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Al5083재 TIG용접부의 잔류응력이 피로균열전파거동에 미치는 효과
이억섭,박찬영,Lee, Ouk-Sub,Park, Chan-Young 대한기계학회 1999 大韓機械學會論文集A Vol.23 No.6
The welded structure unnecessarily remains residual stress due to the very high heating of local region and lastly cooling. The residual stress sometimes causes fracture initiation of welded structures. In this paper, distribution and magnitude of tensile and compressive residual stresses in the TIG(Tungsten Inert Gas) welded aluminum alloy such as Al5083-H112 are measured by using the hole-drilling method. Furthermore, the effects of residual stresses in the TIG welded aluminum CCT(Center Crack Tension) and SEN(Single Edge Notched) Specimens on the fatigue crack propagation behavior are analyzed. The fatigue cracks initiated at residual stresses region are influnced by tensile and compressive residual stresses. However, the effects are found to be released fast for both cases according to the cyclic loads and extension of crack length.
Ultrasonic Nondestructive Evaluation(NDE) of Cornposite Materials - A Review -
이억섭,Lee, Ouk-Sub The Korean Society for Nondestructive Testing 1989 한국비파괴검사학회지 Vol.9 No.2
This essay is a general review of the application of ultrasonic NDE techniques to the performance assessment and characterization of composite materials. A brief review of ultrasonic input-output characterization of a composite plate by shear waves is presented. A theoretical development of ultrasonic wave propagation in isotropic and anisotropic media excited, respectively, by a circular transducer and an oscillatory point source is summarized. Some experimental results are described in which ultrasonic velocity and attenuation measurements give insight into material degradation of fatigued composite laminates. Ultrasonic determination of the elastic constants of a composite plate and an experimental attempt at ultrasonic testing of an isotropic plate containing a crack are also included. A recent effort for the characterization of viscoelastic materials using the ultrasonic NDE technique is outlined. Finally, the reliability of ultrasonic NDE is briefly touched upon.
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.
SHPB 기법과 확률이론을 이용한 고분자재료의 동적거동특성 및 건전성 평가
이억섭(Ouk Sub Lee),김동혁(Dong Hyeok Kim) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.9
The conventional Split Hopkinson Pressure Bar (C-SHPB) technique with aluminum pressure bars to achieve a closer impedance match between the pressure bars and the specimen materials such as hot temperature degraded POM (Poly Oxy Methylene) and PP (Poly Propylene) to obtain more distinguishable experimental signals is used to obtain a dynamic behavior of material deformation under a high strain rate loading condition. An experimental modification with Pulse shaper is introduced to reduce the nonequilibrium on the dynamic material response during a short test period to increase the rise time of the incident pulse for two polymeric materials. For the dynamic stress strain curve obtained from SHPB experiment under high strain rate, the Johnson-Cook model is applied as a constitutive equation, and we verify the applicability of this constitutive equation to the probabilistic reliability estimation method. The methodology to estimate the reliability using the probabilistic method such as the FORM and the SORM has been proposed, after compose the limit state function using Johnson-Cook model. It is found that the failure probability estimated by using the SORM is more reliable than those of the FORM, and the failure probability increases with the increase of applied stress. Moreover, it is noted that the parameters of Johnson-Cook model such as A and n, and applied stress affect the failure probability more than the other random variables according to the sensitivity analysis.