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Dielectric measurements have been used to infer the average moisture content of aluminum adhesive joints bonded with three commercial epoxy adhesives. Measurements were made on both aluminum-adhesivealuminum joints and aluminum-adhesive specimens in order to assess the influence of moisture diffusion gradients. Similar experiments were also performed with foil electrodes embedded in the bondline. For average water concentrations less than approximately 2%, there existed a linear relationship between the permittivity and the average moisture level which was independent of the spatial nonuniformity produced by water diffusion. At higher moisture levels, the dielectric response varied considerably from one adhesive to another, but, in general, could be approximated as a linear dependence on the average moisture concentration. The dielectric response was recoverable upon drying.

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