• 한국해양공학회지
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• 제3권2호
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• pp.108-117
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• 1989

This paper deals with a fatigue life prediction of a surface crack based on the experimentally obtained relationship between surface crack length ratio $a/a_{f}$ and cycle ratio $N/N_{f}$ using micro computer. Firstly $a/a_{f}$-$N/N_{f}$ curves obtained from experimental tests, were assumed as three curves UC(the upper limit curve), LC(the lower limit curve) and MC(the middle curve), and these were utilized to predict the fatigue life. Comparing the calculated values which represent the characteristics of crack growth behaviors from the three assumed curves with the experimental ones, it has been found that in the stable crack growth region, they coincide reasonably well each other. And the differences between the fatigue lives obtained from the assumed curves and the experimental fatigue life did not exceed 20%. Using the characteristics of $a/a_{f}$-$N/N_{f}$ curves, it is possible to predict the da/dN-Kmax curves and the S-$N_{f}$ curves.

• 대한기계학회논문집A
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• 제25권2호
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• pp.275-282
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• 2001

The reactor pressure vessel is usually cladded with stainless steel to prevent corrosion and radiation embrittlement. Number of subclad cracks may be found during an in-service-inspection due to the presence of cladding. It is specified, in ASME Sec. XI, that a subclad crack is characterized as a surface crack when the thickness of the clad is less than 40% of the crack depth. This condition is provided to keep the crack integrity evaluation conservative. In order to refine the fracture assessment procedures for such subclad cracks under a pressurized thermal shock condition, three dimensional finite element analyses are applied for various subclad cracks existing under cladding. A total of 36 crack geometries are analyzed, and the results are compared with those for surface cracks. The resulting stress intensity factors for subclad cracks are 6 to 44% less than those for surface cracks. It is proven that the flaw characterization condition as specified in ASME Sec. XI can be overly conservative for some subclad cracks.

• 한국가스학회지
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• 제3권1호
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• pp.1-7
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• 1999

알루미늄합금(5083-0)의 표면균열시험편의 관통전후의 피로거동을 조사하였다. 관통전의 피로균열형상은 거의 반타원형이며, 측정된 형상비는 Newman-Raju식의 K를 이용하여 계산한 값보다 더 크다. 관통후의 뒷면에서의 피로균열성장거동은 거의 유사하였으며 3영역으로 나누어졌다. 표면균열길이가 긴 경우, 피로균열전파법칙을 사용함으로서 표면균열재의 판두께 관통후의 피로균열 전파특성을 정량적으로 평가될 수 있음을 알 수 있었다.

• 한국산학기술학회논문지
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• 제7권6호
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• pp.1012-1020
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• 2006

철도차량의 차륜에서 발생하는 크랙은 표면으로부터 개시하는 표면크랙, 내부에서 개시하는 내부크랙으로 나눌 수 있고, 이들 크랙은 철도의 안전운행에 위험요소가 된다. 그러므로 이들 크랙의 성장수명 판단은 매우 중요하다. 본 연구에서는 철도차륜의 표면크랙 및 내부크랙의 응력분포상태, 변위 및 성장수명을 연구하였다. 특히 내부 및 표면크랙에 대해 유한요소해석을 실시하여 크랙선단의 응력상태, 변위, 응력확대계수를 찾아내었고, 이를 바탕으로 Paris 공식을 사용하여 성장수명을 예측하였다.

• 대한기계학회논문집
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• 제12권5호
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• pp.1097-1103
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• 1988

본 연구에서는 이 좁은 벤트내에 자료가 모이는 피로균열의 특성을 이용하여 표면피로균열의 성장거동을 파괴역학적으로 해석, 연구하여 균열의 성장특성과 $S-N_{f}$ 곡선의 추정을 마이크로 컴퓨터로 계산하였다.

• 대한기계학회논문집
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• 제3권3호
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• pp.116-123
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• 1979

On the basis of optical microscope and electro microscope observation for the fatigue fracture process of medium corbon martensitic structure produced by rapid heat treatment, mainly the abstracts of the studied results for the morphology of fatigue crack initiation process of high hardened steel are summarized as follows. Fatigue crack initiated from inclusion on the surface or subsurface. Above all the crack which initiated from inclusion exposed on the surface in as follows. (1) fatigue crack initiated from the boundary of the matrix and inclusion. (2) fatigue crack initiated at surrounding of small pit by drop out of inclusion.

• Computers and Concrete
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• 제4권1호
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• pp.49-66
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• 2007

The objective of this paper is to provide experimental data on the propagation of curved crack-surfaces and the respective load-displacement diagrams for the validation of numerical models for cracking of concrete, subjected to three-dimensional stress states. To this end beam-shaped specimens are subjected to combined bending and torsional loading, leading to the formation of a spatially curved crack-surface. The experimental data contain the evolution of the load and of the strains at selected points in terms of the crack mouth opening displacement and the propagation of the crack surface.

• 대한기계학회논문집
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• 제7권4호
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• pp.425-433
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• 1983

Fatigue tests by axial loading (R=0.1) were carried out to investigate fatigue crack growth properties of small surface cracks in mild steel at room temperature, 250.deg. C and 400.deg. C, by using flat specimens with a small artificial pit. All the data of the fatigue crack growth rate obtained in the present tests are determined as a function of the stress intensity factor range, so that the applicability of liner fracture mechanics to the fatigue crack growth of surface cracks at elevated temperatures is investigated and discussed in comparison with the data of type 304 stainless steel at room temperature and elevated temperature. The obtained results are as follows: 1) Relations of both surface fatigue crack length and its depth to cycle ratio fall within a narrow scatter band in spite of different stress levels. 2) The .DELTA. .sigma. .root. .pi. a-da/dN relation of surface fatigue crack growth at room temperature is independent of the stress level and can be plotted as a straight line at log-log diagram, but the relation at 400.deg. C depends partly on the stress level. 3) Relations of the fatigue crack growth into depth d(2b)/dN and is stress intensity factor range .DELTA. $K_{I}$, accounted for the aspect ratio variation, fall within a narrow scatter band for wide range of the applied stress levels. And .DELTA. $K_{I}$E-d(2b)/dN relations of mild steel at different stress level coincide relatively well with the data of type 304 stainless steel. 4) The value of aspect ratio obtained by a beach mark method and a temper coloring method approaches about 0.9 in common with crack growth and it is independent of stress level and temperatures. 5) The equi-crack length curve is parallel to S-N$_{f}$ curve at elevated temperatures.s.s.s.

• 대한기계학회논문집
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• 제11권3호
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• pp.355-361
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• 1987

본 연구에서는 고온기기의 부재로 널리 사용되는 304스테인리스강을 사용하여 기기의 사용조건을 고려한 538.deg. C(1000.deg. F), 593.deg. C(1100.deg. F)및 650.deg. C(1200.deg. F)의 세가지 온도레벨하의 대기중에서 크리이프-피로시험을 실시하여 작은 인공표면결함으로부터 발생.성장하는 표면균열의 성장거동을 조사 연구하였다. 또한 주파수의 영향을 조사 하기 위하여 538.deg. C에서 고온피로시험을 실시하여 이 결과를 크리이프 및 크리이프피로 시험의 결과와 비교.검토하였다.

• Tribology and Lubricants
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• 제18권2호
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• pp.160-166
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• 2002

In case of rough contact fatigue, the accurate calculation of surface tractions is essential to the prediction of crack initiation life. Accurate Surface tractions influencing shear stress amplitude can be obtained by contact analysis based on the morphology of contact surfaces. In this study, to simulate rough contact under sliding condition, gaussian rough surface generated numerically in the previous study was used and to calculate clack initiation life in the substrate, dislocation pileup theory was used.