Properties and Modeling of Ultra-High-Performance Concrete Subjected to Multiple Bullet Impacts

In this study, ultra-high-performance concrete (UHPC) was reinforced by hybrid fibers and corundum aggregates. The dynamic behavior of UHPC against multiple bullet impacts was researched. The penetration damage to concrete targets was measured, and the fracture patterns of targets and bullets were observed after each impact. The effects of hybrid fibers and corundum aggregates on bullet penetration depth and damage to UHPC subjected to multiple bullet impacts were researched. An empirical model was proposed to predict bullet penetration depths in UHPC based on the formula developed by Gomez. The fracturing of UHPC was simulated by the finite-element method. Results show that UHPC resistance to multiple penetrations was improved by the hybrid fibers and corundum aggregates (Moh's hardness of 9.0). The calculated penetration depths were very close to the experimental data using the proposed model and the finite-element method. Simulation showed that depth decreased as erosion strain increased, so an optimal strain for each concrete was determined and used in modeling the hybrid fiber-reinforced cementitious specimens. Concrete target peak pressure varied with depth, and maximum pressure appeared near the penetration end and then gradually dropped until the bottom of the target was reached.