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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.

Starting in the late '90s, a new and innovative brake disk technology entered the high performance passenger car market. Approx. 2 years later, small volume production of carbon-ceramic brake disks started. In the past ten years the number of cars equipped with the new generation of ceramic matrix composite (CMC) brake disks has continuously increased, with main usage in low volume, high horse power applications. The goal of this paper is to give an overview of the system specific boundary conditions as well as today's and tomorrow's targets and aspects of friction material development used in CMC-disk based brake systems. Starting with a description of the system component properties, a comparison of typical CMC vs. standard gray cast iron disk (GCI) applications will be made. The impact of the component properties, especially the disk as friction counterpart to the pad, will be shown by comparing industry standard test scenarios.