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Material Modeling and Springback Prediction of Ultra Thin Austenitic Stainless Steel Sheet
Rahul K. Verma,Satoko Murakoso,Kwansoo Chung,Toshihiko Kuwabara 한국소성가공학회 2010 기타자료 Vol.2010 No.6
The constitutive model with combined isotropic-kinematic hardening along with hardening stagnation (or permanent softening) [Verma, Kuwabara, Chung, Haldar: Int. J. Plasticity (submitted)] was used here for modeling the tension-compression behaviors of a 0.1 mm thick austenitic stainless steel sheet (SUS304), which was observed in a recent work [Kuwabara and Murakoso: Proc. CIRP 2010 Conf. (submitted)]. Springback was also experimentally measured for a shallow drawn rectangular cup here and it was verified using the above model. It was found that this model can successfully predict the Bauschinger effect and hardening stagnation. As for springback, it was found that in this particular case it depends on, other than the material model, factors like boundary conditions, in the finite element analysis (FEA), during unloading. It was also observed that incorporation of the Bauschinger effect and permanent softening is a key for accurate springback prediction and, therefore, the present model performs better than the one which is based only on isotropic hardening without any hardening stagnation.
Verma, Rahul K.,Chung, Kwansoo,Kuwabara, Toshihiko The Iron and Steel Institute of Japan 2011 ISIJ international Vol.51 No.3
<P>Modeling non-monotonous and/or non-proportional deformation is challenging partly because of lack of constitutive equations and more so because of unavailability of sufficient experimental data. In the present work, two different experiments involving non-monotonous/non-proportional deformation have been proposed. The model based on combined isotropic-kinematic hardening with permanent softening was utilized to simulate the deformation behavior under such deformation conditions and it was found that the above model was capable of correctly predicting the deformations for both cases considered here. It was also noticed that the incorporation of permanent softening often observed during reverse loading, is important for accurately predicting the deformation when bending-unbending (or strain reversals) takes place.</P>
Rahul K. Verma,Yuki Ogihara,Toshihiko Kuwabara,Kwansoo Chung 한국소성가공학회 2011 기타자료 Vol.2011 No.8
In this work, as non-proportional/non-monotonous deformation experiments, two-stage and tension-compression-tension uniaxial tests were performed, respectively, for a cold rolled ultra high strength dual phase steel sheet: DP780. Deformation behaviors under such deformation paths were found different than those of the ultra low carbon single phase steels observed by Verma et al. (Int. J. Plast. 2011, 82-101). To model the newly observed deformation behaviors, the combined type constitutive law previously proposed by Verma et al. (Int. J. Plast. 2011, 82-101) was successfully applied here. Permanent softening observed during reverse loading was properly characterized into the isotropic and kinematic hardening parts of the hardening law using tension-compression-tension test data. The cross effect observed in two-stage tests was also effectively incorporated into the constitutive law.
Numerical modeling for accurate prediction of strain localization in hole expansion of a steel sheet
Lee, Jeong-Yeon,Lee, Ki-Jung,Lee, Myoung-Gyu,Kuwabara, Toshihiko,Barlat, Fré,dé,ric Elsevier 2019 International journal of solids and structures Vol.156 No.-
<P><B>Abstract</B></P> <P>The hole expansion of a low carbon steel sheet shows an interesting feature that localized thinning and subsequent crack initiation are observed inside the specimen, and not at the hole edge as is typically expected. The present work investigated a numerical modeling approach to predict this localization behavior within the framework of a finite element (FE) analysis. Plastic anisotropy of the sheet was taken into account using the anisotropic yield functions Yld2000-2d and Yld2004-18p for the plane stress and three-dimensional elements, respectively. Careful examination of the FE model revealed that the influence of the out-of-plane stress is very small, suggesting that shell elements can be efficiently used in the analysis. The influence of friction was also found to be negligibly small. However, the constitutive description exhibited a significant influence in that even a slight change in the yield function parameters resulted in a considerable difference in the prediction. For this reason, several sets of parameters were obtained based on the different material properties, and their influences on the hole expansion simulation were analyzed. In particular, the prediction accuracy could be greatly improved when the yield function parameters were optimized such that the flow stresses and plastic strain rate ratios in uniaxial and plane strain states were well captured.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A numerical modeling approach to predict the localization behavior of sheet was investigated. </LI> <LI> Plastic anisotropy of the sheet was taken into account using non-quadratic anisotropic yield functions. </LI> <LI> Constitutive description exhibited a significant influence on the hole expansion formability even with slight change in the yield function parameters. </LI> <LI> The computational accuracy was significantly improved when the yield function parameters were optimized based on flow stresses and plastic strain rate ratios. </LI> </UL> </P>