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드로잉-아이어닝 공정의 귀생김 예측을 위한 유한요소해석
김석년(S. N. Kim),이명규(M. G. Lee),Fre deric Barlat(F. Barlat) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5
The earing predictability of the finite element (FE) analysis in the drawing-ironing process was evaluated by using a quadratic anisotropic yield function developed by Hill and a non-quadratic anisotropic yield function developed by Barlat and his coworkers. High anisotropic aluminum alloy (AA5042) and low anisotropic steel (AKDQ; aluminum killed drawing quality) steel were experimentally investigated in NUMISHEET 201 I for benchmark problem. From the mechanical properties provided by the benchmark, the anisotropic coefficients for the yield functions were calculated and the forming process was simulated by using the FE-code, ABAQUS with UMAT. The FE simulations for the earing profiles along the material directions and the punch force-stroke behaviors were compared with experimental results.
Themo-Mechanical and Microstructural Modeling of Friction Stir Welding of 6111-T4 Aluminum Alloys
김지훈,Barlat Frederic Gerard,Frédéric Barlat,김종민 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.1
Plastic deformation and thermal history as well as microstructure evolution of friction stir welded 6111-T4 aluminum alloys were numerically simulated. Material and heat flow during friction stir welding were calculated considering the momentum balance equation and energy balance equation under the steady state condition. Based on the calculated temperature history, the coupled nucleation, growth, and coarsening of precipitates were simulated using microstructural modeling, as proposed by Myhr et al. [7,8]. Finally, the distribution of precipitates was used to calculate the mechanical properties of the weld zone, particularly the yield stress, based on the dislocation theory. The results compared well with the measurements, suggesting that the method can be applicable to predict yield stress.
Lee, J.Y.,Lee, J.W.,Lee, M.G.,Barlat, F. Pergamon Press ; Elsevier Science Ltd 2012 International journal of solids and structures Vol.49 No.25
In this work, a constitutive model based on anisotropic hardening was used in the finite element (FE) simulations of springback and its performance was compared with that of conventional hardening laws. The homogeneous yield function-based anisotropic hardening (HAH) model (Barlat et al., 2011), considered in this work, describes a partial distortion of the yield surface under plastic loading. Although it does not use the concept of kinematic hardening, the HAH model was able to predict the complex material behavior upon load reversals such as the Bauschinger effect, transient hardening and permanent softening. For the application to springback, FE simulations were conducted for U-draw/bending of base (as-received) and pre-strained DP780 steel sheets, which was recently proposed as one of the Numisheet 2011 benchmark problems. The predictions with the HAH model, combined with a non-quadratic anisotropic yield function and a plastic strain-dependent unloading modulus, were in good agreement with experimental results for both as-received and pre-strained DP780 sheets.
Effect of slide motion on springback in 2-D draw bending for AHSS
Majidi, O.,Barlat, F. d.,Lee, M. G. Springer Science + Business Media 2016 International journal of material forming Vol.9 No.3
<P>The springback behavior of two advanced high strength steel (AHSS) grades, DP 780 and DP 980, after different forming conditions, was investigated. 2-D draw bending experiments were performed using a direct-drive digital servo-press in three operation modes, conventional (V-mode), relaxation mode (Stepwise and U-mode) and the attach-detach (A-D mode). Numerical simulations were conducted to in an attempt to reproduce the results and to perform parametric studies. The material behavior was captured using the homogeneous anisotropic hardening (HAH) distortional plasticity approach together with the chord elastic modulus model. In addition, the stress relaxation effects were implemented in the code by using a creep law in order to study the influence of a stepwise slide motion mode as well as holding at the bottom dead center. Both experimental and finite element (FE) simulation results demonstrate that detachment of tools from the work-piece was effective to reduce the springback while the effect of stress relaxation was insignificant. The numerical analysis was validated and successfully explained the importance of a forming path change on the final stress state. Based on the result of this study, a new method to reduce springback was introduced.</P>
Kim, Hwigeon,Barlat, Fré,dé,ric,Lee, Yongmoon,Zaman, Shakil Bin,Lee, Chong Soo,Jeong, Youngung Elsevier 2018 International journal of plasticity Vol.111 No.-
<P><B>Abstract</B></P> <P>In the present study, a viscoplastic self-consistent crystal plasticity model (VPSC-RGBV), which accounts for various microstructural features, including the accumulation and annihilation of dislocations due to slip activity and latent hardening originated from interactions between gliding dislocations on different slip planes, is described. The simulation results of the VPSC-RGBV model are compared with those of a macro-mechanical distortional plasticity model, the so-called homogeneous anisotropic hardening (HAH), and experimental data pertaining to metals undergoing complex loading histories. The differences between the simulated and experimental results under non-proportional loading, including 1) the stress-strain curve, 2) instantaneous r-value after strain-path change, and 3) yield surface evolution, are discussed. Finally, potential improvements are suggested for VPSC-RGBV model.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A crystal plasticity model (VPSC-RGBV) was used to describe the anisotropic features under non-proportional loading. </LI> <LI> The constitutive parameters of the VPSC-RGBV model were identified by numerical optimization. </LI> <LI> The applicability of the VPSC-RGBV model to an actual multiphase alloy (DP780) was investigated. </LI> <LI> The simulation results of the VPSC-RGBV model were compared with those of a macro-mechanical model and experimental data. </LI> </UL> </P>
Thermal Effects on the Enhanced Ductility in Non-Monotonic Uniaxial Tension of DP780 Steel Sheet
Omid Majidi,Frederic Barlat,Yannis P. Korkolis,Jiawei Fu,Myoung-Gyu Lee 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.6
To understand the material behavior during non-monotonic loading, uniaxial tension tests were conducted inthree modes, namely, the monotonic loading, loading with periodic relaxation and periodic loading-unloadingreloading,at different strain rates (0.001/s to 0.01/s). In this study, the temperature gradient developing duringeach test and its contribution to increasing the apparent ductility of DP780 steel sheets were considered. In order toassess the influence of temperature, isothermal uniaxial tension tests were also performed at three temperatures(298 K, 313 K and 328 K (25 °C, 40 °C and 55 °C)). A digital image correlation system coupled with an infraredthermography was used in the experiments. The results show that the non-monotonic loading modes increasedthe apparent ductility of the specimens. It was observed that compared with the monotonic loading, the temperaturegradient became more uniform when a non-monotonic loading was applied.