Observation of notch effect in Al6061-T6 specimens under tensile loading using digital image correlation and finite element method

The fracture of ductile materials such as Al6061-T6 usually starts from void nucleation. In this study, we investigated strengthening effect and stress triaxiality behavior in notched Al alloy specimens. Various specimens, one un-notched and two with different U-types of notch, one with large diameter (L-notched) and another with small diameter (S-notched), having the same width were selected. The distribution of strain in the full-field was examined using the digital image correlation (DIC) method. Under the tensile test, S-notched specimens showed a more pronounced strengthening effect than the L-notched specimens. The results of DIC confirmed that the notch tip of the S-notched specimen experienced high strain, while the L-notched specimen experienced high strain at the center. The maximum stress triaxiality moved rapidly from the notch tip to the center with the increase in notch radius over 10 mm. The results of the stress triaxiality analysis by finite element method were in good agreement with the above DIC measurement results and predicted the void generation and fracture sites in L-notched and S-notched specimens.