UPDATED THEORY OF THE X-RAY DIFFRACTION RESIDUAL STRESS MEASUREMENT COMPARING COS-ALPHA AND SIN²PSI TECHNIQUES – BIAXIAL VERSUS TRIAXIAL

Author:  Mohammed Belassel1, James Pineault1, Michael Brauss2 1 PROTO MANUFACTURING LIMITED, Canada 2 PROTO MANUFACTURING INC, USA
Source:  ICSP14 Milan
Doc ID:  2022100
Year of Publication:  2022
Abstract:  
Abstract When applying the Sin²ψ technique to x-ray diffraction (XRD) based residual stress measurements, both the normal and shear stress components can be easily and accurately evaluated in the direction(s) of interest. The Sin²ψ technique was developed and refined over several decades along with many other advances so as to achieve high accuracy residual stress measurement results in a wide variety of circumstances and material conditions. With the introduction of the Cosa technique, only the biaxial stress field was considered in the calculation of the stress tensor components and as such, is susceptible to significant errors often resulting in unreliable residual stress measurements. In the present study, the Sin²ψ and Cosa techniques were compared and evaluated. It is shown that the biaxial based Cosa technique leads to erroneous stress data when in-plane shear stress is present, and results are found to be equivalent to the two-tilt Sin²ψ technique. In other words, the Cosa technique used in only one orientation could not reproduce the correct results as obtained via the Sin²ψ technique with multiple tilts. Thus, the only viable solution is to assume a triaxial stress tensor and to collect data with tilts distributed evenly over the half-space when using the Cosa technique. Keywords: Residual Stress, Shear stress, CosAlpha, Single Exposure, Sin2Psi, Standard