Department of Aerospace Engineering, Iowa State University, Ames, IA 50011, USA.
Proc Natl Acad Sci U S A. 2012 Aug 14;109(33):13204-7. doi: 10.1073/pnas.1203285109. Epub 2012 Jul 30.
Generation and motion of dislocations and twinning are the main mechanisms of plastic deformation. A new mechanism of plastic deformation and stress relaxation at high strain rates (10(9)-10(12) s(-1)) is proposed, under which virtual melting occurs at temperatures much below the melting temperature. Virtual melting is predicted using a developed, advanced thermodynamic approach and confirmed by large-scale molecular dynamics simulations of shockwave propagation and quasi-isentropic compression in both single and defective crystals. The work and energy of nonhydrostatic stresses at the shock front drastically increase the driving force for melting from the uniaxially compressed solid state, reducing the melting temperature by 80% or 4,000 K. After melting, the relaxation of nonhydrostatic stresses leads to an undercooled and unstable liquid, which recrystallizes in picosecond time scales to a hydrostatically loaded crystal. Characteristic parameters for virtual melting are determined from molecular dynamics simulations of Cu shocked/compressed along the 〈110〉 and 〈111〉 directions and Al shocked/compressed along the 〈110〉 direction.
位错和孪晶的产生和运动是塑性变形的主要机制。在高应变速率（10(9)-10(12) s(-1)）下，提出了一种新的塑性变形和应力松弛机制，在这种机制下，虚拟熔化发生在远低于熔点的温度下。使用开发的先进热力学方法预测了虚拟熔化，并通过冲击波传播和单晶体和缺陷晶体准等熵压缩的大规模分子动力学模拟得到了证实。在冲击波前缘的非静水压力的功和能量极大地增加了从单轴压缩固态熔化的驱动力，使熔化温度降低了 80%或 4000 K。熔化后，非静水压力的松弛导致过冷和不稳定的液体，在皮秒时间尺度内重新结晶为承受静水压力的晶体。从沿着〈110〉和〈111〉方向冲击/压缩的 Cu 和沿着〈110〉方向冲击/压缩的 Al 的分子动力学模拟中确定了虚拟熔化的特征参数。
