• Title/Summary/Keyword: CT Specimen

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A Study on the Evaluation of the Pipe Fracture Characteristic (실배관 파괴특성 평가에 관한 연구)

  • Park Jae-Sil;Kim Young-Jin;Seok Chang-Sung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.1 s.232
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    • pp.107-114
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    • 2005
  • In order to analyze the elastic-plastic fracture behavior of a structure, the fracture resistance curve of the material should be known first. The standard CT specimen was used to obtain the fracture resistance curves of a piping system. However, it is known that the fracture resistance curve by the standard CT specimen is very conservative to evaluate the integrity of a structure. Also the fracture resistance curve is effected by the specimen geometry and the dimensions because of the constraint effect. The objective of this paper is to be certain the conservativeness of the fracture resistance curve by the standard CT specimen and to provide an additional safety margin. For these, the fracture tests using a real pipe specimen and the standard CT specimen test were performed. A 4-point bending jig was manufactured for the pipe test and the direct current potential drop method was used to measure the crack extension and the length for the pipe test. Also finite element analyses were performed with a CT specimen and a pipe in order to prove the additional safety margin. From the result of tests and analyses of the pipe and the standard CT specimen, it was observed that the fracture analysis with the standard CT specimen is conservative and the additional safety margin was proved.

A Study on the Evaluation of the Pipe Fracture Characteristic (I) (실배관 파괴특성 평가에 관한 연구 (I))

  • Park, Jae-Sil;Seok, Chang-Sung
    • Proceedings of the KSME Conference
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    • 2001.06a
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    • pp.345-350
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    • 2001
  • In order to perform elastic-plastic fracture mechanical analyses, fracture resistance curves for concerned materials are required. 1T-CT specimen was used to obtain fracture resistance curves. But the fracture resistance curve by the 1T-CT specimen was very conservative to evaluate the integrity of the structure. And fracture resistance curve was affected by the specimen geometry and crack plane orientation. The objective of this paper is to be certain the conservativeness of the fracture resistance curve by the 1T-CT specimen and to provide the additional safety margin. For these, the fracture tests using the real pipe specimen and standard 1T-CT specimen test were performed. 4-point bending jig was manufactured for pipe test and direct current potential drop method was used to measure the crack extension and length for pipe test. From the pipe and the 1T-CT specimen test results, it was observed that the J-integral of the 1T-CT specimen test at the crack initiation point was very small compare to that of the pipe specimen test.

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Estimation of the Fracture Resistance Curve for the Nuclear Piping Using the Standard Compact Tension Specimen (표준 CT시험편을 이용한 실배관 파괴저항 곡선 예측)

  • Park, Hong-Sun;Heo, Yong;Koo, Jae-Mean;Seok, Chang-Sung;Park, Jae-Sil;Cho, Sung-Keun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.33 no.9
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    • pp.930-937
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    • 2009
  • The estimation method of the fracture resistance curve for the pipe specimen was proposed using the load ratio method for the standard specimen. For this, the calculation method of the load - CMOD curve for the pipe specimen with the common format equation(CFE) was proposed by using data of the CT specimen. The proposed method agreed well with experimental data. The J-integral value and the crack extension were calculated from the estimated load - CMOD data. The fracture resistance curve was estimated from the calculated J-integral and the crack extension. From these results, it have been seen that the proposed method is reliable to estimate the J-R curve of the pipe specimen.

Measurement of Deformation field in CT specimen using Laser speckle (레이저 스페클을 이용한 CT 시험편의 변형장 측정)

  • Jean, Moon-Chang;Kang, Ki-Ju
    • Proceedings of the KSME Conference
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    • 2001.11a
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    • pp.192-197
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    • 2001
  • To obtain $A_2$ experimentally in the $J-A_2$ theory, deformation field on the lateral surface of a CT specimen was to be determined using Laser speckle method. The crack growth was measured using direct current potential drop method and most procedure of experimental and data reduction was performed according to ASTM Standard E1737-96. Laser speckle images during crack propagation were monitored by two CCD cameras to cancel the effect of rotation and translation of the specimen. An algorithm to pursue displacement of a point from each image was developed and successfully used to measure $A_2$ continuously as the crack tip was propagated. The effects of specimen thickness on J-R curve and $A_2$ were explored.

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A Study on the Evaluation of Fracture Resistance Characteristics of Large Pipe by using the Curved CT Specimen (대형배관의 Curved CT 시편을 이용한 파괴저항특성평가에 관한 연구)

  • Kim, Ik Hyun;Shin, In Hwan;Park, Kweon Tae;Hong, Suk Woo;Park, Seon Soon;Yoon, Seon Hyun;Koo, Jae Mean;Seok, Chang Sung
    • Journal of the Korean Society for Precision Engineering
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    • v.31 no.7
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    • pp.623-626
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    • 2014
  • The LBB (Leak Before Break) concept is based on evaluating the fracture toughness. NUREG 1061, Vol.3 announced that the specimen for evaluating fracture resistance needs to have same thickness or thicker than pipe. Therefore, it is difficult to collect specimen from pipe which has same thickness as a pipe. So, ASTM standard suggested the use of standard specimen with 1 inch thickness. However, it has been known that an application of LBB by test results of standard specimen is conservative compare with that by real pipe. In this study, to supplement such conservatism, the evaluation of fracture resistance characteristics was performed with curved CT specimen, which has same thickness and curvature as a pipe. In addition, fracture resistance characteristics of curved CT specimen were compared with those of CT specimen. For this, shape factor F, hpl and g were obtained from FEM analysis using the limit load method.

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.

Fracture Study due to Various Core at Compact Tension Specimen Made of Carbon Fiber Reinforced Plastic (탄소성유강화플라스틱으로 만들어진 소형 인장 시험편에서 여러 종류의 심재에 따른 파손 연구)

  • Kim, Jae-Won;Cho, Jae-Ung
    • Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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    • v.8 no.3
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    • pp.589-596
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    • 2018
  • Transportation or structure has the important role at clothing, food, and housing at modern society. If even the small crack happens and propagates at transportation or structure, the parts are fractured and they can cause a disaster. CT specimen was used in order to investigate the damage trend due to the crack propagation at this study to prevent this situation. As the material of CT specimen, the unidirectional carbon fiber reinforced plastic of the composite material in the limelight nowadays. The laminate angle designated in order of [60/-60/60/-60] was applied to the specimen model with the unidirectional fiber. As the analysis condition, the forced displacement was applied to the hole of upper part after fixing the hole of lower part. At the result of this study, the equivalent stress and shear stress was shown to be higher in order of the structural steel, copper, titanium and aluminum. This study result is thought to be utilized usefully at verifying the damage of CT specimen made of inhomogeneous material.

A Study on Accuracy of J-Resistance Curves Measured with Curved Compact Tension Specimen of Zr-2.5Nb Pressure Tube (Zr-2.5Nb 압력관의 휘어진 CT시편으로 측정한 J 저항곡선의 정확도에 관한 연구)

  • Yoon, Kee-Bong;Park, Tae-Gyu;Kim, Young-Suk
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.11
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    • pp.1986-1996
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    • 2003
  • Methodology based on the elastic-plastic fracture mechanics has been widely accepted in predicting the critical crack length(CCL) of pressure tubes of CANDU nuclear plants. A conservative estimate of CCL is obtained by employing the J-resistance curves measured with the specimens satisfying plane strain condition as suggested in the ASTM standard. Due to limited thickness of the pressure tubes the curved compact tension(CT) specimens taken out from tile pressure tube have been used in obtaining J-resistance curves. The curved CT specimen inevitably introduce slant fatigue crack during precracking. Hence, effect of specimen geometry and slant crack on J-resistance curve should be explored. In this study, the difference of J integral values between the standard CT specimens satisfying plane strain condition and the nonstandard curved CT with limited thickness (4.2mm) is estimated using finite element analysis. The fracture resistance curves of Zr-2.5Nb obtained previously by other authors are critically discussed. Various finite element analysis were conducted such as 2D analysis under plane stress and plane strain conditions and 3D analysis for flat CT, curved CT with straight crack and curved CT with slant crack front. J-integral values were determined by local contour integration near the crack tip, which was considered as accurate J-values. J value was also determined from the load versus load line displacement curve and the J estimation equation in the ASTM standard. Discrepancies between the two values were shown and suggestion was made for obtaining accurate J values from the load line displacement curves obtained by the curved CT specimens.

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 Shape Parameter Effect on the J-R Curve of Curved CT Specimen Using Limit Load Method (한계하중법을 이용한 Curved CT 시험편의 파괴저항곡선에 미치는 형상변수 영향 평가)

  • Shin, In Hwan;Park, Chi Yong;Seok, Chang Sung;Koo, Jae Mean
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.7
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    • pp.757-764
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    • 2014
  • In this study, the effect of shape parameters on the J-R curves of curved CT specimens was evaluated using the limit load method. Fracture toughness tests considering the shape factors L/W and $R_m/t$ of the specimens were also performed. Thereafter, the J-R curves of the curved CT specimens were compared using the J-integral equation proposed in the ASTM (American Society for Testing and Materials) and limit load solution. The J-R curves of the curved CT specimens were also compared with those of the CWP (curved wide plate), which is regarded to be similar to real pipe and standard specimens. Finally, the effectiveness of the J-R curve of each curved CT specimen was evaluated. The results of this study can be used for assessing the applicability of curved CT specimens in the accurate evaluation of the fracture toughness of real pipes.