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일반 구조용강 열간 압연 박판에 대한 K-R 곡선 결정
이억섭(Ouk Sub Lee),이계승(Gye Seung Lee),백준호(Joon Ho Baek),편장식(Jang Sik Pyun) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
Some materials exhibit a rising R curve, while the R curve for other materials is flat. The shape of the R curve depends on material behavior and, to a lesser extent, on the configuration of the cracked structure. The R curve for an ideally brittle material is flat because the surface energy is an invariant material property. When nonlinear material behavior accompanies fracture, however, the R curve can take on a variety of shapes. Five different hot-rolled thin plates are tested to investigate R-curve behavior. A special experimental apparatus is used to prevent specimen buckling.
표면 균열이 있는 천연가스 수송용 고장력 강관의 신뢰성 평가
이억섭(Ouk-Sub Lee),김홍민(Hong-Min Kim),김동혁(Dong-Hyeok Kim),최혜빈(Hye-Bin Choi) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
The demand in the natural gas has continuously been increasing in the world owing to the environmental problems and its high efficiency. The natural gas is usually transported to the end-users through the high strength pipeline. One of the notable problems for these pipelines is the brittle fracture initiated at various defects due to the extremely low temperature(-162℃) of the transported natural gas. It is, thus, required to evaluate the effect of the defect of pipeline in terms of the on economical and social losses. In this paper, the reliability of the high strength pipeline with a semi-elliptical crack along the surface is estimated. The failure probability is calculated by using the probabilistic methods, such as the FORM(First Order Reliability Method). The reliability analysis is conducted for the API 5L X65. Furthermore, the effects of probability distribution characteristics of random variables in LSF(Limit State Function) such as the normal distribution on the failure probability are systematically studied.
Issues When Estimating Fatigue Life of Structures
Lee, Ouk-Sub,Chen, Zhi-wei Korean Society for Precision Engineering 2000 International Journal of Precision Engineering and Vol.1 No.2
When estimating fatigue crack growth (FCG) life of structures, the use of crack growth models and knowledge of the values of their corresponding parameters are of vital importance. Inconsistency in using models with appropriate parameters can lead to enormous errors in FCG life prediction. In this paper examples are analyzed and compared with test results to show the possible problems, Consistency checks are necessary for avoiding some pitfalls, and also necessary for verifying the correct performance and accuracy of the used computer program.
Dynamic Mixed Mode Crack Propagation Behavior of Structural Bonded Joints
Lee, Ouk-Sub,Park, Jae-Chul,Kim, Gyu-Hyun The Korean Society of Mechanical Engineers 2000 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.14 No.7
The stress field around the dynamically propagating interface crack tip under a remote mixed mode loading condition has been studied with the aid of dynamic photoelastic method. The variation of stress field around the dynamic interface crack tip is photographed by using the Cranz-Shardin type camera having $10^6$ fps rate. The dynamically propagating crack velocities and the shapes of isochromatic fringe loops are characterized for varying mixed load conditions in double cantilever beam (DCB) specimens. The dynamic interface crack tip complex stress intensity factors, $K_1\;and\;K_2$, determined by a hybrid-experimental method are found to increase as the load mixture ratio of y/x (vertical/horizontal) values. Furthermore, it is found that the dynamically propagating interface crack velocities are highly dependent upon the varying mixed mode loading conditions and that the velocities are significantly small compared to those under the mode I impact loading conditions obtained by Shukla (Singh & Shukla, 1996a, b) and Rosakis (Rosakis et al., 1998) in the USA.
Failure Probability of Corrosion Pipeline with Varying Boundary Condition
Ouk Sub lee,Jang Sik Pyun 대한기계학회 2002 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.16 No.7
This paper presents the effect of external corrosion, material properties, operation condition and design thickness in pipeline on failure prediction using a failure probability model. The predicted failure assessment for the simulated corrosion defects discovered in corroded pipeline is compared with that determined b<br/>
The Reliability Estimation of Pipeline Using FORM, SORM and Monte Carlo Simulation with FAD
Ouk Sub Lee,Dong Hyeok Kim 대한기계학회 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.12
In this paper, the reliability estimation of pipelines is performed by employing the probabilistic method, which accounts for the uncertainties in the load and resistance parameters of the limit state function. The FORM (first order reliability method) and the SORM (second order reliability method) are carried out to estimate the failure probability of pipeline utilizing the FAD (failure assessment diagram). And the reliability of pipeline is assessed by using this failure probability and analyzed in accordance with a target safety level. Furthermore, the MCS (Monte Carlo Simulation) is used to verify the results of the FORM and the SORM. It is noted that the failure probability increases with the increase of dent depth, gouge depth, operating pressure, outside radius, and the decrease of wall thickness. It is found that the FORM utilizing the FAD is a useful and is an efficient method to estimate the failure probability in the reliability assessment of a pipeline. Furthermore, the pipeline safety assessment technique with the deterministic procedure utilizing the FAD only is turned out more conservative than those obtained by using the probability theory together with the FAD. The probabilistic method such as the FORM, the SORM and the MCS can be used by most plant designers regarding the operating condition and design parameters.