Improvement of the tensile properties of laminated composites reinforced with Heli-Coil forms of carbon nanotubes

The traditional composite laminated structures suffer from the absence of reinforcements in the thickness direction between the laminae and microfibers, which will result in poor interaction between the laminae, individual microfiber filaments, and the resin. In addition, out-of-the-plane properties are generally dominated and controlled by poor matrix properties ( e.g., mechanical, electrical, and thermal). Most prior investigations were focused on the use of straight carbon nanotubes ( CNTs), graphene, or nanomaterials in particle forms to improve the resin properties. Our previous research has shown that CNTs with helical (Heli-Coil) geometries ( HCNTs) are more effective as a nanoscale reinforcement to improve the properties of polymeric resins. Because of their inertness, the interfacial bonding between CNTs and the resin is generally weak, and they can be easily pulled out of the resin (inefficient load transfer) if the CNTs are in their straight forms. However, the helical geometries of HCNTs can provide unique mechanical-interlocking mechanisms between the constituents that can substantially improve their effectiveness as a nanoscale reinforcement, leading to improvements in composite performance, properties, and multifunctionality. In this research, HCNTs at low concentrations below 0.1 wt% were processed and then used to fabricate nanocomposite laminates. Tensile test specimens were carefully prepared following the ASTM D3039/ D3039M standard and then tested, analyzed, and evaluated. Additionally, the fractured test specimens were inspected and analyzed using optical and 3D scanning laser-confocal-microscopy imaging. The test results showed improvements of 12.3%, 11.3%, and 17.5% for the tensile strength, modulus, and strain-to-failure, respectively. In conclusion, traditional fiberreinforced composites can considerably benefit from the helical forms of HCNTs.

Automated summary

Traditional composite laminated structures lack reinforcements in the thickness direction between the laminae and microfibers, resulting in poor interaction and weak load transfer. This research demonstrates that using helical carbon nanotubes (HCNTs) as nanoscale reinforcement can substantially improve the performance of polymeric resins. The nanocomposite laminates fabricated with HCNTs showed significant improvements in tensile strength, modulus, and strain-to-failure.