Dielectric spectroscopy as a non-destructive technique to assess water sorption in composite materials

Over the last ten years, the application of high frequency dielectric spect roscopy techniques for the assessment of composite structures has been inve stigated. Novel approaches to assess non-destructively the evolution during ageing of adhesively bonded carbon fibre reinforced plastic (CFRP) structu res and bulk glass fibre reinforced plastic (GRP) structures are presented in this paper and the results are critically assessed. The applicability and limitations of dielectric measurements, in both frequ ency and time domain, to the monitoring of water ingress at 30 degrees C an d 60 degrees C are examined. The correlation between gravimetric and high f requency dielectric spectroscopy data demonstrates the suitability of the t echniques regarding the assessment of water uptake in composites structures and illustrates its potential as a non-destructive evaluation (NDE) techni que. The dielectric time domain response (TDR) study of adhesively bonded s tructures indicates a new way to assess such structures. The approach for f requency domain analysis of bulk GRP using a coaxial probe technique indica tes the potential portability of the technique for in-situ measurements.