• Title/Summary/Keyword: CT 시험편

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A Study on a Relationship Between the Surface Roughness of Fracture CT Specimen Broken by Fatigue Crack Growth and the Moments (피로균열성장에 의해 파단된 CT시험편의 표면조도와 모멘트의 관계에 관한 연구)

  • Kim, Kyun-Suk;Jung, Hyun-Chul;Kim, Kyung-Su;Park, Chan-Joo;Jang, Hos-Seob
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.19 no.4
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    • pp.462-468
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    • 2010
  • Fatigue crack growth caused by surface defects is one of the most important subjects for the evaluation and the assurance of safety in pressure vessels, piping systems, LPG/LNG fuel tank and other various structures. So, this paper aims to investigate the relationship between the surface roughness of fracture CT specimens and the moments on the specimen when doing fatigue test for the evaluation and the assurance of safety of structures from fatigue crack deconstruction. In this experiment, the CT specimens were loaded by a fatigue testing machine with changing loads until they are broken. The surface roughness of the fracture CT specimens was measured using 3D precise shape measuring equipment and digital holography. As a result of this study, It was identified that the average roughnesses are similar at the positions that has a same moments by comparing the results with the moments on the specimen according to the position.

Evaluation of a Back Face Strain Compliance of CT specimen (CT시험편의 Back Face Strain Compliance 평가)

  • Kim, Won Beom
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.17 no.12
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    • pp.686-691
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    • 2016
  • In welded steel structures, there are many stress concentration sites such as weld beads, and welding defects are likely to occur at the welded parts. When a repeated fatigue load acts on a stress concentration site, fatigue crack occurs and propagates, leading to fatigue fracture. Therefore, it is necessary to understand fatigue life, crack initiation life, and crack propagation life in order to prevent fatigue failure. In this study, a compliance method was derived for use in the study of fatigue crack propagation characteristics. This compliance can be used for automated measurement of fatigue cracks. The compliance was calculated using an in-house FEM program for a CT specimen. The results of this calculation are presented in relation to a/W and compared with calculation results using the J integral and a program from a previous study. In addition, the strain distribution in the upward and downward directions was calculated from the center of the back face of the CT specimen. In this distribution, the strain tended to decrease from the center to the top and bottom. The compliance method was achieved from these calculations and can be used for automatic execution of crack propagation tests.

Evaluation of Deterioration of Epoxy Primer for Steel Bridge Coating using Image Processing and Electrochemical Impedance Spectroscopy (화상처리 기법과 전기화학적 임피던스 분광법을 이용한 강교 도장용 에폭시 하도 도료의 열화 평가)

  • Lee, Chan Young;Lee, Sang Hun;Park, Jin Hwan
    • Corrosion Science and Technology
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    • v.8 no.2
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    • pp.53-61
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    • 2009
  • In this study, both evaluations by visual imaging for exterior view of coating and by EIS were executed for epoxy primer coated specimens deteriorated by accelerated test, and comparison and analysis were carried out for 2 evaluation methods. In the comparison between total damaged area ratio acquired by image processing method and deterioration point, higher deterioration points were appeared for rusted specimens than for non-rusted specimens. It is attributed that deterioration point per unit area ratio given for rust is higher than for peeling. In the comparison between total damaged area ratio and EIS result, impedance of coating was largely decreased as about TEX>$10^4{\Omega}{\cdot}cm^2$ or less when rust area ratio is more than about 0.1%, and blistering area ratio is more than about 3%. Charge transfer resistance ($R_{ct}$) and double layer capacitance ($C_{dl}$) values were appeared for all specimens except 2 ones, which shows that water is accumulated and steel substrate is corroded at coated film-steel interface. In the comparison between deterioration point and EIS result, more than 10 points as deterioration point were given for specimens of below $10^6{\Omega}{\cdot}cm^2$ of impedance at low frequency. For specimens deteriorated by NORSOK cyclic test, impedance was lowest of all, though deterioration point was not high. It is thought to be attributed that coating system and accelerated deterioration condition of cyclic tested specimens were different from those of main specimens. From the result, it is thought that coating resistance can be relatively more decreased than deterioration degree estimated from exterior view under more severe corrosion environment or in the present of more complex deterioration factors.

Fracture Mechanics Applied to Fatigue Crack Growth Behavior at Elevated Temperatures (고온 피로균열 성장거동에 관한 파괴역학의 응용에 관한 연구)

  • 서창민;김영호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.6
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    • pp.1552-1560
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    • 1990
  • A general form of the mathematical function in the fatigue crack growth rate law for CT specimens was determined by means of the dimensional analysis at elevated temperatures. The experimental results can be rigorously described by the combination of rate theory and fracture mechanics. The rate theory approach extends the scope of fracture mechanics through the consideration of the temperature. The fatigue crack growth rates are represented by the Arrhenius type equation. This equation explains fairly well the experimental data for Cr-Mo-V rotor steel and A517-F steel in the comparatively wide temperature regions as affected with the temperature and the stress intensity factor range interaction.

Evaluation of the J integral of a CT specimen by FEM (FEM에 의한 CT시험편의 J 적분 해석에 관한 연구)

  • Kim, Won Beom
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.15 no.11
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    • pp.6440-6445
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    • 2014
  • In steel structures, including ships and offshore structures, defects induced during construction or in use causes cracks and damages. Calculation of the stress intensity factor (SIF) K is one method for crack analysis by fracture mechanics approach. In this paper, an evaluation of K was carried out using the J integral. In particular, in this study, a CT specimen was used to calculate the J integral. In the evaluation, 859 nodes and 1618 elements were used for the J integral calculation of the CT specimen by the in-house FEM program. A comparison of the result with the ASTM formula showed that the results from the current research of the J integral was in the 99% coincidence interval. Overall, cracks in this study can be studied satisfactorily by the J integral from the above mesh size.

Depth Sizing of Notch Fatigue Crack Using Diffracted Ultrasonic Wave (회절초음파를 이용한 노치 피로균열의 균열깊이 평가)

  • Jin, Mei-Ling;Lee, Tae-Hun;Park, Byung-Jun;Jhang, Kyung-Young
    • Journal of the Korean Society for Nondestructive Testing
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    • v.29 no.5
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    • pp.405-414
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    • 2009
  • This paper proposed a methodology based on ultrasonic diffraction technique to inspect the depth of a crack initiated from a notch of CT specimen by fatigue test, and its usefulness was verified by experiments. Especially, in order to identify accurately the diffractive waves from the crack tip in the situation where there are extra diffractive elements such as a notch, we have tried imaging by transducer scan and analyzed the propagation path of diffracted wave. Two specimens with and without a crack were experimented. Higher frequency and larger refractive angle of transducer showed a tendency to decrease the error in the measurements, and the measured crack depth showed an error less than 0.38 mm in case of 4 MHz $60^{\circ}-60^{\circ}$. The proposed methodology is applicable to weak diffractive sources, and so that it would be useful to inspect micro cracks and for their depth sizing.

The Effect of Specimen Thickness on the Fatigue Crack Propagation Rate (피로크랙전파율에 대한 시험편 두께의 영향)

  • Koh, Sung-Wi;Um, Yoon-Sung
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.24 no.1
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    • pp.44-49
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    • 1988
  • The paper presents the preliminary results of an esperimental study on crack growth under tension-tension fatigue loading. A purpose of the study is to find the effect of the specimen thickness on crack propagation behaviors. The thickness of the low catbon steel specimens the are used in the experiments are 5, 10, 15,20, and 25 mm. the type of specimen considering in the present study is compact tension specimen.Crack growth behaviors are obseved and measured by travelling microscope. From the study, the followings are found; 1. There is a certain specimen thickness that is the shortest farigue life. The fatigue life of 15mm specimen is the shorter then that of any other opecimen 2. The crack initiation of the thick specimen is slower than that of thin specimen. But the crack propagation rate is just the opposite. 3. The range which is the exponent, m of power law(paris) is 1.98-4.59. the thicker the spec-imen is, the higher the value of m is.

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The Experimental Method of Measuring Q (Q의 실험적 측정법)

  • Kim, Dong-Hak;Lee, Jeong-Hyun;Kang, Ki-Ju
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.285-291
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    • 2003
  • An experimental method to measure Q-parameter in-situ is described. The basic idea comes from the fact that the side necking near a crack tip indicates the loss of stress triaxiality, which can be scaled by Q. From the out-of-plane displacement and the in-plane strain near the surface of side necking, stress field averaged through the thickness is calculated and then Q is determined from the difference between the stress field and the HRR field corresponding to the identical J-integral. To prove the validity, three-dimensional finite element analysis has been performed for a CT configuration with side-groove. Q-value which was calculated directly from the near-tip stress field is compared with that determined by simulating the experimental procedure according to the proposed method, that is, the Q-value determined from the lateral displacement and the inplane strain. Also, the effect of location where the displacement and strain are measured is explored.

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Methods to Evaluate Stress Triaxiality from the Side Necking Near the Crack Tip (균열선단 부근의 측면함몰로부터 응력삼축성의 결정 방법)

  • Kim, Dong-Hak;Kang, Ki-Ju
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.7
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    • pp.1021-1028
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    • 2004
  • Kim et al. suggested an experimental method to determine the Q parameter in situ from the out-of-plane displacement and the in-plane strains on the surface of side necking near the crack tip. In this paper, the procedure to evaluate the stress triaxiality near a crack tip such as the Q parameter is to be polished in the details for simplicity and accuracy. That is, Q and hydrostatic stress are determined only from the out-of-plane displacement, but not using in-plane strain, which is hard to measure. And also, the plastic modulus is determined by an alternative way. Through three-dimensional finite element analyses for a standard CT specimen with 20% side-grooves, the validities of the new procedures are examined in comparison to the old ones. The effect of location where the displacements are measured to determine the stress triaxiality is explored.

Fracture toughnesses of thin sheet materials by using CT specimens (CT 시편을 이용한 박판재료의 파괴인성 특성)

  • Lee, Eok-Seop;Lee, Yun-Pyo;Gang, In-Mo;Kim, Seon-Yong;Kim, Seung-Gwon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.12
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    • pp.2090-2095
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    • 1997
  • The plane stress fracture toughness for thin aluminum alloy(2024-T3 and 7075-T6) specimens are characterized by using compact-tension (CT) specimens. Anti-buckling plates were fabricated on both sides of the thin CT specimens to prevent the buckling phenomena which caused by the 45.deg. C plastic yielding at the crack tip under the plane stress condition. The plane stress fracture toughnesses determined by three different procedures are compared with each others. The plane stress fracture toughnesses are also compared with a few published values which were determined by using center-cracked panel specimens.