• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.8
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• pp.1269-1276
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• 2001

In case of contact fatigue, the accurate calculation of surface tractions and subsurface stress is essential to the predication of crack initiation life. Surface tractions influencing shear stress amplitude have been obtained by contact analysis based on influence function. Subsurface stress has been obtained by using rectangular patch solutions. In this study, to simulate asperity contact under sliding condition, the tip of asperity was simulated by sphere and to calculate crack initiation life in the substrate, dislocation pileup theory was used.

• Journal of the Korean Society for Railway
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• v.12 no.3
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• pp.396-404
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• 2009

With developing the next generation high speed railway, there need to be plans to make sure of running safety though researchs on the crack and break of rail by rolling contact fatigue. Therefore, this study performed the parametric analysis effecting on the fatigue life of rail using simplified equations. It analyzed the internal stress of rail according to the track quality, train velocity, wheel radius, track stiffness, sleeper space, wheel load. For the more, via the finite element method, it analyzed shear force on the rail head which could be changed by the early length of crack, angle of crack and temperature. As a result, this study continued the main parameter effecting on the fatigue life of rail.

• Journal of Auto-vehicle Safety Association
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• v.4 no.1
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• pp.23-26
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• 2012

본 논문은 듀얼클러치 변속기 변속 메커니즘 개발을 위한 동역학적 시뮬레이션 해석 및 피로수명 해석에 관한 연구이다. 캠을 이용한 쉬프트 포크의 이송으로 기어를 변속하는 개념을 갖는 쉬프트 메커니즘의 작동성 및 설계안 검증을 위해 캠의 회전 속도, 접촉면의 경계조건 및 싱크로나이저 슬리브에서의 저항을 반영한 모델링을 구성하여 동역학적 시뮬레이션을 실시하였다. 각 파트의 응력 및 변형률 발생을 해석하여 설계 개선안을 도출하고, 개선안이 반영된 최종 시작모델의 시뮬레이션 상 최대 응력 발생 시점에서 시프트 포크의 각 접촉면 별 외력 작용을 분석하여 이를 적용한 피로 해석을 진행하였다.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.5
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• pp.133-138
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• 2007

Surface pitting is a major failure mode for gears. The contact fatigue life analysis of transmission gear considering running-in process is presented in this paper. Surface roughness change of rolling test is used in a life analysis. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions; the subsurface stress field is obtained using rectangular patch solutions. Mesoscopic multiaxial fatigue criterion which can yield satisfactory results for non-proportional loading is then applied to predict fatigue damage. Suitable counting method and damage rule were used to calculate the fatigue life of random loading caused by rough surface. The life analysis considering running-in is in good agreement with the experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.5
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• pp.375-380
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• 2017

This paper reports the results of an acceleration test to predict the contact-induced failure that could occur at the cylinder-to-hole joint for the fuel rod of a sodium-cooled fast reactor (SFR). To incorporate the fuel life of the SFR currently under development at KAERI (around 35,000 h), the acceleration test method of reliability engineering was adopted in this work. A finite element method was used to evaluate the flow-induced vibration frequency and amplitude for the test parameter values. Five specimens were tested. The failure criterion during the life of the SFR fuel was applied. The S-N curve of the HT-9, the material of concern, was used to obtain the acceleration factor. As a result, a test time of 16.5 h was obtained for each specimen. It was concluded that the $B_{0.004}$ life would be guaranteed for the SFR fuel rods with 99％ confidence if no failure was observed at any of the contact surfaces of the five specimens.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.279-282
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• 2011

The analysis and experimental results for the bellows of gasgenerator liquid oxygen shut-off valve are presented. The analyses are performed using EJMA (Expansion Joint Manufacturing Association) standard and the commercial FE (finite element) analysis program, Abaqus v6.9, at room and cryogenic temperatures. The results include the spring rate, the stress and the fatigue life of the bellows. The effects of the contact and material plasticity on the FE analysis results are also analyzed.

• Tribology and Lubricants
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• v.31 no.6
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• pp.272-280
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• 2015

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.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.11-11
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• 2017

지속적인 고령화 추세에 따라 여성과 고령층의 노동력이 차지하는 비율이 높아지고 있어, 사용하기 편리한 소형농기계의 요구가 증가하고 있는 실정이다. 본 연구에서 사용한 소형 관리기는 정식 작업 전 경운, 정지 등 다양한 작업이 가능한 농기계이다. 본 연구에서는 소형 관리기에 토크 측정 시스템을 구성하였으며, 작업 중 가장 큰 부하를 받는 구굴 작업 부하를 측정하였다. 또한, 작업 시 가장 직접적으로 영향을 받는 PTO (Power Take Off) 기어의 부하 용량(load capacity)을 기어 해석 소프트웨어를 이용하여 분석하였다. PTO 기어의 부하 용량은 안전율, 피로수명을 대상으로 평가하였다. 측정된 부하 데이터는 변동 하중이므로, 부하 크기와 빈도수의 규칙적인 신호로 단순화하기 위하여 레인플로우 카운팅 방법을 사용하였으며, SWT (Smith-Watson-Topper) 방법을 이용하여 공칭 토크를 계산하였다. PTO 기어의 안전율은 ISO 6336, 피로 수명은 마이너 법칙(Miner rule)을 이용하여 계산하였다. PTO의 변속 단수 총 2단이며, 5개의 스퍼 기어로 구성되어 있다. 시뮬레이션 결과, 소형 관리기의 주행 속도 또는 PTO의 회전속도 증가에 따라 PTO에서 발생하는 평균 부하가 크게 나타났다. 또한 주행 단수 및 PTO 기어 단수가 증가할수록 기어의 안전율과 피로 수명이 감소하였으며, 특히 PTO 기어의 안전율은 접촉 응력에서의 안전율보다 굽힘 응력에서의 안전율이 급격하게 감소하였다. 소형 관리기의 PTO 수명은 주행 단수 2단, PTO 단수 2단 일 때 가장 적게 나타났다. 따라서 소형 관리기의 주행 속도와 PTO 회전 속도를 저속으로 작업하는 것이 PTO 기어의 수명에 더 유리할 것으로 판단된다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.1033-1036
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• 2005

The effect of surface roughness on the contact fatigue was investigated in this study. To accomplish this goal, contact analysis based on the influence functions and the rectangular patch solution was performed to obtain the subsurface stress. Mesoscopic multiaxial fatigue criterion is then applied to predict fatigue damage. Suitable counting method and damage rule were used to evaluate the fatigue life of random loading caused by rough surface. As a result of the analysis, relationship between the life and roughness as well as the creack initiation depth was revealed. Below the critical roughness, It is observed that the fatigue life has hardly changed and creack is initiated around the depth at which the maximum shear stress occurs. Different behavior, however, is observed in case that the roughness is above the critical value.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.06a
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• pp.1091-1092
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• 2009