Abstract
A laboratory scale drum winder has been designed and built for the production of pre-preg. Cross-ply hybrid matrix laminates were made from the pre-preg with glass fibres/epoxy resin in the longitudinal plies and glass fibres/epoxy resin-urethane elastomer in the transverse ply. The addition of urethane to the matrix in the transverse plies alone increased the applied strains necessary for the initiation and development of transverse cracking during the extension of cross-ply laminates. This resulted in a smaller reduction in laminate stiffness (due to damage) at a prescribed level of strain. Damage resistance was similar to that in cross-ply laminates with urethane additions to the matrix in both the transverse and longitudinal plies (a uniform matrix laminate). It was found that urethane additions lead to improved damage resistance in cross-ply laminates because they lower the transverse ply modulus and increase the matrix toughness in the transverse ply. During the extension of cross-ply laminates, stable (constrained) transverse cracking was observed in thin transverse plies and unstable (brittle) transverse cracking in thick transverse plies. The effects of urethane additions on the development of constrained transverse cracking and brittle transverse cracking were modelled with a shear lag stress analysis combined with an energy balance and a statistical expression for the transverse ply strength respectively. The ultimate properties of hybrid matrix laminates, having improved damage resistance, were expected to be better than uniform matrix laminates with a similar urethane content in the matrix. However, the tensile strength of circular centre-notched (0,90)s hybrid matrix laminates was lower than uniform matrix counterparts and the compressive strength of (02,902)2s hybrid matrix laminates was similar to uniform matrix counterparts.