• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.144-145
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• 2006

A developed molybdenum hybrid-alloyed steel powder is based on a molybdenum prealloyed steel powder to which molybdenum powder particles are diffusion bonded. The sintered compact made of this powder has a finer pore structure than that of the conventional molybdenum prealloyed steel powder, because the ferritic iron phase $({\alpha}-phase)$ with a high diffusion coefficient is formed in the sintering necks where molybdenum is concentrated resulting in enhanced sintering. The rolling contact fatigue strength of the sintered and carburized compacts made of this powder improved by a factor of 3.6 compared with that of the conventional powder due to the fine pore structures.

• 한국정밀공학회지
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• 제33권7호
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• pp.541-549
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• 2016

Rolling contact fatigue and wear on rails are inevitable in railway operations due to excessive wheel-rail contact stress. The wear is influenced by vehicle speed, contact pressure, environmental conditions, and many other factors. Speeding on a curved track causes many problems such as wear on the gauge of the rail and rolling contact fatigue. Managing environmental conditions can reduce problems on the wheel and rail interface. In this study, the wear characteristics of wheel and rail materials were investigated by twin-disc testing using various parameters. The results of the wear test indicated that the wear rate under dry conditions was larger than that under wet conditions. We found that contact fatigue damage occurred on the rail in dry conditions, however, the surface of the specimen under water remained smooth. Also, the friction coefficient in dry conditions was larger than in wet conditions.

• 대한조선학회논문집
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• 제53권5호
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• pp.380-387
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• 2016

Present research target to develop the procedure of long-term fatigue analysis of the structural details near the upper rolling chock of IMO type B tank by using the time domain modal analysis technique where both the contact and friction behavior can be accurately simulated. In order to perform the time domain analysis focused on the contact and friction, the entire model of the hull and tank was condensed with DOF reduction technique, which is obtained by transforming the global finite element model into its quasi-static modal coordinate. Modal analysis using the quasi-static deformation modes is chosen as a cost effective time domain simulation method and this is based on the fact that the structural response of the tank is quasi-static. Based on the developed cost effective time domain simulation method, the long-term fatigue analysis procedure for the structural details near the rolling chock and key of independent type tank is targeted to be established. The developed fatigue assessment procedure takes into account, wave induced stress and both contact and friction induced stress without loss of accuracy.

• International Journal of Railway
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• 제5권3호
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• pp.129-134
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• 2012

Contact fatigue damages on the rail surface, such as head checks and squats are a growing problem. The fatigue cracks forming on the contact surface grow according to load and lubricating conditions and may end up breaking the rail. Rail fracture can be avoided by preventing the cracks from reaching the critical length. Therefore, the crack growth rate needs to be estimated precisely according to the conditions of the track and load to develop a maintenance plan against rail damages. Therefore, it is important to understand the mechanism of cracks initiation and growth on a rail due to repetitive rolling contact. In this study, we have investigated the crack growth behavior on the rail surface by using the twin-disc tests and the finite element analysis.

• International Journal of Railway
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• 제2권2호
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• pp.43-49
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• 2009

Wear and rolling contact fatigue (RCF) defects are most important causes of rail damage, and often interaction competitive at present railway track. Head check is one of rolling contact fatigue (RCF) defects, and generally occurs in mild circular curves and transition curves that are set at both ends of sharp circular curves. Wear tends to limit the crack growth of head checks by removing the material from the RCF surface. In order to clarify the conditions of the occurrence and growth of head checks, the authors measured the interacting forces between wheels and rails and the angle of attack of wheelset, and carried out contact analyses using the actual profile data of wheels and rails. The effects of the lateral force, the contact geometry, and the wear rate at rail gauge comer on the formation of head checks were also analyzed by using the worn profiles of actual wheels and rails and the data obtained by a track inspection car. Some specific range of wear rate at the gauge comer was identified as having close relation with occurrence of head checks.

• Tribology and Lubricants
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• 제19권1호
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• pp.26-30
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• 2003

The stresses of surface and substrate under the rough surface contact are irregular. Using rainflow counting method for irregular stresses, the fatigue surface crack initiation lift was calculated. With the surface generated by computer, this paper figures out the random load generated by contacting to the rough surface, analyzes the stress of its subsurface, and calculates the fatigue crack initiation life of the rough surface fatigue theory.

• 한국철도학회논문집
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• 제15권2호
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• pp.141-146
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• 2012

차륜과 레일의 반복적인 구름접촉은 레일 표면결함을 유발하고, 레일 표면결함은 충격하중을 유발하여 소음 진동, 레일파단, 궤도파괴로 이어지고 심할 경우 열차사고(탈선)를 발생할 수 있다. 이러한 레일 표면결함을 제어하기 위한 방법으로 레일연마가 시행되고 있다. 본 연구는 KTX차륜과 UIC레일에서 발생하는 최대 접촉압력을 유한요소해석을 통해 산정하였고, 일반레일 및 열처리레일에 대한 구름접촉피로시험을 수행하여 접촉압력 및 반복횟수에 따른 레일표면 경화층 형성 경향을 분석하였으며, 누적통과톤수에 따라 고속철도 레일에서 발생하는 표면 경화층을 제거하여 건전한 레일표면을 유지하기 위해 0.2mm/2천만톤의 적정 레일연마량을 제안하였다.

• Tribology and Lubricants
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• 제20권5호
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• pp.252-258
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• 2004

In this study, using high cycle fatigue (HCF) criteria, the simulation of rolling contact fatigue is conducted under elliptical contact. The HCF criteria fall into three categories: the critical plane approach, the stress invariant approach and the approach based on the mesoscopic scale. The accurate calculation of contact stresses and subsurface stresses is essential to the prediction of crack initiation life. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions and the subsurface stress field is obtained using rectangular patch solutions. The simulation results show that the critical load is decreasing rapidly and the site of crack initiation also moves rapidly to the surface from the subsurface when the friction coefficient exceeds a specific value for all of three fatigue criteria.

• Tribology and Lubricants
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• 제7권1호
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• pp.40-45
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• 1991

Wear performances for dibutyl 3,5-di-t-butyl 4-hydroxy benzyl phosphonate (DBP) were invesitigated using the four ball test machine under sliding and also rolling contact conditions, and compared with ZDDP. DBP showed excellent antiwear performace compared with ZDDP under severe sliding contact. Also, DBP achieved a longer fatigue life than ZDDP under rolling contact conditions. The surface of the worn balls was observed using an optical microscope, and the wear derbis generated was measured using the Particle Quantifier (PQ).

• 한국안전학회지
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• 제22권2호
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• pp.8-14
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• 2007

In this study, tensile and fatigue crack propagation tests machined from actual wheels were performed. FEM analysis also was performed on the crack that was assumed to be 15 mm in depth under the wheel tread surface. The stress intensity factors K I and K II at the crack tip under the stress($P_{max}=911.5MPa$) due to a rolling contact were analyzed for crack growth characteristics. As a result, the perpendicular crack was found to be more dangerous compared to the parallel one. It is found that in the wheel fatigue crack, parallel to the wheel tread surface, the crack with its length 2a = 2.4mm starts to propagate due to the fact that the effective stress intensity factor access to the threshold stress intensity factor($K_{th}=16.04MPa{\sqrt{m}}$) of the wheel.