Hill Engineering has participated in a collaborative, interlaboratory effort to quantify contour method residual stress measurement reproducibility. The study, entitled ‘Interlaboratory Reproducibility of Contour Method Data in a High Strength Aluminum Alloy’ was published through Experimental Mechanics, and is provided open access on Springer Link. The background, objective, and methods from the abstract text are as follows:
Background
The contour method for residual stress measurement has seen significant development, but an experimental reproducibility study utilizing physical samples has not been published.
Objective
A double-blind reproducibility study is reported, having scope beginning with EDM cutting and ending with residual stress calculation.
Methods
A reinforced I-beam sample geometry is identified for its unique residual stress profile when extracted from residual stress bearing quenched aluminum bar (7050-T74). Contour measurements are prescribed on a midplane of symmetry with dimensions 24.0 mm by 50.0 mm. Fourteen identically prepared samples are fabricated from a single long bar with well characterized and uniform residual stress. Five samples throughout the bar are identified for planning measurements to validate sample uniformity and overall suitability of the residual stress field. The planning measurements employ a range of techniques: contour method, neutron diffraction, and hole-drilling. Eight samples are distributed to an international group of participants to execute their standard measurement practice. A double-blind process is followed to provide anonymity.
Results
Results are provided by eight participants: six being self-similar and two being quite different, the latter set aside as outliers. An average residual stress field is established from non-outlying results and the spatial distribution of reproducibility standard deviation is determined. The average stress field ranges from -60 to 70 MPa and the reproducibility standard deviation averages 8.1 MPa on the measurement plane. The average reproducibility standard deviation is about 3 × larger for points within 1.0 mm of plane boundaries (17.6 MPa) than for the remaining points (6.1 MPa).