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## Über dieses Buch

The book includes the research papers presented in the final conference of the EU funded SARISTU (Smart Intelligent Aircraft Structures) project, held at Moscow, Russia between 19-21 of May 2015. The SARISTU project, which was launched in September 2011, developed and tested a variety of individual applications as well as their combinations.

With a strong focus on actual physical integration and subsequent material and structural testing, SARISTU has been responsible for important progress on the route to industrialization of structure integrated functionalities such as Conformal Morphing, Structural Health Monitoring and Nanocomposites.

The gap- and edge-free deformation of aerodynamic surfaces known as conformal morphing has gained previously unrealized capabilities such as inherent de-icing, erosion protection and lightning strike protection, while at the same time the technological risk has been greatly reduced. Individual structural health monitoring techniques can now be applied at the part-manufacturing level rather than via extending an aircraft’s time in the final assembly line. And nanocomposites no longer lose their improved properties when trying to upscale from neat resin testing to full laminate testing at element level.

As such, this book familiarizes the reader with the most significant develo

pments, achievements and key technological steps which have been made possible through the four-year long cooperation of 64 leading entities from 16 different countries with the financial support of the European Commission.

## Inhaltsverzeichnis

### SARISTU: Six Years of Project Management

SARISTU—Smart Intelligent Aircraft Structures—is a large, integrated research and technology project funded by the European Union as part of its 7th Framework Programme. This paper investigates some of the key project management decisions taken in the initiation, preparation and conduct of the project in order to assess the effectiveness of individual management principles, measures and activities. In particular, it investigates the effectiveness of lean project planning when coupled with a bottom-up change process, the impact of structured quality gates in the form of both regular peer reviews as well as progress-driven design reviews. In order to do so, it exploits the one-dimensional nature of “Quality, Time, Cost” and investigates the impact of this principal project management philosophy on a project. Supporting this, the paper outlines the specific deliverable dashboard methodology followed and gives an insight into practical research and development management within a Technology Readiness Level framework. Including a short analysis of financial considerations, the paper concludes by providing some key lessons learned for prospective future managers of large, integrated and hardware-based research and technology projects.

Piet Christof Wölcken, Andreas Kötter, Ben Newman, Rebecca Wadleich, Katrin Genzel

### Morphing Wing Integrated Safety Approach and Results

SARISTU morphing wing is mainly based on three devices: enhanced adaptive droop nose (EADN), adaptive trailing edge device (ATED) and winglet active trailing edge (WATE). All these devices are used together to improve the overall wing efficiency and to reduce the aerodynamic noise. The safety activities described in this paper were performed to verify whether this concept can comply with the standard civil flight safety regulations and airworthiness requirements. The safety analysis was performed in two steps: a functional hazard assessment (FHA) and a system safety assessment (SSA). Both analyses were performed at wing integration level (IS12) and at single morphing wing devices level. A complete mapping between these two levels of analysis was structured from the beginning of the process, starting from the aircraft functional definition, to integrate and harmonize both FHA and fault trees results. FHA was used to assess the severity of the identified Failure Conditions and then allocate safety requirements. Fault tree modelling technique was used to verify the compliance of the system architectures to the quantitative safety requirements resulting from the FHAs. The paper sets out the hypotheses and common data used by the fault trees. A complete but simple example illustrates the safety approach all through the different steps of the safety methodology. Other safety activities commonly performed in the aeronautical field such as the particular risk analysis (PRA), common mode analysis (CMA) and zonal safety analysis (ZSA) were identified in the frame of SARISTU project. This paper concludes with a summary highlighting the main results of these safety activities with some lessons learned from the safety approach adapted to SARISTU context.

Maurizio Verrastro, Sylvain Metge

### Development and Validation of a Bird Strike Protection System for an Enhanced Adaptive Droop Nose

In the frame of IS12 wing integration scenario of the SARISTU project, SONACA was incharge of the development and the validation of bird strike protection systems integrated into an enhanced adaptive droop nose. Numerical simulations were used to elaborate solutions insuring both the downstream actuation (actuator tube) and the spar integrity adding a constraint on system space allocation and converge towards two relevant “iso-mass” concepts: a bird splitter concept and a bird absorber concept. Nonlinear finite elements analyses (NLFEA) using ABAQUS/Explicit were also performed prior the bird strike physical testings to support the test definition and to predict the impact scenario on the structures. With the principal objective to evaluate the efficiency of the bird strike protection systems (BSPS), the bird impact test campaign took place in VZLU test facilities on 21 and 22 April 2015. Three specimens were assembled and subjected to bird impact tests. Two of those specimens were used to compare the behaviour and the efficiency of the splitter and the absorber at “iso-mass” solutions. The third and fourth tests were performed on a representative EADN leading edge structure connected to actuation systems and containing a morphing outer skin in front of a bird strike splitter protection system. Amongst the two investigated BSPS, the bird splitter concept has demonstrated a better efficiency than the bird absorber concept for the assessment of the spar integrity requirement. In a global point of view, except for the bird absorber concept, the test results are in very good agreement with the predicted numerical simulation results. Moreover, all the shots were performed in very good tolerances with no deviations from requirements.

Charles Chary

### Testing Overview of the EADN Samples

The several EADN leading edges were developed and assembled in the application scenario AS01 in the European SARISTU project. VZLU manufactured kinematic parts for wind tunnel model including auxiliary spar and assembled this test article. The functional test was performed for verification of the droop nose components. The second one, longer EADN was assembled for ground testing. All kinematic parts including auxiliary spar were also manufactured at VZLU. The functional test, static test of bending and cyclic test were performed on developed, manufactured and assembled test stand. All tests proved high-quality manufactured parts including the whole assembly and well-satisfied functionality of EADN. The third leading edge with manufactured kinematic parts was assembled for bird strike test. The bird strike tests of leading edge and two splitters were performed at VZLU too. This contribution is the description of assemblies of leading edges and overview of performed testing including results evaluation.

### Enhanced Adaptive Droop Nose—from Computer Model to Multi-functional Integrated Part

The INVENT GmbH rises in the EU project SARISTU under the lead of Airbus and in cooperation with project partners to the challenge to manufacture a composite gapless and flexible droop nose (enhanced adaptive droop nose, EADN) on the basis of computer models and in compliance with standards and requirements of industrial integration. Therefore, various individual disciplines are integrated into one single manufacturing process and, thus, into one multi-functional part. This is an iterative process which develops along the entire range of structural engineering from material and substructure specimen and tests to the design of tooling and processes. Regarding the industrial integration of the morphing wing leading edge, the individual technical disciplines such as protection against erosion, lighting strike and bird strike as well as deicing were selected for SARISTU. Based on the overall design activities of the DLR, INVENT integrates the surface protection of Airbus Group Innovations, deicing of GKN and lightning strike protection into a flexible composite structure.

Olaf Heintze, Stefan Steeger, Alexander Falken, Jürgen Heckmann

### Assessment of the SARISTU Enhanced Adaptive Droop Nose

For the application of laminar flow on commercial aircraft wings, the high-lift devices at the leading edge play a major role. Since conventional leading edge devices like slats do not comply with the high surface quality requirements needed for laminar flow, alternative concepts must be developed. Besides the conventional Krueger device that enables laminar flow on the upper side of the airfoil and additionally implicates an insect shielding functionality, smart droop nose devices are currently being investigated. However, the research on such morphing devices that can deform to a given target shape and provide a smooth, high-quality surface has to give answers to questions of fundamental industrial requirements like erosion protection, anti-/de-icing, lightning strike protection, and bird strike protection. The integration of these functionalities into a given baseline design of a morphing structure is a key challenge for the realization of such devices in the future. This paper focuses on the design drivers, system interdependencies, and effects of the integration of the mentioned functionalities into a smart droop nose device.

Markus Kintscher, Johannes Kirn, Stefan Storm, Fabian Peter

### Adaptive Trailing Edge: Specifications, Aerodynamics, and Exploitation

ATE functional aim is to modify the wing TE shape at high speed in order to obtain an improvement in lift over drag (LoD) ratio in the whole flight envelope, virtually obtaining a wing working always at its actual LoD optimum level. This allows to compensate the weight reduction following the fuel burning and to increase climb and descent A/C performance levels. Initial morphed shapes specification has been obtained by a multidisciplinary optimization process matching the aerodynamic performances and structural loads on wing with a defined level of structural strain for an acceptable duration of skin material life cycle. The so obtained different wing seamless shapes have been further parametrically investigated from aerodynamic point of view so to obtain the most profitable device span and chord extension. Based on these requirements, a full-scale ATE functional concept demonstrator has been designed, sized, and realized, based on reference wing geometry of a 130 Pax jet engines regional A/C with a range of 3000 nautical miles, cruise Mach 0.75, and flight level 35,000 ft. Reference wing aerodynamic studies show the best ATE performances in a relatively high CL range (above 0.5) and for Mach below 0.6. Additional exploitation of ATE has been performed on a light business jet, designed to carry 4 passengers at a speed of Mach 0.65, or fly 1200 nm with 2 passengers. CL range of this A/C is relatively small (below 0.6). In this wing working range, the ATE application seems not to be effective.

Giovanni Marco Carossa, Sergio Ricci, Alessandro De Gaspari, Cedric Liauzun, Antoine Dumont, Moshe Steinbuch

### Structural Design of an Adaptive Wing Trailing Edge for Large Aeroplanes

The structural design process of an adaptive wing trailing edge (ATED) was addressed in compliance with the demanding requirements posed by the implementation of the architecture on large aeroplanes. Fast and reliable elementary methods combined with rational design criteria were adopted in order to preliminarily define ATED box geometry, structural properties, and the general configuration of the embedded mechanisms enabling box morphing under the action of aerodynamic loads. Aeroelastic stability issues were duly taken in account in order to safely assess inertial and stiffness distributions of the primary structure as well as to provide requirements for the actuation system harmonics. Results and general guidelines coming from the preliminary design were then converted into detailed drawings of each box component. Implemented solutions were based on designer’s industrial experience and were mainly oriented to increase the structural robustness of the device, to minimize its manufacturing costs, and to simplify assembly and maintenance procedures. The static robustness of the executive layout was verified by means of linear and nonlinear stress analyses based on advanced FE models; dynamic aeroelastic behaviour of the stress-checked structure was finally investigated by means of rational analyses based on theoretical mode association.

Rosario Pecora, Marco Magnifico, Francesco Amoroso, Leonardo Lecce, Marco Bellucci, Ignazio Dimino, Antonio Concilio, Monica Ciminello

### Distributed Actuation and Control of a Morphing Wing Trailing Edge

In a morphing wing trailing edge device, the actuated system stiffness, load capacity, and integral volumetric requirements drive flutter, actuation strength, and aerodynamic performance. Design studies concerning aerodynamic loads, structural properties, and actuator response provide sensitivities to aeroelastic performance, actuation authority, and overall weight. Based on these considerations, actuation mechanism constitutes a very crucial aspect for morphing structure design because the main requirement is to accomplish variable shapes for a given trailing edge structural mechanism within the limits of the maximum actuation torque, consumed power, and allowable size and weight. In this work, a lightweight and compact lever driven by electromechanical actuators is investigated to actuate the morphing trailing edge device. An unshafted distributed servoelectromechanical actuation arrangement driven by a dedicated control system is deployed to realize the transition from the baseline configuration to a set of design target ones and, at the same time, to withstand the external loads. Numerical and experimental investigations are detailed to demonstrate system effectiveness and reliability using a feedback sensing data from integrated FBG sensors.

Ignazio Dimino, Monica Ciminello, Antonio Concilio, Rosario Pecora, Francesco Amoroso, Marco Magnifico, Martin Schueller, Andre Gratias, Avner Volovick, Lior Zivan

### Elastomer-Based Skin for Seamless Morphing of Adaptive Wings

Elastomeric materials are developed for adaptive wings focusing on the elasticity at minus 55 °C to ensure morphing at cruise altitudes. In order to optimize fatigue and ageing properties of this new multi-material device, FEM simulations and mechanical tests are carried out. Two large skin panels are finally manufactured and successfully assembled into a true-scale wind tunnel demonstrator for the experimental validation of adaptive trailing edge device functionality in simulated operative conditions.

Oliver Schorsch, Andreas Lühring, Christof Nagel

### Manufacturing and Testing of Smart Morphing SARISTU Trailing Edge

Increasing environmental awareness and increasing fuel prices push aircraft industry to enhance aircraft efficiency. Morphing is considered a promising technology for future and next-generation aircrafts. Morphing aircraft changes its external geometry significantly during flight which moderates the design requirements. Adaptive Trailing Edge Device (ATED) is designed and manufactured under SARISTU (Smart Intelligent Aircraft Structures) project. The main challenge is to design and manufacture the smart ATED structure able to support the necessary loads, but it is also capable of changing its geometry. The structure design and actuation system are interrelated. Integration methodology drives multi-disciplinary thinking group from the preliminary design phase. In essence, this considerably amplifies the overall complexity of this work. After manufacturing the ATED, functionality tests have been performed successfully.

Yasser Essa, Federico Martin de la Escalera Cutillas, Ignazio Dimino, Monica Ciminello, Antonio Concilio

### Design, Optimization, Testing, Verification, and Validation of the Wingtip Active Trailing Edge

Andreas Wildschek, Stefan Storm, Martin Herring, Danijel Drezga, Viken Korian, Olaf Roock

### Winglet Design, Manufacturing, and Testing

With respect to the SARISTU project (Smart Intelligent Aircraft Structures), a wingtip active trailing edge (WATE) within the application scenario AS03 has been developed. Full-scale demonstrator has been manufactured and successfully tested to prove the maturity of such a device and its technology. This paper contributes to the overview of design, manufacturing, and testing aspects of WATE demonstrator.

Danijel Drezga, Viken Korian, Olaf Roock, Bernardo Lopez, Arne Fiedler, Stefan Storm, Vladimir Snop

### Seamless Morphing Concepts for Smart Aircraft Wing Tip

Morphing concepts were investigated for a wingtip with active trailing edge (WATE) in an adaptive wing. The basic functionality is to take up geometric gap changes in order to maintain a smooth transition between connected parts. A specific material was tailored in order to meet a set of initially formulated requirements, which involve low modulus, high fatigue life, and stability against physical aging in a temperature range from −55 to +80 °C. A variety of material samples and joints were prepared and tested in order to provide a database for numerical simulation and sizing. One of the proposed solutions was developed until the physical sub-component level. Finally, morphing parts were prepared and delivered for assembly in ground test and true-scale wind tunnel demonstrators.

Christof Nagel, Arne Fiedler, Oliver Schorsch, Andreas Lühring

### Dynamic Aircraft Model with Active Winglet, Effects of Flight Mechanics and Loads Analysis

This paper presents the background, development, and applications of simplified loads models for characterizing the loads related to SARISTU activities in application scenario AS03. The models have been developed from the initial SARISTU wing model of Alenia Aermacchi (AAM). A mass model of the fuel has been reconstructed from the aircraft data, and an aircraft model has been developed using an aircraft sizing tool. With the completion of the winglet design, the SARISTU winglet and the winglet active trailing edge (WATE) model have also been integrated in the loads model. The loads analysis for design purposes includes manoeuvre as well as gust loads. To support the evaluation of WATE device for the gust load alleviation system (GLAS), a state-space aeroservoelastic model of the SARISTU aircraft is developed. The methodologies and models developed within SARISTU have been successfully employed in the design of GLAS and WATE controller optimization and investigations to verify possible wing structure mass reductions. The approach and dynamic loads models developed in SARISTU can be applied straightforward in future R&D projects for structure loads assessments (aeromechanical), control design and optimization, loads, and Structural Health Monitoring (SHM).

Toni Kanakis, Bimo Prananta, Hans van Tongeren, Rob Huls

### Influence of H 2 and $${{\mathcal{L}}}_{\infty }$$ Criteria on Feed-Forward Gust Loads Control Optimized for the Minimization of Wing Box Structural Mass on an Aircraft with Active Winglets

This chapter presents the estimation of potential wing box mass saving enabled by means of active loads alleviation on a regional aircraft equipped with winglet control surfaces. As for the investigated aircraft, the inner wing is sized by maneuvers, and the minimization of structural weight of the wing box by active gust loads alleviation primarily affects the outer wing. Vice versa the minimization of structural weight of the inner wing can mainly be achieved by maneuver loads alleviation. The presented loads alleviation optimization directly minimizes the wing box mass required to sustain maneuver and gust loads. It is shown that the choice of the cost function has a significant influence on this optimum and the resulting wing box mass. Both

H

2

and

$${\mathbf{\mathcal{L}}}_{\infty }$$

criteria are investigated. Based on the optimization results, a potential total wing box mass saving is proposed for further aircraft performance assessment.

Andreas Wildschek

### Evaluation of the Performance Benefits of the Winglet Active Trailing Edge in AS03

An engineering demonstrator of the winglet active trailing edge (WATE) concept was manufactured by AS03 partners in SARISTU. In parallel, simulation activities were used to investigate the performance benefits of active winglets. A study made by AS03 partners (led by AGI-G) assessed the capacity of the WATE—with a suitably designed controller—to alleviate loads due to gust encounters, and this was used to estimate a structural mass saving of around 2 %. A separate study (performed by AGI-UK and ONERA) investigated the potential for an improvement of the lift-to-drag ratio for off-design conditions. This paper brings together the benefits of the structural mass reduction, and the lift-to-drag improvement, using a form of the well-known Breguet range equation to make estimates of the fuel that can be saved over a given mission. This has been combined with typical fleet operation statistics to estimate that the WATE concept (including the structural mass saving effects) could deliver a 1 % reduction in daily fuel costs for a representative airline fleet. For much of the analysis, simplifying assumptions and models have been used in order to meet the project time and cost objectives. Uncertainty in the precise level of benefit is a risk associated with further development of the WATE technology, but the activities in SARISTU AS03 have demonstrated the potential which makes the WATE concept interesting for further development.

Martin Herring

### Ribbon Tapes, Shape Sensors, and Hardware

For fiber optic sensors to be integrated in aerospace structures and for these sensors to provide data that can be used for structural health monitoring (SHM), development work has been performed in the SARISTU project. This particular chapter describes the inclusion of fiber optic sensors in a tape format, called ribbon tape, for damage detection and load monitoring with a secondary bonding procedure to install these in an aerospace structure. The ribbon tapes can be installed on composite structures either by co-bonding or secondary bonding techniques. Both procedures have been applied to composite coupons that have been tested in different environmental conditions. Moreover, a damaged tape repair procedure is developed. This chapter also describes the development of a fiber optic sensor to be used as a shape sensor inside a morphing aerospace structure to provide feedback on the structures shape. The hardware required to analyze and format the sensor readings for use in SHM is also provided in this chapter.

Matthijs Bosboom, Martijn van Wijngaarden, Rolf Evenblij, Paolo Bettini, Theodoros Loutas, Vassilis Kostopoulos, Dimitrios Habas, Moshe Tur, Nahum Gorbatov, Arik Bergman, Uri Ben Simon, Iddo Kressel, Christos Koimtzoglou, Monica Ciminello, Alexander Weisser, Christophe Paget

### Methodologies for the Damage Detection Based on Fiber-Optic Sensors. Applications to the Fuselage Panel and Lower Wing Panel

Damages in aircrafts start as local cracks or delaminations, which, even though they do not change strongly the overall strain field, form initiation points for an eventual failure. Fiber-optic sensors act primarily as strain sensors, so unless damage happens to be close to the sensor location, the changes in the strain data may be very slight and damage may go undetected. Three main independent algorithms were developed for damage detection from strain measurements: (1) a strain field pattern recognition technique, based on principal component analysis, from which damage indices were defined. The validity and accuracy of the approach was proven by experimental tests, as well as by simulations. (2) the extension of the Modal Strain Energy Damage Index algorithm, as a suitable method to identify skin–stringer debonds and optionally larger impact-induced damages in a CFRP composite structure with stiffeners, by using the strain data obtained during vibration tests from wisely distributed fiber Bragg grating (FBG) sensors; and (3) a strain difference-based algorithm which is threefold consisting of the following parallel methodologies: (i) strain difference limit method, (ii) Mahalanobis distance-based method, and (iii) statistical hypothesis testing-based method. These developments were put together on two realistic full-size aircraft structures, to validate the methodologies. In addition to the discretely located FBGs, distributed fiber-optic sensing was also used in the final testing, accurately measuring the strain signatures of damages caused by applied impacts.

Alfredo Güemes, Julian Sierra, Frank Grooteman, Toni Kanakis, Pavlos Michaelides, Dimitrios Habas, Moshe Tur, Nahum Gorbatov, Christos Koimtzoglou, Nikolaos Kontis

### Load Monitoring by Means of Optical Fibres and Strain Gages

This chapter describes the development of load monitoring systems integrated in the demonstrator of a smart wing structure. A monitoring system has been designed and installed on composite spars, with the aim of mapping the load conditions along the axes of such components. Such system is based on optical fibres embedded in ribbons, which have been externally bonded to the spars according to a specific optical architecture. A second system, based on conventional strain gages, has been designed to provide the sectional loads on the whole wing during wind tunnel testing and to interact with an aerodynamic load model. Both monitoring systems have been defined by using detailed FE models of the spar and of the whole wing box. Algorithms for the identification of internal and sectional loads have been developed. Finally, a third type of system is conceived to evaluate the possibility of damage detection into composite spars by using a denser network of sensors. The numerical procedures followed for the design and the calibration of the systems are discussed to assess a methodology for the development of health and usage monitoring systems to be applied in advanced aerospace structures.

Alessandro Airoldi, Giuseppe Sala, Rolf Evenblij, Christos Koimtzoglou, Theodoros Loutas, Giovanni Marco Carossa, Pasquale Mastromauro, Toni Kanakis

### Shape Sensing for Morphing Structures Using Fiber Bragg Grating Technology

Shape sensing is one of the versatile applications in a wide market spread, made practical with the use of fiber-optic (FO) sensors for strain sensing. The properties and capabilities of optical fibers with regard to both strain sensing and data transmission, their high endurance, and chemically inertness allow successful implementations in harsh environments such as aerospace. In the SARISTU project, a FO sensing-based approach for chord-wise shape reconstruction of an adaptive trailing edge device (ATED) is realized with the extrinsic implementation of fiber Bragg grating sensors. With this implementation, the capability is provided for a closed-loop control of the morphing mechanism for a given set of the target shapes. This paper describes the development and implementation of the FO sensing system as well as the applied methodology using Frenet–Serret formulas for shape reconstruction, including component and functional model testing results for validation.

Rolf Evenblij, Frank Kong, Christos Koimtzoglou, Monica Ciminello, Ignazio Dimino, Antonio Concilio

### Methodologies for Guided Wave-Based SHM System Implementation on Composite Wing Panels: Results and Perspectives from SARISTU Scenario 5

Within the SARISTU project, the Application Scenario 5 (AS05) was devoted primarily to the development of methodologies based on ultrasonic guided waves for Structural Health Monitoring (SHM) implementation on wing structural elements made of composite materials for detecting BVID or hidden flaws. These methodologies have been mainly developed by the authors of this paper, technologically integrated, and applied on small-scale structural elements within Scenario 5 (unstiffened and stiffened plates) focusing, at the end of the work, also on statistical assessment of damage thresholds levels for each methodology propaedeutic to a probability of detection (POD) evaluation of each approach. The paper will shortly present the methodologies developed and implemented, the main experimental and numerical results in terms of damage detection, and the statistical assessment of threshold damage detection levels. Finally, a short comparison about pros and cons of the methodologies as well as the migration strategy of the methodologies to the Integration Scenario 12 for full-scale wing implementation will be presented.

Ernesto Monaco, Natalino Daniele Boffa, Vittorio Memmolo, Fabrizio Ricci, Nicola Testoni, Luca De Marchi, Alessandro Marzani, Jan Hettler, Morteza Tabatabaeipour, Steven Delrue, Van Den Abeele Koen

### An Electromechanical Impedance-Based Mobile System for Structural Health Monitoring and Reliability Check of Bonded Piezoelectric Sensors

In many novel industrial applications, piezoelectric transducers (PZT) are used in sensing or actuating systems. These applications could be, for example, piezo-based structural health monitoring systems for aircrafts or active vibration reducing systems for automotive. Due to the fact that PZT materials are brittle, depolarize at high-temperature exposure or that the bonding layer to host structures for bonded transducers can degrade, monitoring of the reliability of these transducers is crucial to guarantee proper system operation. The electromechanical impedance (EMI) method allows monitoring of structural changes with only a single PZT applied to the surface of a structure. In the data analysis, it is furthermore possible to distinguish whether the host structure, the PZT material itself, or the bonding between PZT material and host structure is affected by damage. Object of this work is the implementation of the electromechanical impedance method on a compact, electronic node. Investigations of the EMI method and verification of the electronic node are conducted on an aerospace conform fiber reinforced plastic structure. Furthermore, the temperature effect on the measurement results is investigated, and methods for temperature effect compensation are applied.

Mihail Lilov, Thomas Siebel

### PAMELA SHM System Implementation on Composite Wing Panels

Aernnova developed a methodology for structural health monitoring (SHM) by use of multiple ultrasonic wave-based PAMELA SHM™ system wirelessly controlled. The possibility to perform automated NDT tests with no human presence required enables a large number of inspections and total test time reduction. The capability of this system to detect and characterize the effects on ultrasonic wave responses of several types of damages on different materials as metallic or composite structures is utmost importance for efficient and reliable SHM during structure life cycle. A study of this capability, tools descriptions, and damage detection results are presented in the paper, with the recommendations for future actions, aimed to make easier interpretation and identification of these structural damages. Several different damage detection methodologies and algorithms will be addressed attending to describe the advantages and particularities of each applied to both materials metallic and composites.

Angel Alcaide, Federico Martin, Eduardo Barrera, Mariano Ruiz

### Toward the Upscaling of Guided Waves-Based NDE and SHM in Aeronautics

In this work, we report on some research developments to support the upscaling of nondestructive evaluation and structural health monitoring (SHM) approaches, mainly based on ultrasonic guided waves, for aeronautical applications. In particular, first a spiral-shaped piezoelectric sensor sensitive to the wave direction of arrival (WDA) of guided waves propagating in plate-like structures is described. Next, a miniaturized sensor node capable to perform locally signal processing algorithms, as those developed for the spiral sensors, is presented. The sensor node weights 4 g, measures approximately 20 × 24 mm, is characterized by a low power consumption and exploiting a data-over-power (DoP) network communication reduces to a minimum the need for cabling. At such the spiral sensors and sensor node result to be suitable for the upscaling of SHM approaches devoted to locate impacts as well as delaminations in aircrafts fuselage and wings. Next, impact and/or damage coordinates are passed to an augmented reality (AR) framework that allows the NDT inspector, if equipped with a proper visual device, to see in real time directly on the structure the position of the impact/damage. In the end, by guiding the technician directly to spots potentially damaged this could speed up the NDT visual inspection phase as well as it should reduce the possibility that damages would go undetected. Applications of the above methodologies/technologies for impact localization on an aluminum plate are presented.

Nicola Testoni, Luca De Marchi, Alessandro Marzani

### Damage Identification in Composite Panels—Methodologies and Visualisation

A methodology for the identification of an impact damage using guided waves on a composite structure is implemented. Both numerical and experimental results are used, and a graphical user interface is developed to visualise the potentially damaged area. The latter allows, on top of detection, an assessment of the location and severity of the damage. The input can be experimentally based or calculated with the help of numerical models. Within this work, two numerical models are presented, based on stacked-shell finite element approach and on spectral element approach in time domain. The graphical interface allows the user to choose the most suitable approach from various damage identification methods using pitch-catch acousto-ultrasonics. The numerical models allow us to test a variety of damage locations with variable extents. The quality of the models is shown by a comparison of simulated and experimental data in time domain and respective damage indices. Finally, the visualisation allows to focus on specific areas, enhancing the analysis of multiple damages in a structure. The damage identification tool is a powerful tool in understanding the effects of various damage scenarios on the time response data and together with the numerical model provides a valuable input for model-assisted probability of detection (MAPOD).

Richard Loendersloot, Inka Buethe, Pavlos Michaelides, Maria Moix-Bonet, George Lampeas

### Manufacturing of CFRP Panels with Integrated Sensor Network and Contacting of the Network

Structural health monitoring systems are considered nowadays as ones of the most promising technologies for improving the economics of commercial aircrafts. An ideal SHM system could be capable of indicating the type of damage, its size, location, severity, and estimate the remaining lifetime of the structure. Until now, several technological approaches have been implemented under the scope of SHM systems. One of the most efficient methodologies is the application of guided ultrasonic waves (Lamb waves). This paper will focus on the Lamb wave technique and describe the road map followed along with the instrumentation developed to process the derived signals. For the implementation of such system, two types of piezoelectric sensors have been tackled. The “Smart Layer” provided by Acellent and the DuraAct™ sensors fabricated by Invent GmbH. The “Smart Layer” is based on polyimide layers. At specific spots, PZT are embedded in the layer and they are connected to the main connector by means of a copper circuit. On the other hand, DuraAct™ sensors are piezocomposites which consist of piezoceramic materials embedded in a ductile polymer. In order to study the performance of these systems, physical demonstrators have been manufactured. Representative composite fuselage structures incorporating curved skin panels with omega stringers made from CFRP materials have been designed and produced. Arrays of both types of PZT sensors have been integrated onto these structures inserting by this mean sensors at certain positions which could identify a potential damage. After the finalization of the production process, the panels were impacted and a damage detection analysis was performed based on the acquired data of the Lamb wave propagation through the manufactured panels. Under this analysis, the two different sensor networks were evaluated in terms of reliability, repeatability, and probability of detection by determining the allowable damage size (a

90/95

), which will be detailed in associated papers of AS06.

Dimitrios Habas, Daniel Schmidt, Nicolas Dobmann

### Damage Assessment in Composite Structures Based on Acousto-Ultrasonics—Evaluation of Performance

This work focuses on the damage detection and assessment of barely visible impact damages that occur after impacting a composite stiffened structure through the acousto-ultrasonics technique. Delaminations and debondings have been introduced in two stiffened panels and afterwards interrogated with an integrated structural health monitoring (SHM) network within the project. In order to perform the damage assessment, a methodology for the identification of damages along with a graphical user interface is developed. The performance of the developed methodology is evaluated and a damage assessment based on several damage indices and actuation frequencies is carried out. The most suitable parameters for the given structure and damage types are finally reported.

Maria Moix-Bonet, Peter Wierach, Richard Loendersloot, Martin Bach

### Path-Based MAPOD Using Numerical Simulations

Probability-based methods for the consideration of detection rates and associated damage sizes have been state of the art in NDT. For structural health monitoring (SHM) systems, the quantification of detection capabilities needs to be addressed to enable the industrial implementation. Due to the fixed mounting of SHM systems on structures, experimentally based investigation is particularly difficult and resource consuming. Therefore, the use of numerical simulations is suggested to generate additional data for probability studies. Within this paper, two methods of model-assisted probability of detection (MAPOD) are presented. For the use case of carbon fibre-reinforced plastics (CFRP) panels, tested with acousto-ultrasonics, a path-based analysis was chosen. After a short description of the underlying numerical models, the used probability-based methods are explained. Their application is shown in detail using a 3D and a 2D model for a CFRP panel.

Inka Buethe, Nicolas Dominguez, Henning Jung, Claus-Peter Fritzen, Damien Ségur, Frédéric Reverdy

### Flat and Curved Panel Manufacturing

This paper describes the manufacturing of flat test panels and curved stiffened test panels for the multi-site damage assessment of CFRP structures. Unidirectional carbon fibre prepreg has been used to laminate and autoclave the test panels. The flat panels in sizes 300 × 300 mm and 600 × 600 mm have been produced to provide a low-cost simple test article. The majority of the manufacturing effort has gone into the production of the curved test panels to be used for compression tests after having been subjected to multi-site damage. Tooling has been manufactured to be used in the various processing steps, which involve stringer autoclave consolidation, stringer machining, cobonding the stringers to the still-to-be-consolidated curved skin panel, application of reinforcement plies for load introduction, potting of the stringer ends, machining of the panel contour, potting the complete panel in a potting jig, machining the potting within tolerance for compression testing and quality control using NDI and dimensional verification. The finished panels have been shipped in custom crates which store the panel throughout its logistic and testing program. From KVE, the panels have been shipped to Premium AEROTEC GmbH (PAG) for assembly of the metallic parts also described in this report. PAG shipped the panels to the test location at Imperial College London (ICL).

Martijn van Wijngaarden

### Compression After Multiple Impacts: Modelling and Experimental Validation on Composite Coupon Specimens

This research investigates the post-impact behaviour of CFRP coupon specimens subjected to multisite impacts. Sequential low-velocity impacts at different locations were performed on coupons with different thicknesses. The impact load history was recorded, and the extent of damage was assessed by ultrasonic inspection. The residual strength in compression was then measured in a compression after impact rig which was specially modified for the testing of thin composites. High-speed video and digital image correlation records were taken for a number of specimens during testing. The experimental results were used to validate a finite element mesomechanical modelling approach which accounts for both intralaminar damage and interlaminar damage.

Spyridon Psarras, Raul Muñoz, Mazdak Ghajari, Paul Robinson, Domenico Furfari

### Compression After Multiple Impacts: Modelling and Experimental Validation on Composite Curved Stiffened Panels

This research investigates the post-impact behaviour of composite fuselage panels subjected to multi-site low-velocity impacts. Large curved stiffened panels (1.2 m × 0.8 m, with composite skins/stiffeners and aluminium frames) of two different skin thicknesses were subjected to sequential drop-weight impacts at locations previously determined to be critical in FE simulations. After assessment of the impact damage, each panel was tested in compression. High-speed video, strain gauges, digital image correlation and acoustic emission were used to monitor the failure development and to provide data for comparison with the FE simulations. The FE models, which were based on a mesomechanical approach, showed a good agreement with both the impact damage and the subsequent compression performance.

Spyridon Psarras, Raul Muñoz, Mazdak Ghajari, Paul Robinson, Domenico Furfari, Arne Hartwig, Ben Newman

### Multisite Damage Assessment Tool

Composites generally are not damage-tolerant, and impact damage can significantly degrade the compressive strength of a composite laminate. Even when no visible impact damage is observed at the surface (energies below barely visible impact damage (BVID)), matrix cracking and interlaminar failure can occur and the carrying load of the composite laminates might be considerably reduced (de Freitas et al in Compos Struct 42(4):365–373, 1998). The aim of the multisite damage assessment tool is to give quick answers with regard to remaining airworthiness and further investigations after hail strikes and reducing aircraft on ground time. To clarify the remaining airworthiness of an aircraft after multisite damage (MSD), mainly caused by hail strikes, an assessment tool is developed based on physical and virtual testing as well as accuracy factors of structural health monitoring (SHM) information.

Tulug Pince

### Piezochromic Compounds Able to be Used in Shock Detecting Paints

The work of the ICMCB has dealt with the inorganic piezochromic pigments improvement. Our activities can be divided in three main points. From the state of the art on AMoO

4

piezochromic molybdates (this state of the art is described in the introduction paragraph), the first point has consisted in the synthesis and characterization of the piezochromic oxides and in qualifying pigments mixtures able to mark a shock (the pressure of the shock) without knowing the temperature at which has occurred the shock. In a second point, in order to vary the shock pressure inducing a change of color of the piezochromic pigments, new synthesis routes were developed in order to significantly vary the crystallites size of the piezochromic pigments. Indeed, it was shown that the crystallite size modifies in a large way the piezochromic behavior of the pigments. This point is very important for

SARISTU

project in order to get a palette of morphologies fitting with the requirements of the aeronautic piezochromic paints. In a last (third) point, the exploration of new potential systems was made. In particular, we have focused on doped calcium carbonates able to change their luminescent properties depending on the applied pressure and/or the temperature. This last part has opened new possibilities which have to be more investigated in a near future. The most important results obtained concerning the three above points are here summed up and discussed.

Manuel Gaudon, Alain Demourgues, Veronica Blanco-Gutierrez, Silvere Barut

### Brittle Coating Layers for Impact Detection in CFRP

The detection of possible impacts in carbon-fiber-reinforced plastic (CFRP) structures is important for the evaluation of structural integrity of CFRP. Sol–gel-based sensitive coatings for impact detection on CFRP substrates have been developed and investigated by University of Aveiro (UAVR). The coatings are based on hybrid sol–gel formulations with tunable mechanical properties, i.e., brittleness adjusted for a defined range of impact energy. This sensitive layer allows the identification and location of mechanical impacts under visible light and without supplementary tools or conditions for its detection. A systematic study was performed to enhance the coating response for the defined impact threshold. A set of different parameters such as composition, fillers, curing conditions, surface roughness, and chemistry of the surface were tested and optimized.

Frederico Maia, Kiryl Yasakau, Joao Tedim, Mikhail L. Zheludkevich

### Coating for Detecting Damage with a Manifest Color Change

Carbon fiber-reinforced plastic (CFRP) structures are used in modern airliner. An impact may damage the inner structure of the composite without any visible marks on its surface. So, the solution that is investigated by CATALYSE is the application of a coating that would reveal impacts. This technology is based on microcapsules with a manifest color change (under visual and UV light). Different types of capsules were tested with different active components.

Laura Monier, Karel Le Jeune, Isabelle Kondolff, Gil Vilaça

### Sensitive Coating Solutions to Lower BVID Threshold on Composite Structure

The objectives of the 8th Application Scenario in SARISTU project is to develop sensitive coating for impact detection. This coating is to be applied on composite structural parts and reveal internal impacts from a certain threshold. Several solutions in terms of “sensors” and matrices have been investigated and improved in order to lower the BVID threshold while respecting durability criteria and environmental, health and safety constraints.

Silvere Barut

### Use of Carbon Nanotubes in Structural Composites

Carbon nanotubes (CNT) possess excellent intrinsic characteristics such as exceptionally high mechanical and conductive properties which make them the prime candidate to reinforce high-performance composite structures. However, location and dispersion state of the CNTs are of particular importance to achieve the mechanical and electrical enhancement of carbon-reinforced composites. In the frame of European Project SARISTU, different approaches were investigated by the different partners (e.g., veils, powdered doped prepreg, and doped adhesives). Each approaches required specific dispersion solution. Along its existence, Nanocyl has developed a large experience in incorporation of CNTs in different resins (thermoplastics, thermosets, etc.) using improved innovative mixing process, CNT surface modification (functionalization) or by adding some dispersing agents or compatibilizers. Applying this expertise to SARISTU context, the requested products were delivered in the suitable form for each scenario. As an example, ground CNT/thermoplastics compounds were produced for powdered doped prepreg and different grades of doped thermoplastics for veils production.

Daniel Bonduel, Nadir Kchit, Michael Claes

### Enhancement of Primary Structure Robustness by Improved Damage Tolerance

The aim of SARISTU is to take forward to higher TRL level from previous research of various technologies and methods that realize measurable improvements in aircraft damage tolerance and weight reductions. AS09 aims to evaluate toughening of composite materials through additives such as multiwall carbon nanotubes (MWCNT) and various types of polymer interleaf veils. This scenario works alongside AS10 to deliver multifunctional composite materials. The goal was the improvement in damage tolerance and electrical isotropy. The proposition is that nanoparticle introduction in materials could bring significant positive impact on environment. This positive impact would be by the way of weight reduction in structures and therefore would lead to a reduction in fuel consumption and gas emissions. Several strategies were addressed, and their integration into composite materials and the influence on the damage tolerance were studied. The technologies were studied in terms of mechanical properties and electrical conductivity during the Phase I. The best-performing technologies (thermoplastic veils and MWCNT-treated prepreg) were further characterized in Phase II at RT and HW at coupon level and a sub-element level. This paper reviews the technologies studied and their contribution to the improvement of damage tolerance.

Sonia Flórez, Jorge Gayoso

### Enhancement of Infused CFRP Primary Structure Mechanical Properties Using Interleaving Thermoplastic Veils

Damage tolerance of aircraft primary structures is important to prolong the life of the structure and reduce maintenance costs. For composite structures, this is particularly crucial; unlike metallic structures which are largely made up of multiple components which can be easily visually inspected and replaced where necessary, advanced composite structures are frequently one piece, e.g. wingskins, fuselage sections, and therefore cannot be replaced. Inspection of these components require complex and time-consuming non-destructive inspection testing to check for delaminations within the laminates and any damage would require complex and costly repairs. Since this work focuses on infused CFRPs, it should also be noted that prepreg CFRPs in comparison are inherently more damage tolerant and hence one objective is to narrow the ‘performance gap’ between the two technologies. By including thermoplastic veils between the layers of a composite laminate stack, this reduces the brittleness of the matrix between reinforcement layers and also acts to reduce crack propagation, thus drastically reducing damage sizes as a result of an impact. Subsequently, residual CAI strengths are increased which for many aircraft structures is the primary design allowable. This paper outlines the mechanical performance evaluation of a toughened fabric by addition of interlaminar thermoplastic veils infused with epoxy resin. The objective of the toughened materials is to maximise the performance enhancements, particularly damage tolerance, whilst minimising any knock-downs in hot/wet performance, preform permeability for infusion and also electrical conductivity due to the additional insulating layers. This project work within AS09 evaluates the materials at coupon and sub-component level and feeds into IS12 for the materials of choice to manufacture the Bombardier lower wingskins.

Daniel Breen

### Multi-scale-Reinforced Prepregs for the Improvement of Damage Tolerance and Electrical Properties of Aeronautical Structures

Within the AS09 scenario, partners developed and investigated means by which the damage tolerance of carbon fiber-reinforced polymer (CFRPs) can be improved. This scenario worked alongside AS10 to deliver multifunctional composite materials. The goal was on the improvement in damage tolerance and electrical isotropy which in turn can produce a reduction in weight at the aircraft structure level. Nanoparticle introduction in composite materials compromised the main technological field studied, aiming to advance their Technology Readiness Level against more traditional methods (e.g., thermoplastic veils). Multi-scale modification technology for conventional prepregs developed by Applied Mechanics Laboratory at University of Patras was one of the investigated routes. The resulted MWCNT powder-treated prepreg proved to be one of the two best performing technologies during Phase 1 testing and was further selected to be further characterized (RT and HW) in Phase 2 at coupon level and at sub-element level. Moreover, the MWCNT powder-treated prepreg was down-selected to be used for lower panel production in IS13. In parallel, various industrialization aspects of the technology were investigated such as supply chain management, material handling, and process optimization during composites production. A laboratory production line was established and approximately 1000 m

2

of base prepreg material were treated and delivered. This chapter reviews the work performed on multi-scale modification technology for conventional prepregs during the course of SARISTU project (AS09, AS10 and IS13) summarizing key engineering developments and results.

A. Vavouliotis, G. Sotiriadis, V. Kostopoulos

### Improvement of the Electrical Isotropy of Composite Structures—Overview

The aim of SARISTU is to take forward to higher TRL level from previous research various technologies and methods that realise measurable improvements in aircraft damage tolerance and weight reductions. AS10 claims to evaluate three technologies: multiwall carbon nanotubes (MWCNT), metallic strips and metallic coatings for structural capability integration in order to demonstrate the manufacturability of CFRP parts with improved electrical conductivity. AS10 worked alongside AS09. The improved electrical conductivity should deliver composite laminates showing damage tolerance as it is pursued within AS09. This chapter reviews the technologies studied and their contribution to the improvement of electrical isotropy of CFRP laminates.

Sonia Flórez, Idoia Gaztelumendi, Jorge Gayoso

### Fabrication of Carbon Nanotubes-Doped Veils

Non-woven fabrics (veils) are structural materials consisting of randomly arranged thin fibres. They are used as an interlayer in the laminate fabrication process to improve mechanical properties of composites, especially their fracture toughness. A new role of such veils could be the enhancement of the electrical conductivity of laminate. For this purpose, veils should be doped with a conductive additive enabling them to maintain a high level of mechanical performance as well. Thermoplastic polymers doped with carbon nanotubes could be the best potential candidate materials for electroconductive veil fabrication. This is due to their low weight and the outstanding properties of carbon nanotubes. Moreover, there is no competitive material on the market yet. Commonly known are non-conductive veils produced from neat polymers or those obtained from carbon fibres covered by metal and stick together with chemical binder. From the technical point of view, the last two steps are undesired by product end-users. Hence, a much effort is focused on development of fabrication process of conductive veils from polymer and carbon nanotubes. The proposed technology is the melt blown manufacturing process. It allows fabrication of the final product (veil) through a highly cost-effective one-step route starting from polymer pellets/powder. There is no need to use solvents, processing compounds or binders for sticking fibres together. However, the incorporation of carbon nanotubes in the polymer network leads to a significant increase in the viscosity and decrease in the flow ability of the material. There are huge obstacles to its further processing. Therefore, it is necessary to make an appropriate selection of the polymer matrix and to control the properties of carbon nanotube-doped polymers at each stage of production. Especially, the polymer should have low viscosity (high MFI) and should be able to form fibres. As mentioned, conductive lightweight veils are not present on the market in an amount able to cover industry demand. Therefore, the next step is to increase the existing pilot plant for doped veil production for composite parts in the relevant environment (from TRL 4 to TRL 6). A semi-continuous pilot line for the industrial production of doped veils will be designed and the manufacturing layout will be developed. The main area in which electroconductive veils are highly desired is the aerospace industry or electronic sectors. Such materials could be applied in electromagnetic shielding or in lighting strike protection instead of presently used metallic meshes or tapes. Due to their low weight, the total mass of the aircraft could be reduced and its mechanical properties, i.e. fracture toughness, may be improved.

Paulina Latko, Anna Boczkowska

### Finite Element Modelling of CNT-Doped CFRP Plates for Lightning Strike Damage

The neat and CNT-doped CFRP-laminated plates to be used in aerospace structures are considered for the behaviour of lightning strike damage. Material properties of both the neat and CNT-doped T800/M21 are obtained experimentally. Quasi-isotropic rectangular plates are modelled in ABAQUS finite element program. Coupled electrical and thermal analysis is carried out using multi-physics. Steady-state electrical analysis and transient heat transfer analysis are conducted at each time increment by the application of Joule heat generation. The damage region is estimated by considering the decomposition temperature of the resin. The coupled analysis shows that the damage region of the CNT-doped laminate substantially decreases when compared to the neat laminate. Next, fully coupled electrical–thermal–mechanical analysis is carried out in order to further understand the damage initiation and estimation of material failure before the decomposition of the resin. The damage initiation is estimated by considering thermal stress level and Tsai–Wu material failure criterion. The finite element simulations indicate that more electrical current can be applied to the CNT-doped laminate or that there would be less damage under the same electrical current because the electrical conductivity through the thickness of the plate plays a significant role for the lightning strike damage.

Omer Soykasap, Sukru Karakaya, Yelda Akcin, Mehmet Colakoglu

### Metallic Strip Details for Validation of ESN Technologies

The aim of AS10 is to evaluate technologies that can be integrated directly into structures with the target of creating an electrical structural network (ESN) while reducing weight and improving survivability of composite structures. These investigations are based on various technologies and materials from nanomaterials to metallic strips and coatings. The metallic strip concept is based on the merging of materials at macro- and meso-element scale level, using conventional manufacturing technologies. The innovative development consists of a preassembled semi-product composed of an aluminium strip and a nonvulcanized rubber that is cobonded to the composite frame part while curing the structure. This paper presents the metallic strip design and manufacturing choice, the thermomechanical experimentation and modelling conclusion, the impact coupon test results and conclusion on damage tolerance and detectability of impacts, the electrical current distribution simulation and test and finally the electrothermal behaviour results and conclusion.

Richard Perraud, Olivier Urrea, Thierry Pelegrin, Michel Bermudez, Michel Fouquembergh, Stephane Guinard, Christoph Breu

### Morphing Value Assessment on Overall Aircraft Level

In order to assess the benefit of the morphing devices developed in the framework of SARISTU, integration in an overall aircraft model is required. For this purpose, the relevant input data regarding the adaptive leading-edge, trailing-edge and winglet devices are gathered with specific focus on weight and aerodynamic performance. Different levels of detail are applied. For weight and actuation power, the methods range from geometry (e.g. span and chord)-dependent methods to absolute delta values which are for instance subtracted from components weights as wing structure weight. Methods for aerodynamic data reach from subtractions of absolute values from the lift to drag ratio, constant for the flight phases (i.e. climb, cruise, decent), towards changes to the induced drag polars specific for each mission increment and dependent on the explicit lift coefficient. For an objective assessment, several aircraft models are compared. The assessment and comparison of these aircraft AC models take place on standard overall aircraft-level parameters as block fuel or maximum take-off weight.

Fabian Peter, Eike Stumpf, Giovanni Marco Carossa, Markus Kintscher, Ignazio Dimino, Antonio Concilio, Rosario Pecora, Andreas Wildschek

### Implementation of Morphing, Structural Health Monitoring and Nanomaterials on an Outer Wing Box

This paper presents the implementation of morphing, structural health monitoring and nanotechnology on the demonstrator wing. The goal is to reduce aerodynamic drag and improve bearing capacity, damage detection, damage tolerance allowable and internal load control. The morphing system developed intends to minimize the impact on the aerodynamic drag through variation in shape and help increase the overall efficiency of the wing and the plane. The structural health monitoring system can control a network of piezoelectric transducers and optical fibres that are surface mounted on the structure, to control damage, internal load and the shape of the morphing surfaces. Furthermore, the paper describes the construction and assembly of the wing demonstrator and outer manhole design/manufacturing for improved damage tolerance. This is achieved by using CFRP in combination with nanotechnology and the monitoring of the load in the wing box by means of optical fibres integrated on the spars of the wing box.

Giovanni Marco Carossa, Michelangelo Giuliani, Alan Johnston, Christina Altkvist, Alessandro Airoldi, Zahra Sharif Khodaei, M. H. Aliabadi

### Implementation of a Structural Health Monitoring System for a Composite Wing Box Skin

This paper reports on the implementation of a structural health monitoring (SHM) system devoted to delamination detection on the wing box demonstrator. The developed SHM system is capable to control a network of up to 160 piezoelectric transducers that are surface mounted on the structure. The SHM system is able to perform both electromechanical impedance (EMI) measurement at each transducer to check their reliability and their bonding strength to perform an active guided wave (GW) screening. This latter operation exploits the damage detection methodologies that have been developed in the AS05/IS12 scenario to detect damages. Some information and results of a first experimental test carried out at the ALENIA facilities will be given.

Alessandro Marzani, Nicola Testoni, Luca De Marchi, Ernesto Monaco, Zahra Sharif Khodaei, M. H. Aliabadi, Julio Viana

### Value at Risk for a Guided Waves-Based System Devoted to Damage Detection in Composite Aerostructures

The need of reducing aircrafts’ fuel consumption and emissions has led the aircraft industry to the design of smart structural elements, which are composite panels with built-in multisensors monitoring systems. The potential economic benefit in terms of maintenance and inspection planning strongly depends on the performances of the built-in monitoring system. The discrimination between damaged and not damaged structural components based on monitoring outcomes is indeed the result of a decision process, in which the state of the structure is assessed based on observations, affected by uncertainties. These might lead to erroneous estimation of the structural damage with consequent strong influence on the maintenance portfolio. In this paper, a reliability-based optimization of the life cycle cost of a smart aircraft component is proposed in the framework of a Bayesian damage update methodology by following a damage-tolerant approach. The methodology is applied to the delamination detection due to impacts on a composite component. The statistical models for the monitoring performance depend on a multilevel defect classification based on the five classes of events in accordance with the FAA AC No: 20 107B. Multiclass ROC analysis and threshold optimization are introduced in the perspective of the maintenance portfolio. A cost model accounting for the calculation of the value at risk (VAR), meant as the potential loss associated with the maintenance portfolio, is implemented.

Luca De Marchi, Alessandro Marzani, Nicola Testoni, Ulrike Heckenberger, Alfonso Apicella

### Fuselage Demonstrators: An Overview of the Development Approach

Effective technology development relies on data in order to make informed decisions. In moving through the levels of a test pyramid, from small-scale initial investigations up to large, and ultimately (in the case of aerospace) flight test or full-scale static and fatigue test, demonstrators, the cost and criticality of generating these data increase accordingly. This paper reviews the approach taken in the work linking, and delivering, to the SARISTU fuselage demonstrators, and some of the key decisions taken to minimize risk, to exploit synergies and opportunities, and to streamline the development.

Ben Newman

### Development of a Door Surround Structure with Integrated Structural Health Monitoring System

Structural health monitoring (SHM) based on Lamb waves, a type of ultrasonic guided waves, is a promising method for in-service inspection of composite structures. Lamb waves can be excited and received using a network of actuators and sensors, which are permanently attached to the structure. By analysing the sensor signals, different kinds of structural defects can be detected and located through the interaction of the Lamb waves. This paper presents the development and manufacturing of a full-scale composite fuselage panel with a door surround structure and integrated SHM system. The SHM system consists of piezoceramic sensor arrays, which are integrated into the composite manufacturing process in the form of semi-finished parts. With this approach, the manufacturing steps and costs can be reduced.

Daniel Schmidt, Andreas Kolbe, Robert Kaps, Peter Wierach, Stefan Linke, Stefan Steeger, Friedrich von Dungern, Juergen Tauchner, Christoph Breu, Ben Newman

### Damage Introduction, Detection, and Assessment at CFRP Door Surrounding Panel

Acousto-ultrasonics (AU) is a Structural Health Monitoring (SHM) technique based on a permanently installed piezoelectric transducer network, which actuates and receives ultrasonic guided waves to provide information concerning the structure integrity. In order to verify AU approach, a full-scale CFRP panel is manufactured including a co-bonded transducer network. In this paper, the verification approach is described, starting with the test procedure including damage introduction and reference NDI. The verification procedure is followed by data interrogation of the transducer network using a commercial interrogation unit and respective data evaluation by probability-based imaging methodology, which has been integrated into a Graphical User Interface (GUI) in the SARISTU project. In this paper, the methodology is verified against requirements concerning the minimum damage size to be detected, the accuracy of damage size assessment, and the accuracy of localization of damage. Damage-type differentiation, like delamination or debonding is not aimed in the course of the methodology.

Martin Bach, Nicolas Dobmann, Maria Moix-Bonet

### Installation of Metallic Strip on CRFP Frames: Assessment of IS13 Mechanical and Electrical Performance

The extended use of CFRP material in airframes led to a loss of the ability to use the aircraft superstructure for electrical tasks such as lightning strike protection, systems bonding and grounding. So, to replace metallic fuselage inherent electrical functions in composite aircrafts, an internal metallic structure called electrical structure network or ESN is introduced. The aim of AS10 is to evaluate technologies that can be integrated directly into structures with the aim of creating an electrical structure network (ESN) whilst reducing weight and improving survivability of composite structures. The innovative development consists of a pre-assembled semi-product composed of an aluminium strip and a non-vulcanized rubber that is co-bounded to the composite frame part early at the manufacturing stage. Evaluations of the technology were done at coupon level to check thermal, mechanical and electrical requirements. This paper presents the activity related to IS13 demonstrator and its damage tolerance and electrical performance assessment. For electrical aspects, a numerical model is built, allowing analysing the impact of strip installation versus current solution with the AD2 cable. Numerical results will have to be confirmed with measurements.

Richard Perraud, Olivier Urrea, Thierry Pelegrin, Michel Bermudez, Stephane Guinard, Christoph Breu

### Benefit Analysis Value and Risk Assessment of New SARISTU-Technologies

The value and risk assessment investigates whether the SARISTU aim of improving aircraft efficiency has been met by achieving a reduction in the total weight and operating costs. Process times for manufacturing steps, together with pertinent weight data and weight impact calculations, are used to enable this assessment. The focus lies on processes established in the manufacturing of coupons, elements and details of the SARISTU-test pyramid in AS04 and AS06-10, as integrated into the sub-component technology demonstrators in IS13. A tool has been developed that allows results to be upscaled to component level and allows a comparison of SARISTU-technologies against state-of-the-art manufacturing methods for carbon fibre reinforced fuselages. Serial production and operational impacts have been considered. Additional technologies have been included, such as structural health monitoring (SHM), which was utilized for improving damage detection capabilities.

Sevgi Batal, Stephne du Rand

### Manufacturing of Nano-treated Lower Panel Demonstrators for Aircraft Fuselage

Improved robustness is seen as a key technology enabler for reducing the required thicknesses of composite structural parts; this reduction would, in turn, lead to direct savings in the structural mass. The aim of this study was to produce one reference and two nano-treated lower panel demonstrators for investigating the effect of nano-reinforcement on the damage tolerance behaviour of skin, stringers, bondline and on the electrical conductivity of CFRP. The selected technology, resulting from development and experiments undertaken within the SARISTU project, is carbon nanotube (CNT)-integrated prepreg material M21/34%/UD194/T800S, which is treated by University of Patras. The studies on damage tolerance improvement performed within the scope of Application Scenario 09 were used as input during determination of the manufacturing parameters for the selected co-bonding process. The demonstrators are curved panels whose overall dimensions are 2868 mm length and 1120 mm width, and that are stiffened with four omega stringers and four mechanically fastened frame pieces. This chapter reviews the design and fabrication of manufacturing tooling, the design and production of the various individual components, integration of the DiAMon Plus™ online cure monitoring system by INASCO and the assembly at TAI of the stiffened skin with the composite mousehole frames designed and manufactured by SABCA.

Feride Nur Sasal, Aysun Dogangun Akın, Ayhan Kılıc, Guray Erteği, Caglayan Duygu, Emre İşler, Ben Newman, Christos Koimtzoglou, Panagiotis Maroulas, Patrick Bara, Antonios Vavouliotis, George Sotiriadis, Vassilis Kostopoulos

### Design and Manufacturing of WP135 Side Panel for Validation of Electrical Structure Network (ESN) Technologies

Design and manufacturing of a curved stiffened panel has been carried out within WP135 in SARISTU Integration Scenario IS13. The aim of this fuselage panel is the integration and validation of electrical structure network (ESN) technologies developed within Application Scenario AS10. The assembled panel includes premanufactured braided frames with cocured metallic strips aimed at improving electrical performance, impact detectability and damage tolerance. The panel will be subjected to electrical testing to verify the ESN solution, with additional frames used for impact testing and evaluation.

Christina Altkvist, Jonas Wahlbäck, Juergen Tauchner, Christoph Breu
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