Improvement of the dynamic failure behavior of concrete subjected to projectile impact using user-defined material model

The RHT model, one of the concrete material models, is embedded in commercial tools, and is mainly used for impact and explosive analysis with high strain rates. The original RHT model showed sufficiently similar results for the penetration depth measured by experiments in the low impact velocity. However, as the impact velocity increases, the original model has limitations in expressing the dynamic response of the concrete because yield surfaces and fracture behavior, depending on the strain rate, were underestimated. Although previous studies were conducted to improve the RHT model, the input parameters constituting the RHT model were either adjusted to approximate the experimental data. In this study, we propose a model that can express the improved dynamic tensile failure behavior by reflecting the strain rate-dependent parameters. Unlike the methods used in previous studies, the modified model was established that formulates important parameters to fit well with the experiment using user-defined functions. Based on experimental observations, we introduced a nonlinear crack softening model that reflects strain rate-dependent tensile strength and fracture energy to realistically express fracture strain and impact resistance against dynamic loads. In addition, we embedded a damage model that represents the irreversible volumetric deformation caused by pore collapse as the confinement pressure increases. For the verification of the proposed model, numerical simulations for the two experimental tests (i.e., penetration of thick concrete targets and perforation of thin concrete slabs) were performed. The proposed model shows good agreement with the experimental results, and in particular, it showed that the penetration depth and residual velocity are well estimated. Thus, we confirmed that it is superior in representing the resistance and fracture behaviors of the concrete target.