Micro-slotting, a micro-scale relaxation residual stress measurement technique, has been shown in recent years to be a reliable method for measuring local residual stresses in metallic materials. This technique employs an SEM-focused ion beam system for milling and imaging, digital image correlation software to track displacements due to residual stress relaxation, and finite element analysis for interpolation of the original local stress state. In this research, a micro-slotting procedure was established using finite element models and was used to obtain sub-surface residual stress measurements on machined and shot peened planar Ti-6Al-4V samples. These measurements were compared to macro-scale XRD residual stress measurements, and discrepancies between the results of the two techniques were discussed. The measurement procedure was then applied to as-drilled and cold-expanded holes for near-edge measurement of residual hoop stresses. Comparison of the measured residual stress distributions with plastic strain data obtained using EBSD allowed for interpretation of fatigue life differences and crack growth behavior. Next, a grid of measurements was performed in a sub-surface region of the shot peened sample, and EBSD was used to acquire microstructure information in the measurement regions. Comparison of the measured displacements and interpolated residual stress values with the local microstructure allowed for novel qualitative observations regarding residual stress orientation and microstructure effects on the measured residual stress relaxation. Last, the use of the micro-slotting technique was demonstrated for measurement of local residual stress in additive manufactured components. Series of measurements were performed across two interfaces in a complex Ti-6Al-4V build, and post-measurement optical microscopy allowed for analysis of the residual stress data at the microstructural level --Abstract, page iv
