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

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

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

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 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

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.

Experiencias de Aprendizaje-Servicio en la UPM: 2021 y 2022

La Oficina de Aprendizaje-Servicio (ApS) de la UPM, constituida en sesión del Consejo de Gobierno de diciembre de 2019 tiene, como misión fundamental, promover en el ámbito de las enseñanzas de esta universidad la metodología ApS. Con esta finalidad se vienen realizando convocatorias de proyectos de impacto social alineados con los ODS como un mecanismo más para la contribución a la Agenda 2030, y se colabora intensamente con las diversas oficinas constituidas con el mismo objetivo en otras universidades. Nuestra oficina pretende impulsar progresivamente la colaboración con entidades ajenas a la UPM, y atender demandas y necesidades sociales en las que nuestros estudiantes y profesores brinden sus conocimientos para la construcción de una mejor y más justa sociedad. Con este propósito, se han puesto en marcha numerosas iniciativas y colaboraciones con Ayuntamientos, Asociaciones, ONG, Fundaciones y centros de enseñanza, con el fin común de plantear mejoras y trabajar con entornos desfavorecidos, y colectivos vulnerables de nuestro entorno. Cabe destacar la muy positiva acogida que, progresivamente se está logrando, en lo relativo a la diseminación de estas iniciativas en el ámbito de la UPM, viéndose incrementada la participación e interés de nuestros docentes y estudiantes en los llamamientos que se realizan desde la oficina. Desde la constitución de la oficina, son ya más de 100 actividades desarrolladas con la participación de más de 500 profesores. Uno de los compromisos de la Oficina ApS de la UPM es dar visibilidad por su carácter meritorio a las experiencias realizadas por el profesorado y los estudiantes de nuestra universidad y, es por ello, que nos complace la presentación de esta primera edición del ebook, en el que se recogen algunas de las experiencias realizadas en nuestra universidad y que confiamos ampliar periódicamente con futuras ediciones. Nuestro más sincero agradecimiento a todos los profesores que habéis hecho posible esta primera publicación con vuestras contribuciones

Mortality after surgery in Europe: a 7 day cohort study

Background: Clinical outcomes after major surgery are poorly described at the national level. Evidence of heterogeneity between hospitals and health-care systems suggests potential to improve care for patients but this potential remains unconfirmed. The European Surgical Outcomes Study was an international study designed to assess outcomes after non-cardiac surgery in Europe.Methods: We did this 7 day cohort study between April 4 and April 11, 2011. We collected data describing consecutive patients aged 16 years and older undergoing inpatient non-cardiac surgery in 498 hospitals across 28 European nations. Patients were followed up for a maximum of 60 days. The primary endpoint was in-hospital mortality. Secondary outcome measures were duration of hospital stay and admission to critical care. We used χ² and Fisher’s exact tests to compare categorical variables and the t test or the Mann-Whitney U test to compare continuous variables. Significance was set at p<0·05. We constructed multilevel logistic regression models to adjust for the differences in mortality rates between countries.Findings: We included 46 539 patients, of whom 1855 (4%) died before hospital discharge. 3599 (8%) patients were admitted to critical care after surgery with a median length of stay of 1·2 days (IQR 0·9–3·6). 1358 (73%) patients who died were not admitted to critical care at any stage after surgery. Crude mortality rates varied widely between countries (from 1·2% [95% CI 0·0–3·0] for Iceland to 21·5% [16·9–26·2] for Latvia). After adjustment for confounding variables, important differences remained between countries when compared with the UK, the country with the largest dataset (OR range from 0·44 [95% CI 0·19 1·05; p=0·06] for Finland to 6·92 [2·37–20·27; p=0·0004] for Poland).Interpretation: The mortality rate for patients undergoing inpatient non-cardiac surgery was higher than anticipated. Variations in mortality between countries suggest the need for national and international strategies to improve care for this group of patients.Funding: European Society of Intensive Care Medicine, European Society of Anaesthesiology