Cone cracking and fragmentation of alumina plates under high-speed penetration: Experiments and modeling

Abstract

Ballistic damage and fragmentation of alumina ceramic plates are investigated with ballistic impact experiments and numerical simulations. Ballistic impact tests are conducted with steel spherical projectiles (5 mm diameter) at 274–1040 m s⁻¹ using one- and two-stage gas guns along with high-speed photography. The postmortem targets are characterized with optical imaging, three-dimensional (3D) laser scanning and scanning electron microscopy. As the impact velocity increases, ceramic targets show damage modes as radial cracks (without cones), cone cracks, cone spallation, and cone fragmentation in sequence. The diameter, volume, and surface angles of the conical bullet holes (or ceramic cones) increase, while the height of ceramic cone decreases, with the increase of impact velocity. In the impact region, the shock compression-induc ed and tension-induced damage produce granular and coarse fragments, respectively, with the fragment size distribution following a power law. Numerical ballistic simulations are performed using the smooth particle hydrodynamics and finite element methods (SPH-FEM) along with the Johnson–Cook and Johnson–Holmquist constitutive models. The SPH-FEM fixed coupling model can capture the failure mechanisms and fragmentation characteristics of ceramic targets, including the 3D morphology evolution of ceramic cones. The angle deflection of the cone cracks is attributed to the stress wave interactions from the projectile and target free surfaces, altering the stress state at the crack tip and thus crack propagation direction.