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Die vorliegende Arbeit beschreibt empirische, analytische und numerische Untersuchungen an zylindrischen Klebstoffverbindungen unter Biegebelastungen. Die Klebstoffverbindung zwischen dem isotropen und anisotropen Fügepartner ist als zylindrische Überlappverbindung ausgeführt. Der äußere Fügepartner besteht aus einer Aluminiumlegierung während der innere Fügepatrner aus glasfaserverstärktem Kunststoff im Filament-Winding-Verfahren hergestellt ist. Die Klebstoffschicht des hochtemperaturvernetzenden Epoxidklebstoffs hat eine Schichtdicke zwischen 0,1 mm und 0,2 mm. Die Biegebelastung wird, analog eines Kragträgers, durch eine Querkraftbelastung und eine feste Einspannung in der Verbindung hervorgerufen.
Ziel dieser Arbeit ist die Identifizierung und Qualifizierung von konstruktiven Einflussfaktoren, welche für die Dimensionierung maßgebliche Bedeutung besitzen. Die Grundlage bildet dabei ein analytisches Berechnungsverfahren welches die Schubspannungsverteilung in der Klebstoffschicht vereinfacht beschreibt.
Umfangreiche Materialcharakterisierungen des Klebstoffsystems sowie des glasfaserverstärkten Kunststofffügepartners stellen die Grundlage der analytischen und numerischen Berechnungsverfahren. Aufbauend auf einer globalen Betrachtung des Kraftübertragungsmechanismus werden detaillierte Untersuchungen der Fügepartnersteifigkeiten, des Anisotropiegrads sowie der Überlappungslänge durchgeführt. All diese Parameterstudien werden hinsichtlich ihrer Wirkprinzipien diskutiert und mit umfangreichen experimentellen Untersuchungen abgeglichen.
Es zeigte sich eine generell gute Übereinstimmung zwischen den Resultaten des analytischen Modells, den Finite-Elemente-Simulationen und den experimentellen Befunden. Im Rahmen einer Verformungsanalyse zeigte sich der Effekt einer lokalen Sekundärbiegung der Verbindung, welcher durch die exzentrische Anordnung der Fügeteile hervorgerufen wird.
In Bezug auf die Längsverzerrungen der Fügepartner und die resultierenden Schubspannungen in der Klebstoffschicht wurde eine klare Analogie zu ebenen und axial belasteten Überlappverbindungen erkannt. Fundamentale Zusammenhänge, wie die konvergierende Abhängigkeit zwischen der maximalen Schubspannungsspitze und der Überlappungslänge oder der Beziehung zwischen den Fügeteilsteifigkeiten und der Schubspannungsverteilung, sind entsprechend der Untersuchungen auch für zylindrische Überlappverbindungen gültig. Bei Biegebelastung sind jedoch die Flächenträgheitsmomente und nicht die Querschnittsflächen der Fügepartner für den Schubspannungsverlauf in der Klebstoffschicht prägend.
Darüber hinaus wurde gezeigt, dass der Radius der zylindrischen Verbindung bei axialer Belastung in einer indirekt proportionalen Beziehung zum mittleren Schubspannungsniveau steht. Bei Biegebelastung ist diese Beziehung jedoch indirekt quadratisch, wodurch der Durchmesser der zylindrischen Verbindung in diesem Kontext einen deutlich höheren Einfluss aufweist. In Bezug auf den anisotropen Fügepartner wurde dessen Längssteifigkeit als prägend für die Schubspannungsverteilung identifiziert.
Additive manufacturing (AM), particularly laser powder bed fusion (L-PBF), provides unmatched design flexibility for creating intricate steel structures with minimal post-processing. However, adopting L-PBF for high-performance applications is difficult due to the challenge of predicting microstructure evolution. This is because the process is sensitive to many parameters and has a complex thermal history. Thin-walled geometries present an added challenge because their dimensions often approach the scale of individual grains. Thus, microstructure becomes a critical factor in the overall integrity of the component. This study focuses on applying cellular automata (CA) modeling to establish robust and efficient process–structure relationships in L-PBF of 316L stainless steel. The CA framework simulates solidification-driven grain evolution and texture development across various processing conditions. Model predictions are evaluated against experimental electron backscatter diffraction (EBSD) data, with additional quantitative comparisons based on texture and morphology metrics. The results demonstrate that CA simulations calibrated with relevant process parameters can effectively reproduce key microstructural features, including grain size distributions, aspect ratios, and texture components, observed in thin-walled L-PBF structures. This work highlights the strengths and limitations of CA-based modeling and supports its role in reliably designing and optimizing complex L-PBF components.
The utilisation of 3D printing processes in the fabrication of continuous fiber-reinforced composites confers a multitude of advantages, in particular flexible design based on structural requirements. In order to achieve greater flexibility, there is a necessity for 3D printing systems that allow for customisable material selection and fiber positioning. This paper presents the design of a robot-based 3D printing system that incorporates an in-situ impregnation line and flexibility regarding the machine code generation for fiber positioning. The development of the system enabled the attainment of an average fiber volume content of up to 37.12%. In the tensile tests, material characteristics up to E1 = 24.7 GPa and strength of up to RM1 = 0.51 GPa were determined.
The aim of this paper is to present practical steps for utilizing a validated multiphysics approach for fracture control in CO2 pipelines within the framework of Carbon Capture Transport and Storage (CCTS). Ensuring the arrest of running ductile fracture (RDF) is a crucial safety requirement for the transportation of dense-phase CO2. However, current standards rely on outdated and restrictive methods, imposing severe limitations on pipeline material and structural design. As a result, projects that fall outside these standards face the need for extremely costly tests, often leading to delays or cancellations of CCTS initiatives.
This study introduces an advanced, validated, fully-coupled fluid-structure interaction (FSI) model designed to accurately predict fracture propagation in CO2 pipelines. A key advantage of this approach is its use of robust and reproducible calibration and validation procedures combined with high-quality material characterization data. The full coupling of structural, fluid, and backfill models is essential for obtaining precise results, not only in determining arrest occurrence but also in analyzing properties such as fracture velocity history, 3D pressure distributions behind the propagating crack, wall thinning, and crack tip opening angle. The FSI model has demonstrated its value as a cost-effective tool for safety assessments, enabling the development of fracture control plans that specify minimum required material properties and fluid compositions for optimized pipeline design, both onshore and offshore. Additionally, performing virtual studies with the parameterized FSI model enables the generation of synthetic data for training and validating a machine learning surrogate model. This surrogate model can be integrated into industrial practices, facilitating the application of multiphysics modeling without the need for extensive expertise.
Test Setup for Investigating the Impact Behavior of Biaxially Prestressed Composite Laminates
(2024)
Instrumented impact testing and compression-after-impact testing are important to adequately qualify material behavior and safely design composite structures. However, the stresses to which fiber-reinforced plastic components are typically subjected in practice are not considered in the impact test methods recommended in guidelines or standards. In this paper, a test setup for investigating the impact behavior of composite specimens under plane uniaxial and biaxial preloading is presented. For this purpose, a special test setup consisting of a biaxial testing machine and a specially designed drop-weight tower was developed. The design decisions were derived from existing guidelines and standards with the aim of inducing barely visible impact damage in laminated carbon fiber-reinforced plastic specimens. Several measurement systems have been integrated into the setup to allow comprehensive observation of the impact event and specimen behavior. A feasibility test was performed with biaxially prestressed carbon fiber-reinforced plastic specimens in comparison with unstressed reference tests. The compressive-tensile prestressing resulted in lower maximum contact forces, higher maximum deflections, higher residual deflections and a different damage pattern, which was investigated by light microscopic analysis. Finally, the functionality of the experimental setup is discussed, and the results seem to indicate that the test setup and parameters were properly chosen to investigate the effect of prestresses on the impacts behavior of composite structures, in particular for barely visible subsequent damages.
The pandemic caused by the SARS-CoV-2 virus has claimed more than 6.5 million lives worldwide. This global challenge has led to accelerated development of highly effective vaccines tied to their ability to elicit a sustained immune response. While numerous studies have focused primarily on the spike (S) protein, less is known about the interior of the virus. Here we propose a methodology that combines several experimental and simulation techniques to elucidate the internal structure and mechanical properties of the SARS-CoV-2 virus. The mechanical response of the virus was analyzed by nanoindentation tests using a novel flat indenter and evaluated in comparison to a conventional sharp tip indentation. The elastic properties of the viral membrane were estimated by analytical solutions, molecular dynamics (MD) simulations on a membrane patch and by a 3D Finite Element (FE)-beam model of the virion's spike protein and membrane molecular structure. The FE-based inverse engineering approach provided a reasonable reproduction of the mechanical response of the virus from the sharp tip indentation and was successfully verified against the flat tip indentation results. The elastic modulus of the viral membrane was estimated in the range of 7-20 MPa. MD simulations showed that the presence of proteins significantly reduces the fracture strength of the membrane patch. However, FE simulations revealed an overall high fracture strength of the virus, with a mechanical behavior similar to the highly ductile behavior of engineering metallic materials. The failure mechanics of the membrane during sharp tip indentation includes progressive damage combined with localized collapse of the membrane due to severe bending. Furthermore, the results support the hypothesis of a close association of the long membrane proteins (M) with membrane-bound hexagonally packed ribonucleoproteins (RNPs). Beyond improved understanding of coronavirus structure, the present findings offer a knowledge base for the development of novel prevention and treatment methods that are independent of the immune system.
Maintaining dimensional accuracy is a major challenge of laser powder bed fusion (L-PBF) preventing its application for more complex and filigree L-PBF structures in industrial practice. Previous studies have shown that residual stresses and distortion of benchmark L-PBF components may be predicted by sequential thermo-mechanical analyses. However, the reliability of these analyses for more complex structures must be critically questioned, as comprehensive validation and sensitivity analyses are scarce. In this paper, we present a calibrated and validated low-fidelity sequential thermo-mechanical finite element analysis (FEA) of a tubular L-PBF lattice structure, i.e., an aortic stent, where pronounced local deformation is expected. As a first step, the finite element model was extensively calibrated using experimental data to ensure reproducibility of the simulation results. Thereupon, geometric features critical to the distortion of L-PBF lattice structures and measures to compensate for the distortion, such as inversion of the distorted L-PBF structure, were investigated. It was found that the distortion of the L-PBF lattice structures can be reduced, but not completely prevented, by increasing the strut angles, increasing the strut thickness, and decreasing the transition radius in the area of merging struts. FEA-based inversion of the numerically predicted deformed structure minimized distortion, resulting in the L-PBF aortic stent approximating the intended CAD geometry even with a small strut thickness. This work shows that low-fidelity sequential thermo-mechanical FEA can be used not only for the analysis and deformation compensation of reference structures, but also for the analysis of more complex filigree structures with pronounced local deformation.
The mechanical properties of additively manufactured plastic components, i. e. strength and stiffness, can limit their use as load-bearing structures. In particular, the use of continuous reinforcing fibers can significantly improve the mechanical properties of additively manufactured components and enable the production of load-bearing fiber composite structures. In this context, it seems reasonable to develop the required equipment and process workflows, but also procedures for the load-optimized positioning of fiber paths inside the component and its design. In this paper, the current challenges in the field of technology development of continuous-fiber reinforced 3D printing are highlighted. Possible solutions for the development of a 3D printing system and the generation of necessary toolpaths are presented on the basis of the FIBER-PRINT 3 project. Contents from a subsequent project present a design strategy for a load-optimized positioning of the continuous fiber reinforcement within the component and the implemented calculation of principal stress trajectories as a step towards optimization of the fiber positioning.
Additive Fertigung hat sich in zahlreichen industriellen Anwendungen etabliert und bildet eine wichtige Schlüsseltechnologie. Im Gegensatz zu metallischen Werkstoffen, haben additiv gefertigte Bauteile aus Kunststoffen geringere Festigkeit und Steifigkeit, sodass sich ihre Verwendung als lasttragende Strukturen schwierig gestaltet. Insbesondere der Einsatz von endlosen Verstärkungsfasern kann die mechanischen Eigenschaften additiv gefertigter Strukturen signifikant verbessern und die Fertigung hochbelastbarer Faserverbundstrukturen im 3D-Druckverfahren ermöglichen. Daher gilt es aktuell notwendige Anlagen und Prozessketten für den Fertigungsprozess aber auch Vorgehensweisen für die belastungsoptimierte Auslegung der Faserverläufe innerhalb des Bauteils zu entwickeln, um so das Themengebiet „Endlosfaserverstärkter 3D-Druck“ weiter voranzutreiben. Für mehr räumliche Freiheit bei der Positionierung der Druckbahnen können industrieroboterbasierte Systeme eingesetzt werden, um so das Potenzial gerichteter Bauweise von Faserverbundstrukturen auch im additiven Fertigungsprozess vollumfänglich ausschöpfen zu können. Dabei ermöglicht ihr Einsatz auch eine räumliche Ablage der Faserverstärkung, wobei für die Materialablage ein geeigneter 3D-Druckkopf erforderlich ist. Für die Implementierung der Faserverstärkung ist zudem eine dem Lastfall entsprechende Auslegung des Bauteils sowie die Ermittlung einer sinnvollen Faserpositionierung innerhalb des Bauteils erforderlich, wobei unterschiedliche Variablen aus den Bereichen Material, Struktur und Fertigungsprozess berücksichtigt werden müssen. Im Rahmen des Vortrages werden die Herausforderungen der Technologieentwicklung des endlosfaserverstärkten 3D-Drucks aufgegriffen sowie auf eine belastungsorientierte Faserpositionierung näher eingegangen. Aktuelle Erkenntnisse werden diskutiert sowie eine Entwurfsmethodik für die Prozesspfadgenerierung vorgeschlagen.
