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  • Title/Summary/Keyword: Thermal-mechanical Fatigue

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DEVELOPMENT OF GREEN'S FUNCTION APPROACH CONSIDERING TEMPERATURE-DEPENDENT MATERIAL PROPERTIES AND ITS APPLICATION

  • Ko, Han-Ok;Jhung, Myung Jo;Choi, Jae-Boong
    • Nuclear Engineering and Technology
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    • v.46 no.1
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    • pp.101-108
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    • 2014
  • About 40% of reactors in the world are being operated beyond design life or are approaching the end of their life cycle. During long-term operation, various degradation mechanisms occur. Fatigue caused by alternating operational stresses in terms of temperature or pressure change is an important damage mechanism in continued operation of nuclear power plants. To monitor the fatigue damage of components, Fatigue Monitoring System (FMS) has been installed. Most FMSs have used Green's Function Approach (GFA) to calculate the thermal stresses rapidly. However, if temperature-dependent material properties are used in a detailed FEM, there is a maximum peak stress discrepancy between a conventional GFA and a detailed FEM because constant material properties are used in a conventional method. Therefore, if a conventional method is used in the fatigue evaluation, thermal stresses for various operating cycles may be calculated incorrectly and it may lead to an unreliable estimation. So, in this paper, the modified GFA which can consider temperature-dependent material properties is proposed by using an artificial neural network and weight factor. To verify the proposed method, thermal stresses by the new method are compared with those by FEM. Finally, pros and cons of the new method as well as technical findings from the assessment are discussed.

A Study on the 430C Degradation Behavior of Cast Stainless Steel(CF8M)(II)-Evaluation of Low Cycle Fatigue Characteristics- (주조 스테인리스강 CF8M의 430C 열화거동에 관한 연구 (II) -저사이클 피로특성 평가-)

  • Gwon, Jae-Do;U, Seung-Wan;Park, Jung-Cheol;Lee, Yong-Seon;Park, Yun-Won
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.9 s.180
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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(εta), 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.

High Temperature Creep-Fatigue Behavior of 25Cr-13Ni Stainless Steel (25Cr-13Ni 스테인리스강의 고온 크리프-피로거동에 관한 연구)

  • Song, Jeon-Young;Ahn, Yong-Sik
    • Journal of the Korean Society for Heat Treatment
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    • v.28 no.2
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    • pp.68-74
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    • 2015
  • The low cycle fatigue (LCF) and creep-fatigue (hold time tension fatigue, HTTF) tests were performed on the modified 25Cr-13Ni cast stainless steel, which was selected as a candidate material for exhaust manifold in automotive engine. The exhaust manifold is subjected to an environment in which heating and cooling cycle occur due to the running pattern of automotive engine. Several types of fatigue behaviour such as thermal fatigue, thermal mechanical fatigue and creep-fatigue are belong to the main failure mechanisms. High temperature tensile test was firstly carried out to compare the sample with the traditional cast steel for the component. The low cycle fatigue and HTTF tests were carried out under the strain controlled condition with the total strain amplitude from ±0.6 to ±0.7 at 800C. The hysteresis loops of HTTF tests showed significant stress relaxation during tension hold time. With the increase of tension hold time, the fatigue life was remarkably deceased which caused from the formation of intercrystalline crack by the creep failure mechanism.

Effects of Alpha Phase on the Fatigue Properties of Fe-29%Ni-17%Co Low Thermal Expansion Alloy (Fe-29%Ni-17%Co 저열팽창 합금의 피로 특성에 미치는 알파상의 영향)

  • Kim, Min-Jong;Gwon, Jin-Han;Cho, Kyu-Sang;Lee, Kee-Ahn
    • Korean Journal of Materials Research
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    • v.24 no.9
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    • pp.481-487
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    • 2014
  • The effect of alpha phase on the fatigue properties of Fe-29%Ni-17%Co low thermal expansion alloy was investigated. Two kinds of alloys (Base alloy and Alpha alloy) were prepared by controlling the minimal alloy composition. Microstructure observation, tensile, high-cycle fatigue, and low-cycle fatigue results were measured in this study. The Base alloy microstructure showed typical austenite γ phase. Alpha alloy represented the dispersed phase in the austenite γ matrix. As a result of tensile testing, Alpha alloy was found to have higher strengths (Y.S. & T.S.) and lower elongation compared to those of the Base alloy. High cycle fatigue results showed that Alpha alloy had a higher fatigue limit (360MPa) than that (330MPa) of the Base alloy. The Alpha alloy exhibited the superior high cycle fatigue property in all of the fatigue stress conditions. SEM fractography results showed that the alpha phase could act to effectively retard both fatigue crack initiation and crack propagation. In the case of low-cycle fatigue, the Base alloy had longer fatigue life in the high plastic strain amplitude region and the Alpha alloy showed better fatigue property only in the low plastic strain amplitude region. The fatigue deformation behavior of the Fe-29%Ni-17%Co alloy was also discussed as related with its microstructure.

A Study of Fatigue Lifetime Evaluation on the Interconnect of Semiconductor Pressure Sensor According to the Various Materials (재료에 따른 반도체 압력 센서 배선의 피로 수명 평가에 관한 연구)

  • Shim Jae-Joon;Han Dong-Seop;Han Geun-Jo;Lee Sang-Suk
    • Journal of Navigation and Port Research
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    • v.29 no.10 s.106
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    • pp.871-876
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    • 2005
  • Application of semiconductor sensors has been widely spreaded into various industries because those have several merits like easy miniaturization and batch production comparison with previous mechanical sensors. But external conditions such as thermal and repetitive load have a bad effect on sensors's lifetime. Especially, this paper was focused on fatigue life of a interconnect made by various materials. Firstly we implemented the stress analysis for interconnect under thermal load and wording pressure. And the fatigue lifetime of each material was induced by Manson & Coffin Equation using the plastic stress-strain curve obtained by the plastic-elastic Finite Element Analysis. The Fatigue lifetime in its bottom is smaller than others and bending load have not an effect on the fatigue lifetime of the interconnect but the stress distribution.

Development of Reliability Design Technique and Life Prediction Model for Electronic Components (취성/연성 파괴에 대한 수명예측 모델 및 신뢰성 설계)

  • Kim, Il-Ho;Lee, Soon-Bok
    • Proceedings of the KSME Conference
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    • 2007.05a
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    • pp.1740-1743
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    • 2007
  • In this study, two types of fatigue tests were conducted. First, cyclic bending tests were performed using the micro-bending tester. A four-point bending test method was adopted, because it induces uniform stress fields within a loading span. Second, thermal fatigue tests were conducted using a pseudo power cycling machine which was newly developed for a realistic testing condition. The pseudo-power cycling method makes up for the weak points in a power cycling and a chamber cycling method. Two compositions of solder are tested in all test condition, one is lead-free solder (95.5Sn4.0Ag0.5Cu) and the other is eutectic lead-contained solder (63Sn37Pb). In the cyclic bending test, the solder that exhibits a good reliability can be reversed depending on the load conditions. The lead-contained solders have a longer fatigue life in the region where the applied load is high. On the contrary, the lead-free solder sustained more cyclic loads in the small load region. A similar trend was detected at the thermal cycling test. 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. A constitutive model which includes both creep and plasticity was employed. Thermal fatigue was occurred due to the creep. And plastic deformation is main damage 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.

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Study for the Deformation and Fatigue Life of a PEMFC (고분자 전해질 연료전지 막의 변형 및 피로수명)

  • Yang, Jeong-Hwan;Park, Jung-Sun
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.39 no.5
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    • pp.400-407
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    • 2011
  • The stress distribution and stress amplitude of a membrane are major factors to decide the mechanical fatigue life of PEMFC (Polymer Electrolyte Membrane Fuel Cell). In this paper, mechanical stresses under operating hygro-thermal condition of the membrane are numerically modelled. Contact analysis between gas diffusion layer (GDL) and the membrane is performed under various temperature-humidity conditions. The structural model has nonlinear material properties depending on temperature and relative humidity. Several geometric conditions are applied to the model. The numerical analysis results indicate that deformations of the membrane are strongly related with assembly conditions of the fuel cell. The fatigue life is predicted for practical operating condition through experimental data.

Thermal Stress Analysis for a Ventilated Disk Brake of Railway Vehicles (철도 차량용 제동디스크의 열응력 해석)

  • Lee Y.M.;Park J.S.;Seok C.S.;Lee C.W.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2005.06a
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    • pp.1617-1621
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    • 2005
  • In this study, as a basic research to improve braking efficiency of a ventilated disk brake, we carried out a thermal stress analysis. From analysis result, we knew that a maximum mechanical stress by braking pressure and friction force is applicable to 5 percent of yield strength and has no effect on a fatigue life's decrease for brake disk material. While, a maximum thermal stress by frictonal heat is applicable to 43 percent of yield strength and locates on a friction surface. So, we have found that a thermal stress is the primary factor of crack initiation on a friction surface of disk brake

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