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- Friction stir welding and explosive welding of aluminum/copper: process analysisPublication . Carvalho, G. H. S. F. L.; Galvão, I.; Mendes, R.; Leal, R. M.; Loureiro, A.The 6082 aluminum alloy was welded to copper-DHP by friction stir welding and explosive welding. The effect of each welding process on the microstructural evolution, the intermetallic phases distribution, and the mechanical behavior of both types of welds was analyzed and compared. The microstructural changes proved to be much more expressive in friction stir welding due to the larger area under plastic deformation, the stirring and mixing of the alloys, the longer time under high temperature, and the longer interaction times between the base materials during welding. As explosive welding process is much faster, it avoids extensive microstructural changes and significant interaction of the materials, reducing the intermetallic volumes and their distribution along the interface. The friction stir welds presented Cu-rich intermetallics while the explosive welds presented Al-rich intermetallics. For alloys that can easily form brittle intermetallic phases, excessive interaction during the welding process leads to a very poor mechanical behavior of the joints.
- Influence of tool shoulder geometry on properties of friction stir welds in thin copper sheetsPublication . Galvão, I.; Leal, Rui M.; Rodrigues, D.M.; Loureiro, A.The aim of this work is to study the influence of the shoulder geometry on friction stir welding of 1mmthick copper-DHP plates. The welds were produced using three different shoulder geometries, flat, conical and scrolled, and varying the rotation and traverse speeds of the tool. The flat shoulder tool proved to be inadequate for performing welds, because many defects were produced for all welding conditions. In turn, the scrolled shoulder tool is more effective than the conical one in the production of defect free welds. However, both geometries required a minimum rotational speed to avoid internal defects. For the same welding parameters, greater grain refinement, higher hardness and improved strength are also achieved in the nugget of the welds, using the scrolled tool.
- The role of digital health technology in tuberculosis control: a systematic literature review and comparative analysis based on the WHO guidelinePublication . Netto, Joaquim Teixeira; Melanie Raimundo Maia; Marcela Lopes Bhering da Silva; Valéria Teresa Saraiva Lino; Monica Kramer de Noronha Andrade; Pernencar, Cláudia Alexandra da CunhaThis study presents a systematic review with the objective of evaluating the utilisation of digital technology in the surveillance of Tuberculosis (TB) within the context of public health, and of determining the extent to which this practice aligns with the World Health Organization (WHO) recommendation. The methodology was divided into two distinct phases. In the initial phase, a systematic literature review was conducted utilising the Prism and the Parsifal tool. Subsequently, the digital technologies identified in the selected articles were analysed in accordance with WHO documentation and a patient-centred approach. From an initial pool of 2090 articles, nine studies were meticulously selected, including impactful research from regions such as India, China, Uganda, Sudan, Indonesia, Ukraine, Tanzania, South Africa an Philippines. These studies demonstrate that digital technologies have a beneficial impact. The digital technologies that have been highlighted as offering the most promising advancements in the field of TB surveillance, addressing existing challenges and integrating digital solutions seamlessly into TB control programmes, remain pivotal. In order to eradicate TB as a global health threat, future endeavours must focus on refining digital interventions, overcoming barriers and ensuring equitable access.
- Low-profile, extremely wideband, dual-band-notched MIMO antenna for UWB applicationsPublication . Bhattacharya, Ankan; Roy, Bappadittya; Caldeirinha, Rafael F. S.; Bhattacharjee, Anup K.In this article, an extremely wideband, isolation-enhanced, low-profile “Multiple-Input-Multiple-Output” (MIMO) antenna along with dual-band-notched features has been investigated. The antenna proposed herein, possesses two mutually orthogonal staircase-etched radiators for achieving a wide bandwidth. The radiating elements are placed mutually perpendicular in order to achieve polarization diversity and high isolation, i.e. for minimization of mutual coupling effect between adjacent radiating elements. The antenna exhibits an extremely wide frequency bandwidth covering 1.2–19.4 GHz except two frequency band notches centered at 3.5 and 5.5 GHz, respectively, originated due to the incorporation of a “Rectangular Complementary Split Ring Resonator (RCSRR)” structure and by etching dual “L-shaped” slits in the ground plane. The center frequency of the notched bands is adjusted by fine tuning of the dimensions of the incorporated band-notching structures. Isolation level (S21) better than −20 dB has been obtained due to the insertion of a “T-shaped” parasitic element as a decoupling structure. A prototype of the proposed antenna having dimension of 20 mm × 20 mm (0.08 λo × 0.08 λo) is fabricated and the antenna responses have been measured. Obtained results show that the miniaturized MIMO diversity antenna is undoubtedly a capable contender for communications supporting an extremely wide impedance bandwidth along with band-notched features for WLAN and WiMAX.
- Influence of Tool Geometry and Process Parameters on Torque, Temperature, and Quality of Friction Stir Welds in Dissimilar Al AlloysPublication . Manuel, Neves; Beltrão, Daniel; Galvão, Ivan; Leal, Rui M.; Costa, José D.; Loureiro, AltinoIn the current investigation, the influence of the tool geometry, the position of the materials in the joint, the welding speed on the temperature and torque developed, and on the quality of the welds in dissimilar and tri-dissimilar T joints were analysed. The aluminium alloys used were AA2017-T4, AA6082-T6, and AA5083-H111 and the friction stir welds were performed with identical shoulder tools, but with either a pin with simple geometry or a pin with progressive geometry. Progressive pin tools proved to be a viable alternative in the production of dissimilar and tri-dissimilar welds, as they provide a larger tool/material friction area and a larger volume of dragged material, which promotes an increase in the heat generated and a good mixing of the materials in the stir zone, although they require a higher torque. Placing a stronger material on the advancing side also results in a higher temperature in the stir zone but requires higher torque too. The combination of these factors showed that tools with a progressive pin provide sound dissimilar and tri-dissimilar welds, unlike single-pin tools. The increase in the welding speed causes the formation of defects in the stir zone, even in tri-dissimilar welds carried out with a tool with a progressive pin, which impairs the fatigue strength of the welds.
- Effect of shoulder cavity and welding parameters on friction stir welding of thin copper sheetsPublication . Leal, R. M.; Sakharova, N.; Vilaça, P.; Rodrigues, D. M.; Loureiro, A.The aim of this investigation was to study the influence of shoulder cavity and welding parameters on torque, defect formation, microstructure and mechanical properties of friction stir welds in very thin sheets of deoxidised copper. Three types of tools were used: a flat shoulder tool and two tools with conical shoulder cavities of 3 and 6° respectively. The welding parameters analysed were tool rotation and traverse speeds. It was observed that the torque, the microstructure and hardness and the formation of defects in the welds are influenced mainly by tool rotation speed and, to a lesser extent, by the traverse speed and shoulder cavity. The tensile properties of welds carried out at high rotation speeds are little affected by the shoulder cavity.
- 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.
- Weldability of aluminium-copper in explosive weldingPublication . Carvalho, G. H. S. F. L.; Galvão, I.; Mendes, R.; Loureiro, A.; Leal, RuiA large number of aluminium-copper explosive welds were produced under different welding conditions to perform a broad analysis of the weldability of this combination. The influence of the explosive mixture and the relative positioning of the plates on the welding results were analysed. When the aluminium alloy is positioned as the flyer plate, continuous interfacial melting occurred under the low values of energy lost by the collision, and collision point velocity. This proved that the weldability of the aluminium-copper combination is higher when the copper is positioned as the flyer. A mismatch between the experimental results and the existing theories that define the requirements for achieving consistent welds was noticed. Especially for welds produced using the aluminium alloy as the flyer, the experiments proved to be more restrictive than the theories. These theories, despite being widely applied in dissimilar welding literature, present several limitations concerning aluminium-copper welding. New approaches considering the formation of intermetallic phases at the interface, the properties of both welded metals, and/or the difference in their properties should be developed
- Effect of explosive ratio on explosive welding quality of copper to aluminiumPublication . Loureiro, A.; Mendes, R.; Ribeiro, J. B.; Leal, R. M.The goal of this research is to study the influence of the ratio of an explosive composed of 80% ANFO and 20% matrix on the quality of dissimilar explosive welds of Cu-DHP copper to aluminium alloy 5083-H11, in flat configuration. It is analysed the influence of four explosive ratios (1.4, 1.8, 2.3 and 2.6) on the microstructure and mechanical properties of welds. It was observed that the increase in the explosive ratio gives rise to an increase of the collision point velocity (Vc) and the impact velocity (Vp) and consequently reduces the thickness of the flying plate after welding as well as produces wavy interfaces of greater amplitude. Microstructural analysis showed the formation of hard and brittle intermetallic compounds in the interface region, more obvious in welds made with higher ratio of explosive.
- Influence of base material properties on copper and aluminium–copper explosive weldsPublication . Carvalho, G. H. S. F. L.; Galvão, I.; Mendes, R.; Leal, Rui; Loureiro, A.The influence of base material properties on the interfacial phenomena in copper and aluminium–copper explosive welds was studied. Two explosive mixtures with different detonation velocities were tested. Sound aluminium–copper joints with effective bonding were achieved by using an explosive mixture with a lower detonation velocity. High energy explosives led to extensive interfacial melting, preventing the production of consistent dissimilar welds. Unlike to the similar copper joints, the aluminium–copper welds presented very asymmetrical interfacial waves, rich in intermetallic phases and displaying a curled morphology. The interaction of the materials in dissimilar welding was found to be completely different depending on the positioning of each alloy in the joint, i.e. positioned as the flyer or as the baseplate.
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