A Comparison of Isotropic (*MAT_224) and Anisotropic (*MAT_264) Material Models in High Velocity Ballistic Impact Simulations

To improve the modeling of metals in high velocity impacts, there have been many developments in constitutive material modeling for LS-DYNA ® . One such advancement is the development of the Tabulated Johnson-Cook material model (*MAT_224). *MAT_224 is a tabulated material model with strain rate and temperature dependency. Additionally, this model includes a failure criteria as a function of triaxiality, Lode parameter, temperature, strain rate and element size. This model has been used successfully in the simulation of numerous materials in high velocity ballistic impact load cases. One drawback to the original Tabulated Johnson-Cook material model is that it is implemented with von Mises isotropic plasticity. Therefore, this material model is not ideal for simulating metals that are anisotropic or asymmetric. Subsequently, an anisotropic and asymmetric version of the Tabulated Johnson-Cook model was developed to simulate these materials. The *MAT_264 material model maintains all the capabilities of the *MAT_224 model, but it adds the ability to define the material response in the 0-degree, 45-degree, 90-degree and thickness directions. Additionally, it allows for directional tension-compression asymmetry in the material. Strain rate dependency, temperature dependency, and the failure model are retained from the Tabulated Johnson-Cook model. By using a previously developed failure model and limited material specimen testing, an industrial material characterization was developed for a 6.35 mm thick Ti-6Al-4V rolled plate. Specimen testing of this titanium alloy plate reveals that this material exhibits some anisotropy and asymmetry. NASA cylindrical ballistic tests were simulated with both the *MAT_224 and *MAT_264 material models. First, the isotropic implementation of the *MAT_264 material model is compared to the *MAT_224 model. Second, the anisotropic implementation of the *MAT_264 model is compared to the isotropic *MAT_224 model. Multiple impact velocities are simulated and the resulting exit velocities, internal energies and eroded internal energies are used to compare each material model.