Investigation of Different Techniques to Evaluate the FLC from Experiments and FE Simulations

Abstract:

The formability of sheet metal is highly related to the materials resistance to strain localisation and fracture. The Forming Limit Curve (FLC) is one way to evaluate the tendency to instabilities during the forming operation of a material for different strain states. The Nakazima test is a common technique used to experimentally determine the limiting strains. In this paper a slightly modified version of the proposed ISO-standard used at Outokumpu/Avesta Research Centre (ARC) is presented. The method considers the limiting principal strains before and after failure has occurred. The obtained results from the present approach are compared with previous internal methods used at the company. The previous internal methods consisted of evaluating the limiting principal strains at the maximum punch force before fracture or at a set punch distance before fracture. An austenitic stainless steel grade (254 SMO^®) is used in the study. The method will in this work be called the Interpolation Method (IM). A Finite Element (FE) model of the Nakazima test is modelled in LS-DYNA^® with the goal to be able to simulate the experimental test. In order to compare the FLC between the experimental and the numerical results, one instability indicator is proposed based on the onset of fracture in the FE model.The Barlat YLD2000 model [1] using 6 parameters based on proof stresses and anisotropic values for different material directions is applied as a constitutive model. The Interpolation Method is promising and will be used during a trial period at Outokumpu ARC in the future testing. Further development is needed for the simulation model.

• Periodical: Key Engineering Materials (Volumes 611-612)
• Pages: 41-48
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.611-612.41
• Online since: May 2014
• Authors: Anders Groth*, Erik Schedin, Ramin Moshfegh
• Keywords: Finite Element Analysis (FEA), Forming Limit Curve, Forming Limit Evaluation, Nakazima Test, Sheet Metal Forming, Stainless Steel (SS)

References

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