LNM, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China.
School of Engineering Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
Phys Rev Lett. 2019 Feb 1;122(4):045501. doi: 10.1103/PhysRevLett.122.045501.
The motion of dislocations bridges the atomistic-scale deformation events with the macroscopic strength and ductility of crystalline metals. In particular, screw dislocations, whose Burgers vector is parallel to the line, play crucial roles on plastic flow. Nevertheless, their speed limit and its stress dependence remain controversial. Using large-scale molecular dynamics simulations, we reveal that full screw dislocations and twinning partial screw-type dislocations can glide steadily at the speed of shear wave velocity. Such a scenario is excluded in existing theories due to energy dissipation singularity. We conclude that both types of screw dislocations can move supersonically. We further observe that the motion of a screw dislocation also depends on the shear stress components, which do not contribute to the resolved shear stress (RSS), in contrast to the conventional Schmid's law, which states that the motion of a dislocation is determined by the RSS.
位错的运动将原子尺度的变形事件与晶体金属的宏观强度和延展性联系起来。特别是位错的柏氏矢量与位错线平行，它们在塑性流动中起着至关重要的作用。然而，它们的速度极限及其与应力的关系仍然存在争议。利用大规模分子动力学模拟，我们揭示出完全位错和孪生部分位错可以以剪切波速度稳定地滑移。由于能量耗散奇点，这种情况在现有的理论中是被排除的。我们的结论是，这两种类型的位错都可以超音速运动。我们进一步观察到，位错的运动也取决于切应力分量，这些切应力分量与 resolved shear stress (RSS) 无关，这与传统的 Schmid 定律相反，该定律指出位错的运动是由 RSS 决定的。
