Forming limits prediction using rate-independent polycrystalline plasticity R. Knockaert *, Y. Chastel, E. Massoni CEMEF, E Â cole des Mines de Paris, BP 207, 06904 Sophia-Antipolis Cedex, France Received in ®nal revised form 24 July 2000 Abstract The purpose of this paper is the prediction of forming limits computed from an initial defect approach combined with a rate-independent polycrystalline plasticity model. The algorithm used for the integration of the material behaviour inside and outside the localiza- tion band is presented. Results are compared with the forming limit curves at necking and at failure for 6116-T4 aluminium. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Polycrystalline plasticity; Forming limit curves; Initial defect approach; Formability 1. Introduction Various approaches have been developed in the literature for the theoretical computation of forming limit curves. Some of them are coupled with polycrystalline plasticity in order to deal with more physical material models. For example, a per- turbation method is presented in Boudeau et al., 1998). Another method was developed in Toth et al., 1995) where the perturbation analysis is carried out with Hill's quadratic model ®tted on the yield potential of a viscoplastic polycrystal. Marciniak and Kuczynski have developed another method by assuming the presence of an initial defect Marciniak and Kuczynski, 1967). This defect consists in a band in which the initial thickness of the sheet is smaller. The stretching is then computed for a sheet with such a defect. The calculated forming limits strongly depend on the magnitude of this initial defect. However, for a given imperfection factor, this approach allows to compare the eect of various material models. Moreover, International Journal of Plasticity 18 2002) 231±247 www.elsevier.com/locate/ijplas 0749-6419/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0749-641900)00077-2 * Corresponding author. Fax: +33-4-93-65-43-04. E-mail address: robert.knockaert@cemef.cma.fr R. Knockaert).