Using the fracture efficiency to compare adhesion tests

This paper reports the use of a novel concept, the fracture efficiency, to evaluate adhesion tests by deciding whether a particular test would be more or less likely to cause gross yielding or rupturing in the adherend/coating before the fracture condition is satisfied. Because of the technical importance and the difficulty in obtaining meaningful debond energies for coatings, much of the paper is devoted to the coating adhesion measurement problem. The fracture efficiency of the general coating delamination contiguration is investigated and its theoretical limit is determined. The study suggests that it is unlikely to devise a new test with a significantly higher fracture efficiency than the existing tests. New experimental or analytical techniques considering the inelastic energy dissipation are needed for coating adhesion measurement. In addition to the fracture efficiency, the fracture mode mixity of the general coating delamination problem is also investigated. The conditions which may result in the contact of crack surfaces near the crack tip region are identified. The preferred configurations which would tend to induce interfacial delamination are also discussed. Finally, from the viewpoint of fracture efficiency, guidelines are given to aid in the selection of appropriate test geometries for coating adhesion measurement. Copyright 0 1996 Elsevier Science Ltd.