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    PublicationAccess status: Open Access ,
    Identifizierung von geschädigten Komponenten an Schienenfahrzeugen basierend auf Beschleunigungsmessungen
    (2025)
    Jung, Henningorcid-logo
    The focus of this dissertation relates to the research field of Structural Health Monitoring (SHM) with the aim to develop new methods for damage diagnosis and prediction based on acceleration measurements. The monitoring of bogie components of railway vehicles is chosen as an application example. Railway vehicles are typically designed for an operationel service life of 30 years or more. In order to ensure a safe and reliable operation over this period, regular maintenance actions must be carried out, which nowadays are based on fixed, predefined intervals. These intervals are limited by a certain operating time or after a defined mileage has been reached. Structural damages that occur between two maintenance actions are rarely detected and, in extreme cases, can lead to derailment. Such events are unpredictable and always result in costly corrective maintenance activities. To avoid such derailment scenarios, the intervals are therefore defined according to a conservative approach (short time intervals, less mileage). Increasing the number of maintenance activities not only raises maintenance costs but also leads to inefficient utilization of components, which are often replaced before the end of their technical service life. Therefore, an intelligent, conditionbased maintenance strategy using an SHM system for damage diagnosis and prediction presents a promising approach to reducing the number of maintenance activities while simultaneously increasing safety, reliability, and cost-effectiveness. Structural damages affect the vibration behavior. Railway vehicles are exposed to constant vibrations during operation, primarily caused by the rolling contact between wheel and rail. The main focus of this research thesis is on the automated evaluation and assessment of vibration measurements concerning defective components. For this purpose, a new method based on Stochastic Subspace Identification (SSI) and kernel density estimation is developed and presented. The core of this method is the Modal Parameter Density Estimation Function (MoDE-F). A key innovation is the use of a large number of different stochastic excitation scenarios in combination with kernel density estimation to determine the modal parameters. This approach leads to the minimization of incorrect identification results that arise from a violation of the white noise assumption for the system excitation – as used in the derivation of the SSI –. The automated evaluation and classification of the generated MoDE-F is realized by using the Jensen-Shannon divergence metric (JSDM). Based on the current state of research, the mode of operation is theoretically analyzed and presented. Numerical simulations show the general applicability to realistic operating conditions. The new method is then applied to a real bogie.
    Source Type:Doctoral Thesis
    DOI:10.25819/ubsi/10744
    Series:Schriftenreihe der Arbeitsgruppe für Technische Mechanik im Institut für Mechanik und Regelungstechnik - Mechatronik
    Volume number:22
      1  3
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    Ursachenforschung, Monitoring und Kompensation des Axialdrifts von rotationssymmetrischen Werkstücken auf Rollendrehvorrichtungen
    (2022)
    Vitt, Sven 
    In this work, the mechanical system of turning roll devices is studied and filtered with regard to possible influencing factors on the drift movement occurring during operation. The results of these fundamental investigations flow into the creation of a multi-body simulation model with which the findings are verified. The developed model test rig on a reduced scale is developed based on the observations during a technical measurement on a reel turning device in original size, the examined patent documents, the derived influencing factors in the mechanical system of the reel turning devices, as well as the performed multi-body simulations. The model test rig enables singular investigations of the various causes of the drift movement. As a result, control algorithms could be developed and implemented on the model test rig, which show that the drift movements can curatively be minimized very much. In addition, the algorithms, which access measurement values from the 3D force sensors, that have also been developed and implemented on the model test rig, offer approaches for preventive drift compensation. The investigations can be demonstrated with the multi-body simulation model and the developed model test rig, while the results can be transferred to a prototype of reel turning devices in original size and verified there. During the upscaling process from the model to the original a call back to the multi-body simulation model can be done.
    Source Type:Doctoral Thesis
    DOI:10.25819/ubsi/10115
    Series:Schriftenreihe der Arbeitsgruppe für Technische Mechanik im Institut für Mechanik und Regelungstechnik - Mechatronik
    Volume number:20
      1  8
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    PublicationAccess status: Open Access ,
    Referenzfreies ultraschallbasiertes Verfahren zur Zustandsüberwachung rotierender Bauteile - Anwendung auf Radsätze von Schienenfahrzeugen
    (2021)
    Reitz, Tobias 
    In this research work a baseline-free method for Acousto-Ultrasonics (AU)-based Structural Health Monitoring (SHM) of mechanically loaded and rotating axles is proposed, which can be used for condition monitoring of wheelset axles of railway vehicles. The novel “Dynamic Reference Method” utilizes the difference that is generated in the ultrasonic wave propagation due to the crack breathing mechanism of a mechanically loaded and rotating axle. Due to their physical properties, ultrasonic waves can propagate through a structure and interact with discontinuities within the material, making them particularly suitable for permanent condition monitoring with SHM methods. In order to extract the changes due to damage, most SHM systems first need to collect data from the structure in healthy condition to build the so-called baseline. With the help of signal processing and feature extraction, the structural health condition is assessed through the comparison of the baseline and the newly acquired data. In real operation, structures are exposed to varying Environmental and Operational Conditions (EOCs), especially wheelset axles of railway vehicles, which are considered in this thesis. Different studies on the stability and the influence of EOCs on AU-based SHM methods using a previously collected baseline have shown that these lead to errors in the results of condition monitoring. This is due to the fact that it is difficult or impossible to distinguish the effects due to EOCs from the effects of structural damages. It is in some cases not economically feasible to collect data and to construct a baseline model for each combination of all possible EOCs for each structure. In consideration of such a practical limit, the development of a baseline-free SHM method is necessary and is focused in this thesis. The results of the condition monitoring during the crack initiation and propagation in wheelset axles of railway vehicles demonstrate the effectiveness of the proposed baseline-free SHM method. Cracks can be detected, the crack propagation can be observed during fatigue tests and the approximate circumferential position of the crack can be localized by the proposed method. In addition, it is proved that the introduced SHM method is able to detect a fatigue crack during measurement runs on a full-scale roller test rig for railway vehicles without a previously collected baseline. The proposed baseline-free SHM method could be used to complete the safety level of the periodically performed non-destructive inspections during the operation of wheelset axles, as the permanent condition monitoring prevents unforeseeable damages. This innovative technology contributes to the climate-friendly mobility of the future by increasing the acceptance of rail transport.
    Source Type:Doctoral Thesis
    DOI:10.25819/ubsi/9978
    Series:Schriftenreihe der Arbeitsgruppe für Technische Mechanik im Institut für Mechanik und Regelungstechnik - Mechatronik
    Volume number:19
      1  11
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    Frequency-domain fatigue analysis of wind turbine structures and fatigue damage detection: performance evaluation of spectral-based methods against the rainflow counting algorithm
    (2021)
    Chaaban, Rannam
    Fatigue failure of metallic structures such as wind turbine towers is a problem that affects their remaining service life. Fatigue cracks are most likely to initiate in the structural hot spots such as holes or welded joints. The time-domain approach in dealing with the fatigue analysis problem is the industry standard of fatigue load certification and fatigue damage assessment on wind turbines systems. The time-domain approach is based on time domain cycle counting and a linear fatigue accumulation rule to estimate a cumulative fatigue damage index. By comparing this index to a reference value, fatigue failure prediction and fatigue life estimation are possible. The development of an equivalent formulation to the time-domain fatigue analysis problem has been an active topic of research in the past few years. This equivalent formulation is based on the random vibration fatigue theory where fatigue analysis is done in the frequency domain. The frequency-domain fatigue analysis has found it’s way into many applications subject to random loading. However, the frequency-domain fatigue analysis is developed under certain assumptions that are hard to meet in the case of wind turbine loading. This includes for example the stationarity of the loading, the assumption of zero-mean and the Gaussian amplitude distribution of the stochastic loading. This thesis sets three objectives. The first objective is to address systematically the assumptions required by the spectral fatigue analysis methods in order to be able to accept the obtained results. To achieve this objective, the theoretical basis of the spectral fatigue analysis is reviewed and the limitations of the frequency-domain methods are addressed. Furthermore, a new strategy that enables using the spectral methods for wind turbine fatigue analysis is developed. The second objective is the performance assessment of the equivalent formulations of fatigue analysis problem, the frequency-domain against the industry standard time-domain. This is achieved using two different data-sets: simulation and operational. The simulation-based dataset is generated using hi-fidelity wind turbine simulation tool and aims to replicate the integrated design process at early stages; while the operational data-set is obtained from tower loading measurements of an operating small and utility-scale wind turbines and used to evaluate the performance of different spectral fatigue analysis methods against the well-established rainflow cycle counting method in time domain. The third objective is to explore the potentials of using comparative sensor data approach in the early detection in structural failure. This approach is based on monitoring the linear correlation of the measured strain or estimated fatigue damage at pre-defined sensor locations. An experimental validation of this method is presented in this thesis, and the obtained results demonstrate the possibility of using this technique for structural failure detection. The proposed objectives aim to meet the challenges of optimizing wind turbine structures in terms of cost, fatigue damage and service life time by developing new approaches capable of saving time, computational effort, resources in addition to reducing cost of energy.
    Source Type:Doctoral Thesis
    DOI:10.25819/ubsi/9962
    Series:Schriftenreihe der Arbeitsgruppe für Technische Mechanik im Institut für Mechanik und Regelungstechnik - Mechatronik
    Volume number:18
      679  904
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    Mechanical and pathophysiological in vivo characterization of the individual aortic wall based on 4D ultrasound imaging
    (2020)
    Wittek, Andreasorcid-logo
    This work focuses on the development of new non-invasive methods for the in vivo characteri-zation of the individual elastic behavior of the human aortic wall. Due to the physiological func-tion of the elastic properties within the cardiovascular system and its change with degenerative processes, this knowledge is of direct diagnostic relevance. In addition, the individual material properties are an important, prior to the work presented here unknown, determinant of patient-specific finite element models, which have been developed to calculate the maximum wall stress and to estimate the rupture risk of abdominal aortic aneurysms. Using a modified device that provides time resolved 3D echocardiography with speckle tracking (4D ultrasound), a non-invasive in vivo full field measurement of human aortic wall motion was established in cooperation with industrial and clinical partners. It provided highly resolved mo-tion functions of discrete material points and derived in-plane strain tensors for wall surface segments with a sizes between 1 and about 20 mm^2. This new measurement of displacement and strain was validated in an in vitro experiment with respect to its agreement with optical full field measurements and to its reproducibility under identical conditions (test-retest reliability). Two different methods for the analysis of aortic wall motion were developed and applied to different patient cohorts in clinical studies. A comparison of the cyclic three-dimensional de-formation of the proximal ascending and the abdominal aorta in terms of length and diameter change and twist provided deepened insight in the physiological “Windkessel” function of the ascending aorta. Statistical analysis of the distributions of local in-plane strains was used to ob-tain measures for size and heterogeneity of elastic aortic wall deformation (‘strain distribution indices’). A comparative clinical study in young volunteers and two groups of aged cardiovascular patients without and with abdominal aortic aneurysm showed that aortic walls reliably can be classified according to their cardiovascular health state by use of the obtained strain distribution indices and that these, therefore, are suited as new biomarker for cardiovascular health. Two approaches were developed to characterize and model the individual elastic properties of the aortic wall. Firstly, a local distensibility coefficient has been introduced to linearly ap-proximate and identify the heterogeneous local functional elastic properties in the physiological range in vivo. Secondly, an iterative Finite Element Model Updating approach to the inverse identification of the individual orthotropic and hyperelastic constitutive behavior of geometrical-ly irregular aneurysmal walls was developed. It could be shown that constitutive parameter identification based on heterogeneous full field strain data is feasible even though only two load cases are accessible non-invasively in vivo. The approach was verified numerically and the effect of the measurement uncertainty on the constitutive parameter identification was examined. Finally, the approach was applied exemplarily to in vivo data of three patients of different age and cardiovascular health state.
    Source Type:Doctoral Thesis
    DOI:10.25819/ubsi/10045
    Series:Schriftenreihe der Arbeitsgruppe für Technische Mechanik im Institut für Mechanik und Regelungstechnik - Mechatronik
    Volume number:17
      4  9
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    Lösungsstrategien für dünnbesetzte inverse Probleme im Bereich der Strukturüberwachung
    (2019)
    Ginsberg, Daniel
    Der Fokus dieser Forschungsarbeit liegt auf der Analyse inverser Probleme der schwingungsbasierten Strukturüberwachung. Strukturüberwachungssysteme helfen u.a. dabei die Integrität einer Struktur beurteilen zu können oder eine Vorhersage der Restlebensdauer zu treffen. Im Rahmen dieser Arbeit werden neuartige Überwachungsstrategien entwickelt und untersucht. Die Ergebnisse zeigen das große Potential von Lösungsansätzen für dünnbesetzte inverse Probleme in diesem Bereich. Von dünnbesetzten Problemen spricht man, falls ein Lösungsvektor existiert, welcher nur sehr wenig Elemente ungleich null besitzt. Solche Lösungsstrategien helfen dabei die benötigte Messinformation zu reduzieren und die Rekonstruktionsqualität zu steigern bzw. beizubehalten. Für eine kontinuierliche Strukturüberwachung werden Sensoren permanent an der mechanischen Struktur angebracht. So könnnen die mechanischen Schwingungen dauerhaft gemessen werden. Geeignete Algorithmen müssen dann diese Messdaten verarbeiten, um das gewünschte Überwachungsergebnis zu erzielen. Allerdings spiegeln die Schwingungsmessungen lediglich die Wirkung einer meist unbekannten Ursache wider. Zur Überwachung ist daher eine Invertierung des Ursache-Wirkungsprinzips erforderlich. Das bedeutet, dass die Überwachungsalgorithmen in der Lage sein müssen diese inverse Problemstellung zu lösen. Zur Lösung inverser Probleme ist es zweckmäßig Vorkenntnisse der gesuchten Größen zu berücksichtigen, um mechanisch sinnvolle Ergebnisse zu erhalten. Die charakteristischen Eigenschaften der Strukturanregung und der Schädensmuster können dazu genutzt werden, die jeweils auftretende inverse Problemstellung in ein dünnbesetztes Gleichungssystem zu überführen. Die Lösung solcher Gleichungssysteme kann mittels der L1-Regularisierung sehr effizient generiert werden. Speziell für Lastrekonstruktionsverfahren ist durch die Anwendung von L1-minimierenden Algorithmen eine Lokalisation und eine Kraftverlaufsrekonstruktion mit einer deutlich geringeren Anzahl an Sensoren als bislang möglich. Die Stabilität der Rekonstruktionsalgorithmen ist auch bei verrauschten Messdaten und Modellabweichungen gegeben. Für Schadensidentifikationsalgorithmen sind Lösungsstrategien für dünnbesetzte Probleme ebenfalls gewinnbringend im Hinblick auf die benötigte Messinformation und die erreichbare Schadensidentifikationsqualität. Dies gilt sowohl für Verfahren im Frequenzbereich, als auch für Methoden im Zeitbereich. Mit Hilfe von Lösungsstrategien für dünnbesetzte inverse Probleme ist es außerdem möglich Ansätze für die kombinierte Identifikation von Strukturschäden und externen Lasten zu realisieren. Alle untersuchten Rekonstruktionsalgorithmen erreichen eine Reduktion der benötigten Messinformation, wodurch u.a. ein Beitrag zur günstigeren und praxistauglicheren Anwendung von Strukturüberwachungssystemen geleistet werden kann.
    Source Type:Doctoral Thesis
    DOI:10.25819/ubsi/489
    Series:Schriftenreihe der Arbeitsgruppe für Technische Mechanik im Institut für Mechanik und Regelungstechnik - Mechatronik
    Volume number:16
      2  14
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    PublicationAccess status: Open Access ,
    Online force reconstruction for Structural Health Monitoring
    (2018)
    Niu, Yan
    The knowledge of the external load acting on the structure under investigation is important for Structural Health Monitoring (SHM). The history of the external load can be used for updating the earlier lifetime prediction of the structure. An easy and direct way to get the external load information is to measure it directly using a certain type of force transducer. However, there are still many practical cases in which a direct measurement of the external load is physically or economically not feasible. For those cases, a possible solution is to reconstruct the external load using structural response measurements, e.g. displacement, strain, velocity, and acceleration. This process is defined as force reconstruction. It is a kind of inverse problem which often tends to be ill-posed, in the sense that the measurement noise and the modeling error can be amplified and can cause large deviations in the reconstructed force. Online force reconstruction is a research topic which studies how to realize force reconstruction in real-time. The thesis focuses on online force reconstruction. The basic idea which is adopted in this thesis for online force reconstruction is to apply a real-time executable state and input estimation algorithm. The methodology for online force reconstruction consists of two stages, an offline stage and an online stage. In the offline stage, the modal parameters of the structure are identified, and a state-space model of the structure is constructed. In the online stage, a real-time executable state and input estimation algorithm is applied to provide an estimate of the force. The ill-posedness in the process of force reconstruction is relaxed by the convergence of the estimate error of the force. Together with the force, the structural responses at different positions can be reconstructed, too. In this thesis, modifications to some of the available real-time executable state and input estimation algorithms are proposed, so that these algorithms are theoretically more suitable for online force reconstruction. In the earlier research studies, some algorithms have already been proposed for online force reconstruction. All the available algorithms, including the proposed modified algorithms, are potential candidates for online force reconstruction. In case there is a practical need for online force reconstruction, it is reasonable to raise the question which algorithm to choose. In this thesis, a study on application-oriented algorithm selection is performed. The assumptions and the mathematical conditions in the algorithms are translated into practical requirements. A benchmark study is performed in which a laboratory structure is taken as the benchmark structure. The modal parameters of this benchmark structure are identified using an Experimental Modal Analysis (EMA) technique. Two types of widely used sensors are installed on this benchmark structure, including strain gauge and accelerometer. Three different types of input forces are considered, including a quasi-static force, impact forces, and a wind load which is generated by an electric fan. In total eight different algorithms are tested. Based on the results from the benchmark study, an application oriented guidance for algorithm selection is extracted. As an example of practical application, the presented methodology for online force reconstruction is applied for wind load reconstruction for the 600 meter tall Canton Tower. The field measurement data are recorded by the SHM system of the Canton Tower, including the data which were recorded during the Typhoon Nanmadol in 2011 and the Typhoon Kai-tak in 2012. The modal parameters of the Canton Tower during the Typhoon Nanmadol are identified by using an Operational Modal Analysis (OMA) technique. The available reduced-order Finite Element (FE) model of the Canton Tower is first modified to reflect the height adjustment of the Canton Tower, and then is updated according to the identified modal parameters. In consideration of the characteristics of the wind load and the sensor availability in the SHM system, a suitable algorithm is selected with the help of the application oriented guidance which is extracted from the benchmark study. The wind load on the Canton Tower during the Typhoon Kai-tak is reconstructed. The mean value of the wind load is calculated with the wind speed measurements and the aerodynamic force coefficients which are identified from a wind tunnel test. The dynamic part of the wind load is reconstructed by using the selected algorithm and the acceleration measurements. To validate the reconstruction results, two acceleration channels are selected. The acceleration measurements from these two channels are not used in wind load reconstruction. The strategy for the validation is to compare the reconstructed acceleration for these two channels with the real acceleration measurements. The validation results show that the reconstructed wind load is acceptable. Finally, a summary of this thesis is provided, and some open topics are described. These open topics can be considered in future study on online force reconstruction.
    Source Type:Doctoral Thesis
    Series:Schriftenreihe der Arbeitsgruppe für Technische Mechanik im Institut für Mechanik und Regelungstechnik - Mechatronik
    Volume number:15
      3  14
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    Mechanismenbasierte Modellierung und Simulation des VHCF-Wechselverformungsverhaltens austenitischer Edelstähle
    (2017)
    Hilgendorff, Philipp-Malte
    In this work, a model describing the VHCF deformation behaviour of a metastable and a stable austenitic stainless steel is presented and solved by means of a boundary element method. Based on the experimental examination of the fatigue behaviour of both alloys until very high number of loading cycles (very high cycle fatigue, VHCF) characteristic mechanisms of plastic deformation in shear bands and of deformation-induced phase transformation from the austenite to the α`-martensite are described. A 2-D boundary element method is extended regarding the description of elastic anisotropic properties and the calculation of spatial deformation. Solving the model by using the boundary element method allows simulating the cyclic plastic deformation within two-dimensional microstructures. In extended studies, the effect of a predeformed condition and of a moderate increase of temperature is also considered. Simulation results are directly compared to the observed deformation evolution on real fatigue specimen surfaces and, in addition, a comparison is carried out on the basis of the resonant behaviour of fatigue specimens and of modelled microstructures. Good accordance of results confirms the model assumptions and thereby provides a more profound understanding of the VHCF deformation behaviour of both austenitic stainless steels.
    Source Type:Doctoral Thesis
    Series:Schriftenreihe der Arbeitsgruppe für Technische Mechanik im Institut für Mechanik und Regelungstechnik - Mechatronik
    Volume number:14
      1  5
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    Simulation der mikrostrukturbestimmten Kurzrissausbreitung unter dem Einfluss lokaler Phasenumwandlung
    (2017)
    Kübbeler, Martin
    In various practical situations, structures and components are exposed to high-cycle fatigue loading. In such conditions, their lifetime is determined by the growth of microstructurally short fatigue cracks. In order to increase the resistance of materials against short crack propagation, understanding its mechanisms is an important basis. Hence, this thesis presents a new two-dimensional model representing short crack growth in a metastable austenitic steel. It is influenced by phase transformation, provided two intersecting slip systems are activated at the crack tip. Due to the increased volume of the transformed material, the crack is closed for a longer part of the load cycle compared to transformation-free crack growth. This reduces the cyclic crack tip slide displacement determining the crack propagation rate and results in an increased lifetime of components. Based on experimental investigations, crack propagation and phase transformation – both occurring at the same time – are modelled performing the following main steps: • The stress field in the vicinity of the crack tip is evaluated during one load cycle. If it activates two slip systems, slip planes with the determined orientations are introduced at the crack tip. They represent elastic ideal-plastic material behaviour. • Crack propagation and the increase of transformed material at the crack tip are determined resulting from slip which has been computed along the slip planes. • Crack extension and the increased transformed regions are included into the model and subsequently, a new load cycle is simulated. In order to solve the model numerically, a boundary element method is used, which couples two types of boundary elements: Those with absolute displacements enclose the martensite regions which allows to assign volume increase to these areas. Elements with relative displacements discretise the crack and the slip planes. The model is applied to simulate the growth of microstructrually short cracks. Besides of phase transformation, barrier effects of grain boundaries and individual isotropic stiffnesses of the grains of a microstructure are considered. Effects of short crack propagation resulting from these features are highlighted and parameter studies are performed. Besides of other results, reduction of cyclic crack tip slide displacement due to phase transformation is reproduced. Exemplarily, the propagation of a real crack is simulated yielding a good agreement with the experiment.
    Source Type:Doctoral Thesis
    Series:Schriftenreihe der Arbeitsgruppe für Technische Mechanik im Institut für Mechanik und Regelungstechnik - Mechatronik
    Volume number:13
      3  7
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    Distributed piezoelectric transducers and their applications in structural health monitoring
    (2017)
    Yang, Cheng
    Structural Health Monitoring (SHM) is an upcoming technology, which combines disciplines of smart materials, structural dynamics, structural engineering, Non-Destructive Testing (NDT), sensor and actuator development, signal processing and more. It deals with the development and implementation of techniques where monitoring, inspection and damage detection becomes an integral part of a structure. Piezoelectric materials have been explored and applied in many fields since its first discovery. Recently, with the rapid growth of piezoelectric transducers, they have become an essential part of an SHM system due to many of their prior advantages, for instance, light weight, low cost, ability to be integrated into a structure, easy to apply and so forth. Generally, the conventional piezoelectric transducers used in SHM are discrete piezoelectric ceramic sensors. They are widely accepted in many SHM applications due to the above- mentioned features. However, they are also known for their brittleness, hardness, unable to be applied on a single or multi-curved structural surface, difficult to cover a large area, as well as error performance due to bonding layer failure. These drawbacks compromise the reliability of a SHM system. The research presented here focuses on the investigation and development of a new type of smart material - the distributed piezoelectric transducer, with a target application in SHM fields where the traditional piezoelectric ceramics are not suitable anymore. One of the main focuses is the development of a piezoelectric ceramic and polymer based flexible piezoelectric composite: the piezoelectric paint. The production of a high quality piezoelectric paint is investigated and its material properties are characterized. To enhance the low piezoelectricity, which is the main drawback of a piezoelectric paint, its improvement is studied. The enhanced piezoelectric paint is compared with traditional strain gauges and ceramic sensors. Afterwards, its applications in SHM as strain sensors for strain measurement, modal sensors for modal filtering, vibration sensors for modal analysis are demonstrated. Besides, its thermal properties are studied as well. Since the piezoelectric paint contains a polymer phase, its applications are limited for ambient temperature applications, therefore, another group of piezoelectric material for high temperature SHM applications - Aluminum Nitride (AlN), is explored. This part focuses on a three-layer structure, AlN, Diamond, gamma Titanium Aluminide (γ-TiAl). AlN is deposited on the substrate as distributed Surface Acoustic Wave (SAW) transducer. Numerical calculation of the structure is performed to study the dispersion features of SAW on the three-layer structure. With the help of the Finite Element Method (FEM), the propagation of SAW is demonstrated by modeling and simulation. Structural flaws are simulated to illustrate that with the combination of Interdigital Transducers (IDT), AlN can be used as distributed SAW sensors in high temperature SHM applications.
    Source Type:Doctoral Thesis
    Series:Schriftenreihe der Arbeitsgruppe für Technische Mechanik im Institut für Mechanik und Regelungstechnik - Mechatronik
    Volume number:12
      5  17