Friction Riveting (FricRiveting) as a new joining technique in GFRP lightweight bridge construction

The present work demonstrates the feasibility of the innovative Friction Riveting joining technique on glass fiber reinforced composite/lightweight alloy overlap joints for structural engineering applications. Glass-fiber-reinforced-polymer (GFRP) bridges can be an efficient solution for emergency bridges, which are of vital importance in humanitarian missions following natural disasters or accidents. One of the main problems in the construction with composite structural materials is the joining technology. It is a case study of a glass fiber reinforced polyetherimide emergency bridge with friction-riveted (titanium grade 2 rivets) profiles connected by aluminum shoes (Al 2198-T851). Friction-riveted bridge joints would benefit of advantages such as high strength, short joining cycles and the absence of complex surface preparation. The recorded temperature history during FricRiveting revealed peak temperatures of up to 600 °C, offering an important insight on the formation of the joint (plasticizing of the metallic rivet and physical-chemical structural changes). Microstructural investigation showed the formation of the rivet anchoring zone (the deformed rivet tip with increased diameter) without extensive thermal changes in the matrix and mechanical destruction of the fiber woven. Hybrid friction-riveted composite/titanium grade 2/aluminum overlap joints were successfully produced and optimized via design of experiments, revealing lap shear strengths of up to approximately 200 MPa and final fracture through shear of the metallic rivet. Results were compared with bolted connections in a similar configuration and testing conditions; experimental investigation indicated that joints produced by FricRiveting have comparable mechanical behavior and strength to bolted joints. The load requirement of a 25 m span truss girder GFRP bridge with the proposed friction-riveted connections was calculated by finite element analysis, leading to a number of 162 necessary M5 rivets for the joints with maximum axial forces of 760 kN. This work has partially demonstrated the potential of Friction Riveting for structural engineering applications.