Understanding and Modeling of Void Closure Mechanisms in Hot Metal Forming Processes: A Multiscale Approach

After casting, metal ingots may contain voids of different shapes and sizes which need to be eliminated in order to deliver a sound material. Hot metal forming processes are regularly used in the industry to reach this goal, but the calibration of these processes to get a complete closure of internal voids is still an issue. Existing models in the literature are either based on explicit full-field approaches or micro-analytical approaches. Both approaches have significant limitations regarding industrial issues. A new multiscale approach is thus proposed here. Based on realistic macroscopic loading conditions, extracted from the process scale, meso-scale simulations are conducted on a representative volume element containing an ellipsoidal void. The ellipsoidal void's shape factor and orientation with respect to the loading direction are considered in the void closure evolution law in addition to the classical mechanical parameters (equivalent plastic strain and stress triaxiality ratio). Several process and void morphological parameters are analyzed regarding void closure and the proposed mean field model is validated by comparison with explicit full field simulations of hot rolling.