Influence of Resin Type on the Delamination Behavior of Carbon Fiber Reinforced Composites Under Mode-II Loading

In this study, the delamination fatigue behavior of two different aeronautical quality composites under mode-II notched flexure loading has been experimentally investigated with the aim of analyzing the effect of the resin type used. Both composites contain the same unidirectional AS4 carbon reinforcement, though embedded in two different matrices: an 8552 epoxy with improved toughness and an unmodified brittle 3501-6 epoxy. The end notched flexure test was found suitable for promoting fatigue delamination under mode-II loading. First, the ΔG-N fatigue curves were determined as the number of cycles necessary for crack onset at a given energy release rate. Then the crack growth rate was obtained for different fractions of the critical energy release rates, Gcr. Calculations of the shear toughness were carried out in accordance with the methods proposed in the ESIS protocol. Critical experimental details are reviewed and the influence of the different procedures proposed for the data assessment of results is analyzed. The results confirm, on the one hand, the influence of the manufacturing process on fatigue crack initiation, and, on the other, the improved performance of the modified resin, both in terms of crack initiation and growth rate.