Limit of Ultra-high Strain Rates in Plastic Response of Metals

Abstract

Increase in strain rate requires an increase in density of lattice defects (dislocations) necessary for plastic relaxation of the increasing shear stress. Irradiation of metals by intensive femtosecond laser pulses creates compression waves with durations of tens of picoseconds and ultra-high strain rates up to an inverse nanosecond. At such strain rates, multiplication and motion of the initially existing dislocations become not enough for restriction of the shear stress, which can grow up to the limit of homogeneous nucleation of dislocation loops. We investigate regularities of the homogeneous nucleation of dislocations in metals with FCC, BCC and HCP lattices using the molecular dynamic simulations. Then we generalize these regularities in the form of continuum model of plasticity with nucleation and apply the model for simulation of shot compression pulses. It allows us to investigate the transition between the common mode of multiplication and the nucleation-controlled mode of plasticity.