Downscaling for disc-brake wear testing using a thermomechanical approach

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Brake wear has been identified to be an important source of non-exhaust emissions in transportation. The high dissipated energy in the contact not only results in large frictional heat dissipation in the brake components but also in the generation of debris, particles and gases produced by the wear of both pads and disc. Numerical simulation or tribological tests at the material scale are still not sufficient to predict wear. Experiments at the original scale of the brake system are necessary, with a significant implementation time, high costs and with a limited scope. The aim of the present work is a downscaling strategy to design experiments at reduced scale (i.e. pin-on-disc tribometer scale) taking care of the thermomechanical characteristics of the full-scale braking situation in the case of a railway application. This approach requires a complete understanding of the thermomechanical processes occurring during braking, with respect to the contact loading, the thermal localizations (migrating hot bands), the kinematics of contact opening and closing, and the couplings with the tribological circuit and the wear processes. Their apprehension is based on tests carried out on a full-scale bench equipped with the studied railway brake. A numerical model has been developed to interpret the experiment with respect to the kinetics of contact location and opening-closing, and to identify the relative determinants, key to wear. The transposition of the brake configuration to the tribometer configuration is based on these determinants in the design of a wear-preserving tribosystem. For example, the design of the disc has been adjusted on the reduced scale pin-on-disc system to fit with the kinetical parameters of contact location previously described related to the wear determinants.