The stress–strain response of nanocrystalline metals: A quantized crystal plasticity approach

This paper develops a finite element-based model with quantized crystal plasticity (QCP) to study distinctive features of nanocrystalline (nc) metal behavior, including an enhanced flow stress, extended plastic transition strain and propensity for strain localization. The QCP feature is motivated by molecular dynamics simulations of dislocation loop propagation across nc grains, showing that the grain-averaged plastic strain jumps by discrete amounts. Further, a simple geometric analysis suggests that the magnitude of the jumps is ∼1/grain size, thereby incorporating a grain size effect. QCP simulations of 1000-grain polycrystals can reproduce the unique experimental stress–strain features of nc metals, but only if the probability density distribution for a slip event increases abruptly at a threshold stress ∼1/grain size. Possible explanations for such a unique signature are discussed in terms of dislocation loop expansion conditions that become important in the nc limit.