Leonardo Lecce

A Novel SMA-based Concept for Airfoil Structural Morphing

The adaptive structures concept is of great interest in the aerospace field because of the several benefits which can be accomplished in the fields including noise reduction, load alleviation, weight reduction, etc., at a level in which they can be considered as compulsory in the design of future aircraft. Improvements in terms of the aerodynamic efficiency, aeroelastic behavior, stability, and manoeuvrability performance have already been proved through many international studies in the past. In the family of the Smart Materials, Shape Memory Alloys (SMA) seem to be a suitable solution for many static applications. Their high structural integrability in conjunction with actuation capabilities and a favorable performance per weight ratio, allows the development of original architectures. In this study, a morphing wing trailing edge concept is presented; morphing ability was introduced with the aim of replacing a conventional flap device. A compliant rib structure was designed, based on SMA actuators exhibiting structural potential (bearing external aerodynamic loads). Numerical results, achieved through a FE approach, are presented in terms of trailing edge induced displacement and morphed shape.

Airfoil Structural Morphing Based on S.M.A. Actuator Series: Numerical and Experimental Studies

Multiple flight regimes during typical aircraft missions mean that a single unique optimized configuration, that maximizes aerodynamic efficiency and maneuverability, cannot be defined. Discrete components such as ailerons and flaps provide some adaptability, although they are far from optimal. Wing morphing can significantly improve the performance of future aircraft, by adapting the wing shape to the specific flight regime requirements, but also represents a challenging problem: the structure has to be stiff to maintain its shape under loads, and yet be flexible to deform without collapse. One solution is to adopt structural elements made of smart materials; Shape Memory Alloys (SMAs) have demonstrated their suitability for many static applications due to their high structural integration potential and remarkable actuation capabilities. In this work, the airfoil camber at the wing trailing edge on a full scale wing of a civil regional transportation aircraft is controlled by substituting a traditional split flap with a hingeless, smooth morphed flap. Firstly, the development and testing of an actuator device based on a SMA ribbon, capable of a net rotation of 5 deg, is presented. Then, a flap bay is designed and experimentally tested in presence of static loads, based on a compliant rib built as a series repetition of the proposed actuator. An aero-thermo-mechanical simulation within a FE approach was adopted to estimate the behavior and performance of the compliant rib, integrating both aerodynamic loads, by means of a Vortex Lattice Method (VLM) code, and SMA phenomenology, implementing Liang and Rogers’ constitutive model. The prototype showed good actuation performance even in presence of external loads. Very good numerical-experimental correlation is found for the unloaded case, while some fatigue issues emerged in presence of static loads.

Wing Shape Control through an SMA-Based Device:

Based on numerical and experimental analyses, this article proposes an application of the smart structure concept aimed at realizing a bump on an airfoil profile, finalized to reduce transonic drag, through the use of shape memory alloys (SMAs). The ability of morphing the wing profile is functional to maximize the aerodynamic efficiency in different mission conditions. The use of the so-called smart materials allows a favorable actuation performance per weight ratio, also leading to simple and integrated devices. Currently, to model their mechanical behavior is still an open issue and this work presents some original ideas about this. Numerical results and experimental tests herein presented, demonstrate the efficacy of the developed concept device, calling for further studies on real structures; their correlation also validate the implemented simulation procedure.

Experimental and Numerical Activities on Damage Detection Using Magnetostrictive Actuators and Statistical Analysis

The purpose of this work is to present the formulation of a new experimental procedure to employ in problems of damage analysis of structural elements. The proposed method is based on the acquisition and comparison of Frequency Response Functions (FRFs) of the monitored structure before and after damage occurred. Structural damages modify the dynamic behaviour of the structure and consequently its FRFs making possible calculation of a representative “Damage Index.” The experimental activity was carried on using two prototypes of magnetostrictive actuators developed within the European Commission funded project named MADAVIC (Magnetostrictive Actuators for Damage Analysis and VIbration Control). Three kinds of damages have been simulated on two beam-like structures: little mass disturbances, partial cuts of the beam sections and constraint yielding. Two expressions of damage indices were calculated and analysed. The main target of the work was to assess the reliability of the damage identification by using a “repetitiveness index.” This index is related to the lowest measurable damage extension and the statistical t-test, in order to verify if each calculated index was really representative of a structural damage, rather than of unforeseen differences between the FRFs. A simple Finite Element Model (F.E.M.) of the second test-article has also been developed for numerically simulating the experimental tests and comparing the corresponding results.

Airfoil Morphing Architecture Based on Shape Memory Alloys

The adaptive structures concept is of great interest in the aeronautical field because of the several benefits which can be accomplished in the design of future aircraft. Improvements in terms of aerodynamic efficiency, aero-elastic behaviour and manoeuvrability were proved by many international studies. The development of new structural architectures implementing and integrating innovative materials is mandatory for succeeding in these critical tasks. The so-called Smart Structure idea is more and more taken into account in aerospace applications Among the family of Smart Materials, Shape Memory Alloys (SMAs) certainly represents a convenient solution for many static applications. In this work, an application for a morphing wing trailing edge is presented as alternative for conventional flap devices. A compliant rib structure has been designed, based on SMA components working both as actuators, controlling wing chamber, and as structural elements, sustaining external aerodynamic loads. Achievable performance has been estimated by a FE approach; SMA behaviour has been modelled through a dedicated routine implementing the Liang & Rogers’ model for evaluating the internal stress and the minimum temperature necessary for activation. The numerical results have been presented in terms of induced displacements and morphed shape.Copyright

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.

Non deterministic approaches for the evaluation of the mistune effects on the rotor dynamics

In this job new approaches to the mistune effects evaluation on turbomachine are presented that cannot be classified neither deterministic neither statistical: they are based on the employment of artificial neural networks and of genetic algorithms. In the first case, a net is trained to predict the blade displacements when the rotor is mistuned, correlating the structural response to the introduced mistune pattern. The target is that the net learns the rotor dynamics with an amount of examples sufficient to make fast and reliable predictions on the configurations not included in the learning database. In the second case, a genetic algorithm has been developed to find the structural mistuned configuration that leads to the maximum value of blade vibration amplitude: the target is to perform a smart search of the worst mistuned configuration. In both analyses, a simple test case, representing a twenty blades disc, has been employed and one thousand forced frequency response analyses have been performed. The investigation has demonstrated the applicability of this new possible engineering approaches to the study of system with uncertain properties.

Experimental approach in studying temperature effects on composite material structures realized with viscoelastic damping treatments

This paper presents a study aimed at evaluating how viscoelastic materials embedded in composite plates affect structural damping during the flight of a civil aircraft. The vibro-acoustic responses of composite fuselage structures realized with embedded viscoelastic damping treatments have been experimentally characterized at different temperature conditions. The real influence of viscoelastic materials on composite structures has been investigated, focusing the investigations on aspects still unknown, related mostly to temperature effects. In order to simulate the temperature level of commercial transport aircraft in cruise flight conditions, tests were performed using a climatic room where temperature and humidity were controlled. Vibrational tests were performed on two composite fuselage skin coupons: one treated with embedded viscoelastic damping treatments and the other one untreated. The tests were performed at temperatures of - 35 ∘ C for the untreated composite fuselage structure, and 15 ∘ C , - 20 ∘ C , - 25 ∘ C and - 35 ∘ C for the treated composite fuselage structure. The damping values were carried out by the impulse response decay method and the loss factor was obtained as an average of many repeated acquisitions. In order to maximize the damping effect, the best temperature interval for the treated composite fuselage skin coupon was evaluated, and the behavior for both composite fuselage structures (treated and untreated) was characterized. Thanks to the high number of tests, a statistical analysis was performed in order to validate the approach used.

Multi-tone Switching Shunt Control by a PZT Network Embedded into a Fiberglass Panel: Design, Manufacture, and Test

Research in noise and vibration control has partially focused on semi-active attenuation techniques such as switching shunt control (SSC) systems. Among the various methods, SSC architectures exhibit several interesting advantages such as low power absorption and intrinsic adaptive capabilities. This approach may represent an acceptable compromise between passive and active solutions. In previous work the authors implemented and validated 1D and 2D numerical models, addressed to describe continuous simple isotropic structures under tonal excitations controlled by single-element SSC system. Further efforts were then directed to extend the applicability of those models to non-isotropic structures and to multi-tone control devices. In this article, a 6-PZT network multi-tone SSC system is presented, and embedded into a balanced fiberglass laminate. The network geometry is defined according to an optimization process following modal information. The former 1-channel control circuit was extended to drive up to four independent channels. The complete system dynamics was simulated by assembling the structural matrices into a Matlab code, where both the electromechanical coupling and the control circuit behavior were taken into account. The structure was excited by broadband sweep signals in a selected range. Numerical and experimental results were compared and discussed.

Health Monitoring: New Techniques Based on Vibrations Measurements and Identification Algorithms on an Aeronautical Composite Panel

Purpose of the paper is to present a new application of a Non Destructive Test based on vibrations measurements, developed by the authors and already tested for analysing damage of many structural elements. The proposed new method is based on the acquisition and comparison of Frequency Response Functions (FRFs) of the monitored structure before and after an occurred damage. Structural damage modify the dynamical behaviour of the structure such as mass, stiffened and damping, and consequently its FRFs, making possible to identify and quantify a structural damage. The activities, presented in the paper, mostly focused on a new FRFs processing technique based on a dedicated neural network algorithm aimed at obtaining a “recognition-based learning”; this kind of learning methodology permits to train the neural network in order to let it recognise only “positive” examples discarding, as a consequence, the “negative” ones. Within the structural NDT a “positive” example means “healthy” state of the analysed structural component and, obviously, a “negative” one means a “damaged” or perturbed state. The developed NDT has been tested for identifying and analysing damage on an aeronautical composite panel to validate the method and calibrate the neural network algorithm. These tests have permitted to understand the influence of environmental parameters on the neural network training capability. Thanks to these new techniques it is possible to carry out a smart Health Monitoring system which is going to lead to the reduction of time and maintenance cost and to the increase of the aeronautical structure safety and reliability.