• Title, Summary, Keyword: Surface Crack

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Evaluation of Surface Crack and Blind Crack by Induced Current Focusing Potential Drop(ICFPD) Technique (집중유도형 교류전위차법에 의한 표면결함 및 이면결함의 평가에 관한 연구)

  • Kim, Hoon
    • Journal of the Korean Society for Nondestructive Testing
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    • v.16 no.2
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    • pp.86-94
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    • 1996
  • In the life management safety evaluation of constructs base on a fracture mechanics, the size of defect is the very important parameter. ICFPD (Induced Current Focusing Potential Drop)technique has been developed for detecting and sizing of defects that exist not only on surface but also inside and interior of structural components. The principle of this technique is to induce a focusing current at an exploration region by a straight induction wire through which an alternating current (AC)flows that has constant amplitude and frequency. The potential distributed on the surface of metallic material is measured by potential pick-up pins that are settled on the probe. In this paper, this NDI technique was applied to the evaluation of surface cracks and blind cracks in plate specimens. The results of this study show that in the case of surface crack, the distribution of potential drop is varied with the inched angle of surface crack, and the potential drops in the crack region and the crack edge region are varied with the inclined angle and depth of crack. The distribution of potential drop for the blind crack is distingulished from that for the surface crack, and the potential drop in the crack region is varied with the depth of crack.

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Analysis of Shape Change of a Surface Crack during Stable Fatigue Growth (안정피로성장 중인 표면균열 형상변화의 해석)

  • Chu, Seok-Jae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.9
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    • pp.2843-2853
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    • 1996
  • The multi-point procedure is developed to predict the shape change of a semi-elliptical surface crack during stable fatigue crack growth. 3-D stress intensity factors along a crack front are calculated using the simplified 3-D J-intergral. Crack growth rate coefficient in the Paris law is assumed to be constant along the crack growth. Crack growth rate is set to be the distance between the two parallel tangent lines on the two semi-elliptic crack fronts before and after crack growth.

Crack Analysis of Concrete Gravity Dam Using Surface Integral Method (표면적분법을 이용한 콘크리트 댐의 균열 해석)

  • 진치섭;이영호;손기석
    • Journal of the Korea Concrete Institute
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    • v.12 no.3
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    • pp.31-37
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    • 2000
  • When a crack is produced in a concrete structure, a micro crack zone of fracture process zone (FPZ) appears at the crack tip. To investigate the behaviour of this the micro crack zone, nonlinear fracture mechanics (NLFM) must be applied. However, when a massive concrete structure such as a concrete gravity dam is considered, the micro crack zone can be neglected and the structure can be assumed to have linear elastic fracture mechanics (LEFM) behaviour. This study is divided into two main topics : (1) Calculating stress intensity factor (SIF) at the crack tip by surface integral method and (2) Investigating the propagation of the initial crack. If the initial crack propagates, the angle of the propagation is calculated by using maximum circumferential tensile strength theory. This study, also, contains the effects of body forces and water pressures on the crack face.

Experimental Study on the Surface Defects of Scribed Glass Sheets (절단 유리판의 표면결함에 관한 실험적 연구)

  • Kim, Chung-Kyun
    • Tribology and Lubricants
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    • v.24 no.6
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    • pp.332-337
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    • 2008
  • This paper presents the surface defect analysis based on the experimental investigation of scribed glasses. The scribing process by a diamond wheel cutter is widely used as a reliable and inexpensive method for sizing of glass sheets. The wheel cutter generates a small median crack on the glass surface, which is then propagated through the glass thickness for complete separation. The surface contour patterns in which are formed during a scribing process are strongly related to wheel cutter parameters such as wheel tip surface finish, tip angle and wheel diameter, and cutting process parameters such as scribing pressure, speed and tooling technique. The scribed surface of a glass sheet provides normal Wallner lines, which represent regular median cracks and crack propagation in glass thickness, and abnormal surface roughness patterns. In this experimental study, normal and abnormal surface topographic patterns are classified based on the surface defect profiles of scribed glass sheets. A normal surface of a scribed glass sheet shows regular Wallner lines with deep median cracks. But some specimens of scribed glass sheets show that abnormal surface profiles of glass sheets in two pieces are represented by a chipping, irregular surface cracks in depth, edge cracks, and combined crack defects. These surface crack patterns are strongly related to easy breakage of the scribed glass imposed by external forces. Thus the scribed glass with abnormal crack patterns should be removed during a quality control process based on the surface defect classification method as demonstrated in this study.

Stress Intensity Factor Analysis for Surface Crack in Inhomogeneous Materials (비균질재료의 표면균열에 대한 응력확대계수 해석)

  • 김준수;이준성
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.816-819
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    • 2002
  • Accurate stress intensity factor analyses and crack growth rate of surface-cracked components in inhomogeneous materials are needed for reliable prediction of their fatigue lift and fracture strengths. This paper describes an automated system for analyzing the stress intensity factors of three-dimensional (3D) cracks in inhomogeneous materials. 3D finite element method (FEM) was used to obtain the stress intensity factor for subsurface cracks and surface cracks existing in inhomogeneous materials. To examine accuracy and efficiency of the present system, the stress intensity factor for a semi-elliptical surface crack in a plate subjected to uniform tension is calculated, and compared with Raju-Newman's solutions. Then the system is applied to analyze cladding effect of subsurface cracks in inhomogeneous materials. The results were compared with those surface cracks in homogeneous materials. It is clearly demonstrated from these analyses that the stress intensity factors for subsurface cracks are less than those of surface cracks.

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Reliability Assessment of Buried Pipelines with a Circumferential Surface Elliptical Crack under Axial Stress (축직각 표면타원균열이 존재하는 매석배관의 축방향응력에 대한 건전성 평가)

  • 이억섭;황인현
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.417-420
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    • 2000
  • The theoretical analyses for stresses induced in axial direction in the buried pipelines are reviewed. The influences of the axially directed stresses on the surface elliptical crack are studied in detail and thus some engineering technical informations are provided to use reliability assessment of buried pipelines. The change in temperature, the effect of inner pressure and soil friction in the buried pipeline constrained in axial direction are included to determine the axial stresses in the buried pipeline. Furthermore, the stress induced by the pipeline bending are also considered. The stress intensity factors calculated by two models such as a simple plane crack and an elliptical surface crack for a circumferential surface elliptical crack are compared.

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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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    • 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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Reference Stress Based J-Integral Estimates Along the Semi-Elliptical Surface Crack Front (반타원 표면균열 선단을 따른 참조응력 기반의 J-적분 예측)

  • Kim, Jin-Su;Shim, Do-Jun;Kim, Yun-Jae;Kim, Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.6
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    • pp.701-708
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    • 2004
  • This paper discusses applicability of the enhanced reference stress method to estimate J-integral along the semi-elliptical surface crack front. It is found that angular variations of normalized J­integral are strongly dependent on the geometry, loading mode and loading magnitude. As application of the reference stress approach to semi-elliptical surface cracks implies proportional increases in the normalized J-integral, the present results pose a question in applicability of the reference stress approach. However, investigation of the error in the estimated J-integral in the present work suggests that the enhanced reference stress approach, recently proposed by authors, provides an effective engineering tool fur estimating crack driving force along the semi-elliptical surface crack front.

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.

A Study on the Fatigue Crack of Material by Surface Non-Traditional Machining (표면특수가공에 따른 재료의 피로균열에 관한 연구)

  • 이태연;이승호;강진식
    • Transactions of Materials Processing
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    • v.10 no.3
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    • pp.179-184
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    • 2001
  • The influence of the fatigue crack propagation by shot peening was studied in this paper. Fatigue tests were carried out on the unpeened and shot peened CT specimens. The changes of mechanical properties, residual stress, fatigue fracture surface etc. by shot peening were investigated. The mechanical properties, residual stress, fatigue surface etc. by shot peening were investigated. The mechanical peened specimen improved in fatigue life up to 14% by shot peening. The reason of increase in the fatigue life was closely related with the compressive residual stress, which was 519.7MPa on surface. Another reason was the constraint on crack opening on surface region, it is due to the decrease in slope of crack propagation direction.

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