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이명한(M. H. Lee),김헌영(H. Y. Kim),오수익(S. I. Oh) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.10
Forming limit diagram (FLD) is often used as a failure criterion in the sheet metal forming. To obtain the FLD, generally, there are two methods, analytical and experimental method. The experimental method requires much time and effort because various forming paths and proper yield criterion should be considered to get the FLD. The analytical FLD is based on Marciniak-Kuczynski (M-K) theory and proper yield criterion according to the material, but forming speed cannot be easily incorporated. In this study, numerical method was suggested for getting the FLD. In the numerical method, initial imperfection of material are needed to simulate the failure or necking behavior, which were made by using a random thickness distribution. The numerical method was verified to be able to provide a good guide for getting the FLD. And the numerical FLD considering strain rate effect could be obtained through the simulation of various forming speeds.
마그네슘 합금 판재의 온간 성형 해석에서 FLD를 이용한 성형성 평가
이명한(M. H. Lee),김흥규(K. K. Kim),김헌영(H. Y. Kim),오수익(S. I. Oh) 한국소성·가공학회 2008 소성가공 : 한국소성가공학회지 Vol.17 No.7
In this study, a forming magnesium alloy circular cup was simulated accounting for heat transfer at elevated temperatures. In order to predict the failure of magnesium alloy sheet during simulation, the forming limit diagram, which is used in sheet metal forming analysis to determine the criterion for failure, was investigated. For the failure prediction in the simulation accounting for heat transfer, the forming limit diagram for a temperature the same as the temperature of the blank element was used. The result of the simulation showed that the drawn depth increases with the increase of the dieholder temperature, and is in accord with the experimental results above the die-holder temperature of 150˚C. The forming limit diagram provided a good guide for the failure prediction of warm forming simulation accounting for heat transfer. In addition, the effect of the tool shoulder radius on the drawn depth at various tool temperatures is verified using the simulation conditions which agreed with the experimental results.
[차량운동성능부문] 풍동에서 횡풍 안정성의 시험방법론과 공력의 영향력
김대훈(D.H. Kim),이강덕(K.D. Ih),이명한(M.H. Lee) 한국자동차공학회 2000 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
It was investigated to analyze on cross-wind stability in full-scale wind tunnel. Some aerodynamic factors regarded the stability previous studies. front and rear lift had to consider assessing of stability as well as other aerodynamic forces. lift can change the vehicle center of gravity and weight simultaneously. And it was found that the effective method of analysis in cross-wind stability by means of wind tunnel test. This method provides some directions of stability improvement in aerodynamic styling concept and vehicle dynamic system.