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This review systematically examines the use of additive manufacturing (AM), also known as 3D printing (3DP), in the various aspects of military applications such as firearms, armor and ballistic resistant structures, including those bioinspired. The main goal is to provide a comprehensive exploration of AM in armor and military applications. The materials and structures created using AM technologies are analyzed and reported. Dynamic loading, and impact via Charpy and Izod tests were also explored in the search, although not considered in the armor results to be tests typically conducted at low strain rates, far from a real ballistic solicitation. Recently, an increase in military applications has been found, particularly gun prototypes fabricated in diverse materials with AM. Although the innovation, low costs, and manufacturing are clear advantages of these devices via 3D printing, there are limitations, such as the worrying panorama of unclear regulations that prevent these weapons from eventually reaching ordinary citizens. Current perspectives, opportunities, and challenges are discussed.

This study focuses on the characterization and evaluation of a photoluminescent asphalt coating made from recycled expanded polystyrene (EPS) and strontium aluminate particles. The aim is to provide an alternative use for the significant volumes of EPS waste present in landfills worldwide. Two diluent mixtures, ethyl acetate and acetone, were used for the degradation of recycled EPS. The objective was to develop a coating that absorbs light emitted by cars at night, thereby enhancing road visibility, particularly in developing countries. The characterization of the coating involved various techniques including photoluminescence spectrophotometry (PL), color analysis, scanning electron microscopy (SEM), x-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), thermogravimetric tests (TGA), as well as tensile and shear tests. The findings indicate that the developed coating is not only technically feasible for solving nighttime lighting challenges but also offers a potential large-scale solution for managing EPS solid waste. The coating has the potential to be used in road demarcation, improving road safety, reducing energy consumption during nighttime, and enhancing the aesthetic appeal of roads by providing artificial lighting without the need for electricity consumption.

Poly(dicyclopentadiene) (poly-DCPD) is a thermoset with potential for high-performance applications. In this research, epoxy resin was blended with different concentrations of fly ash class F particles at 0.0, 1.0, 10.0, and 50.0 wt.%, aiming to improve its use as a high-volume structural material by decreasing costs and reducing its negative environmental impact through using fly ash particles. A planetary Thinky mixer was used to initially mix the resin with the curing agent, followed by incorporating a Grubbs catalyst. The microstructures were analyzed using scanning electron microscopy (SEM), where particles were found to be homogeneously distributed over the polymer matrix. The thermomechanical behavior was evaluated via curing, compression, dynamic mechanical analysis (DMA), and thermo-gravimetric analysis (TGA). Nanoindentation tests were also conducted. Fly ash was found to decelerate the curing of the resin through the release of calcium ions that enhanced the exothermic reaction.

Additive manufacturing has shown advantages for nanocomposite fabrication. Despite VAT-photopolymerization being one of the first developed 3D printing technologies, high device costs made it a technology that was difficult to access. The massive production of these devices in recent years has opened this technology to everyone. Stereolithography and Digital light processing are the most prominent technologies used in this field. This systematic review studied 217 articles regarding SLA and DLP for additive manufacture of nanocomposites. The main finding of this systematic review shows that further research on circular economy and life cycle assessment of the SLA and DLP technologies is urgently needed. Also, a deeper discussion on the technology and material costs is recommended in order to give a more detailed insight on the final cost of these 3D-printed nanocomposites.

The growth of consumer culture entails a series of harmful results for the different natural environments, one of these evils being the high rate of waste generation, an example, expanded polystyrene (EPS) today has become a major problem due to the high rates of generation of this type of waste. This study presents the results of EPS waste characterization, obtained by the degradation of EPS with solvent mixtures of acetone and ethyl acetate in different proportions, for possible use as an asphalt adhesive. For the characterization of these EPS waste mixtures, stress tests of the asphalt adhesive were carried out and they were complemented with tests of resistance to cutting, stickiness, rheology and thermogravimetric. The results obtained in this work show that the EPS waste obtained by dissolution with acetone and ethyl acetate solvent mixtures, present greater mechanical resistance, although these wastes have a higher apparent viscosity and a faster drying as it increases the acetone content present in the solvent. Tests showed that this material could be used as an asphalt coating film or adhesive binder.

This research is a comprehensive review of the sustainability of additive manufacturing, from the circular economy and recycling of materials to other environmental challenges involving the safety of materials and manufacturing. There has been important progress in this area, with an increasing number of papers that cover diverse environmental aspects, including the circular economy, recycling and the life cycle assessment of materials. This increase is due to the importance that scientists, industry, government and society are now giving to these topics. This review seeks to develop a greater awareness in relation to the possibilities and implications in the use of the AM, as well as to encourage sustainable development by raising awareness in relation to the taking of necessary actions to achieve compliance of the Sustainable Development Goals. Similarly, current trends are examined in relation to the practices that are currently being adopted in order to ensure that AM is consolidated as a sustainable and convenient practice in the economic, social and environmental spheres. In general, polymers, ceramics, metals and composite materials are now undergoing intensive research to improve their use. Although this research shows that significant progress has been made on several relevant issues, using materials optimization to minimize energy and waste is still far from a global solution.

This study examined an Organic Rankine Cycle powered by a parabolic trough collector and a two-tank thermal storage system based on the development of a mathematical model, for the conditions of the city of Itajubá in Brazil. First, geometrical optics and heat transfer models of the collector–receiver set were used to determine the thermal equilibrium of the solar thermal collector system and parameters such as the efficiency of the solar field, heat and optical losses, and thermal energy of the outlet fluid. Next, the thermal equilibrium of the Organic Rankine Cycle was found in order to establish its operational parameters. Finally, the behavior of the thermal storage system was analyzed through its modeling. Once the characterization of the storage system was completed, the integrated operation of the proposed system was evaluated. Given Itajubá’s weather conditions, the results indicate that an electricity generation system can be implemented with the Solel UVAC Cermet selective coating for the absorber tube, water as the heat transfer fluid, and R-245fa as the working fluid. Based on the solar irradiation profile (1 March 2019), the parabolic trough collectors provided 63.3% of the energy required by the Organic Rankine Cycle to generate 7.4 kW, while the thermal storage system provided 36.4% of the energy demanded by the power generation block. Additionally, the results demonstrate the main conclusions that the turbine’s efficiency was influenced by parameters such as rotational speed, which is affected by the turbine inlet temperature, which, in turn, depends on the behavior of the solar irradiation profile onsite.

The usability of Force Sensing Resistors (FSRs) has been thoroughly demonstrated in [...]

Force Sensing Resistors (FSRs) are manufactured by sandwiching a Conductive Polymer Composite (CPC) between metal electrodes. The piezoresistive property of FSRs has been exploited to perform stress and strain measurements, but the rheological property of polymers has undermined the repeatability of measurements causing creep in the electrical resistance of FSRs. With the aim of understanding the creep phenomenon, the drift response of thirty two specimens of FSRs was studied using a statistical approach. Similarly, a theoretical model for the creep response was developed by combining the Burger’s rheological model with the equations for the quantum tunneling conduction through thin insulating films. The proposed model and the experimental observations showed that the sourcing voltage has a strong influence on the creep response; this observation—and the corresponding model—is an important contribution that has not been previously accounted. The phenomenon of sensitivity degradation was also studied. It was found that sensitivity degradation is a voltage-related phenomenon that can be avoided by choosing an appropriate sourcing voltage in the driving circuit. The models and experimental observations from this study are key aspects to enhance the repeatability of measurements and the accuracy of FSRs.