The study of model polydiacetylene/epoxy composites

Abstract

A mode composite system consisting of one polydiacetylene single crystal fibre in an epoxy resin matrix has been subjected to tensile strain parallel to the fibre direction. The strain at all points along the length of the fibre was determined by resonance Raman spectroscopy while that of the matrix was measured by conventional techniques. Comparison of the fibre and matrix strain showed two distinct regions. Below about 0.5% matrix strain the composite followed Reuss-type behaviour with equal stress in the fibre and the matrix. At higher matrix strain the composite followed Voigt-type behaviour with any increase in matrix strain matched by an equal increase in fibre strain. In this region the strain distribution along the length of the fibre could be approximately described by the shear-lag model of Cox. The critical length of the fibre was found to increase linearly with fibre diameter as predicted by that model. Good qualitative agreement was found with the predictions of a calculation based on finite element analysis over the full range of applied stress.