Effect of Fibre Volume Fraction on Mixed-Mode Fracture of a Fabric Carbon/Epoxy Composite

Abstract

Variation in fibre volume fraction is a common characteristic of composites made by an injection moulding process. The effect of this variation on fracture toughness is not yet fully investigated. This paper examines the fracture in fabric carbon/epoxy composite laminates under a wide range of combined mode-I and mode-II delamination. A total of 60 double cantilever beam and edge-notched flexure specimens are manufactured by resin transfer moulding with two different fibre volume fractions. It was observed that increasing the fibre volume fraction decreased the initiation fracture toughness in all mixed-mode ratios. This behaviour is believed to relate to the fact that the initiation fracture energy is dominantly absorbed by the resin-rich regions at the delamination tip. In contrast, an increase in fibre volume fraction was found to increase the propagation fracture toughness at high mode-I contribution where the fibre bridging is believed to be the major energy dissipating mechanism. Fractographic analysis also demonstrated that an increase in contribution of mode-II delamination is accompanied by a decrease in fibre bridging and an increase in shear hackles.