Mapping bulk triaxial residual stress fields by combination of synchrotron x-ray diffraction and contour method measurements

A novel approach for determining bulk triaxial residual stress fields by coupling energy dispersive x-ray diffraction and contour method measurements is provided and demonstrated. Synchrotron x-ray diffraction (SXRD) can readily map 3D bulk elastic strain and stress fields. Three orthogonal elastic strain components are typically required for stress determination via isotropic Hooke’s law when the plane stress or plane stress assumptions are not appropriate. However, one of the required strain components can be indeterminable when sample geometry is prohibitively large, such as for typical engineering geometries. The transmission geometry required for monochromatic and energy dispersive SXRD can produce long path lengths and excessive attenuation of the x-ray beam. As an example, for a plate-like sample geometry where the thickness is relatively thin, it is trivial to measure the longitudinal and height direction elastic strain components but obtaining the through thickness component is often not possible as the x-ray beam path must be nearly parallel to one of the large dimensions of the plate. To overcome these limitations, this work applies a combination of SXRD and the contour method (a mechanical relaxation technique which is not limited by sample dimensions in the same sense), to determine a multiaxial stress state. This measurement approach is applied to various samples including those produced by additive manufacturing, and an aluminum plate featuring a fastener hole processed by cold expansion. Comparisons with independent measurement techniques show similar trends and magnitudes as the SXRD and contour method coupling measurements and motivates further validation studies.