Numerical simulation of elastic-plastic contact between anisotropic rough surfaces

Abstract

A numerical simulation technique is used to study contact between rough surfaces, allowing for the onset of plasticity at individual asperities. The model treats rough surfaces as anisotropic random processes, with Gaussian height distributions and Gaussian correlation functions. The simulation technique is combined with an iterative method for determining the final surface contact state for a specified applied load. This leads to the explicit calculation of all the contact areas for individual rough surfaces. From this, the authors obtain information on not only the average values for contact parameters such as the number of contact regions, surface separation and true contact area, but also on the fluctuations expected in these quantities because of the statistical nature of rough surface contact. Results from the model are compared with the predictions of a purely elastic model, showing how allowing for the onset of plasticity principally affects the number and size of the contact areas. The effects of strong surface anisotropy on contact parameters are also presented, showing the effects to be generally small in the mixed elastic-plastic regime, because of competing effects within plasticity. The conventional plasticity index is determined for the parameters used in the model calculations, confirming that the model predictions agree with this index as a definition of the average extent of elastic and plastic contact. The model may be used to calculate the friction coefficient for any contact state, assuming adhesion to be the only friction mechanism present. Sample results are compared with experimental friction measurements, showing that the incorporation of plasticity improves agreement between theory and experiment.