A mechanistic criterion for the mixed-mode fracture of unidirectional polymer matrix composites

Abstract A mechanistic fracture criterion has been developed to predict the mixed mode through thickness (translaminar) fracture behaviour of unidirectional (UD) polymer composites. This criterion is energy based and is able to predict the toughness of UD composites. The prediction requires only UD composites constituents and interfacial properties. In order to develop the criterion, the through-thickness fracture behaviour of bulk polymer (epoxy) and UD composite (glass fibre epoxy) along with their fracture surface have been investigated. The fracture testing of glass fibre epoxy and neat epoxy under various in-plane loading is performed using compact tension shear (CTS) fixture. The loading ranges from pure mode I to different mixed mode I/II ratios and pure mode II. To consider the energy absorbed during the plastic deformation of reinforced matrix, the fracture surface morphologies of glass epoxy and neat epoxy were investigated which show an increase by the increase in the shear mode. This effect was included in the developed criterion as well. Consequently, the predictions from the criterion show very good match with the CTS experimental results.