Investigation and Compensation of Biaxial Pre-strain During the Standard Nakajima- and Marciniak-test Using Generalized Forming Limit Concept

One of the most important tasks in sheet metal forming is the prediction of formability. The common criterion for ductile fracture in industrial application is the evaluation of the so-called Forming Limit Curve (FLC). The determination of FLCs is standardized in the international standard 12004-2 by two different experimental methods, the Marciniak- and the Nakajima-test. Several effects, for example bending or contact pressure, are leading to biaxial pre-forming and to a slightly non-linear load path. This results in inaccuracies of the FLC. The so-called Generalized Forming Limit Concept (GFLC) is a phenomenological approach, which was introduced to predict the local necking of non-linear load paths. The accuracy and robustness of the GFLC has already been shown in several papers. In this investigation the GFLC was used to compensate the biaxial pre-forming and to calculate a linear FLC. Input parameters are the Marciniak- and Nakajima-FLCs of the material HC340LA.