Strain localization in titanium investigated via in situ digital image correlation with multiscale speckles

Strain localization in commercially pure titanium under uniaxial tension is investigated with in situ digital image correlation (DIC) at different length scales. Speckles in three different sizes are prepared on the surface of titanium specimens, referred to as microscale, mesoscale and macroscale speckles. The microscale and mesoscale speckles for scanning electron microscopy DIC analysis are fabricated by different electro-polishing procedures, and spray painting is used to prepare the macroscale speckles for the optical DIC measurement. Electron back scattering diffraction (EBSD) characterization is conducted for the microscale speckle case. The strain fields obtained at different length scales combined with the microscale EBSD examination establish the relationship between microscale strain localization and macroscale strain concentration bands. Strain localization tends to form at grain boundaries and inside deformation twins, especially at the large-angle grain boundaries, and the amplitude and rate of strain accumulation at grain boundaries are higher than inside deformation twins. The microscale strain-localized regions dispersed at grain boundaries and within deformation twins present themselves as the strain concentration bands observed with the macroscale speckles, and both the strain localization regions and strain concentration bands are at ±45∘ with the tensile direction.