Force-control Friction Riveting of Ti-6Al-4V/ carbon-fiber reinforced polyether-ether-ketone overlap jointsThursday (29.09.2016) 12:30 - 12:45 Part of:
The use of lightweight metal-composite structures has increased in the aircraft industry to reduce weight and satisfy gas emission policies. Current available joining technologies for such hybrid structures are either too expensive, with limited performance, or not environmental friendly. Friction Riveting was recently introduced as an alternative joining technique for aircraft composites. The technology uses frictional heat and pressure to plasticize and deform a cylindrical metallic rivet into composites plates to produce overlap joints. Joining mechanisms are mechanical interference and adhesion forces. The force-control process variant used in this work is composed of a frictional phase limited by rivet displacement. No forging phase is applied (axial pressure was kept constant); a short consolidation phase limited by time was used. Joining cycles were inferior to 2 s. Case-study overlap joints on Ti-6Al-4V rivet and carbon-fiber reinforced polyether-ether-ketone laminates were investigated in terms of microstructure and quasi-static mechanical performance. Average ultimate lap shear forces of unclamped joints were up to 4.2 ± 0.09 kN. Clamping forces of 5N (nut and washer) increased joint mechanical performance to 52%. Overlap joints failed by rivet pull-out with a mixture of adhesive and cohesive micro-failure modes between the composite plates. Microstructural analysis showed the formation of a thin reconsolidated polymeric layer between the composite plates and micro-mechanical interlocking of carbon fibers entrapped by plasticized titanium rivet. Finally, the joining mechanisms for composite overlap joints were evaluated by scanning electron microscopy, showing a complex pattern including macro- and micro-mechanical interlocking, and adhesion forces at the metal-composite interface.
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