Evaluation of strains in a U-bend specimen by neutron diffraction

Abstract

Neutron diffraction measurements have been made on a 304 stainless steel U-bend specimen using the General Purpose Powder Diffractometer on the Intense Pulsed Neutron Source at Argonne National Laboratory. This experiment was undertaken as a demonstration to show the capabilities of neutron diffraction for the evaluation of strain fields in a stressed specimen. Collimation masks were positioned around the specimen to define the volume from which scattering was observed. Data were obtained from five different positions through the U-bend thickness by shifting the specimen position in the incident neutron beam between data runs. Diffraction data were analyzed for six different crystallographic planes for each data run: (111), (200), (220), (311), (331) and (420). Although the data clearly show variations in strain vs position, additional runs would be needed to completely map the strain field through the thickness and some improvement in resolution would be desired. Although the data may not warrant it, a least squares procedure was applied to the strain data to obtain the principal strains, radial and transverse, as a function of position. Results obtained vary as generally expected, but additional data are needed to clarify some of the detail observed. This report is tutorial in its presentation,more » intended for those having no experience in neutron diffraction. Valuable experience was obtained which would be useful in planning and executing additional experiments at IPNS. 9 tabs.« less