CDRsp - Artigos em revistas internacionais
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- Sustainable Electrospinning of Nanoscale FibresPublication . Alazab, Mohamed; Mitchell, Geoffrey R.; Davis, Fred J.; Mohan, Saeed D.Electrospinning is an effective technology for the preparation of nano and micro scale fibres for diverse application in oil recovery, medical devices, and filters. It is achieved by injecting a charged solution of polymeric material through a needle into a region of high electric field. Under these conditions, the expelled jet follows a chaotic, whip like trajectory towards a grounded collection plate. At low polymer concentrations, the high forces experienced by the jet prior to becoming grounded on the collection plate, result in the formation of undesirable discrete droplets of material, rather than fibres. At higher concentrations, above the critical entanglement limit for the polymer, the polymer chains are stretched and orientated whilst the solvent rapidly evaporates, delivering high aspect ratio fibres. The resulting mesh of overlapping fibres frequently has useful properties such as high surface area and porosity, which has led to their investigation for a range of applications including filtration membranes and tissue scaffolds. One of the major challenges in the development of electrospinning as a manufacturing technology is the use of organic solvents. Typically, fibres are spun from relatively dilute solutions containing 95% solvent. It is clear that systems which use water as a solvent offer many advantages in terms of safety, cost and sustainability. In this work we optimise the conditions for effectively preparing nano/micro fibres of polyethylene oxide from aqueous solutions. We contrast the fibres produced with those prepared using volatile organic solvents.
- Part Specific Applications of Additive ManufacturingPublication . Khan, Imran; Mateus, Artur; Lorger, Christina S. Kamma.; Mitchell, Geoffrey R.Additive manufacturing is one of the most important technological advances which has been implemented and recognised as a modern manufacturing technology with many advantages over conventional approaches. Fused deposition modelling is an additive manufacturing technology commonly used for modelling, prototyping, and production applications. In this work sample holding grips are designed and printed using fused deposition modelling. These are used in time-resolved experiments which require a dedicated system to study one to one structure-property relationships in electrically conductive nanocomposites under uniaxial strain. The grips serve not only to hold the sample during stretching but also have electrodes to measure the electric current and the voltage drop across the sample under uniaxial strain, as they are insulated from the rest of the tensiometer assembly. In such kind of experimental work, the success of the experiment strongly depends upon the grips as the fracture or slip of the sample during the experiment can ruin the data and lead to a loss of confidence on measurement. The use of additive manufacturing was a particular advantage in the optimization of the design of the grips.
- The Fourth “R” - The Reversion of Objects as a Way of Reducing WastePublication . S. GonçalvesGiven the evident inefficiency of the policies and mechanisms established to deal with environmental degradation, it is essential to understand the reasons for their failures and to try alternative ways to mitigate the environmental problems associated with the replacement of objects. The ideas behind the so-called “3 R’s” policy, born of a sequence of two defining moments in the definition of environmental policies in Europe, - Agenda XXI in 1992 [1] and the 5th European Environment and Development Program of 1993 - have produced encouraging results since their creation, but failed to halt the increasing degradation of the environment on a planetary level. One of the problems derives from the fact that any of r's is strongly dependent on the environmental conscience, or even ethics, of the citizens responsible for the decisions regarding the products in their different moments of existence - from their design and production to their use and subsequent destination. This dependence leads to a high fallibility of environmental policies, insofar as western society suggests, in the way it behaves, a direction opposite to that which they advocate. It is thus important to reflect on ways of designing and producing things whose environmental performance is less dependent on the environmental consciousness of the end user, so that this awareness is not so decisive in the impact resulting from the disposal of objects. The present work tries to analyse the response of a group of students of design to the introduction of a “4thR”, that we call Reversion, and that is to think products of daily use whose form is conditioned by the necessity of its components can be, when dismantled of the system, seen as raw material directly usable for another purpose, easily determined by the user, and not as a technical component of an obsolete system. Functional prototypes will be realized in order to evaluate and validate the products regarding their effective performance in terms of production and use, as well as the possibility of reuse of their components in contexts other than those for which the objects were designed.
- Water Assisted Injection Molding for Single and Multi-branched Tubular ComponentsPublication . Oliveira, D.; Mateus, A.; Carreira, P.; Simões, F.; Malça, C.To produce hollow polymeric parts with complex geometries the Fluid Assisted Injection (FAI) technology is currently used. In this technology water and gas can be employed with or without the aid of a projectile. The process consists in the injection of water at high pressures, after the closing of the mold and polymer injection, and up to the filling of the whole molding zone. The injection of water at high pressures will force the polymer from the core to be expelled to a reservoir. This material expulsion is possible, not only thanks to the high water pressures, but also because the polymer is still in a viscous state, thus facilitating the evacuation. Even though the FAI technology is by direct injection of water/gas or with aid of a projectile, there is a common limitation, which is the inability to produce hollowed parts with forking channels. However, even if creating these branches is possible, there is the impossibility of them being geometrically complex and/or extensive. In these cases, the branches are created with inserts inside the mold, meaning that they will always be limited by a molding insert, and not controlled by the water jet. For cases where it is desired to add complex and/or extensive ramifications, subsequent steps of production and assembling must be added, influencing the overall production time. This work aims, therefore, at studying a new approach for the production of hollow parts with extensive branched channels and complex geometries within a single injection cycle, and thus eliminating subsequent processes that are currently required. The first approach is the application of several water injectors, guided towards the respective branches where hollow sections are intended to be produced. This innovation will have an impact on the serial production of high complexity tubular type parts, reducing the production time with the elimination of subsequent processes. Furthermore, a saving of raw materials is achieved by eliminating the necessity of a creation of additional molds. In this work, a detailed experimental study of the water assisted injection process was done to serve as a knowledge base to the concept of the new process named Multi-Path.H2O.
- Numerical modelling of the Young’s modulus of syntactic foamsPublication . Antunes, F.V.; Ferreira, J.A.M.; Capela, C.Syntactic foams are particulate composites obtained by filling a polymeric matrix with hollow solid inclusions. Numerical simulations are an important tool to predict material behaviour and optimize the mechanical properties. The aim of this work is to develop a multi-phase numerical model to predict stiffness of the syntactic foams. The numerical parameters were identified and optimized, and the numerical predictions were validated with experimental results from 3-point bending tests. Different physical parameters were then studied, namely the volume fraction and the size of the filler, the elastic properties of filler and matrix and the inclusion's thickness. A sensitivity analysis was developed to quantify the importance of these different parameters, and the rigidity of the matrix was found to be the most influent. The parametric space was scanned and a numerical interpolation procedure implemented based on shape functions of finite element method. The procedure is an interesting tool for design and was used to identify the particles having stiffness equal to the matrix.
- Augmented Reality: An Enhancer for Higher Education Students in Math's Learning?Publication . Coimbra, MMath. Teresa; Cardoso, Teresa; Mateus, ArturIn this text, we intend to answer to the following question: is Augmented Reality an enhancer for Higher Education students in math's learning? For this purpose, we define augmented reality and present a state of the art mapped mainly by studies that focus AR in educational contexts. We also describe our research, including methodological aspects in data collection and the creation of 3D contents in AR. Then, we synthesize the analysis of some preliminary data, briefly presenting perceptions and practices of students in math's learning with AR contents. Finally, we conclude that the challenges that are nowadays put to teaching methods, acquisition and subsequent knowledge consolidation may be met, to some extent, by the application of available technologies. These, in turn, should enhance a more complete understanding of contents, leading to knowledge endogenization and also to the internalization of more sustained competencies. Among those technologies, we highlight augmented reality since it can encourage motivation, comprehension and a higher involvement with the contents to be learned. Thus, it may increase the use of information and the access to knowledge, improving digital and info-inclusion.
- Relative Contribution of Arms and Legs in 30 s Fully Tethered Front Crawl SwimmingPublication . Morouço, Pedro, G.; Marinho, Daniel A.; Izquierdo, Mikel; Neiva, Henrique; Marques, Mário C.The relative contribution of arm stroke and leg kicking to maximal fully tethered front crawl swimming performance remains to be solved. Twenty-three national level young swimmers (12 male and 11 female) randomly performed 3 bouts of 30 s fully tethered swimming (using the whole body, only the arm stroke, and only the leg kicking). A load-cell system permitted the continuous measurement of the exerted forces, and swimming velocity was calculated from the time taken to complete a 50 m front crawl swim. As expected, with no restrictions swimmers were able to exert higher forces than that using only their arm stroke or leg kicking.
- Processing and Characterization of Thin Wall and Biodegradable Injected PotsPublication . Santos, Cyril; Mateus, Artur; Mendes, Ausenda; Malça, CândidaCurrently, the industry of molds seeks new markets with diversified products and added value. The concept associated with the production by injection of biodegradable pots is therefore of particular significance. Furthermore, environmental factors are increasingly decisive in choosing a product by the consumer, either because of imposed legislation or by the growth of a global awareness of the harmful effects than conventional polymers induce in our quality of life present and future. The general goal of this work was the design, the development and characterization of a thin walled pot for germination of plants made of biodegradable material. In this paper the processing and characterization of the bioplastic selected, the Bioplast GS 2189, is presented. Experimental results confirmed that the biodegradable material undergoes changes during its processing, which is attested by the QIS difference as well as in the reduction of the glass transition temperature, which in the post-processed (injected pot) is lower than the pre-processed material (Bioplast GS 2189). From these results it can be concluded that the injection processing of the Bioplast GS 2189 material affects its properties inducing its degradation process. This behavior can be due to the shear forces and thermal variations to which the material is submitted during the injection process. It was demonstrated that the development of future products in very thin-walled and biodegradable materials obtained by thermoplastic injection process is a competitive and effective solution for molds industries.
- Star-multiplicative graphs in pointed protomodular categoriesPublication . Martins-Ferreira, N.Protomodularity, in the pointed case, is equivalent to the Split Short Five Lemma. It is also well known that this condition implies that every internal category is in fact an internal groupoid. In this work, this is condition (II) and we introduce two other conditions denoted (I) and (III). Under condition (I), every multiplicative graph is an internal category. Under condition (III), every star-multiplicative graph can be extended (uniquely) to a multiplicative graph, a problem raised by G. Janelidze in [10] in the semiabelian context. When the three conditions hold, internal groupoids have a simple description, that, in the semiabelian context, correspond to the notion of internal crossed module, in the sense of [10].
- New Tools for Understanding Complex Polymer BehaviourPublication . Mitchell, Geoffrey R.; Maetus, Artur; Davis, Fred; Mohan, Saeed; Gkourmpis, THomas; Youngs, TristanThe process of manufacturing with polymers usually involves shaping in the melt followed by a transition to the solid to preserve that shape and provide the required mechanical properties. The development of an understanding of those transitions is critical to the optimisation of materials and manufacturing technology. For synthetic polymers there are three key length scales in any phase transition such as crystallisation: the first involves the thin (~10nm) lamellar crystals, the second is the crystal planes in the unit cell (~1nm) and the third the regular local chain conformation (~0.1nm). We are using the extended Q range available with NIMROD at the ISIS Facility in the UK to obtain neutron scattering data which follows the transformation pathways of these three length scales simultaneously. We are using computational modelling procedures to analyse these data to develop a firm understanding of the multiscale processes involved in crystallisation. This paper describes the methodology and some of the experimental challenges using data drawn from this study. This work is part of the FCT funded programme UC4EP.