• Title, Summary, Keyword: Surface Crack

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Variation of Surface Crack Shape in Pressure Vessel Materials (압력용기 소재에서의 표면균열의 형상변화)

  • 허용학;이주진;이해무
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.3
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    • pp.617-623
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    • 1990
  • Cracks present in pressure vessels have been reported to be mostly semi-elliptic surface cracks. The fatigue crack growth rates(FCGR) of surface cracks in the pressure vessel materials, API5A-K55 and SPV 500, used in this study were showed to be different depending on the direction of propagation of the surface crack. An equation for the prediction of the shape change of the surface crack was obtained by combining the Paris' relations for each direction of surface crack extension and agreed well with the experimental data. And also FGGR in both materials were evaluated and prediction of the shape change of surface crack were made using averaged stress intensity factor.

Stress Intensity Factors and Possible Crack Propagation Mechanisms for a Crack Surface in a Polyethylene Tibia Component Subject to Rolling and Sliding Contact (구름마찰 접촉하중시 Polyethylene Tibia 표면균열의 응력확대계 수와 복합전파거동에 관한 연구)

  • Kim, Byung-Soo;Moon, Byung-Young
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.12
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    • pp.2019-2027
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    • 2003
  • Pitting wear is a dominant from of polyethylene surface damage in total knee replacements, and may originate from surface cracks that propagate under repeated tribological contact. In this study, stress intensity factors, K$\_$I/and $_{4}$, were calculated for a surface crack in a polyethylene-CoCr-bone system under the rolling and/or sliding contact pressures. Crack length and load location were considered in determination of probable crack propagation mechanisms and fracture modes. Positive K$\_$I/ values were obtained for shorter cracks in rolling contact and for all crack lengths when the sliding load was apart from the crack. $_{4}$ was the greatest when the load was directly adjacent to the crack (g/a=${\pm}$1). Sliding friction caused a substantial increase of both K$\_$I/$\^$max/ and $_{4}$$\^$max/. The effective Mode I stress intensity factors, K$\_$eff/, were the greatest at g/a=${\pm}$1, showing the significance of high shear stresses generated by loads adjacent to surface cracks. Such behavior of K$\_$eff/ suggests mechanisms for surface pitting by which surface cracks may propagate along their original plane under repeated rolling or sliding contact.

Determination of Stress Intensity Factors for Embedded Elliptical Crack in Turbine Rotor (터빈축차내에 내재된 타원균열의 응력세기계수 결정)

  • 이강용;김종성;하정수
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.5
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    • pp.1229-1242
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    • 1995
  • The thermal shock stress intensity factors of semi-elliptical surface crack in finite plate and the stress intensity fractors of embedded elliptical crack in turbine rotor is determined by means of Vainshtok weight function method. In case of semi-elliptical surface crack, the solution is compared with previous solution. The stress intensity factor for embedded elliptical crack in turbine rotor loaded by centrifugal and thermal loading is also determined. In this case, the value of stress intensity factor is larger at crack contour near internal radius surface and is almost constant at the crack contour farther from internal radius surface.

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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Acoustic emission during fatigue crack penetration behavior of surface cracked plate (표면균열재의 피로균열 관통거동에 따른 어코스틱에미션)

  • 남기우;김선진;오세규;이건찬;오정환;이주석
    • Journal of Ocean Engineering and Technology
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    • v.11 no.3
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    • pp.29-38
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    • 1997
  • Crack penetration behavior by fatigue crack propagation and measurements of AE before-and-after crack penetration were examined using SS41 steel plate. Experimental crack shape of SU type was in good agreement with calculated shape rather than S type. Crack propagation behavior on the front surface appears not to change markedly after penetration. However, crack growth on the back surface appears to accelerate as reported by author. As a crack propagates, AE occurred heavily just before penetration. Then, it decreases and crack is penetrating. A transition from plane strain to plane stress was observed by fractographic study. At this time, separation of fracture surface was shown which affects AE occurrence.

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A Study on the Design of Fatigue Strength using Fractal Character of Surface Micro-crack (표면미소균열의 프랙탈 특성을 이용한 피로강도설계에 관한 연구)

  • Cho, Seok-Swoo;Joo, Won-Sik
    • Journal of the Korean Society for Precision Engineering
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    • v.16 no.12
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    • pp.143-151
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    • 1999
  • The shape of surface micro-crack is very irregular due to nonhomogeneous microstructure but is very important in respect to qualitative estimation of fatigue life. Fractal geomety can quantify the shape of surface mciro-crack. Fractal dimension is measured for surface micro-cracks with coast line and box counting method and estimates cycle ration in Al 2024-T3. The average fractal dimension $D_{favg}$ of surface micro-cracks has 3-parameter weibull distribution and location parameter is nearly constant but shape parameter decreases as cycle ration increases. The fractal dimension by coast line method is measured for individual surface micro-crack but the fractal dimension by box countin method is measured for all the surface micro-cracks under sampling area. Therefore, This paper shows fractal dimension $D_{fb}$ can predict cycle ratio $N/N_f$ more convenient than fractal dimension $D_{favg}$.

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A Study on Fractal Character of Surface Micro-crack under In-plane Bending (평면굽힘하중을 받는 표면미소균열의 프랙탈 특성에 관한 연구)

  • 박승용;주원식;장득열;조석수
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.521-527
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    • 1997
  • Irregular shapes and growth behavior of surface micro-crack showed very complex and nonlinear propeties and many investigators have performed theoretical analysesand experiments on them to characterize fatigue strength. They had difficulties in estimating fatigue life due to random distribution, growth and coalescence of surface micro-cracks. The straightness of crack growth along intergranular and transgranular was prevented from irregular microstructure and precipitates. Euclid geometry can't quantify shape of surface micro-crack but ftractal geometry can. Therefore, it is suggested that average fractal dimension of surface micro-cracks is able to estimate fatigue life but fractal dimension of maximum surface micro-crack is not in Al 2024-T3 alloy.

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Prediction of the crack aspect change in twin surface cracks (2개의 대칭표면구열의 구열형상변화 예측)

  • 최용식;김재원
    • Journal of the korean Society of Automotive Engineers
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    • v.14 no.2
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    • pp.65-75
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    • 1992
  • An analytical scheme for predicting the crack aspect pattern of materials which contain twin surface cracks was developed. Fatigue tests were performed on twin surface cracked PMMA plate specimens to obtain the interaction factor accounting for the interference effect of adjacent cracks. Here, the interaction factor is defined as the ratio of the stress intensity factor for twin surface cracks to that for a single surface crack. From the analysis of the fatigue test result, the interaction factor was presented as the ninth-order polynomial expression having a function of dimensionless crack spacing ratio. Then the polynomial expression was incorporated into the prediction program of the crack aspect pattern for twin surface cracked materials. And, the interaction effect and the coalescence condition of adjacent cracks were simplified in the newly developed prediction scheme of the crack aspect pattern. The predicted crack growth pattern using the prediction scheme was compared with test data from PMMA specimen. The predicted pattern agreed well with the test data.

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Study for Possible Crack Propagation Mechanisms for a Surface Cracked in a Polyethylene Tibia Component Subject to Rolling and Sliding Contact (구름마찰접촉하중 시 Polyethylene tibia 요소의 표면균열 복합전파 거동에 관한 연구)

  • Kim, B.S.;Moon, B.Y.
    • Proceedings of the KSME Conference
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    • pp.1222-1227
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    • 2003
  • Pitting wear is a dominant form of polyethylene surface damage in total knee replacements, and may originate from surface cracks that propagate under repeated tribological contact. In this study, stress intensity factors, $K_{I}$ and $K_{II}$, were calculated for a surface crack in a polyethylene - CoCr - bone system under the rolling and/or sliding contact pressures. Crack length and load location were considered in determination of probable crack propagation mechanisms and fracture modes. Positive $K_{I}$ values were obtained for shorter cracks in rolling contact and for all crack lengths when the sliding load was apart from the crack. $K_{II}$, was the greatest when the load was directly adjacent to the crack $(g/a={\pm}1)$. Sliding friction caused a substantial increase of both $K_{I}^{max}$ and $K_{II}^{max}$. The effective Mode I stress intensity factors, $K_{eff}$, were the greatest at $g/a={\pm}1$, showing the significance of high shear stresses generated by loads adjacent to surface cracks. Such behavior of $K_{eff}$ suggests mechanisms for surface pitting by which surface cracks may propagate along their original plane under repeated rolling or sliding contact.

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A Study on Parameters Affected the Fatigue Crack Growth in Steel Structure Members( II ) -The Effect of Surface Residual Stress for Crack Closure- (강구조 부재의 피로균열성장에 미치는 제인자에 관한 연구( II ) -표면잔류응력이 균열닫힘에 미치는 영향-)

  • Choi, Young Jae;Kyung, Kab Soo
    • Journal of Korean Society of Steel Construction
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    • v.8 no.3
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    • pp.3-11
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    • 1996
  • To investigate the effect of fatigue crack growth due to the surface residual stress, it is measured the residual stress distribution by x-ray diffraction at the crack tip each constant crack growth in the notch specimens, and quantitively assessed the effect of crack closure caused to the distribution of compressive stress at the crack tip from evaluating crack openning stress using the finite element analysis. It is concluded that the degree of the residual stress distribution at the crack tip is decreased with increasing the crack length. From the fact that it is similar to the crack openning stress ratio, it is found that the compressive residual stress distribution and size is related to the crack closure effect and surface residual stress field with propagating crack in the notch specimens depends on the stress intensity factor range at the crack tip.

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