Influence of corrosion on the mechanical properties of hybrid sandwich structures with CFRP face sheets and aluminum foam core

Hybrid materials, such as sandwich structures consisting of an aluminum foam core and CFRP face sheets, offer high lightweight design potential. However, conductive pairing of two materials with different electrochemical potential bears the risk of galvanic corrosion inside an electrolytic environment. Due to the nature of the manufacturing process, the sandwich structures investigated within this contribution are susceptible to corrosion. Multiple specimen variants with differing foam core layers were exposed to a salt spray environment for up to 240 h. These corroded specimens were mechanically characterized using the flatwise tension test. Their mechanical properties were compared to reference specimens without corrosion. It was found that both open and closed cell sandwich specimens showed significant reductions in both strength and stiffness. Comparisons to alternative sandwich specimens consisting of a Nomex honeycomb core and CFRP face sheets, which underwent the same corrosion procedure, seem to prove that the mechanical degradation was indeed a result of corrosion, as the Nomex specimens did only show a significantly smaller decrease in strength, which probably resulted from material scatter superposed with water absorption. The erosion of the metallic core layer should be quantifiable by the determination of mass reduction. Therefore, a chemical cleaning procedure in order to remove any corrosion products from the specimen surface was applied. However, the procedure either led to a further mass decrease by chemical removal of the aluminum structure, or to mass increase by a chemical reaction of the detergent with the face sheets. Thus, complementary X-ray measurements by μ-CT were carried out. Specimens were scanned before and after corrosion, the respective volumetric densities were compared in order to verify material erosion. However, no significant change in volumetric density could be observed.