• Computers and Concrete
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• 제30권4호
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• pp.277-287
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• 2022

Due to the scarcity of extortionate experimental data, fatigue failure of the reinforced concrete (RC) element might be achieved economically adopting nonlinear finite element (FE) analysis as an alternative approach. However, conventional implicit dynamic analysis is expensive, quasi-static method overlooks interaction effects and inertia, direct cyclic analysis computes stabilized responses. Apart from this, explicit dynamic analysis may provide a numerical operating system for factual long-term responses. The study explores the fatigue behavior based on a simplified explicit dynamic solution employing nonlinear time domain analysis. Among fourteen RC beams, one beam is selected to validate under static loading, one under fatigue with the experimental study and other twelve to check the detail fatigue behavior. The SWOT (Strength, Weakness, Opportunities, Threats) analysis has been carried out to pinpoint the detail scenario in the adoption of numerical approach as an alternative to the experimental study. Excellent agreement of FE and experimental results is seen. The 3D nonlinear RC beam model at service fatigue limits is truthful to be used as an expedient contrivance to envisage the precise fatigue behavior. The simplified analysis approach for RC beam under fatigue offers savings in computation to predict responses providing acceptable accuracy rather than the complicated laboratory investigation. At higher frequency, the flexural failure occurs a bit earlier gradually compared to the repeated loading case of lower frequency. The deflection increases by 6%-10% at the end of first cycle for beams with increasing frequency of cyclic loading. However, at the end of fatigue loading, greater deflection occur earlier for higher load range because of more rapid stiffness degradation. For higher frequency, a slight boost in concrete compressive strains at an initial stage of loading has been seen indicating somewhat stepper increment. Stiffness degradation in larger loading cycle at same duration escalates the upsurge of the rate of strain in case of higher frequency.

• Structural Engineering and Mechanics
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• 제77권2호
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• pp.197-215
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• 2021

Under a severe environment of multiple hazards such as earthquakes and winds, the life-cycle performance of engineering structures may inevitably be deteriorated due to the fatigue effect caused by long-term exposure to wind loads, which would further increase the structural vulnerability to earthquakes. This paper presents a framework for evaluating the lifetime structural seismic performance under the effect of wind-induced fatigue considering different sources of uncertainties. The seismic behavior of a high-rise steel-concrete composite frame with buckling-restrained braces (FBRB) during its service life is systematically investigated using the proposed approach. Recorded field data for the wind hazard of Fuzhou, Fujian Province of China from Jan. 1, 1980 to Mar. 31, 2019 is collected, based on which the distribution of wind velocity is constructed by the Gumbel model after comparisons. The OpenSees platform is employed to establish the numerical model of the FBRB and conduct subsequent numerical computations. Allowed for the uncertainties caused by the wind generation and structural modeling, the final annual fatigue damage takes the average of 50 groups of simulations. The lifetime structural performance assessments, including static pushover analyses, nonlinear dynamic time history analyses and fragility analyses, are conducted on the time-dependent finite element (FE) models which are modified in lines with the material deterioration models. The results indicate that the structural performance tends to degrade over time under the effect of fatigue, while the influencing degree of fatigue varies with the duration time of fatigue process and seismic intensity. The impact of wind-induced fatigue on structural responses and fragilities are explicitly quantified and discussed in details.

• 대한기계학회논문집A
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• 제28권9호
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• pp.1297-1305
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• 2004

Reliability of MEMS devices is receiving more attention as they are heading towards commercial production. In particular are the reliability and long-term stability of wafer level vacuum packaged MEMS gyroscope sensors subjected to cyclic mechanical stresses at high frequencies. In this study, we carried out several reliability tests such as environmental storage, fatigue, shock, and vibration, and we investigated the failure mechanisms of the anodically bonded vacuum gyroscope sensors. It was found that successful vacuum packaging could be achieved through reducing outgassing inside the cavity by deposition of titanium as well as by pre-taking process. The current gyroscope structure is found to be safe from fatigue failure for 1000 hours of operation test. The gyroscope sensor survives the drop and vibration tests without any damage, indicating robustness of the sensor. The reliability test results presented in this study demonstrate that MEMS gyroscope sensor is very close to commercialization.

• 한국포장학회지
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• 제16권1호
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• pp.1-4
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• 2010

The compression strength of corrugated fiberboard containers for packaging the agricultural products rapidly decreases because of various environmental conditions during distribution of unitized products. Among various environmental conditions, the main factors affecting the compression strength of corrugated fiberboard are absorption of moisture, long-term accumulative load, and fatigue caused by shock and vibration. An estimated rate of damage for fruit during distribution is about 30~40% owing to the shock and vibration. This study was carried out to characterize the durability of corrugated fiberboard containers for packaging the fruits and vegetables under simulated transportation environment. After the packaging freight was vibrated at various experimental conditions, the compression test for the packaging was performed. The compression strength of corrugated fiberboard containers decreased with loading weight and vibration time. The multiple nonlinear regression equation ($R^2$ = 0.9198) for predicting the decreasing rate of compression strength of corrugated fiberboard containers were developed using four independent variables such as input acceleration level, input frequency, loading weight and vibration time.

• 한국도로학회논문집
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• 제15권4호
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• pp.117-125
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• 2013

PURPOSES : The purpose of this study is to evaluate of field application and laboratory performance of warm-mix asphalt (WMA) according to the dosage rate of organic-based WMA additive. METHODS: Three asphalt mixtures, i.e., hot mix asphalt (HMA), WMA with the dosage rate of 1.5%, WMA with the dosage rate of 1.0%, were sampled from the asphalt plant when the field trial project were constructed. With these mixtures, the laboratory testings were performed to evaluate the linear viscoelastic characteristics and the resistance to moisture, rutting and fatigue damage. RESULTS : From the laboratory test results, it was found that the WMA with the reduced dosage rate of additive would be comparable to HMA and WMA with the original dosage rate in terms of the dynamic modulus, tensile strength ratio, rutting resistance. However, the fatigue reisistance of WMA with the reduced dosage rate was slightly worse but it should be noted that the fatigue performance is necessarily predicted by combining the material properties and pavement structure. CONCLUSIONS: Through the field construction and laboratory testings, the dosage rate of organic-based WMA additive could be reduced from 1.5% to 1.0% without the significant decrease of compactability and laboratory performance. The long-term performance of the constructed pavement will be periodically monitored to support the findings from this study.

• 대한기계학회논문집A
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• 제34권9호
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• pp.1265-1272
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• 2010

최근 들어 화력발전소는 잦은 기동과 부하 변동 하에서 안정적인 운전 및 관리에 대한 요구가 높아지고 있다. 특히 터빈, 보일러와 같이 고온 고압의 조건에서 운전되는 발전 설비의 경우 크리프 및 피로 손상의 영향으로 설비의 수명이 감소하게 된다. 보다 안전한 발전소 운영을 위해 설비의 정확한 수명평가가 중요하며 현재까지 다양한 방법이 개발되어 적용되고 있다. 그러나 현재까지는 표준화된 가이드라인이나 절차 없이 정성적/준정량적 분석에 의해 주요 설비의 수명을 평가하고 있다. 본 연구에서는 크리프 및 피로 손상기구에 근거하여 국내 화력발전 주요 설비의 수명 소비율을 평가하는 표준화된 기준을 개발하였고 실제 설비에 적용하여 평가 기준의 활용성을 검증하였다. 본 기준은 2010 전력기술기준에 수록될 예정으로 수명평가의 정확성 향상과 수명관리 표준화에 기여할 것이다.

• International Journal of Ocean System Engineering
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• 제3권4호
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• pp.209-217
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• 2013

This paper presents a mooring design procedure for a floating offshore wind turbine. Offshore environmental data for Jeju are taken from KHOA (Korea Hydrographic and Oceanographic Administration) and used for the environmental conditions in numerical analyses. A semi-submersible-type floating wind system with a 5-MW-class wind turbine studied by the DeepCwind Consortium is applied. Catenary mooring with a studless chain is chosen as the mooring system. Design deliverables such as the nominal sizes of chain and length of the mooring line are decided by considering the long-term prediction of the breaking strength of the mooring lines where a 100-year return period is used. The designed mooring system is verified using a fatigue calculation based on rain-flow cycle counting, an S-N curve, and a Miner's damage summation of rule. The mooring tension process is obtained from time-domain motion analyses using ANSYS/AQWA.

• Journal of Biosystems Engineering
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• 제30권2호
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• pp.89-94
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• 2005

The compression strength of corrugated fiberboard container for packaging the agricultural products rapidly decreases because of various environmental conditions during distribution of unitized products. Among various environmental conditions, the main factors affecting the compression strength of corrugated fiberboard are absorption of moisture, long-term accumulative load, and fatigue caused by shock and vibration. An estimated rate of damage for fruit during distribution is about from 30 to 40 percent owing to the shock and vibration. This study was carried out to characterize the durability of corrugated fiberboard container for packaging the fruit and vegetables under simulated transportation environment. The vibration test system was constructed to simulate the land transportation using truck. After the package with corrugated fiberboard container was vibrated by vibration test system at various experimental conditions, the compression test for the package was performed. The compression strength of corrugated fiberboard container decreased with loading weight and vibrating time. The multiple nonlinear regression equation for predicting the decreasing rate of compression strength of corrugated fiberboard containers were developed using four independent variables such as input acceleration level, input frequency, loading weight and vibrating time. The influence of loading weight on the decreasing rate of corrugated fiberboard container was larger than other variables.

• 대한조선학회논문집
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• 제30권4호
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• pp.74-82
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• 1993

본고에서는 type B 독립구형 방식 LNG 탱크의 피로균열 발생 및 진전에 대한 구조안전성 평가 기법을 연구하였다. 이는 다음과 같은 3단계의 검토과정으로 구성된다. 1) 탱크에 작용하는 파랑응력의 장기분포 평가 및 피로균열 발생수명해석 과정은 이미 제1보에서 상세히 다룬 바 있으며 2) 초기 결함이 탱크판을 관통할 수 없음을 표면균열 진전해석을 통하여 증명한다. 3) LBF(Leak Before Failure) 이론을 바탕으로 관통균열의 진전해석을 수행하여 급속 취성파괴에 대한 안전성을 검증한다.

• KEPCO Journal on Electric Power and Energy
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• 제4권1호
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• pp.19-24
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• 2018

가스터빈 동익에 대한 지속적인 국산화 개발이 추진되어, 국내 정밀 주조 기술을 향상시키고, 동익의 유지 보수 비용을 낮추는 등의 직간접적인 긍정적 효과를 가져왔지만, 여전히 국산화 개발품이 발전소에서 안정적인 실사용이 가능한지에 대한 우려가 존재한다. 향상된 소재와 주조기술을 바탕으로 조직학적, 기계적 성질에서 충분한 품질을 확보하였더라도, 개발품을 대상으로 다양한 신뢰성 검증이 요구되는 이유이다. 고속회전시험기는 로터, 디스크 등의 회전체에 원심력을 가하여, 이에 따른 제품의 특성을 분석하기 위한 시험장비로 일반적으로 과속도시험을 통한 최종적인 품질검사에 주로 사용된다. 본 논문에서는 전력연구원에 구축된 고속회전시험기를 활용한 가스터빈 동익에 대한 과속도시험을 포함한 저주기피로시험 사례를 중심으로 신뢰성 시험 및 평가 결과를 기술하였다.