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Infuence of Evolution in Anisotropy During Strain Path Change on Failure Limits of Sheet Metals
Kaushik Bandyopadhyay,Shamik Basak,Hongjin Choi,Sushanta K. Panda,Myoung‑Gyu Lee 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.9
Effects of evolution in anisotropy during plastic deformation under strain path changes on the formability and failure wereinvestigated in the present study. The evolution in anisotropic property of the extra deep drawing steel was considered byimplementing the non-quadratic anisotropic yield function Yld2000-2d as a function of effective plastic strain, and the correspondingforming behaviour in two-step forming processes was analysed. For the strain path effect, pre-strain was appliedunder biaxial mode using Marciniak in-plane stretch forming set-up, followed by the secondary deformation using the outof-plane stretch forming tool. For failure prediction of the proposed two-step forming, different failure limit approaches wereinvestigated. First, a strain based forming limit diagram (FLD), proposed as the Marciniak–Kuczynski model was modifiedto include the evolution in anisotropic yield function. The dynamic shift in FLD was also determined by taking strain pathchange into consideration. In addition, the influence of evolution of yield function on the strain path independent failure limitcriteria was also assessed in terms of stress based forming limit diagram. Finally, the prediction accuracy of the failure limitcriteria was compared among different models in terms of failure location and limiting dome height (LDH). It was observedthat the incorporation of evolution in anisotropic yield surface improved the prediction of formability in terms of the LDHand strain distribution for the investigated material.
Improved formability prediction by modeling evolution of anisotropy of steel sheets
Bandyopadhyay, Kaushik,Basak, Shamik,Prasad, K. Sajun,Lee, Myoung-Gyu,Panda, Sushanta Kr.,Lee, Joonho Elsevier 2019 International journal of solids and structures Vol.156 No.-
<P><B>Abstract</B></P> <P>Depending on the experimental observations, the Marciniak–Kuckzinki (MK) model was modified incorporating the evolution in the Yld2000-2d anisotropic yield function as a function of plastic work for two ferritic stainless steel sheets. The numerically estimated FLDs were validated with the strain limits evaluated by stretch forming experiments. Moreover, FE simulations were conducted to predict limiting dome heights (LDH) and limiting drawing ratios (LDR) by both models with and without considering the anisotropy evolutions. Additional formability performances such as surface strain distributions over the deformed cup surfaces and earing profile were also compared with experimental results. It was observed that the accuracy of predictions for formability could be significantly improved in the FE simulations when both initial and its subsequent evolution in yield function were included in the modeling. Further, microstructural analysis of parent sheets and stretch formed cups were performed to understand the effect of microstructure change on the anisotropy and formability. It was found that the preferred orientations along rolling and transverse directions changed differently with deformation. Orientation distribution function and Taylor factor maps were analyzed to confirm non-proportional evolution in stress directionality for both the materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Estimation of directional evolution in flow stress with increase in effective plastic strain. </LI> <LI> Description of yield function evolution based on directional flow stress in FE and MK FLD model. </LI> <LI> Texture analysis confirms interdependency of directional hardening with deformed microstructure. </LI> <LI> Experimental validation of MK based FLD prediction incorporating yield shape evolution. </LI> <LI> Successful prediction of LDH and strain distribution applying yield evolution in FE model. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>