Scale and strain-rate effects on single-crystal face-centered cubic metals were examined. Simple-shear molecular dynamics simulations were performed by applying the embedded atom method to a model of monocrystalline Ni comprising 100 to 100 million atoms and using strain-rates ranging from 107 to 1012/s. The simulation results were compared with experimental data obtained from interfacial force microscopy, nano-indentation, micro-indentation and small-scale torsion experiments. The data were found to scale with a geometrical length scale parameter which was defined by the ratio of sample volume to surface area. The simulations revealed that dislocations which nucleated at free surfaces were critical in causing micro-yield and macro-yield in pristine materials. An increase in flow stress, with increasing strain-rate, resulted from phonon drag. A simple model was developed in order to demonstrate this. Another aspect of the study revealed that plasticity, as reflected by the global average stress¯strain behavior, was characterized by 4 different length-scales: below 104 atoms, between 104 and 106 atoms, between 2 and 300μm and above 300μm.

Length Scale and Time Scale Effects on the Plastic Flow of FCC Metals. M.F.Horstemeyer, M.I.Baskes, S.J.Plimpton: Acta Materialia, 2001, 49[20], 4363-74