Abstract The development of plastic strain localization in a stretching tantalum sheet in the form of necking under dynamic loading conditions was investigated by crystal plasticity simulation in the aim of evaluating the role of phenomena taking place at the scale of the material microstructure. Both equi-biaxial and plane strain stretching have been computed and two grain sizes have been considered. As expected from previous studies at the macroscopic scale, pronounced necking is observed for mean deformations much higher than the one for which a maximum force condition is met. Interestingly, a transition between “Mott-type” fragmentation process and instability-driven necking is observed as a function of the grain size. For large grains (i.e. low number of grains in the sheet thickness) and moderate strain rate, the localization of the plastic strain pattern emerging at the grain scale in the early stages, partly correlated with local slip resistance, seems to play the role of the weakest links in what resembles an obscuration controlled defect interaction process. A pronounced texture may strengthen the role of the local behavior on strain concentration by combining the effects of slip system Schmid factors and self and latent hardening. In contrast, for smaller grains, the memory of the initial strain pattern is much less clear and, for high strain rate, the final neck formation is preceded by the development of strain modulations of larger wavelengths and higher amplitudes than the initial grain-wise heterogeneity. These modulations could be interpreted as unstable perturbation modes of the structure.

中文翻译：

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用晶体塑性方法在拉伸片材中局部化塑性变形：最薄弱环节和不稳定模式控制过程之间的竞争

摘要 通过晶体塑性模拟研究了动态加载条件下颈缩形式的拉伸钽片中塑性应变局域化的发展，目的是评估在材料微观结构尺度上发生的现象的作用。计算了等双轴和平面应变拉伸，并考虑了两种晶粒尺寸。正如先前在宏观尺度上的研究所预期的那样，对于比满足最大力条件的平均变形高得多的平均变形，观察到明显的颈缩。有趣的是，观察到“莫特型”碎裂过程和不稳定驱动的颈缩之间的转变是晶粒尺寸的函数。对于大晶粒（即板材厚度中的晶粒数量少）和中等应变速率，早期在晶粒尺度上出现的塑性应变模式的局部化，部分与局部抗滑性相关，似乎在类似于遮光控制的缺陷相互作用过程中发挥了最薄弱环节的作用。通过结合滑移系统施密特因子和自硬化和潜在硬化的影响，明显的纹理可以加强局部行为对应变集中的作用。相比之下，对于较小的晶粒，初始应变模式的记忆不太清楚，并且对于高应变率，最终颈部形成之前是比初始晶粒不均匀性更大波长和更高振幅的应变调制的发展. 这些调制可以解释为结构的不稳定扰动模式。