A New Mechanical Method for Biaxial Residual Stress Mapping

This paper describes a residual stress measurement approach that determines a two-dimensional map of biaxial residual stress. The biaxial measurement is a combination of contour method and slitting measurements and a computation to determine the effects of out-of-plane stress on a thin slice. The measurement approach uses only mechanical stress release methods, which is advantageous for some measurement articles. The measurement approach is verified with a numerical experiment and validated with independent confirmation measurements. Biaxial mapping measurements are performed in a long aluminum bar (77.8 mm width, 51.2 mm thickness, and 304.8 mm length) that has residual stresses induced with quenching. The measured stresses are consistent with quench induced residual stress, having peak magnitude of 150 MPa and a distribution that is tensile toward the center of the bar and compressive around the boundary. The validating confirmation measurements showed good agreement with the biaxial map. An uncertainty assessment, performed for each step of the experimental procedure, shows that the overall combined uncertainty is low, maximum of 21 MPa for longitudinal stress and maximum of 6 MPa for transverse stress, indicating that the new biaxial mapping approach has excellent measurement precision.