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Development and Applications of Residual Stress Measurements Using Neutron Beams

The deep penetration and selective absorption of neutrons make them a powerful tool in nondestructive testing of materials with large samples or objects. Residual stress formed in a material during manufacturing, welding, utilization or repairs can be measured by means of neutron diffraction. In fact, neutron diffraction is the only non-destructive testing method, which can facilitate 3-D mapping of residual stress in a bulk component. Stress measurement using neutron beams is a technique that enables such high-quality non-destructive investigations, and provides insight into material strain and stress state deep within engineering components and structures under various conditions representative of those which might be experienced in service. Such studies are of importance to improve the quality of industrial components in production and to optimise design criteria in applications. Anisotropies in macroscopic properties like thermal and electrical conductivities, for instance of fuel elements, and mechanical properties of materials depend on the textures developed during their preparation or thermal treatment. Such textures also can be studied using neutron diffraction techniques. At the present time there is a substantial scientific and industrial demand for high-quality nondestructive residual stress measurements, and the continuing competitive drive to optimize performance and minimize weight in many applications indicates that this demand will continue to grow. As such, this technique is an increasingly important tool for mechanical and materials engineering in the search for improved manufacturing processes to reduce stress and distortion. Considering this trend, and in accord with its purpose of promoting the peaceful use of nuclear applications, in 2006-2009 the IAEA coordinated a cooperative research programme on the “Development and Application of the Techniques of Residual Stress Measurements in Materials” (CRP 1314). This project counted with the participation of practitioners from highly specialised user facilities from various Member States, including the including the Czech Republic, Germany, Hungary, India, the Netherlands, Pakistan, Romania, Russian Federation, and South Africa. This document is the culmination of the project, and its purpose is to relate guidance on the basic principles, requirements, preparation, design, execution and standardization of residual stress measurements using neutron beams in a single document. The publication includes details of experimental techniques, associated equipment and instrumentation, their commissioning and calibration, control and data acquisition. A separate chapter is dedicated to data analysis and interpretation. At the end, the document provides with a number of selected examples for applications of residual stress measurements as well as future trends for development and use of this powerful technique. Finally, all necessary information on Round Robin exercise with standard samples as well as an extensive data base containing detailed information on a dozen of residual stress instruments world-wide has been included. Ultimately, the report is intended to promote use of neutron beams in residual stress measurements; facilitate preparation, design and standardization process at less well equipped smaller research centres around the world; serve as a guidance document for young researchers and graduate students new to the field.