In mechanical braking systems, there are hot spots on the surface of a braking disc due to thermal deformation with a high thermal gradient. Controlling such hot spots is important for extending the life of a braking disc. In this study, surface temperatures of railway brake discs were monitored using infrared (IR) thermal imaging technique. A highspeed infrared camera with a maximum speed of 380 Hz was used to monitor surface temperature changes of the braking disc. Braking tests were performed with a full-scale dynamometer. During the braking test, the surface temperature change of the braking disc were monitored using a high-speed infrared camera. Hot spots and thermal damage observed on the surface of railway brake discs during braking tests were quantitatively analyzed using infrared thermographic images. Results revealed that monitoring disc surface temperature using IR thermographic technique can be a new method for predicting surface temperature changes without installing a thermocouple inside the disc.

The magnetorheological material changes its characteristics according to the external magnetic field. Magnetorheological elastomer existing in the solid phase has micrometer-sized magnetically responsive particles inside. When a magnetic field is applied by a permanent magnet or electromagnet nearby, it can exhibit stiffness that changes according to the strength of the magnetic field. Many previous studies focused on verifying the variability of the material"s characteristics. However, this study newly proposed a variable stiffness joint for the suspension system of railway vehicles using a magnetorheological elastomer, as a basic study of magnetorheological elastomer for a mechanical component. Based on the characteristics test of the magnetorheological elastomer, the variable joint was designed to have the same structure as the conventional guide arm joint of a railway vehicle. Particularly, to overcome the low magnetic field strength, which may be a problem in the previous research, and to implement uniform magnetic field distribution, the electromagnet was designed to make direct contact with the magnetorheological elastomer. A mathematical model was established and a finite element method verified the model, resulting in an average magnetic flux density of 300 mT, which means 30% stiffness change at 15% shear strain.

The sanding device support bracket is part of the axle box and is one of the railway vehicles parts that must withstand extremely harsh environments. Conventional welded structure type brackets were cracked at welds during operation, requiring design changes. To minimize harsh environments and manufacturing errors, this review was conducted from the design stage, and design changes were made through several trial and error. In this paper, the optimal design was derived by performing topology optimization on the model designed and manufactured through trial and error and applied to the actual vehicle. The comparison of the existing model with the empirically designed model confirmed the improvement of the optimal design using the topology optimization. The optimized design was verified by the analysis and the vibration test of IEC 61373 was satisfied. The test parts based on the optimal design were applied to the actual vehicle and the performance was verified. In the optimum design process, the shape and material as well as the weight analysis were performed and finally the brackets were designed to be light in weight and improved in strength.

Conventional railroad vehicles, that run on a line with high frequency of sharp curves, have problems such as wheel noise and wear, from insufficient passive steering. To solve this problem, real-time curvature measurement technology must be developed for realizing active steering. In this study, we propose a uniaxial curvature measurement sensor considering applicability to actual railroad vehicles, and analyze its validity in terms of active steering control. Required characteristics of the curvature sensor according to steering control performance, were determined through railroad vehicle dynamics simulations, and actual vehicle driving information. Measurement range of curvature radius is 200 m to 600 m; measurement accuracy is ±3%, and measurement bandwidth is 0.85 Hz. Effectiveness of the developed curvature sensor was analyzed based on behavior of the car body, the bogie and its installation on the vehicle, and curvature of the track was measured in real time on an actual urban railroad vehicle. As a result of the field test, curvature measurement error was obtained within 3%, validating the feasibility of active steering control for the next generation railroad vehicles.

The self-locking nuts that are used in high-speed railway-vehicle bogies and car-body connections are key components of the fastening system. These bogies and connection systems should withstand the high vibrations and shocks that are generated by high-speed operations. Since the first high-speed railway was developed, the antiloose nuts that are globally used in all of the high-speed rail-vehicle bogies and car-body connection systems are single-use limited to prevent nutloosening accidents during train operations. In this study, we developed a double reusable nut for the self-locking nuts of high-speed rail vehicles with a 100-% lifetime improvement. The proposed nut design was subjected to the KS R 9144 and NAS 3350 vibration-performance evaluation tests, and following the DIN 65151 method, a Junker test was performed for an impact-performance test. As the final step, a practical-application test was performed to assess the reusability of the proposed nut for which the self-locking nut of the HEMU-430X high-speed rail vehicle was utilized, and two reusability tests were subsequently carried out to evaluate the safety