Dielectric and mechanical studies of the durability of adhesively bonded CFRP structures subjected to aging in various solvents

Dielectric and mechanical tests of adhesively bonded carbon fibre reinforced plastic (CFRP) joints aged in a series of solvents are reported. The solvent systems include; deicing fluids (ethylene Glycol), aviation fuel, moisture, brine and paint strippers and solvents (dichloromethane and butanone). These measurements indicated that the ingress of the solvent leads to swelling of the joints and plasticization of the adhesive with consequential changes in the mechanical properties. A study of the drying process after the joints have been aged indicated that in certain cases it was possible for the mechanical properties of the joints to be recovered to almost their original values. In other cases the recovery was limited and reflected changes occurring within the adhesive layer. It was difficult to establish an unambiguous correlation between the dielectric constant of the bond and the change in the mechanical strength although in the case of water and ethylene glycol a correlation does appear to exist. The paper discusses the usefulness of the dielectric method for monitoring the ageing of CFRP adhesively bonded joints.