• Nuclear Engineering and Technology
• /
• 제50권5호
• /
• pp.758-766
• /
• 2018

We developed numerical models to efficiently simulate the low-cycle fatigue behavior of a pipe elbow. To verify the model, in-plane cyclic bending tests of pipe elbow specimens were conducted, and a through crack occurred in the vicinity of the crown. Numerical models based on the erosion method and tie-break method are developed, and the numerical results are compared with experimental results. The calculated results of both models are in good agreement with experimental results, and the model using the tie-break method possesses two times faster calculation speed. Therefore, the numerical model based on the tie-break method would be beneficial to evaluate the strength of piping systems under seismic loadings.

• Nuclear Engineering and Technology
• /
• 제53권8호
• /
• pp.2600-2609
• /
• 2021

Low cycle fatigue behaviors of SA508-3 low-alloy steel were investigated in room-temperature air, high-temperature air and in light water reactor (LWR) water environments. The fatigue mean curve and design curve for the low-alloy steel are developed based on the fatigue data in room-temperature and high-temperature air. The environmental fatigue model for low-alloy steel is developed by the environmental fatigue correction factor (F_en) methodology based on the fatigue data in LWR water environments with the consideration of effects of strain rate, temperature, and dissolved oxygen concentration on the fatigue life.

• 대한금속재료학회지
• /
• 제50권4호
• /
• pp.271-279
• /
• 2012

9-12% Cr steels have been used in thermal power plants which repeat start and stop operations. Major factors of fatigue life are temperature, frequency, stress ratio, holding time, microstructure, and environment. Normally, fatigue life decreases at high temperature, low frequency, high stress ratio, and long holding time conditions. A Mod.9Cr-1Mo steel, called G91, was developed at ORNL (Oak Ridge National Laboratory, USA) and was adopted as a high-temperature structural material in the ASME Code in 2004. However, its low-cycle fatigue and fatigue crack growth characteristics have been rarely studied. In this work, we have investigated the low-cycle fatigue crack growth behaviors of G91 steel under various test conditions in terms of temperature and stress ratio. As temperature and stress ratio increase, the crack growth rate becomes faster and striation distance also increases. On the other hand, the number of branch cracks decreases.

• 한국압력기기공학회 논문집
• /
• 제6권1호
• /
• pp.50-56
• /
• 2010

Fatigue has been known as a major degradation mechanism of ASME class 1 components in nuclear power plants. Fatigue damage could be accelerated by combined interaction of several loads and environmental factors. However, the environmental effect is not explicitly addressed in the ASME S-N curve which is based on air at room temperature. Therefore many studies have been performed to understand the environmental effects on fatigue behavior of materials used in nuclear power plants. As a part of efforts, we performed low cycle fatigue tests under various environmental conditions and analyzed the environmental effects on the fatigue life of SA508 Gr. 1a low alloy steel by comparing with higuchi's model. Test results show that the fatigue life depends on water temperature, dissolved oxygen and strain rate. But strain rate over 0.4%/s has little effect on the fatigue life. To find the cause of different fatigue life with ANL's and higuchi's model, another test performed with different heat numbered and heat treated materials of SA508 Gr. 1a. On a metallurgical point of view, the material with bainite microstructure shows much longer fatigue life than that with ferrite/pearlite microstructure. And the characteristics of crack propagation as different microstructure seem to be the main cause of different fatigue life.

• 한국강구조학회 논문집
• /
• 제10권2호통권35호
• /
• pp.221-232
• /
• 1998

본 연구에서는 지진 등과 같이 소성변형의 범위가 큰 Low-Cycle-Fatigue 범주에서 구조물의 응력변동을 중심으로 사용되는 기존의 피로곡선인 S-N선도 보다 실질적으로 간단하게 측정하여 분석할 수 있는 소성회전각에 의한 피로곡선을 제시하였다. 이는 소성힌지가 생성되는 곳의 소성변형율과 구조물의 소성회전각이 서로 정비례를 이루는 상관관계임을 입증하여, 실험을 통하여 밝혀진 소성변형율의 피로곡선의 기울기와 소성회전각의 기울기가 서로 같은 값을 가짐을 보여 주었다. 이론은 Manson과 Coffin의 변형을 피로곡선을 도입하였고, 실험은 ECCS 주관하에 실시하였으며, 수치해석을 통하여 소성힌지 부위의 위치와 정확한 소성변형율을 산정할 수 있었다.

• 한국안전학회지
• /
• 제8권1호
• /
• pp.59-63
• /
• 1993

It is very difficult to find not only optimized welding condition but also fatigue characteristics of the dissimilar weld. In this study. Low carbon steel (SS41) and austenitic stainless steel (STS304) were welded by GTAW welding with STS309 stainless wire rod and Single Edge Notch specimens were used for the examination of fatigue behavior on welding heat cycle. The fatigue crack growth rate in HAZ of SS41 was the highest. The second was in STS304 bond line and the lowest was in HAS of STS304.

• 한국기계연구소 소보
• /
• 통권12호
• /
• pp.3-10
• /
• 1984

• 대한기계학회논문집
• /
• 제9권2호
• /
• pp.140-149
• /
• 1985

본 연구는 오오스테나이트계 STS 316 스테인레스강에 대하여 온도 550.deg. C의 대 기중에서, 변형율제어에 의한 인장-압축에 크리이프 유지시간을 갖는 고온저사이클 피 로시험을 하여 변형율폭 및 크리이프 유지시간이 피로수명에 미치는 영향과 파단면을 주사형 전자현미경으로 관찰하여 크리이프-피로 상호작용이 피로파단면에 미치는 크리 이프 효과를 실험 고찰하였다.

• 대한기계학회논문집A
• /
• 제28권4호
• /
• pp.427-434
• /
• 2004

Ferritic stainless steel is recently used in high temperature structures because of its good properties of thermal fatigue resistance, corrosion resistance, and low price. Tensile and low-cycle fatigue (LCF) tests on 429EM stainless steel used in exhaust manifold were performed at several temperatures from room temperature to 80$0^{\circ}C$. Elastic Modulus, yield strength, and ultimate tensile strength monotonically decreased when temperature increased. Cyclic hardening occurred considerably during the most part of the fatigue life. Dynamic strain aging was observed in 200~50$0^{\circ}C$, which affects the cyclic hardening behavior. Among the fatigue parameters such as plastic strain amplitude, stress amplitude, and plastic strain energy density (PSED), PSED was a proper fatigue parameter since it maintained at a constant value during LCF deformation even though cyclic hardening occurs considerably. A phenomenological life prediction model using PSED was proposed considering the influence of temperature on fatigue life.

• Composites Research
• /
• 제31권6호
• /
• pp.332-339
• /
• 2018

섬유 금속 적층판(Fiber metal hybrid laminate, FML)은 금속재료와 FRP의 접합으로 기존의 금속 소재가 가지지 못했던 뛰어난 물성과 가벼운 무게로 경제적인 구조용 재료로 사용된다. 그러나 섬유의 형태와 종류, 적층조건에 따라 물성의 차이가 크며, 파괴거동을 예측하기 어렵다는 단점이 있다. 본 논문에서는 Al6061-T6 합금에 직조형태의 유리섬유 플라스틱(GFRP, GEP118)을 적층피막한 복합재의 파손거동에 대해 연구한다. Al합금에 GFRP 1, 3, 5 겹을 피막한 3가지 조건으로 성형하고, 피막의 적층수를 변수로 정적시험과 저주기 피로시험을 병행하여 파손거동을 분석하였다. 저주기 피로시험에서는 변형률-수명 해석, 전변형률 에너지밀도법을 사용하여 분석하고, 피로수명을 예측하여 하이브리드 재료에 대한 수명예측성을 분석하였다. 인장해석 결과, GFRP 피막으로 인한 강화효과는 없었고, 피로시험시 나타나는 히스테리시스 형상은 GFRP피막 유무와 피막 수에 상관없이 모재인 Al합금의 거동을 따랐다. 저주기 피로시험 결과 GFRP의 피막으로 피로강도가 증가하였지만, GFRP의 두께에 따라 비례하여 증가하지는 않았다.