Abstract We demonstrate that the conditions for plastic instability, which are traditionally obtained from solid mechanics considerations, also follow from linear stability analysis of the intrinsic evolution laws for the dislocation density. However, the strain rate sensitivity effect enters these conditions in a way different to the known Hart criterion. The necking strain predicted from the dislocation-based models shows good agreement with experimental data, highlighting the primary role played by dynamic dislocation recovery in the stability of uniform plastic flow. In particular, a sharp drop of ductility after plastic deformation to modest strains has been accounted for. A result of special interest with regard to ultrafine-grained materials is the predicted increase of their tensile ductility with increased strain imparted to them by prior severe plastic deformation. Importantly, ductility of such materials was found not to be governed primarily by increased strain rate sensitivity of the flow stress, as is commonly assumed in literature. Rather, it emerges as a result of a decrease in the rate of dynamic recovery of dislocations and the history of the pre-processing by severe plastic deformation.

中文翻译：

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是什么决定了超细晶粒金属的延展性？基于微观结构的缩颈不稳定性方法

摘要 我们证明了塑性不稳定的条件，传统上从固体力学考虑中获得，也遵循位错密度内在演化规律的线性稳定性分析。然而，应变率敏感性效应以不同于已知 Hart 准则的方式进入这些条件。从基于位错的模型预测的颈缩应变与实验数据非常吻合，突出了动态位错恢复在均匀塑性流动稳定性中的主要作用。特别是，塑性变形到适度应变后延展性急剧下降已被考虑在内。对超细晶粒材料特别感兴趣的一个结果是，随着先前严重塑性变形赋予它们的应变增加，它们的拉伸延展性预计会增加。重要的是，如文献中通常假设的那样，发现此类材料的延展性主要不受流动应力应变率敏感性增加的影响。相反，它的出现是位错动态恢复率降低和严重塑性变形预处理历史的结果。