Effect of characteristics of materials on fracture behavior and modeling using graphite-related materials with a high-velocity steel sphere

In order to investigate the impact fracture behavior of graphite-related materials, high-velocity steel spheres accelerated by a two-stage light gas gun were impacted onto three kinds of polycrystalline graphites and a 2D-C/C composite. The polycrystalline graphites have different maximum particle sizes and static dissipation energies. The in situ observation of impact fracture was performed by taking photographs with high-speed framing cameras of the impacted (front) surfaces of those specimens. High pressure caused by shock wave produced a gush of fine fragments in a fluidlike manner immediately after the impact. The apparent volume of fragments was dependent on the maximum particle size, but independent of the thickness of the specimen. The crack patterns of the impacted surface were closely related to the static dissipation energy. The fracture behavior of graphite having the lowest dissipation energy was classified into two cases: with and without fracturing on the rear surface. In the latter case, the time of crack appearance was a function of impact velocity. However, in the former case, both impact velocity and specimen thickness influenced the time of crack appearance.