Experimental Identification of Brake Lining Material Properties Subjected to Combined Static and High Frequency Loading - A Step Towards a Better Prediction of Disc Brake Squeal?

Brake lining material is one of the main factors influencing brake squeal. Actual simulation of brake squeal suffers on the missing of correct material parameters identified under conditions relevant for squeal. The comparison of different measurement methods for friction material characterization, e.g. compressibility tests, modal analyses or ultrasonic measurements shows that the material properties strongly vary depending on the testing conditions which are static preload, dynamic amplitude, frequency range and the loading direction. The different results obtained from these various test procedures show a nonlinear and transversely isotropic material behavior of the brake lining. In order to identify the correct material parameters for successful brake squeal simulation it is necessary to reproduce the operating conditions during the squealing state as close as possible in experimental setups. The present paper introduces a measurement technique and an identification procedure for brake lining material properties in the out-of-plane direction reproducing the load parameters typical for brake squeal. These are preloaded configurations corresponding to squeal typical brake pressures and sinusoidal dynamic loading producing displacements in the micrometer range with frequencies in kHz-range corresponding to the noise emitting oscillations. Furthermore the identified linear and nonlinear brake lining material properties are presented and discussed.