Papers by Author: Hyun Mu Hur

Abstract: For the high quality of wheel, the railway wheel has standardized such as UIC, KS, and JIS code but the chemical composition, the mechanical property and the hardness is merely requested. Although the standard of railway wheel has sustained, 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. 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 threshold stress intensive factor, fracture toughness and impact energy depended on temperature have tested. The result shows that the standard of railway wheel has to supplement fracture toughness and impact energy depended on low temperature in order to reduce the wheel damage.

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.

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.

Abstract: Railway wheels and axles have been one of the most critical components in a railway vehicle. The service conditions of railway vehicles have became more severe in recent years due to the increase of the speed. It is very important to evaluate the reliability of wheels with regard to safety, because wheel failure can cause derailment with loss of life and property. One of the major reasons of the railway wheel damage is the contact zone failure by wheel/rail contact. One of the methods for preventing the failure and increasing the fatigue life is to grind periodically the contact surface before reaching the failure. The increase or decrease of the contact fatigue life by the surface removal of the contact surface were shown by many researchers. However, the reason why fatigue life increases or decrease has not been investigated obviously. In this study, the effect of the surface removal depth on the contact fatigue life for a railway wheel is evaluated through the employment of rolling contact fatigue tests and the finite element analysis. It is found that the contact fatigue life increased with the removal depth. But in the case that the removal depth is greater than the optimal depth, the contact fatigue life decreased. It seems to be obvious that the residual strain is the main factor determining the fatigue life according to the removal depth