The fibre kinking fracture toughness of laminated composites under combined compression and shear

Compact compression specimens with off-axis fibres are employed in this paper, to investigate the effect of in-plane shear stress on the fibre kinking compressive fracture toughness of laminates. The strain distribution on the surface of the specimen was analysed using the digital image correlation method, and the damage process was monitored with thermal imaging. It was noted that the in-plane shear stress introduced by off-axis angle fibres caused an increase in the values of the R-curves when the off-axis angle was 10° or more. The microscopic morphology reveals that as the off-axis angle of the fibres increases, there is an increasing splitting of large fibre bundles, followed by the fibre compression failure within these bundles. This multi-step damage process may be responsible for the increase in energy dissipation.