Papers by Keyword: Strain Rate Sensitivity (SRS)

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Authors: Yannick Champion, Cyril Langlois, Sandrine Guérin, Sylvie Lartigue-Korinek, P. Langlois, Martin J. Hÿtch
Abstract: Based on the Taylor theory, a critical length scale is defined as the minimum dislocations cell size obtained at the maximum work-hardening for metals and alloys. When grain size is smaller than this length scale, corresponding also to a critical dislocation mean free path, new behaviours occur; such as ductility and strength, near perfect elasto-plasticity, high strain-rate sensitivity. Bulk samples are fabricated from Cu nanopowders (particle size 50 nm) by powder metallurgy techniques. The final grain size is comprised between the critical mean free path, evaluated at 130 nm and the size where transition to the so-called nano regime occurs (when unit dislocation no longer exists below 30 nm for Cu). Tensile tests are carried and microstructural analysis are performed before and after deformation.
Authors: G. Fribourg, Alexis Deschamps, Yves Bréchet
Abstract: This paper presents a detailed study of the microstructure and mechanical properties of AA7449 alloy during the two step heat treatment leading to the industrial T7651 temper. It is first shown that reproducing the heat treatment without a deformation step as used in the T7651 industrial temper leads to 2-fold decrease of the precipitation kinetics due to the absence of dislocations, while the resulting mechanical properties (if this change in kinetics is accounted for) are very similar. The work hardening rate is shown to strongly evolve during the heat treatment, and this evolution has been correlated to the evolution of microstructure using a Kocks-Mecking-Estrin analysis. Finally, an analysis in terms of activation volume of the strain rate sensitivity allows for the determination of the dislocation / precipitate interaction in the overaged temper.
Authors: Sheng En Hsu, M.T. Yeh, I Chien Hsu, Sam K. Chang, Yong Chao Dai, J.Y. Wang
Authors: Zane Wyatt, Sreeramamurthy Ankem
Abstract: Within the past decade, it has been shown that twinning in α, β, and α + β titanium alloys can occur at speeds much lower than the speed of sound by many orders of magnitude. This is related to the twinning deformation mechanisms controlled by the diffusion of oxygen as compared to simply a shear process. Very recent developments, such as strain-rate effects on twinning, support a recent hypothesis that the twinning in these materials is controlled by a slow diffusion process, resulting in time-dependent twinning. These recent developments, along with the ramifications of the findings will be outlined in this article.
Authors: Terence G. Langdon
Abstract: The origin of true laboratory-scale superplasticity may be traced to a publication appearing seventy-five years ago in 1934. This overview examines the subsequent major developments in obtaining a fundamental understanding of superplastic flow and then looks to the future to summarize very new developments that provide the potential for invigorating the field of superplastic research.
Authors: Lu Li, Fang Wang
Abstract: Backward extrusion process of aluminum-alloy wheel forging is analyzed by the finite element method. The influence of punch speed and forming temperature on the backward extrusion height of 6061 aluminum alloy wheel is discussed. Studies show that the backward extrusion height increases with increasing forming temperature, and with decreasing punch speed at the same deformation load. It is indicated that when the ranges of forming temperature is from 450 to 500°C and the punch speed is 0.5-1 mm/s, the aluminum alloy wheel has the optimal forming quality. The analysis and conclusions in this paper are helpful in developing the hot extrusion technology specification of 6061 aluminum alloy.
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