Experimental verification of residual stress models using neutron strain scanning

Few experimental methods exist for the non-destructive measurement of internal strains in engineering components and most are capable of providing only restricted datasets which are of limited use in validating model calculations. Neutron strain scanning is a non-destructive technique that uses the diffraction of a beam of thermal neutrons to determine the average spacings of atoms within a small gauge volume inside polycrystalline materials. The technique has been developed over the last decade or so and is similar to the longer established X-ray technique but neutrons are in general much more penetrating and can be used to scan at depths of several centimeters in most engineering materials in contrast to the 10 {micro}m or so possible using X-rays. In principle strain data can be collected, subject to absorption constraints, at any point, in any direction within a component that may be scanned to generate an accurate and continuous residual stress contour pattern that is particularly suitable for the rigorous verification of model predictions. Examples are given of internal residual stress distributions measured in a weld and a railway rail. Comparison is made with a finite element model with which good agreement is observed.