• Journal of the Korean Society for Railway
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• v.11 no.3
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• pp.272-279
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• 2008

The importance of maintenance of rail surface defects is increasing more according to the KTX operation. That is because during high speed operation of rolling stock, rail surface defects may cause shortened fatigue life of rail, acceleration of track degradation and reduced ride comfort. The paper was intended to study the establishment of rail grinding criteria of high-speed railway lines considering the KTX operation circumstances. For this, the specimens of UIC 60 rail on Kyeong-Bu high-speed operation lines were collected and they were tested for metallographic structure and measured for the hardness. As the factors affecting RCF causing the defects of rail surface, passing tonnage, running speed and track condition are considered.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1996.10a
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• pp.207-212
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• 1996

The shotpeening treatment were conducted for improving the strength of rolling contact fatigue of machine element like a gear. This paper was undertaken to analyze the influence of shotpeening treatment for inner race of ball bearing on the roiling contact fatigue. Shotpeening treatment were applied to the full hardened and the carbonitrided bearing. And the rolling contact fatigue life test and X-ray diffraction test were carried out. The results of this study showed that the fatigue life of ball bearing in the clean and the contaminated oil could be improved by shotpeening treatment. This effect was found to be more pronounced to the full hardened bearing.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.714-719
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• 2004

Railway wheels and axles belong to the most critical components in railway vehicles. The service conditions of railway vehicles became more severe in recent years due to the increase of speed. Therefore, a more precise evaluation of wheel/set life and safety has been requested. One of the major reasons of railway wheel damage is a contact zone failure by wheel/rail contact. In this paper, we conducted a rolling contact fatigue test for wheels using a specimen of wheel/rail. the behavior of hardeness and residual stress below the contact surface of the test pieces in the fatigue process were analyzed. Finally, the relation between fatigue life and contact pressure was obtained.

• Tribology and Lubricants
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• v.17 no.3
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• pp.209-215
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• 2001

In view of the effects of the hardness of material on fatigue, rolling contact fatigue process in hard metals seems to differ from it in soft metals. This paper has been aimed to compare the rolling contact fatigue process according to the hardness of materials. Rolling contact fatigue tests using the ball bearings assembled with the inner race of four different hardness have been carried out. In addition, residual stress and half-value breadth on/below the inner raceway during individual rolling contact fatigue have been measured by X-ray diffraction. The results of this study showed that the change of residual stress and half-value breadth during the rolling contact fatigue on race way in hard metals is the same as in soft metals. However, plastic deformation by rolling contact in hard metals is in microscopic scale but only for soft metals in macroscopic scale.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.11a
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• pp.44-49
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• 2000

Recently, PM-high speed steel(PM-HSS) has reportedly been a good alternative material for rolling mill because of its superior peformance to conventional HSS. This paper has been aimed to investigate the possibility for application to rolling contact element for PM-HSS by X-ray diffraction technique. The X-ray elastic constant for PM-HSS has been found by X-ray diffraction during the four-point bending test. Residual stress and half-value breadth on the contact surface during rolling contact fatigue process by X-ray diffraction have also been measured. The result of this study shows that the application of X-ray diffraction technique to PM-HSS could be as possible alternative material as conventional HSS. Half-value breadth on rolling contact surface by X-ray diffraction is not changed during rolling contact fatigue process. On the other hand, the residual stress is changed. This suggests that dislocation reaction has been hardly occurred in rolling contact, depending on supersaturated carbon in PM-HSS.

• Tribology and Lubricants
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• v.13 no.2
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• pp.39-45
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• 1997

The shot peening treatment were conducted for improving the strength of rolling contact fatigue of machine element like a gear. This paper was undertaken to analyze the influence of shot peening treatment for inner race of ball bearing on the rolling contact fatigue. Shot peening treatment were applied to the full hardened and the carbonitrided bearing. And the rolling contact fatigue life test and X-ray diffraction test were carried out. The results of this study showed that the fatigue life of ball bearing in the clean and the contaminated oil could be improved by shot peening treatment. This effect was found to be more pronounced to the full hardened bearing. These facts might be due to the generation of compressive residual stress and the strain hardening of surface layer by shot peening treatment. The failure of the shot peened bearing were presumed to initiate at surface.

• Tribology and Lubricants
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• v.31 no.1
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• pp.1-5
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• 2015

In this study, we apply an ultrasonic nanocrystal surface modification (UNSM) technique to radial journal bearings (JBs) and disks made of SUJ2 and SCM440, respectively. We investigate frictional properties of untreated and UNSM-treated specimens using a ball-on-disk tester. We construct the Stribeck curve at the boundary, under mixed and full hydrodynamic lubrication conditions for the specimens using friction data obtained from JB tests. The friction at the boundary lubrication condition and the transition period to mixed lubrication condition on the UNSM-treated specimens is reduced, which improves the service life of JBs. The major effects of this reduction in the three lubrication regimes can be explained in the terms of improved mechanical properties and the presence of micro dimples. Moreover, we estimate the friction and fatigue properties of SCM440 specimens using a ball-on-disk specimen under dry and oil-lubricated conditions. Friction test results reveal that the UNSM-treated specimens show lower friction coefficient than the untreated specimens under both dry and oil-lubricated conditions. We evaluate the fatigue properties of SCM440 specimens by calculating the Hertzian stress with respect to the failure cycles. Fatigue tests results also reveal that the UNSM-treated specimens possess a longer fatigue life than the untreated specimens. The improved properties are effective in increasing the energy efficiency of bearings.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.6
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• pp.1012-1020
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• 2006

The crack that occurs on the wheels of railroad cars can be categorized into a surface crack that starts from the surface or a subsurface crack that starts from the inside and can be detrimental to safe railroad operations. Therefore, estimating the growth life span of this type of crack is very important. In this research, the stress distributions, displacements, and the growth-life spans of both surface cracks and subsurface cracks have been studied. By using the finite element analysis, especially in the life span prediction process, the stress conditions and the stress intensity factors of the crack tip have been discovered. The Paris formula has been used to analyze the growth-life span prediction.

• Journal of the Korean Society for Railway
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• v.13 no.4
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• pp.447-454
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• 2010

The defects of rail head induced by fatigue and deterioration are mainly classified by two types ; one occurred on the surface of rail head the another occurred on the inner rail head. This study performed the surface irregularity measurement of rail head according to the passing tonnage in the urban railway. Also, we carried out microscopic structure test, chemical component test and micro-hardness test for the specimen which is the used rail on metro line by accumulated passing tonnage. As a result of this study, for new rail, it should be performed initial grinding in order to remove 0.3mm of de-carbonized layer. The preventive-cyclic grinding for preventing RCF defects is proposed two options : grinding by the whole line and grinding by specified sections.

• Tribology and Lubricants
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• v.35 no.4
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• pp.237-243
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• 2019

Through this study, we investigate the effects of ultrasonic nanocrystal surface modification (UNSM) technology on the fatigue life of needle roller bearings. The fatigue life of untreated and UNSM-treated needle roller bearings is evaluated using a roller fatigue tester at various contact stress levels under oil-lubricated conditions. We can ascertain that the fatigue life of an UNSM-treated needle roller bearing was extended by approximately 34.3% in comparison with an untreated one, where the effectiveness of UNSM technology diminishes with increasing contact stress. The surface roughness and surface hardness of needle roller bearings before and after being treated by UNSM technology are compared and discussed to understand the role of UNSM technology in improving the fatigue life of needle roller bearings. In addition, a fractograph of the damaged bearings is observed using a scanning electron microscopy to shed light on the fracture mechanisms of bearings under different contact stress levels. We can therefore conclude that the application of UNSM technology to the needle roller bearings improves the fatigue life by reducing the friction coefficient and increasing the wear resistance; this may be attributed to a reduction in surface roughness from 0.5 to $0.149{\mu}m$ and an increase in surface hardness from 58 to 62 HRc.