Abstract in English:ABSTRACT Acute wound dressings can be based on PVA hydrogels, which present many characteristics of an ideal dressing, e.g., fluid uptake, a moisturized environment, etc. The lack of antimicrobial properties leads to the addition of natural active agents. The present work aims to manufacture and compare PVA gels loaded with Barbatimão bark extract, Leucaena bark extract, Aloe vera, and Lavender essential oil. They were characterized by FTIR, swelling tests, SEM, actives release. There were interactions between PVA and the active agents. The addition of Leucaena and Barbatimão increased the PVA ability to swell, but the opposite was found for Aloe vera and Lavender essential oil. PVA-Lavender essential oil samples presented interconnected pores, while samples with essential oil or extracts presented high crystallinity. Lavender essential oil and Aloe vera presented the highest release. The Barbatimão and Leucaena samples’ release may be related to the samples’ swelling, but the initial release of Aloe vera and Lavender samples was diffusion controlled by swelling. Their long-term release was dose-dependent for Aloe vera, while it was a non-Fickian diffusion for Lavender essential oil related to the hydrogel’s relaxation step. There is a synergistic effect when Aloe vera and Lavender essential oil are loaded in PVA hydrogels.
Abstract in English:ABSTRACT Fused deposition modeling (FDM) has gained popularity recently due to its versatility and low cost. Considering that the quality of printed parts depends on many variables, a 3^3 factorial design of experiments was conducted, where three influential parameters in the process were studied: layer height (0.15, 0.2, and 0.25 mm), infill percentage (30%, 60%, and 90%), and shell count (2, 3, and 4), using polylactic acid as the material. Their effects on tensile strength, flexural strength, printing time, and interactions were measured. The maximum tensile and flexural stress obtained were 33.5 MPa and 87.3 MPa, respectively, at a 90% infill percentage. It was found that layer height does not significantly affect mechanical strength, while infill percentage has the most significant influence, followed by the number of shells. The latter two factors show a meaningful interaction. Furthermore, all the studied parameters have a significant impact on printing time.
Abstract in English:ABSTRACT Economic development based on cleaner industrial technologies has been increasingly studied in recent years. Cementitious composites reinforced with lignocellulosic fibers can be a sustainable alternative for use in engineering. The study aimed to evaluate the technological properties of cementitious composites produced from natural and industrial coconut fiber to compare the reinforcement with wood particles. Physical tests (density, water absorption, and thickness swelling) and mechanical tests (static bending) were carried out in four treatments, which varied the fiber and cement contents. It was found that treatment with natural coconut fiber had the lowest density value, 0.59 g/cm3, and treatment with industrial coconut fiber had the lowest water absorption value for the times and times of 2 and 24 h, 0.19, and 0.38%, respectively, and the treatment with wood particles, the highest values of modulus of elasticity and rupture, 1,897 MPa and 2.44 MPa. The study of the use of lignocellulosic materials as protection in cementitious composites is essential for applications in building constructions to reduce the environmental impacts generated by the generation of waste and use of non-renewable materials and to promote sustainable development.
Abstract in English:ABSTRACT The cavitation phenomenon is an important factor affecting the safe and stable operation of hydraulic machinery units. The cavitation of the hydraulic machinery units can lead to the increased vibration, reduced efficiency, and cavitation erosion of blades. Therefore, a method is needed to determine the incipient cavitation of hydraulic machinery runner blades. This study is initiated from the acoustic characteristics of bubbles generated by the cavitation of model hydraulic turbines and the characteristics of radiated sound energy during cavitation. The characteristics of cavitation noise are studied. After the qualitative analysis of the high- and low-frequency energy distribution patterns of cavitation noise signals before and after cavitation, a mathematical model of the time-frequency characteristics of these signals is proposed using the energy distribution analysis method. The feature information is extracted from the cavitation noise signals and used to judge the occurrence of incipient cavitation in model turbine runner blades. Based on this method, an online cavitation monitoring system is constructed, and comparative tests are carried out on a model pump turbine and Francis turbine. It is found that the results of the proposed method for the judgment of incipient cavitation are highly consistent with those of traditional methods.
Abstract in English:ABSTRACT Concrete is a material that is often used in the construction industry due to its strong compressive strength and durability. Currently, a lot of research is being done to find new ways to increase performance. One of these ideas is what led to the creation of self-compacting. Concrete is accepted as the most cutting-edge development in the concrete building industry. Currently, a lot of research is being done to find new ways to increase performance. Self-Compacting Concrete is becoming more and more popular for usage in overloaded reinforced concrete constructions with difficult casting circumstances. High rise buildings with multi storey construction need light weight concrete so there is a need to investigate on lightweight concrete. The mechanical and physical properties of self-compacting, self-curing, and light-weight concrete are created in this study by replacing natural aggregate with fly ash and expanded clay at percentages of 0%, 10%, 20%, 30%, 40%, and 50%. Calotropis gigantia, a self-curing agent, is incorporated in 4% of the volume of cement and super plasticizer in order to maintain the workability of concrete of M30 grade concrete. The mix proportion of light weight self-compacting concrete is 1:2.04:1.17 with water cement ratio of 0.4.
Abstract in English:ABSTRACT The distribution of residual stress in three different directions of synthetic diamond grains brazed with Ni-Cr brazing filler metal having different embedding depth was measured by Raman spectroscopy to investigate the influence of embedding depth on residual stress of diamond-metal joints and optimize the embedding depth of synthetic diamond grains in brazed synthetic diamond tools. The results show that the residual stress is stable without remarkable gradient in the core zones of brazed synthetic diamond grains. However, in the region of both end of central axis, the margin region of the central plane and the margin region of the section plane between the brazed synthetic diamond grains and the surface of Ni-Cr brazing filler metal, the stress distribution gradient is rather great. The maximum tensile stress always exists in the margin region of the section plane and it has the most important effect on the mechanical property of brazed synthetic diamond grains. The embedding depth of synthetic diamond grains in brazed synthetic diamond tools is optimized at 40–50% based on the maximum tensile stress and the requirement of machining process.
Abstract in Portuguese:RESUMO Estudos já demonstraram que a anodização de zamac é uma alternativa para minimizar os efeitos corrosivos da liga. Outros estudos, em alumínio, demonstraram que quando anodizado e selado pelo processo à quente, promove aumento da sua resistência à corrosão. No entanto, não se tem relatos na literatura sobre selagem à quente em zamac anodizado. O objetivo deste trabalho é identificar o efeito da selagem, quanto a resistência de corrosão, sobre zamac anodizado. Para tanto, peças de zamac 5 lixadas e polidas industrialmente foram anodizadas em eletrólito 0,3 M de ácido oxálico em diferentes tempos (5, 30 e 60 minutos), e posteriormente seladas em H2O destilada à 90ºC por uma hora. As peças foram analisadas por técnicas morfológicas e de corrosão. Os resultados mostraram que com o aumento do tempo de anodização os cristalitos maiores dissolvem-se originando cristalitos menores até a formação de camada lisa. Além disso, o processo de selagem promoveu a hidratação dos produtos anodizados do zamac. No entanto, com o aumento do tempo de anodização, a camada de óxido ficou mais compacta, devido aos menores cristalitos, com diminuição da espessura, devido à camada lisa. Isso resultou no melhor desempenho anticorrosivo da amostra anodizada por 5 minutos e selada.
Abstract in English:ABSTRACT Studies have already shown that zamac anodizing is an alternative to minimize the corrosive effects of the alloy. Other studies, in aluminum, demonstrated that when anodized and sealed by the hot process, it promotes an increase in its resistance to corrosion. However, there are no reports in the literature about heat sealing in anodized zamac. The objective of this work is to identify the effect of sealing, in terms of corrosion resistance, on anodized zamac. For this purpose, industrially sanded and polished pieces of zamac 5 were anodized in 0.3 M oxalic acid electrolyte at different times (5, 30 and 60 minutes), and subsequently sealed in distilled H2O at 90ºC for one hour. The parts were analyzed using morphological techniques and corrosion tests. The results showed that with increasing anodization time, the bigger crystallites dissolve, originating smaller crystallites until the formation of a smooth layer. In addition, the sealing process promoted hydration of the anodized zamac products. However, with increasing anodizing time, the oxide layer became more compact, due to smaller crystallites, with a decrease in thickness, due to the smooth layer. This resulted in the best anti-corrosive performance of the 5-minute anodized and sealed sample.
Abstract in English:ABSTRACT This work aimed to analyze the influence of treatment pressure on the interaction between stearic acid and an Argon-Oxygen plasma. The fixed variables were the applied RF plasma power (50 W), treatment time (30 min), and treatment starting temperature (273 K). The pressure was varied as follows: 0.2, 0.6, and 1.0 Torr. For all treatment conditions, the etching of the samples was observed, as evidenced by the mass loss of the specimens and by following the gaseous by-products of reactions employing a mass spectrometer coupled to the reaction chamber. Optical emission spectroscopy followed the emission lines of oxygen active species. Functionalization of the specimens was also observed, as shown by the results obtained by Fourier-transform infrared spectroscopy (FTIR) and through XRD analysis. A liquid phase was formed for samples treated at 0.6 and 1.0 Torr, which favored the functionalization process and broadened the band present in the region from 1750 to 1700 cm–1, resulting in amorphous phases. An increase in the intensity of the characteristic peaks of esters was also observed. It can be concluded that the higher pressure favors the formation of a liquid phase and reaction kinetics, resulting in higher functionalization and lower etching.
Abstract in English:ABSTRACT This study analyzed the fatigue failure of a parabolic spring made of 51CrV4 steel. A fracture mechanics approach was used to quantify the driving force and resistance for different loading configurations, inclusion sizes, and residual stresses. The analysis considered surface and internal initiation processes, including the impact of residual stresses introduced by shot peening. Key findings include the ability of the methodology to analyze the variables influencing fatigue resistance and failure configuration, the competition between surface and internal fracture processes, the limitation of residual stresses, the importance of minimizing the maximum inclusion size, and the potential for enhancing the propagation threshold for long cracks. The employed methodology facilitates not only the quantification but also the comprehension of the influence of the intrinsic material resistance on the fracture process.
Abstract in Portuguese:RESUMO Estudos mostraram que o Zamac contendo revestimentos obtidos por eletrodeposição, utilizado como metal sanitário, apresenta baixa resistência à corrosão, o que foi atribuído à formação de porosidade na liga devido ao processo de obtenção por injeção sob pressão. Nesse caso, os revestimentos eletrodepositados não cobrem satisfatoriamente a porosidade superficial do Zamac injetado sob pressão. Pesquisas mostraram que a anodização em zamac tem minimizado ou fechado essas porosidades. Este trabalho tem por objetivo verificar o comportamento das camadas eletrodepositadas em amostras de zamac sem e com anodização. Para tanto, amostras de Zamac foram anodizadas em eletrólito de ácido oxálico 0,3 M, com parâmetros de processo de 100 V, 10 mA/ cm2, por 300 s, em uma fonte de potencial × corrente (300 V, 500 mA) e posteriormente eletrodepositadas em banhos de cobre alcalino, cobre ácido, níquel e cromo. As amostras foram avaliadas ao MEV (Microscopia Eletrônica de Varredura) por análises de topo, seção transversal e por Energy Dispersive Spectroscopy- EDS. Os resultados mostraram que o processo de anodização permite melhor nivelamento do revestimento de cobre alcalino e cobre ácido eletrodepositados no Zamac, impactando em revestimentos finais (até a eletrodeposição de cromo) com maior espessura quando comparados aos obtidos no processo industrial.
Abstract in English:ABSTRACT Studies have shown that Zamac containing coatings obtained by electroplating, used as sanitary metal, has low resistance to corrosion, which was attributed to the formation of porosity in the alloy due to the pressure injection process. In this case, the electrodeposited coatings do not satisfactorily cover the surface porosity of the Zamac injected under pressure. Research has shown that zamac anodizing has minimized or closed these porosities. This work aims to verify the behavior of electrodeposited layers in zamac samples with and without anodization. For this, Zamac samples were anodized in 0.3 M oxalic acid electrolyte, with process parameters of 100 V, 10 mA/cm2, for 300 s, in a source of potential × current (300 V, 500 mA) and subsequently electrodeposited in alkaline copper, acid copper, nickel and chromium baths. The samples were evaluated by SEM (Scanning Electron Microscopy) by top analyses, cross section and by Energy Dispersive Spectroscopy - EDS. The results showed that the anodizing process allows for better leveling of the alkaline copper and acid copper coating electrodeposited in Zamac, impacting final coatings (up to chrome electrodeposition) with greater thickness when compared to those obtained in the industrial process.
Abstract in Portuguese:RESUMO Nesta pesquisa foi avaliado o efeito da adição de três tipos de escória de fornos cubilô na deformação a quente de núcleos de areia. Além da avaliação de distorção a quente, foram avaliadas propriedades como resistência a tração imediata e resistência a tração após 30 minutos. Comparativamente, avaliou-se para cada tipo de escória, misturas com a adição 8, 12, 20, 40 e 70% em peso de escória sobre uma areia de sílica da região sul do Brasil. Os resultados mostraram uma redução na resistência à tração imediata dos núcleos de areia, independente do tipo de escória utilizada. A adição de escória granulada de cubilô, devidamente processadas, reduziu a deformação máxima a quente dos núcleos de areia, observou-se também que deformação foi diferente para cada tipo de escória utilizada. De uma maneira geral, os melhores resultados de deformação máxima foram obtidos para as misturas com 70% de adição, seguidas das misturas com 40% de escória. A adição progressiva das escórias também reduz a taxa de deformação, sendo que as escórias verde e preta apresentaram redução de 58%. Os resultados obtidos no ensaio de distorção a quente mostraram um potencial de utilização da escória de cubilô para melhorar o desempenho dos núcleos de areia em relação a defeitos motivados pela expansão da areia de sílica.
Abstract in English:ABSTRACT In this research, the effect of adding three types of cupola furnace slag in sand was evaluated on the hot distortion test. In addition, properties like as immediate tensile strength and tensile strength after 30 minutes were evaluated. Comparatively, mixtures with the addition of 8, 12, 20, 40 and 70% by weight of slag on silica sand from southern Brazil were evaluated for each type of slag. The results showed a reduction in the immediate tensile strength of the sand cores, regardless of the type of slag used. The addition of granulated cupola slag, duly processed, reduced the maximum hot deformation of the sand cores. It was also observed that the deformation was different for each type of slag used. In general, the best maximum deformation results were obtained for mixtures with 70% addition, followed by mixtures with 40% slag. The progressive addition of slag also reduces the deformation rate, with the green and black slag showing a 58% reduction. The results obtained in the hot distortion test showed a potential use of cupola slag to improve the performance of sand cores in relation to defects caused by the expansion of silica sand.
Abstract in English:ABSTRACT While excavation activities in mountain terrain regions, the exposure of carbonaceous mudstone could deteriorate the strength under the water-rock interaction, which impacts slope stability and affects the safety of the engineering project. The present study conducted the Point Loading Test (PLT), Acoustic Emission (AE), and Scanning Electron Microscope (SEM) to investigate the degradation of its mechanical properties under the water-rock interaction. The results reveal that: (1) The Total Organic Carbon (TOC) content and water content correspond to a negative correlation, and the carbonaceous mudstone possesses a softening boundary which makes the mudstone strength decay rapidly resulting in the strength decrease by 80% once the water content exceeds the boundary value; (2) Water-rock interaction weakens the acoustic emission capacity and the acoustic emission characteristic in the failure process of carbonaceous mudstone with different TOC can reflect the influence of water-rock interaction on its macroscopic strength and fracture structure deterioration, and the damage degree under immersion is over 50%; (3) The inhomogeneity of water-rock interaction causes unbalanced forces in the rock, as dissolved soluble minerals and oxidation-reduction of organic matter accelerate the deterioration of carbonaceous mudstone making the water-rock interaction is slowed down by the water-swelling filling of minerals in a time period. Therefore, this study has investigated the strength deterioration of carbonaceous mudstone subjected to water-rock interaction from macro-scale and micro-scale perspectives, which provides a reference for preventing and controlling carbonaceous mudstone deterioration resulting from catastrophes.
Abstract in Portuguese:RESUMO O trabalho teve como objetivo determinar as propriedades físicas e mecânicas de painéis LVL de paricá (Schizolobium parahyba var. amazonicum (Huber x Ducke)) colados com resina ureia-formaldeído. Foram produzidos 6 painéis LVL com 17 lâminas de 2,5 mm de espessura, sendo 14 lâminas de paricá e 3 lâminas de marupá (Simarouba amara Aubl.). Para a condição de umidade padrão de 12%, foram realizados ensaios de teor de umidade, densidades aparente e básica (caracterização física), resistências à compressão paralela e perpendicular às fibras, tração paralela às fibras, cisalhamento na linha de cola e flexão estática flatwise e edgewise (caracterização mecânica). Na condição de saturação total da madeira, foram realizados ensaios de compressão paralela às fibras e cisalhamento na linha de cola do LVL. Os resultados mostraram que os painéis LVL se enquadram na classe de resistência D30, caracterizado com média densidade. Foi observado o modo de ruptura do tipo frágil em todos os ensaios mecânicos, exceto nos ensaios de compressão paralela e perpendicular às fibras. O aumento do teor de umidade, decorrente da saturação total da madeira, influenciou de forma negativa nas resistências à compressão paralela às fibras e ao cisalhamento na linha de cola. O LVL apresentou desempenho mecânico compatível com as solicitações estruturais.
Abstract in English:ABSTRACT The objective of this work was to determine the physical and mechanical properties of paricá (Schizolobium parahyba var. amazonicum (Huber x Ducke)) LVL panels bonded with urea-formaldehyde resin. Six LVL panels were produced with 17 sheets of 2.5 mm thick, 14 sheets of paricá and 3 sheets of marupá (Simarouba amara Aubl.). For the standard temperature condition of 12%, tests were carried out on moisture content, apparent and basic densities (physical characterization), resistance to resistance parallel and perpendicular to the fibers, traction parallel to the fibers, shearing in the glue line and flatwise static bending and edgewise (mechanical characterization). In addition, saturation tests parallel to the fibers and shear tests were carried out in the LVL glue line in the condition of total saturation of the wood. The results appreciated that the LVL panels fall within the D30 strength class and medium density. The brittle type failure mode was observed in all mechanical tests, except in the parallel and perpendicular compression tests to the fibers. The increase in moisture content, due to the total saturation of the wood, negatively influences the resistance to the slope parallel to the fibers and to the shear strength in the glue line. The LVL presented a mechanical performance compatible with the substitute.
Abstract in English:ABSTRACT The development of lightweight geopolymer concrete is the main goal of this research work, and the outcomes were evaluated in comparison to the control mix. In this work, geopolymer concrete was produced using fly ash as a binder, synthetic sand as M-sand as fine aggregate, and coconut shell as well as palm shell ash for coarse aggregate. For the purpose of selecting a mix proportion via trial mixes, an initial investigation was conducted. The quantity among binder, fine and coarse aggregate, sodium hydroxide molarity, sodium silicate: sodium hydroxide ratio, the alkaline binder ratio is some of the significant variables taken into account in the current study. Investigation of the effects of various factors on the engineering characteristics of geopolymer concrete. The trial mixes were utilized to evaluate the characteristics for geopolymer concrete with a ratio of 1: 2.36 :1.02 and a Molarity of 16 with binder ratio 0.6 The key findings of this investigation is to that the coconut shell waste and palm shell can be replaced instead of fine aggregate. In-depth research was done on the mechanical behavior with geopolymer concrete, such as the mechanical and durability characteristics with control mix.
Abstract in Portuguese:RESUMO O atrito nas interfaces ferramenta/cavaco e ferramenta/peça é complexo dificultando a determinação do coeficiente de atrito nos processos de usinagem. Assim, vários ensaios tribológicos foram desenvolvidos para simular as condições de corte e determinar o coeficiente de atrito. Este trabalho apresentou análise comparativa do coeficiente de atrito entre o aço ABNT 1045 e WC-10Co revestido com AlCrN por meio de dois métodos: ensaio de torneamento e ensaio de compressão de anel à quente. O ensaio de torneamento foi realizado com corte oblíquo nas velocidades de corte 150 e 220 m/min. A aquisição dos sinais das componentes de força da usinagem por meio de um dinamômetro. O ensaio de compressão de anel foi realizado nas temperaturas de 200 e 400 °C. Os coeficientes de atrito foram obtidos por meio de modelos matemáticos. A análise estatística do coeficiente de atrito apontou equivalência do coeficiente de atrito no ensaio de torneamento na velocidade de corte 150 m/min com o ensaio de compressão de anel à quente 200 °C. Assim como no ensaio de torneamento na velocidade de corte 220 m/min com o ensaio de compressão de anel à quente 400 °C. A análise macrográfica do anel após a deformação no ensaio de compressão de anel observou a influência da temperatura de ensaio no deslocamento do raio neutro. A análise superficial dos anéis e das matrizes do ensaio de compressão foi realizada por meio de microscopia óptica (MO) e rugosidade Ra, onde observou-se o aumento da rugosidade após o ensaio e a presença de desgaste abrasivo.
Abstract in English:ABSTRACT Friction at the tool-chip and tool-workpiece interfaces is complex, making it difficult to determine the coefficient of friction in machining processes. Thus, several tribological tests were developed to simulate the cutting conditions and determine the coefficient of friction. This work presents a comparative analysis of the coefficient of friction between ABNT 1045 steel and WC-10Co coated with AlCrN using two methods: machining test and hot ring compression test. The machining test was carried out with an oblique cut at the cutting speeds used in the test were 150 and 220 m/min. The acquisition of the signals of the machining force components by means of a dynamometer. The ring compression test was carried out at temperatures of 200 and 400 °C. Friction coefficients were obtained through a mathematicals models. The statistical analysis of the coefficient of friction showed equivalence of the coefficient of friction in the oblique machining test at a cutting speed of 150 m/min with the hot ring compression test at 200 °C. As well as in the machining test at a cutting speed of 220 m/min with the hot ring compression test at 400 °C. The macrographic analysis of the ring after deformation in the ring compression test observed the influence of the test temperature on the displacement of the neutral radius. The surface analysis of the rings and matrices of the compression test was performed using optical microscopy (OM) and roughness Ra, where an increase in roughness was observed after the test and the presence of abrasive wear.
Abstract in Portuguese:RESUMO No presente estudo, lotes de placas de zircônia estabilizada com 8% mol de ítrio (TZ8Y) foram fabricados pela técnica de colagem de fita, variando entre eles a composição da suspensão, como o volume de sólidos e os teores de ligantes, de plastificante do tipo I e de plastificante do tipo II com o intuito de verificar a influência destes parâmetros e do comportamento tixotrópico da suspensão sobre o empenamento do produto final. Após sinterizadas, a topografia das placas foi mapeada por meio de um relógio comparador, tomando medidas sobre a superficia das placas em um sistema de coordenadas, e, a partir desse sistema, foi definido um índice numérico que quantifica a planicidade das amostras. A influência foi investigada através de uma análise estatística bivariada, relacionando o índice de planicidade com cada um dos parâmetros alvo. A análise apresentou uma correlação negativa forte e significativa pelo teste de Spearman (⍴ ≅ 0,95 e valor-p < 10–3) entre o teor de plastificante do tipo I e a planicidade das placas produzidas, porém para os outros parâmetros analisados a correlação não pôde ser considerada estatisticamente significativa. Além disso, os resultados mostraram também que a utilização de um pós processamento nas fitas à verde, como uma laminação, melhorou substancialmente a planicidade das placas após a sinterização.
Abstract in English:ABSTRACT In the present study, 5 batches of tapes made of stabilized zirconia with 8% mol of yttrium (TZ8Y) were produced by the tape casting technique, varying among them the composition of the slurry, such as solids load and the contents of binder, type I plasticizer and type II plasticizer in order to verify the influence of these parameters and the thixotropic behavior of the slurry on the occurrence of warping. After sintering, the topography of the tapes was mapped using an indicator, taking measurements across the entire surface of the tapes in a coordinate system, and, from these maps, a numerical coefficient that quantifies the flatness of the samples was defined. The influence was investigated using a bivariate statistical analysis, relating the flatness coefficient to each of the target parameters. The analysis showed a strong and significant negative correlation using the Spearman coefficient (⍴ ≅ 0,95 e p-value < 10–3) between the type I plasticizer content and the flatness of the produced slabs, but for the other parameters analyzed the correlation could not be considered statistically significant. In addition, the results also showed that the use of a post processing on the green tapes, such as a lamination, substantially improved the flatness of the plates after sintering.
Abstract in English:ABSTRACT This study investigates the feasibility of low-grade hard asphalt in high-temperature regions. We conducted an analysis of the high-temperature rheological properties of asphalt before and after short-term and long-term aging using the dynamic shear rheological (DSR) test and multi-stress creep recovery (MSCR) test. Additionally, the road performance of the asphalt mixture was studied by rutting test and low temperature beam bending test. The results indicate that the 30# asphalt demonstrates superior anti-rutting performance compared to the 50# asphalt. Furthermore, the rutting factor and fatigue factor of the 30# asphalt during aging are significantly higher than those of the 50# asphalt. With increasing temperature, stress level, and stress action time, the strain of the asphalt gradually increases. The unrecoverable creep compliance of the 50# asphalt exceeds that of the 30#. Although the high-temperature performance of the 30# asphalt mixture outperforms that of the 50# asphalt mixture, it exhibits lower flexural tensile strength and deformation ability at low temperatures compared to the 50# asphalt mixture. Overall, low-grade asphalt demonstrates relatively stable stress variations and exhibits good high-temperature stability.
Abstract in English:ABSTRACT Graphene oxide (GO) has attracted more and more attention in asphalt pavement due to its excellent performance. However, most current research is limited to GO modified base asphalt, and the modification effect is insignificant. In this paper, GO / SBS-modified asphalt was prepared by high-speed shearing. The effects of GO on the physical properties, storage stability, low-temperature performance, and aging resistance of SBS-modified asphalt were studied. A low-temperature beam bending test analyzed the low-temperature performance of GO / SBS composite modified asphalt mixture before and after aging. The results show that adding GO improves SBS-modified asphalt’s high-temperature performance, aging resistance, and storage stability. When the content of GO is 0.75%, the physical properties of modified asphalt are the best. The low-temperature rheological properties of modified asphalt with GO before aging are slightly lower than those of SBS-modified asphalt. However, adding GO improves the low-temperature rheological properties of GO/SBS modified asphalt after aging. GO-modified asphalt slightly improves the low-temperature toughness of the mixture under non-aging and short-term aging. However, it still makes the mixture maintain good low-temperature performance under long-term aging. GO / SBS modified asphalt mixture has excellent low-temperature crack resistance before and after aging, and GO / SBS composite modified asphalt can effectively alleviate the damaging effect of aging on the low-temperature crack resistance of asphalt mixture and prolong the service life of the pavement.
Abstract in Portuguese:RESUMO O alumínio é um metal muito utilizado comercialmente e normalmente com tratamento superficial de anodização. A anodização também é um processo consolidado e difundido, principalmente uma técnica potenciostática conhecida como Mild Anodization, que utiliza ácidos orgânicos como eletrólitos com aplicação de baixos potenciais para gerar camadas de óxidos semicondutoras. Por outro lado, o licor pirolenhoso, que é um subproduto da produção de carvão vegetal, oriundo da condensação da fumaça dos fornos de pirólise como processo de controle de poluição atmosférica, é pouco conhecido nos meios tecnológicos sendo utilizado basicamente para fins agrícolas e tem principalmente ácidos orgânicos em sua composição, como o ácido acético, o alcatrão e cetonas. Por outro lado, os processos de anodização são feitos normalmente em eletrólitos que demandam tratamento de efluentes dispendiosos e descarte controlado. Assim, o objetivo deste estudo é avaliar o comportamento do licor pirolenhoso como eletrólito de anodização para alumínio 6061, em diferentes concentrações. Para tanto, foram definidos parâmetros de processo (densidade de corrente, temperatura, tempo) e três níveis de concentração do eletrólito – 10%, 25% e 50% v/v. Comparativamente, os mesmos parâmetros de processo foram utilizados para o eletrólito de ácido acético (em concentrações de 0,4%, 1% e 2% v/v). As superfícies após o tratamento eletroquímico foram avaliadas por sua morfologia, através de microscopia eletrônica de varredura, e quanto à molhabilidade, pelo método da gota séssil. Verificou-se que houve anodização do alumínio em licor pirolenhoso, enquanto que em ácido acético houve eletropolimento da superfície. No caso do licor pirolenhoso, os resultados mostraram que, nas condições de anodização propostas, o desempenho do processo foi melhor na concentração de 10% v/v.
Abstract in English:ABSTRACT Aluminum is a metal widely used commercially and usually with surface anodizing treatment. Anodizing is also a consolidated and widespread process, mainly a potentiostatic technique known as Mild Anodization, which uses organic acids as electrolytes with application of low potentials to generate semiconductor oxide layers. On the other hand, the pyroligneous liquor, which is a by-product of the production of charcoal, arising from the condensation of smoke from pyrolysis ovens as a process for controlling atmospheric pollution, is little known in technological means, being used primarily for agricultural purposes and has mainly organic acids in its composition, such as acetic acid, tar and ketones. On the other hand, anodizing processes are normally carried out in electrolytes that require expensive effluent treatment and controlled disposal. Thus, the aim of this study is to evaluate the behavior of pyroligneous liquor as an anodizing electrolyte for 6061 aluminum at different concentrations. Therefore, process parameters (current density, temperature, time) and three levels of electrolyte concentration were defined – 10%, 25% and 50% v/v. Comparatively, the same process parameters were used for the acetic acid electrolyte (at concentrations of 0.4%, 1% and 2% v/v). The surfaces after electrochemical treatment were evaluated for their morphology, through scanning electron microscopy, and for wettability, by the sessile drop method. It was verified that aluminum was anodized in pyroligneous liquor, while in acetic acid there was surface electropolishing. In the case of the pyroligneous liquor, the results showed that, under the proposed anodizing conditions, the process performance was better at the concentration of 10% v/v.
Abstract in English:ABSTRACT In the restoration of lost or misaligned dental pieces, dissimilar dental alloys are frequently used in the oral cavity, which form galvanic couples that corrode due to the effect of saliva and dentin fluids. In this work, the microstructure of ten non-precious dental alloys was analyzed by optical microscopy, the open-circuit corrosion potential of each alloy was measured against a saturated calomel electrode, they were subjected to accelerated corrosion processes in aerated artificial saliva and plotted the potentiodynamic polarization curves of these alloys. Then, the corrosion potential and current density of the galvanic couples formed by stainless steels 304 and 316L with non-precious dental alloys of Ni-Cr, Co-Cr, and Cu base alloys (Cu-Ni, Cu-Zn and Cu-Al), using the Evans method whose results were not compatible with the principle of galvanic couples, so the Mansfeld equations were used with which results consistent with the aforementioned principle were obtained.
Abstract in Portuguese:RESUMO Análise de tensões residuais realizada em juntas soldadas pelo processo TIG utilizando metal de base ASTM A131 AH36 comparando diferentes projetos de junta. Uma parte com chanfro usinado em formato de “V” e outra em forma de “U”. Também foi correlacionado variáveis de acabamento com passe único oscilante ou com passe duplo retilíneo. O resultado das tensões foi obtido através do método DPC (deslocamento de pontos coordenados). Os corpos de prova foram soldados segundo as normas (fabricação e qualificação) AWS D1.1. Após a soldagem foram realizadas furações na zona termicamente afetada nas mediações centrais do eixo de soldagem em uma mesa de medição por coordenadas. As soldas foram submetidas a tratamento térmico para alívio de tensões (TTAT) e mensurou-se os deslocamentos dos furos causados pelo TTAT, possibilitando o cálculo das tensões residuais. Os resultados demostraram menores níveis de tensões juntas em “U” e boa aplicabilidade do método DPC.
Abstract in English:ABSTRACT Analysis of residual stresses in welded joints by TIG process using base metal ASTM A131 AH36 comparing different joint design, some specimens were machined with joint in “V” shape and others in “U” shape. It was also correlated with finishing with a single oscillating pass or with straight double pass. The results were performed using the DCP method (displacement of coordinated points). The specimens were welded according to the standards (manufacturing and qualification) AWS D1.1. After welding, holes were made in the thermally affected zone in the central region of the welding axis, which were then referenced on a coordinate measuring table. Then, the welds were subjected to a post weld heat treatment (PWHT) and measured the displacements of the holes caused after PWHT in coordinate plan, allowing the calculation of the residual stresses. The results demonstrated lower stress levels in “U” design joints and good applicability of the DPC method.
Abstract in English:ABSTRACT The loads acting on mechanical components are usually complex, and the more traditional fatigue analysis criteria may be non-conservative, especially in out-of-phase and non-proportional loadings. Many multiaxial fatigue models have been developed and need to be experimentally validated. This work describes the load control mechanism of a low-cost electromechanical multiaxial fatigue testing machine, which applies variable axial and torsional loads. A load cell interconnected to the motor control system was manufactured and instrumented with extensometers. For the axial load, a four-bar mechanism coupled to a power screw was designed to apply alternating axial loads, thus ensuring a higher load frequency and preservation of the motor, which will not need to alternate its direction of rotation. The machine’s control system, focused on out-phase loading, is based on the data sent by the load cell and pulse encoders per degree for each motor, ensuring good accuracy in applied loads. Tests were carried out to check the system’s response, in which it was possible to apply load curves of torque and axial force in different phase shift angle. Therefore, several existing multiaxial fatigue models can be tested with good reliability.
Abstract in English:ABSTRACT The physical and mechanical properties of ceramic blocks are affected by the firing process of the primary raw material, in this case, clay or clay minerals. Consequently, this study sought to characterize different types of silty clays for ceramic block production and determine the effect of firing time and mineral content on their mechanical and physical properties. Characterization was conducted in two stages: pre and post-firing. Pre-firing evaluations were granulometric distribution, Attenberg limits, chemical composition, mineral composition and thermal behavior. Post-firing evaluation made use of 30 specimens subjected to temperatures of 800 °C, 900 °C and 1,000 °C. Results showed that firing temperatures greatly affected mechanical properties. Higher burn temperatures increased tensile strength and reduced water absorption while causing linear shrinkage. This increase in shrinkage raised the possibility of damage to the ceramic material and reduction of overall quality.
Abstract in English:ABSTRACT The double punch test (DPT) is increasingly used internationally for quality control of steel fiber reinforced shotcrete (SFRS). This study intends to verify the influence of the DPT specimens’ diameter on the residual strength behavior of the SFRS. The experimental program aims to evaluate the dynamics of the test in terms of the results obtained from the analytical conversion of the axial displacement into total circumferential opening displacement (TCOD). The results are compared to those obtained through the 3D digital image correlation (DIC3D) to evaluate its applicability as a quality control method of the SFRS. The results demonstrated that the TCOD could be easily obtained by analytical conversion with reliable accuracy. The analysis of the DPT results could consider the crack opening level to obtain constitutive equations. The diameter of the DPT specimens directly influences the structural parameters of the SFRS. Smaller specimens may show a 35% reduction in residual strength associated with the service limit state. As the coefficient of variation of the residual strength associated with the ultimate limit state practically doubles when smaller specimens are used, for the same reliability, the sample sizing of the specimens of 10 cm is twice the quantity of the 15 cm.
Abstract in English:ABSTRACT Engineering machinery is characterized by high load frequency, large amplitude, and long continuous working time, which requires high anti-loosening performance of bolts. In this paper, based on DIN65151, a transverse vibration test is designed. By changing the surface roughness, hardness, and coating thickness of the connected parts, the specimens with different surface process parameters were obtained. Tightening and transverse vibration experiments were carried out to monitor the changes in preload force and to study the surface process parameters of the connected parts to investigate their effect on the anti-loosening performance of threaded fasteners. The research results show that the smaller the surface roughness, the higher the surface hardness, and the smaller the coating thickness, the better the anti-loosening performance of the bolt.
Abstract in Portuguese:RESUMO O aço galvanizado por imersão a quente é bastante utilizado no controle da corrosão das estruturas em concreto armado expostas à ambientes agressivos. O que torna importante a análise do comportamento deste aço no desempenho estrutural destas estruturas. A literatura apresenta incertezas e poucos trabalhos sobre este tema. Assim, o objetivo deste trabalho foi analisar a influência da corrosão inicial do aço galvanizado devido à alta alcalinidade do concreto fresco na tensão de aderência do concreto armado. Para análise foram utilizados corpos de prova compostos por um cubo de concreto com uma barra localizada no centro com comprimento de aderência definido, utilizando barras em aço (galvanizado e não galvanizado) nos diâmetros de 10 mm e 20 mm. A aderência foi avaliada através do ensaio de arrancamento simples (pull-out test). Os resultados mostraram que, a perda de espessura da camada de galvanização para todas as barras devido a corrosão inicial oriunda do contato com o concreto fresco, não acarretou prejuízo significativo na proteção proporcionada por esta camada ao aço e nem diminuição na sua tensão de aderência ao concreto. Desta forma pode-se concluir que essa corrosão inicial do zinco não afeta o desempenho estrutural do concreto armado.
Abstract in English:ABSTRACT Hot-dip galvanized steel is widely used to control corrosion in reinforced concrete structures exposed to aggressive environments. This makes it important to analyze the behavior of this steel in the structural performance of these structures. The literature presents uncertainties and few studies on this topic. Thus, the objective of this work was to analyze the influence of initial corrosion of galvanized steel due to the high alkalinity of fresh concrete on the bond strength of reinforced concrete. For analysis, specimens composed of a concrete cube with a bar located in the center with a defined length of adhesion were used, using steel bars (galvanized and non-galvanized) in diameters of 10 mm and 20 mm. Adherence was evaluated using the simple pull-out test. The results showed that the loss of thickness of the galvanizing layer for all bars due to initial corrosion arising from contact with fresh concrete did not cause significant damage to the protection provided by this layer to the steel, nor did it decrease its adhesion stress to the steel. concrete.
Abstract in Portuguese:RESUMO A investigação teve por objetivo analisar a viabilidade técnica de incorporação do resíduo proveniente do filtro prensa do processo de beneficiamento do carvão mineral (TFP) e de cinzas pesadas (CP) advindos de uma termoelétrica, em massa cerâmica na escala laboratorial. Foram realizados ensaios de caracterização físico-química e de classificação dos resíduos. Posteriormente foram desenvolvidas dez formulações através de planejamento experimental por delineamento de misturas simplex centroide, incorporando esses resíduos a uma massa padrão de cerâmica vermelha. Os corpos-de-prova foram conformados por extrusão sem vácuo e submetidos a tratamento térmico em estufa e queima em forno mufla a 900 °C. As propriedades tecnológicas avaliadas foram: retração térmica linear de secagem e de queima, absorção de água e resistência mecânica à compressão e por fim, foram realizados testes de eflorescência e análise fitotoxicológica. Os resultados de classificação dos resíduos, indicaram esses como não sendo perigoso – Classe II-B – inerte. Os testes físicos dos corpos-de-prova mostram que comparados a formulação base de cerâmica vermelha (STD), as demais formulações obtiveram resultados dentro dos parâmetros técnicos, que podem ser posteriormente realizados em um ensaio de escala industrial. Embora os ensaios mecânicos das provas com incorporação de resíduo ficaram abaixo da formulação base (STD), não se descarta uma prova em escala similar a industrial. No ensaio de eflorescência, observou-se que não houve presença de sais solúveis. E por fim, no ensaio fitotoxicológico, com Allium cepa L. de uma formulação com agregação de todas matérias-primas juntas, apresentou um resultado próximos ao padrão, se mostrando apto a reprodução em escala industrial.
Abstract in English:ABSTRACT The investigation aims to analyze the technical viability of addition the waste from the filter-press from the mineral coal treatment process (TFP) and bottom ash from a thermoelectric (CP), in ceramic paste on the laboratory scale. Physical-chemical characterization and waste classification tests were carried out. Subsequently, ten formulations were developed through the mixture design (DoE), incorporating these residues into a standard clay ceramic paste (STD). The samples were formed by extrusion without vacuum and subjected to heat treatment in an oven and fired in a muffle at 900 °C. The evaluated technological properties were: shrinkage of drying and firing, water absorption and mechanical resistance and, finally, efflorescence tests and phytotoxicological analysis were performed. The results of solid waste classification, indicated these as not being dangerous (Class II-B - inert). The technical analysis of the samples show that compared to the clay ceramic standard formulation (STD), the other mixtures obtained results within the technical parameters, which can later be carried out in an industrial scale test. Although the mechanical tests with waste incorporation were below the standard formulation (STD), a test on an industrial scale is not discarded. In the efflorescence test, it was observed that there was no presence of soluble salts. And finally, in the phyto-toxicological test, with Allium cepa L. of a formulation with aggregation of all raw materials, it presented a result marginally similar to the standard, proving itself capable of reproduction on an industrial scale.
Abstract in Portuguese:RESUMO Foram caracterizadas micro estruturalmente e mecanicamente a liga Ti-6Aℓ-4V obtida através da metalurgia do pó em atmosfera não controlada variando os parâmetros de sinterização. As amostras foram compactadas em uma prensa uniaxial à 874 MPa, 999 MPa e 1124 MPa, e sinterizadas sem atmosfera protetora ou vácuo, nas temperaturas de 675 °C, 750 °C e 850 °C. Ao sinterizar o material, houve influência dos óxidos nos resultados devido à alta afinidade que o titânio tem por elementos intersticiais, promovendo um aumento na densidade e elevados valores de dureza. A partir dos resultados verificou-se que o tratamento realizado na pressão de 1124 MPa e temperatura de 750 °C foi o que apontou a maior dureza na fase beta (β), sendo o valor de 1165,1 HV. Na fase alfa (α), o maior valor foi de 1321,3 HV, apresentado pelo tratamento realizado na pressão de 999 MPa e temperatura de 850 °C. Os elevados valores na dureza observados na liga estão associados ao reforço promovido pela dissolução átomos de Fe. Materiais com elevada dureza possuem uma vasta aplicação nas indústrias aeroespaciais e biomédicas, que buscam sempre por melhores resultados de resistência mecânica, aumentando assim a vida útil e a aplicabilidades de seus produtos.
Abstract in English:ABSTRACT Were characterized microstructurally and mechanically the Ti-6Aℓ-4V alloy obtained through powder metallurgy in an uncontrolled atmosphere, varying the sintering parameters, arose. The samples were compacted in a uniaxial press at 874 MPa, 999 MPa, and 1124 MPa, and sintered without a protective atmosphere or vacuum, at 675 °C, 750 °C, and 850 °C. When sintering the material, the oxides influenced the results due to titanium’s high affinity for interstitial elements, promoting increased density and high hardness values. Based on the results, the treatment carried out at a pressure of 1124 MPa and a temperature of 750 °C showed the highest hardness in the beta phase (β), with a value of 1165.1 HV. In the alpha phase (α), the highest value was 1321.3 HV, presented by the treatment performed at a pressure of 999 MPa and a temperature of 850 °C. The high hardness values observed in the alloy are associated with the reinforcement promoted by the dissolution of Fe atoms. Materials with high hardness values use in the aerospace and biomedical industries, which always look for better mechanical resistance results, thus increasing their products’ useful life and applicability.
Abstract in English:ABSTRACT Due to its combination of high mechanical properties, good formability, and low production cost, steel is a key material with potential for improvement in the metallurgical industry. Based on these conditions, this research evaluated the influence of material composition and incomplete austenitization parameters on the final metallurgical and mechanical properties of high-strength microalloyed steels after cooling in a medium with high severity. The applied cycle was based on the intercritical thermal treatment of microalloyed steels with niobium (Nb) and titanium (Ti) to increase the mechanical resistance and guarantee the tenacity of the material. An experimental study was carried out testing three intercritical temperatures, 806 °C, 775 °C, and 740 °C, with subsequent cooling in polymeric solutions in water. The studies showed that the intercritical temperature variation directly contributed to the difference in the second phase microstructure present in the samples. The heat treatment findings resulted in a microhardness of 434.2 HV0.01, characterizing the low-carbon martensite. The presence of a matrix consisting of ferrite and a second phase of low-carbon martensite promoted the typical behavior of dual phase steel. In the x ray diffraction, the presence of retained austenite was not evidenced, indicating the efficiency of the cooling rate. The experiments confirmed the influence of different engineering parameters and intercritical treatment on the mechanical properties. The study enriches the current knowledge about the development of variables for the development of dual phase steel from microalloying elements.
Abstract in English:ABSTRACT Ba1-xGdxTiO3 thin films have been fabricated at different Gd3+ ionic concentrations, film thicknesses, and annealing temperatures using the sol-gel method. The refractive index of the Ba1-xGdxTiO3 films on a silicon substrate is characterized using Spectroscopic Ellipsometry (SE), where the ellipsometry angles Ψ and Δ are fitted very well with the Cauchy dispersion model. The results show that the refractive index at 632.8 nm decreases from 2.18 to 1.892 with the increase of the Gd3+ ratio, while it increases with film thickness and annealing temperature. This trend for refractive index variation is explained based on interatomic spacing and density densification of the films. Using Wemple–Di Domenico (WDD) model shows that the dispersion energy increases with film thickness and annealing temperature and decreases with Gd3+ doping. The relatively high refractive index of the samples supports the possibility of using Ba1-xGdxTiO3 thin films as AR coating for solar cells.
Abstract in English:ABSTRACT To meet the present needs of concrete consumption, it is the need of the hour to discover different alternatives and unique techniques. By Incorporating the latest trends, Polymer Concrete (PC) and Fibre-Reinforced Concrete (FRC) are being used to improve the strength of concrete. It is proposed to produce M30 grade Fibre Reinforced Polymer Concrete (FRPC) with the help of Polyester Resins (PR), Polypropylene Fibres (PF) and Recycled Waste Plastics (RWPA). FRPC is a combination of three different variables of different replacement percentages, which requires extensive and detailed experimentation to optimize each variable used in this investigation. In this study (research), optimization was done by keeping the two variables constant. To reduce the number of experiments, optimization of ingredients was done by statistical modelling technique of Central Composite Design (CCD). In conclusion, the optimal input parameters for achieving a 28-day CS are determined to be 12.05% PR, 2.19% PF, and 30% RWPA. These findings are based on the analysis of experimental results, statistical modelling, and the CCD approach, demonstrating the successful optimization and correlation between the input parameters and the desired CS output.
Abstract in English:ABSTRACT River sand is becoming increasingly scarce. As a result, an alternative material is required to replace river sand in order to save river sand. In the construction of quality concrete, artificial aggregate is now frequently employed as a substitute for river sand. Coconut fibre ash (CFA) aggregate obtained from Coconut fibre is prevalent in India. Partially replacing river sand (fine aggregate) with presaturated CFA aggregate for self curing purpose is presented in the paper. Fine aggregates were replaced by CFA aggregate by 5%, 10%, 15%, 20% and 25% by volume. The workability and strength characteristics of the concrete are studied. Internal curing is the solution to today's water scarcity's insufficient curing. During compared to other mixtures, test results show that the concrete mix with 20% CFA aggregate produced better results when self curing.
Abstract in English:By performing tensile tests in the temperature range of 800°C to 1200°C, the thermoplastic behavior of microalloyed and unmicroalloyed new martensitic low-density steels were investigated, and the mechanism of the effect of Nb and V microalloying on the thermoplasticity was revealed. The results showed that both microalloyed and unmicroalloyed steels have good thermoplasticity and the plasticity increased with increasing deformation temperature. The microalloyed steels above 1000°C could have their high-temperature plasticity significantly enhanced by Nb, V microalloying, while the microalloyed steels at or below 1000°C could have their plasticity reduced. When the deformation temperature exceeds 1000°C, complete recrystallization occurs in both microalloyed and unmicroalloyed steels. The Nb, V microalloys were able to refine the recrystallized grains, which could obtain a stronger resistance to crack expansion and give the microalloyed steels better high-temperature plasticity. When the deformation temperature at or below 1000°C, the unmicroalloyed steel exhibited significant recrystallization. The presence of numerous small-sized NbC precipitation phases, abundant in the microalloyed steel, hindered the recrystallization. This made dynamic recrystallization of microalloyed steels almost non-existent when deformation occurred at lower temperatures, which lead to lower plasticity compared to the unmicroalloyed steel.