Determination of local constitutive behavior of AA6061–T6 friction stir welds using digital image correlation

The local constitutive behavior of aluminum alloy 6061–T6 friction stir welds was characterized by uniaxial tensile tests using digital image correlation. The global tensile stress–strain relations for friction stir weld specimens were determined using a conventional testing machine equipped with an extensometer. The digital image correlation method was simultaneously applied to measure the full-field strain distributions over a 30 mm gauge length of the friction stir weld specimens during loading. The global specimen strains over the gauge length were determined by superimposing local strains measured by digital image correlation using the “inverse rule of mixtures” for composites. The Hollomon and Ludwik constitutive models were used to describe the local flow curves for the weld zones. The global true stress–true strain curves obtained from uniaxial tensile tests were compared with those constructed by superimposing local strains measured using digital image correlation. Both the global mechanical responses were in good agreement with each other. It is shown that the global true stress–true strain curves can be constructed using the inverse rule of mixtures method from the local constitutive equations for the different weld zones determined by the uniaxial tensile tests using digital image correlation.