Focused Ion Beam and Digital Image Correlation (FIB-DIC) Assisted Numerical Residual Stress Field Reconstruction in Laser-Welded Ti-6Al-4V

Residual stress in engineering components is a strong influencer in their mechanical responses, yet most experimental characterization techniques cannot describe the full-filed stress distribution in a wide range of geometries because of finite spatial resolution, limited measurable stress components, etc. Laser welding features low heat input and narrow heat-affected zones, which raises challenges for stress measurements since most laboratory-based techniques, exemplified by X-ray diffraction (XRD), have millimeter-scale spatial resolution or above. In this work, a residual stress field reconstruction technique was demonstrated on laser-welded Ti-6Al-4V combining focused ion beam and digital image correlation (FIB-DIC) to describe the residual stress distribution at micron-scale spatial resolution, synchrotron XRD for the extent of the strain incompatibility, and an automated finite element (FE) approach to iteratively perform full-filed stress reconstruction from incomplete measurements. Transmissive diffraction characterized a strain incompatible zone of width 5.0 mm centered about the weld centerline. 5 × 15 FIB-milled ring-cores were incrementally milled over a quarter of the incompatible zone, which corresponded to circa 14% of the total sample area. The FE-based reconstruction, executed on ABAQUS, was demonstrated successful in returning the stress profile in the unknown area after 10 iterations upon experimental confirmation. A tolerance test based on purely FE-generated input dataset showed the method is sensitive to the definition of the strain incompatible zone. This work shows that FIB-DIC combining FE method can reconstruct the residual stress field from incomplete measurement in laser butt welds, providing sufficient information on the extent of the incompatible zone and the stress distribution within. The method is promising for efficient stress analysis in components where inelastic processes are confined in limited volume, as well as textured polycrystals that are unsuitable for XRD measurements.