Mitigation of Cutting-Induced Artificial Stresses in Contour Method Analysis of Irregular Components

The contour method is a destructive technique to reconstruct residual stresses that are released when cut with wire electro-discharge machining. This cutting process can potentially introduce artifacts when cutting through components with non-rectangular cross sections. This is most apparent when the instantaneous cross section of the workpiece changes with respect to the cutting orientation. Typically, sacrificial material is employed to regularize the cutting cross section to mitigate artifacts. A further correction method has been realized employing a reference sample in a near stress-free state intended to correct for cutting artifacts without the use of sacrificial material. This new approach is illustrated with residual stress manifesting in two aluminum alloy 7050 friction stir welded T-sections. Measurements made employing neutron diffraction, contour method with sacrificial material and with the new approach are compared and contrasted. While the sacrificial material approach remains the best approach for dealing with the subject component and cross section, the use of a reference sample is shown to reduce errors in the resolved residual stress. Neutron diffraction results have been employed, showing that errors can be reduced as compared to an uncorrected result in some regions, but further errors can be introduced if the reference cut has not been well controlled. This is particularly important for components which may not be able to have sacrificial material applied.