Alaelson Vieira Gomes

Evaluation of Ballistic Armor Behavior with Epoxy Composite Reinforced with Malva Fibers

In the present study, we used natural fibers malva (Urena lobata, Linn) in 0, 15 and 30 vol.% as reinforcement of epoxy matrix composites to ballistic application. Ballistic efficiency of these composites was assessed by measuring the energy absorbed and residual velocity after impact 9 mm FMJ ammunition projectile, aiming to compare with traditional materials, such as: aramid fabric Kevlar™ used in vests for personal protection. The results showed by visual analysis and scanning electron microscopy (SEM) that the main active failure mechanisms in composites were delamination layers and fiber rupture. In test groups can be seen that the absorbed energy and the residual velocity varies with the fiber percentage used. Compared to aramid there is both a gain in weight and cost of the ballistic armor, which makes the fiber malva a promising material applications involving personal protection against 9 mm caliber ammunition.

Organic Binder Burnout in Alumina Processing

Incomplete binder removal may introduce severe defects during ceramic processing. This work presents a new method to eliminate polyethylene glycol used as a binder in pre-sintering steps of alumina parts. The effectiveness of the proposed method was evaluated by density and pore size measurements, as well as thermogravimetry (TG), differential thermal analysis (DTA), volumetric physical adsorption analyzer (BET), and Fourier transformed infrared spectroscopy (FTIR). The results show that the new method, although relatively slow in comparison with traditional procedures, yields smaller pore sizes and better mechanical properties of the final products.

Ballistic Performance in Multilayer Armor with Epoxy Composite Reinforced with Malva Fibers

A multilayer armoring system (MAS) is commonly formed by three layers. The initial layer is normally composed by a ceramic with high compressive strength, which absorbs most of the kinetic projectile energy. The subsequent composite layer was formed by epoxy matrix reinforced with natural malva fibers (Urena lobata, Linn), in the form of pure or hybrid fabric with jute fibers, in order to absorb part of the kinetic energy, and to retain ceramic and projectile shrapnel. A third layer formed by aluminum alloy, was included as a penetration restrictor for bullet and fragments by plastic deformation. The ballistic efficiency was evaluated by penetration of the 7.62 × 51 mm ammunition into a clay witness backing the armor. The results showed a great potential by epoxy composites reinforced with malva fabric as compared to other natural fibers and materials traditionally used in personal protection, such as Kevlar™ aramid.

CARACTERIZAÇÃO DE NANOCOMPÓSITOS COM PARTÍCULAS DE CARBETO DE BORO DISPERSAS EM MATRIZ DE POLIETILENO DE ULTRA ALTO PESO MOLECULAR

Flávio James Tommasini Édio Pereira Lima Junior Sergio Neves Monteiro Alaelson Vieira Gomes Marcelo H Prado da Silva Carla S Cosenza Resumo O estudo teve como objetivo a produção de corpos de prova de nanocompósitos baseados em uma matriz polimérica de polietileno de ultra alto peso molecular (UHMWPE) com carga de carbeto de boro dispersas, nas proporções de 0,0625%; 0,125%; 0,25%; 0,5%; 1% e 2%, respectivamente. As respectivas misturas entre os materiais, polímero e carga inorgânica, foram moldadas em prensa hidráulica quente à partir do estado fundido da matriz polimérica. A caracterização dos nanocompósitos com as cargas sem tratamento foi realizada pelas análises de difração de raio-x (DRX) e calorimetria diferencial de varredura (DSC), o que possibilitou a identificação dos planos cristalográficos característicos dos materiais, o grau de cristalinidade da matriz orgânica e suas respectivas temperaturas de fusão. As microestruturas dos materiais, morfologia da carga e adesão interfacial foram observadas através da microscopia eletrônica de varredura (FEGSEM). Através desse estudo foi possível o sugerir o comportamento do polímero com cargas de carbeto de boro dispersas em diversas proporções. Palavras-chave: Nanocompósitos; Carbeto de Boro, Polietileno de Ultra Alto Peso Molecular, Polímero, Estado Fundido.

Comparative Study of Solid-Phase and Liquid-Phase Assisted Sintering of Nb2O5-Doped Alumina

This work investigated the sintering behavior of alumina doped with 4wt% niobia. Three sintering temperatures were investigated: 1400°C, 1450°C and 1500°C. The first temperature leads to solid-phase assisted sintering (SSS) while the other ones develop liquid-phase assisted sintering (LPS). The presence of liquid phase in the second case is due to an eutectic reaction occurring at 1440°C ± 20°C in the alumina-niobia system. The sintering behavior was assessed by measuring the final densities. The results indicated that the 1400°C solid-state sintering, comparatively, was better. This paper proposes that defects associated to the substitution of Al+3 by Nb+5 in the alumina cation sub-lattice, fostered diffusion and SSS. Sintering at 1500°C presented the lowest density, apparently due to niobate (liquid phase) loss, at this temperature as observed by XRD results.

Processing and Properties of Niobia-Doped Alumina Sintered at 1400oC

Niobia is used as a sintering additive in alumina processing because it lowers the sintering temperature. This work investigated the influence of sintering dwell time at 1400oC on the properties of 4 wt% niobia doped alumina. The sintered ceramics were characterized by scanning electron microscopy (SEM), and X rays diffraction (XRD) with Rietveld refinement. Measurements of density, average grain size, hardness, and elastic constants were also performed. The results showed that the porosity depend on the time sintering and this influence on the elastic properties. Longer sintering times improved densification and with this the Youngs Modulus.

Effect of Milling Medium on Alumina Additivated with Niobia

Niobia has been successfully used as sintering additive to alumina in order to lower its sintering temperature. This effect can also be obtained by reducing the ceramic particle size. This work investigated the effect of the particle size on the ceramic final density of alumina with 4 wt% niobia. For that two milling media were used. The as-received powders were submitted to ball and planetary milling and then sintered at 1450°C. The planetary milling medium was more efficient in reducing particle size when compared to ball milling. However, planetary milling caused significant contamination in the niobia powder, from the alumina balls used as milling agents. It forced composition balance in order to keep the original proposed formulation. The planetary milled sintered samples showed better densification and lower grain size in comparison with ball milled ones. It could be concluded that the milling medium choice directly affected both microstructure and properties of the sintered alumina with 4wt% of niobia. .

Effect of LiF and CaO Additions on MgAl2O4 Dynamic Behavior

Lithium fluoride as well as calcium oxide were used as sintering additives to magnesium aluminate ceramics in order to provide both transparency and better densification. This work assessed the dynamic behavior of MgAl2O4 by performing split Hopkinson bar dynamic tests. The total amount of additives was 1.5 wt% in which the percentage of LiF and CaO varied from 0 to 100 wt% with an increment of 25 wt%. The obtained results indicated that CaO low concentrations induced low strength values to the ceramics of different compositions. By increasing the amount of CaO, the MgAl2O4 dynamic strengths were higher. The strain rate was reduced as the amount of CaO increased, indicating a higher trend of energy absorption corroborated by KIc measured values. On the other hand, the ceramic strain increased with the increment CaO additions.