Stress analysis in thin coatings and substrate subjected to point contact loading (mechanics of scratch test)

In this article, a model is developed to predict the stresses in thin coatings induced by a point concentrated load in continuation of articles in describing the tribological contact analysis of coated systems. This solution can be used as a suitable analytical model for mechanics of scratch test. Despite the lack of fully satisfactory analytical model of its mechanics, the scratch test is widely used to quantitatively evaluate the adhesion of coating and substrate. In this test an indenter is drawn across the surface of a coating under an increasing (continuous or step-wise) load. In order to develop an analytical model for scratch test in elastic zone, the fundamental solutions were obtained for concentrated point forces acting perpendicular and parallel to the layer surface. The stress and displacement fields were calculated for the coatings and the substrate due to these forces. These results were compared with the results of finite element method (FEM) by using ANSYS software, as well as with the results of uncoated elastic half-space. These results are also useful for ranking the coating–substrate adhesion of different coated systems, or for estimating the critical mean stress for interfacial failure.