Observation of braking systems shows that macroscopic thermal localizations significantly influence wear, vibration and particle emissions. In particular, thermal localizations, such as hot spots, introduce out-of-plane deformations and consequently contact load bearing variations, with contact openings and closures, which have a major influence on the friction, wear and particle emission mechanisms. The trend towards lighter brake discs, with slender geometries (low thickness and large diameter), is bringing back cases of thermal localizations. Brake discs may be subject to several types of hot spots. A first type only appears for ventilated discs, whose may be subject to a well-known mechanism related to non-uniform heat diffusion with a link between the number of hot spots and the ventilation geometry. The second type appears more spontaneously for every disc geometries. The basis for the explanation of the appearance of this second type is the thermoelastic instabilities (TEI) introduced by Burton and Barber in the 60s, with the study of the growth in time of a sinusoidal disturbance in the pressure or temperature field of the contact as a function of the sliding speed. More recent models study progressive out-of-plane wave distortion (PWD) from the deformation arising from the geometric asymmetry of the systems or from the loading. The development proposed here aim to unify PWD and TEI approaches by a 3D transient finite element analysis to study the evolvement of a periodic or non-periodic location. The principle is to carry out coupled thermo-mechanical modelling with contact and to detect the threshold of propagation of the initial localization. The interest is, on the one hand, not to be sensitive to the introduced perturbation and, on the other hand, to be able to simulate complex geometries and non-linear material behavior. Results are above all compared with literature models remaining for example the influence of the thickness or radius of the disc. The contribution of the proposed model is then exploited, by showing the influence of the geometry of the fastener, the non-linear behavior of the materials in contact or the effect of the superposition of a radial contact location of the hot band type. Different parametric analyses are finally carried out to give partial recommendations of geometries aiming at reducing the risks of occurrence of these localizations or their amplitude. REFERENCES: Burton, R. A., Nerlikar, V., & Kilaparti, S. R. (1973). Thermoplastic Instability in a Seal-Like Configurarion. Wear(24), 177–188. Lee, K., & Barber, J. R. (1993). Frictionally Excited Thermoelastic Instability in Automotive Disk Brakes. Journal of Tribology, 115(4), 607–614. https://doi.org/10.1115/1.2921683 Panier, S., Dufrénoy, P., Brunel, J. F., & Weichert, D. (2004). Progressive Waviness Distortion: A New Approach of Hot Spotting in Disc Brakes. Journal of Thermal Stresses, 28(1), 47–62. https://doi.org/10.1080/01495730490498638

Mr. Valentin Bruant, PhD Student, University of Lille; Dr. Jean-François Brunel, maitre de conférence, université de Lille; Prof. Philippe Dufrenoy, professeur des universités, université de Lille