A Method to Combine Residual Stress Measurements from XRD and IHD using Series Expansion

Abstract

It is common practice to use various residual stress measurement methods to complement each other and fully define a through-thickness stress distribution. Incremental hole-drilling (IHD) and X-ray diffraction (XRD) are two of the most widely used techniques. Although IHD readily provides stress data to some depth, the method is susceptible to large stress uncertainties near the surface. XRD, in contrast, is most suited to finding near-surface stresses. Constrain the residual stress distributions obtained through series expansion by using XRD measurements, thereby obtaining full depth stress measurements with reduced uncertainty near the surface. The proposed method enforces suitable relationships between the amplitude coefficients of the series expansion such that the resultant stress distributions match the XRD measurements. The method is demonstrated on an aluminium alloy 7075 specimen of 10 mm thickness that underwent laser shock peening treatment. Strong correlation in calculated residual stress distributions was found between the proposed method, standard series expansion and the regularized integral method. The proposed method has reduced stress uncertainty near the surface when compared to both standard series expansion and integral methods of IHD due to its incorporation of near-surface XRD data. The proposed method allows XRD measurements to be rigorously incorporated into IHD results. The effect of XRD uncertainty on the overall IHD stress distribution is localised to the near-surface measurements.