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  • Title/Summary/Keyword: Thermal-mechanical Fatigue

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Fatigue Evaluation of Steam Separators of Heat Recovery Steam Generators According to the ASME Boiler and Pressure Vessel Code (ASME Boiler & Pressure Vessel Code에 따른 배열회수보일러 기수분리기의 피로 평가)

  • Lee, Boo-Youn
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.17 no.4
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    • pp.150-159
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    • 2018
  • The present research deals with a finite element analysis and fatigue evaluation of a steam separator of a high-pressure evaporator for the Heat Recovery Steam Generator (HRSG). The fatigue during the expected life of the HRSG was evaluated according to the ASME Boiler and Pressure Vessel Code Section VIII Division 2 (ASME Code). First, based on the eight transient operating conditions prescribed for the HRSG, temperature distribution of the steam separator was analyzed by a transient thermal analysis. Results of the thermal analysis were used as a thermal load for the structural analysis and used to determine the mean cycle temperature. Next, a structural analysis for the transient conditions was carried out with the thermal load, steam pressure, and nozzle load. The maximum stress location was found to be the riser nozzle bore, and hence fatigue was evaluated at that location, as per ASME Code. As a result, the cumulative usage factor was calculated as 0.00072 (much less than 1). In conclusion, the steam separator was found to be safe from fatigue failure during the expected life.

Service Life Analysis of Control Valve far Automatic Turbine Startup of Thermal Power Plant (화력 발전소 증기 터빈의 자동기동을 위한 주증기 제어 밸브 수명해석)

  • Kim, Hyo-Jin;Gang, Yong-Ho
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.1
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    • pp.1-6
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    • 2002
  • The automatic turbine startup system provides turbine control based on thermal stress. During the startup, control system monitors and evaluates main components of turbine using damage mechanism and life assessment. In case of valve chest, the temperature of inner/outer wall is measured by thermo-couples and the safety of these values are evaluated by using allowable △T limit currie during the startup. Because allowable ΔT limit curve includes life assessment, it is possible to apply this curve to turbine control system. In this paper, low cycle fatigue damage, combined rupture and low cycle fatigue damage criterion were proposed for yielding the allowable ΔTf limit curve of CV(control valve) chest. To calculate low cycle fatigue damage, the stress analysis of valve chest has been performed using FEM. Automatic turbine startup to assure service life of CV was achieved using allowable ΔT limit curve.

Thermal Ratchetting of the Conductive Adhesives Joints Subjected to the Thermal Cycles (전도성 접착제의 열경화 응력에 대한 해석)

  • 박주혁;서승호
    • Proceedings of the International Microelectronics And Packaging Society Conference
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    • 2002.05a
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    • pp.208-213
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    • 2002
  • When a thermoset conductive adhesive joints are subjected to the thermal cycles, the thermal stresses are developed around the joints. Most of in-plane, hi-axial components of these residual stresses induces large tensile peel stresses and weakens adhesive joints. Also these stresses vary with thermal cycles, and result in thermal fatigue loading and debonding propagation. In this study, the thermal ratchetting effect in conductive adhesive joints are evaluated by the finite element analysis with the viscoelastic material model. In order to Investigate the relationship between thermal ratchetting and glass transition temperature, the mathematical material model has been developed experimentally by dynamic mechanical analysis. These material models are implemented to the finite element analysis with thermal loading cycles. And the stress profiles around the conductive adhesive joints are calculated. It has been observed that the thermal ratchetting occurs when the maximum temperature of thermal cycles is above the glass transition temperature. The peel and shear stress components increase as the thermal loading time increases. This will contributes to thermal fatigue fracture of the joints.

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A Study on the Contact Fatigue Life Evaluation for Railway Wheels Considering Residual Stress Variation (잔류응력 변화를 고려한 철도차량 차륜의 접촉피로 수명평가)

  • Seo, Jung-Won;Goo, Byeong-Choon;Choi, Jae-Boong;Kim, Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.9
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    • pp.1391-1398
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    • 2004
  • Railway wheels and axles belong to the most critical components in railway vehicles. The service conditions of railway vehicles became more severe in recent years due to the increase of speed. Therefore, a more precise evaluation of wheelset life and safety has been requested. Wheel/rail contact fatigue and thermal cracks due to braking heat are two main mechanisms of the railway wheel failure. In this paper, an evaluation procedure for the contact fatigue life of railway wheel is proposed. One of the main sources of the contact zone failure is the residual stress. The residual stress on wheel is formed during the manufacturing process which includes a heat treatment, and then is changed by contact stress developed by wheel/rail contact and thermal stress induced by braking. Also, the cyclic stress history for fatigue analysis is determined by applying finite elements analysis for the moving contact load. The objective of this paper is to estimate fatigue life by considering residual stress due to heat treatment, braking and repeated contact load, respectively.

Effects of Maximum Strain and Aging Conditions on the Fatigue Life of Vulcanized Natural Rubber (가황 천연고무의 피로수명에 미치는 최대 변형률과 노화도 영향)

  • 우창수;김완두;김완수;권재도
    • Transactions of the Korean Society of Automotive Engineers
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    • v.12 no.4
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    • pp.181-190
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    • 2004
  • The interest of the fatigue life of rubber components such as engine mounts is increasing according to the extension of warranty period of the automotive components. Automotive engine mounts get damaged due to thermal and mechanical loadings. This paper discusses a fatigue life prediction of the 3-dimensional dumbbell specimens for natural rubber compound considering the effects of maximum strain and heat aging temperature. Displacement controlled fatigue life tests were performed using specimens with different levels of maximum strain and various hardness. The basic mechanical properties test and the fatigue test of aged rubber specimen under normal and elevated temperature were executed. A procedure to predicted the fatigue life of vulcanized natural rubber material based on the maximum strain method was proposed, and then this curve was in good agreement with fatigue test data less than 200% error range.

Fabrication of Ti(Al,O)Al2O3 Powder Feedstock for Thermal Spraying and Evaluation of the Composite Coating

  • Cao, Peng;Gabbitas, Brian;Zheng, Ling;Zhang, Deliang
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09a
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    • pp.49-50
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    • 2006
  • [ Ti(Al,O)Al2O3 ] composite powders were produced by high energy mechanical milling of a mixture of Al and TiO2 powders followed by a combustion reaction. The powders were subsequently thermally sprayed on H13 steel substrates. Microstructural examination was conducted on the composite powders and thermally sprayed coatings, using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The performance of the coatings was evaluated in terms of micro-hardness and thermal fatigue. The thermally sprayed coatings performed very well in the preliminary thermal fatigue tests and showed no wetting tendency to molten aluminum.

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FATIGUE ANALYSIS OF A REACTOR PRESSURE VESSEL FOR SMART

  • Jhung, Myung-Jo
    • Nuclear Engineering and Technology
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    • v.44 no.6
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    • pp.683-688
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    • 2012
  • The structural integrity of mechanical components during several transients should be assured in the design stage. This requires a fatigue analysis including thermal and stress analyses. As an example, this study performs a fatigue analysis of the reactor pressure vessel of SMART during arbitrary transients. Using heat transfer coefficients determined based on the operating environments, a transient thermal analysis is performed and the results are applied to a finite element model along with the pressure to calculate the stresses. The total stress intensity range and cumulative fatigue usage factor are investigated to determine the adequacy of the design.

Finite element analysis of inelastic thermal stress and damage estimation of Y-structure in liquid metal fast breeder reactor (액체금속로 Y-구조물의 비탄성 열응력 해석 및 손상평가에 관한 유한요소해석)

  • Kwak, D.Y.;Im, Y.T.;Kim, J.B.;Lee, H.Y.;Yoo, B.
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.7
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    • pp.1042-1049
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    • 1997
  • LMFBR(Liquid Metal Fast Breeder Reactor) vessel is operated under the high temperatures of 500-550.deg. C. Thus, transient thermal loads were severe enough to cause inelastic deformation due to creep-fatigue and plasticity. For reduction of such inelastic deformations, Y-piece structure in the form of a thermal sleeve is used in LMFBR vessel under repeated start-up, service and shut-down conditions. Therefore, a systematic method for inelastic analysis is needed for design of the Y-piece structure subjected to such loading conditions. In the present investigation, finite element analysis of heat transfer and inelastic thermal stress were carried out for the Y-piece structure in LMFBR vessel under service conditions. For such analysis, ABAQUS program was employed based on the elasto-plastic and Chaboche viscoplastic constitutive equations. Based on numerical data obtained from the analysis, creep-fatigue damage estimation according to ASME Code Case N-47 was made and compared to each other. Finally, it was found out that the numerical predictio of damage level due to creep based on Chaboche unified viscoplastic constitutive equation was relatively better compared to elasto-plastic constitutive formulation.

Experimental Estimation of Thermal Durability in Ceramic Catalyst Supports for Passenger Car (승용차용 세라믹 촉매 담체의 열적 내구성의 실험적 평가)

  • Baek, Seok-Heum;Kim, Sung-Yong;Seung, Sam-Sun;Yang, Hyup;Joo, Won-Sik;Cho, Seok-Swoo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.12
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    • pp.1157-1164
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    • 2007
  • Ceramic honeycomb structures have performed successfully as catalyst supports for meeting hydrocarbon, carbon monoxide and nitrous emissions standards for gasoline-powered vehicles. Three-way catalyst converter has to withstand high temperature and thermal stress due to pressure fluctuations and vibrations. Thermal stress constitutes a major portion of the total stress which the ceramic catalyst support experiences in service. In this study, temperature distribution was measured at ceramic catalyst supports. Thermal durability was evaluated by power series dynamic fatigue damage model. Radial temperature gradient was higher than axial temperature gradient. Thermal stresses depended on direction of elastic modulus. Axial stresses are higher than tangential stresses. Tangential and axial stresses remained below thermal fatigue threshold in all engine operation ranges.

Assessment of Internal Leak on RCS Pressure Boundary Valves (원자로냉각재계통 압력경계밸브 내부누설 평가)

  • Park, Jun-Hyun;Moonn, Ho-Rim;Jeong, Ill-Seok
    • Proceedings of the KSME Conference
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    • 2001.06a
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    • pp.322-327
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    • 2001
  • The internal leaks of RCS pressure boundary valves may cause thermal fatigue crack because of the TASCS in RCS branch line. After experienced unisolable piping failures in several PWR plants, many studies have peformed to understand these phenomena and various methods were applied to ensure the structural integrity of piping. In this paper, the cause of unisolable piping failures and the alternatives to prevent recurrence of failure were reviewed. Also, the severity of piping failure including susceptibility of valve leaks was evaluated for the Westinghouse 2-loop plant. The length of turbulent penetration on RHR inlet piping was measured and, thermal fluid analysis and fatigue analysis was performed for this piping. As a means of ensuring the structural integrity, temperature monitoring and specialized UT and other alternatives were compared for the further application.

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