Effect of Galvanic Current on the Physicochemical, Electrochemical and Mechanical Properties of an Aerospace Carbon Fiber Reinforced Epoxy Composite

Abstract

Carbon fiber reinforced epoxy (CFRE) composites are joined with aluminum alloys in aerospace assets through either adhesive bonding or mechanical fastening. The carbon fibers are noble relative to the alloy so when these materials are electrically connected through a thin electrolyte layer, galvanic current can flow. Oxygen reduction occurs at the exposed carbon fibers leading to the formation of H2O2 that could build up in the gap between the two. Electrochemical methods were used to characterize a standard airframe composite before and after a 7-day (i) neutral salt-spray (ASTM B117) and (ii) moist SO2 atmospheric (ASTM G87) test when joined with AA2024-T3. The electrochemical properties of the composite were also assessed before and after the imposition of applied cathodic currents from −1 to 1000 μA. Finally, electrochemical methods were used to study the effect of a 14-day H2O2 exposure on the composite properties. Horizontal shear stress testing was performed to determine how the mechanical strength of the composite specimens was impacted by full immersion (14 days) in H2O2 solutions at 25 and 55°C. The composite is damaged under the cathodic conditions and appears linked to H2O2. The dominant consequence is epoxy and or fiber sizing degradation, which leads to debonding and cracking.