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- A new methodology to fabricate polymer–metal parts through hybrid fused filament fabricationPublication . Silva, Sofia F.; Rosado, Pedro M. S.; Sampaio, Rui F. V.; Pragana, João P. M.; Bragança, Ivo M. F.; Assunção, Eurico; Silva, Carlos M. A.; Bragança, IvoThis paper introduces a new methodology that enables the production of polymer–metal parts through hybrid additive manufacturing. The approach combines fused filament fabrication (FFF) of polymers with adhesive bonding of metal inserts, applied during layer-by-layer construction. The work is based on unit cells designed and fabricated using eco-friendly materials—polylactic acid (PLA) and aluminum—which were subsequently analyzed for build quality and for mechanical performance under tensile lap-shear and three-point bending tests. The acquired knowledge in terms of optimal processing parameters for attaining strong polymer–metal bonds was then applied for the fabrication and testing of prototypes representing modular corner connectors for framing applications. Results on build quality demonstrate that issues, such as lumps and warping, can be solved by finetuning the 3D printing stages of the proposed methodology. In terms of destructive testing, significant improvements in the mechanical performance of PLA can be achieved, demonstrating the feasibility of the proposed methodology in integrating the lightweight properties of polymers with the stiffness of metals. This enables the development of innovative, sustainable and eco-friendly solutions that align with the growing demand for eco-friendly materials and processes in manufacturing.
- A new deformable self-clinching fastenerPublication . Pragana, João P. M.; Sampaio, Rui F. V.; Clara, Ricardo G.; Bragança, Ivo M. F.; Silva, Carlos M. A.; Martins, Paulo A. F.; Bragança, IvoThis work proposes a novel deformable self-clinching fastener for producing hidden lap joints suitable for both structural and electric power distribution applications. The fastener, characterized by an axisymmetric concave shape, is employed to fabricate hybrid busbar joints between electrically conductive strips of different materials and thicknesses. The self-clinching process with the new deformable fastener involves machining dovetail holes in both conductors and applying a squeezing force to the fastener to create a form-closed mechanical joint. The work encompasses both experimental investigations and numerical modeling using finite element analysis and is carried out on unit cells made from aluminum and copper conductors, which are representative of the joining process. The investigation evaluates force requirements, conducts destructive testing, and performs thermo-electric characterization of the new joints to conclude on the suitability of the new deformable self-clinching fastener for electric power distribution applications. Results indicate that while copper fasteners necessitate greater squeezing forces, they offer superior mechanical and thermo-electrical performance compared to aluminum fasteners in hybrid busbar joints.
- A dieless Nakajima test for additively deposited materialsPublication . Sampaio, Rui F. V.; Rosado, Pedro M. S.; Pragana, João P. M.; Bragança, Ivo M. F.; Nielsen, Chris V.; Silva, Carlos M. A.; Martins, Paulo A. F.; Bragança, IvoThis paper focuses on a novel Nakajima test for characterizing the formability of additively deposited materials without extracting sheet blanks. Material is deposited by wire-arc additive manufacturing in the form of ‘Π-shaped’ vertical walls, and the testing regions are then machined to the desired thickness and shapes for subsequent deformation with a hemispherical punch in a press. Digital image correlation is used to obtain the strain loading paths of the deposited material up to failure. The novel test eliminates the need for the special-purpose tool setup of conventional Nakajima tests, simplifying the overall procedure and reducing costs.
- A complete characterization of the fracture forming limits in bulk forming by means of an upset geometry sequencePublication . Sampaio, Rui F. V.; Pragana, João P. M; Bragança, Ivo M. F.; Bragança, I.M.F.; Silva, Carlos M. A.; Martins, Paulo A. F.This paper presents an upset geometry sequence to determine the fracture forming limits in a wide variety of strain loading paths ranging from uniaxial compression to equibiaxial tension. The strains at fracture in principal strain space are obtained by combination of digital image correlation and experimental evolutions of the compression force versus time, and their representation in the effective strain versus stress triaxiality space is accomplished by means of a new analytical framework that uses the instantaneous slope of the strain loading paths. Modeling of the experimental strains at fracture by means of an uncoupled ductile fracture criterion built upon combination of the Cockcroft-Latham and McClintock criteria and fractography analysis using a scanning electron microscope allow understanding and characterizing the crack opening modes by shear and tension as well as the uncertainty region inside which mixed crack opening modes are observed. Results confirm that the overall philosophy and objectives underlying the new upset geometry sequence for determining the fracture forming limits in bulk forming resemble those of the Nakajima test that is commonly used in sheet forming.
- Finite element analysis of non-uniform functionally graded multi-cracked Timoshenko beams using an equilibrium-based formulationPublication . Freixial Argente dos Santos, Hugo Alexandre; Silberschmidt, V. V.A novel finite element formulation is introduced for the static analysis of non-uniform functionally graded multi-cracked Timoshenko beams with small deformations. The cracks, assumed to remain open, are modelled using the so-called discrete spring approach, in which Dirac delta generalized functions are introduced into the bending flexibility of the beams. The formulation is derived on the basis of a complementary variational approach that involves only the elements' shear forces and bending moments as the fundamental unknown fields. The corresponding element flexibility matrix is obtained in closed-form, with the crack contributions explicitly separated from the standard bending and shear flexibility terms. The numerical solutions produced by the formulation are strictly equilibrated, i.e., they satisfy all equilibrium conditions of the associated boundary-value problem in strong form. The effectiveness and accuracy of the formulation are numerically assessed through its application to several benchmark problems. The obtained results are analysed and compared, where possible, to exact (or reference) solutions and solutions given by the standard displacement-based finite element formulation, clearly illustrating the capability of the formulation to deliver highly accurate results for both thin and thick beams, even on meshes with only a few degrees-of-freedom.
- Plane frame structures: optimization and design solutions clusteringPublication . Gaspar, Joana S. D.; Loja, Amélia; Barbosa, JoaquimThis work aims to constitute a framework dataflow based on the prediction, optimization, and characterization of optimal solutions. To this purpose, a metaheuristic optimization method is used to obtain the optimal design solutions for discrete plane frame structures considering as objective function the minimization of their maximum resultant displacement, subjected to side and behavioral constraints. The design variables that lead to the optimal solutions are constituted into datasets which are subsequently submitted to a clustering analysis. The results obtained provide pertinent insights about the optimal solutions clusters’ ranges, giving effective support to a specific solution selection.
- Energy production from landfill gas: short-term managementPublication . Soares Domingues, Nuno AlexandreAn increasing lack of raw materials, resource depletion, environmental impacts and other concerns have changed the way the population faces garbage disposal and municipalities implement waste management strategies. The aggravated global rise in municipal solid waste (MSW) generation has led to a new stage in full development, with objectives and targets set by the European Union regarding reducing the production of MSW. The targets also include the increasing selective collection, reuse, recycling and recovery (organic and energetic) of the waste produced. At the same time, the European Union has also set caps for the greenhouse gas emissions and for increasing the use of alternative renewable energy sources. In this context, one of the sources of renewable energy that is beginning to be used to produce electricity in our country is biogas. Finally, AD promotes the development of a circular economy. The present study introduces the formalism for a computer application that simulates the technical-economic behaviour of the short-term management of biogas for the conversion of electricity, and the mathematical model is formulated as a mathematical programming problem with constraints. A simulation for a case study of short-term management is given using the real landfill data available. The case study proves the ability of the LandGEM, despite some authors' support that the Tabasaran-Rettenberger model provided a more reliable estimate, especially when compared to actual landfill data. The present paper is a contribution to the optimisation of the management of electricity from the use of biogas, namely the second phase of the Strategic Plan for Urban Waste. In addition to complying with the legislation in force, the use of biogas to produce electricity is an added value for the concessionaires of waste treatment and final destination units, as this alternative energy source can provide not only self-sufficiency in electricity for these units but also the export of surplus energy to the National Electricity Grid, thus contributing to the self-sustaining management and energy flexibility that is intended for these infrastructures.
- A hybrid decision support system using rule-based and AI methods: the OnCATs knowledge-based frameworkPublication . Soares Domingues, Nuno AlexandreBackground and significance: Clinical decision support systems (CDSS) can improve evidence-based oncology care, but many rely on opaque AI models that limit transparency and reproducibility. Rule-based approaches provide interpretability but often lack adaptability, a critical issue in prostate cancer where decisions depend on tumor stage, PSA, Gleason score, comorbidities, and life expectancy. Bridging explainability and adaptability is essential for trustworthy decision support. Objective: To develop and evaluate OnCATs, a modular, explainable, hybrid-ready CDSS that encodes prostate cancer management guidelines in a machine-readable and auditable format. Materials and methods: Evidence from 23 international guidelines was formalized into a JSON-based rule base executed through a forward-chaining inference engine. OnCATs supports three decision layers: (1) risk stratification, (2) treatment-pathway recommendation, and (3) prescription-level assistance for radiotherapy, brachytherapy, androgen deprivation therapy, and surgery. Feasibility was tested using ten published case reports. Performance was assessed with precision, recall, F1 scores, and descriptive concordance. Results: OnCATs achieved perfect concordance for risk stratification (precision = 1.00, recall = 1.00, F1 = 1.00). Treatment-pathway concordance was 0.80 (F1 = 0.80). Prescription-level agreement ranged from 0.67 to 0.75 (mean F1 = 0.71). Divergences primarily reflected simplified life-expectancy modeling and incomplete case data. Discussion: OnCATs demonstrates that transparent, rule-based reasoning can reproduce guideline-defined prostate cancer decisions with traceability. Limitations include the small sample size and reliance on secondary data. Conclusion: OnCATs operationalizes multi-source guidelines into an explainable, modular CDSS, providing a reproducible foundation for future integration of probabilistic and machine-learning methods.
- Harnessing renewable energy sources in CO2 refrigeration for eco-friendly fish cold storagePublication . Semedo, Arian António Tavares; Garcia, João Nuno Pinto MirandaThis study explores innovative strategic solutions within a sustainability framework, focusing on four viable options for an integrated refrigeration system designed for fish preservation in Tarrafal de Santiago, Cape Verde. Tarrafal is a coastal town on Santiago Island, characterized by its reliance on fishing activities and the challenges posed by limited energy infrastructure and local environmental vulnerabilities. The evaluated solutions range from grid-dependent systems to fully autonomous configurations powered by renewable energy sources, incorporating various refrigeration facility designs adapted to regional conditions. The primary objective is to assess the energy efficiency, economic viability, and environmental impact of these options within the specific geographic and socioeconomic context of Tarrafal de Santiago. Four approaches were analyzed: Strategy A involves two R134a refrigeration systems powered by conventional grid electricity; Strategy B employs a transcritical CO2 (R744) system combined with grid electricity; Strategy C integrates an R744 refrigeration system powered by autonomous renewable energy sources; and Strategy D utilizes R744 refrigeration combined with seawater-based heat exchange and autonomous renewable energy generation. The results indicate that Strategy D offers the greatest advantages, with emissions amounting to 15,882 kg of CO2 equivalent and a return on investment within five years. Autonomous electricity generation in Strategy D leads to a 95% reduction in CO2 emissions. Although Strategy C entails a higher initial cost, it proves financially viable and significantly enhances energy sustainability. Its autonomous energy production results in a reduction of 360,697 kg of CO2 emissions compared to conventional systems, highlighting the substantial environmental benefits of integrating local renewable energy sources into coastal communities such as Tarrafal de Santiago.
- Assessment of influential operational parameters in the mitigation of CO2, emissions in a power plant: case study in PortugalPublication . Balanuta, Vítor; Baptista, Patrícia; Carreira, Fernando; Duarte, Gonçalo O.; Casaca, Cláudia S. S. L.The European decarbonization goals and requirement for energy independence are mostly relying on intermittent renewable energy sources for electrification. A numerical model was developed to simulate the operation of a steam generator, allowing a study of the potential impacts of retrofitting existing coal-fired power plants to operate with biomass or coal–biomass mixtures on combustion parameters and CO2 emissions. The results obtained using the operational parameters of the Sines power plant indicate that a mixture of 25% coal and 75% pine sawdust allow operation at λ = 1.8, demonstrating that a small amount of coal allows operation near the coal combustion parameters (λ = 1.9). These conditions have the drawback of a reduction of 8.7% in adiabatic flame temperature but a significant reduction of 57.5% in CO2 emissions, considering the biomass as carbon-neutral.