Analysis of the Effect of Diffraction Peak Positioning Method on Residual Stress Measurement, Using the Standard XRD Technique

The standard XRD (X-ray diffraction) technique is one of the most useful non-destructive residual stress measurement methods, especially in military and in nuclear and aerospace industries. The XRD method uses the distance between crystallographic planes (d-spacing) as a strain gauge. According to the Bragg’s law, the precision of d-spacing measurement depends on the precision of measured diffraction angles (2θ). So the precision of the XRD residual stress measurement depends strongly on how precise the 2θ values are measured. In this paper, to show the importance of the peak positioning method on accuracy of the standard XRD method and to present how diffraction peaks are analyzed, three more common peak positioning methods, C.G(center of gravity), Gaussian and parabola are used to determine diffraction peak position of a two-layer Al/Cu cold rolled plate. Then, residual stresses and standard deviations are calculated for all mentioned methods. Also, the effects of various parameters, such as background correction, absorption coefficient, Lorentz polarization factor, and kα2 striping are considered on the results of all peak positioning methods. The results of XRD residual stress measurement technique are also verified by the drilling residual stress measurement method. The results show that the residual stress analyzing by XRD technique is very sensitive to the peak positioning method and for residual stress measurement by this method in rolled plates C.G. method has the highest accuracy and the lowest standard deviation respect to other peak positioning methods. Considering various parameters showed that kα2 stripping and background correction have the highest effects on the results of all peak positioning methods.