• Title/Summary/Keyword: CT Specimen

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Effect of Specimen Orientation on Fatigue Crack Growth Behavior in Friction Stir Welded Al7075-T651 Joints (마찰교반용접된 Al7075-T651 용접부의 피로균열전파 거동에 미치는 시험편 채취방향의 영향)

  • Jeong, Yeui Han;Kim, Seon Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.12
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    • pp.1317-1323
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    • 2014
  • The aim of this paper is to investigate the effects of crack orientation on fatigue crack growth behavior in friction stir welded (FSWed) Al 7075-T651. Fatigue crack growth testing was conducted on compact tension (CT) specimens machined from the friction stir welds and the base metal under constant stress intensity factor range control. Tests were performed with the crack propagating nominally perpendicular to the weld line (termed the TL specimen) and the crack propagating in a parallel direction of the weld line (termed the LT specimen), and with three different constant stress intensity factor ranges. Both these specimen orientations were found to have a considerable effect on the fatigue crack growth behavior. Paris's law was adopted for the analysis of experimental results; the exponent m of the WM-LT specimen was determined to be 3.56, which was the largest value in this experimental conditions.

Creep Crack Propagation Properties of Rotor Steel under Constant Load and Constant Ct Condition (일정하중 및 일정Ct에서 로터강의 크리프 귤열전파 특성)

  • Jeong, Soon-Uk
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.5
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    • pp.105-111
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    • 2001
  • The creep crack growth properties in 3.3NiCrMoV steel were investigated at 55$0^{\circ}C$ by using CT specimen under constant load and constant Ct condition that was held during crack growth of Imm distance. Ct lelied on load line displacement rate, C*usually increased with crack length though load is reduced in order to maintain constant Ct value as crack growth and appeared scatter band. At constant load and Ct region, crack growth slope was 0.900 and 0.844 each, on the other hand C* slope was 0.480. Fully coalesced area(FCA) ahead of crack tip increased as Ct increase to the critical value, and after that value FCA decreased. For the tertiary creep stage of crack growth test, the most of displacement was due to the steady state creep, except only small part due to the primary creep and other effects. Therefore, tests were mainly interrupted in the tertiary stage to obtain high value of Ct.

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Modular Fasciitis Mimicking Malignant Tumor on $^{18}F$-FDG PET/CT ($^{18}F$-FDG PET/CT 영상에서 악성종양으로 오인되었던 결절성 근막염)

  • Lee, Seok-Mo
    • The Korean Journal of Nuclear Medicine
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    • v.39 no.4
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    • pp.263-265
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    • 2005
  • A 25 years old male patient with Hodgkin's disease, considered as complete remission, underwent $^{18}F$-FDG whole body PET/CT. $^{18}F$-FDG whule body PET/CT showed unexpected hypermetabolic nodule in left quadratus femoris muscle suggesting local recurrence. Subsequent MRI also revealed well-enhancing nodular lesion with intermediate and high signal intensity on T1WI and T2WI, respectively. The lesion was confirmed as nodular fasciitis by pathologic examination of the excited specimen.

Esophageal Leiomyoma with intense FDG uptake on $^{18}F-FDG$ PET/CT ($^{18}F-FDG$ PET/CT에서 강한 FDG 섭취를 보인 식도근종)

  • Lee, Seok-Mo;Bae, Sang-Kyun
    • Nuclear Medicine and Molecular Imaging
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    • v.42 no.5
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    • pp.410-413
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    • 2008
  • A 56 years old woman referred to our hospital with dysphagia and epigastric soreness. Gastroendoscopy revealed huge submucosal tumor with ulceration extending from distal esophagus to lesser curvature of stomach. Subsequent computed tomography(CT) demonstrated soft tissue mass encircling distal esophagus, and 18F-FDG PET/CT demonstrated intense $^{18}F-FDG$ accumulation in it. Finally this case was diagnosed as esophageal leiomyoma based on pathologic evaluation of the surgical specimen.

Development and Performance Evaluation of an Ultra-Compact CT with Auto Calibration of Detector Center Axis (검출기 중심축을 자동 보정하는 초소형 CT 개발 및 성능평가)

  • Byeong-Woo Kwak;Keun-Ho Rew
    • Journal of the Korean Society of Radiology
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    • v.17 no.5
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    • pp.651-662
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    • 2023
  • In this study, we designed and fabricated an ultra-compact CT that automatically calibrates the detector's center axis and verified its performance. The three-dimensional reconstruction performance was evaluated using 3D CAD data and X-ray data acquired by manually calibrating the center axis of the CT detector. The results showed that tilting the center axis by more than 0.25° causes circle break phenomenon, which rapidly degrades the quality of the 3D reconstructed image. By applying the automatic calibration device of a detector center axis, the 3D reconstruction performance was enhanced by calibrating the detector center axis to match the specimen rotation axis.

Analysis of the Residual Stress due to Cold Expansion and Stress Intensity Factor in CT Specimen Using Finite Element Method (유한요소법을 이용한 CT 시편의 홀확장 잔류응력 및 응력확대계수 해석)

  • Jang, Jae-Soon;Yang, Won-Ho;Kim, Cheol;Ko, Myung-Hoon;Cho, Myoung-Rae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.5
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    • pp.890-895
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    • 2002
  • Cold expansion method is retarded of crack initiation due to the compressive residual stress developed on the hole surface. Previous research has just been study about residual stress distribution in the hole surrounding. But, The purpose of this study was to improve the understanding of the residual stress effect in hole surrounding as crack growth from another hole. In this paper, it is shown that residual stress is redistributed due to the application of cold expansion process for CT specimen using finite element method. It is further shown that tensile stress increases in proportion to cold expansion ratio in the vicinity of crack. It is thought that stress intensity factor increases with cold expansion ratio.

An Evaluation of Fracture Toughness for SS400 Steel by R-curve and DCPD (R-곡선과 직류전위차(DCPD)에 의한 SS400강의 파괴인성 평가)

  • Jang Seok-Ki;Han Min-Su
    • Journal of Advanced Marine Engineering and Technology
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    • v.29 no.8
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    • pp.855-861
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    • 2005
  • Fracture toughness defined near the initiation of stable crack growth is investigated by R-curve and Direct Current electric Potential Determination(DCPD) under mode I plane strain conditions for CT specimen with 25.4mm thickness of SS400 steel. Fracture toughness. $J_{IC}$lit near crack tip of CT specimen by R-curve is 17.14 $kg_{f}/mm$ and however. its value by DCPD is 22.82 $Rg_{f} mm$ The value of fracture toughness by DCPD is larger than that by R-curve. Therefore, it is suggested that the evaluation of fracture toughness by R-curve is optimum than by DCPD, when considering amount of crack growth about each of fracture toughness.

Influence of Evaluation Methods for Fatigue Crack Growth Process (피로균열 성장과정에 대한 평가방법의 영향)

  • 안철봉
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.8 no.1
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    • pp.119-125
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    • 1999
  • The distribution of fatigue crack growth rate is subjected to the measuring interval and calculated method of growth rate. In this paper, in order to establish the method of determining the distribution of fatigue crack growth rate, which ignores those influences, a series of fatigue crack growth experiments and measuring intervals of crack length calculated reasonable are presented. The main conclusions obtained are summarized as follows: 1) As a result of the ΔP constant test and ΔK constant test, it is thought that an approximate measuring interval of 0.3~0.7mm is reasonable, which allows for few errors and is little subjected to the calculated method of crack growth rate. 2) After generally comparing the error estimation by using the experimental data of CCT specimen with the error rating of the CT specimens, it is possible that the fatigue test has few errors within the measuring interval, ξ(Δa/W)=0.0067~0.017, regardless of the dimension of specimen geometry.

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A Stochastic Study on Fatigue Crack Propagation and Retardation Behavior of Pressure Vessel Steel (압력용기용강의 피로균열전파 및 지연거동에 관한 확률통계적 연구)

  • 김선진;남기우;김부안
    • Journal of Ocean Engineering and Technology
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    • v.9 no.1
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    • pp.132-141
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    • 1995
  • The purpose of the present study is to investigate the statistical characteristics of m and C in the fatigue crack propagation law, da/dN=C(.DELTA.K)/sup m/ and to studies on the randomness of fatigue crack propagation and retardation behavior. Fatigue tests were perfomed on 32 CT specimens of SPV50 steel under the same one condition. First, the value of m and C were determined for each specimen, and all the data were analyzed statistically. second, the material's resistance to fatigue crack propagation is modeled as a stchastic process, which varies randomly along the crack path. The statistical analysis of the material resistance is performed with the data obtained by constant load controlled tests. Finally, retardation behavior was examined experimentally by using a CT specimen, and a retardation parameters were analyzed statistically.

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A method of Determination of Fracture Toughness of Reactor Pressure Vessel Steel by J Integral (J적분을 이용한 원자력 압력용기강의 파괴인성치의 결정)

  • 오세욱;임만배;김진선
    • Journal of Ocean Engineering and Technology
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    • v.9 no.1
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    • pp.111-119
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    • 1995
  • The elastic-plastic fracture toughness($J_{IC}$) and fracture resistance (J-R curve) of SA508-3 alloy steel used for nuclear reactor pressure vessel are investigated by using CT-type specimens. Fracture toughness tests are conducted by unloading compliance method and multiple specimen method at room temperature, -2$0^{\circ}C$ and 20$0^{\circ}C$. The apparent negative crack growth phenomenon which usually arises in partial unloading compliance test is well known. The negative crack growth phenomenon in determining J sub(IC) or J-R cure from partial unloading compliance experiments may be eliminated by the offset technique. In this study, the evaluation of $J_{IC}$ multiple specimen method recommended by the JSME gives the most reliable results by using half-size CT(similar-type) specimens.

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