• Title/Summary/Keyword: 저주기 피로

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Damage Analysis for Last-Stage Blade of Low-Pressure Turbine (저압터빈 최종단 블레이드 손상해석)

  • Song, Gee Wook;Choi, Woo Sung;Kim, Wanjae;Jung, Nam Gun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.37 no.12
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    • pp.1153-1157
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    • 2013
  • A steam turbine blade is one of the core parts in a power plant. It transforms steam energy into mechanical energy. It is installed on the rim of a rotor disk. Many failure cases have been reported at the final stage blades of a low-pressure (LP) turbine that is cyclically loaded by centrifugal force because of the repeated startups of the turbine. Therefore, to ensure the safety of an LP steam turbine blade, it is necessary to investigate the fatigue strength and life. In this study, the low cycle fatigue life of an LP steam turbine blade is evaluated based on actual damage analysis. To determine the crack initiation life of the final stage of a steam turbine, Neuber's rule is applied to elastic stresses by the finite element method to calculate the true strain amplitude. It is observed that the expected life and actual number of starts/stops of the blade were well matched.

High Temperature Fatigue Behavior of A356 and A319 Heat Resistant Aluminum Alloys (A356 및 A319 내열 알루미늄 합금의 고온 피로 변형 거동)

  • Park, Jong-Soo;Sung, Si-Young;Han, Bum-Suck;Jung, Chang-Yeol;Lee, Kee-Ahn
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2009.10a
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    • pp.467-469
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    • 2009
  • In this study, fatigue samples were prepared from cylinder head parts that are actually used in domestic (A) and foreign (B) automobiles; high-temperature, high-cycle, and low-cycle fatigue characteristics were then evaluated and compared. A study on the correlation between the microstructural factor and high temperature fatigue characteristic was attempted. The chemical compositions of the heat resistant aluminum alloys above represented A356 (A) and A319 (B), respectively. The result of the tensile strength test on material B at $250^{\circ}C$ was higher by 30.8MPa compared to material A. On the other hand, elongation was 8.5% higher for material A. At $130{\circ}C$, material B exhibited high fatigue life given high cycle fatigue under high stress, whereas material A showed high fatigue life when stress was lowered. With regard to the low-cycle fatigue result ($250^{\circ}C$) showing higher fatigue life as ductility is increased, material A demonstrated higher fatigue life. Through the observation of the differences in microstructure and the fatigue fracture surface, an attempt to explain the high-temperature fatigue deformation behavior of the materials was made.

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Improvement of Fatigue-Proof Characteristics of Link Members Under Impact Loadings by a Spring-Actuated Mechanism (스프링구동 메커니즘의 충격 하중을 받는 링크부재의 내피로 특성 향상)

  • 안길영;박상후;이부윤;김원진;오일성
    • Journal of the Korean Society for Precision Engineering
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    • v.20 no.4
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    • pp.158-164
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    • 2003
  • The air circuit breaker (ACB) with the spring-actuated mechanism was studied to improve the fatigue-proof characteristics of its link. The low-cycle fatigue fracture phenomenon occurred on the critical link, called h-link, of ACB from the repeated rapid closing and opening operations. To analyze the cause of failure, dynamic FE-analysis on the b-link part of ACB was performed considering tile velocity and acceleration of the links per time as boundary conditions, which were obtained by using ADAMS. Also, the S-N curve obtained by experiments was used to investigate requirement on the fatigue-proof characteristics. Then, to reduce the maximum tensile stress on the h-link, three types of h-link were examined and one of them was selected.

Mechanical Behavior Evaluation and Structural Analysis of 316 Stainless Steel at High Temperature (316 스테인리스강의 고온 물성 연구 및 구조 평가)

  • Rhim, Sung-Han;Lee, Kwang-Ju;Kim, Jin-Bae;Yang, In-Young
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2008.11a
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    • pp.181-184
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    • 2008
  • Austenitic stainless steel is used as high temperature components such as gas turbine blade and disk because of its good thermal resistance. In the present investigation, tensile and low cycle fatigue behavior of 316 stainless steel was studied at wide temperature range $20^{\circ}C{\sim}750^{\circ}C$. In the tensile tests, it was shown that elastic modulus, yield strength, ultimate tensile strength decreases when temperature increased. The effect on fatigue failure of the parameters such as plastic strain amplitude and plastic strain energy density was also investigated. With the experimental results, a structural analysis of turbine blades of 316 stainless steel were carried out.

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A Proposal of Parameter to Predict Biaxial Fatigue Life for CF8M Cast Stainless Steels (CF8M 주조 스테인리스강의 2축 피로수명 예측을 위한 파라미터의 제안)

  • Park Joong Cheul;Kwon Jae Do
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.6 s.237
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    • pp.815-821
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    • 2005
  • Biaxial low cycle fatigue test was carried out to predict fatigue life under combined axial-torsional-loading condition which is that of in-phase and out-of-phase for CF8M cast stainless steels. Fatemi-Socie(FS) parameter which is based on critical plane approach is not only one of methods but also the best method that can predict fatigue life under biaxial loading condition. But the result showed that, biaxial fatigue life prediction by using FS parameter with several different parameters for the CF8M cast stainless steels is not conservative but best results. So in this present research, we proposed new fatigue life prediction parameter considering effective shear stress instead of FS parameter which considers the maximum normal stress acting on maximum shear strain and its effectiveness was verified.

Damage Analysis of Turbopump Turbine considering Creep-Fatigue effects (크리프-피로 영향을 고려한 터보펌프 터빈의 손상해석)

  • Lee, Mu-Hyoung;Jang, Byung-Wook;Kim, Jin-Han;Jeong, Eun-Hwan;Jeon, Seong-Min;Lee, Soo-Yong;Park, Jung-Sun
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.18 no.1
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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.

Application of Damage Index for Limit State Evaluation of a Steel Pipe Tee (강재 배관 Tee의 한계상태 평가를 위한 손상지수의 적용)

  • Kim, Sung-Wan;Yun, Da-Woon;Jeon, Bub-Gyu;Kim, Seong-Do
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.26 no.4
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    • pp.30-39
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    • 2022
  • Maintaining structural integrity of major apparatuses in a nuclear power plant, including piping system, is recognized as a critical safety issue. The integrity of piping system is also a critical matter related to the safety of a nuclear power plant. The actual failure mode of a piping system due to a seismic load is the leakage due to a fatigue crack, and the structural damage mechanism is the low-cycle fatigue due to large relative displacement that may cause plastic deformation. In this study, in-plane cyclic loading tests were conducted under various constant amplitudes using specimens composed of steel straight pipes and a steel pipe tee in the piping system of a nuclear power plant. The loading amplitude was increased to consider the relative displacement generated in the piping system under seismic loads, and the test was conducted until leakage, which is the limit state of the steel pipe tee, occurred due to fatigue cracks. The limit state of the steel pipe tee was expressed using a damage model based on the damage index that used the force-displacement relationship. As a result, it was confirmed that the limit state of the steel pipe tee can be quantitatively expressed using the damage index.

Low Cycle Fatigue Life Prediction of Reusable Experimental Liquid Rocket Engine (재사용이 가능한 실험용 액체로켓엔진의 저주기 피로수명예측)

  • 한풍규;송준영
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2002.04a
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    • pp.8-9
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    • 2002
  • 액체로켓엔진의 연소기는 고온고압의 연소가스에 의해 벽면온도가 매우 높은 수준에 도달하기 때문에, 연소기가 열적으로 안정적으로 작동할 수 있는 메카니즘이 필요하게 되며, 따라서 이러한 방식의 하나로서 추진제를 이용한 재생냉각방식이 널리 사용되고 있다. 일반적으로 재생냉각형 연소기의 내벽은 열전도도가 우수한 구리 또는 구리합금 계열이 많이 사용되고 있다. 이러한 내벽 재질의 내구성은 주로 creep rupture, low cycle thermal fatigue, thermal-mechanical ratcheting에 의해 결정되는데, 사각형태의 냉각채널의 연소기에서는 thermal-mechanical ratcheting 특성이 수명 결정 주요 인자이다. Thermal-mechanical ratcheting은 그림 1과 같이 연소가스 영역과 냉각제 영역을 분리하는 벽면에서 국부적인 부풀음이 일어나면서 벽면두께가 감소하는 소성변형 형태로 나타나는데, 이러한 것을 Dog- house 형상이라 한다.

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A Prediction Model for Low Cycle Fatigue Life of Pre-strained Fe-18Mn TWIP Steel (Fe-18Mn TWIP강의 Pre-strain에 따른 저주기 피로 수명 예측 모델 연구)

  • Kim, T.W.;Lee, C.S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2009.10a
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    • pp.259-262
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    • 2009
  • The influence of pre-strain in low-cycle fatigue behavior of Fe-18Mn-0.05Al-0.6C TWIP steel was studied by conducting axial strain-controlled tests. As-received plates were deformed by rolling with reduction ratios of 10 and 30%, respectively. A triangular waveform with a constant frequency of 1 Hz was employed for low cycle fatigue test at the strain amplitudes in the range of ${\pm}0.4{\sim}{\pm}0.6$ pct. The results showed that low-cycle fatigue life was strongly dependent on the amount of pre-strain as well as the strain amplitude. Increasing the amount of prestrain, the number of reversals to failure was significantly decreased at high strain amplitudes, but the effect was negilgible at low strain amplitudes. A new model for predicting fatigue life of pre-strained body has been devised adding a correction term of ${\Delta}E_{pre-strain}$ to the energy-based fatigue damage parameter.

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Fatigue Damage Behavior in TIG Welded Joint of F82H Steel under Low Cycle Fatigue Loading (저주기 피로부하에서 F82H 강 TIG 용접 접합부의 피로손상거동)

  • Kim, Dong-Hyun;Park, Ki-Won
    • Journal of Welding and Joining
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    • v.33 no.6
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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.