MODE-I FRACTURE-BEHAVIOR OF ADHESIVE JOINTS .1. RELATIONSHIP BETWEEN FRACTURE ENERGY AND BOND THICKNESS

The fracture properties of adhesive joints of aluminium were investiga ted using a rubber-modified tough epoxy resin system (G(IC) = 2.76 kJ/ m(2)) as adhesive material. Compact tension (CT) adhesive joints were manufactured for a wide range of bond thickness t (from 0.05 mm to 10 mm) and fracture tests conducted under static load. Scanning electron microscopy (SEM) was used to examine the fracture surface morphology. A large deformation elastic- plastic finite element model was develope d to evaluate the J-integral value for different bond thickness. The f racture energy, J(C), was found to be highly dependent on the bond thi ckness and was lower than that of the bulk adhesive. As the bond thick ness was increased J(C) also increased, though not monotonically, towa rds the fracture energy of the bulk adhesive. This result was caused b y the complicated interactions between the stress and strain fields, p lastic deformation of the adhesive around the crack tip, constraint fr om the adherends and the failure path. It was shown that values of J(C ) as a function of bond thickness correlated well with the variation o f plastic zone height. Scanning electron micrographs from the fracture surfaces of the CT adhesive joints illustrated that the failure path was mainly cohesive through the centre-plane of the adhesive layer. Br ittle fracture mechanisms were observed for thin bonds (0.04 mm < t < 0.5 mm) but tough fracture mechanisms were identified for thick bonds (t > 1 mm).