Evaluation of fracture limit in automotive aluminium alloy sheet forming

In finite element simulation of auto-body panels forming, an accurate forming limit criterion is very important. To evaluate accurately the formability of automotive aluminium alloy sheet, in this paper, a ductile fracture criterion developed by the author is introduced in finite element simulation. Based on Barlat’s yield function and Hollomon’s hardening equation, the simulations of aluminium alloy sheet forming are carried out. Material constants in the ductile fracture criterion are determined by means of uniaxial tension and hemispherical punch stretching tests. The critical punch strokes of the aluminium alloy sheets X611-T4, 6111-T4 and 5754-O in cylindrical complex forming, which includes deep drawing and stretching modes, are calculated by the ductile fracture criterion. The comparison of the calculated results with the experimental values shows that the critical punch strokes of the three sheets mentioned above are predicted successfully by the ductile fracture criterion.