Neutron strain scanning

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Abstract
Strains in engineering components are commonly classified into two types, microstrains and macrostrains. Microstrains vary over distances that are short relative to the scale of the microstructure and are of considerable importance in the characterization of engineering materials, such as composites and alloys containing secondary phases where differences in expansion coefficients cause stresses to be generated in the separate constituents. In most types of microstrain measurement their short range generally precludes their spatial resolution and data from each phase is integrated from the entire volume of the specimen. Macrostrains, in contrast, vary with location and can be spatially resolved. They usually relate to the shape of a component and are particularly significant near discontinuities such as at sharp bends, defects, or surfaces where stress concentrations occur or stress gradients are often steep. Their spatial variation may be determined by sampling small discrete wolumes throughout a specimen using an appropriate strain gauge. This article is concerned with the use of neutrons for macrostrain scanning.