차륜/레일의 구름접촉을 위한 유한요소모델 및 접촉피로 수명평가

서정원,전현규,배영훈,여인호 한국도시철도학회 2022 한국도시철도학회논문집 Vol.10 No.1

Fatigue damage on the rail surface is caused by repeated rolling contact between the wheel and the rail. Such damage to the rail surface affects ride comfort, noise and driving safety. If proper maintenance is not performed, the rail may break and cause a major accident. It is important to evaluate and predict fatigue damage caused by rolling contact for safety and maintenance of rail. In this paper, a procedure and a finite element model were developed to evaluate the rolling contact fatigue damage of rail. A submodel technique was used to accurately evaluate the repeated rolling contact and the elasto-plastic behavior of the material. Since the surface of the rail undergoes plastic deformation in rolling contact with the wheel, the shape of the contact surface changes, so the contact pressure was obtained through elasto-plastic analysis. From the rolling contact fatigue life evaluation, it was found that cracks occurred at a depth of 2.4 mm from the rail surface, parallel to the surface and almost perpendicular to the rolling direction. 레일 표면의 피로손상은 차륜과 레일의 반복적인 구름접촉에 의해서 발생한다. 이러한 손상은 승차감, 소음 및 주행안전성 등에 영향을 미친다. 만일 적합한 유지보수가 수행되지 않으면 레일의 파단이 발생하여 대형사고를 일으킨다. 레일의 안전성 확보와 유지보수를 위해서는 구름접촉에 의해서 발생하는 피로손상을 평가하고 예측하는 것이 중요하다. 본 논문에서는 레일의 구름접촉피로손상을 평가하기 위한 절차 및 유한요소모델을 개발하였다. 반복적인 구름접촉과 재료의 탄소성 거동을 정확하게 평가하기 위하여 서브모델 기법을 사용하였다. 레일의 표면은 차륜과의 구름접촉으로소성변형이 발생하고, 레일의 접촉면 형상이 변화하므로 탄소성 해석을 통하여 접촉압력을 구하였다. 접촉피로수명평가로부터, 균열은 레일 표면에서 2.4mm 떨어진 깊이에서 표면과 수평이고, 구름방향의 거의 직각인 방향로 발생함을 알 수 있었다.

수분오염 윤활환경 하에서 구름접촉 피로손상의 미시적 관찰

심충기,김홍석,신기훈,정성균 한국기계기술학회 2017 한국기계기술학회지 Vol.19 No.2

Rolling contact fatigue(RCF) is a major cause of failure that appears in components of rolling contacts. In the recent years, the fatigue propagation and failure have been an important issue in respect of the safe operation and to reduce the noise and vibration of the rolling contact components. The water-contaminated lubrication is known to be one of the significant factors that reduces the lifetime of the rolling contact components. Thus, in this study, the effect of water-contaminated lubrication environment on the rolling contact fatigue was investigated. Bearing life testing was performed in two different lubrication conditions (i.e. normal lubrication environment and water-contaminated lubrication environment). The effect of the debirs on the rolling contact fatigue could be eliminated by establishing the debris filter system. Microscopic features of the rolling contact surfaces were examined using energy dispersive spectrometry and non-contact 3D measurement system. In the case of the water-contaminated lubrication, the increase of surface roughness values up to 17.6% was observed. The oxidation state and pattern of the rolling contact surfaces were very different depending on the lubrication environment. It was also found that the bearing rating life, L10 , was decreased significantly in the watercontaminated lubrication condition. The amount of reduction was about 49.7%.

구름접촉을 고려한 레일표면균열발생수명 예측 S/W 개발

김동욱(Dong-Wook Kim),전현규(Hyun-Kyu Jun) 한국철도학회 2016 한국철도학회 학술발표대회논문집 Vol.2016 No.10

구름접촉에 의한 레일표면에서의 손상은 고속화와 축중의 증가로 인해 가속화되고 있는 추세이다. 표면손상이 발생하는 시기를 아는 것은 레일의 유지보수 및 안전성을 확보하는데 매우 중요하나, 이를 위해서는 매우 복잡한 유한요소모델의 생성과 매우 높은 컴퓨팅 파워를 요구하며, 또한 고가의 해석 프로그램이 필요하므로, 균열발생정보가 필요한 현장에서는 시도조차 할 수 없는 상황이다. 이러한 이유로 본 연구에서는 특별한 해석프로그램이 필요하지 않도록 윈도우즈 운영체제에서 단독으로 구동되는 레일표면균열발생 수명 예측 소프트웨어를 개발하였다. 이를 위하여 다양한 손상모델을 프로그래밍 하였으며 구름접촉하중뿐 만 아니라 레일온도차이에 의해 발생하는 선팽창하중, 잔류응력 등의 효과도 고려할 수 있도록 하였다. 따라서 이러한 소프트웨어를 이용하면 열차운행 현장에서도 레일의 대략적인 균열발생시기를 예측할 수 있을 것으로 기대한다. Fatigue damage at the surface of railway rail under rolling contact fatigue is increasing with the increase of axle load and vehicle speed. Although it is very important to know the moment of surface damage initiation for the proper rail maintenance and the secure of railway safety, it is very hard to perform the fatigue damage assessment in field because the analysis require very complex modeling of finite element analysis, high computing power and very expensive analysis software. For this reason, in this study, we developed a standalone computing software for the prediction of fatigue damage initiation life at railway surface under rolling contact fatigue. For this purpose, several fatigue life models were programmed. By using this software, we expect that it is possible to predict the damage initiation life even though in the field by railway engineer who is not a fatigue expert.

응력 구배 효과를 고려한 구름 접촉 모델의 피로수명해석

조인제(InJe Cho),유용훈(YongHun Yu),이보라(Bora Lee),조용주(YongJoo Cho) 한국트라이볼로지학회 2015 한국윤활학회지(윤활학회지) Vol.31 No.6

Recently, Luu suggested fatigue life equation that uses every term of the Crossland equation with stress gradient effect. Luu’s model, however, has a limit of being unable to coverage small radii that are less than a specified length. Furthermore, rolling model has a very small contact area compared to the rolling element size, and fatigue failure occurs on the small radius such as surface asperity by cyclic loading. Therefore, it is necessary to modify fatigue life equation in order to enable fatigue analysis for a small radius. In this paper, the fatigue life considering a stress gradient effect in rolling contact was obtained using Luu’s modified equation. Fatigue analysis was performed to study the effect of stress gradient on the fatigue life using newly adopted equation and to compare the results with pervious models. In order to do this, a series of simulation such as surface stress analysis, subsurface stress analysis, and fatigue analysis are conducted for two rolling balls of same size that contact each other. Through such a series of processes, the fatigue life can be calculated and equation that is proposed in this paper evaluates the fatigue life in case the contact area is small.

레일손상에 의한 윤중증가를 고려한 표면균열 성장예측

전현규(Hyun Kyu Jun),최진유(Jin Yu Choi),나성훈(Sung Hoon Na),유원희(Won Hee You) Korean Society for Precision Engineering 2011 한국정밀공학회지 Vol.28 No.9

Prediction of a minimum crack size for growth, which is defined as a crack size that grows fast enough to keep ahead of its removal by contact wear and periodic grinding, is the most demanding work to prevent rail from fatigue failure and develop cost effective railway maintenance strategy. In this study, we investigated the wheel load increment due to a rail defect during a train ran over it, and its effect on the minimum crack size for growth. For this purpose, we developed simulation software based on the Fletcher and Kapoor’s “2.5D” model and measured wheel load increment during a train passed over a defect. A maximum contact pressure and contact patch size were calculated by 3D FEM and crack growth analyses were performed by varying two of dominant contact contributors; surface friction coefficient(0.1, 0.2, 0.3 and 0.4) and crack aspect ratio. The minimum crack sizes for growth were calculated from 0.29 to 1.44㎜ depending on the contact conditions. They were decreasing with increasing surface friction coefficient and decreasing with crack aspect ratio(a/b).

White etching layer 의 두께변화에 따른 접촉피로수명 평가

서정원(Jung Won Seo),권석진(Seok Jin Kwon),전현규(Hyun Ku Jun),이동형(Dong Hyong Lee) Korean Society for Precision Engineering 2010 한국정밀공학회지 Vol.27 No.8

White Etching Layer(WEL) is a phenomenon that occurs on the surface of rail due to wheel/rail interactions such as excessive braking and acceleration . Rolling Contact Fatigue(RCF) cracks on the surface of rail have been found to be associated with WEL. In this study, we have investigated RCF damages of white etching layer using twin disc testing and fatigue analysis. These tests consist of wheel flat tests and rolling contact fatigue tests. WEL has been simulated by wheel flat test. It has been founded that the WEL with a bright featureless contrast is formed on the surface of specimen by etching. Rolling contact fatigue test was conducted by using flat specimens with the WEL generated by the wheel flat test. It has been observed that two types of cracks occur within the specimen. The contact fatigue test was simulated in 2D elastic-plastic FE simulations. Based on loading cycles obtained from the finite element analysis, the fatigue life analysis according to the thickness variation of WEL was carried out. The longest fatigue life was observed from the thickness of 20㎛.

구름접촉에서 표면의 크랙전파에 관한 수치적 연구

양진승,최성만 明知大學校 産業技術硏究所 1999 産業技術硏究所論文集 Vol.18 No.-

Rolling contact fatigue cracks are of the most common of failure in gears, bearings and railway track. There are two different forms of contact fatigue crack. The cracks may be initiated at the contacting surface, and thereafter propagate at a shallow angle to the surface; alternatively they may be initiated at large non-metallic inclusions below the surface, in the region of maximum cyclic shear stress. In both cases, the cracks continue to propagate in this region before either detaching lumps of material or changing direction to case catastrophic failure. A two-dimensional Finite element model for the rolling contact surface crack subjected to Hertzian pressure distribution has been developed in this thesis. The model takes into account the effect of frictional locking between the faces of the crack. The stress intensity factors for and lubricated surface cracks subjected to a Hertzian loading are calculated by the finite element method. The effect of crack face friction on stress intensity factors is considered for lubricated surface cracks.

구름접촉피로시험을 통한 고속철도 레일연마량 분석

성덕룡(Deok-Yong Sung),장기성(Ki-Sung Chang),박용걸(Yong-Gul Park) 한국철도학회 2012 한국철도학회논문집 Vol.15 No.2

레일표면손상이 접촉피로수명에 미치는 영향

서정원(Jung-Won Seo),이동형(Dong-Hyong Lee),함영삼(Young-Sam Ham),권성태(Sung-Tae Kwon),권석진(Seok Jin Kwon),최하영(Ha-Yong Choi) Korean Society for Precision Engineering 2012 한국정밀공학회지 Vol.29 No.6

Rails are subjected to damage from rolling contact fatigue, which leads to defects such as cracks. Rolling contact fatigue damages on the surface of rail such as head check, squats are one of growing problems. Another form of rail surface damage, known as “Ballast imprint” has become apparent. This form of damage is associated with ballast particles becoming trapped between the wheel and the surface of rail. These defects are still one of the key reasons for rail maintenance and replacement. In this study, we have investigated whether the ballast imprint is an initiator of head check type cracks and effect of defect size using Finite element analysis. The FE analysis were used to investigate stresses and strains in subsurface of defects according to variation of defect size. Based on loading cycles obtained from FE analysis, fatigue analysis for each point was carried out.

와전류 열화상 전산시뮬레이션에 의한 구름접촉피로 결함의 열적 구배 특성 분석

이승주,정윤재,김원태 한국비파괴검사학회 2019 한국비파괴검사학회지 Vol.39 No.4

Rolling-contact fatigue(RCF) is a typical rail-failure-type defect and is mainly caused by excessive stress. This failure affects the durability and fatigue life of the rail, which in turn leads to rupture. Eddy current thermal imaging is a technique that locates an electromagnetic pulse on a conductor, locally generates resistance heat in the defective part, and measures the heat using an infrared camera. In this work, an eddy current thermal imaging model is developed, and the thermal-contrast characteristics of the RCF defects are analyzed. A simulation was performed considering the conditions of excitation frequency, current intensity, and distance between the coil and specimen using FEA(Software ANSYS 19.2 Maxwell 3D, Steady-State Thermal). Thus, the current-density and temperature-gradient data were extracted and comparatively analyzed. Rolling-contact fatigue(RCF)는 레일의 결함 발생 유형 중 대표적인 결함이며 주로 과도한 응력에 의해 발생한다. 이로 인해 레일의 내구성과 피로 수명에 영향을 미치게 되며 결과적으로 파단으로 이어진다. 와전류 열화상이란 전자기 펄스를 전도체에 가진하면 국부적으로 결함부에 저항열이 발생하며 이때 발생된 열을 적외선 열화상 카메라로 측정하는 기술이다. 본 논문에서는 와전류 열화상 시뮬레이션 모델러를 개발하였으며 RCF 결함의 열적 구배 특성 분석을 수행하였다. FEA(Software ANSYS 19.2 Maxwell 3D, Steady-State Thermal)를 활용하여 가진 주파수, 전류의 세기 및 거리의 변수 조건으로 시뮬레이션을 수행하였으며 결과로서 전류 밀도와 온도 구배 데이터를 추출하여 이에 대한 비교 분석을 수행하였다.