Multi-scale Computational Approach for Modelling Spallation at High Strain Rates in Single-Crystal Materials

Abstract

A multi-scale model has been developed to generate and validate spallation (dynamic fracture) model parameters for metallic single crystals. The model uses Molecular Dynamic (MD) simulations at the atomic scales to obtain parameters for a dynamic fracture model called the Nucleation and Growth (NAG) model. The parameters obtained from MD are then used to describe the nucleation and growth of voids in macroscopic hydrodynamic simulations of material impact and spallation. The spall strength and thickness have earlier been computed and compared with the experimental results for single crystal copper (Cu), Molybdenum (Mo) and Niobium (Nb). A good match with the experiments was obtained for Cu and Mo. The mismatch in case of Nb has been dealt in present work. The potential used in MD simulations for Nb has been replaced by a more sophisticated stiff potential and a more accurate Equation of State (EOS) has been used in the hydrodynamic simulations. The spall model parameters obtained this way result in a good match between hydrodynamic simulations and experiments. It is seen that the growth threshold for voids is the important factor in determining the spall strength of single crystals rather than the nucleation threshold for voids.