Influence of Helical Carbon Nanotubes Reinforcement on Short-Beam Shear Strength of Composite Laminates (SAE Paper 2021-01-0027)

Fiber reinforced epoxy composites are widely used in many industries for various applications, which includes aerospace, automotive, renewable industries. Of all the industries aerospace industry is the largest consumer of high-performance composite materials. They are primarily used to fabricate airframe structures such as skin, stringers, and frames. Traditional laminated composites typically use continues fibers as reinforcement and a resin system as a bonding agent, which are known to have excellent mechanical properties such as high stiffness and high strength, while maintain their light weight. One of the main disadvantages of traditional composite laminated structures is their poor interlaminar strength and lack of reinforcement in out-of-plane direction that may result in debonding of the lamiane (delamination and disintegration), when they are subjected to external out-of-plane loads. Various techniques and processes were developed in past decades to improve mechanical performance of the composite structures and assemblies; one such method includes the use of nanoscale reinforcements in between the laminae and within the resin system. However, most prior research has been focused on use of straight carbon nanotubes (CNTs) and other nanomaterials in particle forms. The goal of this research was to improve the interfacial bonding effectiveness and the shear strength between the laminae using nanoscale reinforcements. Because of their inertness, CNTs� interaction with the resin system is generally weak. In this research we have used CNTs with various geometrical configuration (straight and helical geometries) and various weight percentages as an additional reinforcement. The objective was to investigate the effectiveness of helical geometries of the CNTs to form interlocking mechanisms with the resin and the traditional microfiber reinforcements to improve the overall performance of the composite structures and assemblies. In this study, ASTM D2344/2344M-16 is used to study the short beam strength of the laminated nanocomposites and evaluate the benefit of the mechanically interlocked helical CNTs reinforcement. Overall, three sets of composite laminates (i.e., with neat epoxy, straight CNTs reinforced epoxy, and Helical CNTs reinforced epoxy) were fabricated per ASTM standard D2344/2344M-16. Adequate test specimens were cut and then they were tested on a universal testing machine, using a three-point bending fixture with a short span per ASTM D2344 standard. The test results were analyzed ad evaluated to determine the effects of helical CNTs on short beam strength of the laminated nanocomposites.