Effect of the friction riveting process parameters on the joint formation and performance of Ti alloy/short-fibre reinforced polyether ether ketone joints

• FricRiveting of carbon-fibre reinforced PEEK/titanium joints was demonstrated.
• The correlation between process parameters and joint properties was investigated.
• Optimised joints display similar tensile strength than rivet material (10.7 kN).
• An analytical model correlating rivet geometry/anchoring performance was introduced.

The feasibility of friction riveting on short carbon fibre-reinforced thermoplastic polymers was investigated in this work. A design of experiments (DoE) was used to investigate the impact of rotational speed, friction time, friction pressure and forging pressure on joint formation and performance. The joint formation was studied using the mushrooming efficiency, the rivet penetration depth and the mechanical energy input. The tensile pull-out force was used to describe the mechanical performance of the investigated metallic-insert joints made of grade 3 titanium and short carbon fibre-reinforced polyether ether ketone (PEEK). All samples were scanned with X-rays before any mechanical testing to acquire the dimensions of the anchored rivet inside the reinforced polymer, elucidating their correlations with the mechanical performance. The DoE model can be used to tailor joint formation and performance. A parameter-set that improves the pull-out performance was determined using an analysis of variance. The analysis revealed that high rotational speed, friction time and forging pressure caused high pull-out forces. The metallic-insert joints reached high pull-out tensile strength between 6.3 kN and 10.7 kN. The dimensions of the deformed metallic rivet were correlated with the mechanical performance of the joint: the larger the widening of the rivet tip, the higher the pull out force was. Furthermore, widening of the rivet tip by 70% led to the maximal tensile pull-out force (10.7 kN), corresponding to the base material strength of the titanium rivet (10.7 kN). At this threshold value (70%), the failure mode also changed from failure mode III (pull-out of rivet) to failure mode I (rivet failure).