Dielectric spectroscopy technique to assess the durability of adhesively bonded composite joint structures

摘要

In a previous communication at DURACOSYS'99, the capability of the high frequency dielectric technique as a non-destructive evaluation (NDE) method for composite structures was demonstrated. Information related to the integrity of the bond line was retrieved using the time domain reflectometry mode. This paper presents new results concerning the use of dielectric spectroscopy to assess the degradation that occurs in adhesively bonded composite structures subjected to hot/wet environments. The frequency spectrum has been enhanced allowing new insight into the understanding of the degradation process occurring in the adhesive. The frequency domain mode gives access to relaxation processes related to the degradation of the adhesive layer expressed in terms of dipolar and ionic contributions. The mechanical shear strength has also been investigated showing the degradation of the adhesively bonded structure. The dielectric data have been related to gravimetric results as well as mechanical shear strength data. A master curve for the system studied in this work is presented showing the dielectric-mechanical strength relationship.