Identification of forming limit curve at fracture in incremental sheet forming

Computer-aided manufacturing technology is widely used in the sheet-forming industry to predict forming performance. Strain-based forming limit criterion is popularly used for this purpose. In incremental sheet forming, the forming limit curve at fracture (FLCF) is a line from the equi-biaxial strain-point to plane strain-point and is high in comparison with those in conventional press forming methods. This study aims to empirically define the FLCF, specifically the equi-biaxial strain at fracture which has yet to be experimentally defined. In addition, to confirm the experimental measurement results, the finite element simulation by ABAQUS/Explicit was performed wherein the fitted flow curve of the large-strain range, accompanied with non-associated flow rule yield behaviour, demonstrates good agreement with the experiment. A new stress-strain equation is thus introduced to describe the flow curve in a large-strain range.