A study of the interlaminar fracture toughness of a carbon-fiber/epoxy composite containing surface-modified short Kevlar fibers

Abstract

Short Kevlar fibers (SKF) were distributed in the midplane of a continuous carbon-fiber/epoxy laminate before processing at the point where an initial crack is introduced in an interlaminar fracture toughness test. Two extreme cases of SKF/epoxy interfaces were obtained by oxygen-plasma-treated SKF (P-SKF) or silicone-release-agent-treated SKF (S-SKF). The mode I (G(IC)) and mode II (G(IIC)) interlaminar fracture toughnesses of the modified carbon-fiber/epoxy composites were then investigated. The fracture surface was studied by scanning electron microscopy and optical microscopy. The interfacial shear strengths of the SKF/epoxy interfaces were measured by fiber pull-out tests. G(IIC) increased with increasing crack length because of the presence of SKF bridging in the wake of the propagating crack. The fiber-bridging phenomenon may be influenced by the amount and orientation of SKF. However, fiber bridging was not observed in mode-II tests on P-SKF and S-SKF composites, irrespective of the amount of Kevlar fibre. G(IC) showed no significant effect with SKF, P-SKF and S-SKF with no fiber bridging. (C) 1998 Elsevier Science Ltd. All rights reserved.