Fatigue life assessment for brake disc of railway vehicle

Abstract

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.

Development of compacted vermicular graphite cast iron for railway brake discs

“…They also conducted mechanical property and friction tests on these materials. Kim et al [4] analyzed the contact pressure and thermal stress of brake discs for railway vehicles to infer the linear relationship between temperature and thermal stress. They also calculated the remaining life of vehicles using data on the changing temperature of brake discs for railway vehicles in operation.…”

Effects of Nb and Tempering Time on Carbide Precipitation Behavior and Mechanical Properties of Cr–Mo–V Steel for Brake Discs

“…During the braking process, the brake disc absorbs most friction heat resulting from the kinetic energy of railways. Therefore, the brake disc surface bears large heat load and its temperature increases sharply, especially in case of an emergency braking . Moreover, with the increase of train speed, a higher heat energy is generated during braking.…”

Microstructural evolution and thermal fatigue resistance of grey cast iron

“…Thermal fatigue is a common failure mechanism in brake discs. Some published research papers deal with this specific problem from experimental and numerical perspectives, whereas others focus on failure analysis aspects . Temperature gradients and the intrinsic tangential constraint related to disc geometry are responsible for the formation of thermal stresses that, together with continued environmental exposure, can affect the fatigue life and the overall performance of brake discs in service, causing premature failures.…”

“…Thermal fatigue is a common failure mechanism in brake discs. Some published research papers deal with this Nomenclature: Ac 1 , Ac 3 = critical temperatures of steels; FEM= finite element method; H1= heated area 1; H2= heated area 2; H3= heated area 3; R= stress ratio; Term= definition; ThF= thermal Fatigue; σ a = stress amplitude; σ m = Mean stress value specific problem from experimental and numerical perspectives, [9][10][11][12][13][14][15] whereas others focus on failure analysis aspects. [16][17][18][19] Temperature gradients and the intrinsic tangential constraint related to disc geometry are responsible for the formation of thermal stresses that, together with continued environmental exposure, can affect the fatigue life and the overall performance of brake discs in service, causing premature failures.…”