An investigation of the effect of a Kevlar-29 composite cover layer on the penetration behavior of a ceramic armor system against 7.62 mm APM2 projectiles

•Ballistic tests of bilayer ceramic/composite armor structures with a Kevlar-29 composite cover layer were conducted at different velocities.•3D finite element models were developed to elucidate the covering effect through the definition of a cohesive surface at the interface between the cover layer and the ceramic tile.•Ballistic resistance of covered and uncovered armor structures was compared through numerical simulation.•Two major mechanisms in covered armors were identified to have a positive effect on their ballistic resistance. High hardness ceramics are commonly used in lightweight armor systems to defeat the intrusion of high-speed armor piercing (AP) projectiles. However, bare ceramic tiles are intrinsically brittle, and fragments of various sizes can be generated when subjected to impact, which can cause secondary impact to the wearer and surroundings. In a typical armor design, the ceramic tile is usually covered with a compliant thin sheet to mitigate fragments splattering. In this study, the effect of a Kevlar-29 composite cover layer on a bilayer ceramic/composite armor system is investigated through a combined approach of experimental testing and finite element (FE) simulation. In the experiments, 7.62 mm APM2 projectiles were used to impact single Kevlar-29 composite layer covered ceramic/composite armor systems at three different velocities: 884 m/s, 1070 m/s and 1164 m/s. The restraining effect of the cover layer on the ceramic fragments was clearly observed. A 3D FE model was further developed to analyze the covering effect through the definition of a cohesive surface behavior at the interface between the cover layer and the ceramic tile. The FE model successfully captured the peeling behavior of the cover layer and dominant fracture patterns in the ceramic tile. It shows that, the cover layer can improve the ballistic resistance of the armor system through two major mechanisms: the energy dissipation by itself and its effect on fracture process of the ceramic tile. A high bond strength at the interface can also improve the energy dissipating capability of the armor system.