Investigation of mechanical behavior of dissimilar material FSBR joints exposed to a marine environment

The focus of this research is the mechanical behavior of dissimilar material friction stir blind riveted (FSBR) joints after a 6-month exposure to a marine environment with two different material configurations, i.e., CFRP (carbon fiber-reinforced plastic) composite/Al and Mg/CFRP composite. Quasi-static tensile tests along with fractographic and acoustic emission (AE) analyses were employed to explore the effect of corrosion on the mechanical behavior of each individual constituent material and the entire joints. All the exposed constituent materials showed significant degradation in terms of maximum load and nominal stiffness, along with the change in failure mode for the exposed joints. However, the exposed joints exhibited similar strengths as the as-fabricated ones, where the fracture area of all joints was localized at the joining region between the rivet and workpiece (tension failure mode). The joint strengths were similar because of the metallurgical bonding and mechanical interlocking (occurred during the stirring process) which consequently eliminated the gap and prevented the corrosion at the bonding interface between the rivet and workpieces. This observation revealed FSBR as a promising joining technology for the dissimilar material joining applications in corrosion prone environments. In addition, compared to the as-fabricated joints, more AE hit signals were observed during the tension test for the exposed joints due to the fracture of introduced brittle corrosion products.