Influence of Lode angle on modelling of void closure in hot metal forming processes

The presence of voids after casting processes of large metal workpieces requires the use of adapted hot metal forming processes to deliver sound products. Yet, there is at present a lack of knowledge regarding void closure mechanisms and there is no reliable model that can accurately predict void closure. The main aim of this work is to develop a highly accurate mean field model able to predict the evolution of the voids volume after each forming stage. This proposed model is accounting for both stress triaxiality ratio Tx and Lode angle θ in order to override the hypothesis of axisymmetric loading, which is generally considered in the existing models handling void closure in the literature. Based on an advanced multiscale approach, this model also accounts for voids shape and orientation. An optimization method, using a database of explicit RVE simulations, is developed in order to calibrate the new proposed model. Several void morphological parameters and an industrial range of mechanical loading parameters are analyzed regarding void closure. The proposed mean field model is validated by comparison with explicit full field simulations and with a recent pre-existing mean field model, named Cicaporo1 model hereafter (Saby et al., 2015 [19]). In comparison with Cicaporo1, the new model, named Cicaporo2 hereafter, uses less constants and is more accurate.