Impact resistance of boron carbide ceramics from hypersonic and supersonic impacts: A large-scaled molecular dynamics simulation study

Abstract

Boron carbide ceramics are considered to be ideal bullet-resistant materials in the manufacture of lightweight bulletproof armor due to their low density, chemical inertness, high thermal stability, and high hardness. The amorphous transformation of boron carbide subjected to a high velocity impact most likely results in a decrease in the impact strength and impact-fatigue resistance of the material due to cracks that initiate from an amorphous band under an impact load. Here, by simulating impact tests from a diamond bullet on a boron carbide monocrystal slab of the most abundant polymorph, we demonstrate that impact-induced amorphization of a boron carbide crystal can be simulated by using the new Stillinger–Weber (SW) potential. Impact-induced longitudinal and transverse wave fronts travel at speeds ranging from 33.5 to 35 km/s and 7.2 to 9 km/s in boron carbide. The simulation results show that the amorphization of boron carbide is caused mainly by impact-induced temperature increase and, thus, confined to the impact point. The loss of the integrity of the crystal structure began with the bending of the C–B–C three-atom chains, followed by the icosahedron deformation. Most icosahedrons in the boron carbide maintain their cage structures without decomposing after amorphization, which maintains the hardness of the material. This result demonstrates an excellent repeated impact-fatigue resistance of boron carbide against non-hypersonic bullets. Through the analysis of impacts with different angles and speeds, we demonstrate that boron carbide slab ceramic armor shows good resistance to impact from non-frontal and non-hypersonic projectiles and can avoid violent amorphization.