Evaluation of thermal crack propagation for low alloy steel brake disk

Abstract

Very high-speed trains are usually equipped with railway brake disks. During braking, frictional heat is generated by rubbing on the disk surface. Because of non-uniform contact, the frictional heat is localized, and the disk surface temperature rapidly increases in that local area, which is known as the hot spot. This hot spot causes damage such as cracking, which affects the disk life. Therefore, to enhance the disk life or to optimize maintenance intervals, accurately predicting crack propagation behaviours is necessary. This study aims to clarify the relationship between the disk crack propagation rate and braking conditions. Braking tests were conducted by using a reduced-sized brake dynamometer under various braking conditions. The tests revealed that the crack propagation rate decreased under two higher braking energy conditions. Fewer crack propagations were considered because surface cracks were removed as a result of higher wear rates. Furthermore, wear rates could be described by equations as functions of the power with the braking energy. The crack propagation behaviour was predicted using a developed equation that includes the rates of both crack propagation and wear. The crack propagation rates were assessed based on the fracture mechanics using the residual and thermal stress distributions calculated by finite element analysis. The test and predicted results were in close agreement. Thus, the braking conditions that accelerate crack propagation were clarified. This method contributes to the development of long-life disks or provides reasonable maintenance intervals.