MOISTURE EFFECTS ON MODE-II DELAMINATION BEHAVIOR OF CARBON EPOXY COMPOSITES/

Moisture effects on Mode II interlaminar fracture in T300/914C and T30 0/M10 carbon/epoxy composites were investigated by using ENF specimens exposed to different hygrothermal conditions. Crack growth behavior, interlaminar shear strength, glass transition temperature and fractogr aphs of the materials were examined toward establishing the possible m echanisms of moisture effects. It was found that Mode LI fracture toug hness of T300/M10 is more sensitive to moisture than that of T300/914C . For T300/914C, the matrix was plasticized by water and thus G(IIc) i ncreased slightly. With further moisture absorption, swelling action w eakened the interface and led to reduction of fracture toughness. For T300/M10, moisture primarily weakened the interfacial strength and res ulted in decrease in G(IIc). It seemed that water plasticization contr ibuted to the enhancement of delamination toughness of the fiber-matri x system with strong interface, and degraded the toughness of the syst em with weak interface due to a decrease of the fracture area. However , for both of the two systems, the swelling action, which weakened the interface bond, always reduced the delamination resistance.