Neutron Residual Strain Surface Scans - Experimental Results and Monte Carlo Simulations

Abstract

Precise determination of diffraction peak positions is of particular importance for the evaluation of residual strains. Neutrons are commonly used to probe residual strains from material volumes in depths of several millimetres under the sample surface. However, neutron strain analyses are critical for the near surface region. When scanning close to a sample surface, aberration peak shifts arise, which can be of the same order as the peak shifts related to residual strains [1]. Series of Monte Carlo (M.C.) simulations using the software package RESTRAX/SIMRES [2] were carried out to simulate the peak shift as a function of gauge volume depth, monochromator curvature and other instrumental parameters, which can be used to quickly optimise the experimental setup for direct measuring residual strains near the sample surface at an arbitrary surface orientation. The M.C. simulations were compared and agree very well with the experimental data, not only for a stress free steel sample but as well for a deep rolled steel sample, measured at the STRESS-SPEC diffractometer at the research reactor FRM II, Garching (Germany).