Mechanics and Adaptronics – serie

The novel finite element formulations fall into the category of geometrically exact Kirchhoff-Love beams. Furthermore, the numerical efficiency of the new beam formulations is compared to other beam elements that allow for or suppress shear deformation.

The novel finite element formulations fall into the category of geometrically exact Kirchhoff-Love beams. Furthermore, the numerical efficiency of the new beam formulations is compared to other beam elements that allow for or suppress shear deformation.

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.

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.

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.

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. 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.

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. 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.

This book offers extensive knowledge and characterization methods for Ultraviolet light curable piezoelectric 0-3 composites for researchers and industry.

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.

Current methodologies used to design lightweight structures made of CFRP materials under static thermomechanical conditions often rely on simplified approaches.

Therefore, this thesis investigates the potential of multifunctional bondlines, combining structural bonding, disbond arrest features, and structural health monitoring. The approach is adding discrete multifunctional disbond arrest features, functionally integrating disbond arrest and sensor functions, to epoxy bondlines.

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.

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.

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.

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.

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.

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.

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.