Assessment of local microscale residual stresses induced by variable uncut chip thickness in turning using large-field FIB-DIC

Variable uncut chip thickness in turning induces spatially heterogeneous thermomechanical loadings that strongly affect residual stress (RS) generation. Conventional techniques, such as laboratory X-ray diffraction (XRD), provide spatially averaged RS values over millimetre-scale areas and cannot resolve local surface RS gradients. This work introduces a large-field Focused Ion Beam-Digital Image Correlation (FIB-DIC) methodology using slits and ring-cores to quantify local microscale RS, combined with stereo profilometry to correlate stresses with surface topography in turned Ti-6Al-4V ELI. The results reveal peak-to-valley RS variations up to 1000 MPa, undetectable by XRD, highlighting their potential impact on fatigue, corrosion, and surface-driven component performance.