This paper presents a new model for analysis of non-conformal rough surface contacts where one or both of the contacting bodies are coated with a multilayered coating. The model considers elastic contact of arbitrary geometry with real measured roughnesses and both normal and tangential surface loads. It predicts contact pressure distribution, surface deformations and full subsurface stress field. As such, the model offers an optimisation tool for analysis and development of multilayered coatings. Influence coefficients approach is utilised to obtain contact pressures and subsurface stresses while the contact solver is based on standard conjugate gradient method. To improve model efficiency, a semianalytical approach is devised, where the influence coefficients for displacements and stresses are expressed explicitly by solving the fundamental equations in the frequency domain. Fast Fourier Transforms in conjunction with discrete convolution are then utilised to provide the solution in spatial domain. Selected results are presented to first validate the model and then illustrate the potential improvements that can be achieved in the design of multilayered coatings through application of the model. A s -Influence coefficient matrix for general stress, SE* (1) -Equivalent elastic modulus based on properties of counter face and layer (1), 's parameters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 4 1 Introduction Surface coatings are widely employed in tribological components with the primary aim of protecting contacting surfaces from damage and/or reducing friction, particularly under poor lubrication conditions. Bearings, piston rings, fuel injectors and cams and followers are some of the mechanical components were tribological coatings are often employed. Relative to a homogenous contact, presence of a coating in general modifies the contact mechanics in two ways: contact pressures and areas are either increased or decreased depending on the coating properties relative to the substrate and the subsurface stress fields are modified not least due to the mismatch in elastic properties of the coating and the substrate. When carefully controlled, such changes can offer superior contact performance but when poorly understood they can lead to premature failure of coated contacts through mechanisms that may not have been expected in the equivalent homogenous contact, such as fracture, fatigue and delamination. Many modern coatings possess a multilayered structure, where the properties of each coating layer can be chosen to optimise the prevalent contact mechanics for ...

A recently developed thermo-mechanical model was used to investigate the influence of surface roughness characteristics on the maximum contact temperature rise as well as shear stresses in rough surface contacts subjected to normal and tangential loading. In order to identify prevailing trends clearly the surfaces were modelled as having idealised sinusoidal roughness. Following a brief description of the numerical model, results are presented to illustrate the dependence of contact temperature and stresses on roughness parameters such as wavelength and amplitude as well as the contact Peclet number. An attempt is made to explain the observed trends in terms of variation in predicted pressure distribution and real contact areas for different surfaces.

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