Rom. J. Techn. Sci. − Appl. Mechanics, Vol. 59, N° 3, P. 265−277, Bucharest, 2014 LIMIT STRAINS VARIABILITY WITH RESPECT TO MATERIAL SCATTER LIANA PĂRĂIANU, DAN SORIN COMSA, DOREL BANABIC ∗1*∗ Abstract. In this paper a study regarding to the effect of the variability of the mechanical parameters on the prediction of the limit strain have been presented. The necking criterion used in the analyses is the one proposed by Marciniak-Kuczinsky [M-K]. The inelastic behaviour of the sheet metal has been described by BBC2005 yield criterion and Hill48 yield criterion respectively. The Swift’s formulation has been used in order to describe the hardening of the material. The material investigated in this paper is DC04 steel sheet (0.85 mm thickness). Key words: metal forming, failure, sheet metal. 1. INTRODUCTION The automotive industry reported that a large number of rejected parts owe to the fact that the parameters of the sheet metal forming processes are not strictly constants. Col [1] emphasized the most important sources of scatter in a stamping process: material parameters, tooling, process and lubrication. During the last fifteen years, researchers paid attention to studying the variability of the mechanical parameters of both simulation plastic deformation processes and constitutive models. The variability of the mechanical parameters cannot be neglected in a robust sheet metal forming process analysis. Gerlach et al. [2] is one of the first paper to do well on this issue. Karthik et al. [3] performed two kinds of tests on three types of steel in order to determine the variability of the mechanical parameters. These analyses emphasise the fact that the mechanical parameters are affected by the variability not only from lab-to-lab but also from coil-to-coil and test-to-test. More recently, after an in-depth study with conclusions published in [4–6], Carleer and his co-workers incorporated the variability of the mechanical parameters in the simulation of the sheet metal forming process. Since variability of the mechanical parameters became so important to virtual fabrication, AutoForm developed the Sigma module. The implementation of the stochastic modelling in the finite CERTETA Research Center on Sheet Metal Forming, Technical University of Cluj Napoca, 400140 Cluj Napoca, Romania *