Determinación de compuestos fenólicos en frutillas (Fragaria x ananassa Duch.) por HPLC con detección por arreglos de diodo (DAD)

simultánea de compuestos fenólicos en muestras de frutillas y estudiar su correlación con el método de Folin-Ciocalteu (F-C). Los análisis se realizaron antes y después de una hidrólisis ácida sobre las muestras, utilizando metanol como extractante, con el objetivo de determinar los compuestos fenólicos libres y conjugados. Las condiciones de hidrólisis ácida (4 mol L-1 HCl, 50 min a 90 °C) demostraron ser aptas tanto para los compuestos fenólicos estándares como para los extractos de frutilla. La fase móvil consistió en un gradiente preparado a partir de ácido fórmico en agua (2%, pH 3) y ácido fórmico en metanol (2%, pH 3), y una velocidad de flujo de 0,7 ml min-1 a 25 °C. La separación se realizó en una columna Supelcosil LCABZ de 150 x 4,6 mm, 5 μm. Los compuestos fenólicos estándares utilizados fueron a) Flavonoides: quercetina, rutina y kaempferol (flavonoles); catequina y epicatequina (flavanoles) y cianidina y pelargonidina (antocianidinas), y b) Ácidos fenólicos: ácidos gálico y elágico (derivados del ácido hidroxibenzoico) y ácidos ferúlico, cumárico y cinámico (derivados del ácido hidroxicinámico). La validación del método, utilizando soluciones estándares de compuestos fenólicos incluyó estudios de linealidad, límites de detección y cuantificación y determinación de la sensibilidad analítica y de calibración. La precisión y exactitud del método se realizó sobre extractos de fruta. Los resultados indicaron que el método desarrollado fue lineal, sensible, preciso y exacto, y que el metanol puede sustituir al acetonitrilo (más comúnmente usado). El método fue empleado para identificar y cuantificar el perfil de compuestos fenólicos en cinco cultivares de frutillas de Italia (Favetta, Camarosa, Chandler, Darselect y Maya) y dos de Argentina (Camarosa y Selva). Las medianas de los compuestos fenólicos (mg 100 g-1 fruta fresca) antes y después de la hidrólisis ácida fueron: ácido gálico (2,79; 10,22), catequina (2,41; 0,95), epicatequina (-; 10,84), ácido ferúlico (-; 1,03), ácido cumárico (-; 1,55); cianidina (-; 4,46), pelargonidina (-; 18,67), rutina (1,00; 0,11), ácido cinámico (0,14; 0,96), ácido elágico (0,75; 11,70), quercetina (-; 0,32) y kaempferol (-; 0,09). Se analizó, además, el contenido fenólico total antes y después de la hidrólisis ácida por el método de F-C. El contenido de compuestos fenólicos obtenidos para los siete cultivares de frutillas estuvieron dentro de los rangos reportados por otros investigadores. Por otra parte, el contenido fenólico total obtenido como la suma de cada compuesto fenólico analizado por HPLC-DAD, presentó buena correlación con el contenido fenólico total analizado por el método de F-C, antes (0,73) y después de la hidrólisis ácida (0,86)

On the Challenges of Upscaling Damage Monitoring Methodologies for Stiffened Composite Aircraft Panels

Health management methodologies for condition-based maintenance are often developed using sensor data collected during experimental tests. Most tests performed in laboratories focus on a coupon level or flat panels, while structural component testing is less commonly seen. As researchers, we often consider our experimental tests to be representative of a structure in a final application and consider the developed methodologies to be transferrable to these real-life structures. Yet, structures in their final applications such as wind turbines or aircraft are often larger, more complex, might contain various assembly details, and are loaded in complex conditions. These factors might influence the performance of developed diagnostic and prognostic methodologies and should therefore not be ignored.In our work, we consider the aspects of upscaling structural health monitoring (SHM) methodologies for stiffened composite panels with the design of the panels inspired by an aircraft wing structure. For this, we examine two levels of panels, namely a single- and multi-stiffener composite panel, where we consider the single-stiffener panel to be a representative lower-level version of the multi-stiffener panel. Multiple SHM sensors (acoustic emission, Lamb waves, strain sensing) were installed on both composite panels to monitor damage propagation during testing. We identify and analyse challenges and further discuss considerations that must be taken during upscaling of diagnostics and prognostics, and with that, aid in the development of health management methodologies for condition-based maintenance

Strategies for Embedding Optical Fiber Sensors in Additive Manufacturing Structures

The use of optical fiber sensors (OFS) has spread in the Structural Health Monitoring (SHM) community for their ability to detect many different physical quantities, robustness against electromagnetic disturbances, light weight and embedding possibilities. The last point has been widely investigated for different types of materials, but only recently researchers considered the possibility to embed optical fibers in 3D printed structures. Additive Manufacturing (AM) offers new opportunities in terms of design, for the manufacturing of structures with complex geometries in a relatively low amount of time. However, new challenges must be considered, including innovative embedding solutions for different types of sensors. As a first step, this work discusses current embedding strategies for optical fiber sensors in structures produced with the Fused Deposition Modeling (FDM) technique. A novel methodology to embed OFS is introduced and then tested through the production of specimens at three different filling densities and six different loads. The experimental results, where both distributed OFS and strain gauges were used, were also compared with the data obtained from a numerical model developed in Abaqus/CAE in which the filling pattern of the specimens was accurately reproduced. Finally, the results were critically discussed, highlighting both agreements and discrepancies with respect to the expected data

Preliminary experimental study on the electrical impedance analysis for in-situ monitoring of the curing of carbon/epoxy composite material for aeronautical and aerospace structures

International audienceThis paper concerns the electrical characterization of T700/M21 unidirectional composite materials using sensors developed specifically for this study. It proposes a reliable and reproducible protocol for the characterization of the material during curing. Prior to the characterization, an analysis was carried out to assess the impact of parasitic access elements (resistance of the electrode/fibre interface or of the feed wire), which was reduced to a minimum by appropriate dimensioning of the electrodes. A study of the electrical conduction in relation to the direction of the fibres made it possible to establish a suitable approach to homogenized measurement of the material. Thermo-electric coupling by self-heating was also evaluated, with a view to obtaining measurements that were not influenced by this phenomenon. Finally, the use of electrical impedance spectral analysis allowed in-situ monitoring of the curing process. The results obtained are compared with those of a rheological analysis of the same material. These results highlight the value of the proposed protocol and demonstrate that, with the aid of these sensors, complete automation of the manufacturing process of composite structures is feasible (optimization of the cure cycle by real-time automatic control)