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변형률에너지법에 의한 1Cr-0.5Mo-0.1V강의 피로손상평가
고승기(S.K. Koh),나의균(E.G. Na),하정수(J.S. Ha) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
In order to represent and evaluate the fatigue damage of 1Cr-0.5Mo-0.1V steel used for high strength pressure vessels, strain-controlled fatigue tests using uniaxial specimens were performed. Based on the fatigue test results from different strain ratios of -2, -1, 0, 0.5, 0.75, the fatigue damage of the steel was evaluated by using a strain energy density. Mean stress relaxation depended on the magnitude of the applied strain amplitude. The high pressure vessel steel exhibited the cyclic softening behavior. Total strain energy density consisting of the plastic strain energy density and the elastic tensile strain energy density described fairly well the fatigue life of the steel, taking the mean stress effects into account. Fatigue lives predicted by the strain energy density correlerated very well with the experimental fatigue lives within factors of 3 to 4, compared to other fatigue damage parameters.
고승기(Koh.S.K),류창훈(Ryu.C.H),이정준(Lee.z.J),나의균(Na.E.G),백태현(Baek.T.H),전경락(Jeon.K.L.) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
A failure analysis of holddown spring screw was performed using fracture mechanics approach. The<br/> spring screw was designed such that it was capable of sustaining the loads imposed by the initial<br/> tensile preload and operational loads. In order to investigate the cause of failure, a stress analysis of<br/> the top nozzle spring assembly was done using finite element analysis and a life prediction of the<br/> screw was made using a fracture mechanics approach. The elastic-plastic finite element analysis<br/> showed that the local stresses at the critical regions of head-shank fillet and thread root significantly<br/> exceeded than the yield strength of the screw material, resulting in local plastic deformation. Primary<br/> water stress corrosion cracking life of the Inconel 600 screw was predicted by using integration of<br/> the Scott model and resulted in 1.42 years, which was fairly close to the actual service life of the<br/> holddown spring screw.
WEB기반의 3차원 유동속도 원격 계측시스템 개발에 관한 연구
오석형(S. H. Oh),김장권(J. K. Kim),나의균(E. G. Na) 한국동력기계공학회 2009 한국동력기계공학회 학술대회 논문집 Vol.2009 No.6
This paper shows the development process for measuring three-dimensional flow velocity components in a web-browser. The system is developed in an embeddable C/C++ interpreter Ch and Ch-CGI toolkit. The interface for the web-based measurement system consists of a set of web html files and Ch files for CGI. All of data in web browser are passed to Ch-CGI script to generate the output of new html file. PC-Server and PC-Client can submit measurement parameters and receive the text/graphical results each other. PC-Client can control the test equipment by using a parameters that received from PC-Server. It also can pass the test results between the web-based measurement system. In summary, the designed measurement system is evaluated, the outputs shown well on the web browser.
고승기(S.K. Koh),연문흠(M.H. Yeon),나의균(E.G. Na) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.5
Application of a very high internal pressure on the thick-walled cylinder induces beneficial compressive tangential residual stresses near the bore of the cylinder after unloading the internal pressure. However, a reverse yielding due to the Bauschinger effect during the unloading process causes the reduction of the compressive residual stress near the bore. In order to evaluate the autofrettage residual stress distributions of the thick-walled cylinder, the Bauschinger effects were considered. Magnitudes of the compressive residual stresses at the cylinder bore determined by considering the Bauschinger effects decreased by about 25 percent, compared to the case of linear elastic unloading, I.e., without Bauschinger effects. Measured residual stress distuibutions agreed?fairly well with the calculated distributions considering the Bauschinger effects
박찬중(Park C.J.),고승기(Koh S.K.),나의균(Na E.G.),백태현(Baek T.H.) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
Autofrettage analysis of a bend in the fuel injcetion pipe has been performed to investigate the distribution of residual stresses due to pipe bending and autofrettage processes. The pipe bending was simulated by metal forming analysis using finite element method, and residual stress distribution after bending was found. Autofrettage following the pipe bending was performed by applying the hydrostatic internal pressures of 603 ㎫, 535 ㎫, 500 ㎫ on the pipe bend, corresponding to theoretical 26 %, 14 %, 9 % overstrain levels, respectively. Residual stress distributions due to bending and autofrettage were evaluated.