Static friction behavior of spherical contact with ultrathin soft coating

A surprising behavior of ultrathin soft coating is described in the relevant literature showing discontinuity (sharp drop) between the static friction coefficients before and after an ultrathin soft coating is applied on a harder substrate. Existing finite element (FE) models are unable to explain this unusual behavior since they suffer from convergence problem due to excessive distortion of elements in such ultrathin films. To address this problem, an FE model based on the coupled Eulerian-Lagrangian (CEL) method is presented. This method is able to capture the unexpected behavior of ultrathin soft coatings and hence, to provide a reliable scientific explanation to the experimental observation reported in the literature.