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- Aluminum-to-Steel Cladding by Explosive WeldingPublication . Carvalho, Gustavo H. S. F. L.; Galvão, Ivan; Mendes, Ricardo; Leal, Rui M.; Loureiro, AltinoThe production of aluminum-carbon steel and aluminum-stainless steel clads is challenging, and explosive welding is one of the most suitable processes to achieve them. The present work aims to investigate the coupled effect of two strategies for optimizing the production of these clads by explosive welding: the use of a low-density interlayer and the use of a low-density and low-detonation velocity explosive mixture. A broad range of techniques was used to characterize the microstructural and the mechanical properties of the welds, specifically, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, electron backscatter diffraction, microhardness and tensile-shear testing with digital image correlation analysis. Although aluminum-carbon steel and aluminum-stainless steel have different weldabilities, clads with sound microstructure and good mechanical behavior were achieved for both combinations. These results were associated with the low values of collision point and impact velocities provided by the tested explosive mixture, which made the weldability difference between these combinations less significant. The successful testing of this explosive mixture indicates that it is suitable to be used for welding very thin flyers and/or dissimilar materials that easily form intermetallic phases.
- Explosive welding of aluminium to stainless steel using carbon steel and niobium interlayersPublication . Carvalho, G.H.S.F.L.; Galvão, I.; Mendes, R.; Leal, R. M.; Loureiro, A.This work aimed to study aluminium to stainless steel explosive welds produced using two different interlayers: carbon steel and niobium. The use of each interlayer was analysed and compared microstructurally and mechanically using many characterisation techniques. The final joints using both interlayers presented favourable interfacial microstructure: waves on both interfaces. However, the joint using the carbon steel interlayer showed the best mechanical properties compared to the joints using the niobium interlayer. All interfaces found on both welds were wavy. However, depending on the metallic alloy combination, the shape of the wave is completely different. The results suggest that the shape of the waves is influenced by the shock impedance mismatch of the materials being welded. The impedance mismatch parameter (IMP) developed for explosive welding in this work proved to be a compelling method to order metallic combinations in a single axis to estimate the tendency to form typical or curled waves. Typical symmetrical waves tend to develop less quantity of IMCs than curled waves. However, the mechanical tests performed did not detect differences that could have been caused by this difference.
- Effect of the flyer material on the interface phenomena in aluminium and copper explosive weldsPublication . Carvalho, G.H.S.F.L.; Mendes, R.; Leal, R. M.; Galvão, I.; Loureiro, A.The effect of physical and mechanical properties of three different flyers on the interface phenomena of partially overlapped explosive welds, using the same base plate material, was studied. Flyers of Copper Cu-DHP and aluminium alloy 6082 (tempers T6 and O) were welded to AA6082-T6 base plates. The morphology of the weld interface is strongly influenced by the physical and mechanical properties of the flyer. In the interface of the aluminiumwelds, the use of a flyer of lower hardness and yield strength than the base plate results in asymmetrical waves, with bigger amplitude and smaller wavelength than the weld series of similar temper, and higher mechanical properties. The copper-aluminium welds presented flat interfaces, mainly because of the significant differences inmelting temperature and density between the copper flyer and the aluminiumbase plate. Considering these results and analysing several dissimilar welds carried out by other authors itwas found thatwhen the product of density and melting temperature ratios between the flyer and the base plate exceeds a certain value, there is no formation of waves at the interface of the metals. Furthermore, for the Cu-Al welds, the CuAl2 (θ) intermetallic phase was formed on the bond zone.
- Effect of friction stir processing parameters on the microstructural and electrical properties of copperPublication . Leal, Rui; Galvão, I.; Loureiro, A.; Rodrigues, D. M.Friction stir processing (FSP) is an innovative technology, based on friction stir welding (FSW) operative principles, which can be used for changing locally the microstructure and the mechanical properties of conventional materials. In this work, the copper alloy C12200 was friction stir processed using two distinct tools, i.e. a scrolled and a conical shoulder tool, in order to promote different thermomechanical conditions inside the stirred volume, and consequently, varied post-processed microstructures. The influence of the tool geometry and tool rotation and traverse speeds on the microstructural and electrical properties of the processed copper alloy was analysed. The processing conditions were found to have an important influence on the electrical conductivity of the processed material. The differences in electrical conductivity were explained based on dislocations density effects. The effect of the dislocations density on electrical conductivity of the processed material was found to prevail over the effect of the grain boundaries.
- Effect of explosive mixture on quality of explosive welds of copper to aluminiumPublication . Loureiro, A.; Mendes, R.; Ribeiro, J.B.; Leal, Rui; Galvão, I.The aim of this research is to investigate the influence of explosive ratio and type of sensitizer on the quality of explosive welds between copper and aluminium alloy plates. The welds were performed on a partially overlapping joint configuration using an emulsion explosive (EE) with two different sensitizers, hollow glass microspheres (HGMS) and expanded polystyrene spheres (EPS). Welds with an improved surface were achieved by using the HGMS sensitizer. A higher wave amplitude was registered in welds produced with the EPS sensitizer. In turn, the dimension of the molten pockets was influenced by the explosive ratio, increasing in size with increases in the values of this parameter. The intermetallic content of these zones varied according to the sensitizer type.Unlike the CuAl2 phase, the Cu-richer phases CuAl and Cu9Al4were only identified inwelds performed using the EPS sensitizer. An increase in hardness was observed at the interface of all welds, which resulted from both the presence of intermetallic phases and the plastic deformation of the materials promoted by the impact. This effect was most evident on the aluminium alloy side. All the welds had a greater strength than copper, i.e. the weakest material of the joint.
- The many faces of a face: Comparing stills and videos of facial expressions in eight dimensions (SAVE database)Publication . Garrido, Margarida V.; Lopes, Diniz; Prada, Marília; Rodrigues, David; Jerónimo, Rita; Mourão, Rui P.This article presents subjective rating norms for a new set of Stills And Videos of facial Expressions—the SAVE database. Twenty nonprofessional models were filmed while posing in three different facial expressions (smile, neutral, and frown). After each pose, the models completed the PANAS questionnaire, and reported more positive affect after smiling and more negative affect after frowning. From the shooting material, stills and 5 s and 10 s videos were edited (total stimulus set = 180). A different sample of 120 participants evaluated the stimuli for attractiveness, arousal, clarity, genuineness, familiarity, intensity, valence, and similarity. Overall, facial expression had a main effect in all of the evaluated dimensions, with smiling models obtaining the highest ratings. Frowning expressions were perceived as being more arousing, clearer, and more intense, but also as more negative than neutral expressions. Stimulus presentation format only influenced the ratings of attractiveness, familiarity, genuineness, and intensity. The attractiveness and familiarity ratings increased with longer exposure times, whereas genuineness decreased. The ratings in the several dimensions were correlated. The subjective norms of facial stimuli presented in this article have potential applications to the work of researchers in several research domains. Fromour database, researchers may choose the most adequate stimulus presentation format for a particular experiment, select and manipulate the dimensions of interest, and control for the remaining dimensions. The full stimulus set and descriptive results (means, standard deviations, and confidence intervals) for each stimulus per dimension are provided as supplementary material.
- Formation of intermetallic structures at the interface of steel-to-aluminium explosive weldsPublication . Carvalho, G.H.S.F.L.; Galvão, I.; Mendes, R.; Leal, Rui; Loureiro, A.The formation of intermetallic structures at the interface of carbon steel to 6082 aluminium alloy explosive welds and their influence on the weldability of these two materials were studied. The morphology, the microstructure, the chemical and phase compositions of the welds were characterised by several types of microscopy techniques. The interface characterisation proved that explosive mixtures with a lower detonation velocity were revealed as being more suitable for achieving consistent welds since jet entrapment was prevented and continuous molten layers were not formed at the weld interface. It was also found that the physical properties of the intermetallic phases generated at the weld interface have a strong influence on the weldability of steel-to-aluminium explosive welds. Specifically, it was shown that the formation of aluminium-rich intermetallic phases at the weld interface increases the solidification time of the interfacial molten material, decreasing the weldability of these two materials. The formation of these intermetallic compounds should be avoided by reducing the interaction between the flyer and the baseplate as well as by avoiding excessive molten layers.
- Influence of friction stir welding parameters on the microstructural and mechanical properties of AA 6016-T4 thin weldsPublication . Rodrigues, D.M.; Loureiro, A.; Leitão, C.; Leal, Rui; Chaparro, B.M.; Vilaça, P.In present work friction stir welds produced in 1 mm thick plates of AA 6016-T4 aluminium alloy, with two different tools, were analysed and compared concerning the microstructure and mechanical properties. For each tool, the welding parameters were optimized in order to achieve non-defective welds. Assuming a relation between the welding parameters and the energy input per unit of length of the weld [Seidel TU, Reynolds AP. Visualization of the material flow in AA2195 friction stir welds using a marker insert technique. Metall Mater Trans A 2001;32A:2879-84; Sato YS, Urata M, Kokawa H. Parameters controlling microstructure and hardness during friction stir welding of precipitation-hardenable aluminum alloy 6063. Metall Mater Trans A 2002;33(3):625-35; Lim S, Kim S, Lee CG, Kim S-J. Tensile behavior of friction-stri-welded Al 6061-T651. Metall Mater Trans A 2004;35(9):2829-35; Yang B, Yan J, Sutton MA, Reynolds AP. Banded microstructure in AA2024-T351 and AA2524-T351 aluminum friction stir welds: Part I. Metallurgical studies. Mater Sci Eng A 2004;364(1-2):55-65; Peel MJ, Steuwer A, Withers PJ, Dickerson T, Shi Q, Shercliff H. Dissimilar friction stir welds in AA5083-AA6082. Part I: process parameter effects on thermal history and weld properties. Metall Mater Trans A 2006;37:2183-193; Gerlich A, Su P, Yamamoto M, North TH. Effect of welding parameters on the strain rate and microstructure of friction stir spot welded 2024 aluminum alloy. J Mater Sci 2007;42(14):5589-601; Lombard H, Hattingh DG, Steuwer A, James MN. Optimising FSW process parameters to minimise defects and maximise fatigue life in 5083-H321 aluminum alloy. Eng Fract Mech 2008;75(3-4):341-54], the welds produced were classified as "hot" and "cold welds". The results obtained showed that the "hot" welds, obtained with the maximum tool rotational speed and the minimum traverse speed, have improved mechanical properties relative to the "cold" welds that were in undermatch condition relative to the base material. The differences in mechanical properties between the two types of welds are explained based in TEM microstructural analysis. Despite the undermatched characteristics of the "cold" welds relative to the base material, formability tests demonstrated that these welds improve the drawing performance of the welded sheets.
- Mechanical behaviour of similar and dissimilar AA5182-H111 and AA6016-T4 thin friction stir weldsPublication . Leitão, C.; Leal, Rui; Rodrigues, D.M.; Loureiro, A.; Vilaça, P.The tensile behaviour of similar and dissimilar friction stir welds in 1 mm thick sheets of two aluminium alloys (AA5182-H111 and AA6016-T4) is analysed in this paper. The heterogeneity in properties across the welds was studied by performing microhardness tests and microstructural analysis. The tensile tests were performed in samples extracted longitudinal and transverse to the weld direction. It was found that the tensile behaviour of the welds depends mainly on the grain size in the TMAZ, for the AA5182-H111 alloy, and on precipitate distribution, for the AA6016-T4 alloy. In all types of welds, the HAZ preserves the same properties of the base materials. The global mechanical behaviour of the AA5182-H111 similar welds is very similar to that of the base material. However, for the AA6016-T4 similar welds and for the AA6016-T4-AA5182-H111 dissimilar welds a 10-20% strength reduction relative to the base materials and important losses in ductility were reported.
- Desenhos animados e narrativa sequencial para crianças Surdas – Procurando comunicar, entre ouvir e visualizarPublication . Marques, Nuno fragata; Conde e Sousa, Joana; Esteves Rodrigues, AndreiaOs desenhos animados são uma forma de entretenimento apreciada por crianças e adultos em todo o mundo e desempenham um papel significativo no desenvolvimento cognitivo, emocional e social das crianças. Iremos procurar relacionar a criação de desenhos animados gestuantes em diálogo com formas de narrativa sequencial, a banda desenhada e o storyboard, como comunicação direcionada a dois públicos distintos, crianças surdas e crianças ouvintes. Partimos de um ponto de vista inclusivo que as coloca em ponto de igualdade como público-alvo a favor da identificação de pistas que ajudem à criação de narrativas e conteúdos em cinema de animação. Exploraremos a importância dos desenhos animados para crianças Surdas, fonte de acessibilidade linguística, estímulo visual e cognitivo, representação e educação. Por meio de um estudo exploratório, via pesquisa, análise e produção, procura-se perceber possibilidades visuais para explorações da representação do som. Apresentamos, como resultados, um conjunto de considerações a seguir a favor da criação de desenhos animados gestuantes, representativos da cultura surda.