Determination of Johnson-Cook plasticity model parameters for CoCrMo alloy
Lorcan O’Toole, Ravi Sankar Haridas, Rajiv S. Mishra, Fengzhou Fang
Abstract
Numerical modelling of Cobalt-Chromium-Molybdenum (CoCrMo) alloys allows for rapid and economical evaluation of machining processes, such as grinding, turning, and micro-milling. In order to develop a numerical model using Finite Element Method (FEM), it is necessary to implement a constitutive model of the workpiece material which achieves accurate results both under quasi-static and dynamic loading conditions, as well as at elevated temperatures. Subsequently, the Johnson-Cook (JC) parameters for the JC constitutive material model were experimentally determined and validated using FEM. This model was adopted due to its suitability for high strain rate applications, such as machining and high velocity impacts. In this article, quasi-static mechanical testing of ISO 5832–4 CoCrMo shear compression specimen (SCS) experiments were conducted at room temperature, and elevated temperatures (213 °C and 416 °C) to determine the strain effect and thermal softening effect, respectively. Dynamic mechanical testing at room temperature was then carried out using a Split-Hopkinson Pressure Bar (SHPB) apparatus at high strain rates (1000 – 3000 s−1) to determine the strain rate effect of the material. An FEM model was then successfully built in Abaqus CAE using the JC plasticity model, to simulate quasi-static and dynamic mechanical testing of the SCS and validate the determined experimental JC parameters for CoCrMo. The determined JC parameters were then optimised using the FEM numerical model, which are A, B, n, m, and C with values of 611.2 MPa, 775.1 MPa, 0.6, 2.1 and 0.05 respectively. The developed FEM model can be used to further optimise the JC parameters for even higher strain rate and temperature applications.