A numerical study of contact damage and stress phenomena in curved porcelain/glass-filled polymer bilayers

Finite Element Analysis is used to examine contact damage induced by Hertzian indentation of a porcelain coating on a glass-filled polymeric substrate. Different forms of cracking in the porcelain coating are studied –“Hertzian” cone cracks close to the indenter, more distant “outer” cone cracks, and “radial” cracking at the coating/substrate interface. The effects of porcelain coating thickness and radius of curvature on the critical stresses for initiation of these cracks are examined. The predicted critical load curves suggest that for systems with compliant substrates (relative to the coating) with a given radius of curvature, there is an optimum porcelain coating thickness that maximises the critical load for cone cracking. Conversely, for a given coating thickness, the effects of curvature vary significantly – for thinner coatings, where outer cone cracks are dominant, highly convex surfaces are more resistant to cracking, whereas for thicker coatings, which are more prone to Hertzian cone cracking, concave surfaces produce a higher predicted critical load. Curvature is observed to have little effect on the critical load for the formation of radial cracks, which remains the dominant mode of failure in cases of thin coatings on compliant substrates.