Dynamic behaviours of a metalic material under high speed loading, such as in the case of high speed cutting, have a close relationship with the rate dependent microstructure evolution during plastic deformation. This fact is not taken into account in the conventional phenomenological modelling like Johnson-Cook (J-C) model. Gao-Zhang (G-Z) model, which is based on thermally activated dislocation motion theory, has thus been proposed to characterize the mechanical behaviours of material at high strain rates even beyond 10^4s^<-1>. This paper aims to compare the G-Z and J-C models over a wide range of strain rates. It was found that at a low strain rate (10^3s^<-1>-10^4s^<-1>), both the models give results close to the experimental; but that only the G-Z model makes correct predictions when the strain rate is greater than 10^4s^<-1>.
