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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.
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.
박판합금재료의 피로균열 전파특성에 대한 피로수명예측과 활용
이억섭(Ouk Sub Lee),김승권(Seung Gwon Kim) Korean Society for Precision Engineering 2007 한국정밀공학회지 Vol.24 No.2
In fatigue life prediction, it is important that fatigue life is affected by crack closure phenomenon in thin sheet Al alloy. In this research, we attempt to (l)analyze the characteristics of fatigue crack propagation in constant loading condition for thin sheet Al 2024-T3 alloy which is generally used in transportation structures, (2)identify the crack closure phenomenon in thin sheet comparing experimental results of thin and thick sheet specimen under same fatigue loading condition. In using the fatigue related material constants from these fatigue crack propagation analysis, we attempt to (3)operate the fatigue life estimating process with considering crack closure phenomenon and (4)analyze the experimental and prediction results offatigue life in thin sheet AI alloy.
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.
이억섭(Ouk Sub Lee),윤해룡(Hai Long Yin) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
It is a well-known that fatal damages in buried pipeline generally are caused by the corrosion or crack defects. The buried pipeline having these defects becomes more dangerous when it receives external load. This paper presents the effect of varying vehicle load on buried pipeline having external corrosion defects and various boundary condition by using FEM analysis.