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Disc brake squeal is a very complicated phenomenon, and the influence of insulators in suppressing squeal is not fully understood. The aim of this paper is increase the understanding of the effect of insulators. A previous paper [1] presented an experimental technique for measuring the frequency- and temperature- dependent properties of viscoelastic materials currently used in insulators. The present work continues by considering the coupled vibrations of the brake pad and insulator. A comparison of natural frequencies found from experimental modal analysis and finite element modeling indicates agreement to with 5%. Experimentally determined modal loss factors of the brake pad vary dramatically with frequency, changing by a factor of 2 over the frequency range 2-11 kHz. A method for including this frequency dependence, as well as the frequency dependence of the insulator material, in state-of-the-art finite element software is proposed.

Introducing a rubbercoated steel plate - a shim - on the backing plate of a brake pad often solves squeal problems in disc brakes. This may be attributed to one or more of several effects exerted by the shim: Isolation or decoupling of brake components Alteration of the force configuration The addition of damping The effect of damping may be active in either or both of the following ways: In the direction of the normal force exerted by the piston As a constrained layer damping of the bending vibration of the pad This paper will deal with the constrained layer damping effect introduced by applying a viscoelastic material and an additional steel plate on top of the backing plate. This paper reviews some theories on constrained layer damping and extracts information on the effect of varying important parameters such as layer thickness, stiffness of the constrained material etc.