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During friction it is well known that the real contact area is much lower to the theoretical one and that it evolves constantly during braking. It influences drastically the system’s performance. Conversely the system behavior modifies the loading conditions and consequently the contact surface area. This interaction between scales is well-known for the problematic of vibrations induced by friction but also for the thermomechanical behavior. Indeed, it is necessary to develop models combining a fine description of the contact interface and a model of the whole brake system. This is the aim of the present work. A multiscale strategy is propose to integrate the microscopic behavior of the interface in a macroscopic numerical model. Semi-analytical resolution is done on patches at the contact scale while FEM solution with contact parameters embedded the solution at the microscale is used. Asperities and plateaus are considered at the contact interface.

Brake squeal noise has been under investigation by automotive manufacturers for decades due to consistent customer complaints and high warranty costs. Sound in a squealing brake is excited by the contact between pads and the disc. It is well known that the material friction pad consists of several components making it a heterogeneous material. It is also well known that a part of the wear particles agglomerate at the surface leading to non uniform contact properties. The aim of this paper is to investigate the effect of heterogeneities of the friction material on the dynamic behavior of the brake. For this, an analytical model with three degrees of freedom (a translation and a rotation for the pad and a translation for the disc) has been developed including friction at the disc-pad surface contact surface.

Friction materials for braking applications are made of a great number of components. Mineral Roxul®1000 fibres have been widely used as a reinforcement product for such materials. Especially in NAO/non-steel disc pad applications these fibres are an important component of the new generation formulations. In this paper, specific material formulations have been tested on an inertia braking tribometer. It is shown that the NVH performances may be strongly affected by the fibre type. Especially, a rubber coating on the surface of Roxul®1000 fibres reduces the squeal of NAO/non-steel disc pads significantly. Numerical simulations of the braking system have been also developed to better understand the effect of the material. Results show that the squealing modes are selected among instable modes corresponding to coupling between the pad-disc modal frequencies in frictional conditions.

The determination of the heat gradients in friction brakes is precious data in the analysis of the friction brake performances. However, in calculations, the assumption of uniform contact pressure on the apparent friction surface is often retained. It is proposed in this paper to give a progress report on the various types of heat gradients met in the friction brakes using experimental analysis (flash temperatures, hot bands, gradients on hot bands, macroscopic hot spots, large thermal gradients due to non uniform heat exchanges, etc.), and secondly to discuss on the explanation of their origin and on the techniques of modelling. It is shown that macroscopic models may lead to satisfactory predictions on the main thermal localizations, but only if complex couplings are introduced.

Squeal noise is defined as noise at frequency upper than 400 Hz and occurs if the system has a very high amplitude mechanical vibration. All systems with sliding contact are prone to squeal: curve squeal noise of railway wheels, disc brake squeal, etc. It is well known that squeal phenomenon depends on the local kinematics in the contact patch. A multi-scale approach is proposed to identify the mode selection mechanism. Contact surfaces waves are initiated under pressure and sliding velocity conditions leading to self-excitation. Disc brake squeal is treated with this approach.