Universität Stuttgart
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Item Open Access Alumina and zirconia-reinforced polyamide PA-12 composites for biomedical additive manufacturing(2021) Nakonieczny, Damian S.; Kern, Frank; Dufner, Lukas; Antonowicz, Magdalena; Matus, KrzysztofThis work aimed to prepare a composite with a polyamide (PA) matrix and surface-modified ZrO2 or Al2O3 to be used as ceramic fillers (CFs). Those composites contained 30 wt.% ceramic powder to 70 wt.% polymer. Possible applications for this type of composite include bioengineering applications especially in the fields of dental prosthetics and orthopaedics. The ceramic fillers were subjected to chemical surface modification with Piranha Solution and suspension in 10 M sodium hydroxide and Si3N4 to achieve the highest possible surface development and to introduce additional functional groups. This was to improve the bonding between the CFs and the polymer matrix. Both CFs were examined for particle size distribution (PSD), functional groups (FTIR), chemical composition (XPS), phase composition (XRD), and morphology and chemical composition (SEM/EDS). Filaments were created from the powders prepared in this way and were then used for 3D FDM printing. Samples were subjected to mechanical tests (tensility, hardness) and soaking tests in a high-pressure autoclave in artificial saliva for 14, 21, and 29 days.Item Open Access Statistical power analysis in reliability demonstration testing : the probability of test success(2022) Grundler, Alexander; Dazer, Martin; Herzig, ThomasStatistical power analyses are used in the design of experiments to determine the required number of specimens, and thus the expenditure, of a test. Commonly, when analyzing and planning life tests of technical products, only the confidence level is taken into account for assessing uncertainty. However, due to the sampling error, the confidence interval estimation varies from test to test; therefore, the number of specimens needed to yield a successful reliability demonstration cannot be derived by this. In this paper, a procedure is presented that facilitates the integration of statistical power analysis into reliability demonstration test planning. The Probability of Test Success is introduced as a metric in order to place the statistical power in the context of life test planning of technical products. It contains the information concerning the probability that a life test is capable of demonstrating a required lifetime, reliability, and confidence. In turn, it enables the assessment and comparison of various life test types, such as success run, non-censored, and censored life tests. The main results are four calculation methods for the Probability of Test Success for various test scenarios: a general method which is capable of dealing with all possible scenarios, a calculation method mimicking the actual test procedure, and two analytic approaches for failure-free and failure-based tests which make use of the central limit theorem and asymptotic properties of several statistics, and therefore simplify the effort involved in planning life tests. The calculation methods are compared and their respective advantages and disadvantages worked out; furthermore, the scenarios in which each method is to be preferred are illustrated. The applicability of the developed procedure for planning reliability demonstration tests using the Probability of Test Success is additionally illustrated by a case study.Item Open Access iWindow - Intelligentes Maschinenfenster(Düsseldorf : VDI Verlag, 2018) Sommer, Philipp; Verl, Alexander; Kiefer, Manuel; Rahäuser, Raphael; Müller, Sebastian; Brühl, Jens; Gras, Michael; Berckmann, Eva; Stautner, Marc; Schäfer, D.; Schotte, Wolfgang; Do-Khac, Dennis; Neyrinck, Adrian; Eger, Ulrich; Sommer, PhilippDas Verbundforschungsprojekt iWindow: Intelligentes Maschinenfenster beschäftigte sich mit der visuellen Unterstützung von Maschinenbedienern an Werkzeugmaschinen. Diese konnten bisher nur auf wenige bis keine Systeme, die sie bei ihren täglichen Aufgaben direkt an der Werkzeugmaschine unterstützen, zurückgreifen. Das Forschungsprojekt verbindet reale und virtuelle Welt in der Werkzeugmaschine durch Technologien wie Virtual und Augmented Reality, digitaler Zwilling, Simulation und Mehrwertdienste. Durch Nutzung jeweils für die aktuelle Arbeitssituation passender Dienste, werden Mitarbeiter befähigt, sich an die steigende Individualisierung der Produkte und die flexiblere Produktion anzupassen. Kunden und Geschäftspartner werden durch die Möglichkeit eigene mehrwertgenerierende Dienste zu entwickeln und anderen Anwendern zur Verfügung zu stellen in den Wertschöpfungsprozess eingebunden. Diese Publikation beleuchtet die im Rahmen des Forschungsprojekts erarbeiteten Ergebnisse hinsichtlich für ein intelligentes Maschinenfenster benötigter Technologien und Entwicklungen.Item Open Access Comprehensive study of failure mechanisms of field-aged automotive lead batteries(2023) Conradt, Rafael; Schröer, Philipp; Dazer, Martin; Wirth, Jonathan; Jöris, Florian; Schulte, Dominik; Birke, Kai PeterModern vehicles have increasing safety requirements and a need for reliable low-voltage power supply in their on-board power supply systems. Understanding the causes and probabilities of failures in a 12 V power supply is crucial. Field analyses of aged and failed 12 V lead batteries can provide valuable insights regarding this topic. In a previous study, non-invasive electrical testing was used to objectively determine the reasons for failure and the lifetime of individual batteries. By identifying all of the potential failure mechanisms, the Latin hypercube sampling method was found to effectively reduce the required sample size. To ensure sufficient confidence in validating diagnostic algorithms and calculating time-dependent failure rates, all identified aging phenomena must be considered. This study presents a probability distribution of the failure mechanisms that occur in the field, as well as provides insights into potential opportunities, but it also challenges diagnostic approaches for current and future vehicles.Item Open Access Abschaltung von dezentralen Erzeugungsanlagen infolge von Unterspannungen im Kontext von LFSM-O(2022) Schöll, Christian; Lehner, Joachim; Weidner, Johannes; Lens, HendrikBei einer Überfrequenz jenseits von 50,2 Hz müssen sämtliche Erzeugungsanlagen ihre in das Netz eingespeiste Wirkleistung reduzieren. In den zumeist resistiv geprägten Verteilungsnetzen der Mittel- und Niederspannung führt diese überfrequenzbedingte Leistungsreduktion zu einer lokalen Absenkung des Spannungsprofils. Unterschreiten die Spannungen die Vorgaben aus den Netzanschlussbedingungen, unter denen dezentrale Erzeugungsanlagen die Verbindung zum Netz aufrechterhalten müssen, kann es zu unterspannungsbedingten Schutzabschaltungen kommen. Theoretisch könnten diese bei großflächigem Auftreten zu einer Umkehr des ursprünglichen Überfrequenzereignisses in ein Unterfrequenzereignis führen. Anhand von simulationsbasierten Untersuchungen wird in diesem Beitrag jedoch aufgezeigt, dass unter realitätsnahen Annahmen und unter Berücksichtigung der nationalen Richtlinien sowie der zugehörigen netzplanerischen Leitplanken kein besonderes Risiko hinsichtlich der Anregung der beschriebenen Wirkungskette vorliegt.Item Open Access Anti-adhesive surfaces inspired by bee mandible surfaces(2023) Saccardi, Leonie; Schiebl, Jonas; Balluff, Franz; Christ, Ulrich; Gorb, Stanislav N.; Kovalev, Alexander; Schwarz, OliverPropolis, a naturally sticky substance used by bees to secure their hives and protect the colony from pathogens, presents a fascinating challenge. Despite its adhesive nature, honeybees adeptly handle propolis with their mandibles. Previous research has shown a combination of an anti-adhesive fluid layer and scale-like microstructures on the inner surface of bee mandibles. Our aim was to deepen our understanding of how surface energy and microstructure influence the reduction in adhesion for challenging substances like propolis. To achieve this, we devised surfaces inspired by the intricate microstructure of bee mandibles, employing diverse techniques including roughening steel surfaces, creating lacquer structures using Bénard cells, and moulding resin surfaces with hexagonal patterns. These approaches generated patterns that mimicked the bee mandible structure to varying degrees. Subsequently, we assessed the adhesion of propolis on these bioinspired structured substrates. Our findings revealed that on rough steel and resin surfaces structured with hexagonal dimples, propolis adhesion was significantly reduced by over 40% compared to unstructured control surfaces. However, in the case of the lacquer surface patterned with Bénard cells, we did not observe a significant reduction in adhesion.Item Open Access Additively manufactured transverse flux machine components with integrated slits for loss reduction(2022) Kresse, Thomas; Schurr, Julian; Lanz, Maximilian; Kunert, Torsten; Schmid, Martin; Parspour, Nejila; Schneider, Gerhard; Goll, DagmarLaser powder bed fusion (L-PBF) was used to produce stator half-shells of a transverse flux machine from pure iron (99.9% Fe). In order to reduce iron losses in the bulk components, radially extending slits with a nominal width of 150 and 300 µm, respectively, were integrated during manufacturing. The components were subjected to a suitable heat treatment. In addition to a microscopic examination of the slit quality, the iron losses were also measured using both a commercial and a self-developed measurement setup. The investigations showed the iron losses can be reduced by up to 49% due to the integrated slits and the heat treatment.Item Open Access Finite element based design of timber structures(2023) Töpler, Janusch; Schweigler, Michael; Lemaître, Romain; Palma, Pedro; Schenk, Martin; Grönquist, Philippe; Tapia Camú, Cristóbal; Hochreiner, Georg; Kuhlmann, UlrikeItem Open Access Lateral torsional buckling of glulam beam-columns : axial compression and bending verification(2024) Töpler, Janusch; Kuhlmann, Ulrike; Schänzlin, JörgItem Open Access Rheology, dispersion, and cure kinetics of epoxy filled with amine‐ and non‐functionalized reduced graphene oxide for composite manufacturing(2021) Ackermann, Annika C.; Carosella, Stefan; Rettenmayr, Markus; Fox, Bronwyn L.; Middendorf, PeterThis study evaluates the effect of plasma surface functionalization of reduced graphene oxide particles on the processing characteristics and homogeneity of dispersion of a bisphenol A‐(epichlorhydrin) epoxy matrix and amine‐based hardener with varying weight fractions from 0.00 to 1.50 wt%. It was observed that amine‐functionalized reduced graphene oxide leads to a more drastic viscosity increase of up to 18‐fold of the uncured suspensions and that its presence influences the conversion rates of the curing reaction. Optical microscopy of thin sections and transmission electron microscopy analysis showed that a more homogeneous dispersion of the particles could be achieved especially at higher weight fractions by using an appropriate surface functionalization. This knowledge can be used to define suitable processing conditions for epoxies with amine‐based hardeners depending on the loading and functionalization of graphene‐related particles.