• Title/Summary/Keyword: crack arrest

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Fatigue crack propagation of buried pipe steel under mixed model loading (혼합모드하중을 받는 매석배관강의 피로균열전파 거동)

  • 이억섭;최용길
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2000.11a
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    • pp.473-476
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    • 2000
  • Recently, many studies focus on mixed-mode fatigue-fracture characteristics of characteristics of materials. In order to reveal crack initiation and propagation mechanisms in combined -mode fatigue. This paper investigates the initiation and propagation behavior of the fatigue crack of the STS304 specimens under mixed mode loading conditions. moreover crack arrest and branch phenomena were analyzed with respect to the change do the angle of inclined loading. The relationship between the angle of inclined loading and the angle of branched crack was studied. A greate number of cycles are necessary to initiate a new crack from the initial crack. The direction of the new crack propagation is determined by MTS theory.

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Fatigue Crack Growth Retardation after Single Overload Cycle in High Strengh Aluminium Weldments (고강도 알루미늄 합금 용접부에 있어서의 피로균열전파에 미치는 과하중 효과)

  • 이택순;김상태;김인식
    • Journal of Welding and Joining
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    • v.6 no.1
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    • pp.46-52
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    • 1988
  • Retardation or delay in fatigue crack growth due to overloads are important for the accurate prediction of fatigue lives of structural materials. In this study, retardation of fatigue crack growth in Al 6061-T6 weldments and heat affected zones (HAZ) after single overload cycle had been investigated. Retardation in both weldments and HAZ was observed. It was concluded that retardation in both weldment and HAZ was greater than in base metal due to microstructural change and crack branching and crack closure were major governing factor in retardation.

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A Proposal of Round Specimen for the Determination of Crack Arrest Toughness (균열정지 인성치결정을 위한 원형시편의 제안)

  • 이억섭;김상철;송정일;이규철
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.5
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    • pp.1472-1478
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    • 1991
  • 본 연구에서는 Rectangular Computer Tension(CT) 시편을 수정하여 만든 표준 시편인 MRL-CLWL시편(material research laboratorycrack line wedge loaded specimen )으로 균열정지 인성치를 결정하였다. 그리고 CT시편과 같은 효과를 갖는 Newman등 이 제안한 round compact tension(RCT)시편을 수정한 Round-CLWL 시편으로 균열정지인 성치를 결정하여 상호 비교평가하였다. Round-CLWL 시편은 시편제작시 round-bar를 절단하여 시편으로 가공할 수 있으므로 가공성이 좋으며 따라서 가공비가 적게 든다. 특히 균열 위치 및 방향을 임의로 선택하여 가공하기가 용이하므로 방향성이 있는 소 재의 균열정지 인성치를 결정하는 데 매우 편리한 시편이라 생각된다. 본 논문에서 는 Round-CLWL 시편으로 $K_{1a}$ 값을 계산하는데 필요한 형상계수를 결정하였으며, Polymethylmethacrylate(PMMA)를 사용하여 Round-CLWL 시편 채택의 타당성 확인을 위 한 MRL-CLWL과 Round-CLWL 시편 채택의 타당성 확인을 위한 MRL-CLWL과 Round-CLWL시 편의 $K_{1a}$결정 실험을 하였다.하였다.

Effects of Microstructure on the Fatigue Crack Propagation Resistance in Dual Phase Steel (複合組織鋼 의 피勞균열進展抵抗 에 미치는 微視組織 의 영향)

  • 김정규;황돈영;박승락
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.8 no.1
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    • pp.34-40
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    • 1984
  • In this study, martensite-ferrite dual phase steel composed of martensite in hard phase and ferrite in soft phase is made as model material, and the difference of fatigue crack propagation behavior resulted from the structural size is investigated by fracture mechanics and microstructural method. The main results obtained are as follows; 1)Fatigue crack propagation rate is influenced by ferrite grain size. In other words, in the low .DELTA. K region fatigue crack propagation rate is decreased with decreasing of grain size but the difference of propagation rate resulted from the structural size is decreased as .DELTA.K is increased. 2)The above result is explained by the degree of crack arrest effect of second phase for fatigue crack propagation depending on the ratio of reversed plastic zone size to ferrite grain size.

Crack arrestability of thick plates for shipbuilding (조선용 극후물재의 취성균열 정지 특성 평가)

  • An, Gyu-Baek;Park, Jun-Sik;Jeong, Bo-Yeong;Lee, Jong-Bong
    • Proceedings of the KWS Conference
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    • 2007.11a
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    • pp.3-5
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    • 2007
  • In recent time there are vigorous requirement for the use of thick steel plate in various industrial fields including shipbuilding industry. Especially, with the continual increases in marine transportation volumes on a global scale, the steel of container ships have become thicker and thicker with the increased size of ships. In addition to, the brittle crack arrestability of heavy thick plates were big issue, in recently. In this study, crack arrest test were conducted in order to investigate the crack arrestability of thick plates for shipbuilding steels, where test plate thickness were 50mm and 80mm. This paper introduce the brittle crack arrestability of heavy thick plates for shipbuilding.

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Dynamic Fracture Behavior of Some Polymeric Materials (고분자재료의 동적 파괴거동에 관한 연구)

  • 이억섭;한정우;한문식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.7
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    • pp.1630-1641
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    • 1995
  • The dynamic stress intensity factors (DSIF ; $K_{I}$$^{dyn}$) were studied in some polymeric materials using caustics method with a high speed camera system. Also crack tip propagation speed was measured by dynamic crack propagation velocity measuring device. To calculate DSIF a finite element analysis program-INha Stress Analysis Moving CRack(INSAMCR) was utilized. Dynamic fracture characteristics were investigated to verify a relationship between DSIF and crack tip propagation speed and acceleration in PMMA, Homalite-100 and Polycarbonate. The relationship between dynamic stress intensity factor and crack tip velocity revealed typical shapes. Measured crack tip acceleration data envelope converges to the zero level with increasing DSIF. Equivalently crack tip velocities show a wide spread range at low values of DSIF, but become a constant with a higher DSIF. $1.2MPa{\sqrt{m}}$, $1.4MPa{\sqrt{m}}$ and $1.3 MPa{\sqrt{m}}$ were obtained as $K_{I}$$^{dyn}$ values to arrest the dynamic crack for PMMA, Homalite-100 and Polycarbonate, respectively. INSAMCR was run to verify experimental results in PMMA and shows good agreementment.

Dynamic Stress Intensity Factor and Dynamic Crack Propagation Velocity in Nuclear Pressure Vessel Steels (원자로압력용기강의 동적 응력확대계수와 동적 균열전파속도)

  • Lee, O.S.;Han, M.K.;Han, M.S.
    • Journal of the Korean Society for Precision Engineering
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    • v.15 no.11
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    • pp.251-257
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    • 1998
  • 동적 파괴인성치 측정시스템과 동적 2차원 유한요소해석 프로그램을 개발하여 원자로압력용기에 사용하는 강(SA508 cl.3, SA516 gr.70)의 동적 파괴인성치와 동적 균열정지인성치를 평가하고 이에 대한 유용성을 확인하였으며, 이 시스템 을 이용하여 재료의 동적 파괴특성을 규명하였다. SA508 cl.3와 SA516 gr.70의 동적 균열전파속도(a)에 대응하는 동적 응력확대계수 (K(a))에 대한 실험식을 얻었으며, 동적 응력확대계수와 동적 균열전파속도와의 관계는 전형적인 "$\Gamma$" 형으로 나타남을 확인하였다.

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Properties of Fatigue Crack Initiation and Arrest in Structural Steel Under Acid Fog (산성안개 하의 구조용강에서 피로균열의 발생 및 정류특성)

  • Kim, Min-Geon;Kim, Jin-Hak;Kim, Myeong-Seop;Ji, Jeong-Geun;Gu, Eun-Hoe
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.2
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    • pp.374-379
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    • 2002
  • Corrosion fatigue tests were carried out to clarify the influence of acid fog as environmental factor on the fatigue strength of SM55C using rotary bending fatigue tester. The fatigue strength of acid fog specimen extremely decreased about 80% compared to that of distilled water specimen. In acid fog environment, a number of cracks commenced at corrosion pit and coalesced with the adjacent cracks during they propagate, and they formed a single non-propagating circumferential crack under the endurance stress of N=5$\times$10$\^$7/ cycles. Also, the depth of the crack is smaller than that of normal fatigue crack, so the crack has a veil small aspect ratio. The reason of this peculiar crack growth characteristics is that the crack opening-closure behaviors are hindered by corrosion products on the surface crack faces, and hence it is thinkable that the strong corrosion action like anodic dissolution for crack growth in depth direction is weaker compared with surface, resulting from faint pumping action of crack during loading-shedding processes.