Elastic–plastic stress/strain response of friction stir-welded titanium butt joints using moiré interferometry

Abstract An experimental investigation is conducted to examine, evaluate, and characterize the fundamental elastic–plastic stress/strain response of friction stir-welded butt joints in thin-sheet, fine grain Ti–6Al–4V titanium alloy under normal tensile loading using the full-field optical strain analysis technique of moire interferometry. It was found that the overall strength of friction stir-welded Ti–6Al–4V is comparable to the accepted values for pure mill-annealed Ti–6Al–4V and the overall strain performance of friction stir-welded Ti–6Al–4V is roughly half that of the accepted values for pure mill-annealed Ti–6Al–4V. In addition, friction stir-welded Ti–6Al–4V demonstrates a consistent pattern of strain localization between the onset of yielding and ultimate failure. The resolvability of such strain localizations and their impact on far-field behavior can only be realized with full-field measurements such as those obtained using the moire interferometry technique.