A Unified Approach to Modeling Material Behavior and Microstructure Evolution in Machining of OFHC Copper

At a fundamental level, the thermo-mechanical response of metals in dynamic deformation processes such as machining is governed by dislocation processes and associated microstructure evolution. However, the most commonly used material constitutive models in machining are phenomenological (e.g. Johnson-Cook) or semi-phenomenological (e.g. Zerilli-Armstrong) and do not explicitly account for the dependence of material flow stress on dislocation and microstructure evolution processes in a unified manner. The fidelity of machining simulation models is dependent on the amount of micro-scale physics captured in the development of the material constitutive law, microstructure evolution law(s), and the unifying scheme integrating microstructure evolution into the constitutive law. This paper presents a unified material modeling approach that explicitly accounts for dislocation and microstructure evolution processes underlying the finite deformation process. The corresponding evolution laws are formulated and integrated into the constitutive model, which is derived from thermal activation theory and is an additive decomposition of athermal and thermal components of flow stress representing the effects of long-range and short-range obstacles to dislocation motion, respectively. The unified scheme is implemented as a user-defined subroutine in the AdvantEdge™ software (Third Wave Systems LLC) and used to simulate the orthogonal cutting of OFHC copper.