Experimental Investigations of Wave and Fracture Phenomena in Impacted Ceramicsand Glasses

摘要

Four types of glass which differ in their chemical composition, hardness andmaterial density and tiles of SiC, TiB2, and Al203 were impacted edge-on with blunt steel projectiles at striking velocities between 20 m/s and 1000 m/s. The propagation of shock waves and primary and secondary cracks and crack systems and the growing of crack systems from nucleated centers were visualized by means of a Cranz-Schardin high-speed camera within the first 20 microseconds before the projectile penetrated the target more than a few millimeters. The concept of damage velocity was introduced to describe the different damage processes quantitatively. All four types of glass revealed a similar behavior. The damage velocity equaled terminal crack velocity at low loadings, rose to transversal wave velocity when nucleation occurred and approached longitudinal wave velocity with very high loadings. Unlike glass, the ceramics generated different types of cracks, and different fracture velocities were observed at one impact velocity in one specimen. One had to distinguish between the velocity of continuously growing cracks, including the secondary cracks with sharp edges, fuzzy crack traces and crack fronts. In each of the ceramics, the damage velocity increased with increasing striking velocity and approached the longitudinal wave velocity at high loadings. A terminal crack velocity was found for one type of fracture in SiC. Ceramographical investigations of TiB2 fragments have shown that cracks within large grains as well as intercrystalline cracks are generated by coalescence of voids. jg.