| Computer simulations have been in use for decades in the modeling of hypervelocity impacts and general large deformation problems. Several computer codes have been developed to simulate this type of problems under a variety of geometric configurations and for any number of materials. These codes make use of several constitutive material models to simulate the response of the material under a variety of thermo-mechanical conditions. The Johnson-Cook constitutive model is widely used in the simulation hypervelocity impacts for the simulation of crater formation and even perforation of target structures. This thesis presents the results of a sensitivity study of this plasticity model and the effects on the cratering process by the perturbation of its material constants. In this study, a silica particle is simulated in the CTH hydrocode to impact aluminum and steel plates for characterization of the damage under the influence of +/- 20% variation of the material parameters of the Johnson-Cook model. The study is performed under 3 different impact velocities, at 4, 6, and 10 km/s. The sensitivity study includes the initial yield stress, strain hardening, and strain-rate hardening constants, as well as the thermal softening exponent. |
