ENHANCING BALLISTIC IMPACT RESISTANCE OF POLYMER MATRIX COMPOSITE ARMORS BY ADDITION OF MICRO AND NANO-FILLERS

Improving the ballistic impact resistance of hybrid polymer matrix composites through addition of micro- and nano-particles as fillers is the principal goal of this research. Development of light-weight ballistic plates, made of polymer matrix composites with improved ballistic resistance, can offer a solution of shielding with lighter, thinner, stronger and less expensive materials than the conventional ballistic plates. The use of micro- and nano-particles in low concentrations can achieve this goal without compromising the density or strength of the new armor plates. Firstly, laminated hybrid composites consisting of aluminum alloy plates, epoxy resin and Kevlar® fabrics were developed. Shear thickening fluid (STF) made of nano-particles of colloidal silica (SiO2) was impregnated into Kevlar® fabrics to determine its effect on the energy absorption behavior of the composites. STF decreased the tendency of Kevlar® fibers to rupture during projectile penetration, and thus, increased its impact energy absorption performance when compared to the samples made of Kevlar® neat fabrics (containing no STF). Similar laminated hybrid composites were subsequently built through impregnation of micro- and nano-particles of aluminum, gamma alumina, silicon carbide, colloidal silica and potato flour into Kevlar fabrics by mixing these particles with polyethylene glycol. The obtained laminates were evaluated to determine their impact resistance and energy absorption capabilities under ballistic impact. The plates containing aluminum and colloidal silica nano-powders have the highest energy absorption capability of between 679 up to 693 J for plate thickness and areal density of about 10.8 mm and 1.9 g/cm2, respectively. These laminates can meet the protective requirements for levels IIA, II, and IIIA to resist ballistic impact from pistols caliber 9 mm. In another approach, hybrid composite armor plates based on high density polyethylene (HDPE) were prepared by using 10 wt.% of Kevlar® short fibers, and 20 wt.% chonta palm wood, potato flour, colloidal silica or gamma alumina particles. Addition of colloidal silica and gamma alumina nano-particles improve stiffness by 43.5% and increase impact energy absorption capability by 20%, compared to control sample, which is HDPE containing 10 wt.% Kevlar® short fibers. Hybrid bio-composites made of 10 wt.% Kevlar® short fibers and varying amount of chonta wood particles (10, 20, 30 wt. %), as additional reinforcement, were also developed and investigated. The hybrid composite plates containing 10 wt.% chonta palm wood micro-particles exhibited the highest energy absorption capability of 62.4 J, which is equivalent to 19.5 % improvement over control specimens: HDPE reinforced with 10 wt.% Kevlar® short fibers. Finally, bio-composites made of HDPE reinforced with varying fractions of micro-particles of chonta palm wood (10, 20, 25, and 30 wt. %) were developed and characterized. The ballistic impact performance of the biocomposites containing 25 wt.% chonta palm wood particles exhibited the highest energy absorption of 53.4 J, which represents a 41.3% improvement over the unreinforced HDPE specimens with similar thickness and density

Qualitative study in Loop Quantum Cosmology

This work contains a detailed qualitative analysis, in General Relativity and in Loop Quantum Cosmology, of the dynamics in the associated phase space of a scalar field minimally coupled with gravity, whose potential mimics the dynamics of a perfect fluid with a linear Equation of State (EoS). Dealing with the orbits (solutions) of the system, we will see that there are analytic ones, which lead to the same dynamics as the perfect fluid, and our goal is to check their stability, depending on the value of the EoS parameter, i.e., to show whether the other orbits converge or diverge to these analytic solutions at early and late times.Comment: 12 pages, 7 figures. Version accepted for publication in CQ

Brane cosmology from observational surveys and its comparison with standard FRW cosmology

Several dark energy models on the brane are investigated. They are compared with corresponding theories in the frame of 4d Friedmann-Robertson-Walker cosmology. To constrain the parameters of the models considered, recent observational data, including SNIa apparent magnitude measurements, baryon acoustic oscillation results, Hubble parameter evolution data and matter density perturbations are used. Explicit formulas of the so-called {\it state-finder} parameters in teleparallel theories are obtained that could be useful to test these models and to establish a link between Loop Quantum Cosmology and Brane Cosmology. It is concluded that a joint analysis as the one developed here allows to estimate, in a very convenient way, possible deviation of the real universe cosmology from the standard Friedmann-Robertson-Walker one.Comment: 19 pages, 6 figures. arXiv admin note: text overlap with arXiv:1206.219

On the liquid-glass transition line in monatomic Lennard-Jones fluids

A thermodynamic approach to derive the liquid-glass transition line in the reduced temperature vs reduced density plane for a monatomic Lennard-Jones fluid is presented. The approach makes use of a recent reformulation of the classical perturbation theory of liquids [M. Robles and M. L\'opez de Haro, Phys. Chem. Chem. Phys. {\bf 3}, 5528 (2001)] which is at grips with a rational function approximation for the Laplace transform of the radial distribution function of the hard-sphere fluid. The only input required is an equation of state for the hard-sphere system. Within the Mansoori-Canfield/Rasaiah-Stell variational perturbation theory, two choices for such an equation of state, leading to a glass transition for the hard-sphere fluid, are considered. Good agreement with the liquid-glass transition line derived from recent molecular dynamic simulations [Di Leonardo et al., Phys. Rev. Lett. {\bf 84}, 6054(2000)] is obtained.Comment: 4 pages, 2 figure

Nanocellulose from Spanish Harvesting Residues to Improve the Sustainability and Functionality of Linerboard Recycling Processes

The hornification processes undergone by the fibers in the paper industry recycling processes lead to the loss of properties of the final products, which exhibit poor mechanical properties. Among the most promising solutions is the reinforcement of secondary fibers with cellulose nanofibers. The present work addresses two important issues: the efficient production of cellulose nanofibers from scarcely exploited agricultural wastes such as horticultural residues and vine shoots, and their application as a reinforcement agent in recycled linerboard recycling processes. The effect of the chemical composition and the pretreatment used on the nanofibrillation efficiency of the fibers was analyzed. Chemical pretreatment allowed a significantly higher nanofibrillated fraction (45–63%) than that produced by mechanical (18–38%), as well as higher specific surface areas (>430 m2/g). The application of the nanofibers as a reinforcing agent in the recycled linerboard considerably improved the mechanical properties (improvements of 15% for breaking length, 220–240% for Young’s modulus and 27% for tear index), counteracting the loss of mechanical properties suffered during recycling when using chemically pretreated cellulose nanofibers from horticultural residues and vine shoots. It was concluded that this technology surpasses the mechanical reinforcement produced by conventional mechanical refining used in the industry and extends the number of recycling cycles of the products due to the non-physical modification of the fibers

Structural and Electronic Properties of Graphene Oxide for Different Degree of Oxidation1

In the last year, the investigation of two-dimensional materials as graphene oxide is a fundamental goal to produce innovative devices with wide range of applications in many areas. In the present work, we report a systematic study of structural and electronic properties of graphene oxide for different oxidations levels (25%, 50%, 75%, 100%) using density functional calculations for electronic ground state and a statistical approach on carbon-carbon bond length obtained after the geometric optimization of graphene covered with epoxide and hydroxyl functional groups. The theoretical models proposed and studied here are accord with the well-known experimental data. Our statistical results of the carbon-carbon bond length shown that hydroxyl groups disturbs the structure of graphene more than epoxide groups, however, both hydroxyl and epoxide groups are responsible of the change of hybridization sp2 to sp3, while the degree of oxidation increase. In addition, our electronic structure calculations confirm that with low degree of oxidation, the graphene oxide is semiconductor, and with full degree of oxidation graphene oxide is an insulating material. The minimum of total energy is found when the graphene oxide has full coverage. This work can contribute to understand the plasticity and ductility properties of graphene oxide recently reported

Погляд на архіви

The history of string theory started around 1970 when Nambu, Nielsen, and Susskind realized that Veneziano’s 1968 dual model, devised to explain the particle spectrum of the strong interactions, actually describes the properties of quantum mechanical strings. A few years later, QCD appeared as a superior model for the strong interactions; furthermore, in 1974 it was realized that strings contain gravitons in their spectrum. For these reasons, many lost interest in the theory, while for some it made an interesting candidate as a unifying theory of gravity and quantum field theory

Superflares on Ordinary Solar-Type Stars

Short duration flares are well known to occur on cool main-sequence stars as well as on many types of `exotic' stars. Ordinary main-sequence stars are usually pictured as being static on time scales of millions or billions of years. Our sun has occasional flares involving up to $\sim 10^{31}$ ergs which produce optical brightenings too small in amplitude to be detected in disk-integrated brightness. However, we identify nine cases of superflares involving $10^{33}$ to $10^{38}$ ergs on normal solar-type stars. That is, these stars are on or near the main-sequence, are of spectral class from F8 to G8, are single (or in very wide binaries), are not rapid rotators, and are not exceedingly young in age. This class of stars includes many those recently discovered to have planets as well as our own Sun, and the consequences for any life on surrounding planets could be profound. For the case of the Sun, historical records suggest that no superflares have occurred in the last two millennia.Comment: 16 pages, accepted for publication in Ap