Mode I transverse intralaminar fracture in glass fiber-reinforced polymers with ductile matrices

The fracture toughness of laminated composite materials is a very important property for damage-tolerant design, but remains poorly understood under transverse mechanical loading conditions. In this study, the transverse intralaminar fracture in unidirectional laminates with ductile polymer matrices is investigated. The presence of a ductile matrix calls for the use of concepts of nonlinear fracture mechanics for the accurate determination of the resistance of the composite to crack propagation. Unidirectional glass fiber-reinforced polymers with a polyurethane (PU) matrix are studied and compared to a benchmark epoxy (EP). The fracture toughness of these composites was evaluated through the determination of R-curves using the J-integral method, whereas the underlying fracture mechanisms were investigated through in situ testing in a scanning electron microscope. The results suggest stronger adhesion of the polyurethane matrix onto the glass fibers as compared to the epoxy-based polymer. This enables full exploitation of the ductile behavior of the PU matrix, ultimately endowing the laminate with outstanding fracture toughness. The investigated PU matrix has thus the potential to generate laminated composite parts with significantly higher damage tolerance than its epoxy counterpart.