BRITTLE INTERFACE LAYERS AND THE TENSILE-STRENGTH OF METAL MATRIX-FIBER COMPOSITES

The influence of brittle layers on the ultimate tensile strength of metal matrix composites is discussed. An equation has been derived to calculate the first critical thickness of the layer. The brittle layers have two effects on the fracture of the fibre, one of which is the value of the local stress near the tip of the crack, situated at the fibre-layer interface. Methods have been developed for the theoretical calculation of the critical stress intensity factor, KIC, of brittle materials. Experimental results with B-SiC fibres have shown that their tensile strength is reduced with increasing thickness of the SiC layer. The critical thickness of the layer, tl*,for B-SiC fibres is about 1.0 to 7.5 μm, which coincides well with the theoretical value of tl*. © 1979 Chapman and Hall Ltd.