Impediments to efficient through-surface strain scanning

Abstract

The efficient measurement of through-surface residual strains using multidetector neutron strain scanners is constrained by instrumental effects which arise when the ‘gauge volume’ is only partly immersed in the sample. The three principal causes, wavelength variation across the incident beam, lateral displacement of the ‘effective centre’ of the gauge volume relative to the detector, and asymmetric clipping of the diffracted peak profile are discussed and quantified. Results are described of a systematic quantitative investigation of the instrumental aberrations that affect the L-3 spectrometer operating in its strain scanning mode at the NRU reactor at AECL, Chalk River, Canada. Comparisons are made with theoretical models which accurately predict the observed aberrations. Techniques for reducing and correcting for the effects are discussed.