• Title, Summary, Keyword: Surface Crack

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Assessment for Propagation Behavior and Fracture Surface of Mixed-mode Fatigue Crack by Fracture Surface-Roughness Induced Crack Closure (파면거칠기 유도 균열닫힘에 의한 혼합모드 피로균열의 전파거동 및 파면에 대한 평가)

  • Seo, Ki-Jeong;Lee, Jeong-Moo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.4
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    • pp.432-440
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    • 2007
  • In this study, we have investigated the closure behavior of fatigue cracks in SAPH440 steel plates under a mixed-mode I+II loading. A crack image capturing system as a direct measuring method was used to measure the closure levels at a crack tip. The crack closure levels in the fluctuation and stable sections were increased with the increase of the mode mixture ratio. The mode mixture ratio independent fatigue crack propagation rates equation was calculated by considering mixed-mode crack closure levels. The equation was examined according to the application method of crack opening ratio. The fracture surface analysis by C-scan method was also performed in order to investigate the closure mechanism and propagation mode of crack under the mixed-mode I+II loading. The crack closure under the mixed mode I+II is confirmed as a surface roughness closure by the quantitative analysis of fracture surface using the proposed surface roughness parameter.

An analysis of an elastic solid incorporating a crack under the influences of surface effects in plane & anti-plane deformations

  • Kim, Chun Il
    • Interaction and multiscale mechanics
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    • v.4 no.2
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    • pp.123-137
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    • 2011
  • We review a series of crack problems arising in the general deformations of a linearly elastic solid (Mode-I, Mode-II and Mode-III crack) and, perhaps more significantly, when the contribution of surface effects are taken into account. The surface mechanics are incorporated using the continuum based surface/interface model of Gurtin and Murdoch. We show that the deformations of an elastic solid containing a single crack can be decoupled into in-plane (Mode-I and Mode-II crack) and anti-plane (Mode-III crack) parts, even when the surface mechanics is introduced. In particular, it is shown that, in contrast to classical fracture mechanics (where surface effects are neglected), the incorporation of surface elasticity leads to the more accurate description of a finite stress at the crack tip. In addition, the corresponding stress fields exhibit strong dependency on the size of crack.

The Correlation between Fatigue Fracture Crack Surface Friction and Crack Closure Effect in Crack Growth under Mixed-mode loading (혼합모드 하중 하에서의 균열성장 중 피로파단면 마찰과 균열닫힘효과의 상호관계)

  • Seo, Ki-Jeong;Song, Sam-Hong;Lee, Jeong-Moo
    • Proceedings of the KSME Conference
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    • pp.214-219
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    • 2004
  • Crack tip behavior of single mode loading condition(mode I)depend on tensile loading component but one of mixed mode loading condition(mode I+II) have influenced on shear loading component like the practical structure. Because crack closure is caused by shear loading component under mixed-mode loading a research on the behavior in the stage of crack initiation and propagation require to be evaluate about crack closure effect by fatigue crack surface friction. For that reasion we examined the behavior at the crack tip by direct measuring method. Measured behavior at the crack tip was analyzed through vector crack tip displacement. As a result, crack propafation equation was corrected by considering with crack closure effect. In addition we compared fatigue fracture crack surface and crack closure level.

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A Study on Fatigue Crack Growth Characterization Of Surface Crack In Pressure Vessel Materials (압력용기 소재에서의 표면균열의 피로균열 성장특성에 관한 연구)

  • 허용학;이주진;한지원;김종집;문한규
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.1
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    • pp.96-102
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    • 1990
  • Cracks found in pressure vessels have been reported to be mostly semi-elliptic surface cracks. The fatigue crack growth behaviour of the surface cracks on pressure vessel materials, SPV 50Q and API 5A-K55, was studied with the consideration of the crack opening character. To determine the crack opening loads for the surface cracks, the displacement/strain were measured at three positions; the center and the side of the surface crack, the back face of the specimen using CMOD gauge and strain gauges. The experimental results showed that the crack opening load levels measured at the side of the surface crack were generally a little higher than those measured at the back face. As for the crack growth rates at the different parts of the surface crack, the experiments also showed that, if .DELTA.K$_{eff}$ is used, the exponent n of the Paris' law obtained were the same for the rear and the side parts of the surface cracks.

Prediction of Growth Behavior of Initially Semicircular Surface Cracks under Axial Loading (축하중을 받는 초기 반원 표면피로균열의 진전거동 예측)

  • 김종한;송지호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.8
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    • pp.1536-1544
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    • 1992
  • A relatively simple prediction method is proposed for initially semicircular surface crack growth under axial loading. The method takes into account the difference in surface crack closure behavior at the depth point and at the surface intersection point, and also the relationship of crack closure for surface crack and through-thickness crack. The prediction method provides conservative estimation for fatigue life within factor of two, and the predicted crack geometry variations agree well with the observed results. As a result, the prediction method proposed here is considered to be useful for engineering application.

Relationship between Pattern of Fatigue Crack Surface and Fatigue Crack Growth Behavior under $K_{III}$ Mode-Four Point Shear in Al 5083-O

  • Kim Gun-Ho;Won Young-Jun;Sakakur Keigo;Fujimot Takehiro;Nishioka Toshihisa
    • Journal of the Korean Society of Marine Engineering
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    • v.30 no.4
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    • pp.474-482
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    • 2006
  • Generally almost all fatigue crack growth is affected by mode I. For this reason a study on mode I has concentrated in the field of fracture mechanics. However the fatigue crack initiation and growth in machines and structures usually occur in mixed mode loading. If there is any relationship between the cause of fracture in mixed mode loading and fracture surface, fracture surface pattern will be the main mean explaining reasons of fatigue fracture and obtaining further information about fracture process. In this paper low point shear-fatigue test with Aluminum alloy hi 5083-O is carried out from this prospect and then the mixed mode distribution of fracture surface is examined from the result after identifying the generation of fatigue crack surface pattern. It was found from the experimental results that the fatigue crack surface pattern and the fatigue crack shear direction are remarkably consistent. Furthermore It is possible that the analysis of distribution of mixed mode through the fatigue crack surface pattern.

Relationship between Pattern of Fatigue Crack Surface and Fatigue Crack Growth Behavior under $K_{III}$ Mode-Four Point Shear in Al 5083-O (Al 5083-O재에 있어서 $K_{III}$ 모드 4점 전단 하에서의 피로파단면 무늬와 피로균열진전거동의 관계)

  • Kim, Gun-Ho;Won, Young-Jun;Sakakura, Keigo;Fujimoto, Takehiro;Nishioka, Toshihisa
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • pp.43-44
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    • 2006
  • Generally almost all fatigue crack growth is affected by model. For this reason a study on model has concentrated in the field of fracture mechanics. However the fatigue crack initiation and growth in machines and structures usually occur in mixed mode loading. If there is any relationship between the cause of fracture in mixed mode loading and fracture surface, fracture surface pattern will be the main mean explaining reasons of fatigue fracture and obtaining further information about fracture process. In this paper four point shear-fatigue test with Aluminum alloy Al 5083-O is carried out from this prospect and then the mixed mode distribution of fracture surface is examined from the result after identifying the generation of fatigue crack surface pattern. It was found from the experimental results that the fatigue crack surface pattern and the fatigue crack shear direction are remarkably consistent. Furthermore It is possible that the analysis of distribution of mixed mode through the fatigue crack surface pattern.

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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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ON CRACK INTERACTION EFFECTS OF IN-PLANE SURFACE CRACKS USING ELASTIC AND ELASTIC-PLASTIC FINITE ELEMENT ANALYSES

  • Kim, Jong-Min;Huh, Nam-Su
    • Nuclear Engineering and Technology
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    • v.42 no.6
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    • pp.680-689
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    • 2010
  • The crack-tip stress fields and fracture mechanics assessment parameters for a surface crack, such as the elastic stress intensity factor or the elastic-plastic J-integral, can be affected significantly by the adjacent cracks. Such a crack interaction effect due to multiple cracks can alter the fracture mechanics assessment parameters significantly. There are many factors to be considered, for instance the relative distance between adjacent cracks, the crack shape, and the loading condition, to quantify the crack interaction effect on the fracture mechanics assessment parameters. Thus, the current assessment codes on crack interaction effects (crack combination rules), including ASME Sec. XI, BS7910, British Energy R6 and API 579-1/ASME FFS-1, provide different rules for combining multiple surface cracks into a single surface crack. The present paper investigates crack interaction effects by evaluating the elastic stress intensity factor and the elastic-plastic J-integral of adjacent in-plane surface cracks in a plate through detailed 3-dimensional elastic and elastic-plastic finite element analyses. The effects on the fracture mechanics assessment parameters of the geometric parameters, the relative distance between two cracks, and the crack shape are investigated systematically. As for the loading condition, an axial tension is considered. Based on the finite element results, the acceptability of the crack combination rules provided in the existing guidance was investigated, and the relevant recommendations on a crack interaction for in-plane surface cracks are discussed. The present results can be used to develop more concrete guidance on crack interaction effects for crack shape characterization to evaluate the integrity of defective components.

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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