Comparison of 2 methodologies developed for the determination of residual stresses through X-ray diffraction: application to a textured hcp titanium alloy

For polycrystalline materials, the experimental determination of residual stresses neglects the so-called 2nd order fluctuations arising from e.g. plastic or thermal incompatibilities from grain to grain. This constitutes a serious limitation of the classical measurements methods, since these 2nd residual stresses are known to have a major influence on the mechanical behavior of metallic alloys, especially if these are strongly textured. In the present paper, a new methodology for the treatment of the measured data is described and compared to classical ones. In order to do so, the simulation of a tensile test is performed using a self-consistent elasto-plastic model, in order to constitute a virtual experimental data set. The 1st and 2nd order stresses are extracted from the simulation for various macroscopic stress levels. Two approaches (the classical sin2ψ method and a method based on the simultaneous analysis of several X-ray diffraction peaks) are then used to quantify the 1st order stresses from these “experimental” data. It is clearly shown that the method based on multi-peak analysis allows to minimize the error made by neglecting the so-called 2nd order stresses and leads to a better quantitative estimation of the 1st order stresses.