Bendability enhancement of an age-hardenable aluminum alloy: Part II — multiscale numerical modeling of shear banding and fracture

In this study, the sequence of microstructural events leading to failure and the relationship between crystallographic texture, shear band development, micro-crack initiation and propagation during wrap-bending of monolithic AA6016 and composite AA6016X sheet alloys are studied using crystal plasticity based finite element methods (CPFEM). The numerically predicted results for texture evolution, shear bands development and fracture behavior after wrap bending show good agreement to the corresponding experimental observations. It is shown that failure during bending of AA6016 is controlled by the development of intense shear bands that emanate from surface low cusps along the outer tensile edge and provide a minimum energy path for micro-cracks to propagate, promoting a predominant transgranular failure. Upon intersection with another shear band, the advancing crack tip alternate from a less critical localization condition to a more critical one, as it requires lesser energy for the creation of new fracture surfaces while sustaining the imposed plastic deformation. Grains with Cube or near Cube texture are rather resistant to shear banding and crack propagation whereas the contrary is true for grains with near S and near Goss orientations. It is also shown that the ductile clad layers within the composite AA6016X alloy act as an efficient barrier against the development and propagation of shear bands within the less ductile inner core, thereby significantly enhancing the bendability of the alloy. Through a systematic study, it is further shown that the bendability of AA6016 alloy can be improved significantly through proper engineering of the microstructure.