• Title/Summary/Keyword: 유효 응력확대계수

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A Study on Evaluation of Crack Opening Point in Fatigue Crack Propagation Course (II);Parameter Sensitivity Study of Crack Opening Ratio by Using Numerical Calculation (피로크랙 진전과정에서의 크랙열림점 평가에 관한 연구(II))

  • 최병기;윤한용;박창언;정태권
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.3
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    • pp.931-935
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    • 1991
  • 본 연구에서는 유효응력확대계수로서 피로크랙 진전수명을 평가할 수 이용되 는 크랙열림비(본 논문에서는 후술하는 최대응력에 대한 크랙 열림응력의 비를 크랙 열림비로 하다)가 진전수명에 미치는 영향을 평가하기 위한것으로서, 제1보에서는 실 험에 의하여 크랙 열림점을 실측한 결과 측정입치에 따라 다른 값을 나타내며 수명평 가법 크랙 선단으로부터 떨어진 곳(크립게이지를 이용한 크랙마우스등)에서 측정한 크 랙 열림점 값을 이용함이 보다 정확함을 밝혔다.본 제2보에서는 크랙열림비가 수명 평가에 미치는 영향을 상기의 파라미터 영향도 평가수법을 이용하여 평가하고자 한다.

A Study on Fatigue Behavior Considering Effects of Redistributing Tensile Residual Stress and Crack Closure in SS330 Weldment (SS330 용접재에서 재분포 잔류응력 및 균열닫힘영향을 고려한 파로거동에 관한 연구)

  • Lee, Yong-Bok;Jeong, Jin-Seong;Jo, Nam-Ik
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.7
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    • pp.2234-2245
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    • 1996
  • In this study residual stress in weldment was considered about the effect on the fatigue propagation and about the effect of redistribution of residual stress. Then, fatigue tests were conducted by the center notched specimens machined with welded plate. The residual stress and its redistribution after the crack growth were measured by the magnetizing stress indicator and hole-drilling method. Fatigue crack propagation was estimated by the specimens having residual stress redistributed after the cracks growth and having the effects of crack closure. Crack growth rates were predicted and compared with experimental results. It had been found that the predicted crack propagation rates have a good agreement with experimental results when the redistribution of residual stress was considerd.

Numerical Analysis and Experimental Verification of Relaxation and Redistribution of Welding Residual Stresses (용접잔류응력의 이완과 재분포 해석 및 실험적 검증)

  • Song, Ha-Cheol;Jo, Young-Chun;Jang, Chang-Doo
    • Journal of the Society of Naval Architects of Korea
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    • v.41 no.6
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    • pp.84-90
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    • 2004
  • For the precise assessment of the effect of welding residual stresses on structural strength and fatigue crack growth behavior, new FE analysis algorithms for the estimation of residual stress relaxation due to external load and redistribution due to fatigue crack propagation were proposed in this paper. Initial welding residual stress field was obtained by thermal elasto-plastic analysis considering temperature dependent material properties, and the amount of residual stress relaxation and redistribution were assessed by subsequent elasto-plastic analysis In the analysis of fatigue crack propagation, the applied SIF(Stress Intensity Factor) range was evaluated by $\frac{1}{4}$-point displacement extrapolation method, and the effect of welding residual stresses on crack propagation was considered by introducing the effective SIF concept. The test results of crack propagations were compared with the predicted data obtained by the analysis.

Behaviour of Fatigue Crack Propagation under Mixed Mode(I+II) with variation of Angle and Crack Length (혼합모드(I+II)하에서 각도와 균열길이 변화를 갖는 피로균열 전파 거동)

  • 정의효
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.9 no.5
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    • pp.73-79
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    • 2000
  • The applications of fracture mechanics have traditionally concentrated on cracks loaded by tensile stresses, and growing under an opening or mode I mechanism. However, many cases of failures occur from growth of cracks subjected to mixed mode loading. Several criteria have been proposed regarding the crack growth direction under mixed mode loadings. This paper is aimed at investigation of fatigue crack growth behaviour under mixed mode(I+II) with variation of angle and pre-crack length in two dimensional branched type precrack. Especially the direction of fatigue crack propagation was predicted and effective stress intensity factor was calculated by finite element analysis(FEA. In this paper, the maximum tangential stress(MTS) criterion was used to predict crack growth direction. Not only experiment but also finite element analysis was carried out and the theoretical predictions were compared with experimental results.

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A Study on the Microscopic Model for Fatigue Crack Closure Behavior (피로균열 개폐구거동의 미시적 모델에 관한 연구)

  • O, Se-Uk;Gang, Sang-Hun
    • Journal of Ocean Engineering and Technology
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    • v.4 no.1
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    • pp.81-87
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    • 1990
  • Fatigue crack closure levels based on the behavior of residual displacements on crack surfaces, are determined analytically according to the microscopic crack closure mechanisms, i.e., whether the first contact of crack surfaces takes place at the very crack tip or on the surfaces near the tip. The comparative analysis on the two models is carried out empirically by the constant amplitude fatigue tests on 2024-T3 aluminum alloy plate, and it shows that under negative stress ratio, the case of the first contact at crack tip gives better agreement with the experimental results than the other.

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A Study on the Microscopic Model for Fatigue Crack Closure Behavior (피로균열 개폐구거동의 미시적 모델에 관한 연구)

  • O, Se-Uk;Gang, Sang-Hun
    • Journal of Ocean Engineering and Technology
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    • v.4 no.1
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    • pp.87-87
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    • 1990
  • Fatigue crack closure levels based on the behavior of residual displacements on crack surfaces, are determined analytically according to the microscopic crack closure mechanisms, i.e., whether the first contact of crack surfaces takes place at the very crack tip or on the surfaces near the tip. The comparative analysis on the two models is carried out empirically by the constant amplitude fatigue tests on 2024-T3 aluminum alloy plate, and it shows that under negative stress ratio, the case of the first contact at crack tip gives better agreement with the experimental results than the other.

Crack Growth Analysis and Crack Arrest Design of Stiffened Panels(III) - Experimental Evaluation of Crack Arrest Design Chart (보강판의 균열거동해석과 Crack Arrest 설계(III) - Crack Arrest Design 차트의 실험평가)

  • Rhee, Eui-Jong;Rhee, Hwan-Woo
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.5 no.2
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    • pp.42-48
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    • 2006
  • In order to assess the validity of fatigue crack arrest design charts obtained from our previous numerical approach to fatigue crack arrest condition, an extensive fatigue crack growth/arrest test was performed using CT-type integrally stiffened panels. The results are presented as fatigue crack growth rate and non-dimensional crack length relationship, and these are compared with numerically simulated crack growth rates. The measured values of da/dN at the moment of fatigue crack arrest occurred in stiffened panels are good agreement with those numerically simulated crack growth rates.

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A Study on Patch Design Technique for Fatigue Life Prolongation of Cracked Structures (균열진 구조물의 피로수명 연장을 위한 Patch 설계기법에 관한 연구)

  • M.S. Han
    • Journal of the Society of Naval Architects of Korea
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    • v.29 no.2
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    • pp.79-91
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    • 1992
  • This paper develops the compliance approach to the problem of load sharing between a cracked plate and a patch used to bridge the crack. The theory is validated by using calculated stress intensity factors for the patched and unpatched case to reduce experimentally observed growth rates to common base, Calculations are then made on the effect of patch dimension on fatique life technique. The optimum design of the patch considered the life expectancy and fracture strength of the cracked structure can be performed simply by using this technique.

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A Quantitative Analysis of ΔK Conversion Method for the Retardation Behavior of Fatigue Crack Growth in Varying Thickness of Al 2024-T3 Sheet Alloy (판재 Al 2024-T3 합금재료에서 나타나는 두께별 피로균열진전지연거동에 관한 ΔK환산법의 정량적분)

  • Kim, Seung-Gwon;Lee, Ouk-Sub
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.11
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    • pp.1415-1422
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    • 2011
  • Sheet aluminum alloys used in manufacturing of machine structures for transportation show the difference of crack growth speed depending on thickness under the constant fatigue stress condition. The referred thickness effect is a major fatigue failure property of sheet aluminum alloys. In this work, we identified the thickness effect in fatigue test of thick plate and thin plate of Al 2024-T3 alloy under the constant fatigue stress condition, and presented the thickness effect to a correlative equation, $U_{i}^{equ}=f(R_t)$ which is determined by the shape factor, thickness ratio, $R_t$ and the loading factor, equivalent effective stress intensity ratio depending on thickness, $U_{i}^{equ}$. And we analyzed quantitatively the crack growth retardation behavior in thin plate compared to thick plate by the thickness effect using ${\Delta}K$ conversion method. We obtained such values as decrement of thickness(DoT), decrement of stress intensity factor range, ${\Delta}K$ (DoS) and identified the relation between them to present the nature of thickness effect in this work.

Fatigue Crack Propagation and Fatigue Life Evaluation of High-Performance Steel using Modified Forman Model (수정 Forman 모델을 이용한 고성능 강재의 피로균열전파와 피로수명평가)

  • Choi, Sung-Won;Kang, Dong-Hwan;Lee, Jong-Kwan;Kim, Tae-Won
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.11
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    • pp.1361-1368
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    • 2011
  • Fatigue crack propagation behavior and the fatigue life in-high performance steel were investigated by means of fatigue crack propagation tests under constant loading conditions of 'R=0.1 and f=0.1 Hz', 'R=0.3 and f=0.3 Hz', and 'R=0.5 and f=0.5 Hz' for the load ratio and frequency, respectively. A modified Forman model was developed to describe the fatigue crack propagation behavior for the conditions. The modified Forman model is applicable to all fatigue crack propagation regions I, II, and III by implementing the threshold stress intensity factor range and the effective stress intensity factor range caused by crack closure. The results show that predicted fatigue lives of Forman and modified Forman models were 8,814 and 12,292 cycles, respectively when the crack propagated approximately 5.0 mm and the load ratio and frequency were both 0.1. Comparison of the test results indicates that the modified Forman model showed much more effective fatigue crack propagation behavior in high-performance steel.