6H-SiC脆性切削声发射响应的分子动力学研究

Acoustic Emission Response to Brittle Cutting of 6H-SiC Using Molecular Dynamics

摘要:

采用分子动力学方法研究了6H-SiC脆性切削的声发射响应。研究了原子尺度下6H-SiC的微变形和裂纹形核，同时对加工过程中的声发射源进行了识别，分析了其相应的声发射特征。结果表明，6H-SiC在77 nm切削深度下的脆性变形过程简单但不寻常；在6H-SiC切削过程中位错不会连续扩展，变形后的工件在刀具挤压作用下被分割成块，并由位错的快速扩展引发裂纹。对于影响声发射源特征的因素研究发现：初始压应力会导致声发射功率的下降；频率-能量分析中可见的3种声发射源分别是晶格振动、位错扩展和裂纹扩展。此外，在1 K温度下，2次明显的位错传播的声发射响应比晶格振动具有更高的频率特性，但总能量水平最低。相反地，裂纹扩展的声发射响应具有更为明显的频率分布特性和能量特性。

Abstract:

The acoustic emission (AE) response to brittle cutting of 6H-SiC was studied by molecular dynamics simulation. The micro-deformation and crack formation at atomic scale were analyzed. Furthermore, the AE sources in machining were distinguished and their corresponding AE characteristics were discussed. The results show that the brittle deformation process of 6H-SiC at cutting depth of 77 nm is simple but unusual. The deformation possesses discontinuous dislocation propagation and divides the deformed workpiece into pieces, and then the crack is initiated from a fast dislocation propagation. The compressive stress results in the decline of AE power initially. Three AE sources clustered in the frequency-energy analysis are lattice vibration, dislocation propagation and crack propagation. In addition, the AE response of two times of dislocation propagation shows a higher frequency characteristic than lattice vibration does at temperature of 1 K, with the lowest energy occupation in total. On the contrary, the AE response of crack propagation has apparent frequency and energy accumulation characteristics.