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변형률속도 효과를 고려한 AZ31B 판재의 온간 성형한계도 예측 -Ⅱ
최선철(S. C. Choi),김헌영(H. Y. Kim),김형종(H. J. Kim) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.10
The purpose of this study is to predict the forming limit diagram (FLD) of strain-rate sensitive materials on the basis of the Marciniak and Kuczynski (M-K) theory. The strain-rate effect is taken into consideration in such a way that the stress-strain curves for various strain-rates are inputted into the formulation as point data, not as curve-fitted models such as power function. Tensile tests and R-value tests were carried out at several levels of temperature and strain-rate from 25℃ to 300℃ and 0.16 to 0.00016/s, respectively to obtain the mechanical properties of AZ31B magnesium alloy sheet. The FLD of this material was experimentally obtained by limit dome height tests with the punch velocity of 0.1 and 1.0 mm/s at 250℃. The M-K theory-based FLD predicted using Yld2000-2d yield criterion was compared with the experimental results.
변형률속도 효과를 고려한 AZ31B 판재의 온간 성형한계도 예측
최선철(S. C. Choi),김형종(H. J. Kim) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5
The purpose of this study is to predict the forming limit diagram(FLD) of strain-rate sensitive materials on the basis of the Marciniak and Kuczynski (M-K) theory. The strain-rate effect is taken into consideration in such a way that the stress-strain curves for various strain-rates are inputted into the formulation as point data, not as curve-fitted models such as power function. To solve the nonlinear system of equations derived from the equilibrium and constraints in the groove region and the safe zone, the Newton-Raphson method is used. The theoretical FLDs using four different yield criteria, that are von Mises, Hill (1948), Hill (1979), Logan and Hosford, are compared with the experimental, numerical (FEA) and other theoretical results. A new trial is made where a modified M-K model having n-step grooves is introduced to describe a real localized neck.
Yoshida-Uemori 모델을 이용한 Al 판재의 스프링백 예측
서오석(O. S. Seo),이은국(E. G. Lee),홍석무(S. M. Hong),최선철(S. C. Choi),유수열(S. Y. Ryu),이명규(M. G. Lee),김헌영(Heon Young Kim) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5
Springback is caused by the recovery of elasticity of a flat-rolled metal, which occurs when the forming force is released from a flat-rolled metal. Springback takes place in a large degree when a high strength steel plate or AI alloy sheet is processed. It has been known that hardening model is the most efficient for the prediction of springback. Recently, various researches have been carried out. In particular, Yoshida-Uemori model has been proved to be the most suitable for forecasting the springback of a high strength steel plate. In this paper, Uniaxial tension tests and cyclic loading tests(T-C-T, C-T-C) were conducted on the 1050 Al alloy sheet, 3003, and 5052 series. And based on the test results, coefficients required for Yoshida-Uemori model have been figured out. In addition, the test results were put into commercial finite element program PAM-STAMP to predict the springback of Al Alloy sheet and the outcome has been proved to be quite accurate.