Composite pressure vessels for commercial applications

A new generation of composite pressure vessels for large scale market applications has been studied in this work. The vessels consist on a plastic liner wrapped with a filament winding glass fibre reinforced polymer matrix structure. A polyethylene (PE) was selected as liner for water at room temperatures applications and a thermosetting resin was used as matrices in the glass reinforced filament wound laminate. For applications having higher service temperatures, such as, termal accumulators and solar panel vessels, thermoplastics presenting greater temperature performance, for example, polypropylene (PP), polyamide (PA), polycarbonate (PC) Polyvinylidene difluoride (PVDF) or even thermosettings are being studied for application as vessel liners.Agencia de Inovação (ADI) através do projeto QREN 21538 – HERMOCOMPRESS e Fundação para a Ciência e a Tecnologia (FCT

CFRP bioinspirados para melhoria da resistência ao impacto e autossensorização

Os compósitos reforçados com fibras de carbono (CFRP) são cada vez mais usados em aplicações de elevado desempenho devido às excelentes propriedades mecânicas e baixo peso que apresentam. A resistência interlaminar continua, no entanto, a ser uma das maiores limitações do seu desempenho mecânico [1-3]. Recentemente, tem-se vindo a tentar superar o problema aplicando nos CFRP mecanismos semelhantes aos que garantem um elevado desempenho ao impacto em organismos vivos, p.e., o exosqueleto dos artrópodes que apresenta uma estrutura fibrosa laminada helicoidal (Bouligand) à escala micrométrica [4-6]. Sistemas sensoriais estudados em seres vivos também têm inspirado o desenvolvimento de compósitos multifuncionais [7], sendo ainda um desafio a criação de tecnologias de fabrico capazes de replicar estas estruturas/sistemas. Neste trabalho fabricaram-se CFRPs com desempenho mecânico melhorado, usando laminados bioinspirados com fibras orientadas helicoidalmente (tipo Bouligand) e nanotubos de carbono (CNT) como sensores capazes de lhes conferiram multifuncionalidade (monitorização de dano). Produziram-se por infusão por vácuo, usando uma resina epóxída reforçada com fibras contínuas de carbono, placas CFRP (550x180x4 mm) com empilhamentos helicoidal e standard que, para comparação de propriedades, foram sujeitas a ensaios de impacto e de compressão após-impacto. Para garantir a multifuncionalidade, transferiram-se florestas de CNT verticalmente alinhados (VA-CNT) obtidas por deposição química a vapor (CVD) para o laminado. Usaram-se ainda técnicas não-destrutivas (NDT) de ultrassons (C-Scan) na análise da microestrutura e avaliação dos danos produzidos após impacto. Os resultados evidenciam as dificuldades encontradas em fabricar as placas e as melhorias que a integração de estruturas bioinspiradas conferem às características e multifuncionalidade dos compósitosProjeto IAMATinfo:eu-repo/semantics/publishedVersio

Thin veils strategically interleaved to reduce low velocity damages on CFRP

Low velocity impact (LVI) events on carbon fibre reinforced polymers (CFRP) are one of the most problematic issues in composite applications for advanced markets, such as aeronautic, aerospace and army. Due to their own brittleness and layer-by-layer nature, when exposed to LVI solicitations, composites tend to develop internal damages that may be barely visible at naked eye. The high complex field of internal stresses developed in composite laminates during impact usually causes crack initiation and defects between layers, which may propagate (delamination) due to the low toughness that this unreinforced resin rich region exhibits. In this work, to try minimizing this propagation problem, thin veils of different materials (glass, carbon, aramid and polyester), were interleaved between different layers of a carbon/epoxy laminate typically used to produce aircraft components. In addition, to decide between which layers could be better interleave the above referred veils a theoretical study was carried out to evaluate the stresses distribution across laminate thickness when a bending moment is applied, on a carbon/epoxy laminate under study. The new carbon/epoxy laminates using the thin interleaved veils were produced by vacuum bag infusion and their mechanical characteristics and LVI responses compared with those obtained on a non-interleaved one produced in the same processing conditions. Interlaminar shear strength (ILSS) and LVI tests at four different energy impact levels were performed in order to evaluate the respective characteristics of the laminates, their damage tolerance and impact response. All laminates studied were also observed under scanning electron microscopes (SEM) for assessing their processing quality.FCT, Programa MIT Portugal, projeto “IAMAT – Introduction of advanced materials technologies into new product development for the mobility industries

Bioinspired architectures toward improving damage resistance on CFRP laminates

Carbon fibre reinforced polymers (CFRP) are widely used in advanced applications due to their high performance and low weight, however, under certain conditions, they tend to develop internal damages that may compromise the component performance in service. Low velocity impact (LVI) events are one of the most common and dangerous solicitations that CFRP laminates must face during their life time, under these conditions they tend to develop so-called barely visible impact damages (BVID) that may propagate in service. To improve damage tolerance to LVI events, three new bioinspired CFRP laminates were developed and their mechanical properties and impact behaviour were compared to a typical aeronautic standard laminate in this work. All these studied laminates, having approximately the same thickness of 4 mm, were produced by vacuum bag infusion and observed under scanning electron microscopes (SEM) for assessing their processing quality. Tensile, interlaminar shear strength (ILSS) and LVI tests were performed in order to evaluate their Young’s modules, global delamination resistance and impact response. LVI tests were performed for all laminates at the four different impact energy levels of 13.5, 25, 40 and 80 J and damage shape and areas were subsequentially evaluated by ultrasonic C-scan. SEM observations and the good agreement between theoretical and experimental Young’s modules results demonstrated a processing quality. ILSS results have shown that the bioinspired hybrid laminate (HYB) presented better global resistance to delamination when compared to the other laminates. LVI tests and C-scan inspection have also demonstrated that HL and HL_S laminates exhibited higher resistance to damage propagation and smaller damaged area, respectively.FCT, Programa MIT Portugal, projeto “IAMAT – Introduction of advanced materials technologies into new product development for the mobility industries

Strain sensors based on knocked down carbon nanotubes and bucky papers thin films

Recently, carbon nanotubes (CNTs) thin films have been widely applied in sensing applications due to their piezoresistive response. Furthermore, CNT anisotropic electric properties, due to its alignment, can provide useful information regarding strain direction. We present a comparative study between knocked down vertically aligned CNT based sensor, reported in our previous work [1], and CNT bucky papers (BP) based sensors. For this purpose, commercial multi-wall carbon nanotubes (MWCNTs) were dispersed in two different solvents, dimethylformamide (DMF) and ethanol, vacuum filtrated and dried. From these freestanding BP thin films, 10x10 mm squares were cut off and transferred to polyimide (PI) films. The relative electric resistance response and sensitivity of the strained samples was measured and compared with the knocked down CNT/PI based sensor. Moreover, the morphology of the samples was characterized by scanning electron microscopy (SEM). The results showed a high sensitivity to strain, however knocked down CNT/PI based sensor presented better mechanical performance and an anisotropic behaviour that can be used to infer strain direction.FCT, Programa MIT Portugal, projeto "IAMAT (Introduction of Advanced Materials Technologies into New Product Development for the Mobility Industries

Impact damage mitigation using bioinspired CFRP laminate architectures

Carbon fibre reinforced polymers (CFRP) are widely used in advanced applications due to their high performance and low weight. However, when exposed to some conditions, as shear, dynamic and impact loading, they may develop interlaminar damages. One of the most common and dangerous solicitations that they must face in service is low velocity impact (LVI) events. To improve damage tolerance to LVI events, three new bioinspired CFRP laminates were developed and tested in the present work to assess and compare their behaviour to the one presented by a typical aeronautic standard laminate. All these studied laminates, having approximately the same thickness of 4 mm, were produced by vacuum bag infusion and observed under deflexion and scanning electron microscopes (SEM) for assessing their processing quality. Interlaminar shear strength (ILSS) and LVI tests were performed in order to evaluate their delamination resistance and impact response. LVI tests were performed for all laminates at the three different impact energy levels of 13.5 J, 25 J and 40 J. Those tests have shown that the bioinspired hybrid laminate (HYB) and all bioinspired ones presented higher interlaminar shear strength and energy absorption for the 40 J impact energy than the standard CFRP laminate (LS), respectively.FCT projeto do Programa MIT Portugal "IAMAT – Introduction of advanced materials technologies into new product development for the mobility industries

Quasi static mechanical study of vacuum bag infused bouligand inspired composites

Three novel Bouligand inspired composites were produced by vacuum bag infusion manufacturing process and their quasi-static mechanical performance were compared to a conventional aircraft laminate. A morphologic/physical study was first conducted for all configurations and their mechanical response under tensile, three-point bending (3-PB) and interlaminar shear strength (ILSS) tests were then evaluated and discussed. No significant number of voids were detected into laminates, however, a rough and poor defined interlaminar region was observed in both Bouligand-like configurations. Under quasi-static mechanical solicitations, and when compared to reference layup, bioinspired configurations have shown similar and 18% higher tensile and flexural modulus. However, the progressive and translaminar failure mode, typically observed in these configurations, led to a lower load bearing capability. Despite presented similar interlaminar resistance than reference, finite element models built have revealed a good correlation between cross-section stress field and failure mode observed experimentally.Fundação para a Ciência e Tecnologia (FCT), Projetos UIDB/05256/2020, UIDP/05256/2020 e MITP-TB/PFM/0005/201

Aligned carbon nanotube based sensors for strain sensing applications

This paper presents an aligned carbon nanotube (CNT)-based strain sensor. Vertical aligned carbon nanotubes (VA-CNT), synthesized by chemical vapour deposition (CVD), were knocked down onto polymeric films, in order to obtain a thin 10 × 10 × 0.05 mm CNT patch. Different polymeric substrates, ADEXepoxy, polyethylene terephthalate (PET) and polyimide (PI) were used. The samples’ morphology before and after the knock down process, specifically their alignment, was observed by scanning electron microscopy (SEM). The good quality of the synthesized VA-CNT was assessed by Raman spectroscopy. Furthermore, transmission electron microscopy (TEM) analysis was carried out to determine the average wall number and diameters (inner and outer) of the VA-CNT. A MATLAB software with an adapted Van der Pauw method for anisotropic conductors was developed to determine the electric properties of the obtained samples, which were strained in the transverse (X) and parallel (Y) directions with respect to the CNT alignment. The electric anisotropy, defined as electric resistance ratio between obtained measurements along the X (Rxx) and Y (Ryy) -axes, decreases with deformation increment when the sample was strained in the Y-direction, while it increases when strained in the X-direction. Moreover, the obtained Gauge factor values showed a much sensitive response to deformation, i.e., approximately 47% increase in GF values, when the samples are strained transversely to CNT alignment. These results showed that the piezoresistive CNT/polymeric based sensor produced is suitable for strain sensing applications.This work was funded under the project "IAMAT -Introduction of advanced materials technologies into new product development for the mobility industries", with reference MITP-TB/PFM/0005/2013, under the MIT-Portugal program exclusively financed by FCT - Fundacao para a Ciencia e Tecnologia. This work was carried out in part using the Advanced Electron Microscopy, Imaging and Spectroscopy Facility (TEM) of INL - Iberian Nanotechonology Laboratory

Nationwide access to endovascular treatment for acute ischemic stroke in portugal

Publisher Copyright: Copyright Ordem dos M dicos 2021.Introduction: Since the publication of endovascular treatment trials and European Stroke Guidelines, Portugal has re-organized stroke healthcare. The nine centers performing endovascular treatment are not equally distributed within the country, which may lead to differential access to endovascular treatment. Our main aim was to perform a descriptive analysis of the main treatment metrics regarding endovascular treatment in mainland Portugal and its administrative districts. Material and Methods: A retrospective national multicentric cohort study was conducted, including all ischemic stroke patients treated with endovascular treatment in mainland Portugal over two years (July 2015 to June 2017). All endovascular treatment centers contributed to an anonymized database. Demographic, stroke-related and procedure-related variables were collected. Crude endovascular treatment rates were calculated per 100 000 inhabitants for mainland Portugal, and each district and endovascular treatment standardized ratios (indirect age-sex standardization) were also calculated. Patient time metrics were computed as the median time between stroke onset, first-door, and puncture. Results: A total of 1625 endovascular treatment procedures were registered. The endovascular treatment rate was 8.27/100 000 inhabitants/year. We found regional heterogeneity in endovascular treatment rates (1.58 to 16.53/100 000/year), with higher rates in districts closer to endovascular treatment centers. When analyzed by district, the median time from stroke onset to puncture ranged from 212 to 432 minutes, reflecting regional heterogeneity. Discussion: Overall endovascular treatment rates and procedural times in Portugal are comparable to other international registries. We found geographic heterogeneity, with lower endovascular treatment rates and longer onset-to-puncture time in southern and inner regions. Conclusion: The overall national rate of EVT in the first two years after the organization of EVT-capable centers is one of the highest among European countries, however, significant regional disparities were documented. Moreover, stroke-onset-to-first-door times and in-hospital procedural times in the EVT centers were comparable to those reported in the randomized controlled trials performed in high-volume tertiary hospitalspublishersversionpublishe

Different strategies towards the mitigation of low velocity impact damages in advanced composites

Programa doutoral em Ciências e Engenharia de Polímeros e CompósitosOs polímeros reforçados com fibras de carbono (CFRP) são hoje em dia utilizados numa vasta gama de aplicações avançadas, tais como, aeronáutica, aeroespacial e militar. No entanto, e apesar da sua baixa densidade e elevado desempenho mecânico, eles continuam ainda a apresentar algumas debilidades, como a fraca resistência interlaminar. Quando sujeitos a condições de carregamentos dinâmicos, de impacto e de corte, eles tendem a formar no seu interior micro-fissuras que podem propagar-se na região interlaminar, comprometendo desta forma o desempenho mecânico de peça. Numa tentativa de superar este problema, muitas estratégias têm sido estudadas, tais como o reforço através da espessura (por exemplo, preformas fibrosas 3D, Z-pinning e stitching), modificação da matriz e/ou reforço, e ainda reforço interlaminar. Tendo isto em consideração, este trabalho de pesquisa visa estudar diferentes estratégias para melhoria da resistência e tolerância ao dano de compósitos avançados quando submetidos a impactos de baixa velocidade. Para esse fim, um conjunto de novos laminados carbono/epóxi serão produzidos por infusão por vácuo, com o objetivo de comparar e analisar as suas características morfológicas bem como o seu desempenho mecânico. Neste sentido, novas configurações bioinspiradas assim como diferentes estratégias, estruturas e materiais para reforço interlaminar serão consideradas como potenciais abordagens para mitigação do dano para uma nova geração de compósitos laminados. A campanha de teste terá como especial foco testes de impacto de queda de dardo, a fim de avaliar e caracterizar a resistência e tolerância a danos de novos laminados, bem como a sua resposta mecânica. Posteriormente, a fim de avaliar os danos inferido, inspeções visuais e testes não destrutivos (NDT) serão realizados para medir e avaliar o dano dos provetes. Além disso, os compósitos serão caracterizados quanto à sua espessura e fração volúmica dos seus diferentes componentes. Visualizações em microscópicas serão realizadas de modo a instigar a adesão matriz/fibras, morfologia dos laminados e conteúdo de vazios. Também serão realizados ensaios mecânicos quasi-estaticos para avaliar e comparar o desempenho e os modos de falha dos novos compósitos.Carbon fibres reinforced polymers (CFRP) are nowadays widely used in advanced applications, such as aeronautic, aerospace and army. Even though these materials possess light weight and high mechanical performance, they are still presenting some critical weaknesses, namely low interlaminar resistance. When submitted to dynamic, impact and shear loading conditions, they usually tend to develop internal micro-cracks that may propagate throughout the interlaminar region, compromising the whole composite part performance. In order to overcome this problem many strategies have been studied, such as through thickness reinforcements (e.g., 3D-wovens, Z-pinning and stitching), matrix and/or reinforcement modifications, and interlaminar toughening. With this in mind, this research work aims to study different strategies to improve low velocity impact (LVI) damage resistance and tolerance, of advanced laminated composites. To this end, several novel vacuum bag infused carbon/epoxy laminates were manufactured, and their morphologic characteristics and mechanical performances were compared and analysed. Therefore, new bioinspired configurations and different strategies, structures and materials to interleaf conventional laminates were adopted as potential damage mitigation approaches for a new composite laminate generation. Test campaign had specially focus in drop weight impact tests in order to evaluate and characterise new laminates damage resistance and tolerance, as well as their mechanic response. In order to evaluate impact damages, visual inspections and non-destructive testing (NDT) were carried out to measure and evaluate specimens’ damage. Besides this, composites were characterised according their thickness and components volume fraction. Microscopy visualisations were performed to instigate matrix/fibres adhesion, laminates morphology and voids content. In-plane mechanical tests were also performed to evaluate and compare the performances and failure modes of the new composites.To the project “IAMAT—Introduction of advanced materials technologies into new product development for the mobility industries”, with reference MITP-TB/PFM/0005/2013, under the MIT-Portugal program exclusively financed by FCT—Fundação para a Ciência e Tecnologia, for the finantial support