Failure Mechanisms and Fracture Energy of Hybrid Materials

Fibre hybridisation is a well-established methodology to enhance the failure strains of fibre reinforced composites. In a hybrid fibre composite, the matrix is reinforced by two or more types of fibres, with typically a large stiffness contrast. When exactly two types of fibres are used for reinforcement, the fibres with greater stiffness are conventionally called the low extension (LE) fibres, while those with greater compliance are called high extension (HE) fibres. Hybrid fibre composites are typically divided into three cate- gories. If layers of LE and HE fibres are stacked over one other, an interlayer or layer-by-layer configuration is obtained. If yarns of LE and HE fibres are co-woven to form a hybrid fibre composite, an intralayer or yarn-by-yarn configuration is obtained. Finally, if the LE and HE fibres are randomly mixed together, the intrayarn or fibre-by-fibre configuration is obtained. From a manufacturing perspec- tive, it is most difficult to produce intrayarn composites, and easiest to produce interlayer composites.

Hybridisation seeks to combine the advantages of both fibre types and alleviate some of the disadvantages. As an example, carbon fibre reinforced plastic (CFRP) composites exhibit good strength to weight ratio, but undergo brittle failure leading to low fracture toughness. On the other hand, glass fibre reinforced plastic (GFRP) composites exhibit ductile failure, but suffer from a relatively higher density than CFRPs, resulting in a lower strength to weight ratio. By combining the carbon fibres and glass fibres at a microscopic level, intermediate properties can be achieved.