• Title/Summary/Keyword: 응력 확대계수 범위

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Fatigue Characteristics of Non Load-Carrying Fillet Welded Joints according to Post-Processing in Weld Bead Toes (용접지단부의 후처리에 따른 하중비전달형 필렛용접부의 피로특성)

  • Hong, Sung Wook;Kyung, Kab Soo;Choi, Dong-Ho;Yong, Hwan Sun
    • Journal of Korean Society of Steel Construction
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    • v.12 no.6
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    • pp.701-713
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    • 2000
  • In this study, the 4-point bending test been performed in order to estimate effect of grinding on fatigue characteristics quantitatively for as-welded specimen, grinding specimen & TIG-dressing specimen for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue tests, fatigue strength at $2{\times}106$cycles of grinding specimen and TIG-dressing specimen has been increased compared with as-welded specimen and satisfied the grade of fatigue strength prescribed in specifications of domestics and AASHTO & JSSC. As a result of beachmark test, fatigue cracks on all specimens have occurred at several points where stress

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An Experimental Study on Fatigue Crack Growth Characteristics of Welded High-Strength Steels (용접구조용 고강도강재의 피로균열성장특성에 관한 실험적 연구)

  • Hong, Sung Wook;Kyung, Kab Soo;Nam, Wang Hyun;Jung, Young Hwa
    • Journal of Korean Society of Steel Construction
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    • v.14 no.6
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    • pp.773-782
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    • 2002
  • In this study, a series of fatigue tests are performed in order to estimate quantitatively the characteristics of fatigue crack growth rate according to the base metal, heat affected zone(HAZ) and weld metal, and the welding method and grade of strength of object steels, and the influence on fatigue crack growth rate according to the direction of welded line for high strength steels of SM570, POSTEN60, and POSTEN80 steels. From the fatigue test results, the retardations of fatigue crack growth rate are remarkable in case that the direction of notch is parallel to welded line than in case that the direction of notch is perpendicular to welded line because of compresive residual stress in weld metal & HAZ. And the characteristics of fatigue crack growth rate according to welding method are that the dispersion of fatigue crack growth rate in case of FCAW method is smaller than that of SAW method. Also, it knows that the fatigue crack growth rate converges in high stress intensity factor range. Meanwhile, fatigue safety is guaranteed sufficiently in the object steels because the fatigue crack growth rate in the range of fatigue crack propagation has a similar tendency to the test results & existing results.

Effect of Stress Ration on Fatigue Crack Propagation Behavior of Pressure Vessel Steel SA516-Grade70 at Higt Temperature. (원자로 압력용기용 강의 고온피로특성에 미치는 응력비의 영향)

  • 박경동;정찬기;김정호
    • Journal of Advanced Marine Engineering and Technology
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    • v.25 no.5
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    • pp.1108-1114
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    • 2001
  • The fatigue crack propagation behavior of the SA516-Grade 70 steel which is used for pressure vessels was experimentally examined under the condition of at room temperature, $150^{\circ}C$, $250^{\circ}C$ and $370^{\circ}C$ with stress ration of R=0.1 and 0.3. The fatigue crack propagation rate , da/dN, related with the stress intensity factor range, $\vartriangle$N, was influenced by the stress ration within the stable growth of fatigue crack(Region II) with an increase in $\vartriangle$N. The resistance to the fatigue crack growth at high temperature is higher in comparison with that at room temperature, and the resistance attributed to the extent of plasticity-induced by compressive residual stress according to the cyclic loads. Fractographic examinations revels that the differences of the fatigue crack growth characteristics between room and high temperatures are mainly explained by the crack and oxide-induced by high temperature.

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The Mixed Mode fatigue Crack Propagation Behavior with the Variation of Stress Ratio (응력비 변화에 따른 혼합모드 피로균열 전파거동)

  • Song, Sam-Hong;Choi, Ji-Hoon;Lee, Jeong-Moo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.11
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    • pp.2287-2296
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    • 2002
  • Most cracks in the structure occur under mixed mode loading and those fatigue crack propagation behavior heavily depends on the stress ratio. So, it is necessary to study the fatigue behavior under mixed mode loading as the stress ratio changes. In this paper, the fatigue crack propagation behavior was respectively investigated at stress ratio 0.1, 0.3, 0.5, 0.7 and we changed the loading application angle into 0$^{\circ}$, 30$^{\circ}$, 60$^{\circ}$ to apply various loading mode. The mode I and II stress intensity factor of CTS specimen used in this study was calculated by the displacement extrapolation method using FEM (ABAQUS). Using both the experiment and FEM analysis, we have concluded the relationship between crack propagation rate and stress intensity factor range at each loading mode due to the variation of stress ratio. Also, when the crack propagated under given stress ratio and loading mode condition, we have concluded the dominant factors of the crack propagation rate at each case.

Mixed Mode Fatigue Crack Propagation Behavior due to The Variation of Stress Ratio (응력비의 변화에 따른 혼합 모드 피로 균열 전파 거동)

  • Song, Sam-Hong;Choi, Ji-Hoon;Lee, Jeong-Moo
    • Proceedings of the KSME Conference
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    • 2001.11a
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    • pp.286-291
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    • 2001
  • Most cracks in the structure occur under mixed mode loadings and those propagation depend on the stress ratio very much. So, it is necessary to study the fatigue behavior under mixed mode loading as stress ratio changes. In this paper, fatigue crack propagation behavior was investigated respectively at stress ratio 0.1, 0.3, 0.5, 0.7 and we change loading application angle to $0^{\circ},\;30^{\circ},\;60^{\circ}$ to apply various loading. mode. The mode I and II stress intensity factors of CTS specimen used in this study were calculated by displacement extrapolation method using FEM(ABAQUS). Using both the study through the experiment and the theoretical study through FEM analysis, we studied the relation between crack propagation rate and stress intensity factor range at each loading mode due to the variation of stress ratio. Also, when the crack propagated under given stress condition and given loading mode condition, we studied what the dominant factors of the crack propagation rate were at each case.

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Fatigue Characteristics according to the Shape of Cover Plate in Steel Plate Girders (강판형의 덮개판 형상에 따른 피로특성)

  • Jung, Young Hwa;Hong, Sung Wook;Kim, Ik Gyeom;Jung, Jin Suck
    • Journal of Korean Society of Steel Construction
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    • v.12 no.2 s.45
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    • pp.111-122
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    • 2000
  • In this study, A series of fatigue tests have been performed on the fillet welded joints of cover plates in steel plate girders in order to quantitatively assess the fatigue characteristics according to the shapes of cover plates. From the results of fatigue tests, it has been shown that the fatigue strengths were slightly different according to their shapes, but satisfied the fatigue design curves in Korea and other countries. Also, from the results of beachmark tests, it has been confirmed that the points of fatigue crack initiation were closely related to the shapes of weld bead toes, and fatigue cracks simultaneously initiated from several points in weld bead toes have been grown as semi-elliptical surface cracks, and these cracks have been coalesced each other, and grown as through thickness cracks, and finally reached to fracture. Besides, from the results of fracture mechanics approaches, stress gradient factors were the most dominant factors among crack correction factors obtained from the existing equations and finite element analysis, and the fatigue life on fillet welded joints of cover plates could be estimated using the relations between fatigue crack growth rate and stress intensity factor range obtained from finite element analysis.

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Growth Characteristics and Life Prediction of Single Surface Fatigue Crack with the Variation of crack Configuration Ratios (균열 형상비 변화에 따른 단일표면파로균열의 성장특성과 수명예측)

  • 서창민;서덕영;정정수
    • Journal of Ocean Engineering and Technology
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    • v.7 no.2
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    • pp.173-181
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    • 1993
  • This work has been investigated the ralationship between single surface crack length and crack depth have influence on the fatigue life. The simulation based on experimental results of 2.25 Cr-1Mo steel at various crack configuration ratios has enabled successful prediction of fatigue life at room temperature. The effect of crack depth should be considered for predicting fatigue crack growth rates as well as that of surface crack length. It is also shwn that the crack growth mechanisms are in good agreement with expreimental data according to the interaction of crack length and crack depth.

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A Study on Fracture Mechanism of Torsion-Mounted Type Turbine Blade (비틀림 마운트형 터빈 블레이드의 파괴기구에 관한 연구)

  • Hong, Soon-Hyeok;Lee, Dong-Woo;Jang, Deuk-Yul;Cho, Seoks-Woo;Joo, Won-Sik
    • Proceedings of the KSME Conference
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    • 2001.06a
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    • pp.585-590
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    • 2001
  • Turbine blade is subject to torsional load by torsion-mount, centrifugal load by rotation of rotor and repeated bending load by steam pressure. Turbine with partially cracked blade has normal working condition at initial repair time but vibratory working condition at middle repair time due to crack growth. Finite element analysis on turbine blade indicates that repeated bending load out of all loads is the most important factor on fatigue strength of turbine blade. Therefore, this study shows root mean square roughness has linear relation with stress intensity factor range in 12% Cr steel and can predict loading condition of fractured turbine blade.

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A Study on Failure Analysis of Turbine Blade Using Surface Roughness and FEM (표면거칠기와 유한요소법을 이용한 터빈 블레이드의 파손해석에 관한 연구)

  • 홍순혁;이동우;이선봉;조석수;주원식
    • Transactions of the Korean Society of Automotive Engineers
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    • v.9 no.6
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    • pp.170-177
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    • 2001
  • Turbine blade is subject to torsional load by torsion-mount, centrifugal load by rotation of rotor and repeated bending load by steam pressure. Turbine with partially cracked blade has normal working condition at initial repair time but vibratory working condition at middle repair time due to crack growth. Finite element analysis on turbine blade indicates that repeated bending load out of all loads is the most important factor on fatigue strength of turbine blade. Therefore, this study shows root mean square roughness has linear relation with stress intensity factor range in 12% Cr steel and can predict loading condition of fractured turbine blade.

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A Study on the Fatigue Crack Growth Characteristics for the Weldment of Carbon steel-Stainless steel (탄소강-스테인리스강 용접부의 피로균열진전 특성에 관한 연구)

  • 권재도;김우현;김길수;박중철;배용탁;김중형
    • Journal of Welding and Joining
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    • v.16 no.4
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    • pp.47-54
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    • 1998
  • Various equipments in plants are welded with two different materials and it is required to investigate the effects of fatigue crack propagation on the neighborhood of a welded portion. The characteristics of fatigue crack growth in the base metal of carbon and stainless steel, in the carbon and stainless steel sides located in the neighborhood of welded portion (carbon/stainless steel), respectively and welded portion, are investigated. The results show that the crack growth in the welded portion (carbon/stainless steel) is an average value of the crack growths in the carbon and stainless steel respectively located in the neighborhood of the welded portion. It is found that the crack growth in the welded portion is not significantly different from those in the carbon and stainless steel sides. Hence it can be concluded that the structure welded with two different materials wold not impede the integrity based on the fatigue crack growth.

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