Bridging Interactions in Ceramics and Consequences on Crack Path Stability

An important fracture mechanics parameter governing path stability of growing cracks is the biaxiality ratio, i.e. the ratio of the T-stress and stress intensity factor. It is well known in general fracture mechanics that crack growth under positive biaxiality ratios is path-unstable. Any unavoidable mode-II loading must result in an increasing deviation from the initial straight crack plane. This holds for the most fracture mechanics test specimens used in tests on ceramic materials, for instance, edge-notched bending bars, CT, and DCB specimens. The theoretically predicted crack path stability is in disagreement with experimental findings reported in the literature on R-curve measurements, where R-curves were measured for crack lengths yielding high positive biaxiality ratios. Two possible reasons for this astonishing discrepancy between theory and experiments will be discussed.