The oil and gas industry faces constant problems with internal corrosion in pipelines and the integrity of structures and pipes. In these environments, the presence of carbon dioxide (CO2) acts as a contaminant that intensifies corrosive processes, a phenomenon known as sweet corrosion. This type of corrosion occurs when dissolved CO2 reacts with water to form carbonic acid, which contributes to lowering the pH and increasing the aggressiveness of the environment. A characteristic aspect of this mechanism is the formation of iron carbonate (FeCO3), which can act as a protective barrier, reducing the corrosion rate. However, corrosion in CO2 environments can manifest itself in different ways, mainly as generalized corrosion and localized corrosion. Generalized corrosion occurs uniformly, resulting in the continuous loss of material, while localized corrosion is more severe and unpredictable, concentrating in specific areas and forming pitting. Both mechanisms are affected by flow, as local turbulence can cause rapid variations in wall shear and turbulent kinetic energy, which influences the mass transfer process and, consequently, the precipitation and adhesion of FeCO3 films. This study evaluated the behavior of API X65 carbon steel under static conditions, varying parameters such as temperature, CO2 pressure and acetic acid concentration, by means of autoclave immersion tests. The most aggressive condition (60 °C temperature, 10 bar CO2 pressure, 60000 ppm NaCl and 1000 ppm HAc) was also evaluated in dynamic tests using a rotating cage (RC) at 800 rpm. To assess the effect of flow, artificial defects were machined into the RC specimens. The results indicated that the different experimental conditions caused variations in the morphology and adhesion of the iron carbonate (FeCO3) films, directly affecting the corrosion rate of the carbon steel. In addition, it was observed that in the dynamic condition, the generalized corrosion rate increased sharply and the emergence of the localized corrosion mechanism was observed. In this condition, the detachment of the FeCO3 film and an increase in the size of the artificial defects were identified, possibly due to the combined effect of the more aggressive environment and the flow over the surface of the specimen.

A manufatura aditiva tem ganhado forte espaço no setor produtivo atualmente devido a flexibilidade que apresenta em relação a fabricação de produtos complexos. Pode-se dizer que a manufatura aditiva é uma nova tecnologia que permite a criação de objetos a partir de um modelo virtual gerado em ferramentas CAD. Desta forma, os itens são criados a partir da adição de materiais em camadas e esses materiais podem ser filamentos ou pós de polímeros ou metais. O processo denominado MADA que consiste na Manufatura Aditiva por Deposição a Arco é um processo que envolve deposição direta de material, utilizando matéria-prima na forma de arame e o arco elétrico como fonte de energia. Esta tecnologia foi proposta e vem sendo, algum tempo, estudada por pesquisadores, mas ganhou maior notoriedade com a popularização da impressão 3D e com a indústria 4.0. Neste trabalho o processo MADA foi estudado utilizando-se o processo MIG/MAG com o objetivo de construir corpos de prova com diferentes velocidades de arame e velocidades de deposição. A rugosidade das paredes produzidas foi analisada como resposta. Os resultados demonstram que tanto a velocidade de deposição como a velocidade de deslocamento exercem forte influência não apenas na rugosidade como também na estrutura da parede formada.

The present study aimed to analyze the oxidation behavior of refractory high-entropy alloys (RHEAs) in the Al-Cr-Ta-Ti-Mo system, with the goal of developing materials with greater resistance to high-temperature environments. Two compositions were investigated: an equiatomic alloy AlCrMoTaTi and a non-equiatomic alloy 13Al19Cr20Mo31Ta17Ti, referred to as alloy A and alloy B, respectively, through isothermal tests at 1000 °C for 20, 100, and 300 hours. During the tests, the mass variation of the samples was monitored, and the formed oxide layers were analyzed using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD). It was observed that elements with higher melting points, such as Ta and Mo, concentrated in dendritic regions, while Al and Ti, with lower melting points, accumulated in interdendritic regions. Regarding the oxidation results, alloy A showed less mass gain and formed a thinner, more uniform, and adherent oxide layer, whereas alloy B presented a thicker and apparently more irregular oxide layer, which explains the greater mass gain observed in this composition. The results also indicated the predominant formation of TiO₂ and CrTaO₄ oxides, and possibly Al₂O₃ and Cr₂O₃. Overall, it was clear that the chemical composition and internal structure of the alloys are crucial factors in determining oxidation resistance. Alloy A, with its more stable oxide layer, proved to be more promising for applications in high-temperature environments. It is suggested to explore new alloy compositions, test even more severe conditions (such as temperatures above 1000 °C and longer exposure times), and assess the performance of these alloys in different atmospheres, closer to those found in industrial settings.

Plasma cutting is widely used in industry to process conductive materials, such as SAE 1020 steel, due to its versatility in complex cutting, cost-effectiveness, and efficiency. However, the surface quality of the cut varies depending on operational settings, influencing technical applications and productivity. Research in this area not only contributes to these improvements but also helps standardise operations in CNC systems, increasing process efficiency. Therefore, this study aimed to evaluate the surface quality of plasma cutting on SAE 1020 carbon steel, considering two directions of coordinate table movement (longitudinal and transverse) and the influence of parameters such as speed, current, and nozzle-to-material distance. The experiments were performed with an ESAB Handyplasma 45i hand plasma source coupled to a CNC coordinate motion system. The nozzle movement speed, source current, and nozzle height relative to the material were varied. Surface roughness was measured with a Mitutoyo SJ-400 roughness meter in the longitudinal (X-axis) and transverse (Y-axis) directions. The response surface method (RSM) and analysis of variance (ANOVA) were used as analytical techniques to define the interaction between the parameters and identify the optimal conditions. The results show that lower roughness values were obtained with reduced travel speeds (heat flux optimisation), higher currents (generating greater arc stability), and a shorter nozzle-to-material distance (improved precision). Conversely, the transverse (X-axis) direction presented lower average roughness compared to the longitudinal (Y-axis) direction. The study shows that adjustments in speed, current, and nozzle height are decisive for the quality of plasma cutting on SAE 1020 steel. The combination of low speed, high current, and a shorter nozzle distance minimises roughness, favouring industrial applications that require precision. The study of kerf dimension and inclination demonstrated that higher current values and lower travel speeds provide the best combinations for improving the quality of the cut region.

The primary objective of this work — to develop and characterise pyramidal truss structures
using bamboo struts and 3D-printed nodes — was fully achieved, successfully balancing
sustainability, low weight, and adequate mechanical performance for engineering applications.
The study validated the potential of bamboo as a structural element, which demonstrated high
tensile strength (≈126 MPa), ductile behaviour (≈2.55% strain), and competitive compressive
properties. The feasibility of the bamboo-to-node interface using PLA was established, with the
castor oil resin adhesive proving satisfactory and crucial for structural integrity, achieving an
average pull-out force of ≈115 N. The comparative analysis between the structures with short
struts (P30) and long struts (P40) revealed a clear trade-off between mechanical and physical
properties. The P30 structures consistently showed the best overall mechanical performance,
with higher strength and toughness (≈7 kJ/m3 ) in the unit cells, and the TR-P30 beams
sustained the highest maximum flexural load (≈122 N). Conversely, the P40 structures excelled
in mass optimisation, achieving the lowest equivalent density (0.045 g/cm3 in the beam),
representing a mass reduction of approximately 43%, in addition to exhibiting more stable post-
peak behaviour. In summary, the work validates the concept of hybrid bamboo/additive
manufacturing trusses, highlighted by their ability to combine low weight with competitive
mechanical performance. The results demonstrate that this architecture is a promising
alternative for light and sustainable engineering, with potential applications in sandwich panels
and space frames.

Currently, machining has been the process of metal-mechanical transformation of great importance and use, demanding several developments of technologies that aim at better efficiency of operations. As technology advances, consumers demand products with better cost/benefit, which in machining, impact on cutting tools with longer life, or in reducing operating costs such as the use of cutting fluids. However, in some cases, special needs outweigh these requirements, such as the presence of cutting oil in products from the oil/gas sector, making it important to search for techniques that can replace emulsions and increase tool life. In this sense, this work analyzed the use of the air-cooled system in the internal turning of a product from the oil and gas sector, compared with the use of emulsion and dry cutting. For this, the responses of forces in the cut, roughness and cylindricity in cutting conditions similar to those used in the industrial environment were evaluated. The results showed that, although the use of emulsion provides better responses, in some cases, there is improvement in the cutting forces with the replacement of the air cooled system. But, there was a worsening in the geometric deviation responses, roughness and cylindricity, due to the air flow.

Superalloys are widely used in high temperature applications and harsh environments. Inconel 625 is one of the most applied superalloys due to its high resistance to oxidation and mechanical properties. In this work, the microstructure and oxidation mechanism at 900 and 1000 °C of the Inconel 625 superalloy manufactured by the directed energy deposition (DED) and conventionally manufactured (CNV) additive manufacturing process were studied. The samples were cyclically oxidized for up to 100 cycles and isothermally oxidized at 900 °C for 200 hours and at 1000 °C for 100h. Each thermal cycle consisted of 60 minutes at the oxidation temperature and 10 minutes in which the samples were exposed to room temperature for cooling. To characterize the oxidized layers, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) analyzes were carried out. The microstructure of the DED samples alternated between fine equiaxed grains and columnar grains, with Nb and Mo segregations located in the dendritic and interdendritic regions. At 900 °C the oxidation rate was similar for both materials, both in the cyclic and isothermal tests, but was clearly higher for the DED material at 1000 °C in both tests. Inconel 625 (CNV and DED) showed detachment at 900 and 1000 oC in cyclic tests. The oxide layer was identified as predominantly Cr2O3 under all conditions, providing good resistance to oxidation. In addition, oxides such as NbCrO4 as well as NiCr2O4 were identified for the CNV and DED samples. In isothermal tests, the delta phase Ni3(Nb,Mo) was observed for the CNV and DED alloys at the grain boundaries at 900 °C and at the metal/oxide interface for both temperatures as a result of chromium depletion. Finally, Inconel 625 produced by DED showed lower resistance to oxidation, being related to the microstructure, the segregation and the open porosity observed in the samples produced by DED.

Sustainability is one goal for all industrial process nowadays. The great challenge is to have more and more cleaned and optimized processes. Considering the negative impact of mineral or vegetal coolant on the environment and operator health, the target of this study was to provide an alternative cooling method with cold air to replace the liquid coolant. In advanced process with high cutting speeds, the function of cooling the cutting region is much more important than lubrication. To analyze the differences between the cooling methods, tests were performed using vegetal coolant, as traditional method and cold air in two different conditions, with the air flow directed to the rake surface and also directing the air to the rake surface and flank surface. The temperatures, cutting forces and average surface roughness (Ra) were measured as responses and ANOVA was used as method of analysis. The preliminary results indicate that there are no significant differences in cutting forces and surface roughness, but the cold air didn’t have the same or better cooling efficiency. New tests including liquid nitrogen will be performed in an attempt to improve the cooling efficiency keeping in the way of clean cooling methods, mainly because the results for cutting forces and surface finishing were satisfactory.

The helical milling process has been explored in the production of holes for various industries,
standing out biomedical and aerospace. Due to the high precision required and the difficulty of
machining the titanium alloy Ti-6Al-4V, the cutting parameters need to be defined in order to obtain
acceptable levels of quality and precision for such applications. Helical milling, when compared to
conventional drilling, is recommended because it presents low levels of cutting forces and better
quality due to the kinematics of the process. In this work, the main objective was to study the helical
milling to obtain holes in the titanium alloy Ti-6Al-4V. For this purpose, a Box Behnken Design
(BBD) planning was used, enabling the obtaining of second-order regression models capable of
optimization, as a function of the cutting parameters of helical milling, being them, the axial and
tangential feeds per tooth and the cutting speed. The average roughness Ra, circularity (Ront) and
material removal rate (MRR) responses were evaluated. The models obtained for the Ra and Ront
analysis presented adjustments of 87.99% and 84.92% successively, corroborating a good
proportion of explanation of the data variability, having sufficient reliability for a greater
evaluation of the effects of the variables on the responses presented. Finally, for optimization, the
multiobjective optimization method by adaptive geometry estimation (AGE-MOEA) was used to
determine a set of Pareto optimal solutions for the finishing response and the material removal rate.
According to the optimization, to minimize roughness and circularity, it is necessary to adopt as
feeds: fza = 0.71 µm/tooth and fzt = 0.06 mm/tooth and a cutting speed: vc = 59.16 mm/min, while
for greater productivity, it is necessary: fza = 1.20 µm/tooth and fzt = 0.07 mm/tooth and a cutting
speed: vc = 59,16 mm/min. As analyzed through scanning electron microscopy (SEM) images, it
was possible to conclude that for low fza levels, combined with a low cutting speed, inferior surface
quality was observed due to the dragging and adhesion of removed material, as a consequence of
the difficulty in evacuating the chip.

Currently, austenitic stainless steels are produced in large quantities, possessing good mechanical properties, including high toughness and cold workability, with nickel as the primary phase stabilizer. For economic reasons, however, some alloys use manganese as a partial or total substitute for nickel, such as FeMnSiCrNi, which offer relatively low cost, good workability, and ease of processing. Nevertheless, at high temperatures, manganese preferentially reacts with oxygen rather than chromium, preventing the formation of a protective Cr2O3 layer; furthermore, Cr2O3 tends to volatilize at higher temperatures, thus compromising the alloy's oxidation resistance. In contrast to chromium oxide, alumina (Al2O3) is more stable under such conditions; however, the amount of aluminum required to form a protective layer would result in unacceptable mechanical properties. This study evaluated the effect of a coating obtained by pack aluminizing on the oxidation resistance of an FeMnSiCrNi alloy. Cyclic and isothermal oxidation tests were conducted at temperatures of 900 and 1000 °C. At 900 °C, the coating significantly improved the alloy’s oxidation resistance, delaying degradation due to spallation. In the isothermal regime, the aluminized samples showed no spallation; despite manganese diffusion the aluminized coating remained intact. At 1000 °C, however, both aluminized and non-aluminized samples presented loss of mass under both cyclic and isothermal conditions. Compared to other studies, although, the aluminized alloys oxidized at 900 °C achieved significantly better results, given that the tests were conducted under more severe conditions of regime and temperature.

.

EVALUATION OF LOCALIZED CORROSION AND FORMATION OF FeCO3 WITH THE PRESENCE OF FLOW IN DIFFERENT CONCETRATIONS OF SODIUM CHLORIDE

Composite materials can have excellent mechanical properties between the combination of materials and fiber orientation in order to produce optimized and specific structures for each application. When considering factors such as low cost, low density and the search for biodegradable materials, natural fibers and resins obtained from renewable sources has gained relevance in the production of composite structures. Thus, the present work aims to investigate, through a complete 2² factorial design, the effect of the matrix phase, epoxy resin or castor oil, and the reinforcement stage arrangement, unidirectional staple fibers or bidirectional fabric, on the physical and mechanical performance of polymer composites reinforced with jute staple fibers. The reinforcement phases jute staple fibers and bidirectional jute fabric were characterized by mechanical tensile test. The composite materials were characterized in tensile, bending, impact, apparent density, apparent porosity and water absorption tests. The mechanical behavior of composites reinforced with unidirectional staple fibers for three-point bending was investigated through numerical simulation with a nonlinear implicit and incremental formulation. The experimental study indicated that the use of castor oil as a matrix phase reduced the apparent density of the composites and increased the impact resistance. However, it also provided an increase in apparent porosity and water absorption, and reduced the flexural strength of the composites. The alteration of phase reinforcement in materials from bidirectional fabric to unidirectional staple fibers caused expressive increase in all mechanical properties. The averages of physical properties of apparent density, apparent porosity and water absorption were not statistically altered by changing the arrangement of cords. The composite made of epoxy resin and unidirectional staple jute fibers presented the best mechanical behavior in tensile and bending tests. Numerical simulations were well correlated with experimental tests for small displacements. The tensile modulus for the jute fiber obtained by numerical simulation was in line with the values found in the literature. The manufactured composite materials proved to be a sustainable and economical alternative for engineering applications, mainly those manufactured with unidirectional staple jute fibers, which exhibited satisfactory mechanical properties.

The employing the principle to drilling holes in metal is a more recent development. Friction drilling, also known as flow drilling or friction drilling, is an unconventional manufacturing process in which a tapered-tipped carbide rotating tool is pressed into a material, usually metallic. With the contact between tool and part, there is an increase in temperature, and consequently, a decrease in the resistance to deformation of the material due to its flow, thus causing the hole to be made. In this process, there is no chip formation, what occurs is the formation of a bushing due to the flow of the material. The bushing can be used, for example, as a fixing point by brazing or be threaded, serving as a connection point for screw fixings. With different possibilities of applications, the possibility of performing the drilling procedure by friction in different materials is also highlighted, among them, the material studied here is commercially pure titanium, known to be a promising material in applications in the naval and aeronautical industries, and for being considered one of the best biocompatible metallic materials. In this context, this work evaluates the geometric deformations caused in the height of the bushing and diameter of the hole formed in the process of drilling by friction. For that, the rotation speed and the feed were compared, both in dry and lubricated conditions.

Most composite materials are heterogeneous when observed microscopically. However, ordinary finite element analyses of composites do not consider the influence of phases on the mechanical behaviour of the material. This work evaluates different composites using a sequential multiscale methodology, which models each phase with a micromechanical computational analysis of the representative volume element (RVE) and brings the homogenised results to the macroscale. Three types of composites are made with epoxy matrix phase and are classified as silica particle-reinforced polymer (SPRP), carbon fibre-reinforced polymer, and carbon fibre silica particle- reinforced polymer or hybrid. RVE uses a 3D Finite Element (FE), and it is restricted with different boundary conditions. The macroscale represents the geometry of ASTM specimens fabricated for experimental testing with the FEM. A User Material subroutine (UMAT) reproduces the behaviour of micromechanical analyses at the higher scale. Experimental analysis characterise and validate numerical results. In particular, for the SPRP, the results were taken from literature. For fibrous composites, a hand layup method is performed considering the fibre volume fraction of 30%. In addition, the hybrid configuration considers 9wt% of the particles in relation to the total mass of the matrix. Tensile, compression, and in-plane shear tests are performed. Unidirectional laminates are characterised in the longitudinal (0º) and transverse (90º) directions for tensile and compression tests, while a 45º/-45º ply configuration is employed for the shear test. The results show good accuracy for elastic and inelastic responses when compared to experimental and numerical mechanical behaviours. This methodology can support future researches in the same field.

The search for materials with less environmental impact has driven mainly biodegradable and those derived from renewable sources. Biodegradable foams and resins derived from vegetable oils have been investigated and applied in different areas of engineering. Manufacturers stipulate the “ideal” ratio between polyol and prepolymer (a certain ratio taken as the best) associated with a range of applications. However, the various applications focus on the characterization of composites, that is, on the study of the proportions between the phases, but it does not provide purely characterization of the matrix phase. Knowledge about the physical and mechanical properties of matrices prepared with different proportions between polyol and prepolymer can help better understand the performance of the manufactured composite as well as the most appropriate indication of the proportions between the proportions of the adhesive for cases of requests and conditions in different application. This work describes the mechanical and physical properties of biodegradable castor-based foams composed of 2 polyols and 1 pre-polymer. Statistical planning design is used to identify the combined effect of polymeric components on mechanical and physical properties. Contour graphs are obtained, capable of describing the material properties according to the mass percentages of each component. The specimens are obtained through the reactive expansion of the constituents in only one direction, allowing them to obtain anisotropic properties. The results show that it is possible to obtain variations of up to 80% in the mechanical properties. The increase in P2 concentration leads to lower specific properties of the foam. P2 does not affect the final mechanical properties, but the foam density increases considerably. On the contrary, the P1 component increases the density along with the mechanical properties, while PP reduces the density and mechanical properties of the foams. Finally, mathematical models can optimise the mix of the components to achieve a particular performance. The transverse properties (perpendicular direction to the expansion) are higher than the longitudinal ones.

The growing exploitation of natural resources and their unconscious use by man
emphasizes a worldwide trend to develop sustainable and resistant materials, such as sandwich
panels. Recycling and reusing products reduce the need for raw material extraction, conserving
natural resources and eliminating environmental impacts. In addition, variations in core
geometry and materials are investigated to improve the final mechanical properties. This work
presents the development and characterisation of a sustainable sandwich panel of recycled
aluminium skins bonded to an arch-shaped core obtained from reused aluminium cans. A full
factorial design was performed to identify the effects of three factors: type of adhesive (two
epoxies and one polyurethane), the average thickness of the adhesive (0.8 and 1.5 mm), and
the orientation of core arches (aligned and alternated). The sandwich panels were tested under
a three-point bending test, from which the main flexural properties were obtained. The
properties were statistically verified using Analysis of Variance (ANOVA) and the Tukey test.
The results showed the feasibility of the proposed sustainable structure, in which more
satisfactory results of strength and stiffness were obtained for panels made with epoxy polymer
type C (Epoxy RenLam-M + HY951), greater average adhesive thickness (1.5 mm), and
alternate core orientation. The panels showed to be promising for secondary structural
applications, having low weight, cost and presenting an alternative route for the reuse of
components highly discarded in nature.

Superalloys are mainly used because of their exceptional properties, such as mechanical strength and oxidation resistance. The oxidative process is commonly observed in engineering applications and it is usually accentuated under conditions involving high temperatures. These alloys are often used in operations involving high temperatures and stresses, such as gas turbines. This makes the study of oxidation for superalloys relevant. The main objective of this work was to study the oxidation process in the MAR-M247 superalloy, followed by a complementary analysis of the conventional MAR-M246 and Nb-modified MAR-M246 superalloys. MAR-M247 superalloy was exposed to isothermal tests at 1.000 and 1.100 °C for up to 300 hours. This alloy has also been tested cyclically at 1.000 °C for up to 200 cycles and at 1100 °C for up to 219 cycles. The superalloys MAR-M246 (Ta) and MAR-M246 (Nb) were evaluated in relation to cyclic oxidation at 1.100 °C, for up to 219 cycles, in order to study the influence of the replacement of Ta by Nb. The oxidation kinetics and the characterization of the oxidation products were evaluated. The characterization of the samples was performed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and optical microscopy (OM). Some of the conclusions obtained in this work are: NiO, Al2O3, TiO2, Co3O4, NiCr2O4 e CoCr2O4 are common oxidation products for MAR-M247; the MAR-M247 alloy proved to be the most resistant to the oxidation process, followed by MAR-M246 and MAR-M246 (Nb), the last one exhibited the lowest resistance among the alloys.

Internal corrosion is one of the main failure mechanisms in oil and gas (O&G) pipelines. In order to protect the integrity of the pipelines, several researchers are dedicated to reproducing in the laboratory the environments to which the pipelines in the O&G sector are constantly exposed. Currently, the rotating cage (GR) of the ASTM G170-06 standard is one of the most used methodologies for testing the vulnerability of materials in corrosive media or the efficiency of corrosion inhibitors under turbulent flow regimes. However, the GR is a very conservative methodology and there are several factors responsible for this conservatism, for example, the non-uniformity in the loss of mass in the specimens. The objective of the present study is to evaluate, through a computational study, changes in the geometric attributes of the GR of the ASTM G170-06 standard, in order to verify the possibility of obtaining a more uniform distribution of the shear stresses in the specimens.

The growing demand for materials that promote sustainable development and the preservation of the environment make natural fibres stand out in the development of composite materials. In order to improve the properties of these materials, much research has focused on several natural fibres, manufacturing techniques and process parameters. This work investigates the mechanical performance of papaya fibre-reinforced polymeric composites based on epoxy and castor-oil biopolymer. Design of Experiment (DoE) and analysis of variance (ANOVA) techniques are used to analyse the influence of papaya fibre type (inner and intermediate), fibre morphology (without holes, with alternating or coincident holes, and randomly-oriented ground fibres) and fibre orientation (longitudinally or transversally oriented fibres relative to the load). Papaya fibres are also characterised. The specimens are manufactured by hand lay-up, followed by cold uniaxial compaction, and characterized by tensile, flexural and impact drop tower tests. For epoxy-papaya composites, longitudinally oriented provide superior mechanical properties relative to transversely oriented fibres. Composites with longitudinally oriented fibres, without holes, exhibit better mechanical properties. Randomly-oriented short fibres provide much lower reinforcing levels compared to the other morphologies. The Tukey’s test reveals that the morphologies, composites without holes and with alternating holes, are statistically equivalent for traction and flexion properties. In the drop tower test, in contrast, short random fibres provide greater energy absorption. The density of papaya fibres, among the lowest in the plant kingdom, varies according to the fibre layer.

Studies to improve the understanding of machining processes are important for efficient production. The performance of these processes depends on several factors, operational parameters, and other variables. Among the various processes, grinding stands out for its versatility and high dimensional accuracy. Although widely used, it still has some shortcomings, as chip removal is more complex when compared to conventional machining processes with defined geometry tools. In this context, this work aimed to monitor the electrical power of the main motor of the machine, correlating with the dimensional deviation and surface roughness in Ra and Rz parameters of AISI H13 steel in the process of tangential plane grinding process. The input variables tested were working penetration at three levels (0.015; 0.03 and 0.05 mm) and workpiece speed at two levels (10 and 22 m/min). A vitrified aluminium oxide wheel in three conditions was used, being in worn condition, and dressed with two dressing overlap ratios (1 and 5) correlating the dressing parameters and the wheel topography. The results showed that the increase of the working penetration caused an increase in the power signals, the dimensional deviations, and the surface roughness for the three conditions of the grinding wheel. Increasing the workpiece speed also caused an increase in the power; however, regarding the dimensional deviation and surface roughness, the values obtained were lower. The worst results were presented for the conditions imposed on the wheel while worn. In contrast, when dressed, the same wheel had a substantial performance improvement. Higher electrical power values, lower-dimensional deviations, and lower surface roughness were observed significantly when increasing the dressing overlap ratio. The results showed that the electrical power signal was sensitive to variations of the input parameters analysed. Its relationship with possible dimensional deviations and surface roughness values may be able to analyse and diagnose distortions that affect the final quality of the ground parts.

Geopolymers are a materials class, conceived thru the aluminosilicate alkaline activation. Could be obtained by industrial residue calcination (fly ash, bottom ash, ground granulated blast furnace slag, etc.) or calcinated materials (metakaolin). Exhibiting low cost, great availability and good chemical and mechanical properties. Cheap, with good workability and environment friendly materials have been a necessity in the construction industries. with this in mind this work aims on the development of a new mortar (constituted by diffrents weigth proportions), with better workability, mechanical and structural properties thru epoxy resin incorporation in the metakaolin based geopolymer. Were investigated the effects of 0, 15, 20 and 25% resin addiction by weight in relation to the base polymer in mortar with sand in 0:1, 1:1, 2:1 and 3:1 weight proportions by the base geopolymer or with resin content, in the mechanical properties 28 days after production, with 60‰initial cure. A 24 estatistcal planning was used. Were analyzed also the structural modification of the precursor and base polymer thru MEV and EDS. Even with both being significative and with interaction between them, the most influent factor in the process was sand percentage. All investigated response variables, had their properties changed with the resin percentage increase to 15, 20 and 25%. So in this work a superior substitute to CPT was found.

Biocompatible alloys are important for the biomedical industry as they offer alternatives in different treatments. The Ti-6Al-7Nb alloy has excellent mechanical properties and can be used in implants, which can be require holes. The helical milling, compared to drilling, is recommended because presenting low levels of cutting efforts, better finishing, lower temperatures in the cutting region, all this, as a consequence of the kinematics of the process. In this dissertation, the main objective was to study the process of helical milling to obtain holes in biocompatible titanium alloy. In this study, cental composite design was used, making it possible to obtain second-order regression models, which can be optimized, depending on the cutting parameters of helical milling, namely, cutting speed, axial feed per tooth and tangencial feed per tooth. Surface roughness responses were evaluated. Principal component analysis was used to allow the transformation of a set of original intercorrelated variables was enough to represent all the roughness responses. A second-order model for the transformed response was obtained. Finally, for optimization, the NSGA-II bi-objective evolutionaty optizimation method was used to determined a set of optimal Pareto solutions for the surface quality response and material removal rate (MRR). Therefore, according to the optimization, the best values to obtain the best surface quality parameters should be set at 𝑓𝑧𝑎 = 0,033 µm/tooth and 𝑓𝑧𝑡 = 3,65 µm/tooth. While for greater productivity the factors need to be defined at 𝑓𝑧𝑎 = 0,04 µm/tooth and 𝑓𝑧𝑡 = 2,99 µm/tooth. As analyzed the images of scanning eléctron microscopy (SEM) it was possible to conclude that the ploughing effect had na influence on the deterioration of the surface quality at low levels of feed.

Avaliação da resistência à corrosão na indústria química do revestimento com Nb₂O₅ aplicado por aspersão térmica.

Studies show that porous titanium alloys promote osteointegration at the implant-bone interface improving the mechanical stability. However, researches on bioactive coatings that induce the formation of new bone tissue on the surface of metal implants have been gaining prominence, being calcium phosphate (CaP) coatings of great potential. In this work, samples of Ti35Nb were produced by powder metallurgy and coated with calcium phosphate (CaP) by biomimetic method, for use in orthopedic or dental implants. High purity titanium and niobium powders were mixed and uniaxially compacted. For fabrication of macroporous samples, a pore former additive was added in the mixture (Ammonium Bicarbonate – AB). The sintering of samples was performed at 1300 ºC for 2 h in an ASTRO furnace under argon atmosphere. The samples underwent a chemicalthermal treatment for bioactivate the surface by means of the formation of a sodium titanate interlayer. Then, the samples were immersed in a simplified biomimetic solution with ionic CaP-forming composition, for periods of 14 and 21 days. The samples were characterized in terms of density and porosity, as well as chemical, physical and mechanical analyzes were performed by SEM / EDS, SEM / FEG, XRD, RAMAN, XPS, SEM / FIB, TEM, Profilometry and Ultra Microhardness. In general, the formation of micro and macroporous Ti-β alloys were observed. The deposited coatings were identified as biocompatible hydroxyapatite phase. According to the literature hydroxyapatite is the most desired phase for implants application because it presents chemical composition closer to the bone.

The use of composite materials has been growing in various industrial sectors. Sandwich panels are structural composites with high flexural rigidity and low weight, consisting of faces, core and adhesive. Honeycomb cores composed of circular or tubular cells have been shown to be superior to hexagonal cells in terms of energy absorption under deformation, flexural strength and structural rigidity. On the other hand, there is currently a great debate about the amount of solid waste generated by the population worldwide, mainly polymeric waste. In this context, the present work proposes the direct use of polyvinyl chloride (PVC) tubes for the manufacture of sandwich panels with ISO 1200 aluminum faces. It is investigated the effects of the outside diameter of the tube (20 and 32 mm), type of packing (cubic and orthotropic) and type of connection between tubes (with or without mechanical interlocking) on the physical and mechanical properties of panels subjected to three-point bending. The properties are evaluated statistically through Analysis of Variance (ANOVA). The panels with orthotropic packing, 32 mm tubes and without interlocking present a better mechanical performance in relation to other conditions. Interlocking is not an efficient strategy due to the large increase in the density of the structure. The viability of using PVC pipes to fabricate sandwich panels is shown in this study, being a sustainable and economical alternative use of these solid residues from civil construction.

The lubrication is an important parameter for the success or failure of a deep drawing operation. The formulation of traditional lubricants uses mineral oils, which are harmful to the operator's health and difficult to discard. Recent studies have proved the lubricating potential of vegetable oils in deep drawing, and seek for solid additives that can complement the properties of these base oils. The deep drawing of a composite material is highly applicable for the metal industry, meeting the multifunctional needs that steels cannot satisfy. The current work presents an experimental study using vegetable oils with silica micro particles in the deep drawing process of a composite in a sandwich arrangement, formed by a SAE 1006 steel blank, an electrolytic copper blank and a thin PVC inner layer. For the lubrication, were chosen the castor, cotton and canola oils, two samples of silica of different particle sizes, and three different concentrations 1, 3 and 5%. As a final product of the deep drawing, a cup with an internal diameter of 22 mm and a height of 10 mm was shaped. The effect of the lubrication on the deep drawing process was evaluated by the maximum stamping force and the surface finish of the cup, by the roughness parameters Ra and Rz measured on the side and bottom of the cup. The studied composite showed consistency with other materials for stamping. The maximum force values corresponded to previous studies, influenced only by the different types of silica. The influence of the lubrication on the roughness was observed only on the side of the cup. The best surface finish was obtained with the silica of greater granulometry, and sub-angular geometry, using the oils of castor and cotton, and by the addition of silica in lower proportions.

Reis, R. A., (2020). Study of the behavior of conventional and niobium-modified MAR- M246 superalloy cyclically oxidized at 900 and 1.000 ºC. Dissertation (Master Degree) – Universidade Federal de São João Del Rei, 2020.

The oxidation process consists of the reaction of metal alloys with gaseous atmospheres forming an oxide layer on the material surface. At the industrial processes, there are a series of engineering components exposed to oxidation (among them those made with nickel- based superalloys) with temperature changes, different heating and cooling rates and different frequencies. It configures the cyclic oxidation process. Therefore, this research aims to carry out a comparative study of conventional MAR-M246 superalloys, and, also, the same alloy, with tantalum replaced by niobium, to evaluate the formation of oxidized layers in cyclic oxidation tests and characterize them. To test, it was used an oven with an automated system, with cycles of 1 hour of heating and maintenance at high temperature and 10 minutes of cooling in air. The samples were tested for 120, 180 and 240 thermal cycles at 900 ºC and for 24, 120 and 180 at 1,000 ºC. To characterize the oxidized layers, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X- Ray Spectroscopy (EDS) were performed. The tests results at 900 ºC showed mass gains very close to both alloys, with the superalloy MAR-M246 modified with niobium it was showed slightly higher mass gain. In tests at 1,000 ºC, sulfur contamination in the atmosphere was detected, which became the environment more degrading, causing failure of the stainless steel support. However, even so, the two alloys proved to be quite resistant, with greater stability for the alloy containing niobium. Protective oxides, Cr₂O₃ and Al₂O₃ were identified in all test conditions, as well as TiO₂, NiO and Ni(Co)Cr₂O₄. Internal oxidation of Al₂O₃ was identified at both test temperatures, but in greater amounts in samples oxidized at 900 ºC and, at this temperature, the modified MAR-M246 superalloy appeared to have less internal oxidation. It was noticed that the two superalloys had a very similar behavior in terms of mass gain, along with the oxidized layers. This fact suggests an advantage of using niobium for applications with cyclic oxidation at a temperature of 900 ºC due to its lower density and cost. The advantage in the use of niobium could not be affirmed for the temperature of 1.000 ºC due to the sulfur contamination of the cyclic oxidation oven, however, suggested a good behavior for both alloys in sulphidizing environments.

Desenolvimento e caracterização de compósitos cerâmicos e cerâmico-poliméricos destinados à restauração de monumentos históricos fabricados em esteatito (pedra-sabão)