Fragmentation analysis of glass fibres in model composites through the useof Raman spectroscopy

Raman spectroscopy has been used to monitor deformation micromechanics in a model discontinuous fibre composite comprising a single glass fibre in an epoxy resin. The glass fibre was coated with a diacetylene-containing ureth ane copolymer that was subsequently cross-polymerised thermally. During com posite deformation, the stress-induced Raman band shifts of the polydiacety lene sequences in the cross-polymerised coating were used to map the distri butions of strain along glass fibres inside the epoxy resin matrix. The fra gmentation of the fibre has been followed in detail and the behaviour analy sed using classical shear-lag analysis. Values of the interfacial shear str ess along fibre fragments were determined from the measured fibre strain di stributions and were shown to be limited by the shear yield stress of the m atrix. The effect of adhesion between the coating and the fibre upon the st rain distributions has been investigated in detail. The fibre strain distri butions can only be determined accurately when the adhesion is good. Howeve r, in the case of poor adhesion, although the strain distribution in the co ating follows that of the matrix, the fragmentation process can still be mo nitored. (C) 2001 Elsevier Science Ltd. All rights reserved.