• Title/Summary/Keyword: Crack Branching

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A Study on Corrosion Fatigue Properties of Welded Joints for TMCP High Strength Steels (TMCP 고장력강 용접부의 부식도영 특성에 관한 연구)

  • 이택순;이휘원;김영철
    • Journal of Ocean Engineering and Technology
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    • v.10 no.3
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    • pp.14-23
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    • 1996
  • The corrosion fatigue test were carried out to evaluate the fatigue characteristics of accelerated cooled (ACC) TMCP high tensile strength steels and weld joint with high heat input by one side one run submerged are welding. In this paper, the fatigue crack growth behaviors were investigated with the center crack tension specimen of base metal and heat affected zone in substitute sea water and air, respectively Main results obtained are sunnarized as follows: 1. The fatigue crack growth rates in sea water faster than those in air environment for the different heat input values, crack growth rate of base metal is very fast and effect of heat input is not remarkable. 2. In HAZ (82kJ/cm, 116kJ/cm), the crack branching phenomena were observed in both air and sea water environment, 3. In SEM observation, the corrosion effect on base metal was larger than that on HAZ in corrosion environment.

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Intensity Factors for a Branched Crack in a Semi-Infinite Plate Under Tension and Bending Moments (인장과 굽힘을 받는 반 무한 평판내의 분기균열에 대한 강도계수)

  • 김유환;범현규;박치용
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2000.11a
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    • pp.461-464
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    • 2000
  • A branched crack in a semi-infinite plate under tension and bending moment is considered. Intensity factors of the stress and moment for the branched crack are evaluated. The stress intensity factors are obtained by using the finite element method and the J-based mutual integral. The moment intensity factors are calculated by extrapolating the values of the moment near the crack tip. Approximate expressions are also obtained as functions of the branched crack length and branching angle.

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Fatigue Crack Growth Behavior of Ni-Cr-Mo Steel under Acid Fog Environment (산성안개 환경하에서 Ni-Cr-Mo 강의 피로크랙전파거동)

  • Kim, Min-Geon;Im, Yong-Ho;Kim, Man-Gu
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.7 s.178
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    • pp.1841-1846
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    • 2000
  • To examine the effect of acid fog on the corrosion fatigue behavior in structural steel, fatigue tests under acid fog atmosphere were carried out in comparison with distilled water. The corrosive c omponents contained in acid fog pile up the corrosion products on crack face and show a crack branching and crack tip blunting. Therefore, due to these workings crack growth rate was reduced by decreasing the effective stress range in crack tip rather than under distilled water. Also the effect of sulfuric acid, which is the main component of acid fog, and testing speed on fatigue crack growth were examined. It was found that corrosion behavior was remarkably dependent upon pH and Hz rather than components of acid fog. According as pH and testing speed decrease below a specific value, crack growth was accelerated in comparison with distilled water. This reveals that due to liquid having strong acidity and slow speed of test the crack face dissolution was promoted, so crack closure was disturbed in the process of stress descent.

Behavior of Stress Corrosion Cracking in Structural Steel under Acid Fog Environment (산성안개하에서 기계·구조용강의 응력부식균열 거동)

  • Lim, Yong Ho;Kim, Min-Gun
    • Journal of Industrial Technology
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    • v.17
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    • pp.291-295
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    • 1997
  • The tests of stress corrosion cracking in structural carbon steel were carried out under the conditions of acid fog and general water. As the result of measurement SCC rupture time under acid fog was observed to be much shorter than that of general water at the same stress level. Therefore, acid fog drops the SCC strength in structural carbon steel due to strong corrosion. In the SCC process by acid fog, crack initiation was caused by pit corrosion and local stress concentration, and distinctive feature of crack growth shows branching since crack grows to the corrosion direction. Moreover, corrosion products were observed by clevage corrosion on the crack surfaces.

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해수환경에서 강 용접부의 환경강도평가에 관한 연구 1

  • 정세희;김태영;나의균
    • Journal of Welding and Joining
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    • v.6 no.2
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    • pp.56-63
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    • 1988
  • The effects of PWHT (poste weld heat treatment) and stress simulating the residual stress during PWHT in weld HAZ of low and high strength steels on corrosion fatigue crack growth were evaluated. The obtained results are summarized as follows. 1. Fatigue crack growth rate of HAZ in air and 3.5% NaCl solution was slower than that of parent due to the signgularity in weld HAZ. 2. In the case of HT-80, 3.5% NaCl solutio nacts to accelerate the crack growth for all specimens, and the sensitivity of as-weld to corrosion environment was the greatest among other PWHT specimens. 3. Corrosion fatigue crack growth of parent, as-weld and PWHT speciments ofr SS41 as well as SM53B was retarded in comparison with the fatigue crack growth in air. 4. There was a tendency that crack growth of PWHT specimens subjected $10kg/mm^2$ was faster than that of PWHT specimens without stress during PWHT. 5. The retardation phenomenon of crack growth in corrosion environment is attributed to the crack branching decreased .DELTA.K due to the corrosion products and multi-cracks.

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Analysis of a Branched Crack in a Semi-Infinite Plate Under Tension and Bending Moment (인장과 굽힘을 받는 반무한 평판내의 분기균열 해석)

  • 김유환;범현규;박치용
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.15 no.3
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    • pp.433-440
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    • 2002
  • A branched crack in a semi-infinite plate under uniform tension and bending moment is considered in this study By using the superposition, the stress and moment intensity factors for the branched crack subjected to uniform tension and bending moment we evaluated. The stress intensity factors we obtained by using the finite element method and the J-based mutual integral. The moment intensity factors are calculated by extrapolating the values of the moment new the crack tip. Numerical results lot the normalized stress and moment Intensity factors we shown as functions of the ratio of branched crack length to main crack length and the branching angle.

Boundary element analysis of stress intensity factors for Z-shaped cracks (Z형상 균열의 응력세기계수에 대한 경계요소 해석)

  • 이강용;원동성;최형집
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.1
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    • pp.36-43
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    • 1987
  • Stress intensity factors are computed by the boundary element method employing the multiregion technique along with the double-point concept. To demonstrate the validity of the current method, the stress intensity factors of the well-known simple models such as a slanted edge crack and an arcular crack are determined, in advanced, which are proved to be in good agreement within 5% with the pre-existing solutions. Z-shaped cracks are analyzed with various branch crack lengths and branching angles.

Fracture Toughness and Failure Behavior of WC-Co Composites by Fracture Surface Analysis (파괴표면분석을 통한 WC-Co복합재료의 Fracture Toughness측정방법과 Failure Behavior)

  • ;J.J Mecholsky, Jr.
    • Journal of the Korean Ceramic Society
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    • v.26 no.5
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    • pp.645-654
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    • 1989
  • Specimens of WC-Co were indented to measure the resulting crack size and unindented samples were fractured in 3-point flexure to obtain the strength and to measure characteristic features on the fracture surface. Fracture toughness was determined using fractography and compared to those determined using identation techniques. We show that principles of fracture mechanics can be applied WC-Co composites and can be used to analyze the fracture process. The fracture surfaces were examined by scanning electron microscopy and optical microscopy. Characteristic feature observed in glasses, single crystals and polycrystalline materials known as mirror, mist, hackle, and crack branching were identified for these composites. We discuss the importance of fracture surface analysis in determining the failure-initiating sources and the failure behaviorof WC-Co composites.

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Properties of Electrical Discharge Machinable $SiC-TiB_2$ Composites

  • Kim, Young-Wook;Park, Heon-Jin;Lee, June-Gunn;Lee, Soo W.;Chung, Soon-Kil
    • The Korean Journal of Ceramics
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    • v.1 no.3
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    • pp.125-130
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    • 1995
  • Electrical discharge machinable $SiC-TiB_2$ composites were fabricated by hot-pressing. Their mechanical and electrical properties were determined as a function of $TiB_2$ content. The addition of $TiB_2$ to SiC matrix increased the strength and toughness and decreased electrical resistivity. The flexural strength and fracture toughness of SiC-40 vol% $TiB_2$ composited were approximately 50% higher than those of monolithic SiC ceramics. Microstructural analysis showed that the toughening was mainly due to the crack deflection, with some possible contribution from crack branching or microcracking.

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AN EXPERIMENTAL STUDY ON THE FATIGUE FRACTURE OF LAMINATE PORCELAIN (치과용 라미네이트 도재의 피로파괴에 관한 실험적 연구)

  • Park Charn-Woon;Bae Tae-Sung;Lee Sang-Don
    • The Journal of Korean Academy of Prosthodontics
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    • v.31 no.4
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    • pp.482-505
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    • 1993
  • The purpose of this study was to evaluate the fracture characteristics and the effect of resin bonding of laminate porcelain. In order to characterize the indentation-induced crack, Young's moduli and characteristic indentation dimensions were measured. The fatigue life under three point flexure test was measured using the electro-dynamic type fatigue machine, and the crack propagation with thermocycling was investigated on the condition of 15 second dwell time each in $5^{\circ}C\;and\;55^{\circ}C$ bath. The Vickers indentation pattern and the fracture surface were examined by an optical microscope and a scanning electron microscope (SEM). The results obtained were summarized as follows ; 1. Young's moduli(E) of the laminate porcelain and the resin cement used in this experiment were $62.56{\pm}3.79GPa$ and $15.01{\pm}0.12GPa$, respectively. 2. The initial crack size of the laminate porcelain was $69.19{\pm}5.94{\mu}m$ when an indentation load of 9.8N was applied, and the fracture toughness was $1.065{\pm}0.156MPa\;m^{1/2}$. 3. The fatigue life of laminate porcelain showed the constant fracture range at the stress level 27.46-35.30MPa. 4. When a cyclic flexure load was applied, the fatigue life of resin-bonded laminate porcelain was more decreased than that of laminate porcelain. 5. When a thermocycling was conducted, the crack growth rate of resin-bonded laminate porcelain was more increased than that of laminate porcelain. 6. Fracture surface showed the radial crack, the lateral crack, and the macroscopic crack branching region beneath the plastic deformation region when an indentation load of 9.8N was applied.

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