Micro-scale energy dissipation mechanisms during dynamic fracture in natural polyphase ceramic blocks

The dynamic fracture of natural polyphase ceramic (granite) blocks by high-speed impact at 207 m/s, 420 m/s and 537 m/s has been investigated. An electromagnetic railgun was used as the launch system. Results reveal that the number of fragments increases substantially, and the dominant length scale in their probability distributions decreases, as the impact energy is increased. Micro-scale studies of the fracture surfaces reveals evidence of localized temperatures in excess of 2000 K brought on by frictional melting via fracturing and slip along grain boundaries in orthoclase and plagioclase, and via transgranular fracture (micro-cracking) in quartz. The formation of SiO2- and TiO2-rich spheroids on fracture surfaces indicates that temperatures in excess of 3500 K are reached during fracture.