Impact fracture behavior of polycrystalline graphites and C/C composites using high velocity steel sphere

In order to investigate impact fracture behavior of carbons, the following processes were carried out. A high velocity steel sphere accelerated by a two-stage light gas gun was impacted on three kinds of polycrystalline graphites having different maximum particle sizes and a C/C composite. In-site observation of impact fracture was performed by using a high-speed framing camera, taking pictures of those specimens in front, rear and side views. As a result, the following are obtained. In spite of similar density and elastic modulus graphites, the graphites of the biggest and the middle maximum particle size have similarity in little cracks on their front surface, differing from one of the smallest. On the contrary, the graphites of the smallest and the middle maximum particle size have similarity in brittle fracture on their rear surface, differing from one of the biggest. The gushing fine fragments were recognised in all specimens on side view. Their lengths depend on maximum particle size of the specimen.