Influence of Void Coalescence by Direct Impingement on Spall Response of Polycrystalline Metal

It is well known that the spall response of ductile metal is sensitive to its initial microstructures. The present work is focused on the grain size effect and void coalescence during the damage evolution. According to the geometric relationship between voids derived from the porosity and voids size, a criterion for the onset of void coalescence was proposed. Then, we propose an extended damage formulation combining void coalescence by direct impingement, which can describe the increase of porosity rate in view of the reduction of void number and increase of void size after the void coalescence. Our simulations show that the pull-back velocity increases with grain size. Besides, the void coalescence will enhance the magnitude of the spall peak and the acceleration rate after the pull-back minimum. These numerical results are in qualitative agreement with the corresponding experiment data.