CDRsp - Artigos em revistas internacionais
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- Relationship Between Tethered Forces and the Four Swimming Techniques PerformancePublication . Morouço, Pedro; Keskinen, Kari L.; Vilas-Boas, João Paulo; Fernandes, Ricardo JorgeThe purpose of the current study was to identify the relationships between competitive performance and tether forces according to distance swam, in the four strokes, and to analyze if relative values of force production are better determinants of swimming performance than absolute values. The subjects (n = 32) performed a 30 s tethered swimming all-out effort. The competitive swimming velocities were obtained in the distances 50, 100 and 200 m using official chronometric values of competitions within 25 days after testing protocol. Mean force and velocity (50 m event) show significant correlations for front crawl (r = .92, p < .01), backstroke (r = .81, p < .05), breaststroke (r = .94, p < .01) and butterfly (r = .92, p < .01). The data suggests that absolute values of force production are more associated to competitive performance than relative values (normalized to body mass). Tethered swimming test seems to be a reliable protocol to evaluate the swimmer stroking force production and a helpful estimator of competitive performance in short distance competitive events.
- Analysis of friction in the ejection of thermoplastic mouldingsPublication . Correia, Mário Simões; Miranda, Antonio Sousa; Oliveira, Marta Cristina; Capela, Carlos Alexandre; Pouzada, Antonio SergioThe ejection force of injection-moulded thermoplastics depends on the contact conditions at the moment of ejection. Replication of the polymer part surface occurs onto the mould surface during injection of the melt. Ejection takes place in a very short time, hence the static coefficient of friction must be considered for modelling the ejection process. To understand the contribution of the mechanisms involved in the friction during the ejection stage, a mixed approach was followed: analytical simulation of the ploughing, numerical simulation of the deformation, and experimental inference of the adhesion. The relevance of roughness, temperature and contact pressure in the coefficient of friction was evidenced.
- Functionalized Coatings by Electrospinning for Anti-oxidant Food PackagingPublication . Dumitriu, Raluca P.; Mitchell, Geoffrey R.; Davis, Fred J.; Vasile, CorneliaThe development of advanced formulations used for food packaging applications, which behave as protection or preservation materials and improve consumers’ health offers a route to reduced food wastage. The present study deals with investigations on the possibility of obtaining functionalized coatings by electrospinning of poly(ɛ-caprolactone), a synthetic biodegradable polymer together with vitamin E (α-tocopherol), selected as plant-based phenolic antioxidant. In this approach electrospinning allows the production of high surface area materials and thus offering an increased antioxidant activity. The electrospun fibres of poly(ɛ-caprolactone)/vitamin E were obtained, studied and their antioxidant properties were evaluated by measuring the fibre reactivity with 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical. The potential for extending the shelf-life of food products by using this approach is discussed.
- Mechanical behaviour of PVC/CaCO3 Particulate Composites – Influence of TemperaturePublication . Costa, J. D. M.; Capela, C.; Ferreira, J. A. M.This paper is concerned with the study of temperature influence on Young’s modulus, ultimate strength and fracture toughness properties of PVC/CaCO3 particulate composites with different volume fractions. The tests were performed in three- and four-point bending. The resonant technique was also used to analyse the influence of both volume fraction and temperature on Young’s modulus. Significant decrease of ultimate strength, fracture toughness and Young’s modulus was observed with the increase of the temperature. Ultimate strength decreases with the increase of particle volume fraction at room temperature. For the other temperatures, this decreasing trend is less clear. PVC/CaCO3 flexural Young’s modulus calculated for a much lower loading segment increases with volume fraction. The same trend was obtained using the resonant technique. However, as the loading segment used to calculate the Young’s modulus was increased a significant decrease of Young’s modulus was obtained as a result of a progressive debonding at the particle-matrix interface. A 2D simplified FE simulation also confirms such trend. The dependence of Young’s modulus relatively to the loading segment increases as the volume fraction is increased, leading to composite Young’s modulus below matrix value for higher volume fractions and higher loading segments. Fracture toughness decreases with volume fraction.
- Development of Heterogeneous Structures with Polycaprolactone-Alginate Using a New 3D Printing System – BioMED βeta : Design and ProcessingPublication . Biscaia, S.; Dabrowska, E; Tojeira, A.; Horta, J.; Carreira, P; Morouço. P; Mateus, A.; Alves, N.Direct Digital Manufacturing of implantable biomedical devices is the strategy for designing and constructing three dimensional (3D) structures. DDM (i.e., biomanufacturing) technologies have been widely used to construct complex 3D structures (scaffolds), where chemicals, biomaterials, and cells are deposited in a layer-by-layer fashion. These technologies control size, microarchitecture and pores interconnectivity in scaffolds, essential to transporting oxygen and nutrients for cell survival. As the Tissue engineering field progresses, new types of printers have been designed to accomplish functional engineered tissue constructs. However, the availability of innovative 3D biomanufacturing technologies for hard tissue and organ engineering is scarce and with several equipment limitations. In this work, a new biomanufacturing system, BioMEDBeta, composed of three different fabrication modules (thermoplastic micro-extrusion, multi-head deposition of hydrogels and electrospinning) was used to fabricate (3D) scaffolds using layer-by-layer alternated deposition of polycaprolactone and alginate hydrogel. The BioMEDBeta system demonstrates the possibility of obtaining scaffolds with well-defined architecture, using both natural and synthetic polymers. Nevertheless, there are still parameters to optimize related with the design of 3D constructs and materials processing.
- Optimization of a Wood Plastic Composite for Architectural ApplicationsPublication . Martins, G.; Antunes, F.; Mateus, A.; Malça, C.The actual demand for sustainable construction has fostered the research of alternative products made of new materials, such as composites based on renewable resources obtained directly from nature or, most importantly in this context, from the wastes of industries thus encouraging the implementation of recycling processes. This study reports the optimization of wood plastic composites (WPC) made of industrial residues of pine sawdust, high density polyethylene (HDPE) and maleic anhydride-grafted-polyethylene (PE-g-MA) as coupling agent. These composites were specifically designed for the production of an innovative shading system to apply in the forefront of buildings, thus requiring an adequate combination of material properties concerning resistance to weather conditions, with mechanical and functional performance of the final products. The composites were optimized to enable their production and the fabrication of the shutter units through sequential extrusion processing. The optimization of the composites started with a thorough characterization of the raw materials and the mixtures were prepared after analysing the effect of the concentration of pine sawdust in the polymeric matrix, with variable amounts of the coupling agent. Torque rheometry was used to determine the most adequate viscosities for extrusion processing. The composites with optimized contents of pine sawdust and additives were characterized using SEM, FTIR, DSC-TGA, tensile testing, measurements of water contact angle and water absorption capacity. This allowed determining the respective microstructure, chemical interactions, thermal stability, mechanical properties, surface wettability and swelling capacity.
- Quasistatic and fatigue behavior of an AISI H13 steel obtained by additive manufacturing and conventional methodPublication . Garcias, José F.; Martins, Rui F.; Branco, Ricardo; Marciniak, Zbigniew; Macek, Wojciech; Pereira, Cândida; Santos, CyrilThis work aims to compare the mechanical behavior of an AISI H13 steel obtained by additive manufacturing with that obtained by conventional manufacturing methods. The average values of the ultimate tensile strength (UTS) and ductility obtained for the specimens produced by the conventional method were equal to 658 MPa and 18%, respectively, which compares with 503 MPa and 0.75% registered for the selective laser melting (SLM) specimens. Inversely, the average hardness value determined for the SLM specimens was higher, 450 HV, than the observed for the conventional, 200 HV. In addition, the maximum applied stress corresponding to a fatigue limit's endurance of 2 × 106 cycles was equal to 340 and 85 MPa for conventional and SLM specimens, respectively. Therefore, from a fatigue design point of view, it was possible to infer that σmax/UTS = 0.17 for the SLM specimens tested. Porosity and lack of fusion influenced the static and the fatigue strength negatively in the SLM specimens.
- 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.