Research on serrated chip morphology for turning Ti6Al4V titanium alloy by considering damage evolution

The cutting process of titanium alloy Ti6Al4V is accompanied by high strain, high strain rate, and high-temperature thermal-force coupled deformation. A suitable constitutive model is critical for whether the finite element simulation can accurately reflect the elastic-plastic deformation behavior during the actual machining process. To solve the problem that the conventional Johnson-Cook constitutive model cannot accurately describe the material strain softening effect when turning Ti6Al4V, and the applicability of the model included in the material library of commercial ABAQUS finite element software is limited, a simulation research of turning Ti6Al4V based on the TANH constitutive model was conducted. Firstly, the secondary development subroutine of the TANH constitutive model is written by combining the traditional elastic-plastic theory, Newton's iterative method, and the damage evolution criterion based on equivalent plastic displacement and embedded into the two-dimensional orthogonal cutting finite element model. Then the material properties were defined using the J-C constitutive and self-programmed TANH constitutive models, respectively. The experimental data of cutting force and chip morphology were compared. The TANH constitutive model subroutine simulation results were more accurate than those using the J-C constitutive model. The average cutting force error was improved by 3.8 %. The error of chip serration degree was 17.4 %, indicating that the TANH constitutive model subroutine can better describe the material deformation behavior during cutting Ti6Al4V titanium alloy. In addition, the effects of TANH constitutive model parameters and damage evolution characteristics parameters on cutting simulation are also analyzed based on the constructed finite element model, which can provide a reference for improving the accuracy of metal cutting finite element simulation and exploring the mechanism of serrated chip formation.