In recent years, anti-penetration materials have been more widely used for armor, bulletproof vests, and micrometeoroid and orbital debris protection layers for space-suits, space vehicles, and structures. Micrometeoroids develop very high kinetic energies as they travel through space, and pose a significant hazard to spacecraft and astronauts. The velocities of micrometeorites can reach 20 kilometers per second prior to impact on the lunar surface. Therefore, a new protective system utilizing new materials is needed to effectively shield the space vehicles and structures against the high-kinetic-energy penetrators as well as provide penetration-resistant spacesuits. In order to maximize the protection ability against high-kinetic-energy penetrators, the following two major material properties should be considered: high hardness for rebounding and/or gross mechanical deformation of the penetrator, and high toughness for effective energy absorption during the mechanical deformation (and heating) of the protecting materials.
In order to increase both the hardness and toughness, boron nitride nanotubes (BNNT), boron nitride nanoparticles (BNNP), carbon nanotubes (CNT), graphenes, or their combinations can be incorporated into matrices of polymer, ceramic, or metals. Fibers, yarns, and woven or nonwoven mats of BNNT are used as toughening layers to maximize energy absorption and/or high hardness layers to rebound or deform penetrators. They also can be used as reinforcing inclusions, combining with other polymer matrices to create composite layers like typical reinforcing fibers such as Kevlar, ceramics, and metals.
BNNT possess high strength-to-weight ratio, high oxidative temperature resistance (above 800 °C in air), piezoelectric properties, and radiation shielding capabilities. These mechanical and thermal properties of BNNT are believed to make it an ideal material with which to develop a novel lightweight and high-performance anti-penetrator material. These high-aspect-ratio nanomaterials can also provide unique wear properties because the material systems that incorporate these BNNT have displayed increased hardness and toughness, especially at elevated temperatures approaching 900 °C.
A multi-layered composite film was fabricated using BNNT and CNT layers infused with polyurethane (PU) resin. The elastic modulus of the pristine PU was only 60.9 MPa, but that of the multi-layered composite was 756.9 MPa, showing an increase of more than 1140%. The increased modulus of the BNNT/CNT composite promises the increase of toughness before fracture, which is another critical property for the anti-penetrator protection.
BNNT fibers or BNNT woven or non-woven mats can be used for the protection layer by infusing a polymer, ceramic, or metal into the BNNT fibers or mats. A multi-layered composite containing both increased hardness and toughness can greatly enhance the anti-penetration protection and increase the wear resistance. A top high-hardness layer consisting of BNNT, c-BNNP, or other high-hardness materials provides initial protection against penetrators by bouncing or deforming them. The combination of various toughened layers such as a Kevlar fabric (mat), BNNT-reinforced Kevlar woven or non-woven mat, and BNNT or CNT composite layer offers superior toughness enabling effective absorption of the impact energy.