Expression of uncertainty during measurement of X-ray diffraction residual stress

In the present work, a general method to calculate the uncertainty in X-ray stress analysis is proposed. It is in agreement with the current practice in metrology [1, 2, 3]. The uncertainty, expressed by a standard deviation is decomposed into several variance terms that can be calculated either from statistical experimental data or from physical modelling of the errors. The proposed model takes into account random errors due to the counting statistics and temperature fluctuations as well as systematic errors due to goniometer adjustment (beam and specimen alignment, W offset). A method to assess the uncertainty due to the X-ray elasticity constants is also presented. Each term is expressed by a simple formula that enables the operator to identify and quantify easily the influence of the acquisition parameters on the uncertainty and allow him to make choices in order to reduce it.