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Single high-performance fibers (Kevlar® K129, Twaron® 2040, Technora® T200, Dyneema® SK76, Zylon® AS, Vectran® HT, and S-glass) are subject to lateral cutting action by an industrial blade. Due to the inherent variability of such testing, 40–60 replicate experiments were performed for each fiber type, at each of three different loading orientations, and the data were fit with a generalized extreme value distribution to summarize likelihood of failure under each condition. The results show that when organic fibers are cut at an angle that introduces shear loads, cut resistance drops by 60–90% compared to normal-incidence cut loading. This trend is driven by the highly oriented and fibrillar nature of organic fibers, in contrast to the isotropic S-glass fibers which show comparatively little change in cut resistance with blade orientation. Overall, the Vectran fibers provide the best resistance to normal loading, while the S-glass fibers are most resistant to non-normal loading. Micrographs show that, for organic fibers, shear loads lead to more localized failure compared to normally loaded fibers. [ABSTRACT FROM AUTHOR]

Fully dense thermite foils, commonly referred to as Redox Foils, provide a unique opportunity to enable exothermic brazing of components by utilizing the molten metallic product of the thermite reaction as a braze. Due to the propensity of thermites to produce gas, however, Redox Foils must be diluted to eliminate metal vapor formation. This dilution can lead to foils that react too slowly to fully propagate in a bonding configuration, and therefore the reactivity of the foils must be improved. To do so, we milled the constituent powders (Al, CuO, and Cu) before we mechanically consolidated them into dense Redox Foils. The milling process decreases the reactant spacing, or the distance between the fuel (Al) and oxide (CuO), thereby enhancing oxygen transfer between the fuel and the oxide. Two fabrication strategies are employed: milling the thermite reactants (Al and CuO) without the Cu diluent, then adding the diluent before consolidation into Redox Foils, and the second is milling all components (Al, CuO, and Cu) together before consolidation. Both milling processes results in foils that propagate faster and release heat earlier than foils consolidated from unmilled, single-phase powders of Al, CuO and Cu, due to decreased reactant spacings. However, only the second milling strategy is capable of suppressing the production of Cu metal vapor during the reaction of the foils, as confirmed using emission spectroscopy. The lack of Cu vapor in these foils is attributed to a more uniform distribution of Cu diluent that is verified using digital analysis of foil microstructures. [ABSTRACT FROM AUTHOR]

Conformal atomic layer deposition (ALD) of Al2O3 and TiO2 thin films on Kevlar®, poly(p-phenylene terephthalamide) (PPTA) fibers at 50 and 100 °C affects the fiber cut resistance. Systematic studies of ALD coatings between 10 to 400 A thick formed at 50 and 100 °C revealed excellent conformality, and trends in cutting performance depended on materials and process details. Å 50 Å/50 Å TiO2/Al2O3 bilayer formed at 50 °C increased cut resistance of PPTA by 30% compared to untreated fiber materials. In situ infrared analysis shows that trimethylaluminum (TMA) Al2O3 precursor reacts sub-surface with PPTA and tends to degraded mechanical performance. The TiCl4 TiO2 precursor reacts to form a barrier that limits TMA/PPTA interactions, allowing a harder Al2O3 layer to form on top of TiO2. The thin ALD coatings do not substantially affect durability, flexibility, or weight of the PPTA, making ALD a potentially viable means to enhance the protective properties of Kevlar and other polymer fiber systems. [ABSTRACT FROM AUTHOR]