Compression Strength of Carbon Fiber Laminates Containing Flaws with Fiber Waviness

Recent studies of carbon fiber and carbon/glass hybrid laminates have reported compression strengths and failure strains which are borderline for wind turbine blade designs, depending upon the reinforcement architecture, matrix resin, and environment. Compressive strength is known to be sensitive to the straightness of the fibers, with even relatively small degrees of waviness or misalignment causing significant decreases in compression properties. The effects of fiber waviness, induced by infusion processes and inherent in fabric architectures, on compressive strength, have been investigated. Structural details such as ply drops and ply joints can cause significant levels of fiber misalignment, depending on parameters such as ply thickness, fraction of plies dropped, ply drop location, ply joint gap, and mold geometry and pressure. These parameters have been varied in the study reported in this paper, with compressive properties determined in each case. The results show that prepreg laminates containing p ly drops and joints can provide adequate compressive strength, but that severe knockdowns can occur for geometries where large misalignments are induced.