Composite intelligent à base de fibre de carbone et matrice époxy pour les pales d’éoliennes offshores. Modélisations numérique et analytique en multi-échelles

Smart structures have been developed as to monitor structures that have to operate in demanding industrial applications with includes harsh environments (Aeronautics and aerospace, Civil engineering, nuclear and chemical power plants…), too. Current study is focused on the suggestion of new smart composite materials that can be successfully used for wind blade structures in offshore energy generation farms. Indeed, to bring expectable energy-generation performances, new generation wind blades have to exceed 100m length, which is a hardly achievable target given that actual constitutive composite materials are based on glass-fibers, that are notably known to be very heavy and lacking stiffness. Therefore, the switch to carbon fibers (lighter and stiffer) becomes mandatory. In this thesis, we propose the implementation of a smart composite material that is based on carbon fibers and epoxy matrix (here called parent material). Fiber Optic Sensors (FOS) and Quantum-Resistive Sensors (QRS) will be used for detection of over-strained areas all over the structure. This choice is expected to enable for accurate documentation and instant sending of critical information to engineers. To achieve this goal of development of a new smart material for a critical application in offshore wind generation, we have chosen to illustrate it in a research document that is grouping several aspects, summarized in 5 chapters. The thesis is conducted using numerical and analytical modelings. The document is not having the ambition to be exhaustive. It is intended to present a pragmatic research that emphasize how areas of mechanical weakness can be diagnosed, what are the solutions that can be suggested and how we can support them, what are the issues pertaining to the use of embedded sensors and some experimental results that give appraisal of current performance status and what could be future trends.Les structures intelligentes fondées sur des matériaux composites ont été développées pour surveiller les structures qui doivent fonctionner dans des applications industrielles exigeantes, dans des environnements difficiles comme c’est le cas de l’aéronautique, de l’aérospatiale, du génie civil, des centrales nucléaires et chimiques ...). L'étude actuelle est axée sur la suggestion d’un nouveau matériau composite intelligent qui peut être utilisé avec succès dans les pâles d’éoliennes offshore de nouvelle génération. En effet, pour accentuer leur rendement, les pales de nouvelle génération doivent dépasser une longueur de 100m, ce qui représente actuellement une cible hors d’atteinte étant donné que les matériaux composites constitutifs sont fondés sur des fibres de verre, notamment connues pour être lourdes et dépourvues de rigidité significative. Par conséquent, le passage aux fibres de carbone (plus légères et 3 fois plus rigides) devient obligatoire. Dans cette thèse, nous proposons la mise en place d'un matériau composite intelligent à base de fibres de carbone et de matrice époxy (ici appeler matériau parent). Les capteurs à fibre optique (FOS) et les capteurs à résistance quantique (QRS) seront utilisés pour la détection de déformation dans toute la structure. Ce choix devrait permettre une documentation précise et un envoi instantané d'informations critiques aux ingénieurs. Pour atteindre cet objectif de développement d'un nouveau matériau intelligent pour une application critique dans la production d’énergie éolienne offshore, nous avons choisi de proposer un document de recherche regroupant plusieurs aspects du sujet, résumés en 5 chapitres. La thèse est fondée sur des modélisations numériques et analytiques. Le document n'a pas l'ambition d'être exhaustif. Il est destiné à présenter une recherche pragmatique qui met l'accent sur la façon dont les domaines de faiblesse mécanique peuvent être diagnostiqués, quelles sont les solutions qui peuvent être suggérées et comment nous pouvons les soutenir, quelles sont les questions relatives à l'utilisation de capteurs intégrés et les résultats expérimentaux qui permettent l'évaluation du statut actuel de la performance du matériau et les moyens d’en améliorer les performances

Fatigue Behavior of Smart Composites with Distributed Fiber Optic Sensors for Offshore Applications

Continuous inspection of critical zones is essential to monitor the state of strain within offshore wind blades, thus, enabling appropriate actions to be taken when needed to avoid heavy maintenance. Wind-turbine blades contain various substructures made of composites, sandwich panel, and bond-joined parts that need reliable Structural Health Monitoring (SHM) techniques. Embedded, distributed Fiber-Optic Sensors (FOS) are one of the most promising techniques that are commonly used for large-scale smart composite structures. They are chosen as monitoring systems for their small size, being noise-free, and low electrical risk characteristics. In recent works, we have shown that embedded FOSs can be positioned linearly and/or in whatever position with the scope of providing pieces of information about actual strain in specific locations. However, linear positioning of distributed FOS fails to provide all strain parameters, whereas sinusoidal sensor positioning has been shown to overcome this issue. This method can provide multiparameter strains over the whole area when the sensor is embedded. Nevertheless, and beyond what a sensor can offer as valuable information, the fact remains that it is a “flaw” from the perspective of mechanics and materials. In this article and through some mechanical tests on smart composites, evidence was given that the presence of embedded FOS influences the mechanical behavior of smart composites, whether for quasi-static or fatigue tests, under 3-point bending. Some issues directly related to the fiber-architecture have to be solved

Fatigue Behavior of Smart Composites with Distributed Fiber Optic Sensors for Offshore Applications

Continuous inspection of critical zones is essential to monitor the state of strain within offshore wind blades, thus, enabling appropriate actions to be taken when needed to avoid heavy maintenance. Wind-turbine blades contain various substructures made of composites, sandwich panel, and bond-joined parts that need reliable Structural Health Monitoring (SHM) techniques. Embedded, distributed Fiber-Optic Sensors (FOS) are one of the most promising techniques that are commonly used for large-scale smart composite structures. They are chosen as monitoring systems for their small size, being noise-free, and low electrical risk characteristics. In recent works, we have shown that embedded FOSs can be positioned linearly and/or in whatever position with the scope of providing pieces of information about actual strain in specific locations. However, linear positioning of distributed FOS fails to provide all strain parameters, whereas sinusoidal sensor positioning has been shown to overcome this issue. This method can provide multiparameter strains over the whole area when the sensor is embedded. Nevertheless, and beyond what a sensor can offer as valuable information, the fact remains that it is a “flaw” from the perspective of mechanics and materials. In this article and through some mechanical tests on smart composites, evidence was given that the presence of embedded FOS influences the mechanical behavior of smart composites, whether for quasi-static or fatigue tests, under 3-point bending. Some issues directly related to the fiber-architecture have to be solved

Numerical simulation analysis as a tool to identify areas of weakness in a turbine wind-blade and solutions for their reinforcement

Offshore wind energy is one of the main sources of renewable energy that can benefit from new generation materials that exhibit good oxidation resistance and mechanical reliability. Composite materials are the best consideration for harsh environment and deep sea wind turbine manufacturing. In this study, a numerical simulation was implemented to predict the stress distribution over a wind turbine-blade and to determine areas with high stress concentration. Finite Element Analysis (FEA) was used to find optimal material and bonding techniques to construct the blade. By using Abaqus commercial software, a finite element model of wind turbine blade was analyzed under bending-torsion coupled with a static-load condition in flap-wise direction. Structural damage in critical zones varies according to ply orientation and stack thickness as a result of composite orthotropic nature. This study leads existing scenarios and techniques which would provide a new and better solutions for wind turbine blade designers. The root section and trailing edge were found to be critical zones in the wind turbine blade. The root section failure can be reduced by (1) adjusting the thickness of the structure or increasing the number of plies in the composites laminate stacking and by (2) adjusting the bonding technique to prevent trailing-edge failure. Transverse-stitch method and the carbon cord tying methods are most effective for trailing edge reinforcement. Both solutions are proposed to reduce failures in wind turbine blades and proven by step-by-step numerical study. The goal of this study is to deliver a good reference for wind turbine blade designers and to improve the accuracy during design phase as well as to avoid failure

Fiber Optic Sensor Embedment Study for Multi-Parameter Strain Sensing

The fiber optic sensors (FOSs) are commonly used for large-scale structure monitoring systems for their small size, noise free and low electrical risk characteristics. Embedded fiber optic sensors (FOSs) lead to micro-damage in composite structures. This damage generation threshold is based on the coating material of the FOSs and their diameter. In addition, embedded FOSs are aligned parallel to reinforcement fibers to avoid micro-damage creation. This linear positioning of distributed FOS fails to provide all strain parameters. We suggest novel sinusoidal sensor positioning to overcome this issue. This method tends to provide multi-parameter strains in a large surface area. The effectiveness of sinusoidal FOS positioning over linear FOS positioning is studied under both numerical and experimental methods. This study proves the advantages of the sinusoidal positioning method for FOS in composite material’s bonding

Finer SHM-Coverage of Inter-Plies and Bondings in Smart Composite by Dual Sinusoidal Placed Distributed Optical Fiber Sensors

Designing of new generation offshore wind turbine blades is a great challenge as size of blades are getting larger (typically larger than 100 m). Structural Health Monitoring (SHM), which uses embedded Fiber Optics Sensors (FOSs), is incorporated in critical stressed zones such as trailing edges and spar webs. When FOS are embedded within composites, a ‘penny shape’ region of resin concentration is formed around the section of FOS. The size of so-formed defects are depending on diameter of the FOS. Penny shape defects depend of FOS diameter. Consequently, care must be given to embed in composites reliable sensors that are as small as possible. The way of FOS placement within composite plies is the second critical issue. Previous research work done in this field (1) investigated multiple linear FOS and sinusoidal FOS placement, as well. The authors pointed out that better structural coverage of the critical zones needs some new concepts. Therefore, further advancement is proposed in the current article with novel FOS placement (anti-phasic sinusoidal FOS placement), so as to cover more critical area and sense multi-directional strains, when the wind blade is in-use. The efficiency of the new positioning is proven by numerical and experimental study

Numerical simulation analysis as a tool to identify areas of weakness in a turbine wind-blade and solutions for their reinforcement

Offshore wind energy is one of the main sources of renewable energy that can benefit from new generation materials that exhibit good oxidation resistance and mechanical reliability. Composite materials are the best consideration for harsh environment and deep sea wind turbine manufacturing. In this study, a numerical simulation was implemented to predict the stress distribution over a wind turbine-blade and to determine areas with high stress concentration. Finite Element Analysis (FEA) was used to find optimal material and bonding techniques to construct the blade. By using Abaqus commercial software, a finite element model of wind turbine blade was analyzed under bending-torsion coupled with a static-load condition in flap-wise direction. Structural damage in critical zones varies according to ply orientation and stack thickness as a result of composite orthotropic nature. This study leads existing scenarios and techniques which would provide a new and better solutions for wind turbine blade designers. The root section and trailing edge were found to be critical zones in the wind turbine blade. The root section failure can be reduced by (1) adjusting the thickness of the structure or increasing the number of plies in the composites laminate stacking and by (2) adjusting the bonding technique to prevent trailing-edge failure. Transverse-stitch method and the carbon cord tying methods are most effective for trailing edge reinforcement. Both solutions are proposed to reduce failures in wind turbine blades and proven by step-by-step numerical study. The goal of this study is to deliver a good reference for wind turbine blade designers and to improve the accuracy during design phase as well as to avoid failure