SHEET METAL FORMABILITY LIMITS USING HILL'S CRITERION AND SEGMENTWISE LINEARISATION BASED ON TENSILE DATA

Abstract

The yield locus expands until instability occurs and such yield locus is called Forming Limit Stress Curve (FLSC). While FLSC is independent of the loading history, the Forming Limit Curves (FLCs) of materials depend on the prestrain and strain path. In this paper, a new method has been adopted to construct the FLCs, which utilises the readily measurable material properties from a tensile test. From the knowledge of a single limit yield stress, a segmentwise linear yield stress locus, i.e. FLSC, can be determined, assuming the material follows Hill's yield criterion and isotropic hardening model up to localized neck. Strain path dependent FLCs can now be developed using Hollomon strain hardening equation, Hill's anisotropy yield criteria and Levy-Mises equation. The FLCs derived from the segmentwise linear yield loci are compared with the FLCs derived from Hill's yield criterion. The results showed that the FLCs derived using segmentwise linear yield loci are in good agreement with the experimental results compared with those obtained using the Hill's yield loci.