• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2007년도 추계학술대회 논문집
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• pp.85-86
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• 2007

• 한국안전학회지
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• 제20권3호
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• pp.34-41
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• 2005

For assessing residual lift of the steam pipe in fossil power plants, inspections and analysis are usually focused on the critical locations such as butt welds, elbows, Y-piece and T-piece of the steam pipes. In predicting the residual life of T-piece, determination of local stress near welds considering system load as well as internal pressure is not a simple problem. In this study, stress analysis of a T-piece pipe was conducted using a three-dimensional model which represents the T-piece of a domestic fossil power station. Elastic and elastic-creep analysis showed the maximum stress level and its location. Residual creep rupture life was also calculated using the stress analysis results. It was argued that the calculated life is reasonably same as the measured one. The stress analysis results also support life prediction methodology based on in-field replication technique.

• 대한기계학회논문집A
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• 제27권10호
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• pp.1676-1685
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• 2003

Tensile and low cycle fatigue tests on prior cold worked 3l6L stainless steel were carried out at various temperatures ftom room temperature to 650$^{\circ}C$. Fatigue resistance was decreased with increasing temperature and decreasing strain rate. Cyclic plastic deformation, creep, oxidation and interactions with each other are thought to be responsible for the reduction in fatigue resistance. Currently favored life prediction models were examined and it was found that it is important to select a proper life prediction parameter since stress-strain relation strongly depends on temperature. A phenomenological life prediction model was proposed to account for the influence of temperature on fatigue life and assessed by comparing with experimental result. LCF failure mechanism was investigated by observing fracture surfaces of LCF failed specimens with SEM.

• 한국자동차공학회논문집
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• 제13권3호
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• pp.117-122
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• 2005

Titanium alloy has widely been used as material for glasses frame parts because it has high specific strength. It is also light and harmless to human body. However, we have little design data about the mechanical properties such as the creep behaviors of the alloy. Therefore, in this study, creep tests under four constant stress conditions have been conducted with four different temperature conditions. A series of creep tests had been performed to get the basic design data and life prediction of titanium products and we have gotten the following results. First, the stress exponents decrease as the test temperatures increased. Secondly, the creep activation energy gradually decrease as the stresses became bigger. Thirdly, the constant of Larson-Miller parameter on this alloy was estimated as about 2.5. Finally, the fractographs at the creep rupture showed the ductile fracture due to the intergranullar rupture and some dimples.

• 대한기계학회논문집A
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• 제25권5호
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• pp.823-833
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• 2001

In recent years, the subject of remaining life assessment has drawn considerable attention in chemical plants, where various structural components typically operate at high temperature an pressure. Thus a life prediction methodology accounting for high temperature creep fracture is increasingly needed for the components. Critical defects in such structures are generally found in the form of semi-elliptical surface crack, and the analysis of which is consequently an important problem in engineering fracture mechanics. On this background, we first develop an auto mesh generation program for detailed 3-D finite element analyses of axial and circumferential semi-elliptical surface cracks in a piping system. A high temperature creep fracture parameter C-integral is obtained from the finite element analyses of generated 3-D models. Post crack growth module is further appended here to calculate the amount of crack growth. Finally the remaining lives of surface cracked pipes for various analytical parameters are assessed using the developed life assessment program.

• 한국신뢰성학회지:신뢰성응용연구
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• 제7권2호
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• pp.45-55
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• 2007

In this study, two types of fatigue tests were conducted. Firs, cyclic bending tests were performed using the micro-bending tester. Second, thermal fatigue tests were conducted using a pseudo power cycling machine which was newly developed for a realistic testing condition. A three-dimensional finite element analysis model was constructed. A finite element analysis using ABAQUS was performed to extract the applied stress and strain in the solder joints. Creep deformation was dominant in thermal fatigue and plastic deformation was main parameter for bending failure. From the inelastic energy dissipation per cycle versus fatigue life curve, it can be found that the bending fatigue life is longer than the thermal fatigue life.

• 한국가스학회지
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• 제4권4호
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• pp.25-33
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• 2000

최근 들어 가혹한 온도 및 압력조건에서 운전이 요구되는 고온배관들의 잔여수명예측은 상당히 중요한 관심사로 부각되고 있다. 이에 고온손상을 정량적으로 평가하여 설비를 안전하게 사용하기 위한 유지기술 및 수명평가 기술을 확보하는 것은 매우 중요하다. 한편 이러한 고온배관내 대부분의 균열은 반타원 표면균열의 형태로 형상화되어 파괴역학의 실제응용에서 발견할 수 있는 가장 복잡한 형상과 하중특성을 갖게 된다. 이를 배경으로 본 연구에서는 먼저 축방향 및 원주방향 반타원 표면균열이 존재하는 직관의 완전 3차원 유한요소망 자동생성 프로그램을 작성하였다. 이렇게 생성된 유한요소 입력자료를 이용하여 3차원 유한요소 해석을 수행하면 반타원 표면균열선단을 따른 고온 크리프 파괴 지배변수 $C^{\ast}$-적분값을 구할 수 있다. 또한 $C^{\ast}$-적분값에 준해 균열진전량을 계산하는 후처리 균열진전 모듈을 추가하여 사용자 편의 수명평가 프로그램을 개발하였다. 최종적으로 개발된 통합 수명 평가 프로그램을 이용하여 여러 가지 해석변수들의 반타원 표면균열을 갖는 고온 직관 수명에 대한 영향을 살펴보았다.