Model-driven determination of Johnson-Cook material constants using temperature and force measurements

In this paper, an original approach was presented to identify the Johnson-Cook material constants (J-C constants). The Johnson-Cook model is one of the simplest models to describe the material behavior in machining. The five J-C constants are related to strain hardening effect, stain rate hardening effect, and thermal softening effect. The approach was developed based on a chip formation model in orthogonal cutting and Johnson-Cook model. This paper used process variables including the temperature at the primary shear zone, the temperature of the chip, cutting conditions, and the estimations of the material constants as inputs. The machining forces were calculated with the chip formation model using all estimated material constants that were being changed within intervals of 50% of the references. The five J-C constants were determined by searching minimum differences between the calculated forces and measured forces under each cutting condition. The workpiece material properties such as thermal conductivity, specific heat, and melting temperature were not required because of the measurements of the temperatures. The proposed approach has advantages of low experimental cost, low time cost, less experimental complexity, and less mathematical complexity. The determined J-C constants of AISI 1045 steel and 42CrMo4 alloy were compared to their J-C constants from Split-Hopkinson Pressure Bar (SHPB) tests respectively. Close agreements were found for both materials.