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Residual stress analysis

Stress, PANalytical

Improving safety

X-ray diffraction (XRD) is a well-established, non-destructive method for the determination of residual stress in polycrystalline materials. Induced by thermal treatment or machining, for example, stress can accumulate during the lifetime of a material and cause unexpected failure of a technical component in a mechanical construction. The control of residual stress is therefore essential to improve a material’s safety and durability.

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

Versatile applications for metals, ceramics, thin films and more

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 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.

PANalytical's instrumentation and software solutions for residual stress analysis

The Empyrean multi-purpose XRD platform is PANalytical’s most versatile instrument for stress measurements. The system supports the side inclination (chi-stress) and iso-inclination (omega-stress) modes, as well as thin film stress analysis under grazing incidence. It uses a three-axes cradle to carry large and heavy samples, such as engineered components, for chi-stress analysis. A five-axes cradle enables multiple sample analysis without user intervention by using the x and y axes as sample changers.

With the Empyrean, residual stress analysis can be done under non-ambient (high-temperature) conditions and performed with several geometries, from a cost-effective slit-based solution to advanced optical modules for parallel beam geometries. These more complex optics employ X-ray mirrors and lenses to allow for more accurate measurements and a larger choice of reflections for the residual stress determination. A stress-free tungsten sample is available as a reference material.

X'Pert³ MRD (XL) also offers all stress measurement options, including a half-circle cradle for chi-stress measurements. It is particularly well suited for stress analysis in thin films.

The X'Pert³ Powder XRD system offers the same manifold options as the Empyrean, with the exception of the side-inclination method.

Stress is PANalytical’s XRD software module for analyzing residual stress measurements using the classical single-{hkl} sin²ψ method. Supporting uni-directional as well as multi-directional (full tensor) stress determination Stress also includes a database for the X-ray elastic constants.

Stress Plus additionally supports grazing incidence and/or multiple-{hkl} stress analysis for the determination of residual stress in polycrystalline coatings.

Stress software is comprehensive, easy to automate and easy to use.

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