• 한국강구조학회 논문집
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• 제8권3호통권28호
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• pp.107-116
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• 1996

The studies are conducted to investigate the fatigue and fracture, behavior of preflex girder. In this work, the fatigue tests using by constant amplitude fatigue loading and 4-point-loading to maintain pure bending condition in the mid-span of preflex girder will be performed. It is expected from the results of the studies to provide the fatigue strength and the S-N curve of preflex girders. In addition, it will be ensured that fracture initiation occurs in the welded part of horseshoe-type shear connector as well as in other welded joints.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2000년도 KIASC Conference 2000 / 2000년도 학술대회 논문집
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• pp.104-108
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• 2000

In this study, the fatigue test at room temperature and residual resistivity measurement test at 12K were carried out, respectively, using a 0 strand Cu-Ni/NbTi/Cu composite cable, in order to investigate how the annealing treatment effects on critical properties due to fatigue damage. Through a fatigue test of a 0 strand Cu-Ni/NbTi/Cu composite cables, a conventional S-N curve was obtained even though there existed a possibility of fretting among strands. From the resistivity measurement of a NbTi strand after fatigue tests, it was found that the RRR for annealed cables was 3 times more than that for as-received one, but with increase of the repeated number the RRR decreased which was resulted from the accumulation of damage such as lattice defects dislocation within the Cu stabilizer.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1999년도 특별강연 및 춘계학술발표대회 개요집
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• pp.237-240
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• 1999

In this study, residual stresses of the weldment were calculated by finite element analysis(FEA) and experiment. And, the crack closure behaviour and fatigue crack growth characteristics in field of residual stress of A106 Gr B steel pipe weldment were investigated under various stress ratio. Obtained results are as follows. I) $K_{op}$ was independent of $K_{max}$, and load ratio in fatigue crack growth. 2) In variation of load ratio, the scatter band of crack growth curve was reduced by half considering crack closure. and 3) Neglecting crack closure behaviour, actual fatigue crack growth rate can be underestimated' and Actual fatigue crack growth rate can be overestimated by $K_{res}$, in tensile residual stress field.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.108-113
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• 2004

According to our fatigue tests carried out at 20 Hz, R=0.1 on transversely butt~welded joints, fatigue strengths of as-welded specimens, that is, specimens having residual stress are higher than those of annealed specimens in short life range, but vice verse in long life range. This behavior seems to be concerned mainly with residual stress relaxation by applied loading. After analyzing the welding process, we conducted finite element analysis to quantify the degree of residual stress relaxation. By taking into account residual stress relaxation, modified Goodman diagram, and nominal stress, we evaluated the fatigue life of the welded joint from the S-N curve for the parent material. The estimated results are in a good agreement with the experimental results.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 춘계학술대회 논문집
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• pp.263-268
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• 1999

With HAZ of A 106 Gr B steel weldment, fatigue test in air, electrochemical polarization test and corrosion fatigue test in 3.5wt.% NaCl solution were performed changing load ratio. Obtained results are as follows. 1) K$\sub$op/ was independent of K$\sub$max/ and load ratio in fatigue crack growth. 2) In variation of load ratio, the scatter band of crack growth curve was reduced by half considering crack closure 3) In the result of electrochemical polarization test, current density was increased abruptly when potential was larger than corrosion potential. 4) Fatigue crack growth rate in corrosive environment was markly higher than the rate in air because of corrosion characteristics of the material and anodization of inner surface crack.

• 한국해양공학회지
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• 제22권2호
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• pp.58-64
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• 2008

Large-scale tests of welded tubular K-joint sunder balanced in-plane bending braces were carried out to observe the fatigue behavior of the API 2W Gr.60 steel plate produced by POSCO. Toe grinding and weld profiling were used to improve the fatigue life of a tubular K-joint. The effects of the steel grade and chord wall thickness on the fatigue life were also investigated. The present results were compared with the UK DEn design curve.

• 한국정밀공학회지
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• 제14권5호
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• pp.128-133
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• 1997

Due to their high strength and good wear resistance, nitro-carburizing materials have been used for many machine components. However, the nitro-carburizing materials are found to have one disadvantage ; that is, their strength and fatigue life show larger scatter than those of non-heated metals. In this paper, therfore, the statistical chracteristics of non-heated and nitro-carburized specimens for SCM415 are investi- gated under two different of stress levels 1.15 .sigma. /sub .omega. / .leq. / .sigma. / sub .alpha. / .leq. / 1.25 .sigma. /sub .omega. /. Seven specimens at each stress level are tested by using rotating bending fatigue tester. The relation between a crack length and fatigue cycles can be arranged for Weibull distribution, and S-N curve using 95% reliability function is obtalined for nitro-carburized specimen.

• 한국항공운항학회지
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• 제18권1호
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• pp.1-10
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• 2010

Structures under high temperature may have creep behavior and fatigue behavior. Durability study of the structures need the damage analysis with the creep-fatigue effects. In this paper, the damage analysis is studied for a turbine blade in the turbopump for a liquid rocket engine which is operated under high temperature condition. First of all, the load cycle is required for defining the operational characteristics of turbopump. The thermal stress analysis is done for a turbine blade of the turbopump. The stress analysis results are used to judge damage due to the creep and the fatigue. The strain-life method with miner rule is used for fatigue damage analysis. The Larson-Miller parameter master curve and robinson rule are used for the creep damage analysis. The linear damage summation method is used to consider creep-fatigue effects of turbopump turbine. Finally, the analysis results for fatigue and the influence are compared to figure out the damage phenomenon of the turbopump turbine.

• 대한기계학회논문집A
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• 제21권11호
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• pp.1965-1971
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• 1997

The relaxation of stress concentration in notched members can be very significant in the improvement of notched strength and fatigue life. This paper investigated the relationship of stress concentration factor, and notched strength and fatigue life. The stress concentration factors were analyzed by FEM. Uniaxial tensile and fatigue tests were carried on plain woven composite specimens which have a main hole and two defence holes. From experimental results, the notched strength and the fatigue limit increased up to about 50% and 30% respectively due to the reduction in stress concentration. The fatigue lives predicted by Juvinall's approach were underestimated than test results and this trends were remarkable as nothed strength increased. This is because of the underestimation of a coefficient. A in S-N curve (.sigma.$_{ar}$ =A $N_{f}$ $^{B}$). Therefore, considering notched strength the coefficient A was modified. The fatigue lives by this process were agreed well with the experimental results.sults.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.44-48
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• 2001

API 5L X65 배관의 모재 기리 및 원주방향, 심용착금속, 원주용착금속에 대한 고주기피로시험 결과를 요약하면 다음과 같다. (1) 모재 길이방향이 원주방향보다 항복강도 및 항복비가 높게 나타난 압연 방향에 따라 피로특성이 다르게 나타났고, 항복비가 작아질수록 피로강도가 작아졌다. (2) 모재의 피로강도는 항복강도보다 높게 나타났지만 용착금속의 피로강도는 낮게 나타났다. (3) 용착금속은 모재보다 항복강도 및 인장강도가 상당히 높았지만 피로강도는 오히려 작게 나타났다.