Modeling of Thermally Induced Material Softening in Uncoupled Constitutive Equations for the Application in Metal Cutting Simulations

Thermally induced softening of workpiece material during chip formation has a significant impact on the cutting process in terms of forces, chip formation and related results like stresses at the cutting tool. For metal cutting simulations it is therefore of importance to exactly describe the softening behavior of the specific workpiece material to get accurate simulation results. Widely used uncoupled constitutive equations treat the influence of the thermal and mechanical loads on the flow stress as separate, independent functions. This allows for an investigation of the strain, strain rate and temperature dependent effects on the material in separated experiments. By use of hot compression tests thermal softening curves of AISI 1045 steel are developed. The data serves as basis for the comparison of five different preselected mathematical functions suitable for the description of the thermal softening effects. The comparison discusses the differences between the models in terms of the goodness of the fit and the amount of independent material parameters. Based on the comparison a promising softening model is chosen and integrated into a commercial FE code. The simulation results with this modified model and the widely used Johnson-Cook model are compared to experimental results from linear-orthogonal cutting tests for several cutting conditions. The results of the modified model show a positive effect on the simulation results in terms of the chip thickness.