No abstract

The dynamic Mohr–Coulomb behavior of silicon carbide (SiC) was inferred from symmetric pressure/shear plate-impact experiments which entail planar impact of two SiC plates inclined at 15° to the impact direction. The transverse velocity of the free rear surface of the target plate was recorded using a laser Doppler velocimeter system, and the experiments were simulated using a postulated viscoplastic constitutive model that accounts for comminution and dilatancy. Model parameters were varied until the computed and measured velocity histories agreed. The results indicate that comminution occurred soon after loading, and thus the experiment measures the behavior of granulated material at shear strain rates of ≊105 s−1 and mean stress ranging from 1 to 9 GPa. A friction coefficient of 0.23 was obtained, which is about half the value for quasistatic compression of precomminuted ceramic reported in the literature. The simulation results were strongly affected by the values chosen for the friction coefficient and yield strength parameters; changes in the dilatancy, rate-sensitivity, and strain-hardening parameters had a lesser effect.

Incursion of high density penetrators into ceramic armor is preceded by the formation of a finely comminuted rubble bed at the penetrator tip, the Mescall zone. The deformation and failure processes that result in the Mescall zone are critical to understanding penetration resistance and to modeling penetration behavior. Transmission electron microscopy (TEM) was used to examine shock loaded material in the vicinity of an explosive detonation in α-Al2O3 and to infer the phenomenology of plasticity and fracture occurring at the tip of an advancing penetrator in ceramic armor. Comminution proceeds by intergranular fracture until the fragment size approaches the grain size. Further fragmentation proceeds by transgranular cracks, which nucleate at preexisting microvoids and at intersections of basal twins and primary and secondary slip bands.