Dynamic material behavior modeling using internal state variable plasticity and its application in hard machining simulations

Work materials experience large strains, high strain rates, high temperatures, and complex loading histories in machining. The problem of how to accurately model dynamic material behavior, including the adiabatic effect is essential to understand a hard machining process. Several conventional constitutive models have often been used to approximate flow stress in machining analysis and simulations. The empirical or semi-empirical conventional models lack mechanisms for incorporating isotropic/kinematic hardening, recovery, and loading history effects. In this study, the material constants of AISI 52100 steel (62 HRc) were determined for both the Internal State Variable (ISV) plasticity model and the conventional Johnson-Cook (JC) model. The material constants were obtained by fitting the ISV and JC models using nonlinear least square methods to same baseline test data at different strains, strain rates, and temperatures. Both models are capable of modeling strain hardening and thermal softening phenomena. However. the ISV model can also accommodate the adiabatic and recovery effects, while the JC model is isothermal. Based on the method of design of experiment, FEA simulations and corresponding cutting tests were performed using the cutting tool with a 20 deg chamfer angle. The predicted chip morphology using the ISV model is consistent with the measured chips, while the JC model is not. The predicted temperatures can be qualitatively verified by the subsurface microstructure. In addition, the ISV model gave larger subsurface von Mises stress, plastic strain, and temperature compared with those by the JC model.