Keywords: heat dissipation, discrete elements, breaking systems, contact interface, third body, friction.

In frictional braking systems, the thermal problem is of an eminent importance. The heat generated during braking involves a temperature rise in the brake components that affects brake performance and modifies the friction properties and wear of materials. Moreover, two major difficulties remain in studying the thermal problem of frictional problems: the coupling phenomena between tribological, mechanical and thermal behaviour with material degradation; and the multi-scale aspect, from the local heat generation to the volumetric thermal dissipation.

The aim of the work in this paper is to model the heat dissipation for the braking systems. Under severe external loading, one first observes the bodies' surface degradation, which involves debris generation (third bodies in tribology) during the braking procedure. These third bodies are an operator that transmits the load of the first bodies and accommodates the velocity. Different studies also show a complex recirculation, agglomeration and formation of micro-plates of detached particles. The granular nature of the interface is considered by using the discrete element method (DEM) which could help the understanding of the physical phenomena at fine-scale and to approach contact variations over time.

Initially, the dynamic behaviour of the contact interface will be modelled using a dry granular material subjected to shearing at an imposed velocity at a micrometer scale at which these third bodies are observed experimentally. This part examines the behaviour of effective friction and velocity accommodation. The conversion of mechanical energy to heat at each particle contact is shown. The thermal implementation in the computational software allows us to link data (shear rate, contact force, geometry and nature of particles, etc.) to the heat transfer. Then, the heat evolution is examined with respect to time and its distribution in the third bodies (appearance and localisation of hot spots). The investigation of the problem of heat evacuation by conduction in first bodies and by convection in the interface is considerd. All these points are analysed by using our computational software based on the discrete element method whose originality consists in using the bipotential contact method as the solver. The evolution of temperature and its distribution in the interface are compared with the results of a model based on the finite element method.

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