Fatigue life assessment of cast nodular iron disc brakes for railway vehicles

Disc brakes, not only for railway applications but generally in all vehicle applications count as safety components. Therefore, their reliability during service is essential. A disc brake is submitted to different loadings: braking, including emergency braking; horizontal and vertical wheel forces and forces on driving over switches; mass forces acting in the attachment of the disc brakes to the wheels due to relative displacements and centrifugal forces during rolling of the wheel at higher speeds. In the present work, only the influence of thermal strains/stresses caused by braking on the fatigue life will be discussed. For the disc brake of the cast nodular iron EN-GJS-400-15 considered in this study, the other loadings were proved to be not critical. Because of the continuous distortions of a disc brake after each brake operation due to heating, calculated local strains had to be verified experimentally by strain and temperature measurements. The experiments were carried out in a special test rig of the manufacturer where a spectrum of braking operations from the speeds 200, 160 and 90 km/h were investigated. With the preliminary design, the required fatigue life could not be achieved but the fatigue critical areas were recognized. After the redesign of the discs, fatigue failures were prevented.