CHARACTERIZATIONS OF SIZE EFFECT AND OVERALL MECHANICAL BEHAVIOR OF NANOCRYSTALLINE METALS

Abstract

A systematical study of size effects and mechanical behaviors for the nanocrystalline (nc) metals is performed. The grain boundary fracture process is considered and described by the mixed-mode interface cohesive model. The grain material is characterized by the conventional theory of strain gradient plasticity. In the present investigation, the effects of five important parameters on the overall mechanical behavior are studied systematically, which include the grain size, critical separation strength, energy release rate of interface separation, mixity of separation strength, as well as the mixity of separation energy release rate. A finite element method (FEM) covering the above characteristics within the grain and on the grain boundary is developed. The present results show that the overall strength and ductility of the nc metals strongly depend on the grain boundary features described by the mixed-mode cohesive interface model, and there is a competition of deformation of grain boundary with that of grain interior.