Enabling more sustainable sealing solutions via multiscale friction modelling

A reliable and accurate seal friction model is paramount in optimizing sealing products towards energy-efficient and sustainable sealing systems. In seals, depending on the contact conditions, boundary and mixed lubrication regimes are as prevalent as the full-film regime due to, for example, rougher contacting surfaces, lubricant starvation, low speed, severe contact pressure, temperature, etc. Although the research on full-film lubrication regime is well matured, a reliable predictive model for rubber dry friction, contributing to boundary and mixed lubrication regimes, is still lacking, therefore hindering the friction and wear models accuracy for sealing applications. In this work, a predictive analytical model to estimate temperature and speed dependent rubber dry friction is proposed. The model is inspired by a multiscale representation of a metallic counterface combined with a first-order analytical approximation of contact stresses and rubber deformation. The counterface is decomposed into different scales of roughness and the rubber dissipation energy is then determined on each scale. The transition between different scales is also modeled, which is important to correctly estimate the contribution from each scale. Subsequently, a cumulative frictional energy loss is estimated to predict the friction force. The resulting model is able to predict temperature and sliding speed dependent friction coefficient and shows a good correlation with in-house experiments. The proposed dry friction model can be combined with the lubricant viscous shearing friction model to predict the overall friction more reliably in the sealing contact, thereby accelerating the design of more sustainable and energy-efficient sealing solutions.