• Title, Summary, Keyword: Surface Crack

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Generation of Pseudo-Random Load Waves and Preliminary Study on Surface Fatigue Crack Growth under Random Loading (유사랜덤하중파형 작성과 이를 이용한 랜덤하중하의 표면피로 균열진전에 관한 기초적 검토)

  • 송지호;김종한;김정엽
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.1
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    • pp.125-134
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    • 1989
  • Pseudo-random load waves for fatigue testing were generated by personal computer simulation and preliminary study was performed on the growth behavior of surface fatigue crack under random ladings. The closure behavior and growth rates of surface fatigue crack were significantly influenced by the characteristics of random waves. It was also found that the growth rates of surface fatigue crack under random loadings could not be always described by the effective stress intensity factor based on the concept of crack closure.

Development of the DCPD Method Based on Finite Element Analysis for Measuring Semi-Elliptical Surface Cracks (반타원 표면균열 형상측정을 위한 유한요소 전기장 해석에 기초한 직류전위차법의 개발)

  • Kim, Yeong-Jin;Sim, Do-Jun;Choe, Jae-Bung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.7
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    • pp.1147-1154
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    • 2001
  • One of major problems in analyzing failure mechanism of real components is the accurate measurement of crack size and shape. The DCPD(Direct Current Potential Drop) method has been widely used for the crack measurement of a structure and finite element analysis has been used for the derivation of calibration equations, which relates the potential drop with the crack depth. In this paper, finite element analyses were performed for semi-elliptical surface cracks with various crack shapes(a/c) and crack depths(a/t). As a result, a calibration equation has been derived for the measurement of a semi-elliptical surface crack in wide plates. Analytical results are compared with experimental results to evaluate the validity and the applicability of the derived equation. The proposed method is expected to provide efficient and accurate measurement of a surface crack during crack growth.

A study on the development of solution for the Crack Free Hard Chromium Deposits (Crack free 경질 크롬 도금욕 개발에 관한 연구)

  • 추현식;이홍로
    • Journal of the Korean institute of surface engineering
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    • v.25 no.4
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    • pp.181-186
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    • 1992
  • To investigate how to produce the crack free and chromium deposits, bath compositions, additives, electrolysis conditions and other electroplating parameters, such as cathodic current efficiency, surface hard-ness, crack density and corrosion rate of deposits were examined carefully. The crack free chrome deposits were well obtained using both wetting agents and two kind of additives. At 60 A/d$\m^2$, $60^{\circ}C$ electrolysis condition, crack free bright hard chromium deposits were well obtained to a thickness $300\mu\textrm{m}$ in Additive-I and Additive-II added solution.

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Evaluation of Stress Intensity Factor after Penetration of Plate with Long Surface Crack (긴 표면균열재의 관통후 응력확대계수 평가)

  • Nam Kiwoo;Lee Jongrark
    • Journal of the Korean Institute of Gas
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    • v.4 no.1
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    • pp.33-39
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    • 2000
  • Stress intensity factor after penetration was discussed experimentally using long surface pre-cracked specimens of aluminum alloy 5083. The propagation behavior evaluation of long surface crack by equation proposed at penetration of short surface crack could be need modification to evaluate precisely because the error was high as aspect ratio is little. The modification of stress intensity factor with consideration of aspect ratio at penetration of long surface crack can be analyzed the behavior of crack penetration quantitatively.

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Analysis of Mixed Mode Surface Crack in Finite-Width Plate Subjected to Uniform Shearing by Boundary Element Method (경계요소법에 의한 포물선형 인장과 비틀림을 받는 유한폭 판재의 혼합 Mode 표면균열에 대한 해석)

  • Park, Seong-Wan;Hong, Jae-Hak
    • Journal of the Korean Society for Precision Engineering
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    • v.7 no.4
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    • pp.103-116
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    • 1990
  • The mixed mode surface crack in finite-width plate subjected to uniform shearing has been analyzed in 3-D problem by using boundary element method. The calculations were carried out for the surface crack angles (${\alpha}$) of $0^{\circ}, 15^{\circ}, 30^{\circ}, 45^{\circ}, 60^{\circ}, and 75^{\circ}, $ and for the aspect ratio(a/c) of 0.2, 0.4, 0.6 and 1.0 to get stress intensity factors at the boundary points of the surface crack. For the aspect ratio of 1.0 and the surface crack angles, finite element method was used to check the results in this in this study. Comparison of the results from both method showed good agreement.

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Analysis of Mixed Mode Surface Crack in Finite-Width Plate Subjected to Uniform Shearing by Boundary Element Method (경계요소법에 의한 포물선형 인장과 비틀림을 받는 유한폭 판재의 혼합 Mode 표면균열에 대한 해석)

  • Park, Seong-Wan;Hong, Jae-Hak
    • Journal of the Korean Society for Precision Engineering
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    • v.7 no.4
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    • pp.117-129
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    • 1990
  • The mixed mode surface crack in finite-width plate subjected to uniform shearing has been analyzed in 3-D problem by using boundary element method. The calculations were carried out for the surface crack angles (${\alpha}$) of $0^{\circ}, 15^{\circ}, 30^{\circ}, 45^{\circ}, 60^{\circ}, and 75^{\circ}, $ and for the aspect ratio(a/c) of 0.2, 0.4, 0.6 and 1.0 to get stress intensity factors at the boundary points of the surface crack. For the aspect ratio of 1.0 and the surface crack angles, finite element method was used to check the results in this in this study. Comparison of the results from both method showed good agreement.

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The Numerical Analysis for the Surface Crack Behavior in the Planar Solid Oxide Fuel Cell (평판형 고체산화물 연료전지 표면균열거동에 관한 수치해석)

  • Park, Cheol Jun;Kwon, Oh Heon;Kang, Ji Woong
    • Journal of the Korean Society of Safety
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    • v.33 no.5
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    • pp.1-8
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    • 2018
  • A fuel cell is an energy conversion device that converts a chemical energy directly into an electrical energy and has higher energy efficiency than an internal combustion engine, but solid oxide fuel cell (SOFC) consisting of brittle ceramic material remains as a major issue regarding the mechanical properties as the crack formation and propagation. In this study, the stress distribution and crack behavior around the crack tip were evaluated, due to investigated the effects of the surface crack at the operating condition of high temperature. As a result, the difference of the generated stress was insignificant at operating conditions of high temperature according to the surface crack length changes. This is because, the high stiffness interconnect has a closed structure to suppress cell deformation about thermal expansion. The stress intensity factor ratio $K_{II}/K_I$ increased as the crack depth increased, at that time the effect of $K_{II}$ is larger than that of $K_I$. Also the maximum stress intensity factor increased as the crack depth increased, but the location of crack was generated at the electrolyte/anode interface, not at the crack tip.

A Fundamental Study on the Method Repair for Crack in Concrete by Corrosion of Steel Reinforcing (콘크리트 내부 균열에 대한 보수기법의 기초적 연구)

  • Lim, Nam-Gi;Paik, Min-Su;Kwon, Young-Jin;Choi, Eung-Kyoo;Chung, Lan;Jung, Sang-Jin;Choi, Mun-Shik
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.579-584
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    • 1997
  • This experimentation is to apperciation an efficiency of repair for processing crack by corrosion of steel reinforcing, Crack on concrete by corrosion of steel reinforcing is the fact that the first crack appear on the surface of water because of supplying is of oxygen and water. The crack processing is on surface to be contacted by air and to bottom as mainly the vertical direction from a surface of water. The experimentation gives rise to crack in model by electricity. Crack by corrosion of steel reinforcing is more internal crack than external crack. since it is so. crack by corrosion of steel reinforcing have to attention to repair or intermal crack.

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Finite Element Analysis of Subsurface Multiple Horizontal Cracks Propagation in a Half-space Due to Sliding Contact (유한요소법을 이용한 미끄럼 접촉시 내부 복수 수평균열 전파해석)

  • 이상윤;김석삼;권영두
    • Tribology and Lubricants
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    • v.16 no.5
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    • pp.373-380
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    • 2000
  • Finite element analysis is performed on the subsurface crack propagation in brittle materials due to sliding contact. The sliding contact is simulated by a rigid asperity moving across the surface of an elastic half-surface containing single and multiple cracks. The single crack, coplanar cracks and parallel cracks are modeled to investigate the interaction effects on the crack growth in contact fatigue. The crack location is fixed and the friction coefficients between asperity and half-space are varied to analyze the effect of surface friction on stress intensity factor for horizontal cracks. The crack propagation direction is predicted based on the maximum range of shear and tensile stress intensity factors. With a coplanar crack, the stress intensity factor was increased. However, with a parallel crack, the stress intensity factor was decreased. These results indicate that the interaction of a coplanar crack increases fatigue crack propagation, whereas that of a parallel crack decreases it.

강용접부의 표면균열 성장거동에 관한 연구 1

  • 정세희;박재규;이종기
    • Journal of Welding and Joining
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    • v.6 no.2
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    • pp.30-39
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    • 1988
  • Generally, as the welded region of weld structures has the incomplete bead and welded deposit which are able to behave like the surface cracks occasinally, there is a high possibility that the fatigue fracture of the weld structures is due to the surface cracks on the wlded region. This study was done to investigate the effects of post weld heat treatment (PWHT) on the fatigue behaviors of the surface crack of the heat affected zone (HAZ) for the multi-pass welds under the repetitive pure bending moment. The obtained results are summarized as follows : 1. The crack grows to the depth direction initially as the number of cylces increase, the amount of crack length is increased for the surface dir3ction and cive versa for the depth direction. 2. The fatigue life is increased in a order of as weld, PWHT specimens and parent. 3. As the number of cycles increase, the crack length is increased to th surface direction. The increase of the depth length is blunted at the center of specimen thickness. 4. The fatigue crack growth of PWHT specimens to the surface direction is dependent upon the holding time and applied stress during PWHT. In order words, the crack growth rate decreases with the holding time and increases with the applied stress during PWHT. 5. As the crack grows, the aspect formed in the course of crack propagation approaches to semicircle for parent and ellipse with the largest semidiameter for PWHT ($1/4hr, 15kgf/mm^2$) 6. At depth direction, it is difficult to apply to the paris' equation because of the scattered data between the crack growth rate and the stress intensity factor range.

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