THE EFFECTS OF FABRIC WEAVE AND SURFACE TEXTURE ON THE INTERLAMINAR FRACTURE-TOUGHNESS OF ARAMID EPOXY LAMINATES

The mode I interlaminar fracture toughness of woven aramid-fibre/epoxy resin laminates has been investigated as a function of the fabric weave and the fabric surface texture used in the construction of the laminates. The experimental values of G(IC) were found to increase significantly with increasing crack length for all the materials investigated. This behaviour is ascribed to the presence of fibre bridging during crack propagation. The presence of fibre bridging in the cracks has been observed directly. The maximum values of G(IC) determined were in the range of 0.5-3.0 kJ/m2, depending upon both the fabric weave and the surface texture. The largest values of G(IC) were obtained for those composites in which the surface of the fabric used in their construction contained a high density of fibre ends. Among the weave variations studied, larger values of G(IC) were found for the composites containing the coarser plain fabric weaves. The fracture performance of the materials studied was interpreted as being related to the local fibre/resin distributions in the laminates, and in particular the ability of fibres, or fibre ends, to migrate into the resin-rich interply zones during fabrication. An optical comparison of sections of these laminates confirmed an enhanced concentration of fibre ends in the resin-rich interply zones for the fabrics with the most obvious concentration of fibre ends in their surface. This type of fabric surface texture provided a more homogeneous fibre distribution in the composite which resulted in enhanced levels of fibre bridging and, as a consequence, enhanced fracture toughness.