Modelling of fracture effects in the sheet metal forming based on an extended FLC evaluation method in combination with fracture criterions

The industrial based prediction in sheet metal forming bases still on the Forming Limit Diagrams (FLD) as formally proposed by Goodwin [1]. The FLD are commonly specified by the Nakajima tests and evaluated with the so called cross section method. Although widely used, the FLC concept has numerous serious limitations. In the paper the possibilities for a specific prediction of crack limits based on an extended FLC concept (X-FLC) will be discussed. The new concept demonstrates that the Nakajima tests are not only appropriate for the evaluation of the necking instability but for the detection of the real crack strains too. For the evaluation of the crack strains a local thinning method as proposed by Gorji et al. [3] is applied and tested for special 6xxx and 5xxx Al-alloys as well as for the corresponding multilayer FUSION material. (paper)