Influence of femtosecond laser treated surfaces on the mode I fracture toughness of carbon-epoxy bonded joints

Abstract The influence of laser surface treatments on mode I fracture toughness of carbon fibre reinforced composites bonded joints is addressed in this work. Five different surface treatments considering several combinations of laser fluence and scanning speeds were applied prior to bonding of the adherents, aiming to increase the adhesion and, consequently, the fracture resistance of the bonded joint. Mode I fracture characterisation considering Double Cantilever Beam tests was subsequently performed to assess the influence of the several treatments on the critical fracture toughness under pure mode I loading. A suitable compliance based data reduction scheme was used to obtain the resistance curves as function of the equivalent crack length. It was verified that a laser treatment based on an interference scheme is the most effective surface preparation concerning maximization of the mode I fracture energy. A finite element analysis including cohesive zone modelling was performed to validate the procedure and experimental conclusions.