The effect of transverse compressive stresses on tensile failure of carbon fibre/epoxy composites

A novel test configuration has been developed to induce combined stress-states of in-plane longitudinal tension and transverse compression in thin-ply, unidirectional (UD) composite layers. Three different multi-directional laminates have been designed incorporating UD carbon/epoxy plies embedded in angle-ply blocks of the same material. The scissoring deformation of the angle-ply blocks induces transverse compression in the central UD layers when the composite is strained in the 0 degrees fibre direction. The amount of transverse compressive stress was estimated from the measured surface strain of the laminates to be up to about 140 MPa. Negligible effect was found on the tensile failure strain despite the very high in-plane transverse compressive strains generated in the laminates. These were much higher than those typically attained in multi-directional laminates, exceeding the strain at which compressive failure would occur in any 90 degrees plies. The results of this study suggest that in practice fibre direction tensile failure is unlikely to be significantly affected by transverse compressive stresses.