Influence of mode ratio and hygrothermal condition on the delamination toughness of a thermoplastic particulate interlayered carbon/epoxy composite

Double cantilever beam, end-notched flexure and single leg bending tests were used to determine the effects of temperature and moisture on the toughness of a thermoplastic particulate-toughened carbon/epoxy composite. Tests were performed on both dry and moisture-saturated specimens at temperatures of −43 °C, 21 °C and 98 °C, and on dry specimens only at 125 °C. In-situ observations and post-test scanning electron microscopy showed increasing matrix ductility with increasing temperature and moisture content. This correlated to an increase in the mode I and a decrease in the mode II toughness. The mixed-mode toughness data and fracture surface morphologies displayed a blend of the mode I and mode II behaviors.