多晶锗塑性切削机制和力学特性的仿真研究

为探究多晶锗纳米尺度的塑性切削机制和力学特性,采用分子动力学方法(MD)模拟金刚石刀具纳米切削多晶锗过程,对材料的晶体结构,位错分布及演变,应力传导和切削力波动规律进行详细分析;并研究不同切削参数对加工过程的影响。结果表明:晶体结构的非晶转变和晶界与晶体滑移,位错等缺陷相互作用,导致切削力周期性波动;切削过程中非晶体区沿晶界扩展,但晶界阻碍非晶体区跨晶界扩展;位错仅存在晶界附近,而位错类型和数量随晶界处的原子运动和破坏程度发生改变,材料塑性去除主要由晶粒内部的非晶转变和晶界的位错运动所致;晶界的等效应力比晶粒大,分布和传导方向与非晶体原子的一致;切削速度增加使切削区温度上升、应力和切削力减小;切削深度增加易使缺陷原子数量上升,位错线长度降低。通过Diamond结构多晶的研究结果证实多晶锗切削仿真的正确性。

Simulation on ductile cutting mechanism and mechanical properties of polycrystalline germanium

In order to explore the plastic cutting mechanism and mechanical properties of polycrystalline germanium(P-Ge) on nanoscale,the molecular dynamics method was used to simulate the nano-cutting process of P-Ge with diamond tool. The crystal structure,dislocation distribution and evolution,stress conduction and cutting force fluctuation were analyzed in detail, and the influence of different cutting parameters on the machining process was studied. Results show that:Amorphous transformation of the crystal structure and interaction between grain boundaries and defects such as crystal slip and dislocation lead to periodic fluctuation of cutting force. During the cutting process,the amorphous region easily spreads along the grain boundary, but the grain boundary hinders the expansion of the amorphous region across the grain boundary. Dislocations only exist near the grain boundary,and the type and number of dislocations will change with the atomic movement and damage degree at the grain boundaries. Therefore,the plastic removal of the material is mainly induced by the amorphous transformation inside the grain and the dislocation movement of the grain boundary. In addition,the equivalent stress of the grain boundary is larger than that of the grain, and its distribution and conduction direction are consistent with those of the amorphous atom. With the increase of cutting speed, the temperature of cutting zone increases,the stress and cutting force decrease. The number of defective atoms increases with the cutting depth,but the length of the dislocation line decreases. The correctness of P-Ge cutting simulation was confirmed by the research results of diamond structure polycrystalline.