The effect of modal damping on brake squeal instability

"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 generation of squeal is due to an unstable behaviour of the system during the braking phase. Many researchers associate the squeal phenomena to the coalescence of two eigenfrequencies of the system: when two modes, characterized by large deformation at the contact surface, couple at the same frequency, one of them becomes unstable leading to increasing vibration. The present experimental analysis is focused on correlating the propensity to instability of a system mode with its modal damping. Because of the complexity of real brake systems, a simplified experimental set-up is proposed. The set-up is a valid tool that permits to control easily and modify its dynamics. A clear distinction is obtained between the dynamics of the friction pad and the caliper. Different conditions of unstable coupling between a mode of the brake disc and a mode of the caliper or the pad are analyzed. Two opposite roles of the modal damping are detected. A large modal damping can either prevent the rise of squeal instabilities or enlarge the squeal propensity of the brake apparatus. Moreover, the add of damping, aimed to prevent a specified squeal condition, can cause the rise of different squeal events.