Crack growth along heterogeneous interface during the DCB experiment

Interface and bondline heterogeneities are inherent parts of laminated materials. Recently, these otherwise unwanted features are gaining importance enhanced by the surface patterning techniques. In the present contribution, a double cantilever beam adhesion experiment is performed on joints with patterned interfaces. Weak/strong adhesion bands perpendicular to the crack growth direction are produced along the bonded surfaces. A vast range of specimens with different but systematic weak/strong zone ratios is tested. A novel analytical model, including a rule of mixture scaling, is developed to gain phenomenological insights into the data obtained. Two specific cases are addressed: a single strong/weak transition and multiple transitions. The new model proves a very good agreement with the experimental data obtained for any configuration tested. The role of three length scale parameters, weak, strong and process zone sizes, and their interactions, are emphasized. For instance, once small (in comparison to the process zone size) weak/strong zones are present, a substantial decrease in the fracture energy is recorded. This observation may be of importance in understanding both natural (e.g. geckos feet) and industrial (laminated and bonded materials) bondline discontinuities including the role of fillers, voids or kissing bonds.