Analysis of Micro-cutting Mechanisms using Continuum-Mechanics-Controlled Molecular Dynamics

1.基于分子动力学的分级耦合和Ⅱ型裂纹位移场的解析表达式，提出了一种研究单晶铜剪切变形原子尺度机制的模拟方法.模拟结果表明，存在一个临界状态，在该状态下，剪切变形由外力引起的性质转变为自发的性质。这一结果与单晶滑移变形理论和Piispanen卡片模型的描述相吻合.在临界状态之前的过程中，材料中的许多地方反复发生交叉滑移，每次都增加其幅度。这些横向滑移阻碍了宏观剪切滑移.宏观剪切滑移发生在由无序原子排列组成的区域从晶体的一端延伸到另一端的临界状态。所产生的宏观剪切发生在晶体中滑移面的方向上，因为上面提到的区域仅向这些方向发展。利用基于赫兹接触理论的解析位移，将受控分子动力学应用于微米级赫兹压痕.即使在没有预先存在缺陷的单晶硅中，也会在压痕过程中引发导致环形裂纹的缺陷。缺陷是由从试样中的非晶区域传递的动态力与试样表面上的静态拉伸应力的耦合而引发的。耦合力缓慢地使表面上的晶体结构松动并触发交叉滑移，这导致表面上的谷状缺陷。

1. A method of simulation to study atomistic scale mechanism existing in a shear deformation of a monocrystal copper has been proposed based on the hierarchical coupling of molecular dynamics and the analytical expression of the displacement field around a mode-II crack.2. The result of the simulation shows that there is a critical state at which a shear deformation changes its nature from that caused by an external force to that progressing by itself. This result agrees well with the description of the slip deformation theory of a monocrystal and/or the Piispanen card model for microcutting.3. During, the process before the critical state, cross slips occur in many places in a material repeatedly, each time increasing their magnitute. These cross slips block a macroscopic shear slip.4. A macroscopic shear slip occurs at the critical state where the area composed of disordered atomic arrangement has stretched from one end to the other end of a crystal. The resultant macroscopic shear occurs in the directions of the slip planes in a crystal because the area above mentioned develops only to those directions.5. Controlled molecular dynamics has been applied to micrometer-scale Hertz indentation using the analytical displacements derived on the basis of the Hertz contact theory.6. Defects that will cause a ring crack can be initiated during indentation even in monocrystalline silicon with no preexisting defect.7. Defects are initiated by the coupling of the dynamic force transmitted from an amorphous area in the specimen with the static tensile stress on the specimen surface. The coupled forces slowly loosen the crystal structure on the surface and triggers cross slips, which result in valley-like defects on the surface.