A recent study indicates that low-speed friction riveting of carbon-Kevlar and aluminum could enhance joint strength in aerospace engineering.

The study, conducted by a research team from India, demonstrated how friction riveting optimized the strength and reliability of carbon-Kevlar polymer composites combined with AA 7075 aluminum alloy. 

Friction riveting is known for enhancing the strength-to-weight ratio using rotation heat and pressure to bond polymers and metals. More importantly, it achieves this without needing mechanical fasteners or adhesives that affect the weight and performance of aerospace vehicles and impact the environment.

The team found that hybrid materials have joint capacities of 5.83 kN in tensile strength and 2.95 kN for shear pull-out tests. They also discovered through hybrid Taguchi-Grey relational analysis the following ideal conditions, wherein the rivet speed influences joint strength the most:

• Rivet speed: 6000 rpm

• Reaming pressure: 0.2 MPa

• Reaming time: 6 seconds

The friction process generated significant heat of up to 189°C at the interface, which softened the aluminum rivet. This improved ductility and created a stronger bond with the composite material, resulting in better joint formation.

Through microstructural analysis, researchers learned that carbon fibers bond well with aluminum because of effective mechanical interlocking and potential chemical bonding. On the other hand, Kevlar fibers showed weaker interlocking and tended to experience more frequent fiber pull-out during tensile tests. The findings suggest that more improvements in carbon-Kevlar composites are needed to maximize their strength in friction-riveted joints. 

The team sees the need for more long-term durability studies to examine the longevity and performance of these joints when exposed to different environmental conditions like humidity and corrosion exposure. They also believe more experimentation will not only lead to optimized joining designs but also explore alternative polymer-metal combinations. 

Read the full article here to learn more about the optimized friction riveting method. 

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