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Introduction: The finite element method has become popular to determine fracture mechanics parameters, but this type of numerical analysis may or not lead to accurate results, depending on the model quality and the implementation of the established methods. Objective: Implement and validate the calculation of the stress intensity factor and the J integral through the displacement extrapolation, domain integral and interaction integral methods, through finite element modeling of cracked part problems in 2D and 3D. Materials and methods: The stress intensity factor and the integral J were calculated in a compact cracked specimen and a plate with a semi-circumferential surface crack, by means of 2D and 3D finite element models, and these results were verified with those obtained by means of published analytical expressions. Results and Discussion: The error of the results provided by the finite element models does not exceed 3% for the two-dimensional models and 7% for the three-dimensional ones, which demonstrates their quality and precision. Conclusions: The implementation of the calculation of the fracture mechanics parameters is considered validated, which makes it possible to extend its use in the future for constructions and equipment that present cracking in service. [ABSTRACT FROM AUTHOR]

Because thermowells are prone to fatigue damage in petroleum cracking gas pipelines, in this paper, the LES method is used to simulate the flow around thermowells through two-way thermal-fluid-solid coupling, the internal causes of thermowell damage are explored, and measures for improving the thermowell safety are proposed. According to this study, when high-speed, high-temperature gas passes the thermocouple bushing, the main factors affecting the structural safety of the thermocouple bushing are the alternating stress caused by the vortex falling off, the thermal stress cycle due to the temperature gradient, and the pressure gradient impacted by the gas. Furthermore, this paper proposes improving the thermowell safety by installing the interference devices and optimizing the installation angle. The improvement measures were studied by conducting a two-way thermal fluid-structure coupling simulation. The results of this study show that after installing the interference device and optimizing the installation angle the displacement deformation of the thermowell and the equivalent stress is reduced by 57.2% and 72.1%, respectively, which indicates the safety improvement of the thermowell structure and the effectiveness of the method. The research contents of this paper can provide guidance for the installation and use of thermocouple bushing. [ABSTRACT FROM AUTHOR]

The tension test was used for studying the effect of stress variance on stress corrosion cracking susceptibility of low carbon steel immersed in 0.1 M of the sulphuric acid solution. Three unequal values of stress applied on three similar specimens after preparing and grinding them in three metal frames that were manufactured for this purpose were used for 30 days of exposure. The stress increased and the acidic solution effect caused more corrosion and cracking so, the weight loss was more. The relation between stress and weight loss variance was approximately linearly dependent. The corrosion rate was calculated using the weight loss method, and its value was also increased because of the increase of weight loss. The sulphuric acid solution was a good corrosive medium for low carbon steel because of the high percentage of Iron (Fe) which is approximately 98, and a low percentage of Cr and Mo minerals. [ABSTRACT FROM AUTHOR]

A model describing crack length distribution is proposed on the basis of experimental laws governing the formation and growth of fatigue cracks in a flat specimen with multiple stress raisers. The density of this distribution corresponds to that of Pareto and can be used to describe the accumulation of scattered defects in a wide range of cracking scale. The critical values of Pareto distribution exponent, which correspond to the limit states of the multiple fracture of solid bodies, have been substantiated. [ABSTRACT FROM AUTHOR]

Two ferrite-austenite duplex medium manganese steels with very similar phase fractions and grain sizes were subjected to cold rolling. The 10Mn steel presented a much better cold rollability compared with the 7Mn steel, which is believed to stem from two critical factors. Firstly, the larger strain partitioning in the 10Mn steel resulted in a less deformation accommodated by the brittle δ-ferrite, which delayed or even inhibited micro-crack formation inside the ferrite phase. Secondly, the deformation twinning activated in the austenite of the 10Mn steel during rolling effectively enhanced the ductility of the austenite-martensite (γ-α′) mixed phase. [ABSTRACT FROM AUTHOR]

Strain Hardening Cementitious Composites (SHCC) are materials exhibiting tensile hardening behavior up to several percent strain accompanied by the formation of fine multiple cracks. Their tensile ductility is governed by the spacing and opening of cracks, which depend on the stress transfer between the fibers and the matrix. In this article, a new analytic model which takes into consideration the effects of non-uniform matrix strength, post-cracking increase in fiber bridging stress and fiber rupture on stress transfer and multiple cracking behavior of SHCC is developed. Using material parameters within the range reported in the literature, simulation results can reach reasonable agreement with test data on SHCC for two different fiber contents. The effect of fiber length on tensile behavior of SHCC is then simulated to illustrate the applicability of the model to material design. The new model should be helpful to the micromechanics-based design of SHCC for various ductility requirements. [ABSTRACT FROM AUTHOR]

Abstract: This research has been conducted to elucidate the mechanisms of brass die casting failure. A die was examined and we have evaluated the causes of crack failure mechanisms after use in brass die casting. The dominating failure mechanism in the investigated die was thermal fatigue cracking. Crack initiation is associated to accumulation of the local plastic strain that occurs during each casting cycle. The crack growth is facilitated by a number of elements: oxidation of the cracks’ surfaces, filling of brass and softening of the die material. [Copyright &y& Elsevier]

Abstract: Finite element analysis of kink band formation in wood is carried out using an anisotropic failure criterion. The criterion is capable of describing the mixed mode I/mode II crack development observed in the kinked region. The evolution of cracking is simulated with the help of the so-called smeared crack approach. As for the finite rotation of the fibers in the kinked material, it is implemented in the finite element code through a hypo-elastic law characterized by an objective derivate using the rotation of the fibers. This formulation enables to follow strictly the matter under finite strain; which means that the evolution of the orthotropic directions is correctly described. Numerical results, such as the predicted load carrying capacity of wood under compression and its post-cracking behavior, prove to have a good agreement with the experimental observations. Further, the applicability of softening orthotropic plasticity under finite strain conditions for simulating compressive failure modes in wood is established. [Copyright &y& Elsevier]

Abstract: A plane crack problem of nonhomogeneous materials with interfaces subjected to static thermal loading is investigated. A modified interaction energy integral method (IEIM) is developed to obtain the mixed-mode thermal stress intensity factors (TSIFs). Compared with the previous IEIM, the original point of this paper is: the domain-independence of the modified IEIM still stands in nonhomogeneous materials with interfaces under thermal loading. Therefore, the modified IEIM can still be applied to obtain the TSIFs of nonhomogeneous material even if the integral domain includes interfaces. The modified IEIM is combined with the extended finite element method (XFEM) to solve several thermal fracture problems of nonhomogeneous materials. Good agreement can be obtained compared with the analytic solutions and the domain-independence of the IEIM is verified. Therefore, the present method is effective to study the TSIFs of nonhomogeneous materials even when the materials contain interfaces. The influence of the discontinuity of the material properties (thermal expansion coefficient, thermal conductivity and Young’s modulus) on the TSIFs is investigated. The results show that the discontinuity of both thermal expansion coefficient and Young’s modulus affects the TSIFs greatly, while the discontinuity of thermal conductivity does not arouse obvious change of the TSIFs. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to propose a novel methodology for determining dynamic fracture toughness (DFT) of materials under mixed mode I/II impact loading. Previous experimental investigations on mixed mode fracture have been largely limited to qusi-static conditions, due to difficulties in the generation of mixed mode dynamic loading and the precise control of mode mixity at crack tip, in absence of sophisticated experimental techniques. In this study, a hybrid experimental–numerical approach is employed to measure mixed mode DFT of 40Cr high strength steel, with the aid of the split Hopkinson tension bar (SHTB) apparatus and finite element analysis (FEA). A fixture device and a series of tensile specimens with an inclined center crack are designed for the tests to generate the components of mode I and mode II dynamic stress intensity factors (DSIF). Through the change of the crack inclination angle β (=90°, 60°, 45°, and 30°), the K II/K I ratio is successfully controlled in the range from 0 to 1.14. A mixed mode I/II dynamic fracture plane, which can also exhibit the information of crack inclination angle and loading rate at the same time, is obtained based on the experimental results. A safety zone is determined in this plane according to the characteristic line. Through observation of the fracture surfaces, different fracture mechanisms are found for pure mode I and mixed mode fractures. [Copyright &y& Elsevier]

The Neuber-Novozhilov approach is used to obtain necessary and sufficient fracture criteria. Using a modified Leonov-Panasyuk-Dugdale model, simple relations for the critical fracture parameters are derived for opening mode edge cracks for the case where the diameter of the prefracture zone coincides with the diameter of the plasticity zone. These relations are suitable for studying fracture where the crack length is negligibly small. A fracture diagram using critical stresses under both criteria is proposed for a wide range of crack length. At a certain level of loading, three regions are identified, in the first of which the crack is stable, in the second, the crack extends but remains stable, and in the third, the crack is unstable. Experimental data on the fracture of specimens with edge cracks are obtained. It is established that the theoretical critical fracture curves are in good agreement with the obtained critical parameters for flat tensile specimens with two collinear edge cracks. [ABSTRACT FROM AUTHOR]

Abstract: Stress analysis is carried out in an orthotropic strip containing a Volterra-type screw dislocation. The distributed dislocation technique is used to construct integral equations for an orthotropic strip weakened by multiple smooth cracks under time-harmonic anti-plane deformation. These equations are of Cauchy singular type at the location of dislocation, which are solved numerically to obtain the dislocation density on the faces of the cracks. The dislocation densities are employed to determine stress intensity factors for multiple smooth cracks under anti-plane deformation. Several examples are solved and the stress intensity factors are obtained. The effects of the geometric parameters, cracks location and orientation on the stress intensity factors of cracks are investigated. [Copyright &y& Elsevier]

Abstract: Radial fretting tests on human femur cortical bone with a ball-on-flat configuration were carried out in vitro under different normal contact loads. The kinetics behaviors and damage characteristics of the cortical bone were analyzed using the load versus displacement (F–D) curves. The fretting scars were examined using laser confocal scanning microscopy (LCSM) and scanning electron microscopy (SEM). A nano-indenter was used to characterize the mechanical property of the osteon of the cortical bone. Morphologies showed that the primary damage form was due to micro-cracking. Around the osteon, three kinds of micro-crack configurations were observed; i.e. annular cracks—located at the concentric lamellae; radial cracks—initiated from the Harversion canal; and interstitial cracks—initiated and propagated between the interstitial lamellae. Plenty of interstitial cracks occurred in the wear scar, which indicated that the interstitial tissue was the weak zone in the structure of cortical bone. In addition, the contact stresses under the radial fretting condition were calculated by the finite element method analysis (FEMs) and the behaviors of cracking were explained. The results demonstrated that the stress concentration that occurred around the Harversian canal and osteon system resulted in a better resistance than that from the interstitial tissue. The concentric lamellae presented a better radial-fretting resistance and contact fatigue resistance than that from the interstitial lamellae. [Copyright &y& Elsevier]

Abstract: A numerical model for the calculation of fretting fatigue crack initiation is presented and compared with experiments. The model is focused on smooth sphere-on-plane contact in partial and gross slip conditions. It is based on Hamilton’s explicit stress equations and the multi-axial Dang Van and Findley fatigue criteria enhanced with a statistical size factor concept. Promising correlation was found between the model and the experimental results with quenched and tempered steel 34CrNiMo6. The model assumptions, limitations and general application are also discussed. [Copyright &y& Elsevier]

Creep studies were carried out on 2.25Cr-1Mo steel base metal and its fusion-welded weldments at 823 K over the stress range 100-240 MPa. The weldment possessed lower creep rupture strength than the base metal due to type IV failure at the outer edge of the heat-affected zone (HAZ). Premature failure of the weldment was associated with pronounced creep cavitation accompanied with localized creep deformation in the soft intercritical region of the HAZ that was sandwiched between relatively higher creep deformation-resistant microstructural regions. The cavitation was associated with coarse intergranular precipitates in the intercritical region of the HAZ. The type IV cracking in the intercritical region of the HAZ was found to initiate deep inside the weldment and propagate towards the specimen surface. Finite element analysis of stress and strain distributions across the weldment was carried out considering the micro-mechanical strength inhomogeneity across it to explain the observed features of type IV cracking. The estimated higher von-Mises and principal stresses deep inside the intercritical region of the HAZ of the weldment led to the localized creep deformation and preferential cavity nucleation and growth, resulting in type IV failure of the weldment. The role of intergranular precipitate particles in the intercritical region of the HAZ in facilitating creep cavity nucleation by the exhaustion of creep ductility of the material close to the precipitate was corroborated from finite element analysis of stress and strain distribution around the precipitates. [ABSTRACT FROM AUTHOR]

criterion was proposed to predict brittle fracture in engineering components containing sharp V-shaped notches and subjected to mixed mode I/II loading. The criterion, called SV-MTS, was developed based on the maximum tangential stress (MTS) criterion proposed originally for analyzing crack problems. The curves which are obtained from the SV-MTS criterion could be used conveniently to predict the fracture resistance and also the notch bifurcation angle in sharp V-notched components under pure mode II and also mixed mode loading. To evaluate the validity of the proposed criterion, a set of fracture tests were conducted on a new test specimen, called sharp V-notched Brazilian disc (SV-BD), under mixed mode loading conditions. It is shown that the experimental results obtained from PMMA specimens are in very good agreement with the curves of SV-MTS criterion. [ABSTRACT FROM AUTHOR]

Abstract: Pre-stressing scratching tests have been preformed on polished surfaces of Al2O3 ceramic under a Rockwell diamond indenter which moved with uniform speed and constant normal load to investigate how the pre-stress contributes to the material removal mechanism. With the measurement of acoustic emission signals as well as indenter tangential forces, surface damages and cross-section of grooves of Al2O3 ceramic were evaluated under the action of different values of pre-stress. It was found that the scratched groove width was increased with the increasing of pre-stress when same normal loads were applied. The existence of pre-stress tends to restrain the crack propagation along the direction of pre-stress, and obvious plastic deformation at the bottom of scratched groove has been observed. Moreover, the fluctuation of tangential force was obviously enhanced, and the magnitude of tangential force in the test of pre-stress was higher than that of without pre-stress. The acoustic emission signals showed that fewer damages were produced in the process of scratching with an appropriate pre-stress. However, the continuing increase of pre-stress would aggravate the machining process. [Copyright &y& Elsevier]

Abstract: A three-dimensional methodology for simulation of fatigue crack propagation is presented. The method is leveraged by the use of enriched crack tip elements to compute the mixed-mode stress intensity factors. The crack growth model used and the crack propagation life calculation are also described. As examples, fatigue crack propagation of a mode-I surface crack and crack advancements of mixed-mode surface cracks are simulated. The predicted results showed excellent agreement with experimental data from the literature. Thus, it is concluded that the crack propagation method developed allows efficient and accurate simulation of three-dimensional fatigue crack propagation problems. [Copyright &y& Elsevier]

Abstract: Cracking is a major problem during large diameter crystal growth. The objective of this work is to design an effective hot zone for a controlled growth of Yb:S–FAP [Yb3+:Sr5(PO4)3F] laser crystal by the Czochralski technology and effective cooling that can reduce stress. Theoretical and numerical analyses are performed to study the causes of cracking, mitigate the major cracking, as well as reduce cooling time. In the current system, three locations in the crystal are prone to crack, such as the top shoulder of the crystal, the middle portion above the crucible edge, and the bottom tail portion. Based on numerical simulations, we propose a new hot zone design and cooling procedure to grow and cool large diameter crystal without cracking. [Copyright &y& Elsevier]

An experimental technique that deals with the detection of weak electric signals emitted during the application of temporal uniaxial stress on solid materials has been applied on cement mortar samples. These electric signals are met in the literature as Pressure Stimulated Currents (PSC). Two different stress techniques were applied: uniaxial compressional stress at a) a low and b) at a high rate. Both qualitative and quantitative characteristics of the PSC are correlated with the mechanical state of the samples with respect to crack creation and propagation in the bulk of the material and consequently with the stages of composite damage. [ABSTRACT FROM AUTHOR]

model of a three-dimensional elastic body containing a rigid inclusion and a crack located on the interface between the inclusion and the body is considered. Natural boundary conditions are imposed on the crack. A derivative of the energy functional with respect to the perturbation parameter is derived for an arbitrary, rather smooth perturbation of the domain, in particular, the Griffith formula is obtained. [ABSTRACT FROM AUTHOR]

Abstract: The analysis of crack growth in magnesium single crystal was performed using molecular dynamics simulation with Embedded Atom Method (EAM) potentials. The twinning process at the crack tip was analyzed. Four specimens with increasing sizes were used to investigate the influences of material length scale on crack growth of magnesium single crystals. Furthermore, the effects of temperature, and the loading strain rate were also verified. The specimens were subjected to uniaxial tension strain up to the total strain level of 0.2 with a constant strain rate. In the simulation of each specimen, the averaged stress strain curve was monitored. The simulation results show that the specimen size, loading strain rate, and temperature strongly influence the peak stress point at which the twin nucleated and subsequently the crack grew. The initial slope of the averaged stress strain curve is independent of the loading strain rate and temperature. Moreover, high temperatures induce increased atomic mobility, and thereby atom reorganization, which, in turn, releases the stress at the crack tip. [Copyright &y& Elsevier]

Abstract: The aim of this study was to investigate the Coefficient of Thermal Expansion (CTE) of anodic films on 7175 T7351 aluminium alloy and to evaluate the influence of the film characteristics on this value. In particular, effects of porosity and post-treatments, such as coloring and sealing, were studied. Beam bending analysis was used as the experimental method and a numerical finite element model was developed to verify theoretical relationships hypotheses. In particular, the errors induced by the use of theoretical relationships between the curvature of the sample and stresses in the film were not negligible. A relation based on a finite element model was then developed and used to calculate stresses. The experimental value of CTE obtained by beam bending test was then validated by comparing the experimental cracking temperature of anodic films with a theoretical value directly depending on the previously determined CTE. The CTE of anodic films was found to be 13.0±1.010−6 K−1 independent from the porosity of the films and from the post-treatment (inorganic coloring and sealing). [ABSTRACT FROM AUTHOR]

Abstract: Most modellings found in literature for the multiple cracking process of 1D composites can be categorised into three different approaches: a Continuous Approach (CA) that assumes an infinitely long composite, and two random approaches that consider composites of finite length. The Random Strength Approach (RSA) rests on a spatial discretization of the composite on which a strength distribution is applied, whereas the Random Crack Approach (RCA) generates the location and the strength of each new crack without any discretization. The first part of the paper lays the model and its statistical foundations. They are used to demonstrate that the three approaches should provide consistent results. The three approaches are then introduced, with special emphasis on the RCA as it is implemented for the first time without any approximation. Finally, the results provided by the three approaches are compared, confirming their full consistency. [Copyright &y& Elsevier]

Abstract: 3D (three-dimensional) wafer stacking technology has been developed extensively recently. One of the many technical challenges in 3D stacked wafers, and one of the most important, is wafer warpage. Wafer warpage is one of the root causes leading to process and product failures such as delamination, cracking, mechanical stresses, within wafer (WIW) uniformity and even electrical failure. In this study, the wafer warpage of thinned Si wafers in stacked wafers has been evaluated. Si wafer or glass was used as a thick substrate, and Cu or polyimide was used as the bonding material. The top Si wafer in the bonded stack was ground down to 20–100μm, and wafer curvature was measured. Wafer curvature and how it relates to bonding material, substrate material of the stacked layers, and thickness of thinned Si wafer will be discussed. [ABSTRACT FROM AUTHOR]

Abstract: This paper is dedicated to simulation of dynamic analysis of fixed cracks in orthotropic media using an extended finite element method. This work is in fact an extension to dynamic problems of the recently developed orthotropic extended finite element method for fracture analysis of composites. In this method, the Heaviside and near-tip enrichment functions are used in the framework of the partition of unity for modeling crack discontinuity and crack-tip singularities within the classical finite element method. In this procedure, elements that include a crack are not required to conform to crack edges. Therefore, mesh generation can be performed without any need to comply to crack edges and the method is capable of modeling the crack propagation without any remeshing. To determine the fracture properties, mixed-mode dynamic stress intensity factors (DSIFs) are evaluated by means of domain separation integral (J ′-integral) method. Results of the proposed method are compared with other available analytical and computational results. [ABSTRACT FROM AUTHOR]

Abstract: Fatigue crack growth and fracture toughness characteristics of laser rapid manufactured (LRMed) Inconel 625 compact tension specimens of thickness 12 and 25mm were investigated. Fatigue crack propagation in all the specimens investigated in the stress intensity range (ΔK) of 14–38MPa√m, exhibited stage II crack growth in Paris’ regime with nearly same slopes of crack growth per cycle versus ΔK plot. Fatigue crack growth rates in the LRMed specimens of present study were found to be lower than the reported values for wrought Inconel 625 in the ΔK range of 14–24MPa√m and above this range they tended to coincide. X-ray diffraction patterns of the fractured surfaces revealed that the crack propagated along the growth direction of the specimens which was predominantly along the (111) plane. The fracture toughness values (J 0.2) for LRMed Inconel 625 specimens were found to be in the range of about 200–255kJ/m2. The LRMed specimens exhibited stable crack growth during the J-integral test. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this paper was to address the effect of the residual stresses within the brittle film on the substrate on the film strength, fracture energy, and interfacial shear strength (IFSS). Special analyses were performed on the SiO x film/polyethulene terephthalate substrate systems. The residual stresses were evaluated by using the curvature method. The film strength, fracture energy, and IFSS were estimated on the basis of the multiple cracking analyses. In the multiple cracking analyses, the system was subjected to the combination of the residual stresses and the unidirectionally applied stress. Results showed that the relationship between the crack density in the film and the applied strain can be predicted by adopting the energy criterion on the basis of the knowledge on the residual stress distributions in the film segment. The film strength and fracture energy for the initiation of film cracking were almost proportional to the compressive residual stresses in the film. With increasing the compressive residual stresses within the film, the IFSS also increased. [ABSTRACT FROM AUTHOR]

In the present paper, we investigate the influence of corrosion driving forces and interfacial toughness for a coated material subjected to mechanical loading. If the protective coating is cracked, the substrate material may become exposed to a corrosive media. For a stress corrosion sensitive substrate material, this may lead to detrimental crack growth. A crack is assumed to grow by anodic dissolution, inherently leading to a blunt crack tip. The evolution of the crack surface is modelled as a moving boundary problem using an adaptive finite element method. The rate of dissolution along the crack surface in the substrate is assumed to be proportional to the chemical potential, which is function of the local surface energy density and elastic strain energy density. The surface energy tends to flatten the surface, whereas the strain energy due to stress concentration promotes material dissolution. The influence of the interface energy density parameter for the solid–fluid combination, interface corrosion resistance and stiffness ratios between coating and substrate is investigated. Three characteristic crack shapes are obtained; deepening and narrowing single cracks, branched cracks and sharp interface cracks. The crack shapes obtained by our simulations are similar to real sub-coating cracks reported in the literature. [ABSTRACT FROM AUTHOR]

The need for investigation of temperature-induced deformations of frozen soils is demonstrated. Basic concepts associated with temperature-induced stresses and strains are cited. The influence of the 'aftereffect' of temperature-induced deformations, which are closely associated with the rheology of frozen soils developed by S. S. Vyalov and his students, is briefly described. [ABSTRACT FROM AUTHOR]

This paper introduces a research project the authors have proposed. The project aims to gather non-destructive testing data of stress corrosion cracking specimens and present them as benchmark data freely available to researchers in the field. Round-robin test using seven austenitic stainless steel plate specimens with artificial stress corrosion cracking is carried out, and they are measured using various non-destructive testing methods. The data measured are made available together with the results of destructive tests to confirm the true profile of the cracking. [ABSTRACT FROM AUTHOR]

The article focuses on the assessment of adaptive finite element method and photoelastic technique in identifying stress intensity factors, crack propagation and trajectory which are essential to predict the life of a product. It states the use of single, double and slant-edge crack plates as standard problems to assess the performance of both techniques. Moreover, results show that both methods provide accurate prediction of the stress intensity factors and initial crack trajectory.

Predicting fatigue crack growth after its detection during in-service inspection is necessary to prevent a loss of serviceability, such as the oil and/or water tightness of critical compartments. This paper focuses on the most typical fatigue cracks that start at the weld joint between a flat bar stiffener on a transverse web frame and the flange of a longitudinal stiffener on a bottom plate or inner bottom plate. An experiment is carried out to observe the fatigue crack propagation for two kinds of flat bars at the abovementioned connection. The experimental results, especially the surface crack growth on the flange (which dominates during the total fatigue life of the longitudinal stiffener), are compared with crack growth curves predicted using a few existing formulas. Based on the comparative study, a formula that shows the best agreement with the experiment results is selected. Weld toe magnification factors for the web stiffener are computed from the crack propagation rates measured in the experiment, and two equations for the magnification factors versus crack depth are developed for two types of web stiffeners. The selected existing formula and the proposed equations are applied to two connections at the inner bottom and side longitudinal bulkhead of an LNG carrier. The equivalent stress approach based on a long-term distribution is employed to avoid the complexity involved in dealing with the actual stress history. Using this prediction, the remaining service life until an oil or water leakage occurs at a tank boundary can be estimated when a fatigue crack at the connection is detected. [ABSTRACT FROM AUTHOR]

We study the interaction of a rigid die with a base of any shape and the surface of an elastic half space containing cracks in the presence of friction in the contact zone. The solution of the plane contact problem of the theory of elasticity is obtained by the method of singular integral equations. The detailed analysis of the problem is performed for the case where the base of the die is parabolic and a crack is rectilinear and appears on the surface of half space. We also investigate the effects of the friction coefficient, crack length, its orientation, and location on stress intensity factors KI and KII at the crack tip and the distribution of contact stresses under the die. [ABSTRACT FROM AUTHOR]

Abstract: Elimination of edge cracking is one of the major challenges in flanging of advanced high-strength steels (AHSS). Several studies show that edge cracking occurs at lower strains than those predicted by the forming limit curves (FLC) and it is influenced significantly by the sheared or blanked edge quality. This study focuses on FEM modeling and experiments on blanking and hole expansion of AHSS DP590. The FEM model of blanking was developed to characterize the edge quality for different punch/die clearances. Hole expansion was simulated to demonstrate the effect of sheared edge upon stretchability. Thus, it was possible to demonstrate how metal flow, strains and stresses in blanking affect the part quality and potential edge cracking in stretch flanging. [Copyright &y& Elsevier]

The behavior of four parallel non-symmetric cracks with different lengths in a functionally graded material plane subjected to anti-plane shear stress loading was studied by the Schmidt method. The problem was formulated through Fourier transform into four 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 displacements across the crack surfaces were directly expanded as a series of Jacobi polynomials. The results show that the stress intensity factors at the crack tips depend on the crack lengths, spacing of cracks and the material parameters. It was also revealed that the crack shielding effect presents in functionally graded materials. [ABSTRACT FROM AUTHOR]

The influence of technological parameters on the cracking performance of concretes with regards to mixture design, curing, and use of admixtures in normal-strength concretes (NSC) and high-strength concretes (HSC) was investigated. It is concluded that shrinkage and cracking sensitivity are largely independent of the water-cement ratio (w/c) and cement content in NSC. Yet, the internal shrinkage-induced stresses are higher in the lower w/c concrete, but because its strength is also higher, cracking sensitivity is not different than that of a higher w/c concrete. HSC is much more sensitive to cracking than NSC but this sensitivity can be mitigated by either sealed curing or incorporation of shrinkage-reducing admixtures (SRA). Combination of the two results in concretes with very little buildup of internal stresses upon drying. The integrated criterion for cracking sensitivity, based on combining the criteria of time to cracking and stress rate, was shown to be more reliable for the classification than the individual ones. [ABSTRACT FROM AUTHOR]

Stress corrosion cracking (SCC) behavior of 2205 duplex stainless steel (DSS) in H2S–CO2 environment was investigated by electrochemical measurements, slow strain rate test (SSRT), and scanning electron microscopy (SEM) characterization. Results demonstrated that the passive current density of steel increases with the decrease of solution pH and the presence of CO2. When solutions pH was 2.7, the steel SCC in the absence and presence of CO2 is expected to be a hydrogen-based process, i.e., hydrogen-induced cracking (HIC) dominates the SCC of the steel. The presence of CO2 in solution does not affect the fracture mechanism. However, the SCC susceptibility is enhanced when the solution is saturated simultaneously with H2S and CO2. With elevation of solution pH to 4.5, the hydrogen evolution is inhibited, and dissolution is involved in cracking process. Even in the presence of CO2, the additional cathodic reduction of H2CO3 would enhance the anodic reaction rate. Therefore, in addition to the hydrogen effect, anodic dissolution plays an important role in SCC of duplex stainless steel at solution pH of 4.5. [ABSTRACT FROM AUTHOR]

The effect of zirconium alloy strength on stress corrosion cracking for cladding tubes prepared from these materials is studied. Structure-phase transformations and the nature of failure during high-temperature oxidation, i.e. simulation of critical situations with loss of heat carrier (LOCA) for zirconium cladding tubes, are studied. Areas are analyzed for improving zirconium cladding tubes for fuel rods intended for a new generation of heat generation systems. [ABSTRACT FROM AUTHOR]

Fatigue crack closure is strongly influenced by the plastic wake developed because of the action of precedent cycles. It is related to the load sequence and is an additional difficulty for its determination. Finite-element method has been an alternative for the study of crack closure, commonly in constant-amplitude loading. However, such analyses are complex and computationally expensive, the length of the wake simulated being a critical parameter. In this paper, a comprehensive study of the effect of the plastic wake in fatigue crack closure is made. It is structured in two parts: one regarding the correct numerical modelling process and the other focussed on the influence of the wake under moderate variable-amplitude loading. After a brief description of the numerical methodology, results for different wake lengths are reported. The plastic wake is modelled with a new approach in which the final crack tip is fixed. Information regarding potential error is provided. Second, the load sequence effect is discussed. Crack closure is obtained for several load ratios, with wakes developed with different stress ratios. This permits the analysis of the influence of the load sequence over the crack-driving force compared with constant-amplitude loading. [ABSTRACT FROM AUTHOR]

Laboratory experiments on rock samples have shown electric signal emissions when the samples are subjected to temporal stress increase especially when the samples approach failure. These electric signals are attributed to the generation and propagation of microcracks that guide the sample to mechanical failure. In this work the temporal evolution of electric charge release is studied for marble samples subjected to stress at a constant rate up to fracture and it is correlated to the respective recordings of the yielded strain. The results exhibit a systematic linear correlation between electric charge and deformation, with a constant proportionality factor independent of stress rate magnitude. This linear correlation, which is in accordance with the Moving Charged Dislocations (MCD) model, exists from the instant that the marble samples are driven to the non-linear region of mechanical behaviour due to the applied stress, and more precisely to the Crack Propagation Zone (CPZ) up to the prefailure phase. [ABSTRACT FROM AUTHOR]

On the physical nature, most crack tips are not ideally sharp but have a small curvature radius. Both surface energy and crack-root curvature affect the stress and displacement fields in the vicinity of the crack tip. In the present paper, a numerical method, which incorporates the effect of surface elasticity into the finite element method, is employed to study the surface effects on the mode-II crack tip fields. It is found that when the curvature radius of the crack root decreases to micro-/nanometers, surface elasticity has a significant influence on the stresses near the crack tip. For a mode-II crack, surface effects alter both the magnitude and position of the maximum stresses, as is different from a mode-I crack, in which case only the stress magnitude is influence by surface stresses. [ABSTRACT FROM AUTHOR]

In this article, we investigate the domain switching near crack tips in O.62Pb(Mg[sub1/3Nb[sub2/1])O[sub3]- O.38PbTiO[sub3] (PMNT[sub62/38]) single crystal poled along the [001] orientation by polarized-light microscopy. The experimental results reveal that cyclic electric fields stimulate cyclic domain switching near a crack tip. Though the applied electric field is far lower than the coercive electric field, the intensive electric field is able to induce domain switching at a crack tip. Such switched domains are reversible after removal of the applied field. [ABSTRACT FROM AUTHOR]

Stress corrosion cracking (SCC) tests were conducted on American Petroleum Institute (API) grade X-70 line pipe steel using smooth specimens in a standard near neutral pH solution, NS4. Both constant loading and cyclic loading conditions were employed. There were some SCC cracks on the surfaces of specimens under constant loading conditions when the applied load and test duration were appropriate. These cracks were related to stress concentration at corrosion pits. Generally, the local strain rate around corrosion pits in constant load tests was not high enough for the transition from pits to cracks to take place, and so long test times were needed for crack initiation. In contrast, cyclic loading tests facilitated near neutral pH SCC by making the local strain rate at the crack tip change under the applied load spectrum and by enhancing the crack tip local strain rate, which appreciably shortened the crack initiation incubation. [ABSTRACT FROM AUTHOR]

In this paper the passive layer cracking process that occurs under tensile stresses and anodic polarization conditions on AA1050, AA5052, AA5056, and AA7005 aluminum alloys was examined by means of direct current (dc) technique, dynamic electrochemical impedance spectroscopy (DEIS), and acoustic emission (AE). Research revealed the advantage of DEIS and AE methods over the dc one. It was also possible to determine the exact moment of the passive layer cracking on investigated aluminum alloys. [ABSTRACT FROM AUTHOR]

A simple model is presented to account for the effects of void-type damage on crack initiation and propagation in ductile steels under plane strain conditions by virtue of elementary fracture mechanics solutions. Multiple primary voids from large inclusions are uniformly distributed ahead of the crack tip. The growth of these primary voids is followed by nucleation of a large population of secondary voids from second-phase particles. A critical accumulative damage based on the length ratio of the damage zone to the spacing of primary voids, is employed as a failure criterion, including contributions from two populations of voids. Damage accumulation depends much on the strain and stress states such as stress triaxilities, which are extracted from existing results instead of detailed computation. Results show the dependence of fracture toughness on the size of damage zones associated with constraints. Initiation of crack growth is insensitive to the constraints since nucleation of fine voids is determined by local deformation. The model captures the transition in mechanisms from void-by-void growth to multiple void interactions in terms of a decreasing trend in the slopes of fracture resistance curves. At high constraints and large damage zone, a steady-state crack advance is identified with constant toughness. Damage accumulation from the growth of primary voids determines subsequent crack growth resistance and the study demonstrates its dependences on the crack-tip constraints. [ABSTRACT FROM AUTHOR]

A periodic array of cracks in a functionally graded coating bonded to a homogeneous substrate is considered. The medium is subjected to transient or static mechanical loads. The problem is formulated in terms of a singular integral equation with the crack face displacement as the unknown variable. In addition to the time-varied stresses and stress intensity factors for various parameters of the problem, the effect of periodic cracking on the relaxation of the transient stress on the coating surface is discussed. Also included is the influence of the material gradient (material nonhomogeneity) on the crack tip intensity factors and stresses. Solutions for a single graded layer and a graded coating bonded to an infinite substrate are given. [ABSTRACT FROM AUTHOR]

This article investigates applicability of slow strain rate testing (SSRT), which is a common testing technique for determining susceptibility to caustic cracking/stress corrosion cracking (SCC). The results suggest the need for investigating a wide range of strain rates, while investigating the role of other test/process variables. The findings of this investigation provide recommendations of thorough testing with carefully selected test parameters, in order for SSRT to provide caustic cracking susceptibility data that can be confidently used by the alumina processing industry. [ABSTRACT FROM AUTHOR]

The multiple-cracking phenomenon of the Fe-Zn intermetallic coating layer on the hot-dip galvannealed (GA) steels under thermal and tensile stresses was studied experimentally by tensile tests and analytically by means of the finite-element analysis. The multiple cracking of the coating layer had occurred in the as-supplied samples, and it progressed with increasing applied strain. Based on the calculated dependence of the stress of the coating layer on the crack spacing and applied strain, the multiple cracking in the as-supplied samples was accounted for by the thermally induced residual stress, and the further multiple cracking with increasing applied strain was accounted for by the increased stress of the coating layer. The experimentally observed decrease of the average crack spacing with increasing applied strain was described well, and the tensile strength of the coating layer was estimated to be 260 MPa, by application of the calculated relation between the increased stress of the coating layer and applied strain. The influences of the thickness of the coating layer and the substrate material on the multiple cracking were discussed based the stress analysis. It was revealed that the thinner the coating layer and the higher the flow stress of the substrate, the higher the stress of the coating layer becomes and, therefore, the smaller the crack spacing becomes. [ABSTRACT FROM AUTHOR]