Free-edge delamination location and growth montoring with an embedded distributed fiber optic network

Delamination is the most characteristic damage found in composite materials. Low velocity impacts may lead to delamination onset, likely to occur during manufacturing processes or in operating service life.Furthermore, areas near the free-edge of the structures,as well as ply drop off and integrated reinforcements have demonstrate a high vulnerability to impacts. This paper focuses on the delamination detection based on an embedded or fixed fiber optic network in a composite laminate. The sensor network uses the Rayleigh scattering through an Optical Backscatter Reflectometer (OBR)that it obtains a continuous strain monitoring on a bare opical fiber. For this purpose, several optical fibers were attached on the structure surface close to the free edge of the specimens in order to identify the first-ply failure and the delamination growth. Experimental results were compared to an ultrasonic C-Scan inspection which present a good agreement with the data of sensor network

Removal of NO at low concentration from air in urban built environments by activated miscanthus biochar

This work presents an innovative and sustainable approach to remove NO emissions from urban ambient air in confined areas (underground parking areas or tunnels) using low-cost activated carbons obtained from Miscanthus biochar (MSP700) by physical activation (with CO2 or steam) at temperatures ranging from 800 to 900 °C. The NO removal capacity of the activated biochars was evaluated under different conditions (temperature, humidity and oxygen concentration) and compared against a commercial activated carbon. This last material showed a clear dependence on oxygen concentration and temperature, exhibiting a maximum capacity of 72.6% in air at 20 °C, whilst, its capacity notably decreased at higher temperatures, revealing that physical NO adsorption is the limiting step for the commercial sample that presents limited oxygen surface functionalities. In contrast, MSP700-activated biochars reached nearly complete NO removal (99.9%) at all tested temperatures in air ambient. Those MSP700-derived carbons only required low oxygen concentration (4 vol%) in the gas stream to achieve the full NO removal at 20 °C. Moreover, they also showed an excellent performance in the presence of H2O, reaching NO removal higher than 96%. This remarkable activity results from the abundance of basic oxygenated surface groups, which act as active sites for NO/O2 adsorption, along with the presence of a homogeneous microporosity of 6 Å, which enables intimate contact between NO and O2. These features promote the oxidation of NO to NO2, which is further retained over the carbon surface. Therefore, the activated biochars studied here could be considered promising materials for the efficient removal of NO at low concentrations from air at moderate temperatures, thus closely approaching real-life conditions in confined spaces.J. Fermoso gratefully acknowledges the financial support from the Comunidad de Madrid through the Talent Attraction Programme (2018-T1/AMB-10023)

Strain monitoring on a composite aircraft cabin with fiber optic sensors

An integral composite aircraft cabin had been instrumented with two different technologies: distributed fiber optic sensors (DFOSs) and Fiber Bragg Gratings (FBGs). This structural test aims at strain field monitoring in any part of structure when cabin pressurization is applied in order to simulate flight conditions. The Distributed fiber optic network used is based on Rayleigh scatter ing using an Optical Backscatter Reflectometer (OBR). The OBR provides a large number of strain sensor s with high spatial and strain accuracy with a plain optical fiber. DFOSs prove to be the most suitable technology for this test due to their capability to cover large areas with an important amount of strain data. Moreover, the technology of Fiber Bragg Grating sensors has been also applied for the monitoring of the cabin structural integrity. This type of sensors enable a continuous monitoring during the pressurization tests. 24 FBG sensors in four fiber optic circuits were installed on cabin surface . This test allows to correlate distributed and discrete fiber optic sensors and evaluate their damage detection capabilities. Several static pressure tests were conducted in order to detec t structural damage and static loads at the cabin structure

Structural health monitoring in aeronautical structures by means of distributed fibre optic sensing networks

Asegurar la fiabilidad de las estructuras aeronáuticas durante toda su vida operativa ha sido siempre uno de los principales retos que se ha ido cumpliendo a través de complejas y minuciosas operaciones de mantenimiento en la aeronave. Por ello, el desarrollo de técnicas de monitorización que aseguren la integridad estructural y sean capaces de predecir un fallo temprano en la estructura, aportaría una mayor fiabilidad de las estructuras basada en el estado real de la misma, a la vez que significaría un importante ahorro en los planes y tareas de mantenimiento de la aeronave. El tema principal de esta tesis se centra en la explotación de los datos de medida distribuida a través de sensores de fibra óptica para la detección de daño en estructuras aeronáuticas. La técnica de medida distribuida seleccionada ha sido aquella que permite la extracción de datos en deformaciones y/o temperatura a través de la medida de la dispersión de Rayleigh en la fibra óptica. Esta técnica, a diferencia del resto de técnicas de medida distribuida, presenta la mayor resolución espacial con relación a la precisión en la medida de deformaciones y temperatura. Por estos motivos, esta reciente y próspera técnica ha abierto nuevas posibilidades en la monitorización de la salud estructural, y especialmente, debido a sus altas prestaciones, en el campo aeronáutico. En esta tesis, la detección de daño a través de la medida distribuida en deformaciones se ha llevado a cabo desde dos puntos de vista: detección de daño local y detección de daño global. Por un lado, la detección de daño local se ha demostrado en diferentes ensayos de laboratorio para servir como base de aprendizaje y validar los algoritmos desarrollados para la detección y localización de daño a través de la medida en deformaciones. Por otro lado, la detección de daño global se ha probado sobre dos paneles de material compuesto rigidizado representativo del fuselaje de una cabina de avión regional. Sobre estas estructuras se ha analizado el crecimiento de daños inducidos artificialmente durante un ensayo a fatiga. A continuación, los paneles han sido ensayados a cortadura para llevar a cabo la detección y localización de pandeo a través de la medida distribuida en deformación y comparándolo a su vez con técnicas convencionales de sensorización. Con esta finalidad se ha desarrollado una nueva metodología basada en la detección de no linealidades a través de la segunda derivada del campo de deformaciones obtenido mediante la técnica de medida distribuida. De igual importancia ha sido la aplicación de un filtro Savitzky-Golay adecuado a los parámetros de condicionamiento de la señal con el objetivo de reducir el ruido generado al obtener las derivadas de la medida. A su vez, esta técnica ha sido comparada con el método clásico de “Bifurcación” para detectar el inicio del pandeo a través de la comparación de medidas de deformación discretas en ambos lados de la estructura. A través de esta tesis se puede concluir que la medida distribuida ofrece múltiples posibilidades para la monitorización de la salud estructural con muy alta resolución y permitiendo explotar los datos de una manera sencilla y eficiente. ----------ABSTRACT---------- Ensuring the reliability of the aeronautical structures throughout its entire operating life has always been one of the most important challenges achieved by complex and thorough aircraft maintenance tasks. Therefore, the development of monitoring techniques to ensure the structural integrity and the ability to predict the structural failure at an early stage would help to improve its reliability. Furthermore, a maintenance plan based on the real aircraft usage leads to significant savings in terms of cost and time. The major subject of this thesis focuses on the exploitation of the data from distributed measurements of fibre optic sensing networks to detect damage in aeronautical structures. Rayleigh scattering-based sensing technique has been selected to obtain strain and/or temperature distributed measurements. This technique, unlike the rest of the distributed sensing techniques by fibre optic sensors, is the one which enables the best spatial resolution regarding the strain and temperature accuracy. This recent and thriving technique has opened up to new possibilities for structural health monitoring, especially due to its performances in the aerospace field. In this thesis, the detection of damage through distributed strain measurements has been addressed from two aspects: local and global damage approaches. On the one hand, the local damage detection approach has been demonstrated in different laboratory tests in order to develop and validate all the algorithms necessary to detect and locate damage from the strain measurements. On the other hand, the global damage detection approach has been evidenced for two composite stiffened panels representative of a cockpit fuselage skin for a regional aircraft cabin. Artificial damages have been induced in both panels in order to analyse its growth throughout a fatigue experimental test. Moreover, panels have also been tested under shear loads to carry out the buckling detection and location by means of distributed strain measurements in comparison to conventional sensing techniques. For this purpose, a novel methodology has been developed based on a non-linear events detection by means of a second derivative analysis of the distributed strain measurements. The application of a Savitzky-Golay filter based on the signal conditioning parameters has become a key to reduce the signal noise generated by the derivatives of the distributed strain measurements. Furthermore, this methodology has also been compared with the so-called “Bifurcation” classic method to detect the buckling onset by comparing discrete strain measurements on both sides of the structure. Finally, this thesis concludes that this technique offers extensive possibilities for structural health monitoring with very high resolution and allowing the data exploitation in a simple and efficient manner

Speciation of mercury in fly ashes by temperature programmed decomposition

[EN] Mercury (Hg) is a toxic trace element which is emitted mostly in gas phase during coal combustion, although some Hg compounds may be retained in the fly ashes depending on the characteristics of the ashes and process conditions. To improve the retention of Hg in the fly ashes a good knowledge of the capture mechanism and Hg species present in the fly ashes is essential. The temperature programmed decomposition technique was chosen to identify the Hg species present in fly ashes obtained from two Pulverized Coal Combustion (PCC) plants and a Fluidized Bed Combustion (FBC) plant. The fly ashes were then used as Hg sorbents in a simulated flue gas of coal combustion and gasification. The Hg compounds found in the fly ash from the FBC plant after elemental mercury retention were mainly HgCl2 and HgSO4. The Hg species present in the two fly ashes from the two PCC plants were HgCl2 and Hg0. The Hg species formed in the coal gasification atmosphere was HgS for all three fly ashes. The only Hg compound identified in the fly ashes after the retention of mercury chloride was HgCl2.The financial support for this work was provided by the projects CTM2004-04252.CO2-02/TECNO and MERG-CT-2004-516524 and the Ministerio de Ciencia e Innovacion (programme of postdoctoral contracts abroad).Peer reviewe

Free-edge delamination location and growth montoring with an embedded distributed fiber optic network

Delamination is the most characteristic damage found in composite materials. Low velocity impacts may lead to delamination onset, likely to occur during manufacturing processes or in operating service life.Furthermore, areas near the free-edge of the structures,as well as ply drop off and integrated reinforcements have demonstrate a high vulnerability to impacts. This paper focuses on the delamination detection based on an embedded or fixed fiber optic network in a composite laminate. The sensor network uses the Rayleigh scattering through an Optical Backscatter Reflectometer (OBR)that it obtains a continuous strain monitoring on a bare opical fiber. For this purpose, several optical fibers were attached on the structure surface close to the free edge of the specimens in order to identify the first-ply failure and the delamination growth. Experimental results were compared to an ultrasonic C-Scan inspection which present a good agreement with the data of sensor network

Structural Health Monitoring in Composite Structures by Fiber-Optic Sensors

Fiber-optic sensors cannot measure damage; to get information about damage from strain measurements, additional strategies are needed, and several alternatives are available in the existing literature. This paper discusses two independent procedures. The first is based on detecting new strains appearing around a damage spot. The structure does not need to be under loads, the technique is very robust, and damage detectability is high, but it requires sensors to be located very close to the damage, so it is a local technique. The second approach offers wider coverage of the structure; it is based on identifying the changes caused by damage on the strain field in the whole structure for similar external loads. Damage location does not need to be known a priori, and detectability is dependent upon the sensor’s network density, the damage size, and the external loads. Examples of application to real structures are given

Strain monitoring on a composite aircraft cabin with fiber optic sensors

An integral composite aircraft cabin had been instrumented with two different technologies: distributed fiber optic sensors (DFOSs) and Fiber Bragg Gratings (FBGs). This structural test aims at strain field monitoring in any part of structure when cabin pressurization is applied in order to simulate flight conditions. The Distributed fiber optic network used is based on Rayleigh scatter ing using an Optical Backscatter Reflectometer (OBR). The OBR provides a large number of strain sensor s with high spatial and strain accuracy with a plain optical fiber. DFOSs prove to be the most suitable technology for this test due to their capability to cover large areas with an important amount of strain data. Moreover, the technology of Fiber Bragg Grating sensors has been also applied for the monitoring of the cabin structural integrity. This type of sensors enable a continuous monitoring during the pressurization tests. 24 FBG sensors in four fiber optic circuits were installed on cabin surface . This test allows to correlate distributed and discrete fiber optic sensors and evaluate their damage detection capabilities. Several static pressure tests were conducted in order to detec t structural damage and static loads at the cabin structure

A-BASE-DE-PROS: una implementación práctica de los Objetivos de Desarrollo Sostenible en la Universidad Politécnica de Madrid

A lo largo de los últimos años hemos visto cómo los Objetivos de Desarrollo Sostenible (ODS) han ido permeando las distintas capas de la sociedad, estableciendo nuevas prioridades tanto en las políticas públicas como en las empresariales. La educación no ha quedado ajena a este cambio, sino que también se está alineando con las metas anteriores. En este capítulo se describen las principales actividades realizadas en el marco del proyecto APS22.2003 “Aprendizaje BAsado en SErvicio DE ODS relacionados con una PROducción y consumo responsableS (A-BASE-DE-PROS)”, en el que el ODS 12 se toma como eje central para concienciar a estudiantes universitarios y de secundaria de la importancia de la Agenda 2030. En general, hemos comprobado que el proyecto ha permitido dar a conocer los ODS y que la mayoría de los estudiantes, tanto universitarios como de secundaria, han valorado la experiencia como positiva.