ON USE OF DOUBLE CANTILEVER BEAM FOR COATINGS AND ADHESION TESTS

The compliance model of Double Cantilever Beam (DCB) for testing coati ngs and adhesion has been proposed and verified experimentally. The mo del is based on the assumption that the coating modifies the stiffness of a foundation of DCB onto which the beam is fixed, according to a s imple series-spring law. The model includes multi-coated specimens, in particular the specimen with thermal sprayed ceramic coating, with an additional layer of epoxy adhesive for attachment of a symmetrical DC B arm. It was found, that the compliance of DCB specimens with a coati ng is significantly increased for a coating thickness larger than simi lar to 1% of the arm thickness, and a coating Young's modulus smaller than similar to 50% of the arm modulus. The model results, verified by experiment, have profound consequences on calculations of the strain energy release rate in fracture tests for coatings, brazed joints etc. The total compliance of the arm and coating assembly scales with the coating stiffness, and thus the model can be utilised for rigidity eva luation of a variety of coatings on standard substrates, e.g. paints o r polymer coatings on metals.