• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.30-34
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• 2007

Structural integrity of railway vehicles should last for a long period against various and continuous fatigue loadings, and the carbody structures of railway vehicle are manufactured by applying multiform welding types for each material. Since the most of cracks are occurred and proceeded at the vicinity of welding area during the lifetime of carbody structure, the fatigue strength evaluation for welding area of carbody structure should have been carried out. Rotem Company has evaluated lifetime and fatigue strength of carbody structure according to the fatigue analysis based on the international standard and/or inner-official regulation. This study introduces the fatigue analysis method that we have evaluated and calculated the damages for the welding areas of carbody structure under various fatigue loading conditions using cumulative fatigue damage rule(Miner's rule) to verify whether the cumulative damage does exceed unity. This study contains the fatigue test of specimens to derive stress-life relations(S-N curve), sub-modeling analysis and the calculation of cumulative damages under fatigue loading. The fatigue analysis verifies the welding area shall be capable of withstanding under fatigue loading, identifies how critical area shall be selected and presents the principles to be used for design verification.

• 항공우주시스템공학회지
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• 제3권4호
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• pp.27-34
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• 2009

This paper deals with the lifetime prediction of Aircraft Flaperon Joint made of AISI 4130 steel. Reviews are performed on the published damage models at first. And three different damage models are used for predicting the fatigue life of the structure subjected to variable amplitude fatigue loading. These models require no increase in complexity of use, nor do they require additional material property or mission loading information to achieve the improved accuracy. Finally a comparison among the fatigue results is performed. It is observed that the Miner's rule could predict longer life than other cumulative damage models which take into account loads below the endurance limit.

• 한국기계가공학회지
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• 제21권1호
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• pp.73-80
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• 2022

Sensors are applied to small aviation platforms for various purposes. Radio frequency (RF) antennas, which are representative sensors, are available in many forms but require the application of slot array RF antennas to ensure high performance and designation. Slot RF array antennas are applied to dip brazing techniques, but the yield and production time are determined by the proficiency of production personnel in a labor-intensive form. Unmanned aerial vehicles or drones, which are representative small aviation platforms, are continuously exposed to various random vibrations because propellers and multiple power sources are used in them. In this study, the fatigue life of slot array RF antennas applied with additive manufacturing was evaluated through the cumulative damage method (Miner's rule) in a vibration environment with a small aviation platform. For the evaluation, an S N curve obtained from a fatigue strength test was used.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권1호
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• pp.9-20
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• 2018

Due to integrated stochastic wind and wave loads, the supporting platform of a Floating Offshore Wind Turbine (FOWT) has to bear six Degrees of Freedom (DOF) motion, which makes the random cyclic loads acting on the structural components, for instance the tower base, more complicated than those on bottom-fixed or land-based wind turbines. These cyclic loads may cause unexpected fatigue damages on a FOWT. This paper presents a study on short-term fatigue damage at the tower base of a 5 MW FOWT with a spar-type platform. Fully coupled time-domain simulations code FAST is used and realistic environment conditions are considered to obtain the loads and structural stresses at the tower base. Then the cumulative fatigue damage is calculated based on rainflow counting method and Miner's rule. Moreover, the effects of the simulation length, the wind-wave misalignment, the wind-only condition and the wave-only condition on the fatigue damage are investigated. It is found that the wind and wave induced loads affect the tower base's axial stress separately and in a decoupled way, and the wave-induced fatigue damage is greater than that induced by the wind loads. Under the environment conditions with rated wind speed, the tower base experiences the highest fatigue damage when the joint probability of the wind and wave is included in the calculation. Moreover, it is also found that 1 h simulation length is sufficient to give an appropriate fatigue damage estimated life for FOWT.

• 한국구조물진단유지관리공학회 논문집
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• 제22권1호
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• pp.129-136
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• 2018

대형 용접 구조물에 대한 피로설계 수명의 예측은 일반적으로 Palmgren Miner과 등가손상도 방법 또는 선형누적손상도 방법을 사용한다. 또한 용접 구조물에서 피로 균열이 발생되면 잔존 수명은 S-N 곡선과 선형 파괴역학에 기초하여 예측되고 있다. 본 연구에서는 면외거셋 용접이음의 3차원 피로균열 진전거동과 피로수명을 예측하기 위하여 피로 시험을 실시하였다. 면외거셋 용접이음의 3차원 피로균열진전해석은 NX NASTRAN 및 FRANC3D를 이용하여 유한요소 해석을 실시하였다. 면외거셋 용접이음의 균열 형상비, 초기균열 크기 및 응력비에 미치는 영향을 검토하기 위하여 피로균열진전 해석을 실시하였다. 또한 초기균열크기, 균열 형상비와 응력비의 변화에 따른 3차원 피로균열진전 해석 결과와 피로시험결과를 비교하였다. 피로균열진전 해석결과, 피로균열 진전속도와 응력확대계수와의 관계에서 피로시험과 유사하게 나타남을 확인하였으며, 면외거셋 용접이음의 피로수명을 추정할 수 있음을 확인하였다.