ESTGV - DEMGI - Artigo em revista científica, indexada ao WoS/Scopus
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- A study of mixed mode interlaminar fracture on nanoclay enhanced epoxy/glass fiber compositesPublication . Silva, H.; Ferreira, J. A. M.; Costa, J. D. M.; Capela, C.Fiber reinforced laminate are widely used in aerospace, automobile and marine industries, despite its poor interlaminar fracture toughness (IFT), as consequence of the absence of fibers to sustain transverse load. One way recently explored with relative success in order to improve IFT is the use of nanoparticles to reinforce the matrix. Present paper intends to assess and discuss the fracture toughness on mixed mode loading of fiber glass mats/nanoclay enhanced epoxy matrix laminates. The matrix used was the epoxy resin Biresin® CR120 combined with the hardener CH120-3, the fiber glass was triaxial mats ETXT 450 and the nanoparticles were montmorillonite nanoclay (NC). The results were discussed in order to understand the effects of the percentage of nanoclay and the shear load quantified in terms of the GII/GI ratio on the total fracture toughness G. The incorporation of a small quantity of NC into matrices improves significantly mixed-mode IFT for all loading mode ratios GII/G. The total fracture toughness G increases with the mode II loading component and a linear mixed-mode fracture criteria reproduces the Gc against GII/G relationship.
- Fatigue behaviour of glass fibre reinforced epoxy composites enhanced with nanoparticlesPublication . Borrego, L.P.; Costa, J.D.M.; Ferreira, J.A.M.; Silva, H.Nanoparticle reinforcement of the matrix in laminates has been recently explored to improve mechanical properties, particularly the interlaminar strength. This study analyses the fatigue behaviour of nanoclay and multiwalled carbon nanotubes enhanced glass/epoxy laminates. The matrix used was the epoxy resin Biresin CR120, combined with the hardener CH120-3. Multiwalled carbon nanotubes (MWCNTs) 98% and organo-montmorillonite Nanomer I30 E nanoclay were used. Composites plates were manufactured by moulding in vacuum. Fatigue tests were performed under constant amplitude, both under tension–tension and three points bending loadings. The fatigue results show that composites with small amounts of nanoparticles addition into the matrix have bending fatigue strength similar to the obtained for the neat glass fibre reinforced epoxy matrix composite. On the contrary, for higher percentages of nanoclays or carbon nanotubes addition the fatigue strength tend to decrease caused by poor nanoparticles dispersion and formation of agglomerates. Tensile fatigue strength is only marginally affected by the addition of small amount of particles. The fatigue ratio in tensio –tension loading increases with the addition of nanoclays and multi-walled carbon nanotubes, suggesting that both nanoparticles can act as barriers to fatigue crack propagation.
- Interlaminar Adhesive Strength of Nano-Reinforced Glass/Epoxy LaminatesPublication . Silva, H.; Ferreira, J. A. M.; Costa, J. D. M.; Capela, C.Interlaminar fracture is significantly influenced by the adhesive strength of fiber=matrix interfaces. Critical strain energy release rate (GC) is the most common parameter used to quantify the interfacial strength. However, subcritical debonding can occur at lower mechanical loads than those required for interlaminar fracture toughness (IFT). This study was performed using nanoclayreinforced epoxy=glass fiber laminates in order to analyze the influence of the addition of nanoclay and hydro aging on IFT and subcritical crack growth. Hydro aging was done immersinga batch of specimens in distilled water at 25 C for 30 days. Mode I IFT was significantly improved by the incorporation of nanoclays into the resin, the improvement reaching 31% for 3% of nanoclays content. The results of subcritical debonding were plotted in terms of da=dt versus G curves, for dry materials and long term hydro aged composites. Hydro aged composites exhibit not only a reduction of GIc, of about 14% for 3% of nanoclays, but also a higher subcritical crack propagation rate. The addition of nanoparticles reduces subcritical crack propagation rate.
- Mixed Mode interlayer fracture of glass fiber/nano-enhanced epoxyPublication . Silva, H.; Ferreira, J. A. M.; Capela, C.; Richardson, M.O.WIncreasing interlaminar fracture toughness (IFT) has long been an important goal in the fiber reinforced composites field. For that purpose some research has recently explored the use of nanoparticle reinforced matrices to improve interlaminar strength. In this present paper a small quantity of nanoclays (NC) and multiwalled carbon nanotubes (MWCNT) were used in order to enhance the IFT of glass fiber/epoxy composite laminates. The composites sheets were produced by a vacuum molding process. Mode I, Mode II, and Mixed-Mode I/II tests were performed to determine critical strain Energy release rates, using double cantilever beam, end-notched flexure, and Mixed-Mode Bending specimens, respectively. Significant improvements in IFT were obtained for all loading modes by the incorporation of NC into the epoxy resin, whilst MWCNT produced only moderate improvements. For Mode I, IFT improvement by the incorporation of nanoparticle fillers, reached about 31% for 3 wt% of NC and 17% for 1 wt% of MWCNT. In Mode II the increase was about 50% for 3 wt% of NC and 30% for 1 wt% of MWCNT. The dispersion of small quantities NC and MWCNT into matrices significantly improved Mixed-Mode IFTs for all loading mode ratios GII/G. The total fracture toughness G increased under Mode II loading components and linear Mixed-Mode fracture criteria reproduced the Gc versus Mode ratios GII/G and GI versus GII relationship.
- Aplicação da metodologia DMAIC em uma empresa produtora de componentes de borrachaPublication . Almeida, Ricardo; ANTUNES VAZ, PAULO JOAQUIM; Gomes da Silva, Rosa Maria; AlmeidaIntrodução: Nas últimas décadas, foram feitos grandes desenvolvimentos na indústria. As empresas aprimoraram-se para fazer o produto final com mais qualidade e com grande redução de custos. As metodologias Lean foram implementadas em todos os tipos de indústrias e negócios, rompendo com o tipo de produção que se praticava na época, que se baseava em grandes volumes e pouco flexíveis. As metodologias Lean começaram quando os funcionários e engenheiros da Toyota começaram a desenvolver procedimentos e ferramentas para permitir a produção lean, com desperdício zero e sistemas de produção altamente flexíveis. Objetivo:A reorganização do layout do departamento de manutenção, assim como, a melhoria do processo de gestão das spare partse a criação de fluxos para a reparação de equipamentos e ferramentas. Métodos: A ferramenta utilizada foi o DMAIC, esta subdivide o processo de resolução de problemas em cinco etapas, tais como: Definir, Medir, Analisar, Melhorar, Controlar. Resultados: Com a aplicação desta ferramenta foi possível uma redução do número de deslocações e da distância percorrida, (que por sua vez, permitiu também a diminuição do tempo necessário para a sua realização) deste modo o tempo necessário para a sua realização também diminuiu. As spare parts estão mais organizadas, cada bancada de trabalho possui as peças de substituição de maior consumo. A pontuação obtida nas auditorias 5’S também apresentaram um aumento face aos resultados obtidos antes da intervenção. Conclusão: Conclui-se que a causa raiz e as soluções definidas impactaram positivamente a eliminação da causa e problema iniciais.
- An integrated and interoperable AutomationML-based platform for the robotic process of metal additive manufacturingPublication . Babcinschi, Mihail; Freire, Bernardo; Ferreira, Lucía; Señaris, Baltasar; Vidal, Felix; Vaz, Paulo; Neto, PedroIncreasingly, industry is looking to better integrate their industrial processes and related data. Interoperability is key since the organizations need to share data between them, between departments and the different stages of a given technological process. The problem is that many times there are no standard data formats for data exchange between heterogeneous engineering tools. In this paper we present an integrated and interoperable AutomationML-based platform for the robotic process of metal additive manufacturing (MAM). Data such as the MAM robot targets and process parameters are shared and edited along the different sub-stages of the process, from Computer-Aided Design (CAD), to path planning, to multiphysics simulation, to robot simulation and production. The AutomationML neutral data format allows the implementation of optimization loops connecting different sub-stages, for example the multi-physics simulation and the path planning. A practical use case using the Direct Energy Deposition (DED) process is presented and discussed. Results demonstrated the effectiveness of the proposed AutomationML-based solution.
- A Simulation of Data Censored Rigth Type I with Weibull DistributionPublication . Gaspar, Daniel; Andrande Ferreira, LuisIn the maintenance and reliability field, there are frequent analyses with data being censored. In reliability research, many articles do simulation, but few explain how they do it. the loss of information resulting from the unavailable exact failure times will impact negatively the efficiency of reliability analysis. This paper presents four different algorithms to generate random data with a different number of censored values. The four algorithms are compared, and tree parameters are used to select the best one. The Weibull distribution is used to generate the random numbers because it is one of the most used in reliability studies. The results of the algorithm chosen are very relevant; with a sample of n = 50 and a number of cycles of simulations m = 1000, the standard deviation is higher when the shape factor of Weibull distribution is beta = 0.5 and slowly decreases until the shape factor equals 5. The percentage error (PE), one of the indicators selected, is much higher when the percentage of censored data is c = 5%, then goes down when the shape factor increases. There is a different behaviour when censored data is C = 20% and the percentage error (PE) is higher when shape factor is beta = 1.5. This article presents an algorithm that it considers the best for simulating right-censored type-I data. The algorithm has excellent accuracy, random data i.i.d and excellent computational performance.
- Reliability Estimation Using EM Algorithm with Censored Data: A Case Study on Centrifugal Pumps in an Oil RefineryPublication . Silva, José; VAZ, PAULO; Martins, Pedro; Ferreira, LuísCentrifugal pumps are widely employed in the oil refinery industry due to their efficiency and effectiveness in fluid transfer applications. The reliability of pumps plays a pivotal role in ensuring uninterrupted plant productivity and safe operations. Analysis of failure history data shows that bearings have been identified as critical components in oil refinery pump groups. Analyzing historical failure data for such systems is a complex task due to censored data and missing information. This paper addresses the complexity of estimating the Weibull distribution parameters using the maximum likelihood method under these conditions. The likelihood equation lacks an explicit analytical solution, necessitating numerical methods for resolution. The proposed approach presented in this article leverages the expectation maximization (EM) algorithm for estimating the Weibull distribution parameters in a real-world case study of a complex engineering system. The results demonstrate the superior performance of the EM algorithm with censored data, showcasing its ability to overcome the limitations of traditional methods and provide more accurate estimates for reliability metrics. This highlights the importance of obtaining results through these methodologies in the analysis of reliability and in facilitating more informed decision making in complex systems
- Comparative analysis of welding processes using different thermoplasticsPublication . Trindade, Adelino; Guimarães, AndréThis study examined and contrasted three widely utilized welding techniques for modern thermoplastics: hot gas welding, laser beam welding, and friction stir welding. These techniques were employed to join various thermoplastic materials, particularly focusing on polypropylene, polyethylene, and polyvinyl chloride. The weld quality was evaluated using visual inspections and tensile strength tests. Additionally, Vickers hardness tests were performed on the welded joints to detect microstructural alterations. The research aimed to deepen the understanding of the mechanisms behind these welding processes and assess the welded joints' strength.
- Optimizing Database Performance in Complex Event Processing through Indexing StrategiesPublication . Abbasi, Maryam; Bernardo, Marco V.; ANTUNES VAZ, PAULO JOAQUIM; Silva, José; Martins, PedroComplex event processing (CEP) systems have gained significant importance in various domains, such as finance, logistics, and security, where the real-time analysis of event streams is crucial. However, as the volume and complexity of event data continue to grow, optimizing the performance of CEP systems becomes a critical challenge. This paper investigates the impact of indexing strategies on the performance of databases handling complex event processing. We propose a novel indexing technique, called Hierarchical Temporal Indexing (HTI), specifically designed for the efficient processing of complex event queries. HTI leverages the temporal nature of event data and employs a multi-level indexing approach to optimize query execution. By combining temporal indexing with spatial- and attribute-based indexing, HTI aims to accelerate the retrieval and processing of relevant events, thereby improving overall query performance. In this study, we evaluate the effectiveness of HTI by implementing complex event queries on various CEP systems with different indexing strategies. We conduct a comprehensive performance analysis, measuring the query execution times and resource utilization (CPU, memory, etc.), and analyzing the execution plans and query optimization techniques employed by each system. Our experimental results demonstrate that the proposed HTI indexing strategy outperforms traditional indexing approaches, particularly for complex event queries involving temporal constraints and multi-dimensional event attributes. We provide insights into the strengths and weaknesses of each indexing strategy, identifying the factors that influence performance, such as data volume, query complexity, and event characteristics. Furthermore, we discuss the implications of our findings for the design and optimization of CEP systems, offering recommendations for indexing strategy selection based on the specific requirements and workload characteristics. Finally, we outline the potential limitations of our study and suggest future research directions in this domain.