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Amir Hossein Shamdani - One of the best experts on this subject based on the ideXlab platform.
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An experimental-finite element analysis of the Plane Stress local torsion
Journal of Materials Science, 2013Co-Authors: Shahin Khoddam, Amir Hossein ShamdaniAbstract:The Plane Stress local torsion (PSLT) is an attractive method to strengthen the material in the areas of interest. A closed form solution of the problem is complex and an interpretation of the measured raw torque–twist data into the effective Stress and strain is not straightforward. These hinder the optimization and control of the technique. In this study, the PSLT test was performed using Ti-IF steel specimens and their torque–twist response and radial distortion were compared with those obtained from an elastic–plastic model of the PSLT developed by the commercial finite element software, ABAQUS. The resultant microstructure in the samples as a result of large local shear strains and the extent of deformation were studied using SEM and a grid distortion technique, respectively. Mechanical property changes after the PSLT processing were characterized in samples of different geometry using a dedicated formulation based on the similarity theory. The micro shear punch tests allowed characterizing the gradient of the reinforcement in the radial direction of the samples.
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microstructure and mechanical properties of if steel deformed during Plane Stress local torsion
Journal of Materials Science, 2012Co-Authors: Amir Hossein Shamdani, Shahin Khoddam, P F Thomson, Ali DehghanmanshadiAbstract:Mechanical joints are inherently vulnerable to failure because the presence of the joint hole causes a Stress concentration in the vicinity of the hole. The need for improvement of material strength around a fastener hole can be satisfied by severe plastic deformation (SPD) to produce ultrafine grains. The ultrafine grained (UFG) alloys produced by SPD processing possess higher strengths than their coarse-grained counterparts as a result of the reduced grain size. However, in some circumstances such as SPD processing of Al–Zn and Al–Mg alloys the decomposition of supersaturated solid solutions competes with the Hall–Petch effect and leads to a more pronounced softening of the material [1]. Another drawback of SPD processes is that they involve bulk deformation and large energy consumption [2]. It is therefore desirable to enhance the global behaviour of the material by limiting improvement of the material property by SPD to the location at which it is needed. Localized severe plastic deformation (LSPD) techniques, such as forward spiral extrusion [3] and friction stir processing [4], involve lower energy consumption. They modify the properties of materials locally and create a gradient of grain refinement, resulting in significant improvement in the mechanical properties of the processed samples. However, these techniques cannot be used for strengthening the material around fastener holes, and thus a method for improving the strength of material around the hole is needed. To reinforce the mechanical properties of material around a hole, the Plane Stress local torsion (PSLT) process, which involves a Plane Stress axi-symmetric torsional loading, is introduced. The PSLT takes advantage of large shearing strains induced around the intended hole position, through torsional deformation [5]. As a result, the material flows plastically within a thin annular zone around the fastener hole (AZFH). Because of the limited penetration of the flow localization zone into the material, a major proportion of deformation energy is consumed within the AZFH. The PSLT therefore consumes much less energy than do bulk grain refinement techniques.
J W Hancock - One of the best experts on this subject based on the ideXlab platform.
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elastic perfectly plastic asymptotic mixed mode crack tip fields in Plane Stress
International Journal of Solids and Structures, 2006Co-Authors: M Rahman, J W HancockAbstract:Elastic perfectly-plastic asymptotic Plane Stress crack tip fields have been constructed by assembling elastic, constant Stress and fan sectors under a complete range of mixed mode I/II states of loading. The angular Stress distributions are fully continuous, and do not contain the Stress discontinuities which have been a feature of many previously proposed solutions. The analytic solutions are verified by finite element solutions under contained yielding conditions. The structure of the elastic perfectly-plastic fields is compared to the structure of the asymptotic strain hardening fields.
Shahin Khoddam - One of the best experts on this subject based on the ideXlab platform.
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An experimental-finite element analysis of the Plane Stress local torsion
Journal of Materials Science, 2013Co-Authors: Shahin Khoddam, Amir Hossein ShamdaniAbstract:The Plane Stress local torsion (PSLT) is an attractive method to strengthen the material in the areas of interest. A closed form solution of the problem is complex and an interpretation of the measured raw torque–twist data into the effective Stress and strain is not straightforward. These hinder the optimization and control of the technique. In this study, the PSLT test was performed using Ti-IF steel specimens and their torque–twist response and radial distortion were compared with those obtained from an elastic–plastic model of the PSLT developed by the commercial finite element software, ABAQUS. The resultant microstructure in the samples as a result of large local shear strains and the extent of deformation were studied using SEM and a grid distortion technique, respectively. Mechanical property changes after the PSLT processing were characterized in samples of different geometry using a dedicated formulation based on the similarity theory. The micro shear punch tests allowed characterizing the gradient of the reinforcement in the radial direction of the samples.
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microstructure and mechanical properties of if steel deformed during Plane Stress local torsion
Journal of Materials Science, 2012Co-Authors: Amir Hossein Shamdani, Shahin Khoddam, P F Thomson, Ali DehghanmanshadiAbstract:Mechanical joints are inherently vulnerable to failure because the presence of the joint hole causes a Stress concentration in the vicinity of the hole. The need for improvement of material strength around a fastener hole can be satisfied by severe plastic deformation (SPD) to produce ultrafine grains. The ultrafine grained (UFG) alloys produced by SPD processing possess higher strengths than their coarse-grained counterparts as a result of the reduced grain size. However, in some circumstances such as SPD processing of Al–Zn and Al–Mg alloys the decomposition of supersaturated solid solutions competes with the Hall–Petch effect and leads to a more pronounced softening of the material [1]. Another drawback of SPD processes is that they involve bulk deformation and large energy consumption [2]. It is therefore desirable to enhance the global behaviour of the material by limiting improvement of the material property by SPD to the location at which it is needed. Localized severe plastic deformation (LSPD) techniques, such as forward spiral extrusion [3] and friction stir processing [4], involve lower energy consumption. They modify the properties of materials locally and create a gradient of grain refinement, resulting in significant improvement in the mechanical properties of the processed samples. However, these techniques cannot be used for strengthening the material around fastener holes, and thus a method for improving the strength of material around the hole is needed. To reinforce the mechanical properties of material around a hole, the Plane Stress local torsion (PSLT) process, which involves a Plane Stress axi-symmetric torsional loading, is introduced. The PSLT takes advantage of large shearing strains induced around the intended hole position, through torsional deformation [5]. As a result, the material flows plastically within a thin annular zone around the fastener hole (AZFH). Because of the limited penetration of the flow localization zone into the material, a major proportion of deformation energy is consumed within the AZFH. The PSLT therefore consumes much less energy than do bulk grain refinement techniques.
Paul F Joseph - One of the best experts on this subject based on the ideXlab platform.
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mixed mode fracture in power law hardening materials for Plane Stress
Journal of The Mechanics and Physics of Solids, 2020Co-Authors: Adrian Loghin, Paul F JosephAbstract:Abstract The classic nonlinear fracture problem of a fully yielded, mixed mode stationary crack in a power law hardening material for conditions of Plane Stress under small-scale yielding is reconsidered. It has been determined that two different asymptotic solutions are required to represent the full range of mixed mode loading. Neither asymptotic solution has the double root of the linear elastic counterpart, i.e., the nonlinear Plane Stress problem does not have a mixed mode asymptotic solution. The mode II dominant asymptotic solution consists of two terms. The leading term is the pure mode II HRR term, while the second term is symmetric with an eigenvalue slightly weaker than the HRR eigenvalue. This two-term solution applies to a relatively large range of mixed mode loading. The mode I dominant asymptotic solution also consists of a symmetric and an antisymmetric term with different eigenvalues, and has a limited range of applicability near mode I. The pure mode I HRR term is the symmetric term. Contrary to expected behavior based on energy considerations and experience with higher order solutions, the antisymmetric term has an eigenvalue that is stronger than the HRR eigenvalue. This antisymmetric asymptotic solution, which cannot exist without the presence of the mode I HRR term, depends on two small parameters: the distance from the crack tip, r, and the ratio of mode II to mode I loading, K2/K1. The interpretation is that this two-term asymptotic solution exists for small r in the limit as K2/K1 approaches zero. An unusual feature of the second term is that it does not exist in the limit as r approaches zero, and therefore from a mathematical point of view this term does not cause the J-integral to be infinite. The asymptotic results are confirmed with full-field finite element analysis by using the J2 deformation theory of plasticity using a computational domain that covers eleven decades of radial detail. This validates the asymptotic solutions and shows that a two-parameter fracture theory can be used very near mode I and near mode II. The transition from one asymptotic solution to the other, which is demonstrated to occur near mode I, gives rise to a loss of dominance of these two-term asymptotic solutions. The hardening exponent, “n”, plays an important role in the ranges of validity of the two asymptotic solutions. Finally, the asymptotic solutions are shown to agree with solutions from the non-hardening limit, and the comparisons are consistent with those of the full-field results.
M Rahman - One of the best experts on this subject based on the ideXlab platform.
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elastic perfectly plastic asymptotic mixed mode crack tip fields in Plane Stress
International Journal of Solids and Structures, 2006Co-Authors: M Rahman, J W HancockAbstract:Elastic perfectly-plastic asymptotic Plane Stress crack tip fields have been constructed by assembling elastic, constant Stress and fan sectors under a complete range of mixed mode I/II states of loading. The angular Stress distributions are fully continuous, and do not contain the Stress discontinuities which have been a feature of many previously proposed solutions. The analytic solutions are verified by finite element solutions under contained yielding conditions. The structure of the elastic perfectly-plastic fields is compared to the structure of the asymptotic strain hardening fields.
