• 대한기계학회논문집A
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• 제24권9호
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• pp.2183-2190
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• 2000

A thermal aging is observed in a primary reactor cooling system(RCS) made of a casting stainless steel when the RCS is exposed for long period at the reactor operating temperature, 290~3300C An investigation of effects of thermal aging on a low cycle fatigue characteristics included a stress variations caused by a reactor operation and trip, is required. The purpose of the present investigation is to find an effect of a thermal aging of the CF8M on a low cycle fatigue life. The specimen of CF8M are prepared by an artificially accelerated aging technique holding 300 and 1800hr at 4300C respectively. The low cycle fatigue tests for the virgin and two aged specimens are performed at the room temperature for various strain amplitudes($\varepsilon$ta), 0.3, 0.5, 0.8, 1.0, 1.2 and 1.5% strain. Through the experiment, it is found that the fatigue life is rapidly reduced with an creasing of the aging time. The experimental fatigue life estimation formulas between the virgin and two aged specimen are obtained and are proposed to a analysis purpose.

• 대한기계학회논문집A
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• 제32권2호
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• pp.177-185
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• 2008

Low-cycle environmental fatigue tests of cast austenitic stainless steel CF8M at the condition of fatigue strain rate 0.04%/sec were conducted at the pressure and temperature, 15MPa, $315^{\circ}C$ of a operating pressurized water reactor (PWR). The used test rig was limited to install an extensometer at the gauge length of the cylindrical fatigue specimen inside a small autoclave. So the magnet type LVDT#s were used to measure the fatigue displacement at the specimen shoulders inside the high temperature and high pressure water autoclave. However, the displacement and strain measured at the specimen shoulders is different from the one at the gauge length for the geometry and the cyclic strain hardening effect. Displacement of the fatigue specimen gauge length calculated by FEM (finite element method) used to modify the measured displacement and fatigue life at the shoulders. A series of low cycle fatigue life tests in air and PWR conditions simulating the cyclic strain hardening effect verified that the FEM modified fatigue life was well agreed with the simulating test results. The process and method developed in this study for the environmental fatigue test inside the small sized autoclave would be so useful to produce reliable environmental fatigue curves of CF8M stainless steel in pressurized water reactors.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.77-80
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• 2008

Low-cycle fatigue (LCF) tests were carried out to investigate the effect of loading direction on the cyclic deformation behavior and fatigue resistance of rolled AZ31 magnesium alloy. The as-received alloy showed a strong basal texture indicating that the most of basal planes of hexagonal close-packed structure were located parallel to the rolling direction. Two types of specimens whose loading directions were oriented parallel (RD) and vertical (ND) to the rolling direction. respectively, were used for the comparison. It was found that RD specimens yielded at much lower stresses during compression, while vice versa for the ND specimens, which was mainly attributed to the formation of primary twins. This anisotropic deformation behavior resulted in the different mean stresses during the cycling of RD and ND specimens, affecting the fatigue resistance of two specimens. The ND specimen showed a superior fatigue resistance as compared to the RD specimen under strain-controlled condition.

• Journal of Welding and Joining
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• 제33권6호
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• pp.42-48
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• 2015

Reduced activation ferritic/martensitic steels are recognized as the primary candidate structural materials for fusion blanket systems. Welding is an inevitable for breeding blanket for pressure tightness and radioisotope confinement. Especially, TIG welding was chosen for sealing because it has the largest gap allowance compared to the other welding methods, and its properties are controllable by feed wire and welding conditions. In this study, the low cycle fatigue test using two-type gage such as extensometer and strain gage was applied to the TIG welded joint of F82H steel, for evaluating fatigue damage accumulation behavior of the HAZs. As the result, the over-tempered HAZ have shown a higher fatigue damage accumulation compared with other materials at all the testing conditions.

• Nuclear Engineering and Technology
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• 제52권8호
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• pp.1724-1731
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• 2020

Low cycle fatigue tests on the hydrogenated welding seam of Zr-Sn-Nb alloy at room temperature and 360 ℃ had been carried out by using the funnel-shaped flat specimens. The relationships between nominal stress & strain directly measured across the funnel and local stress & strain at the root of the funnel are given by considering cyclic plasticity correction. The results show that the fatigue resistance of welding seam at room temperature is only slightly better than that at 360 ℃. Probabilistic fatigue life curves are obtained by using a two-parameter power function.

• 대한토목학회논문집
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• 제12권4_1호
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• pp.23-32
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• 1992

본 연구의 목적은 지진에 의한 강구조 부재의 소성피로손상 및 파괴에 크게 영향을 미치는 중요한 인자를 추출하여 그들간의 정량적 관계를 규명하는 것이다. 이를 위해, 앵글 강부재에 대하여 5~30 사이클 정도의 극저사이클 피로파괴실험을 실시하였다. 실험은 축방향 상대변위에 의해 제어된 반복 하중하에서 행하였으며, 앵글 시험체는 재하초기에 비탄성 전체좌굴 또는 국부좌굴이 발생하였다. 실험결과, 극저사이클 피로파괴하에서 강부재의 에너지 흡수능력은 재하이력과 파괴모우드에 따라 크게 변한다는 것을 알 수 있었고, 균열발생부에서 잔류 국소변형률의 최대치는 재하패턴 변형모우드 폭두께비에 관계없이 25~40% 정도였다.

• 한국추진공학회지
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• 제26권5호
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• pp.1-10
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• 2022

로켓엔진용으로 개발된 구리크롬 합금에 대해 저주기 피로시험을 수행하고 여러가지 피로수명 예측방법을 이용해 예측수명을 구하여 이를 시험수명과 비교하여 보았다. 피로수명 예측방법으로는 Coffin-Manson 관계식, 소성 및 전 변형률 에너지 밀도 관계식, Smith-Watson-Topper 관계식, Tomkins 관계식, Jahed-Varvani 관계식 등 총 6가지 방법을 이용하였다. 피로 예측수명을 계산한 결과 모든 방법에서 시험수명 대비 분산범위 2 이내를 만족하였다. 예측수명 편차의 정량적 확인을 통해 전 변형률 에너지 밀도 관계식이 가장 우수한 결과를 나타냈다.

• 열처리공학회지
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• 제22권4호
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• pp.217-222
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• 2009

The effects of severe plastic deformation by equal channel angular pressing (ECAP) and subsequent heat treatment on the low cycle fatigue behaviors of Al-Mg-Si alloy were investigated. The specimens which were peak aged at $175^{\circ}C$ after solution treatment showed cyclic hardening at all strain amplitudes, while the specimens ECAPed after solution treatment showed cyclic softening at all strain amplitudes during fatigue. The specimens aged at $100^{\circ}C$ after ECAP showed slight cyclic hardening. Various changes of cyclic fatigue behavior after severe plastic deformation and/or heat treatment were discussed in terms of the microstructural changes and precipitation conditions.

• 대한기계학회논문집A
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• 제34권10호
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• pp.1403-1409
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• 2010

니켈기 초내열합금은 고온 강도를 지속적으로 증가시키며 현재 비행기 엔진, 선박 엔진 및 발전용 가스터빈 고온 부품 등을 만드는 가장 중요한 소재로 오래전부터 사용되어져 왔다. 이러한 부품의 수명을 연장하기 위해서는 사용 환경과 유사한 조건에서의 피로수명 예측이 매우 중요하다. 따라서 본 연구에서는 가스터빈 블레이드 소재인 니켈기 초내열합금 IN738LC에 대하여 실제운전환경과 유사한 조건을 설정하여 다양한 변형률 범위와 온도에서 시험을 수행하였다. 저주기 피로수명을 예측하기 위하여 변형률 에너지 밀도와 파단 사이클과의 관계를 사용하였다. 수명의 예측은 시험결과를 토대로 변형률 에너지법과 Coffin-Manson법에 의하여 예측을 하였다.

• 대한조선학회논문집
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• 제43권2호
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• pp.213-219
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• 2006

Low cycle fatigue cracks are mainly detected at discontinuous welded locations with high stresses under repeated cyclic static loads due to cargo leading and unloading. Theoretical and analytical methods have been used for evaluation of local stress and strain which have an effect on a prediction of fatigue life, but those have difficulties of considering stress concentration at notched location and complicated material behavior of welded joint or heat affected zone. Electronic speckle pattern interferometry(ESPI) system is nondestructive and non-contact measurement system which can get the relatively accurate full field strain at critical positions such as welded zone and structural discontinuous location. In this study, local strain was measured on welded cruciform joint by ESPI system and then low cycle fatigue test was performed. Effect of local strain on low cycle fatigue life was examined by measured values using ESPI system. Moreover, experimental fatigue life was compared with established S-N curves using theoretical local strain and stress calculated by Neuber's rule.