Experimental studies on the interfacial shear-transfer mechanism in discontinuous glass-fibre composites

Interfacial stress/strain distributions in discontinuous glass-fibre/epoxy composites have been determined experimentally for the first time by the simultaneous use of tensile deformation measurements and Raman spectroscopy. Model single-fibre composites were used and the glass fibres were coated with a diacetylene-urethane copolymer which was thermally cross-polymerised. During composite deformation, the stress-induced band shifts of C≡C in the polydiacetylene phases of the coating were used to map the strain distribution along a fibre as a function of overall matrix strain up to fibre fracture. Measured strain distributions in fibres were analysed by using classical shear-lag theory to determine interfacial shear-stress distributions. Fibre fragmentation was monitored in detail up to saturation, and the limiting value of interfacial shear stress is shown to be determined by the shear yield stress of the matrix.