The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Huajian Gao - One of the best experts on this subject based on the ideXlab platform.
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Is Stress Concentration relevant for nanocrystalline metals
Nano letters, 2011Co-Authors: Sandeep Kumar, Aman Haque, Huajian GaoAbstract:Classical fracture mechanics as well as modern strain gradient plasticity theories assert the existence of Stress Concentration (or strain gradient) ahead of a notch tip, albeit somewhat relaxed in ductile materials. In this study, we present experimental evidence of extreme Stress homogenization in nanocrystalline metals that result in immeasurable amount of Stress Concentration at a notch tip. We performed in situ uniaxial tension tests of 80 nm thick (50 nm average grain size) freestanding, single edge notched aluminum specimens inside a transmission electron microscope. The theoretical Stress Concentration for the given notch geometry was as high as 8, yet electron diffraction patterns unambiguously showed absence of any measurable Stress Concentration at the notch tip. To identify possible mechanisms behind such an anomaly, we performed molecular dynamics simulations on scaled down samples. Extensive grain rotation driven by grain boundary diffusion, exemplified by an Ashby-Verrall type of grain switching process, was observed at the notch tip to relieve Stress Concentration. We conclude that in the absence of dislocations, grain realignment or rotation may have played a critical role in accommodating externally applied strain and neutralizes any Stress Concentration during the process.
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is Stress Concentration relevant for nanocrystalline metals
Nano Letters, 2011Co-Authors: Sandeep Kumar, Aman Haque, Huajian GaoAbstract:Classical fracture mechanics as well as modern strain gradient plasticity theories assert the existence of Stress Concentration (or strain gradient) ahead of a notch tip, albeit somewhat relaxed in ductile materials. In this study, we present experimental evidence of extreme Stress homogenization in nanocrystalline metals that result in immeasurable amount of Stress Concentration at a notch tip. We performed in situ uniaxial tension tests of 80 nm thick (50 nm average grain size) freestanding, single edge notched aluminum specimens inside a transmission electron microscope. The theoretical Stress Concentration for the given notch geometry was as high as 8, yet electron diffraction patterns unambiguously showed absence of any measurable Stress Concentration at the notch tip. To identify possible mechanisms behind such an anomaly, we performed molecular dynamics simulations on scaled down samples. Extensive grain rotation driven by grain boundary diffusion, exemplified by an Ashby–Verrall type of grain swit...
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Stress Concentration at slightly undulating surfaces
Journal of the Mechanics and Physics of Solids, 1991Co-Authors: Huajian GaoAbstract:Abstract T his paper presents a first-order perturbation analysis of the Stress Concentration effects caused by slightly undulating surfaces. The perturbation approach that we use treats the undulating surfaces as being perturbed from a reference state in which the surface is perfectly flat. The magnitude of the perturbation is assumed to be sufficiently small compared to other length scales of the bulk material so that a half-plane model can be used for simplification. First-order-accurate perturbation solutions have been derived for the Stress distribution along a sinusoidally wavy surface and for the attenuation of the Stress Concentration away from the undulating surface. The interactions among different surface perturbation waves are investigated by comparing the result of Stress Concentration factor at the trough of a single wave perturbation along an otherwise flat surface to that for periodically wavy surface. We also examine some of the 3-D effects by using the perturbation algorithm to calculate the Stress Concentration at undulating surfaces of elastic half-spaces. In all cases, it is found that wavy surfaces can magnify the bulk Stress easily by a factor of 2 or 3 when the surface profile does not deviate substantially from flatness. This Stress Concentration effect is significant especially for already highly Stressed heteroepitaxial semiconductor thin films, suggesting that the surface morphology of the film surfaces can play an important role in nucleating dislocations and crack-like surface flaws before the bulk Stress reaches a critical level.
Sandeep Kumar - One of the best experts on this subject based on the ideXlab platform.
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Is Stress Concentration relevant for nanocrystalline metals
Nano letters, 2011Co-Authors: Sandeep Kumar, Aman Haque, Huajian GaoAbstract:Classical fracture mechanics as well as modern strain gradient plasticity theories assert the existence of Stress Concentration (or strain gradient) ahead of a notch tip, albeit somewhat relaxed in ductile materials. In this study, we present experimental evidence of extreme Stress homogenization in nanocrystalline metals that result in immeasurable amount of Stress Concentration at a notch tip. We performed in situ uniaxial tension tests of 80 nm thick (50 nm average grain size) freestanding, single edge notched aluminum specimens inside a transmission electron microscope. The theoretical Stress Concentration for the given notch geometry was as high as 8, yet electron diffraction patterns unambiguously showed absence of any measurable Stress Concentration at the notch tip. To identify possible mechanisms behind such an anomaly, we performed molecular dynamics simulations on scaled down samples. Extensive grain rotation driven by grain boundary diffusion, exemplified by an Ashby-Verrall type of grain switching process, was observed at the notch tip to relieve Stress Concentration. We conclude that in the absence of dislocations, grain realignment or rotation may have played a critical role in accommodating externally applied strain and neutralizes any Stress Concentration during the process.
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is Stress Concentration relevant for nanocrystalline metals
Nano Letters, 2011Co-Authors: Sandeep Kumar, Aman Haque, Huajian GaoAbstract:Classical fracture mechanics as well as modern strain gradient plasticity theories assert the existence of Stress Concentration (or strain gradient) ahead of a notch tip, albeit somewhat relaxed in ductile materials. In this study, we present experimental evidence of extreme Stress homogenization in nanocrystalline metals that result in immeasurable amount of Stress Concentration at a notch tip. We performed in situ uniaxial tension tests of 80 nm thick (50 nm average grain size) freestanding, single edge notched aluminum specimens inside a transmission electron microscope. The theoretical Stress Concentration for the given notch geometry was as high as 8, yet electron diffraction patterns unambiguously showed absence of any measurable Stress Concentration at the notch tip. To identify possible mechanisms behind such an anomaly, we performed molecular dynamics simulations on scaled down samples. Extensive grain rotation driven by grain boundary diffusion, exemplified by an Ashby–Verrall type of grain swit...
Aman Haque - One of the best experts on this subject based on the ideXlab platform.
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Is Stress Concentration relevant for nanocrystalline metals
Nano letters, 2011Co-Authors: Sandeep Kumar, Aman Haque, Huajian GaoAbstract:Classical fracture mechanics as well as modern strain gradient plasticity theories assert the existence of Stress Concentration (or strain gradient) ahead of a notch tip, albeit somewhat relaxed in ductile materials. In this study, we present experimental evidence of extreme Stress homogenization in nanocrystalline metals that result in immeasurable amount of Stress Concentration at a notch tip. We performed in situ uniaxial tension tests of 80 nm thick (50 nm average grain size) freestanding, single edge notched aluminum specimens inside a transmission electron microscope. The theoretical Stress Concentration for the given notch geometry was as high as 8, yet electron diffraction patterns unambiguously showed absence of any measurable Stress Concentration at the notch tip. To identify possible mechanisms behind such an anomaly, we performed molecular dynamics simulations on scaled down samples. Extensive grain rotation driven by grain boundary diffusion, exemplified by an Ashby-Verrall type of grain switching process, was observed at the notch tip to relieve Stress Concentration. We conclude that in the absence of dislocations, grain realignment or rotation may have played a critical role in accommodating externally applied strain and neutralizes any Stress Concentration during the process.
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is Stress Concentration relevant for nanocrystalline metals
Nano Letters, 2011Co-Authors: Sandeep Kumar, Aman Haque, Huajian GaoAbstract:Classical fracture mechanics as well as modern strain gradient plasticity theories assert the existence of Stress Concentration (or strain gradient) ahead of a notch tip, albeit somewhat relaxed in ductile materials. In this study, we present experimental evidence of extreme Stress homogenization in nanocrystalline metals that result in immeasurable amount of Stress Concentration at a notch tip. We performed in situ uniaxial tension tests of 80 nm thick (50 nm average grain size) freestanding, single edge notched aluminum specimens inside a transmission electron microscope. The theoretical Stress Concentration for the given notch geometry was as high as 8, yet electron diffraction patterns unambiguously showed absence of any measurable Stress Concentration at the notch tip. To identify possible mechanisms behind such an anomaly, we performed molecular dynamics simulations on scaled down samples. Extensive grain rotation driven by grain boundary diffusion, exemplified by an Ashby–Verrall type of grain swit...
C.m. Wang - One of the best experts on this subject based on the ideXlab platform.
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A practical method to estimate the Stress Concentration of notches
International Journal of Fatigue, 1994Co-Authors: Chow-shing Shin, K.c. Man, C.m. WangAbstract:Abstract Knowledge of Stress Concentration factor and Stress distribution of notches is important to engineers engaged in the design or fracture life assessment of engineering components. In a previous paper, it was pointed out that knowledge of the relevant solutions for Stress analysis of cracks may be used to advantage to estimate the Stress Concentration factor and Stress distribution ahead of a notch via the Creager-Paris Stress field solution for notches. It was shown that this method accurately predicted the Stress Concentration factors and notch-tip Stress distribution in a number of double- and single-edge-notched plates. Finite-element Stress analysis results for plates with multiple notches are recently available. Stress Concentration factors for a variety of notch configurations have also been collected from relevant handbooks. In the current work, a comparison was made between the finite element results and handbook solutions with estimates from fracture mechanics data, and reasonable agreement was found. A number of approximate expressions have been proposed to estimate notch-tip Stress distributions. These estimates were also compared with finite element results, and a guideline is suggested for the choice of approximate expressions to ensure maximum accuracy.
Wen S. Chan - One of the best experts on this subject based on the ideXlab platform.
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Stress Concentration reduction in a plate with a hole using piezoceramic layers
Smart Materials and Structures, 1994Co-Authors: D K Shah, Shiv P. Joshi, Wen S. ChanAbstract:The use of piezoelectric patches to reduce Stress Concentration around a hole in an isotropic plate is investigated. The objective of the research is to reduce Stress Concentration in the vicinity of the hole without exceeding the reduced Stress Concentration value anywhere else in the plate. Finite-element analysis is performed on a finite plate with a central circular hole under far-field applied tensile load. Piezoelectric patch placement in the tensile and compressive regions around the hole are considered. It is found that application of an electric field to produce inplane expansion of the piezoelectric patch can alter the compressive zone in such a way that it results in reduction of Stress Concentration in the tensile zone. For the given geometry, a one-third reduction in Stress Concentration can be achieved. The results demonstrate the feasibility of reducing Stress Concentration around a hole by active piezoelectric patches.
