Search

Bioactive ceramics such as tricalcium phosphate (TCP) doped with metal ions are often used to replace natural bone in orthopedic and dental function, both in structural and coating applications. Although the addition of different ions to TCP has been correlated with improved mechanical performance, as well as pro-osteogenic and osteointegrative biological activities, the effect of combining different ions in single biomaterial formulations is poorly described. Here, design of experiments (DoE) was used to assess the effect of the addition of three metallic ions - Mn2+, Zn2+ and Fe3+ - to TCP doped with 10 mol% Mg2+, in combinations comprising one, two and three ions with varying ratios. Our results showed that the TCP could be doped by combinations of metallic ions and β-TCP and hydroxyapatite constitute the main crystalline phases. Additionally, the simultaneous effect of metal ions influenced the structural and physical properties of the TCP composite. Overall, for up 1 mol% of Mn2+, up to 3.75 mol% of Zn2+ and more than 2 mol% of Fe3+, compositions 2 and 6, a dense microstructure and good defined grain boundaries improve the mechanical properties. Furthermore, the ion-doped TCP composites, namely the one prepared from equal amounts of substituting ions besides Mg2+, did not elicit a cytotoxic effect indicating that these materials could be of interest for tissue engineering applications published

Three composite materials with different CaZrO3/MgO fractions (2/3, 1/2, 1/3) and two single-phase materials (CaZrO3 and MgO) were fabricated and their thermal conductivity was investigated. Complete thermal and mechanical characterizations (thermal expansion coefficient, thermal diffusivity, specific heat, hardness and toughness) of the materials were performed. Values of the thermal conductivity up to 480 °C of the composites were compared with those calculated with the main analytical models. From the real microstructures of the three composites, representative volume elements (RVE) were built and used for finite element modelling (FEM) of thermal conductivity using conductivities of the single-phase materials as inputs. The FEM results showed no differences for the 3 spatial directions of the RVE, nor for the different edge lengths (11, 14 and 17 μm). Results of all analytical models are statistically different from the experimental ones, being those from the Bruggeman model the closest. Results of the proposed FEM are statistically coincident with the experimental ones, showing sensitivity to temperature variation.

A water treatment sludge (WTS) was characterized in order to evaluate if its properties would be suitable for use as liner of earthworks or for strengthening a clay soil. A WTS and a clayey soil was characterized in terms of granulometry, cumulative volumes, specific surface, density, plastic limit, liquid limit, water content, hydraulic conductivity, and characteristics of compaction (optimal water content and dry density). This study aimed to exhibit and evaluate these investigated parameters of WTS, soft soil and mixed proportions between the materials for liners’ material production while evaluating soft soils’ reinforcement feasibility. The results have shown WTS’s contribution with its fine granulometry and compaction characteristics, indicating filling properties and possible feasibility as soft soils additions for liners’ material production while being applicable for soils‘ reinforcements, corroborating with existing literature on the subject. Thus, the currently developed investigation has exposed WTS as a potential addition for these applications while also attending society’s new demands towards a more sustainable future.

The demand for high-strength steel welds, as observed in civil and transport engineering, is related to a mass reduction in vehicles. Container-type trucks are examples of this kind of transport means because their boxes are able to be produced using Hardox grade steels. Therefore, this study reflects on the properties of welds in the MAG welding of Hardox 450, obtained through an innovative micro-jet cooling process with helium. This joining technology aims to reduce the formation of defects and to obtain a joint with very good assumed mechanical properties. Structural components of grade steel require welds with acceptable mechanical parameters with respect to operational loading conditions. That is, this study focuses on selecting welding parameters for the Hardox 450 steel and determining the weld quality with respect to microstructural observations and mechanical tests, such as the Charpy, tensile and fatigue tests. Weld fracturing under increasing monotonic force was examined and was strongly related to both stress components, i.e., axial and shear. The joint response under fatigue was expressed through differences in the fracture zones, i.e., at a stress value lower than the proportional limit, and weld degradation occurred in the shear and axial stress components. The data indicate that the hourglass specimen, with the weld in the centre zone of the measurement section, can be directly used to determine a weld response under cyclic loading. The impact test results showed attractive behaviour in the tested joint, as represented by 47 J at −20 °C. The recommended MAG welding parameters for Hardox 450 steel are low-oxygen when using an Ar + 18% CO2 shielding mixture. The collected results can be directly used as a guide to weld thin-walled structures (6 mm) made of Hardox grade steel, while the data from mechanical tests can support the modelling, designing and manufacturing of components made from this kind of steel grade.

Starting from synthetic raw materials (CaZrO3 and MgO), microstructural and mechanical properties were optimised in order to obtain dense multiphasic ceramic, then finite element method (FEM) of an equimolar (1:1) CaZrO3-MgO composite was performed in order to obtain the effective elastic modulus. Composite presents two main phases of orthorhombic CaZrO3 (81.5 wt.%) and cubic MgO (18.5 wt.%); For 1500 °C, relative density of 99.9%, characteristic strength of 168 MPa, hardness of 7.8 MPa and toughness of 2.5 MPa.m1/2 were obtained. FEM simulation was performed using two representative volume elements (RVE’s) with edge lengths of 14 μm (933 grains) and 17 μm (1670 grains), using isotropic elastic model, and anisotropic on specific set of crystallographic planes. The results of FEM using isotropic approach for the two RVE’s are perfectly aligned with the experimental (245 GPa), while the anisotropic model shows a difference of 6.5%.

The article presents the process of welding of steel movable platform supports. There is a growing demand for the welding of difficult-to-weld fine grain steels used in civil engineering and transport. An example of this could be the use of high-strength movable platform supports. The recently used material in the production of movable platform supports are fine-grained steels due to their high tensile strength of 1000 MPa. The joints formed using them, however, are characterized by much lower strength than the native material. In this article, the most appropriate parameters were selected for welding the movable platform supports made of difficult-to-weld fine-grained steel S960 MC.

Two epoxy resins with different viscosities were enhanced up to 1 wt.%, applying a simple method with carbon nanofibers (CNFs). These were characterized in terms of static bending stress, stress relaxation, and creep tests. In bending, the contents of 0.5 wt.% and 0.75 wt.% of CNFs on Ebalta and Sicomin epoxies, respectively, promote higher relative bending stress (above 11.5% for both) and elastic modulus (13.1% for Sicomin and 16.2% for Ebalta). This highest bending stress and modulus occurs for the lower viscosity resin (Ebalta) due to its interfacial strength and dispersibility of the fillers. Creep behaviour and stress relaxation for three stress levels (20, 50, and 80 MPa) show the benefits obtained with the addition of CNFs, which act as a network that contributes to the immobility of the polymer chains. A long-term experiment of up to 100 h was successfully applied to fit the Kohlrausch–Williams–Watts (KWW) and Findley models to stress relaxation and creep behaviour with very good accuracy.

In this work a methodology to reconstruct three-dimensional microstructures, representative of real biphasic ceramics using Neper free software is proposed. Finite element analysis in Ansys was implemented in order to calculate the effective elastic modulus of the simulated microstructures. Fine grained and dense zirconia toughened alumina (ZTA) materials with 5 and 40 vol.% of Yttria Stabilized Zirconia (YTZP) have been chosen to validate the proposed methodology. First, the effects of the size of the representative volume elements (RVEs) and the characteristics of the grain shapes are analysed. Second, the compliance with the isotropic condition is also verified. Agreement between the numerical and experimental values of the elastic modulus of the considered ZTA materials has been found. For these materials, zirconia fractions higher than 10 vol.% lead to bi-continuous microstructures which make the elastic properties deviate from the Voigt limit due to the increased number of contacts between zirconia grains.

In welding elements of the supporting structure of the means of transport, attention is paid to the high strength and good plastic properties of the welded joint. In the construction of transport means, DOCOL 1200M steel from the AHSS group is increasingly used due to their high tensile strength of steel at the level of 1200 MPa. The welds have much lower strength than the native material. In this paper, it was decided to check the weldability of DOCOL 1200M steel with the use of micro-jet cooling

The demand for new welding technologies in civil engineering and transport is increasing. An example of this is the tendency to increase the operating range of a mobile platform mounted on motor vehicles while maintaining the weight of the vehicle. The most commonly used material in the production of mobile platforms are AHSS steels due to their high tensile strength at the level of 1400 MPa. However, the joints created with their use are characterized by much lower strength than the native material. In this article, the most appropriate parameters for welding elements of a mobile platform from difficult-to-use steel AHSS were selected.

This work aims to better comprehend the mechanical behaviour, including failure sequence and failure modes, of differently surface-treated CFRP T-joints when subjected to out-of-plane loadings. Specimens consisted in two CFRP adherends – skin and stiffener – adhesively bonded with a structural film adhesive. The adherends' untreated and treated (by peel ply or abrasion) surfaces were firstly characterized using scanning electron microscopy (SEM), profilometry and wettability measurements. Stiffener pull-off tests (SPOT) were then experimentally conducted under quasi-static loading. The fractured surfaces were analysed by fractography to identify the failure mechanisms. The peel ply treatment has led to the worst results in terms of maximum load, while the abrasion-treated specimens performed the best of the three series. Surface characterization and fractography analysis were properly correlated with the SPOT results. Fracture damage typically initiates as mode I within the tip of the stiffener's flange, but as the fracture extends along the stiffener's foot, it does it under predominant mode II.

The biofunctionalization of metal implants with bioactive ceramics arises as an appealing strategy for promoting their osseointegration, without impairing implants’ good mechanical resistance. In this work, biocomposites of hydroxyapatite - CaZrO3 were obtained by rate controlled sintering and their microstructure, mechanical properties, biological as well as the effect of stoichiometric calcium zirconate dopant on the decomposition of HA were analysed. The results obtained showed that the addition of CaZrO3 stabilizes the hydroxyapatite at least up to 1300 °C and inhibits the appearance of the α- and β-TCP phases. Moreover, the mechanical properties of the hydroxyapatite were improved with 10 wt% of CaZrO3, despite the increase of porosity. The in vitro assays demonstrated that the biocomposites were biocompatible, since they favoured human osteoblast cells adhesion and proliferation. All the data obtained emphasize the potential of these biocomposites for the aimed biomedical application.

Thermosetting polymers are very popular in the automotive and aeronautic industry, in particular epoxy resin is widely used as matrix thermoset in carbon and glass fibre reinforced composites. The properties of these epoxy-based polymers can be improved with the addition of particulate or small fibre materials in order to construct a lightweight material with enhanced mechanical and structural response. This work aimed to manufacture and characterize epoxy resin reinforced composites with iron (II, III) oxide (magnetite, Fe3O4) in amounts of 0.25, 0.5 and 1 wt%, and 2 and 4 wt% of fumed silicon dioxide (silica, SiO2). Mechanical properties were investigated by three-point bending flexural test, fracture toughness, flexural stress relaxation. In addition, apparent porosity, apparent density and Differential Scanning Calorimetry tests were performed. The results showed that the addition of Fe3O4 does not contribute significantly to the improvement of mechanical properties. However, fumed SiO2 promotes a considerable improvement in the mechanical properties. Keywords: Composite, epoxy resin, Fe3O4, SiO2, mechanical properties

Despite environmental pressures and intrinsic recycling potential, spent refractories waste is generally considered an economically unattractive waste stream. This work proposes an upgraded view of the debris recovered from dismantled spinel-bonded high-alumina linings of steel induction furnaces, demonstrating that it can be reused in the form of vibratable and self-flowing castable systems. The recovered material retains the microstructural distribution of in situ spinel formation without the corresponding disruptive expansion, mirroring the use of pre-formed spinel without the onus of a pre-firing. The mechanical performance after firing was found to be always best for the self-flowing system, which is also less affected by changes in added-water content. There is potential for large usages of cleaned waste (50–60 wt%), which helps reducing the supply risk for major refractory primary raw materials as well as landfilling costs.

An attractive way to obtain low cost calcium zirconate (CaZrO3) composites is mixing natural limestone or dolomite with zirconia. These CaZrO3 based ceramic composites were often investigated as a promising high refractory for casting metal alloys, cements, thermal and environmental barrier coating. In this study the sliding wear, fracture mechanism and friction properties of a CaZrO3-MgO-ZrO2 ceramic against ZrO2 and steel counter bodies was carried out. Wear and fracture surface mechanisms, influence of its impurities and individual phases are discussed. The composite presents a coefficient of friction higher in ceramic/metal than in ceramic/ceramic pair, but the specific wear it is significantly higher when tested with the ZrO2 ball. The fracture surfaces presenta dominant transgranular fracture when tested with steel and intergranular fracture against ZrO2. Fil: Silva, Abílio. Instituto de Cerámica y Vidrio de Madrid; España. Consejo Superior de Investigaciones Científicas; España Fil: Booth, Raul Fernando Nicolas. Instituto de Cerámica y Vidrio de Madrid; España. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentina Fil: Garrido, Liliana Beatriz. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentina Fil: Aglietti, Esteban Fausto. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentina Fil: Pena, Pilar. Consejo Superior de Investigaciones Científicas; España. Instituto de Cerámica y Vidrio de Madrid; España Fil: Baudín, Carmen. Consejo Superior de Investigaciones Científicas; España. Instituto de Cerámica y Vidrio de Madrid; España

Manufacturers of welding equipment strive to develop the most efficient, cost-effective and easy to process welding methods. This necessity is also related to welding of new, often hard-to-weld steel types. The article aims to present the possibility of welding a high-strength S700MC steel with an increased yield point using MAG (135) process and a blowtorch with an intelligent arc control. The blowtorch allows to reduce input energy and reduce splinters while maintaining the mechanical properties of the material. The S700MC steel has been selected for the tests purposefully, as it may create welding problems in order to maintain high strength and increased yield point. The applied technology provided lower power consumption compared to traditional welding machines and joints with very good mechanical properties were achieved.

Resumo Nas minas da Panasqueira (Covilha, Portugal) acumulam-se montes de residuos (agregados) provenientes da extracao de tungstenio sem qualquer aplicacao. Este trabalho pretende contribuir para implementar um novo uso para estes residuos integrando-os como revestimento refratario no processo de moldacao a verde da fundicao de metais nao ferrosos. Os resultados mostram o potencial do uso destes residuos da fundicao de metais nao ferrosos.

Submitted by Ilídio Correia (icorreia@ubi.pt) on 2018-03-21T16:23:01Z No. of bitstreams: 1 2017 de Sá IJPMPM.pdf: 1428720 bytes, checksum: 7a5eb756f5c872a802ebadbdcef464d8 (MD5) Approved for entry into archive by Paulo Pessoa (pfep@ubi.pt) on 2018-03-21T16:36:46Z (GMT) No. of bitstreams: 1 2017 de Sá IJPMPM.pdf: 1428720 bytes, checksum: 7a5eb756f5c872a802ebadbdcef464d8 (MD5) Approved for entry into archive by Paulo Pessoa (pfep@ubi.pt) on 2018-03-21T16:39:05Z (GMT) No. of bitstreams: 1 2017 de Sá IJPMPM.pdf: 1428720 bytes, checksum: 7a5eb756f5c872a802ebadbdcef464d8 (MD5) Made available in DSpace on 2018-03-21T16:39:05Z (GMT). No. of bitstreams: 1 2017 de Sá IJPMPM.pdf: 1428720 bytes, checksum: 7a5eb756f5c872a802ebadbdcef464d8 (MD5) Previous issue date: 2016-09-10 info:eu-repo/semantics/publishedVersion

A new type of luminescent optical fibre sensor for structural health monitoring of composite laminates (CFRP) is proposed. The Nd3+ doped multi-core doubleclad fibre incorporated in composite structure was used as a distributed temperature sensor. The change of luminescence intensity (Nd3+ ions) at the wavelength of 880 nm (4F3/2 → 4I9/2) and 1060 nm (4F3/2 → 4I11/2) was used for internal temperature monitoring. The special construction of optical fibre was used as it assures an efficient pumping mechanism and, at same time, it increases the measuring sensitivity. The linear response with relative sensitivity 0.015 K−1 was obtained for temperature range from 30 up to 75ºC. The manufacturing process of CFRP with embedded optical fibre sensor is also discussed.

The design and production of scaffolds for bone tissue regeneration is yet unable to completely reproduce the native bone properties. In the present study new alginate microparticle and microfiber aggregated scaffolds were produced to be applied in this area of regenerative medicine. The scaffolds' mechanical properties were characterized by thermo mechanical assays. Their morphological characteristics were evaluated by isothermal nitrogen adsorption and scanning electron microscopy. The density of both types of scaffolds was determined by helium pycnometry and mercury intrusion porosimetry. Furthermore, scaffolds' cytotoxic profiles were evaluated in vitro by seeding human osteoblast cells in their presence. The results obtained showed that scaffolds have good mechanical and morphological properties compatible with their application as bone substitutes. Moreover, scaffold's biocompatibility was confirmed by the observation of cell adhesion and proliferation after 5 days of being seeded in their presence and by non-radioactive assays.

The experimental investigation has been carried out to evaluate process stability for two rutile types of electrode supplied with two types of DC power sources: traditional 3 phase thyristor and inverter type. Initially to understand the maximum range of outcomes high quality and defective electrodes, with lower arc stability, were selected for both. During welding tests current and voltage signals were recorded separately with the aid of A/D converter and 5 kHz of sampling frequency. On the basis of digital signals obtained from each electrode type and power sources, a number of statistical indicators have been computed. Furthermore voltage and current histograms have been determined (defined as a density distribution of welding arc voltage and current values). Statistical indicators of voltage signals have proved to be more useful for process stability evaluation, particularly mean voltage (Uśr) and histograms as well as voltage coefficient of variation (KvU).

Mining and quarrying activities in Europe generate approximately 55% of total industrial wastes, according to a recent Eurostat report. Most of these wastes are directly dumped on land or deposited in landfill sites. The first solution may lead to negative environmental impacts on land (removal of vegetation, deforestation, land slope changes and increased risk of erosion), water (pollutant transport through surface runoff, soil infiltration and contamination of water resources), may lead to the contamination of agricultural goods and may impose risks on human health. In Portugal, about 20% of industrial waste produced originates from mines and quarries, particularly from Panasqueira mining, one of the largest tungsten mines in the world. Currently, Panasqueira mining generates almost 100 tonnes of waste-rock, per day. Such waste-rock have accumulated over a number of years into very large heaps and it is desirable to seek new economic solutions that can contribute towards their reuse. In this context, this work discusses the potential for reuse of waste-rock piles of Panasqueira tungsten mine, which may be a case statement to be followed. The proposed solution described in this paper consists in developing innovative polymer-based composite materials, obtained from non-contaminated waste-rock tailings. Such materials must have suitable properties for technical-artistic value added applications, such as conservation, restoration and/or rehabilitation of historic monuments, sculptures, decorative and architectural intervention, or simply as materials for building revetments.

Alumina, with high melting point (2050°C), high hardness and mechanical strength, and excellent abrasion resistance, is one of the most common raw materials used in self-flow refractory castables (SFRC) for monolithic linings and is commercially available in various fine to coarse size classes. However, the performance of the refractory lining depends not only on the properties of its ingredients but also on its easy installation (good flowability). The aim of this work was to evaluate the relationship between the flowability index (FI) of fresh castable and the specific surface area (SSA) of its particles, which is mostly determined by the finer particles content. The results obtained showed that, by controlling the proportion between matrix and aggregate, it is possible to control the SSA of the refractory castable and find a mathematical relationship between the specific surface area and the minimum flowability index required to obtain a self-flow refractory castable. It is, thus, possible to optimize the refractory castable size composition and obtain an estimate for FI as a function of SSA. Using a minimum 45 wt.% matrix content in the castable mixture, a SSA value above 2.215 m2/g is obtained, which leads to FI ≥ 80%, the recommended value for self-flow.

The goal of this research is to choose the proper method of car body welding. Properties of weld metal deposits depend on many conditions. First of all, this paper attempts to study the role of oxide inclusion sites on the transformation of austenite to acicular ferrite in steel weld metal deposits and their toughness. Safety and exploitation conditions of welded steel structure depend on many factors. The most significant of those factors are connected with materials, welding technology, state of stress and temperature. Because of that a good selection of steel and welding method is crucial to obtain proper steel structure. Car body elements of higher durability are made of low carbon and low alloy steel, very often with small amount of carbon and the amount of alloy elements such as Ni, Mn, Mo, Cr and V in low alloy steel and their welds. In the terms of the kind of steel it is used a proper welding method and adequate filler materials. In the present paper the influence of Mn, Ni, Mo, in WMD on the behaviour of steel structure for low temperature service was tested.

The success of a refractory castable is largely due to the quality of its properties and ease of application. Self-flow refractory castables (SFRC), with high flowability index (>130%), can be easily accommodated in a mould without the application of external energy, being ideal for the manufacture of monolithic linings. SFRC castables without cement require a matrix of very fine particles, which guarantees improved rheological behaviour and performs the role of the binder in the absence of the refractory cement. The presence of the aggregate (coarse particles) hinders the flowability index, but improves the castable mechanical strength and reduces firing shrinkage, and also contributes to the reduction of the castable costs. The control of the maximum paste thickness (MPT) allows the reduction of the coarse particles interference, minimizing the number of contact points among the grains and avoiding the formation of an aggregate skeleton that impairs the flowability of the mixture. In the present work, 100% alumina SFRCs without cement were produced with a fixed matrix of fine particles, whose particle size distribution was optimized using statistical techniques (mixtures design and triangular response surfaces). Different aggregate particle size distributions were used, with several MPT values, with the objective of evaluating which was the mean distance that maximized the flowability index, simultaneously ensuring good mechanical strength for the refractory castable. Ensuring a minimum surface area of 2.22m2/g, the mixtures reach the self-flow turning point with a minimum water content and the maximum flowability is obtained for an aggregate particle size distribution modulus of q=0.22, and consequently an optimized MPT value. SFRC with high mechanical strength (>60MPa) were obtained.

Primary energy sources exhibited regular long-term logistic substitution trends from the mid-19th century through the third quarter of the 20th century. This analysis, based on an extension of the Fisher–Pry substitution model, accounted for the observed historical shifts of primary energy use from sources of wood, coal, oil, natural gas, and nuclear. In the mid-1980s the substitution dynamics was replaced by a relatively constant contribution from oil, natural gas, coal, nuclear power, and hydropower. However, a major factor in energy use dynamics in this recent period was substitution of conservation and efficiency for actual fuel use. The energy efficiency is measured as the ratio of economic activity to the rate of energy use (energy intensity). To incorporate these data into the logistic analysis, a method for estimating the fraction of energy saved by the increased efficiency was used. With this interpretation, energy efficiency fits within the substitution model. Furthermore, to identify indications of future energy scenarios, as well as to test the logistic substitution analysis, another statistical approach using ternary diagrams was developed. The consistent results from both logistic substitution and statistical analysis are compared with recent energy projections, trends in decarbonization, Kondratieff waves, and other efficiency measures. While the specific future mix of renewables and nuclear energy sources is uncertain, the more general logistic dynamics pattern of the energy system seems to be continuing as it has for about 150 years now.

In this work, commercial alumina fine powders were used as raw materials, namely two tabular alumina fractions (–500 mesh and –230 mesh) and a reactive alumina. Statistical modelling and the Response Surface Methodology (Statistica, Mixtures Designs and Triangular Surfaces module) were applied to three-component mixtures and used to calculate the various property-composition surfaces. To that aim, the various mixtures were prepared, cast, dried, fired and characterised. The particle size distribution modulus, q, was determined for all mixtures using the software LISA. The various response surfaces were then combined, so that the water content in the mixture could be minimised and the matrix flowability maximised. The properties of the resulting test-bricks (linear shrinkage, mechanical strength, apparent density and porosity) were also modelled and response surfaces were obtained. Combined results enabled the definition of an optimised particle size composition range, which guarantees the presence of a low water flow-bed that enables the aggregate self-flow.

The purpose of this investigation is to evaluate quantitatively and comparatively the effect of embedding optical fibers (OF) on the mechanical behavior of a carbon fiber-epoxy composite in order to verify whether their presence can possibly degrade the mechanical performance of the host material. The existing literature on this subject is not conclusive about the nature and intensity of this effect. Adding more reliable data to our systematic study contributes to this discussion favoring the conclusion about a harmful influence as a consequence of optical fiber embedment. Three kinds of mechanical tests have been performed in this work: impact tests, static flexural tests, and fatigue tests. The results of some experiments point to a possible detrimental influence related to the presence of the OF, being it different in nature and intensity for each of these tests. The mechanical behavior in static loading conditions seems to be not significantly affected as a consequence of the presence of the OF, while that in impact and fatigue tests are strongly affected, even though this influence being physically distinct from each other. Based on these results, some discussion is made about the possible failure mechanisms that can explain the detected differences.

A self-flow refractory castable (SFRC) without cement requires a matrix of fine particles and a broad size distribution of coarse particles (aggregate). The matrix ensures the rheological behaviour and performs the binding role of the absent refractory cement. The presence of the aggregate coarse particles hinders the flowability index (FI), but improves the castable mechanical strength and reduces firing shrinkage. A new methodology of SFRC particle distribution design was developed, using response surface statistical modelling and commercial alumina powders (reactive and tabular). First, the composition of the fine matrix was optimised, seeking minimum water content and maximum IF. To this matrix, various aggregate distributions, combining six tabular alumina size fractions and with different Andreasen distribution modulus, q, between 0.18 to 0.28, were added, to identify the composition with maximum FI. The results obtained show that a minimum specific surface area (SSA) of 2.22m2/g is necessary to reach the self-flow turning point, after which the largest FI requires the maximisation of the aggregate maximum paste thickness (MPT), corresponding to a distribution with q=0.22. The optimised castable composition presents high mechanical strength (>60MPa) and low shrinkage.

In the processing of any particulate system (including refractory castables), the finer sized particle fraction (matrix or filler) is mostly responsible for the final system properties. Alumina fine powders were used in this work as raw materials, namely two tabular alumina fractions (–500 mesh and –230 mesh) and a commercial reactive alumina. Statistical modelling and the Response Surface Methodology (Statistica, Mixtures Designs and Triangular Surfaces module) were used to optimise the particle size composition of the three-component mixtures leading to matrix maximum flowability. The mixing methodology, aimed at minimising the water content, was kept constant. No-cement alumina castables produced with the various fine size powder mixtures, were used to prepare test-pieces. After drying and sintering, their mechanical resistance (MoR), density, porosity, water absorption, thermal shock behaviour and microstructure were evaluated. The results obtained evidenced the relevance of variables such as the water content per unit specific surface area, needed to reach the self-flow “turning point”, and validated the statistical optimisation method used. Moreover those results showed the existence of a matrix composition range, which favours the formation of a flow-bed that enables the aggregate self-flow.

Purpose In this work, an alumina scaffold was produced through a new method to be used in a near future as a bone substitute. Methods In vitro and in vivo studies were performed in order to characterize the mechanical and biological properties of the scaffold. Results The results obtained showed that this scaffold has high mechanical resistance and a porous surface that allows human osteoblast cells to adhere and proliferate. The in vivo studies revealed no systemic reaction. Conclusions The alumina scaffold produced herein has the mechanical and biological properties that are compatible with its application in bone therapy.