Inelastic response of confined aluminium oxide under dynamic loading conditions

Previous efforts to explore the compressive strength of ceramics as a function of confining pressure at high strain rates have been limited by the maximum hydrostatic pressure that could be achieved within the experimental apparatus. An alternate procedure, using an autofrettaged confinement ring, has been designed to achieve higher confining pressures. A 6.2 GPa stress pulse, of approximately 20 μs duration, was used to load a 99.5% pure cylindrical aluminium oxide specimen under a hydrostatic load of approximately 650 MPa. The specimen remained intact and showed no evidence of fracture under scanning electron microscopy (SEM). Transmission electron microscopy (TEM), however, showed extensive evidence of plastic flow; the microcracks that were observed were associated with dislocation arrays. Static and dynamic yield strengths as a function of strain rate are compared.