• Title, Summary, Keyword: Fatigue crack length

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Influences of Fiber Laminate Orientation on the Behavior of Fatigue Delamination in GLARE (GLARE 의 섬유층 배향이 피로층간분리 거동에 미치는 영향)

  • 황진우;송삼홍;김철웅
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.479-482
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    • 2004
  • The behavior of fatigue delamination in a GLARE(Glass Fiber Reinforced Metal Laminates) under fatigue loading conditions investigated. The behavior of fatigue delamination was examined basing on investigation of the crack and delamination using a SAM (Scanning Acoustic Microscope). The crack and delamination behavior on the relationship among a-N, SAM images and crack length-delamination length were considered. The test results indicated the features of different fatigue delamination and crack growth according to each fiber orientation angle and also obtained to more increase delamination than crack through the relationship between crack length and delamination length in GLARE.

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Quantitative Study on Threshold Condition of Critical Non-propagating Crack (임계정류피로크랙의 하한계 전파조건의 정량적 고찰)

  • Kim, Min-Gun
    • Journal of Industrial Technology
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    • v.30 no.B
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    • pp.17-23
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    • 2010
  • Since the propagation of a short fatigue crack is directly related to the large crack which causes the fracture of bulk specimen, the detailed study on the propagation of the short crack is essential to prevent the fatigue fracture. However, a number of recent studies have demonstrated that the short crack can grow at a low applied stress level which are predicted from the threshold condition of large crack. In present study, the threshold condition for the propagation of short fatigue crack is examined with respect to the micro-structure and cyclic loading history. Specimens employed in this study were decarburized eutectoid steels which have various decarburized ferrite volume fraction. Rotating bending fatigue test was carried out on these specimens with the special emphasis on the "critical non-propagating crack length" It is found that the reduction of the endurance limit of their particular micro-structures can be due to the increase of the length of critical non-propagating crack, and the quantitative relationship between the threshold stress ${\sigma}_{wo}$ and the critical non-propagating crack length $L_c$ can be written as ${\sigma}_{wo}{^m}{\cdot}L_c=C$ where m,C is constant. Further experiments were carried out on cyclic loading history on the length of critical non-propagating crack. It shown that the length of critical non-propagating crack is closely related to cyclic loading history.

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The Fatigue Behavior by Variety of Crack Length of Surface Cracked Plate with Stress Concentration Part (응력집중부를 갖는 표면균열재의 균열길이 변화에 따른 피로거동)

  • 남기우;김선진
    • Journal of Ocean Engineering and Technology
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    • v.9 no.1
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    • pp.83-91
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    • 1995
  • Surface defects in structural members are apt to be origins of fatigue cracks growth, which may cause serious failure of whole structures. Most structure has a part where stress concentrates such as welded joints, corner parts, etc. And then, analysis on crack growth and penetration from these defects, therefore, is one of the most important subjects for the reliability of LBB design. The present paper has performed an experimental and analysis on the fatigue crack propagation by variety in crack length of surface cracked plate with stress concentration part. The crack growth behavior can be explained quantitatively by using Newman-Raju equation and the stress partitioning method proposed by ASME B&P Code Sec. XI. The stress concentration factor $K_t$ has affected on the crack growth. The crack growth after penetration depends upon the initial front side crack length.

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A Study on the Fatigue Behavior of Resistance Spot Welded Part of 5182 Aluminum Aloy Sheet (5182 Al합금판의 전기저항 점용접부 피로거동에 관한 연구)

  • 신현일;박용석;강성수
    • Journal of Welding and Joining
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    • v.16 no.2
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    • pp.84-92
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    • 1998
  • On this study, the variations of hardness and microstructure were observed at he spot-welded part of 5182 alminum alloy sheets with thickness of 1.2 mm. The hardness of spot-welded part of aluminum alloy indicated the lowest value at nugget center. Also, the position where fatigue crack exists was investigated by surveying microstructure of the spot-welded sections. Mean load-deformation diagrams were obtained from static tensile test. Fracture was occurred completely within 5 mm after transforming elastic into plastic area. Fatigue test was stopped when the specimens of fatigue test had the final displacement of 0.2mm and measured fatigue bending angle and crack length. This study utilized them, investigated the relations between fatigue bending angle and fatigue crack length and made a estimation of the fatigue fracture life of resistance spot welded part of 5182 aluminum alloy sheet. The relative equation o fatigue crack length and fatigue failure life can be represented by {TEX}$L_{C}${/TEX}=α{TEX}$N_{f}^ {β}${/TEX}.

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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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Threshold Condition for the Propagation of Short Fatigue Crack (炭素鋼 微小疲勞크랙 전파의 不限界條件)

  • 김민건
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.3
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    • pp.505-512
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    • 1988
  • Since the propagation of a short fatigue crack is directly related to the large crack which causes the fracture of bulk specimen, the detailed study on the propagation of the short crack is essential to prevent the fatigue fracture. However, a number of recent studies have demonstrated that the short crack can grow at a low applied stress level which are predicted from the threshold condition of large crack. In present study, the threshold condition for the propagation of short fatigue crack is examined with respect to the microstructure and cyclic loading history. Specimens employed in this study were decarburized eutectoid steels which have various decarburized ferrite volume fraction. Rotating bending fatigue test was carried out on these specimens with the special emphasis on the '||'&'||'quot;critical non-propagating crack length.'||'&'||'quot; It is found that the reduction of the endurance limit of their particular microstructures can be due to the increase of the length of critical non-propagating crack, and the quantitative relationship between the threshold stress .DELTA. .sigma. $_{th}$ and the critical non-propagating crack length Lc can be written as .DELTA. .sigma. $_{th}$, Lc=C where m, C is constant. Further experiments were carried out on the effect of pearlitic structure and cyclic loading history on the length of critical non-propagating crack. It is shown that the length of critical non-propagating crack is closely related to both pearlite interlamellar spacing and cyclic loading history.ory. cyclic loading history.

Fatigue Crack Growth Analysis of Steel Deckplates Under Bending Stress (휨응력을 받는 바닥강판의 피로균열진전해석)

  • Choi, Jun Hyeok;Kyung, Kab Soo;Choi, Dong Ho;Chang, Dong Il
    • Journal of Korean Society of Steel Construction
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    • v.11 no.4
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    • pp.409-416
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    • 1999
  • The fatigue crack growth analysis based on the fracture mechanics is useful to the estimation of the fatigue life on welded structures under cyclic loading. The analysis procedure in fatigue crack growth under uniform axial loading is applicable to bending fatigue problem as well. The intent of the present study is to show the procedure for calculating the fatigue crack propagation lifetimes of deckplates under bending stress and to explain the crack growth rates for the two dimensional crack problems. It is shown that the fatigue crack grows at a decreasing rate and the fatigue life depends on the initial crack length and the crack shape. The numerically predicted crack growth agree with the experimental data.

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Fatigue Crack Initiation and Propagation at Notches (노치 에서의 피로 균열 발생 과 전파 에 관한 연구)

  • 이강용;이택성
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.8 no.2
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    • pp.141-144
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    • 1984
  • The fatigue limits of crack initiation and propagation on the edge elliptical notched semi-infinite plate under completely reversed fatigue stress are determined theoretically. Assuming that the crack initiation and propagation occur when stress intensity factors of notched plate reach the critical values obtained from critical micro-crack length under plain fatigue limit loading and the threshold stress intensity factory, respectively, the fatigue limits of crack initiation and propagation are obtained. The induced theoretical fatigue limit of crack initiation is expressed in terms of plain fatigue limit, critical micro-crack length and notch shape. The one of crack propagation is in terms of threshold stress intensity factor, plain fatigue limit and notch shape. These theoretical results are showed to be in good agreement of Frost's experimental data.

A Basic Study on Growth Characteristics of the Small Surface Crack in 21/4 Cr-1 Mo Steel (2 1/4 Cr-1Mo강의 작은 표면균열의 성장에 관한 기초적 연구)

  • 서창민;강용구
    • Journal of Ocean Engineering and Technology
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    • v.1 no.1
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    • pp.104-110
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    • 1987
  • Fatigue tests by axial loading (R = 0.05) were carried out to investigate fatigue crack growth characteristics of small surface cracks in 2 1/4 Cr-1 Mo steel at room temperature by using flat specimens with a small artificial pit. All the data of the fatigue crack growth rate obtained in the present test are determined as a function of the stress intensity factor range about a semi-elliptical crack, so that the application of linear fracture mechanics to the surface fatigue crack growth and to the fatigue crack growth into depth, and all the data obtained from tests were discussed in comparison with the data of Type 304 stainless steel and two type of mild steel under the same test conditions. The obtained results are as follows: 1)When the cycle ratios are same, surface fatigue crack length and its depth are almost same and fall within a narrow scatter band in spite of different stress levels. 2)Relations of the surface fatigue crack growth rate (da/dN) and fatigue crack growth rate into depth (db/dN) to its stress intensity factor range ($\Delta K_{Ia}, \Delta K_{Ib}$) can be plotted as a straight line at log-log diagram without dependence of stress level and coincide with the data of part-through crack in various steels.

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Analysis of Fatigue Life and Fracture Toughness Using Probabilistic Finite Element Method (확률 유한요소해석법을 이용한 피로수명 및 강도해석)

  • 이현우;오세종
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.6
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    • pp.1448-1454
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    • 1994
  • Data which gathered and used in the field of fatigue and fracture mechanics have a lot of uncertainties. In this case, those uncertainties will make scatter band in evaluation of fatigue life and fracture toughness. Thus, the probabilistic analysis of these data will be needed. For determining the fatigue life in mixed mode, using crack direction law and fatigue crack growth law, the problem is studied as a constrained life minimization. Stress intensity factor(SIF) is computed by approximate solution table(Ewalds/Wanhill 1984) and 0th order PFEM. The variance of fatigue life and SIF are computed by differentiation of tabulated approximate solution and 1st order PFEM. And these are used for criterion of design values, principal parameter determination and modelling. The problem of center cracked plate is solved for checking the PFEM model which is influenced by various parameters like as initial crack length, final crack length, two fatigue parameters in Paris Equation and applied stress.