AbstractMeasurements have been made of the tensile force required to pull a disk of a model viscoelastic adhesive away from an inert rigid substrate. Over a wide range of temperature and rate of deformation of the adhesive the results were found to yield a single master relation in terms of deformation rate by means of the Williams, Landel and Ferry rate—temperature equivalence for viscous materials. Thus, the strength of adhesion is due mainly to dynamic effects in the adhesive of a viscous nature, in a similar way to the cohesive strength of viscoelastic materials. This similarity is attributed to a common failure mechanism: initial failure at a highly stressed point, followed by spreading of the failure zone under local stresses which are governed by the dynamic response of a compliant material. An increase in the strength of adhesion is observed with decreasing thickness of the adhesive layer. This is also explained by the proposed failure mechanism if failure starts at a critical amount of local deformation energy, a form of Griffith's fracture criterio