| Summary: | Modern tribological coatings often possess a multilayered structure, where the properties of each layer can be chosen to optimise the tribological performance of the coating. Such structure can offer advantages over a single layer coating in terms of improved coating durability and reduced contact friction and wear. The behaviour of such complex contacts cannot be fully analysed with current contact models, especially when real surface roughness is considered. Therefore, there is a need for an improved contact analysis model that is able to predict the contact behaviour and sub-surface stresses for real rough multilayered contacts. The work presented in this thesis provides a complete three-dimensional numerical model for non-conformal multilayered real rough surface contacts, which offers a powerful tool for analysis and optimisation of such coated contacts. The model can be used to predict the contact pressure distribution and deformations as well as sub-surface stress field due to applied normal and tangential loads. The contacting bodies are modelled to have an arbitrary geometry, possessing real rough surfaces thus avoiding any assumptions about asperity distribution or shape. The model is based on linear elastic theory and utilises the influence coefficients approach to solve for contact pressures and deformations in a rough contact. The influence coefficients are obtained by utilizing Fourier transforms to solve the Navier’s generalized equation for displacement and stress fields, for an imposed set of boundary conditions pertinent to a multilayered contact. An iteration scheme is set up to obtain the full distribution of pressure and displacement for a rough contact given the applied normal loading, friction coefficient and material properties. The model is validated by comparing its predictions for a set of carefully chosen cases to those obtained with existing analytical and numerical solutions. Results are presented to illustrate the capabilities of the model and its potential applications. These results illustrate how the contact performance, in terms of surface and sub-surface stress, can be enhanced by carefully selecting the properties of each of the layers in a complex multilayered coating. Such enhancements could lead to improved durability and efficiency of machine components, such as rolling element bearings.
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