Determination of the constants of material models by optimization and numerical simulation

Abstract
Material models are essential requirements in numerical simulation of mechanical behavior of materials in particular at high strain rates and at elevated temperatures. The models involve a number of constants to be determined normally by experiment. In this investigation a combined experimental, numerical and optimization technique is employed to obtain the constants of Johnson-Cook model in tension. The experiments are conducted on a high rate tensile testing apparatus called “Flying Wedge”. The apparatus is also simulated using finite element method. The experiments are simulated using the same specimen geometries and the apparatus. The differences between the deformed shapes of the specimens from the experiments and the numerical simulations are taken as the objective function for optimization purposes. The simulations of the tensile tests are repeated for various values of the material constants which are the variable vector in optimization. The optimum constants are then obtained using generic algorithm. The results verified by a number of measures prove to be very encouraging. The results also suggest that the approach given in this work can substitute expensive instrumentations usually used for capturing stress-strain curves at high strain rates and elevated temperature.