Strain gradient plasticity analysis of the strength and ductility of thin metallic films using an enriched interface model

摘要

The mechanical response of thin metallic films is simulated using a two-dimensional strain gradient plasticity finite-element model involving grain boundaries in order to investigate the effect of the thickness, grain shape and surface constraint on the strength, ductilityand back-stress. The grain boundaries and surface layers are modeled as initially impenetrable to dislocations while allowing for relax-ation at a critical stress level. The model captures the variation of the strength with grain size, film thickness, and with the presence or notof constraining surface layers, in agreement with experimental results on Al and Cu films. A decrease in the uniform elongation is pre-dicted with decreasing film thickness due to a loss of strain-hardening capacity and the possible presence of imperfections. These twoeffects dominate over the stabilizing contribution of the plastic strain gradients. Accounting for the relaxation of the interface constraint affects the magnitude of the back-stress as well as the drop in ductility.