Papers by Author: Young Sam Ham

Abstract: The lexical meaning of derailment shall be the wheels of trains going off the track and it is an important factor for the running safety of railway vehicles. For the measurement of interaction forces between the wheel and the rail, wheel set is used with normal method and the vibration accelerometer is used with simplified method to assess the safety of a railway vehicle in the derailment process. The result has been recorded by measuring vibration acceleration.

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.

Abstract: In this study, the tempering effect on the wear characteristics of induction-hardened SPS5 steel was investigated. For this purpose, three tempering conditions were applied to control the hardness and microstructure of heat-treated SPS5 steel. Ball-on-disk wear tests have been performed using zircornia balls on the tempered specimens to determine the variation of wear characteristics. The results showed that friction coefficient decreased with increasing hardness for induction-hardened SPS5 steel. This seems to occur because real contact area between specimen and mating ball was affected by the specimen hardness. Also, we observe the wear type changes from the plowing wear to the adhesive wear as the hardness increases and the adhesive wear particles act as an obstacle to the transmission of the force of friction, reducing the coefficient of friction and the wear rate.

Abstract: As there are many wear parts in the bogie of freight car, the cost of maintenance is high. Also there are many problems to change the wear plates. In case of welded structure bogie, wear plates are attached 30 positions. Especially, the occurrence of the wear quantity at the side of axle box is higher than any other wear plates. Wear parts needs the low wear and high strength. But the repeated load of carbody has acted on wear parts up down direction continually, the friction force defects at their surfaces. At present, the life of wear plates at the side of axle box is about 3~4 years. So we need the new development of wear plate over ten years life to improve the durability and find the new composite material for maintenance free.

Abstract: Railways are a mass transportation system with high safety and punctuality. These strengths have been well proved by tests and evaluations. Railways are an integrated system with cars, power, signal, communication, line structures and operation. Among many safety standards of these systems, contact force between wheels and lines can be chosen since a derailment coefficient evaluated by contract force is the most important fact that decides the safety of railways. Especially regarding express trains, since they run twice faster than conventional ones, the evaluation of a derailment coefficient is more important than any other criteria. Currently, Korean express trains between Seoul and Pusan use the same stations as conventional trains in Daejeon and Dong-Daegu; therefore, express trains run on conventional lines from express lines. This paper describes test results acquired by increasing the train speed where express lines and conventional lines are connected. Test results tell that it is safe with under 0.8 derailment coefficient and running time is reduced by 10~30 seconds in each section.

Abstract: The important factor to evaluate the running safety of a railway vehicle would be the interaction force between wheel and rail(derailment coefficient), for which is one of important factors to check the running safety of a railway vehicle that may cause a tragic accident. Especially, a newly developed vehicle that first runs commercially requires necessarily the measurement and evaluation of derailment coefficient for securing the safety of a vehicle while measuring the derailment coefficient in view of securing running safety could be the more important factor than any other factors. In the meanwhile, it should be also measured the interaction force between wheel and rail in view of track maintenance as well as running safety because increased weight of a vehicle while it is running over a railway may cause damages or destruction on track components such as rails, sleepers and etc consisted of track and any rapid distortion of track. For the reason, the study was intended to evaluate the curving performance and the running safety from the analyses of dynamic running properties, manufacturing wheel axes to measure the working operation of wheels/rail, static load test, derailment coefficient calculated by running test on main track, ratio of wheel unloading, lateral force tolerance of the vehicle that is newly manufactured and commercially running on Gwangju Urban Railway and describe the results.

Abstract: Bogie is the connection device between carbody and wheel in railway vehicles. It is the core part that exert a important effect on the passenger safety and running safety. Bogie largely consists of the bogie frame, suspension, air brake system and wheel set. A static and dynamic load have acted on it complexly. When the bogie is designed, a finite element method, static load test, fatigue test, running test should be considered. A welded structure type bogie was developed for high speed freight car. But some bogie frames have the problems in end beam. There were some cracks ine end beams. The crack situation of the end beam have a bad effect on the brake system. In that case, the cars would be in danger of derailment. This report shows the cause of end beam crack, improvement method. In order to clear the crack cause, many tests were tried. The test result concludes that the crack cause of the end beam is not the brake load but the vibration at the real line running on the track. It is estimated that the improved car which end beam was reinforced was safe enough within permitted life of the car (25years). On the basis of the results, the existing end beam was improved. The safe of the improved end beam was proved by real line test on the track. The operation of freight car have no problems any more.

Abstract: Among welded structure bogies used for high speed freight cars, failures in an end beam have been found in a number of bogies manufactured in between 1999 and 2000. A freight car suffers from a harsher loading condition and it uses a tread brake without a secondary suspension system. It is presumed that the cause of the failure on the end beam is not the vertical loading by the cargo and the vehicle but the force exerted by the brake. The failure at the end beam makes the brake system useless and can cause a derailment in the worst case. In this study, we propose a simple torsion-free brake shoe holder hanger to remove torsion of hanger bracket. Also performed are the finite element analysis and the on-board test for the developed part. Comparison tests verified the applicability of the torsion-free brake shoe holder hanger.