| In October 2015, after the discovery of liquid water on the surface of Mars, NASA declared that the coming decades will see a renewed push to establish "a sustainable human presence beyond Earth, not just to visit but to stay". A challenge for deep-space missions to Mars and beyond will be the construction of space vehicles, habitats, and extra-vehicular activity (EVA) suits capable of withstanding the threats from micrometeoroids and orbital debris (MMOD). MMOD particles, while typically small in size, travel at extraordinary velocities in low-earth orbit (LEO)---on the order of 1-15 km/s (~2,200-33,000 mph)---rendering them highly energetic and dangerous to exposed astronauts performing EVAs.;This dissertation explores using a novel soft body armor technology that intercalates colloidal shear thickening fluids (STFs) into protective textiles, i.e., STF-ArmorT(TM), to improve the resistance of EVA suits to hypervelocity MMOD threats. STF-Armor(TM) has previously been demonstrated to improve resistance to puncture, ballistic, and shock threats--all elements inherent to MMOD projectiles. Under the terrestrial testing conditions explored in this dissertation, incorporation of STF-Armor(TM) into the EVA suit significantly enhanced the resistance to puncture threats and increased specific energy absorption when the projectile was traveling at velocities sufficiently high enough to induce fragmentation upon impact. These results demonstrate proof-of-concept and advance the Technology Readiness Level (TRL) of STF-Armor(TM) to the point where the next step of technology validation will take place in the actual LEO environment on the exterior of the International Space Station.;The intended application motivates some fundamental questions about the effect of confinement on the measured deviatoric stress---the shear stress and the first and second normal stress differences---within the underlying colloidal dispersion. Improved experimental measurements of these viscometric functions were obtained via controlled-stress rheometry. The magnitude and scaling of the viscometric functions were found to be consistent with expectations from Stokesian Dynamics simulations, Dissipative Particle Dynamics simulations, and theory that properly accounts for hydrodynamic interactions between particles at high shear rates. In STF-Armor(TM), concentrated colloidal dispersions are confined to micron-sized gaps between yarn fibrils, a degree of confinement not accessible with current rheometry techniques. A novel experimental approach was developed to study the effects of extreme confinement on the measured deviatoric stress, where the colloidal dispersion was confined not between the plates of a rheometer tooling, but rather between the surfaces of large, non-deformable non-Brownian particles at high packing fractions. At high shear rates, confinement was found to lead to stronger shear thickening and enhanced normal stress differences. Ultimately, the findings of this dissertation help to advance fundamental understanding of the flow behavior of suspensions consisting of both colloidal and non-Brownian particles, which has broad and far-reaching value for applications beyond the soft body armor technology considered here. |
