Chapter 5. Damage Modes Correlated to the Dynamic Response of SiC-N

Summary

The damage modes in a hot-pressed silicon carbide (SiC-N) specimen have been correlated to its dynamic compressive response at high strain rates. We employed a novel dynamic loading/reloading experimental technique modified from a split Hopkinson pressure bar (SHPB) to determine the dynamic properties and to record the damage/failure modes in the ceramic specimen, in which a ceramic specimen was loaded by two consecutive stress pulses. The first pulse determines the dynamic response of the intact ceramic material and then crushes the specimen to a desired damage level. The second pulse then determines the dynamic compressive constitutive behavior of the damaged but still interlocked ceramic specimen. The first pulses were varied slightly to control the damage levels in the ceramic specimen while the second pulse was maintained identical. The results show that the compressive strengths of damaged ceramics depend on a critical level of damage, below which the specimen retains its axial load-bearing capacity and only axial cracks are observed in the specimen. When the specimen is critically damaged, axial cracks and isolated pulverized regions are observed. When the specimen is damaged beyond the critical level, the ceramic specimen is crushed into cracked particles with pulverized (comminuted) materials along the particle boundaries, which displays a granular flow behavior in its stress-strain curve.