Residual stress analysis

Residual stress induces small changes in the crystal lattice spacing of a material, which can be revealed by XRD analysis with a very high sensitivity. 

In practice, the position of a suitable diffraction peak is measured in a certain spot under various orientations of the sample relative to the incident X-ray beam. From this the lattice spacings in different directions, and the related elastic strain can be determined. 

Tensile stress or compressive stress can then be calculated from the strain data taking into account the elastic constant of the material.

X-ray diffraction (XRD) residual stress analysis can be applied to a wide variety of polycrystalline materials, such as hardened steel, welded joints or ceramics. It is used as a quality control tool as well as in academic and industrial research. Often no special sample preparation is required.

With X-ray diffraction (XRD), it is the near-surface residual stress - typically in a depth of a few microns - which is being probed. Films and coatings with sub-micron thickness can also be investigated by using a grazing incidence geometry. This technique also allows for depth profiling. 

It is also possible to map stress across the surface of a material by using an incident X-ray beam with a very small spot size. Additionally, solutions exist for measuring bulky and heavy samples, small curved samples, or uneven sample surfaces.