Effects of Helical Carbon Nanotubes on Mechanical Performance of the Composite Bonded Joints 2020-01-0029
Most composite assemblies and structures generally fail due to the poor performance of their bonded joints that are assembled together with an adhesive layer. Adhesive failure and cohesive failure are among the most commonly observed failure modes in composite bonded joint assemblies. These failure modes occur due to the lack of reinforcement within the adhesive layer in transverse direction. The overall performance of any composite assembly largely depends on the performance of its bonded joints. Various techniques and processes were developed in recent years to improve mechanical performance of the composite bonded joints, one of which includes the use of nanoscale reinforcements within the adhesive layer in between the adherends. However, most prior research have been focused on use of straight carbon nanotubes (CNTs) and other nanomaterials in particle forms. The goal was to improve the properties of the adhesive film and their interfacial bonding effectiveness. Because CNTs are inert in nature, they should be covalently functionalized, before incorporating them into adhesive resins. CNTs can be functionalized using different chemicals to improve their interactions with the adhesive polymer molecules and enhances their dispersion homogeneity. In addition to functionalization, the geometrical configuration of CNTs do also play an important role in their effectiveness, when they are used as nanoscale reinforcements in adhesive layers that used for bonding of load carrying structures. Overall, there are several factors that can influence the effectiveness of the nanoscale reinforcements in adhesive resins, e.g., nanomaterials’ geometry, weight percent inclusion, functionalization method, processing parameters, and the way they interact with the adhesive resin molecules and the adherends. In this research study, helical carbon nanotubes (HCNTs) were chemically functionalized using a mixture of strong acids (e.g., nitric, sulfuric, and/or hydrochloric acids) and then incorporated into an adhesive resin in various weight percentages for bonding of composites. Single lap joint test specimens were prepared based the ASTM Standard (e.g., D1002-10, D5868-01, D3163-01, and/or D4896-01) and then tested to investigate the effectiveness of the chemically functionalized HCNTs (FHCNTs) for improvement of the composite bonded joint assemblies.