Comparison of two X-ray residual stress measurement methods: sin2 ψ and cos α, through the determination of a martensitic steel X-ray elastic constant

X-ray diffraction technique for residual stresses measurement is usually associated to the sin2 ψ method, a method based on the interception of the diffraction cone and line detectors. To overcome this loss of information, the cos α method is an alternative method which uses a single exposure to collect the entire diffraction cone via a 2D detector. The present paper compares both sin2 ψ and cos α methods, through the X-ray elastic constant (XEC) determination of a quenched and tempered martensitic steel. The full-cone measurement method demonstrates a smaller scatter and a better repeatability of the measurements. This latter point is of considerable interest since larger scatter in XEC may result in large variation in residual stress values, especially at high stress levels.