• Title/Summary/Keyword: 균열선단 열림변위

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Crack Growth Instability for Ductile Material Using the Compact Tension Specimen (컴팩트 인장 시편을 이용한 연성 재료의 불안정 균열 성장에 관한 연구)

  • 이홍서;김희송
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.5
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    • pp.928-937
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    • 1989
  • Applicability of $T_{\delta}$ proposed by Shin et al as an instability parameter for ductile material is investigated, Both general fracture test and instability fracture test are performed using compact tension specimens of structural alloy steel(SCM4), The values of ( $T_{\delta}$)$_{app}$(applied tearing modules) estimated from the real load vs. crack growth curve measured from experiments are compared with those estimated from the limit load vs. crack growth curve. The results are:(1) the $T_{\delta}$ parameter may be used as a crack instability parameter:(2) the use of ( $T_{\delta}$)$_{app}$ estimated from the load-crack growth curve, proposed in this study is reasonably justified.ified.d.

Microscopic fracture criterion of crack growth initiation (연성 균열성장 개시의 미시적 파괴조건)

  • 구인회
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.5
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    • pp.740-745
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    • 1987
  • For the prediction of the crack growth initiation from a blunt notch or a precrack in a prestrained material under plane strain tension and small-scale yielding conditions, a microscopic fracture criterion is proposed in terms of the crack tip opening displacement(COD) needed for the attainment of fracture strain at a microstructural distance. Smooth blunting of a crack tip with an initial root radius is assumed, and strain distributions on the crack-line axis are calculated at each deformation stage until the distributions against an original distance normalized to the COD are insensitive to an initial root radius. This case of no initial-root-radius effect is taken as for a sharp crack tip, on which the criterion is applied to determine the characteristic length of material from a critical COD for a fatigue-precracked specimen. The predicted COD at the fracture initiation from a crack with an initial root radius or a prestraining shows reasonable agreement with experimental values.

A Modification of the $C^*$ Integral Considering the Effect of Crack Growth (균열 진전의 효과를 고려한 $C^*$ 적분의 수정)

  • 최영환;방종명;염윤용;송지호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.1
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    • pp.77-86
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    • 1989
  • A modified $C^{*}$ integral as load parameter in creep fracture is proposed considering the effect of crack growth. It is shown that the parameter does not depend on crack velocity. By performing experiment using STS 304 stainless steel at 600.deg.C the validity of the parameter is investigated. The results show that the parameter is a good measure as a load parameter in creep fracture and the rate of crack tip opening displacement can also be a creep load parameter for STS 304 at 600.deg. C.C.

Design of δ5 Clip Gage for CTOD Measurement (CTOD 측정용 δ5 Clip Gage 설계)

  • Park, Tai-Heoun;Nahm, Seung-Hoon;Kim, Am-Kee
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.4
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    • pp.343-351
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    • 2004
  • The flaw assessment method based on ${delta}_5$ parameter was recently proposed and put to the practical use. However: since it is almost impossible to measure the ${delta}_5$ by the existing commercial clip gager, we need to develope the specially designed gages which are suitable for that purpose. In this research, a double cantilever type ${delta}_5$ clip gage with the traveling distance of 4mm was developed by the finite element analysis and the construction of Wheatstone bridge circuit including strain gages. The linearity of developed ${delta}_5$ clip gage was evaluated by the MTS extensometer calibrator with the proper adapters which allow the 6s clip gage to sit on the calibrator. Consequently, the 6s clip gage revealed the good linearity between the output voltage and the traveling distance of gage.

Evaluation of Fracture Behavior on Particle Reinforced Composite Using Digital Image Correlation (DIC를 이용한 입자강화 복합재료의 파괴거동 평가)

  • Hong, Sang-Hyun;Lee, Jeong-Won;Kim, Jae-Hoon;Lee, Sang-Yeon;Park, Jae-Beom;Jung, Gyoo-Dong
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.46 no.7
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    • pp.535-541
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    • 2018
  • In this study, wedge splitting tests were performed to evaluate fracture behavior of particle reinforced composite materials. Crack resistance was evaluated by using CTOD (crack tip opening displacement) and crack tip opening angle (CTOA). The particle reinforced composites were tested under various temperature ($-60^{\circ}C{\sim}50^{\circ}C$) and load speed (5~500mm/min). Also, digital image correlation method (DIC) was used to analyze the strain field at crack tip. Test results showed that the fracture energy increased with decreasing temperature and crack resistance increased with increasing load velocity.

Comparison of the Characteristics of FCAW and SAW for the Brittle Crack Propagation of Welded Parts of BCA Steel in Container Ships (컨테이너선의 후 물재 용접부 취성 균열 전파에 대한 FCAW와 SAW의 비교 특성에 관한 연구)

  • Choi, Kyung-Shin;Lee, Sang-Hoon;Choi, JeongJu
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.20 no.3
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    • pp.24-32
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    • 2021
  • The size of container ships is increasing to increase the cargo loading capacity. However, container ships are limited in terms of the hull longitudinal strength. To overcome this limitation, brittle crack arrest steel can be used. This study was aimed at examining the influence of the heat input on the welding procedures of flux cored arc welding and submerged arc welding. In the experiment, the crack tip opening displacement test, which pertains to a parameter of fracture mechanics, was performed, and a 3-point bending tester was adopted. Based on the results, the crack measurement method was presented, and the stress expansion coefficient value for the pre-fatigue crack length was derived according to the heat input after the pre-cracking length was measured. It was noted that the heat input affected the crack tip opening displacement of brittle crack arrest steel.

Fatigue Crack Closure and Propagation Behavior Under Mixed-Mode Loading Observed by the Direct Measuring Method (직접측정법을 이용한 혼합모드 하중 하에서 피로균열의 닫힘과 전파거동)

  • Song Sam Hong;Seo Ki Jeong;Lee Jeong Moo
    • Journal of the Korean Society for Precision Engineering
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    • v.22 no.6 s.171
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    • pp.152-158
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    • 2005
  • The stress conditions acting on the practical structure are complex, and thus most cracks existing in the practical structures are under mixed-mode loading conditions. The effect of shear load component of mixed-mode loading acts more greatly in the stage of crack initiation and initial propagation than crack propagation stage. Hence, research on the behavior in the stage of crack initiation and initial propagation need to be examined in order to evaluate behavior of mixed-mode fatigue cracks. In this study, the crack tip displacement(CTD) was measured by using the direct measuring method(DMM). We examined the behavior at crack tip by determining crack opening load$(P_{op})$. From the test results, the propagation behavior of mixed-mode fatigue cracks was evaluated by considering mixed-mode crack closure. Also, we examined the characteristic of crack propagation under mixed-mode loading with crack propagation direction.

Study of Brittle Crack Propagation Welding for EH40 Steel Plate in Shipbuilding Steel (조선용 EH40 강판의 용접부 취성 균열전파정지에 관한 연구)

  • Choi, Kyung-Shin;Lee, Sang-Hoon;Chung, Won-Jee;Hwang, Hui-Geon;Hong, Seok-Han;Hong, Ji-Ung
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.18 no.5
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    • pp.9-16
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    • 2019
  • Recent economic trends are worsening and becoming longer, and Korean shipbuilding is focused on high value added and high technology, especially for LNG carriers and large container ships. Both ship types increased in size in the 2010s but have requirements such as high strength, toughness at low temperatures and continuous weldability for preventing brittle fractures at service temperatures. In particular, as container ships become larger, the International Classification Society (IACS) has established a provision (IACS UR S33) that mandates the use of BCA (Brittle Crack Arrest) certified vessels for large container vessels contracted after 2014 to ensure safety. Therefore, studies on BCA 47Y.P are currently being undertaken, but BCA 40Y.P has not been actively studied yet. We will test BCA 40Y.P to verify why it can be applied to a large container ship and measure fatigue cracking.

Estimations of Strain-Based J-integral and CTOD for Circumferential Outer Surface Crack in the Weld of Gas Pipeline Under Axial Displacement (축방향 변위가 작용하는 가스 파이프라인 용접부에 존재하는 원주방향 외부표면균열의 변형률 기반 J-적분 및 CTOD 계산)

  • Kim, Kyoung-Min;Park, Ji-Su;Moon, Ji-Hee;Jang, Youn-Young;Park, Seung-Hyun;Huh, Nam-Su
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.16 no.1
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    • pp.100-109
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    • 2020
  • Pipelines subjected to ground movement would be easily exposed to large-scale deformation. Since such deformations may cause the pipeline failure, it is important to ensure the safety of pipelines in various operation conditions. However, crack in weld metal have been considered as one of the main causes that can deteriorate the structural integrity of the pipeline. For this reason, the structural integrity of the pipe containing the crack in the weld should be obtained. In order to assess cracked pipe, J-integral and crack-tip opening displacement(CTOD) have been applied widely as the elastic-plastic fracture mechanics parameters representing crack driving force. In this study, engineering solutions to calculate the J-integral and CTOD of pipes with a circumferential outer surface crack in the weld are proposed. For this purpose, 3-dimensional elastic-plastic finite element(FE) analyses have been performed considering the effect of overmatch and width of weld. The shape of the weld was simplified to I-groove, and axial displacement was employed as for loading condition. Based on FE results, the effects of crack size, material properties and width of weldment on J-integral and CTOD were investigated. Additionally, the J-integral and CTOD for I-groove were compared with those for V-groove to examine the effects of the weld shape, and a proportionality coefficient of J-integral and CTOD was calculated from the results of this paper.