Fracture-toughness/notch-sensitivity correlation for metal- and ceramic-based fibrous composites

The fracture toughness of a material is given by the critical stress intensity factor KIC used in linear fracture mechanics to evaluate the ultimate load on a structural element containing a crack-like defect. However, KIC can hardly be applicable to the failure analysis of elements made of fibrous composites. Hence, an apparent value of the critical stress intensity factor, K*, for composites are normally experimentally measured to evaluate only the damage tolerance of composite materials. The measurements of the ratio of the flexural strength of specimens with and without a notch (σN/σ0) serve the same purpose. The analysis of K* and σN/σ0 data obtained by testing various oxide/molybdenum composites as well as those for oxide/oxide and C-fibre/SiC-matrix composites published recently along with older data for boron/aluminium reveals a linear correlation between these two characteristics of composites.