Strain localization and damage mechanisms during bending of AA6016 sheet

The bendability of AA6016 sheets is a critical parameter for many automotive applications. In this experimental study the origins of damage and its evolution are characterized using interrupted and in-situ bending tests to correlate microstructural evolution with damage development. Local strains were estimated by optical and scanning microscopy (EBSD). Together with the load-displacement plots, they provided a set of physical parameters characterizing crack initiation. In particular, it is shown that(1)crack initiation occurs at the maximum of the rigidity–displacement curve;(2)cracking is preceded by strain localization in the form of macro-shear bands which induce surface roughening. Local necking then occurs in some surface grains and leads to ductile intergranular crack propagation. The sequence of microscopic changes at the grain scale up to and beyond crack initiation have been characterized and quantified in terms of local grain strains, coarse intragranular slip and shear band evolution over several grains.