Impact of Mineral Fibres on Brake Squeal Occurrences

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 level of friction coefficient and material bulk properties obtained experimentally seem to correspond to the conditions leading to instabilities. Results also show relationship between squeal occurrences and friction conditions at the disc-pad interface. SEM observations reveal very different morphologies between silent and noisy rubbing surfaces, indicating strong interactions between the coupling involved in the origin of squeal noise and the friction mechanisms at the interface.