• Title/Summary/Keyword: Surface Crack

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Study on the Near-Surface Fatigue Crack Initiation Life under Spherical Contact (구 접촉시 표면근처의 피로균열 시작수명에 관한 연구)

  • 설광조;김태완;조용주
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 2001.11a
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    • pp.172-178
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    • 2001
  • Using dislocation pileup theory, the near surface crack initiation life was calculated. The crack initiation life calculted in the previous study is not a real life strictly and just for the cracking in substrate. In this study, two life equations which can be applied for each near-surface and substrate were used for a comparative study. The downward tendency of life at near surface and substrate was similar and the crack initiation life at near-surface was much shorter than the life in substrate. The improvement of the crack initiation life equations which were proposed by W. Cheng was discussed.

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Fracture Behavior of Ceramic Coatings Subjected to Thermal Shock (열충격에 의한 세라믹코팅재의 파괴거동)

  • Han, Ji-Won
    • Journal of the Korean Society of Safety
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    • v.18 no.4
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    • pp.39-43
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    • 2003
  • An experimental study was conducted to develop and understanding of fracture behavior of ceramic thermal barrier coating when subjected to a thermal shock loading. The thermal loading was applied using a 1.5kW $CO_2$ laser. In the experiments, beam-shaped specimens were subjected to a high heat flux for 4sec and cooling of 7sec in air. The interface crack length was increased as the crack density, the surface pre-crack legth and the coating thickness were increased. The center surface crack length was increased as the maximum surface temperature got higher and the surface pre-crack length for shorter.

Finite Element Simulation of Surface Pitting due to Contact Fatigue (접촉피로에 의한 표면피팅의 유한요소 시뮬레이션)

  • Rhee, Hwan-Woo;Kim, Sung-Hun
    • Journal of the Korean Society for Precision Engineering
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    • v.27 no.3
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    • pp.80-88
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    • 2010
  • A simple computational model for modeling of subsurface crack growth under cyclic contact loading is presented. In this model, it is assumed that the initial fatigue crack will initiate in the region of the maximum equivalent stress at certain depth under the contacting surface. The position and magnitude of the maximum equivalent stress are determined by using the equivalent contact model, which is based on the Hertzian contact conditions with frictional forces. The virtual crack extension method is used for simulation of the fatigue crack growth from the initial crack up to the formation of the surface pit due to contact fatigue. The relationships between the stress intensity factor and crack length are then determined for various combinations of equivalent contact radii and loadings.

Development of the Advanced NDI Technique Using an Alternating Current : the Evaluation of surface crack and blind surface crack and the detection of defects in a field component (교류전류를 이용한 새로운 비파괴탐상법의 개발;표면결함과 이면결함의 평가 및 실기 부재의 결함 검출)

  • Kim. H.;Lim, J.K.
    • Journal of Welding and Joining
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    • v.13 no.2
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    • pp.42-52
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    • 1995
  • In the evaluation of aging degradation on the structural materials based on the fracture mechanics, the detection and size prediction of defect are very important. Aiming at nondestructive detection and size prediction ol defect with high accuracy and resolution, therefore, an lnduced Current Focusing Potential Drop(ICFPD) technique has been developed. The principle of this technique is to induce a focusing current at an exploratory region by an induction wire flowing an alternating current(AC) that is a constant ampere and frequency. Defects are assessed with the potential drops that are measured the induced current on the surface of metallic material by the potential pick-up pins. In this study, the lCFPD technique was applied for evaluating the location and size of the surface crack and blind crack made in plate specimens, and also for detecting the defects existing in valve, a field component, that were developed by SCC etc. during the service. The results of this present study show that surface crack and blind crack are able to defect with potential drop. these cracks are distinguished with the distribution of potential drop, and the crack depths can be estimated with each normalized potential drop that are parameters estimating the depth of each type crack. In the field component, the defects estimated by experiment result correspond with those in the cutting face of the measuring point within a higher sensitivity.

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Fatigue Crack shape Variations by a Residual Stress and Fatigue Life Predition (잔류응력에 의한 피로균열면 형상변화 및 수명예측)

  • 강용구;서창민;박원종
    • Journal of Ocean Engineering and Technology
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    • v.7 no.2
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    • pp.68-78
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    • 1993
  • Fatigue crack shape variation by a residual stress during crack growth and life predition are studied. An analytical method is presented to predict the influence of a residual stress due to heattreatment on crack shape variations. Computer simulation results using this me thod are graphically shown that crack growth rate to surface direction are decreased due to compressive residual stress exisiting in surface area. These results are commpared with experimental results. The fatigue life is also predicted by computer simulation of crack aspect ratio variation which is based on the surface crack length increment per unit cycle calculated from a-N diagram. Predited life is about 12 percent lower than experimental life.

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Prevention of Exit Crack in Mirco-drilling of Soda-lime Glass (유리의 미세구멍 가공시 출구 크랙 발생 방지)

  • 박병진;최영준;주종남
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2001.04a
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    • pp.1052-1055
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    • 2001
  • In micro-drilling of brittle materials including glass, cracks occur at the exit surface. In drilling glass, the main type of crack is cone crack. Cone crack is generated by thrust force acting at the bottom surface of the workpiece. Cone crack size could be reduced by changing cutting conditions, but cone crack still existed. Two methods were proposed to prevent crack formation and perfect hole shapes were obtained. One method is attaching two glass plates with water and the other method is constraining two glass plates. The proposed methods eliminated tensile stress acting on the exit surface of glass and prevented crack propagation.

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Study on the Fatigue Crack Initiation Life under 3-Dimensional Rough Contact (3차원 거친 접촉하에서의 피로균열 시작수명에 관한 연구)

  • 이문주;구영필;조용주
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 2000.11a
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    • pp.72-79
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    • 2000
  • In case of rough contact fatigue, the accurate calculation of surface tractions is essential to the prediction of crack initiation life. Accurate Surface tractions influencing shear stress amplitude can be obtained by contact analysis based on tile morphology of contact surfaces. In this study, to simulate rough contact under sliding condition, gaussian rough surface generated numerically in the previous study was used and to calculate crack initiation life in the substrate, dislocation pileup theory was used.

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The analysis of fracture stress using reflection coefficient of surface acoustic wave (탄성표면파의 반사계수를 이용한 파괴응력의 해석)

  • Shin, J.S.;Kim, J.K.;Jun, K.S.
    • The Journal of the Acoustical Society of Korea
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    • v.10 no.3
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    • pp.13-18
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    • 1991
  • In this study, the analysis technique of fracture stress using the reflection coefficient of SAW reflected from a brittle solid with surface crack has been studied. Fracture stress of brittle solid with surface crack has been obtained by the function of the critical stress intensity factor and the maximum normalized stress intensity factor of the crack in the body. And the maximum normalized stress intensity factor of a surface crack can be inferred from a measurement of reflection coefficient of SAW. In experiment, the surface cracks ranging from 0.5mm to 0.9mm in crack depth has been made at the center of each Pyrex disc, and the SAW wedge transducer has been set up for the pitch-catch mode. It has been compared the theoretical values of the fracture stress calculated from the reflection coefficient of SAW with the values of the fracture stress measured from UTM.

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Propagation Characteristics of a Surface Crack on a Semi-Infinite Body Due to Frictional Heating (마찰열에 의한 반무한체 표면균열의 전파특성)

  • Park, Jun-Ho;Park, Eun-Ho;Kim, Chae-Ho;Kim, Seock-Sam
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.10
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    • pp.3126-3134
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    • 1996
  • In this paper, to examine the propagation of inclined surface crack due to frictional heating, analytic model is considered as the semi-infinite elastic body subjected to the thermo-mechanical loading of an asperity moving with a high speed. Considering the moving of frictional heat source and convection on a semi-infinite surface having inclined crack, theoretical analysis was carried out to estimate the propagation characteristics of thermo-mechanical crack. Numerical results showed that stress intensity factor $K_\prod/P_0\sqrt{c}$ is increasing with increasing velocity and frictional coefficient, inclined degree, decreasing crack length and the maximum value of it is positioned at the trailing edge. So it is shown that the propagation probability of surface crack is high at the trailing edge of contact area as increasing velocity and frictional coefficient, inclined degree, as decreasing crack length.

Influence of crack geometry on fatigue crack growth behavior in 5083- H113 aluminium alloy (5083-H113 A1 합금의 피로균열진전거동에 미치는 균열형태의 영향)

  • 김정규;신용승;윤의박
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.4
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    • pp.781-789
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    • 1988
  • The fatigue crack growth and crack closure behavior of long through-thickness cracks and small half-penny shaped surface cracks were investigated in 5083-H113 Aluminum alloy under constant amplitude testing by the unloading elastic compliance method. It was found that, in the Region II, the crack growth behavior of both through-thickness and surface cracks exhibited the tri-linear form with two transitions and no concern with stress ratio R. In the Region I $I_{ab}$ and I $I_{b}$, through-thickness cracks grew faster than surface cracks in length direction, but at .DELTA. K .leq.4 MPa.root.m for R=0.1 the growth rates of surface cracks in depth direction, grew faster than those of through-thickness cracks. When the crack closure was considered, the growth rates of through-thickness cracks lay between the growth rates of depth direction and the growth rates of length direction in surface cracks. It is suspected that this was caused by the difference of crack closure at depth and length direction of surface cracks.s.