Validation And Optimization Of Dynamic Constitutive Model Constants With Taylor Test

Obtaining and validating constants for dynamic material strength models is an issue frequently encountered in computer simulations of engineering applications under impact and explosion loads. The application of Taylor test on this issue is studied, and a method for validating and optimizing constants for dynamic strength models is proposed by comparing the numerical simulation results using initial and refined constants with test results.The criterion which is basically the average difference between measurement results (diameters and final length of the rod) and code simulation output is adopted to validate constants or determine if optimization is reached. And a main program created by coupling the nonlinear least squares optimization code UNLSF, a modified Lenvenberg-Marquardt method, with the LS-DYNA finite element analysis software is developed in this dissertation. It validates and determines the "best" set of constants for dynamic material strength model by running LS-DYNA in a loop, varying the model constitutive parameters, and minimizing the difference between the Taylor test profile of the calculation and experiment.In this dissertation, a successful application of this methodology is described to validate and optimize initial OFHC copper constants for Johnson-Cook model which are obtained from some other experimental techniques. With optimized OFHC constants for JC model, the computational simulation results for different impact velocities and different slenderness ratios can be reached, which are concordant with the results of Taylor impact test. Besides the material flow stress of different stains and stain ratios, obtained from optimized material constants, is evaluated by comparing with the results of static test and phase theory.Considering some inevitable factors in Taylor impact test which may affect the result of constants validation and optimization, it is necessary to carry out the uncertainty analysis of these factors which include the uncertainty of velocity measure, impact attitude, bar profile measure etc. The result of analysis provides the different influence degree of these uncertain factors and shows that it is reasonable for validating and optimizing material constants for dynamic constitutive model with this method.