Pre-strain correction of forming limit curves

Inherent features of the Nakajima test to determine forming limit curves (FLC) are inevitable bending strains and pre-strains originating from evolving punch contact in the early stage. Both effects are very annoying and bias the resulting FLC considerably, so that a direct comparison of materials with different gauges is impossible. In the present work, a simple computational procedure is developed to remove both effects from FLC data. Application examples demonstrate its capabilities.