Measurements of the fracture energy of the coating/substrate interfacial region through radial-notched cylindrical specimens

Measurements of the adhesive strength are normally conducted using the dire ct pull test. However, in the direct pull test failure often occurs at the location of the polymeric adhesive used to prepare the direct pull rest spe cimen when the adhesive strength of the coating/substrate interface is stro nger than the strength of the polymeric adhesive. Even when failure does oc cur at the coating/substrate interface, the direct pull test provides ill-d efined properties since the measured failure strength is strongly affected by the strength-controlling defects present at the interface before the tes t. In this paper we have developed a new test specimen geometry that ensure s the propagation of the crack along the coating/substrate interface or the interfacial region, depending on the properties of the interface and the i nterfacial region. Furthermore, the new specimen provides well-defined prop erties, i.e. the fracture energy of the coating/substrate interface or the interfacial region. The proposed specimen is validated using oxide coatings on steel substrates prepared via the thermal spray technique. (C) 2000 Els evier Science S.A. All rights reserved.