アコースティックエミッション計測による自動車用ブレーキ材料の摩擦特性評価

抄録

Since acoustic emissions (AEs) are elastic stress waves resulting from deformation and fracture of materials, the detected AE signals include a lot of information from deformation and fracture phenomenon. The AE waves generated from the interaction of frictional surfaces can be detected as AE signals using an AE sensor attached to the objective material. Although friction force is mostly used for the evaluation of frictional properties of tribomaterials, it is difficult to gain high sensitivity because the rigidity of the friction system could easily be changed by the installation of a spring. On the other hand, the AE signal measurement has a high sensitivity against microscopic deformation and fracture phenomena comparing with frictional resistance measurement. In this study, the relationships between the frictional properties and the AE signals were examined in two experiments: the in situ observation experiments with a pin-on-block sliding friction tester and the long sliding distance experiments with a pin-on-disk-type sliding friction tester. It was found from the results that microscopic deformation and fracture between the sliding surfaces are mainly caused by a crack growth (slip deformation) and separation of brake pad materials, abrasion of the rotor material, and adhesion of metallic fiber to the rotor material. The difference in the fluctuations of the AE signal is caused by the rapid fracture immediately under the sliding surface. In addition, the fluctuations in the AE signals increase because of the deformation and fracture of the tribofilm. It was also found that the average friction force has a correlation with the AE signals mean amplitude value because the amplitude of AE signals vary with the scale of the phenomenon.