Mesoscale Modeling of 3-d Voids Evolution in Large Ingot during Multi-Hit Deformation

Abstract

Due to non-uniform solidification, internal void defects (like porosity and shrinkage) often exist in the large ingot and behave as sources of damage in the materials performance. Multi-stage forging process, like stretching swaging and upsetting, is often used to eliminate the voids. However, the material with voids inside often undertakes loading from different direction in different forging stage, which may results in closure-reopen effects of the voids. Therefore, modeling the 3-d deformation behavior of the voids is of great significance in multi-hit deformation of the ingot. A 3-d voids evolution modeling is presented by using mesoscale representative volume element (RVE). In the RVE, the deformation of the void is expressed as a function of the remote stress, remote effective strain-rate and the void aspect parameter. The coefficients of the model are determined from the finite element (FE) calculations of the RVE. In this model, the change of void radius is influenced by the mean stress and the deviatoric stress in the corresponding direction. The relationship between the void radius deformation rate and the void aspect parameter in the corresponding direction are heuristically established as inverse proportional functions. As a consequence, the volume and shape of the voids can be obtained by integrating the material deformation history. By combining the void evolution model with macroscopic finite element simulation of the multi-stage forging process, the voids evolution can be efficiently predicted and the condition for closing the voids can be obtained. This model is validated by laboratory experiments and applied in industry.