• 대한조선학회논문집
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• 제56권3호
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• pp.231-241
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• 2019

In this study, a simplified analysis method was developed to evaluate the fatigue damage of an ice-going ship under broken ice condition. The global ice load, which is essentially calculated at the design stage of the Arctic vessel, and the hull form information were used to estimate the local ice load acting on the outer-shell of the ship. The local ice load was applied to the finite element analysis model, and the Weibull parameters for the target fatigue point were derived. Finally, fatigue damage was evaluated by applying the S-N curve and the Palmgren-Miner rule. For the verification of the proposed method, numerical analyses using direct approach were performed for the same conditions. A numerical model that implements the interaction between ice and structure was introduced to verify the local ice load and the stress calculated from the proposed method. Finally, the fatigue analyses of the Baltic Sea for actual ice conditions were performed, and the results of the proposed method, the method using numerical analysis, and the LR method were compared.

• Restorative Dentistry and Endodontics
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• 제43권2호
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• pp.25.1-25.10
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• 2018

Objectives: To evaluate the mechanical properties and metallurgical characteristics of the M3 Rotary and M3 Pro Gold files (United Dental). Materials and Methods: One hundred and sixty new M3 Rotary and M3 Pro Gold files (sizes 20/0.04 and 25/0.04) were used. Torque and angle of rotation at failure (n = 20) were measured according to ISO 3630-1. Cyclic fatigue resistance was tested by measuring the number of cycles to failure in an artificial stainless steel canal ($60^{\circ}$ angle of curvature and a 5-mm radius). The metallurgical characteristics were investigated by differential scanning calorimetry. Data were analyzed using analysis of variance and the Student-Newman-Keuls test. Results: Comparing the same size of the 2 different instruments, cyclic fatigue resistance was significantly higher in the M3 Pro Gold files than in the M3 Rotary files (p < 0.001). No significant difference was observed between the files in the maximum torque load, while a significantly higher angular rotation to fracture was observed for M3 Pro Gold (p < 0.05). In the DSC analysis, the M3 Pro Gold files showed one prominent peak on the heating curve and 2 prominent peaks on the cooling curve. In contrast, the M3 Rotary files showed 1 small peak on the heating curve and 1 small peak on the cooling curve. Conclusions: The M3 Pro Gold files showed greater flexibility and angular rotation than the M3 Rotary files, without decrement of their torque resistance. The superior flexibility of M3 Pro Gold files can be attributed to their martensite phase.

• 한국강구조학회 논문집
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• 제15권2호
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• pp.137-145
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• 2003

본 연구에서는 국산 PS 강봉의 직경, 반복최소응력 및 반복최대응력 등을 실험변수로 하여 직접 인장 피로실험을 수행하였다. 정적 인장실험 결과, 국산 PS 강봉의 응력 - 변형률 곡선과 극한강도 등을 얻었다. 또한, 피로실험에서의 특징적인 실험결과는 PS 강봉의 직경은 피로 수명에 중요한 인자가 아니며, 반복 최소응력의 크기는 국산 PS 강봉의 피로수명에 매우 큰 영향을 미치는 것으로 나타났다. 이러한 피로실험결과를 통계 분석하여 PS 강봉의 응력 범위 및 반복 최소응력 등을 변수로 하는 피로강도 예측식을 제안하였다. 피로실험 중, 시편중앙에 설치한 Extensometer를 이용하여, 변형률의 변화를 측정하였으며, 측정된 변형률 변화현상에서 탄성계수의 변화현상을 구하였다. 변형률 증가현상은 3단계의 형태 즉, 초기에 급격한 증가 후 서서히 증가하며 파괴 직전에 급격하게 증가하는 형태로 나타났다. 탄성계수의 변화현상은 변형률 변화현상과 유사하게 감소하는 것으로 나타났으며 응력수준은 탄성계수 변화에 큰 영향을 주지 않는 것으로 나타났다.

• 대한조선학회논문집
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• 제48권4호
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• pp.299-307
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• 2011

The offshore plants such as FPSO are subjected to combination loading of environmental conditions (swell, wave, wind and current). Therefore the fatigue damage is occurred in the operation time because the units encounter the environmental phenomena and the structural configurations are complicated. This paper is a research for frequency domain fatigue analysis of wide-band random loading focused on accuracy of fatigue damage estimation regarding the proposed methods. We selected ideal bi-modal spectrum. And comparison between time-domain fatigue analysis and frequency-domain fatigue analyses are conducted through the fatigue damage ratio. Fatigue damage ratios according to Vanmarcke's bandwidth parameter are founded for wide-band. Considering safety, we recommend that Jiao-Moan and Tovo-Benasciutti methods are optimal way at the fatigue design for wide-band response. But, it is important that these methods based on frequency-domain unstably change the accuracy according to the material parameter of S-N curve. This study will be background and guidance for the new frequency-domain fatigue analysis development in the future.

• 오토저널
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• 제12권6호
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• pp.11-17
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• 1990

자동차용 변속기의 설계에 있어서 적용 Engine의 출력 및 차량 성능에 부합하는 동력전달 요소의 전달 용량 및 내구 수명을 고려해야 한다. 특히 자동차가 고속 경량화됨에 따라 변속기의 설계에 있어서도 동력전달 요소들의 소형 고용량화가 요구되며 이를 위해서는 설계시 동력전달 요소들의 정확한 강도 및 피로수명 예측이 필수적이다. 본 보고서에서는 Gear의 굽힘응력 계산식에 대한 고찰 및 Gear의 피로시험을 통하여 Helical 치차의 Bending stress에 대한 피로수명 곡선의 시험식을 도출하였다.

• 한국기계가공학회지
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• 제14권2호
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• pp.75-80
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• 2015

The rebar factory production process involves the repetitive bending of rebars. Therefore, the fatigue failure of the rebar bending machine needs to be considered. In this paper, fatigue analysis of the rebar machine was performed using the commercial software DAFUL, which is based on MFBD (Multi Flexible Body Dynamics). The rotating roller, fixing roller and rebar were modeled by the finite element method. The rebar bending process is simulated and the mechanical stresses on the rollers are calculated. Structural analysis of the rebar bending roller was performed using the maximum bending angle of $180^{\circ}$ and maximum processing rebar diameter of ${\Phi}19mm$. Then, for fatigue analysis, the S-N curve of STD-11 was. The fatigue life of rollers is estimated by modified Goodman diagram. The fatigue life range of the rotating roller is $2.99961{\times}10^5{\sim}1{\times}10^8$ while that of the fixed roller is $2.53142{\times}10^5{\sim}1{\times}10^8$. STD-11 has an infinite life cycle after $1{\times}10^8$. Therefore, the rollers of the rebar bending machine may be expected to suffer fatigue failure. Thus, we performed a parameter study of fatigue life according to various axial radii of the fixed roller and rotating roller, and redesign of the rebar bending machine. Consequently, the axial radius of the fixed roller and rotating roller was found to be 35~37.5mm and 30~35mm, respectively, and an infinite life cycle was confirmed at these.

• 대한기계학회논문집A
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• 제34권6호
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• pp.757-762
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• 2010

탄소섬유강화 복합재료는 금속재료에 비하여 높은 비강성과 비강도 등의 우수한 기계적 성질을 나타내고 있으며, 이러한 이유로 최근 경량화가 요구되는 항공기용 재료와 자동차용 재료 등으로 그 사용이 급격히 증가하여 금속재를 대체하고 있다. 그러나 대부분의 기계구조물에서는 반복하중에 의한 피로 파손이 주로 발생하고 있다. 그러므로 섬유강화 복합재를 사용한 기계구조물의 내구성을 확보하기 위해서는 이에 대한 피로 해석 및 내구성 평가가 필요하다. 따라서 피로 손상 모델을 이용하여 피로 시험으로부터 구한 손상량을 이용하여 피로손상 누적곡선을 획득하고 해석하였다.

• Journal of Welding and Joining
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• 제12권1호
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• pp.102-115
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• 1994

This paper is to evaluate the fatigue strength of lap joints of materials applied to LNG carrier cargo containment of GAZ-TRANSPORT(GT) type, which was welded by manual and automatic TIG welding process. The thicknesses of lapped members were 1.5mm/1.5mm or 1.5mm/0.7mm in Invar to Invar joint, and 1.5mm/8.0mm in Invar to stainless steel joint, respectively. These lap joints were mainly applied to the membrance fabrication of GT-LNG carrier. Fatigue tests of Invar/Inar lap joints were conducted under the stress ratio R=0 at room temperature. The effect of mean stress and cumulative fatigue damage on the allowable stress of Invar lap joint was evaluated on the basis of test results. Fatigue test was also conducted on Inver/Stainless steel lap joints welded by automatic TIG process without filler metals. The fatigue test of the joint was carried out under the same conditions as those of Invar/invar lap joints. The fatigue strength of the joint welded without filler metal was comparable to those welded with filler metal quoted from reference. The fatigue strength of Invar/stainless steel lap joint was only dependent on the lap throat thickness, and not on the welding process. Based on test results, the applicability of TIG welding process without filler metal in Invar/stainless steel lap joint was reviewed by controlling welding variables to assure the valid throat thickness of lap joints.

• 한국항공우주학회지
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• 제39권12호
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• pp.1107-1114
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• 2011

본 논문에서는 레이저 피닝(Laser peening) 구조물에 대한 피로 수명을 예측하였다. 레이저 피닝에 의해 생성된 압축잔류응력(Compressive residual stress)을 계산하기 위해서 유한 요소 시뮬레이션(Finite element simulation)을 수행하였고, 피로 수명 예측 시에 압축잔류응력 효과를 고려하기 위해서 수정된 Goodman 식을 사용하였다. 또한, S-N 선도 모델 불확실성(Model uncertainty)을 고려한 피로 수명 예측을 위해 부가 적응 인자 접근법(Additive adjustment factor approach)을 적용하여 예측된 피로 수명의 신뢰 구간(Reliable bounds)을 결정하였다.

• 한국기계가공학회지
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• 제14권3호
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• pp.131-140
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• 2015

The purpose of this study is to predict the fatigue life of a planet carrier of a slewing reducer for a tower crane. To predict the fatigue life of the carrier, the inertia endurance test was carried out, and then the input torque profile for the reducer was obtained. The load profile acting on the planet pins that assembled the carrier was calculated from the measured input torque profile using commercial gearbox analysis software. The stress profiles of the carrier weak points were analyzed from the calculated load profile and boundary conditions using commercial FE software, and the stress cycles were determined using the rainflow counting method. Finally, the fatigue life of the carrier was predicted using the equivalent stress range by considering the effect of mean stress, and an S-N curve was drawn up using the GL guideline and the cumulative damage law.