Papers by Author: Seok Jin Kwon

Paper TitlePage

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: Dong Hyung Lee, Seok Jin Kwon, Won Hee You
Abstract: This paper presents the results of an experimental investigation of fretting wear characteristics on the contact surface of press-fitted shaft subjected to a cyclic bending load. A series of interrupted fretting wear tests with press-fitted specimens were carried out by using a rotating bending fatigue test machine. The evolution of contact surface profile of press-fitted shaft due to fretting wear were measured with a profilometer. The local wear coefficient during the running-in period is discussed from experimental results and FE analysis. It is found that the maximum depth of fretting wear by repeated slip between shaft and boss occurred at the close of contact edge at the early stage of fatigue life and the regions of worn surface are expanded to the inner side of contact edge as increasing number of fatigue cycles. The initial fretting wear rate at the early stage of fatigue life increased rapidly at all loading condition. After steep increasing, the increase of wear rate is nearly constant in the low bending load condition. The local wear coefficient in running-in period decrease dramatically at the early stage of fretting wear.
1269
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: Seok Jin Kwon, Kazuhiro Ogawa, Tetsuo Shoji
Abstract: In general, the S-N curve in railway axles was mainly carried out under 107-108 cycles, while the service area of a railway axle is 108-109 cycles. The strain gages using electrical resistance have been used to measure stresses in railway vehicle wheelsets. However, there are some problems with strain gages using electrical resistance for railway axles. For example, the measured data is for special or limited intervals only. Strain gage installation is complicated, that is, it requires lead wires for measurement. The design of railway axles makes use of data that was obtained many years ago. The applied stresses in wheelsets running for a long time and in new railway vehicle wheelsets have not been studied clearly yet. It is necessary to carry out stress monitoring for more than 108 cycles to evaluate the safety of railway wheelset. Therefore, it is necessary to develop new stress monitoring techniques that can easily measure the working stress of the wheelset. In the present paper, the stress measurement technique of copper electroplating is considered because of its high potential for this purpose.
84
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: 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.
2495
Showing 1 to 10 of 22 Paper Titles