Preliminary investigation of the effect of roughness in Dynarat simulation

Surface roughness has a significant effect on how loads are transmitted at the contact interface between solid bodies. It causes high local pressures in the contacting roughness peaks, i.e., asperities. Even for a low friction coefficient the surface roughness will still play an important role in the early surface wear. A dynamic ratcheting model (Dynarat) for studying the wear rate of ductile materials in rolling/sliding contact is presented. The material is divided into equal-sized rectangular elements (or ‘bricks’). Each material brick accumulates plastic shear strain when the orthogonal shear stress exceeds the brickʹs shear yield stress. When the accumulated plastic strain exceeds a critical value, the ductility is exhausted and the material is deemed to have failed. Inclusion of surface roughness and refinement of the near-surface brick size cause earlier failure of bricks very close to the surface. In order to model surface roughness, brick size needs to be reduced to, at most, a few microns. The purpose of this investigation is to study the effect of surface roughness in the Dynarat model by comparing the model prediction with the results from two different rolling sliding wear testing machines. Further development of the model is needed, such as more inclusive representations of microstructural behaviour. In addition to that, the ratcheting equation, which drives the Dynarat model, needs to be improved to cover other rail materials and more loading configurations.