Effects of Multi-Axis Oscillations in Residual Stress Measurements via X-Ray Diffraction

X-Ray Diffraction (XRD) has been used for the measurement of residual stress (RS) since the 1920s, with numerous advancements in accuracy, precision, and speed heretofore. XRD methods rely on the queried material to be quasi-isotropic, homogeneous, and to have a near-random grain orientation distribution; however, often this is not the case. When the coherent domain size is large relative to the irradiated volume, a non-random grain orientation distribution may be sampled, and the diffraction Debye ring may become “spotty.” The presence of a spotty Debye ring introduces errors in the apparent diffraction peak position and, by extension, results in errors in the determination of RS. Traditionally, oscillations have been conducted in the same plane as the tilting plane in either Omega (Iso-inclination) or Chi (Side-inclination) modes to minimize experimental errors. However, there is no existing literature on Omega oscillations while measuring RS in Chi mode, or vice versa, or the use of simultaneous oscillations in both planes during measurements. In this study, experimental data were collected in both modes, with oscillations in both planes over a range of angles. Simulation and modeling were employed to compare with experimental data with the goal of optimizing RS measurement accuracy.