Spallation caused by the diffusion and agglomeration of vacancies in ductile metals

Abstract

In this work, the spallation processes in the ductile metals are systematically discussed in theory.By employing the phase transition theory and non-equilibrium transport theory, the spallation processes of ductile metals under dynamic loading may be mainly determined by the diffusion and agglomeration of generated vacancies. And through the theoretical analysis on the dynamic spallation processes, it is found that (1)the spallation critical behaviors exist; (2)both the damage evolution rate and the void growth velocity in the spallation planes are monitored by the grain sizes, the tensile strain rate and the temperature of the metal after shocking, i.e., a larger grain size and tensile strain rate and higher temperature will cause a larger damage evolution rate and void growth velocity; (3)there exists the characteristic size for the voids and the characteristic stress on the void boundary, which are dependent of vacancy excitation energy and the average volume occupied by the metal atom; (4)both the stress and temperature close to the void are high and may cause the melting, and they decrease quickly as the distance away from the void increases; (5)the plastic zone surrounding the formed voids is obtained and found to be governed by the characteristic stress; (6)the void growth in the spallation processes may arise from the agglomeration of vacancies rather than the emitting of dislocations. Most of the theoretical results are novel and obtained first. And they are found to be in agreement with the experimental results and the simulated results.