Degradation in Tensile Properties with Overlapped and Discontinuous Fabric Preforms

Abstract

Measured tensile properties including the modulus, strength and elongation of resin transfer molded composites, which were fabricated using several fabric preforms through the normal, overlapped and discontinuous models, were compared. As expected, the overlapped and discontinuous models had lower tensile modulus and strength than the normal model; these values were functions of the effective fiber-volume fraction. The differences were examined and used to predict the overlap-damage and discontinuous-damage parameters, which were developed from the energy method, rule of mixture and failure modes. Also, the results showed that the final failures of the overlapped and discontinuous models were either interfacial bond failure or breaking fibers depending on the overlapped and discontinuous lengths. Since discontinuous fabrics in the preform cannot be avoided in designing and manufacturing composites, the ratio of the discontinuous gap to the gauge length (L G /L) should be less than 0.05. Also, the ratio of the discontinuous length to the gauge length (L D /L) should be large to minimize the influence of the stress concentration. Also, in light of the fiber-volume fraction, composites designed with the overlapped preform are better than those with the discontinuous preform.