Preliminary Study on Adhesive Strength of CFRP Patched Aluminum Alloy Plate Immersed in Salt Water

CFRP composite patches have been widely used to repair damaged structural components of metallic aircrafts. Though CFRP is well-known as a corrosion-resistant material, once the carbon fibers of CFRP are in direct contact with aluminum alloy, the galvanic interaction between CFRP and aluminum induces the corrosion of aluminum alloy resulting decrease of the joint strength. In this study, tensile specimens made of two pieces of aluminum alloy plates joined with a single-lap cocured patch of unidirectional CFRP prepreg were immersed in salt water for 49 days maximum. For some of the specimens, silicon sealant was applied around the edge of the joint for waterproofing. Every 7 days of immersion, changes in electric potential and in electric resistance were measured followed by the tensile testing. After 49 days of immersion, the joint strength of sealed specimen was found to be more than four times higher than that of unsealed one. The relationship of the joint strength with the change in electric potential and that with the change in electric resistance were obtained. The joint strength was successfully estimated by the change in electric potential and electric resistance.