A High Flux Neutron Generator for Measuring Bulk Residual Stress via Diffraction

ABSTRACT: Residual stresses can be created in engineered components by most common fabrication processes (e.g., welding, joining, machining, casting, heat treating, press fitting, etc.). They are of particular concern to the aerospace industry because they are difficult to measure and can lead to premature failure of flight-critical components. There are several established methodologies for characterizing the residual stresses within a component, but those that are widely available either require the destruction of part or can only measure near-surface stresses. The only technique that allows deep, non-destructive interrogation of residual stresses is neutron diffraction. However, this technique is not widely utilized by industry because suitable neutron sources and instrumentation are only available at a handful of national labs and university sites, which require a major time and monetary commitment to access. In this project, a compact, high-flux neutron generator platform will be developed, permitting neutron diffraction-based residual stress measurements to be made in a factory or laboratory setting. BENEFIT: The fabrication costs of critical aerospace components for which residual stresses are an important concern (e.g. bulkheads) can be in excess of $100,000. Currently, the only techniques available in commercial production facilities to measure bulk residual stress (not just near-surface residual stress) require the destruction of the part. The widely accepted"gold standard"for nondestructive measurement of bulk residual stresses is neutron diffraction; however, access to this technique is quite limited, available at only a handful of national lab and university facilities nationwide. Commercial entities can purchase instrument time at these facilities, but it is costly (approximately $20,000 per day), requires travel, and is subject to the scheduling issues that are inherent in a shared-use facility. As such, the technique is used sparingly in the aerospace industry, despite the need for accurate bulk residual stress measurements. In this proposal, a laboratory-scale neutron diffraction measurement platform will be designed. Such a device will dramatically and directly impact the engineering and manufacturing processes of aerospace components. Residual stresses in components could be measured during the development process, permitting real-time optimization of manufacturing processes. The increased amount of data correlating manufacturing processes and residual stresses will also allow researchers to develop accurate models to predict the residual stresses that a given process will generate. The net result will be aerospace components that are stronger, lighter, and have lifetimes that can be predicted with a high degree of accuracy. The commercial potential for such a device has already been proven by similar technologies, such as X-ray diffraction platforms for the measurement of near-surface residual stresses.