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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]

In this paper, we report a novel method of free-space passive optical coupling to completely embedded, transmission-based fiber Bragg grating (FBG) sensors. Fiber optic sensors (FOS's) have attracted intense research and commercial interest. A major challenge in implementing embedded FOS's, however, is improving upon the cumbersome and fragile ingress/egress techniques commonly used for bringing the sensing light into and out of the structures. In this paper, we successfully couple free-space light into and out of an embedded FBG sensor, without the use of physical connectorization. This coupling is enabled by splicing a multimode fiber (MMF) to a single mode fiber Bragg grating (SMFBG), and using hand polishing to integrate 45° mirrors onto the ingress and egress points of the MMF and SMFBG, respectively. We determine the total loss of the system to be 23 dB, which is considerably better than previous studies that did not use this hand polishing technique. We also demonstrate the application of this free-space coupling technique to strain measurement with a maximum strain of about 2000 [variant_greek_epsilon]. With this approach, no "pigtailing" of optical fibers is needed, and the FBG sensors can be completely embedded inside the structures, greatly increasing system simplicity and robustness. [ABSTRACT FROM AUTHOR]

The energy absorbed in ballistic fabrics is modeled by assuming yarn pull-out, including yarn uncrimping and translation, as the primary energy absorption mechanism. Using a semi-empirical model of yarn pull-out bassed on laboratory tests, predictions of fabric ballistic performance are compared to ballistic test results. The study demonstrates that quasi-static pull-out results can be correlated quantitatively with yam pull-out during ballistic impact. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials can uniquely span the physical dimensions of a surrounding compositematrix in the limit ofmaximum reinforcement. However, the alignment and assembly of continuous 2D components at high volume fraction remain challenging.We use a stacking and folding method to generate aligned graphene/polycarbonate composites with as many as 320 parallel layers spanning 0.032 to 0.11millimeters in thickness that significantly increases the effective elasticmodulus and strength at exceptionally lowvolume fractions of only 0.082%. An analogous transverse shear scrolling method generates Archimedean spiral fibers that demonstrate exotic, telescoping elongation at break of 110%, or 30 times greater than Kevlar. Both composites retain anisotropic electrical conduction along the graphene planar axis and transparency.These composites promise substantial mechanical reinforcement, electrical, and optical properties at highly reduced volume fraction. [ABSTRACT FROM AUTHOR]

Reversible Diels-Alder chemistry was utilized to manipulate the surface energy of glass substrates. Hydrophobic dieneophiles were prepared and attached to glass slides and capillaries to yield a nonwetting surface. Thermal treatment of the surfaces cleaved the Diels-Alder linkage, and resulted in the fabrication of a hydrophilic surface. Preliminary analysis utilized contact angle (CA) measurements to monitor the change in surface energy, and observed a hydrophilic state (CA - 70 +/- 3 degrees) before attachment of the dieneophile to a hydrophobic state (CA - 101 +/- 9 degrees) followed by regeneration of the hydrophilic state (CA - 70 +/- 6 degrees) upon cleavage of the Diels-Alder linkage. The treatments were then applied to glass capillaries, with effective treatment confirmed by fluid column measurements. Patterned treatments were also demonstrated to provide effective flow gating. Finally, attempts to create self-pressurizing capillaries were unsuccessful due to pronounced contact angle hysteresis for the hydrophobic surface treatment.

The penetration behavior of Kevlar fabric intercalated with dry particles and shear thickening fluids (STF), highly concentrated fluid-particle suspensions, is presented. In particular, the role of particle hardness is explored by comparing fabric treatments containing SiO(2) particles, which are significantly harder than Kevlar, to treatments containing softer poly(methyl methacrylate) (PMMA) particles. The fabric testing includes yarn pull-out, quasi-static spike puncture, and ballistic penetration resistance, performed on single fabric layers. It was found that both dry particle and STF treatments resulted in improvements in fabric properties relative to neat or poly(ethylene glycol) (PEG) treated fabrics. On comparison of treatments with different particle hardness, the SiO(2) materials performed better in all tests than comparable PMMA materials, although the SiO(2) treatments caused yarn failure in pull-out testing, reducing the total pull-out energy. In addition, resistance to yarn pull-out was found to be substantially higher for STF-treated fabrics than for dry particle treated fabrics. However, both dry particle addition and STF treatments exhibited comparable enhancements in puncture and ballistic resistance. These observations suggest that viscous stress transfer, friction, and physical entrainment of hard particles into filaments contribute to the demonstrated improvements in the properties of protective fabrics treated with shear thickening fluids.