bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Fatigue and Cumulative Damage Characteristics for Concrete in Freezing-Thawing Environment
Authors: Xiao Qian Hui
Published: November 2012

Through analyzing the characteristic of concrete freezing-thawing cumulative damage, concrete freezing-thawing damage can be with fatigue problems with similar methods to analysis. Coagulation Earth material property discrete and cause damage in a given amount of state natural freeze-thaw cycle times is a random variable, analysis found that it is better to obey three-parameter Weibull distribution. Based on three parameters Weibull distribution model, the test data in had established, on the basis of freezing-thawing environment concrete damage and freeze-thaw cycles of the probability of the relation curve, and regression to obtain different guarantee rate of freezing-thawing damage cumulative model for freezing-thawing environment,which could be provides reference for concrete service life prediction and health diagnosis.
Numerical Simulation of Hypervelocity Impact on Mesh Bumper Causing Fragmentation and Ejection
Authors: Guan Gong Shun , Niu Rui Tao
Published: November 2012

In order to study the fragmentation of projectile and ejection of debris clouds caused by hypervelocity impacting mesh bumper, simulation of aluminum sphere projectile hypervelocity normal impacting aluminum mesh bumper was practiced with SPH arithmetic of LS-DYNA soft. The diameter of projectile was 4mm. Impact velocities of aluminum spheres were varied between 2.2km/s and 6.2km/s. The impact angle was 0°. The relationship between the debris clouds characteristic of projectile and the impact position on aluminum mesh bumper was studied. The effect on fragmentation of projectile from different combination mode of aluminum mesh bumper was analyzed. The results showed that the morphologies of the debris cloud varied with the impact position when a projectile impacted the mesh bumper. The debris clouds as palpus was found, and some local kinetic energy concentrated appeared in the debris clouds. Debris clouds distribution was more uniform when projectile impacted wire across point on the mesh bumper. Debris clouds had more diffuse area and less residual kinetic energy when mesh bumper was combined with interleaving mode. Mesh bumper combined with interleaving mode was helpful in enhancing the protection performance of shields.
Correlation between Alternating Temperature Accelerated Aging and Real World Storage of Composite Propellant
Authors: Ding Biao , Shi Pei , Qiu Xin
Published: November 2012

Alternating temperature accelerated aging test was designed to ensure that accelerated aging could preferably simulate real world storage of HTPB composite propellant. Mechanical properties of HTPB propellant aged for three different periods were measured and analyzed. The results indicate that, the tensile strength increased and the elongation decreased after accelerated aging, showing the same trend of real world storage; the mechanical properties of HTPB propellant is strongly influenced by the rate of temperature change; alternating temperature accelerated aging test is consistent well with real world storage. The results can be very helpful for solid rocket motor life prediction.
Effect of Surface Treatment on Creep Property of Jute Fiber Reinforced Green Composite under Environmental Temperature
Authors: Takemura Kenichi , Miyamoto Satoshi , Katogi Hideaki
Published: November 2012

In this study, effect of surface treatment on creep property of green composite under environmental temperature was investigated. Jute fiber was used as reinforcement. PLA (polylactic acid) was used as matrix. Surface treatments were conducted using 5 % solution of silane coupling agent and PVA (polyvinyl alcohol). The flexural test was conducted under 25°C environment. The flexural creep test was conducted for 50 hours at 25, 40 and 50°C environment. As a result, the flexural property of composite increased by the surface treatments. And the surface treatments affected the adhesion of fiber/resin interface. Creep strains of surface-treated jute fiber/resin composites were lower than that of virgin composite. The creep strain was decreased by the treatments. The effects are confirmed under various temperature conditions.
Impact and Sliding Wear Properties of Single Layer, Multilayer and Nanocomposite Physical Vapour Deposited (PVD) Coatings on the Plasma Nitrided Low-Alloy 42CrMo4 Steel
Authors: Surzhenkov Andrei , Adoberg Eron , Põdra Priit , Sergejev Fjodor , Mere Arvo , Viljus Mart , Mikli Valdek , Antonov Maksim , Kulu Priit
Published: November 2012

Current paper handles the comparison of impact wear and sliding wear properties of the hard PVD single layer TiN and Ti(C,N), multilayer (Ti,Al)N and nanocomposite FiVIc® coatings on the plasma nitrided low-alloy 42CrMo4 steel. All the studied coatings demonstrated a relatively high impact wear resistance at the low (104) and medium (105) number of impacts, however, all the studied coatings vanished at the high number of impacts (106). Most extensive wear among the coatings during the sliding wear test was observed for the (Ti,Al)N coating, the FiVIc® showed the least extensive wear; the most extensive wear of the counterbody (hardened steel ball) was registered for the (Ti,Al)N coating, the lowest – for the FiVIc® and Ti(C,N) coatings. The principle wear mechanism of coatings was tribooxidation and mild abrasion, of the counterbody – plastic deformation
Processing and Characterization of Porous Silica-Ag-Nanoparticle Composites Produced by Pulsed Electric Current Sintering
Authors: Larismaa Juha , Söderberg Outi , Syrén Jesse , Haimi Eero , Hannula Simo Pekka
Published: November 2012

This paper studies influence of the process temperature and time on the properties of the compacts made of Ag-SiO2 powder by the pulsed electric current sintering (PECS). Silica particles doped with Ag nanoparticles were prepared by modified Stöber method, and calcinated at 573 K in air resulting in average silica particle size of ~1.1 µm and agglomerate size up to 32 µm. There was about 7 wt.% of silver in the structure and the diameter of the silver particles on the silica carriers was 30 ±7 nm on average. The composite powder was sintered into porous compacts by PECS at 873, 973, 1073, or 1173 K for 10, 20, or 30 min under pressure of 50 MPa. Samples were characterized by SEM, XRD, UV-vis-spectrometer, and laser diffraction. During PECS compaction grain growth of silver particles was observed and the measured average size of Ag in 873 K and in 1173 K samples were 65 nm and 170 nm, respectively. The porosity of the materials did not show remarkable change, as the relative density ranged from 76 to 79 %. Thus, it is possible to produce porous silica based materials with controlled Ag-nanoparticle size by PECS. These materials may be optimized for, e.g., different kinds of antibacterial filters.
3-D Model of the Periodic Structure Punch Sliding upon the Viscoelastic Base with Incompressible Fluid in the Contact Gap
Authors: Gorycheva I.G. , Shpenev Alexey G.
Published: November 2012

In this paper the problem for a periodic structure punch sliding upon a viscoelastic layer bonded to a rigid half space is considered. The semi-analytical solution of the problem is developed. Influence of incompressible fluid in the gap between two bodies upon friction force, contact size and pressure distribution is analysed. The obtained model can be used in a number of practical applications, for example in accounting of automobile tire aquaplaning upon wet road surface.
The Effects of Heat Treatment and Deformation on the Martensitic Transformation of FeMn (Cr) Steels
Authors: Tranta Ferenc , Weiss Andreas
Published: November 2012

The ε martensite phase was investigated in three types of FeMn (Cr) steels by means of metallographic, EBSD and XRD methods as well as by dilatometric and DSC examinations during heating and cooling. In the course of the latter examinations, the transformation temperatures (Ms, As) of ε martensite were determined in the previously deformed samples as well. The results were also compared to the thermodynamic data published in the references describing the γε and γα transformations.
On the Role of Phenomenology and Dislocations in Modelling of Portevin - Le Chatelier Effect
Authors: Béda Peter B.
Published: November 2012

A strange self-sustained oscillation in plastic uniaxial tension of various materials is called the Portevin Le Chatelier (PLC) effect. In modelling PLC dynamic strain aging is the common way of explanation. It is based mainly on dislocation dynamics. Experimental studies show the negative strain rate dependence (NRS) is always present at PLC. By using continuum mechanics and dynamical systems theory we find that NRS is the essential reason of it.
Development of PA6/HDPE Nanocomposite Blends
Authors: Hargitai Hajnalka , Ibriksz Tamás , Stifter János , Andersen Endre
Published: November 2012

In our experiments polyamide 6/high density polyethylene blends (25/75 wt%) were produced and maleic anhydride grafted polyethylene was used as chemical coupling agent. To get finer microstructure and enhance the mechanical properties the blends were compounded by different nanostructured reinforcements. Two kinds of nanosilicate, the layered structure montmorillonite and the needle like sepiolite were applied in different concentrations and their effect on the mechanical and melting properties were examined.
Development of Carbon Nanotube Reinforced Conductive Polymer Composites for PEM Fuel Cells
Authors: Olah M. , Ronkay Ferenc
Published: November 2012

Investigation of conductive polymer composites have been carried out using polypropylene (PP) and polyphenylene sulfonate (PPS) for matrix compound and graphite, carbon black and multi walled carbon nanotubes (MWCNT) for fillers. The comparison of these matrix materials with respect to the resulting electrical conductivity were investigated in depth. The effect of quantity of nanotubes and their dispersion on electrical conductivity and formability was also investigated. It has been found that PPS composites show much higher conductivity, however the high temperature needed for forming, and high viscosity in case of high filler content (50 wt% <) make the processing difficult, therefore the injection molding of the resulting material is currently not possible. Furthermore in contradiction to the literature the addition of MWCNT did not raise the conductivity significantly, therefore the focus have been kept on filler content instead.
Influence of Composition and Grain Size Distribution on the Properties of Limestone and Dolomite Asphalt Fillers
Authors: Geber Robert , Kocserha István , Gömze László A.
Published: November 2012

The aim of the present research work is to examine the influence of mineral composition and grain size distribution on the properties of limestone and dolomite mineral fillers used in Hungarian road construction. Since these properties fundamentally define the features of asphalt pavements, our research goals were assigned accordingly. Different fractions of two mineral fillers (limestone from Alsózsolca and dolomite from Pilisvörösvár) were compared. We have observed deviations in the grain size distribution of some fractions of fillers that were free of contaminations. While limestone consists of a great amount of fines and a relatively small amount of coarse grains, in case of dolomite it is the opposite, that is, small amount of fines and greater amount of coarse grains. The decrease of the grain size of fractions resulted in a slight increase of specific surface area of fillers. We have observed that by the decrease of the grain size of fillers, the hydrophilic coefficient has also decreased. The increasing presence of fines however, resulted in the decrease of the hydrophilic coefficient.
New Advanced SiC Ceramics Based on Natural Biomaterials
Authors: Gömze László A. , Lipusz Dóra , Gömze Ludmila N.
Published: November 2012

On the basis of several years experiments in investigation of hetero-modulus material structures and using natural biomaterials and high purity quartz powders the authors successfully developed new high porosity low density SiC ceramic cellulars and foams. For the development of new silicon-carbide and carbon-silicon-carbide (C/SiC) cellular ceramic composites and foams the author used high purity SiO2 powders mined in Fehervarcsurgo (Hungary) and a biomaterial reagents made from renewable vegetable under trade-name IG-R1. These low density high porosity silicon-carbides probably can be successfully applied in development of light weight ceramic reinforced metal alloy composites in the future. The structure and X-ray diffraction (XRD) analysis of used raw materials and the achieved by authors new SiC and C/SiC ceramic composites and foams are described and shown in present work.
On the Effects of Mechanical and Thermal Treatment Strategies Regarding the Grain Boundary Structure of Polycrystalline Copper
Authors: Varga P. , Szabó Péter János
Published: November 2012

Commercial Cu-ETP drawn copper bar was both mechanically and thermally treated. Repeated cycles of cold rolling and heat treatment with altered parameters were applied on the specimens. Grain boundary character distribution (GBCD) was calculated from the orientation microscopy data. As regards the processing of the orientation data the coincidence site lattice theory was applied. The evolution of the GBCD is discussed in terms of the parameters of cold rolling and heat treatment processes.
Infiltration Characteristics and Compressive Behaviour of Metal Matrix Syntactic Foams
Authors: Orbulov Imre Norbert , Ginsztler János , Kun Peter
Published: November 2012

The most promising process for metal matrix syntactic foam (MMSF) production is pressure infiltration. In case if it can be advanced to die casting the cost of the MMSFs will drop significantly. The first step on this road is to characterize the kinetics of the pressure infiltration with respect to infiltration pressure and time. Experimental infiltration equipment was built and many preliminary tests were performed on the AlSi12 + SLG system. The load bearing capacity is also important, therefore the compressive behaviour of MMSFs were investigated. According to the results engineering factors (matrix material, size of the microballoons, applied heat treatment, temperature of the tests) have significant effects on the compressive properties.
Incremental Forming: An Innovative Process for Small Batch Production
Authors: Tisza Miklos , Kovács Péter Zoltán , Lukács Zsolt
Published: November 2012

The need for flexible forming processes is of utmost importance in the recent years. Therefore, it is very important to develop new innovative technologies and processes. This is particularly valid for small batch and prototype production. Incremental sheet metal forming may be regarded as one of the promising developments for these purposes. In this paper, first a general overview of main process characteristics of the incremental sheet metal forming will be given. Then some recent results of a joint Eureka project launched by two universities and two SME companies in Hungary and Slovenia will be presented.
Examination of Aluminium Based Automotive Casting
Authors: Godzsák Melinda , Gácsi Zoltán
Published: November 2012

Automotive castings have to meet more and more versatile requirements these days. One of the most important requirements towards suppliers and foundries is producing parts of better quality, higher performance but at the same time of less weight. In order to couple this small weight with high performance and excellent quality these products should meet very strict mechanical standards of automotive parts. There is a constant need for production engineering developments ranging from purity degree - that is producing molten metal with high cleanness - to grain refinement and alloy improving including heat treatment technologies.
A Method for Complete Characterization of the Macroscopic Geometry of Grain Boundaries
Authors: Kiss Á.K. , Lábár J.L.
Published: November 2012

In the current paper a new method is presented that determines the five macroscopic parameters of a grain boundary (GB) from electron diffraction patterns and bright field (BF) images in a transmission electron microscope. Usefulness of the method is demonstrated on a set of GBs measured in laser crystallized Si thin films. To characterize the geometry of a grain boundary, we have to determine the misorientation between the neighboring grains, and the direction of the GB-plane. The misorientation is calculated from two convergent beam electron diffraction (CBED) patterns taken on the neighboring grains, and the plane-normal can be calculated from bright field (BF) images of the GB. The thickness of the sample is also needed and it is measured from a CBED pattern taken in two-beam condition. It has been previously observed in metallic thin films, that the GBs can minimize their energy in two alternative ways in thin films: either forming a GB plane with low energy density or minimizing the area of the plane. In the last case the GB plane is almost normal to the surface of the specimen and has a general index. We found, that boundaries with exact Σ3 misorientation generally adopted low energy-density {111} boundary planes and formed coherent twins. The rest of the boundaries adopted general index planes and minimized the surface area of the boundary. The last group included boundaries with small deviation from 3 misorientation, other special high-angle boundaries with-value>3 and boundaries with general misorientation.
Fabrication of Bi6Fe2Ti3O18 Ceramics by Mixed Oxide Method
Authors: Lisińska-Czekaj Agata
Published: November 2012

In the present study Bi6Fe2Ti3O18 (BFTO) ceramics has been fabricated by solid state reaction from the mixture of simple oxides viz. Bi2O3, TiO2 and Fe2O3. Stoichiometric mixture of the powders was thermally analyzed so parameters of the thermal treatment were determined. The EDS measurements have shown conservation of the chemical composition of the ceramic powder after calcination. Hot-pressing method was used for final densification of ceramic samples. The crystalline structure of the sintered samples was examined by X-ray diffraction method at room temperature. It was found that BFTO ceramics sintered at T=980 °C adopted the orthorhombic structure of Aba2 (41) space group with the following elementary cell parameters: a=5.4567(2)Å, b=49.418(2) and c=5.4826(2). Details concerning the atom’s positions are presented.
Sol-Gel Synthesis and Characterization of Barium Lanthanum Titanate Ceramics
Authors: Osinska Katarzyna , Smalarz Grzegorz , Wodecka-Dus Beata , Czekaj Dionizy
Published: November 2012

The (Ba1-xLax)Ti1-x/4O3 (BLT) ceramics for lanthanum content x in the range 0£x£0.005 were prepared by the sol-gel method. Barium acetate, lanthanum acetate and titanium (IV) propoxide were used as starting materials. Glacial acetic acid and n-propyl alcohol were used as solvents and acetyloacetone was added as stabilizer, followed by hydrolysis. Thermal evolution of the dried gel as well as ceramic powder was studied by simultaneous thermal analysis. The amorphous gel of BLT was calcined in the furnace and pressed into pellets. The compacts were next sintered at temperature T=1100°C. The crystalline structure of BLT ceramics was studied by X-ray diffraction method. Morphology of BLT ceramics was studied by scanning electron microscopy.
Fatigue Resistance and Crack Initiation Mechanisms in Nitrided Steel Treated with Selected Types of Surface Coating
Authors: Černý Ivo , Mikulová Dagmar
Published: November 2012

Surface treatment processes are usually applied to improve surface characteristics and resistance. Particularly duplex processes like nitriding combined with nanostructured based coatings are considered as the most advanced ones, with a large application potential in automotive industry. An example is an application in gear wheels, where fatigue loading in gear teeth roots exists besides contact fatigue on teeth sides. Contact fatigue, has to be therefore well balanced with pure fatigue resistance. Some surface treatments leading to excellent contact properties, wear resistance and extremely low friction coefficient may reduce resistance to pure fatigue crack initiation and subsequent growth to premature failure. In the paper, results of an experimental programme aimed at evaluation of fatigue resistance at repeated loading of nitrided steel after application of two types of coating, (i) nanostructured C-layer deposited by a modified cathodic arc technique according to Microcoat patent and (ii) Cr-WC:H-DLC layer produced according to Hauzer patent [1], are presented and discussed. Fatigue tests were carried out using small samples with 2.1 mm diameter, with nitrided layer of 0.35 mm thickness. Tests were completed with fractographical analyses of initiation areas. Results and analyses showed that coating effects depended on the specific technology and parameters. The Cr-WC:H-DLC layer affected fatigue limit favourably unlike the Microcoat C-layer, which resulted in reduction of fatigue strength. A detailed analysis of recorded data during static tensile tests indicated an occurrence of significant surface and subsurface residual stresses with a strong possible effect on fatigue crack initiation mechanisms. A significant, unfavourable effect of inclusions in the subsurface layer was demonstrated.
Structural Features of Electrodeposited Copper Electrodes for CO2 Conversion
Authors: Reis Machado A. S. , Fernandes T. R. C. , Pardal Tiago , Rangel Carmen M.
Published: November 2012

Direct electrochemical reduction of CO2 is a process that could contribute to the reduction of the emission of greenhouse gases by using CO2 as a raw material for fuel production. This paper focuses on voltammetric studies of functionalized electrodes for the electrochemical conversion of CO2 and reports on its use as a tool for electrode screening and optimization. Nickel substrates modified with copper and ruthenium/copper electrodeposits were studied. Voltammetric experiments indicate that CO2 electroreduction follows a nickel type mechanism in which this electrochemical reaction occurs simultaneously and in competition with hydrogen evolution. A significant inhibition of hydrogen evolution reaction is observed in nickel modified electrodes. Inhibition characteristics and the onset of carbon dioxide conversion are dependent of the type of electrode functionalization. Voltammetry is thus a powerful tool to evaluate electrode modifications and for tuning electrodes for an optimized electrocatalytic performance.
Drilling Delamination Outcomes on Glass and Sisal Reinforced Plastics
Authors: Durão Luís Miguel P. , Gonçalves Daniel J.S. , Tavares João Manuel R. S. , de Albuquerque Victor Hugo C. , Panzera Túlio Hallak , Silva Leandro J. , Vieira A. Aguiar , Baptista A.P.M.
Published: November 2012

Nowadays, fibre reinforced plastics are used in a wide variety of applications. Apart from the most known reinforcement fibres, like glass or carbon, natural fibres can be seen as an economical alternative. However, some mistrust is yet limiting the use of such materials, being one of the main reasons the inconsistency normally found in their mechanical properties. It should be noticed that these materials are more used for their low density than for their high stiffness. In this work, two different types of reinforced plates were compared: glass reinforced epoxy plate and sisal reinforced epoxy plate. For material characterization purposes, tensile and flexural tests were carried out. Main properties of both materials, like elastic modulus, tensile strength or flexural modulus, are presented and compared with reference values. Afterwards, plates were drilled under two different feed rates: low and high, with two diverse tools: twist and brad type drill, while cutting speed was kept constant. Thrust forces during drilling were monitored. Then, delamination area around the hole was assessed by using digital images that were processed using a computational platform previously developed. Finally, drilled plates were mechanically tested for bearing and open-hole resistance. Results were compared and correlated with the measured delamination. Conclusions contribute to the understanding of natural fibres reinforced plastics as a substitute to glass fibres reinforced plastics, helping on cost reductions without compromising reliability, as well as the consequence of delamination on mechanical resistance of this type of composites.
Failure Analysis of a Damaged Helicopter Rescue Hoist Cable
Authors: Morgado Teresa L.M. , Brito Armando Sousa , Branco Carlos M.
Published: November 2012

This paper presents the results and main conclusions of a study made to analyze the cause of failure occurred with an austenitic 304 class stainless steel wire rope of a helicopter rescue hoist. The cable is made up of 19 strands, 12 outside and 7 inside. As each strand contains 7 wires, the whole cable is made up of 133 wires. The study includes the chemical and microstructural characterization of the material, as well as the determination of its hardness, mechanical properties and the fractographic analysis by scanning electron microscopy (SEM). Tensile tests were performed for three velocities simulating different work conditions: 250mm/min, 50mm/min and 5mm/min. The fractographic analysis shows that the cable suffered lateral loss of material due to friction and leading to the failure of the remaining material by ductile mode.
Improving the Dynamical Behaviour of a Laser Cutting Equipment by Using a Carbon Fibre Composite Main Structural Runway Frame
Authors: Vieira Daniel G. , de Meireles José Filipe Bizarro , Nunes João Pedro
Published: November 2012

In order to improve the dynamic behaviour of an industrial laser cutting equipment a sandwich solution, using a carbon fibre reinforced polymer (CFRP) and polyester foam core, was implemented to construct its main runway structural frame, which supports the cutting head and major laser beam mirrors and lens. Nowadays, the commercial competiveness of laser cutting equipments is considerable enhanced by their higher cutting speed and precision, as well as, cost. With the recent available higher power laser beam generators and swifter motors quicker and powerful cuts may be already done. However, at accelerations of 3 and 4 g’s already enabled by linear motors, the lack of stiffness and high mass and consequent inertia of the traditional runway structural frames, made from steel and/or aluminium, do not allow achieving high required cutting precisions. Thus, the present study considered replacing those conventional materials by much lighter advanced CRFP composites to improve the dynamic performance of an existing laser cutting equipment. Advanced numeric Finite Element Method (FEM) calculations by using the ANSYS package software were made to verify the static and dynamic behaviours of the new composite structural frame and compare them to simulations made with the currently used steel solution. The composite structural frame processing method has been also studied and defined in this work. Furthermore, the composite laminate has been optimised by defining the better number of stacking layers and fibre orientations to be used, as well as, the foam core thickness. The failure of the new sandwich structural composite runway frame has been verified through the Tsai-Wu criterion. Finally, an economic analysis of the viability of the new composite solution adopted will be also presented.
Model of TiO2-ZnO Composite Sensors by Impedance Spectroscopy
Authors: Silva Robert , Faia Pedro M. , Santos Mario J. , Ferreira A.R. , Furtado C.S.
Published: November 2012

With the study of composite materials based on the TiO2-ZnO pair, we look for better sensitivity and selectivity to the gases, than those of the sensors made out of only one of those metal oxides. This would be due to the fact that some of the interstitial positions that were initially occupied by the atoms of one of the metals are now occupied by atoms of the other metal: if the single covalent/ionic adsorption is decisive in the observed changes in the materials conductivity, then the electronegativity of the occupying metal atoms may be used to regulate the sensitivity and selectivity. We will present the results obtained for pelletized sensors of the pair TiO2-ZnO, with a 85:15 % volume mol ratio of Titanium and Zinc, sintered at 400º and 500°C. The rather involved behaviour of our sensors is understood by measuring their complex impedance subjected to an external sinusoidal varying electric field, which is being applied in the presence of different relative humidities, at various working temperatures. The main goal of this work here described is the study of the relative humidity influence on the sensing properties of the composite sensors, and the development of an electrical model for the sensor electrical response.
Natural Fibres as Reinforcement Strategy on Cork-Polymer Composites
Authors: Fernandes Emanuel M. , Correlo Vitor M. , Mano João F. , Reis Rui L.
Published: November 2012

Cork powder, the most important sub-product of cork processing, combined with thermoplastic matrixes like, high density polyethylene (HDPE), offer a new class of cork-polymer composite (CPC) materials with high added-value. Therefore, reinforcing strategies must be considered to increase the mechanical performance, especially when high content of cork powder is added to the formulation. Coconut fibres have several advantages, such as, low density, renewable source, low cost and biodegradability. The use of these fibres on the reinforcement of CPC materials will not only contribute to improve the mechanical performance but also for increasing the amount of natural component present on the final composition. The main goal of this work was to prepare HDPE/cork (50-50 wt.%) composites reinforced with discontinuous coconut fibres (5 and 10 wt.%) with and without the addition of coupling agent (2 wt.%) by extrusion. The developed reinforced cork based composites were characterized regarding its morphology and mechanical performance. Optical micrographs have shown a homogeneous distribution of the fibres. The coupling agent effect on CPC performance was also investigated. The tensile strength and tensile modulus of the reinforced composites were significantly improved with the addition of coupling agent. The use of 10 wt.% of coconut fibres in the presence of coupling agent promote an increase on maximum tensile strength of around 41 % comparing with the HDPE/cork (50-50 wt.%) composites. Scanning electron microscopy (SEM) micrographs of the tensile fractured specimens confirmed that the use of coupling agent promoted the interfacial adhesion between the fibres and the thermoplastic matrix. Since, like cork powder, coconut fibres have good thermal and acoustic properties, we consider that the novel reinforced CPC herein described have high potential to be used in building and construction systems and other structural 3D applications.
Water Content Control to Improve Space Charge Storage in a Cork Derivative
Authors: Lança M. Carmo , Cunha Inês , Marques João Paulo , Neagu Eugen R. , Gil Luis , Dias C.J. , Marat-Mendes Jose N.
Published: November 2012

The influence of humidity content on the electrical and dielectric properties of a composite made from recycled TetraPak® containers and granulated cork was studied. The material components have been dried before preparation and after the composite was conditioned by keeping the samples in a dry environment (desiccator) or in an oven at high temperature (70°C in air). The differences observed in electrical properties (investigated by isothermal charge and discharge current measurement) and dielectric properties (measured using dielectric relaxation spectroscopy) show that the thermal treatment at high temperature is more efficient on removing water and slows down the re-absorption rate.
Superhydrophobic to Superhydrophylic Biomimetic Poly(3-Hydroxybutyrate) Surfaces Made by Phase Inversion
Authors: González-Obeso Constancio , Song Wen Long , Rodríguez-Pérez Miguel A. , Mano João F.
Published: November 2012

Biodegradable and biocompatible materials have gained increased attentions because of their applications in biomedicine and tissue engineering. Among them, poly(3-hydroxybutyrate) (PHB), a natural origin polymer, has been employed in biomedical applications as a suitable substitute of synthetic polymers for preparing scaffolds and other devices. In this context it is relevant to understand the interactions between the cells and PHB surfaces, which are governed by aspects such as surface topography and chemical composition. Both, surface topography and chemistry determine surface wettability. The aim of this work is to process PHB surfaces exhibiting extreme wettablility properties, ranging from superhydrophobic (surface contact angle higher than 150º) to superhydrophilic (surface contact angle lower than 5º). A simple phase inversion method was used to fabricate surperhydrophobic PHB surface. Chloroform was used as solvent, and a mixture of water and ethanol as the coagulation bath. The water contact angle was found to be 154.3±2.9º. Furthermore the surface was treated by argon plasma for different times, permitting the control of wettability of the PHB surface from the superhydrophobic to superhydrophilic regime.
Resistance of Polyethylene Geonets against Thermo-Oxidation
Authors: Carneiro José Ricardo , Almeida Paulo Joaquim , Lopes M. Lurdes
Published: November 2012

This paper studies the resistance of two high-density polyethylene geonets (manufactured with or without the additive Tinuvin 783) against thermo-oxidation. The materials were exposed to thermo-oxidation by two methods: oven-ageing tests at 100 °C and a new method developed by our research team. The damages suffered by the geonets were evaluated by tensile tests (determination of tensile strength, elongation at maximum load and toughness). Finally, the results obtained in the oven-ageing tests were compared with the results obtained by the new method.
Visco-Elastic-Plastic Properties of Suture Fibers Made of PLA-PCL
Authors: Vieira A.C. , Medeiros Ricardo , Guedes R.M. , Marques A.T. , Tita Volnei
Published: November 2012

Aliphatic polyesters, like PGA, PLA, PCL and PDO, among others, are biodegradable materials that find applications in many biomedical devices, from fibers for subcutaneous sutures to other regenerative surgery implants. The main concept among these applications is to use a biodegradable device that temporarily replace the biomechanical functions, avoiding this way the chirurgical procedures to remove the device. However, the dimensioning of these devices is complex, not only because the mechanical properties evolve during degradation, but also because these biodegradable materials cannot be assumed as elastic materials. In more precise terms, the response of an elastic material implies that the loading and unloading paths coincide, the material responds instantaneously to an applied load, its behavior is time-independent and the material returns to its former unloaded configuration upon the removal of external loads. In this work, fibers of non-degraded PLA-PCL were submitted to tensile testing at different rates, to load-unloading cycles at different load levels and with or without delay before reloading, creep and fatigue tests at different levels of load. These results elucidate the viscoelastic/viscoplastic nature of this class of materials. The load-unloading cyclic test results allow determining the different components of the strain: elastic, plastic and viscous. The visco-plastic nature was also reflected on the creep and fatigue results. The findings discussed in this work must be taken into account when designing biomedical devices, to avoid common causes of failure such as laxity or premature rupture.
Characterization of Spent Ni-MH Batteries
Authors: Cabral Marta , Margarido Fernanda , Nogueira Carlos A.
Published: November 2012

Spent Ni-MH batteries are not considered too dangerous for the environment, but they have a considerable economical value due to the chemical composition of electrodes which are highly concentrated in metals. The present work aimed at the physical and chemical characterisation of spent cylindrical and thin prismatic Ni-MH batteries, contributing for a better definition of the recycling process of these spent products. The electrode materials correspond to more than 50% of the batteries weight and contain essentially nickel and rare earths (RE), and other secondary elements (Co, Mn, Al). The remaining components are the steel parts from the external case and supporting grids (near 30%) containing Fe and Ni, and the plastic components (<10%). Elemental quantitative analysis showed that the electrodes are highly concentrated in metals. Phase identification by X-ray powder diffraction combined with chemical analysis and leaching experiments allowed advancing the electrode materials composition. The cathode is essentially constituted by 6% metallic Ni, 66% Ni(OH)2, 4.3% Co(OH)2 and the anode consists mainly in 62% RENi5 and 17% of substitutes and/or additives such as Co, Mn and Al.
Historical Heritage: A Study to Conservation
Authors: Borges Cristina , Silva António Santos , Veiga Rosário , Borsoi Giovanni
Published: November 2012

Considering ancient monuments and historical buildings, it seems that these mortars have proved to be durable and reliable materials. The restoration and maintenance of old renders is one of the key aspects of correct rehabilitation practice. The ideal course of action is to replace the damaged material by a material with compatible characteristics.The study in development presents the chemical, physical and morphologic analysis performed for ancient air lime mortars belonging to historical monuments: Santa Marta Fortress in the coast line Lisbon-Cascais dated from XVII century and Defense Wall of Lisbon dated from XI century, which layout could be associated to roman period. It is important to underline that the studied samples of ancient portuguese air lime mortars, have been submitted during centuries to very severe maritime environment that includes daily cycles of wet/dry, wind, friction and the constant presence of salts, generally aggressive. However, they show very good performance and conservation state, unlike most of the new air lime mortars, which are generally considered weak, not very durable, materials. This work is included in a study intending to determine key factors to the durability of these ancient materials in presence of water. Visible reaction rims around some aggregates suggests the occurrence of pozzolanic reactions between aggregates and the lime binder that creates neoformation products, such as calcium-silico-aluminates, which seems be, besides the pores filling, the responsible for the resistance and cohesion of these ancient mortars submitted to aggressive humid environments.
A Possible Nanoreactor: CaFe-L(ayered)D(ouble)H(ydroxide) with Intercalated Cinnamate Derivatives
Authors: Srankó David , Muráth Szabolcs , Sipiczki Monika , Szabó Maria , Kukovecz Ákos , Kónya Zoltan , Sipos Pal , Pálinkó Istvan
Published: November 2012

The synthesis and characterisation of various organic-inorganic nanohybrids are reported in this contribution. The host material was Ca3Fe-LDH prepared by the co-precipitation method. E-cinnamate, E-4-nitrocinnamate or E-2,5-difluorocinnamate anions were the guests. Successful intercalation occurred through the introduction of the guest anion into the interlayer region of the host materials with the dehydration-rehydration method. The obtained nanohybrids were studied by powder X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray fluorescence (EDX) coupled to the SEM instrument and infrared spectroscopy (IR). These methods were used on one hand to prove that intercalation was successful and for the characterisation of the substances on the other. Molecular modelling was used for visualising the possible spatial arrangement of the organic anions.
A Contribution to the Mechanical Characterization of Cu ETP Used in the Electric Motors Industry
Authors: Moreira Pedro M.G.P. , de Figueiredo Miguel A.V. , de Castro Paulo M.S.T.
Published: November 2012

The analysis of Cu ETP of a component of electric motors manufactured by WEG is presented. The work included three main tasks: metallographic analyses at the micro and macro levels; mechanical testing; scanning electron microscopy observations. The objective was the evaluation of the state of bars material before and after service. It was found that material in both conditions presents similar microstructures. This indicates that, despite the rotor working at temperatures above 300°C, no grain recrystallization can be identified. It was verified that the copper bar base material presents higher hardness values of than the copper ring. A decrease of yield and rupture stresses as the temperature increases was observed during tensile tests at different temperatures. During testing, a fatigue life of 107 cycles for a remote stress of approximately 134MPa is estimated. It can be concluded that the material after and before service presents different properties, the first one presenting lower strength. This behavior is reflected in lower hardness, yield and rupture stress of the material taken from the fractured rotor bars. This observation can be a result of the high temperature (above 300°C) that is present in the rotor during each start.
Characterizing the Cyclic Behaviour of Extruded AZ31 Magnesium Alloy
Authors: Reis Luís G. , Anes Vitor , Li Bin , de Freitas Manuel
Published: November 2012

In this paper, the mechanical behaviour of extruded AZ31 magnesium alloys under multiaxial fatigue loading conditions is studied. The monotonic properties of the AZ31 magnesium alloy were determined by tests on the specimens which were machined from extruded rods. Then, the cyclic deformation under multiaxial loading conditions was simulated by ANSYS and a plasticity program with the Jiang & Sehitoglu plasticity model. The fatigue lives were estimated by the critical plane models coupled with Coffin-Manson rule, such as Findley, Fatemi-Socie, Brown-Miller, SWT and Liu models. Four loading paths were considered with different levels of non-proportionality, the results show significant loading path dependence.
Delta Ferrite Formation in Austenitic Stainless Steel Castings
Authors: Padilha Angelo Fernando , Tavares Caio Fazzioli , Martorano Marcelo Aquino
Published: November 2012

The effects of chemical composition and cooling rate on the delta ferrite formation in austenitic stainless steels have been investigated. Ferrite fractions measured by a magnetic method were in the range of 0 to 12% and were compared with those calculated by empirical formulas available in the literature. The delta ferrite formation (amount and distribution) was strongly affected by the steel chemical composition, but less affected by the cooling rate. Among several formulas used to calculate the amount of delta ferrite, the best agreement was obtained with those proposed independently by Schneider and Schoefer, the latter being recommended in the ASTM 800 standard.
Effect of Non-Proportionality in the Fatigue Strength of 42CrMo4 Steel
Authors: Reis Luís G. , Anes Vitor , Li Bin , de Freitas Manuel
Published: November 2012

The unexpected collapse of engineering structures is often caused by the fatigue phenomenon resulting from degradation of mechanical properties of materials due to multiaxial cyclic loadings. The interpretation of such degradation is a topic of intensive research in multiaxial fatigue. The fatigue strength is commonly evaluated by the equivalent stress based on the shear stress in the octahedral plane. However, the use of this kind of equivalent stress in the multiaxial fatigue criteria has been proven to be inappropriate. The degradation of mechanical properties of materials is dependent on several factors, e.g. the loading path has a strong influence on the fatigue strength. Non-proportional loadings cause higher damage in materials than proportional loadings for the same maximum equivalent stress. The purpose of this work is to study the effect of different multiaxial loadings on the 42CrMo4 steel and to improve the understanding about the relation between the fatigue strength and the sequential loading proportionality. The considered loadings were defined with the same history but with different load sequences and equivalent stress. To implement this work a biaxial servo-hydraulic fatigue machine was used. The fatigue life and crack angle were measured for each specimen. An analysis was made in order to correlate the crack initiation and fatigue life with the theoretical models, some remarks regarding these topics are presented.
Evaluation of Functionally Graded Ceramic Crucible for Induction Melting of Titanium Based Alloys
Authors: Gomes Fernando , Barbosa Joaquim , Ribeiro Carlos Silva
Published: November 2012

During the last years a very significant effort to develop a melting crucible for induction melting of Ti based alloys at competitive cost has been carried out by many researchers, where the authors are included. Results obtained so far have shown that no material accomplishes the melting crucibles two main demands: inertness facing titanium alloys and suitable/enough thermal-shock resistance. Until now, yttrium and calcium oxides were those materials that performed best on what concerns to thermodynamic stability. However, in both cases, crucibles thermal-shock resistance was very poor, and there are references to crucibles that cracked during melting. Besides, calcium oxide reveals manipulation problems, due to its high higroscopicity. This paper concerns to the evaluation of zircon based crucibles with Y2O3 inner layer for induction melting of TiAl based alloys. A novel multi layered crucible production technique based in a centrifugally assisted slip casting process followed by a sintering operation is described, and results concerning to crucibles porosity and wall composition and morphology are presented. Crucibles obtained in different processing conditions were used to melt a Ti48Al alloy which was poured in graphite moulds. Experimental results include alloy chemical contamination with residual elements, mainly yttrium and oxygen, microhardness measurement and the presence of yttrium oxide and zircon inclusions in the cast samples. Results concerning to the crucibles behaviour are also presented with particular attention to cracks development. The Y2O3 crucible layer was found to suffer some erosion and be slightly dissolved by the molten alloy and the extent of those phenomena depends on the porosity of the layer surface, for fixed experimental melting conditions.