Characterization of microcracking of NCF composites under accelerated hygrothermal cycles: Influence of the stitching yarn and the style of biaxial NCF

In this paper, an analysis of the evolution of microcracking of Non-Crimp Fabric (NCF) polymer matrix laminates under hygrothermal loading is presented. These composites are reinforced with biaxial NCF styles ([+45/-45], [0/90], etc.) and manufactured by Liquid Resin Infusion (LRI). The samples are subjected to accelerated hygrothermal cycles that cause microcracks in specific resin-rich areas (RRA). Three types of microcracks were found to occur in the heterogeneous morphology of NCF. An experimental method based on 2D microscopic observations was adapted for the characterization of microcracking in several NCF laminates. 3D tomographic X-ray observations were performed to investigate the propagation and location of microcracks in the NCF volume. The influence of humidity on microcracking was investigated. The impact of several parameters on microcracking was discussed, in particular the stitching yarn size and styles of biaxial NCF used in laminates.