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.