Numerical Simulations of Soft Coating Deformation by Particle Method

Abstract

Conformability is one of the most important property for sliding bearings at the initial running-in stage. In order to improve this property, most bearings are coated with a soft overlay by several microns in thickness. The conformability relates closely to the plastic deformation and the slight wear of the coating made of resin or soft metal. To evaluate this conforming process, various tests have been conducted, and at the same time numerical simulations needs to be established. We try to develop a numerical simulation by a discrete particle method for analyzing elastic-plastic deformation of a soft coating. This particle method treats relatively larger space scale (discrete particles at 1 micron intervals) compared to the molecular dynamics simulations (MD). And there is no element consisting of nodes unlike finite element method (FEM). Therefore the particle method is convenient for treating failure behaviors (delamination or adhesion). But until now particle methods have never been applied for tribological soft coatings. So we have established a particle method for analyzing elastic-plastic deformation of the coatings in micron order scale and 3D system. Indentation tests were conducted to evaluate elastic-plastic deformations in several simulations and experiments, because indentation tests are popular for soft or hard tribological coatings to evaluate their elastic and plastic properties. In each test, the indenter is loaded and subsequently unloaded. During the loading-unloading process, the load and indentation depth relations were evaluated. In simulations by the discrete particle method, the elasticplastic deformations were reproduced. These results coincide with the prediction that the elastic deformations relate to both loading and unloading processes whereas the plastic deformations relate to only loading process. These tendencies are confirmed by the relations of load and indentation depth. In addition, compared several simulations with several experiments, the deformations of soft coatings made of resin or soft metal were well described by the discrete particle models with two parameters of Young’s modulus and yield stress.