Conventional engineering stress–strain curve could not accurately describe the local deformability of the tensile necking part because the strain is calculated by assuming that the tensile specimen was deformed uniformly. In this study, we used 3D optical measuring digital image correlation to systematically measure the full strain field and actual flow stress in the necking region of ultrafine-grained (UFG) Al. The post-necking elongation and strain hardening exponent of the UFG Al were measured as 80% and 0.10, slightly smaller than those of the coarse-grained Al (117% and 0.28), suggesting the high plastic deformability of the UFG Al under complex stress state. Microstructural studies revealed the shear and ductile fracture, numerous micro-shear bands, and elongated UFG grains in the UFG Al, which are controlled by cooperative grain boundary sliding and multiple dislocation slips.

中文翻译：

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用数字图像相关技术揭示复杂应力状态下超细晶Al的变形机理和塑性

传统的工程应力-应变曲线无法准确地描述拉伸颈缩部分的局部可变形性，因为应变是通过假设拉伸试样均匀变形来计算的。在这项研究中，我们使用3D光学测量数字图像相关性系统地测量了超细晶粒（UFG）Al颈缩区域的全应变场和实际流应力。UFG Al的颈后伸长率和应变硬化指数分别为80％和0.10，略小于粗晶Al（117％和0.28），表明UFG Al在复杂应力下具有很高的塑性变形能力。状态。显微组织研究表明，UFG Al中存在剪切断裂和延性断裂，大量微剪切带以及细长的UFG晶粒，