Leyes cohesivas en uniones adhesivas: ensayo de desgarro/pelado para la caracterización de películas adhesivas delgadas

Para poder predecir la resistencia de una unión adhesiva de manera precisa es necesario disponer de información adecuada sobre las propiedades mecánicas del adhesivo. Por tanto, es fundamental desarrollar métodos de ensayo fiables para determinar el comportamiento constitutivo de las capas adhesivas. En su uso más habitual, los adhesivos se disponen en películas delgadas. Un adhesivo trabajando en una película delgada se comporta de manera muy diferente de como lo haría el mismo adhesivo en masa. Cuando es cargado, el tamaño de la Zona de Proceso de Fallo (ZPF) en el adhesivo es frecuentemente de mayor tamaño que el espesor de la propia película adhesiva. Por tanto, la condición de una ZPF de pequeño tamaño no se cumple y, por consiguiente, no es aplicable la Mecánica de la Fractura Elástica y Lineal (MFEL). Al mismo tiempo, los experimentos demuestran que las probetas de ensayo tienen tendencia a producir propagación inestables de la grieta, dando lugar a la aparición frecuente de patrones de fallo combinados adhesivo/cohesivo, especialmente cuando la solicitación se realiza en modo mixto (pelado/cortadura). Las leyes de comportamiento cohesivo deben ser tomadas como las propiedades de fractura básicas para la caracterización del adhesivo; las leyes cohesivas han de ser obtenidas experimentalmente. Los efectos de la velocidad de solicitación y del espesor de la capa adhesiva sobre la forma de la ley cohesiva pueden ser investigados de forma experimental. El acoplamiento de los fenómenos de elasticidad, adhesión y fractura hace difícil la interpretación de los resultados de los ensayos, especialmente si el adhesivo es un elastómero, que tiene una deformación de varios cientos por ciento antes de fallar. Un nuevo ensayo, que combina el desgarro del adhesivo y el pelado de la película de su substrato, hace uso de la simplicidad de la geometría para aplicar una metodología de análisis de resultados que desacopla los tres fenómenos. Los valores obtenidos permiten elucidar la rigidez, el trabajo de fractura y la energía adhesiva del sistema adhesivo, que juegan un papel fundamental de manera concurrente durante el ensay

Determination of the mixed-mode fracture energy of elastomeric structural adhesives: evaluation of debonding buckling in fibre-metal hybrid laminates

Fibre–metal hybrid laminates combine layers of metal with laminates made of composites – polymeric matrix reinforced with glass-fibre woven fabric. Interface behaviour plays a fundamental role in the overall properties of the hybrid material, especially in the failure mode by debonding buckling of the outermost metal layer. A proper measurement of adhesive fracture energy is required so as to avoid this early failure mechanism during bending. Tapered double cantilever beam test and dissimilar mixed-mode bending test have been used in obtaining mode I and II contributions to the adhesive fracture energy. Data reduction for elastomeric adhesives has been modified in order to account for the variation in compliance during the test due to nonlinear behaviour of the material

MaLECoN: un nuevo material híbrido laminado fibra-metal para construcción naval.

Existe la necesidad perentoria de nuevos materiales para construcción naval que sean capaces de satisfacerlos requerimientos de diseño y fabricación de estructuras más ligeras, a la vez que resistentes, que permitan velocidades de desplazamiento más elevadas y menores consumos energéticos. El acero presenta una serie de limitaciones que dificultan la mejora continuada en la línea marcada para la fabricación de estructuras ligeras, resistentes y seguras. Los materiales compuestos son livianos y resistentes, pero los sistemas de fabricación son costosos y precisan de más mano de obra especializada; por otra parte, son muy sensibles al daño por impacto y pueden presentar problemas de degradación de sus propiedades mecánicas debido a la absorción de agua. Los materiales híbridos laminados fibra-metal combinan la elevada resistencia al impacto y la durabilidad, junto a la versatilidad en los procesos productivos propios de los materiales metálicos, con la resistencia y rigidez específicas en la dirección de las fibras, así como un buen comportamiento a fatiga, característica de los materiales compuestos. El material híbrido multicapas está formado por láminas metálicas alternando con otras de material compuesto y de adhesivo estructural, consiguiéndose prestaciones en servicio mejoradas. Este material ha sido patentado en la Oficina Española de Patentes y Marcas, junto con su procedimiento de fabricación. La extensión internacional de la patente a más de treinta países ha sido ya presentada y está siguiendo el procedimiento de concesión

The E-ELT first light spectrograph HARMONI: capabilities and modes

Trabajo presentado en SPIE Astronomical Telescopes, celebrado en San Diego (California), del 26 de junio al 1 de julio de 2016HARMONI is the E-ELT's first light visible and near-infrared integral field spectrograph. It will provide four different spatial scales, ranging from coarse spaxels of 60 × 30 mas best suited for seeing limited observations, to 4 mas spaxels that Nyquist sample the diffraction limited point spread function of the E-ELT at near-infrared wavelengths. Each spaxel scale may be combined with eleven spectral settings, that provide a range of spectral resolving powers (R 3500, 7500 and 20000) and instantaneous wavelength coverage spanning the 0.5 - 2.4 ¿m wavelength range of the instrument. In autumn 2015, the HARMONI project started the Preliminary Design Phase, following signature of the contract to design, build, test and commission the instrument, signed between the European Southern Observatory and the UK Science and Technology Facilities Council. Crucially, the contract also includes the preliminary design of the HARMONI Laser Tomographic Adaptive Optics system. The instrument's technical specifications were finalized in the period leading up to contract signature. In this paper, we report on the first activity carried out during preliminary design, defining the baseline architecture for the system, and the trade-off studies leading up to the choice of baseline

Construction progress of WEAVE: the next generation wide-field spectroscopy facility for the William Herschel Telescope

We present an update on the overall construction progress of the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT), now that all the major fabrication contracts are in place. We also present a summary of the current planning behind the 5-year initial phase of survey operations, and some detailed end-to-end science simulations that have been effected to evaluate the final on-sky performance after data processing. WEAVE will provide optical ground-based follow up of ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multi-object (MOS) fibres, 20 integral field units, or a single large IFU for each observation. The fibres are fed to a single (dual-beam) spectrograph, with total of 16k spectral pixels, located within the WHT GHRIL enclosure on the telescope Nasmyth platform, supporting observations at R 5000 over the full 370-1000nm wavelength range in a single exposure, or a high resolution mode with limited coverage in each arm at R 20000. The project has experienced some delays in procurement and now has first light expected for the middle of 2019

COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study

Background: The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms. Methods: International, prospective observational study of 60 109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms. Results: ‘Typical’ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (≤ 18 years: 69, 48, 23; 85%), older adults (≥ 70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each P < 0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country. Interpretation: This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men

Upcycling of agricultural residues for additive manufacturing: corn straw waste as reinforcing agent in acrylonitrile-butadiene-styrene composite matrix

More than 1.2 billion tonnes of corn straw wastes (CSW) are generated worldwide each year. CSW is a fibrous, inexpensive, light material which is highly available. Currently, there are no pathways to manage such amount of CSW, being mainly burned in open field, with the environmental impact that this entails. In this work, the upcycling of CSW as a reinforcement material to be integrated in acrylonitrile-butadiene-styrene (ABS) composite matrix for additive manufacturing applications is proposed. ABS+CSW composite material has been used to manufacture 3D printing filaments, aiming to fabricate products via fused filament fabrication techniques. Standardized tensile and flexural test specimens were manufactured incorporating different contents of CSW (ranging from 1 to 5%, w/w) and glycerol (1%, w/w) to ABS: B1-1% (sample with 1% (w/w) of CSW), B2-3% (sample with 3% (w/w) of CSW), and B3-5% (sample with 5% (w/w) of CSW). The maximum tensile stress of the composites slightly increased by 1.3% (for B1-1%), exceeding 10% when B1-3% was used, compared to ABS. Moreover, it decreased to −3% for the specimen made with B3-5. In general terms, the higher the biomass content, the higher the flexural stress. However, the exception was provided by B1-1%, as the flexural stress decreased by 5% compared to ABS. The maximum flexural stress value was reached at 3% SCW, providing a value above 17%, compared to ABS and above 24%, compared to B1-1%. Furthermore, the incorporation of CSW into the ABS matrix resulted in lighter 3D printing filament materials and products compared to the use of ABS