CT - DEM - Artigos publicados em periódicos

URI Permanente para esta coleçãohttps://repositorio.ufrn.br/handle/1/176

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Evaluation of aging in air of poly (ethylene terephthalat) in oxygen plasma
(Materials Research, 2015-10) Feitor, Michelle Cequeira; Alves Junior, Clodomiro; Bezerra, Clovis Medeiros; Sousa, Rômulo Ribeiro Magalhães de; Costa, Thercio Henrique de Carvalho
Polyester fabric samples – PET (poly (ethylene terephtalate)), were treated with oxygen plasma, in order to alter the hydrophilicity of such material. The process parameters: working pressure, current, tension and temperature were kept constant, varying only the treatment time. In order to evaluate the change caused on samples hydrophilicity, as well as the influence of the treatment time, the vertical wicking test was used. The samples were stored at standard temperature and pressure conditions, and their wettability were measured one day after the treatment and repeated after 30, 60 and 360 days, in order to check the stability of the effects produced. Scanning electron microscopy (SEM), Raman and ATR (Attenuated total reflection) spectroscopies were used to evaluate physical and chemical alterations on the samples surface. The results have shown a substantial improvement on the hydrophilicity of the treated samples compared to the non-treated sample.
Effect of cold plasma treatment on recycled polyethylene/kapok composites interface adhesion
(Composite Interfaces, 2018-11-26) Feitor, Michele Cequeira; Macedo, Murilo José Pereira; Mattos, Adriano Lincoln Albuquerque; Costa, Thércio Henrique de Carvalho; Ito, Edson Noriyuki; Melo, José Daniel Diniz
Composites from recycled polyethylene and kapok fibers were pre- pared using untreated and plasma-treated fibers. Flow properties, mechanical properties and fracture morphology were analyzed in order to evaluate the effects of cold plasma treatment on kapok fibers to improve interfacial bonding between fibers and matrix. Melt flow rate (MFR) measurements indicated a reduction in flow rate of the polymer with the addition of kapok fibers. Storage modulus increased with fiber addition and this effect was more significant when plasma- treated fibers were used. Tanδ obtained from viscoelastic characteriza- tion also suggested improvements in fiber/matrix interface as a result of plasma treatment. Addition of kapok fibers to polyethylene pro- duced a reduction in onset decomposition temperature determined from thermogravimetry curve. However, the decrease in temperature observed does not limit composite processing. Furthermore, the degree of crystallinity of polyethylene increased with the addition of untreated fibers and reduced when plasma treated fibers were added. Morphological analysis of failure surface by Field Emission Gun Scanning Electron Microscopy (FEGSEM) suggest that fiber/matrix adhesion was clearly improved when plasma treated fibers were used. Thus, the oxygen cold plasma treatment proved to be an effec- tive non-polluting approach to enhance matrix/fiber adhesion in poly- ethylene/kapok fiber composites, as opposed to chemical treatments.
Thin tin and tio2 film deposition in glass samples by cathodic cage
(Materials Research, 2015-04) Feitor, Michelle Cequeira; Sousa, Rômulo Ribeiro Magalhães de; Araújo, Francisco Odolberto de; Costa, Thercio Henrique de Carvalho; Nascimento, Igor Oliveira; Santos, Francisco Eroni Paes; Alves Júnior, Clodomiro
Thin nitride and titanium dioxide films were produced using an innovative technique called cathodic cage depositon. Uniformity, three-dimensionality and high rate deposition are some of the advantages of this technique. In this study we discuss the influences of temperature, treatment time and gaseous atmosphere on the characteristics of the deposited films. The TiN (titanium nitride) and TiO2 (titanium dioxide) films were produced using a high deposition rate of 2,5 μm/h at a work temperature and pressure of 400°C and 150 Pa respectively. EDS technique was used to identify the chemical composition of the thin film deposited, whilst Raman spectroscopy indicated the phases present confirmed by DRX analysis. The thickness of the deposited films was studied using electron microscopy scanning. The results based on the deposition parameters confirm the great efficiency and versatility of this technique, which allows a uniform three-dimensional film deposition on any material without the appearance of stress. Compared to other techniques, cathodic cage deposition enables deposition at lower temperatures
Novel synthesis of copper oxide on fabric samples by cathodic cage plasma deposition
(Polymers for Advanced Technologies, 2019-11-11) Feitor, Michele Cequeira; Fernades, Fernanda; Rocha Filho, Edglay; Souza, Ivan; Nascimento, Igor; Sousa, Rômulo; Almeida, Edalmy; Costa, Thércio; Naeem, Muhammad; Iqbal, Javed
The fabrics with copper or copper oxide deposition are of considerable interest because of exceptional antibacterial properties, which are useable in medical, textiles, and hygiene applications. Unfortunately, the conventional techniques take long pro-cessing time, complex equipment, and combination of several processing steps (nano-particles synthesis and their deposition on fabrics). In this novel study, cathodic cage plasma deposition assisted with copper cathodic cage is used for the synthesis of the copper oxide on polyester and polyamide fabrics. For the enhancement of synthesis efficiency, the effect of cathodic cage lid thickness is also investigated. The samples are assessed by using scanning electron microscopy, elemental dispersive spectros-copy, and X‐ray photoelectron spectroscopy. It is found that using cathodic cage plasma deposition, fabrics can be successfully synthesized by the copper oxide with comparatively small treatment time, cost‐effectively, and environmentally friendly. Interestingly, cathodic cage plasma treatment is already proved to be working effec- tively on industrial scale; thus, it is predicted to be of noteworthy importance for fab- rics processing on large‐scale garments manufacturing and hospitals.
Surface modification of tool steel by cathodic cage TiN deposition
(Taylor and Francis, 2019-09-11) Feitor, Michelle Cequeira; Barbosa, M. G. C.; Viana, Bartolomeu C.; Santos, F. E. P.; Fernandes, Fernanda de Melo; Costa, Thércio Henrique de Carvalho; Naeem, Muhammad Salman; Sousa, R. R. M.
The aim of this work is to investigate the effect of titanium nitride coating for various treatment times (0.5–4 h) by cathodic cage plasma deposition (CCPD) on surface properties of AISI D6 tool steel. The obtained results depict micrometric-sized TiN film deposition under all processing condition with improved surface hardness and corrosion resistance. Raman and EDS analysis are used to calculate N/Ti ratios for stoichiometric calculations of samples. This study depicts that the surface properties of tool steel can be effectively improved by TiN film deposition using CCPD, with low processing time, low processing temperature and better uniformity, as compared to conventional techniques. Additionally, the problems associated with the conventional TiN films such as pores and voids are eliminated. This technique is compatible with industrial-scale applications, and thus results from this study are expected to be beneficial for the surface engineering industry
Study of High-Density Polyethylene (HDPE) kinetics modification treated by Dielectric Barrier Discharge (DBD) plasma
(MDPI, 2020-10-21) Feitor, Michelle Cequeira; Medeiros Neto, João Freire de; Souza, Ivan Alves de; Targino, Talita Galvão; Diniz, Gutembergy Ferreira; Libório, Maxwell Santana; Sousa, Rômulo Ribeiro Magalhães; Costa, Thércio Henrique de Carvalho
In this work, the plasma was used in the dielectric barrier discharge (DBD) technique for modifying the high-density polyethylene (HDPE) surface. The treatments were performed via argon or oxygen, for 10 min, at a frequency of 820 Hz, voltage of 20 kV, 2 mm distance between electrodes, and atmospheric pressure. The efficiency of the plasma was determined through the triple Langmuir probe to check if it had enough energy to promote chemical changes on the material surface. Physicochemical changes were diagnosed through surface characterization techniques such as contact angle, attenuated total reflection to Fourier transform infrared spectroscopy (ATR-FTIR), X-ray excited photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Plasma electronics temperature showed that it has enough energy to break or form chemical bonds on the material surface, impacting its wettability directly. The wettability test was performed before and after treatment through the sessile drop, using distilled water, glycerin, and dimethylformamide, to the profile of surface tensions by the Fowkes method, analyzing the contact angle variation. ATR-FTIR and XPS analyses showed that groups and bonds were altered or generated on the surface when compared with the untreated sample. The AFM showed a change in roughness, and this directly affected the increase of wettability
Optical-electrical properties and thickness analysis of TiO2 thin films obtained by magnetron sputtering
(Springer Science and Business Media LLC, 2020-09-23) Feitor, Michelle Cerqueira; S. Sobrinho, V. S.; Miranda Neto, José Queiroz de; Lima, L. L. F.; Souza, Iedo A; Libório, Maxwell Santana; Queiroz, José César Augusto de; Sousa, Rômulo Ribeiro Magalhães de; Almeida, Érika Oliveira de; Costa, Thércio Henrique de Carvalho
The study of thin films with properties that meet specific needs and improve people’s quality of life has been the focus of many researchers. However, knowing and controlling the production techniques of these films have been a challenge for the industry of optical-electronic devices, functional coatings, and energy conservation. The thickness of thin films is a parameter that influences the optical and electrical characteristics of these materials, thus being one of the most important information in the plasma deposition process. Because of the need for precision in measuring the thickness of thin transparent films, this work proposes to evaluate the Swanepoel methods (envelope) and the PUMA, computational method, from optical transmittance curves and compare them with the measurements directly made by microscopy. Scanning electronics for thin films of TiO2 deposited by magnetron sputtering in different conditions. The results of this study showed that the PUMA method is capable of calculating film thicknesses of a few hundred nanometers and with few interference fringes. The PUMA method showed convergence with high precision for films produced with 30 and 60 min of treatment and a difference of 17% for films with 120 min of deposition concerning the measurements made by microscopy
Structural and optical properties of ZnO: Al thin films produced by magnetron sputtering with different oxygen flow: an experimental and Ab initio study
(Wiley, 2020-08-05) Feitor, Michelle Cerqueira; Queiroz, José César Augusto de; Azevedo Filho, João Batista de; Libório, Maxwell Santana; Santos, Edson José da Costa; Souto, Ulisses Borges; Sousa, Rômulo Ribeiro Magalhães de; Costa, Thércio Henrique de Carvalho
This work addresses, in an experimental and theoretical way, the influence of different oxygen pressure values on the physical and electronic properties of thin conductive and transparent oxide films of Al-doped ZnO, with different thicknesses. A series of characterization techniques, which include X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), optical spectrophotometry, and Hall measurements are conducted. All films have a hexagonal wurtzite structure characteristic of ZnO, with preferential orientation along the plane (002) and transmittance values, in the visible range, greater than 80%. The increase in flow oxygen up to 25% provides an increase in the film’s density resulting in a decrease in electrical resistivity from 9.58 103 Ω cm to 8.14 103 Ω cm. The ab initio calculations allow to observe the distortions in the microstructure of the films attributed to the presence of impurities and to obtain the values of the total and formation energies. The values of the Mulliken population and chemical bond length are notoriously influenced by the concentration of oxygen in the atmosphere. The displacement of the valence band (VB) and the Fermi level, together with the decrease in the gap energy, reinforce the influence of oxygen gas on the electronic structure of the films
Estudo de nitretação a plasma e tratamento duplex em brocas de aço rápido
(FapUNIFESP (SciELO), 2020) Feitor, Michelle Cequeira; Serra, Petteson Linniker Carvalho; Barros Neto, João Rodrigues de; Furtado, André Sales Aguiar; Sampaio, Weslley Rick Viana; Costa, Thercio Henrique de Carvalho; Sousa, Rômulo Ribeiro Magalhães de
A nitretação a plasma é realizada em ferramentas de aços rápidos para aumentar a resistência ao desgaste da aresta de corte e reduzir a tendência do material usinado em aderir na ferramenta. O objetivo do presente trabalho é estudar a viabilidade da nitretação a plasma e do tratamento duplex em brocas de aço rápidoanalisnado o desgaste de brocas de aço rápido M2 submetidas a diferentes parâmetros de nitretação a plasma e deposição de filme de nitreto de titânio (TiN). As brocas passaram primeiro pelo tratamento de nitretação com, variando-se a temperatura em 350°C, 400°C, 450°C, 500oC e 550oC, enquanto o tratamento duplex foi dividido em nitretação convencional a 500 °C seguido de deposição de um filme fino de TiN aplicado pela técnica de deposição a plasma com gaiola catódica à temperatura de 400oC e 500 °C. As brocas nitretadas a 400°C ainda foram submetidas ao processo de deposição de um filme de TiN. Todas as brocas foram caracterizadas por microdureza Vickers e foram ensaiadas em centro de usinagem CNC, onde o corpo de prova era de aço AISI 4340. Foi realizada uma análise de desempenho entre os diferentes tratamentos, onde chegou à conclusão que o tratamento que resultou melhor desempenho na usinagem foi o tratamento de nitretação a 450°C. A camada nitretada das brocas foi analisada por perfil de microdureza, Microscopia Eletrônica de Varredura, porém observou-se que o valor de microdureza aumenta com o tempo de tratamento, e que a deposição do filme de TiN teve baixa relevância no desempenho da broca
Application of nitriding and duplex treatment on steel drills-HSS
(JMEST, 2020-04) Feitor, Michelle Cequeira; Serra, Petteson Linniker Carvalho; Sousa, Rômulo Ribeiro Magalhães de; Barros Neto, João Rodrigues de; Libório, Maxwell Santana; Costa, Thércio Henrique de Carvalho
The present study aims to evaluate the application of plasma nitriding (at temperatures of 450° and 500°C) and duplex treatment (conventional nitriding followed by TiN deposition, using the cathodic cage deposition technique). Samples were characterized by Vickers Microhardness Test, Scanning Electron Microscopy-SEM, and Energy Dispersion Spectroscopy-EDS. Drill performance was evaluated after machining SAE1045 steel specimens, using flank wear and hole diameter measurements. The performance test pointed to the viability of the treatment at 450°C, whose treated drill had a longer life than in the untreated drill, in addition to meeting the dimensional quality in all holes. In contrast, the other tools, nitrided at 500°C and submitted to the duplex treatment, they presented performance below the expected, not showing viability for application in these conditions. Additionally, it was observed the existence of a thermal gradient formed during the treatment
Surface modification of PET fabric by plasma pre-treatment for long-lasting permethrin deposition
(Wiley, 2020-05-18) Feitor, Michelle Cequeira; Badaro, Adair Divino da Silva; Libório, Maxwell Santana; Souza, Flaviane camara de; Sousa, Rômulo Ribeiro Magalhães; Santos, Rayane Saory Medeiros dos; Costa, Thércio Henrique de Carvalho; Naeem, Muhammad; Iqba, Javed
The mosquito-transmitted diseases are of serious concern and are affecting several millions of peoples worldwide. Instead of medication afterward the disease initiated, self-protection against the mosquito's is preferable, specifically in endemic areas. For this purpose, the permethrin coated clothing is a suitable choice to avoid mosquitos' bites. Unfortunately, the permethrin coating on fabrics is not long-lasting, and its laundering resistance is very low on hydrophobic fabric. In this study, the effect of plasma surface modification of PET fabric on the adhesion of permethrin and its laundering resistance are evaluated. The plasma processing is carried out in nitrogen, oxygen, and nitrogen–oxygen mixture plasma. The samples are analyzed using Fourier Transform Infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscope and chromatography. The results show that the oxygen plasma pre-treated samples exhibit the higher residual contents of permethrin after 60 wash cycles as compared with other gasses. Without plasma pre-treatment, the 95% loss, whereas the sample with oxygen plasma pre-treatment shows that only 22% loss of initial concentration of permethrin occurs after washing. This study shows that plasma pre-treatment is valuable to improve the absorption of permethrin in PET and its laundering-resistance. As plasma treatment is a cost-effective technique, it needs less processing time and eco-friendly, thus it is a great choice to deposit long-lasting permethrin coating by plasma pre-treatment, instead of conventional binding agents. Remarkably, the plasma treatment technique is a well-established and industrially acceptable technique, thus expected to be of noteworthy importance for insecticide garments manufacturers
Structural analysis of kevlar fabric treated with oxygen plasma
(Index Copernicus, 2020-06-30) Feitor, Michelle Cequeira; Targino, Talita Galvão; Cunha, Rayane Dantas da; Medeiros Neto, João Freire de; Cunha, Ricardo Alex Dantas da; Costa, Thércio Henrique de Carvalho
The purpose of this work was to study the effects of low-pressure oxygen plasma treatment on the surface characteristics of kevlar fabric. For comparison purposes, samples treated with oxygenated plasma were prepared and characterised under different experimental conditions, i.e. a treatment time variation of 10, 30 and 60 minutes under a constant pressure of 4 mBar, using a pulsed current source. We analysed the effects of chemical and physical changes to the surface of the material aiming at improved hydrophilicity attributed to the formation of roughness on the surface of fibres, thus obtaining optimal parameters for future works. Changes in the chemical composition of the surface as well as in the superficial roughness of fibres before and after treatment were determined by FTIR, TGA, XRD and wettability testing. SEM was used as a complementary technique to monitor the changes triggered by the procedures using oxygen plasma
Triple langmuir probe, optical emission spectroscopy and lissajous figures for diagnosis of plasma produced by dielectric barrier discharge of parallel plates in atmospheric pressure
(IOS Press, 2020-06-08) Feitor, Michelle Cequeira; Souza, Ivan Alves de; Medeiros Neto, João Freire de; Nascimento, Igor Oliveira; Matamoros, Efrain Pantaleon; Fernandes, Fernanda Melo; Sousa, Rômulo Ribeiro Magalhães; Costa, Thércio Henrique de Carvalho
This work aimed to characterize a Dielectric Barrier Discharge (DBD) plasma equipment through optical and electrical measurements, seeking to obtain a greater knowledge of the plasma production process and how it behaves through the adopted parameters, such as frequency and voltage applied between electrodes, at a fixed distance of 1.7 mm. In order to measure them, three different characterization techniques were applied. The first method was the Lissajous figures, a technique quite effective for a complete electrical characterization of DBD equipment. The second technique used was the Optical Emission Spectroscopy, a tool used for the diagnosis of plasma, being it possible to identify the excited species produced in discharge in diffuse and filamentary regime in the plasma. And finally, the triple Langmuir probe technique was used to obtain the electron temperature and electron density. Based on this study, it was possible to identify the equipment efficiency in different regimes. The electron temperature measurement for both systems analyzed were 27.96 eV and 20.69 eV to the filamentary and diffuse regimes, respectively. The density of electrons number to these regimes were 1.09 × 1021m−3 and 1.56 × 1021m−3
Avaliação experimental da sensibilidade do biodiesel B5 em motores diesel utilizado em frotas de ônibus urbano e interurbano
(Instituto Federal do Rio Grande do Norte - IFRN, 2012) Oliveira Filho, Manuel Fernandes; Farias, Aline Cristine Mendes de; Barbosa, Cleiton Rubens Formiga; Medeiros, João Telésforo Nóbrega de
O estudo objetiva investigar a consolidação do uso do biodiesel em motores de duas frotas de ônibus, uma urbana e uma interurbana. Entende-se serem necessários estudos para se observar tecnologicamente se o uso do biodiesel apresenta problemas quanto ao desgaste das peças diretamente envolvidas com seu uso e também observar as flutuações, para mais ou para menos, do consumo específico desse combustível. O diesel fóssil – tipo D e Biodiesel B5 foram analisados analiticamente, investigando-se também o teor de enxofre presente. Duas frotas de ônibus urbana e interurbana possuem 41 e 13 veículos, respectivamente. Foram analisadas as planilhas de cada veículo no período de três anos (2008 a 2010) e entrevistados os responsáveis pela manutenção e condução da frota para observar os relatos dos mesmos quanto aos aspectos resultantes da substituição do óleo diesel pelo B5. Segundo uma avaliação do consumo de combustível, houve um aumento não-linear (≈ 5 %) quando da substituição do diesel pelo biodiesel B5, mas não foi observada qualquer manutenção adicional relacionada com a sua utilização; todavia foi compensado pela redução de emissões de compostos químicos de dióxido de nitrogênio e teor de enxofre, como medido por Fernandes (2011). Além disso, a funcionalidade e a vida residual em serviço dos ônibus utilizando misturas diesel são discutidos
Novel antibacterial silver coating on PET fabric assisted with hollow-cathode glow discharge
(Wiley, 2020-07-30) Nascimento, Rubens Maribondo do; Naeem, Muhammad; Felipe, M. B. M. C.; Medeiros, Silvia Regina Batistuzzo de; Costa, Thércio Henrique de Carvalho; Libório, Maxwell Santana; Alves Júnior, Clodomiro; Nascimento, Igor Oliveira; Sousa, R. R. M.; Feitor, Michelle Cequeira
The silver-coated fabrics are of much importance because of their outstanding antibacterial features and are useable in several medical and hygienic applications. The silver deposition on fabrics by conventional techniques is not feasible because of their high processing cost, long processing duration, complex equipment, and multiple steps processing (nanoparticle synthesis and subsequent deposition on fabrics). In this novel study, the antibacterial silver coating is deposited by using a hollow cathode discharge (HCD) capable of generating high-density plasma, and thus it exhibits high-efficiency processing. The silver is deposited on woven and non-woven PET fabrics for various treatment times (10-60 minutes), and their antibacterial performance against E. coli and S. aureus bacterial is tested. The XRD results verified the deposition of silver with (111) preferred orientation, while SEM analysis depicted the uniform/ homogeneous deposition of silver particles. The interfacial free energy of adhesion depicts that after the silver deposition on both fabrics, the surface is actively unfavorable for bacterial adhesion. The antibacterial test revealed that the silver-coated woven and non-woven PET fabrics exhibit exceptional antibacterial activity against E. coli and S. aureus bacteria. As the HCD technique is relatively cost-effective, no need for specific sputtering targets, eco-friendly, and require single-step processing for silver deposition. Thus the results are expected to be of remarkable importance to prepare silver-coated antibacterial fabrics useable in hospitals and other appropriate applications
Avaliação dos processos de fratura em filmes finos através da simulação de ensaios de indentação com penetradores esféricos
(Revista Matéria, 2019) Chaves Filho, Ozias Ferreira; Dias, Avelino Manuel da Silva; https://orcid.org/0000-0001-8974-5137; http://lattes.cnpq.br/1142442322601442; http://lattes.cnpq.br/1554836525880222
Recentes trabalhos propõem a utilização dos ensaios de indentação como uma ferramenta capaz de avaliar características mecânicas de filmes finos, assim como avaliar possíveis falhas em sistemas que conjugam filmes de alta dureza depositados em substratos metálicos em solicitações tribológicas. Entretanto, a implementação da técnica de indentação para a avaliação do comportamento destes sistemas filme/substrato e os seus resultados, continuam ocasionando dúvidas no meio científico. Em função destas incertezas na análise do ensaio de indentação, o uso da análise numérica capaz de avaliar os campos de tensões e de deformações durante o ciclo de indentação pode auxiliar em uma interpretação mais segura deste ensaio. Por isso, este trabalho tem como objetivo utilizar o Método dos Elementos Finitos (MEF) para simular ensaios de indentação em um filme de Nitreto de Cromo e Alumínio (CrAlN) de alta dureza depositado em um substrato de aço carbono. Foram usados dois diferentes modelos de danos para avaliar os processos de fratura que ocorrem nestes ensaios de indentação. O primeiro foi o modelo de trinca difusa e o segundo foi o modelo de delaminação, ambos presentes no software comercial de elementos finitos MARC™. Os processos de fratura observados nestas simulações foram comparados com outros resultados apresentados na literatura especializada. Por fim, o uso concomitantemente dos dois modelos de danos foi uma nova abordagem para o estudo de falhas nos ensaios de indentação em filmes finos.
Experimental-numerical technique to evaluate the thickness of tin thin film
(Materials Research, 2019) Dias, Avelino Manuel da Silva; Silva, Everton Carneiro da; Libório, Maxwell Santana
In this study, the numerical analysis of instrumented indentation testing was combined with the experimental procedure to evaluate the mechanical properties and thickness of a titanium nitride (TiN) film deposited on titanium substrate (Ti) by plasma processing. TiN film thickness is an important parameter for the surface treatment industry. In numerical analysis, the finite elements method (FEM) was applied using Marc™ commercial software. Initially, the mechanical properties of the film and substrate were determined using a numerical-experimental methodology, combining the results of indentation testing with a Berkovich indenter and the same numerical simulation for both the film and substrate. Next, the behavior of instrumented Vickers hardness as a function of maximum indenter penetration depth (hmax) was compared with the numerical results of this hardness as a function of the ratio between penetration depth and film thickness (hmax/t). Both curves were fitted using power law equations, which calculated film thickness applying a new convergence algorithm. Finally, it also was shown that the film thickness obtained agrees with the experimental range reported in the literature.
Determination of film thickness through simulation of vickers hardness testing
(Materials Research, 2017-05) Libório, Maxwell Santana; Dias, Avelino Manuel da Silva; Souza, Roberto Martins
In recent decades, changes in the surface properties of materials have been used to improve their tribology characteristics. However, this improvement depends on the process, treatment time and, essentially, the thickness of this surface film layer. Physical vapor deposition (PVD) has been used to increase the surface hardness of metallic materials. The aim of the present study was to propose a numerical-experimental method to assess the thickness (l) of films deposited by PVD. To reach this objective, Vickers experimental hardness data (HV) assays were combined with numerical simulation to study the behavior of this property as a function of maximum penetration depth of the indenter (hmax) into the film/substrate conjugate. A strategy was developed to combine the numerical results of the H x hmax/l curve with Vickers experimental hardness data (HV). This methodology was applied to a TiN-coated M2 tool steel conjugate. The mechanical properties of the studied materials were also determined. The thickness results calculated for this conjugate were compatible with their experimental data.
Numerical analyses of timber columns reinforced by particulate composite material
(Open Construction and Building Technology Journal, 2016) Carvalho, André Luís Ceravolo de; Leila, Felipe Moretti; Dias, Avelino Manuel da Silva; Christoforo, André Luis; Silva, Diogo Aparecido Lopes; Silveira, Márcio Eduardo; Lahr, Francisco Antonio Rocco
Beams are structural elements commonly used in structure for construction designs. Usually wood is applied as structural elements and its use is very important because it is a material of renewable source, low density and satisfactory mechanical performance. When the wood surface is not properly treated, the structure can be destroyed not only by environmental conditions but also the attack of insects, compromising the structural design. This research presents the use of a particulate composite material of epoxy resin reinforced with white Portland cement in order to be applied as repair in timber columns. The mechanical performance of this material is essentially numerical, based on the Finite Element Method. The wood used in the simulation was the Eucalyptus grandis. The elastic properties were obtained from the specialist literature in the field of timber structures. The results of numerical simulations in terms of tension and buckling loads, the inclusion of the composite in the damaged regions (for all dimensions of the defects studied) provided buckling load results significantly higher than the buckling load values for the conditions without composite, and near to the values of the buckling loads without defect, highlighting the good performance of the particulate composite material in the repair of timber columns.
The interface behavior analysis of thin film during ball indentation testing
(International Journal of Materials Engineering, 2016) Dias, Avelino Manuel da Silva; Silva, Everton Carneiro da
The search for improved tribology properties in materials contributes to the development of processes that extend the useful life of components and their applications in increasingly severe environments. In this respect, thin ceramic films have been used to enhance the properties of components that operate under these conditions. However, expensive experimental assays are needed to assess the behavior of these films and system compounds by films and substrates. These experimental analyses are also destructive, requiring the use of sophisticated equipment and specialized hand tools. On the other hand, with advances in computational mechanics, the application of numerical analysis to solve numerous technological problems has become increasingly common, owing to its low operational costs. This study aims to simulate indentation testing with a spherical penetrator in systems composed of thin CrAlN ceramic film deposited on AISI 4140 metallic substrate using a Finite Element commercial code. The main objective of this study was to evaluate the field behavior of stresses in the contact region of the indenter with the sample and on the film-substrate interface.

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