• International Journal of Automotive Technology
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• 제8권2호
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• pp.243-248
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• 2007

The durability of a cylinder head is influenced by the thermal and mechanical history during the manufacturing process, as well as engine operation. In order to improve the durability of cylinder head, both load from engine operation and the preload conditions from the manufacturing process must be considered. The aluminum cylinder head used for a HSDI diesel engine is investigated to reduce the possibility of high cycle fatigue crack in this study. FE analysis is performed to elucidate the mechanism of high cycle fatigue crack in the HSDI diesel cylinder head. Two separate approaches to increase the durability of the cylinder head are discussed: reducing load from engine operation and re-arranging preload conditions from the manufacturing process at the critical location of the cylinder head. Local design changes of the cylinder head and modification of pretension load in the cylinder head bolt were investigated using FE analysis to relieve load at the critical location during engine operation. Residual stress formed at the critical location during the manufacturing process is measured and heat treatment parameters are changed to re-arrange the distribution of residual stress. Results of FE analysis and experiments showed that thorough consideration of the manufacturing process is necessary to enhance the durability of the cylinder head.

• 한국안전학회지
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• 제16권4호
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• pp.52-57
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• 2001

Fatigue crack growth behaviour of Ti-6A-4V alloy is investigated in air and salt solution environment at room temperature and $200^{\circ}C$. Fatigue crack growth rate is blown to be fast for the formation of corrosive product in hot salt environment. For the effect on corrosion fatigue crack growth behaviour of region II. fatigue crack growth rate in atmosphere had a little gap to both case, $200^{\circ}C$ and room temperature. However, it showed very fast tendency in salt corrosive atmosphere, and it was remarkably accelerated in $200^{\circ}C$ temperature salt environment. When $\Delta$K was approximately 30MPa(equation omitted), fatigue crack growth rate had a little difference between at room temperature and at $200^{\circ}C$ high temperature, however in case of salt corrosive environment the room temperature was 3.5 times Inter and $200^{\circ}C$ high temperature for 16 times than air environment respectively.

• 대한기계학회논문집A
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• 제39권1호
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• pp.11-17
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• 2015

최근에 원자력 발전소 안전 3 등급 배관에 적용되고 있는 고밀도 폴리에틸렌 배관은 융착표면을가열한 후 축방향으로 가압하는 열 융착 공정을 이용하여 맞대기 융착되어진다. 이러한 열 융착공정은 맞대기 융착부에 비드 형상을 발생시킨다. 이러한 비드 형상의 응력집중에 기인하여 피로수명이 줄어들 수 있다. 따라서 피로거동에 미치는 맞대기 열 융착부 비드의 효과를 고찰하는 것이 필요하다. 본 연구에서는 응력 제어 조건 하의 인장 피로 시험과 유한요소 탄성응력 해석을 수행하여 맞대기 열 융착부의 인장 피로 거동을 고찰하였다. 고찰 결과, 중주기 및 고주기 피로 영역에선 피로수명에 미치는 비드의 영향이 미미한 반면 저주기 피로 영역에선 비드의 존재가 피로 수명을 감소시킴을 확인하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.777-781
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• 1997

One of the spring-link mechanisms, the air circuit breaker(ACB), was studied to improve the shock-proof characteristics of it. The low-cycle fatigue fracture phenomenon was occurred on the critical link, called h-link, of ACB for the repeated rapid closing and opening operations. To analyze the cause of failure, dynamic FE-analysis on the h-link part of ACB was accomplished with considered the velocity and acceleration of the links per time as boundary conditions, which were obtained by using ADAMS. Then, to reduce the maximum tensile stress on the h-link, three types of h-link were suggested and one of them was selected. Fmm this study, we suggested the process of analysis on the high-speed motion behavior part related low-cycle fatigue fractures.

• 한국철도학회논문집
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• 제11권1호
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• pp.107-113
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• 2008

최근 생애주기비용 분석이 사회기반 시설물 경제성 평가 분야의 필수적 방법으로 대두됨에 따라 체계적이고 합리적인 방법으로 각 시설물의 생애주기비용을 산정하기 위한 노력이 진행되고 있다. 합리적인 생애주기비용 분석을 위해서는 초기비용 뿐만 아니라 유지관리 비용의 예측이 필요하나 국내에서는 고속철도 구간에 강교량을 가설한지 얼마 되지 않았기 때문에 이에 대한 유지관리 특성 등을 파악하고 있지 못한 실정이다. 이에 본 연구에서는 고속철도 소수주형교의 계측데이터와 Rahgozar 등이 제안한 부식열화를 고려한 피로강도감소계수 및 Miner 손상누적법칙을 이용하여 강교량의 주된 열화의 요인이 되는 부식과 피로의 손상을 고려한 체계신뢰성해석을 실시하였다. 이 체계신뢰성 해석결과를 바탕으로 고속철도 소수주형교의 설계단계 생애주기비용 분석 모델을 제안하였다.

• 한국자동차공학회논문집
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• 제11권3호
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• pp.209-213
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• 2003

It is advantage of accelerated vibration testing to compress service exposures to operating vibration into a reduced laboratory test by increasing the amplitude or frequency of the applied input excitations. This paper proposes an accelerated test method to estimate the high-cycle fatigue life under random excitation. The method consists of conducting a test with amplified input excitation and extrapolating linearly the lift in the accelerated condition into the real lift in field condition. The extrapolation is carried out applying the high-cycle irregular excitation fatigue theory including the rainflow counting, Miner’s damage accumulation rule, and Goodman’s mean stress correction. As a verification, those estimated lift is compared with that acquired by experiment f3r the simple case of spot welding specimen with good agreement. This testing procedure will provide an useful scheme that can reduce testing period associated with developing time schedule of new product.

• 대한기계학회논문집A
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• 제28권7호
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• pp.1014-1020
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• 2004

The present work complies the elastic stress concentration factor for a pipe with local wall thinning, based on detailed three-dimensional elastic FE analysis. To cover practically interesting cases, a wide range of pipe and defect geometries are considered, and both internal pressure and global bending are considered. Resulting values of stress concentration factors are tabulated for practical use, and the effect of relevant parameters such as pipe and defect geometries on stress concentration factors are discussed. The present results would provide valuable information to estimate fatigue damage of the pipe with local wall thinning under high cycle fatigue.

• 한국소음진동공학회논문집
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• 제24권5호
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• pp.407-413
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• 2014

The diesel engine and reduction gear combination is one of the common propulsion system in a naval vessel. Since the diesel engine has torsional vibration caused by reciprocating motion of the mass and gas pressure force of the cylinder, high cycle torsional fatigue can be occurred. Therefore, ROK navy restricts the maximum stress of the propulsion shaft according to MIL G 17859D. In this paper, the root cause for the failure of the diesel engine and reduction gear connecting shaft occurred in typical naval vessel is investigated based on the measured bending and torsional moment according to MIL G 17859D procedure.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.240-244
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• 2017

가스터빈 엔진의 구성품 개발단계에서 블레이드의 Aeromechanics 시험은 블레이드 진동설계와 구조 안정성 검증 프로세스 사이에서 중요한 연결 고리를 제공한다. 이 전제에 근거하여 본 연구에서는 NSMS(Non-Intrusive Stress Measuring Systems)를 축류 압축기 구성품 시험리그에 적용하여 Tip Timing 센서가 장착된 단에서 모든 블레이드의 정적/동적 변위를 시험적으로 측정하였다. 진동 특성 분석을 통해 블레이드 고주기 손상을 유발할 수 있는 피로임계위치(Fatigue Critical Location)에서의 진동 응력을 평가하였으며, 공력가진에 의한 비동기 진동응답 및 개별 블레이드 Mistuning 패턴을 제시하였다.

• 한국소음진동공학회논문집
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• 제20권11호
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• pp.1025-1032
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• 2010

Gas turbine compressor blades used in a combined cycle power plant are possibly damaged and fractured during their operation. There are two possible causes of the failure of compressor blades; one is a defect of material quality which can be detected through some microscopic inspections for the fracture section, the other is high cycle fatigue problem caused by vibration and can be diagnosed by carrying out dynamic characteristics analysis for the blades. In this paper, in order to determine the cause of the failure of compressor blades in a combined cycle power plant, examination of the fracture section and the propagation mechanism of the crack via stress analysis are performed. Dynamic characteristics analysis via FRF estimation is also performed to identify the cause of failure.