Translaminar fracture toughness of carbon fibre reinforced polymer composite laminates with cross-ply configuration under biaxial tensile loading

A novel test method is proposed in this study to investigate the fibre tension fracture toughness of composite laminates under biaxial load. Cruciform specimens with a central pre-crack were prepared and loaded in both longitudinal and transverse directions simultaneously with various load ratios. The J-integral method, based on full-field strain data obtained with digital image correlation (DIC), was employed to calculate fracture toughness during crack initiation and propagation. Crack initiation and propagation have been found dependent on the loading ratio, with the longitudinal fibre tensile fracture toughness increasing with the increasing of transverse stress. Fracture mechanism analysis suggested that this increase in fracture toughness may be attributed to the reduction of stress concentration at the crack tip due to transverse stress, which facilitates the stable growth of the fracture process zone (FPZ) and results in an extended fibre pull-out length.