Estudo e desenvolvimento de um sensor de chuva piezoelétrico para automóveis

A presença de sistemas eletrónicos nos veículos automóveis tem vindo a aumentar de forma considerável nos últimos 30 anos, tornando possível o aumento dos padrões de eficiência, segurança e conforto dos mesmos. Os sistemas de acionamento automático dos limpa-para-brisas, baseados em sensores de chuva óticos, têm registado um crescimento quase exponencial nos últimos 10 a 15 anos; no ano 2000, apenas 5 % dos veículos novos produzidos na Europa estavam equipados com este sistema, hoje é um equipamento amplamente difundido na oferta automóvel existente. O presente trabalho consistiu no estudo de uma solução para deteção de chuva em veículos automóveis com a aplicação de um sensor piezoelétrico, tendo em vista a obtenção de uma solução mais versátil e aplicável em vários pontos do veículo. As reduzidas dimensões, a elevada sensibilidade do sensor e a facilidade de aplicação nas superfícies de ensaio foram fatores que motivaram a escolha deste tipo de equipamento como elemento sensorial. As hipóteses definidas para o procedimento laboratorial basearam-se nas conclusões obtidas em estudos anteriormente desenvolvidos no campo dos sensores de chuva para automóveis e nas capacidades dos materiais piezoelétricos para medição de pluviosidade. Os sensores foram instalados sob as superfícies do veículo que apresentavam, simultaneamente, uma maior exposição à pluviosidade, quando este está em movimento, e um menor risco de sofrer danos. Os resultados obtidos permitiram concluir que a utilização deste tipo de sensores permite detetar elevados níveis de pluviosidade e em superfícies com considerável capacidade de deformação elástica. A sua implementação futura em veículos automóveis exige mais algum trabalho de melhoria dos processos de fixação dos sensores e do condicionamento de sinal utilizados.

Analysis of functionally graded sandwich plate structures with piezoelectric skins, using B-spline finite strip method

Functionally graded materials are composite materials wherein the composition of the constituent phases can vary in a smooth continuous way with a gradation which is function of its spatial coordinates. This characteristic proves to be an important issue as it can minimize abrupt variations of the material properties which are usually responsible for localized high values of stresses, and simultaneously providing an effective thermal barrier in specific applications. In the present work, it is studied the static and free vibration behaviour of functionally graded sandwich plate type structures, using B-spline finite strip element models based on different shear deformation theories. The effective properties of functionally graded materials are estimated according to Mori-Tanaka homogenization scheme. These sandwich structures can also consider the existence of outer skins of piezoelectric materials, thus achieving them adaptive characteristics. The performance of the models, are illustrated through a set of test cases. (C) 2012 Elsevier Ltd. All rights reserved.

Optimization of magneto-electro-elastic composite structures using differential evolution

Magneto-electro-elastic structures are built from materials that provide them the ability to convert in an interchangeable way, magnetic, electric and mechanical forms of energy. This characteristic can therefore provide an adaptive behaviour to a general configuration elastic structure, being commonly used in association with any type of composite material in an embedded or surface mounted mode, or by considering the usage of multiphase materials that enable achieving different magneto-electro-elastic properties. In a first stage of this work, a few cases studies will be considered to enable the validation of the model considered and the influence of the coupling characteristics of this type of adaptive structures. After that we consider the application of a recent computational intelligence technique, the differential evolution, in a deflection profile minimization problem. Studies on the influence of optimization parameters associated to the problem considered will be performed as well as the adoption of an adaptive scheme for the perturbation factor. Results are also compared with those obtained using an enhanced particle swarm optimization technique. (C) 2013 Elsevier Ltd. All rights reserved.

Intrusion of Lamprophyre dyke and related deformation effects in the host rock salt: A case study from the Loulé Diapir, Portugal

A rock salt-lamprophyre dyke contact zone (sub-vertical, NE-SW strike) was investigated for its petrographic, mechanic and physical properties by means of anisotropy of magnetic susceptibility CAMS) and rock magnetic properties, coupled with quantitative microstructural analysis and thermal mathematical modelling. The quantitative microstructural analysis of halite texture and solid inclusions revealed good spatial correlation with AMS and halite fabrics. The fabrics of both lamprophyre and rock salt record the magmatic intrusion, "plastic" flow and regional deformation (characterized by a NW-SE trending steep foliation). AMS and microstructural analysis revealed two deformation fabrics in the rock salt: (1) the deformation fabrics in rock salt on the NW side of the dyke are associated with high temperature and high fluid activity attributed to the dyke emplacement; (2) On the opposite side of the dyke, the emplacement-related fabric is reworked by localized tectonic deformation. The paleomagnetic results suggest significant rotation of the whole dyke, probably during the diapir ascent and/or the regional Tertiary to Quaternary deformation. (C) 2014 Elsevier B.V. All rights reserved.

Dynamic behaviour of soft core sandwich beam structures using kriging-based layerwise models

Sandwich structures with soft cores are widely used in applications where a high bending stiffness is required without compromising the global weight of the structure, as well as in situations where good thermal and damping properties are important parameters to observe. As equivalent single layer approaches are not the more adequate to describe realistically the kinematics and the stresses distributions as well as the dynamic behaviour of this type of sandwiches, where shear deformations and the extensibility of the core can be very significant, layerwise models may provide better solutions. Additionally and in connection with this multilayer approach, the selection of different shear deformation theories according to the nature of the material that constitutes the core and the outer skins can predict more accurately the sandwich behaviour. In the present work the authors consider the use of different shear deformation theories to formulate different layerwise models, implemented through kriging-based finite elements. The viscoelastic material behaviour, associated to the sandwich core, is modelled using the complex approach and the dynamic problem is solved in the frequency domain. The outer elastic layers considered in this work may also be made from different nanocomposites. The performance of the models developed is illustrated through a set of test cases. (C) 2015 Elsevier Ltd. All rights reserved.

The three main marine depositional cycles of the Neogene of Portugal

The present work follows a stratigraphic model for the marine Neogene of Portugal based on the definition of three main marine sedimentary cycles. Conceptually the I, II and III Neogene Cycles can be defined as 2nd order sedimentary sequences with duration ranging from 5 to 8 Ma. The I Neogene Cycle is fully represented only in the Lower Tagus Basin. Ranging from the Early Aquitanian to the Late Burdigalian the I Neogene Cycle testify a transgressive episode in the region of Lisbon and Setúbal Peninsula. Rapid lateral facies variations suggest a shallowmarine basin. This cycle ends with an important Late Burdigalian tectonic compressive event expressed by uplift of the surrounding areas and deformation affecting the Early Miocene deposits of the Arrábida Chain. The II Neogene Cycle includes thick sedimentary sequences covering Paleozoic and Mesozoic formations in the Algarve and Alvalade-Melides regions and it extends as far north as Santarém in the Lower Tagus Basin. Mainly controlled by global eustasy, it was generated by the important positive eustatic trend that characterized the Middle Miocene worldwide to which the Portuguese continental margin acted more or less passively. This cycle ended with a second and the most important compression event starting after the end of the Serravallian affecting the entire Portuguese onshore and shelf areas. This led to an important depositional hiatus of marine sediments for more than 2.5 Ma. During the Early and the Middle Tortonian occurred the clockwise rotation of the Guadalquivir Basin. The thickmarine units deposited afterwards in this basin produced a litostatic load, which seems to have induced subsidence farther west resuming the Neogene marine sedimentation in the Cacela region (Eastern Algarve), during the Late Tortonian. This marks the beginning of the III Neogene Cycle. To the north, in the Sado Basin (Alvalade-Melides region), a similar depositional sequence starts its sedimentation during the Messinian. Further north, in the Pombal-Caldas da Rainha region, marine sedimentation started during the Late Pliocene (Piacenzian). The migration in time, from south to north for the beginning of the marine sedimentation of this cycle is interpreted as reflecting a visco-elastic propagation of the deformation from the Betic chain northwards.

Earthquakes in western Iberia: improving the understanding of lithospheric deformation in a slowly deforming region

Mainland Portugal, on the southwestern edge of the European continent, is located directly north of the boundary between the Eurasian and Nubian plates. It lies in a region of slow lithospheric deformation (< 5 mm yr(-1)), which has generated some of the largest earthquakes in Europe, both intraplate (mainland) and interplate (offshore). Some offshore earthquakes are nucleated on old and cold lithospheric mantle, at depths down to 60 km. The seismicity of mainland Portugal and its adjacent offshore has been repeatedly classified as diffuse. In this paper, we analyse the instrumental earthquake catalogue for western Iberia, which covers the period between 1961 and 2013. Between 2010 and 2012, the catalogue was enriched with data from dense broad-band deployments. We show that although the plate boundary south of Portugal is diffuse, in that deformation is accommodated along several distributed faults rather than along one long linear plate boundary, the seismicity itself is not diffuse. Rather, when located using high-quality data, earthquakes collapse into well-defined clusters and lineations. We identify and characterize the most outstanding clusters and lineations of epicentres and correlate them with geophysical and tectonic features (historical seismicity, topography, geologically mapped faults, Moho depth, free-air gravity, magnetic anomalies and geotectonic units). Both onshore and offshore, clusters and lineations of earthquakes are aligned preferentially NNE-SSW and WNW-ESE. Cumulative seismic moment and epicentre density decrease from south to north, with increasing distance from the plate boundary. Only few earthquake lineations coincide with geologically mapped faults. Clusters and lineations that do not match geologically mapped faults may correspond to previously unmapped faults (e.g. blind faults), rheological boundaries or distributed fracturing inside blocks that are more brittle and therefore break more easily than neighbour blocks. The seismicity map of western Iberia presented in this article opens important questions concerning the regional seismotectonics. This work shows that the study of low-magnitude earthquakes using dense seismic deployments is a powerful tool to study lithospheric deformation in slowly deforming regions, such as western Iberia, where high-magnitude earthquakes occur with long recurrence intervals.

Transverse Vibrations in Beams Supported by a Piece-Wise Homogeneous Visco- Elastic Foundation

Transversal vibrations induced by a load moving uniformly along an infinite beam resting on a piece-wise homogeneous visco-elastic foundation are studied. Special attention is paid to the additional vibrations, conventionally referred to as transition radiations, which arise as the point load traverses the place of foundation discontinuity. The governing equations of the problem are solved by the normalmode analysis. The solution is expressed in a form of infinite sum of orthogonal natural modes multiplied by the generalized coordinate of displacement. The natural frequencies are obtained numerically exploiting the concept of the global dynamic stiffness matrix. This ensures that the frequencies obtained are exact. The methodology has restrictions neither on velocity nor on damping. The approach looks simple, though, the numerical expression of the results is not straightforward. A general procedure for numerical implementation is presented and verified. To illustrate the utility of the methodology parametric optimization is presented and influence of the load mass is studied. The results obtained have direct application in analysis of railway track vibrations induced by high-speed trains when passing regions with significantly different foundation stiffness.

Age related changes in the elastic fiber system of the interfoveolar ligament

In order to evaluate age related changes of the elastic fiber system in the interfoveolar ligament, we studied the deep inguinal ring from 33 male cadavers aged from stillborn to 76 years. Selective and alternated staining methods for elastic fibers were performed to differentiate oxytalan, elaunin, and mature elastic fibers. We confirmed quantitative changes of the elastic fiber system with aging. There was a significant and progressive reduction of the oxytalan fibers (responsible for tissue resistance) and a significant increment in the mature elastic and elaunin fibers (responsible for tissue elasticity). Furthermore, there were structural changes in the thickness, shortness and curling of these mature elastic fibers. These changes induced loss of the elastic fiber function and loss of the interfoveolar ligament compliance. These factors predispose individuals to the development of indirect inguinal hernias that frequently emerge in adults and aged individuals, especially above the fifth decade.

Quantitative analysis of collagen and elastic fibers in the transversalis fascia in direct and indirect inguinal hernia

PURPOSE: Our previous studies demonstrated structural and quantitative age-related changes of the elastic fibers in transversalis fascia, which may play a role in inguinal hernia formation. To verify whether there were differences in the extracellular matrix between direct and indirect inguinal hernia, we studied the amount of collagen and elastic fibers in the transversalis fascia of 36 male patients with indirect inguinal hernia and 21 with direct inguinal hernia. MATERIAL AND METHODS: Transversalis fascia fragments were obtained during surgical intervention and underwent histological quantitative analysis of collagen by colorimetry and analysis of elastic fibers by histomorphometry. RESULTS: We demonstrated significantly lower amounts of collagen and higher amounts of elastic fibers in transversalis fascia from patients with direct inguinal hernia compared to indirect inguinal hernia patients. The transversalis fascia from direct inguinal hernia patients showed structural changes of the mature and elaunin elastic fibers, which are responsible for elasticity, and lower density of oxytalan elastic fibers, which are responsible for resistance. These changes promoted loss of resiliency of the transversalis fascia. CONCLUSION: These results improve our understanding of the participation of the extracellular matrix in the genesis of direct inguinal hernia, suggesting a relationship with genetic defects of the elastic fiber and collagen synthesis.

Studying conformally flat spacetimes with an elastic stress energy tensor using 1+3 formalism

Conformally flat spacetimes with an elastic stress energy tensor having diagonal trace-free anisotropic pressure are investigated using 1+3 formalism. The 1+3 Bianchi and Jacobi identities and Einstein field equations are written for a particular case with a conformal factor dependent on only one spatial coordinate. Solutions with non null anisotropic pressure are obtained.

Mechanical vs. electrical hysteresis of carbon nanotube/styrene-butadiene-styrene composites and their influence in the electromechanical response

The interesting properties of thermoplastics elastomers can be combined with carbon nanotubes (CNT) for the development of large strain piezoresistive composites for sensor applications. Piezoresistive properties of the composites depend on CNT content, with the gauge factor increasing for concentrations around the percolation threshold, mechanical and electrical hysteresis. The SBS copolymer composition (butadiene/styrene ratio) influences the mechanical and electrical hysteresis of composites and, therefore, the piezoresistive response. This work reports on the electrical and mechanical response of CNT/SBS composites with 4%wt nanofiller content, due to the larger electromechanical response. C401 and C540 SBS copolymers with 80% and 60% butadiene content, respectively have been selected. The copolymer with larger amount of soft phase (C401) shows a rubber-like mechanical behavior, with mechanical hysteresis increasing linearly with strain until 100% strain. The copolymer with the larger amount of hard phase (C540) just shows rubber-like behavior for low strains. The piezoresistive sensibility is similar for both composites for low strains, with a GF≈ 5 for 5% strain. The electrical hysteresis shows opposite behavior than the mechanical hysteresis, increasing with strain for both composites, but with higher increase for softer copolymer, C401. The GF increases with increasing strain, but this increase is larger for composites with lower amounts of soft phase due to the distinct initial modulus and deformation of the soft and hard phases of the copolymer. The soft phase shows larger strain under a given stress than the harder phase and the conductive pathway rearrangements in the composites are different for both phases, the harder copolymer (C540) showing higher piezoresistive sensibility, GF≈ 18, for 20% strain.

Simulação numérica do comportamento ao impacto de componentes para calçado de segurança

Dissertação de mestrado integrado em Engenharia Mecânica

Desenvolvimento de modelos numéricos e análise experimental de subestruturas soldadas de transformadores de potência, sujeitas a forças de curto-circuito em regime transitório

Dissertação de mestrado integrado em Engenharia Mecânica