Matéria (Rio de Janeiro), Volume: 15, Issue: 2, Published: 2010
  • Biodegradable polymer composites based on Brazilian lignocellulosic

    Kestur, G. Satyanarayana

    Abstract in English:

    Use of eco friendly and energy saving biomaterials and processes have enabled to overcome the effects of growing urbanization and population along with increasing agro-industrial wastes. This has led to a new approach to the industrial design of products and processes along with the implementation of sustainable manufacturing strategies to "optimize the total material cycle from virgin material to finished material, to component, to product, to waste product and to ultimate disposal". Developing countries such as Brazil possess abundantly available but underutilized biomaterial resources, which may possibly give excellent opportunities for scientists to discover methods for their better utilization. This talk presents attempts made so far on the developments of biodegradable composites based on biomaterials of Brazil, with details on their processing matrix-reinforcement combinations, morphology properties and market. Some results of the studies carried out by the author and his colleagues at UFPR-Curitiba are also included.
  • Evaluation of material properties and design requirements for biodegradable magnesium stents

    Farè, Stefano; Ge, Qiang; Vedani, Maurizio; Vimercati, Gianmarco; Gastaldi, Dario; Migliavacca, Francesco; Petrini, Lorenza; Trasatti, Stefano

    Abstract in English:

    Magnesium represents a very attractive material for biodegradable stents since the process of its natural and gradual dissolution into the human body by a corrosion process would prevent restenosis risks and would allow the progressive transmission of the mechanical load to the surrounding tissues after several months of service. The objective of the present work is to develop a frame of mechanical and microstructural data about several commercially available Mg alloys in view of their use for biodegradable stents. The AZ31, AZ61, AZ80, ZM21, ZK61 and WE43 alloys in the form of extruded bars were thus investigated to compare their mechanical properties and corrosion resistance. Further high-temperature characterization was carried out by compression tests at high temperature (temperature range: 260-450°C, strain rate range: 5•10-4 ÷ 3•10-2 s-1) in order to assess the optimal processing window for stent precursors manufacturing (small tubes 1÷2 mm in diameter) by hot extrusion. The experimental results made available by this investigation were adopted to support the development of a finite element (FE) framework combining a shape optimization procedure and a detailed model for Mg alloy mechanical and corrosion damage behavior.
  • Thermal behavior of buriti biofoam

    Monteiro, Sergio Neves; Rodriguez, Rubén Jesus Sanchez; Costa, Lucas Lopes da; Portela, Tammy Godinho Rodrigues; Santos, Nubia Suely Silva

    Abstract in English:

    A natural biofoam extracted from the petiole of the buriti palm tree has shown values of density and mechanical strength with potential for uses in engineering applications such as automobile interior parts and floating components. Moreover, foams can also be used as insulating materials in packing and building panels. In this case some thermal properties are required. Therefore, the objective of this work was to evaluate the thermal behavior of the buriti biofoam by means of TGA, DTG and DSC analysis. The TGA curves revealed weight loss related to release of humidity and molecular structure decomposition. Peaks in the DTG curves indicated two intervals in temperature associated with different decomposition processes. The only endothermic DSC peak found was attributed to the lignocellulosic water of hydration being lost around 121ºC.
  • Diameter dependence of tensile strength by Weibull analysis: Part I bamboo fiber

    Costa, L.L. da; Loiola, R.L.; Monteiro, S.N.

    Abstract in English:

    Fibers stripped of from the bamboo culm by longitudinal cutting are being considered as reinforcement of polymer composites owing to environmental benefits related to their biodegradable and renewable characteristics. The manual cutting process allows bamboo fibers with different diameters to be extracted from the culm. Since a lignocellulosic fiber usually presents tensile strength dependence with its diameter, this possibility was investigated on bamboo fibers by means of the Weibull statistical analysis. It was found that the smaller the fiber diameter, the greater the tensile strength. Fracture observation of ruptured bamboo fibers by scanning electron microscopy, identified possible mechanisms associated with this inverse strength/diameter correlation.
  • Diameter dependence of tensile strength by Weibull analysis: Part II jute fiber

    Bevitori, A. B.; Silva, I.L.A. Da; Lopes, F.P.D.; Monteiro, S.N.

    Abstract in English:

    The jute fiber is one of the strongest lignocellulosic fibers with applications ranging from simple items such as fabrics and ropes to engineering composites for automobile parts and building panels. Like other lignocellulosic fibers, the jute may have an inverse strength dependence with its diameter. In principle, thinner jute fiber could be comparatively stronger and consequently more effective as a composite reinforcement. Therefore, an attempt to correlate the jute fiber strength obtained in tensile test with its corresponding diameter, precisely measured by means of a profile projector, was carried out. A Weibull statistical analysis confirmed the inverse dependence between the jute fiber tensile strength and the corresponding fiber diameter. Scanning electron microscopy observation of the fracture of selected ruptured fiber revealed possible mechanisms that could justify the strength/diameter inverse dependence.
  • Diameter dependence of tensile strength by Weibull analysis: Part III sisal fiber

    Inacio, W.P.; Lopes, F.P.D.; Monteiro, S.N.

    Abstract in English:

    Environmental aspects and economical advantages are motivating the use of natural fiber as reinforcement of polymer composites in substitution for synthetic fiber composites such as fiber glass. In particular, the sisal fiber is one of the most investigated and being used in engineering systems. By contrast to synthetic fibers, natural fibers have the disadvantage of being heterogeneous in their dimensions specially the diameter. In several natural fibers it has been found that the smaller the diameter, the stronger is the fiber. In this work a Weibull analysis of sisal fibers tensile strength was performed to find a correlation with the diameter. The results revealed an inverse dependence of the tensile strength with the diameter. The observation of ruptured fibers by scanning electron microscopy suggested possible mechanisms that justify a hyperbolic correlation.
  • Charpy impact resistance of alkali treated curaua reinforced polyester composites

    Ferreira, Ailton da Silva; Lopes, Felipe Perissé Duarte; Monteiro, Sergio Neves; Satyanarayana, Kestur Gundappa

    Abstract in English:

    Natural fibers obtained from cellulose-based plants are being used as reinforcement of polymer composite owing to both environmental and technical advantages. One important technical characteristic of most lignocellulosic fibers is the bend flexibility, which allows them to resist impact forces. As a consequence, there is an increasing application of these lignocellulosic fibers in automobile parts that, during a crash event, should absorb the impact energy without splitting into sharp pieces. The present work investigates the toughness behavior of polyester composites reinforced with up to 30% in volume of alkali treated continuous and aligned curaua fibers by means of Charpy impact tests. It was found that the incorporation of treated curaua fibers increased the composite absorbed impact energy but not as much as in composites reinforced with non-treated fibers. Macroscopic observation, and scanning electron microscopy analysis of fracture surface, revealed that the main mechanism for the increase in the Charpy notch toughness is the interfacial rupture between the curaua fiber and the polyester matrix.
  • Titanium dental implant surfaces

    Elias, Carlos Nelson

    Abstract in English:

    Osseointegration has been defined as "a direct structural and functional connection between ordered, living bone and the surface of a load-carrying implant". However, titanium and its alloys cannot directly bond to living bone after being implanted into the body. The osseointegration of titanium dental implants is critically dependent on the implant surface properties. Various surface modifications have been proposed in order to provide commercially pure titanium with bioactive bone bonding ability. In the present work, the titanium dental implant surface morphology was modified by acid etching and electrochemical treatments with the purpose of enhancing tissue response, and decreasing the waiting time for implant loading. The results show that surface morphology, topography, roughness and chemical composition were changed by the treatments and these changes has a significant influence on osseointegration. The best results were observed in the samples submitted to the electrochemical treatment.
  • Modeling of work hardening behaviour of high Mn and low C polycristalline austenitic steel with twip effect

    Spindola, M.O.; Ribeiro, E.A.S.; Gonzalez, B.M.; Santos, D.B.

    Abstract in English:

    The steel of this work, 0.06C-25Mn-3Al-2Si-1Ni steel, presenting TWIP effect, was hot and cold rolled and then annealed at temperatures between 600 and 850ºC. The microstructure examination was focused in the recrystallization during annealing for different temperatures through optical and scanning electron microscopy. The volume fraction and recrystallized grain size measurements were performed. Tensile tests were conducted at room temperature. A polycrystalline model, based on micromechanics and working hardening theory, developed by Bouaziz et al., to predict the behavior of TWIP steels under different loading paths, was applied to the current steel. The results from the model are in good agreement with mechanical test and show a total elongation above 60%, uniform elongation up to 55% and a tensile strength greater than 600 MPa, which highlights the potential of this steel for its various applications, mainly automotive industry. The model parameters are discussed and their limitations are presented.
  • Cement composites reinforced by short curaua fibers

    d'Almeida, A.; Toledo Filho, R.; Melo Filho, J.

    Abstract in English:

    The development of an eco-friendly material that could reduce CO² emission and that could aggregate value to a natural fiber, setting man at the countryside and raising the income of populations from poor regions is a challenge. Lignocellulosic fibers are cheap and are a readily available reinforcement, requiring only a low degree of industrialization for their processing. The main drawback of using cement composites reinforced with lignocellulosic fibers is that the fibers can be mineralized inside the alkaline environment. In this work, Portland cement was partially replaced by metakaolinite in order to produce a matrix free from calcium hydroxide, avoiding thus the problem of fiber mineralization. Cement composites reinforced with 2, 4 and 6% of short curaua fibers, were manufactured. The composites were submitted to four pointing bending tests in order to determine their mechanical behavior. The results obtained were compared with those found for cement composites reinforced with sisal fibers.
  • Effects of temperature and strain rate on the tensile properties of twip steels

    Curtze, S.; Kuokkala, V.-T.

    Abstract in English:

    Three high manganese TWIP steels were produced with stacking fault energies γSFE ranging from 20.5 to 42 mJ/m². The materials were mechanically tested in tension at temperatures and strain rates varying in the ranges of -50°C...80°C and 10-3 s-1...1250 s-1, respectively. Due to the temperature dependence of γSFE, also the mechanical behavior of TWIP steels reveals clear temperature dependence, determined by the prevailing deformation mechanism, i.e., dislocation slip, deformation twinning, or ε-martensite transformation. In addition to the 'ordinary' strain rate sensitivity, an increase in temperature due to adiabatic deformation heating contributes to the stacking fault energy (SFE) at high strain rates, shifting γSFE towards the dislocation slip regime and this way strongly affecting also the mechanical behavior. At stacking fault energies close to the transition between twinning and ε-martensite transformation, lowering the temperature can ultimately result in entering the ε-martensite transformation regime that may bring about further ductility.
  • The dynamic-mechanical behavior of epoxy matrix composites reinforced with ramie fibers

    Margem, Frederico Muylaert; Monteiro, Sergio Neves; Bravo Neto, Jarbas; Rodriguez, Rubén Jesus Sanchéz; Soares, Bluma Guenther

    Abstract in English:

    The exceptional tensile strength of ramie fiber has motivated investigations on its application as reinforcement in polymeric composites. In this study the temperature variation of the dynamic-mechanical parameters of epoxy matrix composites incorporated with up to 30% in volume of ramie fiber were investigated by DMA tests. The parameters were the storage modulus, loss modulus and tangent delta. The investigation was conducted in the temperature from 20 to 200°C in an equipment operating in its flexural mode at 1 Hz under nitrogen. The results showed that the incorporation of ramie fiber tends to increase the viscoelastic stiffness of the epoxy matrix. It was also observed sensible changes in the structure damping capacity when the fraction of fiber is increased in the composite. These results indicate that the segmental mobility of the epoxy chains is affected by interaction with ramie fibers in the composite.
  • Digital microscopy and image analysis applied to composite materials characterization

    Paciornik, S.; d'Almeida, J.

    Abstract in English:

    Digital Microscopy was employed to characterize the microstructure of fiber-reinforced composite tubes manufactured by filament winding. Optical Microscopy was used for void characterization while Scanning Electron Microscopy was used for fiber and layer analysis. Acquired images were assembled in mosaics to reveal the microstructure of different cross-sections of the sample. Image processing was employed to detect either voids or individual fibers and measure their size, shape and spatial distribution. Void spatial distribution was analyzed with two different methods - local analysis and the tessellation method - revealing different behaviors along different cross-sections. Fiber layers were automatically detected and their average winding angle and dispersion were analyzed.
  • Processing and characterization of dual phase steel foam

    Gruttadauria, A.; Mombelli, Davide; Castrodeza, E. M.; Mapelli, C.

    Abstract in English:

    Porous materials featuring cellular structures are known to have many interesting combinations of physical and mechanical properties. Some of them have been extensively used in the transportation field (i.e. balsa wood). Steel foams presented promising theoretical properties for both functional and structural applications in transportation, but processing of such a kind of foams is complex due to their high melting point. Recently a technique for processing Cu-based alloys open-cell foams through the molten metal infiltration of a leachable bed of amorphous SiO2 particles was proposed. A variation of the proposed technique that uses SiC particles as space holder is now presented and was recently successfully applied for dual phase steel foam processing. Results from a processing of dual phase DP500 steel foams, including some morphological, micro-structural and mechanical characterization, are here presented.
  • Tensile behavior of lignocellulosic fiber reinforced polymer composites: Part I piassava/epoxy

    Nascimento, D.C.O.; Lopes, F.P.D.; Monteiro, S.N.

    Abstract in English:

    The fibers extracted from the piassava palm tree, scientifically known as Attalea funifera, are among the stiffest lignocellulosic fibers being considered for polymer composite reinforcement. Characterization of piassava composites have been carried out for different polymeric matrices and mechanical tests. In this work the tensile properties of DGEBA/TETA epoxy matrix composites reinforced with up to 30% in volume of continuous and aligned piassava fibers were evaluated. Tensile specimens post-cured at 60ºC for 4 hours were room temperature tested and the corresponding fracture analyzed by scanning electrons microscopy. The results showed a decrease in both the tensile strength and the elastic modulus of the composites up to 30% with an increase at 40% of piassava fibers to values above those of the pure epoxy. The fracture analysis revealed a weak fiber/matrix interface, which could account for the comparative low performance of these composite in tensile tests up to 30% of volume fraction. The relatively large amount of stronger piassava fibers accounts for the better performance of the composite with 40% in volume fraction.
  • Tensile behavior of lignocellulosic fiber reinforced polymer composites: Part II buriti petiole/polyester

    Portela, T.G.R.; Costa, L.L. da; Santos, N.S.S.; Lopes, F.P.D.; Monteiro, S.N.

    Abstract in English:

    The current interest for natural fibers as an environmentally correct composite reinforcement has motivated the investigation of new possibilities. For instance, the fibers extracted from the petiole of the buriti palm tree were recently found to have adequate mechanical properties to reinforce polymer composites. Therefore, the present work evaluates the tensile properties of polyester composites incorporated with thinner buriti petiole fibers for improved mechanical performance. Composites with up to 40% in volume of buriti petiole fibers embedded in orthophtalic polyester matrix were post-cured and then ruptured in tension. Fracture surfaces were analyzed by scanning electron microscopy. A marked increase in the tensile strength was found with the amount of buriti fibers. The fracture analysis revealed aspects of the bonding condition at the fiber/matrix interface, which could be associated with the composite performance.
  • Tensile Behavior of lignocellulosic reinforced polyester composites: Part III coir fiber

    Santafé Júnior, H.P.G.; Lopes, F.P.D.; Costa, L.L.; Monteiro, S.N.

    Abstract in English:

    The fiber extracted from the husk of a coconut fruit, known as coir fiber, has been extensively investigated as a second phase incorporation into polymer composites. The moderate strength of the coir fiber usually does not represent reinforcement to relatively strong thermoset matrices such as polyester, epoxy and phenolic. However, a selection of thinner coir fibers and a post cure treatment of the composite could improve its mechanical performance. Therefore, this work investigated the tensile properties of post-cured polyester matrix composites incorporated with the thinnest coir fiber. Tensile specimens with up to 40% in volume of long and aligned coir fibers were tested and their fracture analyzed by scanning electron microscopy. A relatively improvement was found in the tensile properties for the amount of 40% of coir fiber. These results were compared with similar composites that were bend-tested. The fracture analysis showed a comparatively better fiber/matrix adhesion.
  • Sensitivity analysis of the ECAE process via 2k experiments design

    Medeiros, Neil de; Moreira, Luciano Pessanha; Bressan, José Divo; Lins, Jefferson Fabrício Cardoso; Gouvêa, Jayme Pereira de

    Abstract in English:

    In this work the theoretical solutions based upon the upper-bound theorem recently proposed by Pérez and Luri [Mech. Mater. 40 (2008) 617] for the equal channel angular extrusion process (ECAE) are analyzed by performing a 25 central composite factorial analysis. The uniaxial mechanical properties of commercial pure aluminium are considered by assuming isotropic nonlinear work-hardening combined to von Mises and Drucker isotropic yield criteria to predict the ECAE load and the effective plastic strain. From the proposed 25 factorial analysis, the main parameters affecting the ECAE pressure may be ranked as: (1) Friction factor, (2) die channels intersection angle, (3) outer and (4) inner die corners fillet radii and lastly, (5) plunger velocity. Alternatively, the effective plastic strain is mainly controlled by the die channels intersection angle and, in a less extent, by the outer and inner die corners fillet radii.
  • Dynamic behavior of gamma-irradiated polycarbonate

    Weber, Ricardo Pondé; Vecchio, Keneth S.; Suarez, João Carlos Miguez

    Abstract in English:

    The aim of the present work was to establish the relationship between dynamic behavior of Bisphenol A polycarbonate (BAPC) and degradation by gamma irradiation. The BAPC was exposed to 340 kGy dose and the molecular weight was evaluated by Size Exclusion Chromatography (SEC). A modified split Hopkinson pressure bar was used to measure stress-strain dynamic relations. The results showed little change in the dynamic behavior of irradiated BAPC in the highest strain rate used in this work, in spite of the high decrease in the molecular weight of irradiated BAPC. The lowest strain rate used in this work produced the highest change in the dynamic behavior of irradiated BAPC.
  • The use of fly-ash and rice-hull-ash in Al/SiCp composites: a comparative study of the corrosion and mechanical behavior

    Pech-Canul, M. I.; Escalera-Lozano, R.; Montoya-Dávila, M. A.; Pech-Canul, M.

    Abstract in English:

    The corrosion characteristics and mechanical behavior of Al/SiCp/spinel composites prepared by reactive infiltration with fly-ash (FA) and rice-hull ash (RHA) -both with recycled aluminum- were investigated. MgAl2O4 is formed in situ during infiltration in the temperature range 1050-1150 °C for 50-70 min in argon atmosphere at a pressure slightly above to that of the atmospheric pressure. Results reveal that both FA and RHA help in preventing SiCp dissolution and the subsequent formation of the unwanted Al4C3. However, FA-composites are susceptible to corrosion via formation of Al4C3 by the interaction of native carbon in FA with liquid aluminum. The foremost corrosion mechanism in both types of composites is attributed to microgalvanic coupling between the intermetallic Mg2Si and the matrix. Microstructure and mechanical characterization show that FA- and RHA-composites possess mechanical properties that are significantly different and that this behavior is due to the original ash and MgAl2O4 morphologies. While RHA composites exhibit higher surface hardness than FA composites, the latter display a higher modulus of rupture.
  • Young's modulus of Al/SiC P/MgAl2O4 composites with different particle size distribution of reinforcements

    Montoya-Dávila, M.; Pech-Canul, M.I.; Escalera-Lozano, R.; Pech-Canul, M.A.

    Abstract in English:

    The effect of particle size distribution of SiC particulate reinforcements coated with colloidal SiO2 on Young´s modulus of Al/SiCp/MgAl2O4 composites fabricated by reactive infiltration was investigated. Composites were prepared from porous preforms of silica-coated α- SiC powders of 10, 54, 86, and 146 μm, 0.6 volume fraction of reinforcements and particle size distribution from monomodal to cuatrimodal. Infiltration tests with the alloy Al-13.3Mg-1.8Si (wt. %) were carried out in Ar→N2 atmosphere at 1100ºC for 60 min. The composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition to density and residual porosity measurements, Young´s modulus was evaluated by ultrasonic techniques. Results show that with increase in particles size distribution, residual porosity decreases and density and Young´s modulus of the composites are improved, the latter from 185.39 ±3.6 to 201.93 ±2.3 GPa. This is attributed to the increased metal-ceramic interfaces and to an enhanced matrix-reinforcement load transmission.
  • Ultrafine grained structure development in steel with different initial structure by severe plastic deformation

    Jozef, Zrnik; Sergey, Dobatkin V.; George, Raab; Martin, Fujda; Libor, Kraus

    Abstract in English:

    The present work deals with grain refinement of medium carbon steel, having different initial microstructure, modified by either thermal and/or thermomechanical treatment (TM) prior severe plastic deformation. In case of TM treated steel, structure refinement was conducted in two steps. Preliminary structure refinement has been achieved due to multistep open die forging process which provided total strain of 3. Uniform and fine recrystallized ferrite structure with grain size of the order of 2-5 μm and with nest-like pearlite colonies was obtained. The further grain refinement of steel samples having different initial structure was accomplished during warm Equal Channel Angular Pressing (ECAP) at 400°C. The microstructure development was analyzed in dependence of effective strain introduced (εef ~2.5 - 4). Employment of this processing route resulted in extensive deformation of ferrite grains where mixture of subgrains and ultrafine grain was found regardless the preliminary treatment of steel. The straining and moderate ECAP temperature caused the partial cementite lamellae fragmentation and spheroidization as straining increased. The cementite lamellae spheroidization was more extensive in TM treated steel samples. The tensile behavior was characterized by strength increase for both structural steel states; however the work hardening behavior was modified in steel where preliminary TM treatment was introduced to modified coarse ferrite-pearlite structure.
  • Processing and characterization of epoxy nanocomposites with Mwcnt's/Cnf's using thinky and 3-roll shear mixing techniques

    Hosur, M.; Barua, R.; Zainuddin, S.; Jeelani, S.; Kumar, A.; Trovillion, J.; Pereza, Y.

    Abstract in English:

    In this work, thinky mixing method was used to disperse multi-walled carbon nanotubes (MWCNT's) and carbon nanofibers (CNF's) in SC-1 epoxy either in isolation or in combination with 3-roll shear mixing. To achieve better dispersion, MWCNT mixing with SC-1 resin directly or pre-mixed with a solvent and then mixed with SC-1 resin after evaporating the solvent. Dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), flexural tests, electrical conductivity tests and micrographic analysis were performed on neat, 0.2 and 0.4wt% MWCNT/CNF infused SC-1 epoxy to observe the loading effect on thermo-mechanical properties of composites. DMA results indicated improvement on storage modulus and glass transition temperature, Tg, while flexural results exhibited enhanced flexural strength and modulus with up to 0.4wt% MWCNT/CNF infused epoxy resin over neat. TGA results revealed improved residue content but almost constant decomposition temperature for nanophased resin compared to neat. However, these enhancements were observed only up to 0.2 wt. % loading after which the properties were seen to either reduce or not significantly improve. These results indicate that the methods used for dispersion is suitable for low weight percent loading only.
  • A general study of commercially pure Ti subjected to severe plastic deformation: microstructure, strength and corrosion resistance

    Mendes Filho, A.A.; Rovere, C.A.; Kuri, S.E.; Sordi, V.L.; Ferrante, M.

    Abstract in English:

    Bars of Titanium Grade 2 were subjected to deformation by Equal Channel Angular Pressing, both at room temperature and at 300°C. Additionally, some specimens were cold rolled up to 70% reduction. From tensile tests, data such as yield, maximum strength, elongation and area reduction were obtained. Results show that the best strength - ductility combination is produced by four passes followed by cold rolling. Finally, the corrosion behavior was assessed following ASTM F2129 and no noticeable difference between the starting material and the ECAP-deformed was detected.
  • Stress-strain curves for steel fiber-reinforced concrete in compression

    Oliveira Júnior, Luiz Álvaro de; Borges, Vanessa Elizabeth dos Santos; Danin, Alice Ribeiro; Machado, Daiane Vitória Ramos; Araújo, Daniel de Lima; El Debs, Mounir Khalil; Rodrigues, Paulo Fernando

    Abstract in English:

    This paper presents a study on the compressive behavior of steel fiber-reinforced concrete. In this study, an analytical model for stress-strain curve for steel fiber-reinforced concrete is derived for concretes with strengths of 40 MPa and 60 MPa at the age of 28 days. Those concretes were reinforced with steel fibers with hooked ends 35 mm long and with aspect ratio of 65. The analytical model was compared with some experimental stress-strain curves and with some models reported in technical literature. Also, the accuracy of the proposed stress-strain curve was evaluated by comparison of the area under stress-strain curve. The results showed good agreement between analytical and experimental data and the benefits of the using of fibers in the compressive behavior of concrete.
  • Dynamic behavior of hydrogen desorption from pure iron and inconel 625 during elastic and plastic deformations

    Takai, K.; Shoda, H

    Abstract in English:

    Dynamic behavior of hydrogen desorption from pure iron with a body-centered-cubic lattice and Inconel 625 with a face-centered-cubic lattice was examined during tensile deformation using a quadrupole mass spectrometer in a vacuum chamber integrated with a tensile testing machine. Hydrogen desorption from hydrogen-charged specimens was detected under various strain rates and cyclic stresses. Hydrogen desorption rarely increased under elastic deformation. In contrast, it increased rapidly at the proof stress when plastic deformation began, reached its maximum, and then decreased gradually with increasing applied strain for both pure iron and Inconel 625. This desorption behavior is closely related to hydrogen dragging by moving dislocations. The thermal desorption analysis results showed that the amount of desorbed hydrogen differed at each strain rate. This difference in the amount of desorbed hydrogen transported by dislocations depends on the balance between the hydrogen diffusion rate and mobile dislocation velocity.
  • Thermodynamic study of non-metallic inclusion formation in SAE 1141 steel

    Bielefeldt, Wagner Viana; Vilela, Antônio Cezar Faria

    Abstract in English:

    The main purpose of this paper is the thermodynamic study of non-metallic inclusion formation in the CC tundish for SAE 1141 steel. The specific purposes are: 1) obtaining inclusions as function of steel composition and casting temperature. 2) establishing steel chemical composition to form less harmful inclusions to the SAE 1141 steel castability. Simulations using the commercial software FactSage and databases were carried out. Results showed both different solid oxides and liquid phase formation in inclusions by varying calcium content in the steel. Thus, it was possible: 1) to determine both the inclusion composition as a function of aluminum and calcium content of SAE 1141 steel. 2) to establish a range of calcium content in which inclusions are formed predominantly by liquid phase. 3) to calculate percentage of liquid and solid phases in inclusions, and oxides composition as well.
  • The effect of specimen dimensions on the propensity to adiabatic shear failure in Kolsky bar experiments

    Rosenberg, Zvi; Ashuach, Yechezkel; Kreif, Rafael

    Abstract in English:

    The issue of adiabatic shearing is discussed in this work and a new interpretation is given to some failure phenomena which are usually termed as adiabatic shears. We propose that only a few materials undergo a truly inherent failure which is due to thermal softening at the shearing zone and that the interplay between microvoids, cracks and narrow shear bands should be taken into account through the temperature rise at the front of advancing cracks. Also, the size of the plastic zone ahead of a crack plays an important role in determining the brittleness of a given specimen and should be taken into account when specimens of different sizes are tested. Experimental results for several alloys in the Kolsky bar system support our approach.
  • Microstructural evolution of AA7050 al alloy processed by ECAP

    Cardoso, E. K.; Guido, V.; Silva, G.; Botta Filho, W.; Jorge Junior, A.

    Abstract in English:

    This work aimed to study the microstructural evolution of commercial aluminum alloy AA7050 in the solution treated condition (W) processed by equal channel angular pressing - ECAP. The analyses were made considering the effects of process parameters as temperature (Tamb and 150°C), processing route (A and B C) and number of passes. Optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for microstructural characterization, and hardness tests for a preliminary assessment of mechanical properties. The results show that the refining of the microstructure by ECAP occurred by the formation of deformation bands, with the formation of dislocations cells and subgrains within these bands. The increase of the ECAP temperature led to the formation of more defined subgrains contours and intense precipitation of η phase in the form of spherical particles. The samples processed by Route B C present a more refined microstructure.
  • Hardness evaluation, stoichiometry and grain size of titanium nitride films obtained with plasma nitriding on Ti-6Al-4V samples

    Vasconcellos, Marcos Antonio Zen; Lima, Saulo Cordeiro; Hinrichs, Ruth

    Abstract in English:

    Titanium nitride films were formed on the surface of Ti-6Al-4V discs by plasma nitriding (glow discharge) in different N2:H2 atmospheres at several substrate temperatures. In this study the influence of the process parameters on dynamic micro-hardness were investigated. Grain sizes of the nitride films, determined with X-Ray Diffraction, were related to the nitriding parameters. TiNx stoichiometry was determined with Nuclear Reaction Analysis and showed a correlation to substrate temperature during the nitriding process. Micro-hardness measurements were taken on the nitrided surfaces. Grain sizes increased for a particular gas composition of 60%N2+40%H2 where hardness was lowest.
  • Gelatin/piassava composites treated by electron beam radiation

    Takinami, P.Y.I.; Shimazaki, K.; Colombo, M.A.; Moura, E.A.B. de; Mastro, N.L. del

    Abstract in English:

    Piassava (Attalea funifera Mart) fiber has been investigated as reinforcement for polymer composites with potential for practical applications. The purpose of the present work was to assess the behavior of specimens of piassava fiber and gelatin irradiated with electron beam at different doses and percentage. The piassava/gelatin specimens were made with 5 and 10% (w/w) piassava fiber, gelatin 25% (w/w), glycerin as plasticizer and acrylamide as copolymer. The samples were irradiated up to 40 kGy using an electron beam accelerator, at room temperature in presence of air. Preliminary results showed mechanical properties enhancement with the increase in radiation dose.
  • Evaluation of polypropylene/saw dust composites prepared with maleated polypropylene (mapp) produced by reactive extrusion

    Trombetta, Ernani; Flores-Sahagun, Thais; Satyanarayana, Kestur G.

    Abstract in English:

    Considering the importance of the environment and fuel economy, the Brazilian automotive industry has focused on the development of lightweight materials based on renewable resources. Replacement of PP- talc composite by PP- saw dust composite is a promising possibility. This paper presents the preparation of maleated polypropylene (MAPP) through reactive extrusion using different amounts of peroxides and maleic anhydride as well its characterization. Using 20% of saw dust coated with different amounts of prepared MAPP, several composites were prepared including one with commercial MAPP. Injection molded samples of all these composites along with that without the compatibilizer were characterized for mechanical properties. These studies indicated fulfilling the proposed objectives: (i) finding the optimal reactive extrusion conditions to prepare MAPP samples; (ii) preparation of PP/saw dust composites with and without MAPP coating; (iii) to arrive at optimized composite to get the best performance through their characterization for various properties of all the produced composites.
  • Effects of microstructure on the fatigue crack growth behavior of light metals and design considerations

    Gavras, Anastasios G.; Chenelle, Brendan F.; Lados, Diana A.

    Abstract in English:

    Fatigue crack growth mechanisms of long and small cracks were investigated in cast and wrought aluminum and titanium alloys with various microstructures (as-cast A535, 6061-T61, and mill-and beta annealed Ti-6Al-4V). In addition, friction stir welded and cold spray processed 6061-T61 were also investigated. The effects of microstructure on the fatigue crack growth response of each material were evaluated. Long crack growth data were generated on compact tension specimens at low and high stress ratios R=0.1 and 0.7, respectively. Small crack growth testing was performed on corner and surface flaw tension specimens at low stress ratio, R=0.1. Fatigue crack growth mechanisms at the microstructural scale of the materials were identified and will be discussed. Closure corrections were applied to long crack growth data, and the results were compared to experimental small crack growth data. Models for small crack growth predictions from long crack growth data will also be presented and discussed.
  • Preparation and characterization of biodegradable composites based on Brazilian cassava starch, corn starch and green coconut fibers

    Ramírez, María Guadalupe Lomelí; Muniz, Graciela I. Bolzon de.; Satyanarayana, Kestur G.; Tanobe, Valcineide; Iwakiri, Setsuo

    Abstract in English:

    Increasing search for new materials with high premium on eco-friendliness, new trend is emerging in materials development such as composites, which are well established for a wide variety of applications. With growing interest and importance of renewable bioresources has led to more stress on the use of locally available materials. This paper presents preliminary results on the preparation and characterization of composites based on Brazilian coconut fibers and starches of cassava and corn. The raw materials were characterized for their morphology, chemical composition, and thermal properties and X-ray diffraction studies. Coir fibers were also tested for their tensile properties showing increasing strength and Young's modulus with decreasing diameter, while the % elongation remaining constant. Lignin content of coir was found to be 35%. Structure and properties of composites containing 0, 5 10, 15% fibers in both the matrices and prepared by compression molding would be compared. For the 2 types of starch, there was an increase in the tensile strength by the increasing proportion of fiber. The effect of moisture in the composite stress affects the strength and percentage elongation. The water absorption was higher in the composites made from cassava starch.
  • A multi-scale investigation of the mechanical behavior of durable sisal fiber cement composites

    Silva, Flávio de Andrade; Toledo Filho, Romildo D.; Mobasher, Barzin; Chawla, Nikhilesh

    Abstract in English:

    Durable sisal fiber cement composites reinforced with long unidirectional aligned fibers were developed and their mechanical behavior was characterized in a multi-scale level. Tensile tests were performed in individual sisal fibers. Weibull statistics were used to quantify the degree of variability in fiber strength at different gage lengths. The fiber-matrix pull-out behavior was evaluated at several curing ages and embedded lengths. The composite's mechanical response was measured under direct tension while crack formation was investigated using a high resolution image capturing procedure. Crack spacing was measured using image analysis and correlated with the applied strain under both the tensile and bending response.
  • Processing of a duplex stainless steel by equal channel angular extrusion

    Farias, F.A.; Pontes, M.J.H.; Cintho, O.M.

    Abstract in English:

    A UNS S32205 duplex stainless steel was processed by ECAE in three different velocities, at room temperature, and heat treated in different temperatures and times to evaluate recrystallization. Attrition forces promoted great deformation heterogeneity in the samples sections, with hardness increase, and morphology changes in the grains and changing orientation through the processed samples. In treated samples surface, two types of distinct structures was formed, with surfaces positioned in 90º and 120º angles, probably because the annihilation of pilled dislocations in ferrite based centered cubic structure and austenite face centered cubic structure, respectively. The induced martensite by cold deformation was also observed. Some samples demonstrate located points of recrystallization in grain boundaries for some treatment conditions, the number of recrystallization nuclei increased with the increase of treatment time.
  • Vegetable fibers as multifunctional materials

    Amico, S.C.

    Abstract in English:

    Concerns related to the ever-growing use of raw-materials from non-renewable sources by modern society is driving the interest of the academic and scientific sectors for a new concept of material, which takes into account not only mechanical performance, cost and availability, but also environmentally-related issues, such as biodegradability, renewability and energy use, along with the promotion of social and economical development of the economically-challenged segment of the population. Vegetable fibers have been used in many home-made objects, such as ropes and artcraft, for perhaps as long as humanity exists. However, these fibers present a combination of interesting properties which enables their use in a wide variety of sectors. This invited article will review the work recently carried out by the author in collaboration with various researchers from UFRGS, UFPR and UCS, and will be divided into three case studies, focusing on the use of vegetable fibers for oil sorption, as infiltration (flow) medium and as reinforcement for polymer composites, promoting their use in more demanding and rewarding applications.
  • Deformation and fracture of an alpha/beta titanium alloy

    Andrade, A.; Morcelli, A.; Lobo, R.

    Abstract in English:

    Titanium alloys are used in the aero-spatial, energy and biomaterial industries among others and exhibit high specific strength and fracture toughness. Their mechanical properties show a strong dependence on the microstructure, especially on the size and morphology of the constituent phases. An experimental evaluation was done to a better understanding of that influence, using some techniques like as transmission electron microscopy (TEM), both low and high resolution (HR), scanning electron microscopy (SEM), coupled to electron back-scattering diffraction (EBSD), X-ray diffraction (XRD) and optical microscopy (OM). Some in-situ TEM deformation studies were also done. The alloy was submitted to two heat treatment conditions to get different phases distribution. An hcp phase (alpha) in coexistence with a bcc phase (beta) was observed after both treatments as well the occurrence of twins, stacking faults and dislocations arrangements. The work then, discusses the influence of these features on the overall alloy strength.
  • Characterization and exploitation of piston ring chips in the rectification process a new recycling proposal

    Teixeira, A.; Dias, J. C.; Silva, E. M. da; Silva, M. R. da; Gontijo, M. R. F.

    Abstract in English:

    The rough grind machine operation in metallic material produce a sub product with the followings components such as: metallic residue, small parts come from the resin grinds, diatomaceous earth material (filter material) and soluble oil in water for tools cooling. According [HU1UH] from ABNT, this sub product is toxic, not inert material, aggress the environment with pollution in the currency water and contaminate the ground when incorrectly go to the municipal solid waste. The final destination of this sub product, is the incineration, in the cements company, being the incorporated the sub product to the cement, during your production. With the qualitative result using the scanning electron microscopy (SEM), coupled to the dispersive energy spectroscopy (EDS), two experiments were made with objective to separate the magnetic material of the non-magnetic material, using a permanent magnet. We conclude that the magnetic material can be used by powder metallurgy process in production of pieces.
  • Effect of electron beam irradiation on mechanical properties of gelatin/Brazil nut shell fiber composites

    Inamura, Patrícia Y.; Shimazaki, Kleber; Colombo, Maria Aparecida; Rosa, Ricardo de; Moura, Esperidiana Augusta Barretos de; Mastro, Nelida L. del

    Abstract in English:

    The use of natural fiber as polymeric matrix reinforcement has attracted interest, as fibers are renewable, of low cost, biodegradable and possesses non-toxic properties. In the present paper, Brazil nuts (Bertholletia excelsa) shell fiber (10% w/w) were mixed with gelatin (25% w/w), glycerin as plasticizer and acrylamide as copolymer to investigate the resultant mechanical properties effects upon ionizing radiation. The samples were irradiated at 40 kGy using a Dynamitron electron beam accelerator, at room temperature in the presence of air. The results showed that samples of gelatin with 10% of Brazil nuts shell fiber and irradiated at 40 kGy presented promising results for mechanical performance.
  • Cell adhesion on different titanium-coated surfaces

    Resende, Cristiane X.; Lima, Ingrid R.; Gemelli, Enori; Granjeiro, José M.; Soares, Glória de A.

    Abstract in English:

    Titanium (Ti) is a biocompatible material, and calcium phosphate coating on titanium is commonly applied in order to obtain faster osseointegration around metallic implant. Osteoblast adhesion on three different Ti surfaces was evaluated. The investigated surfaces were commercially pure Ti (cp Ti), Ti coated with sodium titanate (Na-Ti), and Na-Ti followed by octacalcium phosphate coating (Ti-OCP) done by immersion in a calcium and phosphate-rich solution. The studied materials exhibited different morphology and composition. However, all the surfaces promoted cellular adhesion and showed cytocompatibility. No statistically significant difference was observed among the evaluated samples in relation to the number of cells.
Laboratório de Hidrogênio, Coppe - Universidade Federal do Rio de Janeiro, em cooperação com a Associação Brasileira do Hidrogênio, ABH2 Av. Moniz Aragão, 207, 21941-594, Rio de Janeiro, RJ, Brasil, Tel: +55 (21) 3938-8791 - Rio de Janeiro - RJ - Brazil
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