Dynamic Strengthening of Carbon Nanotube Fibers under Extreme Mechanical Impulses

Abstract

A monofilament fiber spun from individual carbon nanotubes is an arbitrarily long ensemble of weakly interacting, aligned, discrete nanoparticles. Despite the structural resemblance of carbon nanotube monofilament fibers to crystalline polymeric fibers, very little is known about their dynamic collective mechanics, which arise from van der Waals interactions among the individual carbon nanotubes. Using ultrafast stroboscopic microscopy, we study the collective dynamics of carbon nanotube fibers and compare them directly with nylon, Kevlar, and aluminum monofilament fibers under the same supersonic impact conditions. The in situ dynamics and kinetic parameters of the fibers show that the kinetic energy absorption characteristics of the carbon nanotube fibers surpass all other fibers. This study provides insight into the strain-rate-dependent strengthening mechanics of an ensemble of nanomaterials for the development of high-performance fibers used in body armor and other protective nanomaterials possessing exceptional stability in various harsh environments.

High-velocity micro-projectile impact testing

“…In the emergent LIPIT technique, the primary diagnostics is high speed photography either via single-detector multiple exposure with pico/femtosecond laser pulses (Fig. 7b) (107,109,114) or using a high-speed multi-frame camera (Fig. 7c) (108,115).…”

“…14). Using LIPIT, the collective dynamics of a CNT fiber, an ensemble of weakly interacting, aligned CNTs, were directly compared by Xie et al to nylon, Kevlar, and aluminum monofilament fibers under the same supersonic impact conditions (114). Although individual CNTs are an elastic strain-rate-insensitive material, strain-rate-induced strengthening arising from interactions between the individual carbon nanotubes was observed.…”

Growth mechanism and kinetics of vertically aligned carbon nanotube arrays

“…CNT fibers have demonstrated promising performance in composites as well, for example, CNT fiber composites retained 69% of the specific strength of CNT fiber 86 . Recently, it was reported that CNT fibers have superior dynamic tensile strength to aramid fibers under supersonic impacts, and the failure mechanism includes molecular CNT damage under such conditions, indicating that higher fiber strengths can be achieved through better coupling between the constituent CNTs 87 . However, it is the fact that challenges still remain for CNT fibers to become a viable substitute material, and the production rate of CNTs should be increased and the overall cost should be decreased significantly.…”

Extreme Dynamic Performance of Nanofiber Mats under Supersonic Impacts Mediated by Interfacial Hydrogen Bonds

“…Energy-absorbing materials with extreme dynamic performance under ballistic impacts are essential for various protective applicationsfrom armors for soldiers to mitigating microdebris impacts on air and spacecraft. − Superior dynamic performance achieved through lightweight protective materials is critical for agility and fuel efficiency of personal and armored vehicles, drones, hypersonic aircraft, and spacecraft. In this regard, synthetic high-performance fibrous materials, especially polyaramid fibers such as Kevlar (DuPont) and ultrahigh-modulus polyethylene, have been replacing heavy metal protective materials due to their outstanding mechanical properties at low density as well as their manufacturability into wearable textiles and composites. , Recent microballistic tests on nanomaterials have revealed their superior energy dissipation capabilities arising from the distinct deformation mechanisms they employ, suggesting the effective role that the nanoscale building blocks could play toward developing high-performance protective materials. − For instance, the specific penetration energy ( E p * ) of multilayer graphene ( E p * ∼ 1.26 MJ/kg (900 m/s impact)) is about 10 times higher than that of a macroscopic steel plate, originating from its superior in-plane sound speed, strength, and rapidly progressing membrane fracture . In contrast to such stiff materials, softer ultrathin semicrystalline and glassy polymer films show even higher specific penetration energy ( E p * ∼ 3.8 and ∼2.8 MJ/kg, respectively), due to their geometric confinement induced microstructural evolution.…”

“…The stress delocalization efficiency characterizes how fast the impact-induced stress waves travel from the impact zone such that the localized failures can be retarded or mitigated. Nanofibrous materials have the potential to achieve extraordinary performance in extreme loading conditions because of the exceptional intrinsic properties of nanofibers − and their mesoscale structural organization that provides highly interactive morphology with a high surface-to-volume ratio. − For example, the exceptional intrinsic fracture strength of MWCNTs (35–110 GPa) leads to much delayed failure, whereas the high modulus (590–1105 GPa) of MWCNTs furnishes the precursor for high effective wave speed in the material. , The entangled morphology of these MWCNTs at the mesoscale enables rapid stress delocalization, while substantial energy is dissipated through inter-fiber interactions. ,− The self-organized structure of CNTs can also be tailored through various processing techniques for scalable fabrication of bulk yarns, , foams, , and fabrics with superior specific properties.…”