Statistical evaluation of the uncertainty of experimentally characterised forming limits of sheet steel

The experimental measurement of forming limit curves (FLCs) has become common practice in the process of evaluating the formability of sheet steel and other sheet metals. In spite of the considerable amount of time researchers have spent on the subject of FLCs, the question regarding the accuracy and precision with which a forming limit can be determined experimentally still has not been sufficiently analysed. The objective of the current work is to evaluate the intrinsic precision of the experimental procedure. The results of the present work give a reliable estimate of the (precision wise) uncertainty on the locus of an FLC. In addition, an alternative approach for interpreting the results of a forming limit characterisation experiment is evaluated. The new approach is a first attempt to capture the expected tendency of a material to deform along different but linear strain paths for the same geometrical boundary conditions for different sheet steel grades.