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

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

Carbon nanotubes based multi-directional strain sensor

In this work a new carbon nanotubes (CNT) based multi-directional strain sensor capable of quantifying and indicate strain direction is foreseen. This work investigates the electromechanical behavior of an aligned CNT sensing patch strained at 45◦ in order to validate its multi-directional sensing capability. Vertically aligned CNT forests are produced by chemical vapor deposition (CVD) and then mechanically knocked down onto polyimide (PI) films. Two configurations, diamond (D sample) and square (Sq sample), are considered. The relative electrical resistance (ΔR/R0) and the electrical anisotropy (RB/RA) upon strain increments are analyzed and compared to previous work results (0◦ and 90◦ strain direction). Both 45◦ samples, D and Sq, are sensitive to strain. A correlation between electrical anisotropy behavior and strain direction (0◦, 45◦ and 90◦) is established. The results show that with only an aligned CNT small patch it is possible to quantify and indicate strain in three directions.This work was partially 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 – Fundação para a Ciência e Tecnologia. This work was also co-financed by national funds through FCT – Fundação para a Ciência e Tecnologia, with the scope of projects with references UIDB/05256/2020 and UIDP/05256/2020”

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

Effects of Resistance Exercise on Endothelial Progenitor Cell Mobilization in Women

This study aimed to determine the effect of a single bout of resistance exercise at different intensities on the mobilization of circulating EPCs over 24 hours in women. In addition, the angiogenic factors stromal cell-derived factor 1 (SDF-1α), vascular endothelial growth factor (VEGF), hypoxia-inducible factor 1-alpha (HIF-1α) and erythropoietin (EPO) were measured as potential mechanisms for exercise-induced EPCs mobilization. Thirty-eight women performed a resistance exercise session at an intensity of 60% (n = 13), 70% (n = 12) or 80% (n = 13) of one repetition maximum. Each session was comprised of three sets of 12 repetitions of four exercises: bench press, dumbbell curl, dumbbell squat, and standing dumbbell upright row. Blood was sampled at baseline and immediately, 6 hours, and 24 hours post-exercise. Circulating EPC and levels of VEGF, HIF-1α and EPO were significantly higher after exercise (P \u3c 0.05). The change in EPCs from baseline was greatest in the 80% group (P \u3c 0.05), reaching the highest at 6 hours post-exercise. The change in EPCs from baseline to 6 hours post-exercise was correlated with the change in VEGF (r = 0.492, P = 0.002) and HIF-1α (r = 0.388, P = 0.016). In general, a dose-response relationship was observed, with the highest exercise intensities promoting the highest increases in EPCs and angiogenic factors

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

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

In vitro exposure of acer negundo pollen to atmospheric levels of SO2 and NO2: effects on allergenicity and germination

In the last years, a rising trend of pollen allergies in urban areas has been attributed to atmospheric pollution. In this work, we investigated the effects of SO2 and NO2 on the protein content, allergenicity, and germination rate of Acer negundo pollen. A novel environmental chamber was assembled to exposure pollen samples with SO2 or NO2 at two different levels: just below and two times the atmospheric hour-limit value acceptable for human health protection in Europe. Results showed that protein content was lower in SO2- exposed pollen samples and slightly higher in NO2-exposed pollen compared to the control sample. No different polypeptide profiles were revealed by SDSPAGE between exposed and nonexposed pollen, but the immunodetection assays indicated higher IgE recognition by all sera of sensitized patients to Acer negundo pollen extracts in all exposed samples in comparison to the nonexposed samples. A decrease in the germination rate of exposed in contrast to nonexposed pollen was verified, which was more pronounced for NO2-exposed samples. Our results indicated that in urban areas, concentrations of SO2 and NO2 below the limits established for human protection can indirectly aggravate pollen allergy on predisposed individuals and affect plant reproduction