A comparative investigation on theoretical models for forming limit diagram prediction of automotive sheet metals

Determination of sheet metal formability, which is commonly evaluated through a forming limit curve (FLC), is an essential task for part designs in the automotive engineering community. This study provides a coherent comparison among four theoretical FLC criteria including Swift's instability, Hill's localized neck, Storen-Rice bifurcation analysis, and Hora's MMFC. Within these criteria, closed-form solutions for FLC are available for fast and expensiveness explicitly estimating the forming limit diagram (FLD) of sheet metals. According to their closed-form solutions, an empirical suggestion is proposed to improve the accuracy of the theoretical FLC. Quantitative comparisons are then made to evaluate the performance of these criteria for numerous aluminum alloys and steel sheets which are frequently used in automotive industries. Based on the comparisons, the advantages and limitations of each model are discussed from a physical point of view, which appears to be a useful suggestion for selecting a proper theoretical model to evaluate the FLD of sheet metals without conducting experimental tests.