Effect of variation in fibre volume fraction on modes I and II delamination behaviour of 5HS woven composites manufactured by RTM

Composites produced by resin infusion techniques will inevitably suffer from variation in resin distribution due to imprecise fibre placement and distortion of the preform during mould closure and infusion. This paper describes an investigation into the effect of variations in fibre volume fraction (FVF) on mode I and mode II delamination behaviour for 5 harness satin (5HS) woven carbon–fibre/epoxy resin composites manufactured by resin transfer moulding (RTM). Additionally, the effect of satin face tow orientation on interlaminar toughness was investigated. In mode I, it was found that toughness increased with increasing FVF and that a strong correlation between fracture surface damage and measured interlaminar fracture toughness was observed. In mode II, measured toughness values were higher than expected and tests were repeated using a mixed-mode rig with 5% mode I. It was found that fracture toughness measurements in pure mode II are significantly affected by friction or mechanical interlocking between the delamination surfaces.