Modeling Carbon Nanotube Entanglement Load Transfer: Implications for Lightweight Aerospace Structures

Carbon nanotube assemblies such as fibers and sheets are an emerging lightweight material class with potential to enable aerospace structures beyond what is achievable with existing materials. Load transfer within these materials can be attributed to a combination of cohesion, static friction, covalent cross-links, and entanglements. Of these mechanisms, entanglements are the least studied or understood and are not well defined when applied to nanotube materials. In this work, an entanglement is defined with sufficient detail for molecular models to be built and tested. Non-reactive models where the covalent bond topology does not change and reactive models where covalent bonds can form and break were developed. In both model types, entanglement load transfer was observed and can be attributed to buckles (i.e., wrinkles) that form under bending compression. In non-reactive models, there are energy barriers to restructure the shape of the buckles, while reactive models formed covalent bonds at the high-curvature edges of the buckles. Reactive models produced an average load transfer approximately 14 times greater than non-reactive models due to these covalent bonds.