THE PERFORMANCE OF KARAFILLIS-BOYCE YIELD FUNCTION ON DETERMINATION OF FORMING LIMIT DIAGRAMS

Forming Limit Diagrams are useful tools for evaluation of formability in the sheet metals. In this paper the effects of yield criteria on predictions of the right and left-hand sides of forming limit diagrams (FLDs) are investigated. In prediction of FLD, Hosford 1979, Karafillis-Boyce (K-B) and BBC2000 anisotropy yield functions have been applied. Whereas the prediction of FLD is based on the Marciniak and Kuczynski model, thus a numerical approach using the Newton-Raphson method has been used. Forming Limit Diagrams have been obtained for Al 6111-T4 and AA5XXX alloys and results have been compared with published experimental data. Results indicate that predictions of FLD are very sensitive to selection of yield criterion. Also it was found that the FLD of K - B yield function has a better agreement than that by other yield criteria.