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Mr. John Smith

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Friction material elastic bulk and contact properties have always been of major interest in vibro-acoustical NVH behaviour of braking systems. Finite element models of complete disc brake systems give some insight in understanding complex NVH-phenomena related to brake instabilities. Nevertheless, the dynamic response of these complete models can be very sensitive to the set of normal bulk and contact parameters used in brake pad models. Well-known testing as pad compressibility testing is usually used to update brake pad compressibility models with appropriate physical properties. Sometimes, a mono-dimensional simplified analytical model of the compressibility is built and updated before the finite element update process starts. In the context of pre-modelling update, the present work shows a methodology that offers a more robust identification of friction material bulk and contact static properties, which is built on multi-dimensional compressibility measurement basis. The present investigation describes a methodology based on a reduced analytical pad compressibility model fed with a set of compressibility measurements to update bulk and contact stiffness parameters. For this purpose, an equivalent contact model which represent both piston-backplate and friction material-plane contact properties is derived. A 40bars-compressibility measurement protocol assuming homogeneous friction material elastic properties along the thickness is performed on six pads from the same material but with different friction material thicknesses to establish a set of non-redundant measurements. The influence of an underlayer and/or bonding layer is neglected in the study and the quality of friction surface finish is considered from same quality. The reduced pad compressibility model gives mathematical framework for an optimization procedure which takes into account the pad compressibility measurements with different friction material thicknesses. The analysis of optimized compressibility parameters brings numerical values of equivalent contact parameters according to a non-linear exponential contact law as well as friction bulk modulus. After the identification of an equivalent contact model, the correlation of piston-backplate contact properties gives a concrete frame to determine friction material-plane contact properties. The study is derived for the first and the sixth compressibility cycle for the loading phase as well as for the unloading phase without modelling of creep phenomena, even if this effect exists. The use of this optimization procedure in this physical frame can be used to a certain extent to take into account some creep response of friction materials without any specific modelling of it. The way of decomposing the compressibility measurement in a several-dimensional richer measurement basis through the setting of non-collinear elementary models was seldom met in the literature for this task. This makes the approach of correlating compressibility models different and increases the robustness of the identified parameters. This robustness deals with the definition of the experimental set of measurements of the same friction material with different thicknesses.

Rejdych, Gabriel, Chancelier, Thierry, Thouviot, Sylvain; - Chassis Brakes International

Multi-dimensional Compressibility Measurement Basis As Robust Optimization
Method For Bulk And Contact Models Update Of Brake Pads In Finite Element

EB2013-FMC-013 • Paper • EuroBrake 2013 • Friction Material Characterisation (FMC)


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