DIELECTRIC NON-DESTRUCTIVE EXAMINATIONOF AGEING OF ADHESIVELY BONDED STRUCTURES

摘要

This paper describes the use of Dielectric Spectroscopy as a non-destructive method for monitoring,firstly solvent ingress at elevated temperatures within aluminium adhesively bonded joints andsecondly water uptake within carbon fibre reinforced plastic (CFRP) bonded joints. Dielectricmeasurements were carried out in both frequency and time domain, allowing for changes in thedielectric permittivity and loss to be calculated. Frequency domain analysis allows the effect ofsolvent ingress in the bondline to be assessed, whereas time domain analysis allows for theidentification of irregularities found within the bondline. CFRP samples, in addition to ageing, havebeen subjected to thermal spiking at cryogenic temperatures at regular intervals throughout the ageingperiod. Destructive mechanical tests, Mode 1 and Mode 2, were also carried out on the aluminiumand CFRP samples and a correlation with dielectric measurements obtained. The dielectricpermittivity and loss were found to increase throughout the ageing period whereas the mechanicalstrength of the joints was reduced, in some cases quite dramatically as a result of leaching of theadhesive by the solvents. Time domain (TDR) analysis has also shown the presence of defects withinthe bondline of the joint structures.