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김원재(Wonjae Kim),이철환(Chulhwan Lee),김현기(Hyunki Kim),고영우(Youngwoo Koh),정관수(Kwansoo Chung) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.5
In the industrial sheet metal forming, the numerical forming analysis to predict forming failure is commonly utilized to optimize the forming process. In particular, for rather thin cold-rolled automotive sheets which more often than not fail with strain localization, the analysis is conducted using shell elements under the plane stress condition. As for the failure criterion, the strain-based forming limit diagram (FLD) is measured and the measured data is converted into various formulae for numerical applications, which might be insensitive to deformation path history such as the criteria based on failure stress of effective failure strain. In this work, a numerical analysis procedure was newly developed for rather thick hot-rolled advanced high strength sheets in automotive applications, utilizing continuum elements. The procedure involves the numerical inverse method to characterize hardening behavior with its ultimate deterioration before failure as well as to evaluate failure behavior, based on simple tension and hemispherical dome stretch tests. To predict failure, the new method directly evaluated strain localization for (critical) material elements without referring to the forming limit diagram. The new procedure was applied for hot-rolled HB780 sheet and analysis results were experimentally validated.
모재의 방향성에 따른 마찰교반용접 판재의 성형성에 관한 실험적 연구
김대용(Daeyong Kim),이원오(Wonoh Lee),김준형(Junehyung Kim),Chongmin Kim,정관수(Kwansoo Chung) 한국소성·가공학회 2009 소성가공 : 한국소성가공학회지 Vol.18 No.1
In order to investigate the formability of friction stir welded(FSW) tailor welded blanks(TWB) with respect to the base material’s directional combination, aluminum alloy AA6111-T4 sheets were welded with three different conjoining types: RD-RD, TD-RD and TD-TD. Here, RD and TD represent rolling and transverse directions, respectively. For experimental formability study, three tests with gradual complexity were performed: the simple tension test with various weld line directions for uni-axial elongation, the hemisphere dome stretching test for biaxial stretching and the cylindrical cup deep drawing test. As a result, all three forming tests showed that RD-RD type samples exhibited the best formability, while TD-TD type sheets showed the least formability performance.
안강환(Kanghwan Ahn),유동훈(Donghoon Yoo),석동윤(Dong-Yoon Seok),김홍기(HongGee Kim),박성호(SungHo Park),정관수(Kwansoo Chung) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5
In order to overcome drawbacks of the advanced high strength steel such as inferior formability and large springback, the hot press forming process(HPF) has been being applied for forming of automotive sheet parts. Good formability and dimensional accuracy without springback as well as good crash performance of final products are the advantages of the HPF process. In this work, a method to characterize the mechanical properties of the HPF steel was developed based on the simple tension test at high temperatures and its finite element analysis, while it was applied to obtain strain rate and temperature dependent flow curves of the HPF steel. The final flow curves were represented by utilizing the Johnson-Cook type equation both in uniform and post-uniform deformation regions.
AA5083-H18판재의 마찰 교반 점 용접 공정에 대한 전산 해석
김돈건(Dongun Kim),Badarinarayan Harsha,유일(Ill Ryu),김지훈(Ji Hoon Kim),김종민(Chongmin Kim),Okamoto Kazutaka,Wagoner R. H.,정관수(Kwansoo Chung) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5
Thermo-mechanical simulation of the Friction Stir Spot Welding (FSSW) processes was performed for the AA5083-H18 sheets, utilizing commercial Finite Element Method (FEM) and Finite Volume Method (FVM) which are based on Lagrangian and Eulerian formulations, respectively. The Lagrangian explicit dynamic FEM code, PAM-RASH, and the Eulerian Computational Fluid Dynamics (CFD) FVM code, STAR-CD, were utilize to understand the effect of pin geometry on weld strength and material flow under the unsteady state condition Using FVM code, material flow pattern near the tool boundary was analyzed to explain the weld strength difference between the weld by cylindrical pin and the weld by triangular pin, while the frictional energy concept using the FEM code had limitation to explain the weld strength difference.
열간프레스성형에서의 변형 측정장치 개발 및 기계적 거동의 물성화
유동훈(Donghoon Yoo),석동윤(Dong-Yoon Seok),김돈건(Dongun Kim),안강환(Kanghwan Ahn),손현성(Hyun-Sung Son),김교성(Gyo-Sung Kim),정관수(Kwansoo Chung) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.10
As a way to improve the safety of automotive and to reduce the weight of vehicles, new forming technologies and advanced materials are in high demand in the automotive industry. However, the advanced strength steel has inferior formability and large springback. In order to overcome such drawbacks, the hot press forming process (HPF) has been being applied for forming of automotive sheet parts. In this work, new equipment was suggested to measure unlimited displacement range compared to previous one which was able to measure only up to 10mm displacement range. The external extensometer connected with grips by wire was applied to equipment so that total strain range was measured up to failure also in high temperature. And the finite element analysis was conducted to characterize the mechanical properties of the HPF steel. Finally, the flow curves were represented by utilizing the Johnson-Cook type equation both in uniform and post-uniform deformation regions.