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Residual stress analysis

Shot-peened Al2O3-ceramic

Mechanical, thermal and/or chemical surface processing as well as coating introduce residual stresses in the near-surface zone of technical parts, which may influence the material properties significantly. Among the methods for residual stress analysis X-ray, synchrotron and neutron diffraction take up a unique position, because they allow for non-destructive and phase-selective evaluation of stress distributions from the surface down to the volume of the material.

On the photon side, we employ in our department angle-dispersive (AD) X-ray and energy-dispersive (ED) synchrotron diffraction methods to investigate the residual stress depth distribution in polycrystalline materials, technical parts and coating systems. The advantages of ED synchrotron diffraction concerning depth-resolved stress analysis are the short measuring times allowing for fast in-situ studies and the multitude of diffraction lines E(hkl) recorded in each spectrum containing additional depth information.

Rietveld-refined energy-dispersive synchrotron diffraction pattern.

Research activities in the field of X-ray stress analysis (XSA) are aimed at the development of new and advanced measuring methods and data evaluation concepts, which enable the detection, evaluation and assessment of complex residual stress distributions in the materials surface region. Recent and current research topics are for example:

  • Residual stress analysis in multilayer coatings
  • Rietveld-based evaluation of ED diffraction data
  • Separation of stress and composition gradients
  • XSA with high lateral and depth resolution
  • Fast in-situ ED stress analysis of dynamic processes (e.g. during thin film growth).

Comparison of experimental and recalculated d-sin²ψ-profile.

Analysis of very steep residual stress gradients by means of the Universal plot (UP) method and the Rietveld-method.