Alternative means for evaluating fibre-matrix adhesion in composites

This paper presents an alternative means, for evaluating fibre-matrix adhesion in composites, which uses simple unidirectional composites in a test geometry that ensures the predominant composite fracture mechanism is that associated with interfacial failure, thus providing direct information regarding the characteristics of the fibre-matrix interface. We have investigated these interfacial failure events by means of acoustic emission (AE) during tensile testing of simple composites whose fibres are oriented perpendicular to the tensile direction. The strain and stress range over which these AE events occur determine the strength of the fibre-matrix interface, while the relative total number of recorded events give indication as to the interfacial failure mode. By varying the treatment of the fibre surface, this changes the nature of the interfacial bonding and is clearly reflected in the AE and mechanical responses. In general, the results obtained and presented in this paper demonstrate that the method shows good sensitivity to changes in the level of fibre-matrix adhesion in composites, providing information on the nature of fibre-matrix adhesion, the strength of the bonds and the failure mode, all in one experiment.