Materials Science Forum Vol. 1012

Abstract: The objective of this paper is to study Fe65Nb-Cu metal matrices, thus varying the content of the pre-alloyed Fe65Nb powder from 10% to 100%. Therefore, powders of Fe65Nb and Cu were used, innovating in the chemical composition of the commonly used matrices. The objective is to evaluate the substitution of Co (toxic element, commonly used) by Nb (98.2% of reserves are Brazilian). For the sintering of the samples it was used hot pressing technique. The parameters were set at: 850°C / 35MPa / 3min. The sintered bodies underwent SEM/EDS analysis and density and porosity measurements were performed. From the results it is possible to say that the compositions of (10% and 30% Fe65Nb) presented the best physical and mechanical properties. The relative density decreases for the compositions with 40%, 50% and 60% Fe65Nb is justified by the presence of fragile particles in metal matrices, since they require more energy in order to efficiently transport matter (diffusion) in a solid state.

Abstract: The wave propagation in a two-dimensional bio-inspired phononic crystal (PC) is analysed. When composite materials and structures consist of two or more different materials periodically, there will be stop band characteristic, in which there are no mechanical propagating waves. These periodic structures are known as PCs. PCs have shown an excellent potential in many disciplines of science and technology in the last decade. They have generated lots of interests due to their ability to manipulate mechanical waves like sound waves and thermal properties which are not available in nature. The physical properties of PCs are not essentially determined by chemical elements and bonds in the materials, but rather on the internal specific structures. Structures of this type have the ability to inhibit the propagation of vibrational energy over certain ranges of frequencies forming band gaps. The main purpose of this study is to investigate the band structure and especially the location and width of band gaps. For this analysis, it is used the finite element method (FEM) and plane wave expansion (PWE). The results are shown in the form of band structure and wave modes. Band structures calculated by FEM and PWE present good agreement. We suggest that the bio-inspired PC considered should be feasible for elastic vibration control.

Abstract: 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.

Abstract: 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.

Abstract: The search for sustainable materials has been increasingly growing due to the world environmental impacts faced. With the improper disposal of PET packaging and the waste generated by steel making, such as slag, a composite of these materials was created in search of a sustainable product. The composite has as its matrix the polymer and its particles are geopolymeric of the steel slag. The polymer composites were manufactured with concentrations of 0%, 20%, 40% and 60% of geopolymer. The characterizations showed that they are composites with low moisture absorption and that the affinity between the matrix and the reinforcement is impaired as the amount of charge increases. It was possible to realize that composites are good materials for future studies for possible future applications, such as ballistic vests. Composites are great precursors for achieving product sustainability due to the feasibility of reusing waste and disposing of it improperly in the environment.

Abstract: Aiming the development of novel composites reinforced with natural fibers from vegetable origin, it is important the understanding and control of processing parameters in twin-screw extruders. The temperature profile and the screw components, as well as the extrusion speed, compromise the distribution and dispersion of the fibers in the matrix and consequently in their rheological behavior, which reflects in the mechanical, chemical and morphological properties of the composites and products obtained from them. One new tool, used to understand processing parameters in composites, is computer simulation. In this study, we used the WinTXS Software to evaluate the influence of process parameters in the polypropylene matrix composite reinforced with 30 vol% wood flour. Parameters such as shear rate, temperature, melt viscosity, and viscous dissipation were evaluated. It was observed that increasing screw speed, the temperature increased, which results from the viscous dissipation. Under these conditions, the shear rate and melt viscosity were reduced.

Abstract: The high consumption of green coconut water, especially in tropical countries like Brazil, generates an aggravating factor to the environment, which is associated with the waste generated after its consumption. Thus, one of the possible ways of reusing the coconut shell after consumption is through the extraction of its fibers, which are considered for several applications. In general, natural lignocellulosic fibers (NLFs) have been used for many purposes, such as reinforcement filler in composite materials, since they have low cost and good mechanical properties. With the intention of providing a better compatibility between the NLFs and the composite polymeric matrix, different types of surface treatments are carried out on the fibers, including mercerization, a chemical treatment in which a basic solution is used. In this sense, the present work aims to verify the influence of mercerization with 3% sodium hydroxide (NaOH) on coconut fiber. Among the analyses carried out, stands the scanning electron microscope (SEM) on fresh and treated coconut fibers. The SEM analyses, allowed to observe that after treatment via mercerization, the fibers displayed a greater surface roughness. This indicates the partial removal of lignin, hemicellulose and some other extracts present on the outer layer of the coconut fiber. Therefore, mercerization will probably enable a better mechanical anchoring between fiber and matrix. Results obtained suggest the effectiveness of the mercerization process. However, it was also of concern that such treatment tends to generate NaOH residues, which is a negative factor regarding sustainability.

Abstract: Polymeric fibers are used for reinforcement of composites in all kinds of applications, from sport and recreation products to military equipment. Since these fibers have high energy absorption on ballistic impact, the defense industry uses them to manufacture lightweight armor. In many cases, armors are exposed to degradation agents such as heat, humidity, and radiation. The macromolecular changes of polymer fibers exposed to degradation agents can affect the mechanical and ballistic properties of the composite. The present work studies the ballistic performance of aromatic polyamide (aramid) fabric-reinforced composite using two different matrices, degraded by gamma radiation. The results suggest that gamma radiation can change the penetration failure mechanism of the composite in a variety of ways depending on the matrix, compromising its performance.

Abstract: This work investigates the mechanical behavior of a PCLIGHT type of polycarbonate (PC). PC samples display interesting results after thermal degradation at different temperatures. Samples of PC in sheet form were exposed for a period of 5 hours at temperatures of 50, 100, 150 e 200°C. After, thermogravimetric test, flexural, impact and tensile tests were performed. The results show that the samples treated at 200oC have their mechanical performance affected. This indicates that the temperature acts on the PC embrittlement behavior. Thus, it can be inferred that temperatures above 150oC can negatively influence the mechanical behavior of the polycarbonate indicating that this material should not be used in association with high temperatures.