Extraordinary KE Absorption in Multi-walled Carbon Nanotubes Mats under High Strain Rate Deformation

Improving the ability of materials to absorb large amounts of kinetic energy from ballistic impact is important for a broad range of applications including body armor and protection of satellites. Carbon nanotubes (CNTs) have exceptional mechanical properties, especially very high axial stiffness and tensile strength. We investigate the energy absorption characteristics and associated deformation behavior of an initially low modulus, low strength, porous, unoriented nonwoven multi-walled carbon nanotubes (MWCNT) mats. The mats are comprised of unaligned, individual tubes and tube bundles bonded together into networks by both covalent and secondary bonds. Their ultra-high aspect ratios and large surface area enhance physical interactions between tubes. Employing a laser-induced micro-projectile impact test (LIPIT), μ-size silica projectiles are impacted at 200-1000 m/s resulting in extreme strain rates (10⁷ s^-1). The morphology of the MWCNT mat evolves dramatically during the deformation event resulting in strong strain hardening as the tubes and bundles are able to reconfigure and align. The mats exhibit record high specific energy absorption (E_p*), up to 12 MJ/kg, far beyond the of ~1 MJ/kg performance of common protection materials such as Kevlar, Dyneema, steel and aluminum.