Divergent impact study of the compressive failure threshold in SiC and B4C

The compressive failure threshold of boron carbide and silicon carbide ceramics has been studied in impact experiments with an axisymmetric divergent flow, generated by the impact of convex copper flyer plates having velocities in the 550-720 m/s range. The radius of curvature of the flyer plates was in the 88-650 mm range. The sample-window (sapphire) interface velocities or the velocities of the free surface of the nickel witness plate were monitored continuously by VISAR. The maximum shear stress achieved under different radial stresses, just prior to the sample failure, is associated with the compressive failure threshold of the ceramic. The compressive failure threshold of the studied ceramics and the parameters of their inelastic deformation were determined by matching the results of the AUTODYN-2D numerical simulation with the experimentally obtained waveforms. The compressive failure threshold of SiC is characterized by a transition from a brittle-like behavior below a radial stress of about 1.5 GPa, to a ductile-like one at higher radial stresses. Boron carbide, in contrast, displays an apparently brittle failure over the whole studied stress interval.