HIGH-STRAIN-RATE DEFORMATION AND COMMINUTION OF SILICON-CARBIDE

Granular flow of comminuted ceramics governs the resistance for penetr ation of ceramic armor under impact. To understand the mechanism of th e granular flow, silicon carbide was subjected to high-strain, high-st rain-rate deformation by radial symmetric collapse of a thick-walled c ylinder by explosive. The deformation, under compressive stresses, was carried out in two stages: the first stage prefractured the ceramic, while a large deformation was accomplished in the second stage. The to tal tangential strain (-0.23) was accommodated by both homogeneous def ormation (-0.10) and shear localization (-0.13). Three microstructures , produced by different processing methods, were investigated. The mic rostructural differences affected the microcrack propagation: either i ntergranular or transgranular fracture was observed, depending on the processing conditions. Nevertheless, the spacing between shear bands a nd the shear displacement within the shear bands were not significantl y affected by the microstructure. Within the shear bands, the phenomen on of comminution occurred, and the thickness of the shear bands incre ased gradually with the shear strain. A bimodal distribution of fragme nts developed inside the shear bands. The comminution proceeded throug h the incorporation of fragments from the shear-band interfaces and th e erosion of fragments inside the shear band. Outside the shear bands, an additional comminution mechanism was identified: localized bending generated comminution fronts, which transformed the fractured materia l into the comminuted material. The observed features of high-strain-r ate deformation of comminuted SiC can be used for validation of comput er models for penetration process. (C) 1998 American Institute of Phys ics.