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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.
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.
The forming limit diagram of an ultra thin super ferritic stainless steel
Hyuk Jong Bong(봉혁종),Frederic, Barlat,Myung-Gyu Lee(이명규) 한국자동차공학회 2011 한국자동차공학회 부문종합 학술대회 Vol.2011 No.5
The forming limit diagram (FLD) of a 0.1㎜-thick sheet of a ferritic stainless steel was determined using a modified Marciniak test. The conventional ASTM standard test method (ASTM E2218-2) was also tried with almost same conditions. However, the ASTM method produced undesired fracture at upper die radius and draw bead and wrinkling on the sheet specimens. The FLDs determined by the two methods are compared and advantages and disadvantages of the two methods are discussed
Plastic Instability in Complex Strain Paths Predicted by Advanced Constitutive Equations
Marilena.C. Butuc,Frederic Barlat,Jose J. Gracio,Gabriela Vincze 한국소성가공학회 2011 기타자료 Vol.2011 No.8
The present paper aims at predicting plastic instabilities under complex loading histories using an advanced sheet metal forming limit model. The onset of localized necking is computed using the Marciniak-Kuczinsky (MK) analysis [1] with a physically-based hardening model and the phenomenological anisotropic yield criterion Yld2000-2d [2]. The hardening model accounts for anisotropic work-hardening induced by the microstructural evolution at large strains, which was proposed by Teodosiu and Hu [3]. Simulations are carried out for linear and complex strain paths. Experimentally, two deep-drawing quality sheet metals are selected: a bake-hardening steel (BH) and a DC06 steel sheet. The validity of the model is assessed by comparing the predicted and experimental forming limits. The remarkable accuracy of the developed software to predict the forming limits under linear and non-linear strain path is obviously due to the performance of the advanced constitutive equations to describe with great detail the material behavior. The effect of strain-induced anisotropy on formability evolution under strain path changes, as predicted by the microstructural hardening model, is particularly well captured by the model.