Mode II fracture toughness of carbon-epoxy bonded joints with femtosecond laser treated surfaces

Mode II fracture toughness of carbon-epoxy bonded joints considering laser treated surfaces was evaluated using the End-Notched Flexure (ENF) test. Four different surface preparations were performed using distinct processing conditions before bonding the specimen arms. The Resistance-curves of the fracture tests were obtained considering an equivalent crack length based procedure. The influence of the different surface treatments on the mode II fracture behaviour was assessed comparing the average values of the fracture toughness. It was verified that a laser treatment employing two interfering laser beams, which produces a complex multi-scale surface morphology free of contaminants, is the best surface preparation regarding higher values of the mode II fracture energy. A cohesive zone analysis was used aiming to validate the followed procedures. The excellent agreement obtained between numerical and experimental results reveals that the used techniques are sound.