Changes at interfaces of friction components during braking

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Changes at interfaces of friction components during braking

Holinski, R. / Hesse, D.

The energy generated during the braking procedure needs to be dissipated. As a result of energy adsorption, a number of physical and chemical effects occur that result in surface changes of friction elements. These changes determine the service life of friction components and the effectiveness of brakes. Some of the surface changes are detrimental while others are beneficial for a safe braking procedure. Some changes in interfaces have been studied. In particular, during wet seasons, metallization of brake components is encountered, resulting in surface destruction of brake components. It was found that water decomposes at frictional interfaces during braking. Hydrogen diffuses into the rotor surface, resulting in metallurgical changes. Thin metal foils of alpha-iron are sheared from rotor surfaces and are transferred to composite surfaces. Metallization of pad surfaces results in high noise and wear during braking. Transfer of composite material to the rotor surface leads to the formation of layers which reduces wear of friction elements. Controlled transfer of material is essential for good braking performance. It was found that, at rotor temperatures higher than 500 degree C, composite material is no longer transferred to rotor surfaces; rather, the additives in the composite react chemically at rotor surfaces. Decomposition compounds from additives are found on brake discs. Transfer layers and chemical reactions on rotor surfaces have been studied.