High strength, high fracture toughness fibre composites with interface control—A review

The subject of improving the fracture toughness of fibre composites is receiving significant attention because a critical design criterion in damage tolerant fibre composites is the possession of a sufficiently high fracture energy absorption capability, particularly under impact loading conditions. For a given brittle-fibre/brittle-matrix composite, high strength requires a strong interfacial bond, but this may lead to a low fracture energy absorption. However, by proper control of the physical and mechanical properties of the fibre-matrix interface high strength characteristics can be combined with high toughness. In order to fully utilise the potential of such composites without introducing a reduction in strength, it is necessary to understand the failure mechanisms leading to eventual fracture. This paper reviews the existing theories of fracture toughness of fibre composites and the various methods for improving the fracture toughness by means of interface control. Conclusions and generalisations which can be drawn from the literature are presented with discussions of areas in which further research is required.