We report on the use of Fiber Bragg Grating (FBG) sensors integrated onto an aircraft landing gear for remote and realtime load monitoring. Several FBGs strain sensors, both in a linear and tri-axial configuration, have been integrated on different locations of true landing gears (both Main and Nose gears) based on their load condition derived from FEM numerical analysis and exposed to numerous qualification lab tests where the load applied to the gears was varied in the range 0-20kN. To this aim, the gears were mounted on a 25kN hydraulic press, that changed the shock absorber route from 0 mm up to 200 mm (corresponding to the maximum take-off weight,~4600 kg). Obtained results are in good agreement with those provided by reference electrical strain gauges located very close to their optical counterparts, and demonstrate the great potentialities of FBG sensors technology to be employed for remote and real time load measurements on aircraft landing gears.
Use of Shape Memory Alloys (SMA) is more and more frequent in engineering because of their unique properties of completely recovering the imposed deformations after heating, or automatically returning to the unloaded configuration via a super-elastic process after very large strains (till around 10%). The process is regulated by a phase change in the material, shifting between martensite and austenite. Along this transformation, some SMA change their elastic properties by a factor three and damping coefficient by a magnitude. Super-elastic materials exhibit stable hysteresis loops under cyclic loading and dissipate energy without residual deformation thus providing in perspective self-centering capability for use in buildings earthquake protection. The present study investigates the performance of SMA-based devices for seismic protection of reinforced concrete structures. In countries with high seismic hazard, vulnerability assessment of existing constructions and seismic retrofit implementation is a major challenge for both scientific community and public administration. This paper illustrates seismic retrofit of an existing school building in Italy, using dissipating steel braces. Both SMA-wire dampers and mixed devices combining SMA elements and classical buckling-restrained axial dampers are considered for seismic upgrading. Adopted technique effectiveness and reliability are investigated by comprehensive nonlinear static and dynamic analyses. Numerical results show that super-elastic SMA dampers are effective for mitigating building response to strong earthquakes and providing systems self-centering capability with negligible residual strains.
After pioneering examples in the ’70 and the ’80, technology advances have brought aircraft morphing systems close to the exploitation on commercial vehicles. However, in spite of many successes, further steps shall be accomplished before series production lines are entered. They introduce new needs and sometimes exasperate aspects till now under control in the design phase. The increased number and kind of parts pushes for implementing additive manufacturing techniques; their modelling gives rise in turn to important simulation challenges. In case of mechanical, alternative to compliant systems, modelling of elements shall take in consideration behavior that is substantially different from the analogous counterparts on classical devices. Hinges and torsion bars are more diffused and smaller in these architectures. This work deals with hinges modelling inside mechanically-driven architectures for adaptive winglets. Impact of these aerodynamic surfaces on aircraft stability is crucial and accurate models are required to guarantee their correct implementation. Morphing capability emphasizes this occurrence even more. Schematization effects are investigated in terms of both static and dynamic response. The variation of the deformed shape is therefore examined, identifying the strain map and internal forces distribution changes, essential for design purposes and stress analysis. Modal characteristics deviations are then explored, which may substantially influence aeroelastic stability margins. It is envisaged that this approach could be exploited to consider lags effect. A parametric investigation is finally carried out to identify structural behavior sensitivity to such kind of modifications.
Blade geometry and stiffness variations lead to advantages that have been proved in several fields, from aerospace to turbomachinery. The advent of innovative materials as Shape Memory Alloys (SMA), have allowed non-conventional design approaches, targeting adaptive, smooth and extensive modifications of aerodynamic shapes and local stiffness. The Project “Shape Adaptive Blades for Rotorcraft Efficiency” (SABRE) within the EU program H2020, has the main objective of maturing blade morphing technologies and related processes, moving from the assessment of predictive codes integrated with novel philosophies of geometry alterations, till experimental validation within lab and wind tunnel environments. In this paper, an SMA demonstrator for active twist is proposed, aimed at modulating spanwise blade torsion angle for rotorcraft performance improvement. The idea is to combine the reference structure with embedded torque actuators. Quasi-steady operations are targeted because of the low frequency bandwidth of the addressed devices (under 1 Hz). Thus, single flight regimes are considered (hover, climb, forward flight). Actuation authority is a critical aspect for the proper design of that system. It is influenced by many geometrical and physical parameters like the cross section geometry or the materials Young modulus. The presented demonstrator is made of three main elements: an SMA rod system, structural elements representative of the blade body stiffness, and the connecting fixtures. An experimental campaign is carried out to verify the relations among alloys activation temperatures, induced stiffness levels, and forces and installation angles (pre-twist).
The paper presents a preliminary study about a de-icing system using ultrasonic waves. The activity has been developed within the project “SMart On-Board Systems” (SMOS), which is part of Italian Aerospace National Research Program, funded by the Italian Ministry of Education and Research and coordinated by CIRA. Conceived for an aircraft wing leading edge, the system shall be extended to other aircraft components, once its efficiency and reliability will be demonstrated. Herein, the results of a preliminary numerical work on a NACA 0012 profile are presented. Guided waves are generated by a piezoelectric transducer bonded on the structure and they cause shear stresses that induce ice delamination and fracture. The investigation is focused on the selection of most suitable excitation frequency for the actuator. Finite element analyses are performed to demonstrate the effectiveness of this approach.
The object of this work is a numerical model aimed at predicting the electrical conductivity of polymeric matrices filled with Carbon Nano-Tubes (CNT). The model, developed within the GRAPSS, ”Graphene-Polymeric Spray Sensor for Shape Recognition of Super-Deformable Structures” a National Project entirely funded by CIRA, will be used to address the design of a sprayable sensor aimed at measuring large deformations. The phenomenon of the tunneling, at the basis of the electrical and thermal conductivity of CNT filled polymeric matrices, was modeled through the finite element, FE, approach. Each particle was schematized as a cluster of nodes connected by highly conductive elements, in compliance with the large conductivity of the CNTs. When the tunneling condition was verified between two particles, a link was realized; the specific electrical resistance was computed on the basis of parameters like the mutual distance and the tunnel cross section area. The resulting system, a truss-structure network contained within a reference cubic volume, was then solved through a thermal analogy. The inward and outward currents, passing through two opposite faces of the cube, were simulated by applying thermal fluxes of opposite sign; the voltage drop caused by the global resistance was then estimated through a steady heat transfer analysis, giving the temperature gradient between the opposite faces. The ratio between the voltage drop and the inward-upward current (respectively, the temperature and the heat flux) represented then the global resistance of the cube. A parametric investigation was finally performed, finding out the dependence of the gage factor (strain vs resistance variation) on CNT concentration and aspect ratio parameters (curvature, diameter-length ratio) and the electrical conductivity.
The manufacturing and the preliminary numerical and experimental testing results of a fiber optic based sensor, able to recognize different load paths, are herein presented. This device is conceived to identify load directions by strain detection along a circumferential geometry. A demonstrator is realized by manufacturing a circular shaped, flexible glass/epoxy laminate hosting the sensible elements. Three loops of optical fiber, laying at different quotes along its thickness, are there integrated. The sensor system is supposed to be bonded on the structural element and then able to follow its deformations under load. The working principle is based on the comparison of the strain paths detected at each fiber optic loop at homologous positions. Rayleigh backscattering optical technology is implemented to measure high spatial resolution strains. A finite element model is used to simulate the sensor behavior and assess its optimal configuration. A preliminary experimental campaign and a numerical correlation are performed to evaluate sensor performance considering in-plane and bending loads.
Benefits in terms of aerodynamic efficiency, aeroelastic behaviour, stability and manoeuvrability performance coming from the adaptive variation of wing geometric (e.g. thickness and chamber) and mechanical (e.g. rigidity) parameters were widely proved. In this scenario, more and more efficient architectures based on innovative materials like shape memory alloys, piezoelectrics, magneto-rheologic fluids were ideated and related morphing ability was tested. Due to the large transmitted forces and deformations, for static applications, SMA based-on architectures were implemented. The essential idea of all these architectures is to integrate a SMA actuator, lacking of remarkable structural value, within a classical wing structure or within a suitably designed one. The main disadvantage of such architectures derives by the necessity of deforming a classical structure, not designed for reaching large displacements. In order to avoid these problems, in this work, the idea of integrating compliant structures by SMA elements, was considered. Some deformation strategies, focused on the wing aft part morphing, were ideated; related performance in terms of vertical displacement and rotation of the trailing edge was estimated by a FE approach. Each architecture is characterised by SMA rod elements able to guarantee large deformations and shape control under aerodynamic loads.
The aim of this paper, describing a semi-active Mass Damper system based on Magnetorheological (MR) Devices, is the evaluation of the effectiveness of a vibration control system based on semi-active dampers, applied to the case of a typical Italian historical construction subjected to seismic action. The reference model has been extracted from the structural scheme of a long-bay building and the control strategy takes into account a mass damper system. The MR damper design has been dealt with, by considering mechanical, hydraulic and electronic related aspects and problems. A specific logical scheme of the building integrated with the MR device has been analysed by means of the Simulink toolbox. By taking advantage of this model, the performance of the semi-active control system has been evaluated in comparison with the passive control strategy and with the structure without control.
The study of acoustic noise generated by helicopter main rotors is the object of many theoretical and experimental investigations because of the complexity of the related physical phenomena and its strong influence on the vehicle performance. One of the main targets of the FriendCopter European Project is to define technical solutions aimed at improving the helicopter acoustic performance. In this work some related activities are described. The extremely complex operating environment of a helicopter rotor contributes to noise generation through several distinct mechanisms: among them, blade vortex interaction noise (BVI) results extremely annoying when it occurs. One method for BVI alleviation is to increase the separation of the tip vortex from the rotor plane using an adaptive
blade tip (anhedral configuration) to diffuse the tip vortex or to displace it. In this work, as a first step of the investigation, a feasibility study on blade tip morphing will be addressed, neglecting
any aeroacoustic estimation; a specific flight condition will be considered to evaluate the efficiency of a particular smart system based on the coupled action of shape memory alloys (SMAs) and magneto-rheological fluids (MRFs). Such a kind of actuation system has to realise an on-off mechanism through which the tip blade displacement is maximised: the properties of the MR fluid will be exploited to selectively reduce the bending stiffness spanwise so that the SMA actuation is increased. A theoretical model and numerical investigations will be shown to evaluate the reliability and the effectiveness of the integrated system.
Aerodynamic control surfaces efficiency is among the major parameters defining the performance of generic aircraft and is
strongly affected by geometric and stiffness characteristics. A target of the '3AS' European Project is to estimate the eventual
benefits coming from the adaptive control of the torque rigidity of the vertical tail of the EuRAM wind tunnel model. The specific role of CIRA inside the Project is the design of a device based on the “Smart Structures and Materials” concept, able to produce required stiffness variations. Numerical and experimental investigations pointed out that wide excursions of the tail torque rigidity may assure higher efficiency, for several flight regimes. Stiffness variations may be obtained through both classical mechanic-hydraulic and smart systems. In this case, the attainable weight and reliability level may be the significant parameters to drive the choice. For this reason, CIRA focused its efforts also on the design of devices without heavy mechanical parts. The device described in this work is schematically constituted by linear springs linked in a suitably way to the tail shaft. Required stiffness variations are achieved by selectively locking one or more springs, through a hydraulic system, MRF-based. An optimisation process was performed to find the spring features maximising the achievable stiffness
range. Then, the hydraulic MRF design was dealt with. Finally, basing on numerical predictions, a prototype was manufactured and an experimental campaign was performed to estimate the device static and dynamic behaviour.
The transonic aerodynamic field around a wing section is characterized by a large number of peculiarities, which strongly influence the airfoil performance. In particular, a shock wave located on the wing upper surface strongly interacts with the boundary layer, causing a drag increase. Moreover, wave oscillations may give rise to the undesired aeroelastic phenomenon of buffeting. Aerodynamic studies have pointed out that shape airfoil modifications may lead to performance improvements. The aim of the work is to present a procedure to design and realize a tailored and integrated composite actuator made of an aluminium alloy sheet. The geometry of the skin element is modified by the combined action of a uniform pressure load producing static deformations, and tangential piezoelectric ceramic patches bonded through a laminate connection layer, towards one direction, preferably. Glass fiber/epoxy was selected to this target. The design procedure is made of a first part, devoted at the definition of the sheet thickness law (taking into account the ceramics contributions) that assures the deformed shape following the specific aerodynamic requirements, and a second part, applied to optimize the structure-actuators configuration. Analytical and numerical extensions of available models, able to predict the strain actuation on composite elements with variable thickness under different boundary conditions complete the proposed methodology. According to the obtained results and indications, an experimental bump prototype was realized. An experimental campaign is being carried out in order to compare the real behavior of the skin element with the theoretical predictions: static and dynamic bump deflected shape was measured.