Precise Analysis of Near Surface Neutron Strain Imaging Measurements

The lateral resolution of Neutron Strain Imaging Instrumentation for high resolution applications is restricted. A realistic lower limit for reasonably fast measurements is 0.5 mm. The reason is, that in order to achieve maximum neutron flux at the sample position, the beam must be focussed. This is often achieved by double focussing monochromators or focussing guides. As a result the beam-divergence sets a lower limit for gauge volume definition. However, the lateral resolution can be improved for near surface and interface analysis by entering the gauge volume only partially into the material. As a result, the sampled gauge volume is getting smaller and resolution is improved. As a drawback, errors of the detected peak position, usually called surface errors or pseudo-strain, are introduced in the measurements. Such errors are often corrected by repeating the measurement with the sample turned by 180 degrees. This is inefficient, limited in precision and often not possible. This paper describes a more efficient and precise method for near surface stress analysis that requires only one reference measurement, which provides experimental parameters for an analytical model for data correction. The model takes into account curved surfaces and allows precise stress determination as close as 40 micrometres below a surface or interface. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ICM11