• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.7
• /
• pp.757-764
• /
• 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.

• Electronics and Telecommunications Trends
• /
• v.8 no.4
• /
• pp.111-129
• /
• 1993

본 고에서는 가입자 통신 선로의 평형화의 필요성을 선로에 유기되는 유도 잡음과 관련하여 서술하였다. 또한, 세계 각국의 표준기관에서 권고하고 있는 평형도 관련 측정 파라미터와 그 측정법을 조사 분석하였다. 또한 포설된 가입자 선로의 평형도 평가법을 제시하였으며, 현장측정을 통해 본 방법의 타당성을 입증하였다. 본 고에서는 제시된 가입자 선로의 평형도 평가법은 우리나라 기술기준의 일환인 회선 평형도의 평가법으로 적용 가능할 것으로 기대된다.

• Electronics and Telecommunications Trends
• /
• v.11 no.3 s.41
• /
• pp.21-30
• /
• 1996

본 고에서는 최근 비약적으로 발전하고 있는 멀티미디어 서비스의 품질설계와 품질관리에 기초자료로서 활용할 주관 품질평가법의 필요성과 목적을 알아보고, ITU-T Study Group 12 Question 22/12(Audiovisual Quality in Multimedia Services) 에서 추진하고 있는 멀티미디어 서비스의 주관 품질평가법 권고화 동향중, AV 통신에 대한 양방향 주관 품질평가법에 관한 권고(Draft Rec. P.920)를 분석하였다.

• Computational Structural Engineering
• /
• v.24 no.3
• /
• pp.8-18
• /
• 2011

• Proceedings of the Korean Nuclear Society Conference
• /
• 1998.05b
• /
• pp.344-349
• /
• 1998

고리 1호기 원전의 원자로냉각재 배관의 파단전누설개념 적용성을 평가하기 위하여 일반적인 파단전누설 절차 및 기준을 검토하였다. 파단전누설 타당성을 검토하기 위하여는 한계하중방법 및 J-T 방법을 비교검토 하였다. 그리고 원자로냉각재 배관에 대해서는 탄소강일 경우와 스테인레스강에 대하여 분석하였고, 가압기 밀림관에 대해서는 열응력을 계산하였다. 그리고 원자로 냉각재 배관에 가상의 관통균열의 파괴안전성은 유한요소법을 이용한 탄소성파괴역학을 통하여 분석하였다. 분석결과 한계하중법과 J-T 방법 모두 스테인레스강과 탄소강재질에 대해 적용 가능한 것으로 나타났다.

• Journal of the Korean Institute of Gas
• /
• v.15 no.4
• /
• pp.21-26
• /
• 2011

Type-3 cylinder liner has a limitation of machining the standard specimen for fracture toughness test because it has approximately 5 mm in thickness as well as a curvature. Hence, it needs to be employed a miniature specimen test technique to evaluate fracture toughness of the cylinder liner. In this study, small punch (SP) test method was employed to evaluate fracture toughness of the cylinder liner. Load-displacement curve result measured from the SP test showed that the liner material was failed during membrane stretching in the general SP load-displacement curve. Additionally, it was shown that liner material was isotropic although the amount of plastic deformation was different depending on the direction due to manufacturing process characteristics. Fracture toughness, $J_{Ic}$, was evaluated using the SP test data. The value of fracture toughness obtained was $13.0kJ/m^2$. This value was similar to that of the same kind of materials. Therefore, the fracture toughness evaluated using the SP test data was reasonable.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.33 no.11
• /
• pp.1187-1194
• /
• 2009

During the last decade, possibility of flaw occurrences has been rapidly increased world-widely as the increase of operating times of petro-chemical facilities. For instance, from a recent in-service inspection, three different sized surface cracks were detected in welding parts of a spherical oxygen holder in Korea. While API579 code provides corresponding engineering assessment procedures to determine crack driving forces, in the present work, numerical analyses are carried out for the cracked oxygen holder to investigate effects of complex geometry, analysis model and residual stress. With regard to the detailed finite element analysis, stress intensity factors are determined from both the full three-dimensional model and equivalent plate model. Also, as an alternative, stress intensity factors are calculated for equivalent plate model by employing the noted influence stress function technique. Finally, parametric structural integrity evaluation of the cracked oxygen holder is conducted in use of failure assessment diagram method, J/T method and DPFAD method. Effects of the geometry and so forth are examined and key findings from the simulations are fully discussed, which enables to determine practical safety margins of spherical components containing a defect.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2008.06a
• /
• pp.343-344
• /
• 2008

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.1
• /
• pp.96-104
• /
• 1989

The behaviors of acoustic emission emitted in the tests of the fracture toughness and fracture stability are observed by using the specimens of aluminum 2024-T351 and 7039-T6 alloys. The empirical eqution of J-R curve is derived. It is demonstrated from the comparison of the fracture toughness obtained from J-R curve with that from ASTM standard E813-81 that the latter is larger than the former. The discontinuous point in the log-log graph of J-integral vs. total acoustic emission count is observed in between the two offset lines referred from ASTM standard E813-81, but it's physical meaning is uncretain. An empirical material tearing modulus is derived in terms of the total acoustic emission count and proved to be valid in fracture instability test.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1996.05c
• /
• pp.123-130
• /
• 1996

탄소성파괴역학의 발달과 함께 원자력 발전소의 설계시 고려해야 하는 고에너지 배관의 양단파단사고와 같은 극한 가정 대신 파단전누설(LBB : Leak Before Break)개념을 배관설계시 고려할 수 있도록 관련 규제 요건이 완화되어 원자력 발전소 고에너지 계통 설계에 새로운 설계 개념으로 적용할 수 있게 되었다. 파단전누설개념 적용시 균열 안정성 평가에 가장 널리 사용되는 방법은 J-T 방법이다. 본 연구에서는 유한요소법 사용시 균열 선단에서 요소의 크기 및 경계 조건 (Boundary Condition)이 변화할 때 Applied J 적분값에 미치는 영향을 ABAQUS 전산 프로그램을 이용하여 조사하였다.