Aligned carbon nanotube-based sensors for strain monitoring of composites

This paper presents a proof of concept of an aligned carbon nanotube (CNT) based strain sensor tested on the surface of a conventional aeronautic laminate. Two type of strain sensors were produced, type S and type T, in which the CNT alignment was parallel (Y) and transversal (X) to strain direction, respectively. Their electrical resistance response was thoroughly evaluated during cyclic tensile tests. Despite some disparities of the relative electrical resistance behavior in specific strain cycles, probably due to one-off interferences in the CNT conductive mechanism, the obtained gauge factor (GF) values were quite stable. Also, the electrical resistance anisotropy was evaluated and its opposite behavior when the samples were strained in Y- and X-directions may be used as strain direction indicator. Being able to quantify and indicate strain direction with just one 10 x 10 mm CNT patch, this sensor has proven to be suitable for strain sensing applications, namely for structure health monitoring of advanced composites.- Manuscript received March 4, 2021; revised March 25, 2021; accepted March 31, 2021. Date of publication April 5, 2021; date of current version June 30, 2021. This work was supported in part by the Project "Introduction of Advanced Materials Technologies Into New Product Development for the Mobility Industries-IAMAT," under the MIT-Portugal program exclusively financed by Fundacao para a Ciencia e Tecnologia "FCT" under Grant MITP-TB/PFM/0005/2013 and in part by the North Portugal Regional Operational Programme (NORTE 2020) under the Portugal 2020 Partnership Agreements through the European Regional Development Fund (ERDF) Project "Technologies for Sustainable and Smart Innovative Products (TSSiPRO)" under Grant NORTE-01-0145FEDER-000015. The associate editor coordinating the review of this article and approving it for publication was Dr. Cheng-Sheng Huang. (Corresponding author: Ana Raquel Santos.

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

Seedless Cu electroplating on Co-W thin films in low pH electrolyte: early stages of formation

The use of Ta/TaN barrier bilayer systems in electronic applications has been ubiquitous over the last decade. Alternative materials such as Co-W or Ru-W alloys have gathered interest as possible replacements due to their conjugation of favourable electrical properties and barrier layer efficiency at reduced thicknesses while enabling seedless Cu electroplating. The microstructure, morphology, and electrical properties of Cu films directly electrodeposited onto Co-W or Ru-W are important to assess, concomitant with their ability to withstand the electroplating baths/conditions. This work investigates the effects of the current application method and pH value of the electroplating solution on the electrocrystallisation behaviour of Cu deposited onto a Co-W barrier layer. The film structure, morphology, and chemical composition were studied by X-ray diffraction, scanning electron microscopy and atomic force microscopy, as well as photoelectron spectroscopy. The results show that the electrolyte solution at pH 1.8 is incapable of creating a compact Cu film over the Co-W layer in either pulsed or direct-current modes. At higher pH, a continuous film is formed. A mechanism is proposed for the nucleation and growth of Cu on Co-W, where a balance between Cu nucleation, growth, and preferential Co dissolution dictates the substrate area coverage and compactness of the electrodeposited films.Portugal 2020 through European Regional Development Fund (FEDER) in the frame of Operational Competitiveness and Internationalisation Programme (POCI) and in the scope of the project USECoIN with grant number PTDC/CTM-CTM/31953/2017. This work was also supported by FCT, through IDMEC, under LAETA project UIDB/50022/202

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

Combined analysis of weak lensing and X-ray blind surveys

We present a joint weak lensing and X-ray analysis of 4 deg$^2$ from the CFHTLS and XMM-LSS surveys. Our weak lensing analysis is the first analysis of a real survey using shapelets, a new generation weak lensing analysis method. We create projected mass maps of the images, and extract 6 weak-lensing-detected clusters of galaxies. We show that their counts can be used to constrain the power spectrum normalisation $\sigma_8 =0.92_{-0.30}^{+0.26}$ for $\Omega_m=0.24$. We show that despite the large scatter generally observed in the M-T relation derived from lensing masses, tight constraints on both its slope and normalisation $M_*$ can be obtained with a moderate number of sources provided that the covered mass range is large enough. Adding clusters from Bardeau et al. (2007) to our sample, we measure $M_* = 2.71_{-0.61}^{+0.79} 10^{14} h^{-1} M_\odot$. Although they are dominated by shot noise and sample variance, our measurements are consistent with currently favoured values, and set the stage for future surveys. We thus investigate the dependence of those estimates on survey size, depth, and integration time, for joint weak lensing and X-ray surveys. We show that deep surveys should be dedicated to the study of the physics of clusters and groups of galaxies. For a given exposure time, wide surveys provide a larger number of detected clusters and are therefore preferred for the measurement of cosmological parameters such as $\sigma_8$ and $M_*$. We show that a wide survey of a few hundred square degrees is needed to improve upon current measurements of these parameters. More ambitious surveys covering 7000 deg$^2$ will provide the 1% accuracy in the estimation of the power spectrum and the M-T relation normalisations.Comment: MNRAS in press Matches accepted version. References update

Cross preferences and genetic diversity of Psidium interspecific hybrids through morphoagronomic traits and resistance to Meloidogyne enterolobii

Abstract The introgression of M. enterolobii resistance-related genes in guava breeding programs can be compromised by incompatibility among Psidium species. This study aimed to evaluate the female parent preference and genetic diversity of Psidium interspecific hybrids using morphoagronomic traits and resistance to M. enterolobii. There were evaluated cross successes and germination from crosses between accesses of P. cattleyanum, P. guineense and P. guajava and the genetic diversity by Ward-MLM method of hybrids according to descriptors developed for the genus. Crosses were more successful when P. cattleyanum was the female parent. Germination was more successful in crosses involving P. cattleyanum and P. guajava. Four groups were formed. The group IV clustered the most resistant genotypes, composed by genotypes of P. cattleyanum x P. guineense, while the group II was the most susceptible. The groups I and III grouped some genotypes of P. cattleyanum x P. guajava with low levels of susceptibility. There are preferences of female parent species among crosses. Some individuals of groups I and III can be used as source of resistance genes for the breeding program, due the presence of favorable alleles inherited from guava parent. The high susceptibility leads to reduction in root development