Mechanical properties of chemically modified portuguese pinewood

To turn wood into a construction material with enhanced properties, many methods of chemical modification have been developed in the last few decades. In this work, mechanical properties of pine wood were chemically modified, compared and evaluated. Maritime pine wood (Pinus pinaster) was modified with four chemical processes: 1,3-dimethylol-4,5- dihydroxyethyleneurea, N-methylol melamine formaldehyde, tetra-alkoxysilane and wax. The following mechanical properties were assessed experimentally: Modulus of elasticity measured statically, stiffness stabilization efficiency in different climates (30 and 87% of relative humidity), modulus of rupture, work maximum load, impact bending strength, compression, tensile and shear strength at indoor conditions (65% of relative humidity). In both types of active principle of modification, cell wall or lumen fill, no significant changes on the bending stiffness (modulus of elasticity) were found. In the remaining properties analysed significant changes in the modified wood-material took place compared to unmodified wood control: - Cell wall modification was the most effective method to achieve high stiffness stabilization efficiency (up to 60%) and also increased compression strength (up to 230%). However, modulus of rupture, tensile, shear and the impact bending strength were reduced by both resins, but in a varying extent, where the N-methylol melamine formaldehyde endured less reduction than 1,3-dimethylol-4,5-dihydroxyethyleneurea resin. In the latter, reduction up to 60% can take place. - In the lumen fill modification: tetra-alkoxysilane has no effect in the mechanical properties. Although, a slight increase in shear strength parallel to the grain was found. Wax specimens have shown a slight increase in bending strength, compression, tensile and shear strength as well as in the absorption energy capacity.

Experimental characterization of the out-of-plane performance of regular stone masonry walls, including test setups and axial load influence

Stone masonry is one of the oldest and most worldwide used building techniques. Nevertheless, the structural response of masonry structures is complex and the effective knowledge about their mechanical behaviour is still limited. This fact is particularly notorious when dealing with the description of their out-of-plane behaviour under horizontal loadings, as is the case of the earthquake action. In this context, this paper describes an experimental program, conducted in laboratory environment, aiming at characterizing the out-of-plane behaviour of traditional unreinforced stone masonry walls. In the scope of this campaign, six full-scale sacco stone masonry specimens were fully characterised regarding their most important mechanic, geometric and dynamic features and were tested resorting to two different loading techniques under three distinct vertical pre-compression states; three of the specimens were subjected to an out-of-plane surface load by means of a system of airbags and the remaining were subjected to an out-of-plane horizontal line-load at the top. From the experiments it was possible to observe that both test setups were able to globally mobilize the out-of-plane response of the walls, which presented substantial displacement capacity, with ratios of ultimate displacement to the wall thickness ranging between 26 and 45 %, as well as good energy dissipation capacity. Finally, very interesting results were also obtained from a simple analytical model used herein to compute a set of experimental-based ratios, namely between the maximum stability displacement and the wall thickness for which a mean value of about 60 % was found.

Estudo da Resistência Mecânica do Betão com Agregado Cerâmico Vermelho

Os sectores da construção e demolição de edifícios são responsáveis por um elevado volume de produção de resíduos. Estes resíduos são normalmente direcionados para aterros, que se encontram, neste momento, sobrelotados. Esta falta de capacidade de receção de resíduos tem como consequência imediata o aumento dos valores monetários associados ao depósito destes materiais excedentários. Com a elevada produção destes resíduos torna-se importante a sua reciclagem e reutilização. No caso da Engenharia Civil, uma grande produtora de resíduos, seria ainda mais interessante o seu reaproveitamento imediato na área. Nesta investigação, pretendeu-se avaliar o desempenho mecânico de betões com diferentes percentagens de agregados cerâmicos vermelhos. Essa investigação passou numa fase inicial pelo estado fresco do betão, de forma a analisar a sua trabalhabilidade. Na fase seguinte, analisou-se no estado endurecido, a resistência à compressão e resistência à tração por compressão diametral. Para concretização deste objetivo produziram-se três tipos de betões: um de referência (areia fina e brita fina), um betão com incorporação de agregados finos e grossos de cerâmica vermelha, juntamente com a areia fina e a brita fina, e o terceiro, um betão com a substituição total da areia fina por cerâmica fina. A realização desta investigação, demostrou que os betões com a incorporação de agregado cerâmico vermelho apresentam resultados de boa qualidade, sendo plausível a sua utilização em estruturas.

Caraterização das propriedades macânicas e de fratura de um adesivo estrutural de alta ductilidade

As juntas adesivas são uma alternativa viável para substituir ligações comuns como as mecânicas ou soldadas, devido a diversas vantagens como a possibilidade de união de materiais de natureza diferente, maior leveza, menores custos inerentes ao fabrico e ainda prevenção da corrosão galvânica que pode ocorrer nas ligações entre dois materiais metálicos diferentes. A resistência de uma junta depende, para um determinado tipo de solicitação imposta, da distribuição de tensões no interior da junta. Por outro lado, a geometria das juntas, as propriedades mecânicas dos adesivos e os componentes a ligar vão influenciar a distribuição de tensões. O carregamento nas camadas adesivas de uma junta poderá induzir tensões de tração, compressão, corte, arrancamento ou clivagem, ou ainda uma combinação de duas ou mais destas componentes. O objetivo da presente dissertação é a caraterização completa de um adesivo estrutural de alta ductilidade recentemente lançado no mercado (SikaPower® -4720), para facilitar o projeto e otimização de juntas adesivas ligadas com o mesmo. São quatro os ensaios a realizar: ensaios à tração de provetes maciços (também denominados de bulk), ensaios ao corte com a geometria Thick Adherend Shear Test, ensaios Double-Cantilever Beam e ainda ensaios End-Notched Flexure. Com a realização dos ensaios referidos, são determinadas as propriedades essenciais à caraterização mecânica e de fratura do adesivo. Os resultados obtidos para cada ensaio resultaram em propriedades medidas com elevada repetibilidade, da mesma maneira que se revelaram de acordo com os dados disponibilizados pelo fabricante, sempre que estes estavam disponíveis.

Relatório de estágio: intervenção em fisioterapia na sindrome da cirurgia lombar falhada

Introdução: A síndrome da cirurgia lombar falhada (SCLF) caracteriza-se pela persistência ou recidiva da dor ou aparecimento de novos sintomas após discectomia, descompressão de canal estreito ou artrodese lombares. Objectivos: O objectivo deste estudo foi descrever a abordagem em fisioterapia de um caso com Síndrome da Cirurgia Lombar Falhada e avaliar os seus efeitos na funcionalidade e sintomatologia dolorosa neste indivíduo. Metodologia: A amostra foi constituída por um sujeito com 41 anos, trabalhador da construção civil, apresentando dor lombar com irradiação para o membro inferior, após ter sido submetido a discectomia lombar e artrodese, que realizou sessões de fisioterapia convencional antes e depois da cirurgia, e que apresentava sinais compatíveis com compressão radicular. A intensidade da dor foi medida através da escala visual analógica (EVA), as amplitudes com o goniómetro universal, a funcionalidade foi avaliada utilizando o Questionário de Incapacidade Roland-Morris (RMDQ), o estado psicológico foi avaliado através da “Escala de Desânimo Associado à Dor” e do “Inventário de Convicções e Percepções Relacionadas com a Dor”. Resultados: A dor era inicialmente em média de 5,5/10 EVA, sendo de 3,4/10 EVA no final do tratamento. Quanto à funcionalidade (RMDQ) esta variou de 14/24 no início para 17/24 no final. De uma forma geral, após a aplicação de técnicas para diminuir a tensão do piriforme, técnicas neuurodinâmicas e um programa de exercícios para melhoria do controlo motor, o paciente apresentou alívio das queixas de dor na nádega esquerda e anca, aumento da amplitude de rotação medial da coxo-femoral, ausência das parestesias na face plantar do pé esquerdo e melhoria das queixas de dor na face anterior e lateral da coxa. Verificamos que houve diminuição dos índices de dor e melhorias dos níveis de funcionalidade. Conclusão: Neste estudo de caso, foi salientado o processo de raciocínio clínico desenvolvido pelo fisioterapeuta: a interpretação dos dados da história e levantamento das primeiras hipóteses e a realização dos testes no exame objectivo, permitiram estabelecer um diagnóstico funcional e elaborar um plano de intervenção através do qual o utente recuperou parcialmente a sua funcionalidade e diminuiu os seus índices de dor.

Concepção e instalação de tabelas multifunções para recintos desportivos cobertos

Mestrado em Engenharia Electrotécnica – Sistemas Eléctricos de Energia

Influence of the pre-treatments on the properties of biodegradable films from bovine hair

The replacement of conventional synthetic films and coatings by biodegradable alternatives reduces the use of non-renewable resources and waste disposal problems. Considering that Portugal is a major producer of leather, and consequently a large producer of related wastes, in this research, bovine hair was tested for the production of biodegradable films directly by thermo-compression, allowing waste valorisation and reduction of environmental pollution. The aim of this study was to determine the influence of the different pre-treatments performed by two processes (removal by mechanical action and removal by chemical process), applied to bovine hair, in order to obtain a biodegradable film with appropriate properties. Mechanical properties for these films were evaluated, namely strain at break, stress at break and Young modulus. Additionally colour, solubility and swelling in water were also studied. The mechanical removal hair only produced films with Na2S treatment. Chemical removed hair (immunization) depends of the pre-treatment and the degreasing with petroleum ether or sodium sulphide pre-treatment leads better mechanical properties. The results obtained indicated that the pre-treatments have an important role in the final properties of biodegradable films.

Deterioração e reabilitação de estruturas de betão armado

Apesar da enorme evolução tecnológica, os prazos na construção são cada vez mais reduzidos e os custos mais controlados, verificando-se uma despreocupação no que diz respeito a aspetos como a qualidade e durabilidade da construção das estruturas. Desperta assim nos técnicos, donos-de-obra, entidades executantes e projetistas a necessidade de avaliar o estado de conservação das estruturas de betão armado. Esta dissertação tem como objetivo principal abordar as anomalias e os mecanismos de deterioração mais correntes, os métodos de ensaio destrutivos ou parcialmente destrutivos mais utilizados e adequados, e abordar algumas das técnicas de reparação e reforço das estruturas de betão armado. Os principais danos apresentados nas estruturas são devidos a agentes físicos, mecânicos, biológicos e químicos. Podem ser devidos a causas diretas (acidentais ou naturais), que acarretam uma ação concreta sobre os elementos estruturais, e causas indiretas (humanas), diretamente ligadas com erros de projeto. É primordial fazer-se o levantamento de todas as anomalias existentes para se recorrer a um método de inspeção e ensaio. Consoante a necessidade de informação e estado da estrutura são selecionados os ensaios a realizar, podendo ser realizados “in situ” ou em laboratório. As técnicas de reparação e reforço são vistas como métodos para melhorar as condições da estrutura ao nível da segurança, desempenho, habitabilidade e durabilidade, prevenindo a evolução dos mecanismos de deterioração.

Interlimb relation during the double support phase of gait: an electromyographic, mechanical and energy based analysis

The purpose of this study is to analyse the interlimb relation and the influence of mechanical energy on metabolic energy expenditure during gait. In total, 22 subjects were monitored as to electromyographic activity, ground reaction forces and VO2 consumption (metabolic power) during gait. The results demonstrate a moderate negative correlation between the activity of tibialis anterior, biceps femoris and vastus medialis of the trailing limb during the transition between midstance and double support and that of the leading limb during double support for the same muscles, and between these and gastrocnemius medialis and soleus of the trailing limb during double support. Trailing limb soleus during the transition between mid-stance and double support was positively correlated to leading limb tibialis anterior, vastus medialis and biceps femoris during double support. Also, the trailing limb centre of mass mechanical work was strongly influenced by the leading limbs, although only the mechanical power related to forward progression of both limbs was correlated to metabolic power. These findings demonstrate a consistent interlimb relation in terms of electromyographic activity and centre of mass mechanical work, being the relations occurred in the plane of forward progression the more important to gait energy expenditure.

Mismatch negativity in childhood temporal lobe epilepsy: a proposed paradigm for testing central auditory processing

Background: Temporal lobe epilepsy (TLE) is a neurological disorder that directly affects cortical areas responsible for auditory processing. The resulting abnormalities can be assessed using event-related potentials (ERP), which have high temporal resolution. However, little is known about TLE in terms of dysfunction of early sensory memory encoding or possible correlations between EEGs, linguistic deficits, and seizures. Mismatch negativity (MMN) is an ERP component – elicited by introducing a deviant stimulus while the subject is attending to a repetitive behavioural task – which reflects pre-attentive sensory memory function and reflects neuronal auditory discrimination and perceptional accuracy. Hypothesis: We propose an MMN protocol for future clinical application and research based on the hypothesis that children with TLE may have abnormal MMN for speech and non-speech stimuli. The MMN can be elicited with a passive auditory oddball paradigm, and the abnormalities might be associated with the location and frequency of epileptic seizures. Significance: The suggested protocol might contribute to a better understanding of the neuropsychophysiological basis of MMN. We suggest that in TLE central sound representation may be decreased for speech and non-speech stimuli. Discussion: MMN arises from a difference to speech and non-speech stimuli across electrode sites. TLE in childhood might be a good model for studying topographic and functional auditory processing and its neurodevelopment, pointing to MMN as a possible clinical tool for prognosis, evaluation, follow-up, and rehabilitation for TLE.

Tensile behaviour of a structural adhesive at high temperatures by the extended finite element method

Component joining is typically performed by welding, fastening, or adhesive-bonding. For bonded aerospace applications, adhesives must withstand high-temperatures (200°C or above, depending on the application), which implies their mechanical characterization under identical conditions. The extended finite element method (XFEM) is an enhancement of the finite element method (FEM) that can be used for the strength prediction of bonded structures. This work proposes and validates damage laws for a thin layer of an epoxy adhesive at room temperature (RT), 100, 150, and 200°C using the XFEM. The fracture toughness (G Ic ) and maximum load ( ); in pure tensile loading were defined by testing double-cantilever beam (DCB) and bulk tensile specimens, respectively, which permitted building the damage laws for each temperature. The bulk test results revealed that decreased gradually with the temperature. On the other hand, the value of G Ic of the adhesive, extracted from the DCB data, was shown to be relatively insensitive to temperature up to the glass transition temperature (T g ), while above T g (at 200°C) a great reduction took place. The output of the DCB numerical simulations for the various temperatures showed a good agreement with the experimental results, which validated the obtained data for strength prediction of bonded joints in tension. By the obtained results, the XFEM proved to be an alternative for the accurate strength prediction of bonded structures.

H-NAMe: specifying, implementing and testing a hidden-node avoidance mechanism for wireless sensor networks

The hidden-node problem has been shown to be a major source of Quality-of-Service (QoS) degradation in Wireless Sensor Networks (WSNs) due to factors such as the limited communication range of sensor nodes, link asymmetry and the characteristics of the physical environment. In wireless contention-based Medium Access Control protocols, if two nodes that are not visible to each other transmit to a third node that is visible to the formers, there will be a collision – usually called hidden-node or blind collision. This problem greatly affects network throughput, energy-efficiency and message transfer delays, which might be particularly dramatic in large-scale WSNs. This technical report tackles the hidden-node problem in WSNs and proposes HNAMe, a simple yet efficient distributed mechanism to overcome it. H-NAMe relies on a grouping strategy that splits each cluster of a WSN into disjoint groups of non-hidden nodes and then scales to multiple clusters via a cluster grouping strategy that guarantees no transmission interference between overlapping clusters. We also show that the H-NAMe mechanism can be easily applied to the IEEE 802.15.4/ZigBee protocols with only minor add-ons and ensuring backward compatibility with the standard specifications. We demonstrate the feasibility of H-NAMe via an experimental test-bed, showing that it increases network throughput and transmission success probability up to twice the values obtained without H-NAMe. We believe that the results in this technical report will be quite useful in efficiently enabling IEEE 802.15.4/ZigBee as a WSN protocol.

Effect of plug-filling, Testing velocity and temperature on the tensile strength of strap repairs on aluminium structures

In this work, an experimental study was performed on the influence of plug-filling, loading rate and temperature on the tensile strength of single-strap (SS) and double-strap (DS) repairs on aluminium structures. Whilst the main purpose of this work was to evaluate the feasibility of plug-filling for the strength improvement of these repairs, a parallel study was carried out to assess the sensitivity of the adhesive to external features that can affect the repairs performance, such as the rate of loading and environmental temperature. The experimental programme included repairs with different values of overlap length (L O = 10, 20 and 30 mm), and with and without plug-filling, whose results were interpreted in light of experimental evidence of the fracture modes and typical stress distributions for bonded repairs. The influence of the testing speed on the repairs strength was also addressed (considering 0.5, 5 and 25 mm/min). Accounting for the temperature effects, tests were carried out at room temperature (≈23°C), 50 and 80°C. This permitted a comparative evaluation of the adhesive tested below and above the glass transition temperature (T g), established by the manufacturer as 67°C. The combined influence of these two parameters on the repairs strength was also analysed. According to the results obtained from this work, design guidelines for repairing aluminium structures were

Damage evaluation of drilled carbon/epoxy laminates based on area assessment methods

The characteristics of carbon fibre reinforced laminates had widened their use, from aerospace to domestic appliances. A common characteristic is the need of drilling for assembly purposes. It is known that a drilling process that reduces the drill thrust force can decrease the risk of delamination. In this work, delamination assessment methods based on radiographic data are compared and correlated with mechanical test results (bearing test).

Mechanical and tribological characterization of TiB2 thin films

Titanium Diboride (TiB2) presents high mechanical and physical properties. Some wear studies were also carried out in order to evaluate its tribological properties. One of the most popular wear tests for thin films is the ball-cratering configuration. This work was focused on the study of the tribological properties of TiB2 thin films using micro-abrasion tests and following the BS EN 1071-6: 2007 standard. Due to high hardness usually patented by these films, diamond was selected as abrasive on micro-abrasion tests. Micro-abrasion wear tests were performed under five different durations, using the same normal load, speed rotation and ball. Films were deposited by unbalanced magnetron sputtering Physical Vapour Deposition (PVD) technique using TiB2 targets. TiB2 films were characterized using different methods as Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), Electron Probe Micro-Analyser (EPMA), Ultra Micro Hardness and Scratch-test Analysis, allowing to confirm that TiB2 presents adequate mechanical and physical properties. Ratio between hardness (coating and abrasive particles), wear resistance and wear coefficient were studied, showing that TiB2 films shows excellent properties for tribological applications.