Enhancing the short-beam strength of composite laminates using helical carbon nanotubes

Abstract

The main disadvantage of traditional composite laminated structures is the lack of reinforcement in out-of-plane direction in between the laminae and the fiber filaments. This will result in poor interlaminar properties leading to delamination and disintegration of the laminates, when subjected to out-of-plane external loads. Most prior research has been focused on use of straight carbon nanotubes (CNTs) and other nanoparticles as additional reinforcement in resin systems. Our prior research has shown that the helical CNTs are more effective as a nanoscale reinforcement, as compared to other nanomaterials. The goal of this research was to improve the interfacial bonding effectiveness between the laminae using the unique characteristics and coil-like geometry of the helical CNTs. They can wrap around each other, entangle with the micro-fiber reinforcements, and get stuck inside the solidified resin. Because of their inertness, CNTs interaction with the resin is generally weak and the helical geometries of CNTs can provide unique mechanical interlocking mechanisms within the composite material systems. This characteristic can substantially improve their interfacial and out-of-plane properties and introduce additional multifunctionalities. In this research, helical CNTs with various weight percentages were used as additional reinforcements in composite laminates. ASTM standard D2344/2344M − 16 was used to investigate the short-beam strength of the helical CNTs reinforced laminates. Test specimens were fabricated, cut, and tested as per ASTM standard and then analyzed. The comparison of test results showed up to 11.3%, 11.9%, and 6.9% improvements for short-beam strength, tangent modulus, and strain at failure, respectively, for the nanocomposite samples with 0.05 wt% HCNTs loading. These results prove that the use of helical CNTs as additional reinforcement is a promising approach for the improvement of the interlaminar properties of laminated composites and structures.