An evolution model for elliptic-cylindrical void in viscous materials considering the evolvements of void shape and orientation

Abstract

The evolution behavior of the internal voids influences the mechanical property of the materials significantly. Considering the void deformation and rotation, the evolution behavior of the elliptic-cylindrical void in power-law viscous materials was investigated by using the representative volume element (RVE) model. The rigid visco-plastic finite element (FE) method was applied to calculate the velocity field in the RVE under different loading conditions, and the instantaneous changing rate of the void radius and orientation were determined by evaluating the evolving of the void profiles at the instant. The calculated results show the deviatoric stress takes an important role in the void radius evolution, and the shear stress influences the change of the void orientation significantly. Based on the investigation, a void evolution model was established to relate the changing rates of the void radius and orientation to the void aspect ratio and the macroscopic stress/strain conditions. This model was incorporated into the FE code to predict the evolvements of void radius and orientation in each step of the deformation history. The predictions agree well with the results of the numerical simulations containing embedded void geometries in the mesh, which demonstrates that this model is capable to evaluate the void evolution behavior under large deformation. As an application, this model was used to predict the closure behavior of the void defects in the large ingot during the hot forging process.