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Showing papers on "Stress concentration published in 2013"


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the hydrogen embrittlement of a Fe 18Mn-1.2%C (wt.%) twinning-induced plasticity steel, focusing on the influence of deformation twins on hydrogen-assisted cracking.

195 citations


Journal ArticleDOI
TL;DR: In this paper, a new universal fatigue strength formula sigma(w)=sigma(b)(C-P) was established for the first time by combining the variation tendency of fatigue crack initiation sites and the competition of defects, the fatigue damage mechanisms associated with different tensile strengths and cracking sites are explained well.
Abstract: With the development of high-strength materials, the existing fatigue strength formulae cannot satisfactorily describe the relation between fatigue strength sigma(w) and tensile strength sigma(b) of metallic materials with a wide range of strength. For a simple but more precise prediction, the tensile and fatigue properties of SAE 4340 steel with the tensile strengths ranging from 1290 MPa to 2130 MPa obtained in virtue of different tempering temperatures were studied in this paper. Based on the experimental results of SAE 4340 steel and numerous other data available (conventional and newly developed materials), through introducing a sensitive factor of defects P, a new universal fatigue strength formula sigma(w)=sigma(b)(C-P.sigma(b)) was established for the first time. Combining the variation tendency of fatigue crack initiation sites and the competition of defects, the fatigue damage mechanisms associated with different tensile strengths and cracking sites are explained well. The decrease in the fatigue strength at high-strength level can be explained by fracture mechanics and attributed to the transition of fatigue cracking sites from surface to the inner inclusions, resulting in the maximum fatigue strength sigma(max)(w) at an appropriate tensile strength level. Therefore, the universal fatigue strength formula cannot only explain why many metallic materials with excessively high strength do not display high fatigue strength, but also provide a new clue for designing the materials or eliminating the processing defects of the materials. (c) 2012 Elsevier B.V. All rights reserved.

179 citations


Journal ArticleDOI
TL;DR: A review of three-dimensional effects at cracks and sharp notches can be found in this article, where the authors review developments over the past 50 years leading up to the current state of the art.
Abstract: This review is a brief survey of three-dimensional effects at cracks and sharp notches. The overall aim is to review developments over the past 50 years leading up to the current state of the art. The review is restricted to linear elastic, homogeneous, isotropic materials, with any yielding confined to a small region at a crack or notch tip. It is also restricted to static loading and to constant amplitude fatigue loading. An enormous amount of theoretical and experimental information relevant to three-dimensional effects has been published in the past five decades, so the review is, of necessity, highly selective. Theoretical topics covered are linear elastic fracture mechanics, including Volterra distorsioni, stress intensity factors, corner point singularities, crack front line tension, displacement analysis of cracks and notches, and through thickness distributions of stresses and stress intensity factors. Crack path topics covered are fatigue crack path constraints, determination of fatigue crack paths, oscillating crack fronts in thin sheets and the transition to slant crack propagation in thin sheets. Plane strain fracture toughness testing, including standards, is covered. Overall, it can be concluded that the existence of three-dimensional effects at cracks and sharp notches has been known for many years, but understanding has been limited, and for some situations still is. Understanding improved when the existence of corner point singularities and their implications became known. Increasingly powerful computers made it possible to investigate three-dimensional effects numerically in detail. Despite increased understanding, three-dimensional effects are sometimes ignored in situations where they may be important.

171 citations


Journal ArticleDOI
TL;DR: In this article, an investigation of fatigue crack growth of interfacial cracks in bi-layered materials using the extended finite element method is presented, which reveals that the crack propagates into the FGM layer under all types of loads.
Abstract: An investigation of fatigue crack growth of interfacial cracks in bi-layered materials using the extended finite element method is presented. The bi-material consists of two layers of dissimilar materials. The bottom layer is made of aluminium alloy while the upper one is made of functionally graded material (FGM). The FGM layer consists of 100 % aluminium alloy on the left side and 100 % ceramic (alumina) on the right side. The gradation in material property of the FGM layer is assumed to be exponential from the alloy side to the ceramic side. The domain based interaction integral approach is extended to obtain the stress intensity factors for an interfacial crack under thermo-mechanical load. The edge and centre cracks are taken at the interface of bi-layered material. The fatigue life of the interface crack plate is obtained using the Paris law of fatigue crack growth under cyclic mode-I, mixed-mode and thermal loads. This study reveals that the crack propagates into the FGM layer under all types of loads.

102 citations


Journal ArticleDOI
TL;DR: In this article, the authors evaluated the lap shear strength and fatigue properties of friction stir spot welded (FSSWed) dissimilar AZ31B-H24 Mg alloy and Al alloy (AA) 5754-O in three combinations.
Abstract: Lightweighting is currently considered as an effective way in improving fuel efficiency and reducing anthropogenic greenhouse gas emissions. The structural applications of lightweight magnesium and aluminum alloys in the aerospace and automotive sectors unavoidably involve welding and joining while guaranteeing the safety and durability of motor vehicles. The objective of this study was to evaluate the lap shear strength and fatigue properties of friction stir spot welded (FSSWed) dissimilar AZ31B-H24 Mg alloy and Al alloy (AA) 5754-O in three combinations, i.e., (top) Al/Mg (bottom), Al/Mg with an adhesive interlayer, and Mg/Al with an adhesive interlayer. For all the dissimilar Mg-to-Al weld combinations, FSSW induced an interfacial layer in the stir zone (SZ) that was composed of intermetallic compounds of Al3Mg2 and Al12Mg17, which led to an increase in hardness. Both Mg/Al and Al/Mg dissimilar adhesive welds had significantly higher lap shear strength, failure energy and fatigue life than the Al/Mg dissimilar weld without adhesive. Two different types of fatigue failure modes were observed. In the Al/Mg adhesive weld, at high cyclic loads nugget pull-out failure occurred due to fatigue crack propagation circumferentially around the nugget. At low cyclic loads, fatigue failure occurred in the bottom Mg sheet due to the stress concentration of the keyhole leading to crack initiation followed by propagation perpendicular to the loading direction. In the Mg/Al adhesive weld, nugget pull-out failure mode was primarily observed at both high and low cyclic loads.

99 citations


Journal ArticleDOI
TL;DR: In this paper, the authors compared the tensile and fatigue properties of wrought aluminum alloy 2198-T351 and Alloy Alloy 2024-T3 that is currently used in aerostructures and found that the latter was superior in the high cycle fatigue and fatigue endurance limit regimes, especially when considering specific mechanical properties.

93 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of water content, temperature and loading rate on the strength and failure process of rock at sub-zero temperatures were investigated and the results showed that the presence of water in the rock resulted in a marked increase in rock strength and fracture initiation stress.

89 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the cohesive stress transfer during the sub-critical crack growth associated with the debonding of FRP from concrete under fatigue loading using the direct shear test set-up.
Abstract: The cohesive stress transfer during the sub-critical crack growth associated with the debonding of FRP from concrete under fatigue loading is experimentally investigated using the direct shear test set-up. The study focused on high-amplitude/low-cycle fatigue. The fatigue sub-critical crack growth occurs at a load that is smaller than the static bond capacity of the interface, obtained from monotonic quasi-static loading, and is also associated with a smaller value of the interfacial fracture energy. The strain distribution during debonding is obtained using digital image correlation. The results indicate that the strain distribution along the FRP during fatigue is similar to the strain distribution during debonding under monotonic quasi-static loading. The cohesive crack model and the shape of the strain distribution adopted for quasi-static monotonic loading is indirectly proven to be adequate to describe the stress transfer during fatigue loading. The length of the stress transfer zone during fatigue is observed to be smaller than the cohesive zone of the interfacial crack under quasi-static monotonic loading. The strain distribution across the width of the FRP sheet is not altered during and by fatigue loading. A new formulation to predict the debonding crack growth during fatigue is proposed.

88 citations


Journal ArticleDOI
TL;DR: In this paper, a crack propagation criterion was proposed for model I crack in concrete by using the initial fracture toughness K IC ini as an inherent material property, and the crack begins to propagate when the difference, between the stress intensity factors caused by the applied load K I P and that by the cohesive stress K I σ, exceeds KIC ini.

88 citations


Journal ArticleDOI
TL;DR: In this article, three different pit shapes were assumed: round, triangle, and triangle with a notch, and the results showed that the fatigue strength of wires with the triangular pit was lower than that with a round shape.
Abstract: Fatigue tests were conducted for corroded galvanized steel wires on three corrosion levels, showing that fatigue strength of corroded wires lowers as corrosion progresses. Corrosion pits were measured on the corroded specimens, showing severer corrosion produced deeper pits in more condensed areas. Fatigue tests were then conducted for wire specimens with artificial pits whose sizes were decided by the measured corrosion pit data. Three different pit shapes were assumed: round, triangle, and triangle with a notch. The wire specimens with round pits did not break until 1 million cycles in the stress range of 400 MPa. The fatigue strength of wires with the triangular pit was lower than that with a round shape. Triangular pit specimens broke at fewer cycles for shorter pit length. The fatigue strength of wires with a notched triangle further decreased, and critical cycles did not depend on pit length. As the S-N relation of the wire specimens with triangular pits and notched triangular pits has a sim...

87 citations


Journal ArticleDOI
TL;DR: In this article, random fiber packings were modelled using 3D finite element analysis and compared to ordered fibre packings, and significant differences in the stress redistribution were found, and the presence of fibres at smaller distances from the broken fibre explains these phenomena.

Journal ArticleDOI
TL;DR: In this article, a series of three-dimensional pits models were used to predict stress concentration factor, based on the finite element analyses, aspect ratio is the main parameter affecting SCF.

Journal ArticleDOI
TL;DR: In this article, notched specimens with a stress concentration factor common in many structural components have been subjected to severe shot peening process and the results indicate a very significant fatigue strength improvement for severely shot peened specimens in spite of their very high surface roughness.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the corrosion of Ni-Cr-Mo-V high strength steel at different hydrostatic pressures by scanning electron microscopy (SEM) and finite element analysis (FEA).

Journal ArticleDOI
TL;DR: In this article, a multiscale model is provided to assess the toughening improvements in nanoparticle filled polymers caused by the formation of localised plastic shear bands, initiated by the stress concentrations around nanoparticles.
Abstract: In this paper a multiscale model is provided to assess the toughening improvements in nanoparticle filled polymers caused by the formation of localised plastic shear bands, initiated by the stress concentrations around nanoparticles. The model quantifies the energy absorbed at the nanoscale and accounts for the emergence of an interphase zone around the nanoparticles. It is proved that the elastic properties of the interphase, which are different from those of the matrix, due to chemical interactions, highly affect the stress field rising around particles and the energy dissipation at the nanoscale.

Journal ArticleDOI
TL;DR: In this paper, the influence of stress state and plastic anisotropy on the fracture behavior of a rolled AA7075-T651 aluminium plate under quasi-static loading conditions is studied both experimentally and numerically.

Journal ArticleDOI
TL;DR: In this paper, a deformation mechanism is proposed with the help of experimental observations and finite-element simulation, which demonstrates that stress concentrations occur around the precipitates, which promotes a heterogeneous stress distribution and the formation of multiple shear bands.

Journal ArticleDOI
TL;DR: In this article, the authors evaluated the residual stress relaxation and its effect on the fatigue strength of AISI 316L steel ground surfaces in comparison to electro-polished surfaces.

Journal ArticleDOI
01 Apr 2013-Carbon
TL;DR: In this article, the effect of heat treatment on the strength and toughness of a carbon fiber/silicon carbide composite with a thin pyrolytic carbon interphase was investigated.

Journal ArticleDOI
TL;DR: Corrosion fatigue behavior of a medium strength structural material was studied in air and in 3.5% NaCl solution as discussed by the authors, where emphasis was placed on the study of corrosion pit formation and the development of cracks from pits.

Journal ArticleDOI
Xudong Ren1, Q.B. Zhan1, Hong-Yu Yang1, Fengze Dai1, C.Y. Cui1, Sun Guifang1, Liang Ruan1 
TL;DR: In this paper, the effects of residual stress on fatigue behavior and crack propagation from LSP-worked hole were performed in a parametric study on residual stress and stress intensity factor to determine their effect on crack growth propagation.

Journal ArticleDOI
TL;DR: In this article, Acoustic emission (AE) signals were analyzed to identify the classes of reinforced concrete (RC) beam corresponding to a specific crack mode and the relationship between average frequency and RA value indicated clear trend with respect to crack classifications.

Journal ArticleDOI
TL;DR: In this article, the effects of size and shape of a superficial or internal notch on the strength and failure mechanism of CuZr metallic glass (MG) under tensile loading were investigated.
Abstract: Atomistic simulations are performed to study the effects of size and shape of a superficial or internal notch on the strength and failure mechanism of CuZr metallic glass (MG) under tensile loading. Our results show that plastic deformation originating at the notch root reduces the stress concentration there and leads to a notch-insensitive normalized tensile strength. The notch, however, dictates the failure location as the plastic zone at the notch root serves as a nucleation site for shear band (SB) formation. It is shown that when the plastic zone size reaches a critical value, a SB starts to propagate from the notch root across the entire sample, causing the material failure. These results provide useful guidelines for the design, testing, and engineering of MG for structural applications.

Journal ArticleDOI
TL;DR: Finite element simulations were used to quantify load transmission from the clamps to the ROI in biaxial tension and to formulate a correction factor that can be used to determine ROI stresses, which may lead to more accurate representation of the mechanical response of fibrous soft tissue.
Abstract: Planar biaxial tension remains a critical loading modality for fibrous soft tissue and is widely used to characterize tissue mechanical response, evaluate treatments, develop constitutive formulas, and obtain material properties for use in finite element studies. Although the application of tension on all edges of the test specimen represents the in situ environment, there remains a need to address the interpretation of experimental results. Unlike uniaxial tension, in biaxial tension the applied forces at the loading clamps do not transmit fully to the region of interest (ROI), which may lead to improper material characterization if not accounted for. In this study, we reviewed the tensile biaxial literature over the last ten years, noting experimental and analysis challenges. In response to these challenges, we used finite element simulations to quantify load transmission from the clamps to the ROI in biaxial tension and to formulate a correction factor that can be used to determine ROI stresses. Additionally, the impact of sample geometry, material anisotropy, and tissue orientation on the correction factor were determined. Large stress concentrations were evident in both square and cruciform geometries and for all levels of anisotropy. In general, stress concentrations were greater for the square geometry than the cruciform geometry. For both square and cruciform geometries, materials with fibers aligned parallel to the loading axes reduced stress concentrations compared to the isotropic tissue, resulting in more of the applied load being transferred to the ROI. In contrast, fiber-reinforced specimens oriented such that the fibers aligned at an angle to the loading axes produced very large stress concentrations across the clamps and shielding in the ROI. A correction factor technique was introduced that can be used to calculate the stresses in the ROI from the measured experimental loads at the clamps. Application of a correction factor to experimental biaxial results may lead to more accurate representation of the mechanical response of fibrous soft tissue.

Journal ArticleDOI
TL;DR: In this paper, the authors developed some effective numerical techniques for designing stiff structures with less stress concentrations, which is achieved by introducing some specific stress measures, which are sensitive to the existence of high local stresses, in the problem formulation and resolving the corresponding optimization problem numerically in a level set framework.
Abstract: 1. Abstract Although the phenomenon of stress concentration is of paramount importance to engineers when they are designing load-carrying structures, stiffness is often used as the solely concerned objective or constraint function in the studies of optimal topology design of continuum structures. Sometimes this will lead to optimal designs with severe stress concentrations which may be highly responsible for the fracture, creep and fatigue of structures. Thus, considering stress-related objective or constraint functions in topology optimization problems is very important from both theoretical and application perspectives. It has been known, however, that this kind of problem is very challenging since several difficulties must be overcome in order to solve it effectively. The first difficulty stems from the fact that stress constrained topology optimization problems always suffer from the so-called singularity problem. The second difficulty in stress-related optimization problem is due to the high computational cost caused by the large number of local stress constraints. The conventional treatment of this difficulty with use of the so-called global stress measures cannot give an adequate control of the magnitude of local stress level. The third difficulty is related to the accuracy of stress computation which is greatly influenced by the local geometry of structure. The aim of the present work is to develop some effective numerical techniques for designing stiff structures with less stress concentrations. This is achieved by introducing some specific stress measures, which are sensitive to the existence of high local stresses, in the problem formulation and resolving the corresponding optimization problem numerically in a level set framework. In the first global stress measure, local geometry information such as boundary curvature is introduced while in the second global stress measure, stress gradient is employed to locate the hot points of high local stresses automatically. Our study indicates that with use of the proposed numerical schemes and proposed global stress measures, the intrinsic difficulties mentioned above in stress-related topology optimization of continuum structures can be overcome in a natural way. 2.

Journal ArticleDOI
TL;DR: In this article, fatigue damage in carbon black filled natural rubber under uni-and multiaxial loading conditions was investigated at both the macroscopic (mechanical) scale and the microscopic (material) scale.

Journal ArticleDOI
TL;DR: In this article, a wavelet transformation induced multi-time scaling (WATMUS) method is used to perform accelerated cyclic CPFE simulations till crack nucleation, which is otherwise infeasible using conventional time integration schemes.

Journal ArticleDOI
TL;DR: In this article, the authors used modeling and targeted experimentation to quantify the processing conditions which cause recrystallization in a single-crystal superalloy and estimated the total accumulated plastic strain needed for recrestallization to be in the range of 2.

Journal ArticleDOI
TL;DR: In this article, the authors present the first results for stress concentrations in unidirectional hybrid composites, more specifically around a broken carbon fibre, and they show that a small increase of the stress concentration factors on both fibre types is noted with decreasing carbon fibre content.

Journal ArticleDOI
TL;DR: In this article, the authors present a set of equations for accurately describing the crack tip stress components particularly for those cases where the modes I and II stress intensity factors used in combination with the T-stress component, are unable to capture with satisfying precision the complete stress field ahead the cracktip.