Papers by Author: Jung Won Seo

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Authors: Byeong Choon Goo, Jae Hoon Kim, Jung Won Seo, Chang Sung Seok
2302
Authors: Jeong Guk Kim, Sung Cheol Yoon, Sung Tae Kwon, Jung Won Seo, Kyung Taek Park
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.
2766
Authors: Seok Jin Kwon, Jung Won Seo, Dong Hyung Lee, Sung Tae Kwon
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.
194
Authors: Hyun Kyu Jun, Jung Won Seo
Abstract: Repair of damaged rail surface by overlay welding is the common rail maintenance method. But the discontinuity in material between base and weld brings initiation of cracks and they causes a rail fracture. Unfortunately, such cracks are hard to detect on site because the weld boundary prevents the echo signals penetration by reflection. So estimation of the critical crack size (CCS) has been a critical issue in railroad industry to prevent a rail from sudden fracture. In this study, we calculated the critical size of crack which was initiated and propagated underneath of the overlay welded rail by applying linear elastic fracture mechanics. For this purpose, we measured the maximum load carrying capacities of cracked UIC60 by inverted 3 point bend tests and checked the feasibility of the finite element (FE) analysis procedure. We could find the correlation in crack size between the test and 3D FE analysis results and applied the proposed 3D FE analysis model to calculate the CCS of a rail. We calculated the stress intensity factors on cracked rail by increasing the size of crack until the rail broke. The CCS was calculated as around 30.0 mm under the normal railway service operating condition.
1175
Authors: Seok Jin Kwon, Jung Won Seo, Hyun Mu Hur, Sung Tae Kwon
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.
1075
Authors: Seok Jin Kwon, Dong Hyung Lee, Jung Won Seo, Young Sam Ham
Abstract: The defect initiation and crack propagation in wheel may result in the damage of the railway vehicle or derailment. Therefore, it is important to evaluate the characteristics of the wheel tread. In the present paper, the characteristics of wheel tread based on contact positions, running distance and brake pattern are evaluated. To evaluate the damage for railway wheels, the measurement for the replication of wheel surface is carried out. The result shows that the damaged wheel tread is remarkably depended on the contact positions between wheel and rail. It should be noted that the replication test can be applied in new evaluation method of wheel damage.
645
Authors: Seok Jin Kwon, Jung Won Seo, Dong Hyung Lee, Chan Woo Lee
Abstract: The majority of catastrophic wheel failures are caused by surface opening fatigue cracks either in the wheel tread or wheel flange areas. The inclined cracks at railway wheel tread are initiated and the cracks are caused by wheel damage-spalling after 60,000 km running. Because the failured railway wheel is reprofiled before regular wheel reprofiling, the maintenance cost for the railway wheel is increased. Therefore, it is necessary to analyze the mechanism for introduction of crack. In the present paper, the combined effect on railway wheels of a periodically varying contact pressure and an intermittent thermal braking loading is investigated. To analyze damage cause for railway wheels, the measurements for replica of wheel surface and effect of braking application in field test are carried out. The result shows that the surface cracks in railway wheel tread are due to combination of thermal loading and ratcheting.
1047
Authors: Dong Hyung Lee, Seok Jin Kwon, Jung Won Seo, Won Hee You
Abstract: The objective of this study is to clarify the effect of hub contact shape on contact pressure and fatigue life with regard to the selection of a suitable taper design near the end of the fit. A numerical asymmetric-axisymmetric finite element model was developed in order to determine the contact stress state of press-fitted shaft by using four types of tapered contact surfaces on the hub. The variations of fatigue crack initiation life according to the change of tapered contact surfaces on the hub were evaluated by using the Smith-Watson-Topper (SWT) multiaxial fatigue criterion. As the result, comparing with the contact pressure and the fatigue crack initiation life, maximum decrease of contact pressure and maximum increase of fatigue crack initiation life were obtained for the 1/400 m/m tapered hub subjected to a bending load near the fretting fatigue limit. Furthermore, as the change of bending load, the optimal amout of taper in hub which fatigue life gets into maximum is varied. Therefore, we suggest that the best performance, in terms of pressure distribution and fatigue life of press fit, can be obtained by using a proper taper values for the hub element.
1638
Authors: Jung Won Seo, Hyun Mu Hur, Sung Tae Kwon, Jae Boong Choi, Young Jin Kim
Abstract: Damage often occurs on the surface of railway wheels due to wheel-rail contact fatigue. Since the wheel failure can cause derailment causing the loss of life and property, it should be removed prior to the wheel failure. The effect of surface removal on contact fatigue life has been investigated by many researchers, however, the effects of residual stress and traction force have not been reported yet. The railway wheel reserves the initial residual stress due to the manufacturing process, and this residual stress is changed by the thermal stress induced by braking. Also, the traction force is usually applied along with residual stress on wheels of locomotive and electric motor vehicle. In this study, the effect of surface removal on the contact fatigue life for a railway wheel has been evaluated by applying the rolling contact fatigue test. Also, the effect of traction force and change of residual stress on the contact fatigue life has been estimated by applying finite element analysis. It is found that the residual stress is a dominant factor determining the surface removal depth as far as the traction coefficient is less than 0.15. If the traction coefficient is greater than 0.2, however, the surface removal depth is observed to be independent on the residual stress.
1067
Authors: Seok Jin Kwon, Dong Hyung Lee, Jung Won Seo, Sung Tae Kwon
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.
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