Effect of through thickness strain distribution on shear fracture hazard and its mitigation by using multilayer aluminum sheets

The formability of sheet metal is generally accepted to be limited by the so-called Forming Limit Curve (FLC). This is valid for a majority of operations, given that localization immediately precedes fracture. For the characterization of the latter, a microscopy based new method is applied on Nakazima specimens. Furthermore a simple cup deep drawing test is employed to investigate the shear failure phenomenon and extend the fracture limit in the left hand side of the principal strain space. In addition, fracture phenomenon in aluminum alloy AA6016 sheet sample is investigated by using different fracture criteria. The measured principal fracture strains ɛ11f and ɛ22f are then implemented in the FE-code to predict rupture. Moreover, initiation and propagation of cracks in monolithic and multilayer aluminum alloys, are studied. A newly designed triangle shape deep drawing part is used in the framework of this work to validate the constitutive and failure models as well as investigate the advantage of a multilayer material, compared to the monolithic one.