An investigation of the combined size and rate effects on the mechanical responses of FCC metals

The molecular dynamics (MD) simulations are performed with single-crystal copper blocks under simple shear to investigate the size and strain rate effects on the mechanical responses of face-centered cubic (fcc) metals. It is shown that the yield stress decreases with the specimen size and increases with the strain rate. Based on the theory of dislocation nucleation, a modified power law is proposed to predict the scaled behavior of fcc metals, which agrees well with the numerical and experimental data ranging from nanoscale to macro-scale. In the MD simulations with different strain rates, a critical strain rate exists for each single-crystal copper block of given size, below which the yield stress is nearly insensitive to the strain rate. A hyper-surface is therefore formulated to describe the combined size and strain rate effects on the plastic yield strength of fcc metals. The preliminary results presented in this paper demonstrate the potential of the proposed simple procedure for engineering design at various spatial and temporal scales.