Mechanics and Adaptronics – serie

The novel finite element formulations fall into the category of geometrically exact Kirchhoff-Love beams. A prominent characteristic of this category is that the absence of shear deformation is strongly enforced by removing two degrees of freedom. Further, the corresponding beam theories exhibit not only translational but also rotational degrees of freedom and their configurations thus form a non-additive and non-commutative space. Sophisticated interpolation schemes are required that need to be tested not only for locking, spatial convergence behavior, and energy conservation, but also for observer invariance and path-independence. For the three novel beam element formulations all these properties are analytically and numerically studied and confirmed, if applicable. Two different rotation parameterization strategies are employed based on the well-known geodesic interpolation used in many Simo-Reissner beams and the lesser known split into the so-called \textit{smallest rotation} and a torsional part. Application of the former parameterization results in a mixed finite element formulation intrinsically free of locking phenomena. Additionally, the first geometrically exact Kirchhoff-Love beam element is presented, which strongly enforces inextensibility by removing another degree of freedom. Furthermore, the numerical efficiency of the new beam formulations is compared to other beam elements that allow for or suppress shear deformation. When modeling very slender beams, the new elements offer distinct numerical advantages.Standard molecular dynamics simulations, which are commonly used to study polymers, suffer from a lack of a careful mathematical basis and the use of an expensive explicit time integration scheme. To circumvent these shortcomings and to be able to simulate stretching experiments on relevant time scales, the problem is described by a stochastic partial differential equation, which can be solved using the finite element method with a backward Euler temporal discretization. In detail, the polymer is represented by a Kirchhoff-Love beam with a linear elastic constitutive model. Inertial and electrostatic forces are neglected. It is deformed by a distributed load mimicking collisions with molecules of the surrounding fluid. Naturally, this load heavily fluctuates over time and space and mean values need to be computed in a Monte Carlo manner. To vastly speed up the fitting process to experimental data in a Bayesian framework, a surrogate model based on a Gaussian process is set up, which directly computes the mean values for given material parameters. The uncertainties and correlations of the material parameters are studied and compared to the literature.

The novel finite element formulations fall into the category of geometrically exact Kirchhoff-Love beams. A prominent characteristic of this category is that the absence of shear deformation is strongly enforced by removing two degrees of freedom. Further, the corresponding beam theories exhibit not only translational but also rotational degrees of freedom and their configurations thus form a non-additive and non-commutative space. Sophisticated interpolation schemes are required that need to be tested not only for locking, spatial convergence behavior, and energy conservation, but also for observer invariance and path-independence. For the three novel beam element formulations all these properties are analytically and numerically studied and confirmed, if applicable. Two different rotation parameterization strategies are employed based on the well-known geodesic interpolation used in many Simo-Reissner beams and the lesser known split into the so-called \textit{smallest rotation} and a torsional part. Application of the former parameterization results in a mixed finite element formulation intrinsically free of locking phenomena. Additionally, the first geometrically exact Kirchhoff-Love beam element is presented, which strongly enforces inextensibility by removing another degree of freedom. Furthermore, the numerical efficiency of the new beam formulations is compared to other beam elements that allow for or suppress shear deformation. When modeling very slender beams, the new elements offer distinct numerical advantages.Standard molecular dynamics simulations, which are commonly used to study polymers, suffer from a lack of a careful mathematical basis and the use of an expensive explicit time integration scheme. To circumvent these shortcomings and to be able to simulate stretching experiments on relevant time scales, the problem is described by a stochastic partial differential equation, which can be solved using the finite element method with a backward Euler temporal discretization. In detail, the polymer is represented by a Kirchhoff-Love beam with a linear elastic constitutive model. Inertial and electrostatic forces are neglected. It is deformed by a distributed load mimicking collisions with molecules of the surrounding fluid. Naturally, this load heavily fluctuates over time and space and mean values need to be computed in a Monte Carlo manner. To vastly speed up the fitting process to experimental data in a Bayesian framework, a surrogate model based on a Gaussian process is set up, which directly computes the mean values for given material parameters. The uncertainties and correlations of the material parameters are studied and compared to the literature.

During heat treatment in dairy production, the rapid formation of heat-induced fouling deposits on the plant surface leads to reduced efficiency of heat transfer. Therefore, a regular cleaning process is required to soften the heat-induced protein deposits and then remove them from the plant surface. The mechanical property of the deposits is one of the key issues of the cleaning mechanisms since the non-fractured behaviour dominates the deformation of the fouling layer and the failure behaviour has a great impact on the cohesive removal of fouling deposits. Considering the complicated geometry of fouling deposits and their irregular distribution, indentation experiments were carried out on various kinds of protein deposits. The experimental results reveal the significant influence of the thickness of fouling deposits on their mechanical behaviour and the time-dependent nonlinear behaviour of the deposits.Furthermore, heat-induced whey protein gel was used as the modelmaterial for fouling deposits and the non-fractured and fracture behaviour was characterized using compression and wire cutting experiments, respectively. The material parameters identified using the inverse finite element method allow the prediction of fracture behaviour under localized external loads and provide a deeper insight into cohesive removal. To investigate the softening effect during caustic washing, tensile experiments were conducted on chemically treated and untreated whey protein gels. Adequate chemical degradation leads to a softer mechanical response and increased stress relaxation, making whey protein gels more flowable and more resistant to tensile deformation. The experimental results provide useful data on the failure behaviour of chemically treated whey protein gels.

During heat treatment in dairy production, the rapid formation of heat-induced fouling deposits on the plant surface leads to reduced efficiency of heat transfer. Therefore, a regular cleaning process is required to soften the heat-induced protein deposits and then remove them from the plant surface. The mechanical property of the deposits is one of the key issues of the cleaning mechanisms since the non-fractured behaviour dominates the deformation of the fouling layer and the failure behaviour has a great impact on the cohesive removal of fouling deposits. Considering the complicated geometry of fouling deposits and their irregular distribution, indentation experiments were carried out on various kinds of protein deposits. The experimental results reveal the significant influence of the thickness of fouling deposits on their mechanical behaviour and the time-dependent nonlinear behaviour of the deposits.Furthermore, heat-induced whey protein gel was used as the modelmaterial for fouling deposits and the non-fractured and fracture behaviour was characterized using compression and wire cutting experiments, respectively. The material parameters identified using the inverse finite element method allow the prediction of fracture behaviour under localized external loads and provide a deeper insight into cohesive removal. To investigate the softening effect during caustic washing, tensile experiments were conducted on chemically treated and untreated whey protein gels. Adequate chemical degradation leads to a softer mechanical response and increased stress relaxation, making whey protein gels more flowable and more resistant to tensile deformation. The experimental results provide useful data on the failure behaviour of chemically treated whey protein gels.

This thesis works on the topic of fiber-reinforced plastics and discusses the measurement of strain with embedded sensors. Embedding sensors into a structure fundamentally poses challenges arising from the differences in mechanical properties of sensor and structure. This thesis works on the research area of Self-Sensing, where these challenges are overcome by using carbon fibers for both load-carrying and strain-sensing functions. Starting with a literature review, this thesis proposes three research hypotheses, which are targeted to describe the Self-Sensing properties of unidirectional carbon fiber reinforced plastics (CFRPs) for strain measurements. These hypotheses assume, that the electric anisotropy of the material results in a complex voltage distribution within a Self-Sensing specimen. In order to discuss this point further, a two-dimensional piezoresistivity model based on the Laplace equation is introduced. The developed model newly allows to quantify the electricpotential changes in specimens with arbitrary geometrical dimensions and electric anisotropy.Furthermore, this thesis discusses a set of experimental results on the piezoresistive properties of unidirectional CFRP made with the pultrusion process. Overall, the results of the experiments indicate that the most repeatable results are obtained for specimens with electric contacts at their cut-end. This approach allows to manufacture Self-Strain-Sensing rods with a gauge factor of approximately 1.9 that can be used in a multifunctional manner for both load-carrying and strain-sensing purposes. Furthermore, a novel measurement setup is developed, which allows to acquire the electric potential distribution on the surface of electrical conductors with very high spacial resolution. This experimental setup newly reveals that the current flow in specimens can be more complex than assumed in a two-dimensional model.

This thesis works on the topic of fiber-reinforced plastics and discusses the measurement of strain with embedded sensors. Embedding sensors into a structure fundamentally poses challenges arising from the differences in mechanical properties of sensor and structure. This thesis works on the research area of Self-Sensing, where these challenges are overcome by using carbon fibers for both load-carrying and strain-sensing functions. Starting with a literature review, this thesis proposes three research hypotheses, which are targeted to describe the Self-Sensing properties of unidirectional carbon fiber reinforced plastics (CFRPs) for strain measurements. These hypotheses assume, that the electric anisotropy of the material results in a complex voltage distribution within a Self-Sensing specimen. In order to discuss this point further, a two-dimensional piezoresistivity model based on the Laplace equation is introduced. The developed model newly allows to quantify the electricpotential changes in specimens with arbitrary geometrical dimensions and electric anisotropy.Furthermore, this thesis discusses a set of experimental results on the piezoresistive properties of unidirectional CFRP made with the pultrusion process. Overall, the results of the experiments indicate that the most repeatable results are obtained for specimens with electric contacts at their cut-end. This approach allows to manufacture Self-Strain-Sensing rods with a gauge factor of approximately 1.9 that can be used in a multifunctional manner for both load-carrying and strain-sensing purposes. Furthermore, a novel measurement setup is developed, which allows to acquire the electric potential distribution on the surface of electrical conductors with very high spacial resolution. This experimental setup newly reveals that the current flow in specimens can be more complex than assumed in a two-dimensional model.

This book provides findings on the simulation of the valve dynamic to the current technological standards. Above all, it delivers a simulation based and predictive approach on the fatigue strength assessment of four-stroke heavy-duty engine valves. The demand for more efficient combustion engines with fuel flexibility goes along with increasing component requirements regarding strength and durability, while the development costs should remain low. In this context, the present book focuses on the gas exchange valves of heavy-duty engines. Especially, the valves on the exhaust side have an increased risk of fatigue failure. The aim of this book is the generation of a predictive fatigue strength assessment to strengthen the frontloading of the exhaust valve design process and to increase the reliability of the component. In the context of fatigue assessment, this book examines the loads of the exhaust valve during its working cycle. Beside the high temperature and cylinder pressure, further loads act on the exhaust valve like actuation force or an eccentric impact of the valve on the valve seat ring. Furthermore, a bold valve secondary dynamic in the form of valve bending vibrations is observed on the exhaust valves of heavy-duty engines increasing the valve load even more. The cause of this secondary dynamic is unknown. This book investigates the valve loads to get the necessary input for the fatigue strength assessment. With respect to a predictive approach, the determination of valve dynamic and valve loads is based on a multibody simulation model of the valve train. In order to deliver predictive results and a transferable method, this simulation model includes all relevant physical effects to describe the valve dynamic accurately during all valve load phases of the working cycle. With the simulation model, the root cause for the bold valve secondary dynamic is examined iteratively. The model delivers not only the cause for the valve secondary dynamic but most importantly the critical valve loads. These loads deliver the input for the fatigue strength assessment. To ensure the robustness of the load data determined by the simulation model, the sensitivity of influences on the valve load is examined. In this context geometrical misalignment, fluctuations in load data and variable engine operation points are considered. A load collective based on the variation of influences on the valve load is the result of this analysis. All the results of the influence and sensitivity study are generated with the newly developed simulation model of the valve train. Moreover, this book outlines measurements on a testbed engine. In scope of these measurements are temperature and strain measurements of the valve. The generated data validate the simulation model of the valve train. Additionally, the statistical evaluation of the data is used in the subsequent fatigue strength assessment to increase the reliability of the results.

This book provides findings on the simulation of the valve dynamic to the current technological standards. Above all, it delivers a simulation based and predictive approach on the fatigue strength assessment of four-stroke heavy-duty engine valves. The demand for more efficient combustion engines with fuel flexibility goes along with increasing component requirements regarding strength and durability, while the development costs should remain low. In this context, the present book focuses on the gas exchange valves of heavy-duty engines. Especially, the valves on the exhaust side have an increased risk of fatigue failure. The aim of this book is the generation of a predictive fatigue strength assessment to strengthen the frontloading of the exhaust valve design process and to increase the reliability of the component. In the context of fatigue assessment, this book examines the loads of the exhaust valve during its working cycle. Beside the high temperature and cylinder pressure, further loads act on the exhaust valve like actuation force or an eccentric impact of the valve on the valve seat ring. Furthermore, a bold valve secondary dynamic in the form of valve bending vibrations is observed on the exhaust valves of heavy-duty engines increasing the valve load even more. The cause of this secondary dynamic is unknown. This book investigates the valve loads to get the necessary input for the fatigue strength assessment. With respect to a predictive approach, the determination of valve dynamic and valve loads is based on a multibody simulation model of the valve train. In order to deliver predictive results and a transferable method, this simulation model includes all relevant physical effects to describe the valve dynamic accurately during all valve load phases of the working cycle. With the simulation model, the root cause for the bold valve secondary dynamic is examined iteratively. The model delivers not only the cause for the valve secondary dynamic but most importantly the critical valve loads. These loads deliver the input for the fatigue strength assessment. To ensure the robustness of the load data determined by the simulation model, the sensitivity of influences on the valve load is examined. In this context geometrical misalignment, fluctuations in load data and variable engine operation points are considered. A load collective based on the variation of influences on the valve load is the result of this analysis. All the results of the influence and sensitivity study are generated with the newly developed simulation model of the valve train. Moreover, this book outlines measurements on a testbed engine. In scope of these measurements are temperature and strain measurements of the valve. The generated data validate the simulation model of the valve train. Additionally, the statistical evaluation of the data is used in the subsequent fatigue strength assessment to increase the reliability of the results.

This book offers extensive knowledge and characterization methods for Ultraviolet light curable piezoelectric 0-3 composites for researchers and industry. The book provides extensive research on the use of carbon-based conductive nanoparticles to improve the performance of Ultraviolet light curable piezoelectric composites, forming piezoelectric 0-0-3 composites. Materials researched include Barium Titanate (BTO), Sodium Potassium Niobate (KNN), Graphene Nanoplatelets (GNP), Multi-Walled Carbon Nanotubes (MWCNT) and Graphene Oxide (GO). A comprehensive literature review on piezoelectric 0-3 composites focuses on the main influencing factors to achieve high piezoelectric composite performance. The method to characterize the performance of piezoelectric composites using 4-point bending is adopted from literature, is characterized, and adopted for performance measurements.

This book offers extensive knowledge and characterization methods for Ultraviolet light curable piezoelectric 0-3 composites for researchers and industry. The book provides extensive research on the use of carbon-based conductive nanoparticles to improve the performance of Ultraviolet light curable piezoelectric composites, forming piezoelectric 0-0-3 composites. Materials researched include Barium Titanate (BTO), Sodium Potassium Niobate (KNN), Graphene Nanoplatelets (GNP), Multi-Walled Carbon Nanotubes (MWCNT) and Graphene Oxide (GO). A comprehensive literature review on piezoelectric 0-3 composites focuses on the main influencing factors to achieve high piezoelectric composite performance. The method to characterize the performance of piezoelectric composites using 4-point bending is adopted from literature, is characterized, and adopted for performance measurements.

This book presents an investigation on integrating wireless sensor nodes including their antennas into fiber metal laminates (FMLs) for the purpose of enabling wireless, material-integrated structural health monitoring.Within the scope of this work, a digital sensor node is presented, which can be fully integrated into a conductive host material. A stainless steel antenna supplies the system with sufficient power to provide the functions required for its intended use. This system enables the wireless readout of sensor data for the detection of damage in FMLs. The application focuses on aerospace components, for the detection of damage in the inner material layers, which are not or only hardly detectable by optical inspection methods. Guided ultrasonic waves in the form of Lamb waves are used for this. The flexible electronics are inserted into the layers of the target material, while the associated antenna is cut into the outer metal layer. This turns the outer metal layer, which would prevent wireless communication from inside the laminate, into an advantage, as the need for an additional, external antenna is eliminated. Two fundamentally different principles can be used as the sensor element. Piezoelectric sensors were already used extensively in structural health monitoring using ultrasound and recently developed piezoresistive sensors, which are designed to be very small, making them highly suitable for material integration. Both types of sensors can be read out with the presented system so that the most appropriate approach can be chosen depending on the application. The suitability of the wireless sensor system for its intended purpose is verified by material-integrated measurements. At the end of this work, it is shown that the raw data of the measurements reproducibly provide a sufficient resolution of the sensor signal to manually identify changes caused by applied reversible, artificial pseudo-defects from reference measurements without any damage. The intended audience of this book are people from the field which are familiar with the basic concepts of electrical engineering or similar regions, embedded system enthusiasts and all readers who like to follow the process of a complete wireless electronic system design from requirements analysis to final material-integrated measurement demonstrations.

This book presents an investigation on integrating wireless sensor nodes including their antennas into fiber metal laminates (FMLs) for the purpose of enabling wireless, material-integrated structural health monitoring.Within the scope of this work, a digital sensor node is presented, which can be fully integrated into a conductive host material. A stainless steel antenna supplies the system with sufficient power to provide the functions required for its intended use. This system enables the wireless readout of sensor data for the detection of damage in FMLs. The application focuses on aerospace components, for the detection of damage in the inner material layers, which are not or only hardly detectable by optical inspection methods. Guided ultrasonic waves in the form of Lamb waves are used for this. The flexible electronics are inserted into the layers of the target material, while the associated antenna is cut into the outer metal layer. This turns the outer metal layer, which would prevent wireless communication from inside the laminate, into an advantage, as the need for an additional, external antenna is eliminated. Two fundamentally different principles can be used as the sensor element. Piezoelectric sensors were already used extensively in structural health monitoring using ultrasound and recently developed piezoresistive sensors, which are designed to be very small, making them highly suitable for material integration. Both types of sensors can be read out with the presented system so that the most appropriate approach can be chosen depending on the application. The suitability of the wireless sensor system for its intended purpose is verified by material-integrated measurements. At the end of this work, it is shown that the raw data of the measurements reproducibly provide a sufficient resolution of the sensor signal to manually identify changes caused by applied reversible, artificial pseudo-defects from reference measurements without any damage. The intended audience of this book are people from the field which are familiar with the basic concepts of electrical engineering or similar regions, embedded system enthusiasts and all readers who like to follow the process of a complete wireless electronic system design from requirements analysis to final material-integrated measurement demonstrations.

Current methodologies used to design lightweight structures made of CFRP materials under static thermomechanical conditions often rely on simplified approaches. In particular, the temperature-related design case is typically described by assuming a uniform distribution of the worst-case temperature, which is the maximum allowable temperature that can occur simultaneously with the mechanical loads. However, these simplifications can lead to a weight penalty due to their over-conservatism. To address these limitations, the present work describes a novel analysis methodology that accounts for spatial distributions of temperature. This approach allows for a more detailed understanding of the structural behavior under these demanding conditions. As a result, existing load-carrying potentials can be identified and used to fully exploit the advantage of CFRP structures. Moreover, this methodology generates an improved understanding of the variability in the structural behavior under such scattering thermal conditions, which can increase confidence and reliability in the design process and lead to reduce related margins of safety. To accurately model the mechanical behavior of structures at distributed temperature conditions, it is essential to consider the temperature-dependent properties of the material. These properties describing the elastic and strength behavior of the unidirectional ply, are derived from typical material characterization performed at various temperatures. In this approach, a phenomenological model is used to account for the temperature dependence of the material. This model is fitted to the characterization results to consider the individual magnitude of the properties. The resulting property allowables contain typical material uncertainties, as well as the model uncertainty that is defined by assessing the errors between the model and measurement. To determine the stability and strength behavior of structures under different thermal conditions, Finite-Element-Analysis (FEA) is utilized. Variations of thermal load distributions are analyzed to consider the uncertainty in opertational conditions qualitatively and quantitatively. A series of such analyses is conducted at different thermal conditions to determine design values such as buckling loads or failure loads. Based on this data, surrogate modeling leads to design value formulation as a function of the temperature distribution. This approach provides a more comprehensive and reliable assessment of the structural behavior under different thermal conditions and enables to either determine more realistic worst-case behavior or enhanced design values such as probabilistic structural allowables. The final part of the thesis demonstrates the developed analysis methodology on representative skin field structures. The comparison to the common analysis procedure highlights the potentials of structural load carrying capability and reveals deficiencies in the present approach. Thus, a detailed modelling of the temperature distribution leads additionally to an improved reliability of the design process and more efficient and robust structures.

Current methodologies used to design lightweight structures made of CFRP materials under static thermomechanical conditions often rely on simplified approaches. In particular, the temperature-related design case is typically described by assuming a uniform distribution of the worst-case temperature, which is the maximum allowable temperature that can occur simultaneously with the mechanical loads. However, these simplifications can lead to a weight penalty due to their over-conservatism. To address these limitations, the present work describes a novel analysis methodology that accounts for spatial distributions of temperature. This approach allows for a more detailed understanding of the structural behavior under these demanding conditions. As a result, existing load-carrying potentials can be identified and used to fully exploit the advantage of CFRP structures. Moreover, this methodology generates an improved understanding of the variability in the structural behavior under such scattering thermal conditions, which can increase confidence and reliability in the design process and lead to reduce related margins of safety. To accurately model the mechanical behavior of structures at distributed temperature conditions, it is essential to consider the temperature-dependent properties of the material. These properties describing the elastic and strength behavior of the unidirectional ply, are derived from typical material characterization performed at various temperatures. In this approach, a phenomenological model is used to account for the temperature dependence of the material. This model is fitted to the characterization results to consider the individual magnitude of the properties. The resulting property allowables contain typical material uncertainties, as well as the model uncertainty that is defined by assessing the errors between the model and measurement. To determine the stability and strength behavior of structures under different thermal conditions, Finite-Element-Analysis (FEA) is utilized. Variations of thermal load distributions are analyzed to consider the uncertainty in opertational conditions qualitatively and quantitatively. A series of such analyses is conducted at different thermal conditions to determine design values such as buckling loads or failure loads. Based on this data, surrogate modeling leads to design value formulation as a function of the temperature distribution. This approach provides a more comprehensive and reliable assessment of the structural behavior under different thermal conditions and enables to either determine more realistic worst-case behavior or enhanced design values such as probabilistic structural allowables. The final part of the thesis demonstrates the developed analysis methodology on representative skin field structures. The comparison to the common analysis procedure highlights the potentials of structural load carrying capability and reveals deficiencies in the present approach. Thus, a detailed modelling of the temperature distribution leads additionally to an improved reliability of the design process and more efficient and robust structures.

Safe and efficient joints are key for improving the structural efficiency of composite aircraft. Therefore, this thesis investigates the potential of multifunctional bondlines, combining structural bonding, disbond arrest features, and structural health monitoring. The central research question is how to achieve a functionally compliant design. This means ensuring disturbances between these functions do not eliminate their benefits regarding the objective of safe and efficient joints. The approach is adding discrete multifunctional disbond arrest features, functionally integrating disbond arrest and sensor functions, to epoxy bondlines. Experimental results indicate some major challenges such as a stiffness conflict for the integrated functions. Nevertheless, securing the epoxy bondline without disturbing its static strength proves successful in the end. In addition, the thesis provides some new insights regarding the functional compliance concept. For example, it strongly suggests considering temporal aspects, such as transient material properties.

Safe and efficient joints are key for improving the structural efficiency of composite aircraft. Therefore, this thesis investigates the potential of multifunctional bondlines, combining structural bonding, disbond arrest features, and structural health monitoring. The central research question is how to achieve a functionally compliant design. This means ensuring disturbances between these functions do not eliminate their benefits regarding the objective of safe and efficient joints. The approach is adding discrete multifunctional disbond arrest features, functionally integrating disbond arrest and sensor functions, to epoxy bondlines. Experimental results indicate some major challenges such as a stiffness conflict for the integrated functions. Nevertheless, securing the epoxy bondline without disturbing its static strength proves successful in the end. In addition, the thesis provides some new insights regarding the functional compliance concept. For example, it strongly suggests considering temporal aspects, such as transient material properties.

Aviation has a substantial environmental impact, necessitating a shift towards more sustainability. High-aspect-ratio (HAR) wings increase the efficiency of future transport aircraft by significantly reducing induced drag and, consequently, fuel consumption. However, the extended wingspan of HAR wings is accompanied by challenges, including ground operations, structural loads, and aircraft control. Folding wingtips (FWTs) address these challenges by incorporating a hinge at the outboard wing section, enabling the wingtip to fold during ground operations or specific flight scenarios. Wingtip actuators that allow active adjustment of the wingtip's cant angle and hinge stiffness can expand the potential operating modes of FWTs beyond the current state-of-the-art. Possible operating modes include extended load alleviation, mission adaptability, advanced flight control, and active flutter suppression. While most research on FWTs focuses on flight dynamics and aeroelasticity, little attention has been given to the structural design of wingtip actuators. This book introduces an actuator concept that transforms FWTs into multifunctional wingtip devices, referred to as actuated adaptive wingtips. The concept of actuated adaptive wingtips is based on a compliant morphing structure that adapts its mechanical properties by varying the fluid pressure in structure-integrated chambers.

This open access dissertation explores how manufacturing-induced residual stress states in fiber metal laminates (FMLs) affect a structural health monitoring (SHM) system. SHM is a promising technology for monitoring the structural integrity during operation. SHM systems using guided ultrasonic waves (GUWs) enable the detection of damage located inside a laminate and are, therefore, particularly suitable for FMLs due to their complex damage characteristics. Experimental methods for quantifying residual stresses in FMLs are developed and evaluated. This work shows that process strains can be measured throughout manufacturing with sensors integrated into the laminate. The strain measurements verify different modified cure cycles to change residual stress states in FMLs consisting of carbon-fiber-reinforced polymer (CFRP) and steel. To avoid complex sensor technology in industrial manufacturing processes, a robust method is additionally presented that derives a process-specific parameter, the stress-free temperature, from asymmetrical reference laminates. The quantified residual stress states in various CFRP-steel laminates allow the experimental investigation of the influence of stress on the propagation velocity of fundamental GUWs. With laser-scanning-vibrometry, dispersion diagrams for various FMLs over a wide frequency range are experimentally determined. The results show no significant influence of the residual stress states on the phase velocity of the fundamental symmetric and asymmetric GUW modes for the investigated FMLs. In contrast, comparative measurements under external tensile prestress show a considerable increase in phase velocity with increasing prestress for both fundamental GUW. Finally, fatigue tests are performed on CFRP-steel laminates to investigate the influence of different residual stress states on the residual life prediction capabilities of an SHM system. The results show that reducing residual stresses through modified cure cycles delays crack initiation, reduces crack propagation velocity, and, consequently, extends the fatigue life of the investigated FMLs.

Laminar flow control systems promise substantial emission reductions by minimising the viscous drag of transport aircraft. While boundary-layer suction has been proven in wind tunnel and flight tests, no system effectively improving the energy efficiency of transport aircraft is available. This doctoral thesis develops an additively manufacturable suction panel for laminar flow control, reducing the technology's complexity into one integral component decoupled from the aircraft's main structure. The benefit of additive manufacturing is the integration of complex aerodynamic requirements, such as surface curvature and suction rate control, into the suction panel's design.Manufacturing micro-perforations of the same size as the resolution of industrial 3D printers is challenging. This thesis investigates printable perforation geometries for various additive manufacturing technologies. Identifying their porosity and pressure drop characteristics enables the selection of suitable geometries and technologies to produce micro-perforated surfaces for boundary-layer suction. Stereolithography-printed surfaces with quadratic-truncated-cone perforations effectively delay the laminar-turbulent transition in flat-plate wind tunnel tests.Under aerodynamic loading, the micro-perforated surface requires a dense support structure, simultaneously enabling air discharge. However, due to insufficient internal airflow, support structures such as Honeycombs or foams cannot be used. In contrast, triply periodic minimal surfaces offer significant internal airflow while providing dense mechanical support. This thesis investigates the design and mechanical performance of triply periodic minimal surface structures and presents a prediction model based on their relative density. A wing-sizing study employs this model to demonstrate the suction panel's minimal impact on the wing mass.Ultimately, this doctoral thesis presents a design for an additively manufactured suction panel that meets the mechanical and aerodynamic requirements of laminar flow control and aircraft wing design. Successful suction panel component tests result in a design methodology that enables effective transition delay and integrated passive suction rate control. The additively manufactured suction panel reduces complexity and expands the applications of laminar flow control technology. Consequently, the suction panel concept developed in this thesis promises to be a key technology for next-generation transport aircraft with increased energy efficiency.

Im Rahmen der vorliegenden Dissertation werden zwei additiven Fertigungsverfahren, Automated Fiber Placement (AFP) und Additive Layer Manufacturing (ALM) unter Verwendung thermoplastischer Faserverbundwerkstoffe kombiniert. Weiterhin kommt künstliche Intelligenz zur Optimierung und Minimierung der Fehler im Fertigungsprozess zum Einsatz. Durch die Kombination dieser drei Methoden in einem automatisierten Fertigungsprozess lassen sich leichtere und kostengünstigere Faserverbundbauteile in homogeneren Serien herstellen. Endlosfasern wie Kohlenstofffasern können durch ihre mechanischen Eigenschaften die Leistung dieser Methoden signifikant erhöhen

Die vorliegende Arbeit untersucht einen neuen Freiheitsgrad zur Beeinflussung der Reibung, indem ein adaptiver Reibbelag entwickelt wird, dessen Reibung aktiv durch den Einsatz von den Piezoaktoren beeinflusst wird, und zwar primär durch Änderung bzw. Kombination verschiedener Materialpaarungen im Betrieb. Ein tribologisch gezielt beeinflussbares Reibsystem ermöglicht für einen breiteren Anwendungsbereich einen Betrieb mit geringer Reibleistung und geringem Verschleiß, indem die tribologischen Eigenschaften bzw. die Reibung bei Veränderungen der Betriebsbedingungen (z.B. Gleitgeschwindigkeit, Temperatur) durch eine Regelung angepasst werden. Bei trockenlaufenden Tribosystemen tritt für einige Reibmaterialien bei konstanter Normalkraft mit zunehmender Gleitgeschwindigkeit ein Abfall des Reibwertes auf. Dieser Abfall ist häufig unerwünscht, weil er beispielweise zu Reibschwingungen des Gesamtsystems oder zur Verringerung der Effektivität in Bremsen oder Kupplungen führen kann. Ein wesentliches Motiv dieses Vorhabens ist das Bestreben, den Reibwert des trockenlaufenden Reibbelages mit zunehmender Gleitgeschwindigkeit konstant zu halten oder ansteigen zu lassen, indem verschiedene unterschiedliche Reibmaterialien einzeln oder zusammen in Kontakt mit dem Gegenkörper gebracht werden. Reibbeläge mit adaptiven Komponenten, deren Eigenschaften gezielt verändert werden können, eröffnen ein breites Anwendungsspektrum in diversen Bereichen des Maschinenbaus.

Um bei der Fertigung von Faserverbundkunststoffen Zeit, Energie und Kosten sparen zu können, werden möglichst viele Informationen über die Vorgänge während des Fertigungsprozesses benötigt. Die Integration von Foliensensoren in die hergestellten Bauteile ist eine von mehreren Möglichkeiten, diese Informationen zu erhalten. Foliensensoren bestehen aus einer thermoplastischen Folie, auf der metallische Elektroden strukturiert sind. Ihre Integration in das Bauteil bringt unterschiedliche Vor- und Nachteile mit sich. Einerseits sind bauteilintegrierte Sensoren flexibler einsetzbar als werkzeugintegrierte Sensoren und ermöglichen eine feinere räumliche Auflösung der Aushärtevorgänge. Andererseits werden sie bei der Fertigung zum Produktbestandteil. Sie sollten deswegen einfach und kostengünstig sein, sowie die Lasttragfähigkeit nicht beeinträchtigen. Aus mechanischer Sicht bringen Foliensensoren vor allem ein Delaminationsrisiko mit sich. Die Wahl des thermoplastischen Substratmaterials macht dabei den entscheidenden Einflussfaktor aus. Während Sensoren auf Basis des häufig verwendeten Materials Polyimid ein erhebliches Delaminationsrisiko mit sich bringen, ist der Einfluss von Polyetherimid weit weniger schädlich oder verbessert sogar einzelne Festigkeitskennwerte. Neben dem Substratmaterial wirken sich auch die metallischen Sensorstrukturen auf die Belastbarkeit aus. Zur Gestaltung minimalinvasiver Sensoren sollte ein möglichst geringer Metallisierungsgrad angestrebt werden. Das verbreitetste Design für Foliensensoren zur Aushärteüberwachung sind sogenannte Interdigitalelektroden, die eine elektrische Kapazität bilden, deren Impedanz von der direkten Umgebung beeinflusst wird. In variothermen Fertigungsprozessen besteht eine Herausforderung darin, den Einfluss der Temperatur von dem des Aushärtegrades zu trennen. Die an integrierten Sensoren gemessenen Impedanzinformationen müssen dazu eine Verarbeitung durchlaufen, in deren Verlauf die Frequenzabhängigkeit und die Einflüsse von Temperatur und Sensorgeometrie aus den Daten entfernt werden. Für eine variotherme Aushärteüberwachung ist daher die Verwendung eines zusätzlichen Temperatursensors unverzichtbar. Die Sensordaten bieten darüber hinaus Potential für die Ermittlung des Faservolumengehalts oder zur Detektion von Harzfehlanmischungen.

Das Ziel dieses Buches ist die Charakterisierung und Beschreibung des Ausbreitungsverhaltens geführter Ultraschallwellen (GUW) in Faserverbund-Metall-Laminaten (FML). Sie gliedert sich in drei experimentelle Untersuchungen. Im ersten Experiment wird das Phasenverhältnis der Schwingungen an Strukturober – und -unterseite als Maß für die Ähnlichkeit zu den für isotrope Materialien hergeleiteten Lamb-Wellen untersucht. Dazu erfolgt die Entwicklung eines Verfahrens zum Phasenwinkelvergleich, welches auf der Continuous Wavelet Transformation sowie der Short-Time Fourier-Transformation beruht. Damit kann anhand simulierter Zeitsignalverläufe in verschiedenen Strukturen gezeigt werden, dass sich auch in FML die geführten Wellen wie klassische Lamb-Wellen ausbilden. Auch in einer experimentellen Untersuchung an einem FML kann die Beobachtungen für gleichphasige Schwingungen bestätigt und für Schwingungen mit Phasenversatz geschlussfolgert werden. Im anschließenden Experiment wird die Frage adressiert, wie sich das Wellenausbreitungsverhalten im Inneren von FML verhält. Dazu werden auf piezoelektrischem Polyvinylidenfluorid (PVDF)-basierende Foliensensoren gewählt, die sich aufgrund ihrer geringen Abmaße und ihrer geringen akustischen Impedanz gut für die möglichst rückwirkungsarme Integration in flache Strukturen aus Faserverbundkunststoff (FVK) eignen. Die erwartete Wirkweise der PVDF-Foliensensoren unter GUW-Erfassung wird erklärt. Anschließend erfolgt die experimentelle Untersuchung des FML, in deren Rahmen die Wellenmoden identifiziert werden sowie eine Abschätzung des Verschiebungsfeldverlaufes entlang der Strukturhöhe gegeben wird. Die Ergebnisse liefern einen experimentellen Hinweis auf die Modenkopplung im gewählten Laminataufbau. Das dritte und letzte Experiment liefert den konkreten Anwendungsfall der Schadensdetektion und -charakterisierung in FML. Dazu werden im Rahmen einer Parameterstudie ein Referenzlaminat sowie zwei Laminate mit künstlichen Delaminationen bei ansonsten übereinstimmendem Laminataufbau gefertigt. Ziel ist zum einen die Untersuchung, inwiefern sich eine unterschiedliche relative Höhenlage eines Schadens im Wellenfeld der FML zeigt. Zum anderen soll geprüft werden, inwiefern sich Schadensinformationen über einen integrierten Sensor erfassen lassen. Flächige Vergleichsmessungen an den Plattenoberflächen über ein Laser-Doppler-Vibrometer dienen der Abschätzung der über die integrierten PVDF-Foliensensoren und unterstützen die Auswertung. Es kann gezeigt werden, dass anhand des horizontalen Scherwellenmoden zusätzliche Schadensinformation über den integrierten Sensor gewonnen werden kann. Über Wellenausbreitungsszenarien gelingt es das Auftreten einiger Wellenpakete in den Sensorzeitsignalen über Modenkonversion zu erklären. Es erfolgt eine Zusammenfassung der Ergebnisse sowie ein Ausblick auf mögliche Folgearbeiten zu jedem Experiment.

In dieser Forschungsarbeit wird ein neuartiges Enteisungssystemkonzept untersucht, bei dem ein Draht aus einer Formgedächtnislegierung (FGL) in ein Elastomermaterial eingebettet wird, um thermomechanische Effekte zu erzielen. Die besonderen thermischen und mechanischen Eigenschaften von FGL machen sie zu einer vielversprechenden Option für die Integration in Luftfahrtsysteme, um Eisansammlungen auf aerodynamischen Oberflächen zu entfernen. Das Konzept basiert auf der Nutzung des Formgedächtniseffekts (FGL) als Grundprinzip für das Enteisungssegment.

Mobile Roboter besitzen das Potenzial, zu deutlichen Effizienzsteigerungen in der Fertigung kohlenstofffaserverstärkter Kunststoffe zu führen, wenn sie die aktuell üblichen Sondermaschinen ersetzen. Dazu müssen die mobilen Roboter Bahngenauigkeiten im Submillimeterbereich erreichen.  Da stationäre Roboter diese Bahngenauigkeiten mit Modellerweiterungen erreichen können, ist es die Kernfrage dieser Arbeit, ob diese auf mobile Roboter übertragbar sind. Bahngenauigkeitsuntersuchungen zeigen, dass sich die mobile Plattform in erster Linie durch eine herabgesetzte Fundamentsteifigkeit  auswirkt. Weiterhin wird beobachtet, dass die Trägheitskräfte des Roboterarmes genügen können, um eine Bewegung der Plattform relativ zum Hallenboden zu erzeugen.  Die Arbeit zeigt, dass künstliche neuronale Netze in der Lage sind, den Bahnfehler des mobilen Roboters mit einer mittleren Abweichung zum gemessenen Bahnfehler von 0,3mm vorhersagen zu können und damit potentiell dazu geeignet sind, die Bahngenauigkeit eines mobilen Roboters in den Submillimeterbereich zu steigern. Durch den Austausch des Bahninterpolators zwischen der Aufnahme der Trainingsdaten und der Erprobung der Modellerweiterung kann die Arbeit keine Genauigkeitssteigerungen zeigen. Mit einer Erweiterung des Trainingsdatensatzes oder durch den Einsatz nur eines einzigen Bahninterpolators scheint es jedoch möglich zu sein, dass Folgearbeiten die Steigerung der Bahngenauigkeit in den Submillimeterbereich nachweisen können.

Folienlager sind Gleitlager mit einer nachgiebigen Innenkontur. Dies erlaubt die Kompensation der fliehkraft- und temperaturbedingten Wellenexpansion bei hohen Drehzahlen. Die vielen Reibkontakte zwischen den Folien erhöhen zudem die Lagerdämpfung. Mit aerodynamisch wirkenden Folienlagern ausgestattete Turbomaschinen können somit je nach Baugröße mit mehr als 100.000 U/min betrieben werden. Ein wesentlicher Faktor, der die Lebensdauer begrenzt, ist der Verschleiß bei jedem Start-Stop-Zyklus. Unglücklicherweise können Folienlager geometrisch entweder auf einen geringeren Verschleiß beim Anfahren oder eine größere Stabilität bei hohen Drehzahlen optimiert werden. In dem hier vorliegenden Buch wird daher der Ansatz eines aktiv schaltbaren Folienlagers vorgestellt, bei welchem das Lagerspiel und die geometrische Vorspannung (Preload) je nach Betriebszustand eingestellt werden können. Anhand theoretischer Überlegungen und experimenteller Beobachtungen zeigt sich eine grundsätzliche Eignung der im aktiven Lager angestrebten Schaltformen. So ist trotz signifikanter Einflüsse von Fertigungs- und Montageabweichungen eine Verbesserung des Anfahrverhaltens bzw. ein stabiler Betrieb bei hohen Drehzahlen sichtbar. Die Integration der aktiven Komponente, bestehend aus den piezokeramischen Patchaktuatoren und einem geometrisch an eine dreiflächige Lagerbuchse angelehnten Lagerträger, verändern das Betriebsverhalten gegenüber der passiven Prototypen dabei aber erheblich. So verringert sich neben der Lagersteifigkeit auch die Lagerdämpfung. Zudem genügen moderate Lasten und fertigungsbedingte Eigenspannungen, um die aktive Verformung des Lagerträgers zu blockieren. Theoretische Modelle zeigen, dass eine Versteifung der aktiven Komponente durchaus zielführend ist. Eine praktische Umsetzung ist hingegen aufgrund fehlender Aktuatorwerkstoffe aktuell noch nicht möglich.

Zur Effizienzsteigerung im Transportsektor wird häufig Gewicht reduziert, was durch dünnere Strukturen jedoch auch zu erhöhten Schwingungsamplituden und somit Schalleinstrahlung in die Fahrgastzellen führt. Diese Dissertation untersucht einen zuvor publizierten Ansatz zur effizienten Beschreibung dieser Schalleinstrahlung. Ziel der Arbeit ist es, die Anwendbarkeit dieser Methode auf reale Kavitäten wie Flugzeugkabinen zu prüfen. Untersucht werden die Beteiligung stehender Wellen im Innenraum, die Kopplungsstärke zwischen den Teilsystemen Fluid und Struktur sowie geometrische Voraussetzungen des Modellierungsansatzes. Die Studie zeigt das Auftreten stehender Wellen und schlägt ein neues Kriterium zur Identifikation stark und schwach gekoppelter Systeme vor. Die darüber hinaus nachgewiesenen Anforderungen an die Kabinengeometrie erweisen sich jedoch als erhebliche Einschränkung der praktischen Anwendbarkeit.