Failure Mechanisms and Fracture Energy of Hybrid Materials

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

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