Yes / Self-sensing concrete used in coating form for structural health monitoring of concrete structures has the merits of cost-effectiveness, offering protective effect on structural components, enabling electrical measurements unaffected by steel reinforcement and is also convenient to maintain and replace. This paper investigates the feasibility of using self-sensing cement mortar coating containing carbon nanotube-nano carbon black (CNT-NCB) composite fillers (CNCFs) for damage monitoring of concrete beams. The self-sensing cement mortar coated to concrete beams demonstrated outstanding electrical conductivity (resistivity ranging from 18 to 85 Ω·cm). Under monotonic flexural loadings, self-sensing cement mortar coating with 1.8 vol.% CNCFs featured sensitive self-sensing performance in terms of capturing the initiation of vertical cracks at pure bending span of concrete beams, with fractional change in resistivity (FCR) reaching up to 60.6%. Moreover, FCR variations of self-sensing cement mortar coating exhibited good synchronization and stability with the variation of mid-span deflections of concrete beams during cyclic flexural loadings irrespective of the contents of CNCFs and cyclic amplitudes. Remarkably, it was found that FCR of cement mortar coating basically showed a progressive upward tendency, representing irreversible increase in the resistance during cyclic loading. The irreversible residual FCR indicated the crack occurrence and damage accumulation of concrete beams. / National Science Foundation of China (52368031, 51978127 and 52178188) and the China Postdoctoral Science Foundation (2022M710973)

The goal of this work is to investigate the piezoelectricity of composite laminates embedded with layers of zinc oxide (ZnO) nanowires. ZnO nanowire embedded composites have the potential to sense and actuate giving the potential for these smart composites to serve the function of being load bearing structures and monitoring the integrity of the structure. This work examines the piezoelectric characteristics of composite beams by investigating their electromechanical coupling in the form of vibration under the presence of electrical excitation. With the help of a mathematical model, piezoelectric constants are estimated for these samples. A layer of ZnO nanowires were grown on plane woven fiberglass fabric that was incorporated into a carbon fiber epoxy composite. The beam deflection velocity was measured as a varying voltage was applied to the composite. Using Hamilton's Principle and Galerkin's method of weighted residuals, a mathematical model was derived to estimate piezoelectric constants for the composites from the experimental data. Piezoelectric properties were determined using vibrational testing and a mathematical model. Piezoelectric constants h31, g31, and d31 were estimated to be 9.138 E7 V/m, 6.092 E-4 Vm/N, and 2.46 E-14 respectively. To demonstrate the electromechanical coupling, ZnO nanowire composites were bonded to Al beams that were progressively damaged to determine if a change in electrical impedance could be observed to correspond to the change in structural impedance of the host beam. Changes in impedance were detected by a change in root mean squared deviation damage metric M. A significant correlation was shown between increasing damage in the host beam and an increase in damage metric M. / Master of Science / A major problem facing both commercial and military aircraft fleets is aircraft grounded time due to inspection. Inspection times tend to be lengthy since visual inspection cannot detect all types of incurred damage an aircraft may face. In the case of composite aircraft structures, a special type of damage known as delamination (when layers of the composite structure become un-bonded) can occur. Since delamination is not always visible from the surface, and composite structures cannot be taken apart since they are made in one piece; additional damage detection methods are necessary. Impedance-based structural health monitoring (IBSHM) is one technique of nondestructive evaluation (NDE) that examines changes in vibrational response of the structure in order to detect damage. A novel approach to IBSHM is incorporating zinc oxide, a type of piezoelectric material, inside the composites due to its ability to deform in the presence of an electric field or generate a voltage when stressed. The goal of this research is to determine piezoelectric properties of composites with ZnO nanowires grown on inner layers of the laminates. Piezoelectric properties were determined using vibrational testing and a mathematical model. To demonstrate the electromechanical coupling, ZnO nanowire composites were bonded to Al beams that were progressively damaged to determine if a change in electrical impedance could be observed to correspond to the change in structural impedance of the host beam. Changes in impedance were detected by a change in root mean squared deviation damage metric M. A significant correlation was shown between increasing damage in the host beam and an increase in damage metric M.

Detection, characterization and prognosis of damage in civil, aerospace and mechanical structures, known as structural health monitoring (SHM), have been a growing area of research over the last few decades. As several in-service civil, mechanical and aerospace structures are approaching or even exceeding their design life, the implementation of SHM systems is becoming a necessity. SHM is the key for transforming schedule-driven inspection and maintenance into condition-based maintenance, which promises enhanced safety and overall life-cycle cost reduction. While damage detection and characterization can be achieved, among other techniques, by analyzing the dynamic response of the structure under test, damage prognosis requires the additional knowledge of loading patterns acting on the structure. Accurate, nondestructive, and reference-free measurement of the state-of-stress in structural components has been a long standing challenge without a fully-satisfactory outcome. In light of this, the main goal of this research effort is to advance the current state of the art of structural health and loading monitoring, with focus being cast on impedance-based SHM and acoustoelastic-based stress measurement techniques. While impedance-based SHM has been successfully implemented as a damage detection technique, the utilization of electromechanical impedance measurements for damage characterization imposes several challenges. These challenges are mainly stemming from the high-frequency nature of impedance measurements. Current acoustoelastic-based practices, on the other hand, are hindered by their poor sensitivity and the need for calibration at a known state of stress. Addressing these challenges by developing and integrating theoretical models, numerical algorithms and experimental techniques defines the main objectives of this work. A key enabler for both health and loading monitoring techniques is the utilization of piezoelectric transducers to excite the structure and measure its response. For this purpose, a new three-layer spectral element for piezoelectric-structure interaction has been developed in this work, where the adhesive bonding layer has been explicitly modeled. Using this model, the dynamic response of piezoelectric-augmented structures has been investigated. A thorough parametric study has been conducted to provide a better understanding of bonding layer impact on the response of the coupled structure. A procedure for piezoelectric material characterization utilizing its free electromechanical impedance signature has been also developed. Furthermore, impedance-based damage characterization has been investigated, where a novel optimization-based damage identification approach has been developed. This approach exploits the capabilities of spectral element method, along with the periodic nature of impedance peaks shifts with respect to damage location, to solve the ill-posed damage identification problem in a computationally efficient manner. The second part of this work investigates acoustoelastic-based stress measurements, where model-based technique that is capable of analyzing dispersive waves to calculate the state of stress has been developed. A criterion for optimal selection of excitation waveforms has been proposed in this work, taking into consideration the sensitivity to the state of stress, the robustness against material and geometric uncertainties, and the ability to obtain a reflections-free response at desired measurement locations. The impact of material- and geometry-related uncertainties on the performance of the stress measurement algorithm has also been investigated through a comprehensive sensitivity analysis. The developed technique has been experimentally validated, where true reference-free, uncalibrated, acoustoelastic-based stress measurements have been successfully conducted. Finally, the applicability of the aforementioned health and loading monitoring techniques to railroad track components has been investigated. Extensive in-lab experiments have been carried out to evaluate the performance of these techniques on lab-scale and full-scale rail joints. Furthermore, in-field experiments have been conducted, in collaboration with Norfolk Southern and the Transportation Technology Center Inc., to further investigate the performance of these techniques under real life operating and environmental conditions. / Ph. D. / Structural health monitoring (SMH) addresses the problem of damage detection and identification in civil, aerospace and mechanical structures. As several in-service structure are approaching or even exceeding their design life, the implementation of SMH systems is becoming a necessity. Besides Damage identification, a complete assessment of the structure under test requires the knowledge of loading patterns acting on it. Accurate, nondestructive, and reference-free measurement of the state-of-stress in structural components has been a long-standing challenge without a fully satisfactory outcome. This research effort aims to advance the current state-of-the-art of structural health and loading monitoring with the focus being cast on impedance-based SHM and acoustoelastic-based stress measurement techniques. Theoretical models and numerical algorithms have been developed as a part of this work to facilitate impedance-based damage identification and provide a better understanding of a number of factors affecting the perfomance of this technique. A new acoustoelastic-based stress measurement technique has also been developed and experimentally validated. Using the technique, true reference-free, uncalibrated stress measurements have been successfully conducted for the first time. The applicability of the aforementioned techniques to the railroad industry has been investigated, where their perfomance is evaluated under real-life operating and environmental conditions.

Aircraft propulsion systems can be exposed to a variety of solid particulates while operating in either arid or other hazardous environments. For conventional takeoff and landing aircraft, debris can be ingested directly into the gas turbine powerplant which is exposed to the ambient environment. For helicopters and other vertical takeoff and landing (VTOL) aircraft, rotor down wash presents a particular threat during takeoff and landing operations as significant amounts of groundlevel particles can be entrained in the surrounding air and subsequently ingested into the engine. Prolonged exposure to particle ingestion events leads to premature engine wear and, in extreme cases, rapid engine failure. Expanding our current understanding of these events is the first step to enabling engine manufacturers to mitigate these damage mechanisms through novel engine designs. The work described in this dissertation is aimed at increasing the scientific understanding of these ingestion events through the development of two distinct diagnostic instruments. First, an anisokinetic particle sampling probe is designed to be used for in-situ particle sampling inside of a gas turbine engine compressor. Offtake of particles during engine operation in dusty conditions will provide researchers with an improved understanding of particle breakage tendency and component erosion susceptibility. Both experimental and numerical investigations of the probe present a comprehensive realization of probe performance characteristics. Secondly, a novel particle visualization technique is developed to provide users with particle distribution and particle mass flow estimates at the inlet of a gas turbine engine. This technique yields both time-resolved and time-averaged quantities, allowing users to have a comprehensive account of particles entering the engine. / Doctor of Philosophy / Foreign debris ingested into aircraft engines can cause serious damage and degrade their performance. The source of these ingested particles may be from atmospherically suspended ash due to volcanic eruption, high altitude ice crystals, or ground-level sand and dust. Both conventional takeoff and landing aircraft and vertical takeoff and landing (VTOL) aircraft are at risk. In extreme cases, exposure to a particle-laden atmosphere has resulted in catastrophic engine failure and loss of life. For this reason, researchers are intensely focused on mitigating the effects of these harmful particulates. The work described in this dissertation establishes two novel diagnostic capabilities. These are aimed at providing the research community with an increased understanding of how particles enter an aircraft powerplant as well as describe the behavior of these particles as they traverse the initial stages of an engine. The first instrument described is a particle sampling probe which is meant to be inserted into the compressor section of a gas turbine engine. This probe will offtake particles as they enter the engine after they have had an opportunity to interact with the rotating components of the compressor. In doing so, researchers gain an improved understanding of particle breakage tendency and component erosion susceptibility. The second instrument provides a snapshot of particle distribution at the inlet of the engine as well as estimates of total particle mass flow. This capability allows researchers to have a precise understanding of the quantity of ingested material as well as a qualitative understanding of how the inflow distribution of particles looks. Each of the developed tools represent a first step to enabling engine manufacturers to mitigate these damage mechanisms through novel engine designs.

Structural Health Monitoring (SHM) is the implementation of damage detection and characterization algorithms using in vitro sensing and actuation for rapidly determining faults in structural systems before the damage leads to catastrophic failure. SHM systems provide near real time information on the state of the integrity of civil, mechanical and aerospace structures. A roadblock in implementing SHM systems in practice is the possibility of false positives introduced by environmental changes. In particular, temperature changes can cause many SHM algorithms to indicate damage when no damage exists. While several experimentally based efforts have been attempted to alleviate temperature effects on SHM algorithms, fundamental research on the effects of temperature on SHM has not been investigated. The work presented in this dissertation composes of two main parts: the first part focuses on the experimental studies of different mechanical structures of aluminum beams, lug samples and railroad switch bolts. The experimental study of the aluminum lug samples and beams is done to propose and examine methods and models for in situ interrogation and detection of damage (in the form of a fatigue crack) in these specimen and to quantify the smallest detectable crack size in aluminum structures. This is done by applying the electrical impedance-based SHM method and using piezoceramic sensors and actuators. Moreover, in order to better extract the damage features from the measured electrical impedance, the ARX non-linear feature extraction is employed. This non-linear feature extraction, compared to the linear one, results in detection of damages in the micro-level size and improves the early detection of fatigue cracks in structures. Experimental results also show that the temperature variation is an important factor in the structural health monitoring applications and its effect on the impedance-based monitoring of the initiation and growth of fatigue cracks in the lug samples is experimentally investigated. The electrical impedance-based SHM technique is also applied in monitoring the loosening of bolted joints in a full-scale railroad switch and the sensitivity of this technique to different levels of loosening of the bolts is investigated. The second part of the work presented here focuses on the analytical study and better understanding of the effect of temperature on the vibration-based SHM. This is done by analytical modeling of the vibratory response of an Euler-Bernoulli beam with two different support conditions of simply supported and clamped-clamped and with a single, non-breathing fatigue crack at different locations along the length of the beam. The effect of temperature variations on the vibratory response of the beam structure is modeled by considering the two effects of temperature-dependent material properties and thermal stress formations inside the structure. The inclusion of thermal effects from both of these points of view (i.e. material properties variations and generation of thermal stresses) as independent factors is investigated and justified by studying the formulations of Helmholtz free energy and stresses inside a body. The effect of temperature variations on the vibratory response of the cracked beam are then studied by integrating these two temperature-related effects into the analytical modeling. The effect of a growing fatigue crack as well as temperature variations and thermal loadings is then numerically studied on the deflection of the beam and the output voltage of a surface-bonded piezoceramic sensor. / Ph. D.

This thesis describes the test rig and results from a project expanding the field of rotor health monitoring by using Active Magnetic Bearings (AMBs) as actuators for applying a variety of known force inputs to a spinning. Similar to modal analysis and other nondestructive evaluation (NDE) techniques which apply input signals to static structures in order to monitor responses; this approach allows for the measurement of both input and output response in a rotating system for evaluation. However, unlike these techniques, the new procedure allows for multiple forms of force input signals to be applied to a rotating structure. This technique is used on a rotating shaft supported in conventional bearings with an AMB actuator added to the system. This paper presents the results from this project including shaft rub and notch. An EDM notch was also tested to attempt a breathing scenario similar to breathing cracks. / Master of Science

Structural health monitoring (SHM) is the process of using measurements of a structure's response to known excitations and trying to determine if damage has occurred to the structure. This also fits the description of non-destructive evaluation (NDE). The main difference is that NDE takes place while the structure is out of service and SHM is intended to take place while the structure is in service. As such, SHM provides the opportunity to provide early warning against structural failure. This thesis intends to advance the state of the art in SHM by examining two approaches to SHM: vibration based and impedance based, and to associate these with the NDE method of stress intensity factors. By examining these methods the goal is to try and answer some of the important questions in SHM process. The first is to experimentally validate a crack model and to see how small of a crack can be detected by vibration methods. The second is to use the concept of stress intensity factor to perform an SHM type of measurement to determine the remaining life of a structure once the impedance method has determined that damage has occurred. The measurement system considered consists of using several different piezoceramic materials as self-sensing actuators and sensors. The structures are a simple beam and a more complex lug element used in aircraft applications. The approach suggested here is to use the impedance and vibration methods to detect crack initiation and then to use the proposed stress intensity method to measure the stress intensity factor of the structure under consideration. / Master of Science

Für den zielgerichteten Einsatz von präventiven und mitigativen Notfallmaßnahmen sowie zur Beurteilung ihrer Wirksamkeit während auslegungsüberschreitender Unfälle in Druckwasserreaktoren aber auch für Hinweise zum Störfallverlauf und für die Abschätzung der Auswirkungen auf die Anlagenumgebung müssen geeignete Störfallinstrumentierungen vorhanden sein. Insbesondere der Zustand des Reaktordruckbehälterinventars (RDB-Inventar) während der In-Vessel-Phase eines auslegungsüberschreitenden Unfalls lässt sich mit aktuellen Störfallinstrumentierungen nur stark eingeschränkt überwachen, wodurch die o. g. Forderungen nicht erfüllt werden können. Die vorliegende Arbeit beinhaltet detaillierte Untersuchungen für die Entwicklung einer Störfallinstrumentierung, welche eine durchgängige Zustandsüberwachung des RDB-Inventars während der In-Vessel-Phase eines auslegungsüberschreitenden Unfalls ermöglicht. Die Störfallinstrumentierung basiert auf der Messung und Klassifikation von unterschiedlichen Gammaflussverteilungen, welche während der In-Vessel-Phase außerhalb des Reaktordruckbehälters auftreten können. Ausgehend von der Analyse zum Stand von Wissenschaft und Technik wird der modell-basierte Ansatz für Structural Health Monitoring-Systeme genutzt, um eine grundlegende Vorgehensweise für die Entwicklung der Störfallinstrumentierung zu erarbeiten. Anschließend erfolgt eine detaillierte Analyse zu den Vorgängen während der In-Vessel-Phase und eine daraus abgeleitete Definition von Kernzuständen für einen generischen Kernschmelzunfall. Für die definierten Kernzustände werden mittels Simulationen (Monte-Carlo-Simulationen zum Gammastrahlungstransport in einem zu dieser Arbeit parallel laufenden Vorhaben) Gammaflüsse außerhalb des Reaktordruckbehälters berechnet. Die Simulationsergebnisse dienen dem Aufbau von Datenbasen für die Entwicklung und Analyse eines Modells zur Klassifikation von Gammaflussverteilungen. Für die Entwicklung des Klassifikationsmodells kommen drei diversitäre und unabhängig arbeitende Klassifikationsverfahren (Entscheidungsbaum, k-nächste-Nachbarn-Klassifikation, Multilayer Perzeptron) zur Anwendung, um die Identifikationsgenauigkeit und Robustheit der Störfallinstrumentierung zu erhöhen. Die abschließenden Betrachtungen umfassen die Validierung der Störfallinstrumentierung mittels eines Versuchstandes zur Erzeugung unterschiedlicher Gammaflussverteilungen. Im Ergebnis der Untersuchungen konnte die prinzipielle Funktionsweise der entwickelten Störfallinstrumentierung nachgewiesen werden. Unter der Voraussetzung, die Gültigkeit der definierten Kernzustände zu untermauern sowie weitere, nicht in dieser Arbeit betrachtete Kernschmelzszenarien mit in die Entwicklung der Störfallinstrumentierung einzubeziehen, steht somit insbesondere für zukünftige Kernkraftwerke mit Druckwasserreaktoren eine Möglichkeit für die messtechnische Überwachung des RDB-Inventars während auslegungsüberschreitender Unfälle bereit. Die Arbeit leistet einen wesentlichen Beitrag auf dem Gebiet der Reaktorsicherheitsforschung sowie für den sicheren Betrieb von kerntechnischen Anlagen.

This thesis is about using structural-dynamics based methods to address the existing challenges in the field of Structural Health Monitoring (SHM). Particularly, new structural-dynamics based methods are presented, to model areas of damage, to do damage diagnosis and to estimate and predict the sensitivity of structural vibration properties like natural frequencies to the presence of damage. Towards these objectives, a general analytical procedure, which yields nth-order expressions governing mode shapes and natural frequencies and for damaged elastic structures such as rods, beams, plates and shells of any shape is presented. Features of the procedure include the following: 1. Rather than modeling the damage as a fictitious elastic element or localized or global change in constitutive properties, it is modeled in a mathematically rigorous manner as a geometric discontinuity. 2. The inertia effect (kinetic energy), which, unlike the stiffness effect (strain energy), of the damage has been neglected by researchers, is included in it. 3. The framework is generic and is applicable to wide variety of engineering structures of different shapes with arbitrary boundary conditions which constitute self adjoint systems and also to a wide variety of damage profiles and even multiple areas of damage. To illustrate the ability of the procedure to effectively model the damage, it is applied to beams using Euler-Bernoulli and Timoshenko theories and to plates using Kirchhoff's theory, supported on different types of boundary conditions. Analytical results are compared with experiments using piezoelectric actuators and non-contact Laser-Doppler Vibrometer sensors. Next, the step of damage diagnosis is approached. Damage diagnosis is done using two methodologies. One, the modes and natural frequencies that are determined are used to formulate analytical expressions for a strain energy based damage index. Two, a new damage detection parameter are identified. Assuming the damaged structure to be a linear system, the response is expressed as the summation of the responses of the corresponding undamaged structure and the response (negative response) of the damage alone. If the second part of the response is isolated, it forms what can be regarded as the damage signature. The damage signature gives a clear indication of the damage. In this thesis, the existence of the damage signature is investigated when the damaged structure is excited at one of its natural frequencies and therefore it is called ``partial mode contribution". The second damage detection method is based on this new physical parameter as determined using the partial mode contribution. The physical reasoning is verified analytically, thereupon it is verified using finite element models and experiments. The limits of damage size that can be determined using the method are also investigated. There is no requirement of having a baseline data with this damage detection method. Since the partial mode contribution is a local parameter, it is thus very sensitive to the presence of damage. The parameter is also shown to be not affected by noise in the detection ambience.

Aerospace structures comprising of metals and composites are exposed to extreme loading and environmental conditions which necessitates regular inspection and maintenance to verify and monitor overall structural integrity. The timely and accurate detection, characterization and monitoring of structural cracking, corrosion, delaminating, material degradation and other types of damage are of major concern in the operational environment. Along with these, stringent requirements of safety and operational reliability have lead to evolutionary methods for evaluation of structural integrity. As a result, conventional nondestructive evaluation methods have moved towards a new concept, Structural Health Monitoring (SHM). SHM provides in-situ information a bout the occurrence of damage if any, location and severity of damage and residual life of the structure and also helps in improving the safety, reliability and confidence levels of critical engineering structures. While the concepts underlying SHM are well understood, development of methods is still in a nascent stage which requires extensive research that is challenging and has been the main motivating factor for undertaking the work reported in the thesis. Under the scope of the investigations carried out in this thesis, an integrated approach using Ultrasonic (active) and Acoustic Emission (passive) methods has been explored for SHM of metallic and composite plate structures using a distributed array of surface bonded circular piezoelectric wafer active sensors(PWAS). In ultrasonic method, PWAS is used for actuation and reception of Lamb waves in plate structures. The damage detection is based on the interaction of waves with defects resulting in reflection, mode conversion and scattering. In acoustic emission (AE) technique, the same sensor is used to pick up the stress waves generated by initiation or growth of defects or damage. Thus, both the active and passive damage detection methods are used in this work for detection, location and characterization of defects and damage in metallic and composite plates with complex geometries and structural discontinuities. And, thus the strategy adopted is to use time-frequency analysis and time reversal technique to extract the information from Lamb wave signals for damage detection and a geodesic based Lamb wave approach for location of the damage in the structure. To start with experiments were conducted on aluminum plates to study the interaction of Lamb waves with cracks oriented at different angles and on a titanium turbine blade of complex geometry with a fine surface crack. Further, the interaction of Lamb wave modes with multiple layer delaminations in glass fiber epoxy composite laminates was studied. The data acquired from these experiments yielded complex sets of signals which were not easily discern able for obtaining the information required regarding the defects and damage. So, to obtain a basic understanding of the wave patterns, Spectral finite element method has been employed for simulation of wave propagation in composite beams with damages like delamination and material degradation. Following this, time-frequency analysis of a number of simulated and experimental signals due to elastic wave scattering from defects and damage were performed using wavelet transform (WT) and Hilbert-Huang transform(HHT).And, a comparison of their performances in the context of quantifying the damages has given detailed insight into the problem of identifying localized damages, dispersion of multi-frequency non-stationary signals after their interaction with different types of defects and damage, finally leading to quantification. Conventional Lamb wave based damage detection methods look for the presence of defects and damage in a structure by comparing the signal obtained with the baseline signal acquired under healthy conditions. The environmental conditions like change in temperature can alter the Lamb wave signals and when compared with baseline signals may lead to false damage prediction. So, in order to make Lamb wave based damage detection baseline free, in the present work, the time reversal technique has been utilized. And, experiments were conducted on metallic and composite plates to study the time reversal behavior ofA0 andS0Lamb wave modes. Damage in the form of a notch was introduced in an aluminum plate to study the changes in the characteristics of the time reversed Lamb wave modes experimentally. This experimental study showed that there is no change in the shape of the time reversed Lamb wave in the presence of defect implying no breakage of time reversibility. Time reversal experiments were further carried out on a carbon/epoxy composite T-pull specimen representing a typical structure. And, the specimen was subjected to a tensile loading in a Universal testing machine. PWAS sensor measurements were carried out at no load as also during different stages of delamination due to tensile loading. Application of time reversed A 0 and S0 modes for both healthy and delaminated specimens and studying the change in shape of the time reversed Lamb wave signals has resulted in successful detection of the presence of delamination. The aim of this study has been to show the effectiveness of Lamb wave time reversal technique for damage detection in health monitoring applications. The next step in SHM is to identify the damage location after the confirmation of presence of damage in the structure. Wave based acoustic damage detection methods (UT and AE) employing triangulation technique are not suitable for locating damage in a structure which has complicated geometry and contains structural discontinuities. And, the problem further gets compounded if the material of the structure is anisotropic warranting complex analytical velocity models. In this work, a novel geodesic approach using Lamb waves is proposed to locate the AE source/damage in plate like structures. The approach is based on the fact that the wave takes minimum energy path to travel from the source to any other point in the connected domain. The geodesics are computed numerically on the meshed surface of the structure using Dijkstra’s algorithm. By propagating the waves in reverse virtually from these sensors along the geodesic path and by locating the first inter section point of these waves, one can get the AE source/damage location. Experiments have been conducted on metallic and composite plate specimens of simple and complex geometry to validate this approach. And, the results obtained using this approach has demonstrated the advantages for a practicable source location solution with arbitrary surfaces containing finite discontinuities. The drawback of Dijkstra’s algorithm is that the geodesics are allowed to travel along the edges of the triangular mesh and not inside them. To overcome this limitation, the simpler Dijkstra’s algorithm has been replaced by a Fast Marching Method (FMM) which allows geodesic path to travel inside the triangular domain. The results obtained using FMM showed that one can accurately compute the geodesic path taken by the elastic waves in composite plates from the AE source/damage to the sensor array, thus obtaining a more accurate damage location. Finally, a new triangulation technique based on geodesic concept is proposed to locate damage in metallic and composite plates. The performances of triangulaton technique are then compared with the geodesic approach in terms of damage location results and their suitability to health monitoring applications is studied.