Three-dimensional quantitative in situ study of crack initiation and propagation in AA6061 aluminum alloy sheets via synchrotron laminography and finite-element simulations

Ductile crack initiation and propagation in AA6061 aluminum alloy for a fatigue precrack have been studied in situ via synchrotron radiation computed laminography, a technique specifically developed for three-dimensional imaging of laterally extended sheet specimens with micrometer resolution. The influence of the microstructure, i.e. due to the presence of coarse Mg2Si precipitates and iron-rich intermetallics, on the void nucleation process is investigated. Coarse Mg2Si precipitates are found to play a preponderant role in the void nucleation and ductile fracture process. Void growth and void coalescence are then observed and quantified by three-dimensional image analysis during crack initiation and propagation. Parameters for a Gurson-Tvergaard-Needleman micromechanical damage model are identified experimentally and validated by finite-element simulations.