NONDESTRUCTIVE EXAMINATION OF COMPOSITE JOINT STRUCTURES - A CORRELATION OF WATER-ABSORPTION AND HIGH-FREQUENCY DIELECTRIC PROPAGATION

Applications of high-frequency dielectric measurements (300 kHz to 3 G Hz) to the non-destructive examination (NDE) of composite structures a re discussed. Preliminary data indicate that the method, previously us ed for aluminium bonded structures, can be applied to bonded carbon fi bre composite structures. Water ingress into the bond structure was ob served to influence both the time- and the frequency-domain data. Comp arison of exposed and dry joints demonstrated that a good correlation exists between changes with time in the dielectric properties of the c omposites and the extend of water uptake in the matrix. Parallel gravi metric measurements were also performed. Diffusion of water into the c omposite structures is discussed in terms of various models. This pape r demonstrates that this NDE method may be used for assessment of the water content in the matrix and has general applicability to the study of carbon-reinforced matrix materials.