Paper VI (ii) Elastic behaviour of coated rough surfaces

Numerical solutions developed by Chen and Engel for the elastic deformation of layered elastic half spaces are recast in the form of correction factors. These correction factors apply to the load and area at a circular microcontact computed using the Hertz equations when both contacting bodies are composed entirely of the coating material. The values thus corrected are the load and area applicable to the composite material consisting of the coating and the substrate. The correction factors depend on the ratio of the coating thickness to the uncorrected microcontact radius. The amount of the correction thus varies with the height of individual asperities. Using approximating functions for the correction factors and the Greenwood-Williamson microcontact model, a simulation scheme is outlined for determining the total microcontact load and area for coated surfaces. Results are obtained using representative surface characteristics and four values of the ratio of the elastic modulus of the coating to the elastic modulus of the substrate. The values of these ratios are E₁/E₂ = 1/10, 1/3, 3 and 10, and span the range from very soft to very hard coatings.