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Over the last two decades, intensive research in the field of innovative brake rotor materials for high performance vehicles has been done. Due to the market demand for lightweight components with high strength even at elevated temperatures, most new concepts are based on fiber-reinforced materials [1]. The most prominent concept is a silicon carbide matrix material with embedded carbon fibers (C/C-SiC), which penetrated into the market for brake rotors in 2000 [2,3]. Such carbon ceramic brake rotor systems (CKB) have already been made available for a wide range of premium sedans, SUVs and sports cars. In terms of tribology, these rotors pose new challenges for an understanding of the relevant friction phenomena in the boundary layer, as well as for suitable formulations of brake pad materials. The brake system's macroscopic tribological performance with such pads is determined by a closed-loop interaction between heat, wear and sliding resistance on the micro scale.

Brake pad materials in today's commercially marketed vehicles are usually complex phenolic resin based composites with numerous ingredients. Since the abandonment of asbestos fibers, different material classes evolved in Europe (low steel), North America (semimet) and Asia (NAO), which specifically meet the requirements of the respective market [ 1 ]. For these complex materials, no a-priori prediction of friction and wear performance is possible today [ 2 ]. Research over the past decade revealed that friction power and wear debris are interrelated [ 3 ] and that the topography of the friction layer shows a very rich dynamic [ 4 ]. The respective processes can be well described with a family of dynamic friction laws, which is suitable for the description of AK-Master test results [ 5 ], as well as for the understanding of history dependent high frequency effects.

Widely known is the fact that friction and wear characteristics of disk brakes are subject to pronounced temperature dependencies. For systems with organically bound brake pads, many thermally induced material changes can occur, ranging from degassing of the phenolic resin binder up to degradation of fibers and melting of metallic components. All these effects modulate the surface structure between pad and disk. They are a major contributor to friction layer dynamics [1] and directly influence the system's performance. Concerning the calculation of contact temperatures in disk brakes, several attempts have been made in the past. Most of them, however, use drastic assumptions (e.g. homogenous materials and ideal contact), which limit the results to qualitative approximations [2]. Recent studies already include the multi-material structure of brake pads. These give indications on how material mixtures must be changed, in order to modify contact temperatures into a certain direction [3].

A ceramic bound matrix has been investigated to be used as a friction material. The materials were produced by means of ceramic technology using frits containing silicates, and ceramic friction modifiers such as tin oxide, zircon, iron oxide, magnesium oxide. Four formulations were tested by means of a tribometer (pin-on-disc tester) using a gray cast iron counterpart. Test section included speeds between 1 and 12 ms-1, and loads between 25 and 400 N. The coefficient of friction of the tested specimens were between 0.7 and 0.4, and exhibited sensitivity to speed at low loads (25 N), while they are quite stables at high loads (400N). The characterization of the tribolayers was carried out by means of scanning electron microscopy. The four developed materials were named A, B, C, and D. They exhibited different wear rates and coefficients of friction. All the materials exhibited sensitivity to speed, while showed a lower sensitivity to load.