Showing papers on "Stress concentration published in 2010"
15 Jun 2010-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of grain size and grain orientation on deformation twinning in a Fe-22-wt.% Mn-0.6-c TWIP steel was investigated.
Abstract: We investigate the effect of grain size and grain orientation on deformation twinning in a Fe–22 wt.% Mn–0.6 wt.% C TWIP steel using microstructure observations by electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD). Samples with average grain sizes of 3 μm and 50 μm were deformed in tension at room temperature to different strains. The onset of twinning concurs in both materials with yielding which leads us to propose a Hall–Petch-type relation for the twinning stress using the same Hall–Petch constant for twinning as that for glide. The influence of grain orientation on the twinning stress is more complicated. At low strain, a strong influence of grain orientation on deformation twinning is observed which fully complies with Schmid's law under the assumption that slip and twinning have equal critical resolved shear stresses. Deformation twinning occurs in grains oriented close to 〈1 1 1〉//tensile axis directions where the twinning stress is larger than the slip stress. At high strains (0.3 logarithmic strain), a strong deviation from Schmid's law is observed. Deformation twins are now also observed in grains unfavourably oriented for twinning according to Schmid's law. We explain this deviation in terms of local grain-scale stress variations. The local stress state controlling deformation twinning is modified by local stress concentrations at grain boundaries originating, for instance, from incoming bundles of deformation twins in neighboring grains.
567 citations
TL;DR: This review focuses on aspects related to specimen geometry and test mechanics of "macro" shear and tensile bond strength tests, which tend to increase with smaller bonding areas and with the use of high elastic modulus composites.
313 citations
TL;DR: In this paper, the SED is derived directly from nodal displacements, so that also coarse meshes are able to give sufficiently accurate values for it, and the link between local SED and NSIFs is discussed with reference to some typical welded joints and to plates weakened by sharp V-notches.
279 citations
01 Jan 2010
TL;DR: It has been found that the values of K and J obtained from FE simulations are consistent with theoretical solutions and the stress distribution ahead of the crack tip is very close to that of expected from analytical studies for the case of a straight fronted transgranular crack.
Abstract: Methods have been examined to evaluate the fracture mechanics parameters J and K in finite element (FE) analyses on a compact tension, C(T), geometry using a mesh appropriate for the evaluation of both intergranular and transgranular microstructural damage processes. Realistic grain and grain boundary microstructures were modelled using ABAQUS. Both straight and deviating crack profiles were considered, representing transgranular and intergranular crack growth processes, respectively. Elastic and elastic-plastic finite element analyses were performed on a C(T) specimen model with a standard straight and deviating crack profile to derive and compare the stress intensity factor, K, and J parameter values under plane stress and plane strain conditions. Considerations as to the validity of the J domain integral calculations that ABAQUS computes are discussed. It has been found that the values of K and J obtained from FE simulations are consistent with theoretical solutions and the stress distribution ahead of the crack tip is very close to that of expected from analytical studies for the case of a straight fronted transgranular crack. Reasonable values of K and J parameters could also be achieved from the FE contour integral values of a deviating crack when the contours selected were adequately far from the crack tip. However, significant differences were found between the analytical and FE contour integral values of a deviating crack when the crack growth direction was considered to continue at the angle defined by its grain boundary. The values of J obtained by from the load line displacement measurements were uninfluenced by the crack profile and in good agreement with other analytical solutions.© 2010 ASME
223 citations
TL;DR: In this paper, the displacement discontinuity across crack surface is modeled by independent cover functions over different physical covers, while additional functions, extracted from the asymptotic near tip field, are incorporated into cover functions of singular physical covers to reflect the stress singularity around the crack tips.
Abstract: The numerical manifold method is a cover-based method using mathematical covers that are independent of the physical domain. As the unknowns are defined on individual physical covers, the numerical manifold method is very suitable for modeling discontinuities. This paper focuses on modeling complex crack propagation problems containing multiple or branched cracks. The displacement discontinuity across crack surface is modeled by independent cover functions over different physical covers, while additional functions, extracted from the asymptotic near tip field, are incorporated into cover functions of singular physical covers to reflect the stress singularity around the crack tips. In evaluating the element matrices, Gaussian quadrature is used over the sub-triangles of the element, replacing the simplex integration over the whole element. First, the method is validated by evaluating the fracture parameters in two examples involving stationary cracks. The results show good agreement with the reference solutions available. Next, three crack propagation problems involving multiple and branched cracks are simulated. It is found that when the crack growth increment is taken to be 0.5h≤da≤0.75h, the crack growth paths converge consistently and are satisfactory.
183 citations
TL;DR: The stiffer file designs generated higher stress concentrations in the apical root dentin during shaping of the curved canal, which raises the risk of dentinal defects that may lead to apicalRoot cracking.
182 citations
TL;DR: In this article, a fatigue reliability model which integrates the probability distribution of hot spot stress range with a continuous probabilistic formulation of Miner's damage cumulative rule is developed for fatigue life and reliability evaluation of steel bridges with long-term monitoring data.
Abstract: A fatigue reliability model which integrates the probability distribution of hot spot stress range with a continuous probabilistic formulation of Miner's damage cumulative rule is developed for fatigue life and reliability evaluation of steel bridges with long-term monitoring data. By considering both the nominal stress obtained by measurements and the corresponding stress concentration factor (SCF) as random variables, a probabilistic model of the hot spot stress is formulated with the use of the S-N curve and the Miner's rule, which is then used to evaluate the fatigue life and failure probability with the aid of structural reliability theory. The proposed method is illustrated using the long-term strain monitoring data from the instrumented Tsing Ma Bridge. A standard daily stress spectrum accounting for highway traffic, railway traffic, and typhoon effects is derived by use of the monitoring data. Then global and local finite element models (FEMs) of the bridge are developed for numerically calculating the SCFs at fatigue-susceptible locations, while the stochastic characteristics of SCF for a typical welded T-joint are obtained by full-scale model experiments of a railway beam section of the bridge. A multimodal probability density function (PDF) of the stress range is derived from the monitoring data using the finite mixed Weibull distributions in conjunction with a hybrid parameter estimation algorithm. The failure probability and reliability index versus fatigue life are achieved from the obtained joint PDF of the hot spot stress in terms of the nominal stress and SCF random variables.
165 citations
TL;DR: The preliminary results indicate that large von Mises stress occurs where plantar soft-tissue contacts with geometrically irregular bony structures, thus internal stress distribution within the plantarSoft-Tissue was dramatically influenced by bony prominences due to stress concentration.
127 citations
TL;DR: In this article, the authors investigated the effect of water pressure in a pipe on the rate of leakage from leak openings in the pipe and found that pipe stresses are significantly affected by a leak opening, and can easily exceed the material's yield strength in the vicinity of the opening.
Abstract: The effect of water pressure in a pipe on the rate of leakage from leak openings in the pipe is one of the main factors influencing leakage that is still not understood sufficiently. In this study, the behaviours of different types of leak openings (round holes and longitudinal and circumferential cracks) on pressurized pipes were investigated for different pipe materials (uPVC, steel, cast iron and asbestos cement) using finite element analysis. Linear elastic behaviour was assumed. The study found that (1) pipe stresses are significantly affected by a leak opening, and can easily exceed the material's yield strength in the vicinity of the opening; (2) round holes show the smallest expansion with pressure, followed by circumferential cracks and then longitudinal cracks; (3) the areas of all leak openings increase linearly with pressure; (4) longitudinal pipe stresses affect the behaviours of round holes and circumferential cracks, but not that of longitudinal cracks; and (5) the effect of pressure on a l...
122 citations
TL;DR: In this article, the initial stages of fatigue crack formation in the commercial aluminum alloy 7075-T651 were studied under moderately high fatigue loads in a scanning electron microscope, and the experimental conditions were designed to mimic the behavior of fastener holes in the lower wing covers of military attack aircraft, thus the loading parameters were such that local plasticity was expected.
117 citations
TL;DR: In this paper, the S-N line slopes of thin welded structures with actual IIW design lines are derived for the notch stress concept variants with rref = 1.0, 0.3 or 0.05 mm, respectively.
Abstract: An assessment of thin welded structures with actual IIW design lines results in an overestimation of fatigue lives (strengths) at high load levels and a conservative estimation at low load levels, in many cases, independently of the applied fatigue assessment approach (nominal, structural or notch stress). This is mainly due to the slopes of the design S-N line k = 3.0 for normal and k = 5.0 for shear stresses, which are valid for thick and stiff structures. To overcome this inconsistency for welded thin and flexible structures, the slopes k = 5.0 for normal and k = 7.0 for shear stresses are suggested, keeping the already known FAT values derived for the notch stress concept variants with rref = 1.0, 0.3 or 0.05 mm, respectively. However, the slope is not only determined by plate thickness; it is the result of an interaction between thickness, local geometry (stress concentration), structural stiffness, loading mode and last but not least residual stresses. This complexity makes it difficult to identify the driving parameters and to predict the slope of the S-N line in many cases.
TL;DR: In this article, the fatigue characteristics of rolled Mg-3Al-1Zn (AZ31) alloy were investigated by performing the low-cycle fatigue test along the rolling direction; the alloy was found to have a strong basal texture so that the fatigue deformation was predominated by the alternation of twinning and detwinning during each cycle.
TL;DR: In this article, the generalized stress intensity factors are evaluated directly from the scaled boundary finite-element solution for the singular stress field by following standard stress recovery procedures in the finite element method.
TL;DR: The failure behaviour predicted by FE modelling is in good agreement with experimental results, and the reduction in compressive strength owing to the embedding of circular vascules ranges from 13 to 70 per cent, which correlates with vascule dimension.
Abstract: A study of the influence of embedded circular hollow vascules on structural performance of a fibre-reinforced polymer (FRP) composite laminate is presented. Incorporating such vascules will lead to multi-functional composites by bestowing functions such as self-healing and active thermal management. However, the presence of off-axis vascules leads to localized disruption to the fibre architecture, i.e. resin-rich pockets, which are regarded as internal defects and may cause stress concentrations within the structure. Engineering approaches for creating these simple vascule geometries in conventional FRP laminates are proposed and demonstrated. This study includes development of a manufacturing method for forming vascules, microscopic characterization of their effect on the laminate, finite element (FE) analysis of crack initiation and failure under load, and validation of the FE results via mechanical testing observed using high-speed photography. The failure behaviour predicted by FE modelling is in good agreement with experimental results. The reduction in compressive strength owing to the embedding of circular vascules ranges from 13 to 70 per cent, which correlates with vascule dimension.
TL;DR: In this article, the effect of corrosion on the gigacycle fatigue strength of a martensitic-bainitic hot-rolled steel used for manufacturing offshore mooring chains for petroleum platforms was studied.
TL;DR: The cross-sectional design has a greater impact than taper or size of the instrument on the stresses developed in the instrument under either torsion or bending, taking into account the nonlinear mechanical properties of material.
TL;DR: The present study showed that the use of different thread form designs did not affect the von Mises concentration at supporting bone structure, however, the compressive stress concentrations differ by various thread profiles.
Abstract: The biomechanical behavior of implant thread plays an important role on stresses at implant-bone interface. Information about the effect of different thread profiles upon the bone stresses is limited. The purpose of this study was to evaluate the effects of different implant thread designs on stress distribution characteristics at supporting structures. In this study, three-dimensional (3D) finite element (FE) stress-analysis method was used. Four types of 3D mathematical models simulating four different thread-form configurations for a solid screw implant was prepared with supporting bone structure. V-thread (1), buttress (2), reverse buttress (3), and square thread designs were simulated. A 100-N static axial occlusal load was applied to occlusal surface of abutment to calculate the stress distributions. Solidworks/Cosmosworks structural analysis programs were used for FE modeling/analysis. The analysis of the von Mises stress values revealed that maximum stress concentrations were located at loading areas of implant abutments and cervical cortical bone regions for all models. Stress concentration at cortical bone (18.3 MPa) was higher than spongious bone (13.3 MPa), and concentration of first thread (18 MPa) was higher than other threads (13.3 MPa). It was seen that, while the von Mises stress distribution patterns at different implant thread models were similar, the concentration of compressive stresses were different. The present study showed that the use of different thread form designs did not affect the von Mises concentration at supporting bone structure. However, the compressive stress concentrations differ by various thread profiles.
TL;DR: In this article, a generalised plane strain model was used to predict free edge delamination in composite structures. But the results were limited to ( ± 10 ) s, ( ± 20 ) s ) laminates, where the interfacial fracture energy and interlaminar shear strength are known.
TL;DR: In this paper, the effect of constraint induced by the crack depth on creep crack-tip stress field in compact tension (CT) specimens is examined by finite element analysis, and the effects of creep deformation and damage on the Hutchinson-Rice-Rosengren (HRR) singularity stress field are discussed.
TL;DR: In this article, the effects of cutout on the load bearing capacity and stress concentration of flat infinite plates subjected to a uniaxial tension load were investigated. And the results indicated that the stress concentration factor of perforated plates can be significantly changed by using proper cutout shape, bluntness and orientation.
TL;DR: In this paper, the authors analyzed the fatigue crack propagation behavior of a magnesium single crystal using molecular dynamics simulation and found that the growth rate of fatigue crack decreasing with increasing strain rate.
TL;DR: In this article, the effect of shot peening on the fatigue behavior of Al-7075-T651 samples carrying different types of notches was investigated by means of X-ray diffraction (XRD) measurements on plain specimens.
TL;DR: In this paper, a new format of anisotropic gradient elasticity is formulated and implemented to simulate stress concentrations in cortical bone, which is validated numerically in tests with bone fractures in the longitudinal and the transversal directions.
TL;DR: In this paper, the microporosity and mechanism of fatigue damage formation and growth were invested using X-ray computed tomography and scanning electron microscopy, and the variations in the fracture surfaces according to three fatigue damage evolution stages: fatigue crack formation (incubation), microstructurally/physically small cracks, and long cracks.
TL;DR: In this article, a typical fracture surface with a fine concavo-convex pattern called "ODA" was discovered for very high cycle fatigue (VHCF) of high strength steel.
TL;DR: In this article, the use of the Theory of Critical Distances, applied in the form of the Point Method, to estimate the range of the threshold value of the stress intensity factor, Δ K th, as well as the plane strain fracture toughness, K Ic, of conventional engineering materials.
TL;DR: In this paper, the authors show that the bending stress can be reduced significantly by using asymmetric gear teeth and by shape optimizing the gear through changes made to the tool geometry, but the stress reductions found are not very sensitive to small design changes.
TL;DR: In this paper, X-ray computed tomography and metallography are applied to cast AlSi7Mg to characterize the size and morphology of casting pores, and the stress concentration due to the real 3D pore morphology is then investigated with finite element method.
TL;DR: The existence or non-existence of fatigue crack growth thresholds is of practical importance and scientific interest, as is knowledge of the stresses enabling crack formation at the surface and the interior of a specimen as discussed by the authors.
TL;DR: In this article, a lock-in thermographic technique was applied for analysis of stress concentration zones to specimens, made of the same steel, with central flat bottom hole, achieving good predictions.