bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of Stress-Strain Curve through Berkovich Indentation Testing
Authors: Dias A.M.S. , Godoy G.C.D.
Published: January 2010

Instrumented indentation testing is a technique widely used in different materials to evaluate the penetration depth in function of the indenter load. Considering Berkovich indenter, this methodology has been used to determine mechanical properties such as hardness, Young modulus and a stress versus strain curve of the elastic-plastic behaviour under compression of the tested materials. However, the implementation of this technique to evaluate mechanical properties and also its results have still brought doubts on research areas. Nowadays, the use of a numerical methodology able to evaluate the stress and strain fields during indentation cycle can lead to a more secure interpretation. The aim of this work was to simulate the Berkovich indentation testing and to propose a methodology to extract the stress-strain curve through experimental and numerical analyses. The obtained numerical results for the load-displacement curve were quite similar to the experimental curve presented in the literature.
Modelling of a Piezoelectric Polymer Film System for Biosensing Applications
Authors: Inácio Paulo , Marat-Mendes J.N. , Neagu Eugen R. , Dias C.J.
Published: January 2010

Most piezoelectric gravimetric biosensors are based on quartz crystal microbalances or surface acoustic wave devices. In this paper we describe a polymer film system, made of piezoelectric polyvinylidene difluoride (PVDF) and the Immobilon-P membrane (porous PVDF), for biosensing applications. In operation a film is accommodated in a flow cell and connected to an electronic circuit, constituting an oscillatory resonant device; the output signal is its resonance frequency. This device successfully detected the binding between bovine IgG and bovine anti-IgG. Work on the modelling of this film system is presented. Two different approaches are being considered: the finite element method (FEM) and the ABCD matrices. Results comparing theoretical and experimental data are presented.
Elastic Work and Fracture Energy of Concretes Made with Crushed Stones and Pebbles Aggregates
Authors: Ribeiro S. , Santos E.M.B. , Garcia G.C.R. , Rodrigues J.A.
Published: January 2010

This work examines the elastic work and fracture energy of a mortar and two concretes using the wedge splitting method to attain stable crack propagation. A comparison was made of the fracture energy in mortar and concrete using two different aggregates: crushed stone and pebbles, both with sizes between 4.8 and 9.5 mm. The mortar was made of sand, Portland cement and water, using a cement: sand ratio of 1:2. The water content was 0.46 of the cement mass. The samples were molded and then cured for seven days at 25oC in 100% relative humidity. After curing, the samples were dried at 55oC for 48 hours. The concretes were produced using the same procedure, but with the addition of the aggregates. The amount of aggregate was 10 wt.% of the total weight of cement plus sand. After curing and drying, the samples were subjected to the wedge splitting procedure. The tests were carried out at a constant displacement rate of 0.030 mm/min. The following results were obtained: elastic work: 80.4 ± 0.6, 114 ± 9 and 110 ± 12 mJ, and fracture energy: 30.3 ± 0.6, 40 ± 1, and 40 ± 5 J.m-2, respectively, for the mortar and for the concretes containing crushed stone and pebbles. These results allow us to conclude that the aggregates improved the elastic work and the fracture energy of the concretes. However, the type of aggregate did not make any difference to the properties. These findings contradict what is generally known, i.e., “that concrete produced with pebbles is inferior to concrete made with crushed stone”, at least insofar as it concerns the energies associated with the fracture process.
Determination of Calcium Ions in Hydrated Cement Paste at Early Stage
Authors: Hošková Šárka , Tichá Petra , Demo Pavel
Published: January 2010

A novel method that allows determining instantaneous concentration of calcium ions, Ca2+, in hydrated cement paste (HCP) is suggested. EDTA solution (belonging to a group of carboxylic acids/carboxylates and borates) seems to be very effective retarder altering nucleation and subsequent growth of newly forming clusters of calcium minerals. Concentrations of Ca2+ have been determined for various water to cement ratios, at different times and for given temperature.
Quartzite Quarry Waste Recovery: A Case Study
Authors: Lima Rosa Malena Fernandes , Morais R.M.M. , Silva Alexandro Fortes S.
Published: January 2010

The quartzite dimension stones from the region of Ouro Preto, State of Minas Gerais, Brazil are exploited by LPA (local productive agreement). There are about 350 people directly involved in this economic activity. The rock in this region is greatly weathered. Because of this, the final quartzite recovery is only about 30% of the volume, resulting in great amounts of waste which is deposited on land near the pits. At a typical quarry in Passagem de Mariana, near Ouro Preto, fragments and sand from the waste deposits were collected and characterized. The results are presented herein. After studies with three sand samples, it was verified that these sands can be used in civil construction. Also, with proper size classification, it can be utilized by casting industries. Furthermore, after being purified by high intensity magnetic separation and froth flotation, these wastes can be also used in the glass bottle industry. All of these applications are very interesting in the social, economic and environmental point of view.
Role of Combined Water for Determining the Mechanical Behaviour of Class C Fly Ash Belite Cements
Authors: Goñi S. , Guerrero A.
Published: January 2010

The physically-chemically bounded water is an important parameter directly related to the gain of mechanical strength during the hydration of cements. In this work, quantitative determinations of the physically - chemically bounded water of two types of belite cements, called FABC-2-W and FABC-2-N, were carried out by means of thermogravimetry analyses during a period of 180 days of hydration. The hydrated products were characterized by X-ray diffraction and BET surface area. Important direct quantitative correlations were obtained between the combined water and technological characteristics of cements such as the compressive mechanical strength or the BET surface area. TG measurements for hydrated FABC-2-W and FABC-2-N cements were carried out in flowing nitrogen on a TGA/SDTA 851 (Mettler) in the temperature range from 25 to 1100°C with heating rate of 10 °C min-1 and nitrogen flow rate of 25 mL min-1. BET surface area was measured using nitrogen adsorption at 77 K, on an ASAP 2010 (Micromeritics).
Influence of Mineral Additions in the Inhibition of Delayed Ettringite Formation in Cement Based Materials – A Microstructural Characterization
Authors: Silva António Santos , Soares D. , Matos L. , Salta Manuela M. , Divet L. , Pavoine Alexandre , Candeias António Estevao , Mirão José
Published: January 2010

The degradation of concrete structures caused by delayed ettringite formation (DEF) is a problem that affects many concrete structures worldwide [1]. This pathology is due to the formation of expansive ettringite inside the material and is very difficult to deal with, because presently there is no efficient method to repair concrete structures affected by DEF. Hence, there is an urgent need to find preventive methods that may enable the inhibition of DEF in new constructions.
This paper presents the findings of a long-term study [2,3] on the expansion rate and microstructure of heat-cured concretes with different amounts of mineral additions, like fly ash, metakaolin, ground granulated blast-furnace slag, silica fume and limestone filler. For this purpose different concrete compositions were produced using the same binder, water/binder (w/b) ratios and aggregate type. The concretes were prepared and subjected to a heat-curing cycle and subsequently to two drying-humidification cycles. After these cycles the concrete specimens were immersed in water for long-term storage at 20 ± 2°C. Length changes of specimens were measured at regular intervals. The microstructures of old heat curing specimens were investigated by optical microscopy and SEM-EDS analysis. The results of the blended-concrete compositions were compared with control compositions, and the conclusions were extracted.
Influence of the Geometry of Units and of the Filling of Vertical Joints in the Compressive and Tensile Strength of Masonry
Authors: Haach V.G. , Vasconcelos G. , Lourenço Paulo B.
Published: January 2010

Attention is given to the mechanical properties of concrete block masonry, with respect to its compressive and tensile strength. These properties are important parameters in the in-plane lateral behaviour of masonry walls, determining their resistance and ductility. Such properties play also a central role when analytical and numerical analysis is used for simulating or predicting the behaviour of masonry structures. The influence of two selected parameters on the mechanical properties of masonry is discussed, namely the geometry of the units and the filling of the vertical joints. Results show that masonry under compression behaves as a homogeneous material and the stress-strain diagrams can be represented by a parabola similarly to what is suggested for structural concrete. In case of tensile strength, filling of vertical joints appears to influence considerably the tensile strength. The filling of the vertical joints increased the strength but lead to a more brittle behaviour.
The Effect of Chlorides on the Thaumasite Form of Sulfate Attack in Limestone Cement Concrete
Authors: Sotiriadis K. , Nikolopoulou E. , Tsivilis Sotiris
Published: January 2010

In this paper the effect of chlorides on the thaumasite form of sulfate attack in limestone cement concrete is studied. Concrete specimens made from ordinary Portland cement and two Portland limestone cements (limestone content 15% and 35% respectively) were prepared. After 28 days of curing the specimens were immersed in six solutions of various sulfate and chloride content and stored at 5oC. Visual assessment of the specimens, mass measurements and compressive strength tests took place for a period of 24 months. XRD method was used to identify thaumasite in the deteriorated parts of the specimens. All measurements showed that Portland cement concrete exhibits a lower degree of deterioration than Portland limestone cement concrete. Specimen disintegration was more severe, the higher the limestone contents of the cements and the higher the sulfate content of the corrosive storage solutions. Chlorides play an inhibitory role, delaying the deterioration of the concrete specimens. XRD analysis showed the presence of thaumasite at the deteriorated parts of the specimens after nine months of curing.
Development of Permeable Reactive Barrier for Phosphorus Removal
Authors: Oliveira M. , Machado Ana Vera , Nogueira Regina
Published: January 2010

Permeable reactive barriers were developed for phosphorus removal. The barrier consists in an organic-inorganic hybrid material, which allows water and others species to flow through it, while selectively removes the contaminants. Polyethylene oxide (POE) and aluminium oxide (Al2O3) were used as the organic and the inorganic parts, respectively. The hybrid material was obtained by sol-gel reaction, using aluminium isopropoxide as inorganic percursor in order to attain Al2O3. The hybrid material produced was characterized by FT-IR spectroscopy and thermogravimetry. The previous tests for phosphorus removal have shown the effectiveness capacity of the developed material to remove it.
Hydrothermal Synthesis of Na-LTA, Na-X and HS Zeolites from Tunisian Sand and Aluminum Scraps
Authors: Tounsi Hassib , Mseddi Samir , Djemal Samir
Published: January 2010

Na-LTA, Na-X and HS zeolites have been prepared from Tunisian sand and aluminum scraps. The alkaline attack of the sand leads to the metasilicate sol used as a source of silica. The aluminum source was prepared by dissolving aluminum in NaOH solution. The influence of several physicochemical parameters such as temperature, crystallization time and the alkalinity of the reaction mixture on the nature and the purity of the obtained products have been investigated.
Designing Activated Carbons from Natural and Synthetic Raw Materials for Pollutants Adsorption
Authors: Mourão Paulo A.M. , Cansado Isabel P.P. , Carrott Peter J.M. , Ribeiro Carrott Manuela M.L.
Published: January 2010

Over the last decades the literature has shown the possibility of producing activated carbons (AC) from a wide variety of raw materials, and to use them as one of the most environment-friendly solutions for waste disposal [1]. Simultaneously, it has been shown that the adsorption of pollutants from different sources by activated carbons is one of the most efficient techniques for remediating or solving this kind of problem [2]. In this context, phenolic compounds represent one of the most important classes of pollutant present in the environment [3]. In this perspective, we present a study involving the production of AC from cork (Quercus suber L.), PEEK (polyetheretherketone) wastes or granulated recycled PET (polyethyleneterephthalate) and their applicability for the adsorption of phenolic compounds from the liquid phase. All samples were characterised in relation to their structural properties and chemical composition, by different techniques, including nitrogen adsorption at 77 K, elemental analysis (C, H, N, O and S) and point of zero charge (PZC). The activated carbons produced demonstrated high adsorption capacities both in the gas and liquid phase as exemplified by N2 and phenolic compounds adsorption experiments. Based on the structural and chemical properties, and on the kinetic and equilibrium studies of liquid phase adsorption, it is possible to conclude that it is the porous volume of the ACs that predominantly controls the process of phenolic compounds adsorption.
Synthesis and Characterization of Biodiesel from Coconut Oil Using Homogeneous Catalyst
Authors: Sifuentes-Gallardo Pio , Lopez-Rodriguez Angelica S. , Diaz-Flores Laura L. , Hernandez-Rivera Miguel A. , Vazquez-Rodriguez Jose M. , Lopez-Torres Rodolfo
Published: January 2010

The present project explains how crude biodiesel (crude BD) has been obtained by using coconut oil and ethyl alcohol as well as sodium hydroxide as a catalyst. The coconut oil was extracted with water which was submitted to evaporation afterwards. This experiment was carried out by adding the coconut oil in a 500 mL glass flask. The catalyst was dissolved in ethyl alcohol and mixed together with the coconut oil. Once obtained the mixture, this was stirred for 25 minutes at temperatures from 20, 30, 40, 50 to 60 °C. During the reaction, two phases were formed: crude biodiesel (top layer) and crude glycerol (bottom layer). The characterization was done by determination of pH (using an electrode located in the top layer connected to a computer by RS-232 interface system). When the separation concluded, the crude BD was rinsed in order to remove the catalyst. The characterization of washed biodiesel was determined by density and Saybolt viscosity. Fourier Transform Infrared (FTIR) analysis was also made. The results by FTIR indicated the two functional groups of fatty acid ethyl esters (C=O, 1733 cm-1 and C-O, 1154 cm-1) and the OH wide band group of glycerol at 3400 cm-1. When the reaction time ended, the maximum pH value registered was 12.7. The values for pH, density and Saybolt viscosity were acceptable for crude BD and crude glycerol.
Fracture Behaviour of Brazed Soft Martensitic Stainless Steel Joints under Cyclic Loading
Authors: Başer Tanya A. , Leinenbach Christian , Schindler Hans Jakob
Published: January 2010

The fracture behaviour of brazed joints of the soft martensitic stainless steel X3CrNiMo13-4 under cyclic loading is investigated. The fatigue crack propagation curves (da/dN-ΔK) were derived for different load ratios R. The fatigue crack threshold values ΔKth were estimated to be 9 MPa m0.5, 7 MPa m0.5, 6 MPa m0.5 and 4 MPa m0.5 for the R values of 0.1, 0.3, 0.5 and 0.7, respectively. In addition, crack growth curves were derived for different constant loads ΔF. The Paris exponent, n, was estimated for the different R values and found to be very high compared to homogeneous materials. The work was completed with microstructural and fractographic investigation by scanning electron microscope (SEM).
Behaviour of Membrane Construction Materials under Multi-Axial Tensile Loading
Authors: Chen S.H. , Sousa Fangueiro Raul Manuel Esteves , Ding Xin , Yi H.L.
Published: January 2010

This paper focused on the tensile performance of PVC-coated membrane materials under multi-axial loads. Several groups of experiments were carried out to investigate the effect of the specimen configuration and the loading speed on the tensile properties. It could be concluded that the configuration of the specimen plays an important role on the tensile performance of the materials. The suitable configuration for multi-axial loading tests had been identified. It was also found out that the loading speed had certain effect on the tensile failure performance and the tensile response. A loading speed of lower than 20mm/min was suggested to achieve a reasonable result of the multi-axial tensile performance of PVC-coated membrane materials. Another group of tensile experiments with a crack in the center of the specimens under multi-axial loads were performed. It was noticed that the tensile properties in warp direction of the coated membrane materials play an important role in the tensile failure under multi-axial loads, no matter the initial crack length and the crack orientation are.
Electrochemical Formation and Corrosion Properties of Porous TiOx Biomaterials
Authors: Jakubowicz Jarosław , Jurczyk K. , Jurczyk M.
Published: January 2010

Formation of porous TiOx layers on Ti during electrochemical etching in H3PO4, CH3COOH electrolytes modified by HF and NH4F was described. The anodization resulted in porous TiOx formation, useful in tissue growth and bone bonding. The pore dimensions increased due to the increase of HF or NH4F content in H3PO4 electrolyte. During anodization at 10 V for 30 min, when the HF content increased from 0.5 to 10%, the pore diameter increased from 30 nm up to 8 m, respectively. Anodization in CH3COOH electrolyte resulted in non-uniform etching with flat hexagonal islands with nanopores inside surrounded by micropores.
Corrosion properties of the etched samples were investigated in Ringer’s solution at 37oC and were compared to the unetched sample. The best corrosion resistance showed the samples etched at 10 V for 30 min in 1M H3PO4 + 2% HF and 1M H3PO4 + 10% NH4F, what can be attributed to thick oxide layer. We find, that porous sample presented good biocompatibility with human osteoblasts.
Creep and Low Cycle Fatigue Characterisation of IN718 TIG Butt-Welds at 620°C
Authors: Tanner D.W.J. , Becker A.A. , Hyde Thomas H.
Published: January 2010

The testing setups, results and analysis of constant load creep and low-cycle high temperature fatigue tests of tungsten inert gas (TIG) butt-welded, thin-section INCONEL 718 (IN718) specimens are presented. The main objectives were to determine the effect the welds have on failure time and analyse any differences in their failure behaviour. It was found that although welded IN718 may exhibit comparatively little loss of tensile strength, its ductility and creep and high temperature fatigue properties are severely compromised due to its changed microstructure.
Characterization of Fatigue Crack Growth Rate of AA6056 T651 and T6: Application to Predict Fatigue Behaviour of Stiffened Panels
Authors: Moreira Pedro Miguel Guimarães Pires , Richter-Trummer Valentin , Tavares Sérgio M.O. , de Castro Paulo Manuel Salgado Tavares
Published: January 2010

Tensile and fatigue crack growth tests of the 6056 T651 and T6 aluminium alloys were carried out. The fatigue crack propagation tests were performed on compact tension 4mm thick (CT) specimens, under cyclic loading with R ratios 0.1 and 0.5. The resulting data was used to predict the fatigue behaviour of stiffened panels subjected to fatigue loading under similar R ratios. The AA6056-T651 panels were fabricated using High Speed Machining (HSM) starting with 30mm thick plates. AA6056-T651 CT specimens were cut from the panels mentioned above, whereas AA6056-T6 CT specimens were machined from 5mm thick material. It was found that the AA6056-T651 (HSM material) specimens, machined from a 30mm thick plate presented higher rupture and yield stress than the AA6056-T6 material extracted from a 5mm thick plate. When tested at the same R value the AA6056-T6 specimens present higher crack growth rate than the AA6056-T651 specimens.
Use of Guided Waves for Inspection of Composite Skin-Honeycomb Core
Authors: Satour A. , Boubenider F. , Badidi Bouda Ali , Halimi Rachid
Published: January 2010

Sandwich plates, made of two aluminum layers and a metal honey comb core are used in the aircraft industry. The purpose of this study is to show the ultrasonic guided waves sensibility to discover delamination in skin-honeycomb sandwich structures used in aeronautics. Separation between the skin and the core can appear during the manufacture or after use. In this work, Lamb's waves are used to control this kind of plane structure. Indeed, these waves have the advantage to put in vibration the totality of the plate that we want to control and they propagate on long distances without too much attenuation. The revealing, by the guided waves, of the unsticking which can meet on such sandwiches, between the plate and the honeycomb core is studied and commented.
Application of Inverse Methods for Spatial Deconvolution of Pulsed Ultrasound Fields Radiated in Solids
Authors: Djerir Wahiba , Boutkedjirt Tarek , Badidi Bouda Ali , Satour A.
Published: January 2010

When measuring the ultrasound field, the signal provided by the receiving transducer is affected by its spatial properties. Particularly, the displacement normal to its surface is spatially averaged because of the receiver finite size. In this study, we show using a numerical simulation, the effectiveness of the spatial deconvolution of these effects for a rectangular transducer. For that, three methods allowing the inversion of the aperture effect are tested 1) Wiener’s method; 2) the power spectral equalization (PSE) method, and 3) the maximum a posteriori (MAP) method. The obtained results show that the three methods are able to reconstruct the ultrasound field from the spatially averaged values and the quality of the reconstruction depends strongly upon the signal to noise ratio (SNR) and the spatial frequencies of the ultrasound field investigated
Ultrasonic Inspection of Composite Materials Using Minimum Entropy Deconvolution
Authors: Benammar A. , Drai R. , Guessoum A.
Published: January 2010

In this work, the Minimum Entropy Deconvolution (MED) method, developed for ultrasonic signals, is used to address the problem of delamination defect detection in Composite Materials. Standard deconvolution techniques suppose that the wavelet is minimum phase but generally make no assumptions about the amplitude distribution of the primary reflection coefficient sequence. For a white reflection sequence the assumption of a Gaussian distribution means that recovery of the true phase of the wavelet is impossible; however, a non-Gaussian distribution in theory allows recovery of the phase. It is generally recognized that primary reflection coefficients typically have a non-Gaussian amplitude distribution. The minimum entropy deconvolution (MED) method supposes whiteness but seek to exploit the non-Gaussianity. This method do not assume minimum phase. The deconvolution filter is defined by the maximization of a function called the objective. The algorithm is tested on simulated data and also tested on real ultrasonic data from multilayered composite materials.
Machinability of Al-4%wt Mg-Al2O3-Graphite Composites Produced by Compo-Casting Technique
Authors: Hassan Adel M. , Hayajneh Mohammad , Al-Mahasneh M.K.
Published: January 2010

Aluminium-4%wt Magnesium-Alumina-Graphite particulate metal matrix composites, with different percentage weights of alumina and graphite particles, were produced by the process of compo-casting. The method of casting has been briefly described in the present study. The magnesium was added to the aluminium as wetting agent to enhance the bond between the matrix (aluminium) and the reinforcement particles (alumina and graphite). Machinability of the considered composites was indicated by the values of the drilling thrust forces and torques, using a moderate speed drilling machine. The cutting tools were made of high speed steel, while the other cutting parameters were held constant during the drilling process. The results showed that the change in the volume percentage of both alumina and graphite particles have remarkable effect on the measured drilling thrust forces and torques, which in turn affect the machinability of the studied particulate metal matrix composites.
Nanocrystallite Characterization of the MMC 316L-0.3%wtY2O3-3%wtTaC by Rietveld Refinement Method
Authors: de Carvalho W.M. , Gomes Uilame Umbelino , de Souza Carlson P. , Furukava M.
Published: January 2010

The nanocrystallites in a metal matrix composite (MMC) have wide importance in the sintering area. The nanocrystallites have been related with properties such as hardness and density of 316L steel matrixes. The Y2O3 and TaC dispersion in steel crystalline structures affects these properties and the sintering process. This study analyze: the 316L steel, Y2O3 and TaC crystallite size; TaC and Y2O3 dispersion in milled powder composite; MMC nanocrystallite size and micro-strain during milling process of 316L-(CFC) steel and the effects of dispersion in sintered MMC. The alloy was submitted to high energy milling. MMC was characterized by scanning electronic microscopy (SEM) and X-ray diffraction (XRD). The diffraction was analyzed by Rietveld’s refinement method, DBWS 9807 program, and crystallite size and micro-strain were performed using Scherrer’s equation and Williamson-Hall’s method.
Ecodesign Applied to Components Based on Sugarcane Fibers Composites
Authors: Luz Sandra M. , Ferrão Paulo M.C. , Alves C. , Freitas M. , Caldeira-Pires Armand
Published: January 2010

This work evaluates the technical performance and environmental impacts, when sugarcane bagasse is applied as reinforcement of polypropylene in a component instead neat polypropylene (PP). To achieve the goals of this study, the tensile and flexural properties and Life Cycle Assessment (LCA) as a function of fiber content were performed. In addition, different end-of-life (EOL) options for natural fiber composites were proposed, including incineration, recycling (with economic reuse) and discharging (landfill). Besides the good mechanical properties, natural fiber composites showed great environmental performance during the entire life cycle, mainly in the cultivation phase, when sugarcane consumes carbon while growing, contributing to global warming decreases. As a conclusion, sugarcane bagasse fibers production results in lower environmental impacts compared to neat PP and the recycling with economic reuse of sugarcane bagasse-PP composite was the best alternative to minimize environmental impacts after the end-of-life.
Mechanical Behaviour of Sandwich Beams Manufactured with Glass or Jute Fiber in Facings and Cork Agglomerates as Core
Authors: Reis Luís G. , Carvalho P. , Alves C. , de Freitas Manuel
Published: January 2010

The environment is a prominent issue today. Designing environmentally sustainable products is an attempt to address this question. In many cases, natural materials are environmentally friendly for product design manufacturing. The goal of this work is to study the mechanical behaviour of NL10 and NL30 cork agglomerates. Compression, shear and bending tests in sandwich specimens made of glass or jute fiber in facings and cork agglomerates as core were carried out. The sandwich specimens were manufactured by Resin Transfer Moulding (RTM) process. Results show that NL30 has a higher compression strength and shear resistance than NL10 agglomerate due to its manufacturing process, which originates superior density, but the NL30 agglomerate superior density is undesirable. Sandwich test specimens that presented failure by rupture of the core in both types of tests, core shear tests and three point bending tests, showed that the failure is mainly adhesive occurring between the adhesively joined cork grains. Since grains are unaffected and remain intact, it is possible to improve these materials by using better agglutinants and new bonding techniques with the intent of getting cork agglomerates with higher shear and flexural strength.
Thermo-Mechanical Treatment to Improve Properties of Sisal Fibres for Composites
Authors: Motta L.A.C. , John Vanderley M. , Agopyan Vahan
Published: January 2010

The cross section variation, mechanical properties and moisture absorption of vegetable sisal fibres compressed at temperatures of 120, 160 and 200 °C were determined and compared with values obtained in non-compressed fibres. The thermo-mechanical treatment carried out resulted in a relevant increasing of fibre stiffness (elastic modulus) and decreasing of fibre moisture absorption.
Bioactivity and Viscoelastic Characterization in Physiological Simulated Conditions of Chitosan/Bioglass® Composite Membranes
Authors: Caridade Sofia G. , Merino Esther G. , Luz Gisela M. , Alves N.M. , Mano João F.
Published: January 2010

A number of combinations of biodegradable polymers and bioactive ceramics have been used for orthopaedic applications including in hard tissue regeneration. Ideally, composites aimed to be used in orthopaedic applications should combine adequate mechanical properties and bioactivity. Chitosan (CTS) has been widely used for biomedical applications, namely in tissue regeneration or drug delivery. In this sense, membranes of chitosan and chitosan with Bioglass® (BG) were prepared by solvent casting and characterised using Scanning Electron Microscopy. In vitro bioactivity tests were performed in the composite membranes, namely by monitoring their capability to induce the precipitation of apatite upon immersion in simulated body fluid (SBF). The results showed that the addition of BG promoted the deposition of an apatite-like layer. The deposition of apatite could influence the mechanical performance of the material. Therefore, in order to follow this biomineralization, the viscoelastic properties of these composite membranes (immersed in SBF) were evaluated. The change in the storage modulus (E’) and the loss factor (Tan δ) were measured as a function of immersion time using non-conventional dynamic mechanical analysis (DMA) tests, in which the samples were kept in wet conditions and at 37°C during the measurements. The mechanical properties of the chitosan membranes were improved by the addition of BG particles. An increase on the storage modulus was observed by the composite membranes while for the pure chitosan membranes the storage modulus was stable up to 7 days. Clear changes were detected in the composite membranes that contrasted with pure chitosan (CTS) membranes that exhibit stable viscoelastic properties up to 7 days. In addition, this work showed that sample characterization in the hydrated state can be useful to predict the mechanical performance of composites under meaningful physiological conditions.
Exploring the Use of Cork Based Composites for Aerospace Applications
Authors: Silva José M. , Devezas Tessaleno C. , Silva A. , Gil L. , Nunes C. , Franco N.
Published: January 2010

Aerospace components are characterized by having high strength to weight ratios in order to obtain lightweight structures. Recently, different types of sandwich components using composite materials have been developed with the purpose of combining the effect of reinforced face-sheets with low weight core materials, such as honeycombs and foams. However, these materials must combine damage tolerance characteristics with high resistance under both static and dynamic loads. Cork composites can be considered as an alternative material for sandwich components since cork is a natural material with some remarkable properties, such as high damage tolerance to impact loads, good thermal and acoustic insulation capacities and excellent damping characteristics for the suppression of vibrations. The experiments carried out in this investigation were oriented in order to optimize the specific strength of cork based composites for sandwich components. Static bending tests were performed in order to characterize the mechanical strength of different types of cork agglomerates which were obtained considering distinct production variables. The ability to withstand dynamic loads was also evaluated from a set of impact tests using carbon-cork sandwich specimens. The results from experimental tests showed that cork agglomerates performance depends on the cork granulate size, the type of reinforcing elements and the bonding procedure used for the cohesion with the matrix material.
Suitability of Corkrubber Gaskets in Gasoline-Ethanol Blends
Authors: Gil P. , Fernandes J. , Neves M.M. , Reis Luís G.
Published: January 2010

The increasing use of biofuels, namely blends of gasoline with ethanol, requires the identification of its impact on the fuel admission components of internal combustion engines that have not been specially design to work with high levels of ethanol. This paper provides a discussion on performance testing of corkrubber gaskets from a commercial company (ACC – Amorim Cork Composites) to seal these engines using gasoline and gasoline-ethanol blends. In order to evaluate the chemical compatibility of four corkrubber composites, several samples were immersed in different blends of gasoline with ethanol to determine the changes of hardness, volume, thickness and weight. The results of these tests differed between materials, but all of them showed less damage tolerance to blends with low and medium percentages of ethanol (e.g., E5, E10, E25, E50) when compared to gasoline or blends with higher percentages of ethanol (E85).An aggressiveness factor is proposed to compile results from the immersion tests. Validation tests were carried out in conditions as close as possible to the service and accordingly to similar test standards. This study allows concluding on which of these corkrubber composites have adequate sealing properties for gasoline as well as blends of gasoline with ethanol.
Shock Resistance and Compression Analysis of Concrete in Expanded Polystyrene Formworks (EPSFWs)
Authors: Macias-Garcia A. , Diaz-Diez M.A. , Alexandre-Franco M.F. , Fernandez-Gonzalez C. , Cuerda-Correa E.M.
Published: January 2010

Bench-scale and industrial expanded polystyrene formworks (EPSFWs) were prepared and tested in terms of shock resistance and compression analyses. The composition of the EPSFWs was varied and the influence of the substitution of calcium carbonate by granite, kaolin or slate on the mechanical properties of the EPSFWs was analyzed. Bench-scale samples were subjected to a previous selection based on the optimal mechanical behavior. Samples containing large grain sand and slate were chosen for the subsequent industrial scale preparation. The real EPSFWs were also tested from the shock resistance and compression standpoints. The results obtained suggest that the samples showing the best performance among all the tested EPSFWs are those in which calcium carbonate was substituted by slate. This fact is of special interest since large amounts of slate dust are obtained in the area of Spanish Extremadura from local mines. Thus, the preparation of formworks represents a good alternative for the valorization of this by-product.
Ytterbium/Yttrium Oxide Superlattices Sensing Strain under High Temperature
Authors: Lu Ya Lin , Reinhardt Karen A.
Published: January 2010

Rare-earth (RE) doped oxide materials are one of the interesting sensor materials potentially able to remote-sense strain inside an object under high temperature. In contrast to commonly investigated temperature-sensing methods of monitoring temperature-dependent luminescent characteristics of those doped RE ions, sensing strain under high temperatures, however, will be much difficult. This research develops a new strained superlattice that has the potential to sense strain under the high temperature environment, via monitoring the superlattice’s period-dependent luminescence.
Investigations on Humidity Sensing Properties of Thick Films of the TiO2:WO3 System
Authors: Faia Pedro M. , Ferreira A.R. , Furtado C.S.
Published: January 2010

This paper reports the study of the humidity-sensitive electrical properties of TiO2:WO3 thick films. Prototype sensors have been prepared by depositing an emulsion of TiO2 and WO3 powders in acetone with cellulous glue onto an alumina substrate, by a spin coating technique using a low spreading speed (125 r.p.m.). Films were prepared with five different atoms proportions of Ti and W: 100:0, 100:1, 100:6, 100:18 and 100:36. The oxides thick films were successively fired at the temperatures of 600, 700, 900, 1100, and 1300 °C, during 2 hours at each of these temperatures. Measurements were obtained at a constant temperature of 25 °C and at various relative humidities (RHs) in the frequency range of 0.01 Hz – 40 MHz. It was thought that the humidity sensing of the TiO2 matrix would be influenced by the substitution of the Ti4+ ions for higher valence ions, W6+ in the present study. In the measuring frequency range, samples impedance varies of three-four orders of magnitude over the RH range of 10-100 %. It is found to be the sensitivity highly dependent on both the measuring frequency and the sintering temperature. A parameter called characteristic humidity is defined to represent the sensitive response of sensors. This parameter is used to evaluate the influence of the W6+ ions on the sensitivity behaviour of the sensors.
New Composite Membranes Containing Bioactive Glass-Ceramic Nanoparticles and Chitosan for Biomedical Applications
Authors: Luz Gisela M. , Mano João F.
Published: January 2010

In this study a new P-free system applied to the production of Bioactive Glass Nanoparticles (BG-NPs) is proposed, in order to evaluate the effect of suppressing this component, in the bioactivity capability of the materials. The BG-NPs, based on both ternary (SiO2-CaO-P2O5) and binary (SiO2-CaO) systems, were prepared via a sol-gel method. The morphology and composition of the BG-NPs were studied using FTIR and SEM. New composite membranes were produced combining chitosan and the BG-NPs. The bioactive character of the prepared biodegradable membranes was accessed in vitro by analyzing the capability for apatite formation onto the surface after being immersed in simulated body fluid (SBF). EDX and SEM were used to confirm the bioactivity of the materials.
Humidity ITO Thick Film Sensing Behaviour Investigated by Impedance Spectroscopy
Authors: Faia Pedro M. , Santos Mario J. , Furtado C.S.
Published: January 2010

With the study of composite materials based on the In2O3-SnO2 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 a film obtained by sol-gel method and deposited using a slow spin coating process, of the In2O3-SnO2 pair, with a 2:3 mol ratio of Indium and Tin, respectively. The rather involved behaviour of our sample 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 thick film.
Theoretical Study of the Influence of Chemical Defects on the Molecular Properties of Semiconducting Polymers
Authors: Ramos Marta M. D. , Correia Helena M.G. , Barbosa Hélder M.C.
Published: January 2010

Semiconductor polymers are successfully implemented in a broad range of applications such as light emitting diodes, field effect transistors and photovoltaic devices. Most of the achievements reached in the development of these devices were obtained at experimental level, being difficult to identify individually the influence of each factor that limits and controls these devices efficiency. One of the factors that strongly influence the performance of polymer-based devices is the presence of chemical defects in the polymer strands that change their molecular properties. As a result, these polymer strands can work like traps or deep energetic states for charge transport, leading, for instance, to a decrease on charge mobility. At experimental level it is a difficult task to isolate the influence of each type of chemical defects individually on the molecular properties of the polymer strands. It is in this context that theoretical modelling seems to be the most suitable approach to get a deep understanding of the influence of chemical defects on the molecular properties of semiconductor polymers. By performing quantum molecular dynamics calculations we study the influence of chemical defects on the molecular properties of poly(para-phenylenevinylene) (PPV). Our results show clearly a significant difference on the electronic properties of defective polymer strands (e.g. charge carrier localization, ionization potential, electron affinity and electric-field threshold for charge carrier mobility along the polymer backbone) as compared with defect-free strands.
Influence of Oxygen Stoichiometry and Cation Ordering on Magnetoresistive Properties of Sr2FeMoO6±δ
Authors: Kalanda M. , Suchaneck Gunnar , Saad Anis M. , Demyanov S. , Gerlach Gerald
Published: January 2010

This work investigates the influence of initial compound synthesis prehistory on the phase sequence during formation of single-phase Sr2FeMoO6 (SFMO). Analytical-grade SrCO3, Fe2O3 and MoO3 (sample No.1) and partially reduced precursors of SrFeO3-x (SFO) and SrMoO4-y (SMO) (sample No.2) were used as initial reagents. In the latter case, kinetic limitations of SFMO phase formation are resolved by increasing the diffusivity of both of Fe3+ and Mo5+ and decreasing diffusion lengths to the reaction zone. This enhances the double-perovskite growth rate, lowers synthesis temperature and increases the intensity of X-ray reflections of (011) and (013) planes suggesting a superstructural ordering of Fe3+ and Mo5+ cations. Samples No.1 and No.2 have both a Тс ~ 420K while the magnetization value at 77 K in the sample No.2 is higher by a factor 2.3 compared to that of sample No.1. A decrease of the oxygen vacancy concentration by annealing Sr2FeMoO5.82 lowered magnetization of the samples and promoted the formation of a second magnetic phase with Тс = 700 К. We suppose that an increase of oxygen partial pressure during annealing causes formation of clusters with antiferromagnetic coupling in Fe3+-О2--Fe3+ chains. In order to increase the magnetoresistive effect at temperatures relevant for technical application, weak intergrain bonds should be formed.
Electrical and Mechanical Examination of PLZT/PZT Graded Structure for Photovoltaic Driven Piezoelectric Transformers
Authors: Kozielski Lucjan , Plonska Malgorzata , Bucko M.M.
Published: January 2010

Lanthanum-modified lead zirconate titanate (PLZT) ceramic materials have gained considerable attention due to their photostriction, which is the superposition of photovoltaic and piezoelectric effects. Functionally Graded Materials (FGM) implemented in construction of Piezoelectric Transformer (PT) can be used for direct converting photonic energy to electrical one by implementing photostrictive actuators with piezoelectric generator in one graded structure of piezoelectric transformer. Possible application in electronic industry needs thoroughly electrical and mechanical characterisation of this new FGM structure constructed from the PLZT/PZT material. Measurements presented in this work reveal high electrical anisotropy of this graded structure and the Impedance Spectroscopy (IS) proved to be a method capable to present such inequality in form of well separated semicircles. Additionally, dielectric measurements demonstrated that the characteristics of the graded structure are not a simply addition of starting materials parameters but are deeply influenced by a predominantly diffusion direction. Finally, additional nano-mechanical and -electrical methods are used for clarifying the complexity of the integration process of FGMs.
Synthesis and Characterization of Novel Donor-Acceptor Oligothiophenes as Efficient and Thermally Stable Second-Order Nonlinear Optical Chromophores
Authors: Batista Rosa M.F. , Costa Susana P.G. , Belsley Michael , Raposo M. Manuela M.
Published: January 2010

New push-pull thiobarbituric (oligo)thiophene derivatives 1 were synthesized, in good to excellent yields (60-98%), through Knoevenagel condensation of the corresponding formyl-(oligo)thiophenes 2 with 1,3-diethylthiobarbituric acid in dichloromethane, under basic conditions. Evaluation of the thermal and solvatochromic properties of these compounds was carried out and their NLO response was estimated. The values obtained suggest that these (oligo)thiophenes have good potential to be used as novel NLO materials.
Piezoelectric and Ultrasonic Studies of Mixed AgxCu1-xInP2(S,Se)6 Layered Crystals
Authors: Samulionis Vytautas , Banys Juras , Vysochanskii Yulian
Published: January 2010

The paper reviews recent results of ultrasonic and piezoelectric investigation in CuInP2S6 family ferroelectric layered crystals and their solid solutions in the temperature range 100-360 K. It was shown that, Cu substitution by Ag lowers the phase transition temperature. In investigated AgxCu1-xInP2(S,Se)6 crystals above the phase transition (PT) temperature the piezoelectric response was absent and appeared only below the transition. At low temperatures T < 220 K the layered AgxCu1-xInP2Se6 crystals are ferroelectric. Piezoelectric sensitivity in the ferroelectric phase increases with DC field applied along the c-axis, then saturates, and after reversion of voltage the piezoelectric signal decreases, at field near coercive changes sign, and saturates again at high voltage of opposite polarity In the paraelectric phase under external DC electric field, applied along c-axis normal to layers, thin AgxCu1-xInP2Se6 plates can effectively excite and detect ultrasonic waves, due to electrostriction. The same behaviour was observed and in AgxCu1-xInP2S6 crystals. The critical ultrasonic velocity anomalies were observed in the vicinity of PT. In CuInP2S6 crystals with addition of In i.e. indium rich materials the phase transition temperature could be raised to T > 330 K what is important for applications in medical diagnostics ultrasonic transducers. In all these materials the poling conditions were investigated and it was shown that after long time exposing in DC field the piezoelectric sensitivity sufficiently increases and electromechanical coupling constants as high as > 50 % could be obtained.