Stress Evaluation by Neutron Diffraction: Modelling of a Two-axis Spectrometer

Abstract

Neutron stress evaluation is reliable in normal condition where the neutron probe is entirely immersed in the sample. However, near surface measurements are difficult to analyse, due to great parasitic peak shifts which are obtained in such condition. To correct these systematic errors, a numerical modelling of a whole two-axis neutron spectrometer has been developed. The simulation program computes the distribution of intensity and wavelength across the incident beam. The precise shape and size of the probe volume is also calculated. A theoretical diffraction peak is finally built through a modified Monte Carlo simulation method. The whole simulation program allows thus to predict and correct all parasitic shifts of the diffraction peak. To check the limits of the method, the procedure has been applied to the evaluation of the residual stresses induced by surface treatments, such as nitriding and shot peening.