Effect of Nanostructure and Crosslinks on Impact Resistance of Carbon Nanotube Films Under Micro‐Ballistic Impact

Carbon nanotube (CNT) films show great promise as an advanced bulletproof materials due to their excellent energy dissipation ability under impact loadings. However, it is challenging to determine the optimized architecture structure of CNTs to enhance the impact resistance of CNT films. In this study, the impact behavior of CNT films with various architecture structures were studied by micro-ballistic impact experiments and coarse-grained molecular dynamics (CGMD) simulations. The micro-ballistic impact experimental results showed that the cross-ply laminated (CPL) structure enhances significantly the specific energy absorption (SEA) of CNT films compared to that with disordered structure due to the synergistic interactions between covalent bonds in CNT chains. On this basis, four CPL-CNT (CCNT) films with the same areal density (ρ^2D) but different single-layer areal density ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>ρ</mml:mi> <mml:mi>s</mml:mi> <mml:mrow><mml:mn>2</mml:mn> <mml:mi>D</mml:mi></mml:mrow> </mml:msubsup> <mml:annotation>${\rho }_{s}^{2D}$</mml:annotation></mml:semantics> </mml:math> ) and one disordered CNT (DCNT) film with the same ρ^2D as the CCNT films were constructed in CGMD models. The simulation results showed that the SEAs of all the four CCNT films are higher than DCNT film, which is consistent with experiments. In addition, the SEAs of CCNT films increase with decreasing <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>ρ</mml:mi> <mml:mi>s</mml:mi> <mml:mrow><mml:mn>2</mml:mn> <mml:mi>D</mml:mi></mml:mrow> </mml:msubsup> <mml:annotation>${\rho }_{s}^{2D}$</mml:annotation></mml:semantics> </mml:math> . However, too small <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>ρ</mml:mi> <mml:mi>s</mml:mi> <mml:mrow><mml:mn>2</mml:mn> <mml:mi>D</mml:mi></mml:mrow> </mml:msubsup> <mml:annotation>${\rho }_{s}^{2D}$</mml:annotation></mml:semantics> </mml:math> can lead to local plugging failure of the CNT film and therefore decrease SEA of the CNT film. Moreover, adding crosslinks could further increase the SEAs of both the DCNT and the CCNT films due to the strengthened interactions of adjacent CNTs. The crosslinked CCNT films with appropriate ρ^2D is still much higher than the crosslinked DCNT films. Furthermore, it was further found that when the strength of the crosslinks aligns with that of the CNT beads, the CNT film achieves preeminent impact resistance. This study provides a pathway for enhancing the impact resistance of CNT films by optimizing the microstructure and introducing crosslinks between CNTs.