Development and Applications of Residual Stress Measurements Using Neutron Beams

The deep penetration and selective absorption of neutrons make them a powerful tool for the non-destructive testing of large samples of material or large objects. Residual stress that is formed in a material during manufacturing, welding, utilization or repair can be measured by means of neutron diffraction. In fact, neutron diffraction is the only non-destructive testing method which can facilitate three dimensional mapping of residual stress in a bulk component. Stress measurement using neutron beams is a technique that enables this kind of high quality non-destructive investigation, and provides insight into the 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 optimize design criteria in applications. Anisotropies in macroscopic properties such as 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. There is currently substantial scientific and industrial demand for high quality non-destructive 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, the neutron diffraction 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 accordance with its purpose of promoting the peaceful use of nuclear applications, in 2006-2009 the IAEA organized a Coordinated Research Project on the Development and Application of the Techniques of Residual Stress Measurements in Materials. This project relied on the participation of practitioners from highly specialized user facilities from various Member States, including the Czech Republic, Germany, Hungary, India, the Netherlands, Pakistan, Romania, the Russian Federation and South Africa. This report is the culmination of the project, and provides guidance on the basic principles, requirements, preparation, design, execution and standardization of residual stress measurements using neutron beams. It includes details of experimental techniques; associated equipment and instrumentation; their commissioning, calibration and control; and, finally, data acquisition. A separate section is dedicated to data analysis and interpretation. The publication also provides a number of selected examples of applications of residual stress measurements as well as future trends for the development and use of this powerful technique. Finally, complete information on a number of round robin exercises with standard samples, as well as detailed information on a dozen residual stress instruments worldwide, has been included. Ultimately, the report is intended to promote the use of neutron beams in residual stress measurements; facilitate the preparation, design and standardization process at less well equipped smaller research centres around the world; and to serve as a guidance text for young researchers and graduate students new to the field