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Simulation study on cavity growth in ductile metal materials under dynamic loading

Frontiers of physics 2013年第4期8卷 394-404页

作者： Ai-Guo Nu Guang-Cai Zhang Yang-Jun Ying Xi-Jun Yu National Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics P. O. Box 8009-26 Beijing 100088 China

cavity growth in ductile metal materials under dynamic loading is investigated via the material point method. Two typical cavity effects in the region subjected to rarefaction wave are identified：（i） part of material particles flow away from the cavity in comparison to the initial loading velocity, （ii） local regions show weaker negative or even positive pressures. Neighboring cavities interact via coalescence of isobaric contours. The growth of cavity under tension shows staged behaviors. After the initial slow stage, the volume and the dimensions in both the tensile and transverse directions show linear growth rate with time until the global tensile wave arrives at the upper free surface. It is interesting that the growth rate in the transverse direction is faster than that in the tensile direction. The volume growth rate linearly increases with the initial tensile velocity. After the global tensile wave passed the cavity, both the maximum particle velocity in the tensile direction and the maximum particle velocity in the opposite direction increase logarithmically with the initial tensile speed. The shock wave reflected back from the cavity and compression wave from the free surface induce the initial behavior of interracial instabilities such as the Richtmyer-Meshkov instability, which is mainly responsible for the irregularity in the morphology of deformed cavity. The local temperatures and distribution of hot spots are determined by the plastic work. Compared with the dynamical process, the heat conduction is much slower.

关键词： material point method cavity growth dynamic loading interracial instability

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High-strain-rate superplasticity in oxide ceramics:a trial of microstructural design based on creep-cavitation mechanisms

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Acta Metallurgica Sinica(English Letters) 2011年第3期24卷 195-204页

作者： Keijiro HIRAGA Byung-Nam KIM Koji MORITA Hidehiro YOSHIDA Yoshio SAKKA Masaaki TABUCHI National Institute for Materials Science

From existing knowledge about high-temperature cavitation mechanisms, necessary conditions were discussed for the suppression of cavitation failure during superplastic deformation in ceramic materials. The discussion, where special attention was placed on the relaxation of stress concentrations during grain-boundary sliding and cavity nucleation and growth, leaded to a conclusion that cavitation failure could be retarded by the simultaneous controlling of the initial grain size, the number of residual defects, diffusivity, dynamic grain growth and the homogeneity of microstructure. On the basis of this conclusion, high-strain-rate superplasticity （defined as superplasticity at a strain rate higher than 0.01 s^-1） could be intentionally attained in some oxide ceramic materials. This was shown in tetragonal zirconia and composites consisting of zirconia, a-alumina and a spinel phase.

关键词： Grain-boundary sliding Accommodation Stress concentration Diffusional relaxation cavity nucleation cavity growth Dynamic grain growth

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