Predicting forming limit diagrams by numerical simulation of Nakazima and modified Marciniak tests

Forming limit diagram (FLD) is a useful tool for investigation of sheet's formability for designing industrial products. Experimentally extracting FLD requires exact experimental tests, and is time consuming, and expensive. Therefore, several studies have been carried out on the usage of theoretical methods and finite element software for determining these diagram. In this study, FLD for AA3105 aluminum alloy sheet were obtained by simulating the Nakazima and modified Marciniak test in ABAQUS software. In order to numericaly determine FLD of AA3105, Hill yield criterion, Hosford yield criterion and GTN damage model based on Hosford criterion and Voce and power law hardening rules were investigated. Due to the lack of the Hosford yield criterion and the GTN damage model based on Hosford criterion in the ABAQUS software, VUMAT subroutines has been developed and used to determine the behavior of the AA3105 aluminum alloy. The results showed that the predicted FLD based on the Hill criterion, shows large deviation from experimental results. The usage of the Hosford criterion and GTN damage model for aluminum alloys showed a better correlation with experimental results. Also, due to the presence of voids in metals, the GTN damage model which is based on the void volume fraction has a greater physical justification than other yield criterion. Furthermore, by comparing numerical FLDs that obtained from Nakazima and modified Marciniak tests, it was concluded that the limit strains in modified Marciniak test is lower than the Nakazima test.