The aerospace industry is an ever-evolving field that has seen many technological advances over the past decades. The desire for aircraft to be not only efficient and reliable but also cheaper and safer has brought about many proposals across the industry. One of these advances is towards morphing aircraft wings to make wings lighter, more flexible, aerodynamically efficient and structurally stable. One of the key elements of a morphing wing is sensors that monitor the loads and shape of the wing throughout the flight. Within the framework of the SmartX project, the goal and contribution of this study is on the design and development of novel sensing methods for Structural Health Monitoring. This has been performed with a specific focus on shape sensing and load monitoring. This thesis is focussed towards the design and development of a Structural Health Monitoring tool for adaptive aerospace structures and at the same time to reduce the dependency on a high number of sensors. Within the already available fibre optic sensor techniques an identification was made for demonstrating the potential of a higher performing SHM tool involving the combination of FBG spectral sensing and FBG-Pair interferometric sensing. A proposal is made to have a reliable, robust and cost effective sensing methodology for real time monitoring of morphing structures with a simultaneous focus on the SmartX morphing wing demonstrator. The method developed and demonstrated in this thesis is not limited to aerospace (and morphing) structures and can be extended to other engineering structures. Load carrying structures that undergo deformations/deflections can be monitored provided they are properly calibrated. These include, but are not limited to, rotor blades, masts, beam structures and bridges.@en

This article describes the challenges of integrating smart sensing, actuation, and control concepts into an over-sensed and over-actuated technology integrator. This technology integrator has more control inputs than the expected responses or outputs (over-actuated), and its every state is measured using more than one sensor system (over-sensed). The hardware integration platform is chosen to be a wind tunnel model of a low-speed aircraft wing such that it can be tested in a large university-level wind tunnel. This hardware technology integrator is designed for multiple objectives. The nature of these objectives is aerodynamic, structural, and aeroelastic, or, more specifically; drag reduction, static and dynamics loads control, aeroelastic stability control, and lift control. Enabling technologies, such as morphing, piezoelectric actuation and sensing, and fibre-optic sensing are selected to fulfil the mentioned objectives. The technology integration challenges are morphing, actuation integration, sensor integration, software and data integration, and control system integration. The built demonstrator shows the intended level of technology integration.@en

In this paper, with the final aim of shape sensing for a morphing aircraft wing section, a developed multimodal shape sensing system is analysed. We utilise the method of interrogating a morphing wing section based on the principles of both hybrid interferometry and Fibre Bragg Grating (FBG) spectral sensing described in our previous work. The focus of this work is to assess the measurement performance and analyse the errors in the shape sensing system. This includes an estimation of the bending and torsional deformations of an aluminium mock-up section due to static loading that imitates the behaviour of a morphing wing trailing edge. The analysis involves using a detailed calibration procedure and a multimodal sensing algorithm to measure the deflection and shape. The method described In this paper, uses a standard single core optical fibre and two grating pairs on both the top and bottom surfaces of the morphing section. A study on the fibre placement and recommendations for efficient monitoring is also included. The analysis yielded a maximum deflection sensing error of 0.7 mm for a 347 × 350 mm wing section.

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Abstract: Optical fibre sensors and in particular fibre Bragg gratings (FBG) have received a lot of interest for Structural Health Monitoring in different application fields, such as aerospace, pipeline and civil engineering. FBGs are conventionally used to monitor strain and sometimes temperature. In this paper, we propose a new method for load monitoring of a cantilever plate subjected to point loading. The bending of plate is complex due to the interaction between the axial and transverse bending stiffnesses of the material. We use a novel algorithm for interrogating fibre Bragg grating sensors based on both hybrid interferometry and FBG spectral sensing. The method is demonstrated in this paper using a single-mode optical fibre containing four FBG sensors to estimate both the point loading position and the loading magnitude at an arbitrary location on a 1 m² cantilever plate. The algorithm first utilizes point strain information through spectral sensing as well as strain from interferometric sensing over a long path. The gratings are interrogated using Wavelength Division Multiplexing (WDM). We calibrated the system using an experimental model. This model was then verified by using single point static loading tests and comparing the calculated sensing position with the actual position. The method achieved a good estimation of loading position achieving a measurement error of about 9% in a 2D plane. The analysis discusses the possible sources of inaccuracies. This study forms the basis of our future work involving morphing smart-wing sections for the purpose of load monitoring. Article highlights: A new optical sensing configuration is demonstrated for load and structuralhealth monitoring of cantilever structures.The algorithm successfully estimates the position of an arbitrary load on acantilever plate, with an error of 9%.This methodology will be extended to monitor more complex structures, in-cluding morphing aircraft wing sections.

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This work highlights the smart fibre optic sensing methodology developed and incorporated in the SmartXAlpha morphing wing demonstrator. The sensing technology developed here uses a method of incorporating both hybrid interferometry and FBG spectral sensing. This is achieved using a standard single-core optical fibre. The objective of this method is to be able to estimate the deflections of the morphing modules of the wing using the least amount of grating sensors. Apart from the lab environment, the tests were carried out in the wind tunnel to replicate real flight conditions. This was carried out with a focus on bending and torsional deformations of the morphing modules. The method is shown to achieve good accuracy for deflection sensing and to provide vital information for wing load monitoring purposes. @en

This paper presents a study on trailing edge deflection estimation for the SmartX camber morphing wing demonstrator. This demonstrator integrates the technologies of smart sensing, smart actuation and smart controls using a six module distributed morphing concept. The morphing sequence is brought about by two actuators present at both ends of each of the morphing modules. The deflection estimation is carried out by interrogating optical fibers that are bonded on to the wing’s inner surface. A novel application is demonstrated using this method that utilizes the least amount of sensors for load monitoring purposes. The fiber optic sensor data is used to measure the deflections of the modules in the wind tunnel using a multi-modal fiber optic sensing approach and is compared to the deflections estimated by the actuators. Each module is probed by single-mode optical fibers that contain just four grating sensors and consider both bending and torsional deformations. The fiber optic method in this work combines the principles of hybrid interferometry and FBG spectral sensing. The analysis involves an initial calibration procedure outside the wind tunnel followed by experimental testing in the wind tunnel. This method is shown to experimentally achieve an accuracy of 2.8 mm deflection with an error of 9%. The error sources, including actuator dynamics, random errors, and nonlinear mechanical backlash, are identified and discussed.

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The need for real-time shape sensing techniques have increased with the advent of morphing capable structures. Current Fibre optic shape sensing methods determine the bending or curvature of the structure but fail to provide information of the location of the load being applied due to which the change in shape had occurred @en

Over the years, many shape sensing methods have been developed with technologies including optical fibre, PZT and fringe projection. Among them, optical fibres have gained a lot of attention due to their unobtrusive nature when either surface mounted or embedded in the structure. Optical fibre Bragg gratings (FBG) are currently employed for structural health monitoring in civil and aerospace systems and their shape sensing capabilities have been previously reported. In this paper, we propose a novel fibre optic based shape sensor of an isotropic cantilever beam based on the principles of interferometry and FBG sensing. The method described in this paper uses a standard single core single-mode optical fibre and the least number of sensors to estimate the shape, making it comparatively an inexpensive sensing method. On displacing the beam with an unknown magnitude and at an unknown location along the beam, we are able to demonstrate that we can measure the shape of the displaced beam and the magnitude and location of the force applied. The analysis involves using a calibration method and an iterative calculation to measure the two unknowns. An analytical model based on the known beam theories was used to assess the accuracy of the measurements. The preliminary analysis yielded an accuracy of ±1 mm and ±50 mm for the displacement and location, respectively.

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To design and develop a smart sensing-system for load monitoring, shape sensing and damage detection on a morphing wing structure.@en

Study of the interaction of shear horizontal guided mode with defects in the bend region of an isotropic top hat stiffener is presented. Compared with the SH0 wave in a plate, the shear mode in the bend is dispersive and its wavefield characteristics are affected by the curvature of the bend. The scattering studies showed that the sensitivity of the wave to outer surface cracks in the bend increases with increasing frequency compared to inner surface cracks. Further numerical simulations demonstrated that the shear mode is sensitive to the delamination in the bend due to non-zero transverse shear stress. Results of finite element modeling were validated by experiments and reasonably good agreements were obtained.@en