This paper explores the way in which the data obtained from the dielectric study (reported in Part II of this 3-part series of articles), can be related to the mechanical strength of the bonded structure. Exposure of the adhesive bonded joints to a hot and wet environment leads to a loss of strength. Changes are observed in the dielectric properties on exposure to the humid environment, and an attempt is made to relate these observations to the mechanisms leading to loss in the mechanical strength of the bond. The observation of a correlation between the changes in these physical properties indicates the possibility of using dielectric spectroscopy as a powerful nondestructive evaluation (NDE) technique for bonded composite structures.