Bulk Residual Stress and Strain Measurements Near Geometrically Large Holes for Improving Cold Expansion Process Models

We report on a series of measurements of residual stress and residual strain near large cold expanded holes. The work was undertaken to improve engineering models of the hole cold expansion (Cx) process and support more effective use of compressive residual stress treatments that extend fatigue life and/or inspection periods. Measurements were made in samples with a 25.4 mm thickness and a centered 25.4 mm hole, so the features are large relative to typical applications. Measurements use a complement of diverse techniques: the contour method, time-of-flight neutron diffraction (LANL SMARTS instrument), and EDXRD (CHESS FAST instrument). Comparisons of data shows all techniques in agreement. Comparisons of data to outputs from a process simulation are consistent with systematic discrepancies reported in prior publications that have significant effects on forecasts of Cx fatigue benefits. The measurement data therefore provide an engineering basis for making improvements to the process simulation.