Bonding strength is an important property of coating layers and the scratch method is widely used for its evaluation. However, the resistance against one stroke for exfoliating the coating layer is a load bearing capacity rather than bonding strength. A continuous indentation machine with an acoustic emission attachment was designed to detect the initiation of film peeling and the critical value was named Pc. Experiments show that even Pc is closely reated to the smaple hardness, its data are of less deviation and more sensitive to the interfacial condition than the Lc value of scratch test. A better way to evaluate bonding strength is by using contact rolling. Delamination of film occurs after millions of cycles thus stress can be kept in the elastic regime. Under this circumstance, Hertzian analysis can be used to calculate the stress responsible for the peeling of the film. Either cylindrical or spherical contact can be selected for measurement. Since stress concentration is eliminated for ball rolling, the shear stress range at the depth of interface can be precisely determined. The bonding strengths of different coating systems and different film thicknesses can be compared.
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