Mechanical behaviour of polycrystalline BeO, Al2O3 and AlN at high pressure

An investigation of the mechanical behavior of various types of BeO, Al2O3, and AlN at confining pressures up to 1.25 GPa, at 25 C, is presented. The strain rates were 3 to 7 x 10 to the -5th/s; the stress-strain data taken in uniaxial compressive stress loading indicate that BeO aggregates undergo a transition from brittle fracture at low confining pressures to plastic flow at high pressures. Concurrently, the ultimate compressive strength of BeO increases to over 4.0 GPa at 1.0 GPa pressure; alumina is brittle at all pressures up to 1.25 GPa, and its strength increases to over 6.0 GPa at 1.25 GPa confining pressure. The distortional strain energy absorbed by each material during compression was calculated and compared with published data. Alumina has a degraded energy absorption with pressure, but BeO and AlN show increased compressive strength and ductility at moderate pressures; this indicates their suitability as high strength and ductility structural materials for moderate pressures.