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The growing environmental awareness in the last few decades has driven the research and development of composites reinforced with natural fibers as an alternative to replace synthetic fiber composi...

Fiber-reinforced composites are among the most investigated and industrially applied materials. Many studies on these composites using fibers, especially with natural fibers, were made in response to an urgent action for ambient preservation. A particularly relevant situation exists nowadays in the area of materials durability. In this respect, no studies on water-immersion-accelerated aging in fique fiber–epoxy composites are reported. This work aimed to fill this gap by investigating the epoxy matrix composites reinforced with 40 vol% fique fabric. The epoxy matrix and the composite, both unaged and aged, were characterized by weight variation, water absorption, morphology, colorimetry (CIELAB method), Fourier transform infrared spectroscopy (FTIR) and dynamic–mechanical analysis (DMA). The main results were that degradation by water presents appearance of complex microfibril structures, plasticization of epoxy resin, and debonding of the fique fiber/epoxy matrix. The most intense color change was obtained for the water-immersion-aged epoxy by 1440 h. Cole–Cole diagrams revealed the heterogeneity of the materials studied.

Polycaprolactone (PCL) bionanocomposites reinforced with microfibrillated cellulose (MFC), either plain or modified with 2 wt% of zinc oxide (ZnO) nanoparticles, were first time developed for possible application as multifunctional packing. The MFC was obtained by an alkali treatment, a steam explosion process, and ZnO modification applied to parchment (PAR), a husk waste from the coffee industry. X-ray diffraction (XDR), thermogravimetric analysis (TGA/DTG), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), tensile tests, and CO2 permeability characterized the MFCs and the bionanocomposites. As for the MCFs, the crystallinity index of 50.6% measured by XRD for the plain PAR fiber increases with the combined alkaline treatment and steam explosion (CFA/EXP) to 68.2%, and further with ZnO modification (ZnO-CFA/EXP) to 80.1%. TGA/DTG displays a rising onset of thermal degradation from 214 to 306 °C, as well as maximum degradation rate from 330 to 350 °C, for PAR and ZnO-CFA/EXP, respectively. Regarding the nanocomposites, the addition of 3 wt% of alkali/steam explosion and ZnO-modified CFA/EXP contributes to enhancing thermal stability. Tensile tests disclosed improved mechanical properties of the novel nanocomposites as compared to the PCL matrix. In particular, Young's modulus rose from 88.5 to 169.5 MPa for the plain PCL and PCL reinforced with 3(ZnO-CFA/EXP), respectively. SEM images evidenced the participation of cellulose micro and nanofibrils in the PCL matrix. Approximately 20% reduction in the CO2 permeability coefficient of both PCL and its 3CFA/EXP nanocomposite compared with 3(ZnO-CFA/EXP) proved that the ZnO nanoparticles provide a gas barrier to the nanocomposite, a convenient property for food packing.

Among the natural fibers, the hemp fiber extracted from the stem of Cannabis sativa is, after sisal, the second most applied as reinforcement of polymer composites and increasingly used from automotive to civil construction industries. Polypropylene (PP) is the most common hemp fiber-reinforced matrix. Despite numerous papers on the application of natural fibers reinforcing polymer composites for ballistic protection, only one was so far dedicated to hemp fibers/PP with this purpose. In the present work, the main objective is for the first time to investigate the ballistic performance of the epoxy matrix reinforced with up to 30 vol% of hemp fabric. Epoxy is recently emerging as another strong alternative for the hemp fiber/fabric matrix. Due to the great variability in properties, a preliminary investigation was conducted on the basic mechanical and thermal behavior of the composites. The 30 vol% reinforcement with hemp fabric increased by 7.5 times the Izod impact energy as well as by more than 60% the tensile strength and 80% of the elastic modulus as compared to the neat epoxy. For all composites, a decrease of 20% in thermal temperatures (Tonset and Tmax) occurred in comparison to neat epoxy. The absorbed ballistic energy from the impact of 0.22 ammunition was significantly higher (95–108.5 J) than that previously reported of 36 J for hemp fabric/PP composite and others natural fiber/epoxy composites.

As an alternative for ordinary Portland cement, geopolymers are cost effective materials that can be prepared with relatively low energy consumption and substantial reduction of CO2 emissions. In the present study the characteristics of novel hybrid composite of geopolymer foam (GPF)/polylactic acid (PLA) and their efficiency in removing copper(II) and zinc(II) to treat high volumes of polluted water are investigated. Contrary to the conventional methods for removing heavy metals, the newly developed composites are ecological, low-cost, easily available, and economically viable alternatives providing good physical-chemical stability, ion-exchange properties, and a porous structure. Based on the sustainable advantage to produce geopolymers from recycled materials, GPFs were obtained from blast furnace slag (BFS) by reacting 20 mL of an 8 M alkaline solution of sodium metasilicate (Na2SiO3) with BFS particles and later addition of hydrogen peroxide. GPFs were produced with a stoichiometry of 1.4 and 1.6 g/L between BFS/alkali solution with a 1.6 ml solution of hydrogen peroxide 50% to develop porosity into the materials. Finally, the GPFs were coated with PLA. Specimens of GPF/PLA composites were characterized by X-ray fluorescence spectroscopy, Fourier transformed infrared spectroscopy, thermogravimetric analysis, dynamic mechanical analysis, and field emission gun scanning electron microscopy. Adsorption analysis of Cu(II) and Zn(II), as well as ion-exchanges from aqueous solution through the composite with 1.4 and 1.6 stoichiometry, were performed using deionized water containing 0.80% Cu(II) or Zn(II). The test resulted in high performance for retaining Cu(II) and Zn(II). Under CO2 pressure at 50 bar, the gas permeation tests confirmed porous formations into the geopolymer foams coated with molten PLA.

In the present work, two types of composites were produced, both reinforced with 30 vol% of curaua fibers (CF). In the first type, only the fiber was functionalized with graphene oxide (GO), producing the GOCF/EM composite. While in the second, only the epoxy matrix (EM) was functionalized, producing the CF/GOEM composite. The objective of the work was to investigate the influence of functionalization with GO on the tensile properties of these produced composites. In comparison with the non GO-functionalized composite, as control CF/EM, the results revealed an increase in yield strength (64%), tensile strength (40%), Young's modulus (60%) and toughness (28%) of the CF/GOEM composite. The GOCF/EM composites for which the fibers were functionalized with GO also performed better than the CF/EM composite. The ANOVA and Tukey tests confirm this increase. As for ductility, within the standard deviation, no change was observed between samples functionalized by GO and those from the control. For the first time, comparing the results of the composites, it was demonstrated that a polymer matrix functionalized by GO offers superior tensile performance compared to the other types, keeping the same GO concentration in the composite. This fact is corroborated by the analysis of the corresponding fracture mechanisms. Preliminary results of composite with simultaneous functionalization of both fiber and epoxy matrix failed to present superior properties. This might be attributed to high amount of GO, which is apparently not a good reinforcement as the curaua fiber.

Banana fibers are among the natural lignocellulosic fibers with greater potential for use as reinforcement in polymer matrix composites. Attractive mechanical and physical properties as well as low cost of production are considered as the main advantages on the use of such fibers. This works aims to study the mechanical behavior of the banana fiber when used as filler to the two most commonly used thermoset matrices (epoxy and polyester). The specimens were produced with up to 30 vol% of banana fibers for both polymeric matrices. Tensile strength tests as well as macroscopic and microscopic evaluation of the fractured surface were carried out. It was shown that, indeed, the banana fiber provided a substantial reinforcement for both matrices. On the other hand, mechanical strength associated with the composite epoxy/banana was more than 50% higher than the exhibit by the polyester/banana one. Such behavior could be associated with the interfacial strength regarding the fiber and the matrix.

Composite materials are being extensively studied for ballistic armor. Their main advantage is connected to the possibility of deeply reducing weight and costs by maintaining high performances in terms of strength and security. Epoxy composites are reinforced with natural fibers which are replacing other synthetic reinforcement materials. Composites are prepared using polymers as matrix material because of ease of production with different reinforcements. The mechanical strength of the natural fiber reinforced polymer composites has been compared with synthetic fiber reinforced polymer composites and it is found that for achieving equivalent mechanical strength of the material, the volume fraction of the natural fiber should be much higher than synthetic fiber. This work being an experimental study on untreated “as received” fique fabric-reinforced epoxy composites, to demonstrate the potential of this renewable source of natural fiber for use in a number of applications.

The influence of citric acid in the properties of high strength Portland cement pastes and mortars, both in fresh and hardened condition, was evaluated. The content of citric acid varied from 0 to 0.8 wt%. Tests were carried out in cement pastes to determine the water required for normal consistency and initial and final setting times. Mortars cements were tested to define bulk density, consistency index, air content in the fresh condition and compressive strength after 7, 14, and 28 days. Analysis by XRD was also performed. The results showed that the use of citric acid as a retardant additive is a viable procedure, because it increased the mechanical strength after 14 days and improved the mortar workability.

The development of high entropy alloys led to a great scientific interest owing to the fact that these alloys are responsible for presenting previously unexplored possibilities. Not only the breakdown of the classical paradigm of metal alloying development, but also the infinite possibilities on compositions and the unique properties exhibited, attracted the attention of a number of researchers since the "discovery" of high entropy alloys in 2004. Recently, it was suggested that some of these alloys could be suitable for ballistic application. This works aims to study the behavior of a CoCrFeMnNi high entropy alloy against a 271 m/s lean projectile. It is shown for the first time that high entropy alloys might provide a substantial protection against this ammunition threat. Furthermore, the results suggested that this specific alloy could be strengthen by shock-wave propagation and that the main ballistic energy absorption mechanism was the spalling of surfaces.

The incorporation of industrial waste in cementitious materials is an alternative for its adequate disposal. Among the residues that do not yet have adequate disposal are the residues created by the ornamental rock industries. In this context, this work aims to identify and characterize clays of the region where the ornamental rock industry is dominant and to verify the performance of the ceramic masses with the incorporation of the marble and granite residue. Physical and chemical characterization tests were performed on both clay and residues. After the identification of the two best clays, ceramic masses were prepared where it was possible to evaluate the performance of the clays with each of the residues in incorporations up to 20 wt.%. The results indicated that CI-A with 15 wt.% marble incorporation obtained the best performance.

The arapaima is a large Amazonian freshwater fish and an example of a natural protective system against predators such as the piranha fish. In this work, both the plain scales and a 30 vol% of arapaima scales reinforced epoxy composite were characterized for their structure, composition and morphology. The characterization was performed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). The SEM images showed that the surface morphology of the scales was not altered by the flattening process applied before composite manufacturing. The EDS results confirm that the percentage of calcium is higher in the scale outer layer, which also shows the presence of phosphorous. The evidence of collagens in the plain scales as well as the presence of hydroxyl groups and absorption bands related to the epoxy group in the composites were revealed by FTIR. Mechanical bend tests disclosed the toughening contribution of arapaima scales to the composite epoxy matrix. Nanoindentation testing confirms the higher hardness of the scale outer layer associated with calcium participation. These experimental results provide, for the first time, an initial view of the arapaima scales potential for use as reinforcement in novel polymer composites.

Natural lignocellulosic fibers have been studied as cost-effective reinforcements in composites for engineering applications that, in some cases, may require exposure to temperatures above ambient. In the present work a promising fiber extracted from a Brazilian palm tree, the piassava fiber both neat as well as graphene oxide (GO) functionalized, had their thermal behavior analyzed jointly with corresponding epoxy composites. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were for the first time employed to assess the thermal properties of the GO-coated piassava fiber. Dynamic mechanical analysis (DMA) investigated innovative epoxy matrix composites reinforced up to 30 vol% of both neat and GO-coated piassava fiber. TGA/DTG results indicate a limit of thermal stability of about 200 °C for the neat piassava fiber. On the other hand, the hemicellulose and lignin maximum degradation rates occurred at relatively higher temperatures for the GO-coated piassava fibers. The DSC analysis revealed an endothermic peak at about 125 °C for the neat piassava fiber associated with the breakage of molecular bond, which was not found for the GO-coated fibers within the maximum interval of temperature analyzed. The DMA parameters revealed notable changes attributed to the effect of GO coating on the piassava fibers regarding the viscous stiffness and damping capacity of the epoxy composite.

Natural fibers have, in past decades, been increasingly used as reinforcement of polymer matrix composites in substitution for synthetic fibers. This work presents a comparative study on the mechanical properties of both epoxy and polyester composites reinforced with promising hemp fiber. The comparison would allow which of these thermoset matrices is more adequate for novel biocomposites to be used in technological applications. Amounts of 10, 20 and 30 vol% of continuous and aligned hemp fibers were mixed with either epoxy or polyester inside steel molds kept under pressure and cured for 24 h at room temperature. Plain epoxy and polyester plates were also fabricated for control samples. Basic characterization by Fourier transform infrared spectroscopy was preliminarly performed. Mechanical properties were obtained in flexural and tensile tests according to ASTM standards. Results were statistically compared by ANOVA and Tukey tests. Fracture was analyzed by scanning electron microscopy. For higher amount, 30 vol% of reinforcing hemp fiber, the epoxy composites disclosed superior strength than those of polyester composites. Indeed, for epoxy composites the flexural and tensile strength, 76.7 and 50.5 MPa, respectively, are higher than corresponding 49.1 and 25.4 MPa, respectively, for polyester composites. As for the elastic modulus, the flexural of 30 vol% hemp fiber/epoxy composites, 3.8 GPa, was superior to 30 vol% hemp fiber/polyester, with 1.2 GPa. These results indicate a potential application of hemp fiber/epoxy composites as part of multilayered armor systems for personal ballistic protection. Keywords: Hemp fiber, Epoxy composite, Polyester composite, Mechanical properties

In the aluminum industry, the initial operation comprises the production of its oxide, Al2O3 (alumina) from ores, mainly the bauxite. The Bayer process is, in practice, the only used to produce alumina generating a huge amount of hazardous waste known as red mud. Among the proposed alternatives to consider red mud a useful by-product, the incorporation into clay ceramics allows large quantities to be reutilized as construction products. Several research works investigated this alternative but were limited to single clay incorporation without specific application in building construction products. In the present work the possibility of producing bricks and roofing tiles for building construction with plain red mud and incorporations separately, in two different clays, with low and high plasticity, was for the first time investigated. Both red mud and clays were characterized. Corresponding ceramics fired at 850, 950 and 1050°C were evaluated for their technological properties. The results indicated that plain red mud fired at any of these temperatures might be used as bricks according to the Brazilian standards. It could also be used for roofing tiles production when fired at 1050°C. Application in bricks for building construction and a preliminary environmental assessment were for the first time presented. Keywords: Red mud ceramic, Plain ceramic, Clay incorporated ceramic, Bricks and tiles

Engineering applications involving polymer composites reinforced with natural lignocellulosic fibers (NLFs) have greatly increased in recent decades due to advantages associated not only with favorable composite properties but also fiber sustainability and cost-effectiveness. A search for less common NLFs is currently an endeavor for the development of novel composites with improved properties. In particular, for applications above room temperature, the thermal resistance must be characterize. In the present work composites reinforced with up to 30 vol% fabric made of buriti, a relatively unknown natural fiber from Brazil, with limited reported information, were characterized by thermogravimetric/derivative (TG/DTG) and dynamic mechanical analysis (DMA). Preliminarily, the plain buriti fiber was investigated in terms of X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR) and TG/DTG analysis. XRD pattern allowed, for the first time, the evaluation of a microfibril angle of 7° and crystallinity index of 63%. FTIR bands for buriti fibers were also obtained with expected results. TG/DTG results indicate for the buriti fiber a limit degradation temperature around 200 °C and for the buriti fabric epoxy composites at about 250 °C. Dynamic mechanical analysis of composites disclosed similar viscoelastic stiffness values but an increasing glass transition temperature with the amount of buriti fabric. Keywords: Buriti fabric, Epoxy composites, Natural fiber composites, Thermal analysis, Structural characterization

The aim of this work is to characterize properties and microstructure of AISI 316L stainless steel used as a coating on welding of carbon steel sheets. Two carbon steel plates were set as the metal base and the stainless steel coating was applied on the weld bead. The applied process used was the submerged arc welding (SAW) and tests were carried out for the tensile strength and Vickers hardness, in addition to observation of the microstructure by optical microscopy. The results indicated that the stainless-steel coating applied on the weld bead provided relatively high values of tensile strength. Moreover, the hardness values suggest that the investigated innovative material can be applied in corrosive environments. Keywords: Carbon steel, Stainless steel, Coating, Welding

Reinforcement of polymer matrices with natural lignocellulosic fibers (NLFs) is today presenting great potential for the reduction of both product weight and cost in many industrial sectors as well as the advantage of being renewable and eco-friendly materials. For some industrial applications, especially in ballistic armor, the materials are expected to meet technical and mechanical requirements in terms of impact behavior, which motivate the present work. This work conducted a notch toughness assessment by Izod and Charpy impact tests of epoxy matrix composites reinforced with different volume fractions of fique fabric, up to 50 vol%. Statistical analyses indicated significant differences between composites with distinct amount of fique fabric. Failure mechanisms were analyzed by scanning electron microscopy (SEM). The results revealed that composite reinforced with 40 vol% of fique fabric presented the best notch toughness performance. Composites with 15 and 30 vol% of fique fabric display predominantly brittle fracture associated with lower impact energies. With higher amount, 50 vol%, of fique fabric reinforcement both Izod and Charpy impact energy suffered a small decrease according to the Roger and Plumtree model. Keywords: Fique fabric, Impact tests, Epoxy matrix, Natural fiber composite

A spent tire without the legal possibility of running is classified as unserviceable tire waste. In this work, incorporation of rubber tire waste (RTW) in clay ceramics used in the production of bricks and roofing tiles was for the first time evaluated. The raw materials were initially characterized in terms of its mineralogical and chemical composition by X-ray diffraction (XRD) and X-ray fluorescence (XRF), respectively. Physical and mechanical properties of RTW incorporated ceramics such as bulk density, water absorption, linear shrinkage, flexural and compressive strength were determined. Besides, thermal analyses by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were carried out in the plain RTW. Different ceramic compositions were prepared with amounts of 0.5; 1; 1.5 and 2 wt% RTW incorporated into the clay ceramic. Prismatic specimens were prepared by uniaxial pressing and then sintered at 850 and 950 °C. The results indicate that the investigated waste contributes to a saving in energy during the ceramic sintering due to its high amount of carbon. An increase in the ceramic porosity above 1.5 wt% of RTW was responsible for increasing the water absorption. Within standard deviations, both the shrinkage and strength were not impaired. The clay ceramic with 1 wt% of RTW sintered at 950 °C was the most suitable condition observed. Hence, these results showed a viable alternative to RTW, turning it into an environmentally friendly by-product for civil construction materials. Keywords: Tire waste, Waste incorporation, Clay ceramic, Physical properties

The ballistic performance of multilayered armor system (MAS) with front ceramic tile, followed by a laminate of up to 50 vol.% of fique fabric-reinforced epoxy matrix and back by a 5062H34 aluminum alloy was evaluated. The backface signature (BFS) caused by the bullet in a block of clay witness behind the target was used to evaluate the MAS ballistic performance according to international standards. The results using high-velocity 7.62 mm ammunition show a BFS similar to a MAS second layers of Kevlar™ laminate with the same thickness. The Weibull analysis statistically provides the reliability of BFS test results. Fracture examinations by scanning electron microscopy (SEM) revealed that the epoxy-fique fabric composite has different types of energy dissipation mechanisms. These are the same capture of ceramic fragments by a mechanic of incrustation presented in Kevlar™ laminate. Among the tested materials, the 40 vol.% fabric composite was found to be a better alternative to replace Kevlar™. The lower cost of the epoxy-fique fabric composite is an additional advantage that favors its substitution for the aramid fabric. Keywords: Fique fiber, Natural fiber composite, Weibull analysis, Ballistic performance

Dynamic mechanical analysis (DMA) is one of the most common methods employed to study a material’s viscoelastic properties. The effect of thermal aging on plain epoxy and a fique fabric-reinforced epoxy composite was investigated by comparing the mass loss, morphologies, and DMA properties of aged and unaged samples. In fact, thermal aging presents a big challenge for the high-temperature applications of natural fiber composites. In this work, both plain epoxy and fique fabric-reinforced epoxy composite were found to have different molecular mobility. This leads to distinct transition regions, with different changes in intensity caused by external loadings from time-aging. Three exponentially modified Gauss distribution functions (EMGs) were applied to loss factor curves of fique fabric-reinforced epoxy composite and plain epoxy, which allowed identifying three possible mobility ranges. From these results it was proposed that the thermal degradation behavior of natural fibers, especially fique fiber and their composites, might be assessed, based on their structural characteristics and mechanical properties.

Polymer composites reinforced with natural fabric have recently been investigated as possible ballistic armor for personal protection against different levels of ammunition. In particular, fabric made of fique fibers, which is extracted from the leaves of the Furcraea andina, was applied as reinforcement for polymer composites used in a multilayered armor system (MAS). The superior performance of the fique fabric composites as a second MAS layer motivated this brief report on the determination of the absorbed energy and capability to limit velocity in the stand-alone ballistic tests. The single plates of epoxy composites, which were reinforced with up to 50 vol% of fique fabric, were ballistic tested as targets against 7.62 mm high-speed, ~840 m/s, impact ammunition for the first time. The results were statistically analyzed by the Weibull method and ANOVA. The absorbed energies of the 200–219 J and limit velocities of 202–211 m/s were found statistically similar to the epoxy composites reinforced with the fique fabric from 15 to 50 vol%. Predominantly, these findings are better than those reported for the plain epoxy and aramid fabric (KevlarTM) used as stand-alone plates with the same thickness. Macrocracks in the 15 and 30 vol% fique fabric composites compromise their application as armor plates. The delamination rupture mechanism was revealed by scanning electron microscopy. By contrast, the integrity was maintained in the 40 and 50 vol% composites, ensuring superior ballistic protection compared to the use of KevlarTM.

Since the mid-2000s, several studies were carried out regarding the development of ballistic resistant materials based on polymeric matrix composites reinforced with natural lignocellulosic fibers (NLFs). The results reported so far are promising and are often comparable to commonly used materials such as KevlarTM, especially when used as an intermediate layer in a multilayer armor system (MAS). However, the most suitable configuration for these polymer composites reinforced with NLFs when subjected to high strain rates still lacks investigation. This work aimed to evaluate four possible arrangements for epoxy matrix composite reinforced with a stiff Brazilian NLF, piassava fiber, regarding energy absorption, and ballistic efficiency. Performance was evaluated against the ballistic impact of high-energy 7.62 mm ammunition. Obtained results were statistically validated by means of analysis of variance (ANOVA) and Tukey’s honest test. Furthermore, the micromechanics associated with the failure of these composites were determined. Energy absorption of the same magnitude as KevlarTM and indentation depth below the limit predicted by NIJ standard were obtained for all conditions.

The titica vine fiber (TVF) (Heteropsis flexuosa) is a natural lignocellulose fiber (NLF) from the Amazon rainforest that was, for the first time, investigated in terms of its basic properties such as dimensions, porosity, and density as well as its chemical composition, moisture content, crystallinity, and microfibrillar angle. In this study, the apparent density of TVF was determined as one of the lowest-ever reported for NLFs). Using both the geometric method and Archimedes’ principle, density values in the range of 0.5–0.6 g/cm3 were obtained. The moisture content was measured as around 11%, which is in accordance with the commonly reported values for NLFs. The TVF exhibited a high porosity, approximately 70%, which was confirmed by SEM images, where a highly porous morphological structure associated with the presence of many voids and lumens was observed. The crystallinity index and microfibrillar angle were determined as 78% and 7.95°, respectively, which are of interest for a stiff NLF. A preliminary assessment on the mechanical properties of the TVFs revealed a tensile strength, Young’s modulus, and elongation of 26 MPa, 1 GPa, and 7.4%, respectively. Furthermore, the fiber presented a critical length of 7.62 mm in epoxy matrix and an interfacial shear strength of 0.97 MPa. These results suggest the TVFs might favors applications where lighter materials with intermediate properties are required.

Buriti Fibers extracted from the leafstalk of palm tree, Mauritia flexuosa, native to the Amazon region, have been investigated as a reinforcement of polymer matrix composites. Recently, the fabric made from buriti fibers was also studied as a possible reinforcement of epoxy composites. In particular, the preliminary results of a 10 vol% buriti fabric epoxy composite in a multilayered armor system (MAS) displayed a satisfactory backface signature (BFS) but the composite target was not able to preserve its integrity after the ballistic impact. This motivated the present work, in which we carry out a complete statistical investigation of the ballistic performance of 10, 20, and 30 vol% buriti fabric epoxy composites as a MAS second layer against 7.62 mm rifle ammunition. BFS, associated with the depth of penetration in a clay witness simulating a human body, disclosed values of 18.9 to 25 mm, statistically similar and well below the lethal value of 44 mm specified by the international standard. Absorbed energy in stand-alone ballistic tests of 163–190 J for armor perforation were also found to be statistically higher than 58 ± 29 J obtained for the conventionally applied synthetic aramid fabric. The 30 vol% buriti fabric composites maintained the integrity of the MAS second layer, as required for use in body armor. Failure mechanisms found for the 10 vol% and 20 vol% buriti fabric composites by macro analysis and scanning electron microscopy confirmed the importance of a higher amount such as 30 vol% in order to achieve effective ballistic protection.

Multilayered armor systems (MAS) with a front ceramic layer backed by a relatively unknown Amazonian guaruman fiber-reinforced (Ischnosiphon koem) epoxy composites, as second layer, were for the first time ballistic tested against the threat of 7.62 mm rifle ammunition. The amount of 30 vol% guaruman fibers was investigated in three distinct configurations: (i) continuous aligned, (ii) 0–90° cross-laid, and (iii) short-cut randomly dispersed. Additionally, single-target ballistic tests were also carried out in the best MAS-performed composite with cross-laid guaruman fibers against .22 caliber ammunition. The results disclosed that all composites as MAS second layer attended the US NIJ standard with corresponding penetration depth of (i) 32.9, (ii) 27.5, and (iii) 29.6 mm smaller than the lethal limit of 44 mm in a clay witness simulating a personal body. However, the continuous aligned guaruman fiber composite lost structural integrity by delamination after the 7.62 projectile impact. By contrast, the composite with cross-laid guaruman fibers kept its integrity for subsequent shootings as recommended by the standard. The single-target tests indicated a relatively higher limit velocity for .22 caliber projectile perforation, 255 m/s, and absorbed energy of 106 J for the cross-laid guaruman fibers, which are superior to corresponding results for other less known natural fiber epoxy composites.

Natural fiber-reinforced polymer (NFRP) composites have obtained significance in recent times due to their wide application in different industries, such as automotive, aerospace, construction, home appliances, and ballistic vest because of the high cost of synthetic fibers and environmental issue. These natural fibers are cheaper and lighter but their mechanical properties are lower than the synthetic fibers. In addition, great efforts have been made to understand the phenomenon of weathering of polymeric materials, which ultimately result in the deterioration of the physical and mechanical properties of the polymer. This work aims to present some research in the degradation area of natural fibers and their composites. The components of NFRP and flexural strength and modulus are revealed in the first part. Afterwards, the second part will be devoted to review some methods of aging treatments applied to natural fiber composites. Eventually, a discussion about the optimal approaches for lifetime prediction of NFRPs will be drawn.

The objective of this work was to evaluate the influence of photodegradation by ultraviolet radiation in composites of epoxy matrix reinforced with sisal fabric in the energy absorption capacity against shots of 0.22-gauge lead projectile. The ballistic tests were performed at subsonic speed using a 150-bar compressed air draft system. The ballistic efficiency was evaluated using the residual velocity technique. Fourier transform infrared spectroscopy (FTIR) was also performed to observe changes after radiation exposure. Exposure to UV radiation, both at 75–225 h, caused changes in the color of the composite plates, in addition to optimizing the energy absorption capacity in level I events by NIJ 0101.04, absorbing about 93% of the projectile energy, showing to be a very easy and fast technique for improving the ballistic properties of composites which in turn are more economically viable than the commonly used synthetic materials.

The replacement of synthetic fibers to natural fibers has been the subject of intense research, particularly as applied in composites. Astrocaryum vulgare is an important palm tree employed for many people along the Amazonian region in handcrafts and other products, by traditional manipulation techniques. The aim of this work is to perform a density Weibull analysis of Astrocaryum vulgare (Tucum) fibers with different diameters. The results obtained may be a database of Astrocaryum vulgare fibers, helping future research that will address its application potential as an alternative fiber applied in polymer composites.

Since the twenty-first century began, environmental concerns related to energetic consumption and pollution have been gaining attention. In part, these could be associated with production and disregard synthetic materials. Using natural materials instead of synthetic aimed to become a trend, which has not happened. Natural lignocellulosic fibers (NLFs) were showed to be capable of replacing synthetic fibers in polymer composites. However, some limitations such as damage from heat can be considered a major constraint for wider application of NLFs/polymer composites. A novel strategy that is suggested to improve this property is the graphene oxide (GO) functionalization of NLFs. This work investigates the thermal behavior of epoxy/NLF composites, with and without GO functionalization. Two different amounts of reinforcement, low (20 vol%) and high (40 vol%), were dynamic mechanically investigated up to 160 °C. Investigated parameters revealed notable changes attributed to GO-functionalization effect on the NLF regarding viscous stiffness and damping capacity of the composite.

In recent decades, the unique characteristics of natural fibers have promoted their use as reinforcement in polymeric composites. This is verified in several industrial sectors, from packaging to automotive and civil construction. Among the natural fibers, the raffia fiber extracted from the palm tree Raphia vinifera and introduced in the Amazon region a long time ago, started to be considered for the production of polymeric composites only in recent years. For the first time, the effect of raffia fiber length and its alkali treatment on the mechanical properties of a polymer composite was disclosed. Tensile tests were performed in composites with raffia fibers randomly dispersed into terephthalate-based unsaturated polyester resin. The results showed an increase in the Young&rsquo, s moduli, confirmed by ANOVA, for the composite with both untreated and alkali-treated fibers in comparison to the plain polyester, which characterizes a stiffening effect. The composites with alkali treated fibers exhibited similar tensile strength values for all lengths, however, their strengths are lower than those for the untreated condition due to a weak raffia fiber/polyester matrix adhesion. Therefore, this work fills the current knowledge gap on raffia fiber incorporation in polyester matrix and valorizes this abundant Brazilian resource, providing additional information towards the use of raffia fiber in polymer composites.

Natural-fiber-reinforced polymer composites have recently drawn attention as new materials for ballistic armor due to sustainability benefits and lower cost as compared to conventional synthetic fibers, such as aramid and ultra-high-molecular-weight polyethylene (UHMWPE). In the present work, a comparison was carried out between the ballistic performance of UHMWPE composite, commercially known as Dyneema, and epoxy composite reinforced with 30 vol % natural fibers extracted from pineapple leaves (PALF) in a hard armor system. This hard armor system aims to provide additional protection to conventional level IIIA ballistic armor vests, made with Kevlar, by introducing the PALF composite plate, effectively changing the ballistic armor into level III. This level of protection allows the ballistic armor to be safely subjected to higher impact projectiles, such as 7.62 mm caliber rifle ammunition. The results indicate that a hard armor with a ceramic front followed by the PALF/epoxy composite meets the National Institute of Justice (NIJ) international standard for level III protection and performs comparably to that of the Dyneema plate, commonly used in armor vests.

A novel class of graphene-based materials incorporated into natural lignocellulosic fiber (NLF) polymer composites is surging since 2011. The present overview is the first attempt to compile achievements regarding this novel class of composites both in terms of technical and scientific researches as well as development of innovative products. A brief description of the graphene nature and its recent isolation from graphite is initially presented together with the processing of its main derivatives. In particular, graphene-based materials, such as nanographene (NG), exfoliated graphene/graphite nanoplatelet (GNP), graphene oxide (GO) and reduced graphene oxide (rGO), as well as other carbon-based nanomaterials, such as carbon nanotube (CNT), are effectively being incorporated into NLF composites. Their disclosed superior mechanical, thermal, electrical, and ballistic properties are discussed in specific publications. Interfacial shear strength of 575 MPa and tensile strength of 379 MPa were attained in 1 wt % GO-jute fiber and 0.75 wt % jute fiber, respectively, epoxy composites. Moreover, a Young’s modulus of 44.4 GPa was reported for 0.75 wt % GO-jute fiber composite. An important point of interest concerning this incorporation is the fact that the amphiphilic character of graphene allows a better way to enhance the interfacial adhesion between hydrophilic NLF and hydrophobic polymer matrix. As indicated in this overview, two basic incorporation strategies have so far been adopted. In the first, NG, GNP, GO, rGO and CNT are used as hybrid filler together with NLF to reinforce polymer composites. The second one starts with GO or rGO as a coating to functionalize molecular bonding with NLF, which is then added into a polymeric matrix. Both strategies are contributing to develop innovative products for energy storage, drug release, biosensor, functional electronic clothes, medical implants, and armor for ballistic protection. As such, this first overview intends to provide a critical assessment of a surging class of composite materials and unveil successful development associated with graphene incorporated NLF polymer composites.

This paper aims to present a comparison on the use of different heat treatment conditions in association with welding of a HSLA-80 steel. This investigation was carried out by multipass welding using the coated electrode process in different heat treatment conditions, with or without pre- or post-weld heating, in order to compare effects on the mechanical properties and microstructure for each condition. After welding was performed, procedures to identify microstructural phases and characterize the mechanical behavior were carried out. The results of mechanical tests and metallographic analysis were conclusive that heat treatments are not necessary to complement welding procedures of this steel. This is especially the case of the post-welding heat treatment. In fact, the application of these treatments did not significantly affect neither the microstructure nor the mechanical characteristics of the material. Keywords: Mechanical properties, Heat treatment, Microstructure, Mechanical testing

Ceramic armors are frequently used for protection against high energy projectiles, such as the 7.62 mm and 5.56 mm. Recently, it has been demonstrated that a modification in the geometry of the impact face, from flat to convex, enlarges the stress distribution zone created by the projectile-target interaction. This effect raises the projectile's energy absorption and might improve the user's safety. In the present work, the objective is to characterize ceramic armor plates with convex impact face, by means of the NIJ-0101.06 (2008) standard methodology, aiming to provide an eventual application in armor vests. The characterization is based on the measurement of the backface signature, a deformation behind armor imprinted in a reference material that simulates the consistency of the human body. The results showed significant improvement in the ballistic performance after the impact geometry modification. Keywords: Ballistic test, Ceramic armor, Multilayered armor system, Impact geometry

Cements from alkali-activated reactions are unleashing opportunities for the future application of inorganic polymers, known as geopolymers. These materials are eco-friendly, since their manufacturing process does not involve carbon dioxide (CO2) emission and it makes possible the use of industrial waste as raw material. In this work, a geopolymeric cement concrete (GCC) was developed through adequate portions of geopolymer components. Its characteristics were compared with Portland cement concrete (PCC), through the establishment of some parameters of design such as consumption of binders, water/aggregates ratio and cement content. The mechanical performance of these concretes was evaluated with emphasis on the fatigue behavior. The results showed a better fatigue performance of CCG in comparison with PCC in several parameters. Better matrix/aggregate adhesion in the CCG in comparison with PCC was also observed in the microstructural analysis, which may explain its superior fatigue performance. Keywords: Geopolymer, Concrete, Fatigue

The several advantages of natural lignocellulosic fibers (NLFs), such as, economical, technical, environmental and social, make these fibers an alternative to replace synthetic fibers in composite materials. The application of NLF as reinforcements in polymeric composites has increased in many industrial sectors from civil construction to automobiles. This demands the characterization of promising fibers, such as those extracted from leaves of pineapple (PALF) and the mesocarp of coconut fruit (coir fiber), for possible application in composites. In the present work, pullout tests were performed to compare the interfacial adhesion with epoxy resin of these two fibers that have greatly different characteristics. Results showed a critical length 70% higher for the coir fiber in comparison to PALF and a interfacial strength 3.5 times smaller, which indicates stronger adhesion of PALF with epoxy resin. This may be justified by the distinct morphological aspects, particularly the rougher surface of PALF. Mechanical tests were also performed in both coir fiber and PALF composites. In these tests, it was observed the superiority of mechanical properties for the composite reinforced with 30 vol% of PALF. Additionally, ballistic tests were carried out. In this evaluation, composites were used in a MAS type III against the 7.62 mm ammunition. The results revealed a relatively low depth of penetration (18.2 mm) for the MAS with PALF composite as well as a depth of penetration (31.6 mm) for MAS with coir composite, both considered efficient according to the personal body armor standard. Therefore, all these results highlight the potential of these fibers as polymer composites reinforcement in ballistic armors. Keywords: Pullout test, Natural lignocellulosic fibers, Critical length, Interface adhesion