 austenitic stainless steel in a boiling MgCl2 solution, and the initiation process of stress corrosion microcrack. Results showed that corrosion process during SCC enhanced dislocation emission, multiplication and motion. Microcracks of SCC were initiated when the corrosion-enhanced dislocation emission and motion reached critical state.   A passive film formed during corrosion of austenitic stainless steel in the boiling MgCl2 solution generated a tensile stress. During SCC, the additive tensile stress generated at the metal/passive film interface helps enhance dislocation emission and motion.

  14. Stress corrosion cracking of copper canisters

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-12-15

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

  15. Inhibition of Ce3+ on Stress Corrosion Crack of High Strength Aluminum Alloy

    Directory of Open Access Journals (Sweden)

    LI Wen-ting

    2017-05-01

    Full Text Available The stress corrosion cracking (SCC susceptibility of 7A04 high strength aluminum alloy in 3.5% (mass fraction NaCl solution and the Ce3+ inhibition of SCC were investigated by slow stress rate test(SSRT, using constant current polarization, electrochemical noise (ECN and electrochemical impedance spectroscopy (EIS techniques. The inhibition mechanism of Ce3+ ions on the initiation and propagation of cracking was also analyzed. The results indicate that both anodic and cathodic galvanostatic polarizations can accelerate the SCC of 7A04, the former increases anodic dissolution but the latter accelerates hydrogen embrittlement of crack tip. SCC susceptibility of 7A04 can be reduced effectively by the addition of cerium ions, the fracture time is delayed and slowed down, but only during the initiation other than the propagation stage of cracking. Ce3+ ions can restrain the initiation of metastable pitting on the surface of 7A04 specimen, which therefore increase the induction time of the cracking since that the micro pits are usually the source of cracking.However, once the crack begins to propagate or the specimen is notched, the addition of cerium ions can rarely inhibit the cracking process. This is possibly attributed to that the radius of Ce3+ ion is too large to diffuse into the crack tip or it is hard to form protective CeO2 layer, Ce3+ ion therefore fails to rehabilitate the active alloy at the crack tip and further reduce the SCC developing rate of 7A04. SEM also indicates that the crack initiation of smooth 7A04 specimens is mainly induced by metastable or stable pits.

  16. Sizing stress corrosion cracks using laser ultrasonics

    Energy Technology Data Exchange (ETDEWEB)

    Rehman, Hamood; McNealy, Rick; Fingerhut, Martin [Applus-RTD. Houston, TX (United States); Klein, Marvin; Ansari, Homayoon [Intelligent Optical Systems, Inc. Los Angeles, CA (United States); Kania Richard [TransCanada. Calgary, AB (Canada); Rapp, Steve [Spectra Energy, Houston, TX (United States)

    2010-07-01

    Despite various efforts, no reliable tools and techniques are available to enable an operator to quantify the impact of an SCC (Stress Corrosion Cracking) colony on the safety and integrity of a pipeline. Reliable non-destructive detection and measurement tools are not available either. There is therefore a large gap between current technology and the needs of the pipeline industry. Recent developments promise that with a concentrated effort, a comprehensive solution can be devised. This paper describes technical work performed to develop and validate both the inspection tool and the time of flight diffraction (TOFD) technique for sizing the depth of SCC. It also presents preliminary results of work on a closely related project that provides, on the basis of this technology, an integrated approach and tool for mapping, sizing, and evaluating SCC, through which significant cracks are filtered from more benign cracks within an SCC colony.

  17. A numerical analysis of stress intensity factors for cracks emanating from an elliptical hole in a rectangular plate under biaxial loads

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Concerns with stress intensity factors for cracks emanating from an elliptical hole in a rectangular plate under biaxial loads by means of a boundary element method which consists of non-singular displacement discontinuity element presented by Crouch and Starfied[6] and crack-tip displacement discontinuity elements proposed by the author. In the boundary elenent implementation the left or the right crack-tip displacement discontinuity element is placed locally at the corresponding left or right crack tip on top of the constant displacement discontinuity elements that cover the entire crack surface and other boundaries. The present numerical results further illustrate that the present numerical approach is very effective and accurate for calculating stress intensity factors of complex cracks in a finite plate and can reveal the effect of the biaxial load and the cracked body geometry on stress intensity factors.

  18. An I-integral method for crack-tip intensity factor variation due to domain switching in ferroelectric single-crystals

    Science.gov (United States)

    Yu, Hongjun; Wang, Jie; Shimada, Takahiro; Wu, Huaping; Wu, Linzhi; Kuna, Meinhard; Kitamura, Takayuki

    2016-09-01

    In the present study, an I-integral method is established for solving the crack-tip intensity factors of ferroelectric single-crystals. The I-integral combined with the phase field model is successfully used to investigate crack-tip intensity factor variations due to domain switching in ferroelectricity subjected to electromechanical loadings, which exhibits several advantages over previous methods based on small-scale switching. First, the shape of the switching zone around a crack tip is predicted by the time-dependent Ginzburg-Landau equation, which does not require preset energy-based switching criterion. Second, the I-integral can directly solve the crack-tip intensity factors and decouple the crack-tip intensity factors of different modes based on superimposing an auxiliary state onto an actual state. Third, the I-integral is area-independent, namely, the I-integral is not affected by the integral area size, the polarization distributions, or domain walls. This makes the I-integral applicable to large-scale domain switching. To this end, the electro-elastic field intensity factors of an impermeable crack in PbTiO3 ferroelectric single crystals are evaluated under electrical, mechanical, and combined loading. The intensity factors obtained by the I-integral agree well with those obtained by the extrapolation technique. From numerical results, the following conclusions can be drawn with respect to fracture behavior of ferroelectrics under large-scale switching. Under displacement controlled mechanical loading, the stress intensity factors (SIFs) decrease monotonically due to the domain switching process, which means a crack tip shielding or effective switching-induced toughening occurs. If an external electric field is applied, the electric displacement intensity factor (EDIF) increases in all cases, i.e., the formed domain patterns enhance the electric crack tip loading. The energy release rate, expressed by the crack-tip J-integral, is reduced by the domain

  19. The concept of the average stress in the fracture process zone for the search of the crack path

    Directory of Open Access Journals (Sweden)

    Yu.G. Matvienko

    2015-10-01

    Full Text Available The concept of the average stress has been employed to propose the maximum average tangential stress (MATS criterion for predicting the direction of fracture angle. This criterion states that a crack grows when the maximum average tangential stress in the fracture process zone ahead of the crack tip reaches its critical value and the crack growth direction coincides with the direction of the maximum average tangential stress along a constant radius around the crack tip. The tangential stress is described by the singular and nonsingular (T-stress terms in the Williams series solution. To demonstrate the validity of the proposed MATS criterion, this criterion is directly applied to experiments reported in the literature for the mixed mode I/II crack growth behavior of Guiting limestone. The predicted directions of fracture angle are consistent with the experimental data. The concept of the average stress has been also employed to predict the surface crack path under rolling-sliding contact loading. The proposed model considers the size and orientation of the initial crack, normal and tangential loading due to rolling–sliding contact as well as the influence of fluid trapped inside the crack by a hydraulic pressure mechanism. The MATS criterion is directly applied to equivalent contact model for surface crack growth on a gear tooth flank.

  20. Stress corrosion cracking resistance of aluminum alloy 7000 series after two-step aging

    Directory of Open Access Journals (Sweden)

    Jegdić Bore V.

    2015-01-01

    Full Text Available The effect of one step-and a new (short two-step aging on the resistance to stress corrosion cracking of an aluminum alloy 7000 series was investigated, using slow strain rate test and fracture mechanics method. Aging level in the tested alloy was evaluated by means of scanning electron microscopy and measurements of electrical resistivity. It was shown that the alloy after the new two-step aging is significantly more resistant to stress corrosion cracking. Values of tensile properties and fracture toughness are similar for both thermal states. Processes that take place at the crack tip have been considered. The effect of the testing solution temperature on the crack growth rate on the plateau was determined. Two values of the apparent activation energy were obtained. These values correspond to different processes that control crack growth rate on the plateau at higher and lower temperatures. [Projekat Ministarstva nauke Republike Srbije, br. TR 34028 i br. TR 34016

  1. Strain energy density-distance criterion for the initiation of stress corrosion cracking of alloy X-750

    Energy Technology Data Exchange (ETDEWEB)

    Hall, M.M. Jr.; Symons, D.M.

    1996-05-01

    A strain energy density-distance criterion was previously developed and used to correlate rising-load K{sub c} initiation data for notched and fatigue precracked specimens of hydrogen precharged Alloy X-750. This criterion, which was developed for hydrogen embrittlement (HE) cracking, is used here to correlate static-load stress corrosion cracking (SCC) initiation times obtained for smooth geometry, notched and fatigue precracked specimens. The onset of SCC crack growth is hypothesized to occur when a critical strain, which is due to environment-enhanced creep, is attained within the specimen interior. For notched and precracked specimens, initiation is shown by analysis to occur at a variable distance from notch and crack tips. The initiation site varies from very near the crack tip, for highly loaded sharp cracks, to a site that is one grain diameter from the notch, for lower loaded, blunt notches. The existence of hydrogen gradients, which are due to strain-induced hydrogen trapping in the strain fields of notch and crack tips, is argued to be controlling the site for initiation of cracking. By considering the sources of the hydrogen, these observations are shown to be consistent with those from the previous HE study, in which the characteristic distance for crack initiation was found to be one grain diameter from the notch tip, independent of notch radius, applied stress intensity factor and hydrogen level.

  2. Stress-corrosion cracking of titanium alloys.

    Science.gov (United States)

    Blackburn, M. J.; Feeney, J. A.; Beck, T. R.

    1973-01-01

    In the light of research material published up to May 1970, the current understanding of the experimental variables involved in the stress-corrosion cracking (SCC) behavior of titanium and its alloys is reviewed. Following a brief summary of the metallurgy and electrochemistry of titanium alloys, the mechanical, electrochemical, and metallurgical parameters influencing SCC behavior are explored with emphasis on crack growth kinetics. Macro- and microfeatures of fractures are examined, and it is shown that many transgranular SCC failures exhibit morphological and crystallographic features similar to mechanical cleavage failures. Current SCC models are reviewed with respect to their ability to explain the observed SCC behavior of titanium and its alloys. Possible methods for eliminating or minimizing stress corrosion hazards in titanium or titanium alloy components are described.

  3. Accelerated Stress Corrosion Crack Initiation of Alloys 600 and 690 in Hydrogenated Supercritical Water

    Science.gov (United States)

    Moss, Tyler; Was, Gary S.

    2017-04-01

    The objective of this study is to determine whether stress corrosion crack initiation of Alloys 600 and 690 occurs by the same mechanism in subcritical and supercritical water. Tensile bars of Alloys 690 and 600 were strained in constant extension rate tensile experiments in hydrogenated subcritical and supercritical water from 593 K to 723 K (320 °C to 450 °C), and the crack initiation behavior was characterized by high-resolution electron microscopy. Intergranular cracking was observed across the entire temperature range, and the morphology, structure, composition, and temperature dependence of initiated cracks in Alloy 690 were consistent between hydrogenated subcritical and supercritical water. Crack initiation of Alloy 600 followed an Arrhenius relationship and did not exhibit a discontinuity or change in slope after crossing the critical temperature. The measured activation energy was 121 ± 13 kJ/mol. Stress corrosion crack initiation in Alloy 690 was fit with a single activation energy of 92 ± 12 kJ/mol across the entire temperature range. Cracks were observed to propagate along grain boundaries adjacent to chromium-depleted metal, with Cr2O3 observed ahead of crack tips. All measures of the SCC behavior indicate that the mechanism for stress corrosion crack initiation of Alloy 600 and Alloy 690 is consistent between hydrogenated subcritical and supercritical water.

  4. Accelerated Stress Corrosion Crack Initiation of Alloys 600 and 690 in Hydrogenated Supercritical Water

    Science.gov (United States)

    Moss, Tyler; Was, Gary S.

    2017-01-01

    The objective of this study is to determine whether stress corrosion crack initiation of Alloys 600 and 690 occurs by the same mechanism in subcritical and supercritical water. Tensile bars of Alloys 690 and 600 were strained in constant extension rate tensile experiments in hydrogenated subcritical and supercritical water from 593 K to 723 K (320 °C to 450 °C), and the crack initiation behavior was characterized by high-resolution electron microscopy. Intergranular cracking was observed across the entire temperature range, and the morphology, structure, composition, and temperature dependence of initiated cracks in Alloy 690 were consistent between hydrogenated subcritical and supercritical water. Crack initiation of Alloy 600 followed an Arrhenius relationship and did not exhibit a discontinuity or change in slope after crossing the critical temperature. The measured activation energy was 121 ± 13 kJ/mol. Stress corrosion crack initiation in Alloy 690 was fit with a single activation energy of 92 ± 12 kJ/mol across the entire temperature range. Cracks were observed to propagate along grain boundaries adjacent to chromium-depleted metal, with Cr2O3 observed ahead of crack tips. All measures of the SCC behavior indicate that the mechanism for stress corrosion crack initiation of Alloy 600 and Alloy 690 is consistent between hydrogenated subcritical and supercritical water.

  5. Threshold Stress Intensity of Hydrogen-Induced Cracking and Stress Corrosion Cracking of High Strength Steel

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The threshold stress intensity of stress corrosion cracking (SCC) for 40CrMo steel in 3.5 % NaCl solution decreased exponentially with the increase of yield strength. The threshold stress intensity of hydrogen-induced cracking during dynamical charging for 40CrMo steel decreased linearly with the logarithm of the concentration of diffusible hydrogen. This equation was also applicable to SCC of high strength steel in aqueous solution. The critical hydrogen enrichment concentration necessary for SCC of high strength steel in water decreased exponentially with the increase of yield strength. Based on the results, the relationship between KISCC and σys could be deduced.

  6. Effects of microstructure on crack tip fields and fracture toughness in PC/ABS polymer blends

    NARCIS (Netherlands)

    Seelig, Thomas; Van der Giessen, Erik

    2007-01-01

    Numerical simulations are performed in order to gain a better understanding of the effects of various microstructural features and toughening mechanisms in amorphous PC/ABS polymer blends. Crack tip loading under global small-scale yielding conditions is considered with the blend microstructure expl

  7. Influence of the crack-tip hydride concentration on the fracture toughness of Zircaloy-4

    Energy Technology Data Exchange (ETDEWEB)

    Bertolino, G. [LMS, CNRS UMR7649, Ecole Polytechnique, 91128 Palaiseau cedex (France)]. E-mail: bertolin@cab.cnea.gov.ar; Perez Ipina, J. [CONICET (Argentina); Universidad Nacional del Comahue, 8300 Neuquen (Argentina); Meyer, G. [Centro Atomico Bariloche, CNEA, 8400 Bariloche (Argentina); CONICET (Argentina)

    2006-01-01

    The influence of a hydrogen concentration gradient at the crack-tip and hydride platelet orientation on the fracture toughness, fracture mode and micromechanisms of a Zircaloy-4 commercial alloy was studied. Fracture toughness was measured on CT specimens and the analysis was performed in terms of J-integral resistance curves at temperatures ranging from 293 to 473 K. Fracture toughness results of specimens containing higher hydrides concentration near the crack-tip region, preferentially orientated in the crack plane, were compared to those obtained from specimens with a homogeneous hydrogen distribution and different platelet orientation; specimens were obtained by charging them in loaded and unloaded condition, respectively. Changes on both macroscopic and microscopic fracture behaviour were observed at temperatures ranging from 293 to 343 K, and the results show the relevance of both hydride concentration and platelet orientation. The existence of a ductile-to-brittle transition is discussed at the light of these new results.

  8. Dislocation formation and twinning from the crack tip in Ni3Al: molecular dynamics simulations

    Institute of Scientific and Technical Information of China (English)

    Xie Hong-Xian; Wang Chong-Yu; Yu Tao; Du Jun-Ping

    2009-01-01

    The mechanism of low-temperature deformation in a fracture process of L12Ni3Al is studied by molecular dynamic simulations. Owing to the unstable stacking energy, the [011] superdislocation is dissociated into partial dislocations separated by a stacking fault. The simulation results show that when the crack speed is larger than a critical speed, the Shockley partial dislocations will break forth from both the crack tip and the vicinity of the crack tip; subsequently the super intrinsic stacking faults are formed in adjacent {111} planes, meanwhile the super extrinsic stacking faults and twinning also occur. Our simulation results suggcst that at low temperatures the ductile fracture in L12Ni3Al is accompanied by twinning, which is produced by super-intrinsic stacking faults formed in adjacent {111} planes.

  9. Mode III interfacial crack in the presence of couple stress elastic materials

    CERN Document Server

    Piccolroaz, Andrea; Radi, Enrico

    2010-01-01

    In this paper we are concerned with the problem of a crack lying at the interface between dissimilar materials with microstructure undergoing antiplane deformations. The micropolar behaviour of the materials is described by the theory of couple stress elasticity developed by Koiter (1964). This constitutive model includes the characteristic lengths in bending and torsion and thus it is able to account for the underlying microstructure of the two materials. We perform an asymptotic analysis to investigate the behaviour of the solution near the crack tip. It turns out that the stress singularity at the crack tip is strongly influenced by the microstructural parameters and it may or may not show oscillatory behaviour depending on the ratio between the characteristic lengths.

  10. Relationship among Parameters Evaluating Stress Corrosion Cracking

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    @@The threshold stress, σc, for sulfide stress corrosion cracking (SCC) of seven pipeline steels and five other steels, the critical stress, SC, for seven pipeline steels and two drill rod steels with various strengths and the susceptibility to SCC, IRA or σf(SCC)/σf, for four pipeline steels, two drill rod steels and five other steels were measured. The results showed that there are no definite elationships among σc, SC and IRA or σf(SCC)/σf. The threshold stress for hydrogen induced cracking (HIC) during charging with loading in the H2SO4 solution, σc(H), decreased linearly with logarithm of the concentration of diffusible hydrogen c0, i.e., σC(H)=A-B Inc0 for four pipeline steels. σc(H) obtained with a special cathodic current ic, which was corresponding to the diffusible hydrogen concentration during immersing in the H2S solution, were consistent with σc for sulfide SCC for four pipeline steels.Therefore, σc for sulfide SCC can be measured using dynamically charging in the H2SO4 solution with the special cathodic current ic.

  11. A Relationship Between Constraint and the Critical Crack Tip Opening Angle

    Science.gov (United States)

    Johnston, William M.; James, Mark A.

    2009-01-01

    Of the various approaches used to model and predict fracture, the Crack Tip Opening Angle (CTOA) fracture criterion has been successfully used for a wide range of two-dimensional thin-sheet and thin plate applications. As thicker structure is considered, modeling the full three-dimensional fracture process will become essential. This paper investigates relationships between the local CTOA evaluated along a three-dimensional crack front and the corresponding local constraint. Previously reported tunneling crack front shapes were measured during fracture by pausing each test and fatigue cycling the specimens to mark the crack surface. Finite element analyses were run to model the tunneling shape during fracture, with the analysis loading conditions duplicating those tests. The results show an inverse relationship between the critical fracture value and constraint which is valid both before maximum load and after maximum load.

  12. 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.

  13. Effects of the Crack Tip Constraint on the Fracture Assessment of an Al 5083-O Weldment for Low Temperature Applications

    Directory of Open Access Journals (Sweden)

    Dong Hyun Moon

    2017-07-01

    Full Text Available The constraint effect is the key issue in structural integrity assessments based on two parameter fracture mechanics (TPFM to make a precise prediction of the load-bearing capacity of cracked structural components. In this study, a constraint-based failure assessment diagram (FAD was used to assess the fracture behavior of an Al 5083-O weldment with various flaws at cryogenic temperature. The results were compared with those of BS 7910 Option 1 FAD, in terms of the maximum allowable stress. A series of fracture toughness tests were conducted with compact tension (CT specimens at room and cryogenic temperatures. The Q parameter for the Al 5083-O weldment was evaluated to quantify the constraint level, which is the difference between the actual stress, and the Hutchinson-Rice-Rosengren (HRR stress field near the crack tip. Nonlinear 3D finite element analysis was carried out to calculate the Q parameter at cryogenic temperature. Based on the experimental and numerical results, the influence of the constraint level correction on the allowable applied stress was investigated using a FAD methodology. The results showed that the constraint-based FAD procedure is essential to avoid an overly conservative allowable stress prediction in an Al 5083-O weldment with flaws.

  14. 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.

  15. 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

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

    Directory of Open Access Journals (Sweden)

    Yongshui Kang

    2014-10-01

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

  17. Analysis of stress corrosion cracking in alloy 718 following commercial reactor exposure

    Science.gov (United States)

    Leonard, Keith J.; Gussev, Maxim N.; Stevens, Jacqueline N.; Busby, Jeremy T.

    2015-11-01

    Alloy 718 is generally considered a highly corrosion-resistant material but can still be susceptible to stress corrosion cracking (SCC). The combination of factors leading to SCC susceptibility in the alloy is not always clear enough. In the present work, alloy 718 leaf spring (LS) materials that suffered stress corrosion damage during two 24-month cycles in pressurized water reactor service, operated to >45 MWd/mtU burn-up, was investigated. Compared to archival samples fabricated through the same processing conditions, little microstructural and property changes occurred in the material with in-service irradiation, contrary to high dose rate laboratory-based experiments reported in literature. Though the lack of delta phase formation along grain boundaries would suggest a more SCC resistant microstructure, grain boundary cracking in the material was extensive. Crack propagation routes were explored through focused ion beam milling of specimens near the crack tip for transmission electron microscopy as well as in polished plan view and cross-sectional samples for electron backscatter diffraction analysis. It has been shown in this study that cracks propagated mainly along random high-angle grain boundaries, with the material around cracks displaying a high local density of dislocations. The slip lines were produced through the local deformation of the leaf spring material above their yield strength. The cause for local SCC appears to be related to oxidation of both slip lines and grain boundaries, which under the high in-service stresses resulted in crack development in the material.

  18. STRESS FIELD AT A TIP OF A PREFABRICATED SPIRAL V-NOTCH

    Institute of Scientific and Technical Information of China (English)

    郑周练; 陈山林; 叶晓明

    2004-01-01

    Based on the tranditional V-notched blasting,a technique of spirally V-notched blasting to loosen earth and rock was presented.Fracture mechanics and Westergaard stress function were adopted to build a complex stress function to derive the plane stress and strain fields at one tip of the crack under a quasi-static pressure.An expression was formulated to define the stress intensity factor of spiral V-notch loosen blasting.Factors that have effects on the stress intensity factor were studied.It is demonstrated that spiral V-notch loosen blasting is an extension of vertical V-notch blasting,straight cracking,and alike theories.

  19. The Dirichlet Problem for the 2D Laplace Equation in a Domain with Cracks without Compatibility Conditions at Tips of the Cracks

    Directory of Open Access Journals (Sweden)

    P. A. Krutitskii

    2012-01-01

    Full Text Available We study the Dirichlet problem for the 2D Laplace equation in a domain bounded by smooth closed curves and smooth cracks. In the formulation of the problem, we do not require compatibility conditions for Dirichlet's boundary data at the tips of the cracks. However, if boundary data satisfies the compatibility conditions at the tips of the cracks, then this is a particular case of our problem. The cases of both interior and exterior domains are considered. The well-posed formulation of the problem is given, theorems on existence and uniqueness of a classical solution are proved, and the integral representation for a solution is obtained. It is shown that weak solution of the problem does not typically exist, though the classical solution exists. The asymptotic formulae for singularities of a solution gradient at the tips of the cracks are presented.

  20. Modeling of Stress Corrosion Cracking for High Level Radioactive-Waste Packages

    Energy Technology Data Exchange (ETDEWEB)

    Lu, S C; Gordon, G M; Andresen, P L; Herrera, M L

    2003-06-20

    A stress corrosion cracking (SCC) model has been adapted for performance prediction of high level radioactive-waste packages to be emplaced in the proposed Yucca Mountain radioactive-waste repository. SCC is one form of environmentally assisted cracking due to three factors, which must be present simultaneously: metallurgical susceptibility, critical environment, and static (or sustained) tensile stresses. For waste packages of the proposed Yucca Mountain repository, the outer barrier material is Alloy 22, a highly corrosion resistant alloy, the environment is represented by the water film present on the surface of the waste package from dripping or deliquescence of soluble salts present in any surface deposits, and the stress is principally the weld induced residual stress. SCC has historically been separated into ''initiation'' and ''propagation'' phases. Initiation of SCC will not occur on a smooth surface if the surface stress is below a threshold value defined as the threshold stress. Cracks can also initiate at and propagate from flaws (or defects) resulting from manufacturing processes (such as welding). To account for crack propagation, the slip dissolution/film rupture (SDFR) model is adopted to provide mathematical formulas for prediction of the crack growth rate. Once the crack growth rate at an initiated SCC is determined, the time to through-wall penetration for the waste package can be calculated. The SDFR model relates the advance (or propagation) of cracks, subsequent to the crack initiation from bare metal surface, to the metal oxidation transients that occur when the protective film at the crack tip is continually ruptured and repassivated. A crack, however, may reach the ''arrest'' state before it enters the ''propagation'' phase. There exists a threshold stress intensity factor, which provides a criterion for determining if an initiated crack or pre

  1. Stress corrosion cracking of AISI 321 stainless steel in acidic chloride solution

    Indian Academy of Sciences (India)

    Yanliang Huang

    2002-02-01

    The stress corrosion cracking (SCC) of AISI 321 stainless steel in acidic chloride solution was studied by slow strain rate (SSR) technique and fracture mechanics method. The fractured surface was characterized by cleavage fracture. In order to clarify the SCC mechanism, the effects of inhibitor KI on SCC behaviour were also included in this paper. A study showed that the inhibition effects of KI on SCC were mainly attributed to the anodic reaction of the corrosion process. The results of strain distribution in front of the crack tip of the fatigue pre-cracked plate specimens in air, in the blank solution (acidic chloride solution without inhibitor KI) and in the solution added with KI measured by speckle interferometry (SPI) support the unified mechanism of SCC and corrosion fatigue cracking (CFC).

  2. Atomistic simulation study of the effect of martensitic transformation volume change on crack-tip material evolution and fracture toughness

    Energy Technology Data Exchange (ETDEWEB)

    Grujicic, M. [Clemson Univ., SC (United States). Dept. of Mechanical Engineering; Lai, S.G. [Clemson Univ., SC (United States). Dept. of Mechanical Engineering; Gumbsch, P. [Max Planck-Institut fur Metallforshung Institut fuer Werstoffwissenshaft, Seestrasse 92, D-7000 Stuttgart I (Germany)

    1997-07-15

    The effect of the sign of the F.C.C.{yields}B.C.C. martensitic transformation volume change in Fe-20Ni on material evolution in a region surrounding the crack tip and the accompanying change in the fracture resistance of the material have been investigated using molecular dynamics simulations. The interaction between atoms has been modeled using the embedded atom method (EAM) interatomic potentials. To obtain both the positive and the negative values of the transformation volume change, small adjustments had to be made in the EAM functions. These changes did not significantly affect of the key materials properties, such as the relative thermodynamic stability of the F.C.C. and B.C.C. structures, elastic constants, (11 anti 2){sub bcc} twin boundary energy, (10 anti 1){sub fcc}/(1 anti 21){sub bcc} interfacial energy, etc. The simulation results show that the sign of the transformation volume change has a profound effect on the material evolution and the path of the advancing crack. When the volume change is negative, the region ahead of the crack tip undergoes the transformation only after the other regions around the crack tip have already transformed. The crack tip undergoes a significant blunting and tends to stay on the original crack plane. In sharp contrast, when the volume change is positive, the region ahead of the crack tip transforms first and significant decohesion along the F.C.C./B.C.C. interfaces takes place. Consequently the crack tends to branch out. The effect of material evolution at the crack tip on the ability of the material to withstand further fracture has been quantified by calculating the Eshelby`s F{sub 1} conservation integral. The sign of the transformation volume change is found to have a major effect on the change of the F{sub 1} integral with the simulation time. (orig.)

  3. Three-dimensional characterization of stress corrosion cracks

    DEFF Research Database (Denmark)

    Lozano-Perez, S.; Rodrigo, P.; Gontard, Lionel Cervera

    2011-01-01

    Understanding crack propagation and initiation is fundamental if stress corrosion cracking (SCC) mechanisms are to be understood. However, cracking is a three-dimensional (3D) phenomenon and most characterization techniques are restricted to two-dimensional (2D) observations. In order to overcome...... the best spatial resolution. To illustrate the power of these techniques, different parts of dominant stress corrosion cracks in Ni-alloys and stainless steels have been reconstructed in 3D. All relevant microstructural features can now be studied in detail and its relative orientation respect...

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

    Directory of Open Access Journals (Sweden)

    L.Y. Yang

    2014-07-01

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

  5. Stress-ratio effect on mode II propagation of interlaminar fatigue cracks in graphite/epoxy composites

    Energy Technology Data Exchange (ETDEWEB)

    Tanaka, Keisuke; Tanaka, Hiroshi [Nagoya Univ. (Japan). Dept. of Mechanical Engineering

    1997-12-31

    The effect of the stress ratio on the propagation behavior of Mode II interlaminar fatigue cracks was studied with unidirectional graphite/epoxy laminates, Toray T800H/{number_sign}3631. End-notched flexure (ENF) specimens were used for fatigue tests under the stress ratios of R = 0.2, 0.5, and 0.6; and end-loaded split (ELS) specimens were used for tests under R = {minus}1.0, {minus}0.5, and 0.2. For each stress ratio, the crack propagation rate was given by a power function of the stress intensity range, {Delta}K{sub 11}, in the region of rates above 10{sup {minus}9} m/cycle. Below this region, there exists the threshold for fatigue crack propagation. The threshold condition is given by a constant value of the stress intensity range, {Delta}K{sub 11th} = 1.8 MPa{radical}m. The crack propagation rate is determined by {Delta}K{sub 11} near the threshold, while by the maximum stress identity factor, K{sub 11max}, at high rates. A fracture mechanics equation is proposed for predicting the propagation rate of Mode II fatigue cracks under various stress ratios. The effect of the stress ratio on the micromechanism of Mode II fatigue crack propagation was discussed on the basis of the microscopic observations of fracture surfaces and near-crack-tip regions.

  6. Imaging in-plane and normal stresses near an interface crack using traction force microscopy.

    Science.gov (United States)

    Xu, Ye; Engl, Wilfried C; Jerison, Elizabeth R; Wallenstein, Kevin J; Hyland, Callen; Wilen, Larry A; Dufresne, Eric R

    2010-08-24

    Colloidal coatings, such as paint, are all around us. However, we know little about the mechanics of the film-forming process because the composition and properties of drying coatings vary dramatically in space and time. To surmount this challenge, we extend traction force microscopy to quantify the spatial distribution of all three components of the stress at the interface of two materials. We apply this approach to image stress near the tip of a propagating interface crack in a drying colloidal coating and extract the stress intensity factor.

  7. Fatigue crack tip damaging micromechanisms in a ferritic-pearlitic ductile cast iron

    Directory of Open Access Journals (Sweden)

    Francesco Iacoviello

    2015-07-01

    Full Text Available Due to the peculiar graphite elements shape, obtained by means of a chemical composition control (mainly small addition of elements like Mg, Ca or Ce, Ductile Cast Irons (DCIs are able to offer the good castability of gray irons with the high mechanical properties of irons (first of all, toughness. This interesting properties combination can be improved both by means of the chemical composition control and by means of different heat treatments(e.g. annealing, normalizing, quenching, austempering etc. In this work, fatigue crack tip damaging micromechanisms in a ferritic-pearlitic DCI were investigated by means of scanning electron microscope observations performed on a lateral surface of Compact Type (CT specimens during the fatigue crack propagation test (step by step procedure, performed according to the “load shedding procedure”. On the basis of the experimental results, different fatigue damaging micromechanisms were identified, both in the graphite nodules and in the ferritic – pearlitic matrix.

  8. Standard test method for crack-tip opening displacement (CTOD) fracture toughness measurement

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2008-01-01

    1.1 This test method covers the determination of critical crack-tip opening displacement (CTOD) values at one or more of several crack extension events, and may be used to measure cleavage crack initiation toughness for materials that exhibit a change from ductile to brittle behavior with decreasing temperature, such as ferritic steels. This test method applies specifically to notched specimens sharpened by fatigue cracking. The recommended specimens are three-point bend [SE(B)], compact [C(T)], or arc-shaped bend [A(B)] specimens. The loading rate is slow and influences of environment (other than temperature) are not covered. The specimens are tested under crosshead or clip gage displacement controlled loading. 1.1.1 The recommended specimen thickness, B, for the SE(B) and C(T) specimens is that of the material in thicknesses intended for an application. For the A(B) specimen, the recommended depth, W, is the wall thickness of the tube or pipe from which the specimen is obtained. Superficial surface machini...

  9. FEM solutions for plane stress mode-I and mode-II cracks in strain gradient plasticity

    Institute of Scientific and Technical Information of China (English)

    邱信明; 郭田福; 黄克智

    2000-01-01

    The strain gradient plasticity theory is used to investigate the crack-tip field in a power law hardening material. Numerical solutions are presented for plane-stress mode I and mode II cracks under small scale yielding conditions. A comparison is made with the existing asymptotic fields. It is found that the size of the dominance zone for the near-tip asymptotic field, recently obtained by Chen et al., is on the order 5% of the intrinsic material length I. Remote from the dominance zone, the computed stress field tends to be the classical HRR field. Within the plastic zone only force-stress dominated solution is found for either mode I or mode II crack.

  10. Transverse shear effects on the stress-intensity factor for a circumferentially cracked, specially orthotropic cylindrical shell

    Science.gov (United States)

    Delale, F.; Erdogan, F.

    1977-01-01

    The problem of a cylindrical shell containing a circumferential through crack is considered by taking into account the effect of transverse shear deformations. The formulation is given for a specially orthotropic material within the confines of a linearized shallow shell theory. The particular theory used permits the consideration of all five boundary conditions regarding moment and stress resultants on the crack surface. Consequently, aside from multiplicative constants representing the stress intensity factors, the membrane and bending components of the asymptotic stress fields near the crack tip are found to be identical. The stress intensity factors are calculated separately for a cylinder under a uniform membrane load, and that under a uniform bending moment. Sample results showing the nature of the out-of-plane crack surface displacement and the effect of the Poisson's ratio are presented.

  11. 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.

  12. Tips for Coping: The Music Educator and Stress.

    Science.gov (United States)

    Radocy, Rudolf E.; Heller, George N.

    1982-01-01

    Discusses sources of stress for music teachers and offers tips for coping with it. Relaxation exercises, physical exercise, and a change of environment are recommended. Teachers should realistically assess their abilities and career prospects. (AM)

  13. 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.

  14. SCATTERING OF HARMONIC ANTI-PLANE SHEAR STRESS WAVES BY A CRACK IN FUNCTIONALLY GRADED PIEZOELECTRIC/PIEZOMAGNETIC MATERIALS

    Institute of Scientific and Technical Information of China (English)

    Liang Jun

    2007-01-01

    In this paper, the dynamic behavior of a permeable crack in functionally graded piezoelectric/piezomagnetic materials is investigated. To make the analysis tractable, it is assumed that the material properties vary exponentially with the coordinate parallel to the crack. By using the Fourier transform, the problem can be solved with the help of a pair of dual integral equations in which the unknown is the jump of displacements across the crack surfaces. These equations are solved to obtain the relations between the electric filed, the magnetic flux field and the dynamic stress field near the crack tips using the Schmidt method. Numerical examples are provided to show the effect pf the functionally graded parameter and the circular frequency of the incident waves upon the stress, the electric displacement and the magnetic flux intensity factors of the crack.

  15. Critical applied stresses for a crack initiation from a sharp V-notch

    Directory of Open Access Journals (Sweden)

    L. Náhlík

    2014-10-01

    Full Text Available The aim of the paper is to estimate a value of the critical applied stress for a crack initiation from a sharp V-notch tip. The classical approach of the linear elastic fracture mechanics (LELM was generalized, because the stress singularity exponent differs from 0.5 in the studied case. The value of the stress singularity exponent depends on the V-notch opening angle. The finite element method was used for a determination of stress distribution in the vicinity of the sharp V-notch tip and for the estimation of the generalized stress intensity factor depending on the V-notch opening angle. Critical value of the generalized stress intensity factor was obtained using stability criteria based on the opening stress component averaged over a critical distance d from the V-notch tip and generalized strain energy density factor. Calculated values of the critical applied stresses were compared with experimental data from the literature and applicability of the LEFM concept is discussed.

  16. On the application of cohesive crack modeling in cementitious materials

    DEFF Research Database (Denmark)

    Stang, Henrik; Olesen, John Forbes; Poulsen, Peter Noe;

    2007-01-01

    Cohesive crack models-in particular the Fictitious Crack Model - are applied routinely in the analysis of crack propagation in concrete and mortar. Bridged crack models-where cohesive stresses are assumed to exist together with a stress singularity at the crack tip-on the other hand, are used....... Further, a quantitative condition is established indicating when a bridged crack model can be approximated with a cohesive crack model with smooth crack closure in terms of the ratio between the energy dissipation associated with the crack tip and the process zone....

  17. The role of local strains from prior cold work on stress corrosion cracking of α-brass in Mattsson's solution

    Energy Technology Data Exchange (ETDEWEB)

    Ulaganathan, Jaganathan, E-mail: jagan.ulaganathan@mail.utoronto.ca; Newman, Roger C., E-mail: roger.newman@utoronto.ca

    2014-06-01

    The dynamic strain rate ahead of a crack tip formed during stress corrosion cracking (SCC) under a static load is assumed to arise from the crack propagation. The strain surrounding the crack tip would be redistributed as the crack grows, thereby having the effect of dynamic strain. Recently, several studies have shown cold work to cause accelerated crack growth rates during SCC, and the slip-dissolution mechanism has been widely applied to account for this via a supposedly increased crack-tip strain rate in cold worked material. While these interpretations consider cold work as a homogeneous effect, dislocations are generated inhomogeneously within the microstructure during cold work. The presence of grain boundaries results in dislocation pile-ups that cause local strain concentrations. The local strains generated from cold working α-brass by tensile elongation were characterized using electron backscatter diffraction (EBSD). The role of these local strains in SCC was studied by measuring the strain distributions from the same regions of the sample before cold work, after cold work, and after SCC. Though, the cracks did not always initiate or propagate along boundaries with pre-existing local strains from the applied cold work, the local strains surrounding the cracked boundaries had contributions from both the crack propagation and the prior cold work. - Highlights: • Plastic strain localization has a complex relationship with SCC susceptibility. • Surface relief created by cold work creates its own granular strain localization. • Cold work promotes crack growth but several other factors are involved.

  18. Tips to Manage Anxiety and Stress

    Science.gov (United States)

    ... Disorder Specific Phobias Obsessive-Compulsive Disorder (OCD) Posttraumatic Stress Disorder (PTSD) Depression Bipolar Disorder Suicide and Prevention Stress Related Illnesses Myth-Conceptions Find ...

  19. Stress analysis of fracture of atherosclerotic plaques: crack propagation modeling.

    Science.gov (United States)

    Rezvani-Sharif, Alireza; Tafazzoli-Shadpour, Mohammad; Kazemi-Saleh, Davood; Sotoudeh-Anvari, Maryam

    2016-12-09

    Traditionally, the degree of luminal obstruction has been used to assess the vulnerability of atherosclerotic plaques. However, recent studies have revealed that other factors such as plaque morphology, material properties of lesion components and blood pressure may contribute to the fracture of atherosclerotic plaques. The aim of this study was to investigate the mechanism of fracture of atherosclerotic plaques based on the mechanical stress distribution and fatigue analysis by means of numerical simulation. Realistic models of type V plaques were reconstructed based on histological images. Finite element method was used to determine mechanical stress distribution within the plaque. Assuming that crack propagation initiated at the sites of stress concentration, crack propagation due to pulsatile blood pressure was modeled. Results showed that crack propagation considerably changed the stress field within the plaque and in some cases led to initiation of secondary cracks. The lipid pool stiffness affected the location of crack formation and the rate and direction of crack propagation. Moreover, increasing the mean or pulse pressure decreased the number of cycles to rupture. It is suggested that crack propagation analysis can lead to a better recognition of factors involved in plaque rupture and more accurate determination of vulnerable plaques.

  20. Stress-induced crack path in Aji granite under tensile stress

    Science.gov (United States)

    Kudo, Yozo; Sano, Osam; Murashige, Naokuni; Mizuta, Yoshiaki; Nakagawa, Koji

    1992-12-01

    The double-torsion test using Aji granite was carried out to investigate the interaction between stress-induced crack path and mineral grains. Crack velocities were controlled at range 10-7 m/s to 10-1 m/s. After the stressed specimens were dyed, we checked the crack path by thin section analysis, using an optical microscope. The stress-induced crack path was divided into two types, transgranular and intergranular cracks, and each path was subdivided with respect to mineral grains. In spite of the extensive range of crack velocities, the ratios between the transgranular and intergranular crack lengths did not change. The crack paths were all jagged, and often showed detour around the grain boundary when faced with obstacles like hard grains or preexisting cracks. That is to say, quartz grain played an important role as an obstacle. Feldspar grain could change the crack path because of its cleavage plane. Biolite grain had a serious effect on the path even if its constitution ratio is very small. Fractal dimensions of the crack paths were calculated by three methods, as indicators of surface roughness. The fractal dimensions were shown in a slight trend with the change of crack velocity. This trend can be explained from the point of limited cracking rate in stress corrosion.

  1. Residual stress in glass: indentation crack and fractography approaches.

    Science.gov (United States)

    Anunmana, Chuchai; Anusavice, Kenneth J; Mecholsky, John J

    2009-11-01

    To test the hypothesis that the indentation crack technique can determine surface residual stresses that are not statistically significantly different from those determined from the analytical procedure using surface cracks, the four-point flexure test, and fracture surface analysis. Soda-lime-silica glass bar specimens (4 mm x 2.3 mm x 28 mm) were prepared and annealed at 650 degrees C for 30 min before testing. The fracture toughness values of the glass bars were determined from 12 specimens based on induced surface cracks, four-point flexure, and fractographic analysis. To determine the residual stress from the indentation technique, 18 specimens were indented under 19.6N load using a Vickers microhardness indenter. Crack lengths were measured within 1 min and 24h after indentation, and the measured crack lengths were compared with the mean crack lengths of annealed specimens. Residual stress was calculated from an equation developed for the indentation technique. All specimens were fractured in a four-point flexure fixture and the residual stress was calculated from the strength and measured crack sizes on the fracture surfaces. The results show that there was no significant difference between the residual stresses calculated from the two techniques. However, the differences in mean residual stresses calculated within 1 min compared with those calculated after 24h were statistically significant (p=0.003). This study compared the indentation technique with the fractographic analysis method for determining the residual stress in the surface of soda-lime-silica glass. The indentation method may be useful for estimating residual stress in glass.

  2. Combined mode I stress intensity factors of slanted cracks

    Science.gov (United States)

    Ismail, A. E.; Rahman, M. Q. Abdul; Ghazali, M. Z. Mohd; Zulafif Rahim, M.; Rasidi Ibrahim, M.; Fahrul Hassan, Mohd; Nor, Nik Hisyamudin Muhd; Ariffin, A. M. T.; Zaini Yunos, Muhamad

    2017-08-01

    The solutions of stress intensity factors (SIFs) for slanted cracks in plain strain plate are hard to find in open literature. There are some previous solutions of SIFs available, however the studies are not completed except for the case of plain stress. The slanted cracks are modelled numerically using ANSYS finite element program. There are ten slanted angles and seven relative crack depths are used and the plate contains cracks which is assumed to fulfil the plain strain condition. The plate is then stressed under tension and bending loading and the SIFs are determined according to the displacement extrapolation method. Based on the numerical analysis, both slanted angles and relative crack length, a/L played an important role in determining the modes I and II SIFs. As expected the SIFs increased when a/L is increased. Under tension force, the introduction of slanted angles increased the SIFs. Further increment of angles reduced the SIFs however they are still higher than the SIFs obtained using normal cracks. Under bending moment, the present of slanted angles are significantly reduced the SIFs compared with the normal cracks. Under similar loading, mode II SIFs increased as function of a/L and slanted angles where increasing such parameters increasing the mode II SIFs.

  3. Stress Corrosion Cracking in Al-Zn-Mg-Cu Aluminum Alloys in Saline Environments

    Science.gov (United States)

    Holroyd, N. J. Henry; Scamans, G. M.

    2013-03-01

    Stress corrosion cracking of Al-Zn-Mg-Cu (AA7xxx) aluminum alloys exposed to saline environments at temperatures ranging from 293 K to 353 K (20 °C to 80 °C) has been reviewed with particular attention to the influences of alloy composition and temper, and bulk and local environmental conditions. Stress corrosion crack (SCC) growth rates at room temperature for peak- and over-aged tempers in saline environments are minimized for Al-Zn-Mg-Cu alloys containing less than ~8 wt pct Zn when Zn/Mg ratios are ranging from 2 to 3, excess magnesium levels are less than 1 wt pct, and copper content is either less than ~0.2 wt pct or ranging from 1.3 to 2 wt pct. A minimum chloride ion concentration of ~0.01 M is required for crack growth rates to exceed those in distilled water, which insures that the local solution pH in crack-tip regions can be maintained at less than 4. Crack growth rates in saline solution without other additions gradually increase with bulk chloride ion concentrations up to around 0.6 M NaCl, whereas in solutions with sufficiently low dichromate (or chromate), inhibitor additions are insensitive to the bulk chloride concentration and are typically at least double those observed without the additions. DCB specimens, fatigue pre-cracked in air before immersion in a saline environment, show an initial period with no detectible crack growth, followed by crack growth at the distilled water rate, and then transition to a higher crack growth rate typical of region 2 crack growth in the saline environment. Time spent in each stage depends on the type of pre-crack ("pop-in" vs fatigue), applied stress intensity factor, alloy chemistry, bulk environment, and, if applied, the external polarization. Apparent activation energies ( E a) for SCC growth in Al-Zn-Mg-Cu alloys exposed to 0.6 M NaCl over the temperatures ranging from 293 K to 353 K (20 °C to 80 °C) for under-, peak-, and over-aged low-copper-containing alloys (alloys (>~0.8 wt pct), they are typically

  4. Modeling Threshold of Stress Intensity Factor in Iodine Induced Stress Corrosion Crack of Zirconium

    Institute of Scientific and Technical Information of China (English)

    SHANG; Xin-yuan; CHEN; Peng

    2013-01-01

    KISCC,which is the threshold of stress intensity factor of iodine induced stress corrosion crack(ISCC)of Zirconium,reflects the susceptibility of ISCC of zirconium.Once the stress intensity factor surpasses the threshold,the cracking propagation modality in material will transform to transgranular from intergranular immediately and the velocity of the cracking will increase rapidly.Four key factors that’s

  5. Crack tip field in functionally gradient material with exponential variation of elastic constants in two directions

    Institute of Scientific and Technical Information of China (English)

    Tianhu Hao

    2005-01-01

    This paper presents an exact solution of the crack tip field in functionally gradient material with exponential variation of elastic constants. The dimensionless Poisson's ratios v0 of the engineering materials (iron, glass... ) are far less than one; therefore, neglecting them, one can simplify the basic equation and the exact solution is easy to obtain.Although the exact solution for the case v0 ≠ 0 is also obtained, it is very complicated and the main result is the same with the case v0 = 0 (it will be dealt with in Appendix Ⅶ).It has been found that the exponential term exp(ax + by) in the constitutive equations becomes exp (ax/2 + by/2 - kr / 2 ) in the exact solution.

  6. Three-dimensional characterization of stress corrosion cracks

    Energy Technology Data Exchange (ETDEWEB)

    Lozano-Perez, S., E-mail: sergio.lozano-perez@materials.ox.ac.u [University of Oxford, Department of Materials, Parks Road, Oxford OX1 3PH (United Kingdom); Rodrigo, P. [Universidad Rey Juan Carlos, Dpto. de Ciencia e Ingenieria de Materiales, c/ Tulipan s.n., 28933 Mostoles (Madrid) (Spain); Gontard, Lionel C. [Danish Technical University, Center for Electron Nanoscopy, Matematiktorvet Building 307, Room 115, 2800 Kogens Lyngby (Denmark)

    2011-01-31

    Understanding crack propagation and initiation is fundamental if stress corrosion cracking (SCC) mechanisms are to be understood. However, cracking is a three-dimensional (3D) phenomenon and most characterization techniques are restricted to two-dimensional (2D) observations. In order to overcome this problem, different approaches to extract 3D information have been used in the recent years. In this work we will present the benefits of using 3D focused ion beam (FIB) slicing and electron tomography. 3D FIB slicing offers a fast and high throughput characterization while electron tomography offers the best spatial resolution. To illustrate the power of these techniques, different parts of dominant stress corrosion cracks in Ni-alloys and stainless steels have been reconstructed in 3D. All relevant microstructural features can now be studied in detail and its relative orientation respect to the strain direction and grain boundary plane accurately measured.

  7. Stress-compatible embedded cohesive crack in CST element

    DEFF Research Database (Denmark)

    Olesen, John Forbes; Poulsen, Peter Noe

    2010-01-01

    A simple element with an embedded strong discontinuity for modeling cohesive cracking of concrete is presented. The element differs from previous elements of the embedded type, in that a consistent stress field is obtained by direct enforcement of stress continuity across the crack. The displacem......A simple element with an embedded strong discontinuity for modeling cohesive cracking of concrete is presented. The element differs from previous elements of the embedded type, in that a consistent stress field is obtained by direct enforcement of stress continuity across the crack....... The displacement discontinuity is modeled in an XFEM fashion; however, the discontinuous displacement field is special, allowing for the direct enforcement of stress continuity. This in turn allows for elimination of extra degrees of freedom necessary for describing the crack deformations, thus the element has...... the same number of freedoms as its continuous basis: CST. The good performance of the element is demonstrated by its ability to simulate threepoint bending of a notched concrete beam. The advantage of the element is its simplicity and the straightforward implementation of it. Handling situations...

  8. Research on mechanisms of stress corrosion cracking in Zircaloy

    Energy Technology Data Exchange (ETDEWEB)

    Knorr, D.B.; Pelloux, R.M.

    1981-06-01

    The results of internal gas pressurization tests, primarily at 320/sup 0/C, on cladding tubes from two suppliers, Supplier A and Supplier B, are presented. The two lots show a substantial difference in iodine SCC susceptibility so a test matrix is used to resolve the relative contributions of surface condition, residual stress, and texture. Additional tests with constant deflection split-ring specimens and with unstressed cladding segments are used to understand crack initiation and the early crack growth stages of SCC. The difference in SCC susceptibility is due to crystallographic texture. Other variables such as surface finish, stress relief temperature, and residual stress have little or no effect. Mechanical properties, crack initiation, and crack propagation all depend on texture. Both initiation and propagation features are analyzed by scanning electron microscopy. A mechanism for crack initiation consistent with most observations in this study and with the work of other investigators is proposed. At 320/sup 0/C, lifetime is crack initiation limited while several tests at 390/sup 0/C indicate that lifetime is less initiation limited at higher temperature. 31 figures, 9 tables.

  9. Evaluation Of Finite Element Mesh Arrangements And Stress Intensity Factor Calculation Methods For Opening Mode Fracture Of Cracked-Cemented Materials

    Directory of Open Access Journals (Sweden)

    Hamid R. Nikraz

    2007-01-01

    Full Text Available Fracture mechanics is a branch of mechanics, which deals with the cracked body. Every construction material that currently in use inevitably is not flawless. The pre-existing crack may grow to cause structure failure due to low stress, which acts to a structure. Stress intensity factor (K is a single parameter in fracture mechanics, which can be used to examine if a crack, would propagate in a cracked structure under particular loading condition. Finite element method is used to analyze the cracked body to provide the displacements data around the crack tip (at quarter point elements due to load prescribed, for stress intensity factor determination. Two methods of stress intensity factor calculation, Quarter Point Displacement Technique (QPDT and Displacement Correlation Technique (DCT, were evaluated. A series of standard fracture testing were undertaken to provide the fracture load data (Pf, which coupled with the stress intensity factor analytical formula to calculate fracture toughness. The results showed that under a particular mesh arrangement, the result of finite element analysis could deviate from the analytical formula calculation result. The QPDT method is suitable for compact tension specimen but DCT seemed to be not. For cracked beam analysis, the QPDT and DCT calculations were in good agreement with the analytical formula as long as coupled with the appropriate mesh arrangement around the crack tip.

  10. Stress analysis and stress-intensity factors for finite geometry solids containing rectangular surface cracks

    Science.gov (United States)

    Gyekenyesi, J. P.; Mendelson, A.

    1977-01-01

    The line method of analysis is applied to the Navier-Cauchy equations of elastic equilibrium to calculate the displacement field in a finite geometry bar containing a variable depth rectangular surface crack under extensionally applied uniform loading. The application of this method to these equations leads to coupled sets of simultaneous ordinary differential equations whose solutions are obtained along sets of lines in a discretized region. Using the obtained displacement field, normal stresses, and the stress-intensity factor variation along the crack periphery are calculated for different crack depth to bar thickness ratios. Crack opening displacements and stress-intensity factors are also obtained for a through-thickness, center-cracked bar with variable thickness. The reported results show a considerable potential for using this method in calculating stress-intensity factors for commonly encountered surface crack geometries in finite solids

  11. Stress analysis and stress intensity factors for finite geometry solids containing rectangular surface cracks

    Science.gov (United States)

    Gyekenyesi, J. P.; Mendelson, A.

    1975-01-01

    The line method of analysis is applied to the Navier-Cauchy equations of elastic equilibrium to calculate the displacement field in a finite geometry bar containing a variable depth rectangular surface crack under extensionally applied uniform loading. The application of this method to these equations leads to coupled sets of simultaneous ordinary differential equations whose solutions are obtained along sets of lines in a discretized region. Using the obtained displacement field, normal stresses and the stress intensity factor variation along the crack periphery are calculated for different crack depth to bar thickness ratios. Crack opening displacements and stress intensity factors are also obtained for a through-thickness, center cracked bar with variable thickness. The reported results show a considerable potential for using this method in calculating stress intensity factors for commonly encountered surface crack geometries in finite solids.

  12. Steady-state propagation of a Mode III crack in couple stress elastic materials

    CERN Document Server

    Mishuris, G; Radi, E

    2012-01-01

    This paper is concerned with the problem of a semi-infinite crack steadily propagating in an elastic solid with microstructures subject to antiplane loading applied on the crack surfaces. The loading is moving with the same constant velocity as that of the crack tip. We assume subsonic regime, that is the crack velocity is smaller than the shear wave velocity. The material behaviour is described by the indeterminate theory of couple stress elasticity developed by Koiter. This constitutive model includes the characteristic lengths in bending and torsion and thus it is able to account for the underlying microstructure of the material as well as for the strong size effects arising at small scales and observed when the representative scale of the deformation field becomes comparable with the length scale of the microstructure, such as the grain size in a polycrystalline or granular aggregate. The present analysis confirms and extends earlier results on the static case by including the effects of crack velocity an...

  13. The effect of couple-stresses on the stress concentration around a moving crack

    Directory of Open Access Journals (Sweden)

    S. Itou

    1981-01-01

    Full Text Available The problem of a uniformly propagating finite crack in an infinite medium is solved within the linearized couple-stress theory. The self-equilibrated system of pressure is applied to the crack surfaces. The problem is reduced to dual integral equations and solved by a series-expansion method. The dynamic stress-intensity factor is computed numerically.

  14. Uncertainty quantification methodologies development for stress corrosion cracking of canister welds

    Energy Technology Data Exchange (ETDEWEB)

    Dingreville, Remi Philippe Michel [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Bryan, Charles R. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2016-09-30

    This letter report presents a probabilistic performance assessment model to evaluate the probability of canister failure (through-wall penetration) by SCC. The model first assesses whether environmental conditions for SCC – the presence of an aqueous film – are present at canister weld locations (where tensile stresses are likely to occur) on the canister surface. Geometry-specific storage system thermal models and weather data sets representative of U.S. spent nuclear fuel (SNF) storage sites are implemented to evaluate location-specific canister surface temperature and relative humidity (RH). As the canister cools and aqueous conditions become possible, the occurrence of corrosion is evaluated. Corrosion is modeled as a two-step process: first, pitting is initiated, and the extent and depth of pitting is a function of the chloride surface load and the environmental conditions (temperature and RH). Second, as corrosion penetration increases, the pit eventually transitions to a SCC crack, with crack initiation becoming more likely with increasing pit depth. Once pits convert to cracks, a crack growth model is implemented. The SCC growth model includes rate dependencies on both temperature and crack tip stress intensity factor, and crack growth only occurs in time steps when aqueous conditions are predicted. The model suggests that SCC is likely to occur over potential SNF interim storage intervals; however, this result is based on many modeling assumptions. Sensitivity analyses provide information on the model assumptions and parameter values that have the greatest impact on predicted storage canister performance, and provide guidance for further research to reduce uncertainties.

  15. Crack nucleation near stress concentrators in quasi-brittle materials

    Science.gov (United States)

    Demeshkin, A. G.; Kornev, V. M.; Kurguzov, V. D.

    2012-02-01

    The results of combined tension (compression) and shear experiments with plexiglass specimens are used to construct a Coulomb-Mohr-type strength curve. Fracture experiments were performed with plexiglass square plates with internal through cuts. The specimens were subjected to compression on a Zwick/Roell testing machine until cracks appeared. In the process of testing, nucleation of symmetric cracks was observed, which propagated as the load was further increased. The fracture character (tensile or shear) could not be decided until a subsequent numerical analysis of the plate stress-strain state was performed by the finite elementmethod. The stress concentration loci were found to coincide with the crack nucleation loci. In the plane ( σ, τ ), Mohr's circles were constructed for the stress states at the stress concentration points. If the point at which Mohr's curve touches the limit curve is known, then one can determine the plane on which the normal and tangential stresses attain critical values, and hence one can determine the crack propagation direction. The experimental results and numerical solutions were found to be in good agreement.

  16. 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.

  17. 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.

  18. 复合材料Ⅰ+Ⅱ混合型周期平行裂纹尖端场%Crack- Tip Field for ModeⅠ + Ⅱ Periodic Parallel Crack of Composite Materials

    Institute of Scientific and Technical Information of China (English)

    余路娟; 张雪霞; 赵文彬; 李婵

    2014-01-01

    研究了裂纹面内均匀载荷作用下的正交各向异性复合材料板周期平行裂纹尖端场问题。利用复变函数方法,将力学问题化为偏微分方程边值问题。根据叠加原理,将偏微分方程边值问题化为Ⅰ型和Ⅱ型两个边值问题求解。在复数域内,利用双曲函数的周期性,通过构造适当的 WestergAArd 应力函数,将周期平行裂纹尖端场问题化为单一裂纹尖端场问题。得到混合型周期平行裂纹尖端附近的应力强度因子和应力场的解析表达式。由于平行裂纹的周期性分布,应力强度因子的大小取决于形状因子。所得结果表明,当裂纹间距趋于无穷大时,应力强度因子退化为含单个中心裂纹时的结果,并且所得到的解析解更好的体现了平行裂纹分布的周期性。研究结果为结构和材料的强度设计提供了有意义的参考。%The problem for periodic pArAllel crAcks in An orthotropic composite plAte subjected to the uniformly dis-tributed loAd within the crAcks surfAce is studied. The complex function method is used to turn the mechAnicAl problem into the boundAry vAlue problem of pArtiAl differentiAl equAtion. The superposition principle is used to con-vert the boundAry vAlue problem of pArtiAl differentiAl equAtion into those of modeⅠAnd modeⅡ. In the complex domAin,by using the periodicity of the hyperbolic function And constructing proper WestergAArd stress function,the tip field problem of periodic pArAllel crAcks is turned into A tip field problem of A single crAck. The AnAlytic expres-sions for stress intensity fActor And stress field of the mixed mode periodicAl pArAllel crAcks-tip Are Achieved. Due to the periodicity of pArAllel crAck distribution,the stress intensity fActor depends on the shApe fActor. The result showed thAt when the distAnce between the crAcks tends to infinity,the stress intensity fActor is degenerAted into A single centrAl crAck situ

  19. Experimental estimation of the heat energy dissipated in a volume surrounding the tip of a fatigue crack

    Directory of Open Access Journals (Sweden)

    G. Meneghetti

    2016-01-01

    Full Text Available Fatigue crack initiation and propagation involve plastic strains that require some work to be done on the material. Most of this irreversible energy is dissipated as heat and consequently the material temperature increases. The heat being an indicator of the intense plastic strains occurring at the tip of a propagating fatigue crack, when combined with the Neuber’s structural volume concept, it might be used as an experimentally measurable parameter to assess the fatigue damage accumulation rate of cracked components. On the basis of a theoretical model published previously, in this work the heat energy dissipated in a volume surrounding the crack tip is estimated experimentally on the basis of the radial temperature profiles measured by means of an infrared camera. The definition of the structural volume in a fatigue sense is beyond the scope of the present paper. The experimental crack propagation tests were carried out on hot-rolled, 6-mm-thick AISI 304L stainless steel specimens subject to completely reversed axial fatigue loading.

  20. Hydrogen-related stress corrosion cracking in line pipe steel

    DEFF Research Database (Denmark)

    Nielsen, Lars Vendelbo

    1997-01-01

    A correlation between hydrogen concentration (C0) and the critical stress intensity factor for propagation of hydrogen-related cracks has been established by fracture mechanical testing of CT-specimens for the heat affected zone of an X-70 pipeline steel. This has been compared with field...

  1. Chemical milling solution reveals stress corrosion cracks in titanium alloy

    Science.gov (United States)

    Braski, D. N.

    1967-01-01

    Solution of hydrogen flouride, hydrogen peroxide, and water reveals hot salt stress corrosion cracks in various titanium alloys. After the surface is rinsed in water, dried, and swabbed with the solution, it can be observed by the naked eye or at low magnification.

  2. Corner Crack Propagation in the Presence of Residual Stresses (Preprint)

    Science.gov (United States)

    2006-05-01

    used to produce compressive residual stresses in regions of a component, such as a bolt hole or blade attachment, that were prone to crack...plasticity burnishing (LPB), have been developed more recently to provide ways of inducing deeper compressive residual stresses while limiting surface...experiments performed for this work were designed to simulate fastener holes like those found in turbine engine components. A double-edge notch tension

  3. Comparative study of fracture appearance in crack tip opening angle testing of gas pipeline steels

    Energy Technology Data Exchange (ETDEWEB)

    Hashemi, S.H., E-mail: shhashemi@birjand.ac.ir [Department of Mechanical Engineering, The University of Birjand, PO Box 97175-376, Birjand (Iran, Islamic Republic of)

    2012-12-15

    The crack tip opening angle (CTOA) experiments were conducted on API X65, X70, X80 and X100 steels using a modified double cantilever beam (MDCB) geometry. The fracture surfaces of the test specimens were examined after fracture tests by optical and scanning electron microscopy. The fracture surfaces of the lower grade X65 and X70 steels had fully ductile features including classic flat and slant fracture characteristics. However, repetitive propagation and arrest of quasi-cleavage in the form of chevron arrow-head fractures was observed on the fracture surfaces of higher grade X80 and X100 steels. Interestingly, the analysis of load-displacement records from the latter steels demonstrated local ragged patterns after the test peak load, associated with the repetitive low energy quasi-cleavage mechanism. Detailed discussion on the micro-fractographs of the tested steels and comparison of the test observations with the only newly published work in this filed conclude the paper.

  4. Elastodynamic Stress Intensity Factor History for a Semi-infinite Crack Under Three-dimensional Transient Loading

    Institute of Scientific and Technical Information of China (English)

    李湘平; 柳春图

    1994-01-01

    The dynamic stress intensity factor history for a semi-infinite crack in an otherwise unbounded elastic body is analyzed. The crack is subjected to a pair of suddenly-applied point loadings on its faces at a distance L away from the crack tip. The exact expression for the mode I stress intensity factor as a function of time is obtained. The method of solution is based on the direct application of integral transforms, the Wiener-Hopf technique and the Cagniard-de Hoop method. Due to the existence of the characteristic length in loading, this problem was long believed a knotty problem. Some features of the solutions are discussed and graphical result for numerical computation is presented.

  5. 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.

  6. Crack tip fields in elastic-plastic and mixed mode I+II+III conditions, finite elements simulations and modeling

    Directory of Open Access Journals (Sweden)

    F. Fremy,

    2015-07-01

    Full Text Available This paper is devoted to the analysis of the load path effect on I+II+III mixed mode fatigue crack propagation in a 316L stainless steel. Experiments were conducted in mode I+II and in mode I+II+III. The same maximum, minimum and mean values of the stress intensity factors were used for each loading path in the experiments. The main result of this set of experiments is that very different crack growth rates and crack paths are observed for load paths that are however considered as equivalent in most fatigue criteria. The experiments conducted in mode I+II and in mode I+II+III, also allowed to show that the addition of mode III loading steps to a mode I+II loading sequence is increasing the fatigue crack growth rate, even when the crack path is not significantly modified.

  7. Calculation of transient dynamic stress intensity factors at bimaterial interface cracks using a SBFEMbased frequency-domain approach

    Institute of Scientific and Technical Information of China (English)

    Z.J.YANG; A.J.DEEKS

    2008-01-01

    A frequency-domain approach based on the semi-analytical scaled boundary finite element method (SBFEM) was developed to calculate dynamic stress intensity factors (DSIFs) at bimaterial interface cracks subjected to transient loading. Be-cause the stress solutions of the SBFEM in the frequency domain are analytical in the radial direction, and the complex stress singularity at the bimaterial interface crack tip is explicitly represented in the stress solutions, the mixed-mode DSIFs were calculated directly by definition. The complex frequency-response functions of DSIFs were then used by the fast Fourier transform (FFT) and the inverse FFT to calculate time histories of DSIFs. A benchmark example was modelled. Good re-sults were obtained by modelling the example with a small number of degrees of freedom due to the semi-analytical nature of the SBFEM.

  8. Crack tip fields and mixed mode fracture behaviour of progressively drawn pearlitic steel

    Directory of Open Access Journals (Sweden)

    J. Toribio

    2015-07-01

    Full Text Available This paper deals with the influence of the cold drawing process on the fracture behaviour of pearlitic steels. To this end, fracture tests under axial loading were performed on steel wires with different drawing degree (from a hot rolled bar to a commercial prestressing steel wire, transversely pre-cracked by fatigue, analyzing in detail the changes in fracture micromechanisms. The deflection angles of the fracture path were measured by longitudinal metallographic sections and the characteristic parameters of the loaddisplacement plot were related to different fracture events. Results allowed a calculation of critical stress intensity factors for different fracture angles and drawing degrees, thus evaluating the strength anisotropy and obtaining a sort of directional toughness.

  9. Mitigation of Intergranular Stress Corrosion Cracking in Al-Mg by Electrochemical Potential Control

    Science.gov (United States)

    McMahon, M. E.; Scully, J. R.; Burns, J. T.

    2017-08-01

    Intergranular stress corrosion cracking in the Al-Mg alloy AA5456-H116 is suppressed via cathodic polarization in 0.6 M NaCl, saturated (5.45 M) NaCl, 2 M MgCl2, and saturated (5 M) MgCl2. Three zones of intergranular stress corrosion cracking (IG-SCC) susceptibility correlate with pitting potentials of unsensitized AA5456-H116 and pure β phase (Al3Mg2) in each solution. These critical potentials reasonably describe the influence of α Al matrix and β phase dissolution rates on IG-SCC severity. Complete inhibition occurred at applied potentials of -1.0 V and -1.1 V versus saturated calomel electrode ( V SCE) in 0.6 M NaCl. Whereas only partial mitigation of IG-SCC was achieved at -0.9 V SCE in 0.6 M NaCl and at -0.9, -1.0, and -1.1 V SCE in the more aggressive environments. Correlation of pitting potentials in bulk environments with IG-SCC behavior suggests an effect of bulk environment [Cl-] and pH on the stabilized crack tip chemistry.

  10. 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

  11. Stress corrosion cracking of titanium alloys

    Science.gov (United States)

    Statler, G. R.; Spretnak, J. W.; Beck, F. H.; Fontana, M. G.

    1974-01-01

    The effect of hydrogen on the properties of metals, including titanium and its alloys, was investigated. The basic theories of stress corrosion of titanium alloys are reviewed along with the literature concerned with the effect of absorbed hydrogen on the mechanical properties of metals. Finally, the basic modes of metal fracture and their importance to this study is considered. The experimental work was designed to determine the effects of hydrogen concentration on the critical strain at which plastic instability along pure shear directions occurs. The materials used were titanium alloys Ti-8Al-lMo-lV and Ti-5Al-2.5Sn.

  12. 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.

  13. Susceptibility to Stress Corrosion Cracking of 254SMO SS

    Directory of Open Access Journals (Sweden)

    De Micheli Lorenzo

    2002-01-01

    Full Text Available The susceptibility to stress corrosion cracking (SCC of solubilized and sensitized 254SMO SS was studied in sodium chloride, and sodium fluoride solutions at 80 °C and sulfuric acid solutions in presence of sodium chloride at 25 °C. The influence of salt concentration, pH values and the addition of thiosulfate was examined. The susceptibility to SCC was evaluated by Slow Strain Rate Tests (SSRT, at 1.5 x 10-6 s-1 strain rate. The behavior of 254SMO was compared to those of AISI 316L SS and Hastelloy C276. 254SMO showed an excellent resistance to SCC in all conditions, except in the more acidic solutions (pH <= 1 where, in the sensitized conditions, intergranular stress corrosion cracking occurred.

  14. Research of stress corrosion cracking of T225NG titanium alloy in loop water of high temperature and high pressure

    Institute of Scientific and Technical Information of China (English)

    Xu Jijin; Yan Keng; Chen Ligong; Jiang Chengyu

    2006-01-01

    Double cantilever beam (DCB) specimens were used to research the stress corrosion cracking of T225NG titanium alloy in loop water of high temperature and high pressure. DCB specimens were forced pre-stress, put into high pressure autoclave, and the stress corrosion and crack expansion of specimens were observed and measured in 500 h, 1 000 h and 2 000h respectively. The results show that small expansion occurred along the direction of pre-cracking. According to calculation,the speed of cracking expansion is lower than 10 -9 m/s in 500 h and the value of KIscc/KI is higher than 0. 75, which proves that T225NG has an excellent corrosion resistance in loop water. The main reason is that there is an oxide film on the surface of specimens. According to the analysis of energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), the oxide film consists of TiO2. Therefore, the oxide film at the crack tip impedes the hydrogen separating out from the cathode to penetrate into titanium alloy and resists hydrogen embrittlement.

  15. Mechanism of biaxial pre-stress method on welding residual stress and hot cracks controlling

    Institute of Scientific and Technical Information of China (English)

    LIU Xuesong; ZHOU Guangtao; WANG Ping; LIU Haoyuan; FANG Hongyuan

    2009-01-01

    Based on the conventional uniaxial pre-tensile stress method during welding, this study presents a new method of welding with biaxial pre-stress. With the help of numerical simulation, experiments were carried out on the self-designed device. Except for the control on residual stress and distortion as-welded, the experimental results also show its effect on the prevention of hot cracks, thus this method can make up for the disadvantage of the conventional pre-stress method. Hot cracks

  16. Computer Simulation of Intergranular Stress Corrosion Cracking via Hydrogen Embrittlement

    Energy Technology Data Exchange (ETDEWEB)

    Smith, R.W.

    2000-04-01

    Computer simulation has been applied to the investigation of intergranular stress corrosion cracking in Ni-based alloys based on a hydrogen embrittlement mechanism. The simulation employs computational modules that address (a) transport and reactions of aqueous species giving rise to hydrogen generation at the liquid-metal interface, (b) solid state transport of hydrogen via intergranular and transgranular diffusion pathways, and (c) fracture due to the embrittlement of metallic bonds by hydrogen. A key focus of the computational model development has been the role of materials microstructure (precipitate particles and grain boundaries) on hydrogen transport and embrittlement. Simulation results reveal that intergranular fracture is enhanced as grain boundaries are weakened and that microstructures with grains elongated perpendicular to the stress axis are more susceptible to cracking. The presence of intergranular precipitates may be expected to either enhance or impede cracking depending on the relative distribution of hydrogen between the grain boundaries and the precipitate-matrix interfaces. Calculations of hydrogen outgassing and in gassing demonstrate a strong effect of charging method on the fracture behavior.

  17. Three dimensional K-Tz stress fields around the embedded center elliptical crack front in elastic plates

    Institute of Scientific and Technical Information of China (English)

    Junhua Zhao; Wanlin Guo; Chongmin She; Bo Meng

    2006-01-01

    Through detailed three-dimensional(3D)finite element(FE)calculations,the out-of-plane constraints Tz along embedded center-elliptical cracks in mode I elastic plates are studied.The distributions of Tz are obtained near the crack front with aspect ratios (a/c) of 0.2,0.4,0.5,0.6,0.8 and 1.0.Tz decreases from an approximate value of Poisson ratio ν at the crack tip to zero with increasing normalized radialdistances (r/a) in the normal plane of the crack front line,and increases gradually when the elliptical parameter angle φ changes from 0°to 90°at the sanle r/a.with a/c rising to 1.0,Tz is getting nearly independent of φ and is only related to r/a.Based on the present FE calculations for Tz,empirical formulas for Tz are obtained to describe the 3D distribution of Tz for embedded center-elliptical cracks using the least squares method in the range of 0.2 ≤ a/c ≤ 1.0.These Tz results together with the corresponding stress intensity factor K are well suitable for the analysis of the 3D embedded center-elliptical crack front field,and a two-parameter K-Tz principle is proposed.

  18. Hierarchical petascale simulation framework for stress corrosion cracking

    Science.gov (United States)

    Vashishta, P.; Kalia, R. K.; Nakano, A.; Kaxiras, E.; Grama, A.; Lu, G.; Eidenbenz, S.; Voter, A. F.; Hood, R. Q.; Moriarty, J. A.; Yang, L. H.

    2008-07-01

    We are developing a scalable parallel and distributed computational framework consisting of methods, algorithms, and integrated software tools for multi-terascle-to-petascale simulations of stress corrosion cracking (SCC) with quantum-level accuracy. We have performed multimillion- to billion-atom molecular dynamics (MD) simulations of deformation, flow, and fracture in amorphous silica with interatomic potentials and forces validated by density functional theory (DFT) calculations. Optimized potentials have been developed to study sulfur embrittlement of nickel with multimillion-to-multibillion atom MD simulations based on DFT and temperature dependent model generalized pseudopotential theory. We have also developed a quasi-continuum method embedded with quantum simulations based on DFT to reach macroscopic length scales and an accelerated molecular dynamics scheme to reach macroscopic time scales in simulations of solid-fluid interfaces that are relevant to SCC. A hybrid MD and mesoscale lattice Boltzmann simulation algorithm is being designed to study fluid flow through cracks.

  19. De-alloying and stress-corrosion cracking. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Sieradzki, K.

    1998-09-01

    This research program has had two major areas of focus that are related: (1) alloy corrosion and (2) the role of selective dissolution in the stress corrosion cracking of alloy systems. These interrelated issues were examined using model systems such as Ag-Au and Cu-Au by conventional electrochemical techniques, in situ scanning tunneling microscopy (STM), in situ small angle neutron scattering (SANS), ultrahigh speed digital photography of fracture events, and computer simulations. The STM and SANS work were specifically aimed at addressing a roughening transition known to occur in alloy systems undergoing corrosion at electrochemical potentials greater than the so-called critical potential. Analytical models of de-alloying processes including the roughening transition were developed that specifically include curvature effects that are important in alloy corrosion processes. Stress-corrosion experiments were performed on the same model systems using rapid optical and electrochemical techniques on 50 {micro}m--250 {micro}m thick sheets and small diameter wires. The primary goal of this work was to develop a fundamental understanding of the corrosion and electrochemistry of alloys and the stress-corrosion cracking processes these alloys undergo. Computer simulations and analytical work identified surface stress and an important parameter in environmentally assisted fracture. The major results of the research on this program since the summer of 1993 are briefly summarized.

  20. Guide for Recommended Practices to Perform Crack Tip Opening Displacement Tests in High Strength Low Alloy Steels

    Directory of Open Access Journals (Sweden)

    Julián A. Ávila

    Full Text Available Abstract: Fracture mechanics approach is important for all mechanical and civil projects that might involve cracks in metallic materials, and especially for those using welding as a structural joining process. This methodology can enhance not only the design but also the service life of the structures being constructed. This paper includes detailed consideration of several practical issues related to the experimental procedures to assess the fracture toughness in high strength low alloy steels (HSLA using the crack tip opening displacement (CTOD parameter, specifically pipeline steels for oil and gas transportation. These considerations are important for engineers who are new in the field, or for those looking for guidelines performing different procedures during the experimentation, which usually are difficult to understand from the conventional standards. We discuss on topics including geometry selection, number of replicate tests, fatigue precracking, test procedure selection and realization, reports of results and other aspects.

  1. Determination of stress intensity factors in half-plane containing several moving cracks

    Institute of Scientific and Technical Information of China (English)

    K. MALEKZADEH FARD; M. M. MONFARED; K. NOROUZIPOUR

    2013-01-01

    The dynamic stress intensity factors in a half-plane weakened by several finite moving cracks are investigated by employing the Fourier complex transformation. Stress analysis is performed in a half-plane containing a single dislocation and without dislocation. An exact solution in a closed form to the stress fields and displacement is ob-tained. The Galilean transformation is used to transform between coordinates connected to the cracks. The stress components are of the Cauchy singular kind at the location of dislocation and the point of application of the force. Numerical examples demonstrate the influence of crack length and crack running velocity on the stress intensity factor.

  2. Fatigue crack propagation behavior in the field of residual stress distribution. 7th Report. Study of fatigue crack propagation based upon RPG load; Zanryu oryokuba ni okeru hiro kiretsu denpa kyodo. 7. RPG kijun ni yoru hiro kiretsu denpa kyodo no kenkyu

    Energy Technology Data Exchange (ETDEWEB)

    Toyosada, M.; Niwa, T. [Kyushu University, Fukuoka (Japan). Faculty of Engineering

    1995-12-31

    In the previous paper, a simulation model of fatigue crack opening and closing phenomena in an arbitrary stress distribution field for the purpose of obtaining RPG load is shown. From the calculation and experimental results of RPG load, the effects of stress ratio and delayed retardation on fatigue crack propagation are quantitatively assessed. Moreover it becomes clear that the stopping condition of fatigue crack propagation is {delta}K{sub RP}{le}0. In this paper, fatigue crack propagation tests in residual stress distribution field are carried out. Two types of center notched specimens are prepared: one is that gas heating is made at the center line of the specimen which leads to tensile residual stress field in the middle part of the specimen, the other at near the edges of the specimen which leads to compressive residual stress field in the middle part of the specimen. It becomes clear that tensile residual stress descends RPG load and compressive residual stress raises RPG load. Moreover if the large compressive residual stress exists, crack closes even when tensile yield zone generates at the crack tip under loading process. In this case, plastic zone could not grow until crack becomes fully open. Simulated RPG load is in good agreement with experimental one even in the field of residual stress distribution. And compressive residual stress has a large effect of decreasing the fatigue crack propagation rate. These effects can be successfully estimated by the simulation model. 6 refs., 9 figs., 2 tabs.

  3. 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.

  4. Application of new experimental methods to pipeline stress corrosion cracking. Annual report, March 1992-February 1993

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, C.G.; Kobayashi, T.; Becker, C.H.; Pound, B.G.; Simons, J.W.

    1993-04-01

    The objective of the investigation is to develop a physically based understanding of the mechanisms of stress corrosion cracking (SCC) in pipeline steels by applying advanced fracture surface and electrochemical characterization techniques to samples taken from fielded pipeline. The investigations found that the effect of pressure fluctuations on the propagation of stress corrosion cracks was readily evident from an analysis of the topographies of conjugate fracture surfaces. Substantial crack blunting was produced under normal pipeline operating conditions. Corrosion deposits were removed from the fracture surfaces of a stress corrosion crack in a pipeline specimen recovered from service. The topography of the underlying metal surface appears to be preserved with little corrosion damage after crack formation. This allowed the cracking process to be reconstructed from the surface topography. In some cases, deposits on the fracture surfaces of stress corrosion cracks contain significant concentrations of metallic elements that are not found in pipeline steels but are likely to be commonplace in the surrounding environment.

  5. POTENTIAL FOR STRESS CORROSION CRACKING OF A537 CARBON STEEL NUCLEAR WASTE TANKS CONTAINING HIGHLY CAUSTIC SOLUTIONS

    Energy Technology Data Exchange (ETDEWEB)

    Lam, P.; Stripling, C.; Fisher, D.; Elder, J.

    2010-04-26

    The evaporator recycle streams of nuclear waste tanks may contain waste in a chemistry and temperature regime that exceeds the current corrosion control program, which imposes temperature limits to mitigate caustic stress corrosion cracking (CSCC). A review of the recent service history found that two of these A537 carbon steel tanks were operated in highly concentrated hydroxide solution at high temperature. Visual inspections, experimental testing, and a review of the tank service history have shown that CSCC has occurred in uncooled/un-stress relieved tanks of similar construction. Therefore, it appears that the efficacy of stress relief of welding residual stress is the primary corrosion-limiting mechanism. The objective of this experimental program is to test A537 carbon steel small scale welded U-bend specimens and large welded plates (30.48 x 30.38 x 2.54 cm) in a caustic solution with upper bound chemistry (12 M hydroxide and 1 M each of nitrate, nitrite, and aluminate) and temperature (125 C). These conditions simulate worst-case situations in these nuclear waste tanks. Both as-welded and stress-relieved specimens have been tested. No evidence of stress corrosion cracking was found in the U-bend specimens after 21 days of testing. The large plate test was completed after 12 weeks of immersion in a similar solution at 125 C except that the aluminate concentration was reduced to 0.3 M. Visual inspection of the plate revealed that stress corrosion cracking had not initiated from the machined crack tips in the weld or in the heat affected zone. NDE ultrasonic testing also confirmed subsurface cracking did not occur. Based on these results, it can be concluded that the environmental condition of these tests was unable to develop stress corrosion cracking within the test periods for the small welded U-bends and for the large plates, which were welded with an identical procedure as used in the construction of the actual nuclear waste tanks in the 1960s. The

  6. Ultrasonic inspection reliability for intergranular stress corrosion cracks

    Energy Technology Data Exchange (ETDEWEB)

    Heasler, P G; Taylor, T T; Spanner, J C; Doctor, S R; Deffenbaugh, J D [Pacific Northwest Lab., Richland, WA (USA)

    1990-07-01

    A pipe inspection round robin entitled Mini-Round Robin'' was conducted at Pacific Northwest Laboratory from May 1985 through October 1985. The research was sponsored by the US Nuclear Regulatory Commission, Office of Nuclear Regulatory Research under a program entitled Evaluation and Improvement of NDE Reliability for Inservice Inspection of Light Water Reactors.'' The Mini-Round Robin (MRR) measured the intergranular stress corrosion (GSC) crack detection and sizing capabilities of inservice inspection (ISI) inspectors that had passed the requirements of IEB 83-02 and the Electric Power Research Institute (EPRI) sizing training course. The MRR data base was compared with an earlier Pipe Inspection Round Robin (PIRR) that had measured the performance of inservice inspection prior to 1982. Comparison of the MRR and PIRR data bases indicates no significant change in the inspection capability for detecting IGSCC. Also, when comparing detection of long and short cracks, no difference in detection capability was measured. An improvement in the ability to differentiate between shallow and deeper IGSCC was found when the MRR sizing capability was compared with an earlier sizing round robin conducted by the EPRI. In addition to the pipe inspection round robin, a human factors study was conducted in conjunction with the Mini-Round Robin. The most important result of the human factors study is that the Relative Operating Characteristics (ROC) curves provide a better methodology for describing inspector performance than only probability of detection (POD) or single-point crack/no crack data. 6 refs., 55 figs., 18 tabs.

  7. Transient stress intensity factors for edge and corner cracks in quench-test specimens

    Science.gov (United States)

    Emery, A. F.; Kobayashi, A. S.

    1980-01-01

    The transient temperature and stress fields in a quenched rectangular bar were computed and used to determine the stress intensity factors for midside and corner-edge cracks. The stress intensity factors, KI, are presented as a function of time, flaw size, and aspect ratio. The variations of KI along the crack edge are given and the self-limiting growth of the crack depth is discussed in relation to the nonlimited surface growth.

  8. CONSIDERATION OF ANISOTROPY AND CONTACT OF CRACKS EDGE AT STRESS CALCULATIONS OF ROLLING BEARINGS

    OpenAIRE

    2014-01-01

    Investigation of influence of anisotropy on stress-deformed state of base (roller bearings track) considering the appearance of cracks with contacting edges in it is done in the work. The boundary integral equation method is used to determine the stresses. Solution of the Integral equation is done numerically by the mechanical quadrature method. At the task solution it is considered that cracks can be located in the compressive stresses areas, wherefore the cracks edges can contact. The unkno...

  9. Stress corrosion cracking of several high strength ferrous and nickel alloys

    Science.gov (United States)

    Nelson, E. E.

    1971-01-01

    The stress corrosion cracking resistance of several high strength ferrous and nickel base alloys has been determined in a sodium chloride solution. Results indicate that under these test conditions Multiphase MP35N, Unitemp L605, Inconel 718, Carpenter 20Cb and 20Cb-3 are highly resistant to stress corrosion cracking. AISI 410 and 431 stainless steels, 18 Ni maraging steel (250 grade) and AISI 4130 steel are susceptible to stress corrosion cracking under some conditions.

  10. 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

  11. Stress corrosion cracking of brass in ammonia solution

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Brass foil with a protective layer formed on one side was deflected during corrosion in an ammonia solution under various applied potentials, and then corrosion-induced stress generated at brass/dezincification layer under different potentials could be measured. At the same time, susceptibility to stress corrosion cracking(SCC) of brass in the ammonia solution under various applied potentials was measured using a single-edge notched specimen. At open-circuit potential, both corrosion-induced tensile stress and susceptibility to SCC(Iσ) had a maximum value. Both tensile stress σp and susceptibility Iσ decreased slightly under anodic polarization, but reduced steeply with the decrease in potential of cathodic polarization. At the cathodic potential of -500  mV(vs SCE), corrosion-induced stress became compressive because of copper-plating layer, correspondingly, susceptibility to SCC was zero. Therefore, the variation of SCC susceptibility with potential is consistent with that of the corrosion-induced additive stress.

  12. Effects of weld residual stresses on crack-opening area analysis of pipes for LBB applications

    Energy Technology Data Exchange (ETDEWEB)

    Dong, P.; Rahman, S.; Wilkowski, G. [and others

    1997-04-01

    This paper summarizes four different studies undertaken to evaluate the effects of weld residual stresses on the crack-opening behavior of a circumferential through-wall crack in the center of a girth weld. The effect of weld residual stress on the crack-opening-area and leak-rate analyses of a pipe is not well understood. There are no simple analyses to account for these effects, and, therefore, they are frequently neglected. The four studies involved the following efforts: (1) Full-field thermoplastic finite element residual stress analyses of a crack in the center of a girth weld, (2) A comparison of the crack-opening displacements from a full-field thermoplastic residual stress analysis with a crack-face pressure elastic stress analysis to determine the residual stress effects on the crack-opening displacement, (3) The effects of hydrostatic testing on the residual stresses and the resulting crack-opening displacement, and (4) The effect of residual stresses on crack-opening displacement with different normal operating stresses.

  13. 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.

  14. Assessment of foam fracture in sandwich beams using thermoelastic stress analysis

    DEFF Research Database (Denmark)

    Dulieu-Barton, J.M.; Berggreen, Christian; Mettemberg, C.

    2009-01-01

    Thermoelastic Stress Analysis (TSA) has been well established for determining crack-tip parameters in metallic materials. This paper examines its ability to determine accurately the crack-tip parameters for PVC foam used in sandwich structures.......Thermoelastic Stress Analysis (TSA) has been well established for determining crack-tip parameters in metallic materials. This paper examines its ability to determine accurately the crack-tip parameters for PVC foam used in sandwich structures....

  15. Stress intensity factors and crack opening areas for axial through cracks in hollow cylinders under internal pressure loading

    Energy Technology Data Exchange (ETDEWEB)

    Ehlers, R.

    1986-01-01

    For a linear-elastic cylinder with an axial through crack subject to internal pressure loading, stress intensity factors and crack opening areas were calculated by the finite element method. Wall thickness and crack length were varied for constant mean radius of the cylinder, thus varying the shell parameter lambda with 2.5 stress intensity factors depend on lambda as well as on R/t and show considerable differences to solutions based on shallow shell theory even for very short cracks. The range of validity of these solutions is discussed. Starting from the observation that the energy release rate for a semi-infinite crack is finite, a simple interpolation formula is given that retains the proper asymptotic behaviour for very long and very short cracks. Crack opening areas are given and compared to an approximate analytical formula from the literature. Some general limitations of the validity of the present results, particularly the required minimum lengths of the cylinder, are discussed.

  16. Study on stress intensity factors for crack on involute spur gear tooth

    Directory of Open Access Journals (Sweden)

    Jian Cai

    2015-03-01

    Full Text Available Investigating the stress intensity factors has a great importance to predict the fatigue damage for the involute spur gears. The aim of this article is to reveal the variation laws of stress intensity factors for crack on the involute spur gear tooth. For this purpose, a three-dimensional finite element model for calculating the stress intensity factors of the involute spur gear containing a surface crack is established using the finite element code ABAQUS. Based on the established three-dimensional finite element model, the influences of several parameters, such as torque, friction coefficient, crack depth, crack initial location, and crack size, on mode I, mode II, and mode III stress intensity factors are investigated numerically. The results of the study provide valuable guidelines for enhanced understanding of stress intensity factors for the crack on the involute spur gear tooth.

  17. 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.

  18. The Effect of Welding Residual Stress for Making Artificial Stress Corrosion Crack in the STS 304 Pipe

    Directory of Open Access Journals (Sweden)

    Jae-Seong Kim

    2015-01-01

    Full Text Available The stress corrosion crack is one of the fracture phenomena for the major structure components in nuclear power plant. During the operation of a power plant, stress corrosion cracks are initiated and grown especially in dissimilar weldment of primary loop components. In particular, stress corrosion crack usually occurs when the following three factors exist at the same time: susceptible material, corrosive environment, and tensile stress (residual stress included. Thus, residual stress becomes a critical factor for stress corrosion crack when it is difficult to improve the material corrosivity of the components and their environment under operating conditions. In this study, stress corrosion cracks were artificially produced on STS 304 pipe itself by control of welding residual stress. We used the instrumented indentation technique and 3D FEM analysis (using ANSYS 12 to evaluate the residual stress values in the GTAW area. We used the custom-made device for fabricating the stress corrosion crack in the inner STS 304 pipe wall. As the result of both FEM analysis and experiment, the stress corrosion crack was quickly generated and could be reproduced, and it could be controlled by welding residual stress.

  19. 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

  20. Hydrogen-increased dezincification layer-induced stress and susceptibility to stress corrosion cracking of brass

    Institute of Scientific and Technical Information of China (English)

    李会录; 高克玮; 褚武扬; 刘亚萍; 乔利杰

    2003-01-01

    Dezincification layer formed during corrosion or stress corrosion cracking (SCC) of brass in an ammonia solution could induce an additive stress. The effect of hydrogen on the dezincification layer-induced stress and the susceptibility to SCC were studied. The dezincification layer-induced stress was measured using the deflection method and the flowing stress differential method, respectively. The latter measures the difference between the flowing stress of a specimen before unloading and the yield stress of the same specimen after unloading and forming a dezincification layer. The susceptibility to SCC was measured using slow strain rate test. Results show that both the dezincification layer-induced stress and the susceptibility to SCC increase with increasing hydrogen concentration in a specimen. This implies that hydrogen-enhanced dezincification layer-induced stress is consistence with the hydrogen-increased susceptibility to SCC of brass in the ammonia solution.

  1. The interaction of two collinear cracks in a rectangular superconductor slab under an electromagnetic force

    Energy Technology Data Exchange (ETDEWEB)

    Gao Zhiwen, E-mail: gaozhw@lzu.edu.c [Key Laboratory of Mechanics on Western Disaster and Environment, Ministry of Education (China); Department of Mechanics and Engineering Science, College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000 (China); School of Mechanical Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Zhou Youhe [Key Laboratory of Mechanics on Western Disaster and Environment, Ministry of Education (China); Department of Mechanics and Engineering Science, College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000 (China); Lee, Kang Yong, E-mail: KYL2813@yonsei.ac.k [School of Mechanical Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of)

    2010-08-01

    The interaction of two collinear cracks is obtained for a type-II superconducting under electromagnetic force. Fracture analysis is performed by means of finite element method and the magnetic behavior of superconductor is described by the critical-state Bean model. The stress intensity factors at the crack tips can be obtained and discussed for decreasing field after zero-field cooling. It is revealed that the stress intensity factor decreases as applied field increases. The crack-tip stress intensity factors decrease when the distance between the two collinear cracks increases and the superconductors with smaller crack has more remarkable shielding effect than those with larger cracks.

  2. Cracks propagation by stress corrosion cracking in conditions of Boiling Water Reactor (BWR); Propagacion de grietas por corrosion bajo esfuerzo en condiciones de reactor de agua hirviente (BWR)

    Energy Technology Data Exchange (ETDEWEB)

    Fuentes C, P

    2003-07-01

    This work presents the results of the assays carried out in the Laboratory of Hot Cells of the National Institute of Nuclear Research (ININ) to a type test tube Compact Tension (CT), built in steel austenitic stainless type 304L, simulating those conditions those that it operates a Boiling Water Reactor (BWR), at temperature 288 C and pressure of 8 MPa, to determine the speed to which the cracks spread in this material that is of the one that different components of a reactor are made, among those that it highlights the reactor core vessel. The application of the Hydrogen Chemistry of the Water is presented (HWC) that is one alternative to diminish the corrosion effect low stress in the component, this is gets controlling the quantity of oxygen and of hydrogen as well as the conductivity of the water. The rehearsal is made following the principles of the Mechanics of Elastic Lineal Fracture (LEFM) that considers a crack of defined size with little plastic deformation in the tip of this; the measurement of crack advance is continued with the technique of potential drop of direct current of alternating signal, this is contained inside the standard Astm E-647 (Method of Test Standard for the Measurement of Speed of Growth of Crack by fatigue) that is the one that indicates us as carrying out this test. The specifications that should complete the test tubes that are rehearsed as for their dimensions, it forms, finish and determination of mechanical properties (tenacity to the fracture mainly) they are contained inside the norm Astm E-399, the one which it is also based on the principles of the fracture mechanics. The obtained results were part of a database to be compared with those of other rehearsals under different conditions, Normal Chemistry of the Water (NWC) and it dilutes with high content of O{sub 2}; to determine the conditions that slow more the phenomena of stress corrosion cracking, as well as the effectiveness of the used chemistry and of the method of

  3. STRESS INTENSITY FACTORS FOR A FINITE PLATE WITH AN INCLINED CRACK BY BOUNDARY COLLOCATION

    Institute of Scientific and Technical Information of China (English)

    Xing Li; Xuemei You

    2005-01-01

    In this paper, we combine the Muskhelishvili's complex variable method and boundary collocation method, and choose a set of new stress function based on the stress boundary condition of crack surface,the higher precision and less computation are reached. This method is applied to calculating the stress intensity factor for a finite plate with an inclined crack. The influence of θ (the obliquity of crack) on the stress intensity factors, as well as the number of summation terms on the stress intensity factor are studied and graphically represented.

  4. Two-dimensional Numerical Estimation of Stress Intensity Factors and Crack Propagation in Linear Elastic Analysis

    Directory of Open Access Journals (Sweden)

    A. Boulenouar

    2013-10-01

    Full Text Available When the loading or the geometry of a structure is not symmetrical about the crack axis, rupture occurs in mixed mode loading and the crack does not propagate in a straight line. It is then necessary to use kinking criteria to determine the new direction of crack propagation. The aim of this work is to present a numerical modeling of crack propagation under mixed mode loading conditions. This work is based on the implementation of the displacement extrapolation method in a FE code and the strain energy density theory in a finite element code. At each crack increment length, the kinking angle is evaluated as a function of stress intensity factors. In this paper, we analyzed the mechanical behavior of inclined cracks by evaluating the stress intensity factors. Then, we presented the examples of crack propagation in structures containing inclusions and cavities.

  5. 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.

  6. In vivo oxide-induced stress corrosion cracking of Ti-6Al-4V in a neck-stem modular taper: Emergent behavior in a new mechanism of in vivo corrosion.

    Science.gov (United States)

    Gilbert, Jeremy L; Mali, Sachin; Urban, Robert M; Silverton, Craig D; Jacobs, Joshua J

    2012-02-01

    In vivo modular taper corrosion in orthopedic total joint replacements has been documented to occur for head-neck tapers, modular-body tapers, and neck-stem tapers. While the fretting corrosion mechanism by which this corrosion occurs has been described in the literature, this report shows new and as yet unreported mechanisms at play. A retrieved Ti-6Al-4V/Ti-6Al-4V neck-stem taper interface, implanted for 6 years is subjected to failure analysis to document taper corrosion processes that lead to oxide driven crack formation on the medial side of the taper. Metallurgical sectioning techniques and scanning electron microscopy analysis are used to document the taper corrosion processes. The results show large penetrating pitting attack of both sides of the taper interface where corrosion selectively attacks the beta phase of the microstructure and eventually consumes the alpha phase. The pitting attack evolves into plunging pits that ultimately develop into cracks where the crack propagation process is one of corrosion resulting in oxide formation and subsequent reorganization. This process drives open the crack and advances the front by a combination of oxide-driven crack opening stresses and corrosion attack at the tip. The oxide that forms has a complex evolving structure including a network of transport channels that provide access of fluid to the crack tip. This emergent behavior does not appear to require continued fretting corrosion to propagate the pitting and cracking. This new mechanism is similar to stress corrosion cracking where the crack tip stresses arise from the oxide formation in the crack and not externally applied tensile stresses.

  7. Weibull Effective Area for Hertzian Ring Crack Initiation Stress

    Energy Technology Data Exchange (ETDEWEB)

    Jadaan, Osama M. [University of Wisconsin, Platteville; Wereszczak, Andrew A [ORNL; Johanns, Kurt E [ORNL

    2011-01-01

    Spherical or Hertzian indentation is used to characterize and guide the development of engineered ceramics under consideration for diverse applications involving contact, wear, rolling fatigue, and impact. Ring crack initiation can be one important damage mechanism of Hertzian indentation. It is caused by sufficiently-high, surface-located, radial tensile stresses in an annular ring located adjacent to and outside of the Hertzian contact circle. While the maximum radial tensile stress is known to be dependent on the elastic properties of the sphere and target, the diameter of the sphere, the applied compressive force, and the coefficient of friction, the Weibull effective area too will be affected by those parameters. However, the estimations of a maximum radial tensile stress and Weibull effective area are difficult to obtain because the coefficient of friction during Hertzian indentation is complex, likely intractable, and not known a priori. Circumventing this, the Weibull effective area expressions are derived here for the two extremes that bracket all coefficients of friction; namely, (1) the classical, frictionless, Hertzian case where only complete slip occurs, and (2) the case where no slip occurs or where the coefficient of friction is infinite.

  8. [TIPS

    Science.gov (United States)

    Brazzini, Augusto; Carrillo, Alvaro; Cantella, Raúl

    1998-01-01

    Esophageal hemorrage due to variceal bleeding in cirrhotic patients represents a serious problem for the physician in charge, especially in this country where liver transplants are inexistent; and also, it is a drama for the patient and its familly. We propose here the Transjugular Intrahepatic Portosystemic Shunt (TIPS). Twenty one patients were part of a study where 23 TIPS were placed, observing an immediate improval in 18 of them, a rebleeding in 2, within the first 24 and 48 hours. An embolization of the coronary veins was performed in the procedure in 15 patients, and a second intervention due to rebleeding in 2 of them. In the latter patients, the embolization of the coronary veins was rutinary.The survival of the patients has been outstanding.We conclude that this interventional procedure is a worldwide reality in the treatment of esophageal hemorrage by variceal bleeding due to portal hipertension, and it does not cut down the probability of liver transplant, unfortunately inexistent in our country. This procedure results in a low morbimortality with an adequate quality of life.

  9. Photoelastic studies of crack propagation and arrest in polymers and 4340 steel

    Energy Technology Data Exchange (ETDEWEB)

    Irwin, G.R.; Fourney, W.L.; Kobayashi, T.; Metcalf, J.T.; Dally, J.W.

    1978-11-01

    Progress is reported concerning the further evaluation of proposed standard procedures for determining arrest toughness; study of crack behavior of 4340 steel with firefringent coatings; comparison of crack behavior in plastic and steel duplex specimen; a dynamic photoelastic study of crack propagation in a ring specimen; characterization of effect of damping on crack behavior; comparison of crack behavior in Araldite B and Homalite 100; and parametric aspects of crack tip stress fields.

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

    Directory of Open Access Journals (Sweden)

    Walter Per-Ole

    2004-11-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1998-11-01

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

  12. Analysis on residual stress after crack arrested by using electromagnetic heating%单边裂纹电磁热止裂强化的残余应力分析

    Institute of Scientific and Technical Information of China (English)

    付宇明; 郑光洁; 郑丽娟; 张金森; 刘会莹

    2012-01-01

    建立带有单边裂纹的无限大金属薄板模型,给出脉冲放电瞬间的温度场,应用一维条件下的热弹塑性理论,导出了单边裂纹金属构件电磁热止裂后的一维残余应力解;对带有单边裂纹的导电薄板脉冲放电后裂纹尖端产生的残余应力进行数值分析,理论与数值分析结果基本吻合;对40CrNiMo试件的残余应力超声波无损检测发现,止裂后残余应力变大.研究表明,在对带有单边裂纹的导电薄板进行电磁热止裂时,裂纹尖端周围温度急剧升高,使得裂纹尖端受热膨胀,由于裂尖受到周围材料的刚性约束,在受热和冷却过程中会残留一个压缩塑性应变,其产生的残余应力可有效的抑制裂纹扩展.%Establishing infinite metal sheet model with an single side crack,giving the temperature field for the pulse discharge,applying heat elastic-plastic theory under the condition of one-dimension, the one dimensional residual stress solution for the metal components with single side crack after electromagnetic heating crack arrest was derived. Numerical analysis on the residual stress at the crack tip of thin conductive plate with single side crack after pulse discharge shows the theoretical calculation is coincide with numerical analysis. The residual stress around the crack tip in 40CrNiMo component before and after pulse discharge was checked by ultrasound contrast method. Results show that the residual stress change greatly after crack arrest. When the side-crack of thin conductive plate is arrested using electromagnetic heating,the temperature around the crack tip rise quickly and the crack tip expands due to heating. The crack tip is rigidly constrained by the surrounding material, so a compressed plastic strain would remain within the heating and cooling process, the residual stress produced would effectively constrain the extending of the crack.

  13. Relationship between localized strain and irradiation assisted stress corrosion cracking in an austenitic alloy

    Energy Technology Data Exchange (ETDEWEB)

    McMurtrey, M.D., E-mail: mdmcm@umich.edu [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109 (United States); Was, G.S. [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109 (United States); Patrick, L.; Farkas, D. [Department of Materials Science and Engineering, Virginia Tech, Blacksburg, VA 24061 (United States)

    2011-04-25

    Research highlights: {yields} Austenitic steel is more susceptible to intergranular corrosion after irradiation. {yields} Simulation and experiment used to study cracking in irradiated austentic steel. {yields} Cracking occurs at random high angle boundaries normal to the tensile stress. {yields} Cracking at boundaries with high normal stress and inability to accommodate strain. {yields} Boundary type, angle, and Taylor and Schmid factors affect strain accommodation. - Abstract: Irradiation assisted stress corrosion cracking may be linked to the local slip behavior near grain boundaries that exhibit high susceptibility to cracking. Fe-13Cr-15Ni austenitic steel was irradiated with 2 MeV protons at 360 deg. C to 5 dpa and strained in 288 deg. C simulated BWR conditions. Clusters of grains from the experiment were created in an atomistic simulation and then virtually strained using molecular dynamic simulation techniques. Cracking and grain orientation data were characterized in both the experiment and the simulation. Random high angle boundaries with high surface trace angles with respect to the tensile direction were found to be the most susceptible to cracking. Grain boundary cracking susceptibility was also found to correlate strongly with slip continuity, indicating that the strain accommodation at the boundary is related to cracking resistance. Higher cracking susceptibility was also found at grain boundaries adjacent to grains with low Schmid factor or high Taylor factor. The basic trends reported here are supported by both the experiments and the simulations.

  14. Evaluation of Fracture Parameters for Cracks in Coupled Thermoelasticity for Functionally Graded Materials

    Directory of Open Access Journals (Sweden)

    Repka M.

    2015-11-01

    Full Text Available The finite element method (FEM is developed for coupled thermoelastic crack problems if material properties are continuously varying. The weak form is utilized to derive the FEM equations. In conventional fracture theories the state of stress and strain at the crack tip vicinity is characterized by a single fracture parameter, namely the stress intensity factor or its equivalent, J-integral. In the present paper it is considered also the second fracture parameter called as the T-stress. For evaluation of both fracture parameters the quarter-point crack tip element is developed. Simple formulas for both fracture parameters are derived comparing the variation of displacements in the quarter-point element with asymptotic expression of displacement at the crack tip vicinity. The leading terms of the asymptotic expansions of fields in the crack-tip vicinity in a functionally graded material (FGM are the same as in a homogeneous one with material coefficients taken at the crack tip.

  15. Cold work effects on sulfide stress cracking of pipeline steel exposed to sour environments

    Energy Technology Data Exchange (ETDEWEB)

    Huang, H.; Shaw, W.J.D. (Calgary Univ., AB (Canada). Dept. of Mechanical Engineering)

    1993-01-01

    Cold work effects on sulfide stress cracking of a pipeline steel were examined for exposure to a sour gas environment. Cold worked steel was found to be sensitive to hydrogen embrittlement. The fracture toughness decreases with increasing cold work. Sufficiently low values of fracture toughness may be achieved to promote plane strain fracture even in relatively thin laboratory specimens after a steady state level of hydrogen has occurred in the material. Sulfide stress cracking failure of steel with low amounts of cold work (<30%) is by transgranular cleavage fracture, while heavily cold worked steel shows secondary cracks and microvoid coalescence. The results indicate that sulfide stress cracking of the steel is a mixture of anodic stress corrosion cracking (SCC) and hydrogen embrittlement. The anodic SCC mechanism is mainly promoted by carbon dioxide and a high level of chloride. (author).

  16. Influence of nitrogen on the stress corrosion cracking resistance of austenitic stainless steels in chloride environment; Influence de l'azote sur la resistance a la corrosion sous contrainte d'aciers inoxydables austenitiques en milieu chlorure

    Energy Technology Data Exchange (ETDEWEB)

    Teysseyre, S

    2001-11-01

    The aim of this study is to investigate the influence of nitrogen additions on the Stress Corrosion Cracking (SSC) resistance of austenitic stainless steel in chloride environment. The investigation was carried out in two part: first, an experimental investigation with model industrial steels was carried out and secondly, numerical simulations based on the Corrosion Enhanced Plasticity Model were developed. Both slow strain rate tensile tests and constant load test of the different steels in boiling MgCl{sub 2} (153 deg C) at free potential show that, for a given plastic strain rate, nitrogen addition increases the critical stress for crack initiation without influencing the crack propagation rate. We observed that the creep rate under constant load was affected by the nitrogen content. As a consequence, the SCC behaviour (cracks density and propagation rate) depends on the nitrogen content. We thus confirm that the nitrogen content influences the corrosion - deformation interaction mechanisms via its positive contribution to the flow stress. These experimental results are reproduced semi-quantitatively by means of numerical simulations at the scale of crack. - dislocation interactions. The presence of nitrogen is modelled by an increased lattice friction stress, which in turn affects the dynamics of crack tip shielding by dislocation pile-ups. We conclude that nitrogen addition in austenitic stainless steels increases the SC crack initiation stress in proportion of the increased flow stress, without penalty in terms of SC crack propagation rate. (author)

  17. 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.

  18. Stress intensity factors of eccentric cracks in bi-materials plate under mode I loading

    Energy Technology Data Exchange (ETDEWEB)

    Ismail, A. E. [Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor (Malaysia)

    2015-05-15

    Bi-material plates were generally used to joint electronic devices or mechanical components requiring dissimilar materials to be attached. During services, mechanical failure can be occurred due to the formation of cracks at the interfacial joint or away from the centre. Generally, linear elastic fracture mechanics approach is used to characterize these cracks based on stress intensity factors (SIF). Based on the literature survey, the SIFs for the central cracks were easily available. However, the SIFs for eccentric cracks were difficult to obtain. Therefore, this paper presented the SIFs for eccentric cracks subjected to mode I tension loading. Three important parameters were used such as relative crack depth, a/L, relative offset distance, b/L and elastic mismatch, E{sub 1}/E{sub 2} or α. It was found that such parameters significantly affected the characteristic of SIFs and it was depend on the location of cracks.

  19. Cooling-dominated cracking in thermally stressed volcanic rocks

    Science.gov (United States)

    Browning, John; Meredith, Philip; Gudmundsson, Agust

    2016-08-01

    Most studies of thermally induced cracking in rocks have focused on the generation of cracks formed during heating and thermal expansion. Both the nature and the mechanism of crack formation during cooling are hypothesized to be different from those formed during heating. We present in situ acoustic emission data recorded as a proxy for crack damage evolution in a series of heating and cooling experiments on samples of basalt and dacite. Results show that both the rate and the energy of acoustic emission are consistently much higher during cooling than during heating. Seismic velocity comparisons and crack morphology analysis of our heated and cooled samples support the contemporaneous acoustic emission data and also indicate that thermal cracking is largely isotropic. These new data are important for assessing the contribution of cooling-induced damage within volcanic structures and layers such as dikes, sills, and lava flows.

  20. Three-dimensional elastic stress and displacement analysis of finite geometry solids containing cracks

    Science.gov (United States)

    Kring, J.; Gyekenyesi, J.; Mendelson, A.

    1977-01-01

    The line method of analysis is applied to the Navier-Cauchy equations of elastic equilibrium to calculate the displacement fields in finite geometry bars containing central, surface, and double-edge cracks under extensionally applied uniform loading. The application of this method to these equations leads to coupled sets of simultaneous ordinary differential equations whose solutions are obtained along sets of lines in a discretized region. Normal stresses and the stress intensity factor variation along the crack periphery are calculated using the obtained displacement field. The reported results demonstrate the usefulness of this method in calculating stress intensity factors for commonly encountered crack geometries in finite solids.

  1. 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.

  2. lnvestigation of Patch Coatings lnfluence on the Stress lntensity Factor for Surface Cracks

    DEFF Research Database (Denmark)

    Lambertsen, Søren Heide; Jepsen, Michael S.; Damkilde, Lars

    2013-01-01

    to damp the free end of the crack, which will reduce the stress intensity factor and subsequently reduce the crack growth. The considered patch consists of a surface layer of 0.2 mm two component adhesive Epoxy, 3M DP 460. The models described in this work contains five different crack sizes with a patch......In this paper, it is investigated how a surface layer of epoxy glue will affect the crack propagation of a surface crack. The intension is to reduce or even stop the crack propagation by means of patch layer coating. When adding a patch layer to the surface with small cracks, the layer will attempt...... layer on the surface. The stress intensity factor is computed by means of the J-integral and the FE-model is setup with a nonlinear material model to establish the upper boundary for the patch stress capacity. A reduction of the stress intensity factor of approximately 2 % and a reduction of the crack...

  3. 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...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-09-15

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

  5. Effect of a Local Reinforcement on the Stress Intensity Factor of a Cracked Plate

    Institute of Scientific and Technical Information of China (English)

    JIANGCui-xiang; ZHA0Yao; LIUTu-guang

    2004-01-01

    Stress intensity factors are calculated for a cracked plate reinforced locally subject to mode I loading.The stiffeners are considered to have both longitudinal and transverse stiffness.There is no relative displacement between the plate and the stiffener.It is considered that the shear stresses are lumped at a finite number of locations,the result is obtained by summation.The influence of the stiffener location and the stiffener relative stiffness on cracked plate is included.The stress intensity factor depends on all these factors.Case study shows that the shear stress acting parallel to the stiffener gives more effect on the stress intensity factor than the shear stress acting perpendicular to the stiffener.To increase the relative stiffness of stiffener avails to reduce the stress intensity factor of the cracked plate.

  6. Combined effect of gamma radiation and stress cracking in polystyrene; Efeito combinado da radiacao gamma e 'stress cracking' no poliestireno

    Energy Technology Data Exchange (ETDEWEB)

    Amorim, Fernando A.; Rabello, Marcelo S., E-mail: marcelo@dema.ufcg.edu.br [Universidade Federal de Campina Grande - UFCG, Campina Grande - PB (Brazil); Silva, Leonardo G.A. [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

    2011-07-01

    This study aimed to evaluate the combined effect of gamma radiation and stress cracking in polystyrene. Three different grades of polystyrene were analysed. The material was submitted to tensile tests and relaxation, analysis of molecular weight and determination of crosslinking. The results showed an increase in tensile strength in the specimens that had been exposed to radiation. The higher the molecular weight polystyrene showed better mechanical properties and after suffering the effects of gamma radiation there was an increase of 5.67% in the resistance to stress cracking effects. (author)

  7. 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.

  8. The mechanism of stress-corrosion cracking in 7075 aluminum alloy

    Science.gov (United States)

    Jacobs, A. J.

    1970-01-01

    Various aspects of stress-corrosion cracking in 7075 aluminum alloy are discussed. A model is proposed in which the continuous anodic path along which the metal is preferentially attacked consists of two phases which alternate as anodes.

  9. The tonoplast intrinsic aquaporin (TIP) subfamily of Eucalyptus grandis: Characterization of EgTIP2, a root-specific and osmotic stress-responsive gene.

    Science.gov (United States)

    Rodrigues, Marcela I; Bravo, Juliana P; Sassaki, Flávio T; Severino, Fábio E; Maia, Ivan G

    2013-12-01

    Aquaporins have important roles in various physiological processes in plants, including growth, development and adaptation to stress. In this study, a gene encoding a root-specific tonoplast intrinsic aquaporin (TIP) from Eucalyptus grandis (named EgTIP2) was investigated. The root-specific expression of EgTIP2 was validated over a panel of five eucalyptus organ/tissues. In eucalyptus roots, EgTIP2 expression was significantly induced by osmotic stress imposed by PEG treatment. Histochemical analysis of transgenic tobacco lines (Nicotiana tabacum SR1) harboring an EgTIP2 promoter:GUS reporter cassette revealed major GUS staining in the vasculature and in root tips. Consistent with its osmotic-stress inducible expression in eucalyptus, EgTIP2 promoter activity was up-regulated by mannitol treatment, but was down-regulated by abscisic acid. Taken together, these results suggest that EgTIP2 might be involved in eucalyptus response to drought. Additional searches in the eucalyptus genome revealed the presence of four additional putative TIP coding genes, which could be individually assigned to the classical TIP1-5 groups.

  10. Stresses due to an adhesion crack in T-shaped junction of two orthotropic plates

    Institute of Scientific and Technical Information of China (English)

    Dai-Heng Chen

    2012-01-01

    The general solution of streesses is derived for a T-shaped junction of two thin plates with an adhesion crack.The plates are orthotropic.A shear force is applied on the crack surface.The analysis is based on the supposition that the stresses in each plate can be approximated by a plane stress condition.The results obtained are verified by numerical calculation of FEM.

  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. INVESTIGATION OF THE SCATTERING OF HARMONIC ELASTIC WAVES BY TWO COLLINEAR SYMMETRIC CRACKS USING THE NON-LOCAL THEORY

    Institute of Scientific and Technical Information of China (English)

    周振功; 王彪

    2001-01-01

    The scattering of harmonic waves by two collinear symmetric cracks is studied using the non-local theory. A one-dimensional non-local kernel was used to replace a twodimensional one for the dynamic problem to obtain the stress occurring at the crack tips. The Fourier transform was applied and a mixed boundary value problem was formulated. Then a set of triple integral equations was solved by using Schmidt's method. This method is more exact and more reasonable than Eringen' s for solving this problem. Contrary to the classical elasticity solution, it is found that no stress singularity is present at the crack tip. The non- local dynamic elastic solutions yield a finite hoop stress at the crack tip, thus allowing for a fracture criterion based on the maximum dynamic stress hypothesis. The finite hoop stress at the crack tip depends on the crack length, the lattice parameter and the circular frequency of incident wave.

  13. The shear-stress intensity factor for a centrally cracked stiff-flanged shear web

    Science.gov (United States)

    Fichter, W. B.

    1976-01-01

    By use of the principle of superposition the stiff-flanged shear web is modeled mathematically by an infinite elastic strip with fixed longitudinal edges. The shear-stress intensity factor for a central longitudinal crack is calculated for various values of the ratio of strip width to crack length, h/a, in the range 0.1-10. The interaction of the crack with the boundaries is illustrated by boundary shear-stress distributions for three values of h/a. Some implications of the results for the design of damage-tolerant shear webs are discussed briefly.

  14. Experimental and theoretical strain distributions for stationary and growing cracks

    Science.gov (United States)

    Gerberich, W. W.; Davidson, D. L.; Kaczorowski, M.

    E XPERIMENTAL strain distributions are determined very near the crack tip in Fe-3wt.%Si single crystals. Both in situ stereoimaging and electron channeling techniques give reasonably reproducible distributions. By growing fatigue cracks on a {100} cleavage plane, the singularity strengths have been determined for both growing and stationary cracks under relatively plane stress and plane strain conditions. This has allowed a comparison to existing theoretical models. It is shown that the HRR singularity (Hutchinson, Rice and Rosengren, 1968) for stationary cracks is very good to within I μm of the crack tip and a hardening model for the growing crack (gao and hwang, Advances in Fracture Research, edited by D. Francois. 5th Int. Conf. on Fracture, Cannes, France, 2, 669, 1981) is surprisingly good. Other issues such as fracture criteria are discussed since strains greater than unity were measured at the crack tip in this relatively brittle material.

  15. 混凝土裂缝扩展过程中裂尖张开口位移(CTOD)与裂缝嘴张开口位移(CMOD)的变化关系分析%RELATIONSHIP BETWEEN CRACK TIP OPENING DISPLACEMENT (CTOD) AND CRACK MOUTH OPENING DISPLACEMENT (CMOD) THROUGHTOUT DEVELOPMENT OF CONCRETE CRACK

    Institute of Scientific and Technical Information of China (English)

    徐世烺; 张秀芳; 卜丹

    2011-01-01

    The crack tip opening displacement and crack mouth opening displacement are two indexes evaluating the magnitude of crack opening during fracture. The current investigation presents a study of relationship between the crack tip opening displacement and crack mouth opening displacement throughout the development of cracks using the wedge splitting compact tension fracture tests. It is found that the relationship between them can be characterized by a tri-linear model, and that the two governing points on the tri-linear model approximately correspond to the cracking and critical unstable propagation of cracks, respectively. Furthermore,the influence of depth of specimens on the crack tip opening displacement and crack mouth opening displacement at the cracking moment and unstable propagation moment is discussed. Subsequently, based on a hinge model, a new formula for calculating the crack tip opening displacement is developed. The comparison between experimental values of the crack tip opening displacement and the calculated shows a good agreement.%裂缝尖端张开口位移(CTOD)和裂缝嘴张开口位移(CMOD)是衡量裂缝张开程度的两个指标.该文进行了楔入式紧凑拉伸混凝土断裂试验,研究了在裂缝扩展的整个过程中裂缝尖端张开口位移和裂缝嘴张开口位移之间的关系.发现,裂缝尖端张开口位移和裂缝嘴张开口位移关系曲线可以用三线性模型来描述,两个转折点与裂缝的起裂和临界失稳扩展相对应.讨论了高度对起裂时和失稳时对应的裂缝尖端张开口位移和裂缝嘴张开口位移的影响规律.根据铰链模型,给出了计算裂缝尖端张开口位移(CTOD)的计算公式,与试验结果吻合较好.

  16. Analysis of stress intensity factor in orthotropic bi-material mixed interface crack

    Institute of Scientific and Technical Information of China (English)

    赵文彬; 张雪霞; 崔小朝; 杨维阳

    2014-01-01

    Adopting the complex function approach, the paper studies the stress intensity factor in orthotropic bi-material interface cracks under mixed loads. With con-sideration of the boundary conditions, a new stress function is introduced to transform the problem of bi-material interface crack into a boundary value problem of partial dif-ferential equations. Two sets of non-homogeneous linear equations with 16 unknowns are constructed. By solving the equations, the expressions for the real bi-material elastic constantεt and the real stress singularity exponentsλt are obtained with the bi-material engineering parameters satisfying certain conditions. By the uniqueness theorem of limit, undetermined coefficients are determined, and thus the bi-material stress intensity factor in mixed cracks is obtained. The bi-material stress intensity factor characterizes features of mixed cracks. When orthotropic bi-materials are of the same material, the degenerate solution to the stress intensity factor in mixed bi-material interface cracks is in complete agreement with the present classic conclusion. The relationship between the bi-material stress intensity factor and the ratio of bi-material shear modulus and the relationship be-tween the bi-material stress intensity factor and the ratio of bi-material Young’s modulus are given in the numerical analysis.

  17. THERMAL FRACTURE OF FUNCTIONALLY GRADED PLATE WITH PARALLEL SURFACE CRACKS

    Institute of Scientific and Technical Information of China (English)

    Yuezhong Feng; Zhihe Jin

    2009-01-01

    This work examines the fracture behavior of a functionally graded material (FGM) plate containing parallel surface cracks with alternating lengths subjected to a thermal shock. The thermal stress intensity factors (TSIFs) at the tips of long and short cracks are calculated using a singular integral equation technique. The critical thermal shock △T_c that causes crack initiation is calculated using a stress intensity factor criterion. Numerical examples of TSIFs and △T_c for an Al_2O_3/Si_3N_4 FGM plate are presented to illustrate the effects of thermal property gradation, crack spacing and crack length ratio on the TSIFs and △T_c. It is found that for a given crack length ratio, the TSIFs at the tips of both long and short cracks can be reduced significantly and △T_c can be enhanced by introducing appropriate material gradation. The TSIFs also decrease dramatically with a decrease in crack spacing. The TSIF at the tips of short cracks may be higher than that for the long cracks under certain crack geometry conditions. Hence, the short cracks instead of long cracks may first start to grow under the thermal shock loading.

  18. 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

  19. Evaluation of residual stress relief of aluminum alloy 7050 by using crack compliance method

    Institute of Scientific and Technical Information of China (English)

    王秋成; 柯映林; 邢鸿燕; 翁泽宇; 杨芳儿

    2003-01-01

    High strength aluminum alloys of 7xxx series have unacceptable levels of quenching residual stresses from solution heat treatment. The residual stress not only results in machining distortion and dimensional instability, but also increases the possibility of stress corrosion cracks. Therefore, it is necessary to reduce the residual stress to an acceptable level. The crack compliance method was adopted to study the influences of various stress relief methods on residual stress patterns in 7050 aluminum alloy. The results show that 90% residual stress can be eliminated by the cold stretching(Tx51) method. And a lower level of residual stress can be achieved by the uphill quenching(Tx53) method or the cold compression(Tx52). However, there is a very steep residual stress gradient normal to exterior surfaces.

  20. Elastic analysis of a mode Ⅱ crack in an icosahedral quasicrystal

    Institute of Scientific and Technical Information of China (English)

    Zhu Ai-Yu; Fan Tian-You

    2007-01-01

    Based on the displacement potential functions, the elastic analysis of a mode Ⅱ crack in an icosahedral quasicrystal is performed by using the Fourier transform and dual integral equation theory. By the solution, the analytic expressions for the displacement field and stress field are obtained. The asymptotic behaviours of the phonon and phason stress fields around the crack tip indicate that the stresses near the crack tip exhibit a square root singularity. The most important physical quantities of fracture theory, crack stress intensity factor and energy release rate, are evaluated in an explicit version.

  1. 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.

  2. Some relationships between the peak stresses and the local strain energy density for cracks subjected to mixed-mode (I+II loading

    Directory of Open Access Journals (Sweden)

    G. Meneghetti

    2015-07-01

    Full Text Available In this work, a link between the averaged strain energy density (SED approach and the peak stress method in the case of cracks subjected to mixed mode (I+II loading has been investigated. Some closed-form expressions of the strain energy density, averaged in a volume of radius R0, as function of the Stress Intensity Factors are provided for plane strain conditions under mixed mode I+II loadings, the material being thought of as isotropic and linear elastic. On the basis of the peak stress method (PSM some expressions useful to estimate the mode I and mode II stress intensity factors (SIFs have been recently derived. These relationships take advantage of the elastic peak stresses from FE analyses carried out by using a given mesh pattern where the element size and type are kept constants. The evaluation of the SIFs from a numerical analysis of the local stress field usually requires very refined meshes and then large computational effort. The usefulness of the PSM-based expressions is that (i only the elastic peak stresses numerically evaluated at the crack tip are needed and not a set of stress–distance data; (ii the employed meshes are rather coarse if compared to those necessary for the evaluation of the whole local stress field. By substituting the PSM-based relationships in the closed-form expressions of the averaged SED it appears that the latter can be directly estimated by means of the elastic peak stresses evaluated at the crack tip. Several FE analyses have been carried out on cracked plates subjected to tension loading considering different geometrical combinations, varying the length 2a and the inclination ϕ of the crack (i.e. the mode mixity as well as the size d of the adopted finite elements, with the aim to evaluate the local SED and the elastic peak stress components σpeak and τpeak. In all cases the numerical values of the SED derived from the FE analyses have been compared with those analytically obtained by using the

  3. Peak Stress Intensity Factor Governs Crack Propagation Velocity In Crosslinked UHMWPE

    Science.gov (United States)

    Sirimamilla, P. Abhiram; Furmanski, Jevan; Rimnac, Clare

    2013-01-01

    Ultra high molecular weight polyethylene (UHMWPE) has been successfully used as a bearing material in total joint replacement components. However, these bearing materials can fail as a result of in vivo static and cyclic loads. Crack propagation behavior in this material has been considered using the Paris relationship which relates fatigue crack growth rate, da/dN (mm/cycle) versus the stress intensity factor range, ΔK (Kmax-Kmin, MPa√m). However, recent work suggests that the crack propagation velocity of conventional UHMWPE is driven by the peak stress intensity (Kmax), not ΔK. The hypothesis of this study is that the crack propagation velocity of highly crosslinked and remelted UHMWPE is also driven by the peak stress intensity, Kmax, during cyclic loading, rather than by ΔK. To test this hypothesis, two highly crosslinked (65 kGy and 100 kGy) and remelted UHMWPE materials were examined. Frequency, waveform and R-ratio were varied between test conditions to determine the governing factor for fatigue crack propagation. It was found that the crack propagation velocity in crosslinked UHMWPE is also driven by Kmax and not ΔK, and is dependent on loading waveform and frequency in a predictable quasi-static manner. The current study supports that crack growth in crosslinked UHMWPE materials, even under cyclic loading conditions, can be described by a relationship between the velocity of crack growth, da/dt and the peak stress intensity, Kmax. The findings suggest that stable crack propagation can occur as a result of static loading only and this should be taken into consideration in design of UHMWPE total joint replacement components. PMID:23165898

  4. Peak stress intensity factor governs crack propagation velocity in crosslinked ultrahigh-molecular-weight polyethylene.

    Science.gov (United States)

    Sirimamilla, Abhiram; Furmanski, Jevan; Rimnac, Clare

    2013-04-01

    Ultrahigh-molecular-weight polyethylene (UHMWPE) has been successfully used as a bearing material in total joint replacement components. However, these bearing materials can fail as a result of in vivo static and cyclic loads. Crack propagation behavior in this material has been considered using the Paris relationship which relates fatigue crack growth rate, da/dN (mm/cycle) versus the stress intensity factor range, ΔK (Kmax - Kmin , MPa√m). However, recent work suggests that the crack propagation velocity of conventional UHMWPE is driven by the peak stress intensity (Kmax ), not ΔK. The hypothesis of this study is that the crack propagation velocity of highly crosslinked and remelted UHMWPE is also driven by the peak stress intensity, Kmax , during cyclic loading. To test this hypothesis, two highly crosslinked (65 kGy and 100 kGy) and remelted UHMWPE materials were examined. Frequency, waveform, and R-ratio were varied between test conditions to determine the governing factor for fatigue crack propagation. It was found that the crack propagation velocity in crosslinked UHMWPE is also driven by Kmax and not ΔK, and is dependent on loading waveform and frequency in a predictable quasistatic manner. This study supports that crack growth in crosslinked UHMWPE materials, even under cyclic loading conditions, can be described by a relationship between the velocity of crack growth, da/dt and the peak stress intensity, Kmax . The findings suggest that stable crack propagation can occur as a result of static loading only and this should be taken into consideration in design of UHMWPE total joint replacement components.

  5. Relativity between corrosion-induced stress and stress corrosion cracking of brass in an ammonia solution

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The susceptibility to stress corrosion cracking (SCC) of brass in an ammonia solution with various pH values or under various applied potentials was measured at slow strain rate tests. The additive stress in the same solution was measured using two methods. The results indicate that the variation of the susceptibility to SCC with pH value or with potential is in an excellent agreement with the corrosion (passive film or dezincification layer)-induced stress. When pH ? 7, the corrosion-induced tensile stress and the susceptibility to SCC have maximum values and hardly change with increasing the pH value. However, when pH < 7, both the corrosion-induced tensile stress and the susceptibility to SCC reduce rapidly with decreasing the pH value. Both the corrosion-induced tensile stress and the susceptibility to SCC have maximum values at the open-circuit potential, decrease slightly under the anodic polarization, and reduce gradually to zero under the cathodic polarization.

  6. Some important considerations in the development of stress corrosion cracking test methods.

    Science.gov (United States)

    Wei, R. P.; Novak, S. R.; Williams, D. P.

    1972-01-01

    Discussion of some of the precaution needs the development of fracture-mechanics based test methods for studying stress corrosion cracking involves. Following a review of pertinent analytical fracture mechanics considerations and of basic test methods, the implications for test corrosion cracking studies of the time-to-failure determining kinetics of crack growth and life are examined. It is shown that the basic assumption of the linear-elastic fracture mechanics analyses must be clearly recognized and satisfied in experimentation and that the effects of incubation and nonsteady-state crack growth must also be properly taken into account in determining the crack growth kinetics, if valid data are to be obtained from fracture-mechanics based test methods.

  7. Fundamental understanding and life prediction of stress corrosion cracking in BWRs and energy systems

    Energy Technology Data Exchange (ETDEWEB)

    Andresen, P.L.; Ford, F.P. [General Electric, Schenectady, NY (United States). Corporate Research and Development Center

    1998-03-01

    The objective of this paper is to present an approach for design and lifetime evaluation of environmental cracking based on experimental and fundamental modeling of the underlying processes operative in crack advance. In detailed this approach and its development and quantification for energy (hot water) systems, the requirements for a life prediction methodology will be highlighted and the shortcomings of the existing design and lifetime evaluation codes reviewed. Examples are identified of its use in a variety of cracking systems, such as stainless steels, low alloy steels, nickel base alloys, and irradiation assisted stress corrosion cracking in boiling water reactor (BWR) water, as well as preliminary use for low alloy steel and Alloy 600 in pressurized water reactors (PWRs) and turbine steels in steam turbines. Identification of the common aspects with environmental cracking in other hot water systems provides a secure basis for its extension to related energy systems. 166 refs., 49 figs.

  8. A Modified Constant-Stress Coupon for Enhanced Natural Crack Start during Fatigue Testing

    Science.gov (United States)

    2016-05-01

    UNCLASSIFIED UNCLASSIFIED A Modified Constant- Stress Coupon for Enhanced Natural Crack Start during Fatigue Testing Witold Waldman, Robert...modified constant- stress coupon for use in fatigue testing . This novel coupon design has a significantly greater surface area along the notch boundary...modified constant- stress coupon for use in fatigue testing . A constant- stress coupon is a novel design that has a significantly greater surface area along

  9. A MOVING CRACK IN A NONHOMOGENEOUS MATERIAL STRIP

    Institute of Scientific and Technical Information of China (English)

    Wang Baolin; Han Jiecai

    2006-01-01

    This paper considers an anti-plane moving crack in a nonhomogencous material strip of finite thickness. The shear modulus and the mass density of the strip are considered for a class of functional forms for which the equilibrium equation has analytical solutions. The problem is solved by means of the singular integral equation technique. The stress field near the crack tip is obtained. The results are plotted to show the effect of the material non-homogeneity and crack moving velocity on the crack tip field. Crack bifurcation behaviour is also discussed. The paper points out that use of an appropriate fracture criterion is essential for studying the stability of a moving crack in nonhomogeneous materials. The prediction whether the unstable crack growth will be enhanced or retarded is strongly dependent on the type of the fracture criterion used. is a suitable failure criterion for moving cracks in nonhomogeneous materials.

  10. Numerical Computation of Stress Intensity Factors for Bolt-hole Corner Crack in Mechanical Joints

    Institute of Scientific and Technical Information of China (English)

    Wang Liqing; Gai Bingzheng

    2008-01-01

    The three-dimensional finite element method is used to solve the problem of the quarter-elliptical comer crack of the bolt-hole in mechanical joints being subjected to remote tension. The square-root stress singularity around the corner crack front is simulated using the collapsed 20-node quarter point singular elements. The contact interaction between the bolt and the hole boundary is considered in the finite element analysis. The stress intensity factors (SIFs) along the crack front are evaluated by using the displacement correlation technique. The effects of the amount of clearance between the hole and the bolt on the SIFs are investigated. The numerical results indicate that the SIF for mode I decrease with the decreases in clearance, and in the cases of clearance being present, the corner crack is in a mix-mode, even if mode I loading is dominant.

  11. Influence of oxide films on primary water stress corrosion cracking initiation of alloy 600

    Science.gov (United States)

    Panter, J.; Viguier, B.; Cloué, J.-M.; Foucault, M.; Combrade, P.; Andrieu, E.

    2006-01-01

    In the present study alloy 600 was tested in simulated pressurised water reactor (PWR) primary water, at 360 °C, under an hydrogen partial pressure of 30 kPa. These testing conditions correspond to the maximum sensitivity of alloy 600 to crack initiation. The resulting oxidised structures (corrosion scale and underlying metal) were characterised. A chromium rich oxide layer was revealed, the underlying metal being chromium depleted. In addition, analysis of the chemical composition of the metal close to the oxide scale had allowed to detect oxygen under the oxide scale and particularly in a triple grain boundary. Implication of such a finding on the crack initiation of alloy 600 is discussed. Significant diminution of the crack initiation time was observed for sample oxidised before stress corrosion tests. In view of these results, a mechanism for stress corrosion crack initiation of alloy 600 in PWR primary water was proposed.

  12. Compression Stress Effect on Dislocations Movement and Crack propagation in Cubic Crystal

    CERN Document Server

    Suprijadi,; Yusfi, Meiqorry

    2012-01-01

    Fracture material is seriously problem in daily life, and it has connection with mechanical properties itself. The mechanical properties is belief depend on dislocation movement and crack propagation in the crystal. Information about this is very important to characterize the material. In FCC crystal structure the competition between crack propagation and dislocation wake is very interesting, in a ductile material like copper (Cu) dislocation can be seen in room temperature, but in a brittle material like Si only cracks can be seen observed. Different techniques were applied to material to study the mechanical properties, in this study we did compression test in one direction. Combination of simulation and experimental on cubic material are reported in this paper. We found that the deflection of crack direction in Si caused by vacancy of lattice,while compression stress on Cu cause the atoms displacement in one direction. Some evidence of dislocation wake in Si crystal under compression stress at high tempera...

  13. SCATTERING OF THE HARMONIC STRESS WAVE BY CRACKS IN FUNCTIONALLY GRADED PIEZOELECTRIC MATERIALS

    Institute of Scientific and Technical Information of China (English)

    Ma Li; Nie Wu; Wu Linzhi; Zhou Zhengong

    2005-01-01

    The present paper considers the scattering of the time harmonic stress wave by a single crack and two collinear cracks in functionally graded piezoelectric material (FGPM).It is assumed that the properties of the FGPM vary continuously as an exponential function.By using the Fourier transform and defining the jumps of displacements and electric potential components across the crack surface as the unknown functions, two pairs of dual integral equations are derived. To solve the dual integral equations, the jumps of the displacement and electric potential components across the crack surface are expanded in a series of Jacobi polynomials.Numerical examples are provided to show the influences of material properties on the dynamic stress and the electric displacement intensity factors.

  14. Study of the Effect of Swelling on Irradiation Assisted Stress Corrosion Cracking

    Energy Technology Data Exchange (ETDEWEB)

    Teysseyre, Sebastien Paul [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2016-09-01

    This report describes the methodology used to study the effect of swelling on the crack growth rate of an irradiation-assisted stress corrosion crack that is propagating in highly irradiated stainless steel 304 material irradiated to 33 dpa in the Experimental Breeder Reactor-II. The material selection, specimens design, experimental apparatus and processes are described. The results of the current test are presented.

  15. Interaction of a crack with crystal defects in solids

    Energy Technology Data Exchange (ETDEWEB)

    Narita, N. [Kyushu Inst. of Tech., Kitakyushu (Japan). Dept. of Materials Science and Engineering; Higashida, K.

    1997-06-01

    The modifications of stress states near a crack tip by interstitial impurities and by dislocations are analyzed using 2-D and 3-D potential methods. In the case of interstitial impurities, the local stress intensity k{sub D} due to impurities is much affected by their location and is altered from crack tip shielding to anti-shielding as their location changes from behind a crack tip to the front. If impurities are mobile, their forward redistribution is induced by crack fields to increase k{sub D} values. The tetragonal strain of impurities also enhances the increase of the k{sub D} values. In dislocation-crack systems, two kinds of screw dislocation arrays are observed on each different slip plane ahead of a crack tip in MgO thin crystals and they mainly induce the mode I stress intensity of shielding type as a result of the mutual cancellation of the other modes. The effect of crack tip shielding/anti-shielding on crack extension is discussed in connection with the experimental observation of fracture toughness. (orig.). 7 refs.

  16. Laboratory evaluation of soil stress corrosion cracking and hydrogen embrittlement of API grade steels

    Energy Technology Data Exchange (ETDEWEB)

    Bueno, A.H.S.; Castro, B.B.; Ponciano, J.A.C. [Federal Univ. of Rio de Janeiro (Brazil). COPPE

    2004-07-01

    Stress corrosion cracking (SCC) in carbon steels is a form of deterioration that can occur during the service life of a pipeline that is exposed to mechanical stress and strains. A study was conducted to investigate SCC and hydrogen embrittlement (HE) of API grade steels in contact with soil. The physical, chemical and bacteriological characteristics of different soil samples were determined. Slow strain rate tests were performed using electrolytes obtained in the soil samples taken from different points near buried pipelines. Stress versus strain curves were obtained at different electrode potentials for API X46, X60 and X80 steels. The results showed the conjoint incidence of SCC and HE, depending on the potential imposed. It was revealed that HE contributes to the initiation of cracking and crack propagation. Cracking morphology was similar to the SCC found in field situations where transgranular cracking was detected in a pipeline that had collapsed as a result of land creeping. The material exhibited signs of secondary cracking and lower ductility, even under cathodic potentials. It was noted that the methodology used in this study was not able to reproduce the possible effect of microbial induced corrosion. 10 refs., 3 tabs., 3 figs.

  17. Molecular Dynamics Simulation of Porous Layer-enhanced Dislocation Emission and Crack Propagation in Iron Crystal

    Institute of Scientific and Technical Information of China (English)

    D. Li; F.Y. Meng; X.Q. Ma; L.J. Qiao; W.Y. Chu

    2011-01-01

    The internal stress induced by a porous layer or passive layer can assist the applied stress to promote dislocation emission and crack propagation, e.9. when the pipeline steel is buried in the soil containing water, resulting in stress corrosion cracking (SCC). Molecular dynamics (MD) simulation is performed to study the process of dislocation emission and crack propagation in a slab of Fe crystal with and without a porous layer on the surface of the crack. The results show that when there is a porous layer on the surface of the crack, the tensile stress induced by the porous layer can superimpose on the external applied stress and then assist the applied stress to initiate crack tip dislocation emission under lowered stress intensity KI, or stress. To respond to the corrosion accelerated dislocation emission and motion, the crack begins to propagate under lowered stress intensity KI, resulting in SCC.

  18. 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)

  19. Tips for Survivors of a Traumatic Event: Managing Your Stress

    Science.gov (United States)

    ... 799-4TTY (4889) Web Site: www.suicidepreventionlifeline.org Workplace Helpline Toll-Free: 1-800-WORKPLACE (967-5752) Web Site: http://dwp.samhsa.gov/ ... 0209 Revised 4/07 Know How To Relieve Stress You can manage and alleviate your stress by ...

  20. 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.

  1. Investigation of the crack problem in non-local piezoelectric materials under combined electromechanical loadings

    Institute of Scientific and Technical Information of China (English)

    Qun Li; Yiheng Chen

    2009-01-01

    The present investigation of the crack problem in piezoelectric materials is performed based on the non-local theory. After some manipulations, the impermeable crack,the permeable crack (the crack gap is full of NaCI solution),and the semi-permeable crack (the crack gap is full of air or silicon oil) are reduced to a uniform formulation by assuming the normal electric displacement on the crack surfaces to be an unknown variable. Thus, a triple integral equation with the unknown normal electric displacement is established. By using the Newton iterative method and solving the triple integral equation, it is found that the normal electric displacement on the crack surfaces is no longer a constant as determined by previous studies, rather, it depends upon the remote combined electromechanical loadings. Numerical results of the stresses and electric displacement fields show that there are no singularities at the crack tips so that the stresses remain finite. It is of great significance that the concrete electric boundary condition on the crack surfaces exerts significant influence on the near-tip fields and in this way plays an important role in evaluating the crack stability in the non-local piezoelectric materials. More specifically, the impermeable crack model always overestimates the finite stresses at the crack tips, whereas the permeable crack model always underestimates them.

  2. Study on cracking of welding overlay based on the theory of diffusion-induced stress

    Institute of Scientific and Technical Information of China (English)

    Xiliang ZHANG; Changyu ZHOU

    2011-01-01

    Hydrogen diffusion in the wall of hydrogenation reactor for three situations,i.e. operating,normal shutdown and abnormal shutdown,was numerically simulated based on the finite element program-ABAQUS. The formula of diffusion-induced stress was deduced for model of the thin walled cylinder. Distribution of diffusion-induced stress in the wall of hydrogenation reactor was studied. The results showed that the maximum stress was at the fusion surface between welding overlay and base metal,and which would increase with cooling rate. The crack will initiate and propagate from fusion surface to welding overlay when the diffusion-induced stress is higher than yield stress,but it will not propagate to the base metal. Diffusion-induced stress is one of the important factors for crack initiation and propagation of welding overlay of hydrogenation reactor.

  3. 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.

  4. Stress corrosion cracking and its anisotropy of a PZT ferroelectric ceramics

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Stress corrosion cracking (SCC) of a PZT ferroelectric ceramics in various media, such as moist atmosphere, silicon oil, methanol, water and formamide, and its anisotropy have been investigated at constant load test using a single-edge notched tensile specimen. The results showed that SCC could occur in all media, and the threshold stress intensity factor of SCC in water and formamide, KISCC, revealed anisotropy. The KISCC for poling direction parallel to the crack plane, was greater than that perpendicular to the crack plane, similar to the anisotropy of fracture toughness KIC; however, the anisotropy factor of KISCC, which was =1.8 (in formamide) and 2.1 (in water), was larger than that of KIC, which is =1.4. The stress-induced 90° domain switching causes the anisotropy of KIC and KISCC, besides, the resistance of SCC also has anisotropy.

  5. Study on an Explosion Treated Steel Weld Metal withPrepared Crack

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A softening zone with recrystallized grain around the prepared crack tip in the shock waves treated C-Mn steel weld metal was observed. It is suggested that a dynamic recovery occurred around the prepared crack tip even at a low explosion pressure (5 GPa) because of the stress and strain concentration at the crack tip when shock waves pass through. This result supports the previous work on the improved mechanical properties of a shock treated welded joint with residual crack from the viewpoint of microstructure.

  6. Tips for Disaster Responders: Preventing and Managing Stress

    Science.gov (United States)

    ... be done safely while on deployment, like walking, stretching, and taking deep breaths. Read or listen to ... Stress Management Techniques Reduce physical tension by exercising, stretching, taking deep breaths, and walking. Use time off ...

  7. A circumferential crack in a cylindrical shell under tension.

    Science.gov (United States)

    Duncan-Fama, M. E.; Sanders, J. L., Jr.

    1972-01-01

    A closed cylindrical shell under uniform internal pressure has a slit around a portion of its circumference. Linear shallow shell theory predicts inverse square-root-type singularities in certain of the stresses at the crack tips. This paper reports the computed strength of these singularities for different values of a dimensionless parameter based on crack length, shell radius and shell thickness.

  8. Modelling probabilistic fatigue crack propagation rates for a mild structural steel

    Directory of Open Access Journals (Sweden)

    J.A.F.O. Correia

    2015-01-01

    Full Text Available A class of fatigue crack growth models based on elastic–plastic stress–strain histories at the crack tip region and local strain-life damage models have been proposed in literature. The fatigue crack growth is regarded as a process of continuous crack initializations over successive elementary material blocks, which may be governed by smooth strain-life damage data. Some approaches account for the residual stresses developing at the crack tip in the actual crack driving force assessment, allowing mean stresses and loading sequential effects to be modelled. An extension of the fatigue crack propagation model originally proposed by Noroozi et al. (2005 to derive probabilistic fatigue crack propagation data is proposed, in particular concerning the derivation of probabilistic da/dN-ΔK-R fields. The elastic-plastic stresses at the vicinity of the crack tip, computed using simplified formulae, are compared with the stresses computed using an elasticplastic finite element analyses for specimens considered in the experimental program proposed to derive the fatigue crack propagation data. Using probabilistic strain-life data available for the S355 structural mild steel, probabilistic crack propagation fields are generated, for several stress ratios, and compared with experimental fatigue crack propagation data. A satisfactory agreement between the predicted probabilistic fields and experimental data is observed.

  9. Stress Corrosion Cracking of Zircaloy-4 in Halide Solutions: Effect of Temperature

    Directory of Open Access Journals (Sweden)

    Farina S.B.

    2002-01-01

    Full Text Available Zircaloy-4 was found to be susceptible to stress corrosion cracking in 1 M NaCl, 1 M KBr and 1 M KI aqueous solutions at potentials above the pitting potential. In all the solutions tested crack propagation was initially intergranular and then changed to transgranular. The effect of strain rate and temperature on the SCC propagation was investigated. An increase in the strain rate was found to lead to an increase in the crack propagation rate. The crack propagation rate increases in the three solutions tested as the temperatures increases between 20 and 90 °C. The Surface-Mobility SCC mechanism accounts for the observation made in the present work, and the activation energy predicted in iodide solutions is similar to that found in the literature.

  10. Chloride stress corrosion cracking of Alloy 600 in boric acid solutions

    Energy Technology Data Exchange (ETDEWEB)

    Berge, Ph. [Electricite de France, 92 - Paris la Defense (France); Noel, D.; Gras, J.M.; Prieux, B. [Electricite de France, 77 - Moret-sur-Loing (France). Direction des Etudes et Recherches

    1997-10-01

    The high nickel austenitic alloys are generally considered to have good resistance to chloride stress corrosion cracking. In the standard boiling magnesium chloride solution tests, alloys with more than 40% nickel are immune. Nevertheless, more recent data show that cracking can occur in both Alloys 600 and 690 if the solution is acidified. In other low pH media, such as boric acid solution at 100 deg C, transgranular and intergranular cracking are observed in Alloy 600 in the presence of minor concentrations of sodium chloride (2g/I). In concentrated boric acid at higher temperatures (250 and 290 deg C), intergranular cracking also occurs, either when the chloride concentration is high, or at low chloride contents and high oxygen levels. The role of pH and a possible specific action of boric acid are discussed, together with the influence of electrochemical potential. (author) 21 refs.

  11. Stress-corrosion cracking of sensitized stainless steel by sulfur-containing compounds

    Energy Technology Data Exchange (ETDEWEB)

    Isaacs, H.S.; Vyas, B.; Kendig, M.W.

    1981-01-01

    The stress corrosion cracking (SCC) of sensitized Type 304 stainless steel in thiosulfate solutions has been studied using constant extension rate tests. Very low concentrations of about 6.10/sup -7/M Na/sub 2/S/sub 2/O/sub 3/ (0.1ppm) gave cracking. With boric acid added, higher concentrations (1ppm) were required. The SCC was shown to be electrochemically controlled. Below -0.5v/sub SCE/ (-0.75/sub SHE/) no SCC took place; above this potential the rate of SCC increased with potential. An induction period was required before SCC continued above -0.5v if the potential was held at or below this value for extended times. This period was associated with the build up of an aggressive solution of thiosulfate decomposition products within the crack. The cracking process has been considered to be controlled by rupture of a salt layer and not a passivating oxide.

  12. Stress corrosion crack initiation of alloy 600 in PWR primary water

    Energy Technology Data Exchange (ETDEWEB)

    Zhai, Ziqing; Toloczko, Mychailo B.; Olszta, Matthew J.; Bruemmer, Stephen M.

    2017-07-01

    Stress corrosion crack (SCC) initiation of three mill-annealed (MA) alloy 600 heats in simulated pressurized water reactor primary water has been investigated using constant load tests equipped with in-situ direct current potential drop (DCPD) measurement capabilities. SCC initiation times were greatly reduced by a small amount of cold work. Shallow intergranular (IG) attack and/or cracks were found on most high-energy grain boundaries intersecting the surface with only a small fraction evolving into larger cracks and IGSCC growth. Crack depth profiles were measured and related to DCPD-detected initiation response. Processes controlling the SCC initiation in MA alloy 600 are discussed. IN PRESS, CORRECTED PROOF, 05/02/2017 - mfl

  13. 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

  14. Numerical Analysis of the Influence of In-Plane Constraints on the Crack Tip Opening Displacement for SEN(B Specimens Under Predominantly Plane Strain Conditions

    Directory of Open Access Journals (Sweden)

    Graba M.

    2016-12-01

    Full Text Available This paper presents a numerical analysis of the relationship between in-plane constraints and the crack tip opening displacement (CTOD for single-edge notched bend (SEN(B specimens under predominantly plane strain conditions. It provides details of the numerical model and discusses the influence of external load and in-plane constraints on the CTOD. The work also reviews methods for determining the CTOD. The new formula proposed in this paper can be used to estimate the value of the coefficient dn as a function of the relative crack length, the strain hardening exponent and the yield strength - dn(n, σ0/E, a/W, with these parameters affecting the level of in-plane constraints. Some of the numerical results were approximated using simple mathematical formulae.

  15. Numerical Analysis of the Influence of In-Plane Constraints on the Crack Tip Opening Displacement for SEN(B) Specimens Under Predominantly Plane Strain Conditions

    Science.gov (United States)

    Graba, M.

    2016-12-01

    This paper presents a numerical analysis of the relationship between in-plane constraints and the crack tip opening displacement (CTOD) for single-edge notched bend (SEN(B)) specimens under predominantly plane strain conditions. It provides details of the numerical model and discusses the influence of external load and in-plane constraints on the CTOD. The work also reviews methods for determining the CTOD. The new formula proposed in this paper can be used to estimate the value of the coefficient dn as a function of the relative crack length, the strain hardening exponent and the yield strength - dn(n, σ0/E, a/W), with these parameters affecting the level of in-plane constraints. Some of the numerical results were approximated using simple mathematical formulae.

  16. Contraction stresses in dental composites adjacent to and at the bonded interface as measured by crack analysis.

    Science.gov (United States)

    Yamamoto, Takatsugu; Nishide, Akihito; Swain, Michael V; Ferracane, Jack L; Sakaguchi, Ronald L; Momoi, Yasuko

    2011-01-01

    The objective of this study was to calculate stresses produced by polymerization contraction in regions surrounding a dental resin composite restoration. Initial cracks were made with a Vickers indenter at various distances from the edge of a cylindrical hole in a soda-lime glass disk. Indentation crack lengths were measured parallel to tangents to the hole edge. Resin composites (three brands) were placed in the hole and polymerized (two light irradiation protocols) at equal radiation exposures. The crack lengths were re-measured at 2 and 10 min after irradiation. Radial tensile stresses due to polymerization contraction at the location of the cracks (σ(crack)) were calculated from the incremental crack lengths and the fracture toughness K(c) of the glass. Contraction stresses at the composite-glass bonded interface (σ(interface)) were calculated from σ(crack) on the basis of the simple mechanics of an internally pressurized thick-walled cylinder. The greater the distance or the shorter the time following polymerization, the smaller was σ(crack). Distance, material, irradiation protocol and time significantly affected σ(crack). Two-step irradiation resulted in a significant reduction in the magnitude of σ(interface) for all resin composites. The contraction stress in soda-lime glass propagated indentation cracks at various distances from the cavity, enabling calculation of the contraction stresses.

  17. 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.

  18. Factors affecting stress assisted corrosion cracking of carbon steel under industrial boiler conditions

    Science.gov (United States)

    Yang, Dong

    Failure of carbon steel boiler tubes from waterside has been reported in the utility boilers and industrial boilers for a long time. In industrial boilers, most waterside tube cracks are found near heavy attachment welds on the outer surface and are typically blunt, with multiple bulbous features indicating a discontinuous growth. These types of tube failures are typically referred to as stress assisted corrosion (SAC). For recovery boilers in the pulp and paper industry, these failures are particularly important as any water leak inside the furnace can potentially lead to smelt-water explosion. Metal properties, environmental variables, and stress conditions are the major factors influencing SAC crack initation and propagation in carbon steel boiler tubes. Slow strain rate tests (SSRT) were conducted under boiler water conditions to study the effect of temperature, oxygen level, and stress conditions on crack initation and propagation on SA-210 carbon steel samples machined out of boiler tubes. Heat treatments were also performed to develop various grain size and carbon content on carbon steel samples, and SSRTs were conducted on these samples to examine the effect of microstructure features on SAC cracking. Mechanisms of SAC crack initation and propagation were proposed and validated based on interrupted slow strain tests (ISSRT). Water chemistry guidelines are provided to prevent SAC and fracture mechanics model is developed to predict SAC failure on industrial boiler tubes.

  19. 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.

  20. Irradiation-Assisted Stress Corrosion Cracking of Austenitic Stainless Steels in BWR Environments

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Y. [Argonne National Lab. (ANL), Argonne, IL (United States); Chopra, O. K. [Argonne National Lab. (ANL), Argonne, IL (United States); Gruber, Eugene E. [Argonne National Lab. (ANL), Argonne, IL (United States); Shack, William J. [Argonne National Lab. (ANL), Argonne, IL (United States)

    2010-06-01

    The internal components of light water reactors are exposed to high-energy neutron irradiation and high-temperature reactor coolant. The exposure to neutron irradiation increases the susceptibility of austenitic stainless steels (SSs) to stress corrosion cracking (SCC) because of the elevated corrosion potential of the reactor coolant and the introduction of new embrittlement mechanisms through radiation damage. Various nonsensitized SSs and nickel alloys have been found to be prone to intergranular cracking after extended neutron exposure. Such cracks have been seen in a number of internal components in boiling water reactors (BWRs). The elevated susceptibility to SCC in irradiated materials, commonly referred to as irradiation-assisted stress corrosion cracking (IASCC), is a complex phenomenon that involves simultaneous actions of irradiation, stress, and corrosion. In recent years, as nuclear power plants have aged and irradiation dose increased, IASCC has become an increasingly important issue. Post-irradiation crack growth rate and fracture toughness tests have been performed to provide data and technical support for the NRC to address various issues related to aging degradation of reactor-core internal structures and components. This report summarizes the results of the last group of tests on compact tension specimens from the Halden-II irradiation. The IASCC susceptibility of austenitic SSs and heat-affected-zone (HAZ) materials sectioned from submerged arc and shielded metal arc welds was evaluated by conducting crack growth rate and fracture toughness tests in a simulated BWR environment. The fracture and cracking behavior of HAZ materials, thermally sensitized SSs and grain-boundary engineered SSs was investigated at several doses (≤3 dpa). These latest results were combined with previous results from Halden-I and II irradiations to analyze the effects of neutron dose, water chemistry, alloy compositions, and welding and processing conditions on IASCC

  1. Residual stress in plasma sprayed ceramic turbine tip and gas path seal specimens

    Science.gov (United States)

    Hendricks, R. C.; Mcdonald, G.; Mullen, R. L.

    1983-01-01

    The residual stresses in a ceramic sheet material used for turbine blade tip gas path seals, were estimated. These stresses result from the plasma spraying process which leaves the surface of the sheet in tension. To determine the properties of plasma sprayed ZrO2-Y2O3 sheet material, its load deflection characteristics were measured. Estimates of the mechanical properties for sheet materials were found to differ from those reported for plasma sprayed bulk materials.

  2. 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.

  3. 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....

  4. Characterizing the effect of creep on stress corrosion cracking of cold worked Alloy 690 in supercritical water environment

    Science.gov (United States)

    Zhang, Lefu; Chen, Kai; Du, Donghai; Gao, Wenhua; Andresen, Peter L.; Guo, Xianglong

    2017-08-01

    The effect of creep on stress corrosion cracking (SCC) was studied by measuring crack growth rates (CGRs) of 30% cold worked (CW) Alloy 690 in supercritical water (SCW) and inert gas environments at temperatures ranging from 450 °C to 550 °C. The SCC crack growth rate under SCW environments can be regarded as the cracking induced by the combined effect of corrosion and creep, while the CGR in inert gas environment can be taken as the portion of creep induced cracking. Results showed that the CW Alloy 690 sustained high susceptibility to intergranular (IG) cracking, and creep played a dominant role in the SCC crack growth behavior, contributing more than 80% of the total crack growth rate at each testing temperature. The temperature dependence of creep induced CGRs follows an Arrhenius dependency, with an apparent activation energy (QE) of about 225 kJ/mol.

  5. A STUDY OF CORROSION AND STRESS CORROSION CRACKING OF CARBON STEEL NUCLEAR WASTE STORAGE TANKS

    Energy Technology Data Exchange (ETDEWEB)

    BOOMER, K.D.

    2007-08-21

    The Hanford reservation Tank Farms in Washington State has 177 underground storage tanks that contain approximately 50 million gallons of liquid legacy radioactive waste from cold war plutonium production. These tanks will continue to store waste until it is treated and disposed. These nuclear wastes were converted to highly alkaline pH wastes to protect the carbon steel storage tanks from corrosion. However, the carbon steel is still susceptible to localized corrosion and stress corrosion cracking. The waste chemistry varies from tank to tank, and contains various combinations of hydroxide, nitrate, nitrite, chloride, carbonate, aluminate and other species. The effect of each of these species and any synergistic effects on localized corrosion and stress corrosion cracking of carbon steel have been investigated with electrochemical polarization, slow strain rate, and crack growth rate testing. The effect of solution chemistry, pH, temperature and applied potential are all considered and their role in the corrosion behavior will be discussed.

  6. Stress/strain distributions for weld metal solidification crack in stainless steels

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    This paper has simulated the driving force of solidification crack of stainless steels, that is, stress/strain field in the trail of molten pool. Firstly, the effect of the deformation in the molten pool was eliminated after the element rebirth method was adopted. Secondly, the influence of solidification shrinkage was taken into account by increasing thermal expansion coefficients of the steels at elevated temperatures. Finally, the stress/strain distributions of different conditions have been computed and analyzed. Furthermore, the driving force curves of the solidification crack of the steels have been obtained by converting strain-time curves into strain-temperature curves, which founds a basis for predicting welding solidification crack.

  7. 49 CFR 192.929 - What are the requirements for using Direct Assessment for Stress Corrosion Cracking (SCCDA)?

    Science.gov (United States)

    2010-10-01

    ... requirements for using Direct Assessment for Stress Corrosion Cracking (SCCDA)? (a) Definition. Stress..., appendix A3, and remediate the threat in accordance with ASME/ANSI B31.8S, appendix A3, section A3.4....

  8. Fatigue crack shape prediction based on vertex singularity

    Directory of Open Access Journals (Sweden)

    Hutař P.

    2008-11-01

    Full Text Available Due to the existence of vertex singularity at the point where the crack intersects the free surface, stress distribution around the crack tip and the type of the singularity is changed. In the interior of the specimen the classical singular behaviour of the crack is dominant and can be described using analytic equations. Contrary to this, at the free surface or in the boundary layer close to free surface the vertex singularity is significant. The influence of vertex singularity on crack behaviour and a crack shape for a three-dimensional structure is described in this paper. The results presented make it possible to estimate fatigue crack growth rate and crack shape using the concept of the generalized stress intensity factor. The estimated fatigue crack shape can help to provide a more reliable estimation of the fatigue life of the structures considered.

  9. Fundamental aspects of stress corrosion cracking of copper relevant to the Swedish deep geologic repository concept

    Energy Technology Data Exchange (ETDEWEB)

    Bhaskaran, Ganesh; Carcea, Anatolie; Ulaganathan, Jagan; Wang, Shengchun; Huang, Yin; Newman, Roger C. [Dept. of Chemical Engineering and Applied Chemistry, Univ. of Toronto, Toronto (Canada)

    2013-03-15

    Phosphorus-doped oxygen-free copper will be used as the outer barrier in canisters that will contain spent nuclear fuel in the proposed Swedish underground repository. The possibility of stress corrosion cracking (SCC) is a concern, in view of isolated reports of cracking or intergranular corrosion of pure copper in sulfide solutions. This concern was addressed in the present work using copper tensile specimens provided by SKB. Methods included slow strain rate testing, constant strain tensile testing, electrochemical and surface analytical studies of corrosion products, and electron backscatter diffraction analysis of grain orientation effects on corrosion. The base solutions were prepared from NaCl or synthetic sea water with addition of varying amounts of sodium sulfide at room temperature and 80 degree Celsius. No SCC was found in any of the testing, for a range of sulfide concentrations from 5-50 mM at room temperature or 8 C, including tests where small anodic or cathodic potential displacements were applied from the open-circuit (corrosion) potential. Neither was SCC found in constant-strain immersion testing with very large strain. The Cu2S corrosion product is generally very coarse, fragile, and easily spalled off in severe corrosion environments, i.e. high sulfide concentration, high temperature, less perfect de aeration, etc. But it could also consist of very fine grains, relatively compact and adherent, on particular grain orientations when it was formed on an electro polished surface in a very well-deaerated solution. These orientations have not yet been identified statistically, although some preference for thin, adherent films was noted on orientations close to (100). The notion that the corrosion reaction is always controlled by inward aqueous-phase diffusion of sulfide may thus not be unconditionally correct for this range of sulfide concentrations; however it is hard to distinguish the role of diffusion within pores in the film. In the actual

  10. 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.

  11. Stress corrosion cracking in canistered waste package containers: Welds and base metals

    Energy Technology Data Exchange (ETDEWEB)

    Huang, J.S.

    1998-03-01

    The current design of waste package containers include outer barrier using corrosion allowable material (CAM) such as A516 carbon steel and inner barrier of corrosion resistant material (CRM) such as alloy 625 and C22. There is concern whether stress corrosion cracking would occur at welds or base metals. The current memo documents the results of our analysis on this topic.

  12. 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.

  13. Salt Stress-induced Programmed Cell Death in Rice Root Tip Cells

    Institute of Scientific and Technical Information of China (English)

    Jian-You Li; Ai-Liang Jiang; Wei Zhang

    2007-01-01

    Salt stressed rice root tips were used to investigate the changes of reactive oxygen species (ROS) and antioxidant enzymes at the early stages of programmed cell death (PCD). The results indicated that 500 mmol/L NaCl treatment could lead to specific features of PCD in root tips, such as DNA ladder, nuclear condense and deformation, and transferase mediated dUTP nick end labeling positive reaction, which were initiated at 4 h of treatment and progressed thereafter. Cytochrome c release from mitochondria into cytoplasm was also observed, which occurred at 2 h and was earlier than the above nuclear events. In the very early phase of PCD, an immediate burst in hydrogen peroxide and superoxide anion production rate was accompanied by two-phase changes of superoxide dismutases and ascorbate peroxidase. A short period of increase in the activity was followed by prolonged impairment. Thus,we conclude that salt can induce PCD in rice root tip cells, and propose that in the early phase of rice root tip cell PCD, salt stress-induced oxidative burst increased the antioxidant enzyme activity, which, In turn, scavenged the ROS and abrogated PCD. Also, when the stress is prolonged, the antioxidant system is damaged and accumulated ROS induces the PCD process, which leads to cytochrome c release and nuclear change.

  14. 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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-07-01

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

  16. Prevention of stress-corrosion cracking in nuclear waste storage tanks

    Energy Technology Data Exchange (ETDEWEB)

    Ondrejcin, R S

    1984-01-01

    Stress corrosion cracking (SCC) has occurred in the early versions of carbon steel primaries of nuclear waste tanks at the Savannah River Plant. (Secondary containment was provided by a vessel surrounding the lower portion of the primary tank.) Evaporated alkaline nitrate wastes in the form of crystallized salts are being dissolved from some of these tanks for transfer to new tanks of a different design. To prevent the SCC sequence from occurring during salt dissolution, the levels of inhibitors required to prevent cracking at yield stresses were determined. Special statistically designed experiments were performed to evaluate the probability of cracking under the combined influences of nitrate, nitrite, hydroxide, and temperature. Experimentlly, samples were tested by a potentially controlled constant extension rate test and by wedge opening loaded samples. Two equations were derived by multivariable regression analyses that correlated probability of cracking as the dependent variable to nitrate, nitrite, and hydroxide concentrations and temperature as the independent variables. From these equations, simple operating standards were developed by setting the probability of cracking equal to zero and solving for the four independent variables. 15 references, 15 figures, 8 tables.

  17. Stress corrosion cracking and hydrogen embrittlement of thick section high strength low alloy steel.

    OpenAIRE

    Needham, William Donald

    1986-01-01

    An experimental study was conducted to evaluate the corrosion performance of weldments of a high strength low alloy(HSLA) steel in a simulated seawater environment. This steel, designated HSLA80, was developed by the United States Navy for use in ship structural applications. Stress corrosion CRACKING(SCC) and hydrogen embrittlement(HEM) were investigated by conducting 42 Wedge-Opening load(WOL) tests as a function of stress intensity and corrosion potential and 33 Slow Strain Rate(SSR) tests...

  18. AN EFFECTIVE BOUNDARY ELEMENT METHOD FOR ANALYSIS OF CRACK PROBLEMS IN A PLANE ELASTIC PLATE

    Institute of Scientific and Technical Information of China (English)

    YAN Xiang-qiao

    2005-01-01

    A simple and effective boundary element method for stress intensity factor calculation for crack problems in a plane elastic plate is presented. The boundary element method consists of the constant displacement discontinuity element presented by Crouch and Starfield and the crack-tip displacement discontinuity elements proposed by YAN Xiangqiao. In the boundary element implementation the left or the right crack-tip displacement discontinuity element was placed locally at the corresponding left or right each crack tip on top of the constant displacement discontinuity elements that cover the entire crack surface and the other boundaries. Test examples ( i. e. , a center crack in an infinite plate under tension, a circular hole and a crack in an infinite plate under tension) are included to illustrate that the numerical approach is very simple and accurate for stress intensity factor calculation of plane elasticity crack problems. In addition, specifically, the stress intensity factors of branching cracks emanating from a square hole in a rectangular plate under biaxial loads were analysed. These numerical results indicate the present numerical approach is very effective for calculating stress intensity factors of complex cracks in a 2-D finite body, and are used to reveal the effect of the biaxial loads and the cracked body geometry on stress intensity factors.

  19. Strain gradient plasticity-based modeling of hydrogen environment assisted cracking

    DEFF Research Database (Denmark)

    Martínez Pañeda, Emilio; Niordson, Christian Frithiof; P. Gangloff, Richard

    2016-01-01

    Finite element analysis of stress about a blunt crack tip, emphasizing finite strain and phenomenologicaland mechanism-based strain gradient plasticity (SGP) formulations, is integrated with electrochemical assessment of occluded-crack tip hydrogen (H) solubility and two H-decohesion models......; it is imperative to account for SGP in H cracking models. Predictions of the threshold stress intensity factor and H-diffusion limited Stage II crack growth rate agree with experimental data for a high strength austenitic Ni-Cusuperalloy (Monel®K-500) and two modern ultra-high strength martensitic steels (Aer...

  20. MULTIPLE PARALLEL SYMMETRIC PERMEABLE MODEL-Ⅲ CRACKS IN A PIEZOELECTRIC/PIEZOMAGNETIC COMPOSITE MATERIAL PLANE

    Institute of Scientific and Technical Information of China (English)

    Zhengong Zhou; Peiwei Zhang; Linzhi Wu

    2010-01-01

    In this paper,the interactions of multiple parallel symmetric and permeable finite length cracks in a piezoelectric/piezomagnetic material plane subjected to anti-plane shear stress loading are studied by the Schmidt method.The problem is formulated through Fourier transform into dual integral equations,in which the unknown variables are the displacement jumps across the crack surfaces.To solve the dual integral equations,the displacement jumps across the crack surfaces are directly expanded as a series of Jacobi polynomials.Finally,the relation between the electric field,the magnetic flux field and the stress field near the crack tips is obtained.The results show that the stress,the electric displacement and the magnetic flux intensity factors at the crack tips depend on the length and spacing of the cracks.It is also revealed that the crack shielding effect presents in piezoelectric/piezomagnetic materials.

  1. 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.

  2. Evolution of residual stress and crack morphologies during 3D FIB tomographic analysis of alumina.

    Science.gov (United States)

    Elfallagh, F; Inkson, B J

    2008-05-01

    Three-dimensional focused ion beam (FIB) tomography is increasingly being used for 3D characterization of microstructures in the 50 nm-20 microm range. FIB tomography is a destructive, invasive process, and microstructural changes may potentially occur during the analysis process. Here residual stress and crack morphologies in single-crystal sapphire samples have been concurrently analyzed using Cr3+ fluorescence spectroscopy and FIB tomography. Specifically, maps of surface residual stress have been obtained from optically polished single-crystal alumina [surface orientation (1 ī 0 2)], from FIB milled surface trenches, from Vickers micro-indentation sites (loads 50 g-300 g), and from Vickers micro-indentation sites during FIB serial sectioning. The residual stress maps clearly show that FIB sputtering generates residual stress changes. For the case of the Vickers micro-indentations, FIB sputtering causes significant changes in residual stress during the FIB tomographic serial sectioning. 3D reconstruction of the crack distribution around micro-indentation sites shows that the cracks observed are influenced by the location of the FIB milled surface trenches due to localized stress changes.

  3. Round robin analysis on stress intensity factor of inner surface cracks in welded stainless steel pipes

    Energy Technology Data Exchange (ETDEWEB)

    Han, Chang Gi; Chang, Yoon Suk [Dept. of Nuclear Engineering, College of Engineering, Kyung Hee University, Yongin (Korea, Republic of); Kim, Jong Sung [Dept. of Mechanical Engineering, Sunchon National University, Sunchon (Korea, Republic of); Kim, Maan Won [Central Research Institute, Korea Hydro and Nuclear Power Company, Daejeon (Korea, Republic of)

    2016-12-15

    Austenitic stainless steels (ASSs) are widely used for nuclear pipes as they exhibit a good combination of mechanical properties and corrosion resistance. However, high tensile residual stresses may occur in ASS welds because postweld heat treatment is not generally conducted in order to avoid sensitization, which causes a stress corrosion crack. In this study, round robin analyses on stress intensity factors (SIFs) were carried out to examine the appropriateness of structural integrity assessment methods for ASS pipe welds with two types of circumferential cracks. Typical stress profiles were generated from finite element analyses by considering residual stresses and normal operating conditions. Then, SIFs of cracked ASS pipes were determined by analytical equations represented in fitness-for-service assessment codes as well as reference finite element analyses. The discrepancies of estimated SIFs among round robin participants were confirmed due to different assessment procedures and relevant considerations, as well as the mistakes of participants. The effects of uncertainty factors on SIFs were deducted from sensitivity analyses and, based on the similarity and conservatism compared with detailed finite element analysis results, the R6 code, taking into account the applied internal pressure and combination of stress components, was recommended as the optimum procedure for SIF estimation.

  4. Round Robin Analyses on Stress Intensity Factors of Inner Surface Cracks in Welded Stainless Steel Pipes

    Directory of Open Access Journals (Sweden)

    Chang-Gi Han

    2016-12-01

    Full Text Available Austenitic stainless steels (ASSs are widely used for nuclear pipes as they exhibit a good combination of mechanical properties and corrosion resistance. However, high tensile residual stresses may occur in ASS welds because postweld heat treatment is not generally conducted in order to avoid sensitization, which causes a stress corrosion crack. In this study, round robin analyses on stress intensity factors (SIFs were carried out to examine the appropriateness of structural integrity assessment methods for ASS pipe welds with two types of circumferential cracks. Typical stress profiles were generated from finite element analyses by considering residual stresses and normal operating conditions. Then, SIFs of cracked ASS pipes were determined by analytical equations represented in fitness-for-service assessment codes as well as reference finite element analyses. The discrepancies of estimated SIFs among round robin participants were confirmed due to different assessment procedures and relevant considerations, as well as the mistakes of participants. The effects of uncertainty factors on SIFs were deducted from sensitivity analyses and, based on the similarity and conservatism compared with detailed finite element analysis results, the R6 code, taking into account the applied internal pressure and combination of stress components, was recommended as the optimum procedure for SIF estimation.

  5. EXPERIMENTAL STUDY ON CRACK CURVING PROPAGATION IN BENDING BEAMS UNDER IMPULSIVE LOAD

    Institute of Scientific and Technical Information of China (English)

    Fang Jing; Yao Xuefeng; Xiong Chunyang

    2000-01-01

    Dynamic fracture behaviour of crack curving in bent beams has been investigated.In order to understand the propagation mechanism of such cracks under impact,an experimental method is used that combines dynamic photoelasticity with dynamic caustics to study the interaction of the flexural waves and the crack.From the state change of the transient stresses in polymer specimen,the curving fracture in the impulsively loaded beams is analyzed.The dynamic responses of crack tips are evaluated by the stress intensity factors for the cracks running in varying curvature paths under bending stress wave.

  6. Lead-induced stress-corrosion cracking of alloy 600 in plausible steam generator crevice environments

    Energy Technology Data Exchange (ETDEWEB)

    Wright, M.D. [Atomic Energy of Canada Limited, Chalk River, Ontario (Canada); Manolescu, A. [Ontario Hydro Technologies, Toronto, Ontario (Canada); Mirzai, M. [Ontario Hydro, Toronto, Ontario (Canada)

    1999-03-01

    Laboratory stress-corrosion cracking (SCC) test environments were developed to simulate crevice chemistries representative of Bruce Nuclear Generating Station A (BNPD A) steam generators (SGs); these test environments were used to determine the susceptibility of Alloy 600 to lead-induced SCC under plausible SG conditions. Test environments were based on plant SG hideout return data and analysis of removed tubes and deposits. Deviations from the normal near-neutral crevice pH environment were considered to simulate possible faulted excursion crevice chemistry and to bound the postulated crevice pH range of 3 to 9 (at temperature). The effect of lead contamination up to 1000 ppm, but with an emphasis on the 100- to 500-ppm range, was determined. SCC susceptibility was investigated using constant extension rate tensile (CERT) tests and encapsulated C-ring tests. CERT tests were performed at 305 degrees C on tubing representative of BNPD A SG U-bends. The C-ring test method allowed a wider test matrix, covering 3 temperatures (280 degrees C, 304 degrees C and 315 degrees C), 3 strain levels (0.2%, 2% and 4%), and tubing representative of U-bends plus tubing given a simulated stress relief to represent material at the tube sheet. The results of this test program confirmed that in the absence of lead contamination, cracking does not occur in these concentrated, 3.3 to 8.9 pH range, crevice environments. Also, it appears that the concentrated crevice environments suppress lead-induced cracking relative to that seen in all-volatile-treatment (AVT) water. For the (static) C-ring tests, lead-induced SCC was only produced in the near-neutral crevice environment and was more severe at 500 ppm than at 100 ppm PbO. This trend was also observed in CERT tests, but some cracking-grain boundary attack occurred in acidic (pH 3.3) and alkaline (pH 8.9) environments. The C-ring tests indicated that a certain amount of resistance to cracking was imparted by simulated stress relief of

  7. Calculation of Stress Intensity Factor KⅠ Using the Exact Solution in an Infinitely Deep Crack in a Half-Plane

    Energy Technology Data Exchange (ETDEWEB)

    An, Deuk Man [Pusan Nat’l Univ., Busan (Korea, Republic of)

    2017-01-15

    In this study, we develop the exact field of modeⅠin an infinitely deep crack in a half-plane. Using this field, we obtain the exact stress intensity factor KⅠ. From the tractions on the crack faces induced by exact field, we calculate the stress intensity factor of this field. We compare the results with the stress intensity factor calculated using Bueckner’s weight function formula and that calculated by using Tada’s formula listed in “The Stress Analysis of Cracks Handbook” It was found that Bueckner’s formula yields accurate results. However, the results obtained using Tada’s formula exhibit inaccurate behavior.

  8. Statistical model of stress corrosion cracking based on extended form of Dirichlet energy

    Indian Academy of Sciences (India)

    Harry Yosh

    2013-12-01

    The mechanism of stress corrosion cracking (SCC) has been discussed for decades. Here I propose a model of SCC reflecting the feature of fracture in brittle manner based on the variational principle under approximately supposed thermal equilibrium. In that model the functionals are expressed with extended forms of Dirichlet energy, and Dirichlet principle is applied to them to solve the variational problem that represents SCC and normal extension on pipe surface. Based on the model and the maximum entropy principle, the statistical nature of SCC colony is discussed and it is indicated that the crack has discrete energy and length under ideal isotropy of materials and thermal equilibrium.

  9. Three-dimensional hybrid-stress finite element analysis of composite laminates with cracks and cutouts

    Science.gov (United States)

    Wang, S. S.

    1985-01-01

    A three-dimensional hybrid-stress finite element analysis of composite laminates containing cutouts and cracks is presented. Fully three-dimensional, hexahedral isoparametric elements of the hybrid-stress model are formulated on the basis of the Hellinger-Reissner variational principle. Traction-free edges, cutouts, and crack surfaces are modeled by imposition of exact traction boundary conditions along element surfaces. Special boundary and surface elements are constructed by introducing proper constraints on assumed stress functions. The Lagrangian multiplier technique is used to enforce ply-interface continuity conditions in hybrid bimaterial composite elements for modeling the interface region in a composite laminate. Two examples are given to illustrate the capability of the present method of approach: (1) the well-known delamination problem in an angle-ply laminate, and (2) the important problem of a composite laminate containing a circular hole. Results are presented in detail for each case. Implications of interlaminar and intralaminar crack initiation, growth and fracture in composites containing cracks and cutouts are discussed.

  10. Theoretical Analysis of Heat Stress Prefabricating the Crack in Precision Cropping

    Directory of Open Access Journals (Sweden)

    Lijun Zhang

    2013-07-01

    Full Text Available The mathematical model of the metal bar in course of heat treatment is built by regarding the convective heat transfer process of the metal bar as the heat conduction boundary condition. By the theory analysis and numerical simulation methods, the theoretical expression of unsteady multidimensional temperature field for the axisymmetric model of metal bar is obtained. Temperature field distribution of bar V-shaped notch equivalent tip is given by ANSYS software. The quantitative relationship between temperature of bar inner key points and the time is determined. Through the polynomial curve fitting, the relation between the ultimate strength and the temperature is also given. Based on it, the influences of the width of the adiabatic boundary and water velocity on the critical temperature gradient of germinating heat crack in the tip of V-shaped notch are analyzed. The experimental results in precision cropping show that the expression of unsteady multidimensional temperature field is feasible in the rapid calculation of crack generation.

  11. Stress intensity factor and load transfer analysis of a cracked riveted lap joint

    Energy Technology Data Exchange (ETDEWEB)

    Moreira, P.M.G.P. [DEMEGI, Faculdade de Engenharia, Universidade do Porto, 4200-465 Porto (Portugal)]. E-mail: pmgpm@fe.up.pt; Matos, P.F.P. de [DEMEGI, Faculdade de Engenharia, Universidade do Porto, 4200-465 Porto (Portugal); Camanho, P.P. [DEMEGI, Faculdade de Engenharia, Universidade do Porto, 4200-465 Porto (Portugal); Pastrama, Stefan D. [Department of Strength of Materials, University Politehnica of Bucharest, Splaiul Independentei nr. 313, Sector 6, Bucharest (Romania); Castro, P.M.S.T. de [DEMEGI, Faculdade de Engenharia, Universidade do Porto, 4200-465 Porto (Portugal)

    2007-07-01

    One of the main problems of aeronautical structures is the onset and growth of defects due to fatigue loading. This phenomenon is accentuated in areas of stress concentration, for example in the connection of components, such as the riveted joints of fuselage panels. Several geometric configurations can be used in riveted joints of fuselage panels. This work is focused on one geometry, a single-lap splice with three rivets rows and one rivet column. A three-dimensional stress analysis using the finite element method was carried out in order to analyze the load transfer as a function of crack geometry and length, and to determine the stress intensity factors for one or two cracks emanating from the edge of the hole located at the critical cross section.

  12. Evaluation of the stress corrosion cracking resistance of several high strength low alloy steels

    Science.gov (United States)

    Humphries, T. S.; Nelson, E. E.

    1980-01-01

    The stress corrosion cracking resistance was studied for high strength alloy steels 4130, 4340, for H-11 at selected strength levels, and for D6AC and HY140 at a single strength. Round tensile and C-ring type specimens were stressed up to 100 percent of their yield strengths and exposed to alternate immersion in salt water, salt spray, the atmosphere at Marshall Space Flight Center, and the seacoast at Kennedy Space Center. Under the test conditions, 4130 and 4340 steels heat treated to a tensile strength of 1240 MPa (180 ksi), H-11 and D6AC heat treated to a tensile strength of 1450 MPa (210 ksi), and HY140 (1020 MPa, 148 ksi) are resistant to stress corrosion cracking because failures were not encountered at stress levels up to 75 percent of their yield strengths. A maximum exposure period of one month for alternate immersion in salt water or salt spray and three months for seacoast is indicated for alloy steel to avoid false indications of stress corrosion cracking because of failure resulting from severe pitting.

  13. 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.

  14. Evolving fracture patterns: columnar joints, mud cracks, and polygonal terrain

    Science.gov (United States)

    Goehring, L.

    2012-12-01

    Contraction cracks can form captivating patterns, such as the artistic craquelure sometimes found in pottery glazes, to the cracks in dried mud, or the polygonal networks covering the polar regions of Earth and Mars. Two types are frequently encountered: those with irregular rectilinear patterns, such as that formed by an homogeneous slurry when dried (or cooled) uniformly, and more regular hexagonal patterns, such as those typified by columnar joints. Once cracks start to form in a thin contracting layer, they will sequentially break the layer into smaller and smaller pieces. A rectilinear crack pattern encodes information about the order of cracks, as later cracks tend to intersect with earlier cracks at right angles. In this manner they relieve the stresses perpendicular to the pre-existing crack. In a hexagonal pattern, in contrast, the angles between all cracks at a vertex are near 120°. In this presentation it will be shown how both types of pattern can arise from identical forces, and that a rectilinear, T-junction dominated pattern will develop into to a hexagonal pattern, with Y-junctions, if allowed to. Such an evolution can be explained as the result of three conditions: (1) if cracks advance through space, or heal and recur, that the previous positions of a crack tip acts as a line of weakness, guiding the next iteration of cracking; (2) that the order of opening of cracks can change in each iteration; and (3) that crack tips curve to maximise the local strain energy release rate. The ordering of crack patterns are seen in a number of systems: columnar joints in starch and lava; desiccation cracks in clays that are repeatedly wetted and dried; cracks in eroding gypsum-cemented sand layers; and the cracks in permafrost known as polygonal terrain. These patterns will each be briefly explored, in turn, and shown to obey the above principles of crack pattern evolution.

  15. Stress corrosion cracking in low-pressure turbine discs in an NaCl solution

    Energy Technology Data Exchange (ETDEWEB)

    Hitomi, Itoh [Mitsubishi Heavy Industries, Ltd., Takasago Research and Development Center (Japan); Takashi, Momoo [Mitsubishi Heavy Industries, Ltd., Takasago Machinery Works (Japan)

    2001-07-01

    From past research, it is known that stress corrosion cracking in low-pressure turbine discs occurs in an environment near that of deaerated pure water. Nevertheless, in units with molar ratio control, there is a possibility of NaCl concentrating as an impurity in the dry/wet boundary region. Long-term immersion tests were conducted at 373 K to 473 K with the NaCl concentration predicted to become 5%. It was found that, when FeCl{sub 3} or other oxidizer was added, corrosion increased remarkably and SCC was initiated. When cracks were initiated, they were primarily transgranular; as the test temperature was decreased, initiation was accelerated but conversely crack propagation was reduced. (author)

  16. The stress distribution in tempered glass due to a crack

    Science.gov (United States)

    Arin, K.

    1976-01-01

    A model describing the failure in tempered glass is proposed and a method of solution is presented. An infinite elastic strip is assumed to represent the glass and the loads vanish everywhere on the boundary as well as at infinity. The problem is solved using the integral equations technique where the input is the residual stresses in the glass.

  17. Effect of proton irradiation on irradiation assisted stress corrosion cracking in PWR

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Han Ok; Hwang, Mi Jin; Kim, Sung Woo; Hwang, Seong Sik [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2014-05-15

    Irradiation assisted stress corrosion cracking (IASCC) involves the cracking and failure of materials under irradiation environment in nuclear power plant water environment. The major factors and processes governing an IASCC are suggested by others. The IASCC of the reactor core internals due to the material degradation and the water chemistry change has been reported in high stress stainless steel components, such as fuel elements (Boiling Water Reactors) in the 1960s, a control rod in the 1970s, and a baffle former bolt in recent years of light water reactors (Pressurized Water Reactors). Many irradiated stainless steels that are resistant to inergranular cracking in 288 .deg. C argon are susceptible to IG cracking in the simulated BWR environment at the same temperature. Under the circumstances, a lot works have been performed on IASCC in BWR. Recent efforts have been devoted to investigate an IASCC in a PWR, but the mechanism in a PWR is not fully understood yet as compared with that in a BWR owing to a lack of data from laboratories and fields. Therefore, it is strongly necessary to review and analyze recent researches of an IASCC in both BWR and PWR for establishing a proactive management technology for the IASCC of core internals in Korean PWRs. The objective of this research to find IASCC behavior of proton irradiated 316 stainless steels in a high-temperature water chemistry environment. The IASCC initiation susceptibility on 1, 3, 5 DPA proton irradiated 316 austenite stainless steel was evaluated in PWR environment. SCC area ratio on the fracture surface was similar regardless of irradiation level. Total crack length on the irradiated surface increases in order of specimen 1, 3, 5 DPA. The total crack length at the side surface is a better measure in evaluating IASCC initiation susceptibility for proton-irradiated samples.

  18. A comparison of methods for calculating notch tip strains and stresses under multiaxial loading

    Directory of Open Access Journals (Sweden)

    M. Lutovinov

    2016-10-01

    Full Text Available Selected methods for calculating notch tip strains and stresses in elastic–plastic isotropic bodies subjected to multiaxial monotonic loading were compared. The methods use sets of equations where hypothetical notch tip elastic strains and stresses obtained from FEM calculations serve as an input. The comparison was performed within two separate groups of methods: the first group consists of the methods intended for cases of multiaxial proportional loading and the second group deals with multiaxial non-proportional loading. Originally, the precision of the methods was validated by comparison with results obtained from elastic–plastic FEM analyses. Since computer performance at the time was lower than nowadays, verification of the proposed methods on FEM models with a finer mesh was needed. Such verification was carried out and is presented in this paper. The effect of various formulations of material stress–strain curve was also evaluated

  19. Mechanism of intergranular stress corrosion cracking in HAZ for super-martensitic stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Miyata, Yukio; Kimura, Mitsuo [Tubular Products and Casting Research Dept., JFE Steel Corporation, 1-1, Kawasaki-cho, Handa (Japan); Nakamichi, Haruo; Sato, Kaoru [Analysis and Characterization Research Dept., JFE Steel Corporation, 1-1, Minamiwatarida-cho, Kawasaki-ku, Kawasaki (Japan); Itakura, Noritsugu [Products Service and Development Dept., Chita Works, JFE Steel Corporation. 1-1, Kawasaki-cho, Handa (Japan); Masamura, Katsumi [Tubular Products Business Planning Dept., JFE Steel Corporation, 2-2-3, Uchisaiwai-sho, Chiyoda-ku, Tokyo (Japan)

    2004-07-01

    Mechanism of intergranular stress corrosion cracking (IGSCC) for heat affected zone (HAZ) of super-martensitic stainless steel was studied using two types of the steel. One was a lean grade, which was Mo free and low Ni, and the other was a high grade, which was Mo added and high Ni. Specimens received heat treatments simulating welding thermal cycles were applied to SCC tests. Cracks were observed in some specimens after U-bend SCC test under low pH environments. Thermal cycle conditions with sensitization were verified from the results. No crack was observed in the specimen with the thermal cycle simulating post welding heat treatment (PWHT) after sensitizing conditions. Therefore, PWHT was clarified to be effective to prevent the cracking. Cr carbides were observed along prior austenite grain boundary intermittently, and Cr depleted zone was confirmed on the grain boundary adjacent to carbides that precipitated on the grain boundary. It is, therefore, concluded that the cracking results from Cr depletion on prior austenite grain boundary accompanied by precipitation of Cr carbides under specific welding conditions. (authors)

  20. A Study on the Residual Stress Improvement of PWSCC(Primary Water Stress Corrosion Cracking) in DMW(Dissimilar Metal Weld)

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Sung Sik; Kim, Seok Hun; Lee, Seung Gun [Korea Institute of Nuclear Safety, Daejeon (Korea, Republic of); Park, Heung Bae [KEPCO Engineering and Construction Company, Daejeon (Korea, Republic of)

    2010-10-15

    Since 2000s, most of the cracks are found in welds, especially in (DMW) dissimilar metal welds such as pressurizer safety relief nozzle, reactor head penetration, reactor bottom mounted instrumentation (BMI), and reactor nozzles. Even the cracks are revealed as a primary water stress corrosion cracking (PWSCC), it is difficult to find the cracks by current non destructive examination. The PWSCC is occurred by three incident factors, such as susceptible material, environmental corrosive condition, and welding residual stress. If one of the three factors can be erased or decreased, the PWSCC could be prevented. In this study, we performed residual stress analysis for DMW and several residual stress improvement methods. As the preventive methods of PWSCC, we used laser peening(IP) method, inlay weld(IW) method, and induction heating stress improvement(IHSI) method. The effect of residual stress improvement for preventive methods was compared and discussed by finite element modeling and residual stress of repaired DMW

  1. High-Performance Laser Peening for Effective Mitigation of Stress Corrosion Cracking

    Energy Technology Data Exchange (ETDEWEB)

    Hackel, L; Hao-Lin, C; Wong, F; Hill, M

    2002-10-02

    Stress corrosion cracking (SCC) in the Yucca Mountain waste package closure welds is believed to be the greatest threat to long-term containment. Use of stress mitigation to eliminate tensile stresses resulting from welding can prevent SCC. A laser technology with sufficient average power to achieve high throughput has been developed and commercially deployed with high peak power and sufficiently high average power to be an effective laser peening system. An appropriately applied version of this process could be applied to eliminate SCC in the waste package closure welds.

  2. 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.

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

    Science.gov (United States)

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

    1974-01-01

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

  4. Electrochemical studies on stress corrosion cracking of incoloy-800 in caustic solution. Part II: Precracking samples

    Directory of Open Access Journals (Sweden)

    Dinu Alice

    2006-01-01

    Full Text Available Stress corrosion cracking (SCC in a caustic medium may affect the secondary circuit tubing of a CANDU NPP cooled with river water, due to an accidental formation of a concentrated alkaline environment in the areas with restricted circulation, as a result of a leakage of cooling water from the condenser. To evaluate the susceptibility of Incoloy-800 (used to manufacture steam generator tubes for CANDU NPP to SCC, some accelerated corrosion tests were conducted in an alkaline solution (10% NaOH, pH = 13. These experiments were performed at ambient temperature and 85 °C. We used the potentiodynamic method and the potentiostatic method, simultaneously monitoring the variation of the open circuit potential during a time period (E corr/time curve. The C-ring method was used to stress the samples. In order to create stress concentrations, mechanical precracks with a depth of 100 or 250 μm were made on the outer side of the C-rings. Experimental results showed that the stressed samples were more susceptible to SCC than the unstressed samples whereas the increase in temperature and crack depth lead to an increase in SCC susceptibility. Incipient micro cracks of a depth of 30 μm were detected in the area of the highest peak of the mechanical precrack.

  5. Weight Function Method for Stress Intensity Factor of Internal Surface Semi-elliptical Crack in Elliptical Holes

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The hatches for inspecting are usually designed with elliptical holes in airplane structures, so computation of the stress intensity factor of three dimensional crack at elliptical holes is pivotal for damage tolerance analysis of these structures. In this paper, weight function is derived for a two dimensional through cracks at elliptical holes by applying a compounding method. Stress intensity factor formulas for an internal surface semi-elliptical crack in elliptical holes are obtained using the three dimensional weight function method. Stress intensity factors for an internal surface semi-elliptical crack in elliptical holes under remote tension are computed. At the same time, research on how radius of curvature for elliptical holes affect stress intensity factors was conducted. Stress intensity factors decrease when radius of curvature increases. Some results and conclusions which are of practical value are given.

  6. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-05-22

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

  8. Residual stress in plasma-sprayed ceramic turbine tip and gas-path seal specimens

    Science.gov (United States)

    Hendricks, R. C.; Mcdonald, G.; Mullen, R. L.

    1983-01-01

    The residual stresses in a ceramic sheet material used for turbine blade tip gas path seals, were estimated. These stresses result from the plasma spraying process which leaves the surface of the sheet in tension. To determine the properties of plasma sprayed ZrO2-Y2O3 sheet material, its load deflection characteristics were measured. Estimates of the mechanical properties for sheet materials were found to differ from those reported for plasma sprayed bulk materials. Previously announced in STAR as N83-28380

  9. 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.

  10. Near-neutral pH Stress Corrosion Crack Initiation under Simulated Coating Disbondment

    Science.gov (United States)

    Eslami, Abdoulmajid

    This research is aimed at understanding near-neutral pH SCC initiation under disbonded coatings of pipeline steels, and the effect of different environmental and operational factors on crack initiation. Understanding near-neutral pH stress corrosion cracking (SCC) could answer many of the primary questions on crack initiation of SCC which have not yet been answered. It could also assist the development of effective mitigative measures dealing with thousands of kilometer of pipelines containing this form of cracking, in addition to preventive action for future pipeline installations. Near-neutral pH SCC usually occurs under polyethylene tape (PE tape) coated pipelines, at locations where the coating becomes disbonded and/or damaged. Ground water can then penetrate under the damaged/disbonded coating, become trapped and form a suitable environment for corrosion and cracking. Despite extensive studies on this topic the details of crack initiation mechanisms in addition to the exact role of environmental and operational factors on crack initiation are not thoroughly understood. Most previous laboratory tests have been done in aggressive loading conditions and ignored the effect of coatings and cathodic protections (CP). In order to simulate the conditions responsible for crack initiation, a novel testing setup capable of simulating the synergistic effects of coating disbondment, cathodic protection and cyclic loading was implemented. Using this setup and long term laboratory tests near-neutral pH SCC initiation mechanisms and the effect of some environmental and operational factors on crack initiation were investigated. It was found that near-neutral pH SCC initiation does not necessarily occur in near-neutral pH environments as commonly believed. Depending on the level of CP and CO2 in the underground environment, different localized environments with varying pH values from near-neutral to high values above 10 can form under the disbonded coatings. This significantly

  11. NEW BOUNDARY ELEMENT METHOD FOR TORSION PROBLEMS OF CYLINDER WITH CURVILINEAR CRACKS

    Institute of Scientific and Technical Information of China (English)

    WANG Yin-bang; LU Zi-zi

    2005-01-01

    The Saint-Venant torsion problems of a cylinder with curvilinear cracks were considered and reduced to solving the boundary integral equations only on cracks. Using the interpolation models for both singular crack tip elements and other crack linear elements, the boundary element formulas of the torsion rigidity and stress intensity factors were given. Some typical torsion problems of a cylinder involving a straight,kinked or curvilinear crack were calculated. The obtained results for the case of straight crack agree well with those given by using the Gauss-Chebyshev integration formulas,which demonstrates the validity and applicability of the present boundary element method.

  12. Interface crack problems for mode Ⅱ of double dissimilar orthotropic composite materials

    Institute of Scientific and Technical Information of China (English)

    Wei-yang YANG; Shao-qin ZHANG; Jun-lin LI; Yu-lan MA

    2009-01-01

    The fracture problems near the interface crack tip for mode Ⅱ of double dissimilar orthotropic composite materials are studied. The mechanical models of interface crack for mode Ⅱ are given. By translating the governing equations into the generalized bi-harmonic equations,the stress functions containing two stress singularity exponents are derived with the help of a complex function method. Based on the boundary conditions,a system of non-homogeneous linear equations is found. Two real stress singularity exponents are determined be solving this system under appropriate conditions about himaterial engineering parameters. According to the uniqueness theorem of limit,both the formulae of stress intensity factors and theoretical solutions of stress field near the interface crack tip are derived. When the two orthotropic materials are the same,the stress singularity exponents,stress intensity factors and stresses for mode Ⅱ crack of the orthotropic single material are obtained.

  13. Scanning electron acoustic microscopy of indentation-induced cracks and residual stresses in ceramics

    Science.gov (United States)

    Cantrell, John H.; Qian, Menglu; Ravichandran, M. V.; Knowles, K. M.

    1990-01-01

    The ability of scanning electron acoustic microscopy (SEAM) to characterize ceramic materials is assessed. SEAM images of Vickers indentations in SiC whisker-reinforced alumina clearly reveal not only the radial cracks, the length of which can be used to estimate the fracture toughness of the material, but also reveal strong contrast, interpreted as arising from the combined effects of lateral cracks and the residual stress field left in the SiC whisker-reinforced alumina by the indenter. The strong contrast is removed after the material is heat treated at 1000 C to relieve the residual stresses around the indentations. A comparison of these observations with SEAM and reflected polarized light observations of Vickers indentations in soda-lime glass both before and after heat treatment confirms the interpretation of the strong contrast.

  14. Investigation of stress intensity factor for internal cracks in FG cylinders under static and dynamic loading

    Directory of Open Access Journals (Sweden)

    Mahmoud Shariati

    2017-01-01

    Full Text Available his paper investigates the variations of mode I stress intensity factor (KI for inner penny-shaped and circumferential cracks in functionally graded solid and hollow thick walled cylinders, respectively with the changes of crack geometry, material gradation and loading conditions. The functionally graded material of cylinders consists of epoxy and glass. It is assumed that the mechanical properties vary with a power law in the radial direction of cylinders. Micromechanical models for conventional composites are used to estimate the material properties of functionally graded cylinders. The equations of motion obtained from the extended finite element discretization are solved by the Newmark method in the time domain. The interaction integral method is employed to calculate the mode I stress intensity factor (KI. The MATLAB programming environment was implemented to solve the problem.

  15. 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.

  16. Scanning electron acoustic microscopy of indentation-induced cracks and residual stresses in ceramics

    Science.gov (United States)

    Cantrell, John H.; Qian, Menglu; Ravichandran, M. V.; Knowles, K. M.

    1990-01-01

    The ability of scanning electron acoustic microscopy (SEAM) to characterize ceramic materials is assessed. SEAM images of Vickers indentations in SiC whisker-reinforced alumina clearly reveal not only the radial cracks, the length of which can be used to estimate the fracture toughness of the material, but also reveal strong contrast, interpreted as arising from the combined effects of lateral cracks and the residual stress field left in the SiC whisker-reinforced alumina by the indenter. The strong contrast is removed after the material is heat treated at 1000 C to relieve the residual stresses around the indentations. A comparison of these observations with SEAM and reflected polarized light observations of Vickers indentations in soda-lime glass both before and after heat treatment confirms the interpretation of the strong contrast.

  17. Stress-Corrosion Cracking of Metallic Materials. Part III. Hydrogen Entry and Embrittlement in Steel

    Science.gov (United States)

    1975-04-01

    Strength Steels," Stress Corrosion Cracking in High-Strength Steels and in Titanium and Altuninum Alloys, Naval Rasearch Laboratory, Washington, D.C...to pickling solutions. In all of these examples, the sulfide, cyanide, etc., caused a hydrogen-related problem that would not have existed in their...desorption reaction. In studying the pickling of low-carbon steel in various strong acids, Hudson’ 4 measured the corrosion rate and amount of hydr-ogen

  18. Stress Mapping in Glass-to-Metal Seals using Indentation Crack Lengths

    Energy Technology Data Exchange (ETDEWEB)

    Buchheit, Thomas E. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Component & Systems Analysis; Strong, Kevin [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Material Mechanics and Tribology; Newton, Clay S. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Material Mechanics and Tribology; Diebold, Thomas Wayne [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Material Mechanics and Tribology; Bencoe, Denise N. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Electronic, Optical and Nano; Stavig, Mark E. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Organic Materials Science; Jamison, Ryan Dale [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Transportation System Analysis

    2017-08-01

    Predicting the residual stress which develops during fabrication of a glass-to-metal compression seal requires material models that can accurately predict the effects of processing on the sealing glass. Validation of the predictions requires measurements on representative test geometries to accurately capture the interaction between the seal materials during a processing cycle required to form the seal, which consists of a temperature excursion through the glass transition temperature of the sealing glass. To this end, a concentric seal test geometry, referred to as a short cylinder seal, consisting of a stainless steel shell enveloping a commercial sealing glass disk has been designed, fabricated, and characterized as a model validation test geometry. To obtain data to test/validate finite element (FE) stress model predictions of this geometry, spatially-resolved residual stress was calculated from the measured lengths of the cracks emanating from radially positioned Vickers indents in the glass disk portion of the seal. The indentation crack length method is described, and the spatially-resolved residual stress determined experimentally are compared to FE stress predictions made using a nonlinear viscoelastic material model adapted to inorganic sealing glasses and an updated rate dependent material model for 304L stainless steel. The measurement method is a first to achieve a degree of success for measuring spatially resolved residual stress in a glass-bearing geometry and a favorable comparison between measurements and simulation was observed.

  19. Stress Mapping in Glass-to-Metal Seals using Indentation Crack Lengths.

    Energy Technology Data Exchange (ETDEWEB)

    Strong, Kevin [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Buchheit, Thomas E. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Diebold, Thomas Wayne [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Newton, Clay S. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Bencoe, Denise N. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Stavig, Mark E. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Jamison, Ryan Dale [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2017-08-01

    Predicting the residual stress which develops during fabrication of a glass-to-metal compression seal requires material models that can accurately predict the effects of processing on the sealing glass. Validation of the predictions requires measurements on representative test geometries to accurately capture the interaction between the seal materials during a processing cycle required to form the seal, which consists of a temperature excursion through the glass transition temperature of the sealing glass. To this end, a concentric seal test geometry, referred to as a short cylinder seal, consisting of a stainless steel shell enveloping a commercial sealing glass disk has been designed, fabricated, and characterized as a model validation test geometry. To obtain data to test/validate finite element (FE) stress model predictions of this geometry, spatially-resolved residual stress was calculated from the measured lengths of the cracks emanating from radially positioned Vickers indents in the glass disk portion of the seal. The indentation crack length method is described, and the spatially-resolved residual stress determined experimentally are compared to FE stress predictions made using a nonlinear viscoelastic material model adapted to inorganic sealing glasses and an updated rate dependent material model for 304L stainless steel. The measurement method is a first to achieve a degree of success for measuring spatially resolved residual stress in a glass-bearing geometry and a favorable comparison between measurements and simulation was observed.

  20. Root elongation, water stress, and mechanical impedance: a review of limiting stresses and beneficial root tip traits.

    Science.gov (United States)

    Bengough, A Glyn; McKenzie, B M; Hallett, P D; Valentine, T A

    2011-01-01

    Root elongation in drying soil is generally limited by a combination of mechanical impedance and water stress. Relationships between root elongation rate, water stress (matric potential), and mechanical impedance (penetration resistance) are reviewed, detailing the interactions between these closely related stresses. Root elongation is typically halved in repacked soils with penetrometer resistances >0.8-2 MPa, in the absence of water stress. Root elongation is halved by matric potentials drier than about -0.5 MPa in the absence of mechanical impedance. The likelihood of each stress limiting root elongation is discussed in relation to the soil strength characteristics of arable soils. A survey of 19 soils, with textures ranging from loamy sand to silty clay loam, found that ∼10% of penetration resistances were >2 MPa at a matric potential of -10 kPa, rising to nearly 50% >2 MPa at - 200 kPa. This suggests that mechanical impedance is often a major limitation to root elongation in these soils even under moderately wet conditions, and is important to consider in breeding programmes for drought-resistant crops. Root tip traits that may improve root penetration are considered with respect to overcoming the external (soil) and internal (cell wall) pressures resisting elongation. The potential role of root hairs in mechanically anchoring root tips is considered theoretically, and is judged particularly relevant to roots growing in biopores or from a loose seed bed into a compacted layer of soil.

  1. Combined effect of matrix cracking and stress-free edge on delamination

    Science.gov (United States)

    Salpekar, S. A.; Obrien, T. K.

    1990-01-01

    The effect of the stress-free edge on the growth of local delaminations initiating from a matrix crack in (0 sub 2/90 sub 4) sub s and (+ or - 45.90 sub 4) sub s glass epoxy laminates is investigated using 3-D finite element analysis. The presence of high interlaminar normal stresses at the intersection (corner) of the matrix crack with the stress-free edge, suggests that a mode I delamination may initiate at the corners. The strain energy release rates (G) were calculated by modeling a uniform through-width delamination and two inclined delaminations at 10.6 deg and 45 deg to the matrix crack. All components of G have high values near the free edges. The mode I component of G is high at small delamination length and becomes zero for a delamination length of one-ply thickness. The total G values near the free edge agreed well with previously derived closed form solution. The quasi-3D solutions agreed well with the 3-D interior solutions.

  2. The effect of a curvature-dependent surface tension on the singularities at the tips of a straight interface crack

    KAUST Repository

    Zemlyanova, A. Y.

    2013-03-08

    A problem of an interface crack between two semi-planes made out of different materials under an action of an in-plane loading of general tensile-shear type is treated in a semi-analytical manner with the help of Dirichlet-to-Neumann mappings. The boundaries of the crack and the interface between semi-planes are subjected to a curvature-dependent surface tension. The resulting system of six singular integro-differential equations is reduced to the system of three Fredholm equations. It is shown that the introduction of the curvature-dependent surface tension eliminates both classical integrable power singularity of the order 1/2 and an oscillating singularity present in a classical linear elasticity solutions. The numerical results are obtained by solving the original system of singular integro-differential equations by approximating unknown functions with Taylor polynomials. © 2013 The Author.

  3. 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.

  4. Crack prediction in EB-PVD thermal barrier coatings based on the simulation of residual stresses

    Science.gov (United States)

    Chen, J. W.; Zhao, Y.; Liu, S.; Zhang, Z. Z.; Ma, J.

    2016-07-01

    Thermal barrier coatings systems (TBCs) are widely used in the field of aerospace. The durability and insulating ability of TBCs are highly dependent on the residual stresses of top coatings, thus the investigation of the residual stresses is helpful to understand the failure mechanisms of TBCs. The simulation of residual stresses evolution in electron beam physical vapor deposition (EB-PVD) TBCs is described in this work. The interface morphology of TBCs subjected to cyclic heating and cooling is observed using scanning electron microscope (SEM). An interface model of TBCs is established based on thermal elastic-plastic finite method. Residual stress distributions in TBCs are obtained to reflect the influence of interfacial roughness. Both experimental and simulation results show that it is feasible to predict the crack location by stress analysis, which is crucial to failure prediction.

  5. A novel soybean intrinsic protein gene, GmTIP2;3, involved in responding to osmotic stress

    Directory of Open Access Journals (Sweden)

    Da Yong eZhang

    2016-01-01

    Full Text Available Water is essential for plant growth and development. Water deficiency leads to loss of yield and decreased crop quality. To understand water transport mechanisms in plants, we cloned and characterized a novel tonoplast intrinsic protein (TIP gene from soybean with the highest similarity to TIP2-type from other plants, thus designated GmTIP2;3. The protein sequence contains two conserved NPA motifs and six transmembrane domains. The expression analysis indicated that this gene was constitutively expressed in all detected tissues, with higher levels in the root, stem and pod, and the accumulation of GmTIP2;3 transcript showed a significant response to osmotic stresses, including 20% PEG6000 (polyethylene glycol and 100 µM ABA (abscisic acid treatments. The promoter-GUS (glucuronidase activity analysis suggested that GmTIP2;3 was also expressed in the root, stem and leaf and preferentially expressed in the stele of root and stem, and the core promoter region was 1000 bp in length, located upstream of the ATG start codon. The GUS tissue and induced expression observations were consistent with the findings in soybean. In addition, subcellular localization showed that GmTIP2;3 was a plasma membrane-localized protein. Yeast heterologous expression revealed that GmTIP2;3 could improve tolerance to osmotic stress in yeast cells. Integrating these results, GmTIP2;3 might play an important role in response to osmotic stress in plants .

  6. Hierarchical Petascale Simulation Framework For Stress Corrosion Cracking

    Energy Technology Data Exchange (ETDEWEB)

    Grama, Ananth

    2013-12-18

    A number of major accomplishments resulted from the project. These include: • Data Structures, Algorithms, and Numerical Methods for Reactive Molecular Dynamics. We have developed a range of novel data structures, algorithms, and solvers (amortized ILU, Spike) for use with ReaxFF and charge equilibration. • Parallel Formulations of ReactiveMD (Purdue ReactiveMolecular Dynamics Package, PuReMD, PuReMD-GPU, and PG-PuReMD) for Messaging, GPU, and GPU Cluster Platforms. We have developed efficient serial, parallel (MPI), GPU (Cuda), and GPU Cluster (MPI/Cuda) implementations. Our implementations have been demonstrated to be significantly better than the state of the art, both in terms of performance and scalability. • Comprehensive Validation in the Context of Diverse Applications. We have demonstrated the use of our software in diverse systems, including silica-water, silicon-germanium nanorods, and as part of other projects, extended it to applications ranging from explosives (RDX) to lipid bilayers (biomembranes under oxidative stress). • Open Source Software Packages for Reactive Molecular Dynamics. All versions of our soft- ware have been released over the public domain. There are over 100 major research groups worldwide using our software. • Implementation into the Department of Energy LAMMPS Software Package. We have also integrated our software into the Department of Energy LAMMPS software package.

  7. Hierarchical Petascale Simulation Framework For Stress Corrosion Cracking

    Energy Technology Data Exchange (ETDEWEB)

    Grama, Ananth

    2013-12-18

    A number of major accomplishments resulted from the project. These include: • Data Structures, Algorithms, and Numerical Methods for Reactive Molecular Dynamics. We have developed a range of novel data structures, algorithms, and solvers (amortized ILU, Spike) for use with ReaxFF and charge equilibration. • Parallel Formulations of ReactiveMD (Purdue ReactiveMolecular Dynamics Package, PuReMD, PuReMD-GPU, and PG-PuReMD) for Messaging, GPU, and GPU Cluster Platforms. We have developed efficient serial, parallel (MPI), GPU (Cuda), and GPU Cluster (MPI/Cuda) implementations. Our implementations have been demonstrated to be significantly better than the state of the art, both in terms of performance and scalability. • Comprehensive Validation in the Context of Diverse Applications. We have demonstrated the use of our software in diverse systems, including silica-water, silicon-germanium nanorods, and as part of other projects, extended it to applications ranging from explosives (RDX) to lipid bilayers (biomembranes under oxidative stress). • Open Source Software Packages for Reactive Molecular Dynamics. All versions of our soft- ware have been released over the public domain. There are over 100 major research groups worldwide using our software. • Implementation into the Department of Energy LAMMPS Software Package. We have also integrated our software into the Department of Energy LAMMPS software package.

  8. Influence of the crack propagation rate in the obtaining opening and closing stress intensity factor by finite element method

    Directory of Open Access Journals (Sweden)

    Luiz Carlos H. Ricardo

    2016-03-01

    Full Text Available Crack propagation simulation began with the development of the finite element method; the analyses were conducted to obtain a basic understanding of the crack growth. Today structural and materials engineers develop structures and materials properties using this technique as criterion design. The aim of this paper is to verify the effect of different crack propagation rates in determination of crack opening and closing stress of an ASTM specimen under a standard suspension spectrum loading from FD&E SAE Keyhole Specimen Test Load Histories by finite element analysis. The crack propagation simulation was based on release nodes at the minimum loads to minimize convergence problems. To understand the crack propagation processes under variable amplitude loading, retardation effects are discussed.

  9. Residual stress and crack initiation in laser clad composite layer with Co-based alloy and WC + NiCr

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Changmin; Park, Hyungkwon; Yoo, Jaehong [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Lee, Changhee, E-mail: chlee@hanyang.ac.kr [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Woo, WanChuck [Neutron Science Division, Korea Atomic Energy Research Institute, Daejeon 305-353 (Korea, Republic of); Park, Sunhong [Research Institute of Industrial Science & Technology, Hyo-ja-dong, Po-Hang, Kyoung-buk, San 32 (Korea, Republic of)

    2015-08-01

    Highlights: • Major problem, clad cracking in laser cladding process, was researched. • Residual stress measurements were performed quantitatively by neutron diffraction method along the surface of specimens. • Relationship between the residual stress and crack initiation was showed clearly. • Ceramic particle effect in the metal matrix was showed from the results of residual stress measurements. • Initiation sites of generating clad cracks were specifically studied in MMC coatings. - Abstract: Although laser cladding process has been widely used to improve the wear and corrosion resistance, there are unwanted cracking issues during and/or after laser cladding. This study investigates the tendency of Co-based WC + NiCr composite layers to cracking during the laser cladding process. Residual stress distributions of the specimen are measured using neutron diffraction and elucidate the correlation between the residual stress and the cracking in three types of cylindrical specimens; (i) no cladding substrate only, (ii) cladding with 100% stellite#6, and (iii) cladding with 55% stellite#6 and 45% technolase40s. The microstructure of the clad layer was composed of Co-based dendrite and brittle eutectic phases at the dendritic boundaries. And WC particles were distributed on the matrix forming intermediate composition region by partial melting of the surface of particles. The overlaid specimen exhibited tensile residual stress, which was accumulated through the beads due to contraction of the coating layer generated by rapid solidification, while the non-clad specimen showed compressive. Also, the specimen overlaid with 55 wt% stellite#6 and 45 wt% technolase40s showed a tensile stress higher than the specimen overlaid with 100% stellite#6 possibly, due to the difference between thermal expansion coefficients of the matrix and WC particles. Such tensile stresses can be potential driving force to provide an easy crack path ways for large brittle fractures

  10. Effect of dissolved oxygen content on stress corrosion cracking of a cold worked 316L stainless steel in simulated pressurized water reactor primary water environment

    Science.gov (United States)

    Zhang, Litao; Wang, Jianqiu

    2014-03-01

    Stress corrosion crack growth tests of a cold worked nuclear grade 316L stainless steel were conducted in simulated pressurized water reactor (PWR) primary water environment containing various dissolved oxygen (DO) contents but no dissolved hydrogen. The crack growth rate (CGR) increased with increasing DO content in the simulated PWR primary water. The fracture surface exhibited typical intergranular stress corrosion cracking (IGSCC) characteristics.

  11. Correlation between tension softening relation and crack extension resistance in concrete

    Institute of Scientific and Technical Information of China (English)

    Xiufang ZHANG; Shilang XU

    2009-01-01

    Changes of the material fracture toughness with crack propagation can be described by a crack extension resistance curve, one of the fundamental fracture criteria in crack mechanics. Recently, experimental observation of the fracture behavior in concrete was used to develop a new fracture criterion, the crack extension GR resistance curve, to analyze crack propagation during the entire concrete fracture process. The variation of the crack extension resistance is mainly associated with the energy consumption in the fracture process zone ahead of the stress-free crack tip. The crack extension resistance is then a function of the softening curve, which is a basic mechanical property in the fracture process zone. The relationship between the softening curve and the crack extension GR resistance curve is then analyzed based on results of three-point bending beams tests. The results indicate that the characteristic points of the crack extension resistance GR curve is closely related to the characteristic point on used tension softening curve.

  12. 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.

  13. Residual stress and crack initiation in laser clad composite layer with Co-based alloy and WC + NiCr

    Science.gov (United States)

    Lee, Changmin; Park, Hyungkwon; Yoo, Jaehong; Lee, Changhee; Woo, WanChuck; Park, Sunhong

    2015-08-01

    Although laser cladding process has been widely used to improve the wear and corrosion resistance, there are unwanted cracking issues during and/or after laser cladding. This study investigates the tendency of Co-based WC + NiCr composite layers to cracking during the laser cladding process. Residual stress distributions of the specimen are measured using neutron diffraction and elucidate the correlation between the residual stress and the cracking in three types of cylindrical specimens; (i) no cladding substrate only, (ii) cladding with 100% stellite#6, and (iii) cladding with 55% stellite#6 and 45% technolase40s. The microstructure of the clad layer was composed of Co-based dendrite and brittle eutectic phases at the dendritic boundaries. And WC particles were distributed on the matrix forming intermediate composition region by partial melting of the surface of particles. The overlaid specimen exhibited tensile residual stress, which was accumulated through the beads due to contraction of the coating layer generated by rapid solidification, while the non-clad specimen showed compressive. Also, the specimen overlaid with 55 wt% stellite#6 and 45 wt% technolase40s showed a tensile stress higher than the specimen overlaid with 100% stellite#6 possibly, due to the difference between thermal expansion coefficients of the matrix and WC particles. Such tensile stresses can be potential driving force to provide an easy crack path ways for large brittle fractures combined with the crack initiation sites such as the fractured WC particles, pores and solidification cracks. WC particles directly caused clad cracks by particle fracture under the tensile stress. The pores and solidification cracks also affected as initiation sites and provided an easy crack path ways for large brittle fractures.

  14. Sensitization, intergranular attack, stress corrosion cracking, and irradiation effects on the corrosion of iron--chromium--nickel alloys

    Energy Technology Data Exchange (ETDEWEB)

    Wu, P.C.S.

    1978-04-01

    A literature review is presented on the sensitization, intergranular attack, and stress corrosion cracking of austenitic stainless steels with emphasis on dilute solutions at temperatures below the boiling point of water. An attempt is made to list the possible sources of contaminants during manufacture, shipping, construction and all phases of operation of the sodium containing components. The susceptibility of the different materials to stress corrosion cracking in the various contaminants is discussed and suggestions to prevent serious problems are made. (GHT)

  15. Cracking Process and Stress Field Evolution in Specimen Containing Combined Flaw Under Uniaxial Compression

    Science.gov (United States)

    Liu, Ting; Lin, Baiquan; Yang, Wei; Zou, Quanle; Kong, Jia; Yan, Fazhi

    2016-08-01

    Hydraulic slotting, an efficient technique for underground enhanced coal bed methane (ECBM) recovery, has been widely used in China. However, its pressure relief mechanism is unclear. Thus far, only limited research has been conducted on the relationships among the mechanical properties, flaw parameters, and crack propagation patterns of coal after hydraulic slotting. In addition, because of the limitations of test methods, an in-depth information is not available for this purpose. In this work, numerical models of specimens containing combined flaws are established based on particle flow code method. Our results provide insights into the effects of flaw inclination angle on the mechanical properties, crack propagation patterns, and temporal and spatial evolution rules of stress field in specimens containing combined flaws during the loading process. Besides, based on the initiation position and underlying mechanism, three types of crack initiation modes are identified from the failure processes of specimens. Finally, the crack propagation pattern is quantitatively described by the fractal dimension, which is found to be inversely proportional to the uniaxial compressive strength and elastic modulus of the specimen. To verify the rationality of the numerical simulation results, laboratory tests were conducted and their results match well with those obtained from the numerical simulation.

  16. Uncommon deformation mechanisms during fatigue-crack propagation in nanocrystalline alloys.

    Science.gov (United States)

    Cheng, Sheng; Lee, Soo Yeol; Li, Li; Lei, Changhui; Almer, Jon; Wang, Xun-Li; Ungar, Tamas; Wang, Yinmin; Liaw, Peter K

    2013-03-29

    The irreversible damage at cracks during the fatigue of crystalline solids is well known. Here we report on in situ high-energy x-ray evidence of reversible fatigue behavior in a nanocrystalline NiFe alloy both in the plastic zone and around the crack tip. In the plastic zone, the deformation is fully recoverable as the crack propagates, and the plastic deformation invokes reversible interactions of dislocation and twinning in the nanograins. But around the crack tip lies a regime with reversible grain lattice reorientation promoted by a change of local stress state. These observations suggest unprecedented fatigue deformation mechanisms in nanostructured systems that are not addressed theoretically.

  17. Effect of layerwise structural inhomogeneity on stress- corrosion cracking of steel tubes

    Science.gov (United States)

    Perlovich, Yu A.; Krymskaya, O. A.; Isaenkova, M. G.; Morozov, N. S.; Fesenko, V. A.; Ryakhovskikh, I. V.; Esiev, T. S.

    2016-04-01

    Based on X-ray texture and structure analysis data of the material of main gas pipelines it was shown that the layerwise inhomogeneity of tubes is formed during their manufacturing. The degree of this inhomogeneity affects on the tendency of tubes to stress- corrosion cracking under exploitation. Samples of tubes were cut out from gas pipelines located under various operating conditions. Herewith the study was conducted both for sections with detected stress-corrosion defects and without them. Distributions along tube wall thickness for lattice parameters and half-width of X-ray lines were constructed. Crystallographic texture analysis of external and internal tube layers was also carried out. Obtained data testifies about considerable layerwise inhomogeneity of all samples. Despite the different nature of the texture inhomogeneity of gas pipeline tubes, the more inhomogeneous distribution of texture or structure features causes the increasing of resistance to stress- corrosion. The observed effect can be explained by saturation with interstitial impurities of the surface layer of the hot-rolled sheet and obtained therefrom tube. This results in rising of lattice parameters in the external layer of tube as compared to those in underlying metal. Thus, internal layers have a compressive effect on external layers in the rolling plane that prevents cracks opening at the tube surface. Moreover, the high mutual misorientation of grains within external and internal layers of tube results in the necessity to change the moving crack plane, so that the crack growth can be inhibited when reaching the layer with a modified texture.

  18. Numerical stress analysis of crack at welded beam-to-column connection

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    In the past, brittle fracture of steel structure was reported rarely under earthquake. However, recent earthquakes, especially Northridge Earthquake (USA) and Hyogoken-Nanbu earthquake (Japan), astonished engineers in the field of construction. The experience from recent earthquakes of USA and Japan shows that brittle fracture of welded steel structure always starts from high stress zone with welded crack[1~5]. As backing bar for grooved weld on beam flange exists, artificial crack is formed because of lack-of-fusion at the root of flange weld. In this paper stress distribution of connection is computed with FEM, and stress concentration at the root of flange weld is also analyzed. Stress intensity factors (SIFs), KI, at the root of flange weld are computed in the method of fracture mechanics. The computation shows that stress intensity factor on bottom flange weld is obviously higher than that on top flange weld. It is proved by the fact that brittle fracture is liable to start at the root of bottom flange weld on actual earthquake[1,4]. Finally measures are brought forward to avoid fracture of weld structure against earthquake.

  19. Effect of Crack Tip Stress Concentration Factor on Fracture Resistance in Vacuum Environment

    Science.gov (United States)

    2015-01-20

    aluminum alloys and a steel in vacuum environment. The materials investigated were peakaged 7075 -T651, overaged 7075 -T7351, 5083-H131, fully sensitized Al...about twice higher than those of the aluminum alloys; (4) the peakaged 7075 -T651 and overaged 7075 -T7351 have comparable fracture resistance; (5...the fracture resistance of 2024-T351 alloy is higher than 7075 alloys; (6) the fracture resistances of as-received 5083-H131 (5083R) and sensitized

  20. 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

  1. 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.

  2. Evaluation of irradiation assisted stress corrosion cracking (IASCC) of type 316 stainless steel irradiated in FBR

    Energy Technology Data Exchange (ETDEWEB)

    Tsukada, T. (Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan)); Jitsukawa, S. (Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan)); Shiba, K. (Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan)); Sato, Y. (Power Reactor and Nuclear Fuel Development Corp., Oarai, Ibaraki (Japan)); Shibahara, I. (Power Reactor and Nuclear Fuel Development Corp., Oarai, Ibaraki (Japan)); Nakajima, H. (Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan))

    1993-12-01

    Type 316 stainless steel from the core of the experimental fast breeder reactor (FBR) JOYO was examined by the slow strain rate tensile (SSRT) test in pure, oxygenated-water and air and by the electrochemical potentiokinetic reactivation (EPR) test to evaluate a susceptibility to the irradiation assisted stress corrosion cracking (IASCC) and the radiation-induced segregation (RIS). The solution annealed and 20% cold-worked materials had been irradiated at 425 C to a neutron fluence of 8.3x10[sup 26] n/m[sup 2] (> 0.1 MeV) which is equivalent to 40 displacement per atom (dpa). Intergranular cracking was induced by the SSRT in water at 200 and 300 C, but was not observed on specimen tested in water at 60 C and in air at 300 C. This indicates that irradiation increased a susceptibility to stress corrosion cracking (SCC) in water. After the EPR test, grain boundary etching was observed in addition to grain face etching. This suggests Cr depletion may have occurred both at grain boundary and at defect clusters during the irradiation. The results are compared with the behavior of similar materials irradiated with different neutron spectrum. (orig.)

  3. 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.

  4. Public inquiry concerning stress corrosion cracking on Canadian oil and gas pipelines

    Energy Technology Data Exchange (ETDEWEB)

    Vollman, K.W.; Cote-Verhaaf, A.; Illing, R.

    1996-11-01

    An comprehensive inquiry was conducted into the serious problem of near-neutral pH stress corrosion cracking (SCC) in Canada`s buried oil and gas pipelines. The inquiry was prompted by evidence of the widespread nature of SCC and awareness that research was producing new insights into the problem. Two major ruptures and fires occurred on the TransCanada system in February and July of 1995. The July rupture was in a location where it was believed SCC could not occur. SCC on pipelines occurs when small cracks develop on the outside surface of the buried pipeline. With time the cracks grow large enough until the pipeline fails or ruptures. SCC results from an interaction of the following three conditions: a potent environment at the pipe surface, a susceptible pipe material, and a tensile stress. Recommendations to resolve the problem included implementation of an SCC management program by pipeline companies, changes to the design of the pipeline, continued research, establishment of an SCC database, improved emergency response practices, and information sharing. 84 refs., 8 tabs., 67 figs.

  5. The Effect of Water on Crack Interaction

    Science.gov (United States)

    Gaede, O.; Regenauer-Lieb, K.

    2009-04-01

    While the mechanical coupling between pore fluid and solid phase is relatively well understood, quantitative studies dealing with chemical-mechanical weakening in geological materials are rare. Many classical poroelastic problems can be addressed with the simple law of effective stress. Experimental studies show that the presence of a chemically active fluid can have effects that exceed the predictions of the law of effective stress. These chemical fluid-rock interactions alter the mechanical properties of the solid phase. Especially chemical-mechanical weakening has important ramifications for many areas of applied geosciences ranging from nuclear waste disposal over reservoir enhancement to fault stability. In this study, we model chemically induced changes of the size of the process zone around a crack tip. The knowledge of the process zone size is used to extend existing effective medium approximations of cracked solids. The stress distribution around a crack leads to a chemical potential gradient. This gradient will be a driver for mass diffusion through the solid phase. As an example, mass diffusion is towards the crack tip for a mode I crack. In this case a chemical reaction, that weakens the solid phase, will increase the size of the process zone around the crack tip. We apply our model to the prominent hydrolytic weakening effect observed in the quartz-water system (Griggs and Blacic, 1965). Hydrolytic weakening is generally attributed to water hydrolyzing the strong Si-O bonds of the quartz crystal. The hydrolysis replaces a Si-O-Si bridge with a relatively weak hydrogen bridge between two silanol groups. This enhances dislocation mobility and hence the yield stress is reduced. The plastic process zone around a crack tip is therefore larger in a wet crystal than in a dry crystal. We calculate the size of the process zone by solving this coupled mechanical-chemical problem with the Finite Element code ABAQUS. We consider single crack, collinear crack and

  6. Stability of cracked pipe under inertial stresses. Subtask 1.1 final report

    Energy Technology Data Exchange (ETDEWEB)

    Scott, P.; Wilson, M.; Olson, R.; Marschall, C.; Schmidt, R.; Wilkowski, G. [Battelle, Columbus, OH (United States)

    1994-08-01

    This report presents the results of the pipe fracture experiments, analyses, and material characterization efforts performed within Subtask 1.1 of the IPIRG Program. The objective of Subtask 1.1 was to experimentally verify the analysis methodologies for circumferentially cracked pipe subjected primarily to inertial stresses. Eight cracked-pipe experiments were conducted on 6-inch nominal diameter TP304 and A106B pipe. The experimental procedure was developed using nonlinear time-history finite element analyses which included the nonlinear behavior due to the crack. The model did an excellent job of predicting the displacements, forces, and times to maximum moment. The comparison of the experimental loads to the predicted loads by the Net-Section-Collapse (NSC), Dimensionless Plastic-Zone Parameter, J-estimation schemes, R6, and ASME Section XI in-service flaw assessment criteria tended to underpredict the measured bending moments except for the NSC analysis of the A106B pipe. The effects of flaw geometry and loading history on toughness were evaluated by calculating the toughness from the pipe tests and comparing these results to C(l) values. These effects were found to be variable. The surface-crack geometry tended to increase the toughness (relative to CM results), whereas a negative load-ratio significantly decreased the TP304 stainless steel surface-cracked pipe apparent toughness. The inertial experiments tended to achieve complete failure within a few cycles after reaching maximum load in these relatively small diameter pipe experiments. Hence, a load-controlled fracture mechanics analysis may be more appropriate than a displacement-controlled analysis for these tests.

  7. Role of pH on the stress corrosion cracking of titanium alloys

    Science.gov (United States)

    Khokhar, M. I.; Beck, F. H.; Fontana, M. G.

    1973-01-01

    Stress corrosion cracking (SCC) experiments were conducted on Ti-8-1-1 wire specimens in hydrochloric and sulfuric acids of variable pH in order to determine the effect of pH on the susceptibility to cracking. The alloy exhibited increasing susceptibility with decreasing pH. By varying the applied potential, it was observed that susceptibility zones exist both in the cathodic and the anodic ranges. In the cathodic range, susceptibility also increased with decreasing applied potential. Corrosion potential-time data in hydrochloric acid (pH 1.7) and sulfuric acid (pH 1.7) indicate that chloride ions lower the corrosion potential of the specimen which, in turn, increases the susceptibility.

  8. Numerical and experimental analysis of the directional stability on crack propagation under biaxial stresses

    Energy Technology Data Exchange (ETDEWEB)

    RodrIguez-MartInez, R; Urriolagoitia-Calderon, G; Urriolagoitia-Sosa, G; Hernandez-Gomez, L H [Instituto Politecnico Nacional Seccion de Estudios de Posgrado e Investigacion (SEPI), Escuela Superior de IngenierIa Mecanica y Electrica (ESIME), Edificio 5. 2do Piso, Unidad Profesional Adolfo Lopez Mateos ' Zacatenco' Col. Lindavista, C.P. 07738, Mexico, D.F. (Mexico); Merchan-Cruz, E A; RodrIguez-Canizo, R G; Sandoval-Pineda, J M, E-mail: rrodriguezm@ipn.m, E-mail: urrio332@hotmail.co, E-mail: guiurri@hotmail.co, E-mail: luishector56@hotmail.co, E-mail: eamerchan@gmail.co, E-mail: ricname@hotmail.co, E-mail: jsandovalp@ipn.m [Instituto Politecnico Nacional Seccion de Estudios de Posgrado e Investigacion (SEPI), Escuela Superior de IngenierIa Mecanica y Electrica (ESIME). Unidad profesional, AZCAPOTZALCO, Av. de las Granjas No. 682, Col. Sta. Catarina Azcapotzalco, C.P. 02550, Mexico D.F. (Mexico)

    2009-08-01

    In this paper, the case of Single Edge Notch (SEN) specimens subject to opening/compressive loading was analyzed; The loads are applied in several ratios to evaluate the influence of the specimen geometry, and the Stress Intensity Factor (SIF) K{sub 1} values on the directional stability of crack propagation. The main purpose of this work is to evaluate the behaviour of the fracture propagation, when modifying the geometry of the SEN specimen and different relationships of load tension/compression are applied. Additionally, the precision of the numerical and experimental analysis is evaluated to determine its reliability when solving this type of problems. The specimens are subjected to biaxial opening/compression loading; both results (numerical and experimental) are compared in order to evaluate the condition of directional stability on crack propagation. Finally, an apparent transition point related to the length of specimens was identified, in which the behaviour of values of SIF changes for different loading ratios.

  9. Stress Corrosion Cracking Behavior of Alloy 22 in Multi-Ionic Aqueous Environments

    Energy Technology Data Exchange (ETDEWEB)

    K.J. King; J.C. Estill; R.B. Rebak

    2002-07-15

    The US Department of Energy is characterizing a potential repository site for nuclear waste in Yucca Mountain (NV). In its current design, the nuclear waste containers consist of a double metallic layer. The external layer would be made of NO6022 or Alloy 22 (Ni-22Cr-13Mo-3W-3Fe). Since over their lifetime, the containers may be exposed to multi-ionic aqueous environments, a potential degradation mode of the outer layer could be environmentally assisted cracking (EAC) or stress corrosion cracking (SCC). In general, Alloy 22 is extremely resistant to SCC, especially in concentrated chloride solutions. Current results obtained through slow strain rate testing (SSRT) shows that Alloy 22 may suffer SCC in simulated concentrated water (SCW) at applied potentials approximately 400 mV more anodic than the corrosion potential (E{sub rr}).

  10. Role of pH on the stress corrosion cracking of titanium alloys

    Science.gov (United States)

    Khokhar, M. I.; Beck, F. H.; Fontana, M. G.

    1973-01-01

    Stress corrosion cracking (SCC) experiments were conducted on Ti-8-1-1 wire specimens in hydrochloric and sulfuric acids of variable pH in order to determine the effect of pH on the susceptibility to cracking. The alloy exhibited increasing susceptibility with decreasing pH. By varying the applied potential, it was observed that susceptibility zones exist both in the cathodic and the anodic ranges. In the cathodic range, susceptibility also increased with decreasing applied potential. Corrosion potential-time data in hydrochloric acid (pH 1.7) and sulfuric acid (pH 1.7) indicate that chloride ions lower the corrosion potential of the specimen which, in turn, increases the susceptibility.

  11. Literature Survey on the Stress Corrosion Cracking of Low-Alloy Steels in High Temperature Water

    Energy Technology Data Exchange (ETDEWEB)

    Seifert, H.P

    2002-02-01

    The present report is a summary of a literature survey on the stress corrosion cracking (SCC) behaviour/ mechanisms in low-alloy steels (LAS) in high-temperature water with special emphasis to primary-pressure-boundary components of boiling water reactors (BWR). A brief overview on the current state of knowledge concerning SCC of low-alloy reactor pressure vessel and piping steels under BWR conditions is given. After a short introduction on general aspects of SCC, the main influence parameter and available quantitative literature data concerning SCC of LAS in high-temperature water are discussed on a phenomenological basis followed by a summary of the most popular SCC models for this corrosion system. The BWR operating experience and service cracking incidents are discussed with respect to the existing laboratory data and background knowledge. Finally, the most important open questions and topics for further experimental investigations are outlined. (author)

  12. Strain Measurements within Fibre Boards. Part II: Strain Concentrations at the Crack Tip of MDF Specimens Tested by the Wedge Splitting Method

    Directory of Open Access Journals (Sweden)

    Jörn Rathke

    2012-08-01

    Full Text Available This is the second part of an article series where the mechanical and fracture mechanical properties of medium density fiberboard (MDF were studied. While the first part of the series focused on internal bond strength and density profiles, this article discusses the fracture mechanical properties of the core layer. Fracture properties were studied with a wedge splitting setup. The critical stress intensity factors as well as the specific fracture energies were determined. Critical stress intensity factors were calculated from maximum splitting force and two-dimensional isotropic finite elements simulations of the specimen geometry. Size and shape of micro crack zone were measured with electronic laser speckle interferometry. The process zone length was approx. 5 mm. The specific fracture energy was determined to be 45.2 ± 14.4 J/m2 and the critical stress intensity factor was 0.11 ± 0.02 MPa.

  13. Strain Measurements within Fibre Boards. Part II: Strain Concentrations at the Crack Tip of MDF Specimens Tested by the Wedge Splitting Method

    Science.gov (United States)

    Sinn, Gerhard; Müller, Ulrich; Konnerth, Johannes; Rathke, Jörn

    2012-01-01

    This is the second part of an article series where the mechanical and fracture mechanical properties of medium density fiberboard (MDF) were studied. While the first part of the series focused on internal bond strength and density profiles, this article discusses the fracture mechanical properties of the core layer. Fracture properties were studied with a wedge splitting setup. The critical stress intensity factors as well as the specific fracture energies were determined. Critical stress intensity factors were calculated from maximum splitting force and two-dimensional isotropic finite elements simulations of the specimen geometry. Size and shape of micro crack zone were measured with electronic laser speckle interferometry. The process zone length was approx. 5 mm. The specific fracture energy was determined to be 45.2 ± 14.4 J/m2 and the critical stress intensity factor was 0.11 ± 0.02 MPa.

  14. Origins of Negative Strain Rate Dependence of Stress Corrosion Cracking Initiation in Alloy 690, and Intergranular Crack Formation in Thermally Treated Alloy 690

    Science.gov (United States)

    Kim, Young Suk; Kim, Sung Soo

    2016-09-01

    We show that enhanced stress corrosion cracking (SCC) initiation in cold-rolled Alloy 690 with decreasing strain rate is related to the rate of short-range ordering (SRO) but not to the time-dependent corrosion process. Evidence for SRO is provided by aging tests on cold-rolled Alloy 690 at 623 K and 693 K (350 °C and 420 °C), respectively, which demonstrate its enhanced lattice contraction and hardness increase with aging temperature and time, respectively. Secondary intergranular cracks formed only in thermally treated and cold-rolled Alloy 690 during SCC tests, which are not SCC cracks, are caused by its lattice contraction by SRO before SCC tests but not by the orientation effect.

  15. Validation of surface crack stress intensity factors of a tubular K-joint

    Energy Technology Data Exchange (ETDEWEB)

    Lie, S.T. [School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, Singapore 639798 (Singapore)]. E-mail: cstlie@ntu.edu.sg; Lee, C.K. [School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, Singapore 639798 (Singapore); Chiew, S.P. [School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, Singapore 639798 (Singapore); Shao, Y.B. [School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, Singapore 639798 (Singapore)

    2005-08-01

    Tubular K-joints are encountered widely in offshore structures, and the prediction of damaged joints depends very much on the accuracy of stress intensity factor solutions (SIFs). No parametric equations and very few results have been proposed and published in the literature for estimating the SIFs of any K-joints subjected to complex loading conditions. In this paper, a mesh generation method proposed previously for the Y-joint and T-joint has been extended to the K-joint. This method is realized by dividing the K-joint into several sub-zones with each zone consisting of different types of elements and mesh densities. This method has a distinct advantage of controlling the mesh quality, and most importantly the aspect ratio of the elements along the crack front. When the mesh of all the sub-zones has been generated automatically and completely, they are merged to form the complete model. The two most commonly used methods, namely the J-integral and displacement extrapolation, are used to evaluate the SIF values along the crack front of a typical K-joint. To validate the accuracy of these computed SIFs, a full-scale K-joint specimen was tested to failure under fatigue loading conditions. The standard alternating current potential drop (ACPD) technique was used to monitor the rate of crack propagation of the surface crack located at the hot spot stress region. Using the given material parameters C and m, the experimental SIFs were deduced, and they are found to be in good agreement with the computed SIFs obtained from the generated models. Hence, the proposed finite element models are both efficient and reliable.

  16. Stress Corrosion Cracking of the Drip Shield, the Waste Package Outer Barrier, and the Stainless Steel Structural Material

    Energy Technology Data Exchange (ETDEWEB)

    G. Gordon

    2004-10-13

    Stress corrosion cracking is one of the most common corrosion-related causes for premature breach of metal structural components. Stress corrosion cracking is the initiation and propagation of cracks in structural components due to three factors that must be present simultaneously: metallurgical susceptibility, critical environment, and static (or sustained) tensile stresses. This report was prepared according to ''Technical Work Plan for: Regulatory Integration Modeling and Analysis of the Waste Form and Waste Package'' (BSC 2004 [DIRS 171583]). The purpose of this report is to provide an evaluation of the potential for stress corrosion cracking of the engineered barrier system components (i.e., the drip shield, waste package outer barrier, and waste package stainless steel inner structural cylinder) under exposure conditions consistent with the repository during the regulatory period of 10,000 years after permanent closure. For the drip shield and waste package outer barrier, the critical environment is conservatively taken as any aqueous environment contacting the metal surfaces. Appendix B of this report describes the development of the SCC-relevant seismic crack density model (SCDM). The consequence of a stress corrosion cracking breach of the drip shield, the waste package outer barrier, or the stainless steel inner structural cylinder material is the initiation and propagation of tight, sometimes branching, cracks that might be induced by the combination of an aggressive environment and various tensile stresses that can develop in the drip shields or the waste packages. The Stainless Steel Type 316 inner structural cylinder of the waste package is excluded from the stress corrosion cracking evaluation because the Total System Performance Assessment for License Application (TSPA-LA) does not take credit for the inner cylinder. This document provides a detailed description of the process-level models that can be applied to assess the

  17. 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

  18. 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.

  19. A Fundamental study of remedial technology development to prevent stress corrosion cracking of steam generator tubing

    Energy Technology Data Exchange (ETDEWEB)

    Park, In Gyu; Lee, Chang Soon [Sunmoon University, Asan (Korea)

    1998-04-01

    Most of the PWR Steam generators with tubes in Alloy 600 alloy are affected by Stress Corrosion Cracking, such as PWSCC(Primary Water Stress Corrosion Cracking) and ODSCC(Outside Diameter Stress Corrosion Cracking). This study was undertaken to establish the background for remedial technology development to prevent SCC. in the report are included the following topics: (1) General: (i) water chemistry related factors, (ii) Pourbaix(Potential-pH) Diagram, (iii) polarization plot, (iv) corrosion mode of Alloy 600, 690, and 800, (v) IGA/SCC growth rate, (vi) material suspetibility of IGA/SCC, (vii) carbon solubility of Alloy 600 (2) Microstructures of Alloy 600 MA, Alloy 600 TT, Alloy 600 SEN Alloy 690 TT(Optical, SEM, and TEM) (3) Influencing factors for PWSCC initiation rate of Alloy 600: (i) microstructure, (ii) water chemistry(B, Li), (iii) temperature, (iv) plastic deformation, (v) stress relief annealing (4) Influencing factors for PWSCC growth rate of Alloy 600: (i) water chemistry(B, Li), (ii) Scott Model, (iii) intergranular carbide, (iv) temperature, (v) hold time (5) Laboratory conditions for ODSCC initiation rate: 1% NaOH, 316 deg C; 1% NaOH, 343 deg C; 50% NaOH, 288 deg C; 10% NaOH, 302 deg C; 10% NaOH, 316 deg C; 50% NaOH, 343 deg C (6) Sludge effects for ODSCC initiation rate: CuO, Cr{sub 2}O{sub 3}, Fe{sub 3}O{sub 4} (7) Influencing factors for PWSCC growth rate of Alloy 600: (i) Caustic concentration effect, (ii) carbonate addition effect (8) Sulfate corrosion: (i) sulfate ratio and pH effect, (ii) wastage rate of Alloy 600 and Alloy 690 (9) Crevice corrosion: (i) experimental setup for crevice corrosion, (ii) organic effect, (iii) (Na{sub 2}SO{sub 4} + NaOH) effect (10) Remedial measures for SCC: (i) Inhibitors, (ii) ZnO effect. (author). 30 refs., 174 figs., 51 tabs.

  20. Dynamics of crack penetration vs. branching at a weak interface: An experimental study

    Science.gov (United States)

    Sundaram, Balamurugan M.; Tippur, Hareesh V.

    2016-11-01

    In this paper, the dynamic crack-interface interactions and the related mechanics of crack penetration vs. branching at a weak interface are studied experimentally. The interface is oriented perpendicular to the incoming mode-I crack in an otherwise homogeneous bilayer. The focus of this investigation is on the effect of interface location and the associated crack-tip parameters within the bilayer on the mechanics of the ensuing fracture behavior based on the optical methodologies laid down in Ref. Sundaram and Tippur (2016). Time-resolved optical measurement of crack-tip deformations, velocity and stress intensity factor histories in different bilayer configurations is performed using Digital Gradient Sensing (DGS) technique in conjunction with high-speed photography. The results show that the crack path selection at the interface and subsequently the second layer are greatly affected by the location of the interface within the geometry. Using optically measured fracture parameters, the mechanics of crack penetration and branching are explained. Counter to the intuition, a dynamically growing mode-I approaching a weak interface at a lower velocity and stress intensity factor penetrates the interface whereas a higher velocity and stress intensity factor counterpart gets trapped by the interface producing branched daughter cracks until they kink out into the next layer. An interesting empirical observation based on measured crack-tip parameters for crack penetration and branching is also made.

  1. 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

  2. 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.

  3. An analytical investigation on singularity of current distribution around a crack in a long cylindrical superconductor

    Science.gov (United States)

    Xue, Feng; Zhou, You-He

    2010-06-01

    This paper presents an analytical investigation to display the distribution of critical current flow and trapped magnetic field around a through crack centrally located in a long cylindrical superconductor on the basis of the Bean model and the Kim model. After a simple conformal mapping is employed to the case of that the superconductor is fully penetrated, the current streamlines, the current density, and the trapped field around the crack in the superconductor without deformation are obtained. It is shown that the crack results in a long-range disturbance of J(r ) on the scale much larger than the crack length 2a and a large stagnation region of magnetic flux near the crack except for the singularity of the critical current at the crack tip. Meanwhile, it is also found that the singularity feature is different from the conventional stress one at the crack tip in a deformable body.

  4. In Situ X-ray Microtomography of Stress Corrosion Cracking and Corrosion Fatigue in Aluminum Alloys

    Science.gov (United States)

    Singh, Sudhanshu S.; Stannard, Tyler J.; Xiao, Xianghui; Chawla, Nikhilesh

    2017-08-01

    Structural materials are subjected to combinations of stress and corrosive environments that work synergistically to cause premature failure. Therefore, studies on the combined effect of stress and corrosive environments on material behavior are required. Existing studies have been performed in two dimensions that are inadequate for full comprehension of the three-dimensional (3D) processes related to stress corrosion cracking (SCC) and corrosion-fatigue (CF) behavior. Recently, x-ray synchrotron tomography has evolved as an excellent technique to obtain the microstructure in 3D. Moreover, being nondestructive in nature, x-ray synchrotron tomography is well suited to study the evolution of microstructure with time (4D, or fourth dimension in time). This article presents our recent 4D studies on SCC and CF of Al 7075 alloys using x-ray synchrotron tomography.

  5. Diffusion-Coupled Cohesive Interface Simulations of Stress Corrosion Intergranular Cracking in Polycrystalline Materials

    Energy Technology Data Exchange (ETDEWEB)

    Pu, Chao; Gao, Yanfei; Wang, Yanli; Sham, T.-L.

    2017-09-01

    To study the stress corrosion intergranular cracking mechanism, a diffusion-coupled cohesive zone model (CZM) is proposed for the simulation of the stress-assisted diffusional process along grain boundaries and the mechanical response of grain boundary sliding and separation. This simulation methodology considers the synergistic effects of impurity diffusion driven by pressure gradient and degradation of grain boundary strength by impurity concentration. The diffusion-coupled CZM is combined with crystal plasticity finite element model (CPFEM) to simulate intergranular fracture of polycrystalline material under corrosive environment. Significant heterogeneity of the stress field and extensive impurity accumulation is observed at grain boundaries and junction points. Deformation mechanism maps are constructed with respect to the grain boundary degradation factor and applied strain rate, which dictate the transition from internal to near-surface intergranular fracture modes under various strain amplitudes and grain sizes.

  6. Modeling of a Curvilinear Planar Crack with a Curvature-Dependent Surface Tension

    KAUST Repository

    Zemlyanova, A. Y.

    2012-01-01

    An approach to modeling fracture incorporating interfacial mechanics is applied to the example of a curvilinear plane strain crack. The classical Neumann boundary condition is augmented with curvature-dependent surface tension. It is shown that the considered model eliminates the integrable crack-tip stress and strain singularities of order 1/2 present in the classical linear fracture mechanics solutions, and also leads to the sharp crack opening that is consistent with empirical observations. Unlike for the case of a straight crack, for a general curvilinear crack some components of the stresses and the derivatives of the displacements may still possess weaker singularities of a logarithmic type. Generalizations of the present study that lead to complete removal of all crack-tip singularities, including logarithmic, are the subject of a future paper. © 2012 Society for Industrial and Applied Mathematics.

  7. Infrared thermography study of the fatigue crack propagation

    Directory of Open Access Journals (Sweden)

    O.A. Plekhov

    2012-07-01

    Full Text Available The work is devoted to the experimental study of heat dissipation process caused by fatigue crack propagation. To investigate a spatial and time temperature evolution at the crack tip set of experiments was carried out using specimens with pre-grown centered fatigue crack. An original mathematical algorithm for experimental data treatment was developed to obtain a power of heat source caused by plastic deformation at crack tip. The algorithm includes spatial-time filtration and relative motion compensation procedures. Based on the results of mathematical data treatment, we proposed a way to estimate the values of J-integral and stress intensity factor for cracks with pronounced the plastic zone.

  8. SIF-based fracture criterion for interface cracks

    Science.gov (United States)

    Ji, Xing

    2016-06-01

    The complex stress intensity factor K governing the stress field of an interface crack tip may be split into two parts, i.e., hat{K} and s^{-iɛ}, so that K=hat{K}s^{-iɛ}, s is a characteristic length and ɛ is the oscillatory index. hat{K} has the same dimension as the classical stress intensity factor and characterizes the interface crack tip field. That means a criterion for interface cracks may be formulated directly with hat{K}, as Irwin (ASME J. Appl. Mech. 24:361-364, 1957) did in 1957 for the classical fracture mechanics. Then, for an interface crack, it is demonstrated that the quasi Mode I and Mode II tip fields can be defined and distinguished from the coupled mode tip fields. Built upon SIF-based fracture criteria for quasi Mode I and Mode II, the stress intensity factor (SIF)-based fracture criterion for mixed mode interface cracks is proposed and validated against existing experimental results.

  9. Tensile stress corrosion cracking of type 304 stainless steel irradiated to very high dose

    Energy Technology Data Exchange (ETDEWEB)

    Chung, H. M.; Ruther, W. E.; Strain, R. V.; Shack, W. J.

    2001-09-01

    Certain safety-related core internal structural components of light water reactors, usually fabricated from Type 304 or 316 austenitic stainless steels (SSs), accumulate very high levels of irradiation damage (20--100 displacement per atom or dpa) by the end of life. The data bases and mechanistic understanding of, the degradation of such highly irradiated components, however, are not well established. A key question is the nature of irradiation-assisted intergranular cracking at very high dose, i.e., is it purely mechanical failure or is it stress-commotion cracking? In this work, hot-cell tests and microstructural characterization were performed on Type 304 SS from the hexagonal fuel can of the decommissioned EBR-11 reactor after irradiation to {approximately}50 dpa at {approximately}370 C. Slow-strain-rate tensile tests were conducted at 289 C in air and in water at several levels of electrochemical potential (ECP), and microstructural characteristics were analyzed by scanning and transmission electron microcopies. The material deformed significantly by twinning and exhibited surprisingly high ductility in air, but was susceptible to severe intergranular stress corrosion cracking (IGSCC) at high ECP. Low levels of dissolved O and ECP were effective in suppressing the susceptibility of the heavily irradiated material to IGSCC, indicating that the stress corrosion process associated with irradiation-induced grain-boundary Cr depletion, rather than purely mechanical separation of grain boundaries, plays the dominant role. However, although IGSCC was suppressed, the material was susceptible to dislocation channeling at low ECP, and this susceptibility led to poor work-hardening capability and low ductility.

  10. Stress corrosion cracking of austenitic weld deposits in a salt spray environment

    Science.gov (United States)

    Cai, J. B.; Yu, C.; Shiue, R. K.; Tsay, L. W.

    2015-10-01

    ER 308L and 309LMo were utilized as the filler metals for the groove and overlay welds of a 304L stainless steel substrate, which was prepared via a gas tungsten arc-welding process in multiple passes. U-bend and weight-loss tests were conducted by testing the welds in a salt spray containing 10 wt% NaCl at 120 °C. The dissolution of the skeletal structure in the fusion zone (FZ) caused the stress corrosion cracking (SCC) of the weld. The FZ in the cold-rolled condition showed the longest single crack length in the U-bend tests. Moreover, sensitization treatment at 650 °C for 10 h promoted the formation of numerous fine cracks, which resulted in a high SCC susceptibility. The weight loss of the deposits was consistent with the SCC susceptibility of the welds in a salt spray. The 309LMo deposit was superior to the 308L deposit in the salt spray.

  11. Microstructural and Stress Corrosion Cracking Characteristics of Austenitic Stainless Steels Containing Silicon

    Science.gov (United States)

    Andresen, Peter L.; Chou, Peter H.; Morra, Martin M.; Lawrence Nelson, J.; Rebak, Raul B.

    2009-12-01

    Austenitic stainless steels (SSs) core internal components in nuclear light water reactors (LWRs) are susceptible to irradiation-assisted stress corrosion cracking (IASCC). One of the effects of irradiation is the hardening of the SS and a change in the dislocation distribution in the alloy. Irradiation may also alter the local chemistry of the austenitic alloys; for example, silicon may segregate and chromium may deplete at the grain boundaries. The segregation or depletion phenomena at near-grain boundaries may enhance the susceptibility of these alloys to environmentally assisted cracking (EAC). The objective of the present work was to perform laboratory tests in order to better understand the role of Si in the microstructure, properties, electrochemical behavior, and susceptibility to EAC of austenitic SSs. Type 304 SS can dissolve up to 2 pct Si in the bulk while maintaining a single austenite microstructure. Stainless steels containing 12 pct Cr can dissolve up to 5 pct bulk Si while maintaining an austenite structure. The crack growth rate (CGR) results are not conclusive about the effect of the bulk concentration of Si on the EAC behavior of SSs.

  12. Stress corrosion cracking of alloy 600 using the constant strain rate test

    Energy Technology Data Exchange (ETDEWEB)

    Bulischeck, T. S.; van Rooyen, D.

    1980-01-01

    The most recent corrosion problems experienced in nuclear steam generators tubed with Inconel alloy 600 is a phenomenon labeled ''denting''. Denting has been found in various degrees of severity in many operating pressurized water reactors. Laboratory investigations have shown that Inconel 600 exhibits intergranular SCC when subjected to high stresses and exposed to deoxygenated water at elevated temperatures. A research project was initiated at Brookhaven National Laboratory in an attempt to improve the qualitative and quantitative understanding of factors influencing SCC in high temperature service-related environments. An effort is also being made to develop an accelerated test method which could be used to predict the service life of tubes which have been deformed or are actively denting. Several heats of commercial Inconel 600 tubing were procured for testing in deaerated pure and primary water at temperatures from 290 to 365/sup 0/C. U-bend type specimens were used to determine crack initiation times which may be expected for tubes where denting has occurred but is arrested and provide baseline data for judging the accelerating effects of the slow strain rate method. Constant extension rate tests were employed to determine the crack velocities experienced in the crack propagation stage and predict failure times of tubes which are actively denting. 8 refs., 17 figs., 5 tabs.

  13. EXPERT PANEL OVERSIGHT COMMITTEE ASSESSMENT OF FY2008 CORROSION AND STRESS CORROSION CRACKING SIMULANT TESTING PROGRAM

    Energy Technology Data Exchange (ETDEWEB)

    BOOMER KD

    2009-01-08

    The Expert Panel Oversight Committee (EPOC) has been overseeing the implementation of selected parts of Recommendation III of the final report, Expert Panel workshop for Hanford Site Double-Shell Tank Waste Chemistry Optimization, RPP-RPT-22126. Recommendation III provided four specific requirements necessary for Panel approval of a proposal to revise the chemistry control limits for the Double-Shell Tanks (DSTs). One of the more significant requirements was successful performance of an accelerated stress corrosion cracking (SCC) experimental program. This testing program has evaluated the optimization of the chemistry controls to prevent corrosion in the interstitial liquid and supernatant regions of the DSTs.

  14. Statistical model of stress corrosion cracking based on extended form of Dirichlet energy: Part 2

    Indian Academy of Sciences (India)

    HARRY YOSH

    2016-10-01

    In the previous paper ({\\it Pramana – J. Phys.} 81(6), 1009 (2013)), the mechanism of stress corrosion cracking (SCC) based on non-quadratic form of Dirichlet energy was proposed and its statistical features were discussed. Following those results, we discuss here how SCC propagates on pipe wall statistically. It reveals that SCC growth distribution is described with Cauchy problem of time-dependent first-order partial differential equation characterized by the convolution of the initial distribution of SCC over time. We also discuss the extension of the above results to the SCC in two-dimensional space and its statistical features with a simple example.

  15. INHIBITION OF STRESS CORROSION CRACKING OF CARBON STEEL STORAGE TANKS AT HANFORD

    Energy Technology Data Exchange (ETDEWEB)

    BOOMER, K.D.

    2007-01-31

    The stress corrosion cracking (SCC) behavior of A537 tank steel was investigated in a series of environments designed to simulate the chemistry of legacy nuclear weapons production waste. Tests consisted of both slow strain rate tests using tensile specimens and constant load tests using compact tension specimens. Based on the tests conducted, nitrite was found to be a strong SCC inhibitor. Based on the test performed and the tank waste chemistry changes that are predicted to occur over time, the risk for SCC appears to be decreasing since the concentration of nitrate will decrease and nitrite will increase.

  16. Intergranular stress corrosion cracking of welded ferritic stainless steels in high temperature aqueous environments

    Energy Technology Data Exchange (ETDEWEB)

    Fukuzuka, Toshio; Shimogori, Kazutoshi; Fujiwara, Kazuo; Tomari, Haruo (Kobe Steel Ltd. (Japan). Central Research and Development Lab.); Kanda, Masao

    1982-07-01

    In considering the application of ferritic stainless steels to heat exchanger tubing materials for moisture separator-reheaters in LWRs, the effects of environmental conditions (temperature, chloride, dissolved oxygen, pH), thermal history, and steel composition (content of C, N, Cr and Ti) on the Inter-Granular Stress Corrosion Cracking (IGSCC) in high temperature aqueous environments, were studied. The IGSCC was proved to depend on steel composition and thermal history rather than environment. From these results, a steel was designed to prevent IGSCC of the welding HAZ for 18Cr and 13Cr steels.

  17. Investigation of stress corre-sion cracking under anodic dissolution control

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    This review is about stress corrosion cracking (SCC) under anodic dissolution control. The section 1 is the methods distinguishing SCC controlled by anodic dissolution from those by hydrogen. The section 2 presents hydrogen-enhanced corrosion and SCC under anodic dissolution con-trol. The section 3 demonstrates corrosion-enhanced local-ized plasticity and corrosion-induced deformation localiza-tion, which are the fundaments of new mechanism of SCC. The section 4 is an overview of the proposed mechanisms of SCC under anodic dissolution control. The last section pro-poses a new mechanism of SCC.

  18. Stress Corrosion Cracking of an Austenitic Stainless Steel in Nitrite-Containing Chloride Solutions

    Directory of Open Access Journals (Sweden)

    R. K. Singh Raman

    2014-12-01

    Full Text Available This article describes the susceptibility of 316L stainless steel to stress corrosion cracking (SCC in a nitrite-containing chloride solution. Slow strain rate testing (SSRT in 30 wt. % MgCl2 solution established SCC susceptibility, as evidenced by post-SSRT fractography. Addition of nitrite to the chloride solution, which is reported to have inhibitive influence on corrosion of stainless steels, was found to increase SCC susceptibility. The susceptibility was also found to increase with nitrite concentration. This behaviour is explained on the basis of the passivation and pitting characteristics of 316L steel in chloride solution.

  19. Report on Status of Shipment of High Fluence Austenitic Steel Samples for Characterization and Stress Corrosion Crack Testing

    Energy Technology Data Exchange (ETDEWEB)

    Clark, Scarlett R. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Leonard, Keith J. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2016-09-01

    The goal of the Mechanisms of Irradiation Assisted Stress Corrosion Cracking (IASCC) task in the LWRS Program is to conduct experimental research into understanding how multiple variables influence the crack initiation and crack growth in materials subjected to stress under corrosive conditions. This includes understanding the influences of alloy composition, radiation condition, water chemistry and metallurgical starting condition (i.e., previous cold work or heat treatments and the resulting microstructure) has on the behavior of materials. Testing involves crack initiation and growth testing on irradiated specimens of single-variable alloys in simulated Light Water Reactor (LWR) environments, tensile testing, hardness testing, microstructural and microchemical analysis, and detailed efforts to characterize localized deformation. Combined, these single-variable experiments will provide mechanistic understanding that can be used to identify key operational variables to mitigate or control IASCC, optimize inspection and maintenance schedules to the most susceptible materials/locations, and, in the long-term, design IASCC-resistant materials.

  20. 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.

  1. Simulation model of fatigue crack opening/closing phenomena for predicting RPG load under arbitrary stress distribution field

    Energy Technology Data Exchange (ETDEWEB)

    Toyosada, M.; Niwa, T. [Kyushu Univ., Fukuoka (Japan)

    1995-12-31

    In this paper, Newman`s calculation model is modified to solve his neglected effect of the change of stress distribution ahead of a crack, and to leave elastic plastic materials along the crack surface because of the compatibility of Dugdale model. In addition to above treatment, the authors introduce plastic shrinkage at an immediate generation of new crack surfaces due to emancipation of internal force with the magnitude of yield stress level during unloading process in the model. Moreover, the model is expanded to arbitrary stress distribution field. By using the model, RPG load is simulated for a center notched specimen under constant amplitude loading with various stress ratios and decreased maximum load while keeping minimum load.

  2. Phase Transformation Stress and Its Influence for Arresting Crack Propagation Using Electro-heating Effect%电热止裂相变应力及其对止裂效果的影响

    Institute of Scientific and Technical Information of China (English)

    王平; 白象忠

    2011-01-01

    对含裂纹的45钢钢板进行了电热效应裂纹止裂(简称电热正裂)实验研究,发现电热止裂后的裂纹尖端附近发生了相变,并对相变组织进行了实验观察.针对裂尖处的相变区域,进行了相变应变的X射线衍射实验测定,采用Eshelby等效夹杂模型,利用等效夹杂理论进行了放电后裂尖处的相变应力场的理论分析计算.计算结果表明,在裂尖处的相变区域,形成了相变压应力场.分析了相变压应力对止裂效果的长效影响,发现相变压应力对裂纹扩展的阻碍影响是非常明显的,其对裂纹扩展速率降低的影响更是显而易见,起到了长期限制裂纹扩展的作用.研究结果表明,电热止裂技术既具有理论的可行性,也具有实际应用的实效性.%An experimental investigation of arresting crack propagation by pulse discharging to a 45 # steel plate with crack was shown herein. Through the microstructure analysis near crack tip after crack prevention by using electromagnetic heating effect, it is found that the phase transformation has been occurred. Also, the residual strain of phase transformation near crack tip has gotten by X-ray diffusion method. The theoretical calculation of the phase transformation stress was finished by Eshelby's model of imaginary cutting method. The affection of the residual stress on the crack propagation was discussed. It is found that the residual stress will have a long term effect for crack prevention. The results obtained show that the technique of arresting crack propagation by using electric magnetic heat effect has both academic feasibility and practicability.

  3. Strain Measurements within Fibreboard. Part III: Analyzing the Process Zone at the Crack Tip of Medium Density Fiberboards (MDF) Double Cantilever I-Beam Specimens

    Science.gov (United States)

    Rathke, Jörn; Müller, Ulrich; Konnerth, Johannes; Sinn, Gerhard

    2012-01-01

    This paper is the third part of a study dealing with the mechanical and fracture mechanical characterization of Medium Density Fiberboards (MDF). In the first part, an analysis of internal bond strength testing was performed and in the second part MDF was analyzed by means of the wedge splitting experiment; this part deals with the double cantilever I beam test, which is designed for measuring the fracture energy as well as stress intensity factor in Mode I. For a comparison of isotropic and orthotropic material behavior, finite element modeling was performed. In addition to the calculation of fracture energy the stress intensity factor was analyzed by means of finite elements simulation and calculation. In order to analyze strain deformations and the process zone, electronic speckle pattern interferometry measurements were performed. The results revealed an elongated process zone and lower results for KIC if compared to the wedge splitting experiment. The Gf numbers are higher compared to the wedge splitting results and can be explained by the thicker process zone formed during the crack propagation. The process zone width on its part is influenced by the stiff reinforcements and yields a similar crack surface as with the internal bond test.

  4. Strain Measurements within Fibreboard. Part III: Analyzing the Process Zone at the Crack Tip of Medium Density Fiberboards (MDF Double Cantilever I-Beam Specimens

    Directory of Open Access Journals (Sweden)

    Gerhard Sinn

    2012-11-01

    Full Text Available This paper is the third part of a study dealing with the mechanical and fracture mechanical characterization of Medium Density Fiberboards (MDF. In the first part, an analysis of internal bond strength testing was performed and in the second part MDF was analyzed by means of the wedge splitting experiment; this part deals with the double cantilever I beam test, which is designed for measuring the fracture energy as well as stress intensity factor in Mode I. For a comparison of isotropic and orthotropic material behavior, finite element modeling was performed. In addition to the calculation of fracture energy the stress intensity factor was analyzed by means of finite elements simulation and calculation. In order to analyze strain deformations and the process zone, electronic speckle pattern interferometry measurements were performed. The results revealed an elongated process zone and lower results for KIC if compared to the wedge splitting experiment. The Gf numbers are higher compared to the wedge splitting results and can be explained by the thicker process zone formed during the crack propagation. The process zone width on its part is influenced by the stiff reinforcements and yields a similar crack surface as with the internal bond test.

  5. Crack instability of ferroelectric solids under alternative electric loading

    Science.gov (United States)

    Chen, Hao-Sen; Wang, He-Ling; Pei, Yong-Mao; Wei, Yu-Jie; Liu, Bin; Fang, Dai-Ning

    2015-08-01

    The low fracture toughness of the widely used piezoelectric and ferroelectric materials in technological applications raises a big concern about their durability and safety. Up to now, the mechanisms of electric-field induced fatigue crack growth in those materials are not fully understood. Here we report experimental observations that alternative electric loading at high frequency or large amplitude gives rise to dramatic temperature rise at the crack tip of a ferroelectric solid. The temperature rise subsequently lowers the energy barrier of materials for domain switch in the vicinity of the crack tip, increases the stress intensity factor and leads to unstable crack propagation finally. In contrast, at low frequency or small amplitude, crack tip temperature increases mildly and saturates quickly, no crack growth is observed. Together with our theoretical analysis on the non-linear heat transfer at the crack tip, we constructed a safe operating area curve with respect to the frequency and amplitude of the electric field, and validated the safety map by experiments. The revealed mechanisms about how electro-thermal-mechanical coupling influences fracture can be directly used to guide the design and safety assessment of piezoelectric and ferroelectric devices.

  6. The role of local strains from prior cold work on stress corrosion cracking

    Science.gov (United States)

    Ulaganathan, Jaganathan

    Several studies have recently reported that cold working exacerbates stress corrosion cracking (SCC) of materials in various environments, including those in which they were previously thought to be immune. While these studies usually consider cold work as a homogeneous effect, the presence of grain boundaries results in local strain concentrations that are inhomogeneously distributed within the microstructure. In order to understand the underlying mechanisms by which the local strains generated by cold work influences SCC, α-brass and Alloy 600 were used in this study. The microscopic changes in the local strains caused by cold work and by SCC were measured using electron backscatter diffraction (EBSD) and polychromatic X-ray microdiffraction (PXM). While the plastic strains were qualitatively expressed through the local misorientation calculated from the orientation data measured by both EBSD and PXM, the elastic strains were determined from the Laue patterns measured by PXM. The interaction between the local strains, and the crack initiation and propagation during SCC was studied by comparing the strain distribution from the same area measured before cold work, after cold work, and again after SCC. In this way, apart from obtaining insights on the interaction, the relative importance of pre-existing strain concentrations and those created by crack propagation can be identified. Additionally, statistical analysis of the EBSD data from uncracked and cracked grain boundaries in Alloy 600 showed the susceptibility of the boundaries to increase when they were surrounded by high local strain concentrations and when the grains sharing the boundary had similar deformation tendency, but to be independent of the grain boundary angle. Finally, one of the contributors for the changes in the strain distribution during SCC can be the corrosion process itself which was examined by intermittently measuring the changes in local strains caused by intergranular corrosion on an

  7. Diffraction analysis of nonuniform stresses in surface layers : Application to cracked TiN coatings chemically vapor deposited on Mo

    NARCIS (Netherlands)

    Sloof, W.G.; Kooi, B.J.; Delhez, R.; Keijser, Th.H. de; Mittemeijer, E.J.

    1996-01-01

    Variations of residual stresses in layers on substrates can occur in directions parallel and perpendicular to the surface as a result of compositional inhomogeneity and/or porosity or cracks. Diffraction methods to evaluate such stress variations are presented. Comparison of the experimental value f

  8. METHOD TO CALCULATE BENDING CENTER AND STRESS INTENSITY FACTORS OF CRACKED CYLINDER UNDER SAINT-VENANT BENDING

    Institute of Scientific and Technical Information of China (English)

    汤任基; 汤昕燕

    2001-01-01

    Using the single crack solution and the regular solution of plane harmonic function, the problem of Saint-Venant bending of a cracked cylinder by a transverse force was reduced to solving two sets of integral equations and its general solution was then obtained. Based on the obtained solution, a method to calculate the bending center and the stress intensity factors of the cracked cylinger whose cross-section is not thin-walled, but of small torsion rigidity is proposed. Some numerical examples are given.

  9. CONVOLUTION OF THE IMPACT THREE-DIMENSIONAL ELASTO-DYNAMICS AND DYNAMIC STRESS INTENSITY FACTOR FOR AN ELLIPTIC CRACK

    Institute of Scientific and Technical Information of China (English)

    孙竹凤; 范天佑; 吴祥法

    2002-01-01

    This paper presents a formulation for three-dimensional elastodynamics with an elliptic crack based on the Laplace and Fourier transforms and the convolution theorem. The dynamic stress intensity factor for the crack is determined by solving a Fredholm integral equation of the first kind. The results of this paper are very close to those given by the two-dimensional dual integral equation method.

  10. Research on Stress Intensity Factors for Weld Root Crack of T-butt Joints%T形焊接接头根部裂纹应力强度因子研究

    Institute of Scientific and Technical Information of China (English)

    宋占勋; 方少轩; 谢基龙

    2013-01-01

    Stress intensity factors (SIFs) for weld root crack of T-butt joints are researched. Semi-ellipse crack models for weld root of T-butt joints are built with finite model. Geometric parameters and boundary conditions are established according to finite model. Singular element method is used to simulate stress singularity of crack tip with finite element calculation. Element size of crack tip is obtained by convergence experiment. Calculation results show that, SIFs of crack tip have regularity for different initial crack size under same load, and the importance of different geometric parameters affect SIF is different. Therefore, some geometric parameters must be focused on fatigue research for weld root of T-butt joint. The simulation results are fitted by multiple linear regression method. These results could provide a valuable reference for further research of crack propagation and fatigue life prediction.%建立T形焊接接头根部裂纹的半椭圆裂纹模型,定义裂纹模型的构形参数以及边界条件,分析裂纹尖端的应力强度因子.采用奇异单元法,通过有限元计算,模拟裂纹尖端的应力奇异性.并通过收敛性检验确定裂纹尖端的单元尺寸.在此基础上,计算裂纹尖端量纲一应力强度因子,并分析其受几何参数影响的变化规律.计算结果表明,对于给定的载荷条件下,不同初始裂纹尺寸时,裂纹尖端的应力强度因子存在一定的规律性,且不同几何参数对应力强度因子的影响程度存在一定差异,因此,对焊接结构疲劳强度研究时需要有一定的侧重点.采用多重线性回归方法拟合仿真计算结果,这些结果为进一步研究T形焊接接头根部裂纹扩展和疲劳寿命预测提供参考.

  11. Assessment of Initial Test Conditions for Experiments to Assess Irradiation Assisted Stress Corrosion Cracking Mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Busby, Jeremy T [ORNL; Gussev, Maxim N [ORNL

    2011-04-01

    Irradiation-assisted stress corrosion cracking is a key materials degradation issue in today s nuclear power reactor fleet and affects critical structural components within the reactor core. The effects of increased exposure to irradiation, stress, and/or coolant can substantially increase susceptibility to stress-corrosion cracking of austenitic steels in high-temperature water environments. . Despite 30 years of experience, the underlying mechanisms of IASCC are unknown. Extended service conditions will increase the exposure to irradiation, stress, and corrosive environment for all core internal components. The objective of this effort within the Light Water Reactor Sustainability program is to evaluate the response and mechanisms of IASCC in austenitic stainless steels with single variable experiments. A series of high-value irradiated specimens has been acquired from the past international research programs, providing a valuable opportunity to examine the mechanisms of IASCC. This batch of irradiated specimens has been received and inventoried. In addition, visual examination and sample cleaning has been completed. Microhardness testing has been performed on these specimens. All samples show evidence of hardening, as expected, although the degree of hardening has saturated and no trend with dose is observed. Further, the change in hardening can be converted to changes in mechanical properties. The calculated yield stress is consistent with previous data from light water reactor conditions. In addition, some evidence of changes in deformation mode was identified via examination of the microhardness indents. This analysis may provide further insights into the deformation mode under larger scale tests. Finally, swelling analysis was performed using immersion density methods. Most alloys showed some evidence of swelling, consistent with the expected trends for this class of alloy. The Hf-doped alloy showed densification rather than swelling. This observation may be

  12. The nonlocal solution of two parallel cracks in functionally graded materials subjected to harmonic anti-plane shear waves

    Institute of Scientific and Technical Information of China (English)

    Jun Liang; Shiping Wu; Shanyi Du

    2007-01-01

    In this paper, the dynamic interaction of two parallel cracks in functionally graded materials (FGMs) is investigated by means of the non-local theory. To make the analysis tractable, the shear modulus and the material den-sity are assumed to vary exponentially with the coordinate vertical to the crack. To reduce mathematical difficulties, a one-dimensional non-local kemel is used instead of a two-dimensional one for the dynamic problem to obtain stress fields near the crack tips. By use of the Fourier transform,the problem can be solved with the help of two pairs of dual integral equations, in which the unknown variables are the jumps of displacements across the crack surfaces. To solve the dual integral equations, the jumps of displace-ments across the crack surfaces are expanded in a series of Jacobi polynomials. Unlike the classical elasticity solu-tions, it is found that no stress singularity is present at the crack tips. The non-local elastic solutions yield a finite hoop stress at the crack tips. The present result provides theoret-ical references helpful for evaluating relevant strength and preventing material failure of FGMs with initial cracks. The magnitude of the finite stress field depends on relevant param-eters, such as the crack length, the distance between two parallel cracks, the parameter describing the FGMs, the fre-quency of the incident waves and the lattice parameter of materials.

  13. 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.

  14. An Enhanced Cohesive Crack Element for XFEM using a Double Enriched Displacement Field

    DEFF Research Database (Denmark)

    Mougaard, Jens Falkenskov; Poulsen, Peter Noe; Nielsen, Leif Otto

    2007-01-01

    Applying the principles of the eXtended Finite ElementMethod a partly cracked cohesive element is developed. The element is based on a double enrichment of the standard displacement field, which allows the element to model equal stresses at the both sides of the crack in the crack-tip element...... element. The performance of the developed element is tested in a Three Point Bending Test, where the partly cracked element gives a good over all structural response. Furthermore the partly cracked element gives results without the often seen zigzag behaviour on the load-deflection curve....

  15. THE CRACK-INCLUSION INTERACTION AND THE ANALYSIS OF SINGULARITY FOR THE HORIZONTAL CONTACT

    Institute of Scientific and Technical Information of China (English)

    陶昉敏; 汤任基

    2001-01-01

    Using the basic solutions of a single crack and a single inclusion, and making use of the principle of linear superposition of elastic mechanics, the interaction problem between a planar crack and a flat inclusion in an elastic solid is studied. The problem is reduced to solve a set of standard Cauchy-type singular equations. And the stress intensity factors at points of crack and inclusion were obtained. Besides, the singularity for the horizontal contact of crack and inclusion was analyzed. The calculating model put forward can be regarded as a new technique for studying the crack and its expanding caused by inclusion tip. Then several numerical examples are given.

  16. A thermo-mechanical study of mode I, small-scale yielding crack-tip fields in glassy polymers

    NARCIS (Netherlands)

    Basu, S.; van der Giessen, E.

    2002-01-01

    The objective of this work is to study the stress and temperature fields ahead of a blunted notch under mode 1, small-scale yielding situations. The investigation is motivated by the observation that certain polymers and polymer blends exhibit a marked increase in fracture toughness with increase in

  17. 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.

  18. Microstructural investigation of vintage pipeline steels highly susceptible to stress corrosion cracking

    Science.gov (United States)

    Torres, Monica

    The use of pipelines for the transmission of gas offers not only efficiency, but a number of economic advantages. Nevertheless, pipelines are subject to aggressive operating conditions and environments which can lead to in-service degradation [1] and thus to failures. These failures can have catastrophic consequences, such as environmental damage and loss of life [2]. One of the most dangerous threats to pipeline integrity is stress corrosion cracking (SCC). Despite the substantial progress that has been achieved in the field, due to the complex nature of this phenomenon there is still not a complete understanding of this form of external corrosion. This makes its detection and prevention a challenge and therefore a risk to pipeline integrity, and most importantly, to the safety of the population. SCC cracks are the result of the interaction between a corrosive environment, applied stresses, and a susceptible microstructure. To date, what defines a susceptible microstructure remains ambiguous, as SCC has been observed in a range of steel grades, microstructures, chemical composition, and grain sizes. Therefore, in order to be able to accurately predict and prevent this hazardous form of corrosion, it is imperative to advance our knowledge on the subject and gain a better understanding on the microstructural features of highly susceptible pipeline materials, especially in the subsurface zone where crack nucleation must take place. Therefore, a microstructural characterization of the region near the surface layer was carried-out utilizing TEM. TEM analysis revealed the dislocation character, ferrite morphology, and apparent carbide precipitation in some grain boundaries. Furthermore, light microscopy, SEM, and hardness testing were performed to expand our knowledge on the microscopical features of highly SCC susceptible service components. This investigation presents a new approach to SCC characterization, which exposed the sub-surface region microscopical

  19. Environmental stress cracking in gamma-irradiated polycarbonate - A diffusion approach

    Science.gov (United States)

    Silva, Pietro Paolo J. C. de O.; Araújo, Patricia L. B.; da Silveira, Leopoldo B. B.; Araújo, Elmo S.

    2017-01-01

    Polycarbonate (PC) is an engineering polymer which presents interesting properties. This material has been also used in medical devices, which is frequently exposed to gamma radiosterilization and to chemical agents. This may produce significant changes in polymer structure, leading to failure in service. The present work brings about a new approach on environmental stress cracking (ESC) processes elucidation in 100 kGy gamma-irradiated PC, by evaluating the diffusion process of methanol or 2-propanol in test specimens and determining the diffusion parameters on solvent-irradiated polymer systems. A comparison of diffusion parameters for both solvents indicated that methanol has a considerable ESC action on PC, with diffusion parameter of 7.5×10-14±1% m2 s-1 for non-irradiated PC and 7.8×10-14±2.8% m2 s-1 for PC irradiated at 100 kGy. In contrast, 2-propanol did not act as an ESC agent, as it did promote neither swelling nor cracks in the test specimens. These results were confirmed by visual analysis and optical microscopy. Unexpectedly, structural damages evidenced in tensile strength tests suggested that 2-propanol is as aggressive as methanol chemical for PC. Moreover, although some manufacturers indicate the use of 2-propanol as a cleaning product for PC artifacts, such use should be avoided in parts under mechanical stress.

  20. Environmental Degradation of Materials: Surface Chemistry Related to Stress Corrosion Cracking

    Science.gov (United States)

    Schwarz, J. A.

    1985-01-01

    Parallel experiments have been performed in order to develop a comprehensive model for stress cracking (SCC) in structural materials. The central objective is to determine the relationship between the activity and selectivity of the microstructure of structural materials to their dissolution kinetics and experimentally measured SCC kinetics. Zinc was chosen as a prototype metal system. The SCC behavior of two oriented single-crystal disks of zinc in a chromic oxide/sodium sulfate solution (Palmerton solution) were determined. It was found that: (1) the dissolution rate is strongly (hkil)-dependent and proportional to the exposure time in the aggressive environment; and (2) a specific slip system is selectively active to dissolution under applied stress and this slip line controls crack initiation and propagation. As a precursor to potential microgrvity experiments, electrophoretic mobility measurements of zinc particles were obtained in solutions of sodium sulfate (0.0033 M) with concentrations of dissolved oxygen from 2 to 8 ppm. The equilibrium distribution of exposed oriented planes as well as their correlation will determine the particle mobility.

  1. Environmental Degradation of Materials: Surface Chemistry Related to Stress Corrosion Cracking

    Science.gov (United States)

    Schwarz, J. A.

    1985-01-01

    Parallel experiments have been performed in order to develop a comprehensive model for stress cracking (SCC) in structural materials. The central objective is to determine the relationship between the activity and selectivity of the microstructure of structural materials to their dissolution kinetics and experimentally measured SCC kinetics. Zinc was chosen as a prototype metal system. The SCC behavior of two oriented single-crystal disks of zinc in a chromic oxide/sodium sulfate solution (Palmerton solution) were determined. It was found that: (1) the dissolution rate is strongly (hkil)-dependent and proportional to the exposure time in the aggressive environment; and (2) a specific slip system is selectively active to dissolution under applied stress and this slip line controls crack initiation and propagation. As a precursor to potential microgrvity experiments, electrophoretic mobility measurements of zinc particles were obtained in solutions of sodium sulfate (0.0033 M) with concentrations of dissolved oxygen from 2 to 8 ppm. The equilibrium distribution of exposed oriented planes as well as their correlation will determine the particle mobility.

  2. The Effect of Microstructure on Stress-Strain Behaviour and Susceptibility to Cracking of Pipeline Steels

    Directory of Open Access Journals (Sweden)

    A. Mustapha

    2012-01-01

    Full Text Available The effect of microstructure on the stress-strain behaviour of pipeline steels was studied. Slow strain rate (2×10-6 s-1 tests were conducted on grade X65 and X100 steels in silicone oil and hydrogen carbonate/carbonate solution. The as-received grade X100 steel at 75°C showed serrated stress-strain curves. The magnitude of the serrations depended upon the strain rate and test temperature. Annealing at 600°C or above removes the serrations, but this increased the susceptibility to transgranular cracking in hydrogen carbonate/carbonate solution at potentials below −800 mV (sce. The removal and reformation of banding in pipeline steels were also studied. Ferrite/pearlite becomes aligned during the hot rolling stage of pipe manufacture and causes directionality in crack propagation and mechanical properties. Heat treatments were carried out which show that banding in grade X65 and X100 can be removed above 900°C. This depends on homogenisation of carbon which also depends on temperature, time, and cooling rate.

  3. Micro-mechanical State at Tip of Environmentally Assisted Cracking in Nickel-based Alloy%镍基合金环境致裂过程中裂尖微观力学特性分析

    Institute of Scientific and Technical Information of China (English)

    薛河; 李永强

    2016-01-01

    Nickel-based alloys and austenitic stainless steels are widely used in the structures of primary circuit of nuclear power plants.Environmentally assisted cracking (EAC) of these materials is one of the most significant potential safety hazards in the primary circuit of nuclear power plants.Researches show that EAC in nickel-based alloy is a process of oxide film rupture and reform at the tip of EAC in the high temperature water environment of nuclear power plants.To understand the micro-mechanical state at the tip of EAC,the stress-strain in the oxide film and the base metal at the EAC tip was simulated and discussed using a commercial finite element analysis code,which provides a foundation to improve the quantitative predication accuracy of EAC growth rate of nickel-based alloys and austenitic stainless steels in the important structures of nuclear power plants.%核电站-回路压力容器、管道及蒸汽发生器等设备和结构中广泛采用镍基合金和奥氏体不锈钢,而这些材料的环境致裂(EAC)却是核电结构的主要安全隐患之一.研究表明,核电高温高压水环境中镍基合金的EAC是裂尖氧化膜破裂和再生成的一个过程.为了深入了解镍基合金EAC裂纹扩展过程中裂尖的力学状况,从理论和数值模拟两方面分析研究了EAC裂尖氧化膜和基体金属区域的应力分布规律,为提高定量预测高温高压水环境中镍基合金EAC扩展速率精度奠定基础.

  4. Investigation on the stress state along the crack front in the fatigue crack growth rate test for thick high strength steel plates%厚钢板疲劳裂纹扩展前缘应力状态试验与数值仿真

    Institute of Scientific and Technical Information of China (English)

    党之凡; 乐京霞; 董岩

    2016-01-01

    Complex environmental loads would unavoidably lead to the fatigue damage in marine struc⁃tures, and the case worsens in high strength steel thick-welded structures which have typical tri-axial stress and the feature of brittleness. To study the stress state along the crack front, a standard fatigue crack growth rate test for high strength steel Q370QE with a thickness of 36 mm is conducted, and the correspond⁃ing material parameters and the threshold of stress intensity factor are obtained. Next, the abnormal behav⁃ior of a crack front during crack growth and the stress state along crack front during crack growth are ana⁃lyzed with the finite element method. Accordingly, the varying tendency of crack front shape could be quali⁃tatively defined. Finally, local constraint factors are introduced in order to quantitatively describe the stress state along the crack front with the growth of fatigue crack based on plasticity analysis, which provides prop⁃er explanation to why the crack front changes from slant to flat with the crack growing. The calculated stress intensity factor could only describe the stress state in the center area, but distortion is inevitable on the sur⁃face, while the local constraint factor can fully describe the stress state along the crack tip zone.%复杂的环境载荷不可避免地会造成海洋结构物的疲劳损伤,而高强度厚钢板典型的三向应力状态会增加结构脆性,更加缩短结构的疲劳寿命。为研究厚板裂纹前缘应力状态沿板厚方向的分布,完成了3组36 mm板厚Q370QE高强度钢的标准疲劳裂纹扩展速率试验,得到了材料参数C,m以及应力强度因子门槛值。接着,应用有限元方法分别基于线弹性分析和塑性分析计算裂纹尖端应力强度因子和裂纹尖端局部约束因子,并解释试验中裂纹前缘由倾斜趋于平直的现象。计算所得裂纹尖端应力强度因子可描述板厚中心部分裂纹前缘的应力

  5. Fatigue crack propagation analysis of plaque rupture.

    Science.gov (United States)

    Pei, Xuan; Wu, Baijian; Li, Zhi-Yong

    2013-10-01

    Rupture of atheromatous plaque is the major cause of stroke or heart attack. Considering that the cardiovascular system is a classic fatigue environment, plaque rupture was treated as a chronic fatigue crack growth process in this study. Fracture mechanics theory was introduced to describe the stress status at the crack tip and Paris' law was used to calculate the crack growth rate. The effect of anatomical variation of an idealized plaque cross-section model was investigated. The crack initiation was considered to be either at the maximum circumferential stress location or at any other possible locations around the lumen. Although the crack automatically initialized at the maximum circumferential stress location usually propagated faster than others, it was not necessarily the most critical location where the fatigue life reached its minimum. We found that the fatigue life was minimum for cracks initialized in the following three regions: the midcap zone, the shoulder zone, and the backside zone. The anatomical variation has a significant influence on the fatigue life. Either a decrease in cap thickness or an increase in lipid pool size resulted in a significant decrease in fatigue life. Comparing to the previously used stress analysis, this fatigue model provides some possible explanations of plaque rupture at a low stress level in a pulsatile cardiovascular environment, and the method proposed here may be useful for further investigation of the mechanism of plaque rupture based on in vivo patient data.

  6. Modeling of stresses at grain boundaries with respect to occurrence of stress corrosion cracking

    Energy Technology Data Exchange (ETDEWEB)

    Kozaczek, K.J. [Oak Ridge National Lab., TN (United States); Sinharoy, A.; Ruud, C.O. [Pennsylvania State Univ., University Park, PA (United States); McIlree, A.R. [Electric Power Research Institute, Palo Alto, CA (United States)

    1995-12-31

    The distributions of elastic stresses/strains in the grain boundary regions were studied by the analytical and the finite element models. The grain boundaries represent the sites where stress concentration occurs as a result of discontinuity of elastic properties across the grain boundary and the presence of second phase particles elastically different from the surrounding matrix grains. A quantitative analysis of those stresses for steels and nickel based alloys showed that the stress concentrations in the grain boundary regions are high enough to cause a local microplastic deformation even when the material is in the macroscopic elastic regime. The stress redistribution as a result of such a plastic deformation was discussed.

  7. Investigation on Dynamic Propagation Characteristics of In-Plane Cracks in PVB Laminated Glass Plates

    Directory of Open Access Journals (Sweden)

    Xiaoqing Xu

    2016-01-01

    Full Text Available Polyvinyl butyral (PVB laminated glass has been widely used as an important component of mechanical and construction materials. Cracks on PVB laminated glass are rich in impact information, which contribute to its impact resistance design. In this paper, a three-dimensional (3D numerical simulation model describing PVB laminated glass under impact loading is firstly established and validated qualitatively and quantitatively compared with the corresponding experimental results recorded by the high-speed photography system. In the meantime, the extended finite element method (XFEM is introduced to analyze the crack propagation mechanism of laminated glass based on dynamic stress intensity factors (DSIFs and propagations of stress waves. Parametric studies are then carried out to investigate the influence of five critical parameters, that is, plate dimension, crack length, impact energy, glass properties, and PVB properties, on crack propagation characteristics of laminated glass. Results show that the interaction between crack tip and stress waves as well as the propagations of stress waves corresponds to the fluctuations of DSIFs at crack tip. Both the structure and material variables are proven to play a very important role in glass cracking DSIFs and thus govern the crack propagation behavior. Results may provide fundamental explanation to the basic crack propagation mechanism on radial cracks in PVB laminated glass under impact loading conditions, thus to instruct its impact design improvement.

  8. Stress-corrosion cracking of steels in ammonia with consideration given to OTEC design: a survey

    Energy Technology Data Exchange (ETDEWEB)

    Teel, R.B.

    1980-03-01

    Carbon steel, alloy steel, and high-strength, quenched and tempered steel, when under applied or residual stress and especially when cold formed and/or welded without subsequent thermal stress relief, are subject to failure by stress-corrosion cracking (SCC) in air-contaminated dry ammonia. Water as well as hydrazine when present in small amounts have been shown to be effective inhibitors in an all steel system. Galvanic corrosion between dissimilar metals and/or accelerated failure by SCC of stressed steel as a result of galvanic coupling may be of concern. Where water has proven effective as an inhibitor of SCC in an all steel system, it may not be adequate in a mixed metal system. With aluminum tubes, the tube sheet will either have to be solid aluminum, aluminum clad steel or some nonconductive coating will be necessary to effectively remove the cathodic alloy from the galvanic circuit. Research is required to determine the severity of the coupling effect between dissimilar alloys in ammonia under OTEC conditions; especially the possibility of accelerated SCC failures of stressed steel where the presence of an inhibitor in the ammonia may not be sufficient to override the galvanic coupling effect.

  9. Unloading Effect on Delayed Hydride Cracking in Zirconium Alloys

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Young Suk; Kim, Sung Soo [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2010-05-15

    It is well-known that a tensile overload retards not only the crack growth rate (CGR) in zirconium alloys during the delayed hydride cracking (DHC) tests but also the fatigue crack growth rate in metals, the cause of which is unclear to date. A considerable decrease in the fatigue crack growth rate due to overload is suggested to occur due either to the crack closure or to compressive stresses or strains arising from unloading of the overload. However, the role of the crack closure or the compressive stress in the crack growth rate remains yet to be understood because of incomplete understanding of crack growth kinetics. The aim of this study is to resolve the effect of unloading on the CGR of zirconium alloys, which comes in last among the unresolved issues as listed above. To this end, the CGRs of the Zr-2.5Nb tubes were determined at a constant temperature under the cyclic load with the load ratio, R changing from 0.13 to 0.66 where the extent of unloading became higher at the lower R. More direct evidence for the effect of unloading after an overload is provided using Simpson's experiment investigating the effect on the CGR of a Zr-2.5Nb tube of the stress states of the prefatigue crack tip by unloading or annealing after the formation of a pre-fatigue crack

  10. Interference of wedge-shaped protrusions on the faces of a Griffith crack in biaxial stress. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Boulet, J.A.M. [Tennessee Univ., Knoxville, TN (United States)

    1992-04-01

    An initial investigation of the influence of protrusion interference on the fracture toughness required to prevent unstable propagation of a Griffith crack in a brittle material is described. The interference is caused by relative shear displacement of the crack faces when subjected to remote biaxial stress with neither principal stress parallel to the crack. It is shown that for room temperature cracks smaller than about one centimeter in silicon carbide, or about one millimeter in silicon nitride, the presence of interference changes the fracture stress. A mathematical model based on linear elasticity solutions and including multiple interference sites at arbitrarily specified positions on the crack is presented. Computations of the change in required fracture toughness and its dependence on wedge geometry (size and vertex angle), applied stresses (orientation and magnitude), and location of the interference site are discussed. Results indicate that a single interference site has only a slight effect on required toughness. However, the influence of interference increases monotonically with the number of interference sites. The two-dimensional model described herein is not accurate when the interference sites are closely spaced.

  11. Lanthanum Prevents Salt Stress-induced Programmed Cell Death in Rice Root Tip Cells by Controlling Early Induction Events

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    In a previous study, a salt stress-induced programmed cell death (PCD) model was established in rice root tip cells. Here,by using Wuyunjing 8th rice seedlings, the effects of lanthanum on salt stress-induced PCD early events were studied. The peroxidase (APX). Imidazole (20 mmol/L), the inhibitor of nicotinamide adenine dinucleotide phosphate-oxidase (NADPH oxidase), could alleviate the occurrence of PCD obviously, and such alleviation could be enhanced by the addition of La3+,indicating the involvement of NADPH oxidase in the salt stress-induced PCD process. Taken together, lanthanum could prevent salt stress-induced PCD occurrence in the rice root tip cells by blocking the calcium influx under stress, which was followed by inhibiting calcium-dependent NADPH oxidase activity to prevent O2·-production and, enhancing the cytosolic antioxidative enzyme activities to scavenge the reactive oxygen species.

  12. Effect of interaction of embedded crack and free surface on remaining fatigue life

    Directory of Open Access Journals (Sweden)

    Genshichiro Katsumata

    2016-12-01

    Full Text Available Embedded crack located near free surface of a component interacts with the free surface. When the distance between the free surface and the embedded crack is short, stress at the crack tip ligament is higher than that at the other area of the cracked section. It can be easily expected that fatigue crack growth is fast, when the embedded crack locates near the free surface. To avoid catastrophic failures caused by fast fatigue crack growth at the crack tip ligament, fitness-for-service (FFS codes provide crack-to-surface proximity rules. The proximity rules are used to determine whether the cracks should be treated as embedded cracks as-is, or transformed to surface cracks. Although the concepts of the proximity rules are the same, the specific criteria and the rules to transform embedded cracks into surface cracks differ amongst FFS codes. This paper focuses on the interaction between an embedded crack and a free surface of a component as well as on its effects on the remaining fatigue lives of embedded cracks using the proximity rules provided by the FFS codes. It is shown that the remaining fatigue lives for the embedded cracks strongly depend on the crack aspect ratio and location from the component free surface. In addition, it can be said that the proximity criteria defined by the API and RSE-M codes give overly conservative remaining lives. On the contrary, the WES and AME codes always give long remaining lives and non-conservative estimations. When the crack aspect ratio is small, ASME code gives non-conservative estimation.

  13. 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.

  14. The nonlocal theory solution of a Mode-I crack in functionally graded materials

    Institute of Scientific and Technical Information of China (English)

    LIANG Jun

    2009-01-01

    The behavior of a Mode-I finite crack in functionally graded materials is investigated using the non-local theory. To make the analysis tractable, it is assumed that the shear modulus varies exponentially with coordinate vertical to the crack. The problem in this paper can be solved through the Fourier transform with the help of two pairs of dual integral equations, in which the unknown variables are jumps of displacements across crack surfaces. To solve dual integral equations, the jumps of displacements across crack surfaces are directly expanded in a series of Jacobi polynomials. Unlike the classical elasticity solutions, it is found that no stress singularities are present at crack tips. The non-local elastic solutions yield a finite stress at crack tips, thus allowing us to use the maximum stress as a fracture criterion. Numerical examples are provided to show the effects of the crack length, the parameter describing the functionally graded materials, the lattice parameter of materials and the materials constants upon the stress fields near crack tips.

  15. The nonlocal theory solution of a Mode-I crack in functionally graded materials

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The behavior of a Mode-I finite crack in functionally graded materials is investigated using the non-local theory. To make the analysis tractable, it is assumed that the shear modulus varies exponentially with coordinate vertical to the crack. The problem in this paper can be solved through the Fourier transform with the help of two pairs of dual integral equations, in which the unknown variables are jumps of dis- placements across crack surfaces. To solve dual integral equations, the jumps of displacements across crack surfaces are directly expanded in a series of Jacobi polynomials. Unlike the classical elasticity solutions, it is found that no stress singularities are present at crack tips. The non-local elastic solu- tions yield a finite stress at crack tips, thus allowing us to use the maximum stress as a fracture crite- rion. Numerical examples are provided to show the effects of the crack length, the parameter describ- ing the functionally graded materials, the lattice parameter of materials and the materials constants upon the stress fields near crack tips.

  16. Gel-free/label-free proteomic analysis of root tip of soybean over time under flooding and drought stresses.

    Science.gov (United States)

    Wang, Xin; Oh, MyeongWon; Sakata, Katsumi; Komatsu, Setsuko

    2016-01-01

    Growth in the early stage of soybean is markedly inhibited under flooding and drought stresses. To explore the responsive mechanisms of soybean, temporal protein profiles of root tip under flooding and drought stresses were analyzed using gel-free/label-free proteomic technique. Root tip was analyzed because it was the most sensitive organ against flooding, and it was beneficial to root penetration under drought. UDP glucose: glycoprotein glucosyltransferase was decreased and increased in soybean root under flooding and drought, respectively. Temporal protein profiles indicated that fermentation and protein synthesis/degradation were essential in root tip under flooding and drought, respectively. In silico protein-protein interaction analysis revealed that the inductive and suppressive interactions between S-adenosylmethionine synthetase family protein and B-S glucosidase 44 under flooding and drought, respectively, which are related to carbohydrate metabolism. Furthermore, biotin/lipoyl attachment domain containing protein and Class II aminoacyl tRNA/biotin synthetases superfamily protein were repressed in the root tip during time-course stresses. These results suggest that biotin and biotinylation might be involved in energy management to cope with flooding and drought in early stage of soybean-root tip.

  17. 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.

  18. 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.

  19. A large-area strain sensing technology for monitoring fatigue cracks in steel bridges

    Science.gov (United States)

    Kong, Xiangxiong; Li, Jian; Collins, William; Bennett, Caroline; Laflamme, Simon; Jo, Hongki

    2017-08-01

    This paper presents a novel large-area strain sensing technology for monitoring fatigue cracks in steel bridges. The technology is based on a soft elastomeric capacitor (SEC), which serves as a flexible and large-area strain gauge. Previous experiments have verified the SEC’s capability to monitor low-cycle fatigue cracks experiencing large plastic deformation and large crack opening. Here an investigation into further extending the SEC’s capability for long-term monitoring of fatigue cracks in steel bridges subject to traffic loading, which experience smaller crack openings. It is proposed that the peak-to-peak amplitude (pk-pk amplitude) of the sensor’s capacitance measurement as the indicator of crack growth to achieve robustness against capacitance drift during long-term monitoring. Then a robust crack monitoring algorithm is developed to reliably identify the level of pk-pk amplitudes through frequency analysis, from which a crack growth index (CGI) is obtained for monitoring fatigue crack growth under various loading conditions. To generate representative fatigue cracks in a laboratory, loading protocols were designed based on constant ranges of stress intensity to limit plastic deformations at the crack tip. A series of small-scale fatigue tests were performed under the designed loading protocols with various stress intensity ratios. Test results under the realistic fatigue crack conditions demonstrated the proposed crack monitoring algorithm can generate robust CGIs which are positively correlated with crack lengths and independent from loading conditions.

  20. Simulated Service and Stress Corrosion Cracking Testing for Friction Stir Welded Spun Formed Domes

    Science.gov (United States)

    Stewart, Thomas J.; Torres, Pablo D.; Caratus, Andrei A.; Curreri, Peter A.

    2010-01-01

    Simulated service testing (SST) development was required to help qualify a new 2195 aluminum lithium (Al-Li) alloy spin forming dome fabrication process for the National Aeronautics and Space Administration (NASA) Exploration Development Technology Program. The application for the technology is to produce high strength low weight tank components for NASA s next generation launch vehicles. Since plate material is not currently manufactured large enough to fabricate these domes, two plates are joined by means of friction stir welding. The plates are then pre-contour machined to near final thicknesses allowing for a thicker weld land and anticipating the level of stretch induced by the spin forming process. The welded plates are then placed in a spin forming tool and hot stretched using a trace method producing incremental contours. Finally the dome receives a room temperature contour stretch to final dimensions, heat treatment, quenching, and artificial aging to emulate a T-8 condition of temper. Stress corrosion cracking (SCC) tests were also performed by alternate immersion in a sodium chloride (NaCl) solution using the typical double beam assembly and with 4-point loaded specimens and use of bent-beam stress-corrosion test specimens under alternate immersion conditions. In addition, experiments were conducted to determine the threshold stress intensity factor for SCC (K(sub ISCC)) which to our knowledge has not been determined previously for Al-Li 2195 alloy. The successful simulated service and stress corrosion testing helped to provide confidence to continue to Ares 1 scale dome fabrication

  1. ELASTIC INTERACTION BETWEEN WEDGE DISCLINATION DIPOLE AND INTERNAL CRACK

    Institute of Scientific and Technical Information of China (English)

    FANG Qi-hong; LIU You-wen

    2006-01-01

    The system of a wedge disclination dipole interacting with an internal crack was investigated. By using the complex variable method, the closed form solutions of complex potentials to this problem were presented. The analytic formulae of the physics variables, such as stress intensity factors at the tips of the crack produced by the wedge disclination dipole and the image force acting on disclination dipole center were obtained.The influence of the orientation, the dipole arm and the location of the disclination dipole on the stress intensity factors was discussed in detail. Furthermore, the equilibrium position of the wedge disclination dipole was also examined. It is shown that the shielding or antishielding effect of the wedge disclination to the stress intensity factors is significant when the disclination dipole moves to the crack tips.

  2. 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

  3. 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

  4. Engineering Solution for the Uniform Strength of Partially Cracked Concrete

    DEFF Research Database (Denmark)

    Hansen, Elin A.; Hansen, Will; Brincker, Rune

    2005-01-01

    Significant computational resources are required to predict the remaining strength from numerical fracture analysis of a jointed plain concrete pavement that contains a partial depth crack. It is, therefore, advantageous when the failure strength can be adequately predicted with an engineering...... solution. Current engineering or closed-form solutions are based on the elastic effective crack approach with the fracture parameters toughness and critical crack tip opening of concrete. The solutions do not directly consider the effect of the distance to the boundary conditions (restrained slab length......) and the cracking process caused by stress softening across the crack. A proposed engineering solution methodology includes these latter variables. The application of the solution is demonstrated on a slab containing a partial depth midslab crack and subjected to in-plane tension. The solution captures the effects...

  5. Parametric Assessment of Stress Development and Cracking in Internally Cured Restrained Mortars Experiencing Autogenous Deformations and Thermal Loading

    Directory of Open Access Journals (Sweden)

    Kambiz Raoufi

    2011-01-01

    Full Text Available A finite element model is used to examine how the properties of cementitious mortar are related to the stress development in the dual ring test. The results of this investigation are used to explain the thermal cracking behavior of mixtures containing prewetted lightweight aggregates (LWA by quantifying the contribution of several material properties individually. In addition to the beneficial effects of using the LWA as an internal curing agent to reduce the autogenous shrinkage of concrete, the LWA also helps to reduce the potential for thermal cracking due to a lower elastic modulus and increased stress relaxation. The rate of stress development, age of cracking, and magnitude of the temperature drop necessary to induce cracking in a dual ring specimen are dependent on a variety of factors, including the coefficient of thermal expansion of both the cementitious mortar and the restraining rings, elastic modulus of the mortar, creep effect of the mortar, and rate of thermal loading. Depending on the rate of cooling, cracking may or may not occur. The slowest rate of cooling (2.5∘C/h minimizes the effects of creep while cooling rates faster than 8∘C/h can produce a thermal gradient through the mortar cross-section that needs to be considered.

  6. Status report: Intergranular stress corrosion cracking of BWR core shrouds and other internal components

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1996-03-01

    On July 25, 1994, the US Nuclear Regulatory Commission (NRC) issued Generic Letter (GL) 94-03 to obtain information needed to assess compliance with regulatory requirements regarding the structural integrity of core shrouds in domestic boiling water reactors (BWRs). This report begins with a brief description of the safety significance of intergranular stress corrosion cracking (IGSCC) as it relates to the design and function of BWR core shrouds and other internal components. It then presents a brief history of shroud cracking events both in the US and abroad, followed by an indepth summary of the industry actions to address the issue of IGSCC in BWR core shrouds and other internal components. This report summarizes the staff`s basis for issuing GL 94-03, as well as the staff`s assessment of plant-specific responses to GL 94-03. The staff is continually evaluating the licensee inspection programs and the results from examinations of BWR core shrouds and other internal components. This report is representative of submittals to and evaluations by the staff as of September 30, 1995. An update of this report will be issued at a later date.

  7. Assessment of NDE Technologies for Detection and Characterization of Stress Corrosion Cracking in LWRs

    Energy Technology Data Exchange (ETDEWEB)

    Meyer, Ryan M.; Ramuhalli, Pradeep; Toloczko, Mychailo B.; Bond, Leonard J.; Montgomery, Robert O.

    2012-12-31

    Stress corrosion cracking (SCC) in light water reactors (LWRs) has been a persistent form of degradation in the nuclear industry. Examples of SCC can be found for a range of materials in boiling and pressurized water reactor environments, including carbon steels, stainless steels, and nickel-base stainless alloys. The evolution of SCC is often characterized by a long initiation stage followed by a phase of more rapid crack growth to failure. This provides a relatively short window of opportunity to detect the start of observable SCC, and it is conceivable that SCC could progress from initiation to failure between subsequent examinations when managed by applying periodic in-service inspection techniques. Implementation of advanced aging management paradigms in the current fleet of LWRs will require adaptation of existing measurement technologies and development of new technologies to perform on-line measurements during reactor operation to ensure timely detection of material degradation and to support the implementation of advanced diagnostics and prognostics. This paper considers several non-destructive examination (NDE) technologies with known sensitivity to detection of indicators for SCC initiation and/or propagation, and assesses these technologies with respect to their ability to detect and accurately characterize the significance of an SCC flaw. Potential strategies to improve SCC inspection or monitoring performance are offered to benefit management of SCC degradation in LWRs.

  8. Effect of Nanostructure Changes on Stress Corrosion Cracking of Proton Irradiated Nuclear Energy Structural Materials

    Directory of Open Access Journals (Sweden)

    M.N. Lunika

    2011-01-01

    Full Text Available Austenitic stainless alloys are used extensively as structural materials in the internal components of light water reactor (LWR pressure vessels because of their relatively high strength, ductility, and fracture toughness. Irradiation-assisted stress corrosion cracking (IASCC is main degradation process that affects LWR internal components exposed to radiation. The existing data on proton irradiated austenitic alloys were reviewed to evaluate the effects of key parameters such as material composition, irradiation dose on IASCC susceptibility of these materials in LWR environments. The significance of deformation nanostructure and stacking fault energy (SFE changes in the material on IASCC susceptibility is also discussed. Results show that the IASCC susceptibility of the alloys increases with increasing irradiation dose and decreasing stacking fault energy. IASCC tends to initiate at locations where slip dislocation channels intersect grain boundaries. Localized deformation in the form of grain boundary sliding due to the interaction of slip channels and grain boundaries is likely the primary cause of the observed cracking initiation. It may play a key role in the underlying mechanism of IASCC in light water reactor core components.

  9. Reconstruction of stress corrosion cracks using signals of pulsed eddy current testing

    Science.gov (United States)

    Wang, Li; Xie, Shejuan; Chen, Zhenmao; Li, Yong; Wang, Xiaowei; Takagi, Toshiyuki

    2013-06-01

    A scheme to apply signals of pulsed eddy current testing (PECT) to reconstruct a deep stress corrosion crack (SCC) is proposed on the basis of a multi-layer and multi-frequency reconstruction strategy. First, a numerical method is introduced to extract conventional eddy current testing (ECT) signals of different frequencies from the PECT responses at different scanning points, which are necessary for multi-frequency ECT inversion. Second, the conventional fast forward solver for ECT signal simulation is upgraded to calculate the single-frequency pickup signal of a magnetic field by introducing a strategy that employs a tiny search coil. Using the multiple-frequency ECT signals and the upgraded fast signal simulator, we reconstructed the shape profiles and conductivity of an SCC at different depths layer-by-layer with a hybrid inversion scheme of the conjugate gradient and particle swarm optimisation. Several modelled SCCs of rectangular or stepwise shape in an SUS304 plate are reconstructed from simulated PECT signals with artificial noise. The reconstruction results show better precision in crack depth than the conventional ECT inversion method, which demonstrates the validity and efficiency of the proposed PECT inversion scheme.

  10. A boundary integral method for a dynamic, transient mode I crack problem with viscoelastic cohesive zone

    KAUST Repository

    Leise, Tanya L.

    2009-08-19

    We consider the problem of the dynamic, transient propagation of a semi-infinite, mode I crack in an infinite elastic body with a nonlinear, viscoelastic cohesize zone. Our problem formulation includes boundary conditions that preclude crack face interpenetration, in contrast to the usual mode I boundary conditions that assume all unloaded crack faces are stress-free. The nonlinear viscoelastic cohesive zone behavior is motivated by dynamic fracture in brittle polymers in which crack propagation is preceeded by significant crazing in a thin region surrounding the crack tip. We present a combined analytical/numerical solution method that involves reducing the problem to a Dirichlet-to-Neumann map along the crack face plane, resulting in a differo-integral equation relating the displacement and stress along the crack faces and within the cohesive zone. © 2009 Springer Science+Business Media B.V.

  11. Cold-Cracking Assessment in AA7050 Billets during Direct-Chill Casting by Thermomechanical Simulation of Residual Thermal Stresses and Application of Fracture Mechanics

    NARCIS (Netherlands)

    Lalpoor, M.; Eskin, D.G.; Katgerman, L.

    2009-01-01

    Thermally induced strains and stresses developed during direct-chill (DC) semicontinuous casting of high strength aluminum alloys can result in formation of micro-cracks in different locations of the billet. Rapid propagation of such micro-cracks in tensile thermal stress fields can lead to

  12. Direct Measurements of Critical Stresses and Cracking in Thin Films of Colloid Dispersions

    Science.gov (United States)

    Man, Weining; Russel, William B.

    2008-05-01

    Useful films can be formed by drying colloidal dispersions, but the negative capillary pressure generated often promotes cracks. Complex lateral flows during drying compromised previous measurements of the pressure required for cracking. Here we report data for the onset of cracking, and the additional cracks that appear at higher pressures, from high-pressure ultrafiltration experiments on homogeneously compressed films. A comparison of the data with expectations from theory confirms that cracking is controlled by elastic recovery, though an energy criterion only provides a lower bound. Our experiments also identify the role of flaws as nucleation sites that initiate cracks.

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

    Science.gov (United States)

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

    2011-01-01

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

  14. Effect of microstructure on the sulphide stress cracking susceptibility of a high strength pipeline steel

    Energy Technology Data Exchange (ETDEWEB)

    Ramirez, E. [Centro de Investigacion en Ingenieria y Ciencias Aplicadas-UAEM, Av. Universidad 1001, 62209-Cuernavaca, Mor. (Mexico); Gonzalez-Rodriguez, J.G. [Centro de Investigacion en Ingenieria y Ciencias Aplicadas-UAEM, Av. Universidad 1001, 62209-Cuernavaca, Mor. (Mexico)], E-mail: ggonzalez@uaem.mx; Torres-Islas, A.; Serna, S. [Centro de Investigacion en Ingenieria y Ciencias Aplicadas-UAEM, Av. Universidad 1001, 62209-Cuernavaca, Mor. (Mexico); Campillo, B. [Intituto de Ciencias Fisicas-Facultad de Quimicas-Universidad Nacional Autonoma de Mexico Cuernavaca, Mor. (Mexico); Dominguez-Patino, G. [Centro de Investigacion en Ingenieria y Ciencias Aplicadas-UAEM, Av. Universidad 1001, 62209-Cuernavaca, Mor. (Mexico); Juarez-Islas, J.A. [Instituto de Investigaciones en Materiales-Universidad Nacional Autonoma de Mexico, Circuito Exterior S/N, Cd. Universitaria, C.P. 04510, Mexico, D.F. (Mexico)

    2008-12-15

    The sulphide stress cracking (SSC) susceptibility of a newly developed high strength microalloyed steel with three different microstructures has been evaluated using the slow strain rate testing (SSRT) technique. Studies were complemented with potentiodynamic polarization curves and hydrogen permeation measurements. Material included a C-Mn steel having Ni, Cu, and Mo as main microalloying elements with three microstructures: martensitic, ferritic and ferritic + bainitic. Testing temperatures included 25, 50, 70 and 90 deg. C. Detailed SEM observations of the microstructure and fracture surfaces were done to identify possible degradation mechanisms. The results showed that in all cases, the corrosion rate, number of hydrogen atoms at the surface and the percentage reduction in area increased with temperature. The steel with a martensitic microstructure had the highest SSC susceptibility at all temperatures, whereas the ferritic steels were susceptible only at 25 deg. C, and the most likely mechanism is hydrogen embrittlement assisted by anodic dissolution.

  15. Corrosion and stress corrosion cracking of ferritic/martensitic steel in super critical pressurized water

    Energy Technology Data Exchange (ETDEWEB)

    Hirose, T. [Naka Fusion Research Institute, JAEA, 801-1 Mukouyama, Naka, Ibaraki 311-0193 (Japan)]. E-mail: hirose.takanori@jaea.go.jp; Shiba, K. [Naka Fusion Research Institute, JAEA, 801-1 Mukouyama, Naka, Ibaraki 311-0193 (Japan); Enoeda, M. [Naka Fusion Research Institute, JAEA, 801-1 Mukouyama, Naka, Ibaraki 311-0193 (Japan); Akiba, M. [Naka Fusion Research Institute, JAEA, 801-1 Mukouyama, Naka, Ibaraki 311-0193 (Japan)

    2007-08-01

    A water-cooled solid breeder (WCSB) blanket cooled by high temperature SCPW (super critical pressurized water) is a practical option of DEMO reactor. Therefore, it is necessary to check the compatibility of the steel with SCPW. In this work, reduced activation ferritic/martensitic steel, F82H has been tested through slow strain rate tests (SSRT) in 23.5 MPa SCPW. And weight change behavior was measured up to 1000 h. F82H did not demonstrated stress corrosion cracking and its weight simply increased with surface oxidation. The weight change of F82H was almost same as commercial 9%-Cr steels. According to a cross-sectional analysis and weight change behavior, corrosion rate of F82H in the 823 K SCPW is estimated to be 0.04 mm/yr.

  16. Localized Deformation as a Primary Cause of Irradiation Assisted Stress Corrosion Cracking

    Energy Technology Data Exchange (ETDEWEB)

    Gary S. Was

    2009-03-31

    The objective of this project is to determine whether deformation mode is a primary factor in the mechanism of irradiation assisted intergranular stress corrosion cracking of austenitic alloys in light watert reactor core components. Deformation mode will be controlled by both the stacking fault energy of the alloy and the degree of irradiation. In order to establish that localized deformation is a major factor in IASCC, the stacking fault energies of the alloys selected for study must be measured. Second, it is completely unknown how dose and SFE trade-off in terms of promoting localized deformation. Finally, it must be established that it is the localized deformation, and not some other factor that drives IASCC.

  17. Stress analysis of the cracked-lap-shear specimen - An ASTM round-robin

    Science.gov (United States)

    Johnson, W. S.

    1987-01-01

    This ASTM Round Robin was conducted to evaluate the state of the art in stress analysis of adhesively bonded joint specimens. Specifically, the participants were asked to calculate the strain-energy-release rate for two different geometry cracked lap shear (CLS) specimens at four different debond lengths. The various analytical techniques consisted of 2- and 3-dimensional finite element analysis, beam theory, plate theory, and a combination of beam theory and finite element analysis. The results were examined in terms of the total strain-energy-release rate and the mode I to mode II ratio as a function of debond length for each specimen geometry. These results basically clustered into two groups: geometric linear or geometric nonlinear analysis. The geometric nonlinear analysis is required to properly analyze the CLS specimens. The 3-D finite element analysis gave indications of edge closure plus some mode III loading. Each participant described his analytical technique and results. Nine laboratories participated.

  18. Stress analysis of the cracked lap shear specimens: An ASTM round robin

    Science.gov (United States)

    Johnson, W. S.

    1986-01-01

    This ASTM Round Robin was conducted to evaluate the state of the art in stress analysis of adhesively bonded joint specimens. Specifically, the participants were asked to calculate the strain-energy-release rate for two different geometry cracked lap shear (CLS) specimens at four different debond lengths. The various analytical techniques consisted of 2- and 3-dimensional finite element analysis, beam theory, plate theory, and a combination of beam theory and finite element analysis. The results were examined in terms of the total strain-energy-release rate and the mode I to mode II ratio as a function of debond length for each specimen geometry. These results basically clustered into two groups: geometric linear or geometric nonlinear analysis. The geometric nonlinear analysis is required to properly analyze the CLS specimens. The 3-D finite element analysis gave indications of edge closure plus some mode III loading. Each participant described his analytical technique and results. Nine laboratories participated.

  19. Chemical contamination of soft drinks in sealed plastic bottles by environmental stress cracking.

    Science.gov (United States)

    Muller, Dan; Israelsohn-Azulay, Osnat

    2009-01-01

    A contamination of soft drinks in sealed bottles by organic solvents is reported: closed bottles full of soft drinks were accidentally placed on a cardboard soaked with thinner and the organic fluid subsequently fissured the bottom of the bottles and penetrated into the soft drinks without any apparent leakage of the soft drinks. Experiments were carried out to simulate the process: the penetration of different organic solvents into soft drinks through the bottom of closed bottles was tested. The penetration occurred only when the closed bottles contained carbonated soft drinks (CSD), indicating that inner pressure is a necessary condition for the fissuring of the bottles. This paper discusses environmental stress cracking of polyethylene terephthalate (PET) bottles by organic solvents and migration of chemicals to CSD. Experiments were conducted to determine the conditions in which PET can be permeable to poisoning organic products.

  20. Hydrogen embrittlement, grain boundary segregation, and stress corrosion cracking of alloy X-750 in low- and high-temperature water

    Energy Technology Data Exchange (ETDEWEB)

    Mills, W. J.; Lebo, M. R.; Kearns, J. J. [Bettis Atomic Power Lab., West Mifflin, PA (United States)

    1997-04-01

    The nature of intergranular stress corrosion cracking (SCC) of alloy X-750 was characterized in low- and high-temperature water by testing as-notched and precracked fracture mechanics specimens. Materials given the AH, BH, and HTH heat treatments were studied. While all heat treatments were susceptible to rapid low-temperature crack propagation (LTCP) below 150 C, conditions AH and BH were particularly susceptible. Low-temperature tests under various loading conditions (e.g., constant displacement, constant load, and increasing load) revealed that the maximum stress intensity factors (K{sub P{sub max}}) from conventional rising load tests provide conservative estimates of the critical loading conditions in highly susceptible heats, regardless of the load path history. For resistant heats, K{sub P{sub max}} provides a reasonable, but not necessarily conservative, estimate of the critical stress intensity factor for LTCP. Testing of as-notched specimens showed that LTCP will not initiate at a smooth surface or notch, but will readily occur if a cracklike defect is present. Comparison of the cracking response in water with that for hydrogen-precharged specimens tested in air demonstrated that LTCP is associated with hydrogen embrittlement of grain boundaries. The stress corrosion crack initiation and growth does occur in high-temperature water (>250 C), but crack growth rates are orders of magnitude lower than LTCP rates. The SCC resistance of HTH heats is far superior to that of AH heats as crack initiation times are two to three orders of magnitude greater and growth rates are one to two orders of magnitude lower.

  1. 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.

  2. 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.

  3. Pacific Northwest National Laboratory Investigation of the Stress Corrosion Cracking in Nickel-Base Alloys, Volume 2

    Energy Technology Data Exchange (ETDEWEB)

    Bruemmer, Stephen M.; Toloczko, Mychailo B.; Olszta, Matthew J.

    2012-03-01

    The objective of this program is to evaluate the primary water stress corrosion cracking (PWSCC) susceptibility of high chromium alloy 690 and its weld metals, establish quantitative measurements of crack-growth rates and determine relationships among cracking susceptibility, environmental conditions and metallurgical characteristics. Stress-corrosion, crack-growth rates have been determined for 12 alloy 690 specimens, 11 alloy 152/52/52M weld metal specimens, 4 alloy 52M/182 overlay specimens and 2 alloy 52M/82 inlay specimens in simulated PWR primary water environments. The alloy 690 test materials included three different heats of extruded control-rod-drive mechanism (CRDM) tubing with variations in the initial material condition and degree of cold work for one heat. Two cold-rolled (CR) alloy 690 plate heats were also obtained and evaluated enabling comparisons to the CR CRDM materials. Weld metal, overlay and inlay specimens were machined from industry mock ups to provide plant-representative materials for testing. Specimens have been tested for one alloy 152 weld, two alloy 52 welds and three alloy 52M welds. The overlay and inlay specimens were prepared to propagate stress-corrosion cracks from the alloy 182 or 82 material into the more resistant alloy 52M. In all cases, crack extension was monitored in situ by direct current potential drop (DCPD) with length resolution of about +1 µm making it possible to measure extremely low growth rates approaching 5x10-10 mm/s. Most SCC tests were performed at 325-360°C with hydrogen concentrations from 11-29 cc/kg; however, environmental conditions were modified during a few experiments to evaluate the influence of temperature, water chemistry or electrochemical potential on propagation rates. In addition, low-temperature (~50°C) cracking behavior was examined for selected alloy 690 and weld metal specimens. Extensive characterizations have been performed on material microstructures and stress-corrosion cracks by

  4. STUDY ON DYNAMIC STRESS INTENSITY FACTORS OF DISK WITH A RADIAL EDGE CRACK SUBJECTED TO EXTERNAL IMPULSIVE PRESSURE

    Institute of Scientific and Technical Information of China (English)

    Chen Aijun

    2007-01-01

    A dynamic weight function method is presented for dynamic stress intensity factors of circular disk with a radial edge crack under external impulsive pressure. The dynamic stresses in a circular disk are solved under abrupt step external pressure using the eigenfunction method.The solution consists of a quasi-static solution satisfying inhomogeneous boundary conditions and a dynamic solution satisfying homogeneous boundary conditions. By making use of FourierBessel series expansion, the history and distribution of dynamic stresses in the circular disk are derived. Furthermore, the equation for stress intensity factors under uniform pressure is used as the reference case, the weight function equation for the circular disk containing an edge crack is worked out, and the dynamic stress intensity factor equation for the circular disk containing a radial edge crack can be given. The results indicate that the stress intensity factors under sudden step external pressure vary periodically with time, and the ratio of the maximum value of dynamic stress intensity factors to the corresponding static value is about 2.0.

  5. Mode-I-crack compression modeling and numerical simulation for evaluation of in-situ stress around advancing coal workfaces

    Institute of Scientific and Technical Information of China (English)

    LIU Wei-qun; ZHU Li

    2009-01-01

    The relatively high stress probably leads to generation of a fractured or even instable area around a working coalface. Also, the generated weak area often evolves into an easy-infiltrating field of water/gas to greatly increase probability of accident occurrence. To reveal the distribution of high stress around working faces, we put forward the mode-I-crack compression model. In this model, the goaf following a working face is regarded as a mode-I crack in an infinite plate, and the self-gravity of overlaying strata is transformed into an uniform pressure applied normal to the upper edge of the model crack. Solving this problem is based on the Westergaard complex stress function. For comparison, the software RFPA-2D is also employed to simulate the same mining problem, and furthermore extendedly to calculate the stress interference induced by the simultaneous advances of two different working faces. The results show that, the area close to a working face or the goaf tail has the maximum stress, and the stress is distributed directly proportional to the square root of the advance and inversely proportional to the square root of the distance to the working face. The simultaneous advances of two neighboring working faces in different horizontals can lead to extremely high resultant stress in an interference area.

  6. On non-singular GRADELA crack fields

    Directory of Open Access Journals (Sweden)

    Elias C. Aifantis

    2014-01-01

    Full Text Available A brief account is provided on crack-tip solutions that have recently been published in the literature by employing the so-called GRADELA model and its variants. The GRADELA model is a simple gradient elasticity theory involving one internal length in addition to the two Lame' constants, in an effort to eliminate elastic singularities and discontinuities and to interpret elastic size effects. The non-singular strains and non-singular (but sometimes singular or even hypersingular stresses derived this way under different boundary conditions differ from each other and their physical meaning in not clear. This is discussed which focus on the form and physical meaning of non-singular solutions for crack-tip stresses and strains that are possible to obtain within the GRADELA model and its extensions.

  7. Effects of Surface State and Applied Stress on Stress Corrosion Cracking of Alloy 690TT in Lead-containing Caustic Solution

    Institute of Scientific and Technical Information of China (English)

    Zhiming Zhang; Jianqiu Wang; En-Hou Han; Wei Ke

    2012-01-01

    The effects of surface state and applied stress on the stress corrosion cracking (SCC) behaviors of thermally treated (TT) Alloy 690 in 10 wt% NaOH solution with 100 mg/L litharge at 330 ℃ were investigated using C-ring samples with four kinds of surface states and two different stress levels. Sample outer surfaces of the first three kinds were ground to 400 grit (ground), shot-peened (SP) and electro-polished (EP) and the last one was used as the as-received state. Two samples of every kind were stressed to 100% and 200% yield stress of Alloy 690TT, respectively. The results showed that the oxide film consisted of three layers whereas continuous layer rich in Cr was not found. The poor adhesive ability indicated that the oxide film could not protect the matrix from further corrosion. Lead was found in the oxide film and the oxides at the crack paths and accelerated the dissolution of thermodynamically unstable Cr in these locations and also in the matrix. The crack initiation and propagation on Alloy 690TT were effectively retarded by SP and EP treatments but were enhanced by grinding treatment, compared with the cracks on the as-received surface. The cracking severity was also enhanced by increasing the externally applied stress. The accelerated dissolution of Cr and the local tensile stress concentration in the near-surface layer caused by cold-working and higher applied stress reduced the SCC-resistance of Alloy 690TT in the studied solution.

  8. Extended displacement discontinuity method for analysis of cracks in 2D thermal piezoelectric semiconductors

    Science.gov (United States)

    Zhao, MingHao; Pan, YiBo; Fan, CuiYing; Xu, GuangTao

    2017-08-01

    The extended displacement discontinuities method has previously been used for crack analysis of elastic materials, piezoelectric media, magneto-electro-elastic media and piezoelectric semiconductors. Here, this method is extended to study cracks in two-dimensional n-type thermal piezoelectric semiconductors. The extended displacement discontinuities include the conventional displacement discontinuity, electric potential discontinuity, carrier density discontinuity, as well as temperature discontinuity across crack faces; correspondingly, the extended stresses represent conventional stress, electric displacement, electric current, and heat flux. Employing a Fourier transform, the fundamental solutions for a line crack under uniformly distributed extended displacement discontinuities on the crack faces are derived under mechanical, electrical, and heat loading. Based on the obtained fundamental solutions, an extended displacement discontinuity boundary element method is developed. The stress and heat flux intensity factors at the crack tip are calculated under different combined loadings.

  9. TEST METHOD OF CRACK TIP OPENING DISPLACEMENT (CTOD) AND THE DUCTILE FRACTURE PROPERTIES OF TURBINE ROTOR MATERIAL%CTOD试验方法与转子材料的延性断裂性能

    Institute of Scientific and Techni