497 research outputs found
A 3D finite element stochastic framework for the failure of tow-based discontinuous composites
No full textTow-Based Discontinuous Composites (TBDCs) combine high manufacturability with good mechanical proper-ties. This work presents a novel 3D approach for the numerical modelling of TBDCs. The framework generates 3D orientation tensors by adding a stochastic component to the orientation tensors deterministically predicted by a process simulation. The actual TBDCs are thus idealised as Equivalent Laminates (ELs), resulting from these stochastic tensors. A physically based 3D failure criterion is presented for the prediction of failure initiation of the ELs. The consequent stiffness reduction is captured by a ply-discount method. The approach is validated for two TBDCs materials, with two different moulding conditions and different amounts of in-mould flow. The proposed approach accurately predicts the characteristic variability of these materials. As a consequence, the predicted strength was in good agreement with the experimental results of both materials tested
Compressive properties of thin tow-based discontinuous composites [Elektronisk resurs]
No full textUltra-thin tow-based discontinuous composites are an emerging class of composite materials which can be used for high performance applications in a wide range of industries. They offer significant advantages compared to continuous composites, such as reduced waste material, enhanced formability and even increased mechanical properties. However, the properties of composite materials under compression are often a limiting factor in structural design. Measuring the compressive properties of composites is also non-trivial, as premature failures are occurring often with the existing testing standards. Finally, the compressive response of discontinuous composites is currently unclear as the existing studies are limited. This work presents a full experimental campaign on the characterization of the compressive response of ultra-thin tow-based discontinuous composites. A uniaxial test is initially employed which reveals instabilities, premature failures and large experimental scatter. Afterwards, a sandwich beam bending test is employed which allows to measure the compressive properties accurately with low variability. The compressive strains measured exceed 1 %, which is also the tensile limit for this material. The agreement between the tensile and compressive strength was investigated by using scanning electron microscopy which revealed that the damage was controlled by matrix deformation in the tow interfaces
Carbon fibre sheet moulding compounds with high in-mould flow: linking morphology to tensile and compressive properties
No full textsponsorship: The research leading to these results has been performed within the framework of the FiBreMoD project and has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 722626. YS acknowledges FWO Flanders for his postdoctoral fellowship. SVL holds the Toray Chair at KU Leuven, the support of which is acknowledged. SP acknowledges her Research Fellowship of the Royal Academy of Engineering on "Multiscale discontinuous composites for high-volume and sustainable applications" (2015-2019). The authors also acknowledge Mitsubishi Chemical Carbon Fiber and Composites GmbH for providing material and related information. The micro-CT images have been acquired on the X-ray computed tomography facilities at KU Leuven, maintained under the supervision of Prof M. Wevers and financed by the Hercules Foundation and the Research Council of KU Leuven (project C24/17/052); help of Dr Jeroen Soete and of technician Johan Vanhulst is gratefully acknowledged. The authors acknowledge Marco Alves (Imperial College London) for several useful discussion on CT analysis of TBDC. The technicians of KULeuven Bart Pelgrims and Kris Van de Staey are acknowledged for their help with the tensile and compressive tests. (European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant|722626, FWO Flanders, Toray Chair at KU Leuven, the Royal Academy of Engineering, Hercules Foundation, Research Council of KU Leuven|C24/17/052)status: Published onlin
Professor Pimenta Claro (1957-2018): Pioneer in dynamics of mechanical systems at the University of Minho
No full textThis work highlights the importance of Professor Pimenta Claro in the genesis and development of a new scientific area at the Department of Mechanical Engineering of the University of Minho, namely Dynamics of Mechanical Systems. Professor Pimenta Claro initiated his academic career in October 1980, coming from industry, where he was a well-recognized engineer in the field of mechanical design. Professor Pimenta Claro concluded his Pedagogical Aptitude and Scientific Capacity Tests (PAPCC) – MSc equivalent – in 1987, with dissertation title “Estudo Comparativo das Previsões Teóricas do Desempenho de Chumaceiras Radiais Hidrodinâmicas com Resultados Experimentais”. Professor Pimenta Claro received his doctorate degree in 1994 with thesis “Reformulação de Método de Cálculo de Chumaceiras Radiais Hidrodinâmicas – Análise do Desempenho Considerando Condições de Alimentação” under the mentorship of Professor Sousa Miranda, which was in fact the first PhD in Mechanical Engineering defended at the University of Minho. In 1997, Professor Pimenta Claro broken with his past background – classical tribology – to open a new research domain – Dynamics of Mechanical Systems. Since then, Professor Pimenta Claro has coordinated and participated in several scientific projects both with national and international partners, as well as projects with industrial partners. Professor Pimenta Claro was author of numerous publications, including scientific papers, books, conference papers, etc., and supervised PhD and MSc students. From 2007 to 2013 he coordinated the research group called Dynamics of Mechanical Systems. Professor Pimenta Claro was also pioneer and responsible for the creation of new courses on dynamics of mechanical systems offered in different degrees at the School of Engineering of the University of Minho. Thus, the main purpose of this work is to highlight Pimenta Claro’s contributions to the vast scientific area of Dynamics of Mechanical Systems at the Department of Mechanical Engineering of the University of Minho
Recycling carbon fibre reinforced polymers for structural applications: Technology review and market outlook
No full text17.01.14 KB. Ok to add accepted version to spiral, Elsevier says ok while mandate is not enforced
Worsening heart failure: progress, pitfalls, and perspectives (Heart Failure Reviews, (2025), 10.1007/s10741-025-10497-z)
No full textPublisher Copyright: © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2025.The order of the authors' first and last names was reversed in the original publication. The correct author names are as follows: Incorrect Author List: Fonseca Cândida · Baptista Rui · Franco Fátima · Moura Brenda · Pimenta Joana · Pedro Moraes Sarmento · Silva Cardoso José · Brito Dulce Correct Author List: Cândida Fonseca · Rui Baptista · Fátima Franco · Brenda Moura · Joana Pimenta · Pedro Moraes Sarmento · José Silva Cardoso · Dulce Brito The original article has been corrected.publishersversionpublishe
Designing and modelling bio-inspired discontinuous composites
No full textThe exponential increase in the use of composites for structural applications in the past decades comes with a constant need to increase their performance for them to remain an attractive substitute to conventional metals. In particular, despite their lightweight and high specific stiffness and specific strength, composites generally suffer from a lack of damage tolerance. Their brittle nature restrains the use of composites in industry, or at least leads to over-conservative designs.
This work aimed at designing and modelling novel discontinuous microstructures, inspired by damage tolerant naturally-occurring discontinuous composites. This was achieved by considering discontinuous hybrid and discontinuous hierarchical microstructures.
In a first part, a virtual testing framework was developed to perform virtual testings of non-hybrid and hybrid aligned-fibre discontinuous composites. The virtual framework, made of analytical models combining statistics and micromechanics, captured and explained different effects such as hybrid effects, size effects, and the effect of variability. The models were used to identify microstructures which maximise the strength, failure strain and stiffness of hybrid discontinuous composites.
In a second part, hierarchical discontinuous carbon-fibre reinforced polymers were designed, modelled numerically and tested experimentally. They exhibited a stable failure mechanism and dissipated energy stably, before failure, through diffuse damage (unlike most conventional composites). This study also showed that non-self-similar microstructures could achieve better damage tolerance and provide a clearer warning before failure than self-similar microstructures.
This work shows the potential for different types of discontinuous composites to overcome the inherent brittleness of conventional composites. The models developed throughout this work can be used to support material design, perform parametric studies and identify optimal designs.Open Acces
ALBERTO PIMENTA: AS CASAS MOVEDIÇAS
No full textThe article discusses part of the most recent production of the poet, essayist and performer Alberto Pimenta from two points: a) the insistent formal instability sought by the author, who with each new project seems to reinvent his work by discarding the previously construction procedures and always looking for new questions and new possible dialogues with literary tradition, the focus of his most recent works, and b) the maintenance, in projects very different from each other, of political commitments and the critical dimension of the author's writings, who turns his gaze, once again, for the lives of the poorest and for the injustices of the contemporary world, especially for what is happening in the world of labor relations in Portugal, in particular, and on the margins of Europe, in general.O artigo discute parte da produção mais recente do poeta, ensaísta e performer Alberto Pimenta a partir de dois pontos: a) a insistente instabilidade formal buscada pelo autor, que a cada novo projeto parece reinventar a sua obra ao descartar os procedimentos construtivos anteriormente utilizados e partir sempre em busca de novas questões e novos diálogos possíveis com a tradição, foco de seus trabalhos mais recentes, e b) a manutenção, em projetos muito diversos entre si, dos compromissos políticos e da dimensão crítica dos escritos do autor, que volta seu olhar, uma vez mais, para a vida dos mais pobres e para as injustiças do mundo contemporâneo, sobretudo para o que se passa no mundo das relações de trabalho em Portugal, em particular, e nas margens da Europa, em geral
Modelling the variability and reliability of high-performance composite materials
No full textCarbon-fibre reinforced polymers (CFRPs) are the material of choice for light-weight structural applications. The microstructure of CFRPs ranges from simple to more complex architectures, allowing them to be tailored for specific applications. However, composite material systems present intrinsic variability which leads to a stochastic mechanical response.
The behaviour of composite materials under different loading conditions (ranging from static to complex cyclic loads) is still to be fully understood.
This study aims to develop models to predict the variability and reliability of different composite architectures, leading to safer and more reliable composite structure designs.
Tow-Based Discontinuous Composites (TBDCs) are an up-and-coming class of high-performance discontinuous composites, which combine high manufacturability and good mechanical properties. Their architecture, composed by randomly oriented carbon fibre tows, results in a microstructure with the most extreme levels of variability. The spatial variability of TBDC strain fields was quantitatively characterised with a new proposed method, which enabled the identification of a relationship between the characteristic length-scales of the strain fields and the material's microstructural features. The intrinsic variability of these materials leads to a notch insensitive behaviour, that was experimentally characterised not only for circular notches of different diameters but also for non-circular notch geometries.
A stochastic Finite Element (FE) framework able to replicate the intrinsic variability of TBDC materials was proposed. The framework considers an implicit representation of the material's microstructure, by using a Stochastic Equivalent Laminate analogy, and predicts the elastic response, damage initiation and final failure of TBDCs under static loading.
The FE framework was validated against experimental results for different TBDC material systems, with both random and preferential fibre orientations.
Numerical models were used to explore the design space of discontinuous composites, in order to identify optimal microstructure designs that maximise their stiffness and strength. Ultra-thin tapes (20 \upmum) of high modulus (425-760 GPa) carbon-fibres were used to manufacture and test TBDC under static loading. The experimental results showed increases of strength up to 100\%, when compared with commercially available TBDC systems, and resulted in a discontinuous composite with mechanical properties that match the strength and overcome the stiffness of aerospace-graded continuous-fibre quasi-isotropic laminates.
Composites are often subjected to cyclic loading, presenting further challenges in predicting their reliability. An analytical model to predict the fatigue response of unidirectional composites was also proposed.
Due to its analytical formulation, the model was able to predict, for the first time in the literature, the evolution of the micromechanical fatigue damage in composites with any number of fibres. Strength reductions throughout fatigue life (up to 10 million cycles) are computed in less than sixty seconds. The model generates stochastic S-N curves and was successfully validated against experiments from the literature.
This work shows the potential of TBDCs to match the mechanical properties of continuous-fibre quasi-isotropic laminates while still having high manufacturability. The models developed
throughout this work can be used to support material design, to identify optimal TBDC microstructures for enhanced mechanical performance.Open Acces
A computationally-efficient hierarchical scaling law to predict damage accumulation in composite fibre-bundles
No full textUnidirectional composites under longitudinal tension develop damage through the accumulation and clustering of fibre–breaks, which may lead to catastrophic failure of an entire structure. This paper uses a hierarchical scaling law to predict the kinetics of fibre–breakage and its effect on the stress–strain response of composites under longitudinal tension; due to its analytical formulation based on the statistical analysis of hierarchical fibre–bundles, the scaling law predicts the response of composite bundles up to virtually any size in less than one second. Model predictions for the accumulation and clustering of fibre–breaks are successfully validated against experiments from the literature. These results show that the present model is a much more computationally–efficient alternative to other state–of–the–art models based on Monte–Carlo simulations, without sacrificing the accuracy of predictions when compared against experiments
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