Determination of Johnson-Cook Model Parameters using Optimization Method

Thus far, the majority of Johnson-Cook (JC) model parameters have been determined by fitting of the experimental data. To achieve this, some values in each test, such as the strain rate and temperature, are assumed to be fixed. After numerous tests with various strain rates and temperatures, the flow stress is fitted as a function of the strain, strain rate, and temperature. However, the fixed test conditions may vary during the test. For example, the strain rate is not constant during a test if the test velocity is constant. In this paper, an optimization method is proposed to determine the model parameters. Tensile tests are performed for various strain rates. A finite element analysis is also conducted for the same conditions, and the model coefficients of the JC model are used as the design parameters. The error is defined as the discrepancy between the experimentally and numerically obtained stress-strain relations. This error is then used as a minimization objective. By this method, the model coefficients can be determined such that the numerically obtained stress-strain relation almost coincides with the experimentally obtained stress-strain relation. Moreover, a determination method of the material model coefficients by optimization is proposed.