Book Description

This thesis is addressed to understand the physics of the instability that is at the origin of squeal noise. Due to the interdisciplinary nature of this issue, involving especially dynamic and tribological aspects, the work is organized into four main branches, developed parallely. i) A linear finite element model is developed to predict the squeal frequencies by a parametrical analysis (complex eigenvalue analysis). ii) The unstable values of the system parameters are introduced into a nonlinear finite element model to study the system vibrations and the behaviour of the contact stresses with and without squeal. iii) A dynamic experimental analysis is performed to understand the macroscopic behaviour of the system and to link the squeal instability with the system dynamics. The design of a simplified brake set-up, characterized by a dynamics that can be simply monitored and modified, allows to highlight the modal coupling (lock-in) phenomenon. iv) A tribological experimental analysis is developed to understand the role of the components of the tribological triplet (mechanism, first bodies, third body). The topography of the contact surfaces allows to validate the numerical results and to evidence fatigue phenomena. The results obtained from the four branches of the research converge together, characterizing the squeal as a dynamic instability of the brake system due to unstable couplings between two modes of the brake components. The coupling occurs at the contact where the oscillations of the local contact stresses and the friction coefficient couple the normal and tangential vibrations of the brake components, causing auto-excited vibrations of the system.