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접촉문제에서의 변분부등식의 유한요소해석과 A Priori 오차계산법
이춘열,Lee, Choon-Yeol 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.9
Governing equations infrictional contact problems are introduced using variational inequality formulations which are regularized to overcome the diffculties of non-differentiability of the friction functional. Also finite element approximations and a priori error estimations are derived based on those formulations. Numerical simulations are performed illustrating the theoretical results.
다공매체를 통과하는 유동문제의 유한요소해석과 부분해석후 오차계산
이춘열,Lee, Choon-Yeol 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.5
A new a posteriori error estimator is introduced and applied to variational inequalities occurring in problems of flow through porous media. In order to construct element-wise a posteriori error estimates the global error is localized by a special mixed formulation in which continuity conditions at interfaces are treated as constraints. This approach leads to error indicators which provide rigorous upper bounds of the element errors. A discussion of a compatibility condition for the well-posedness of the local error analysis problem is given. Two numerical examples are solved to check the compatibility of the local problems and convergence of the effectivity index both in a local and a global sense with respect to local refinements.
고온 고압 환경에서 인코넬 690 재료의 프레팅 마모 특성에 관한 실험적 연구
이춘열(Choon Yeol Lee),이주석(Ju Suck Lee),배준우(Joon Woo Bae) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
In nuclear power plant, fretting wear can make serious problems caused by impact motion between U-tubes and support structures located in steam generators. In order to guarantee the reliability of the steam generator, the damage due to the fretting wear should be throughly investigated. The purpose of this study is to elucidate fretting wear mechanism qualitatively and quantitatively. Hence, fretting wear simulation is performed according to the environment to which the actual steam generators in nuclear power plant are exposed. Initial experimental results are obtained for various experimental parameters and the effect of work rate and temperature on fretting wear is evaluated.
이춘열(Choon Yeol Lee),전리사(Li Si Tian),배준우(Joon Woo Bae),채영석(Young Suck Chai) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
Numerical analysis by influence function method (IFM) is demonstrated in this study in order to investigate the fretting wear problems on steam generator tubes and fuel cells, caused by flow induced vibration. Two-dimensional numerical contact model is developed in terms of Cauchy integral equation. The distributions of normal pressures, shear stresses and displacement fields are derived between two contact bodies with similar elastic properties. The work rate model is adopted to calculate the wear amounts between two materials. The results are compared with the solutions by finite element analyses, which verifies applicability of the present method to fretting wear problems.
이춘열(Choon Yeol Lee),배준우(Joon Woo Bae),윤덕용(Deok Yong Yun),배광훈(Kwang Hoon Bae),채영석(Young Suck Chai) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
In nuclear power plant, fretting wear caused by flow induced vibration (FIV) accompanied with sliding and impact loading can make a serious problem between U-tubes and supports which are located in steam generators. In order to simulate the impact/sliding fretting wear, a fretting wear simulator was developed, which can perform classical fretting wear and impact/sliding fretting wear experiments under high temperature and high pressure environment. Before the complete analyses of impact and sliding fretting wear, finite element models for the dynamic characteristics by impact forces in steam generators are developed in this study. After verification of the finite element models in comparison with existing solutions, dynamic analysis of two dimensional tube-to-plate model is performed. Finally, based on the results by finite element analyses, impact velocity, kinetic energy and impact energy are calculated, which will be correlated with the wear amount measured from the experiments.
설일찬,이춘열,채영석,Seol, Il-Chan,Lee, Choon-Yeol,Chai, Young-Suck 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.7
Single fiber pull-out technique has been commonly used to characterize the mechanical behavior of interface in fiber reinforced composite materials. An improved analysis considering the effects of transversely isotropic properties of fiber and the effects of thermal residual stresses in both radial and axial directions along the fiber/matrix interface is developed for the single fiber pull-out test. Although the stress transfer properties across the interface is not much affected by considering the transversely isotropic properties of fiber, interfacial debonding is notably encouraged by the effect. The interfacial shear stress that plays an important role in interfacial debonding is very much affected by the component of axial thermal residual stress in the bonded region, which can induce a two-way debonding mechanism.
유한 요소법을 이용한 자동차용 다이어프램 스프링의 최적설계
김민관(Min-Kwan Kim),이춘열(Choon- Yeol Lee) 한국자동차공학회 2003 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
A diaphragm spring is an important component of a clutch assembly, characteristics of which depend largely on that of a diaphragm spring. A diaphragm spring is subject to high stress concentration in driving condition, which frequently causes cracks and fracture around finger area. In this paper, behavior of a diaphragm spring is analysed by finite element method to calculate sensitivity of design parameters, which is used to perform optimal design of diaphragm spring shape. As an object function, tangential stresses are taken and minimized to improve durability. Characteristics of the diaphragm is used as equality constraint to maintain the original design purpose and sequential linear programming(SLP) is utilized as an optimization tool. With optimized design, it is verified that concentrated stress is decreased maintaining release load characteristic.
배준우(Joon Woo Bae),이춘열(Choon Yeol Lee),채영석(Young Suck Chai) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.10
Fretting, which is a special type of wear, is defined as small amplitude relative motion along the contacting interface between two materials. The structural integrity of steam generators in nuclear power plants is very much dependent up on the fretting wear characteristics of Inconel 690 U-tubes. A finite element model that can simulate fretting wear was developed in this study in order to investigate the behavior of the phenomenon quantitatively. Two-dimensional and three-dimensional finite element analyses were adopted to investigate the fretting wear problems. Two-dimensional finite element analyses for elastic contact wear problems were performed to demonstrate the feasibility of the finite element method to the fretting wear problems in consideration of frictional contact. A numerical example which has existing solutions was treated. By introducing a control parameter s, which scaled up the wear constant and scaled down the cycle numbers, the algorithm was shown to greatly reduce the time required for the analysis. In the wear model, the work rate model was adopted. The two-dimensional solutions of the study are in good agreement with the previous results by Stromberg. The actual tube-to-tube fretting wear tests in the steam generator were simulated in the three-dimensional finite element analysis. Normal contact pressures and wear depth along the contact surface were plotted under the different values of wear parameters and a number of cycles.
SA312 TP347 재료 협개용접부의 응력부식에 관한 연구
우승완(Seung Wan Woo),이춘열(Choon Yeol Lee),권재도(Jae Do Kwon) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.10
Conventionally, SMAW process was applied to join pipes of RCL, which caused lot of loss in time and cost due to excessive heat input and defects in joining section. Recently, narrow-gap welding(NGW) process was introduced to overcome the disadvantages of SMA W. However, the application of NGW to nuclear power plant is not yet common because safety of NGW process is not proven. In present paper, the welded coupons are made of stainless steel. They are manufactured under different processes; general welding(GW) and repair welding after GW in stainless steel. The stress corrosion cracking(SCC) tests are performed at 50, 80 and 100%,σ<SUB>y</SUB> under 42% MgCl₂ environment. The failure time of SAW base-metal at 100%,σ<SUB>y</SUB> is twice longer than that of welded-material. It is verified that welded-material of stainless steel is largely affected in effect of SCC environment. In addition, The failure time of SAW welded-material is longer than SRW welded-material. It is verified that SA 312 TP 347 welded material is largely exposed in SCC environment when it has repair welding.