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The NVH behavior of brake systems remains a core problem for the brake industry. Many efforts have been made to achieve a better system understanding, but the prediction of noise occurrence based on measurable parameters remains unsatisfactory. By considering the brake pad as one key component within the brake system, until today different measurement methods describing its material properties have been developed. This work analyses the correlation of all important “state of the art” friction material/pad parameter measurement methods to the NVH behavior of a specific brake system on a statistical basis. The answer to the question “does the NVH parameter for friction materials exist” ? will be derived from these correlation results.

It is widely known that friction materials show a load and frequency dependent stiffness. The load dependency can be explained with a geometrical nonlinear material structure, like the existence of porosities that are compressed by increasing the load. The frequency dependency is principally due to the viscoelastic characteristics of the polymer matrix that binds the different components together. Today there are commonly three different measurement systems used to investigate the material stiffness in compression: Ultrasound, which measures in a MHz-range, piezoelectric actuator to measure in a kHz-range, and hydropulser used for low frequency and quasi-static conditions [1]. Comparing the results from different authors it can be observed, that the stiffness does not change dramatically in the frequency range of each system, but between systems. There is a great discrepancy in the observed results, and it is said, due to the material's frequency dependence.