Residual stress measurement

The materials engineering department at SLV Halle GmbH has been equipped with residual stress-measuring technology since 2009, which is used in non-destructive testing on samples and components.  The X-ray diffractometer used combines the benefits of high precision lab measurement with the mobility of a portable device. Residual stress levels often have a major impact on the load capacity permitted in welded structures, making awareness of residual stress essential in state-of-the-art engineering.

High-energy X-ray measurement allows for empirical residual stress analysis in quality and quantity. Crystal lattices in materials undergo microscopic changes manifested in residual stress at the macroscopic scale, so residual stress can only be measured in materials that are either crystalline or partly crystalline. The penetration depth applied in this measuring method only amounts to a few microns, and depends heavily on the material involved.

X-ray diffractometers are used in measuring residual stresses using the above method; there are various designs available on the market. These devices may be stationary or mobile.

Measuring accuracy and times depend mainly on exposure time and angular resolution using this testing method. Typical measurements involve a stress curve in depth profiles taken at a depth of usually only up to a few millimetres into the material, or as stress distribution on the surface of the sample. Measurements at critical points, such as the base of a gear tooth, are also possible using this equipment. The validity and accuracy of the results from any measurement depend heavily on surface condition and preparation of the test piece.

• Near-surface measurements such as residual stress distribution on metal sheet surfaces
• Depth profiles
• Measurement at the SLV Halle lab or on site