Search

Due to their ability to manufacture highly complex geometries, additive manufacturing technologies have applications in several industrial sectors, such as aerospace, automotive, biomedical and electronics. However, parts made of pure polymeric materials may have limitations in their applications because of the shortcomings in their mechanical properties. Thus, polymer matrix composite materials are used as an alternative to obtaining better technical characteristics, especially for parts obtained by additive manufacturing. In this work, the influence of reinforcement and printing orientation on the mechanical behavior of samples manufactured using filaments of PLA/20 wt% Al (Aluminum microparticles) and PLA/20 wt% CF (carbon fiber reinforcement) were studied. The samples were manufactured using fused deposition modelling (FDM) technology. Tests were carried out to analyze the mechanical behavior of the studied materials, such as tensile, compression, and bending. The results obtained from the mechanical tests of the reinforced filaments were compared with the results on the mechanical performance of pure PLA. The results showed the influence of the type of reinforcement, namely short fibers or microparticles, is evident. The tensile strength, compressive strength, and flexural strength were primarily influenced by the type of reinforcement and Young's modulus was predominantly influenced by the printing angle and type of reinforcement. The fracture mechanism of composite specimens was infill gaps and interface. [ABSTRACT FROM AUTHOR]

Polysaccharides have been widely used for the development of drug delivery systems. These systems can be physicochemically modified to enhance their stabilities and control their drug release profiles. However, such modifications cannot alter their biocompatibility or toxicity. Herein, four structurally modified sodium alginate/carboxymethylcellulose blends are synthesized and loaded with prednisone, and the effects of the modifications on their hydrolytic degradation rates, biocompatibilities, toxicities, and drug release profiles are investigated. All the blends are ionically cross‐linked with Ca2+ and Fe3+. Blend 1 is not modified further, blend 2 is additionally reinforced with 8% w/w of cellulose nanocrystals, blend 3 is treated with epoxidized linseed oil to develop a hydrophobic layer, and blend 4 is chemically cross‐linked with epichlorohydrin. Blends 2 and 4 exhibit similar physicochemical characteristics, appropriate hydrolytic degradation rates and drug release patterns, as well as biocompatibility and non‐toxicity. In‐vitro studies using the osteoblasts and CAM assay demonstrate that blends 2 and 4 are also biocompatible and non‐toxic. In contrast, blend 1 exhibits the highest drug release rate, followed by blend 3. [ABSTRACT FROM AUTHOR]

Copyright of DYNA - Ingeniería e Industria is the property of Publicaciones Dyna SL and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Cementitious composites reinforced with silica, silicon carbide or carbon microfibres are designed, manufactured, characterised and tested as porous restrictor for aerostatic bearings. Carbon microfibres are residues obtained from the cutting process of carbon fibre-reinforced polymers. Porosity, permeability, flexural strength and stiffness are quite relevant in the design of aerostatic porous bearings. A 3141 full factorial design is carried out to identify the effects of particle inclusion and water-to-cement ratio(w/c) factors on the physical and mechanical properties of cementitious composites. Higher density material is achieved by adding silicon carbide. Higher porosity is obtained at 0.28 w/c level when silica and silicon carbide are used. Carbon microfibres are not effective under bending loads. Higher compressive strength is reached especially when silica particles are combined with 0.33 or 0.35 w/c. According to the permeability coefficient values the cementitious composites consisted of CMF (0.28 w/c), silica (0.30 w/c) or silicon carbide (0.30 w/c) inclusions are promising as porous restrictor; however, carbon microfibre porous bearings achieved the lowest air gap variation under the tested working conditions. [ABSTRACT FROM AUTHOR]

Over the last few decades, a significant amount of research has been focused on the use of natural fibres as reinforcement in polymers, due to their intrinsic properties such as sustainability, easy availability and processing, biodegradability and moderate mechanical strength. Among natural fibres, coir is a low-cost fibre extracted from coconut palm which is extensively produced in Brazil. A full factorial design was carried out to investigate the effects of the manufacturing and composition parameters on the mechanical and physical properties of short coir fibre-reinforced composites (SCoirFRCs). The random short fibres were mixed with epoxy polymer and compacted by uniaxial pressure. The physical and mechanical responses, namely, apparent density, impact resistance, flexural strength and modulus, were investigated under a design of experiment approach. SCoirFRCs fabricated with 35% of fibre volume fraction, 375 g/m2 of fibre grammage and HY956 epoxy hardener type achieved higher flexural modulus and impact resistance, while those consisting of 30 vol% of coir fibres, HY956 type and 300 g/m2 of grammage revealed higher flexural strength. The findings revealed that the mechanical properties of SCoirFRCs are substantially dominated by the properties of the matrix phase and fibre wettability. [ABSTRACT FROM AUTHOR]

In the vacuum thermoforming process, the group effects of the processing parameters, when related to the minimizing of the product deviations set, have conflicting and non-linear values which make their mathematical modelling complex and multi-objective. Therefore, this work developed models of prediction and optimization using artificial neural networks (ANN), having the processing parameters set as the networks' inputs and the deviations group as the outputs and, furthermore, an objective function of deviation minimization. For the ANN data, samples were produced in experimental tests of a product standard in polystyrene, through a fractional factorial design (2k-p). Preliminary computational studies were carried out with various ANN structures and configurations with the test data until reaching satisfactory models and, afterwards, multi-criteria optimization models were developed. The validation tests were developed with the models' predictions and solutions showed that the estimates for them have prediction errors within the limit of values found in the samples produced. Thus, it was demonstrated that, within certain limits, the ANN models are valid to model the vacuum thermoforming process using multiple parameters for the input and objective, by means of reduced data quantity. [ABSTRACT FROM AUTHOR]

The progress in establishing new classes of biocomposites has led to potential applications in the automotive, aerospace, and construction industries because of their life cycle properties, low cost, lightweight, non‐abrasive, and moderate mechanical strength. The heterogeneity of natural fibers plays an important role in the fiber–matrix adhesion, therefore affecting the mechanical performance and the durability of the composites. This work has described the manufacturing, characterization, and testing of hybrid composites reinforced with sisal fibers and silica nanoparticles. A full factorial design was performed to identify the effects of fiber treatment, fiber orientation and nanosilica inclusion factors on the physical and mechanical properties of hybrid composites. Composites made with unidirectional untreated fibres and silica nanoparticles (2 wt%) provided higher impact resistance. In contrast, the highest strength and stiffness values and the lowest overall porosity were achieved when unidirectional treated fibres with 2 wt% of silica inclusions were considered. POLYM. COMPOS., 39:146–156, 2018. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The present work had as objective the development of a specialist system for use as intelligent tutor, assisting in the training of technicians in refrigeration. We used techniques such as Ishikawa Diagram, Fault Tree Analysis (FTA) and Failure Modes Analysis and their Effects (FMEA) to investigate the main failure modes and corrective maintenance procedures. The heuristic knowledge was programmed into a specialist system using the CLIPS platform. The program interacts with the user providing the path for fault correction in the refrigerator. It was observed that the expert system is an excellent tool for storing heuristic information, and it can be used as a tool to support basic corrective maintenance tasks such as intelligent tutor, or evolve in increments, allowing a continuous improvement of the program. [ABSTRACT FROM AUTHOR]