Creep Damage Mechanisms in Hot-Pressed Alumina

The creep fracture behaviour of two commercially available hot-pressed aluminas has been extensively studied, both in flexure and tension. Three distinct regions are observed. At high stress, failure is by slow crack growth, dominated by a single flaw. At intermediate stresses, widely distributed microcracking is observed. Microcrack linkage differs for flexure and tension, resulting in large increases in lifteime for the flexure geometry. At the lowest stresses, widely distributed cavities are observed. Nonetheless, failure still occurs by the growth of flaw related cracks. The most damaging flaws appear to be large-grained regions.