Showing papers by "Marc A. Meyers published in 1989"

Effect of stress state and microstructural parameters on impact damage of alumina-based ceramics

Abstract: Alumina discs of two grain sizes (4 and 24μm), and three compositions (99.4% purity, 85% purity, alumina + partially stabilized zirconia) were subjected to planar normal impact in a gas gun at a nominal pressure of 4.6GPa. The alumina discs were confined in copper and aluminium capsules, which provided solely compressive and compressive plus tensile pulses in the ceramic, respectively. These experiments were conducted at different pulse durations (controlled by the thickness of the flyer plates). The surface area of cracks per unit volume was measured in order to estimate the impact damage. Compression followed by tension produced significantly more damage than compression alone. The small grain-sized discs exhibited more damage than the large grain-sized discs. The amount of damage increased with the duration of the tensile stress pulse. The addition of partially stabilized zirconia (∼ 14%) did not enhance the resistance to fragmentation of the discs; X-ray diffraction did not reveal an impact-induced phase transformation. Although the pressures generated were below the Hugoniot elastic limit of alumina, considerable fracturing of the specimens took place. Scanning electron microscopy revealed that the fracture was intercrystalline in regions away from the spall plane. In the spall plane energy was sufficient to comminute the grains, producing considerable grain debris and transgranular fracture. Transmission electron microscopy revealed the onset of damage to the structure, in the form of dislocations (present in only a small fraction of grains), microcracks nucleating at voids, and intergranular microcracks.