Hypo- and hyper-inelasticity applied to modeling of compacted graphite iron machining simulations

In the present paper we are concerned with constitutive modeling and validation of the thermomechanically coupled Compacted Graphite Iron (CGI) machining problem. Particular emphasis is placed on the significance of the choice of different hypo-inelastic models induced by different objective stress rate formulations. We also relate to a thermodynamically consistent hyper-elastic–inelastic formulation based on multiplicative decomposition of the deformation gradient. The consequently induced tangent material behavior is then derived in the spatial setting in terms of the Oldroyd stress rate, and it is compared to the hypo–formulations. The Johnson–Cook (JC) model is taken as the main prototype for the modeling of isotropic hardening, strain rate and temperature dependencies, which is considered reframed within the Perzyna visco-plasticity framework, thereby highlighting the quasistatic and rate dependent properties of the model. The different models are compared both on the material point level (simple shear and uniaxial tensile–compressive tests) and on the structural level (FE-analysis of a 2D shear test and in representative CGI-machining simulations) and the resulting mechanical isothermal behavior obtained from the different ways of establishing the objective stress rate are surprisingly similar. Based on the results obtained a hypo-inelastic formulation based on a modified Oldroyd stress rate is proposed due to its link to thermo-mechanical consistency and relative computational efficiency.