Linear and nonlinear numerical approaches to brake squeal noise

"Brake squeal" groups a large set of high frequency sound emissions from brake systems, generated during the braking phase and characterized by a harmonic spectrum. The arising of squeal phenomenon is due to an unstable behaviour that occurs in linear conditions, during the braking phase. Several authors studied brake systems instability through a complex eigenvalues analysis of the system. Squeal then reaches a new limit cycle and the linear models of brake system result useless in order to study the squeal characteristics in such a non-linear phase. This paper presents the integration of two different numerical approaches to identify the mechanism bringing to the dynamic squeal instability, and to study its behaviour. The first approach performs a finite element modal analysis of the brake system, to identify its eigenvalues and to relate them to the squeal occurrence. The second one uses a specific finite element program, Plast3, appropriate for non-linear dynamic analyses in the time domain and particularly addressed to contact problems with friction between deformable bodies. The use of this program allows analyzing the behaviour of contact stresses and the dynamics of the system in the contact surface, both in the linear and in the non-linear range. The two models are compared and the arising of squeal is predicted both in frequency analysis with the linear model and in the time domain simulation with the non linear one. Results on instability prediction, obtained with the two models, are discussed. To simplify the dynamic behaviour of its components, the presented study is carried on a simple model, composed by a disc, a small friction pad and a beam supporting the pad. The geometry of the models is related to an experimental set-up that will be analyzed to validate the models and compare numerical results with the experiments. © 2006 Civil-Comp Press.