On the Impact of Surface Morphology and Transfer Film on Brake System Performance of High-Capacity Metro Train

The brake system of Melbourne’s High-Capacity Metro Train (HCMT) suffers from consistently extended braking distances after repeating a set of high-speed tests and the commission process. The degradation of brake system performance affects the safety of rolling stock and its conformance to the design standard. In this paper, the root cause leading to the degraded brake performance was analyzed. The brake discs and brake pads of the affected train and another train with normal working conditions were removed and a series of examinations was to determine the reason for the change of friction coefficient between friction surfaces. The results revealed that brake disc samples from the affected TS02 trainset suffered from changed transfer film and surface morphology after multiple consecutive high-speed braking applications. The factors that may affect the brake system performance were analyzed in the laboratory. It was found the brake disc surface had a lower hardness level, coefficient of friction, and smaller contacting area with the brake pad when compared to the brake disc and pad samples from another trainset. These factors harmed the performance of the braking system, and the decrease in the braking effort led to a longer braking distance than expected and failed braking tests.