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Este estudo teve como objetivo avaliar a influência da assimetria durante o processo de laminação com reduções de 10% e 20% na espessura empregada à liga de magnésio AZ31, do ponto de vista microestrutural e propriedade mecânica. Diversos estudos têm sido realizados nas ligas de magnésio visando adquirir melhores propriedades mecânicas, sobretudo conformabilidade, pois esta é uma das principais limitações encontradas na liga. Neste trabalho são apresentados os resultados microestruturais e mecânicos para amostras processadas por laminação simétrica e assimétrica nas reduções de 10% e 20% nas temperaturas ambiente, 100 °C, 200 °C, 300 °C e 400 °C. Foi observado que todas as amostras submetidas ao processo de laminação assimétrica apresentaram um valor maior de dureza em relação àquelas laminadas simetricamente. Também, observou-se que as amostras laminadas a 400°C apresentaram grãos refinados, podendo ser um indício de que tenha ocorrido a recristalização. Uma vez que este efeito também pôde ser observado a 300 °C, porém exclusivamente para a amostra laminada assimetricamente, este resultado pode estar relacionado ao processo assimétrico promover uma maior deformação no material.

Adhesive joints are nowadays widely used in fields ranging from packaging to aeronautics. Nevertheless, the absence of accurate failure criteria remains an important obstacle that often prevents the use of adhesive joints in structural applications. The main objective of this work is to be an introduction to the subject, and it was for this to evaluate the factors that most influence the strength of overlap adhesive joints.

The search for lightweight structures increases the demand for non-metallic materials, such as polymers, composites, and hybrid structures. This work presents the dissimilar joining through direct laser joining between polymethylmethacrylate (PMMA) and S235 galvanised steel using a pulsed Nd:YAG laser. The main goal is to determine the influence of processing parameters on joint strength and quality. In addition, the impact of surface conditions on the joint quality was also analysed. Overall, the optimum ranges of process parameters were found, and some are worth highlighting, such as the laser beam diameter and pulse duration, which significantly influenced the joint strength. Failure of the welded samples occurred in PMMA component, demonstrating good joint efficiency. Additionally, a maximum increase of 5.1% of the tensile shear strength was achieved thanks to the mechanical pre-treatment. It is possible to conclude that the joining between PMMA and the S235 galvanised steel can be performed by optimising the process parameters. Additionally, it can be enhanced through surface pre-treatments by exploring the mechanical interlock between both materials.

The heat transfer coefficient and friction factor of Fe3O4/vacuum pump oil nanofluids flowing in a tube with twisted tape inserts were analyzed experimentally. The experiments were conducted for different mass flow rates (0.04 kg/s to 0.208 kg/s), volume concentrations (0.05% to 0.5%), Prandtl numbers (440 to 2534), Graetz numbers (500 to 3000) and twisted tape inserts (H/D = 5, 10 and 15). Results reveal that the Nusselt number is enhanced by 8.94% and 13.48% for the 0.5% nanofluid for the mass flow rates of 0.0416 kg/s and 0.208 kg/s, respectively, relative to the base fluid. For the mass flow rate of 0.208 kg/s with 0.5 vol. % nanofluid, the friction factor penalty is 1.21-times compared to the base fluid. By using twisted tape insert of H/D = 5, the Nusselt number is further enhanced by 23.86% and 39.53% for the 0.5% nanofluid for mass flow rates of 0.0416 kg/s and 0.208 kg/s, respectively, relative to the base fluid. For the twisted tape insert of H/D = 5 with mass flow rate of 0.208 kg/s and 0.5 vol. % nanofluid, the friction factor penalty is 1.44-times compared to the base fluid. New Nusselt number and friction factor correlations are proposed.

Based on global needs for sustainable development, finding new sustainable materials that can replace oil-based ones for mass products is crucial nowadays. This paper focuses on employing an expanded cork-based composite to produce a surfboard. To evaluate the mechanical properties, uniaxial tensile and compression tests were performed on the skin and core materials, respectively. Bending tests were performed on the entire representative composite structure. Numerical models of the tests were arranged and validated from experimental results. From that, a surfboard prototype model was used to simulate some experimental conditions, permitting us to draw promising conclusions. An actual prototype was also produced. It was found that expanded cork performs very well when sandwiched between wood and polyester resin/glass fibre, being able to hold substantial loads and at the same time reduce weight and the environmental footprint of the composite by 62.8%. It can be concluded that expanded cork is an excellent candidate to replace oil-based foams in surfboard manufacturing. Despite a slight increase in weight, this sustainable material aligns with all the philosophies of surf practice worldwide.

We provide an algorithm based on a less-known result about recurrence relations for the determinants of banded matrices. As a consequence, we prove recent conjectures on the determinants of particular classes of pentadiagonal matrices and simple alternative proofs for other results.

An experimental investigation was conducted aiming to determine the heat transfer, friction and instantaneous collector thermal efficiency of a thermosyphon (natural circulation) solar water heating system using as working fluids of water and the Cu/H2O nanofluid. The Cu nanoparticles were synthesized using the chemical reduction method and characterized by the x-ray diffraction and transmission electron microscopy techniques. The stable Cu/H2O nanofluid was prepared for the volume concentrations of 0.1% and 0.3%. The empirical correlations developed for Nusselt number and friction factor for the Cu/H2O nanofluid fit the experimental data with a deviation of less than ±3.5% and ±2.5%, respectively. The results of present experimental investigation were presented at various Reynolds number and particle volume concentrations under thermosyphon conditions. The comparison indicates that the heat transfer enhancement obtained with the Cu/H2O nanofluid for the thermosyphon is higher than that for the plain tube collector and increases with the increase of particle volume concentration. The overall thermal performance of the thermosyphon increases when the operating fluid is Cu/H2O nanofluid as compared to water.

With the widely use of high-strength steel sheets in the automotive industry, the twist springback phenomenon of the steel sheets under multi-step forming conditions has received extensive attention. In this work, the Dual Phase steel DP500 is taken as the research object to investigate the complex non-linear elastoplastic behaviors and twist springback under two-step loading paths. The large specimen with a pre-strain of 4% true strain in rolling direction is carried out on a large tensile testing machine, and several specific blanks are extracted from it at different directions for a subsequent P-channel forming. The influence of twist springback associated with the pre-strain is analyzed. The finite element model based on the non-linear elastic model and the homogeneous anisotropic hardening model (HAH) is also established for the springback prediction and stress analysis. The results indicate that the pre-strain has a considerable impact on the twist springback. The non-linear strain path changes resulted from pre-straining not only influence the residual stress but also affect the elastic modulus distribution.

Heat transfer, friction factor and efficiency of a thermosyphon type flat plate collector with and without twisted tape inserts were analyzed experimentally. Water based Cu nanofluids were used as the absorber fluid to receive the heat from solar radiation into the flat plate collector. The experiments were conducted for volume concentrations of 0.1% and 0.3% and twist ratios of H/D = 5, 10 and 15. Results reveal that the heat transfer rate and efficiency of nanofluids increase with the increase of particle volume concentrations. The Nusselt number of 0.3% nanofluid is enhanced up to 20.46%, and it is further enhanced up to 46.90% with twisted tape insert of H/D = 5 with a maximum friction factor penalty of 1.477-times compared to plain collector. The efficiency of the solar collector with water is 52% and it is enhanced to 58% for 0.3% nanofluid, whereas it is further enhanced to 64% for 0.3% nanofluid with twisted tape insert of H/D = 5. Empirical correlations are proposed based on the experimental data for the friction factor and Nusselt number with a standard deviation of less than ±6.5%. The study indicates that for 100 units of solar flat plate collector the use of 0.1% and 0.3% Cu nanofluids leads to weight savings of 284 kg and 567 kg, respectively. The total weight of 100 units of solar flat plate collector is further saved by 767 kg, 1050 kg and 1250 kg for 0.3% nanofluid with twisted tape inserts of H/D = 15, H/D = 10 and H/D = 5, respectively. The collector cost is reduced by 5.66% and 11.33% for 0.1% and 0.3% nanofluids, and it is further reduced to 25% for 0.3% nanofluid with a twisted tape insert of H/D = 5.

© The Author(s). 2020 Open Access. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data., Background: Preventing childhood obesity is a public health challenge of the twenty-first century and it must be a priority. Governments play a major role in creating and supporting a healthy school environment and should prioritise actions to improve children’s health. Sintra Grows Healthy aims to promote healthy lifestyles to prevent childhood obesity and improve children’s health-related quality of life and social and emotional skills, through the development of a school evidence-based and sustainable model. Methods: This protocol describes a quasi-experimental design and community-based participatory research. The participants included in the study are the school community of Portuguese public primary schools from the municipality of Sintra. Data will be collected on demographic and socio-economic characterization, nutritional status, eating habits and behaviours, physical activity, sedentary behaviours and sleep, health-related quality of life, and social and emotional skills. Discussion: There is evidence to support interventions in school settings as strategies for obesity prevention. Upto-date homogeneous and community-based interventions for preventing childhood obesity are lacking, therefore Sintra Grows Healthy intends to fill this gap. Furthermore, Sintra Grows Healthy aims to contribute with relevant scientific findings that will allow the development of better strategies for policymakers and society to manage this major public health problem., This research is funded by the Municipality of Sintra and co-funded by Gulbenkian Academies for Knowledge, Calouste Gulbenkian Foundation. The Sintra Grows Healthy is promoted by the Municipality of Sintra. The Gulbenkian Academies for Knowledge, Calouste Gulbenkian Foundation, supports the Municipality of Sintra assigning a subsidy in order to promote social and emotional skills but played no role in the study design. The Municipality of Sintra provides financial support to Faculty of Medicine, University of Lisbon,for this institution to undertake the technical and scientific leadership, including the study design validation, development and dissemination of Sintra Grows Healthy, in its various actions

The friction factor, thermal performance, and heat transfer are experimentally analyzed for reduced-graphene oxide/cobalt oxide (rGO/CO3O4) hybrid nanomaterial-based nanofluid circulating in a plain tube with and without twisted tape inserts having different pitches. The reduced-graphene oxide/cobalt oxide (rGO/CO3O4) hybrid nanomaterial is prepared using in situ/chemical reduction technique and then characterized with transmission electron microscope, X-ray diffraction, and magnetometry. The experiments were conducted with different values of particle loading (0.05%, 0.1%, and 0.2%) and Reynolds number (2000–2,020,000). Three twisted tape inserts of helixes 285 mm, 190 mm, and 95 mm were used. The nanofluids was produced from the addition of the hybrid nanomaterial to water yield an increase, as compared to the basefluid (water), of the Nusselt number, which is further enhanced by increasing the nanoparticle loading. Therefore, when compared to water, the Nusselt number is enhanced by 25.65%, with no twisted tape and by 79.16% with twisted tape with helix of 95 mm for the nanofluid of 0.2% volume concentration. However, when compared to water, there is a slight friction factor penalty with the 0.2% particle loading of 1.11-times and 1.49-times for the plain tube and for the 95-mm twisted tape helix, respectively. The thermal performance factor gets enhanced by increasing the nanoparticles concentration of the hybrid nanofluids with or without twisted tape inserts, and it is always higher than one. Based on the experimental data, regression equations were developed for the Nusselt number and friction factor.

Os sistemas de previsão e alerta utilizados na gestão de recursos hídricos e operação de sistemas de drenagem tiveram desenvolvimentos significativos nos últimos anos. Esses desenvolvimentos resultaram da disponibilidade de informações meteorológicas em tempo real, em particular de medições por sensores em satélites, medição através de radar meteorológico e de previsões de modelos atmosféricos para diferentes horizontes temporais. Todos os modelos de previsão ambiental são incertos e essa incerteza é variável no tempo e no espaço. Este trabalho tem como objetivo apresentar os resultados da avaliação da evolução do erro associado a diferentes previsões de curto prazo. A plataforma Delft-FEWS (Flood Early Warning System) foi utilizada para proceder à importação e processamento de dados de observações e previsões disponíveis para a bacia do rio Ave, localizada no norte de Portugal. Os dados meteorológicos medidos foram obtidos no Sistema Nacional de Informações de Recursos Hídricos (SNIRH), em quatro estações meteorológicas instaladas na bacia em estudo e dados de refletividade medidos pelo radar meteorológico operado pela Meteogalicia. As previsões avaliadas correspondem às precipitações simuladas por modelos atmosféricos desenvolvidos pela National Oceanic and Atmospheric Administration (NOAA) e Meteogalicia, nomeadamente os modelos Global Forecast System (GFS), Global Ensemble Forecast System (GEFS) e Weather Research and Forecasting, (WRF) operado pela Meteogalicia. A incerteza associada às precipitações previstas foi avaliada considerando horizontes de previsão de um a quatro dias. Os melhores resultados foram obtidos para o modelo WRF durante eventos de precipitação ocorridos entre janeiro de 2017 e maio de 2018 e apresentaram médias de erros relativos que variaram entre 7% (um dia de previsão) e 29% (quatro dias). O sistema implementado permite, assim, do ponto de vista operacional, antecipar com antecedência de dois dias eventos extremos., The forecasting and warning systems used in water resources management and drainage systems operation have had significant developments in recent years. These developments resulted from the availability of meteorological information in real time, in particular from measurements by sensors in satellites, measurement through meteorological radar and forecasts of atmospheric models for different time horizons. All environmental forecasting models are uncertain and this uncertainty varies over time and space. This work aims to present the results of the evaluation of the evolution of the error associated with different short-term forecasts. The Delft-FEWS (Flood Early Warning System) platform was used to import and process observation and forecast data available for the river Ave basin, located in northern Portugal. The measured meteorological data were obtained from the National Water Resources Information System (SNIRH), at four new meteorological stations installed in the basin and radar reflectivity data measured by the meteorological radar operated by Meteogalicia. The forecasts evaluated correspond to the rainfall simulated by atmospheric models developed by the National Oceanic and Atmospheric Administration (NOAA) and Meteogalicia, namely the Global Forecast System (GFS), Global Ensemble Forecast System (GEFS) and Weather Research and Forecasting (WRF) model operated by Meteogalicia. The uncertainty associated with the predicted rainfall was evaluated considering forecast horizons of one to four days. The best results were obtained for the WRF model during precipitation events that occurred between January 2017 and May 2018 and presented average relative errors that varied between 7% (one forecast day) and 29% (four days). The implemented system thus allows, from an operational point of view, to forecast extreme events in advance of two days., TRATAVE S.A

The material characterization regarding sheet metal formability is usually assessed by the forming limit curve (FLC). The FLC requires specialized and expensive equipment, several samples with different geometries, and can be a very time-consuming procedure for data treatment. Alternatively, the hole expansion test (HET) and the Erichsen Cupping Test (ECT) can be used for routine evaluations of sheet metal mechanical behavior. These formability tests require fewer quantities of material and easy specimen preparation with a fast analysis of results. The HET and ECT procedures provide a proper evaluation of sheet material stretch-flangeability, formability, strength, and ductility. In this work, we developed a low-cost mechanical device capable of performing the HET and ECT tests using a universal testing machine. The equipment is designed to meet the test parameters set by ISO 16630 (HET) and ISO 20482 (ECT) standards. In order to verify its functionality, tests were carried out with the dual-phase steels DP600 and DP780. The corresponding values determined for the hole expansion ratio and the Erichsen index provided reliable results in terms of the accuracy and repeatability of the proposed testing device.

In this short note, we provide a brief proof for a recent determinantal formula involving a particular family of banded matrices.

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A novel multi-output porthole extrusion die for thin-walled aluminum alloy profile is introduced and its thermo-mechanical modeling for the analyses of metal flow and elasto-plastic deformation is developed. In order to explore the sources of undesirable deformations, two key deformation behaviors (non-uniform relative exit velocity of profile and mandrel deflection of extrusion die) which play considerable effects on the metal flow balance are analyzed based on the developed numerical model. Finally, the optimization design of the multi-output porthole extrusion die structure is performed for the improvement of extruded profile quality.

The aim of this study is to investigate the path-dependent elastic-plastic behavior of dual-phase steel and its influence on the prediction of twist springback in the channel forming process. The anisotropic hardening responses of the sheet material for non-proportional loading, as well as the degradation of the elastic modulus in uniaxial and biaxial tension are investigated. A recently proposed distortional plasticity model combined with a dislocation density-based hardening approach was adopted to describe the flow behavior of the material. The results indicate that the present model simultaneously reproduces all of the experimentally observed features for both load reversal and changes of the principal strain axis. This constitutive description is employed in the finite element analysis of the forming of two channels with obvious twist springback characteristics. The complex strain path changes during the forming process are then analyzed using a proposed indicator. Finally, the relevance of the load changes and the stress distribution in the channel regarding twist springback predictions are discussed. The influence of loading path-dependent elastic modulus degradation for the prediction of twist springback is also assessed based on two different application geometries.

This paper aims to identify the mechanisms associated to the transient hardening behaviour of dual phase steels under strain path changes, and to capture the observed material behaviours with appropriate constitutive models. First, three DP steel sheets with different amounts of martensite were tested under monotonic and various strain path changes. Second, microstructural analysis of the materials before and after strain path change were performed by means of SEM, TEM, and EBSD. The contribution of texture evolution on the mechanical behaviour was also assessed using the visco-plastic self-consistent (VPSC) polycrystal plasticity model. Transient hardening behaviour and permanent softening were observed in the tension–tension tests for all the studied DP steels. These behaviours were explained by the development of strain gradients during the first load resulting from strain accommodation incompatibilities between the ferrite and martensite phases. For the purpose of describing the macroscopic material behaviours, the enhanced homogeneous anisotropic hardening (HAH) model (Barlat et al., 2014) integrated with the Yld2000-2d anisotropic yield function were adopted for constitutive modelling. The simulation results were discussed in view of the microstructure evolution.

The focus of this work is to investigate the control strategy of twist springback of an industrial aluminium alloy extruded tube after mandrel-rotary draw bending, which is a complex nonlinear physical process with coupling multi-factor interactive effects. A particularly pronounced twist springback characteristic of an AA6060-T4 hybrid thin-walled bent tube was observed. It leads to difficulty at the assembly stage due to the inaccurate geometry of product. For an accurate modelling of material behaviours, a non-quadratic anisotropic yield criterion integrated with combined isotropic and kinematic hardening model was adopted to describe the strain-stress behaviours including anisotropy, Bauschinger effects and permanent softening. The corresponding mechanical tests, e.g., enhanced forward-reverse simple shear tests, were performed to identify the material parameters. By using the improved and validated finite element model, two process control strategies related to the mandrel nose placement and the axial push assistant loading are proposed for the assessment of the control efficiency. The simulation results indicate that the mandrel nose placement mainly affects the longitudinal angular springback but not twist deformation in the circumferential sections. The angular springback angle firstly increases and then decreases after several tests of forward mandrel nose placement. The other control strategy, additional axial push assistant loading with high boost, is able to reduce twist deformation, but the compensation of angular springback is not attained and even a slight increase is observed. It also leads to the rise of the of wrinkle tendency in the intrados sidewall. Finally, the wipe die rake is put forward to reduce the wrinkle tendency due to the high boost applied for twist control.

Laser processing is a rapidly growing key technology driven by several advantages such as cost and performance. Laser welding presents numerous advantages in comparison with other welding technologies, providing high reliability and cost-effective solutions. Significant interest in this technology, combined with the increasing demand for high-strength lightweight structures has led to an increasing interest in joining high-performance engineering thermoplastics by employing laser technologies. Laser transmission welding is the base method usually employed to successfully join two polymers, a transmitting one through which the laser penetrates, and another one responsible for absorbing the laser radiation, resulting in heat and melting of the two components. In this work, the weldability of solely transmitting high-performance engineering thermoplastic is analyzed. ERTALON&reg, 6 SA, in its white version, is welded by a pulsed Nd:YAG laser. Tensile tests were performed in order to evaluate the quality of each joint by assessing its strength. A numerical model of the joint is also developed to support the theoretical approaches employed to justify the experimental observations.

Currently, welding processes have become one of the most used methods for joining materials in all kinds of industries, thanks to properties such as high speed and high tensile strength. However, despite these advantages, this type of connection method has some drawbacks, for example, residual stress and structural distortion, mainly due to the process thermal cycles. Structural distortion is one of the major concerns of industrial joining practice. In order to decrease distortion, the variation of welding sequence, direction, and clamping conditions, have been applied through several years, by trial and error tests. However, numerical simulation enables virtual examination of the welding, mainly due to the progress on the numerical methods, which stimulated the research on welding simulation models. These models can cover a wide spectrum of physical and thermal processes occurring during, and after welding. The aim of this paper is to provide wider information about types of finite element method (FEM) in fusion welding processes and to demonstrate the accuracy of FEM models results compared to experimental.

To meet the demands of vehicular safety and greenhouse gas emission reduction, the automotive industry is increasingly using advanced high strength steels (AHSS) in the production of the components. With the development of the new generation of AHSS, it is essential to study their behavior towards manufacturing processes used in the automotive industry. For this purpose, the welding capability of newly developed third-generation Gen3 980T steel was investigated using the Nd:YAG (Neodymium:Yittrium Aluminum Garnet) laser-welding with different parameter conditions. The analysis was made by uniaxial tensile tests, micro-hardness, Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The criteria used to evaluate the quality of the weld were the distance between the fracture and the weld bead and the surface finish. A relationship between the quality of the weld and the energy density was observed, expressed by a partial penetration for values below the optimal, and by irregularities in the weld bead and a high number of spatters for the values above the optimal.

Welding is a fundamental process in many industries. It is a fast-changing technology, continuously evolving, with recent developments in laser and robotic welding, virtual reality and machine learning. Focusing on laser welding, there is a significant interest in this technology, as well as an increasing demand for high-strength lightweight structures, replacing metals in some applications. This work presents an experimental study of the mechanical properties of three types of polyamide 6 joints welded by Nd:YAG laser. After welding, tensile tests were carried out in order to evaluate the influence of the joint type and weld passes on joint strength and weld stresses. The results showed that fairly high weld stresses could be achieved, indicating that good-quality welds were achieved.