Mechanics of delamination of a brittle coating strip on a brittle substrate

A shear lag analysis was developed to quantify the nature of the stresses that develop both within a strip of brittle coating adhered to a brittle substrate and at the coating/substrate interface. The results are compared to results obtained using a more rigorous finite element model. As expected from the shear-lag analysis, the maximum interfacial shear stresses predicted by this model was at the coating ends in the coating/substrate interfacial layer, whereas axial compressive stresses within the coating itself were zero at the coating ends and were a maximum at the center of the coating. In this shear-lag model, the magnitude of these stresses as a function of the applied compressive stress was derived in terms of a single non-dimensional parameter, κ, that took into account the elastic and geometric properties of the coating and the substrate. The results of the shear-lag analysis were fully consistent with the finite element model results except at the corner between the coating and the substrate wherein the finite element model predicted a singularity. An approximate expression for the interfacial fracture toughness was obtained in terms of κ and in terms of the compressive stress at the onset of coating delamination using the analysis.