• Title/Summary/Keyword: CT Specimen

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A Study on Fatigue Crack Growth Behavior of Steel Using AE (AE을 이용한 강의 피로균열전파 거동에 관한 연구)

  • Chung, K.Y.;Kim, S.J.;Kim, Y.S.;Oh, M.S.;Kim, Y.D.
    • Journal of Power System Engineering
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    • v.5 no.2
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    • pp.50-56
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    • 2001
  • In this study, the effect of specimen thickness and stress ratio on fatigue crack growth in S45C steel was investigated. Acoustic emission was monitored during the fatigue crack growth test. Both crack closure and AE technique were used in assessing fatigue crack growth behavior. Constant amplitude loading tests were performed on CT type specimen with three different thicknesses and stress ratios. Crack closure was investigated to explain the influence of specimen thickness and stress ratio on the fatigue crack growth in the second growth region. The crack closure effect was decreased with specimen thickness and stress ratio.

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Effect of Specimen Thickness on the Statistical Properties of Fatigue Crack Growth Resistance in BS4360 Steel

  • Kim, Seon-Jin;Itagaki, Hiroshi;Ishizuka, Tetsuo
    • Journal of Mechanical Science and Technology
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    • v.14 no.10
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    • pp.1041-1050
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    • 2000
  • In this paper the effect of specimen thickness on fatigue crack growth with the spatial distribution of material properties is presented. Basically, the material resistance to fatigue crack growth is treated as a spatial stochastic process, which varies randomly on the crack surface. The theoretical autocorrelation functions of fatigue crack growth resistance with specimen thickness are discussed for several correlation lengths. Constant ${\Delta}K$ fatigue crack growth tests were also performed on CT type specimens with three different thicknesses of BS 4360 steel. Applying the proposed stochastic model and statistical analysis procedure, the experimental data were analyzed for different specimen thicknesses for determining the autocorrelation functions and probability distributions of the fatigue crack growth resistance.

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Development and Usefulness of Acrylic Needle for Percutaneous Bone Biopsy (경피적 골생검용 아크릴 바늘의 제작과 유용성)

  • Kim, Tae-Hyung;Shin, Myung-Jin;Shin, Ji-Hoon;Lim, Jin-Oh;Ryu, Ji-Yeon;Oh, Jae-Seon;Woo, Chul-Woong;Nam, Jeung-Hee
    • Journal of radiological science and technology
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    • v.33 no.1
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    • pp.25-29
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    • 2010
  • To evaluate the usefulness of newly designed percutaneous bone biopsy needle for pumpkin's specimen collection. We manufactured three types of biopsy needle with different internal processing which were made of 10 mm-diameter acrylic material. We made the conventional type (Ct) similar to the clinical type then compared the test group. The type a (Ta) made 1 cm-length internal processing from the distal, type b (Tb) made taper, and type c (Tc) made internal processing like spiral configuration. We performed 20 times biopsy to get an 10 mm length specimen from pumpkin's surface and evaluated the success rate of the biopsy, length of the specimen, and determine internal processing type of the most suitable biopsy needle (ANOVA test). Success rates of Ct, Ta, Tb, and Tc were 55%, 80%, 90%, and 100%, respectively. The lengths of the specimen of Ct, Ta, Tb, and Tc were $5.6{\pm}1.1\;mm$, $5.9{\pm}0.87\;mm$, $3.9{\pm}0.77\;mm$, and $9.4{\pm}0.54\;mm$, respectively. All groups were statistically significant (p < 0.05) except the group between Ct and Ta (p = 0.28). Newly designed bone biopsy needle seems to be useful for obtaining enough specimen. Tc may be more effective than other types.

A study on the fracture toughness degradation in cryogenic structural material using single-specimen method (단일 시험편법에 의한 극저온용 구조재료의 파괴인성 저하에 관한 연구)

  • Kwon, Il-hyun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.22 no.2
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    • pp.343-351
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    • 1998
  • This paper was investigated degradation of the fracture toughness caused by sensitizing heat-treatment of the cryogenic structural material JN1 base metal using unloading compliance method reported as useful a method in evaluating the elastic-plastic fracture toughness at cryogenic temperature. The specimens used in this paper were 20% side-grooved 0.5T-CT specimens which were machined in the JN1 base metal. Also, to investigate cryogenic fracture toughness of the fusion line region in the JN1 GTA weldments, it was also used 20% side-grooved 0.5T-CT specimens that was machined fusion line to located in the middle of the specimen. The cryogenic fracture toughness values of the JN1 base metal were significantly decreased with increasing the time and temperature of the heat treatment. The fracture toughness value obtained from the fusion line specimen was invalid, but it was lower value than that of the JN1 base metal. Especially, this value was approximately equal with that obtained from the JN1 650.deg. C-5h heat-treated material.

Variation of the Fracture Resistance Curve with the Change of a Size in the CT Specimen (CT시험편의 크기 변화에 따른 파괴저항곡선의 변화)

  • Seok, Chang-Seong;Kim, Su-Yong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.12
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    • pp.2963-2971
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    • 2000
  • In order to obtain more realistic fracture resistance curve, research is currently underway to introduce new parameter and to quantify the constraint effect. The objective of this study is to investigate the relationship between the constraint effect of a size(plane size and thickness) and the fracture resistance curve. In this paper fracture toughness tests were performed with various plane size and various thickness of specimens in two materials. The test results showed that the effects of plane size in th4 J-R curve were significant and the curve was risen with an increase in plane size. However, relatively weak influence was observed form the change of the specimen thickness and size. The stress fields near the crack tip of th specimen is close to the HRR field according to increasing the plane size and Q stress appears different value according to material properties and the plane size.

X-ray Computed Tomography on Larger Diameter Timber than Digital Detector

  • Kim, Chul-Ki;Lee, Jun-Jae;Oh, Jung-Kwon
    • Journal of the Korean Wood Science and Technology
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    • v.41 no.5
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    • pp.385-391
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    • 2013
  • X-ray computed tomography is a very powerful nondestructive technique in safety inspection of historic timber building. But, in field, various testing condition makes it difficult to carry out X-ray CT testing. Limited size in X-ray digital detector is one of the problems. In this study, a pitch pine disk with two holes was used to know how imperfection in X-ray projection affects CT image resolution. Using various number of projections, CT image was reconstructed by filtered back projection method, and then it was investigated how many projection is required to identify the holes in different location. Two artificial holes could be differently detected according to their location in cross section of specimen. One hole in center part of specimen was identified using more than 9 radiographs, but the other one which located in outer part of cross section could not be detected until more than 36 projections were used. Even though there is data missing in outer part of cross section due to limited size of detector, the center part of CT image could be reconstructed well and the resolution of outer part became higher with increase of the number of projections. For field application, the number of projections for CT image reconstruction needs to be decided with consideration of another nondestructive testing and the location of interest.

A Study on Tensile Property due to Stacking Structure by Fiber Design of CT Specimen Composed of CFRP (CFRP로 구성된 CT시험편의 섬유설계에 의한 적층구조에 따른 인장 특성 연구)

  • Hwang, Gue-Wan;Cho, Jae-Ung
    • Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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    • v.7 no.11
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    • pp.447-455
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    • 2017
  • At the modern industry, the composite material has been widely used. Particularly, the material of carbon fiber reinforced plastic hardened with resin on the basis of fiber is excellent. As the specific strength and rigidity are also superior, it receives attention as the light material. Among these materials, the carbon fiber reinforced plastic using carbon fiber has the superior mechanical property different from another fiber. So, it is utilized in vehicle and airplane at which high strength and light weight are needed at the same time. In this paper, the tensile property due to the fiber design is investigated through the analysis study with CT specimen composed of carbon plastic reinforced plastic. At the stress analysis of CFRP composite material with hole, the fracture trend at the tensile environment is examined. Also, it is shown that the lowest stress value happens and the deformation energy of the pre-crack becomes lowest at the analysis model composed of the stacking angle of 60° through the result due to the stacking angle. On the basis of this study result, it is thought to apply the foundation data to anticipate the fracture configuration at the structure applied with the practical experiment.

3D Analysis of Crack Growth in Metal Using Tension Tests and XFEM (인장 실험과 XFEM을 이용한 금속 균열 성장의 3 차원적 분석)

  • Lee, Sunghyun;Jeon, Insu
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.4
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    • pp.409-417
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    • 2014
  • To prevent the occurrence of fractures in metal structures, it is very important to evaluate the 3D crack growth process in those structures and any related parts. In this study, tension tests and two simulations, namely, Simulation-I and Simulation-II, were performed using XFEM to evaluate crack growth in three dimensions. In the tension test, Mode I crack growth was observed for a notched metal specimen. In Simulation-I, a 3D reconstructed model of the specimen was created using CT images of the specimen. Using this model, an FE model was constructed, and crack growth was simulated using XFEM. In Simulation-II, an ideal notch FE model of the same geometric size as the actual specimen was created and then used for simulation. Obtained crack growth simulation results were then compared. Crack growth in the metal specimen was evaluated in three dimensions. It was shown that modeling the real shape of a structure with a crack may be essential for accurately evaluating 3D crack growth.

The Thickness Effect on the Determination of Fracture Toughness Jic (파괴인성치 Jic 결정에 대한 시험편 두께의 영향에 관한 연구)

  • 고성위
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.24 no.2
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    • pp.83-93
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    • 1988
  • Recent Experimental results show that the J integral can be effectively used to obtain a valid parameter for predicting plane strain and plane stress fracture. However, only a few research results have been reported for the effect of thickness where the plane strain state can not be assumed. A purpose of this study is to find the behavior of fracture touhness and tearing modulus varing the specimen thickness. The type of specimen in the present study is compact tension (CT). The thicknesses of the low carbon steel specimens that are used in the experiments are 5, 10, 15, 20 and 25mm. The measurement of crack length is taken by optical measurements method. From the study, the followings are found; 1) The fracture toughness and the tearing modulus which are obtained by using Yoon's and Simpson's formula show more conservative than that by using Rice's and Merkel's. 2) The fracture toughness is increase in specimen thickness which is reached 15mm. Beyond this thickness the fracture toughness is decreased in specimen thickness. 3) In the case of CT specimen with the thickness ranging from 5 to 25mm, the tearing modulus which is applied the same J integral equation is almost constant. 4) By using Yoon's formula, the correlation of the plane slress fracture toughness J sub(C) with specimen thickness B is expressed as the following formula. J sub(C)/J sub(IC)=1.7-15.1(B/W)+112.9(B/W) super(2) -301.3(B/W) super(3) +260.6(B/W) super(4)

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CT Image Reconstruction of Wood Using Ultrasound Velocities I - Effects of Reconstruction Algorithms and Wood Characteristics -

  • Kim, Kwang-Mo;Lee, Jun-Jae
    • Journal of the Korean Wood Science and Technology
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    • v.33 no.5 s.133
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    • pp.21-28
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    • 2005
  • For the proper conservation of wooden cultural properties, non-destructive evaluation (NDE) method, which can be used to quantitatively evaluate the internal state of wood members, are needed. In this study, an ultrasonic CT system composed of portable devices was attempted, and the capacity of this system was verified by reconstructing the CT images for two phantoms and two artificially defected specimens. Results from this study showed that the sizes of detected defects were enlarged and the shapes were distorted on the CT images. Also, the positions were shifted somewhat toward the surface of specimen, which is regarded due to the anisotropic property of wood. Compared to the filtered back-projection method, SIRT (simultaneous iterative reconstruction technique) method was determined to be more efficient as the algorithm of image reconstruction for wood. A new ultrasonic CT system is thought to be used as a NDE method for wood. However wood characteristics and wave diffraction within wood made it difficult to accurately evaluate the size, shape and position of defects. To improve the quality of CT image of wood, more research including the relationship between wood and ultrasound is needed, and wood properties should be taken into consideration on the image reconstruction algorithm.