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

Carbon nanotube assemblies such as fibers and sheetsare an emerginglightweight material class with potential to enable aerospace structuresbeyond what is achievable with existing materials. Load transfer withinthese materials can be attributed to a combination of cohesion, staticfriction, covalent cross-links, and entanglements. Of these mechanisms,entanglements are the least studied or understood and are not welldefined when applied to nanotube materials. In this work, an entanglementis defined with sufficient detail for molecular models to be builtand tested. Non-reactive models where the covalent bond topology doesnot change and reactive models where covalent bonds can form and breakwere developed. In both model types, entanglement load transfer wasobserved and can be attributed to buckles (i.e., wrinkles) that formunder bending compression. In non-reactive models, there are energybarriers to restructure the shape of the buckles, while reactive modelsformed covalent bonds at the high-curvature edges of the buckles.Reactive models produced an average load transfer approximately 14times greater than non-reactive models due to these covalent bonds.