Development of material models for semi-brittle materials like tungsten carbide

Tungsten carbide is a very special material that exhibits both brittle and ductile properties. While purely brittle and ductile materials in general are well understood, a theory for describing the properties of a hybrid material like tungsten carbide has been elusive. Since this material is often used as the core in projectiles, a better understanding is necessary in order to either optimize the penetration or fragmentation capability or to create optimal protection. The fragmentation properties of a tungsten carbide projectile was studied systematically by doing perforation experiments with different yaw angles. Then numerical simulations of the experiments were performed, in which the tungsten carbide projectile was modelled using three different materials models, including Johnson-Cook and Johnson-Holmquist. The results showed that none of the models were able to reproduce the experimental results. To improve on this situation, a new material model (MTSB) based on theory for growth of microcracks was developed. In addition, the Johnson-Cook model was modified with a new dynamic dependency. Numerical simulations of the yaw experiments using the new models showed good agreement with experiments. MTSB and Modified Johnson-Cook were then put to another test. Oblique impact experiments with tungsten carbide projectile against different steel targets were performed. Numerical simulation of these experiments with both the new material models showed good agreement, in particular for the MTSB. Our conclusion is that both the new models are candidates for being an accurate description of tungsten carbide.