Fibre-matrix interfaces in carbon fibre reinforced PPS composites: damage initiation and propagation in tensile tests

This paper investigates the effect of fibre-matrix adhesion on the local strain development, as measured by the Digital Image Correlation technique, and on damage initiation and propagation in +/- 45 degrees and 0 degrees tensile tests of 5HS carbon fibre reinforced Polyphenylene sulphide. The sides of both +/- 45 degrees and 0 degrees samples have been monitored by a high-speed camera during testing. Scanning electron microscopy (SEM) analysis of cross-sections of samples tested up to different strain levels has been performed to help the identification of the main failure mechanisms. In the case of 0 degrees tensile tests, the fractured samples' sides have been also observed by optical microscopy and the fracture areas have been analysed by SEM. In the +/- 45 degrees tensile tests, strain concentration is observed in the middle of the samples with low fibre-matrix adhesion, where the interface is not able to transfer the load to the fibres in the outer part of the sample, contrary to what happens in samples with good bonding. A fragile failure is observed in samples with good interfacial bonding, whereas a very extensive delamination failure is obtained in samples with poor interface. In the 0 degrees tensile tests, local strain concentrations develop at each weave cross-over points in composites with poor fibre-matrix adhesion. This leads to weft fibre bundle debonding from the resin and eventually to extensive delamination. A more uniform strain field is observed in samples with good fibre-matrix adhesion, where a fragile type of failure is obtained.