Brake squeal noise is generally defined at frequency upper than 1000 Hz and occurs if the system has a very high amplitude mechanical vibration with sound pressure level above 120 dB. It is well-know that the occurrence of squeal depends on many phenomena still relatively unknown. This situation is made difficult by the complexity of the composite raw friction materials, as well as the accumulation of wear debris in the form of a third body at the contact interface. The evolution of the friction material, the third body and the surfaces in contact during braking make even more complex this problem. It is proposed here to provide some potential interactions between the state of the contact surfaces and the potential for triggering the squeal.
One way to understand this phenomenon is to study simplified set-up allowing controlling the dynamic behavior and material and surface parameters. Duboc has developed a simplified set-up made of a plate spring holding a pad-housing, a pad and a disc. An analytical model of the experiment has also been developed. It is three degrees of freedom model (a translation and a rotation for the pad and a translation for the disc) including a disc-pad surface contact model with frictional contact surface. The analytic model is in the same way as developed by Oura . This surface contact analysis model connects the disc with the pad via distributed springs (contact stiffness). From this model, a complex modal analysis is performed to determine the frequencies of the system.
In Magnier, the model previously described has been extended by introducing heterogeneous stiffness and the results show clearly that the distribution heterogeneities play a key role on the mode lock-in. However in this paper, all heterogeneities were square shaped with edges equal to 1.5 mm.
In the present study, we propose to extend the model by considering the influence of the size of the heterogeneities on the potentiality of squeal noise occurrence. Results show that the size of contact localization has also an influence. It also shows what size of heterogeneity it is reasonable to consider. Such information is relevant to interpret the occurrence of noise compared to the sizes of the ingredients of the brake pad and the morphology of surfaces in contact.
V. Magnier,*, J.F. Brunel, K. Bonnay, P. Dufrénoy - Univ Lille Nord de France