Papers by Author: Sung Tae Kwon

Abstract: The temperature monitoring on the surface of the railway brake disc was performed using high-speed infrared (IR) camera. The railway brake disc was developed for disc braking of maximum train speed of 180 km/h. The braking tests were conducted with a full scale dynamometer, and a high-speed infrared camera was employed to monitor temperature evolution on the brake disc during braking operation. The high-speed IR camera provides the measurement of temperature change during braking as well as the images of temperature contour on the brake disc surface. In general, the hot spot generation has been considered the main degradation mechanism in railway brake disc. In this investigation, damage evolution due to generation of hot spots on railway brake disc was investigated using the infrared thermography method.

Abstract: The railway wheel in long-term running had experienced the wheel damage due to fatigue crack and shelling. The damaged wheel in railway vehicle would cause a poor ride comfort, a rise in the maintenance cost and even fracture of the wheel, which then leads to a tremendous social and economical cost. It is necessary to evaluate long-term damage of railway wheel in order to ensure the safety of wheel. To evaluate the damage for railway wheels, the measurements for the replication of wheel surface and residual stress of railway wheel using x-ray diffraction system were carried out. The result shows that the residual stress of wheel is depend on the running distance and thermal gradient during brake application also that the replication test can be applied in new evaluation method of wheel damage.

Abstract: The tensile fracture behavior of polymer matrix composite materials was investigated with the aid of a nondestructive evaluation (NDE) technique. The materials, E-glass fiber reinforced epoxy matrix composites, which are applicable to bogie materials in railway vehicles to reduce weight, were used for this investigation. In order to explain stress-strain behavior of polymer matrix composite sample, the infrared thermography technique was employed. A high-speed infrared (IR) camera was used for in-situ monitoring of progressive damages of polymer matrix composite samples during tensile testing. In this investigation, the IR thermography technique was used to facilitate a better understanding of damage evolution, fracture mechanism, and failure mode of polymer matrix composite materials during monotonic loadings.

Abstract: Upon investigation of the damaged wheels it was determined that the cracking was caused by thermal fatigue during on-tread friction braking. The thermal cracks appear as short cracks oriented axially on the wheel tread. Severe heating of the wheel tread during braking was believed to be a contributing the variation of residual stress which is related to wheel failure. It is necessary to evaluate the residual stress due to deterioration of wheel tread in order to ensure the safety of wheel. In the present paper, the residual stress of railway wheel for deterioration using x-ray diffraction system is evaluated. The result shows that the residual stress of wheel is depend on the running distance and the residual stress needs to be inspected between the wheel diameter of 800 and 780mm.

Abstract: The hot spot generation has been considered as the main degradation mechanism in railway brake disc. Therefore, the understanding of hot spots, also called hot judder, which is undesirable low frequency vibrations developed by non-uniform contact area between brake pad material and brake disc, is important for a better understanding of material design as well as enhancement of materials properties in railway brake disc. Also, infrared (IR) thermography is a powerful NDE technique for the characterization of thermal phenomenon in engineering components and/or systems including engineering materials. The high-speed IR camera provides the measurement of temperature change during brake operation as well as the images of temperature contour on the brake disc surface. In this investigation, damage evolution due to generation of hot spots on railway brake disc was investigated using the infrared thermography method. Moreover, based on obtained thermographic images of hot spots, the hot spots and thermal damage of railway brake disc during braking operation were qualitatively analyzed.

Abstract: Damage evolution due to generation of hot spots on railway brake disc was investigated using the infrared thermography method. A brake disc with gray cast iron, which is currently used in Korea, was employed for this investigation. A high-speed infrared camera was used to measure the surface temperature of brake disc as well as for in-situ monitoring of hot spot evolution. From the thermographic images, the observed hot spots and thermal damage of railway brake disc during braking operation were qualitatively analyzed. Moreover, in this investigation, the previous experimental and theoretical studies on hot spots phenomenon were reviewed, and the current experimental results were introduced and compared with theoretical prediction.

Abstract: The structural strength during static loadings for a carbody of railway container freight car was evaluated to verify the structural strength of newly manufactured carbody. The carbody of freight car was designed with SM490YA steel and stainless steel for the general railway transportation. Prior to the assessment of structural strength, finite element method (FEM) characterization was used for the stress and structural analyses on stress distribution in a carbody of container freight car. The strain gages were attached on the carbody based on the FEM results in order to measure structural strength during static loadings such as vertical and compression loadings. The actual vertical loading test and horizontal compression loading test were conducted, and the results were compared with the previous FEM results. In this investigation, the evaluation method for the structural strength in a structural component has been introduced using several engineering techniques, and experimental and theoretical results were compared.

Abstract: In order to investigate performance characteristics of deteriorated subway rolling stocks, several engineering assessment methods, such as the acceleration, vibration, and braking performance tests, were carried out on subway electric multiple units (EMUs) with over 20 years operation. According to the testing results, in vibration and braking performance of EMUs, the similar performance results were obtained as compared with newly manufactured EMUs. However, in terms of acceleration performance characteristic, below reference value (3.0 km/h/s) has been obtained. This is mainly due to performance deterioration of EMUs including traction motor. In this investigation, the results on precision diagnosis evaluation of deteriorated EMUs were provided through the overall evaluation of corrosion testing and structural performance of car body in subway EMUs.

Abstract: The precision diagnosis of subway electric multiple units (EMUs) was conducted with various types of engineering analysis techniques for the current performance and wear evaluation. The evaluation was conducted on detailed parts of EMUs, such as car bodies, bogies, braking systems, and electrical systems of EMUs. Several characterization means including nondestructive evaluation techniques, corrosion testing, and three-dimensional measurements, were employed for the evaluation of car bodies and bogies. For braking system, degradation and performance tests were conducted, while the functional and degradation tests were performed on electrical system in order to identify the actual performance of the system. Moreover, stress and structural analyses using commercial finite element method (FEM) software provided important information on stress distribution and load transfer mechanisms. In this investigation, various advanced engineering analysis techniques for the safety analysis of subway EMUs have been introduced and the analysis results have been used to provide the critical information for the criteria of safety assessment.

Abstract: Despite of improvement of wheel material for railway vehicle, the damages of railway wheel have been occurred in service running. Because of wheel damage with spalling, shelling and thermal crack, the maintenance cost for the railway wheel has increased. The railway wheel had standardized but the chemical composition, the mechanical property and the hardness with respect to railway wheel is merely established. In order to reduce wheel damage, it is necessary to reinforce the standard of railway wheel. In present study, the fracture mechanics characteristics of railway wheel such as low cycle fatigue, fracture toughness, impact energy depended on low temperature and so on have tested. The result shows that the standard of railway wheel has to supplement fracture toughness and impact energy depended on low temperature etc.