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The aim of this study was to evaluate and compare the fracture resistance of temporary restorations made of polymethylmethacrylate (PMMA), graphene-modified PMMA (GRA), acetal resin (AR) and polysulfone (PS) obtained by a subtractive technique (milling) using a computer-aided design and manufacturing (CAD/CAM) system of a three-unit fixed dental prosthesis (FDP). Methods: Four groups of ten samples were fabricated for each material. Each specimen was characterized by a compression test on a universal testing machine, all specimens were loaded to fracture and the value in Newtons (N) was recorded by software connected to the testing machine. The fracture mode was evaluated on all samples using a stereomicroscope. Results: There were statistically significant differences (p value < 0.005) between PMMA and the other three materials (PMMA: 1302.71 N; GRA: 1990.02 N; RA: 1796.20 N; PS: 2234.97). PMMA presented a significantly lower value than the other materials, and PS showed the highest value. GRA and RA presented a similar range of values but they were still higher than those of PMMA. Conclusions: GRA, RA and PS are presented as valid options within the range of interim milled restorative materials and as alternatives to PMMA.

Corrosion phenomena are usually difficult to recognize without a deep knowledge of the electrochemical properties of materials, this creates difficulties in the analysis of corrosion in practice, control measures are developed through image processing to solve these problems. This article describes a methodology for the analysis of the inner surface of steam pipelines by means of digital image processing (DIP). A classification algorithm is presented that is able to detect four levels of corrosion on the inner surface of steam pipelines. Gray-level co-occurrence matrix GLCM, which analyzes all the attributes of each image texture was employed. The performance of the classification algorithm was evaluated by using a confusion matrix, which showed very reliable classification results by comparing with experimental tests.

In this article, an experimental investigation was conducted to study the effects of 3D printed structured fabrics on the tensile strength of two additive manufacturing technologies: (i) fused deposition modeling (FDM); and (ii) stereolithography (SLA). Three types of structured fabrics were designed in a linked fabric structure, which resembled the main characteristics of a conventional textile. Through computer-aided design (CAD), the textile structures were sketched, which, in a STL format, were transferred to 3D printing software, and consequently, they were printed. The specimens were subjected to tensile tests to analyse the behaviour of the linked structures under tensile loads. The results obtained indicated that the elements structured in a linked fabric pattern showed a statistically significant effect between the design of the 3D printed structured fabric and its tensile strength. Some important properties in textiles, fabric areal density, fineness (tex) and fabric flexibility were also analysed. This study opens an important field of research on the mechanical resistance of textile structures manufactured by 3D printing, oriented for applications in wearables that have a promising future in the fields of medicine, aerospace, sports, fashion, etc.

In this paper, the one-dimensional tensile behavior of Guadua angustifolia Kunth fibre/polypropylene (PP+GAKS) composites is modeled. The classical model of Kelly–Tyson and its Bowyer–Bader’s solution is not able to reproduce the entire stress–strain curve of the composite. An integral (In-Built) micromechanical model proposed by Isitman and Aykol, initially for synthetic fiber-reinforced composites, was applied to predict micromechanical parameters in short natural fiber composites. The proposed method integrates both the information of the experimental stress-strain curves and the morphology of the fiber bundles within the composite to estimate the interfacial shear strength (IFSS), fiber orientation efficiency factor ηFOD, fiber length efficiency factor ηFLD and critical fiber length lc. It was possible to reproduce the stress-strain curves of the PP+GAKS composite with low residual standard deviation. A methodology was applied using X-ray microtomography and digital image processing techniques for the precise extraction of the micromechanical parameters involved in the model. The results showed good agreement with the experimental data This research was funded by Universidad Politécnica Salesiana within the framework of the research project Resolution: N◦ 009-008-2021-11-11

En la presente investigación se determinaron las propiedades mecánicas atracción del material biocompuesto de polipropileno(PP)isotáctico reforzado conhaces defibras cortas de bambú orientadas al azar. Se prepararon muestras del material con diferentes contenidos de refuerzo (20, 30 y 40%), empleando como agente de acople el polipropileno con injertos de moléculas de anhídrido maleico (MAPP). Un grupo de estas muestras fueron sometidas a un tratamiento de envejecimiento térmico acelerado para evaluar el efecto de dicho tratamiento sobre las propiedades a tensióndel biocompuesto. Se realizaron ensayos de tracción a diferentes velocidades de deformación (10 y 50 mm/min) y se obtuvo un aumento de la resistencia a la tracción(de 29a 45 MPa)y del módulo de elasticidad(de 1 a 3GPa)del PP con el contenido de fibras. Para diferentes velocidades de estiramiento, se obtuvo una mejor resistencia a altas velocidades. El envejecimiento térmico durante 24 horas a 100ºC aumentó la resistencia del PP puro. Para los biocompuestos, se obtuvo una baja resistencia en las muestras envejecidas en mayor tiempo (98ºC, 10 días). A través de la microscopia electrónica de barrido se realizó unacaracterización microestructural que permitió explicar el mejoramiento de la resistencia del PP reforzado con fibras, y en algunos casos, la pérdida de resistencia debido al tratamiento térmico

El presente artículo analiza las propiedades tensiles de un material compuesto polimérico reforzado con fibras de carbono empleado en la fabricación del monoplaza para competición Fórmula SAE. Para ello se manufacturaron compuestos a partir de preimpregnados con diferentes orientaciones de fibra mediante un proceso de curado al vacío. Se evaluó el efecto de la orientación de las fibras sobre la resistencia y la rigidez de los compuestos formulados. Se instrumentaron las probetas de tracción con extensómetros biaxiales para obtener un registro real de la deformación y posterior determinación del módulo de Young. Los resultados experimentales fueron comparados con los resultados analíticos obtenidos a partir de la Teoría Clásica de Laminados mediante software especializado. Se desarrolló también un análisis microscópico de la región fracturada de las probetas para evaluar el efecto del proceso de manufactura. El conjunto de información generada a partir de los resultados experimentales y analíticos proporciona un entendimiento de la anisotropía de los materiales compuestos Epoxi-Carbono que permitirá tomar decisiones de diseño en futuros desarrollos dentro del proyecto Fórmula SAE.

The present work has been carried out in order to investigate the sliding wear performance of a Ni-Cr based alloy, containing boron, carbon, silicon and iron, deposited onto a SAE 1045 steel substrate. The coatings were thermally sprayed by means of a High Velocity Oxy-Fuel system and post heat-treated for one hour at 760°C in an argon atmosphere. The relative sliding performance was evaluated under unlubricated dry conditions at different applied normal loads and sliding velocities, in order to analyze the influence of these parameters on the wear response. Test results are discussed and interpreted on the basis of both microstructural evaluations and mechanical properties measurements. The surface morphology and topography of the wear scars have been studied through of a Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) techniques. The results have shown an improved wear resistance of the coated steel samples as compared to the uncoated ones.

The aim of this study was to determine the resistance to fracture of feldspathic restorations with lithium disilicate and crystallized with different ovens and programs. Methods: Sixty monolithic restorations (LD) (EMAX CAD™ LT, Ivoclar-Vivadent™) were designed with the same parameters and milled with a CAD/CAM system (CEREC SW 5.1, CEREC MCXL, Dentsply-Sirona™, Bensheim). Each restoration was randomly assigned by randomization software (RANDNUM) to one of the three groups: (a) (NF) Oven P310 (Ivoclar, Vivadent) normal crystallization program, (b) (FF) Ivoclar P310 oven (Ivoclar-Vivadent™) rapid crystallization program, or (c) (SF) SpeedFire oven (Dentsply-Sirona™). Results: There were statistically significant differences between the groups (ANOVA, p &lt, 0.05). The NF and FF groups showed the highest values of resistance to fracture, with statistically significant differences with the SF group. Conclusions: Using a furnace from the same dental company with predetermined programs from the material manufacturer, as well as using a predetermined program for rapid crystallization, has no effect on fracture resistance, and would save clinical time when performing ceramic restorations with lithium disilicate, while keeping their mechanical properties.

The aim of this study was to evaluate and compare the resistance to fracture of interim restorations obtained through additive techniques (3D impressions) and subtractive techniques (milling) using a computer-aided design and manufacture (CAD/CAM) system of a three-unit fixed dental prosthesis (FDP) to ascertain its clinical importance. (1) Materials and methods: In total, 40 samples were manufactured and divided into two groups (n = 20) using: (1) light-curing micro hybrid resin for temporary crowns and bridges (PriZma 3D Bio Prov, MarketechLabs, São Paulo, Brazil) for the rapid prototyping group (RP) and (2) a polymethylmethacrylate (PMMA) CAD/CAM disc (Vipiblock Trilux, VIPI, São Paulo, Brazil) for the computer-assisted milling (CC). The resistance to fracture was determined with a universal testing machine. (2) Results: The strength and the standard deviation for the computer-assisted milling group were higher (1663.57 ± 130.25 N) than the rapid prototyping (RP) group, which had lower values of (1437.74 ± 73.41 N). (3) Conclusions: The provisional restorations from the computer-assisted milling group showed a greater resistance to fracture than the provisional restorations obtained from the rapid prototyping group.

A polymeric natural fiber-reinforced composite is developed by extrusion and injection molding process. The shrinkage and warpage of high-density polyethylene reinforced with short natural fibers of Guadua angustifolia Kunth are analyzed by experimental measurements and computer simulations. Autodesk Moldflow® and Solid Works® are employed to simulate both volumetric shrinkage and warpage of injected parts at different configurations: 0 wt.%, 20 wt.%, 30 wt.% and 40 wt.% reinforcing on shrinkage and warpage behavior of polymer composite. Become evident the restrictive effect of reinforcing on the volumetric shrinkage and warpage of injected parts. The results indicate that volumetric shrinkage of natural composite is reduced up to 58% with fiber increasing, whereas the warpage shows a reduction form 79% to 86% with major fiber content. These results suggest that it is a highly beneficial use of natural fibers to improve the assembly properties of polymeric natural fiber-reinforced composites.

This research work presents an analysis of the injection molding process of a natural fiber-reinforced composite, from the characterization of its rheological properties by the technique of capillary rheometry. Two of the main parameters of injection molding were estimated: the injection pressure and the clamping force. The rheological coefficients obtained were used as inputs in analytical and finite element models, for the prediction of the injection parameters. The results were compared, and it was observed that there is good agreement between them. The percentage errors between the two estimation methods were less than 5% for injection pressure and less than 10% for the clamping force. Also, the behavior of the material using different natural reinforcing contents (compositions of 20%, 30% and 40% fiber with a coupling agent at 4% and 8%) and the effect of its rheological properties on both the injection pressure and clamping force were evaluated. The study is of particular interest given that from the rheological characterization, the experimental values were adjusted to the Cross-WLF viscosity model and the adjustment coefficients, which contain both the reinforcing and coupling agent effects, were fed into the two methods of estimation of the injection parameters. The methodology used and the results obtained allow the prediction of the main parameters of injection molding of new bio-based composites, facilitating their use on an industrial scale.

The research addresses an analysis of the level of contamination generated by the gases produced when applying low-pressure cold plasma in a cleaning process of metal sheets used in the manufacture of white goods. A mixture of argon and oxygen ionized gases at 50% was utilized to break down the lubricating oil molecules deposited on the surface of the sheet metal. A statistically significant number of samples were selected, with different volumes of oil on the surface, between 6 ml and 34 ml. The samples were later subjected to a plasma discharge with a time of 72 s, a gas pressure of 0.6 bar and 50% power to determine the correlation of the oil volume with the levels of gases generated by the discharge, maintaining the degree of surface cleanliness, as given by contact angle values between 67.5 and 79 degrees, constant. For the analysis of results a Pearson correlation was applied for each detected gas. An analysis was later conducted of the relationship between the degree of cleanliness of the metallic surface, as given by contact angles at 16, 36 and 53 degrees, with the levels of the gases generated by the plasma discharge, keeping the volume of the lubricating oil on the surface constant at 5 ml. For the analyses, statistical tests were carried out to find the correlation between the predictor variables and the dependent variable to establish a multivariate linear statistical model. The results allowed the behavior of the level of contamination to be determined, establishing that the volume of oil does not influence the level of the gases generated by the use of low-pressure cold plasma. The results obtained allow us to understand the relationship between the contact angle that represents the quality of surface cleaning of oil-impregnated sheet metal and the level of contamination generated in the process.

Given the growing request for reusing raw material in new manufactured products in the plastics industry, the present study analyzes the effect of the concentration of recycled materials and pigments on the rheological properties of the polymer blend. It was quantified and analyzed in a statistical way the significance of the effects that these components produce in the rheological properties, such as the melt flow index, the maximum torque and the degradation time on high density polyethylene (HDPE). Knowledge of such properties will optimize processing parameters by using polymer blends with recycled materials and pigments. A minimum effect of the components was evidenced on the melt flow index having the pigment content the greatest impact factor.

En este artículo se presenta la determinación de humedad, elementos solubles e insolubles en agua de la fibra de Carludovica palmata (paja toquilla). Para realizar estos ensayos se utilizan las normas ASTM E871-82, ASTM D1110-84 y ASTM D1107-96. Con la finalidad de determinar su uso pontencial como refuerzo en materiales compuestos y la influencia en la resistencia mecánica. El porcentaje de humedad de la fibra analizada corresponde al 5,33% de su peso. El porcentaje de elementos solubles e insolubles en agua es 0,1042% y 0,3589% respectivamente. This paper presents the determination of moisture and water solubles and insolubles of Carludovica Palmata (paja toquilla) fiber. To perform these tests using ASTM E871-82, ASTM D1110-84 and ASTM D1107-96 standars. In order to determine its use pontencial as reinforcement in composite materials and the influence on the mechanical strength. The moisture content of analyzed fiber corresponds to 5,33% by weight. The percentage of soluble and insoluble components in water is 0,1042% and 0,3589 %, respectively.

Esta revisión presenta los reportes de las investigaciones relacionadas con el desarrollo de nuevos materiales compuestos poliméricos reforzados con fibras naturales y desechos agroindustriales provenientes del Ecuador. Se analizan las fibras vegetales con potencial para ser empleadas como reforzante en compuestos poliméricos. Se sintetizan los resultados relevantes de las diferentes investigaciones analizadas. Aspectos como el tipo de matriz, la morfología de las fibras, los tratamientos superficiales y las propiedades mecánicas son presentados. This review presents the research reports related to the development of new polymeric composites reinforced with natural fibers and agro-industrial wastes from Ecuador. Vegetable fibers with potential are analyzed to be used as reinforcement in polymeric composites. It summarizes the relevant results from the different investigations analyzed. Aspects such as the type of matrix, the fiber morphology, surface treatment and mechanical properties are presented.

This research was carried out a comparative analysis of cleaning of sheet steel, for use in forming processes impregnated with a mixture of SAE 40 oil and diesel by means of low-pressure cold plasma. The plasma discharge was generated by radio frequency energy using two types of gases, argon and oxygen. Cleaning of the surface was evaluated by measuring the contact angle with deionized water, diiodo methane and ethylene glycol, for the calculus of the surface free energy by means of the Fowkes theories and Wu and gas chromatography. The results show that the plasma cleaning is more effective when using a previous cleaning, in this case the immersion in solvent (CH3-OH).

El ACS (Agua Caliente Sanitaria) de uso doméstico es una necesidad imperante debido a las condiciones de temperaturas bajas en la ciudad de Cuenca, para suplir esta necesidad actualmente se utilizan sistemas eléctricos y a base de GLP (Gas licuado de petróleo), los mismos que en su producción y uso emanan dióxido de carbono (CO2) el cual se constituye en el primer factor de contaminación.La energía solar utilizada a través de colectores solares de tubos de vacío para la obtención de ACS, es una tecnología que aporta significativamente a disminuir la utilización de combustibles fósiles; actualmente en el Ecuador se comercializa colectores de este tipo, que han sido copiados o importados de países europeos y norteamericanos, en donde las condiciones meteorológicas y de localización son diferentes a las que se tiene en Ecuador. En el presente estudio se caracteriza un colector solar de tubos de vacío, a través de la verificación de su eficiencia con los datos ambientales, y de localización medidos en el lugar de emplazamiento y se estructura un diseño con características que favorecen su implementación en la ciudad de Cuenca, es decir considerando su localización, datos meteoroló- gicos y condiciones tecnológicas que posibilitan la fabricación de los mismos en la industria local.