Ring-Core Focused Ion Beam Digital Image Correlation for Residual Stress Evaluation

Residual stress (RS) in welds, especially in the localized region where the weld starts or stops, can lead to unexpected performance and distortion, particularly during post-weld machining and heat treatment. Measuring RS is challenging due to resource limitations (e.g. neutron or x-ray beam capabilities and facilities) and destruction of the part of interest (e.g. contour method or hole drilling techniques). This work explores the ring-core focused ion beam digital image correlation (FIB-DIC) method on an electron beam weld. The FIB is used to mill a microscopic, ring-shaped trench into the surface of the part, leaving behind a pillar in the center of the milled ring. DIC then optically measured small displacements on the top surface of this pillar, which can be linked to the released elastic strain from milling. Local compressive and tensile stresses in the start-stop region of the weld were investigated, and the impact of these results with respect to weld development will be presented. This measurement technique has seldom been applied to welds, yet may provide valuable insight into controlling or minimizing RS during weld parameter development, allowing this work to minimize a gap in RS research.