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Residual stresses are in a component before it sees its first load. They arise from casting, welding, heat treatment or machining and add to the load stresses in service. A component can therefore fail even though the calculated limit load was never reached.
Together with our partners, we determine the magnitude and direction of these stresses. This allows load capacity, fatigue strength and manufacturing influences to be assessed. We work with two methods:
Hole-drilling method
Residual stresses over depth. A blind hole a few millimetres in diameter; the load capacity is retained.
X-ray diffraction (XRD)
Residual stresses at the surface, non-destructive. Crystalline materials only; greater depths by stepwise removal.
Mechanical hole-drilling method
A special strain gauge rosette with three measuring grids is applied to the component. We drill a small blind hole through its centre, either slowly with an HSS end mill or with a high-speed air turbine and carbide cutter.
Drilling releases the residual stresses at the edge of the hole and the material springs back. The rosette measures this relaxation step by step. From the data we calculate the residual stresses over the drilling depth.
Procedure
- Define the measuring points together with you
- Prepare the surface, apply and wire the hole-drilling rosette
- Drill the blind hole in steps, recording the strains after each step
- Calculate the residual stresses over the drilling depth
- Results report with incoming documentation of your component
X-ray diffraction (XRD)
For residual stresses near the surface we prefer X-ray diffraction. It is based on the diffraction of X-rays at the lattice planes of a crystalline material: elastic strain changes the spacing of the lattice planes compared with the stress-free state. These strains are converted into stresses using the elastic constants.
X-rays penetrate only a short distance, so the depth resolution is high. For greater depths, material is removed electrochemically in steps and measured again after each step.
Procedure
- Material analysis and incoming documentation of the component
- Definition of measuring positions and stress directions
- Reference measurements
- Measurement, with electrochemical layer removal if required
- Results report
What we need for a quotation
- Component and material, ideally with a drawing
- The question to be answered, for example comparing two manufacturing processes or the cause of a failure
- Desired measuring points and number of components
Related services: strain gauge application, on-site measurement, all services.
Need to clarify residual stresses?
Send us the drawing and your question, we will come back with a proposal: Contact us or request a quotation.