Resumo em Inglês:

Duplex stainless steels are susceptible to the formation of sigma phase at high temperature which could potentially be responsible for catastrophic service failure of components. Thermal treatments were applied to duplex stainless steels in order to promote the precipitation of different fractions of sigma phase into a ferrite-austenite microstructure. Quantitative image analysis was employed to characterize the microstructure and Charpy impact tests were used in order to evaluate the mechanical degradation caused by sigma phase presence. The fracture morphology of the Charpy test specimens were thoroughly observed in SEM, looking for a correlation between the microstructure and the fracture types in UNS S32205 duplex stainless steel. The main conclusion is the strong embrittlement effect of sigma phase since it is possible to observe a transition from transgranular fracture to intergranular fracture as increases the percentage of sigma phase. Thus, the mixed modes of fracture are predominant in the present study with high dependence on sigma phase percentages obtained by different thermal treatments.

Resumo em Inglês:

It was recently shown that the crystallinity of extracted bone mineral samples from the fin bones of zebrafish could increase over storage time. This would have implications in many studies in which the samples need to be stored until analysis. The aim of this study was to further evaluate if the crystallinity of extracted bone mineral increases over storage time. The extracted mineral was a biological bone-like apatite produced in osteoblast cell cultures. The overall characterization of the mineral was done by energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and high-resolution transmission electron microscopy. In order to evaluate possible changes in crystallinity over storage time, the same sample was analyzed by X-ray diffraction immediately after mineral extraction and after 18 months of storage. In conclusion, no statistically relevant changes were observed over storage time, although the occurrence of a slight increase in crystallinity could be discussed in the stored mineral sample.

Resumo em Inglês:

The analysis of phase decomposition was carried out using the nonlinear and linear Cahn-Hilliard equations in a hypothetical A-B alloy system with a miscibility gap. These equations were solved by the explicit finite difference method assuming a regular solution model. The supersaturated solid solution and decomposed phases were considered to have an fcc structure. Different aging temperatures and thermodynamic interaction parameters ΩA-B were used to simulate different alloy systems. The numerical simulation results showed that the growth kinetics of phase decomposition in the alloy with 30at.% A was slower than that of 50 at.% A. Additionally, the start time and modulation wavelength of phase decomposition are strongly affected by the thermodynamic interaction parameter ΩA-B value. The numerical simulation results showed that the growth kinetics of phase decomposition with the linear equation is slower than that with the nonlinear one.

Resumo em Inglês:

Perovskite-type materials have been investigated extensively in the attempt to discover new electrolyte materials for solid oxide fuel cells (SOFC) operating at low temperatures. These materials include LaAlO3-based perovskite, which, when adequately doped, presents high ionic conductivity. However, despite the high conductivity of doped LaAlO3, two characteristics limit its application as solid electrolyte: low sinterability and p-type electronic conductivity in oxidizing conditions. The purpose of this work was to investigate the effect of Pr co-doping on the densification and electrical conductivity of Sr-doped LaAlO3. The addition of Pr eliminated the deficiencies mentioned above. Pr in solid solution acts as a perfect sintering aid because promoted densification without forming secondary phase which should be detrimental for electrical conduction. The addition of Pr also increased the bulk electrical conductivity measured in air atmosphere but had no effect at low oxygen partial pressure. However, the addition of Pr had a strong effect on the grain boundary, improving the ionic grain boundary electrical conductivity at air atmosphere which was attributed to the Pr influence on the space charge layer.

Resumo em Inglês:

This study presents an experimental investigation on surface roughness and chip formation in turning of Al 2219/15SiCp and Al 2219/15SiCp-3Gr (hybrid) composites. Experiments were conducted with different cutting conditions using carbide, coated carbide and polycrystalline diamond (PCD) tools. The results reveal that the surface roughness values are less for coated carbide tools compared to carbide and are minimum for PCD tools. The incorporation of graphite in Al 2219/15SiCp composite increases the surface roughness. This is due to smearing and removal of softer and amorphus graphite particles on the surface of the specimen, creates pits on the machined surface which increases the surface roughness values. The graphitic composite produced discontinuous chips leads to easy machining. PCD tool performs better than carbide and coated carbide tools.

Resumo em Inglês:

The complex dielectric permittivity (ε) and magnetic permeability (µ) of Radar Absorbing Materials (RAM) based on magnetic particles (MnZn ferrite particles) embedded in a dielectric matrix (silicon rubber) have been studied in the frequency range of 2 to 18 GHz. The relative permeability and permittivity of MnZn ferrite-silicon composites for various mass fractions are measured by the transmission/reflection method using a vector network analyzer. The concentration dependence of permittivity and permeability on the evaluated frequency range is analyzed. In a general way, the results show ε' parameter presenting more significant variation among the evaluated parameters (ε", µ", µ'). The comparison of dielectric and magnetic loss tangents (ε"/ε' and µ"/µ', respectively) shows more clearly the variation of both parameters (ε and µ) according to the frequency. It is also observed that higher MnZn ferrite content fractions favor both dielectric and magnetic loss tangents.

Resumo em Inglês:

We reported a study of the structural and magnetic properties of BaZrO3 (BZO) as possible substrate material for the production of YBa2Cu3O7-δ (YBCO) superconducting films. Rietveld analyses of the X-ray diffraction pattern show that BZO crystalizes as a cubic perovskite, space group Pm3m (#221). Chemical stability and crystallographic coupling between BZO and YBCO were examined by characterizing YBCO/BZO (10, 30 and 50 YBCO vol%) polycrystalline composites. Morphological and compositional analyses of composites were performed through scanning electron microscopy and energy dispersive X-ray experiments, respectively. Response of magnetization measurements revealed that the proximity of BZO does not affect the superconducting transition temperature (Tc=90,2 K) of YBCO material. Our results evidenced that the BZO is an excellent candidate to be substrate for the fabrication of YBCO superconducting thin films.

Resumo em Inglês:

Some implant manufactures use Al2O3 instead TiO2 powder to sandblast the machined dental implant, because Al2O3 powder is commercially more easily available and is cheaper than TiO2 powder. However, Al2O3 powder usually leaves aluminum oxide contamination on the surface, which is potentially toxic. In this work, we subjected Ti discs previously sandblasted with Al2O3 powder to 5 different acid etchings in order to verify which treatment is able to remove incorporated particles of Al2O3 from the surface. One group of samples were only sandblasted and served as control. The samples were analyzed by electron microscopy (SEM, EDS), scanning probe microscopy, and grazing incidence XRD. The control group showed presence of Al2O3 on the surface. Three acid etchings were efficient in removing the alumina from the tested samples. Almost all the tested samples showed higher roughness parameters values than the control samples. Titanium hydride was found in almost all test groups. Moreover, the results suggest that there is no incorporation of the whole Al2O3 particle into the titanium surface after the collision, conversely a particle fragmentation occurs and what remains on the titanium surface are Al2O3 residues.

Resumo em Inglês:

The most widely used thermochemical process for surface hardening of steels is case hardening. Using several different heat treatments, martensitic surface layers were formed on SAE 1020 steel into which carbon had been diffused. Case depths were measured by traditional destructive techniques. Barkhausen noise measurements were made and both the RMS Barkhausen pulse envelope and the fast Fourier transform (FFT) were obtained from numerical calculation. The FFT amplitudes, functions of frequency, were associated with distance from the sample surface using the skin depth equation δ = 1/ (πfσµ)½ , where f is the frequency of the electromagnetic wave, s is the electrical conductivity, and µ is the magnetic permeability. We define a normalized power index (NPI) which can be used to estimate case depths. The NPI is discussed in relation to the sample microstructure and it is shown that the case depth is most easily determined when the magnetic properties of the surface layer and core are substantially different.

Resumo em Inglês:

Composites of polydiphenylamine (D-PDPA) and zeolite Y with H+ as the cation (Y_H+) have been fabricated to be used as a sensing material towards non-halogenated and halogenated solvents (hexane, dichloromethane, 1, 2-dichloroethane, chloroform). These composites are toxic towards human and environment and are widely used as solvents in various industries. Polydiphenylamine, zeolite Y, and their composites are characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, particle size analysis, surface area, and pore size analysis. The effects of the Si/Al ratio, zeolite content, and vapor concentrations are investigated. The electrical conductivity sensitivity of the composites towards the solvents is higher than the pristine D-PDPA by ~1 order of magnitude. The composites can discriminate a non-halogenated solvent from halogenated solvents. They possess maximum electrical conductivity sensitivity values towards dichloromethane, but the composites do not respond to hexane. Generally, the sensitivity of the composites increases with increasing zeolite content and vapor concentration. The interactions between the composites and the vapors are investigated by FT-IR spectroscopy and UV-Vis spectroscopy. A mechanism for the interaction between the composites and the solvents is proposed.

Resumo em Inglês:

The present work is focused on ferrous powder metallurgy and presents some results of a development of a suitable masteralloy for use as an additive to iron powder for the production of sintered steels. The masteralloy was produced by melting a powder mixture containing approximately Fe + 20% Ni + 20% Mn + 20% Si + 1% C (wt%), in order to obtain a cast billet that was converted into fine powder by crushing and milling. It was observed presence of SiC in the masteralloy after melting that is undesirable in the alloy. Si element should be introduced by using ferrosilicon. Sintered alloys with distinct contents of alloying elements were prepared by mixing the masteralloy powder to plain iron powder. Samples were produced by die compaction of the powder mixtures and sintering at 1200 °C in a differential dilatometer in order to record their linear dimensional behaviour during heating up and isothermal sintering, aiming at studying the sinterability of the compacts. Microstructure development during sintering was studied by SEM, XRD and microprobe analyses.

Resumo em Inglês:

For good performance of electrical steels it is necessary a high magnetic induction and a low power loss when submitted to cyclic magnetization. A fine dispersion of precipitates is a key requirement in the manufacturing process of Fe- 3%Si grain oriented electrical steel. In the production of high permeability grain oriented steel precipitate particles of copper and manganese sulphides and aluminium nitride delay normal grain growth during primary recrystallization, causing preferential growth of grains with Goss orientation during secondary recrystallization. The sulphides precipitate during the hot rolling process. The aluminium nitride particles are formed during hot rolling and the hot band annealing process. In this work AlN precipitation during hot deformation of a high permeability grain oriented 3%Si steel is examined. In the study, transfer bar samples were submitted to controlled heating, compression and cooling treatments in order to simulate a reversible hot rolling finishing. The samples were analyzed using the transmission electron microscope (TEM) in order to identify the precipitates and characterize size distribution. Precipitate extraction by dissolution method and analyses by inductively coupled plasma optical emission spectrometry (ICP-OES) were used to quantify the precipitation. The results allowed to describe the precipitation kinetics by a precipitation-time-temperature (PTT) diagram for AlN formation during hot rolling.

Resumo em Inglês:

The construction industry keeps on demanding huge quantities of natural resources, mainly minerals for mortars and concrete production. The depletion of many quarries and environmental concerns about reducing the dumping of construction and demolition waste in quarries have led to an increase in the procuring and use of recycled aggregates from this type of waste. If they are to be incorporated in concrete and mortars it is essential to know their properties to guarantee the adequate performance of the end products, in both mechanical and durability-related terms. Existing regulated tests were developed for natural aggregates, however, and several problems arise when they are applied to recycled aggregates, especially fine recycled aggregates (FRA). This paper describes the main problems encountered with these tests and proposes an alternative method to determine the density and water absorption of FRA that removes them. The use of sodium hexametaphosphate solutions in the water absorption test has proven to improve its efficiency, minimizing cohesion between particles and helping to release entrained air.

Resumo em Inglês:

When AISI 316L stainless steels are submitted to the nitriding process at temperatures lower than 450 °C, a high nitrogen content expanded austenite phase is formed, which shows higher hardness and higher pitting corrosion resistance compared to the untreated material. As a result, this material becomes adequate for biomedical application. The conditions of the nitriding technique, such as gas mixture, pressure, time and temperature, play an important role in some properties of the modified layer, including: thickness, hardness and N concentration along the layer. This paper explores a set of six samples of AISI 316L, nitrided at different times and temperatures, whose properties show important differences. The aim of this research is to investigate the correlation between the nitrided layer thickness (in the range of 0.77 to 11 µm) with both X-ray patterns characteristics and hardness measurements, which used two distinct loads. The results of this study show that: whereas the 3.6 gf load was suitable to measure the real hardness for four of the nitrided layers showing thickness ≥ 2.9 µm, the 50 gf load measured a substrate contribution, probably even for the highest thickness, 11 µm. Moreover, analyzing different reflections of the X-ray patterns showed evidence of the clear consistency between the X-Ray depths and the nitrided layer thicknesses: if the layer thickness is lower than the penetration depth of X-rays, two phases (austenite and expanded substrate) are present. If the layer thickness is higher, only the austenite is observed. Finally, concerning the citotoxicity property, all the samples, nitrided or not, were approved in the test for biocompatibility, indicating their potential use for biomedical applications.

Resumo em Inglês:

The strength development of self-compacting mortars (SCM) containing calcined silt (CS) and ground brick waste (GWB) was investigated. The variables are the nature of addition (CS and GWB) in the binder and the heat curing at different temperatures (20 ºC and 60 ºC) at 7 and 14 days of curing. Two temperatures 20 and 60 ºC were applied to samples with intermediate levels (depending on the drying method applied to precast) for 18 hours in total. In this study, a Portland cement (CEMII), Calcined silt (750 ºC for 5 hours), ground waste brick, were used in the binders of SCM. The results show that the compressive strength to 14 days of mortars, increases with annealing (60 ºC) compared to that measured at 20 ºC. Also, values of compressive strength of mortars at 14 days that are close to those obtained without 28 days curing treatment. Indeed, a strength gain of about 20.5% and 27.3% was obtained respectively for the SCM with GWB and the SCM with CS. However, a small change in mass recorded for both types of mortars.

Resumo em Inglês:

In this study Klason lignins from Eucalyptus grandis (LEUG) and Pinus taeda (LPIT) were characterized using Fourier transform infrared (FTIR) spectroscopy and thermogravimetry (TGA). The degradation kinetic parameters were determined by TGA using the Kissinger method. Thermogravimetric results showed that LPIT had higher thermal stability and also higher activation energy than LEUG. FTIR results showed that the average strength of intermolecular interactions and enthalpy of hydrogen bond formation among the phenolic groups are higher for LPIT than for LEUG. The results demonstrated that differences between thermal stability and degradation mechanisms might be associated with differences in hydrogen bonding in lignin.

Resumo em Inglês:

The cobalt-based Stellite 6 coating with a thickness of 0.5 mm was deposited onto 45 carbon steel by electro-spark deposition technology. Microstructure, chemical composition, phase composition, microhardness distribution and wear resistance of the coating were researched by a series of experiments. The results indicate that, the coating with refined and compact microstructure is mainly composed of Co, Cr7C3, Co6W6C and CrCo. The coating makes metallurgical bonding interface with the substrate. Microhardness of the coating is improved significantly with an average value of 827.9 HV0.5, which is about 3.6 times that of the substrate. Under the same experimental condition, mass loss of the substrate is about 4.2-4.5 times that of the coating, so the coating shows excellent wear resistance. Main wear mechanism of the coating is abrasive wear at low speed or low load stage, and fatigue wear at high speed or heavy load condition.

Resumo em Inglês:

The aim of this work was the evaluation of the thermal-rectification process of reforestation wood Corymbia citriodora Hook by measuring of mechanical properties under compression parallel to the grain and also determining of chemical composition. The tested samples were thermally treated in a furnace with nitrogen-atmosphere at heating rate of 0.033 ºC.min-1, at temperatures of 160, 180, 200, 220 and 240 ºC. The chemical components and mechanical properties were affected with the thermal rectification process. The contents ranged from 17.85 to 3.51% extractives, 30.44 to 53.86% lignin, 69.56 to 46.14% holocellulose and 0.31 to 0.47% ashes. The samples strength decreased from 20% to 50% and the elasticity modulus increased about 47%. The characteristic values of strength under compression were determined and these changes were about 23% lower than Brazilian standard. The best mechanical properties of Corymbia citriodora were obtained at 180 ºC.

Resumo em Inglês:

Self-compacting mortar (SCM) is a new generation product and has prospective use as an independent material as well as an integral constituent of self-compacting concrete (SCC). In this paper the flow response of self-compacting mortar is assessed by Taguchi method and ANOVA interaction. Effect of powder material and super-plasticizer on the relative flow index of fresh SCM is evaluated by mortar trial test designed by Taguchi method of optimization. An ANOVA interaction analysis is performed to comprehend the interaction of the factors and their effect on quality characteristic. The relative significance level of powder material and super-plasticizer in governing the flow characteristic is discussed. A modified approach is proposed by incorporation of the error balancing property of statistical central tendency and the assumption of non- variance of mean. Construing contribution of mean, sample size and relative error to Signal to Noise Ratio provides limits of deviations of the same.

Resumo em Inglês:

In order to study the dynamic recrystallization (DRX) behavior of as-extruded 42CrMo high-strength steel, a series of isothermal upsetting experiments were carried out in a temperature range of 1123~1348 K and a strain rate range of 0.01~10 s-1 on Gleeble 1500. It was found that DRX softening is more recognizable at higher temperatures and lower strain rates, and stress level increases with increasing strain rate and decreasing deformation temperature. The types of flow stress evolution were distinguished by the following three characteristics: WH followed by DRX, WH followed by DRV, and WH followed by no dynamic softening. At a fixed temperature, the average grain size refined by DRX linearly decreases with increasing strain rate in log scale. At a fixed strain rate, the average grain size remains almost constant below 1273 K, while it rapidly increases above 1273 K. At a larger strain rate, data set of grain sizes has a smaller standard deviation to the average size value, and data have tightly grouped. This indicates that as strain rate increases, the microstructure becomes more and more uniform. The relationships between the average grain size and Zener-Hollomon parameter were nonlinearly fitted by the equation D A = 319.81202 - 13.6114 lnZ + 0.15322 (lnZ)². The results from this equation show that the average grain size decreases with increasing Zener-Hollomon parameter. On the plot of D A versus lnZ, the regions corresponding to DRV (lnZ 37.8) and DRX (lnZ 37.8) were clarified clearly.

Resumo em Inglês:

Tensile properties and fracture location of AA2139-T351 friction stir welded joints are studied in the as-welded and post-weld aged condition. The experimental results show that when the joints are free of welding defects, they fail on the advancing side of the HAZ exhibiting a large amount of plastic deformation. When the revolutionary pitch exceeds a threshold value, some micro-defects are formed in the weld nugget due to insufficient heat input. In this case, the joints fail near the weld center, and the fracture occurs in a mixed mode, both ductile and brittle. However, being less ductile, post-weld aged joints are less defect-tolerant and, then, they fracture closer to the weld center, showing a reduced elongation at fracture and an UTS within the order of magnitude of the as-welded joints.

Resumo em Inglês:

The acid-base cements are materials developed by means of reactions between an acid component and another basic one. This type cement belongs to the family of the so called "chemically bonded phosphate ceramics" (CBPCs), new types of inorganic materials that have special physico-chemical properties and that, in contrast to most advanced ceramics, are made by processing the material at ambient temperature. In the present work, cylindrical specimens were molded (30 mm × 50 mm) with magnesium phosphate cement and grinding dust (waste from an automobile industry) which was added to ceramic matrices in varied contents (0% to 40% in mass). The influence of this addition with regard to phase formation and to mechanic resistance (axial compression and traction by diametrical compression) of the compositions (3, 7 and 28 days after the molding) was evaluated using a universal test machine. The samples of magnesium phosphate cement mortars containing grinding dust were then analyzed after being subjected to an accelerated aging test for a period of 1200 hours (50 days), equivalent to one year of natural aging. The results obtained showed a decrease in the compressive strength of the mortar between 28 days and 1 year of age but this loss in performance is not associated with the presence of grinding dust and the CBPCs proved highly satisfactory for the encapsulation of hazardous wastes.

Resumo em Inglês:

Montmorillonite clays are of great interest for industrial processes such as catalysis and adsorption. The textural properties of clays can be modified in an attempt to increase their uses. This paper describes the acid treatment of natural montmorillonite clay. The materials were characterized using X-ray diffraction (XRD), atomic absorption spectroscopy (AA) and BET surface area measurements. Three different acids (HCl, HNO3 and H2SO4) were tested, and HCl and H2SO4 were more efficient for removing Fe from the clay. The results indicate that HCl better preserves the material structure because less Al is removed. A central composite design (CCD) 2² was applied to evaluate the treatment using HCl. The temperature and concentration presented positive effects on the removal of Fe, Al and Mg. Combinations of the HCl acid solution concentration and temperature, such as 4 mol.L-1/50 °C and 1 mol.L-1/75 °C, assured that Fe was removed with less damage to the structure.

Resumo em Inglês:

Nanocomposites based on epoxy and a mixture of clays and multi-walled carbon nanotubes (MWCNT) were produced by casting, and also molded by RTM using glass fibers as reinforcement, yielding a hybrid multi-scale micro/nanocomposite material. Two types of montmorillonite clays were used, natural (MMT-Na) and organophilic (MMT-30B). Higher viscosity was obtained for the mixture with MMT-30B and it was observed that this clay did not perform as well as the MMT-Na in helping the dispersion of the carbon nanotubes (CNT). The glass transition temperature (Tg) of the nanocomposites increased in up to 6 °C with the addition of MWCNT and up to 10 °C with the addition of MMT-30B, differently from the MMT-Na which did not alter the Tg of the material. By transmission electron microscopy, it was verified that more homogeneous dispersions and more intercalated structures were obtained with the MMT-30B than with the MMT-Na. Finally, the low clay content used and, especially, the very low MWCNT content, did not significantly alter the studied flexural properties.

Resumo em Inglês:

Multiferroic ceramic solid solutions between the ferroelectric relaxor Pb(Fe2/3W1/3)O3 (PFW) and "normal" ferroelectric PbTiO3 (PT) - PFW-PT have been synthesized by a modified B-site precursor method and characterized by microwave dielectric measurements. A dielectric dispersion occurring in the frequency range of 100MHz-3GHz and in a broad range of temperatures showed to be a powerful tool to detect electrostrictive and magnetostrictive effects. Anomalies in the temperature dependence of the dielectric parameters (fR (characteristic frequency) and the dielectric strength Δε (characteristic of the dispersion)) have been observed at T N and T C for all samples, indicating that the coupling between the ferroelectric and antiferromagnetic orders occurs "via strain" and confirming the high sensitivity of microwave dielectric measurements to probe weak transitions in bulk ceramics.

Resumo em Inglês:

New environmental laws have restricted the use of hardwood trees in overhead power lines structures, such as, poles and cross-arms, leading companies to seek alternative materials. Reforested wood coated with polymeric resin has been proposed as an environmental friendly solution, with improved electrical properties and protection against external agents, e.g. moisture, ultraviolet radiation and fungi. However, the single thin layer of resin, normally applied on such structures reveal to be inefficient, due to be easily damage during handling. In this paper, we present a composite coating, based on geotextile fibers and polyurethane resin that is suitable for wooden structures. Results obtained from two different tree species (from managed and reforested areas) coated with the composite reveal that the additional layer not only provided a stronger adhesion between wood and ccoating layer but also a further improvement in the electrical properties and better protection against abrasion and moisture.

Resumo em Inglês:

This work investigates the correlation between the in-vitro wear resistance and the nanomechanical properties of dental sealants commercially available. Mechanical properties, namely hardness (H) and elastic modulus (E), were assessed by nanoindentation technique. The coated samples presented lower H and E values than the Z250 composite resin substrate. Such measurements were used to calculate H/E ratios. Wear tests were carried out in water by using a pin-on-plate apparatus. Scars formed on the samples were qualitatively examined by optical microscopy, while their wear depths were measured by contact profilometry. Based on the findings, an empirical correlation between the wear depths and H/E was obtained. A high H/E ratio was associated to surfaces with enhanced wear resistance. For the tribological conditions here employed, the H/E ratio could be, therefore, considered a useful parameter for ranking the in-vitro wear of dental sealants.

Resumo em Inglês:

Polycrystalline ITO films with good optoelectronics characteristics and homogeneous surface has been obtained upon annealing at 550 °C in N² atmosphere using a low-cost chemical vapor deposition (CVD) system. The films were evaluated as pH sensors in separative extended gate field-effect transistor (SEGFET) apparatus, exhibiting a sensitivity of 53 mV/pH, close to the expected Nernstian theoretical value for ion sensitive materials. The use of CVD process to synthesize ITO, as described here, may represent an alternative for fabrication of SEGFET pH sensors at low cost to be used in disposable biosensors since H+ ions are the product of several oxireductase enzymes.

Resumo em Inglês:

Experience shows that a damage induced by a given cycle is dependent on the loading history. In this regard, the objective of this paper is to study and describe the phenomenology of the loading history on crack propagation. Different loading configuration has been considered for fatigue crack propagation of XC38 steel; overload cycles followed by underload and vice versa were considered during propagation. Measure of crack opening has been made using compliance method. It is shown that the main parameters which cause retardation are the residual compressive stresses and the crack closure. The finite element modeling is used to calculate the evolution of residual stress profiles before and after application of the overload-underload cycle. It corroborates the hypotheses on the mechanisms behind, including those proposed on the residual stresses at the crack tip.

Resumo em Inglês:

Al-SiC composites were successfully produced with improved mechanical properties. Effect of SiC content, its particles size and shaping method were investigated. Three shaping methods of conventional powder metallurgy (PM), hot press (HP) and hot extrusion (EX) were used. The hardness of the samples was measured by Vickers method. Tensile and compression tests were performed for the characterization of mechanical properties. Microstructure was monitored by optical microscopy. Maximum relative density (RD) was obtained for hot pressed samples. Higher SiC content with smaller particles size had the best effect on the mechanical properties such as yielding point (YP), ultimate tensile strength (UTS) and hardness. Maximum hardness (6.57 GPa) and UTS (212 MPa) were obtained for Al-20%SiC with SiC mesh size of 1000. Maximum YP was obtained for Al-20%SiC in compression test (143.64 MPa) that is larger than it in tensile test (117.96 MPa). Remarkable difference exists between HP and extrusion methods at higher SiC contents. The YP of EX samples are larger than HP samples. Strains at known stress (562 MPa) of EX samples are smaller than HP samples.

Resumo em Inglês:

The success of manufacturing composite parts by liquid composite molding processes with RTM depends on tool designs, efficient heat system, a controlled injection pressure, a stabilized vacuum system, besides of a suitable study of the preform lay-up and the resin system choice. This paper reports how to assemble a RTM system in a laboratory scale by specifying heat, injection and vacuum system. The design and mold material were outlined by pointing out its advantages and disadvantages. Four different carbon fiber fabrics were used for testing the RTM system. The injection pressure was analyzed regarding fiber volume content, preform compression and permeability, showing how these factors can affect the process parameters. The glass transition temperature (Tg) around 203 ºC matched with the aimed temperature of the mold which ensured good distribution of the heat throughout the upper and lower mold length. The void volume fraction in a range of 2% confirmed the appropriate RTM system and parameters choice.

Resumo em Inglês:

The sugar cane bagasse is the most abundant agricultural residue produced in Brazil. It can be used for the production of chipboard panels and as constructive components for several types of environments. The substitution of timber for the bagasse minimizes environmental impacts and contributes to the generation of a new product with lower density and lower thermal conductivity which can improve the thermal conditioning of buildings. This study aims at determining the heat flow through chipboard panels made of sugarcane bagasse and comparing these chipboard panels with similar ones made of Pinus and Eucalyptus. The results show that the heat flow during the heating of the panels is lower for the panels made of sugar cane bagasse and the heat accumulation promoted by this panel is greater than by others. Therefore this product may be suitable to be used as liners, between cavity walls, partition walls and more.

Resumo em Inglês:

The synthesis of porous materials has attracted interest for decades due to their applications in catalysis and gas adsorption. Clay obtained by insertion of mesoporous oligomer [La xAl13-xO4 (OH)24 (H2O)12]7 + (where x equals the molar amount of lanthanum), followed by calcination, may cause variation in the acidic properties. The analyzes showed that increasing the amount of La on oligomer results in a higher acidity shown in the spectrum a characteristic band in the region of 1445 and 1545cm-1 to Lewis and Brönsted respectively, predominantly of the last one. The Mössbauer spectroscopy results showed a relationship between increased symmetry of the octahedral site of iron (Fe3+) and increased lanthanum doping, and consequently a sharp increase in acidity.

Resumo em Inglês:

Computer simulation of simultaneous evolution of individual texture components during recrystallization of an IF steel is carried out. A new methodology has been developed that takes as its starting point experimental data of each texture component evolving during recrystallization. In particular, Magnusson et al. data on IF steel was analyzed in a previous work with the help of the exact analytical tools developed by Rios and Villa for simultaneous transformations. From this analysis parameters such as number of nuclei of each texture component per unit of volume could be obtained and were employed as input for the present computer simulation. From this input 3-d microstructures could then be generated. The methodology proposed here combines experimental data, exact analytical methods and computer simulation and may be employed to extract the maximum information from the experimental data.

Resumo em Inglês:

The aim of this study was to investigate the effects of attack by xylophagous organisms on the physicomechanical properties of Araucaria angustifolia wood from the floor of a historic house in Pelotas, Southern Brazil using two nondestructive methods. To achieve this, samples were collected from the floor for visual assessment by photography in metric scale. All the images were exported to CAD software in order to measure the percentage of the sample's surface attack in relation to its total area. Subsequently, nondestructive tests were performed using an ultrasound with two types of transducers. Mechanical properties of the material was measured through static bending tests and these results were compared with the results of nondestructive methods. The nondestructive methods of computerized visual analysis and ultrasound were efficient for quantifying the surface attack and showed a good relationship with the results obtained in static bending tests.