• Journal of Mechanical Science and Technology
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• 제19권11호
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• pp.1988-1997
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• 2005

This study is concerned with structural integrity evaluations for the interference-fit flywheels in reactor coolant pumps (RCPs) of nuclear power plants. Stresses in the flywheel due to the shrinkage loads and centrifugal loads at the RCP normal operation speed, design overspeed and joint-release speed are obtained using the finite element method (FEM), where release of the deformation-controlled stresses as a result of structural interactions during rotation is considered. Fracture mechanics evaluations for a series of cracks assumed to exist in the flywheel are conducted, considering ductile (fatigue) and non-ductile fracture, and stress intensity factors are obtained for the cracks using the finite element alternating method (FEAM). From analysis results, it is found that fatigue crack growth rates calculated are negligible for smaller cracks. Meanwhile, the material resistance to non-ductile fracture in terms of the critical stress intensity factor (K$_{IC}$) and the nil-ductility transition reference temperature (RT$_{NDT}$) are governing factors for larger cracks.

• 한국주조공학회지
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• 제38권2호
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• pp.48-54
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• 2018

To improve the durability of the turbocharger, it is important to suppress cracking of the turbine housing; therefore, we investigated the initiation and growth of these cracks. First, we initiated a crack in the turbine housing using endurance experiments. After the endurance test, cracks mainly occurred in the valve seat, the nozzle area, and the scroll part of the turbine housing. The results of a fracture analysis of the cracks showed that cracks in the valve seat were initiated by fatigue fracture. This seems to be caused by the accumulation of mechanical and thermal stresses due to vibration of the turbine wheel and high-temperature exhaust gas. Also, cracks in nozzle and scroll area were initiated by intergranular corrosion due to the exhaust gas. Thus, although there are differences in the cause of initiation according to the site, a concentric waveform was observed in all fracture planes. This phenomenon indicates that cracks gradually grow due to repeated stress changes, and the main causes are the temperature difference of the exhaust gas and the vibration caused by the turbine shaft.

• 한국산학기술학회논문지
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• 제14권1호
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• pp.1-6
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• 2013

3차원 균열은 항공기나 압력용기 계통에서 흔히 발견되는 결함중의 하나이다. 균열을 갖는 구조물에 대한 정확한 응력확대계수 해석과 균열성장속도는 파괴강도와 피로수명을 평가하는데 필요로 한다. 3차원 유한요소법은 구조물에 존재하는 표면균열의 응력확대계수를 구하는데 이용되어 진다. 기하모델, 즉 균열을 포함하는 솔리드모델을 정의한 후, 절점이 버켓법에 의해 생성되어 진다. 요소생성은 사변형 솔리드요소를 데라우니 삼각화 기술에 의해 생성하도록 하였다. 시스템의 정확도와 효용성을 체크하기 위해 내압을 받는 원통형용기에 균열이 존재하는 경우의 응력확대계수 해석을 수행하였다. 개발된 시스템을 이용한 해석결과는 ASME 식과 Raju-Newnam식과 비교하여 5%이내의 차이를 보였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.585-590
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• 2001

Turbine blade is subject to torsional load by torsion-mount, centrifugal load by rotation of rotor and repeated bending load by steam pressure. Turbine with partially cracked blade has normal working condition at initial repair time but vibratory working condition at middle repair time due to crack growth. Finite element analysis on turbine blade indicates that repeated bending load out of all loads is the most important factor on fatigue strength of turbine blade. Therefore, this study shows root mean square roughness has linear relation with stress intensity factor range in 12% Cr steel and can predict loading condition of fractured turbine blade.

• 한국수소및신에너지학회논문집
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• 제35권2호
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• pp.216-229
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• 2024

Pipeline steels for hydrogen transmission may cause hydrogen embrittlement due to absorption and diffusion of hydrogen through metals. Hydrogen pipes exhibited similar mechanical properties to atmospheric conditions in terms of tensile and yield strength in a hydrogen atmosphere. This paper aims to provide relevant information regarding hydrogen embrittlement in hydrogen transmission pipeline.

• 대한기계학회논문집A
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• 제25권11호
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• pp.1705-1712
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• 2001

Mechanical component has striation with constant width and SEM can estimate fracture type and loading condition. SEM has benefit to fatigue fracture analysis but striation can be observed according to the kind of material and range of crack growth rate and can't. In this case, it needs AFM that can measure 3-dimensional surface profile with resolution of atomic size. In this study. to find fracture reason of torsion-mounted blade in nuclear plant, we estimate the relation between stress intensity factor range and root mean square roughness in 12% Cr steel by AFM and predict in-service loading condition of turbine blade. failure analysis is performed by finite element method and Goodman diagram on torsion-mounted blade.

• 대한기계학회논문집A
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• 제36권10호
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• pp.1249-1254
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• 2012

원자력발전소의 배관에 대하여 행하는 검사는 배관의 구조건전성에 큰 영향을 미친다. 그러나 검사에는 많은 인력과 비용이 소요되므로 검사의 영향을 평가하여 최적의 검사주기와 검사품질을 결정하는 것이 중요하다. 본 논문에서는 원자력발전소 배관의 파손확률을 평가할 수 있도록 개발된 P-PIE 프로그램을 사용하여 검사의 유무, 검사주기 및 검사품질 등이 배관의 파손확률에 미치는 영향을 살펴보았다. 국내 원전의 배관 데이터를 사용하여 해석하였으며, 피로 및 부식에 의한 균열성장을 고려하였다.

• 소성∙가공
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• 제25권1호
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• pp.36-42
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• 2016

Fiber metal laminates (FMLs) are well known for improved fatigue strength, better impact resistance, superior damage tolerance and slow crack growth rate compared to traditional metallic materials. However, defects and loss of strength of a composite material can occur due to the vertical load from the punch during the joining with a dissimilar material using a conventional clinching method. In the current study, tapered-hole clinching was an alternative process used to join Al 5052 and FMLs. The tapered hole was formed in the FML before the joining. For the better understanding of static and dynamic characteristics, a clinched joining followed by a tensile-shear test was numerically simulated using the finite element analysis. The design parameters were also evaluated for the geometry of the tapered hole by the Taguchi method in order to improve and compare the lateral joining strength of the clinched joint. The influence of the neck thickness and the undercut were evaluated and the contribution of each design parameter was determined. Then, actual experiments for the joining and tensile-shear test were conducted to verify the results of the numerical simulations. In conclusion, the appropriate combination of the design parameters can improve the joining strength and the cross-sections of the tapered-hole clinched joint formed in the actual experiments were in good agreement with the results of the numerical simulations.

• 터널과지하공간
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• 제27권3호
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• pp.121-131
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• 2017

본 연구에서는 암석과 콘크리트의 정적 및 동적 장기강도시험을 통해 이들 재료의 시간 의존적 거동에 대해 연구했으며, 특히 장기강도시험 중 발생한 미소파괴음 신호를 분석하여 장기 안정성 평가에 활용하고자 하였다. 정적 장기강도시험의 경우 임계하 균열성장시험을 활용하여 Mode I과 Mode II에 대한 장기거동과 미소파괴음 발생특성을 분석하였으며, 동적 장기강도시험의 경우, 반복재하 4점 굴곡시험을 통한 장기강도의 한계와 미소파괴음 발생특성을 분석하였다. 미소파괴음 분석결과, 미소파괴음 히트 누적곡선 대 시간에 따른 곡선은 1차, 2차, 3차 구간이 있는 크립곡선의 모양과 유사한 모양을 보였다. 선형구간에 해당하는 미소파괴음 히트 누적곡선의 2차 구간의 기울기와 지연파괴시간과의 로그-로그 관계로부터 암석과 콘크리트의 정적 및 동적 장기 안정성을 평가하는 방안에 대한 가능성을 제시하였다.