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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.

Brake squeal is usually investigated using linearized models and the eigenvalues of the linear equations of motion. Eigenvalues with positive real parts are interpreted as the onset of squeal. Nonlinearities are commonly neglected due to the high effort associated with the corresponding calculations. Following the linear theory, the vibration amplitude should increase exponentially. On the other hand experimental results and overall experience show, that brake squeal is a stationary or quasi-stationary vibration phenomenon with approximately constant amplitude. This can only be explained by introducing nonlinearities into the model. These nonlinearities are limiting the increasing vibration amplitudes to a stationary limit cycle. Considering experimentally identified material properties of the brake lining as the main source of nonlinearities in the system a nonlinear disk brake model is introduced.