• Title/Summary/Keyword: 인공결함

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The Effect of Defect Location Near a Circular Hole Notch on the Relationship Between Crack Growth Rate (da/dN) and Stress Intensity Factor Range (δK) - Comparative Studies of Fatigue Behavior in the Case of Monolithic Al Alloy vs. Al/GFRP Laminate - (원공노치 인근에 발생한 결함의 위치변화가 균열성장률(da/dN) 및 응력확대계수범위(δK)의 관계에 미치는 영향 - 단일재 알루미늄과 Al/GFRP 적층재의 피로거동 비교 -)

  • Kim, Cheol-Woong;Ko, Young-Ho;Lee, Gun-Bok
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.3 s.258
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    • pp.344-354
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    • 2007
  • The objective of this study is to investigate the effect of arbitrarily located defect around the circular hole in the aircraft structural material such as Al/GFRP laminates and monolithic Al alloy sheet under cyclic bending moment. The fatigue behavior of these materials may be different due to the defect location. Material flaws in the from of pre-existing defects can severely affect the fatigue crack initiation and propagation behavior. The aim of this study is to evaluate effects of relative location of defects around the circular hole in monolithic Al alloy and Al/GFRP laminates under cyclic bending moment. The fatigue behavior i.e., the stress concentration factor($K_t$), the crack initiation life($N_i$), the relationship between crack length(a) and cycles(N), the relationship between crack growth rate(da/dN) and stress intensity factor range(${\Dalta}K$) near a circular hole are considered. Especially, the defects location at ${\theta}_1=0^{\circ}\;and\;{\theta}_2=30^{\circ}$ was strongly effective in stress concentration factor($K_t$) and crack initiation life($N_i$). The test results indicated the features of different fatigue crack propagation behavior and the different growing delamination shape according to each location of defect around the circular hole in Al/GFRP laminates.

Evaluation of Weld Defects in Stainless Steel 316L Pipe Using Guided Wave (스테인레스 316L강의 배관용접결함에 대한 유도초음파 특성 평가)

  • Lee, Jin-Kyung;Lee, Joon-Hyun
    • Journal of the Korean Society for Nondestructive Testing
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    • v.35 no.1
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    • pp.46-51
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    • 2015
  • Stainless steel is a popular structural materials for liquid-hydrogen storage containers and piping components for transporting high-temperature fluids because of its superior material properties such as high strength and high corrosion resistance at elevated temperatures. In general, tungsten inert gas (TIG) arc welding is used for bonding stainless steel. However, it is often reported that the thermal fatigue cracks or initial defects in stainless steel after welding decreases the reliability of the material. The objective of this paper is to clarify the characteristics of ultrasonic guided wave propagation in relation to a change in the initial crack length in the welding zone of stainless steel. For this purpose, three specimens with different artificial defects of 5 mm, 10 mm, and 20 mm in stainless steel welds were prepared. By considering the thickness of s stainless steel pipe, special attention was given to both the L(0,1) mode and L(0,2) mode in this study. It was clearly found that the L(0,2) mode was more sensitive to defects than the L(0,1) mode. Based on the results of the L(0,1) and L(0,2) mode analyses, the magnitude ratio of the two modes was more effective than studying each mode when evaluating defects near the welded zone of stainless steel because of its linear relationship with the length of the artificial defect.

Fault Diagnosis of a Rotating Blade using HMM/ANN Hybrid Model (HMM/ANN복합 모델을 이용한 회전 블레이드의 결함 진단)

  • Kim, Jong Su;Yoo, Hong Hee
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.23 no.9
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    • pp.814-822
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    • 2013
  • For the fault diagnosis of a mechanical system, pattern recognition methods have being used frequently in recent research. Hidden Markov model(HMM) and artificial neural network(ANN) are typical examples of pattern recognition methods employed for the fault diagnosis of a mechanical system. In this paper, a hybrid method that combines HMM and ANN for the fault diagnosis of a mechanical system is introduced. A rotating blade which is used for a wind turbine is employed for the fault diagnosis. Using the HMM/ANN hybrid model along with the numerical model of the rotating blade, the location and depth of a crack as well as its presence are identified. Also the effect of signal to noise ratio, crack location and crack size on the success rate of the identification is investigated.

Evaluation of the Fatigue Behavior before and after Wall Thickness Penetration in Carbon Steel Pipes with Circumferential Part Through-Wall Surface Crack (원주방향 미관통 표면결함을 가지는 탄소강 배관의 두께관 통전.후의 피로거동 평가)

  • Seok-Hwan AHN
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.36 no.2
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    • pp.147-154
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    • 2000
  • 실온 대기 중에서 탄소강배관(STS370)의 피로시험을 행하였다. 배관에는 외부결함을 인공적으로 상정하여, 피로균열진전 및 관통의 거동, 균열형상, 누설 및 파단수명, 균열개구변위를 실험과 이론의 양면으로부터 비교·검토하였다. 특히, 배관의 벽두께 관통후에 있어서의 응력확대계수를 평가하기 위하여 새로운 식을 제안하였다. 피로균열이 관벽을 관통하기 전에 있어서는 판모델에 의한 Newman-Raju의 응력확대계수 평가식을 이용하므로서 aspect비와 누설수명 등 관통전의 피로균열성장거동을 평가할 수 있음을 나타내었다. 또한, 피로균열이 관벽을 관통한 후에 있어서는 본 논문에서 제안한 배관모델에 의한 응력확대계수의 평가식을 이용하여 관통후의 균열형상, 파단수명 및 균열개구변위 등 관통후의 피로균열성장거동을 평가하였다.

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Propagation Characteristic of Ultrasonic on Slit Defect in Butt Joint (맞대기 용접부내의 인공 결함에서 초음파의 전파특성)

  • 남영현
    • Journal of Welding and Joining
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    • v.14 no.6
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    • pp.37-47
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    • 1996
  • An ultrasonic testing uses the directivity of the ultrasonic wave which propagates in one direction. The directivity is expressed as the relationship between the propagate direction and its sound pressure. The directivity of ultrasonic wave is related to determination of testing sensitivity, scanning pitch and defect location. This paper investigated the directivity of ultrasonic wave, which scattered from slit defect located in heat-affected zone (HAZ) in butt joint using visualization method. The directivity of shear waves scattered from slit defect were different according to probe direction (far defect, near defect) and probe position (forward movement, maximum echo position, backward movement). The difference of directivity of reflection wave was existed between 2 MHz and 4 MHz angle probes. In the case of 2 MHz angle probe, the directivity of reflection wave was appeared sharp form because of the relation wave length and defect size.

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Design of 1D-Magnetophotonic Crystal (1차원 자성 포토닉 결정의 설계)

  • 박재혁;이종백;조재경
    • Proceedings of the Optical Society of Korea Conference
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    • 2000.08a
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    • pp.180-181
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    • 2000
  • 포토닉 결정이란 굴절률(또는 유전률)이 다른 물질들을 빛의 파장 정도의 크기로 주기적으로 배열한 인공적인 결정이다. 포토닉 결정은 1989년 Yabnolovitch에 의해 제안되어, 새로운 광 매체로서의 가능성을 열었다. 1차원 자성 포토닉 결정이란 1차원 포토닉 결정 내에 결함층으로 자성층을 삽입한 것을 말한다. 1996년 Inoue 등에 의해 제안된 1차원 자성 포토닉 결정은 결함층으로 삽입된 자성층에 빛이 국재화되어 거대한 자기광학효과를 나타낸다는 점에서 주목을 받고 있다$^{(1)}$ . 본 논문에서는 1 차원 자성 포토닉 결정과 포토닉 결정과의 차이점 및 1 차원 자성 포토닉 결정의 설계와 그에 따른 특성에 대하여 논하고자 한다 (중략)

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A Study on Growth of Citrine (황수정 육성에 관한 연구)

  • 박로학;유영문
    • Korean Journal of Crystallography
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    • v.1 no.1
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    • pp.8-13
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    • 1990
  • Synthetic citrines were grown by hydrothermal method. For the establishment of grown conditions of large citrine, various types and/or amount of nutrients, seed orientations, mineralizers, colorants and temperature gradients were studied. For the evaluation of the quality of as grown citrine, color tone, crystal form, macro-and micro-defects were observed and crystal structure and absorption spectrums were analyzed. As a result, large sized citrines of 205mm L x 58mm W x 35mm T with excellent color tone and minium defects were grown.

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Detectability of Pore Defect in Wind Turbine Blade Composites Using Image Correlation Technique (이미지 상관 기법을 이용한 풍력 발전 블레이드용 복합재료의 기공 결함 검출능)

  • Kim, Jong Il;Huh, Yong Hak;Lee, Gun Chang
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.37 no.10
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    • pp.1201-1206
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    • 2013
  • Defects that occur during the manufacturing process or operation of a wind turbine blade have a great influence on its life and safety. Typically, defects such as delamination, pore, wrinkle and matrix crack are found in a blade. In this study, the detectability of the pores, a type of defect that frequently occur during manufacturing, was examined from the full field strain distribution determined with the image correlation technique. Pore defects were artificially introduced in four-ply laminated GFRP composites with $0^{\circ}/{\pm}45^{\circ}$ fiber direction. The artificial pores were introduced in consideration of their size and location. Three different-sized pores with diameter of 1, 2 and 3 mm were located on the top and bottom surface and embedded. By applying static loads of 0-200 MPa, the strain distributions over the specimen with the pore defects were determined using image correlation technique. It was found the pores with diameter exceeding 2 mm can be detected in diameter.

A study on the Change of Uniaxial Compressive Strength and Young's Modulus According to the Specimen Size of Intact Material (무결함 재료의 크기에 따른 강도와 탄성계수의 변화에 관한 연구)

  • Lee, Seung-Woo;Song, Jae-Joon
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.8 no.3
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    • pp.205-217
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    • 2006
  • Rock and discontinuities are main factors consisting of a rock mass and the physical properties of each factor have direct effects on the mechanical stability of artificial structures in the rock mass. Because physical properties of the rock and discontinuities change a lot according to the size of test materials, a close attention is needed when the physical properties, obtained from laboratory tests, are used for the design of field structures. In this study, change of physical properties of intact materials due to the change of their size are studied. Six kinds of artificial materials including crystal, instead of an intact rock, are adopted for the study to guarantee the homogeneity of specimen materials even with relatively large size. Uniaxial strength and Young's modulus of each artificial material are checked out for a size effect and compared with the predicted values by Buckingham's theorem - dimensional analysis. A numerical analysis using PFC (Particle Flow Code) is also applied and primary factors influencing on the size effect are investigated.

Development of an EMAT System for Detecting flaws in Pipeline (배관결함 검출을 위한 EMAT 시스템 개발)

  • Ahn, Bong-Young;Kim, Young-Joo;Kim, Young-Gil;Lee, Seung-Seok
    • Journal of the Korean Society for Nondestructive Testing
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    • v.24 no.1
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    • pp.15-21
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    • 2004
  • It is possible to detect flaws in pipelines without interruption using all EMAT transducer because it is a non-contact transducer which can transmit ultrasonic waves into specimens without couplant. And it ran easily generate guided waves desired in each specific problem by altering the design of coil and magnet. In the present work, EMAT systems have been fabricated to generate surface waves, and selectively the plate wave of $A_1\;or\;S_1$ mode. The surface wave of 1.5MHz showed a good signal-to-noise ratio without distortion in its propagation along a pipeline, while the $S_1$ mode of 800kHz and the $A_1$ mode of 940kHz were distorted according to their dispersive properties. The wider the excitation pulse becomes, the better the mode selectivity of the plate waves becomes. A pipe of 256mm inner diameter and 5.5m thickness with 5 flaws was used for comparing the flaw detectability among the modes under consideration.