Dynamic Material Behavior Modeling Using Internal State Variable Plasticity and Its Application in Hard Machining Simulations

Abstract

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 semiempirical 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.

An experimental investigation of the behaviour of steels over large temperature and strain rate ranges

“…This penalizes numerical analysts who use phenomenological and very simple models (such as the Johnson-Cook model [17]) [26], the identification of which requires only a few tests [5,27] and that have a limited range of validity, which is more restrictive than the range of the rheological parameters observed in machining or forging operations. Also, it is possible to find in the literature different values of the same model parameters for identical materials [28,29]. Contradictions in the experimental results can also be found depending on the different experimental devices used to cover a wide range of rheological parameters.…”

A new material model for 2D numerical simulation of serrated chip formation when machining titanium alloy Ti–6Al–4V

“…No mathematical formulation has been proposed in these studies to take into account the strain-softening phenomenon. Guo et al [11] call this phenomenon adiabatic shearing and, contrary to Hua and Shivpuri [5], asserted that this effect is much more significant at high temperatures.…”

“…Different methods have been used to simulate the sawtooth chip formation in machining such as the pure deformation model without taking into account any fracture criterion [9,10] and many material laws such as the Johnson-Cook (JC) material model, the BaummannChiesa-Johnson (BCJ) law [11], Obikawa and Usui, Rhim and Oh [12,13] models, etc., coupled with a fracture criterion such as the JC damage law [14][15][16][17][18], deformation energy-based criterion [5,19], ductile fracture criterion [12]. Therefore, apart from pure deformation model [9,10], a fracture criterion is implemented in most numerical simulations to obtain the saw-tooth chip geometry [12,[14][15][16][17][18][19]].…”

“…Some attempts have been made to account for microstructural transformations of the material, the history of loading, the kinematic and isotropic hardening and the recrystallisation and recovery phenomena [11,13,21]. For example, an interesting phenomenon called strain softening has been introduced in the flow stress model in order to explain the saw-tooth chip formation [5].…”

MTS model based force prediction for machining of Ti-6Al-4V

“…In the shear zone, the material flow stress not only depends on the current states, the mechanical loading history also influence the material flow stress. A more physical based BCJ model was proposed by Guo et al (Guo, Wen et al 2006) to account for the kinematic hardening and dislocation effects in the adiabatic shear zone. However, the microstructure attributes are not directly calculated from the BCJ model.…”