The fique is a plant typical of the Colombian Andes, from which relatively common items are fabricated. One of these is woven fabric extensively applied in sackcloths. The mechanical strength of fique fabric have motivated recent investigations on possible reinforcement of polymer matrix composites. For this purpose its thermo-mechanical behavior was unveiled. In particular, dynamic mechanical analysis (DMA) of fique fabric reinforced polyester matrix composites disclosed improved viscoelastic behavior in association with change in the glass transition temperature. The present work extends this investigation to epoxy matrix, which is one of the most employed thermoset polymer for composite matrix. Fique fabric volumetric fractions of up to 50% are for the first time incorporated into epoxy composites. It was found that these incorporations significantly increased the viscoelastic stiffness of the composite, given by the storage modulus (E’), in the temperature interval from -50 to 170°C. An accentuated softening in viscoelastic stiffness was revealed for all composites above 75°C. Peaks in both the loss modulus (E”) and tangent delta (tan δ), respectively associated with the lower and upper limits of the glass transition temperature, were shifted towards higher temperatures with increasing amount of fique fabric.

A comparative investigation on the firing behavior of a natural kaolinitic clay from Campos dos Goytacazes, Brazil, and its specific clay fraction was performed. The clay fraction, equivalent diameter less than 2 µm, was separated from the precursor clay by a sedimentation method. Chemical analysis, X-ray diffraction (XRD) and scanning electron microscopy were used to characterize the unfired materials. Thermoanalysis and dilatometry were applied to follow the structural transformations. The firing behavior was studied by water absorption and XRD of samples fired in the temperature range from 400 to 1100°C. Differences were found between the natural kaolinitic clay and its clay fraction. The absence of quartz and smaller particles of the clay fraction result in a comparatively lower temperature for structural consolidation associated with reduced open porosity. This can be attributed to solid state sintering alone, in contrast to a higher temperature liquid phase sintering needed for complete consolidation of the natural kaolinitic clay.

Firearms threat has always been a matter of personal concern, especially to soldiers in armed conflicts as well as police officers and civilians involved with public security. A multilayered armor system (MAS) is intended to personal protection against high kinetic energy ammunition, such as that used in rifles. MAS layers are normally composed of a front ceramic followed by a layer that must show both high impact resistance and low weight. Usually, synthetic fiber fabrics, such as aramid in Kevlar® and ultra-high molecular weight polyethylene (UHMWP) in Dyneema® are commonly used as the second layer. Currently, composites reinforced with natural fibers are also being considered as second MAS layer due to their good performance associated with the advantages of being cheaper and environmentally friendly. The fique is a relatively unknown natural fiber extracted from leaves of a plant native of South American Andes. In the present work, fique fibers and fique fabrics incorporated in polyester composite plates with volume fraction of 10, 20 and 30% were ballistic tested. The calculated projectile loss of energy indicated a relatively large energy dissipation by the composite. The tested specimens were statistically treated by the Weibull analysis and were examined by scanning electron microscopy.

Waste incorporation into clay ceramic is a worldwide accepted recycling procedure for environmentally friendly reuse of spent industrial materials. In the present work a clay ceramic from the city of Campos dos Goytacazes, Brazil, was, for the first time, investigated with different amounts, up to 10 wt%, of a solid waste generated from the “Sulfatreat” natural gas treatment process. Both the waste and the incorporated ceramic were characterized by X-ray fluorescence and X-ray diffraction as well as vibratory sieving, gas chromatography and sedimentation method. Ceramic samples were prepared by uniaxial pressing at 18 MPa and sintered at 850°C. Physical and mechanical properties of these ceramics such as linear shrinkage, apparent density, water absorption and flexural strength were evaluated. Microstructure of the incorporated ceramics was analyzed by optical microscopy. The results showed that, within the standard deviation, the linear shrinkage and apparent density of the clay ceramic were not affected by the waste incorporation. However, the water absorption is benefitted, by decreasing above 5 wt% incorporation, while the flexural strength is impaired for any incorporated amount. Porosity and larger waste particles observed in microstructure are proposed reasons for these advantages and shortcomings.

The Amazonian region of South America is known for its diversified number of plants from which food, medicine, wood and fibers have, since long time, been produced by local natives. A typical example is the guarumã (“guaruman”as suggested English spelling) scientifically identified as Ischinosiphon koem, an abundant plant found in the low lands alongside rivers of the state of Para in Brazil. Fibers extracted from the stem of the guaruman are used in ropes and baskets owing to their strength. In the present work, the possibility of applying guaruman fibers as reinforcement of polymer matrix composites is, for the first time, investigated. Amounts up to 30 vol% of continuous and aligned fibers were incorporates into epoxy matrix composites. Density measurements disclosed the guaruman to be one of the lightest natural fibers. Tensile tests indicate that the guaruman fiber addition was able to improve the composite elastic modulus. However, no significant change was found in the ultimate strength, total strain and resilience. On the other hand, a cost-effective analysis revealed a substantial reduction of ~29% in the epoxy composite price due to the incorporation of fibers. Preliminary ballistic evaluation disclosed a potential for application of guaruman epoxy composites in multilayered armor.

ABSTRACT Environmental considerations in addition to technical, economical and societal benefits are increasingly promoting the substitution of natural fibers for glass fiber in polymer matrix composites. However, natural fibers are heterogeneous in their dimensions, specially the cross section, which plays an important role in their mechanical strength. It has been found that the equivalent diameter of fibers such as sisal, ramie, pineapple and curaua correlates to different levels of tensile resistance. Piassava is a promising stiff natural fiber for composite reinforcement. In this work, a statistical analysis of tensile strength of piassava fibers using the Weibull methodology was performed. An attempt to correlate the fiber strength, obtained in tensile tests, with the diameter, precisely measured by means of a profile projector, was carried out. The results revealed an inverse dependence between the piassava fiber diameter and corresponding tensile strength. Fracture tip observation by SEM suggested a possible mechanism that could justify this inverse correlation.

ABSTRACT Polymer matrix composites have been applied in components such as helmets and shielding for which toughness is a major requirement. Natural fiber presents interfacial characteristics with polymeric matrices that favor a high impact energy absorption by the composite structure. The objective of this work was then to assess the Izod impact resistance of polymeric composites reinforced with different amounts, up to 30% in volume, of a promising high strength natural fiber from the Amazon region known as curaua. Among these, the piassava fiber extracted from a palm tree native of South America stands as one of the most rigid with a potential to be used as composite reinforcement. Therefore, the present work investigates the notch toughness behavior, by Izod impact tests, of epoxy composites reinforced with up to 40 % in volume of continuous and aligned piassava fibers.The results showed a remarkable increase in the notch toughness with the amount of incorporated curaua fibers. This can be attributed to a preferential debonding of the fiber/matrix interface, which contributes to an elevated absorbed energy. . It was found that the incorporation of piassava fibers results in significant increase in the impact energy of the composite. Scanning electron microscopy analysis showed that the nature of the piassava fiber interface with the epoxy matrix is the major responsible for the superior toughness of the composite.

Ornamental stones, such as marble and granite, are worldwide used as pavement cover and lining parts in civil construction. Dwindling deposits and environmental pollution, due to extraction methods, have motivated the replacement of natural ornamental stones by synthetic ones. In particular, artificial ornamental stones are being developed with mineral wastes incorporated into polymeric matrix. In this work, granite particle waste, from a quarry, which supplies plates for building construction, was used in amounts of 85 and 90 wt % together with epoxy resin to fabricate novel artificial stones. Physical and mechanical characterization disclosed superior properties that allow these new developed artificial stones to be applied as pedestrian traffic pavements.

The great environmental impact caused by mineral production has forced mining and ornamental stone industries to acquire new concepts and technical solutions in order to develop eco-friendly and sustainable activities. In this context, this work aims to study the durability of soil-cement block with the incorporation of limestone residues from the processing of marble as an ornamental stone. Specimens were prepared with 30, 40 and 50 vol% of residues added to the soil-cement mixture and analyzed for their physical, chemical and mineralogical properties. After the curing period, the specimens were subjected to mechanical analysis and the established experimental program showed that the addition of residues in the mixture becomes feasible for the preparation of soil-cement blocks, exhibiting improved results when compare to a reference block without residues.

The essential work of fracture (EWF) method provides useful parameters to characterize the fracture toughness of polymers exposed to degrading environments under conditions associated with plane-stress state of failure. Exposure of polymeric engineering materials to ultraviolet (UV) radiation may produce macromolecular changes that impair their fracture toughness. In the present work, for the first time, the EWF method applying a double edge notched tensile specimen was used to quantify the fracture toughness behavior of polycarbonate (PC) exposed to different, 300 h and 600 h, UV irradiation times. In addition, molar weight M ─ n determination, differential scanning calorimetry (DSC), Fourier transformed infrared spectroscopy (FTIR) and tensile tests were also investigated for non-irradiated and UV irradiated PC. The EWF results and scanning electron microscopy analysis revealed a significant reduction (39 % for 300h and 45 % for 600h of UV exposure) in fracture toughness associated with scission of the macromolecular chains. Other investigated properties, such as M ─ n, glass transition temperature, oxidation index and tensile strength, despite decreasing with UV exposure, did not show conclusive values.

The growing interest in natural lignocellulosic fibers (NLFs) is associated not only with environmental benefits but also with technical, economical and social advantages. Among the NLFs, the coir fiber and pineapple leaf fiber (PALF) are low-cost and widely available waste materials. The present work investigated the dynamic mechanical properties, by means of DMA tests, of these two different fibers as reinforcement of epoxy matrix composites. The influence on DMA properties of composites by the volume fraction and the configuration form, mat or aligned coir fiber, were also evaluated. The results showed higher E’ and E” moduli values and an increase in Tg with the incorporation of PALF in epoxy matrix, which indicate a superior dynamic mechanical properties for this composite in comparison to the neat epoxy resin. The experimental data also revealed a stronger interfacial interaction of PALF/epoxy when compared to coir fiber/epoxy. It was also found a lower tan δ value exhibited by higher volume fractions of aligned coir fibers in epoxy matrix.

The response to ballistic impact of alumina-ultra high molecular weight polyethylene (UHMWPE) composites with different relative concentrations of alumina was investigated. The impact tests were carried out at subsonic speed using a compressed air system. The results showed that the depth of penetration (DOP) in a Medium Density Fiberboard (MDF) bulkhead protected by a disk of the composite decreased with increasing concentration of alumina in the composite. Scanning electron microscopy (SEM) images of composites with 80 %, 85 % and 95 % alumina showed transgranular, intergranular and ductile fracture mechanisms.

Shape memory alloys (SMA) are attracting considerable attention owing to possible applications from biomedical to aerospace. In particular, CuAlNi alloys present significant advantages associated with low cost, easy processing and superior thermo-electric conductivity over other SMAs such as the NiTi alloys. Characterization of some properties and structural changes caused by martensitic transformation are still open to investigation. The present work evaluated these characteristics in an as-cast plasma processed shape memory Cu-14wt.%Al4wt.%Ni, which was compression tested until fracture. Experimental results showed that an as-cast ingot presents not only chemical and phase homogeneity, but also microstructures composed of grains with martensitic morphology. Martensites β'1 and γ'1, as well as intermediary martensitic R and high temperature β1 were identified by X-ray diffraction tests. It was found that the compressive deformation does not interfere in the phase composition and martensite morphology. However, compression changes the volumetric fractions and crystallographic orientation of the martensites. The mechanical behavior is characterized by an apparent elastic response until the fracture. The fractured surface exhibits brittle aspect like "river patterns" and evidence of intergranular rupture.

Natural fiber reinforced polymer composites have recently been investigated as a component of multilayered armor system (MAS). These composites were found to present advantages when replacing conventional high strength synthetic aramid fabric laminate composite (KevlarTM, with same thickness, as MAS second layer. Continuous and loose natural fibers were up to now mostly used to reinforce these ballistic composites. Only two natural fabrics reinforced polymer composite were so far used with same purpose. Therefore, this work investigated the possibility of substituting KevlarTM for three other natural fabrics, based on mallow and jute fibers, as reinforcement of epoxy composites. Fabrics made of either pure mallow, or 70%mallow/30% jute or 50%mallow/50% jute fibers were separately mixed with epoxy to produce laminate composite plates. These plates were set as second layer of Al2O3/Nb2O5 front ceramic MAS, that were ballistic tested against relatively high energy 7.62 mm ammunition. Indentation depth values caused by the bullet penetration in clay witness, simulating human body behind the MAS, were always found to be below the safety standard limit. These indentation values were similar to those obtained in MAS with KevlarTM as second layer. However, significant economical advantages favor the investigated natural fabric composites over the synthetic Kevlar.

Due to increasing improvement of weaponry and ammunition, attention is being given to the development of new materials that could more effectively resist to ballistic impact. In order to stop high energy bullets, with speed above 800 m/s, a high strength material is necessary. However, if just one material is used, then a relatively thick piece is required, which might affect negatively the wearer mobility. The objective of this work is to investigate the effect of thickness on the ballistic behavior of aramid fabric laminates, Kevlar®, hit by high energy bullet. The purpose is to find the minimum thickness to avoid perforation. Ballistic tests using conventional 7.62 mm ammunition were performed according to standard procedures. The macro and microscopic aspects of the target specimens were evaluated. The results showed a change in the ballistic behavior of the laminates as their thickness increased. It was found that until the laminate was able to capture the bullet, 96 layers (~50 mm) were required. This is significantly higher than the necessary thickness for a multilayered armor to stop the same 7.62 mm bullet.