Neutron radiographic nondestructive evaluation of aerospace structures

Neutron radiography with source intensities which are moderate relative to those of reactor neutron sources was found to be effective for nondestructive inspection of a variety of aerospace structures. By using either 2 mg of the isotope californium-252, or a 3-MeV Van de Graaff accelerator as neutron source, the technique was found particularly suited to evaluation of adhesive bonds in metal honeycomb and phenolic fiberglas-to-metal structures. Adhesive flaws in a variety of bonded assemblies, including a set of test panels with built-in adhesive voids and unbonds, were detected by neutron radiographic inspection. In addition, detection of corrosion hidden within metal aircraft assemblies appears to be a promising application of neuron radiography. Corrosion products introduced into one such structure in the laboratory to simulate corrosion from a field situation were radiographically imaged for sizes ranging down to 0.030 in. in dia and 0.002 in. in thickness. It is expected that with continued improvements in imaging techniques and mobility of neutron sources for radiography the technique will gain widespread usage for routine nondestructive inspection of many types of structures