During the last years, the research interest in assessing noise and vibration optimization has been addressed on different control typologies, based both on active and passive architectures. Within the paper, some preliminary activities aimed at the realization of a structurally simple, cheap and easily replaceable active control systems is discussed. Under these premises, the paper deals with the assessment of an Enhanced Synchronized Shunted Switch Architecture (SSSA) control architecture, based upon the use of piezoelectric devices, specifically optimized for a cantilver beam structure. Main activities regarded the control system set up and optimization, both under the electronic than the piezo location points of view, and control results under deterministic and stochastic forcing actions. Experimental results have been compared with the numerical one as well as a comparison between the SSSA approach and other active control architectures has been also presented and discussed. Results have shown a good performances of the proposed approach that present also a relative easy implementation if compared with already assessed control technologies.
The development of advanced monitoring system for strain measurements on aeronautical components remain an important target both when related to the optimization of the lead-time and cost for part validation, allowing earlier entry into service, and when related to the implementation of advanced health monitoring systems dedicated to the in-service parameters verification and early stage detection of structural problems. The paper deals with the experimental testing of a composite samples set of the main landing gear bay for a CS-25 category aircraft, realized through an innovative design and production process. The test have represented a good opportunity for direct comparison of different strain measurement techniques: Strain Gauges (SG) and Fibers Bragg Grating (FBG) have been used as well as non-contact techniques, specifically the Digital Image Correlation (DIC) and Infrared (IR) thermography applied where possible in order to highlight possible hot-spot during the tests. The crucial points identification on the specimens has been supported by means of advanced finite element simulations, aimed to assessment of the structural strength and deformation as well as to ensure the best performance and the global safety of the whole experimental campaign.
Nowadays, smart composites based on different nano-scale carbon fillers, such as carbon nanotubes (CNTs), are increasingly being thought of as a more possible alternative solution to conventional smart materials, mainly for their improved electrical properties. Great attention is being given by the research community in designing highly sensitive strain sensors for more and more ambitious challenges: in such context, interest fields related to carbon nanotubes have seen extraordinary development in recent years. The authors aim to provide the most contemporary overview possible of carbon nanotube-based strain sensors for aeronautical application. A smart structure as a morphing wing needs an embedded sensing system in order to measure the actual deformation state as well as to “monitor” the structural conditions. Looking at more innovative health monitoring tools for the next generation of composite structures, a resin strain sensor has been realized. The epoxy resin was first analysed by means of a micro-tension test, estimating the electrical resistance variations as function of the load, in order to demonstrate the feasibility of the sensor. The epoxy dogbone specimen has been equipped with a standard strain gauge to quantify its strain sensitivity. The voltamperometric tests highlight a good linearity of the electrical resistance value as the load increases at least in the region of elastic deformation of the material. Such intrinsic piezoresistive performance is essentially attributable to the re-arrangement of conductive percolating network formed by MWCNT, induced by the deformation of the material due to the applied loads. The specimen has been prepared within this investigation, to demonstrate its performance for a future composite laminate typical of aerospace structures. The future carbon-fiber sensor can replace conventional metal foil strain gauges in aerospace applications. Furthermore, dynamic tests will be carried out to detect any non-reversible changes to the sensing response.
Maintenance tasks and safety aspects represent a strategic role in the managing of the modern aircraft fleets. The demand for reliable techniques for structural health monitoring represent so a key aspect looking forward to new generation aircraft. In particular, the use of more technologically complex materials and manufacturing methods requires anyway more efficient as well as rapid application processes to improve the design strength and service life. Actually, it is necessary to rely on survey instruments, which allow for safeguarding the structural integrity of the aircraft, especially after the wide use of composite structures highly susceptible to non-detected damages as delamination of the ply. In this paper, the authors have investigated the feasibility to implement a neural network-based algorithm to predict the impact event at low frequency, typically due to the bird collision. Relying upon a numerical model, representative of a composite flat panel, the approach has been also experimentally validated. The purpose of the work is therefore the presentation of an innovative application within the Non Destructive Testing field based upon vibration measurements. The aim of the research has been the development of a Non Destructive Test which meets most of the mandatory requirements for effective health monitoring systems while, at the same time, reducing as much as possible the complexity of the data analysis algorithm and the experimental acquisition instrumentation. Future activities will be addressed to test such technique on a more complex aeronautical system.
The present work relates to the assessment and testing of a multifunctional intelligent system, based upon the use of piezoelectric devices, devoted both to the active noise and vibration control and to damage detection f the structure. In the control application, the piezoelectric devices (in form of patches) play the role of actuators; their induced secondary vibration field has the target to reduce the primary one through a specific control algorithm and system. In the health monitoring application, the piezo devices play both the roles of actuators and sensors. In fact the developed technique is primarily based upon the evaluation and comparison of the structure Frequency Response Functions (FRF) that intrinsically contains all the information regarding the structural properties whose change may be correlated with incipient damages. The aforementioned application were investigated and experimentally assessed with good results with reference to a typical partial fuselage structure (three frames, eight stringers and the skin panels: 1.2 m x 1.7 m). On the noise control application side, a height sensors/height actuators control architecture was then assessed and experimentally tested whose results may be synthesized in a 30 dB vibration level reduction at sensors locations and more than 20 dB of reduction of the associated noise field. In the optic of a multifunctional intelligent system, the aforementioned set of piezo's was decided to be used also for health monitoring application. As a preliminary activity, an extensive monitoring was performed on the integer structure to verify the sensibility of the system and the stability of the defined Damage Index (DI) in respect to environmental factor not related to structural real modification. To verify the sensibility of the technique to reveal and locate a typical shear clip damage, a set of rivets were successively cut in the area surrounding the frame shear clip, and relative FRF's were acquired and relative DI calculated. The analysis of the data showed a good sensibility of the system to identify the presence of a damage with maximum values of the DI in the sensor closest to the damage location and with an absolute value of the index growing up with damage extension.
A technique for detecting and locating structural damages is presented in this paper. It is based on the analysis of experimentally evaluated frequency response functions (FRFs) and consists of a comparison of the FRFs of the healthy structure which are assumed as reference and the FRFs collected at different times. A damage detection index interprets the differences between the FRFs. The results obtained by this technique when tested on a partial frame of a commercial aircraft were very interesting. It is possible to detect and locate all damages which were simulated/induced and also gave an indication of the extent of the damage. Moreover, the technique has the basic features required of a new NDE technique such as being non- model related and having the possibility of performing real- time monitoring.
During the last five years, the Dept. of Aeronautical Engineering of the University of Naples, has carried out a lot of work, especially on the experimental side, focused on assessing the feasibility of an active vibration and noise control approach, based on the use of piezoceramic actuators and sensors bonded to different structural elements. This paper concerns an application of this technique relative to a partially curved stiff frame of a medium civil transport jet aircraft. The general procedure, as previously assessed on different test articles, requires as first step, the dynamic characterization of the test article, to best point out the target of control procedure in terms of deformed shapes relative to the frequency of most interest. The use of PZT piezoactuators to be bonded on the structure guarantee at the same time high actuators forces in front of a low weight increment. The hearth of the MIMO (Multi Input Multi Output) feedforward control algorithm that is usually applied, is then represented by an ANN (Artificial Neural Network) control algorithm that use the evaluation of experimental FRF as measured by reference accelerometer, to calculate the optimum control forces to be applied to the actuators to minimize a target cost function. Experimental results provided over 32 dB of overall vibration level reduction in a single controlled mode shape, without any spillover effect.
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