Overall mechanical behavior of nanocrystalline materials accompanied by damage evolution on grain boundaries

In the present research, overall mechanical behaviors of the nanocrystalline materials considering the grain boundary damage evolutions are investigated systematically. A mixed-mode cohesive interface model is used to describe the mixed deformation and fracture process of grain boundaries. Based on the mixed-mode cohesive interface model, the grain boundary damage and damage evolution are defined and characterized. In order to describe the size effect, the strain gradient plasticity theory is used for grain materials. In the present results, the overall stress–strain relations and the corresponding damage evolution curves are obtained as functions of several independent parameters, such as the mixed separation strength, the mixed critical energy release rate, grain size, Young’s modulus as well as strain hardening exponent. The present results show that both the overall strength and ductility of the nanocrystalline materials are closely dependent on the grain boundary strength and the damage evolution behaviors. By means of the damage evolution relations, the features of the overall stress–strain curves can be clearly interpreted.