ABSTRACT
The equilibrium crack growth behaviour of an Al2O3/ZrO2 ceramic composite AS8 (alumina with 8 wt % monoclinic in the form of 15–20 μm polycrystalline clusters) developed by Garvie et al. at the CSIRO Division of Materials Science and Technology, Australia and intended for refractory applications was studied. The crack-resistance (R) curves for three specimen geometries including double-cantilever-beam (DCB), compact tension (CT) and single edge notched beam (SENB) were obtained and their crack toughening mechanisms discussed. In-situ crack growth observations and microscopic studies identified the co-existence of a fracture process zone around the crack tip and crack bridges at the crack wake. Bridging was shown to be a significant toughening mechanism responsible for the pronounced R-curves. Because of the large scale bridging, the R-curves depend on specimen geometry and size. The equivalent crack wake bridging stresses were also determined based on a new crack compliance theory developed in this laboratory.
