Coated contacts: a strain approach

A strain approach for the design of coated contacts is described, allowing a simple evaluation of the risk of coating failure, once the elastic modulus of the coating and the substrate and the coating thickness are known. Examples are provided for hard and soft coatings. The approach is shown to be particularly useful for hard coatings, where failure is mainly related to tensile longitudinal stresses at the interface. Results from the proposed strain approach compare well with data from a standard stress analysis. Finally, the level of approximation introduced by evaluating the strain field for the reference Hertzian case is discussed, showing that the error introduced is not acceptable.