A numerical study on criterion of void coalescence in ductile materials at different strain rates

Abstract
Spalling experiments show that the criterion of void coalescence can be characterized by a rate-independent parameter in some ductile metals and the criterion depends on relative spacing d defined as the distance between two voids divided by the radius of void. In this study, numerical analysis, based on two-dimensional finite element model, will be adopted to study the mechanism of this experimental phenomenon. Considering that hydrostatic stress is a dominant variable depicting the evolution of void nucleation, growth and coalescence in ductile materials, numerical simulations will be performed to obtain the relationship between the spacing d and the hydrostatic stress along the ligament between voids. The numerical results show that the distribution of the hydrostatic stress along matrix ligament is very sensitive to the change in the spacing , furthermore show that criteria of void nucleation and coalescence can be established on the threshold of local hydrostatic stress. Through analyzing these numerical results, it is concluded that the criterion of void coalescence under strain rate loads can be modeled by using a fixed relative spacing that is not sensitive to strain rates. Furthermore, based on the criterion proposed, a reasonable curve describing the relationship between failure strength of ductile materials at various strain rates is also obtained numerically.