• 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.

• 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.

• 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.