Abstract: In order to analyze sheet formability more realistically， a new approach based on the M-K theory was proposed， which predicted the forming limit of aluminum alloy sheets by using different modes of data from the measured stress-strain curve. The forming limits of 6016-T4 and 7075-T6 aluminum alloy sheets were theoretically analyzed using three modes of data， which were the original data of the measured stress-strain curve， the power exponential fitted data and polynomial fitted data of the stress-strain curves， respectively. According to the stress-strain data from tensile test， the ultimate strains were calculated and the theoretical forming limit curves (FLC) were plotted. After comparing the theoretically predicted FLC with experimental data from the bulging test， the results indicate that the predicted forming limits using the data of the original stress-strain curve is the best one， while the forming limits using the data from the power exponential fitted curve has a certain deviation from the experimental one.

Key words: stress-strain curve, M-K theory, forming limit diagram(FLD), theoretical prediction, metal sheet