Elastic Deformation of Coating/substrate Composites in Axisymmetric Indentation

Elastic deformation of coating/substrate composites was examined for axisymmetric indentations with three different geometries of flat-ended cylinder, sphere, and cone. Intensive theoretical considerations were made for the Boussinesq problems not only in its Fredholm integral equation of the second kind, but also in its Green function using the principle of superposition for the approximated contact stress distribution. The agreement and the disagreement between these two different numerical/analytical assessments for elastic surface deformations are discussed. Along with these theoretical considerations, experimental scrutiny was conducted for the theoretical predictions for spherical indentation by the use of a sol-gel-derived MeSiO_3/2 film coated on a soda-lime glass plate. A novel technique is also proposed for estimating in a simultaneous manner the elastic moduli of both the coating film and of the substrate or the elastic modulus of the film and its thickness in spherical indentation tests.