• 대한기계학회논문집A
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• 제38권7호
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• pp.757-764
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• 2014

본 연구에서는 한계하중법을 이용하여 Curved CT 시험편의 J-적분에 미치는 형상변수 영향을 평가하였다. 주요 형상변수인 시험편의 길이와 폭의 비(L/W), 평균곡률반경과 두께의 비($R_m/t$)에 대한 파괴인성시험 후, ASTM 시험법에서 제시한 표준시험편의 J-적분과 한계하중법으로 구한 J-적분을 각각 적용하여 구한 파괴저항곡선을 평가하였다. 또한 배관의 파괴저항곡선을 잘 모사한다고 알려진 휨 광폭평판(CWP) 및 표준시험편의 파괴저항곡선과 비교 고찰하여 최종적으로 Curved CT 시험편의 파괴저항곡선에 대한 유효성을 평가하였다. 본 논문의 결과는 향후 실배관의 정확한 파괴인성을 평가하는 데 있어 Curved CT 시험편의 적용가능성을 평가하는 데에 활용할 수 있다.

• 대한기계학회논문집A
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• 제27권11호
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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.

• 한국정밀공학회지
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• 제31권7호
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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.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2009년도 추계학술대회 논문집
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• pp.475-476
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• 2009

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2010년도 춘계학술대회 논문집
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• pp.1175-1176
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• 2010

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 춘계학술대회 논문집
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• pp.967-968
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• 2012

• 대한기계학회논문집A
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• 제29권8호
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• pp.1118-1122
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• 2005

The direct current potential drop (DCPD) method and the unloading compliance (UC) method with a crack opening displacement gauge were applied simultaneously to the Zr-2.5Nb curved compact tension (CCT) specimens to determine which of the two methods can precisely determine the crack initiation point and hence the crack length for evaluation of their fracture toughness. The DCPD method detected the crack initiation at a smaller load-line displacement compared to the UC method. As a verification, a direct observation of the fracture surfaces on the curved compact tension specimens was made on the CCT specimens experiencing either 0.8 to 1.0 mm load line displacement or various loads from $50\%\;to\;80\%$ of the maximum peak load, or $P_{max}$. The DCPD method is concluded to be more precise in determining the crack initiation and fracture toughness, J in Zr-2.5Nb CCT specimens than the UC method.