Residual stresses arise during almost every manufacturing stage, for example during casting, welding or machining. These internal stresses exist independently of external forces and can significantly affect component properties. While compressive residual stresses make crack initiation more difficult, tensile residual stresses can considerably reduce a component’s service life.
Traditionally, measurement is performed using X-ray diffraction, an established method for determining residual stresses. However, the penetration depth of X-rays in metals is limited to a few micrometres, meaning that only near-surface stresses can be measured. To obtain a complete picture of the stress distribution, additional destructive methods such as electrolytic etching are often required.
With ResiduStress, W.S. Werkstoff Service GmbH offers an innovative solution: residual stress measurement using ultrasound. This method enables non-destructive analysis of the stress distribution throughout the component volume. Polarised ultrasonic waves allow both surface and subsurface stresses to be measured without damaging the component.
Freight wagon wheels are a practical example. In accordance with DIN EN 13262, these should have tangential compressive residual stresses in the wheel rim after manufacture. During braking, the tread is heated intensely by the brake blocks, which can gradually transform these stresses into crack-promoting tensile residual stresses over time.
This phenomenon intensifies the transformation that normally takes place over the service life as the diameter decreases due to wear and reprofiling. Continuous monitoring of residual stresses is crucial to prevent component failure, for example as a result of lateral thermal cracks. Ultrasonic testing provides reliable, non-destructive monitoring.
