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High frequency brake squeal is often suppressed by applying an insulator to the shoe plate of the pad. This may increase the damping and change the coupling conditions in a favorable way, but detailed knowledge about which of the several effects of insulators that are most important is not at hand. A joint effort is needed to increase the understanding of the effects of insulators. This paper describes a new way of measuring the shear stiffness and damping of insulators. The method can be used to measure either the individual layers in an insulator or the complete insulator that is build up of several layers. The method does not rely on the resonant behavior of a structure and it therefore allows for measurements of the parameters over a wide frequency range. The measurement setup can be placed in a temperature chamber and this allows the parameters to be measured over a wide temperature range.

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.