QUANTIFICATION OF MATERIAL AND GEOMETRIC DEFECTS VARIABILITY IN FIBER-REINFORCED COMPOSITES WITH PLY WAVINESS DEFECTS

This article presents the findings of defects in fiber-reinforced polymeric composite laminates manufactured with artificially-induced ply waviness features. The design of the ply waviness mimics defects seen in composites at ply drops and in regions of tow overlaps and gaps. Detailed imaging of the composite microstructure after curing is conducted via optical microscopy, and material and defect variability are quantified. Results confirm that manufacturing of composites with artificially-induced ply waviness causes additional defects at lower material scales, including fiber volume fraction variations, voids/porosity, and ply thickness variations. The consolidation during debulking, flow of the resin, and deformation of the fibers at regions of gaps or overlaps cause these additional defects during the curing. Efforts to understand strength knockdowns in composites due to ply waviness, therefore, must also include such associated defects or look for process improvements that minimize them.