A B S T R A C T The brake disc of a railway should have stability. After long-term use, the brake disc may be seriously damaged by thermal fatigue cracks on the frictional surface. In this study, fatigue tests were carried out for a brake disc material (GC25). Furthermore, in order to determine the cause of the thermal fatigue cracks, contact pressure and thermal stress analyses were performed. From these results, the linear relation between temperature and stress variations was obtained, and the remaining life assessment of the brake disc of a railway vehicle was performed by using it.Keywords disc brake; fatigue life assessment; thermal stress analysis. N O M E N C L A T U R E I N T R O D U C T I O NAs the friction contact occurs between the brake disc of a railway vehicle and the pad pushing the revolving circular brake disc, the friction surface of the brake disc is repeatedly heated and cooled by the convection heat transfer between the surface and the ventilated holes during motion. 1 When it is heated by the frictional energy from braking, thermal expansion occurs. At this instant, because the thermal expansion is restrained by the structural shape of the brake disc and the braking pressure acting on the friction surface, compressive stress occurs on the friction surface. On the contrary, tensile stress occurs during cooling and the residual stress is distributed on the friction surface after cooling. If this braking process is repeated, thermal fatigue cracks occur on the friction surface. 2-4 Further, the wear resulting from repeated braking and the shape distortion caused by the thermal fatigue lead to an irregular contact surface between the brake disc and the lining and concentrate the friction heat on a local area. 5 Table 1 shows the replacement rate of the brake disc by thermal fatigue crack for the SAEMAUL train in Korea. 6 It has actually been reported that thermal fatigue cracks occur on the friction surface after the brake disc is used for 6 months, and the brake disc is often replaced at an interval of 2-3 years rather than that of 5-6 years, which is the typical life time, owing to the thermal fatigue. 6 The fatigue characteristic of the brake disc must be enhanced to resolve such problems, and for this, it is important to collect data on the variations in the temperature of an actual brake disc in operation. Furthermore, it is important to estimate the remaining life sufficiently in advance to prevent casualties resulting from the abrupt destruction of the brake disc. In this study, in order to determine the cause of thermal fatigue cracks, contact pressure and thermal stress analyses were performed. From these results, the linear relation between temperature and stress variations was obtained, and the remaining life assessment for the brake disc of a railway vehicle was performed by using it and the results of the fatigue tests for standard specimens.