Technische Fakultät

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  • Doctoral thesis
    Open Access
    DMAICS-Zyklus zur Digitalisierung in produzierenden Unternehmen
    FAU Studien aus dem Maschinenbau : 439, (FAU University Press, 2024) Selmaier, Andreas
    Digitale Technologien aus den Bereichen Internet der Dinge, cyber-physische Produktionssysteme, Cloud und künstliche Intelligenz eröffnen der Fertigungsindustrie neue Potenziale zur Produkt- und Prozessoptimierung. Mit der Digitalisierung streben Unternehmen nicht nur danach, die klassischen Zielparameter Zeit, Qualität und Kosten zu verbessern, sondern auch die Flexibilität und Reaktionsfähigkeit im Hinblick auf neue Geschäftsmodelle und externe Einflüsse zu erhöhen. Die vollständige digitale Transformation im Produktionsumfeld, die durch eine heterogene Anlagen- und Systemlandschaft gekennzeichnet ist, erfordert sowohl einen technischen als auch einen kulturellen Wandel. Aufgrund sich rasch entwickelnder Technologien sind Unternehmen und ihre Mitarbeiter neben der Aufrechterhaltung der Kernproduktionsprozesse gefordert, zusätzlich eine hohe Veränderungsbereitschaft sowie die Fähigkeit zur Anpassung und Innovation vorzuweisen. Die inhärente soziale und technische Komplexität der digitalen Transformation stellt die Fertigungsindustrie vor Herausforderungen. Gegenstand und Ziel dieser Arbeit ist es, ein methodenbasiertes Vorgehensmodell zu definieren, das den komplexen Transformationsprozess umfassend und anwendungsagnostisch abbildet. Die Formulierung eines integrierten Prozessmodells und dessen methodische Ausgestaltung zielen auf die Lösung praktischer Problemmerkmale im Bereich der Digitalisierung ab. Der beschriebene Lösungsansatz wird in verschiedenen industriellen Anwendungsszenarien validiert. Die erfolgreiche Realisierung von sechs digitalen Lösungen aus den Technologiebereichen Internet der Dinge, Datenanalyse und Cloud Computing beweist die Richtigkeit und Anwendbarkeit der Methodik, deren Spezifikation eine Implementierungsgrundlage für Informationssysteme zur Digitalisierung von Fertigungsunternehmen schafft.
  • Doctoral thesis
    Open Access
    Eigenspannungen beim Voll-Vorwärts-Fließpressen – Entstehung, Einstellung und Stabilität
    FAU Studien aus dem Maschinenbau : 444, (FAU University Press, 2024) Jobst, Andreas
    Kaltmassivumformverfahren wie das Voll-Vorwärts-Fließpressen werden als ressourcen- und energieeffiziente Fertigungsmethode für metallische Bauteile eingesetzt. Inhomogene plastische Dehnungsverteilungen, die dabei typischerweise auftreten, führen jedoch zum Verbleiben von Eigenspannungen im Werkstoff, welche zu unerwünschten Effekten führen und das Ermüdungsverhalten maßgeblich beeinflussen können. Das in dieser Arbeit verfolgte Ziel ist die Erarbeitung einer Methode zur eigenspannungssensitiven Prozessauslegung. Anhand eines Referenzprozesses wurde die Eigenspannungsentstehung beim Voll-Vorwärts-Fließpressen des rostfreien Stahls X6Cr17 numerisch und experimentell untersucht. Darauf aufbauend wurden Steuer- und Störgrößen zur Eigenspannungseinstellung qualifiziert und deren Auswirkungen quantifiziert. Unter zyklisch-mechanischer Bauteilbelastung wurden verschiedene Relaxationsmuster identifiziert. Hinsichtlich der thermischen Belastung wurde ein Prozessfenster erarbeitet, innerhalb dessen stabile Eigenspannungen vorliegen. Darauf aufbauend wurde ein modellbasierter Zusammenhang zwischen der Temperatur, der Belastungsdauer und der Eigenspannungsstabilität abgeleitet. Es konnte gezeigt werden, dass eine Beeinflussung der Betriebsfestigkeit fließgepresster Bauteile durch die Eigenspannungssteuerung bei der Umformung möglich ist. Durch eine Anpassung des Matrizendesigns konnten kostengünstig oberflächennahe Zugeigenspannungen reduziert und die Langzeitfestigkeit erhöht werden.
  • Article
    Open Access
    Towards advanced piezoelectric metamaterial design via combined topology and shape optimization
    (Springer, 2024-02-20) Stankiewicz, Gabriel; Dev, Chaitanya; Weichelt, Michelle; Fey, Tobias; Steinmann, Paul
    Metamaterials open up a spectrum of artificially engineered properties otherwise unreachable in conventional bulk materials. For electromechanical energy conversion systems, lightweight materials with high hydrostatic piezoelectric coupling coefficients and negative Poisson’s ratio can be obtained. Thus, in this contribution, we explore the possibilities of piezoelectric metamaterials design by employing structural optimization. More specifically, we apply a sequential framework of topology and shape optimization to design piezoelectric metamaterials with negative Poisson’s ratio for electromechanical energy conversion under uniform pressure. Topology optimization is employed to generate the initial layout, whereas shape optimization fine tunes the design and improves durability and manufacturability of the structures with the help of a curvature constraint. An embedding domain discretization (EDD) method with adaptive domain and shape refinement is utilized for an efficient and accurate computation of the state problem in the shape optimization stage. Multiple case studies are conducted to determine the importance of desired stiffness characteristics, symmetry conditions and objective formulations on the design of piezoelectric metamaterials. Results show that the obtained designs are highly dependent on the desired stiffness characteristics. Moreover, the addition of the EDD-based shape optimization step introduces significant changes to the designs, confirming the usability of the sequential framework.
  • Article
    Open Access
    Geometrically nonlinear design of compliant mechanisms: Topology and shape optimization with stress and curvature constraints
    (Elsevier, 2022-06-06) Stankiewicz, Gabriel; Dev, Chaitanya; Steinmann, Paul
    In this work, we exploit a sequential topology and shape optimization framework to design compliant mechanisms. We pay particular attention to a refined and exact design of flexure hinges via shape optimization in a geometrically nonlinear setting. We propose improved adaptive shape and domain refinement strategies for the embedding domain discretization method (EDD) to achieve numerically and geometrically accurate designs of the flexure hinges. Furthermore, to account for durability and manufacturability of the flexure hinges, we employed local stress constraints and a curvature constraint. The local stress constraints are integrated into an augmented Lagrange functional together with the output displacement to form a combined objective response. The design update is realized by employing and adapting the traction method for the specifics of the embedded boundary. Hence, the curvature constraint does not appear in a standard response form, but is rather introduced into the auxiliary boundary value problem (BVP) of the traction method via a penalty functional. The novelties of this work include: (1) enhanced adaptive shape and domain refinement strategies for EDD; (2) geometrically nonlinear shape optimization using EDD; (3) adapted traction method with curvature constraint.
  • Bachelor thesis
    Open Access
    Validation of Dune Simulations using OpenFOAM
    Proceedings of the Institute for Multiscale Simulation (2012-03-27) Michelsen, Britt
    In this thesis, the fluid flow around atwo and three-dimensional dune is simulated with the help of the open source C++ library OpenFOAM.The simpleFOAM solver, which is supplied by OpenFOAM, has proven to be reliable and has shown astrong correlation with field measurements conducted in the paper ‘'The role of streamline curvature in sand dune dynamics" by Giles F. S. Wiggs in 1996. It can be shown, that the two-dimensional as well as the three-dimensional calculations are in good agreement with the experimental data. However, in order to get reasonable steady-state results the initial conditions are calculated using the transient solver pimpleFOAM. The Reynolds-averaged Navier-Stokes equation is being used to simulate the time-averaged turbulent fluid flow around the dune and different meshing tools as well as cell geometries are compared. The validation of afluidized model as an alternative to modelling the individual sand particles has proven to be difficult, because sand doesn't show aconventional fluidic behaviour. ------ Im Rahmen dieser Arbeit wurde das Strömungsprofil sowohl um eine zweidimensionale als auch um eine dreidimensionale Düne mit Hilfe der Open-Source C++ Bibliothek OpenFOAM simuliert. Die simpleFOAM Simulationsroutine, welche von OpenFOAM zur Verfügung gestellt wird, stellte sich als verlässlich heraus und zeigte eine starke Relation zu den in "The role of streamline curvature in sand dune dynamics” veröffentlichten Werten von Giles F. S. Wiggs aus dem Jahre 1996. Sowohl der zwei- als auch der dreidimensionale Fall konnte in guter Übereinstimmung mit den Ergebnissen der Veröffentlichung simuliert werden. Allerdings mussten die Anfangswerte mit Hilfe des transienten pimpleFOAM Gleichungslösers approximiert werden und dann anschließend in simpleFoam übernommen werden. Die Reynolds-gemittelten Navier-Stokes-Geichungen wurden zur Approximation der turbulenten Strömungen verwendet und unterschiedliche Diskretisierungsgitter zur Validierung herangezogen. Die Überprüfung der Gültigkeit von fluidisierten Modellen als Alternative zur Simulation einzelner Sandkörner stellte sich als kompliziert heraus, da Sand kein herkömmliches Fluidverhalten zeigt und somit nicht ausreichend vom Strömungsloser erfasst werden kann.
  • Article
    Open Access
    Extracting powder bed features via electron optical images during electron beam powder bed fusion
    (2024-07) Markl, Matthias; Azadi Tinat, Mohammad Reza; Renner, Jakob; Berger, Timo; Körner, Carolin
    Electron beam powder bed fusion offers the unique opportunity to observe the process by measuring scattered electrons on a metal detector. This technique is the state of the art in generating electron optical images of the build area after melting using single- or multi-detector setups. The images enable the detection of surface defects like porosity or material transport by reconstructing the surface topography. Internal defects such as layer-bonding defects cannot be identified. Many of these defects, particularly layer-bonding defects, often originate from an irregular distribution of the powder bed. This work introduces an additional process step by recording an electron optical image after the distribution of the powder bed. Combining this with an electron optical image after melting the previous layer enables extraction of powder bed features such as the current powder bed height. The underlying method bases on the correlation of experimental measurements and numerical simulations of the intensity of the electron optical signal for different powder bed heights. With this approach, it is possible to identify irregular powder distributions, such as uncovered areas of previously molten material or locally varying powder bed heights. This information is crucial for online monitoring and real time process control. Exemplary, this opens the opportunity of healing the powder bed by an additional raking step.
  • Master thesis
    Open Access
    Dynamics of melting solids using SPH
    Proceedings of the Institute for Multiscale Simulation (2017-08-08) Blank, Michael
    In this thesis a meshless multiphysics simulation method based on the smoothed particle hydrodynamics (SPH) method is introduced and is applied to the simulation of dynamic melting processes. For this purpose, models for separate physical phenomena available in an academic SPH code were separately validated. These models include implicit viscous force computation for highly viscous flows and heat transfer for bodies with complex shaped free surfaces. Subsequently, a model for modifying the specific heat capacity which approximates the latent heat over a temperature interval around the melting temperature is implemented. In order to validate the viscosity model used, the coalescence of agglomerate chains with three or six primary spheres under the influence of surface tension is simulated. The time required to obtain a spherical shape through a viscous flow assumption is seen to be less in the case of SPH than that simulated by a surface area minimization algorithm. This could be due to inertial and hydrodynamic effects. The heat transport is then validated with two-dimensional analytical solutions of the heat conduction equation for different boundary conditions. The order of accuracy for this heat transfer model is shown to be more than first order. To determine the accuracy of the moving phase boundary position, an analytical solution of the two-dimensional Neumann problem is used and compared with the corresponding SPH results. The determined average error is between 3.67% and 0.60% as a function of the number of interpolation points and the boundary conditions used. The validated models of the viscosity, the heat conduction and the latent heat are then coupled to models for surface tension as well as rigid body interactions which are already part of the code. Thus, the multiphysics model obtained is used for the simulation of different morphologies with a heat of fusion of 1 J/kg, 1 kJ/kg and 100 kJ/kg, respectively. The surface evolution of complex shaped bodies melting at time scales comparable to the fluid flow time scales is shown to be a highly non-linear phenomena deviating considerably from viscous sintering models in literature. The usefulness of this simulation method for optimizing industrial process designs is thus demonstrated.
  • Bachelor thesis
    Open Access
    Hysteretischer Übergang zwischen Fluidisierungsmoden in horizontal angeregtem Granulat
    Proceedings of the Institute for Multiscale Simulation (2014-12-01) Steub, Laura
  • Bachelor thesis
    Open Access
  • Master thesis
    Open Access
    Kritische Parameter der vertikalen Oszillation für das Einsetzen granularer Konvektion
    Proceedings of the Institute for Multiscale Simulation (2000-05-24) Renard, Simon
  • Master thesis
    Open Access
    Granular Jamming Transition versus Gravitational Acceleration
    Proceedings of the Institute for Multiscale Simulation (2023-10-31) Yu, Qing
    Granular materials are ubiquitous in our everyday life. Yet, some behaviors of granular media continue to surprise us, and a theory predicting granular flows from first principles is still missing. When the granular materials are compressed or sheared, they can change from a flowing fluid-like state to a rigid solid-like state. This change is called the jamming transition. The previous research shows that the granular packing fraction at the jamming point is lower in microgravity than on Earth. This small change in jamming packing fraction could influence the handling of granular materials in microgravity. To investigate this question, we probed the jamming point in microgravity, provided by drop tower Bremen. Additional discrete element method simulations were also performed to complement the practical experiments. Our experiments showed that the average jamming packing fraction in microgravity is 0.0212 lower than on Earth. Simulation results showed that, for a system with 0 friction coefficient, the average jamming packing fraction in microgravity and Earth gravitational acceleration are 0.6032 and 0.6142. For a system with a 0.5 friction coefficient, the average jamming packing fraction in microgravity and Earth’s gravitational acceleration are 0.5336 and 0.5448.
  • Master thesis
    Open Access
    Optimierung der Textur granulatdurchströmter Röhren hinsichtlich des Massenflusses
    Proceedings of the Institute for Multiscale Simulation (2014-03-31) Verbücheln, Felix
  • Master thesis
    Open Access
    Simulation based optimization of granular damping devices
    Proceedings of the Institute for Multiscale Simulation (2015-07-01) Nadjafabadi Farahani, Mohammad Hassan
  • Doctoral thesis
    Open Access
    Damage Tolerance and Failure Analysis of Hierarchically Patterned Materials
    (2024-06-03) Pournajar, Mahshid
    Hierarchically (micro)structured materials contain elements that repeatedly ap- pear on multiple scales in a self-similar manner. Architectures of this type are sup- posed to provide enhanced toughness in materials made from brittle constituents. Network models have been developed to explore the failure behavior of hierar- chical structures. While modeling approaches have confirmed the mechanical advantages of these microstructural arrangements, experimental validation of the viability and applicability of these models remains an open question. In this thesis we apply both simulation and experimental approaches to explore how the hierarchical architecture of materials improves toughness and enhances damage tolerance in different loading modes. Conducting experiments on quasi- two-dimensional materials, we examine the failure behavior of paper sheets as well as polystyrene (PS) sheets as simple prototypes of a disordered quasi-brittle material. Different microstructures are imposed in the form of laser cut hier- archical and non-hierarchical reference slice patterns. Fault tolerance is investi- gated considering both intact samples and samples with pre-existing macroscopic cracks. To simulate fracture in different loading conditions, failure is reached under displacement-controlled tensile loading and time dependant creep constant sub-critical load. We record acoustic emission signals to monitor damage, and we use digital image correlation technique (DIC) to reconstruct surface strain pat- terns. We perform similar tests in two-dimensional (2D) beam network model (BNM) simulations, which allow us to average results over multiple realizations of structural disorder and local strength fluctuations. We demonstrate that hierarchical patterning effectively suppresses strain local- ization and crack propagation. As a result, hierarchical patterned samples show higher failure load, apparent fracture toughness, and work of fracture. Under creep conditions, the hierarchically patterned samples sustain larger creep strains at higher stress levels. Creep curves exhibit peculiar behavior characterized by multiple minima in creep rate, attributed to the repeated arrest of emerging lo- calization bands. Our results indicate that hierarchical patterning enhances fault tolerance by dramatically altering failure mechanisms. In order to further explore the relation- ship between microstructure and fracture behavior, and to investigate how the network structure responds to damage, we implement methods of graph theory to quantify statistical correlation between network measures and failure propensity. We study the possibility of predicting failure locations by quantifying the edge betweenness centrality (EBC) of the load carrying beams in our quasi-brittle sim- ulation models. We evaluate the effectiveness of the EBC metric as a structural predictor of future failure events for varying degrees of local-strength disorder highlighting, as above, the differences between hierarchical and reference systems.
  • Doctoral thesis
    Open Access
    Machine Learning for Stuttering Detection and Classification in Stuttering Therapy
    (2024) Bayerl, Sebastian P.
    This thesis comprehensively explores stuttering detection and classification, lever- aging diverse datasets and methodologies. It emphasizes the importance of stuttering classification in enhancing accessibility for individuals with speech disorders and delivers a structured overview, starting with the foundational elements of speech and machine learning and extending to the new methods developed during the course of this research. The thesis identifies existing research gaps, necessitating a thorough examination of available datasets and a review of historical methods deployed for stuttering detection. It highlights the absence of comparability in the field due to diversity in annotation methods and the scarcity of datasets. This work is a crucial step in advancing the automation of stuttering assessment and therapy evaluation. It introduces and evaluates the speech control index, a new metric to assess stuttering therapy recordings. It goes on to create the Kassel State of Fluency (KSoF) dataset, advancing German stuttering research with optimized annotation protocols and enabling cross-language research initiatives. An in-depth analysis of the Stuttering Events in Podcasts (SEP-28k) brings forth valuable insights into its composition, advocating for quality assurance in research data and speaker exclusivity while splitting data into train, development, and test sets. This thesis investigates speech transformer features for stuttering detection and sets new benchmarks in stuttering classification. It conclusively shows the utility of features learned using English stuttering data on German stuttering recordings. Furthermore, it evaluates end-to-end stuttering classification systems based on speech transformer models. This is done using multi-language and cross-corpus datasets, showing the developed methods’ generalizability and their contribution towards a general stuttering detection system. It does so by evaluating cross-corpus and multi-language stuttering classification systems. While the research concludes with the harder task of multi-label stuttering classification, it underscores the ongoing challenges due to data availability and the inherent ambiguity of stuttering. It advocates for the creation of new multimodal datasets and refinement in the processing of stuttered speech, focusing on improving the accessibility of speech technology. The thesis contains innovative contributions, empirical explorations, and insights, aiming to navigate the future pathway in the field of stuttering detection and classification.
  • Article
    Open Access
    High-Throughput Numerical Investigation of Process Parameter-Melt Pool Relationships in Electron Beam Powder Bed Fusion
    (MDPI, 2023-07-10) Breuning, Christoph; Boehm, Jonas; Markl, Matthias; Körner, Carolin
    The reliable and repeatable fabrication of complex geometries with predetermined homogeneous properties is still a major challenge in electron beam powder bed fusion (PBF-EB). Although previous research identified a variety of process parameter–property relationships, the underlying end-to-end approach, which directly relates process parameters to material properties, omits the underlying thermal conditions. Since the local properties are governed by the local thermal conditions of the melt pool, the end-to-end approach is insufficient to transfer predetermined properties to complex geometries and different processing conditions. This work utilizes high-throughput thermal simulation for the identification of fundamental relationships between process parameters, processing conditions, and the resulting melt pool geometry in the quasi-stationary state of line-based hatching strategies in PBF-EB. Through a comprehensive study of over 25,000 parameter combinations, including beam power, velocity, line offset, preheating temperature, and beam diameter, process parameter-melt pool relationships are established, processing boundaries are identified, and guidelines for the selection of process parameters to the achieve desired properties under different processing conditions are derived.
  • Bachelor thesis
    Open Access
    Röntgentomographische Charakterisierung von Wurzelwachstum in granularer Materie
    Proceedings of the Institute for Multiscale Simulation (2017-10-29) Zoller, Doris
  • Master thesis
    Open Access
    The Dzhanibekov-Effect - an intuitive theoretical and practical approach to understand the rotation of rigid bodies about their intermediate axis
    Proceedings of the Institute for Multiscale Simulation (2023-06-16) Aseervatham, Bijohn Chandrew
  • Master thesis
    Open Access
    Pattern formation in a horizontally vibrated granular submonolayer
    Proceedings of the Institute for Multiscale Simulation (2012-01-26) Krengel, Dominik
    In 1995, Strassburger et al [27] carried out an experiment in which they shook a sub-monolayer of particles horizontally. Their investigations revealed that particles arranged themselves in stripes under the influence of the shaking. To describe this behavior, they developed a simple cellular automaton model: during an impact, all particles jump simultaneously in the direction of impact until they come to rest on a left and a right neighbor. However, the jumping could never be observed experimentally, suggesting that the streaking has a different cause. The aim of this work is to identify the key mechanism for streak formation in a horizontally shaken submonolayer of particles. For this purpose, the experiment of Strassburger et al. is repeated to confirm the effect. Based on the experiment, a force-based multiparticle simulation is performed to specifically investigate the system. It is shown that although particles can jump during the simulation, this is not essential for their streak formation. Friction between particles can be identified as the basis for streak formation, which means that particles in contact can no longer roll freely and move together with the bottom of the shaking container. Furthermore, it is found that streaking only occurs at higher excitation amplitudes and lower excitation frequencies. Other combinations lead to the particles in the system either not being supplied with enough energy to form streaks, or receiving too much energy and assuming a gas-like state. A comparison between the experiment and simulation shows that the non-round particles used in the experiment, which can only roll to a limited extent, lead to deformed stripes within which the particles are quasi-stationary. In the simulation, on the other hand, perfectly round spheres were used and strips with low deformation were generated, within which the particles exhibit high mobility. During the preparation of the simulation, collisions of three-dimensional particles were analyzed. It was found that the normal restitution coefficient can assume negative values. This effect was already known for high-speed impacts of nanoparticles [52]. However, it can be shown that this effect is a general phenomenon resulting from the geometry of the impact. Negative restitution coefficients can be observed for all types of collisions that are determined by finite interaction forces.
  • Master thesis
    Open Access
    Einfluss der Partikelform auf die elektrische Leitfähigkeit granularer Packungen
    Proceedings of the Institute for Multiscale Simulation (2020-06-08) Rabe, Carina
    In dieser Arbeit wird der Einfluss der Partikelform auf die elektrische Leitfähigkeit granularer Packungen untersucht. Mit den Ergebnissen der Simulation eines ereignisbasierten Algorithmus wird eine Routine zur Kontaktdetektion und Auswertung etabliert, die ein Widerstandsnetzwerk aus Kontakten in den granularen 2D- und 3D-Packungen bildet. Hierbei wird zwischen zwei Herangehensweisen zur Netzwerkbildung unterschieden. Um den Einfluss der Partikelform auf die elektrische Leitfähigkeit zu untersuchen, werden Partikel- und Packungseigenschaften geprüft. Die Partikel werden anhand ihres Aspektverhältnisses und ihrer Sphärizität charakterisiert. Kennzahlen, wie die Packungsdichte und die Koordinationszahl, welche zur Charakterisierung der Packung dienen, werden auf ihre Eignung zur Beschreibung des Einflusses der Packung auf die Leitfähigkeit untersucht. In this work, the influence of the particle shape on the electrical conductivity in granular packings is examined. With the results of the simulation of an event-driven algorithm, a contact detection routine is established that forms a resistance network made up of contacts in the granular 2D and 3D packings. A distinction is made between two approaches of network formation. To investigate the influence of the particle shape on the electrical conductivity, particle and packing properties are studied. The particles are characterized on the basis of their aspect ratio and their sphericity. Key figures, such as the packing density and the coordination number, which serve to characterize the packing, are examined on their suitability for describing the conductivity of packings.