To see the other types of publications on this topic, follow the link: Flexible Structural health monitoring.
Dissertations / Theses on the topic 'Flexible Structural health monitoring'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Flexible Structural health monitoring.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Liu, Wei Lin. "Integrated and flexible ultrasonic transducers for structural health monitoring on aircraft structures." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97155.
Full textAbstract:
Fatigue crack initiating from fastener holes in aluminum plates is a typical damagefrequently found on modern aircraft structures. Requirements for life extension of agingaircraft fleets and reduced maintenance costs have been accelerating the developments ofstructural health monitoring (SHM) technologies. This thesis considers the active sensingapproach of SHM that involves the integrated ultrasonic transducer (IUT) and the flexibleultrasonic transducer (FUT). The main component of IUT and FUT was piezoelectriclead-zirconate-titanate composite films which were fabricated using the sol-gel spraytechnique. The crack growth monitoring capability of the IUT and FUT was successfullydemonstrated on aluminum plates with fatigue cracks. The artificial damages on analuminum test article representing aircraft structural complexity were also detected by theFUT array bonded on both planar and curved surfaces. Finally, the design and fabricationof miniature angle beam wedges having low spurious noise are presented. The fatiguecrack on an aluminum thin plate was detected using the FUT bonded onto such anglebeam wedges.<br>Les fissures dues à la fatigue du métal initiées aux trous de fixation dans lesplaques d'aluminium sont des problèmes communs dans les avions modernes. De plus,l'utilisation d'avions de plus en plus âgés et le besoin de réduire leurs coûts d'entretien àaccélérer le développement de la technologie de la surveillance de la santé structurelle(SSS) de ces derniers. Ce mémoire considère l'approche active de la SSS en incorporantla capacité des capteurs intégrés ultrasonores (CIU) et des capteurs flexibles ultrasonores(CFU). L'ingrédient principal des CIU et CFU est des films à base de plomb-zirconatetitanatequi sont fabriqués à partir de la technique sol-gel. La capacité des CIU et CFU àsurveiller la croissance des fissures sur des plaques d'aluminium fissurées par fatigue futdémontrée avec succès. Les défauts artificiels mis dans des échantillons de plaquesd'aluminium représentant la complexité structurelle furent également détectés par unematrice de CFU collée sur des surfaces plane et courbe. Finalement, la conception et lafabrication de coins d'angles miniatures ayant comme caractéristiques de faibles bruitsparasites sont présentées. Les fissures par fatigue sur de minces plaques d'aluminiumfurent détectées en utilisant les CFU collés sur de tels coins.
2
Li, Xinming. "Piezoelectric-based structural health monitoring of flexible beam connection damage." Thesis, University of Ottawa (Canada), 2003. http://hdl.handle.net/10393/26511.
Full textAbstract:
Structural health monitoring is an emerging technology addressing major concerns in the operation of in-service structures, i.e. the reliability of the structures and the cost associated with maintaining reliability. In this thesis, the motivation of structural health monitoring has been discussed within the framework of non-destructive evaluation. To be a common failure mode, connection damage or lap joint damage is chosen as damage signature in a structure, consisting of a flexible aluminum beam jointed on a frame by bolts. To simulate connection damage, the stress relaxing on the bolt is achieved by the action of bolt looseness quantified by rotation angle. The dynamic response of flexible beam system is monitored with a piezoelectric transducer. To produce exciting signal, an electro-mechanical system processes the voltage signal. Response interpretation is carried out on PC or on an embedded DSP chip in real time. The two analysis methods, frequency response method and wavelet analysis method, were explored to identify early "changes" of beam connection so as to reach the goal of structural health monitoring.
3
Enriquez, Karla Cecilia. "Development of an ultra-low power sensor for highway health monitoring." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
Full text
4
Nauman, Saad. "Geometrical modelling and characterization of 3D warp interlock composites and their on-line structural health monitoring using flexible textile sensors." Thesis, Lille 1, 2011. http://www.theses.fr/2011LIL10010/document.
Full textAbstract:
Ce mémoire de thèse de doctorat est structuré en deux parties. Dans la 1ère partie, une nouvelle approche traitant la caractérisation géométrique et mécanique est décrite. La modélisation géométrique de tissu 3D interlock est corrélée avec les paramètres de tissage afin de mieux prendre en compte ces paramètres. Le tissage de tissu 3D interlock est décrit en détail. Par la suite, une étude a été menée pour mieux comprendre les changements qui se produisent dans une mèche de carbone lorsque cette dernière est intégrée dans un renfort. Un coefficient de transfert des propriétés mécaniques a été proposé permettant une meilleure compréhension de l’influence des paramètres structuraux sur les propriétés d’un composite. Dans la 2eme partie du mémoire, un système de mesure in situ pour les composites a été développé. Ce système comporte un capteur souple et un module de traitement de données et d’amplification des signaux. Le capteur fibreux développé durant nos recherches a été inséré pendant le tissage comme un fil de trame. Le système a été testé sur une plaque en composite, contenant les renforts en 3D interlock, en traction. Le capteur suit fidèlement les déformations de la plaque composite jusqu’à la rupture<br>This thesis is divided in two parts. In the first part a geometrical modelling approach has been developed in tandem with weaving parameters. The reinforcements were woven on a modified conventional loom to study the geometry of these structures. Their weaving has been described in detail. The weaving parameters have been correlated to the modelling approach. The meso structural modelling approach is capable of predicting essential reinforcement geometrical characteristics at meso structural level without being too complicated. Furthermore, mechanical characterization of 3D interlock reinforcements has been carried out in such a way that a track of mechanical properties during the complete production cycle has been maintained. A novel parameter called strength transfer coefficient was proposed which allows better understanding of the influence of structural parameters on the final properties of the composite. In the second part of the thesis an online structural health monitoring system which is composed of a textile based sensor and signal amplification and treatment module, has been developed. This system is capable of detecting structural deformations in the composite as the sensor is integrated during the manufacturing of the reinforcement and can follow its deformation pattern when composite is subjected to tensile loading in a real time
5
Suh, Peter M. "Robust modal filtering for control of flexible aircraft." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51780.
Full textAbstract:
The work in this dissertation comprises aeroservoelastic simulation development, two modal filter design case studies and theoretical improvement of the modal filter. The modal filter is made robust to sensor bias. Studies have shown that the states estimated by the modal filter can be integrated into active structural control. The integration of modal filters into aircraft structural control systems is explored.
Modal filters require distributed sensing to achieve accurate modal coordinate estimates. Distributed sensing technology has progressed to the point, where it is being tested on aircraft such as Ikhana and the upcoming X-56A. Previously, the modal filter was criticized for requiring too many sensors. It was never assessed for its potential benefits in aircraft control. Therefore it is of practical interest to reinvestigate the modal filter.
The first case study shows that under conditions of sensor normality, the modal filter is a Gaussian efficient estimator in an aeroservoelastic environment. This is a fundamental experiment considering the fact that the modal filter has never been tested in the airflow.
To perform this case study a linear aeroservoelastic code capable of modeling distributed sensing is developed and experimentally validated. From this code, a computational wing model is fitted with distributed sensing. A modal filtering design methodology is developed and applied.
With distributed sensing and modal filtering feedback control is achieved. This is also compared and contrasted with a controller using state-of-the-art accelerometers. In addition, new methods of active shape control are introduced for warping an aeroelastic structure utilizing the modal filter and control surfaces.
The next case study takes place in a realistic setting for an aircraft. Flexible aircraft bring challenges to the active control community. Increased gust loads, possibility of flutter, and off-design drag may detrimentally affect performance and safety. Aeroservoelastic tailoring, gust load alleviation (GLA) and active flutter suppression (AFS) may be required on future flexible air vehicles. It is found that modal filters can theoretically support these systems.
The aircraft case study identifies additional steps required in the modal filtering design methodology. Distributed sensing, the modal filter and modal reference shape control are demonstrated on the X-56A flutter-unstable simulation model. It is shown that control of deformations at potentially millions of points on an aircraft vehicle can be achieved through control of a few modal coordinates.
Finally modal filter robustness is theoretically improved and computationally verified. State-of-the-art modal filters have high bias sensitivity. In fact, this is so critical that state-of-the-art modal filters may never be certified for aircraft implementation. This is especially true within a flight critical control system. The solution to this problem is found through derivation of the robust modal filter.
The filter combines good properties of concentration algorithms with robust re-descending M-estimation. A new trim criterion specific to the strain based modal sensing system is derived making the filter robust to asymmetric or leverage point outliers. Robust starts are introduced to improve convergence of the modal estimation system to the globally optimal solution in the presence of 100s of biased fiber optic sensors.
6
Shih, Jeanne-Louise. "Flexible ultrasonic tranducers using ferroelectric sol-gel composite films for non-destructive testing and structual health monitoring." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114146.
Full textAbstract:
High temperature (HT) flexible ultrasonic transducers (FUTs) for nondestructive testing (NDT) and structural health monitoring (SHM) were developed using the sol gel spray method. Although the integrated ultrasonic transducer (IUT) is highly desirable as a NDT and SHM solution since it is a technique of directly coupling a fabricated UT to an inspected structure such an on-site fabrication solution may not be particularly attractive. FUTs acting as small and lightweight UTs may be fabricated off-site and then on-site installed. Lead-zirconate titanate composite (PZT-c) and bismuth titanate composite (BIT-c) films were sprayed onto 75 µm or 38 µm thick metallic membranes. At room temperature, these FUTs demonstrate consistently high piezoelectric performance comparable to commercially available UTs when used to perform thickness measurements over flat surfaces. Such FUTs offer the advantage that they may be conformed to curved surfaces. Additionally, these may be fabricated off-site and installed on-site. Therefore, bonding techniques such as glueing and brazing onto pipes were studied with the brazing demonstrating operability at 490ºC, thereby offering a HT, conformable, semi-permanent and on-site installed NDT and SHM solution. Techniques of room temperature selective area Corona poling and expanded area Corona poling were demonstrated, allowing for the patterning of the films and a method for integrating the Corona poling technique to either maintain or repair a network of on-site installed FUTs. The development of these techniques had started with the use of UV to replace the heating of the sol-gel composite film necessary during Corona poling. It was however found that under the same conditions, neither heat nor UV was required for the poling o f the film. Nonethless, this prompted optical studies with respect to some semiconductor and ferroelectric properties of these sol-gel films. Non-bonded FUTs are also presented as dry contact and momentary FUTs. The spray technique used with a shadow mask and other techniques was used to fabricate different devices such as ultrasonic phased-arrays and unimorph, piezoelectric vibrational energy harvesters, meant to be integrated with a battery network of NDT, SHM FUTs as an intermittent, self-sustained power source. These demonstrated an amplification in charge generation with a pre-stressed configuration, allowable by the flexible film and substrate. With such high piezoelectric performance inherent in the sol-gel film, a study into some ferroelectric properties of the film was performed, in particular by the optical approach using UV. The results demonstrated PZT-c films were absorbant between 200 and ~400 nm both before and after crystallization from HT treatment with an approximated bandgap of 2.8-3.1 eV. A photoconductivity of 0.0205 Ω-1cm-1 was measured for a 5 μm thick PZT-c film. An effect in which a lowering of the Curie temperature (Tc) was observed demonstrates that study in relation to the field of photoferroelectrics with such composite films may be of scientific interest. Lastly, the poling of the film in nanoscale using Piezo Force Microscopy (PFM) was demonstrated.<br>Dans cette thèse, des capteurs flexibles ultrasonores (CFU) à haute température (HT) ont été développés pour des applications dans le domaine de l'évaluation non destructive (END) et celui de la surveillance de la santé structurelle (SSS). Alors que les capteurs intégrés (CIU) qui peuvent être fabriqués sur site et qui ne nécessitent pas de couplant sont des solutions attrayantes dans ces domaines, la fabrication sur site peut souvent être difficile ou infaisable selon les conditions. Par contre, les CFUs qui sont petits et légers peuvent être fabriqués à part et installés sur site. Les couches composées piézo-électriques, avec lesquelles les capteurs ultrasoniques à haute température (CUHT) sont fabriqués, sont développés à partir de la technique sol-gel. Ces couches constituées de zirconate titanate de plomb (PZT-c), ou de titanate de bismuth (BIT-c) sont déposées sur des substrats métalliques d'épaisseurs de 75 m ou de 38 m. À la température de la pièce, ces CFUs démontrent une performance piézo-électrique comparable aux capteurs commerciaux lors des mesures d'épaisseur sur des surfaces plates. L'avantage de ces CFUs est que ceux-ci peuvent se conformer à des surfaces courbes. De plus, les CFUs peuvent être fabriqués à part et installés sur-site. De plus, des moyens pour attacher ces capteurs aux structures courbes comme les tuyaux ont été essayés. Des techniques de collage et de brasage ont été démontrées, avec les CFUs opérationnels à ces hautes températures jusqu'à 490ºC, offrant une solution conformable, HT, moyennement permanente, en plus de l'avantage de l'installation sur site. Les techniques de polarisation Corona à température de la pièce qui permettent une polarisation sélective ou à grande surface ont été développées, permettant de polariser des motifs. Le développement de ces techniques avait débuté avec l'utilisation d'ondes UV pour remplacer le chauffage qui était nécessaire durant la polarisation Corona, permettant une polarisation des couches piézo-électriques sol-gel à température de la pièce. Il a cependant été découvert que sous ces conditions, ni le chauffage, ni l'UV n'étaient nécessaires, ce qui a néanmoins motivé des études optiques vis-à-vis ces couches sol-gel par rapport à leurs propriétés semi-conductrices et ferroélectriques. La méthode de sol-gel utilisée avec un masque ainsi que d'autres techniques ont aussi été utilisées pour fabriquer des capteurs de configurations différentes comme le capteur à éléments en phase ou le capteur à contact momentané. Le sol-gel a aussi été utilisé pour fabriquer un capteur d'énergie vibratoire unimorphe dans le but d'être intégré avec un système de batteries et avec le réseau de CFU pour END et SSS come source d'énergie de façon discontinue mais autonome. Ces capteurs démontrent une augmentation de charge générée lorsqu'ils sont mis sous une tension pré-courbée, une configuration possible avec la couche et le substrat flexible. Les résultats optiques ont démontré une absorbance envers les ondes UV (~200-400 nm) dans l'état sol-gel des couches ainsi qu'après cristallisation à HT, avec une structure de bande de 2.8-3.1 eV. Une photoconductivité de 0.0205 Ω-1cm-1 a été mesurée pour une couche de PZT-c d'épaisseur de 5 μm. Un effet où une baisse en température du point Curie (Tc) a été observée sous ondes UV pour les couches de PZT-c démontre que des études dans le domaine de la photoferroélectricité avec ces couches seraient d'intérêt scientifique. La polarisation d'une couche de PZT-c sur une surface 500 nm x 500 nm utilisant la microscopie à force piezo (MFP) a aussi été démontrée.
7
Genari, Helói Francico Gentil. "Damage-Tolerant Modal Control Methods for Flexible Structures." Thesis, Paris, ENSAM, 2016. http://www.theses.fr/2016ENAM0032/document.
Full textAbstract:
Les structures intelligentes sont de plus en plus présentes dans différentes industries et notamment dans les domaines de l'aéronautique et du génie civil. Ces structures sont dotées de fonctions qui leur permettent d'interagir avec leur environnement, d'adapter leurs caractéristiques structurelles (raideur, amortissement, viscosité, etc.) selon les besoins ou de surveiller leur état de santé ou « SHM » (Structural Health Monitoring). Aujourd’hui, les performances des méthodes de contrôle actif peuvent être considérablement dégradées lors de l’apparition d’endommagement. Le contrôle actif tolérant aux dommages ou « DTAC » (Damage Tolerant Active Control) est un champ de recherche récent qui s'intéresse à l'élaboration d'approches intégrées pour réduire les vibrations tout en surveillant l'intégrité de la structure, en identifiant les éventuels dommages, et en reconfigurant la loi de commande.Cette thèse apporte une contribution au DTAC en proposant une approche originale basée sur la norme H∞ modale . Les méthodes proposées se focalisent principalement sur le cas où plusieurs actionneurs et capteurs piézoélectriques non-collocalisés sont utilisés pour atténuer les vibrations des structures endommagées. Le manuscrit comprend quatre parties principales. Le chapitre 2 présente des rappels sur la commande H∞ et sur sa solution sous optimale obtenue par une approche par inégalité matricielle ou « LMI » (Linear Matrix Inequality), sur lesquels s’appuient les développements proposés dans ce travail. Le chapitre 3 décrit la norme H∞ modale introduite pour le contrôle actif des vibrations. Cette commande présente une sélectivité modale élevée, permettant ainsi de se concentrer sur les effets du dommage tout en bénéficiant des propriétés de robustesse qu'offre la commande H∞ vis-à-vis du spillover et des variations de paramètres. Une nouvelle stratégie de rejet des vibrations est proposée au chapitre 4. C'est une approche dite préventive où une prise en compte lors de l'élaboration de la commande H∞ modale, des zones fortement contraintes de la structure, où le risque d’endommagement est élevé est réalisée. Un algorithme SHM est proposé afin d'évaluer la sévérité du dommage pour chaque mode. Le chapitre 5 propose une nouvelle approche modale à double boucle de commande pour faire face à des endommagements imprévisibles. Un premier correcteur est conçu dans ce but pour satisfaire les contraintes de performance et de robustesse sur la structure saine, tandis que le second a pour objectif de conserver un contrôle satisfaisant quand un dommage survient. La loi de commande s'appuie sur un observateur d’état et d'un algorithme SHM pour reconfigurer en ligne le correcteur. Toutes les approches DTAC proposées sont testées en utilisant des simulations (analytiques et éléments finis) et/ou des expérimentations sur des structures intelligentes<br>Smart structures have increasingly become present in different industry applications and particularly in the fields of aeronautics and civil engineering. These structures have features that allow interactions with the environment, adapting their characteristics according to the needs (stiffness, damping, viscosity, etc.), monitoring their health or controlling their vibrations. Today smart structure active control methods do not respond appropriately to damage, despite the capacity of external disturbances good rejection. Damage-tolerant active control (DTAC) is a recent research area that aims to develop integrated approaches to reduce the vibrations while monitoring the integrity of the structure, identifying damage occurrence and reconfiguring the control law of the adopted active vibration control method.This thesis contributes to DTAC area, proposing a novel modal control framework and some applying strategies. Developed methods focus in non-collocated flexible structures, where multiples piezoelectric sensors and actuators are used to attenuate damaged structure vibration. The chapters present four main topics and the conclusions. Chapter 2 reviews the regular suboptimal H∞ problem and its respective solution based on the linear matrix inequality (LMI) approach, which is a fundamental tool for the development of subsequent topics. Chapter 3 introduces the modal H∞-norm based method for vibration control, which reveals high modal selectivity, allowing control energy concentration on damage effects and presenting robustness to spillover and parameter variation. A new control strategy is developed in Chapter 4, taking into account existing knowledge about the structure stressed regions with high probability of damage occurrence, leading to specific requirements in the modal H∞ controller design. A structural health monitoring (SHM) technique assesses each damaged mode behavior, which is used to design a preventive controller. Chapter 5 presents a novel modal double-loop control methodology to deal with the unpredictability of damage, nevertheless ensuring a good compromise between robustness and performance to both healthy and damaged structures. For this purpose, the first loop modal controller is designed to comply with regular requirements for the healthy structure behavior, and the second loop controller is reconfigured aiming to ensure satisfactory performance and robustness when and if damage occurs, based on a state-tracking observer and an SHM technique to adapt the controller online. In all these chapters, simulated (analytical and finite elements based) and/or experimental aluminum structures are used to examine the proposed methodology under the respective control strategies. The last chapter subsumes the achieved results for each different approach described in the previous chapters
8
Webb, Graham Thomas. "Structural health monitoring of bridges." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708027.
Full text
9
Grisso, Benjamin Luke. "Advancing Autonomous Structural Health Monitoring." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/29960.
Full textAbstract:
The focus of this dissertation is aimed at advancing autonomous structural health monitoring. All the research is based on developing the impedance method for monitoring structural health. The impedance technique utilizes piezoelectric patches to interrogate structures of interested with high frequency excitations. These patches are bonded directly to the structure, so information about the health of the structure can be seen in the electrical impedance of the piezoelectric patch. However, traditional impedance techniques require the use of a bulky and expensive impedance analyzer. Research presented here describes efforts to miniaturize the hardware necessary for damage detection. A prototype impedance-based structural health monitoring system, incorporating wireless based communications, is fabricated and validated with experimental testing. The first steps towards a completely autonomous structural health monitoring sensor are also presented. Power harvesting from ambient energy allows a prototype to be operable from a rechargeable power source.
Aerospace vehicles are equipped with thermal protection systems to isolate internal components from harsh reentry conditions. While the thermal protection systems are critical to the safety of the vehicle, finding damage in these structures presents a unique challenge. Impedance techniques will be used to detect the standard damage mechanism for one type of thermal protection system. The sensitivity of the impedance method at elevated temperatures is also investigated.
Sensors are often affixed to structures as a means of identifying structural defects. However, these sensors are susceptible to damage themselves. Sensor diagnostics is a field of study directed at identifying faulty sensors. The influence of temperature on these techniques is largely unstudied. In this dissertation, a model is generated to identify damaged sensors at any temperature. A sensor diagnostics method is also adapted for use in developed hardware. The prototype used is completely digital, so standard sensor diagnostics techniques are inapplicable. A new method is developed to work with the digital hardware.<br>Ph. D.
10
Ward, Jacob Thomas Elliott. "Guided wave structural health monitoring." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.682233.
Full textAbstract:
Routine airframe Non-Destructive Testing (NDT) procedures are costly and prone to human error. Guided wave structural health monitoring (GWSHM) shows great promise to in future assist these carefully regulated aerospace NDT practices. Using automatic GWSHM to both detect and localise damage can better focus the human NDT effort and ultimately lead to safer operation of airframes. The thesis presents structural health monitoring techniques for airframes using measurements of guided waves. Work is presented on both metal plates and carbon fibre reinforced plastic panels. An active GWSHM method is considered in its capability to detect and localise damage by measurements of scattered Lamb waves from artificially placed damage. The contribution to knowledge on active GWSHM has been towards effective and practical strategies for placing a low number of transducers into arrays suitable for global coverage. Much early active GWSHM studies often adopted a uniformly sparse distribution of transducer elements, perhaps in an attempt to gain the best possible global coverage. In this thesis, active GWSHM performance has been evaluated for arrays of different geometry and has shown that a uniformly sparse distribution of transducer elements may not be the most effective strategy when using a minimal number of sensors. Simulated and artificial damage, placed with different orientations over a large area, has been used to test candidate array layouts. It finds the layout optimal for damage detection is not necessarily the layout optimal for damage localisation. The zeroth order anti-symmetric Lamb wave mode has been used at low frequency-thickness. The mode, referred to as the flexural mode when propagating with low frequency-thickness, is favoured for its short wave length and long range. At low frequency-thickness this mode is quickly outrun by its symmetric counterpart, causing coherent noise in the signals recorded. Baseline subtraction is used to suppress the coherent noise before imaging. Benign structural features, that would usually hinder damage-localisation from an image, are actually found to assist damage localisation for some array layouts when using the reference baseline signal subtraction technique. A passive GWSHM method is considered in its capability to localise impacts. Impact events on carbon fibre panels are localised using a low frequency passive array. The technique is suggested for evaluating damage from tyre-burst or propeller debris impacts to airframe surfaces. It is particularly relevant to new airframe designs that have significant usage of composite materials on their outer surface. Historically the aerospace sector has readily adopted time of arrival estimation methods similar to those found on a standard oscilloscope. As an example, acoustic emission monitoring, in recent decades has routinely used threshold-crossing as a means of time of arrival measurement. An alternative is presented requiring the whole time series to be post-processed. It extracts an alternative arrival time from propagating waves resulting from the impact, which can be used in time-difference of arrival algorithms. This method is shown to be more reliable and accurate for impact localisation than historical techniques.
11
Singh, Gurjashan. "Health Monitoring of Round Objects using Multiple Structural Health Monitoring Techniques." FIU Digital Commons, 2010. http://digitalcommons.fiu.edu/etd/330.
Full textAbstract:
Structural Health Monitoring (SHM) techniques are widely used in a number of Non – destructive Evaluation (NDE) applications. There is a need to develop effective techniques for SHM, so that the safety and integrity of the structures can be improved. Two most widely used SHM methods for plates and rods use either the spectrum of the impedances or monitor the propagation of lamb waves. Piezoelectric wafer – active sensors (PWAS) were used for excitation and sensing. In this study, surface response to excitation (SuRE) and Lamb wave propagation was monitored to estimate the integrity of the round objects including the pipes, tubes and cutting tools. SuRE obtained the frequency response by applying sweep sine wave to surface. The envelope of the received signal was used to detect the arrival of lamb waves to the sensor. Both approaches detect the structural defects of the pipes and tubes and the wear of the cutting tool.
12
Brigman, Nicholas (Nicholas Allen). "Structural health monitoring in commercial aviation." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/73846.
Full textAbstract:
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 87-90).<br>The number of aging commercial aircraft in service is steadily increasing as airlines continue to extend the life of their aircraft. Aging aircraft are more susceptible to fatigue and corrosion and require more frequent and intensive inspections and maintenance, which is a financial drain on operators. One way to improve the economics and safety of commercial aircraft is through implementation of a structural health monitoring (SHM) system. An ideal SHM would be able to give be capable of indicating damage type, location, severity, and estimate the remaining life of the structure while the structure is in use. This paper is an overview of how SHM can be applied in commercial aviation including discussion of requirements, implementation, challenges, and introducing several possible SHM systems. The SHM systems introduced in this paper are: vibration based monitoring, fiber optic sensors, and high frequency wave propagation techniques including acoustic emission, ultrasonic, Lamb waves, piezoelectric and MEMS actuator/sensors. The limitations and challenges inhibiting introduction of SHM to industry and recommendations for the future are also discussed.<br>by Nicholas Brigman.<br>M.Eng.
13
Mani, Girindra N. "Structural Health Monitoring of Rotordynamic Systems." University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1144522032.
Full text
14
Ashwin, Belle. "WIRELESS INTELLIGENT STRUCTURAL HEALTH MONITORING SYSTEM." VCU Scholars Compass, 2008. http://scholarscompass.vcu.edu/etd/1626.
Full textAbstract:
Metal structures are susceptible to various types of damages, including corrosion, stress damage, pillowing deformation, cracks etc. These kinds of damages in the metal structures occur mainly due to operational conditions and exposure to the environment. Our research involves a portable integrated wireless sensor system with video camera and ultrasound capabilities which is being developed to investigate corrosion damage on real structures in real time. This system uses images of the metal surfaces, which are captured from an integrated wireless sensor and then quantified and analyzed using computational intelligence. The quantification of the obtained images is done with specialized component analysis software which enhances and performs wavelet transforms on the received images. Through this quantized analysis of the images we can detect and isolate regions of degradation on the metal surface. We believe that the final developed system will allow us to detect damage in metallic structures in its early stages, thereby ensuring proper safety and maintenance of its structural health. This system will further be targeted towards medical applications with capabilities of remote health monitoring. The initial target areas being bone structure and cancer detection and analysis. Applying such a wireless data capture system in these areas will reveal a broad spectrum of the usage of such an application system.
15
Azhari, Faezeh. "Cement-based sensors for structural health monitoring." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/7324.
Full textAbstract:
The purpose of structural health monitoring is to continuously and accurately assess the performance of structures using a sensory system.
Recently introduced, cement-based sensors are piezoresistive and therefore can be used to sense stress/strain, simply by monitoring their electrical resistivity. These sensors, also known as smart (self-monitoring) structural materials can be used as a part or total component of structures and provide both structural capability and response to applied stress and damage.
In this study cement-based sensors are developed using two types of carbon fibres, as well as both single-walled and multi-walled carbon nano-tubes. A wide range of experiments were conducted to pinpoint the most efficient fibre content, frequency, electrode type and resistivity measurement technique. The influence of different parameters such as curing, temperature, moisture and chloride were also investigated.
The resistivity of the specimens increased with curing time, but became almost constant after a certain amount of time. The resistivity values decreased with increasing temperature and increased with the decrease in temperature at a rate of about 22-35 ohm-cm/°C. It was further found that moisture and chloride have a considerable influence on the electrical resistivity of these sensors.
Next, the response of the developed cement-based sensors to compressive, tensile and flexural loading was explored. The resistivity values from the sensors were compared with load and displacement values as well as strain data acquired from conventional strain gauges.
The results indicate that electrical resistivity of the sensors increases reversibly upon tension and decreases reversibly under compression provided that substantial cracking does not occur and the sensor remains in the elastic range. Once a dense field of micro-cracking followed by macro-cracking occurs, these sensors respond distinctly, possibly even prior to the appearance of visible cracks, providing an early prediction of any upcoming failure.
The resistivity measurements under both compressive and tensile stress demonstrated an excellent correlation with strain. The developed sensors offer gauge factors well above those of electrical strain gauges.
It is concluded, therefore, that cement-based sensors can be the future alternative for conventional sensors in the structural health monitoring of concrete structures.
16
Bartoli, Ivan. "Structural health monitoring by ultrasonic guided waves." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2007. http://wwwlib.umi.com/cr/ucsd/fullcit?p3283893.
Full textAbstract:
Thesis (Ph. D.)--University of California, San Diego, 2007.<br>Title from first page of PDF file (viewed December 3, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 311-325).
17
Singh-Levett, Ishan. "Real-time integral based structural health monitoring." Thesis, University of Canterbury. Mechanical Engineering, 2006. http://hdl.handle.net/10092/1171.
Full textAbstract:
Structural Health Monitoring (SHM) is a means of identifying damage from the structural response to environmental loads. Real-time SHM offers rapid assessment of structural safety by owners and civil defense authorities enabling more optimal response to major events. This research presents an real-time, convex, integral-based SHM methods for seismic events that use only acceleration measurements and infrequently measured displacements, and a non-linear baseline model including hysteretic dynamics and permanent deformation. The method thus identifies time-varying pre-yield and post-yield stiffness, elastic and plastic components of displacement and final residual displacement. For a linear baseline model it identifies only timevarying stiffness. Thus, the algorithm identifies all key measures of structural damage affecting the immediate safety or use of the structure, and the long-term cost of repair and retrofit. The algorithm is tested with simulated and measured El Centro earthquake response data from a four storey non-linear steel frame structure and simulated data from a two storey non-linear hybrid rocking structure. The steel frame and rocking structures exhibit contrasting dynamic response and are thus used to highlight the impact of baseline model selection in SHM. In simulation, the algorithm identifies stiffness to within 3.5% with 90% confidence, and permanent displacement to within 7.5% with 90% confidence. Using measured data for the frame structure, the algorithm identifies final residual deformation to within 1.5% and identifies realistic stiffness values in comparison to values predicted from pushover analysis. For the rocking structure, the algorithm accurately identifies the different regimes of motion and linear stiffness comparable to estimates from previous research. Overall, the method is seen to be accurate, effective and realtime capable, with the non-linear baseline model more accurately identifying damage in both of the disparate structures examined.
18
Movva, Gopichand. "Optimal Sensor Placement for Structural Health Monitoring." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc700010/.
Full textAbstract:
In large-scale civil structures, a limited number of sensors are placed to monitor the health of civil structures to reduce maintenance, communication and energy costs. In this thesis, the problem of optimal sensor location placement to infer the health of civil structures is explored. First, a comparative study of approaches from the fields of control engineering and civil engineering is conducted . The widely used civil engineering approaches such as effective independence (EI) and modal assurance criterion (MAC) have limitations because of the negligence of modes and damping parameters. On the other hand, control engineering approaches consider the entire system dynamics using impulse response-type sensor measurement data. Such inference can be formulated as an estimation problem, with the dynamics formulated as a second-order differential equation. The comparative study suggests that damping dynamics play significant impact to the selection of best sensor location---the civil engineering approaches that neglect the damping dynamics lead to very different sensor locations from those of the control engineering approaches. In the second part of the thesis, an initial attempt to directly connect the topological graph of the structure (that defines the damping and stiffness matrices) and the second-order dynamics is conducted.
19
Storozhev, Dmitry Leonidovich. "Smart Rotating Machines for Structural Health Monitoring." Cleveland State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=csu1262724991.
Full text
20
Kolli, Phaneendra K. "Wireless Sensor Network for Structural Health Monitoring." Youngstown State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1274304285.
Full text
21
Fekrmandi, Hadi. "Development of New Structural Health Monitoring Techniques." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/cgi/viewcontent.cgi?article=2923&context=etd.
Full textAbstract:
During the past two decades, many researchers have developed methods for the detection of structural defects at the early stages to operate the aerospace vehicles safely and to reduce the operating costs. The Surface Response to Excitation (SuRE) method is one of these approaches developed at FIU to reduce the cost and size of the equipment. The SuRE method excites the surface at a series of frequencies and monitors the propagation characteristics of the generated waves. The amplitude of the waves reaching to any point on the surface varies with frequency; however, it remains consistent as long as the integrity and strain distribution on the part is consistent. These spectral characteristics change when cracks develop or the strain distribution changes. The SHM methods may be used for many applications, from the detection of loose screws to the monitoring of manufacturing operations.
A scanning laser vibrometer was used in this study to investigate the characteristics of the spectral changes at different points on the parts. The study started with detecting a load on a plate and estimating its location. The modifications on the part with manufacturing operations were detected and the Part-Based Manufacturing Process Performance Monitoring (PbPPM) method was developed. Hardware was prepared to demonstrate the feasibility of the proposed methods in real time.
Using low-cost piezoelectric elements and the non-contact scanning laser vibrometer successfully, the data was collected for the SuRE and PbPPM methods. Locational force, loose bolts and material loss could be easily detected by comparing the spectral characteristics of the arriving waves. On-line methods used fast computational methods for estimating the spectrum and detecting the changing operational conditions from sum of the squares of the variations. Neural networks classified the spectrums when the desktop – DSP combination was used. The results demonstrated the feasibility of the SuRE and PbPPM methods.
22
Pawar, Prashant M. "Structural Health Monitoring Of Composite Helicopter Rotor Blades." Thesis, Indian Institute of Science, 2006. http://hdl.handle.net/2005/273.
Full textAbstract:
Helicopter rotor system operates in a highly dynamic and unsteady aerodynamic environment leading to severe vibratory loads on the rotor system. Repeated exposure to these severe loading conditions can induce damage in the composite rotor blade which may lead to a catastrophic failure. Therefore, an interest in the structural health monitoring (SHM) of the composite rotor blades has grown markedly in recent years. Two important issues are addressed in this thesis; (1) structural modeling and aeroelastic analysis of the damaged rotor blade and (2) development of a model based rotor health monitoring system. The effect of matrix cracking, the first failure mode in composites, is studied in detail for a circular section beam, box-beam and two-cell airfoil section beam. Later, the effects of further progressive damages such as debonding/delamination and fiber breakage are considered for a two-cell airfoil section beam representing a stiff-inplane helicopter rotor blade. It is found that the stiffness decreases rapidly in the initial phase of matrix cracking but becomes almost constant later as matrix crack saturation is reached. Due to matrix cracking, the bending and torsion stiffness losses at the point of matrix crack saturation are about 6-12 percent and about 25-30 percent, respectively. Due to debonding/delamination, the bending and torsion stiffness losses are about 6-8 percent and about 40-45 percent after matrix crack saturation, respectively. The stiffness loss due to fiber breakage is very rapid and leads to the final failure of the blade. An aeroelastic analysis is performed for the damaged composite rotor in forward flight and the numerically simulated results are used to develop an online health monitoring system. For fault detection, the variations in rotating frequencies, tip bending and torsion response, blade root loads and strains along the blade due to damage are investigated. It is found that peak-to-peak values of blade response and loads provide a good global damage indicator and result in considerable data reduction. Also, the shear strain is a useful indicator to predict local damage. The structural health monitoring system is developed using the physics based models to detect and locate damage from simulated noisy rotor system data. A genetic fuzzy system (GFS) developed for solving the inverse problem of detecting damage from noise contaminated measurements by hybridizing the best features of fuzzy logic and genetic algorithms. Using the changes in structural measurements between the damaged and undamaged blade, a fuzzy system is generated and the rule-base and membership functions optimized by genetic algorithm. The GFS is demonstrated using frequency and mode shape based measurements for various beam type structures such as uniform cantilever beam, tapered beam and non-rotating helicopter blade. The GFS is further demonstrated for predicting the internal state of the composite structures using an example of a composite hollow circular beam with matrix cracking damage mode. Finally, the GFS is applied for online SHM of a rotor in forward flight. It is found that the GFS shows excellent robustness with noisy data, missing measurements and degrades gradually in the presence of faulty sensors/measurements. Furthermore, the GFS can be developed in an automated manner resulting in an optimal solution to the inverse problem of SHM. Finally, the stiffness degradation of the composite rotor blade is correlated to the life consumption of the rotor blade and issues related to damage prognosis are addressed.
23
Kuok, Sin Chi. "Ambient effects on structural health monitoring of buildings." Thesis, University of Macau, 2009. http://umaclib3.umac.mo/record=b2099636.
Full text
24
Guan, Hong. "Vibration-based structural health monitoring of highway bridges." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2006. http://wwwlib.umi.com/cr/ucsd/fullcit?p3211821.
Full text
25
Hejll, Arvid. "Civil structural health monitoring : strategies, methods and applications /." Luleå : Division of Structural Engineering, Department of Civil and Mining Engineering, Luleå University of Technology, 2007. http://epubl.ltu.se/1402-1544/2007/10/.
Full text
26
Konstantinidis, Georgios. "Structural health monitoring of plates using lamb waves." Thesis, University of Bristol, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.495779.
Full textAbstract:
It is desirable for any structural health monitoring (SHM) system to achieve maximum sensitivity with minimum sensor density. This may be accomplished using guided waves. The structural health monitoring system described herein is based on the excitation and reception of guided waves using piezoelectric elements as sensors. One of the main challenges faced is that in all but the most simple structures the wave interactions become too complex for the time domain signals to be interpreted directly.
27
Dawood, Tariq Ali. "Structural health monitoring of GFRP sandwich beam structures." Thesis, University of Southampton, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438529.
Full text
28
Amraoui, Mohamed Yacine. "Non-invasive damage detection and structural health monitoring." Thesis, University of Bristol, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271865.
Full text
29
Sharma, Vinod K. "Laser doppler vibrometer for efficient structural health monitoring." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26708.
Full textAbstract:
Thesis (Ph.D)--Aerospace Engineering, Georgia Institute of Technology, 2009.<br>Committee Chair: Hanagud, Sathya; Committee Member: Apetre, Nicole; Committee Member: Engelstad, Steve; Committee Member: Glass, Brian; Committee Member: Kardomateas, George; Committee Member: Ruzzene, Massimo. Part of the SMARTech Electronic Thesis and Dissertation Collection.
30
Jesus, André H. "Modular Bayesian uncertainty assessment for structural health monitoring." Thesis, University of Warwick, 2018. http://wrap.warwick.ac.uk/109522/.
Full textAbstract:
Civil infrastructure are critical elements to a society’s welfare and economic thriving. Understanding their behaviour and monitoring their serviceability are relevant challenges of Structural Health Monitoring (SHM). Despite the impressive improvement of miniaturisation, standardisation and diversity of monitoring systems, the ability to interpret data has registered a much slower progression across years. The underlying causes for such disparity are the overall complexity of the proposed challenge, and the inherent errors and lack of information associated with it. Overall, it is necessary to appropriately quantify the uncertainties which undermine the SHM concept. This thesis proposes an enhanced modular Bayesian framework (MBA) for structural identification (st-id) and measurement system design (MSD). The framework is hybrid, in the sense that it uses a physics-based model, and Gaussian processes (mrGp) which are trained against data, for uncertainty quantification. The mrGp act as emulators of the model response surface and its model discrepancy, also quantifying observation error, parametric and interpolation uncertainty. Finally, this framework has been enhanced with the Metropolis–Hastings for multiple parameters st-id. In contrast to other probabilistic frameworks, the MBA allows to estimate structural parameters (which reflect a performance of interest) consistently with their physical interpretation, while highlighting patterns of a model’s discrepancy. The MBA performance can be substantially improved by considering multiple responses which are sensitive to the structural parameters. An extension of the MBA for MSD has been validated on a reduced-scale aluminium bridge subject to thermal expansion (supported at one end with springs and instrumented with strain gauges and thermocouples). A finite element (FE) model of the structure was used to obtain a semi-optimal sensor configuration for stid. Results indicate that 1) measuring responses which are sensitive to the structural parameters and are more directly related to model discrepancy, provide the best results for st-id; 2) prior knowledge of the model discrepancy is essential to capture the latter type of responses. Subsequently, an extension of the MBA for st-id was also applied for identification of the springs stiffness, and results indicate relative errors five times less than other state of the art Bayesian/deterministic methodologies. Finally, a first application to field data was performed, to calibrate a detailed FE model of the Tamar suspension bridge using long-term monitored data. Measurements of temperature, traffic, mid-span displacement and natural frequencies of the bridge, were used to identify the bridge’s main/stay cables initial strain and friction of its bearings. Validation of results suggests that the identified parameters agree more closely with the true structural behaviour of the bridge, with an error that is several orders of magnitude smaller than other probabilistic st-id approaches. Additionally, the MBA allowed to predicted model discrepancy functions to assess the predictive ability of the Tamar bridge FE model. It was found, that the model predicts more accurately the bridge mid-span displacements than its natural frequencies, and that the adopted traffic model is less able to simulate the bridge behaviour during periods of traffic jams. Future developments of the MBA framework include its extension and application for damage detection and MSD with multiple parameter identification.
31
Shi, Haichen. "On nonlinear cointegration methods for structural health monitoring." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/22301/.
Full textAbstract:
Structural health monitoring (SHM) is emerging as a crucial technology for the assessment and management of important assets in various industries. Thanks to the rapid developments of sensing technology and computing machines, large amounts of sensor data are now becoming much easier and cheaper to obtain from monitored structures, which consequently has enabled data-driven methods to become the main work forces for real world SHM systems. However, SHM practitioners soon discover a major problem for in-service SHM systems; that is the effect of environmental and operational variations (EOVs). Most assets (bridges, aircraft engines, wind turbines) are so important that they are too costly to be isolated for testing and examination purposes. Often, their structural properties are heavily in uenced by ambient environmental and operational conditions, or EOVs. So, the most important question raised for an effective SHM system is, how one could tell whether an alarm signal comes from structural damage or from EOVs? Cointegration, a method originating from econometric time series analysis, has proven to be one of the most promising approaches to address the above question. Cointegration is a property of nonstationary time series, it models the long-run relationship among multiple nonstationary time series. The idea of employing the cointegration method in the SHM context relies on the fact that this long-run relationship is immune to the changes caused by EOVs, but when damage occurs, this relationship no longer stands. The work in this thesis aims to further strengthen and extend conventional linear cointegration methods to a nonlinear context, by hybridising cointegration with machine learning and time series models. There are three contributions presented in this thesis: The first part is about a nonlinear cointegration method based on Gaussian process (GP) regression. Instead of using a linear regression, this part attempts to establish a nonlinear cointegrating regression with a GP. GP regression is a powerful Bayesian machine learning approach that can produce probabilistic predictions and avoid overfitting. The proposed method is tested with one simulated case study and with the Z24 Bridge SHM data. The second part concerns developing a regime-switching cointegration approach. Instead of modelling nonlinear cointegration as a smooth function, this part sees cointegration as a piecewise-linear function, which is triggered by some external variable. The model is trained with the aid of the augmented Dickey-Fuller (ADF) test statistics. Two case studies are presented in this part, one simulated mulitidegree-of-freedom system, and also the Z24 Bridge data. The third part of this work introduces a cointegration method for heteroscedastic data. Heteroscedasticity, or time-dependent noise is often observed in SHM data, normally caused by seasonal variations. In order to address this issue, the TBATS (an acronym for key features of the model: Trigonometric, Box-Cox transformation, ARMA error, Trend, Seasonal components) model is employed to decompose the seasonal-corrupted time series, followed by conventional cointegration analysis. A simulated cantilever beam and real measurement data from the NPL Bridge are used to validate the proposed method.
32
Yang, Chen. "Vibration-based structural health monitoring of composite laminates." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/vibrationbased-structural-health-monitoring-of-composite-laminates(b762020d-f2c6-49ed-84ba-dfc2e3ece187).html.
Full textAbstract:
Over the past three decades, carbon-fibre reinforced plastics (CFRP) and glass fibre-reinforced plastics (GFRP) have been increasingly used in modern engineering designs to make composite laminated structures. This increase is due to their attractive mechanical performances and their stable physical and chemical properties. However, these composites are subjected to distinctive failure modes which are different from those of metallic alloys. These failure modes include delamination, matrix cracking and fibre breakage. Therefore, structural health monitoring (SHM) of composite laminated structures during the operational phase has become increasingly important. This thesis presents the development of vibration-based SHM approaches. A non-contact fibre optic sensor is developed for modal testing and structural health monitoring of composite laminate structures. Signal processing methods are used on the acquired modal data to produce a new damage index. The main investigations and contributions of the thesis are summarised as follows,1) A delamination detection method using additional mass loading and modal frequencies is numerically and experimentally studied. The study shows that the interaction between local inertia and delaminations affects the vibration characteristics of composite laminated beams for delaminations located at different depths. 2) A two-step delamination producing technique through mechanical pull-up is proposed and experimentally validated for composite laminated plates. The proposed technique overcomes the inadequate performance of PTFE inserts approach and shows the ability to produce both near surface and far surface delaminations at inaccessible regions from the boundaries. 3) A delamination detection approach using wavelet coefficients of the multiple-mode modal frequency curve for beam-like structures is developed. The method does not require the knowledge of the intact state nor the use of artificial noise filtering procedures.4) The proposed intact-free wavelet coefficients of modal frequency surface are further applied to two-dimensional composite laminate plate-like structures. In conjunction with the wavelet-based edge detection method in imaging processing, the proposed method shows the satisfactory performance in delamination identification and localisation for laminate plates.5) A cost-effective non-contact fibre optic displacement sensor is developed based on the theoretical model. The parameters of the sensor are calibrated following standard procedures. The sensor shows satisfactory performance in structural modal testing. 6) The application of the developed fibre optic sensor in structural health monitoring for composite laminate structures is demonstrated by experiments and its performance is compared with that of commercial sensors.
33
Dodson, Jacob Christopher. "Guided Wave Structural Health Monitoring with Environmental Considerations." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/27070.
Full textAbstract:
Damage detection in mechanical and aerospace structures is critical to maintaining safe
and optimal performance. The early detection of damage increases safety and reduces cost
of maintenance and repair. Structural Health Monitoring (SHM) integrates sensor networks
and structures to autonomously interrogate the structure and detect damage. The
development of robust SHM systems is becoming more vital as aerospace structures are
becoming more complex. New SHM methods that can determine the health of the structure
without using traditional non-destructive evaluation techniques will decrease the cost
and time associated with these investigations. The primary SHM method uses the signals
recorded on a pristine structure as a reference and compares operational signals to the
baseline measurement. One of the current limitations of baseline SHM is that environmental
factors, such as temperature and stress, can change the system response so the
algorithm indicates damage when there is none. Many structures which can benefit from
SHM have multiple components and often have connections and interfaces that also can
change under environmental conditions, thus changing the dynamics of the system.
This dissertation addresses some of the current limitations of SHM. First the changes
that temperature variations and applied stress create on Lamb wave propagation velocity
in plates is analytically modeled and validated. Two methods are developed for the
analytical derivative of the Lamb wave velocity; the first uses assumes a thermoelastic material
while the second expands thermoelastic theory to include thermal expansion and
the associated stresses. A model is developed so the baseline measurement can be compensated
to eliminate the false positives due to environmental conditions without storage
of dispersion curves or baseline signals at each environmental state. Next, a wave based
instantaneous baseline method is presented which uses the comparison of simultaneously
captured real time signals and can be used to eliminate the influence of environmental effects
on damage detection. Finally, wave transmission and conversion across interfaces in
prestressed bars is modeled to provide a better understanding of how the coupled axial
and flexural dynamics of a non-ideal preloaded interface change with applied load.<br>Ph. D.
34
Simmers, Garnett E. Jr. "Impedance-Based Structural Health Monitoring to Detect Corrosion." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/32636.
Full textAbstract:
Corrosion begins as moisture penetrates the protective barrier of a surface, starting an electrochemical process which over time leads to surface pitting. The combined action of mechanical stresses and corrosion induced pitting reduces structural integrity as the pits enlarge to form nucleation sites for surface cracks, which propagate into through-thickness cracks. In most cases, the total mass loss due to corrosion within the structure is small; however, significant reductions in mechanical strength and fatigue life can occur in the corroded material leading to advanced crack growth rates or fast fracture. Since the structural damage due to localized corrosion pitting is small and the crack growth rates may be large, traditional inspections methods and â find it and fix itâ maintenance approaches may lead to catastrophic mechanical failures.
Therefore, precise structural health monitoring of pre-crack surface corrosion is paramount to understanding and predicting the effect corrosion has on the fatigue life and integrity of a structure. In this first third of this study, the impedance method was experimentally tested to detect and the onset and growth of the earliest stages of pre-crack surface corrosion in beam and plate like structures. Experimental results indicate the impedance method is an effective detection tool for corrosion induced structural damage in plates and beams. For corrosion surface coverages less than 1.5% and pit depths of less than 25 microns (light corrosion), the impedance method could successfully detect corrosion on plates and beams at distances up to 150 cm from the sensor location.
Since the impedance method is a proven tool for corrosion detection, it makes sense to determine how well the method can quantify and track key corrosion variables like location, pit depth, and surface coverage. In order to make fatigue life adjustments for corroded structures it is necessary to quantify those variables. Thus, the second portion of this study uses the impedance method to quantify corrosion location, pit depth, and location. Three separate tests are conducted on beam-like structures to determine how well the damage metrics from the impedance method correlate to the key corrosion variables. From the three tests, it is found that the impedance method correlates best with the changes in corrosion pit depth, so if combined with data from routine maintenance it would be possible to use the impedance method data in a predictive or tracking manner. The impedance method can be correlated to location and surface coverage changes, but the relationship is not as strong. Other NDE techniques like Lamb Waves could use the same sensors to quantify corrosion location, and perhaps surface coverage.
The impedance method can detect and quantify pre-crack surface corrosion which leads to shortened fatigue life in structures; however, the sensors must be robust enough to withstand corrosive environments. The last portion of this study tests the following: corrosive effect on Lead Zirconate Titnate (PZT) and Macro Fiber Composites (MFC) sensors, Kapton protected MFC actuators for corrosion detection, and determines if corrosion damage can be sensed on the side of the structure opposite the damage. Sensor recommendations regarding the use of piezoelectric sensors in corrosive environments are made.<br>Master of Science
35
Anton, Steven Robert. "Baseline-Free and Self-Powered Structural Health Monitoring." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/33731.
Full textAbstract:
The research presented in this thesis is based on improving current structural health monitoring (SHM) technology. Structural health monitoring is a damage detection technique that involves placing intelligent sensors on a structure, periodically recording data from the sensors, and using statistical methods to analyze the data in order to assess the condition of the structure. This work focuses on improving two areas of SHM; baseline management and energy supplies. Several successful SHM methods have been developed in which prerecorded baseline measurements are compared to current measurements in order to identify damage. The need to compare new data to a prerecorded baseline can present several complications including data management issues and difficulty in controlling the effects of varying environmental conditions on the data. Another potential area for improvement in SHM systems deals with their energy supplies. Many SHM systems currently require wired power supplies or batteries to operate. Practical SHM applications often require inexpensive, stand alone sensors, data acquisition, and processing hardware that does not require maintenance.
<p>
To address the issue of baseline management, a novel SHM technique is developed. This new method accomplishes instantaneous baseline measurements by deploying an array of piezoelectric sensors/actuators used for Lamb wave propagation-based SHM such that data recorded from equidistant sensor-actuator paths can be used to instantaneously identify several common features of undamaged paths. Once identified, features from these undamaged paths can be used to form a baseline for real-time damage detection. This method utilizes the concept of sensor diagnostics, a recently developed technique that minimizes false damage identification and measurement distortion caused by faulty sensors. Several aspects of the instantaneous baseline damage detection method are explored in this work including the implementation of sensor diagnostics, determination of the features best used to identify damage, development of signal processing algorithms used to analyze data, and the comparison of two sensor/actuator deployment schemes.
<p>
The ultimate goal in the development of practical SHM systems is to create autonomous damage detection systems. A limiting factor in current SHM technology is the energy supply required to operate the system. Many existing SHM systems utilize wired power supplies or batteries to power sensors, data transmission, data acquisition, and data processing hardware. Although batteries eliminate the need to run wires to SHM hardware, their periodic replacement requires components to be placed in easily accessible locations which is not always practical, especially in embedded applications. Additionally, there is a high cost associated with battery monitoring and replacement. In an effort to eliminate replaceable energy supplies in SHM systems, the concept of energy harvesting is investigated. Energy harvesting devices are designed to capture surrounding ambient energy and convert it into usable electrical energy. Several types of energy harvesting exist, including vibration, thermal, and solar harvesting. A solar energy harvesting system is developed for use in powering SHM hardware. Integrating energy harvesting technology into SHM systems can provide autonomous health monitoring of structures.<br>Master of Science
36
Shiryayev, Oleg V. "Improved Structural Health Monitoring Using Random Decrement Signatures." Wright State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=wright1214234132.
Full text
37
Ullah, Israr. "Vibration-based structural health monitoring of composite structures." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/vibrationbased-structural-health-monitoring-of-composite-structures(f21abb03-5b46-4640-9447-0552d5e0c7d6).html.
Full textAbstract:
Composite materials are in use in several applications, for example, aircraft structural components, because of their light weight and high strength. However the delamination which is one of the serious defects often develops and propagates due to vibration during the service of the structure. The presence of this defect warrants the design life of the structure and the safety. Hence the presence of such defect has to be detected in time to plan the remedial action well in advance. There are a number of methods in the literature for damage detection. They are either 'baseline free/reference free method' or using the data from the healthy structure for damage detection. However very limited vibration-based methods are available in the literature for delamination detection in composite structures. Many of these methods are just simulated studies without experimental validation. Grossly 2 kinds of the approaches have been suggested in the literature, one related to low frequency methods and other high frequency methods. In low frequency approaches, the change in the modal parameters, curvatures, etc. is compared with the healthy structure as the reference, however in the high frequency approaches, excitation of structures at higher modes of the order of few kHz or more needed with distributed sensors to map the deflection for identification of delamination. Use of high frequency methods imposes the limitations on the use of the conventional electromagnetic shaker and vibration sensors, whereas the low frequency methods may not be feasible for practical purpose because it often requires data from the healthy state which may not be available for old structures. Hence the objective of this research is to develop a novel reference-free method which can just use the vibration responses at a few lower modes using a conventional shaker and vibration sensors (accelerometers/laser vibrometers). It is believed that the delaminated layers will interact nonlinearly when excited externally. Hence this mechanism has been utilised in the numerical simulations and the experiments on the healthy and delaminated composite plates. Two methods have been developed here - first method can quickly identify the presence of the delamination when excited at just few lower modes and other method identify the location once the presence of the delamination is confirmed. In the first approach an averaged normalised RMS has been suggested and experimentally validated for this purpose. Latter the vibration data have then been analysed further to identify the location of delamination and its size. Initially, the measured acceleration responses from the composite plates have been differentiated twice to amplify the nonlinear interaction clearly in case of delaminated plate and then kurtosis was calculated at each measured location to identify the delamination location. The method has further been simplified by just using the harmonics in the measured responses to identify the location. The thesis presents the process of the development of the novel methods, details of analysis, observations and results.
38
Cicero, Tindaro. "Signal processing for guided wave structural health monitoring." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/5302.
Full textAbstract:
The importance of Structural Health Monitoring (SHM) in several industrial fields has been continuously growing in the last few years with the increasing need for the development of systems able to monitor continuously the integrity of complex structures. In order to be competitive with conventional non destructive evaluation techniques, SHM must be able to effectively detect the occurrence of damage in the structure, giving information regarding the damage location. Ultrasonic guided waves offer the possibility of inspecting large areas of structures from a small number of sensor positions. However, inspection of complex structures is difficult as the reflections from different features overlap. Therefore damage detection becomes an extremely challenging problem and robust signal processing is required in order to resolve strongly overlapping echoes. In our work we have considered at first the possibility of employing a deconvolution approach for enhancing the resolution of ultrasonic time traces and the potential and the limitations of this approach for reliable SHM applications have been shown. The effects of noise on the bandwidth of the typical signals in SHM and the effects of frequency dependent phase shifts are the main detrimental issues that strongly reduce the performance of deconvolution in SHM applications. The second part of this thesis is concerned with the evaluation of a subtraction approach for SHM when changes of environmental conditions are taken into account. Temperature changes result in imperfect subtraction even for an undamaged structure, since temperature changes modify the mechanical properties of the material and therefore the velocity of propagation of ultrasonic guided waves. Compensation techniques have previously been used effectively to overcome temperature effects, in order to reduce the residual in the subtraction. In this work the performance of temperature compensation techniques has been evaluated also in the presence of other detrimental effects, such as liquid loading and different temperature responses of materials in adhesive joints. Numerical simulations and experiments have been conducted and it has been shown that temperature compensation techniques can cope in principle with non temperature effects. It is concluded that subtraction approach represents a promising method for reliable Structural Health Monitoring. Nonetheless the feasibility of a subtraction approach for SHM depends on environmental conditions.
39
Zhang, Jian. "Advanced signal processing technique for structural health monitoring." 京都大学 (Kyoto University), 2006. http://hdl.handle.net/2433/136142.
Full text
40
Erazo, Kalil. "Bayesian Filtering In Nonlinear Structural Systems With Application To Structural Health Monitoring." ScholarWorks @ UVM, 2015. http://scholarworks.uvm.edu/graddis/513.
Full textAbstract:
During strong earthquakes structural systems exhibit nonlinear behavior due to low-cycle fatigue, cracking, yielding and/or fracture of constituent elements. After a seismic event it is essential to assess the state of damage of structures and determine if they can safely resist aftershocks or future strong motions. The current practice in post-earthquake damage assessment relies mainly on visual inspections and local testing. These approaches are limited to the ability of inspectors to reach all potentially damaged locations, and are typically intended to detect damage near the outer surfaces of the structure leaving the possibility of hidden undetected damage. Some structures in seismic prone-regions are instrumented with an array of sensors that measure their acceleration at different locations. We operate under the premise that acceleration response measurements contain information about the state of damage of structures, and it is of interest to extract this information and use it in post-earthquake damage assessment and decision making strategies.
The objective of this dissertation is to show that Bayesian filters can be successfully employed to estimate the nonlinear dynamic response of instrumented structural systems. The estimated response is subsequently used for structural damage diagnosis. Bayesian filters combine dynamic response measurements at limited spatial locations with a nonlinear dynamic model to estimate the response of stochastic dynamical systems at the model degrees-of-freedom. The application of five filters is investigated: the extended, unscented and ensemble Kalman filters, the particle filter and the model-based observer.
The main contributions of this dissertation are summarized as follows: i) Development of a filtering-based mechanistic damage assessment framework; ii) Experimental validation of Bayesian filters in small and large-scale structures; iii) Uncertainty quantification and propagation of response and damage estimates computed using Bayesian filters.
41
Schubert, Martin, Sabine Friedrich, Daniel Wedekind, Sebastian Zaunseder, Hagen Malberg, and Karlheinz Bock. "3D printed flexible substrate with pneumatic driven electrodes for health monitoring." Institute of Electrical and Electronics Engineers (IEEE), 2017. https://tud.qucosa.de/id/qucosa%3A33148.
Full textAbstract:
Telemedical methods enable remote patient monitoring and healthcare at a distance. Besides, fitness tracker and sport watches are currently trending electronic products to generate awareness of health parameters in daily life. Especially, the long-term and continuous measurement of electrophysiological signals such as electrocardiogramm (ECG) becomes increasingly attractive for telemedical applications. Typically used disposable Ag/AgCl wet electrodes for good skin-electrode contact can potentially cause skin irritation and rashes. This paper presents a low cost, individual and flexible substrate for skin electrodes to be applied in future consumer electronic or professional applications. It enables an alternative contact method of the electrode to the skin by applying a pressure during the measurement and hence good contact. If no measurement is needed pressure can be released and the electrode loses skin contact. The 3D printed polymer module is 4 mm thick and comprises a pressure chamber, silver electrodes and insulation layer. The airtight printed membrane of flexible filament, which expands when inflating the chamber, may be printed in different thicknesses and shapes, much thinner than the present 4mm. This enables a high individuality for various applications. Pressure up to 150 kPa was applied and leads to dilatation of 1400 μm. First tests on skin when measuring electrodermal activity (EDA) show promising results for future applications.
42
Lannamann, Daniel L. "Structural health monitoring : numerical damage predictor for composite structures." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA390997.
Full text
43
Koh, Yeow Leung 1976. "In-situ structural health monitoring of composite repair patches." Monash University, Dept. of Mechanical Engineering, 2002. http://arrow.monash.edu.au/hdl/1959.1/7698.
Full text
44
Silva, Muñoz Rodrigo. "Structural Health Monitoring Using Embedded Fiber Optic Strain Sensors." Fogler Library, University of Maine, 2008. http://www.library.umaine.edu/theses/pdf/SilvaMunozR2008.pdf.
Full text
45
Nayyerloo, Mostafa. "Real-time Structural Health Monitoring of Nonlinear Hysteretic Structures." Thesis, University of Canterbury. Department of Mechanical Engineering, 2011. http://hdl.handle.net/10092/6581.
Full textAbstract:
The great social and economic impact of earthquakes has made necessary the development of novel structural health monitoring (SHM) solutions for increasing the level of structural safety and assessment. SHM is the process of comparing the current state of a structure’s condition relative to a healthy baseline state to detect the existence, location, and degree of likely damage during or after a damaging input, such as an earthquake. Many SHM algorithms have been proposed in the literature. However, a large majority of these algorithms cannot be implemented in real time. Therefore, their results would not be available during or immediately after a major event for urgent post-event response and decision making. Further, these off-line techniques are not capable of providing the input information required for structural control systems for damage mitigation. The small number of real-time SHM (RT-SHM) methods proposed in the past, resolve these issues. However, these approaches have significant computational complexity and typically do not manage nonlinear cases directly associated with relevant damage metrics. Finally, many available SHM methods require full structural response measurement, including velocities and displacements, which are typically difficult to measure. All these issues make implementation of many existing SHM algorithms very difficult if not impossible.
This thesis proposes simpler, more suitable algorithms utilising a nonlinear Bouc-Wen hysteretic baseline model for RT-SHM of a large class of nonlinear hysteretic structures. The RT-SHM algorithms are devised so that they can accommodate different levels of the availability of design data or measured structural responses, and therefore, are applicable to both existing and new structures. The second focus of the thesis is on developing a high-speed, high-resolution, seismic structural displacement measurement sensor to enable these methods and many other SHM approaches by using line-scan cameras as a low-cost and powerful means of measuring structural displacements at high sampling rates and high resolution. Overall, the results presented are thus significant steps towards developing smart, damage-free structures and providing more reliable information for post-event decision making.
46
Niu, Yan [Verfasser]. "Online force reconstruction for Structural Health Monitoring / Yan Niu." Siegen : Universitätsbibliothek der Universität Siegen, 2019. http://d-nb.info/1193252164/34.
Full text
47
Kerrouche, Abdelfateh. "Fibre Optic Distributed Sensors Systems for Structural Health Monitoring." Thesis, City University London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.507411.
Full text
48
Gul, Mustafa. "INVESTIGATION OF DAMAGE DETECTION METHODOLOGIES FOR STRUCTURAL HEALTH MONITORING." Doctoral diss., University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3317.
Full textAbstract:
Structural Health Monitoring (SHM) is employed to track and evaluate damage and deterioration during regular operation as well as after extreme events for aerospace, mechanical and civil structures. A complete SHM system incorporates performance metrics, sensing, signal processing, data analysis, transmission and management for decision-making purposes. Damage detection in the context of SHM can be successful by employing a collection of robust and practical damage detection methodologies that can be used to identify, locate and quantify damage or, in general terms, changes in observable behavior. In this study, different damage detection methods are investigated for global condition assessment of structures. First, different parametric and non-parametric approaches are re-visited and further improved for damage detection using vibration data. Modal flexibility, modal curvature and un-scaled flexibility based on the dynamic properties that are obtained using Complex Mode Indicator Function (CMIF) are used as parametric damage features. Second, statistical pattern recognition approaches using time series modeling in conjunction with outlier detection are investigated as a non-parametric damage detection technique. Third, a novel methodology using ARX models (Auto-Regressive models with eXogenous output) is proposed for damage identification. By using this new methodology, it is shown that damage can be detected, located and quantified without the need of external loading information. Next, laboratory studies are conducted on different test structures with a number of different damage scenarios for the evaluation of the techniques in a comparative fashion. Finally, application of the methodologies to real life data is also presented along with the capabilities and limitations of each approach in light of analysis results of the laboratory and real life data.<br>Ph.D.<br>Department of Civil and Environmental Engineering<br>Engineering and Computer Science<br>Civil Engineering PhD
49
Sun, Zhi. "Wavelet packet based structural health monitoring and damage assessment /." View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202003%20SUN.
Full text
50
Lajnef, Nizar. "Self-powered sensing in structural health and usage monitoring." Diss., Connect to online resource - MSU authorized users, 2008.
Find full textAbstract:
Thesis (Ph.D.)--Michigan State University. Dept. of Civil and Environmental Engineering, 2008.<br>Title from PDF t.p. (viewed on July 2, 2009) Includes bibliographical references (p. 127-133). Also issued in print.