A crack propagation criterion based on local shear strain in adhesive bonds subjected to shear

Direct observations show that the fracture of thin adhesive bonds subjected to shear is characterized by stable crack propagation along the interface followed by catastrophic growth. Other failure processes are observed during the stable growth phase, including crack kinking, development of a large void at the crack tip and formation of a detrimental interface micro-debond ahead of the main crack. The specific choice depends on factors such as the position of the precrack plane within the adhesive layer, the layer thickness and the loading level. Regardless of the specimen geometry, the entire interfacial crack propagation event is controlled by a single parameter - a critical shear strain at the crack tip that is independent of the bond thickness and the shearing direction but is a (decreasing) function of the crack velocity. The results can be useful in the application of fracture mechanics to the design of microlaminates, composites, traditional adhesive bonding and other technologies in which thin adhesive layers are used. Published by Elsevier Science Ltd.