• Journal of Welding and Joining
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• 제11권4호
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• pp.112-124
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• 1993

It has been reported that fatigue damage sometimes occurred at the stress concentrated and dynamic loaded structural members of bulk carrier. In this paper, studies on fatigue strength of hull structures are reviewed, and the program for evaluating fatigue strength is developed. And the fatigue crack initiation and propagation on the end part of cargo hold frame of bulk carrier were calculated by FEM stress analysis and the fatigue strength evaluation program. These method can be applied not only to the crack initiation life but also to crack propagation life for the hull structural members at the hull design stage and be effective as the guideline to prevent the crack initiation or to estimate the fatigue strength for repairing of the fatigue damaged structures of real ships.

• Journal of Welding and Joining
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• 제11권2호
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• pp.42-52
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• 1993

The corrosion fatigue fracture behaviour of dual phase steel was investigated in 3% NaCl solution at 302MPa and 137MPa. Fatigue test was conducted by cantilever type of self-made rotary bending fatigue testing machine. The fatigue strength increased with increasing the hardness of 2nd phase. Corrosion pit originated at the boundary of the 2nd phase. The size and number of corrosion pits were influenced by the 2nd phase hardness, and pits remained constant in size just after they were transited into cracks. The life of crack initiation was effected by stress level. The shape of relation of .DELTA. K and da/dN has smaller scattering in it in 3% NaCl solution than that in air. The higher the 2nd phase hardness is, the greater the corrosion fatigue life becomes. Corrosion fatigue fracture behaviour was primarily effected by mechanical factor in case of high stress(302MPa), but by electro-chemical reaction in a lower stress(137MPa). As stress level got lower and hardness of the 2nd phase got higher, the roughness of fracture surface increased.

• 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.

• Journal of Welding and Joining
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• 제6권1호
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• pp.46-52
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• 1988

Retardation or delay in fatigue crack growth due to overloads are important for the accurate prediction of fatigue lives of structural materials. In this study, retardation of fatigue crack growth in Al 6061-T6 weldments and heat affected zones (HAZ) after single overload cycle had been investigated. Retardation in both weldments and HAZ was observed. It was concluded that retardation in both weldment and HAZ was greater than in base metal due to microstructural change and crack branching and crack closure were major governing factor in retardation.

• Journal of Welding and Joining
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• 제12권3호
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• pp.90-100
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• 1994

In this study the fatigue crack growth behavior was investigated for the surface cracks in aluminum alloy A5083-O plate and its weldment. Several kinds of specimens were tested at room temperature. The Eccentric specimens(E1.0, E2.5) subjected to combined stresses(tension+bending) were tested and the welded specimens with weld toes(TOE1, TOE2) were tested in order to verify the method to consider the stress concentration such as weld toe. It was ascertained that the surface crack growth property in the weld toe could be predicted by the corrected Pang's equation proposed in this study.

• Journal of Welding and Joining
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• 제13권2호
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• pp.60-67
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• 1995

The factors affecting on the fatigue strength of spot_welded specimens have been studied. The influence of initial overloads on the fatigue life of spot_welded tensile_shear specimens is investigated by considering fatigue crack initiation and crack propagation. The change of strain range and the influence of initial overload are correlated on the basis ol strain results. The results of this study are as follows. l) The initial absolute strain range decreased with initial overloads increase, and absolute strain range decreased before transformation of waveform of strain, but increased after transformation of waveform of strain. 2) In case of subsequent point of inflection of offset strain, the increment of this strain decreased with initial overload increase. 3) As initial overloads increase, the deformation behavior of spot welded parts is restricted after overloading.

• 한국공작기계학회논문집
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• 제12권1호
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• pp.38-44
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• 2003

In this study, endurance limit and fatigue behavior of load carrying fillet welded cruciform joints depending on commonly used welding methods such as SMAW, SAW, MIG and FCAW are investigated. In respect of endurance limit SMAW specimen showes highest result, and then MIG, SAW, FCAW in descending order. However, SMAW specimen showes lowest crack growth rate and it followed by MIG, FCAW, SAW. By these results, it is needed to use SMAW or MIG welding methods for welding structures with small welding capacity and SAW or FCAW methods for large welding structures with respect to economic benefits and operation efficiency of welding. It was also shown fatigue crack growth rate was more influenced by the strenght of welding materials than the endurance limit of welding materials.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 춘계학술대회 논문요약집
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• pp.76-76
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• 2004

하이브리드 복합재료 중에서 적충형태의 Al/GFRP는 단일재 알루미늄에 비해 피로특성, 비강도, 비강성 등이 매우 우수하여 Fig. 1과 같이 항공기 주익 구조에 주로 적용된다. 그러나 이러한 Al/GFRP 적층재 역시 장시간에 걸쳐 비행하중을 받게 되면 다양한 형태의 파손이 발생할 수 있다. 이 중 알루미늄층과 섬유층 사이에서 발생하는 층간분리는 Al/GFRP 적층재의 대표적인 피로파손 형태이며, 현재 이러한 파손은 다 방면으로 연구되고 있다.(중략)

• 대한조선학회논문집
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• 제29권2호
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• pp.79-91
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• 1992

본 논문에서는 균열 보수에 사용되는 Patch와 균열진 판 사이에 컴프라이언스 개념을 적용하여 Patch된 균열진 판의 응력확대계수를 이론유도하고, 이에 대한 실험과 균열진전 거동규명을 통하여 그 유효성을 충분히 검증하였다. 또한, 이와같은 컴프라이언스를 이용한 이론방법을 바탕으로 균열진 구조물의 잔존수명이 고려된 Patch를 간단히 설계할 수 있는 기법을 제시하였다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2005년도 추계학술대회 논문집
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• pp.1083-1088
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• 2005

As the industrial society develops rapidly, the weight reduction and high strength are demanded gradually. In case of the welded joint for the rolling stock which receives the repeat load, the structural failure can occur easily. However, if the shot peening technique is applied, the durability and the fatigue characteristics of the rolling stock will be improved because the hardness increases and the residual stress is induced. In this study, the fatigue characteristics of shot peened welled joints for the rolling stock was investigated. The crack initiation was examined and hardness was also evaluated. the results show that the fatigue characteristics of welded joints was improved.