The effect of voids on the flexural fatigue performance of unidirectional carbon fibre composites developed for wind turbine applications

The influence of voids in the initiation and propagation of static flexural and flexural fatigue failures of unidirectional carbon fibre composite was investigated. Vacuum pressure in the vacuum bag oven cure process was varied to produce void levels in the range 0.5–6%. The voids were characterised using image analysis and used to explain the static flexural strengths and flexural fatigue results. It was observed that mean void content and aspect ratios were less effective in explaining the mechanical property results than void size distributions. A strong correlation between large voids (area > 0.03 mm 2) and a detrimental effect on the mechanical properties was found. This was attributed to the effect of these voids on the crack propagation in the resin rich inter-ply regions.