• Title, Summary, Keyword: 파괴저항곡선

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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.

원자력 배관용 스테인레스강의 파괴저항곡선 예측

  • 장윤석;석창성;김영진
    • Proceedings of the Korean Nuclear Society Conference
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    • pp.796-802
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    • 1995
  • 본 연구의 목적은 원자력 배관용 스테인레스강의 J-R곡선을 예측하기 위한 2가지 방법 올 제시하는 것이다. 첫 번째 방법에서는 균열길이/시편폭 비를 변수로 한 탄소성 유한요소해석을 수행하여 파괴변형률에 근거한 P-$\delta$곡선을 얻고, 이 결과로부터 일반궤적법을 응용하여 J-R곡선을 구하였다. 두 번째 방법에서는 $\sigma$-$\varepsilon$곡선과 J-R곡선의 상관관계를 통계처리하여 응력-변형률시험결과로부터 J-R곡선을 예측할 수 있는 실험식을 제시하였다. 본 연구에서 제시한 방법들을 이용하여 구한 예측결과는 실험결과와 대체로 잘 일치하였다.

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Resistance Curves of Concrete CLWL-DCB Specimens (콘크리트 CLWL-DCB 시험편의 저항곡선)

  • 연정흠
    • Journal of the Korea Concrete Institute
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    • v.14 no.3
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    • pp.357-364
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    • 2002
  • The resistance curves (R-curves) for 381 m crack extension of CLWL-DCB specimens had been determined. The average velocities of the crack extension measured with strain gages were 0.70 and 55 ㎜/sec. The measured rotation angle of the notch faces showed the existence of the singularity at least before 171 and 93 mm crack extensions for the 0.70 and 55 ㎜/sec crack velocities, respectively. The maximum slopes of the R-curves occurred between 25 and 89 ㎜ crack extensions for 0.70 ㎜/sec crack velocity and between 51 and 127 ㎜ crack extensions for 55 ㎜/sec crack velocity During the maximum slopes of the R-curves, the micro-crack localization can be expected, and faster crack velocity may form longer micro-cracking and micro-crack localizing zones. The fracture resistance of 0.70 ㎜/sec crack velocity reached a roughly constant maximum value of 143 N/m at 152 ㎜ crack extension, while that of 55 ㎜/sec crack velocity increased continuously to 245 N/m at 254 ㎜ crack extension and then decreased to the value of 0.70 ㎜/sec crack velocity. The R-curve of 55 ㎜/sec crack velocity was similar to that of the small size three-point bend test, and it showed that small size specimen or fast crack velocity could cause more brittle behavior.

A study on the Relations Between Fracture Strain and Fracture Resistance Curve of nuclear Pressure Vessel Steel (압력용기강의 파괴저항곡선의 파괴변형률에 관한 연구)

  • 임만배
    • Journal of Ocean Engineering and Technology
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    • v.14 no.1
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    • pp.44-51
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    • 2000
  • Safety and integrity are required for reactor pressure vessels because they are operated in high temperature. There are single specimen method multiple specimen method and load ratio analysis method which used as evaluation of safety and integrity for reactor pressure vessels. In this study the fracture resistance curve(J-R curve) elastic-plastic fracture toughness($J_{IC}$) and material tearing modulus ($T_{mat}$) of SA 508 class 3 alloy steel used as reactor pressure vessel steel are measured and evaluated at room temperature 20$0^{\circ}C$ and 30$0^{\circ}C$ according to unloading compliance method and load ration analysis method. And then the comparison with experimental $J_{IC}$ and theoretical$J_{IC}$ by local fracture strain is managed.

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Prediction of Fracture Resistance Curves for Nuclear Piping Materials (원자력 배관재료의 파괴저항곡선 예측)

  • 장윤석;석창성;김영진
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.4
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    • pp.1051-1061
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    • 1995
  • In order perform leak-before-break design of nuclear piping systems and integrity evaluation of reactor vessels, full stress-strain (.sigma. - .epsilon.) curves and fracture resistance (J-R) curves are required. However it is time-consuming and expensive to obtain J-R curves experimentally. The objective of this paper is to develop two methods for J-R curve prediction. In the first method, elastic-plastic finite element analyses for a series of crack length / specimen width ratio were performed. Accordingly the load versus load line displacement (P .delta.) curve corresponding to the fracture strain is obtained and the J-R curve based on the generalized locus method is obtained. In the second method, the correlation between .sigma.-.epsilon. curves and J-R curves was statistically analyzed and an empirical equation to predict the J-R curve from the .sigma.-.epsilon. test result is proposed. A good correlation between the predicted results based on the proposed methods and the experimental ones is obtained.

Analyses of the Decrease Phenomenon of Fracture Resistance Curve Under Tension-Compression Loading (인장-압축하중 하의 파괴저항곡선의 감소현상 해석)

  • Yun, Byeong-Gon;Seok, Chang-Seong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.2
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    • pp.378-385
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    • 2000
  • Fracture resistance (J-R) curves, which are used for elastic-plastic fracture mechanics analyses, decreased under tension-compression loading condition. This phenomenon was proved by several former researches, but the causes have not been clear yet. The objective of this paper is to investigate the cause of this phenomenon. On the basis of fracture resistance curve test results, strain hardening hypothesis, stress redistribution hypothesis and crack opening hypothesis were built. In this study, hardness tests, Automated Ball Indentation(ABI) tests, theoretical stress field analyses, and crack opening analyses were performed to prove the hypotheses. From this study, strain-hardening of material, generation of tensile residual stress at crack tip, and crack opening effects are proved as the causes of the decrease hypothesis.

J-R Curve Characterization by Load Ratio Analysis and Unloading Compliance Method for SA508 C-3 steel (SA508-3재의 제하컴플라이언스법과 하중비해석을 이용한 파괴저항곡선 평가)

  • 임만배;차귀준;윤한기;안원기
    • Journal of Ocean Engineering and Technology
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    • v.12 no.1
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    • pp.65-75
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    • 1998
  • The fracture resistance curve is one of most important and design techniques employed in nuclear pressure vessel structures. This study is to evaluate the J-R curve characteristics for the SA508C-3 by the unloading compliance method and load rato analysis. The effect of strain aging for the exponential correlation of the J-R curve in this metal are investigated at room temperature, 20$0^{\circ}C$ and 30$0^{\circ}C$. The load ratio analysis method can evaluate the J-R curve by using the simple tension load-displacement curve only without the repeat of the unloading and loading. Therefore, the analysis by the proposed load ratio method has a merit, in comparison with the unloading compliance method, which can measure the crack length without the precision measurement equipment.

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A Study on Fatigue Crack Growth Behavior and R-Curve Characteristics of Gas Piping Material (가스배관재의 피로균열진전거동과 파괴저항특성곡선에 관한 연구)

  • Son, J.D.;Lim, M.B.
    • Journal of the Korea Society For Power System Engineering
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    • v.11 no.1
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    • pp.127-133
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    • 2007
  • SG-365 steel is an important material and used for manufacturing a pressure vessel which the gas piping. In this investigation, the elastic plastic fracture toughness of this material is evaluated by the unloading compliance method according to the ASTM E813-97 and E1152-97 method on the smooth and side groove 1CT specimens. The effect of smooth and side groove is studied on the elastic plastic fracture toughness. The side grooved specimen is very useful in estimation of the $J_{IC}$. It is much easier than the smooth specimen to the onset of the ductile tearing by the R curve method. Besides, it improves the accuracy of toughness values, decreases a phenomenon of the tunneling and shear lip by the side groove.

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Resistance Curves of Propagating Cracks for Concrete Three-Point Bend Specimens (콘크리트 삼점 휨시험편의 성장하는 균열에 대한 저항곡선)

  • 연정흠
    • Journal of the Korea Concrete Institute
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    • v.13 no.6
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    • pp.568-574
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    • 2001
  • From measured responses of concrete three-point bend tests, the average values of the responses have been calculated. The fracture behavior of continuously propagating concrete crack has been analyzed from the average responses. The experimental parameters of this study were the initial notch sizes of 25.4㎜ and 6.4 ㎜ and the processing times of 2,000 sec. and 20 sec . The different notch sizes were used for the effects of the size of fracture process zone and specimen geometry, and the processing times for those of initial creep. However the load-point displacement rate in this study did not affect the experimental responses seriously. The average loads were calculated from the average external work of a series of tests, and average crack lengths were determined by using strain gages. Before the peak load, the resistance curve could be determined from the size of fracture process zone, but unstable crack propagation of 88㎜ occurred at the load-point displacement of 0.088∼0.154㎜ after the peak load. The average fracture energy density G$\_$F/$\^$ave/ = 115 N/m occurred during the unstable crack propagation. The fracture process zones were fully developed at the crack length of 111㎜, and the sizes of fracture process zone for initial notches of 25.4㎜ and 6.4㎜ were 86㎜ and 105㎜, respectively. Average fracture energy densities of the resistance curves after full development of fracture process zone were 229 N/m for the initial notch of 25.4㎜ and 284 N/m for 6.4㎜. The values were more than twice of G$\_$F/$\^$ave/.

Variation of the fracture resistance curve with the change of a size in the specimen of reduced activation ferritic steel (JLF-1) (저방사화 철강재 (JLF-1)의 시험편 크기 변화에 따른 파괴저항곡선의 변화)

  • Kim, D.H.;Yoon, H.K.;Lee, S.P.;Kohyama, A.
    • Proceedings of the KSME Conference
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    • pp.1240-1245
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    • 2003
  • Reduced activation ferritic steel (JLF-1) is considered as a promising candidate material for blanket or first-wall structure of D-T fusion reactors. The fracture tests of fracture resistance curve (J-R curve) and $J_{IC}$ are desirable to investigate the exact fracture toughness of JLF-1 steel, since it has a high ductility. The fracture toughness of JLF-1 steel is affected by the configuration of test specimen such side groove, specimen thickness or specimen size. In this study, the fracture toughness tests were performed with various size(plane size and thickness) and various side groove of specimens. The test results showed the standard specimen with the side groove of 40 % represented a valid fracture toughness. The fracture resistance curve increased with increasing plane size and decreased with increasing thickness. However, the fracture resistance curve of half size specimen was similar to that of the standard specimen.

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