微尺寸单晶金属应变突变现象的随机有限元分析
A Stochastic Finite Element Simulation of Strain Burst in Single Crystalline Micropillars
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摘要: 微米尺寸单晶柱体的压缩实验发现,在其塑性变形过程中应变会发生突变,致使塑性流动呈现明显的间歇性. 通过随机有限元方法,分析了微米尺寸和块体镍单晶柱体在混合加载方式下的间歇性塑性流动行为. 同时,结合镍单晶柱体的实验数据以及基于经典晶体塑性理论的有限元方法,对近期新建立的理论模型进行了分析研究. 结果表明:新理论模型能够捕捉应变突变的发生;对于块体材料,新模型计算结果与常规晶体塑性有限元结果以及实验结果均比较吻合;当单晶柱体尺寸减小至几十μm左右时,新模型预测结果仍然能够与实验结果保持一致;微柱体的塑性流动是通过一系列的应变突变行为实现的.Abstract: Microcompression tests revealed that a sequence of strain bursts occurred during plastic deformation of single crystal micropillars, leading to obvious intermittent plastic flow behaviors. A stochastic finite element method was presented within crystal plasticity framework to describe the intermittent characteristics of crystal deformation under the hybrid loading mode (HLM) for both micron-sized pillars and bulk crystal. The theoretical model proposed recently was investigated by comparing the simulation results to the experimental observations and the conventional finite element methods using classic continuum models of plasticity. The results show that the new model could well capture the occurrence of the strain burst and describe a smooth macroscopic curve in the compression tests of macro-samples. In addition, as the diameters of micropillar decrease to tens of micrometers, the model could also reproduce the experimentally observed micropillars' intermittent plastic flow behaviors; the plastic flow of the micropillars proceeds through a sequence of intermittent burst slips.
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