http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
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.
Choi, S.H.,Kim, D.H.,Lee, H.W.,Seong, B.S.,Piao, K.,Wagoner, R. Elsevier Sequoia 2009 Materials science & engineering. properties, micro Vol.526 No.1
A visco-plastic self-consistent (VPSC) polycrystal model was employed to simulate the evolution of yield locus shape in a polycrystalline AZ31 Mg alloy sheet under uniaxial loading. Macroscopic velocity gradients were imposed to calculate a full yield locus on the two-dimensional projection of a stress potential. The directions of the plastic strain rate vector were evaluated for various loading directions at the four quadrants of yield locus. The change of yield locus shape during plastic deformation was explained by texture evolution and the variation in the relative activity of each deformation mode. The validity of the polycrystal model for simulation of yield locus in a polycrystalline AZ31 Mg alloy sheet was demonstrated through the comparison of simulated deformation texture and R-value, which is a differential property of yield locus, with the experimental results.
Predicting Shear Failure of Dual-Phase Steels
Ji Hoon Kim,Ji Hyun Sung,D. K. Matlock,Daeyong Kim,R. H. Wagoner 한국소성가공학회 2010 기타자료 Vol.2010 No.6
Dual-phase (DP) steels are being used increasingly to make automotive panels because of their advantageous combinations of high ductility (for forming) and high strength (for service). However, their adoption has been limited because of failures during die tryout that are unpredicted by the usual methods of finite element modeling and forming limit diagrams. The failures, often called “shear failures” occur at regions of high curvature (low R/t) where sheet of thickness t is drawn over a tool radius R. Recent work revealed that the type of failure and the formability of DP steels depend not only on R/t, but also on strain rate, an effect derived from the propensity of these steels to locally heat in areas of high strain when strain rates are sufficiently high to limit heat transfer. The formability is reduced significantly by the thermal effect for rates greater than approximately 0.1/s. This result explains at least partially why forming limit diagrams, which are measured quasi-statically (and thus isothermally) do not reflect the behavior of DP steels formed industrially (at typical strain rates of approximately 10/s). In order to apply laboratory test results of draw-bend formability to industrial forming operations, the inputs to commercial finite element codes (constitutive equations, forming limits) must be adapted to the reality of the material (DP steel) and underlying physics (thermal effects on constitutive behavior). Toward this end, two procedures have been developed and tested, one numerical and one analytical. Together they predict similar forming limits and provide a path for understanding the applied formability of DP steels.
박판 인장 시험에서 가공열의 영향에 관한 유한요소 해석
김용환,Wagoner, R.H. 대한기계학회 1989 대한기계학회논문집 Vol.13 No.4
본 연구의 목적은 2차원 유한요소법을 이용하여 변형과 열전달의 복합된 열소성 문제를 해석하여 재료의 성형성에 대한 가공열의 영향을 연구하는 것이다. 2차원 해석은 종래 단순 인장시험의 해석에 사용되던 1차원 해석에 비해 보다 정확한 해를 가지며 특히 넥킹의 발생 이후의 해석에 유용하다. A numerical method for analyzing non-isothermal plastic deformation of sheet metals has been developed and sheet tensile tests have been analyzed using a two-dimensional finite element formulation. A modified Bishop`s method is used to solve the thermoplasticity problem in decoupled form at each time step. The accuracy of the analysis is confirmed by comparison with experimental data. The uniform elongation is found is drop by 0.1 to 2.7% at moderate strain rates, while total elongation decreases upto 6.0% during tensile testing in air compared to the isothermal case. The effect of deformation heating, becomes more pronounced as necking develops and at higher testing speed.
김용환,Wagoner, R. H. 대한기계학회 1990 대한기계학회논문집 Vol.14 No.5
본 연구에서는 박판의 프레스 성형에 관련된 열소성 문제를 해석할 수 있는 효과적이고, 신뢰도가 높은 수치적 방법을 개발하는 것이다. 박판 성형에서 변형과 열전달이 결합된 문제의 해석을 위하여 3차원 유한 요소 해석을 행하고 그를 이용하여 박판의 스트레치 성형 공정을 해석하였다. 해석 결과를 기존의 실험 결과와 비교하 여 본 해석의 타당성을 보이고, 재료 거동에 영향을 미치는 여러가지 공정 변수의 영 향을 검토하였다. A numerical method for analyzing non-isothermal, rigid-viscoplastic deformation problems has been presented. As an application, a stretch forming of sheet metals, including temperature effect, has been analyzed by a three-dimensional finite element method. Bishop`s step-wise decoupled method is adopted to solve thermomechanical coupling between deformation and heat transfer. Using the method, the effect of temperature on strain distribution during stretch forming is investigated. By comparison of the non-isothermal results with isothermal analysis, the importance of including temperature effects in the analysis of metal forming problems is emphasized. The predicted results were in good agreement with the existing experimental measurements at the different punch temperatures and dome heights investigated. It is also found that any increase of the punch temperature appeared to postpone the strain localization process by lowering the peak strain in the critical punch-sheet contact region and by normalizing strain distribution within the specimen.