Benchmark Sample Design for the Validation of Residual Stress Measurements by Diffraction: Insights and Practicalities

Abstract Non-destructive determination of residual stresses can present significant challenges. Two benchmark samples having the same geometry have been developed which can be measured by diffraction techniques and adapted to other material systems to validate RS measurements. While having the same geometry, one was solely elastically loaded while the other had stresses generated by significant plasticity. Measurements by a neutron diffraction and two synchrotron X-ray diffraction instruments (white beam and monochromatic beam) have been made in the ferrite phase at identical locations on S355 ferrite/pearlite steel benchmark samples. Broadly consistent results (± 30–50 MPa) are obtained across the three diffractometers. These results were corroborated by finite element predictions, with standard deviation on differences between predictions and measurements being ± 22 MPa for benchmarks with elastic sources of stress and ± 77 MPa for the plastically deformed case. Differences in the stresses were found when making near-surface measurements but only when around 80% of the gauge volume was outside the sample. The larger discrepancies between the measurements and the FE model in the plastic case may be due to plastic load transfer from the softer ferrite to the harder cementite during plastic deformation.