ISEL - Eng. Mecan. - Artigos
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- Non-proportional mixed mode plastic zones via finite elements and artificial neural networksPublication . Infante, Virgínia; Miguel Gomes Simões Baptista, RicardoThe plastic zone developed around a fatigue crack tip can affect both fatigue and fracture material behaviour. Predicting the plastic zone shape and size under cyclic conditions can, therefore, enhance fatigue crack propagation analysis. While there are theoretical solutions for the elastic stress and strain fields under pure or mixed mode conditions around the crack tip, solutions for plastic fields must be determined using experimental or numerical approaches. The Compact Tension Shear (CTS) specimen has been extensively used to analyse plastic zones under proportional conditions, but when non-proportional conditions are applied the number of necessary analyses for a reasonable understanding of the plastic zone shape and size around the crack tip can increase exponentially. To address this problem, a combined approach was used to reduce the number of required plastic zone simulations. First, a hand selected number of loading configurations were simulated using the Finite Element Method (FEM), predicting the plastic zone shape and size. Then, an Artificial Neural Network (ANN) was trained to predict the plastic zone under different conditions. Using only 18 configurations for 3 different loading conditions, the trained ANN was able to accurately predict the plastic zone shape and size for both tensile and shear propagation modes. The network can now be used to predict the plastic zone influence on fatigue and fracture behaviour, without the need for further numerical analysis. The paper results also show that crack propagation direction can be correlated and predicted using the applied loads and the resulting plastic zone.
- Reaction path in the mechanosynthesis of calcium phosphates using a biogenic calcium sourcePublication . Ferro, Alberto C.; Seixas, Tomás; Guedes, MafaldaCalcium phosphates were produced by mechanosynthesis, using eggshell, H3PO4 and 6-83 wt%-H2O. Mixtures were milled at 600 rpm during 0.5-12 h. Resulting calcium phosphates occur within specific milling domains; H2O concentration determines onset and stability of monophasic hydroxyapatite. Within the tested conditions, brushite is the first detected calcium phosphate precipitated from solution. In 6, 40 and 56 wt%-H2O, monetite intermediates brushite's transformation to hydroxyapatite; in 71 and 83 wt%-H2O transformation is direct. Hydroxyapatite formation is favoured at the H2O extremes tested, 6 and 83 wt%. CO2 build-up in the confined jar and nucleation-and-growth events during drying are possible obstacles upon control of morphology and composition of synthesised particles. The potential of chicken eggshell as direct biogenic source and the ability of high-energy milling as corresponding processing route to produce calcium phosphates was demonstrated. This signals a route for reliable production of brushite, monetite and hydroxyapatite. A preliminary milling map was built, allowing to obtain desired final product under specific milling conditions.
- A statistical assessment of drilling effects on glass fiber-reinforced polymeric compositesPublication . Martins, Ana; Carvalho, Alda; Bragança, Ivo; Barbosa, Inês; Barbosa, Joaquim; Loja, AméliaFiber-reinforced composites are extensively used in many components and structures in various industry sectors, and the need to connect and assemble such types of components may require drilling operations. Although drilling is a common machining process; when dealing with fiber-reinforced composite materials, additional and specific problems may arise that can com-promise mechanical integrity. So, the main goal of this work is to assess how various input variables impact two main outcomes in the drilling process: the exit-adjusted delamination factor and the maximum temperature on the bottom surface where the drilling tool exits. The input variables include the type of drilling tools used, the operating speeds, and the thickness of the plates being drilled. By using Analysis of Variance (ANOVA), the analysis aims to identify which factors significantly influence damage and exit temperature. The results demonstrate that the influence of tools and drilling parameters is critical, and those selections impact the quality of the hole and the extent of the induced damage to the surrounding area. In concrete, considering the initially selected set of tools, the BZT03 tool does not lead to high-quality holes when drilling medium- and high-thickness plates. In contrast, the Dagger tool shows potential to reduce exit hole damage while also lowering temperature.
- Short-term load forecasting of electricity demand for the residential sector based on modelling techniques: A systematic reviewPublication . Rodrigues, Filipe; Cardeira, Carlos; Calado, João; Melício, RuiIn this paper, a systematic literature review is presented, through a survey of the main digital databases, regarding modelling methods for Short-Term Load Forecasting (STLF) for hourly electricity demand for residential electricity and to realize the performance evolution and impact of Artificial Intelligence (AI) in STLF. With these specific objectives, a conceptual framework on the subject was developed, along with a systematic review of the literature based on scientific publications with high impact and a bibliometric study directed towards the scientific production of AI and STLF. The review of research articles over a 10-year period, which took place between 2012 and 2022, used the Preferred Reporting Items for Systematic and Meta-Analyses (PRISMA) method. This research resulted in more than 300 articles, available in four databases: Web of Science, IEEE Xplore, Scopus, and Science Direct. The research was organized around three central themes, which were defined through the following keywords: STLF, Electricity, and Residential, along with their corresponding synonyms. In total, 334 research articles were analyzed, and the year of publication, journal, author, geography by continent and country, and the area of application were identified. Of the 335 documents found in the initial research and after applying the inclusion/exclusion criteria, which allowed delimiting the subject addressed in the topics of interest for analysis, 38 (thirty-eight) documents were in English (26 journal articles and 12 conference papers). The results point to a diversity of modelling techniques and associated algorithms. The corresponding performance was measured with different metrics and, therefore, cannot be compared directly. Hence, it is desirable to have a unified dataset, together with a set of benchmarks with well-defined metrics for a clear comparison of all the modelling techniques and the corresponding algorithms.
- Ardosia: simulating circuits and robotic systems in a platformPublication . Marnoto de Oliveira Campos, Francisco MateusCircuit simulation, together with practical sessions, is considered a fundamental tool to assist in the teaching of electronics. Robotics offers rich real-world applications that foster student interest in developing engineering projects. Despite the potential benefits of uniting these two realities, software tools that combine circuits and robotic systems in a single simulation platform are scarce. This article presents Ardosia, a simulation software that combines electronics and robotics in a single simulation arena. The electronic aspects of the simulation are handled by the Falstad Circuit Simulator, a software with proven success in promoting student interest and learning outcomes. Importantly, this software features significant interactive and visualization characteristics that are deemed valuable to enhance conceptual understanding. Non-electrical physics simulation is performed by a special-purpose engine, designed to simulate sensor and actuator behavior in a 2-D world. In combination, the two simulation engines yield a model where electronic circuits are embodied in the world through robot sensors and actuators interacting together and with the surroundings. Such a simulator is intended to promote the use of robotics projects in electronics education, since students will be equipped with software to conveniently design and evaluate robotic systems, through simulation, before applying their ideas in an experimental setting. This article presents an overview of Ardosia, complemented with examples of use in electronics education and a validation experiment comparing simulation with real-world data.
- Simulating circuits and robotic systems in a platformPublication . Marnoto de Oliveira Campos, Francisco MateusCircuit simulation, together with practical sessions, is considered a fundamental tool to assist in the teaching of electronics. Robotics offers rich real-world applications that foster student interest in developing engineering projects. Despite the potential benefits of uniting these two realities, software tools that combine circuits and robotic systems in a single simulation platform are scarce. This article presents Ardosia, a simulation software that combines electronics and robotics in a single simulation arena. The electronic aspects of the simulation are handled by the Falstad Circuit Simulator, a software with proven success in promoting student interest and learning outcomes. Importantly, this software features significant interactive and visualization characteristics that are deemed valuable to enhance conceptual understanding. Non-electrical physics simulation is performed by a special-purpose engine, designed to simulate sensor and actuator behavior in a 2-D world. In combination, the two simulation engines yield a model where electronic circuits are embodied in the world through robot sensors and actuators interacting together and with the surroundings. Such a simulator is intended to promote the use of robotics projects in electronics education, since students will be equipped with software to conveniently design and evaluate robotic systems, through simulation, before applying their ideas in an experimental setting. This article presents an overview of Ardosia, complemented with examples of use in electronics education and a validation experiment comparing simulation with real-world data.
- Enhancing the performance of double-flush riveted joints through hybridization with adhesive bondingPublication . Alpendre, João M. B.; Rosado, Pedro M. S.; Sampaio, Rui F. V.; Pragana, João P. M.; Bragança, Ivo; Silva, Carlos M. A.; Martins, Paulo A. F.This paper explores the potential to enhance the mechanical performance of joints created through a new joining-by-forming technique called hybrid double-flush riveting. To achieve this, adhesive bonding is used to form hybrid lap joints with superior mechanical properties. The study focuses on high-strength steel sheets and starts by identifying the appropriate surface conditions necessary for producing strong adhesive-bonded joints. A similar strategy is applied to construct double-flush riveted joints, focusing on the geometric variables involved in the process. Hybrid joints are then created by integrating adhesive bonding with double-flush riveting, with the second carried out before or after curing is completed. The experimental development is supported by finite element analysis conducted with an in-house computer program. The mechanical performance of the hybrid joints is compared to that of purely adhesive-bonded and conventionally double-flush riveted joints through shear and peel destructive testing. Results demonstrate that hybrid joints ultimately provide greater joint strength for both solicitations. This allows showcasing the hybridization of double-flush riveting with adhesive bonding as an effective solution for applications where joint strength and continuity are essential.
- Color evaluation of pre-shaded monolithic zirconia restorations on different substrates and resin cementsPublication . Fonseca, Vanessa; Neves, Cristina Bettencourt; Portugal, Jaime; Anes, Vitor; Chasqueira, Filipa; Roque, Joao CarlosThis study evaluated if the material, the substrate, and the cement have no influence on the color of pre-shaded monolithic zirconia crowns. The specific effect of the cement over each substrate/brand group was also studied. Two commercial brands of zirconia, Amann Girrbach (AG) and Zirkonzahn (ZZ), were used to produce crowns that were placed over three substrates (natural tooth, zirconia, metal) using two different resin cements (Ivoclar AG (Shaan, Liechtenstein) Neutral and Light) or glycerol (as the control) (n = 10). Lightness (L*), chroma (C*), hue (h*), and color difference (ΔE) of each crown were measured using a VITA Easyshade V® spectrophotometer (VITA Zahnfabrik, Bad Säckingen, Germany), following the standardized reference. Since normality was not verified by the Shapiro–Wilk test, data were statistically analyzed using the Kruskal–Wallis test for group comparisons and Tukey’s post-hoc test for multifactorial variance analysis (α = 0.05). ΔE medians ranged between 1.3 in the AG/zirconia substrate/glycerol group and 8.0 in the ZZ/metal substrate/light cement group. In general, lower values of ΔE were recorded in AG restorations compared to ZZ (p < 0.05), zirconia, and natural tooth substrates compared to metal (p < 0.001) and neutral compared to light cements (p < 0.05). Specifically, over the metal substrate, AG crowns with neutral cement and ZZ crowns with neutral cement and glycerol showed lower ΔE values (p < 0.05). Over the zirconia substrate, light cement presented higher ΔE values than glycerol in both brands but similar to neutral cement. Over the natural tooth, no significant differences were observed between cements (p > 0.05) in the AG brand, while in the ZZ group, light cement showed higher ΔE values (p < 0.05). The final color of the restorations was significantly influenced by the zirconia brand, substrate type, and resin cement. Light cement led to greater color variations, particularly in ZZ restorations. These findings highlight the importance of material selection in achieving esthetically pleasing zirconia restorations.
- Energy production from landfill gas: short-term managementPublication . Domingues, Nuno SoaresAn 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.
- Natural gas–hydrogen blends to power: equipment adaptation and experimental studyPublication . Valente, Ruben; Costa, Jorge M.; Soares Domingues, Nuno AlexandreAn experimental study was devised to assess the technical, environmental, and economic impact of incorporating hydrogen into natural gas. The experimental tests were conducted on a GUNT ET 792 demonstration unit, characterized by operating on a gas cycle in a twin-shaft configuration. The equipment was adapted to accommodate natural gas and mixtures of natural gas with hydrogen in volumetric fractions of 5%, 10%, and 20%. The tests carried out ensured the viability of using these mixtures from a safety perspective. On the other hand, it was possible to evaluate the main differences in the use of these fuel gases in terms of the temperatures and pressures that characterize the main points of the gas cycle, fuel injection pressures, air/fuel ratios, excess air, power output, overall cycle efficiencies, NOX and CO2 emissions, and operational cost.