MODE-II FRACTURE OF COMPOSITES INTERLAYERED WITH NYLON PARTICLES

The purpose of this work was to determine the toughening mechanisms in interlayered carbon-fiber/epoxy composites. The primary variables wer e: (I) the diameter of the interlayering particles; (2) the thickness of the interply; and (3) the ductility of the matrix resin. G(IIC) was measured and mechanisms of fracture and toughening were examined by t ransmission optical microscopy and scanning electron microscopy. In a ductile epoxy system, the particles acted primarily to maintain the th ickness of the interlaminar region during processing. Mode II fracture toughness was found to increase linearly with interply thickness, reg ardless of particle incorporation. In two brittle systems, where plast ic deformation ahead of the crack tip was limited, the particles rough ened by two mechanisms, i.e. stress concentration induced plastic defo rmation and particle bridging. In the latter mechanism, the particles first initiated microcracks in the interlaminar region, then bridged t he microcracks. During this bridging process, the particles absorbed e nergy through extensive plastic deformation. In the non-interlayered b rittle-matrix systems, interply thickness played a limited role in aff ecting G(IIC). (C) 1996 Elsevier Science Limited