It was noted that the grain-size effect upon the yield strength and strain hardening of thin film at sub-micron and nanometer scales was closely related to the interactions between grain boundaries and dislocation. Based upon higher-order gradient plasticity theory, the size-effect of multi-grain thin film arising from the grain boundary density under tensile stress was systematically investigated. The developed formulations employing dislocation density and slip resistance were implemented into the finite element program, in which the grain boundary was treated as an interface impenetrable by dislocations. The numerical simulation results reasonably showed that plastic hardening rate and yield strength were linear to the grain boundary density of multi-grain thin film. The aspect ratio of grain size and orientation of slip system had a distinct influence on the grain plastic properties. The research of slip system including homogeneous and nonhomogeneous distribution patterns revealed that the hardening effect of low-angle slip system was greater than that of high-angle slip system. The results agreed well with the experimentally measured data and the solutions by discrete dislocation dynamics simulation.

The Study of Grain Boundary Density Effect on Multi-Grain Thin Film Under Tension. X.C.Zhao, Z.L.Liu, Z.Zhuang, X.Liu, Y.Gao: Computational Materials Science, 2012, 53[1], 175-86