Fernanda Santos da Luz

Ballistic Test of Multilayered Armor with Intermediate Epoxy Composite Reinforced with Jute Fabric

Multilayered armors with a front ceramic followed by aramid fabric (Kevlar™) are currently used against high velocity ammunition. In these armors, a front ceramic layer that shatters and spalls the bullet is followed by an intermediate layer, usually plies of aramid fabric, which dissipates both the bullet and ceramic fragments energy. In the present work, the intermediate aramid fabric layer was replaced by an equal thickness layer of 30 vol% jute fabric reinforced epoxy composite. Ballistic impact test with 7.62 caliber ammunition revealed that both the plain epoxy and the jute fabric composite have a relatively similar performance of the Kevlar™ and also attended the NIJ standard for body protection. The energy dissipation mechanisms of jute fabric composite were analyzed by scanning electron microscopy and found to be the rupture of the brittle epoxy matrix as well as the interaction of the jute fibers with the post-impact fragments. This latter is the same mechanism recently disclosed for aramid fabric. However, the lightness and lower cost of the jute fabric composite are additional advantages that favor its substitution for the aramid fabric.

Influence of the Areal Density of Layers in the Ballistic Response of a Multilayered Armor System Using Box-Behnken Statistical Design

Several works have been dedicated to study the ballistic response of multilayered armor systems (MAS), including those using natural fiber composites as second layer. These composites disclosed good ballistic performance, having economic and environmental advantages. In the present work, the objective was to investigate the effect of areal densities of each MAS layer, in the overall performance of a MAS with an alumina ceramic front, a curaua fabric reinforced composite filling, and an aluminum alloy backing the target. Ballistic “backface signature” tests were conducted, varying the areal densities of the MAS layers according to a Box-Behnken design. The results showed a similar influence of the ceramic and aluminum layers in the MAS “backface signatures”, although deformation and failure mechanisms were significantly different. The composite also showed significant participation in the overall MAS performance. Since the composite is cheaper and lighter, a balance minimizing the other layers would be advantageous.

Limit Speed Analysis and Absorbed Energy in Multilayer Armor with Epoxy Composite Reinforced with Mallow Fibers and Mallow and Jute Hybrid Fabric

Epoxy matrix composites reinforced with up to 10, 20 and 30 vol% of continuous and aligned natural mallow fibers and 30 vol% of mallow and jute hybrid fabric were for the first time ballistic tested as personal armor against class III 7.62 mm FMJ ammunition. The ballistic efficiency of these composites was assessed by measuring the dissipated energy and residual velocity after the bullet perforation. The results were compared with that in similar tests of aramid fabric (Kevlar™) commonly used in vests for personal protections. Visual inspection and scanning electron microscopy analysis of impact-fractured samples revealed failure mechanisms associated with fiber pullout, rupture and layers delamination. When compared to Kevlar™, the mallow fiber and hybrid fabric composite displayed practically the same ballistic efficiency. However, there is a reduction in both weight and cost, which makes both, mallow fiber and hybrid fabric composites, a promising material for personal ballistic protection.

Analysis of Coir Fiber Porosity

Lignocellulosic natural fibers exhibit high variation in mechanical properties values due to their heterogeneity. Recent studies have shown that the dispersion of these properties depends on the diameter of the fiber. A possible explanation for the tendency of low mechanical properties with large diameter is the high probability of defects into the fiber. However, no study has yet investigated the relation between the diameter and defects of natural fibers. Hence, in the present work the total porosity of coir fiber (Cocos Nucifera L.) was estimated. A statistical analysis was carried out on a batch of about 100 fibers and the geometric density was measured by using a stereomicroscope. The closed and open porosity as well as the density of the fiber were quantified by helium pycnometry method. The values obtained were correlated with the diameter of each analyzed fiber. Results made it possible a more detailed knowledge of the porous structure of the fiber.

CARACTERIZAÇÃO MECÂNICA E MICROESTRUTURAL DE CONCRETO GEO POLIMÉRICO SUBMETIDO À FADIGA

Verônica Scarpini Cândido Alisson Clay Rios da Silva Fernanda Santos da Luz Sergio Neves Monteiro Resumo Cimentos provindos de reações álcali-ativadas abrem novas oportunidades para o futuro, como a utilização de polímeros inorgânicos, conhecidos como geopolímeros. Estes materiais são considerados ecologicamente corretos, pois seu processo de fabricação não envolve a emissão de CO2 e é possível utilizar resíduos industriais como matéria prima. Neste trabalho, foi desenvolvido um concreto de cimento geopolimérico (CCG) e sua resistência à fadiga foi comparada com outro concreto correspondente de cimento Portland (CCP). Foram utilizados alguns parâmetros fixos na dosagem de ambos os concretos, como consumo de aglomerantes, relação água/aglomerante e teor de argamassa. O estudo foi realizado por meio de ensaios dinâmicos, avaliando os efeitos de diferentes níveis de tensões, máximas e mínimas, e frequência aplicada. Os resultados de fadiga nas diversas variações realizadas mostraram um melhor desempenho ao comportamento em fadiga do CCG em relação ao CCP. Na análise microestrutural foi observada uma melhor aderência matriz/agregado no CCG quando comparado com o CCP, o que pode explicar sua maior resistência perante a fadiga. Palavras-chave: Geopolímero; Concreto geopolimérico; Fadiga.

Work Hardening and Microstructural Effect during Dynamic Deformation of Polycrystalline Copper

Dynamic deformation of metals in the elevated strain rate interval of elastic-plastic wave propagation is relevant to technological conditions, such as structural response to impact, ballistic effects, and metal forming processes. In the present work, the work hardening of quasi-static and dynamically deformed copper using a split pressure bar was evaluated for two different grain sizes. From slip lines observations in conditions of both dynamic and quasi-static strain rates, as well as an insensitivity to grain size of the yield stress, it is suggested that copper behave like a single crystal under dynamic deformation. It is shown, for the first time, that the work hardening rate during dynamic deformation of polycrystalline copper remains higher up to the fracture.