Mode-I adhesive fracture energy measurement with modified single-lap joint test geometry

Abstract

The adhesive fracture energy or fracture toughness of adhesively-bonded joints comprising carbon-fiber-reinforced polymer composite substrates and three different types of adhesives was detemined using a modified single-lap joint (MSLJ). This joint was made by implanting end pre-cracks in the adhesive layer at the center of the bondline of a conventional single-lap joint (SLJ). This modification ensured that the crack propagated from a sharp starter crack from both ends of the overlap during testing, reducing the effect of spew fillets on the measured adhesive fracture toughness scatter band. The MSLJ specimens were tested to failure and the adhesive fracture energy was calculated using the Kinloch–Osiyemi model. The values of the adhesive fracture energy obtained from the MSLJ tests were compared with those from SLJ and the double-cantilever beam (DCB) test geometries. The fracture energy values obtained from the MSLJ specimens were significantly lower than those from SLJ specimens and agreed well with those from DCB specimens. The three differenent types of aerospace grade film adhesives tested were Redux 322, Redux 335K and Redux 319A.