04 Fakultät Energie-, Verfahrens- und Biotechnik

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/5

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Open Access
Adaptive winding pin and hooking capacity model for coreless filament winding
(2023) Mindermann, Pascal; Gresser, Götz T
Coreless filament winding is a manufacturing process used for fiber-reinforced composites, resulting in high-performance lightweight lattice structures. Load transmission elements, which are assembled from commercially available standardized parts, often restrict the component design. A novel adaptive winding pin was developed, which is made by additive manufacturing and can therefore be adjusted to specific load conditions resulting from its position within the component. This allows to decouple the fiber arrangement from the winding pin orientation, which allows a fully volumetric framework design of components. A predictive model for the pin capacity was derived and experimentality validated. The hooking conditions, pin capacity, and occupancy were considered in the creation of a digital design tool.
Open Access
Automatic joining of electrical components to smart textiles by ultrasonic soldering
(2021) Micus, Sebastian; Haupt, Michael; Gresser, Götz T.
A suitable connection method to automatically produce E-textiles does not exist. Ultrasonic soldering could be a good solution for that since it works with flux-free solder, which avoids embrittlement of the textile integrated wires. This article describes the detailed process of robot-assisted ultrasonic soldering of e-textiles to printed circuit boards (PCB). The aim is to understand the influencing factors affecting the connection and to determine the corresponding solder parameters. Various test methods are used to evaluate the samples, such as direct optical observation of the microstructure, a peeling tensile test, and a contact resistance measurement. The contact strength increases by reducing the operating temperature and the ultrasonic time. The lower operating temperature and the reduced ultrasonic time cause a more homogeneous metal structure with less defects improving the mechanical strength of the samples.
Open Access
Constitutive correlations for mass transport in fibrous media based on asymptotic homogenization
(2023) Maier, Lukas; Kufferath-Sieberin, Lars; Pauly, Leon; Hopp-Hirschler, Manuel; Gresser, Götz T.; Nieken, Ulrich
Mass transport in textiles is crucial. Knowledge of effective mass transport properties of textiles can be used to improve processes and applications where textiles are used. Mass transfer in knitted and woven fabrics strongly depends on the yarn used. In particular, the permeability and effective diffusion coefficient of yarns are of interest. Correlations are often used to estimate the mass transfer properties of yarns. These correlations commonly assume an ordered distribution, but here we demonstrate that an ordered distribution leads to an overestimation of mass transfer properties. We therefore address the impact of random ordering on the effective diffusivity and permeability of yarns and show that it is important to account for the random arrangement of fibers in order to predict mass transfer. To do this, Representative Volume Elements are randomly generated to represent the structure of yarns made from continuous filaments of synthetic materials. Furthermore, parallel, randomly arranged fibers with a circular cross-section are assumed. By solving the so-called cell problems on the Representative Volume Elements, transport coefficients can be calculated for given porosities. These transport coefficients, which are based on a digital reconstruction of the yarn and asymptotic homogenization, are then used to derive an improved correlation for the effective diffusivity and permeability as a function of porosity and fiber diameter. At porosities below 0.7, the predicted transport is significantly lower under the assumption of random ordering. The approach is not limited to circular fibers and may be extended to arbitrary fiber geometries.
Open Access
Design and analysis of methods to connect microelectronics to smart textiles
(2022) Micus, Sebastian; Gresser, Götz Theodor (Prof. Dr.-Ing.)
The smart textiles market shows a high growth potential during the next ten years. However, the integration of conventional electronics in textiles requires a lot of manual work. As a result, the products tend to have very high prices, which inhibits the success. During the production processes, the joining step offers the greatest potential to reduce manual manufacturing, but a suitable connection method for the automated production of E-textiles does not exist, yet. For this reason, this thesis analyses different connection methods for joining electronic components to textile integrated litz wires. The selected processes show a high potential for automation. The chosen methods are thermode soldering, insulation displacement connections (IDCs), anisotropic conductive adhesives (ACA), laser soldering, ultrasonic soldering and ultrasonic welding. Various test methods were developed and used to evaluate the samples in order to ensure the reliability of the joinings, such as direct optical observation of the microstructure, a peeling tensile test, and a four-wire contact resistance measurement. The thesis consists of four peer reviewed paper. Each paper focuses on one or more connection methods. In the first paper, hot bar soldering, IDCs and ACA was investigated. The second paper focuses on the ultrasonic soldering. The third paper presents the development on laser soldering and the final paper shows the results of ultrasonic welding. Hot bar soldering initially showed great results. However, solder was drawn into the strands, which was not possible to prevent. Drawn-in solder has a clear negative effect on the textile properties close to the contact point. IDCs have good preconditions for an automated smart textiles production. The strands can slip into the IDCs even under a certain deviation in position. However, thin wires are important to ensure the textile properties of the smart textile, but the available connectors were not suitable to connect AWG 32 or thinner strand. At the current stage of development, anisotropic conductive bonding methods are only conditionally suitable for the usage in automated production. The bonding process has weaknesses due to inadequate contacting and process time. Ultrasonic soldering works with flux-free solder, which avoids embrittlement of the textile integrated wires trough drawn in solder. The influencing factors of the connection and the corresponding solder parameters were determined. The contact strength increases by reducing the operating temperature and the ultrasonic time. A lower operating temperature and a reduced ultrasonic time cause a more homogeneous metal structure with less defects, resulting in an improved mechanical strength of the samples. Contactless laser soldering is considered to be a good contacting method to reduce the joining zone on the textile. An ytterbium-doped fibre laser (1064 nm) was used and different sets of parameters were investigated by means of different designs of experiment. The copper strands in the textile tape were stripped by the laser and soldered to the printed circuit board (PCB) without any transport. Unfortunately, some conductors were poorly wetted by solder. The connection between flexible textiles and stiff electronic components has always been a structural weakness and a limiting factor to establish smart textiles in our everyday life. Therefore, the next chapter focuses on reliable connections between conductive textiles and conventional litz wires by ultrasonic welding. It shows a promising approach. The electrical and mechanical performance of the samples were investigated after both 15 and 30 wash and dry cycles in a laundry machine. The resistance of the joints increased by more than 300 %, because the silver coated wires suffered under the laundry cycles. While the mechanical strength during the peeling test decreased only about 20 % after 15 cycles and remained the same after 30 cycles. Ultrasonic welding showed good results for connecting conductive textiles to litz wires, which enables the production of smart textiles with textile sensors.
Open Access
Design of fiber-composite/metal-hybrid structures made by multi-stage coreless filament winding
(2022) Mindermann, Pascal; Müllner, Ralf; Dieringer, Erik; Ocker, Christof; Klink, René; Merkel, Markus; Gresser, Götz T.
The methods presented in this study assist in fabricating load-bearing structures with high mass-specific mechanical performance at various scales. Possible applications include primary and secondary structures in engineering, architecture, automotive, or aerospace industries.Additive manufacturing processes, such as coreless filament winding with fiber composites or laser powder bed fusion with metals, can produce lightweight structures while exhibiting process-specific characteristics. Those features must be accounted for to successfully combine multiple processes and materials. This hybrid approach can merge the different benefits to realize mass savings in load-bearing structures with high mass-specific stiffnesses, strict geometrical tolerances, and machinability. In this study, a digital tool for coreless filament winding was developed to support all project phases by natively capturing the process-specific characteristics. As a demonstration, an aluminum base plate was stiffened by a coreless wound fiber-composite structure, which was attached by additively manufactured metallic winding pins. The geometrical deviations and surface roughness of the pins were investigated to describe the interface. The concept of multi-stage winding was introduced to reduce fiber–fiber interaction. The demonstration example exhibited an increase in mass-specific component stiffness by a factor of 2.5 with only 1/5 of the mass of a state-of-the-art reference. The hybrid design approach holds great potential to increase performance if process-specific features, interfaces, material interaction, and processes interdependencies are aligned during the digitized design phase.
Open Access
Development of a novel method and apparatus for analysis of die dynamics of an isothermal thermoset pultrusion process
(2021) Selvarayan, Sathis Kumar; Gresser, Götz T. (Prof. Dr.-Ing.)
Pultrusion is a continuous process to manufacture constant cross-sectional fibre reinforced composite profiles. The profiles take their shape as the continuously moving fibre-matrix combination consolidates inside the cavity of a pultrusion die. The temperature-induced viscosity and volumetric changes of the fibre-matrix during the consolidation as well as the friction between the die wall and the moving fibre-matrix generates shear and normal forces that act on the die wall - phenomena known as “die dynamics”. Quantification and analysis of the die dynamics are crucial to understand and control the pultrusion process. However, state-of-the-art methods available to characterise the pultrusion process have limited capability to record the forces that act on the die wall at each position along the length of the pultrusion die. Further, the on-line measurement techniques demand full-scale pultrusion line which, in general, are resource intensive. In addition, the available methodologies have not considered the impact of process additives on the die dynamics. This research work, therefore, focuses on developing a resource-efficient offline testing method to characterise the die dynamics of a thermoset pultrusion process and to pre-determine the required process parameters for a given fibre-matrix combination. In the newly developed approach, called rotating core method, pre-impregnated rovings wound on a solid core with defined fibre volume fraction rotates about the axis of the core inside a hollow cylindrical heated die. The rotational velocity of the rotating core is set to be identical to the line speed of the pultrusion process. The rotating fibre-matrix undergo temperature-induced polymerisation leading to the transformation of the fibre-matrix into a solid composite within the cylindrical die. This mimic the dominant phenomena that occur inside a pultrusion die in the pultrusion process. An apparatus developed within the scope of this work, the Die Dynamics Simulator (DDS), for the first time allows to continuously measure the torque exerted by the rotating fibre-matrix on the DDS die during the polymerisation process. The measured torque represents the resistive forces that arise within the die during the consolidation of the fibre-matrix combination. Evaluation of the curing kinetics and rheology of the resin formulations facilitates the characterisation of their polymerisation behaviour enabling identification of the components of the resistive forces. Further, this work investigates the influence of the following parameters on die dynamics using the developed apparatus: (1) die temperature, (2) velocity of the fibre-matrix, (3) contact area of the die and the fibre-matrix, (4) part thickness, (5) fibre volume fraction, and (6) process additive - internal mould release (IMR). Subsequently, the developed methodology is validated against the pultrusion process using a lab-scale pultrusion line. The results show the dependency of the resistive forces on the individual and the interactions between multiple parameters. More importantly, the experiments conducted with varying concentrations of IMR permitted to evaluate the implication of the mould release on the evolving resistive forces within the die. The results further provide insight at which phase of the polymerising matrix is the IMR most effective. Comparison of the measured forces on the DDS and from that measured on the pultrusion line show good fit for higher fibre volume fractions of the consolidated composite.
Open Access
Development of an impregnation end-effector with fiber tension monitoring for robotic coreless filament winding
(2021) Mindermann, Pascal; Bodea, Serban; Menges, Achim; Gresser, Götz T.
The manufacturing process of robotic coreless filament winding has great potential for efficient material usage and automation for long-span lightweight construction applications. Design methods and quality control rely on an adequate digital representation of the fabrication parameters. The most influencing parameters are related to the resin impregnation of the fibers and the applied fiber tension during winding. The end-effector developed in this study allows efficient resin impregnation, which is controlled online by monitoring the induced fiber tension. The textile equipment was fully integrated into an upscaled nine-axis robotic winding setup. The cyber-physical fabrication method was verified with an application-oriented large-scale proof-of-concept demonstrator. From the subsequent analysis of the obtained datasets, a characteristic pattern in the winding process parameters was identified.
Open Access
Development of natural fibre-reinforced semi-finished products with bio-based matrix for eco-friendly composites
(2022) Möhl, Claudia; Weimer, Timo; Caliskan, Metin; Baz, Stephan; Bauder, Hans-Jürgen; Gresser, Götz T.
Increasing resource consumption and a growing amount of textile waste increase the importance of a circular economy and recycling in the fashion and apparel industry. Environmentally friendly bio-based composites made from cellulosic fibres obtained from textile waste, and polymers based on renewable raw materials present a possible solution. In this study, the development of textile semi-finished products based on medium-to-long cotton and flax fibres obtained from textile waste in combination with a bio-based thermoplastic matrix for lightweight applications is investigated. For the production of natural fibre-polylactide hybrid yarns, fibre slivers with improved fibre orientation and blending are produced. Subsequently, quasi-unidirectional woven fabrics are produced and consolidated into bio-based composites. Textile and mechanical properties of hybrid yarns as well as bio-composites are analysed with regard to the influence of fibre length, fibre distribution in the yarn, yarn structure and fibre volume content. The results show that the production of bio-based semi-finished products can be a potential way for upcycling textile waste.
Open Access
Entwicklung einer Methode zur kontinuierlichen Bauteilüberwachung von Faserverbundwerkstoffen mittels piezoelektrischer Mehrlagengewebe
(2022) Hofmann, Paul; Gresser, Götz T. (Prof. Dr.-Ing.)
Eine Form der Beschädigung von Faser-Kunststoff-Verbunden (FKV) ist die Delamination. Diese Beschädigung ist durch konventionelle, visuelle Prüfung oft nicht zu erkennen. Methoden, wie das zyklische Austauschen der Bauteile oder regelmäßige Inspektionen, sind zeitaufwendig und vor allem teuer. Daher soll in Zukunft Sensorik direkt in solche Bauteile integriert werden, um die Beanspruchung oder den Zustand der Bauteile kontinuierlich im Betrieb zu überwachen (Condition Monitoring bzw. Structural Health Monitoring). Herkömmliche, elektronische Sensorbauteile, integriert in einem FKV, stellen allerdings einen Fremdkörper in der textilen Verstärkungsstruktur dar und bilden daher eine mechanische Schwachstelle. Gleichzeitig gewinnen dreidimensionale Mehrlagengewebe als textile Verstärkung im FKV aus mechanischen, aber auch wirtschaftlichen Gründen immer mehr an Bedeutung. Diese Arbeit beschreibt daher die Entwicklung und Charakterisierung einer piezoelektrischen Biegesensorik auf Mehrlagengewebebasis als Teil der gewebten Verstärkungsstruktur von FKV. Weil die Verstärkungsstruktur an sich als Sensor fungiert, entstehen durch diese Sensorik keine negativen Einflüsse auf die mechanischen Bauteileigenschaften durch Fehlstellen in der textilen Grundstruktur. Durch grundlegende Analysen zu Sensorprinzip und Sensoraufbau wird eine Methode entwickelt, wie textile Mehrlagenstrukturen partiell sensorisch ausgerüstet werden können. Die piezoelektrische Gewebestruktur wird auf eine möglichst gute sensorische Charakteristik bei möglichst geringem Einfluss auf die mechanischen Bauteileigenschaften hin entwickelt und optimiert. Die gewonnenen Erkenntnisse werden dann an verschiedenen Mehrlagengewebestrukturen umgesetzt, analysiert und verifiziert. Abschließend werden die Sensorsignale der gewebten Piezoelemente an einem mechanischen Berechnungsmodell validiert: Vom Signal der sensorischen Gewebestruktur kann direkt auf die Bauteilbeanspruchung geschlossen werden. Durch die entwickelte textile Sensortechnologie wird eine kontinuierliche Überwachung von dynamisch belasteten Bauteilen während des Betriebs ermöglicht. So können bspw. künftig mit Hilfe der Sensorik aus einer piezoelektrischen Mehrlagengewebestruktur eine mögliche Überlast während des Betriebs erkannt, eventuelle Beschädigungen vermieden bzw. detektiert und damit Wartungs-, Reparatur- und Stillstandkosten erheblich reduziert werden.
Open Access
Entwicklung und Analyse einer selbstkühlenden und substratunabhängigen Beschichtung für technische Textilien unter Nutzung der energiefreien Strahlungskühlung
(2024) Zimmermann, Lea; Gresser, Götz T. (Prof. Dr.-Ing.)
Aufgrund des Klimawandels, des Bevölkerungswachstums und des städtischen Wärmeinseleffekts (UHI) ist der Bedarf an Kühlenergie insbesondere in städtischen Gebieten gestiegen und wird voraussichtlich auch in Zukunft weiter zunehmen. Bisherige konventionelle Kühlsysteme für Gebäude wie Klimaanlagen basieren auf thermodynamischen Kreisläufen, die einen großen Teil des Strombedarfs ausmachen und gleichzeitig Abwärme und Kohlendioxid (CO2) an die Umwelt abgeben. Technologien wie die Strahlungskühlung bieten eine nachhaltige und energiefreie Lösung, indem sie die Wellenlängenbereiche der Atmosphäre, die für elektromagnetische Strahlung transparent sind, das so genannte atmosphärische Fenster (8-13 µm), nutzen, um Wärmestrahlung in den kälteren (3 K) Weltraum abzugeben. Durch die Entwicklung von Beschichtungen, die selektiv Wärme durch die Atmosphäre abstrahlen und weniger Sonnenwärme absorbieren, ist eine Abkühlung unter die Umgebungstemperatur auch tagsüber möglich. Während sich bisherige Veröffentlichungen im Bereich der textilen Gebäudekühlung auf spezifische Faserstrukturen und textile Trägermaterialien sowie komplexe Mehrschichtaufbauten konzentrierten, was den Einsatz für hochskalierte Außenanwendungen einschränkt, zielt diese Arbeit auf die Entwicklung einer neuartigen, substratunabhängigen Beschichtung mit spektral selektiven Strahlungseigenschaften hin. Durch die detaillierte Abstimmung von Beschichtungsparametern wie der Partikelkonzentration, verteilung und -größe in Kombination mit niedrig emittierenden und solarreflektierenden Partikeln sowie einem stark im mittleren Infrarot emittierenden Matrixmaterial, wird eine substratunabhängige Kühlung unter die Umgebungstemperatur erreicht, gezeigt am Beispiel von drei für den Membran- und Zeltbau typischen Gewebetypen. Darüber hinaus ist die Beschichtung so konzipiert, dass sie einfach auf verschiedene textile Materialien appliziert werden kann und gleichzeitig eine geringe Dicke aufweist, um hohe Flexibilität und Skalierbarkeit zu gewährleisten. Um die Funktionsweise des entwickelten Beschichtungssystems weiter zu validieren, wurden Tests im Freien mit einem konzipierten Messaufbau durchgeführt, um Temperaturunterschiede und Kühlleistungen unter realen Wetterbedingungen zu messen. Die Ergebnisse zeigen, dass die Temperatur der Beschichtung (zwischen 7-19 Uhr) an einem heißen Sommertag um durchschnittlich 2 °C unter der Umgebungstemperatur liegt. Darüber hinaus wird ein thermisches Modell an textile Materialien angepasst und validiert, um die Kühlleistung für verschiedene Wetterszenarien zu simulieren und zu berechnen. Damit leistet diese Arbeit einen Beitrag zur Weiterentwicklung nachhaltiger textilbasierter Kühltechnologien und bietet eine vielversprechende Lösung für den wachsenden Bedarf an energieeffizienter Kühlung in städtischen Umgebungen.
Open Access
Flax fibre yarn coated with lignin from renewable sources for composites
(2022) Möhl, Claudia; Weimer, Timo; Caliskan, Metin; Hager, Tom; Baz, Stephan; Bauder, Hans-Jürgen; Stegmaier, Thomas; Wunderlich, Werner; Gresser, Götz T.
The present experimental work analyses the potential of lignin as a matrix for materials made from renewable resources for composite components and the production of hybrid semi-finished products by coating a flax fibre yarn. Natural fibres, due to their low density, in combination with lignin can be a new renewable source for lightweight products. For this purpose, the extrusion process was adapted to lignin as a matrix material for bio-based composites and coating of natural fibre yarns. A commercial flax yarn is the basis for the lignin coating by extrusion. Subsequently, the coated flax yarn was characterised with regard to selected yarn properties. In order to produce composite plates, the lignin-coated flax yarn was used as warp yarn in a bidirectional fabric due to its insufficient flexibility transversely to the yarn axis. The commercial flax yarn was used as weft yarn to increase the fibre volume content. The tensile and flexural properties of the bio-based composite material were determined. There was a significant difference in the mechanical properties between the warp and weft directions. The results show that lignin can be used as matrix material for bio-based natural fibre composites and the coating of natural fibre yarns is an alternative to spun hybrid yarns.
Open Access
Grundlegende Ermittlung von Struktur-Eigenschaftsbeziehungen beim Strukturknäuelprozess für technische Anwendungen
(2022) Haigis, Kathrin; Gresser, Götz T. (Prof. Dr.-Ing.)
Die Strukturknäueltechnik ist eine Technologie, um hochautomatisiert und wirtschaftlich leichte Strukturbauteile herzustellen, bei denen das Garn auf allen Seiten des Dornkörpers abgelegt wird. Die vorliegende Arbeit untersucht erstmalig die Struktur-Eigenschaftsbeziehungen beim Strukturknäuelprozess für technische Anwendungen. Hierfür werden die Einflussfaktoren auf die Strukturknäuelbildung erstmalig definiert und erarbeitet, zu denen neben den knäueltechnologischen Aspekten auch die Maschinenelemente Flyer und Dorn sowie die garnseitigen Einflussfaktoren gehören. Die technologischen Zusammenhänge stellen die Grundlage für ein Berechnungsmodell dar, das in der Arbeit erarbeitet wird. Anhand dieses Modells und der gezeigten recheneffizienten Strategien erfolgt eine auf Dornkörpergrundformen abgestimmte Berechnung der Ablagepunkte.
Open Access
Impact of long-term weathering on the properties of a digestate-based biocomposite
(2021) Gebhardt, Marion; Milwich, Markus; Gresser, Götz T.; Lemmer, Andreas
Natural fibre composites are increasingly used. For many applications, the long-term stability of the mechanical properties is crucial. Therefore, the effects of weathering of a biocomposite made from fibrous digestate and bio-based thermoset are investigated. The fibre component of the composite comes from digestate of a German biogas station which processes hop vines as main substrate. The matrix is a plant-oil-based epoxy resin. The samples were alternately exposed to UV radiation and moisture for various lengths of time. Afterwards, the material strength and water absorption were tested. As a result, the weathering leads to a decrease of strength but not to a high increase of water uptake.
Open Access
Improved micro-oil droplet coalescence for oil-water separation by spider silk-like structures
(2023) Aliabadi, Maryam; Gresser, Götz Theodor (Prof. Dr.-Ing.)
Open Access
The influence of background materials on the radiative cooling performance of semi-transparent and opaque textiles : a theoretical and experimental analysis
(2024) Zimmermann, Lea; Aili, Ablimit; Stegmaier, Thomas; Kaya, Cigdem; Gresser, Götz T.
This paper investigates the theoretical and experimental cooling performance of textile materials utilizing radiative cooling technology. By applying Kirchhoff’s law, the emissivity of surfaces is determined, revealing that materials with high transmission values can achieve comparable cooling performance to those with high reflection values. Notably, materials exhibiting moderate reflectance and transmittance in the solar range tend to absorb minimal solar radiation, thus offering high theoretical cooling performance. However, practical applications like building envelopes or clothing present challenges due to the impact of background radiation on overall cooling capacity. Despite their intrinsic cooling properties, a significant portion of solar radiation is transmitted, complicating matters as the background can significantly affect overall cooling performance. This study provides a solution that accounts for the influence of background materials. Based on spectral data, various background materials and their impact on different semi-transparent comparison materials can be considered, and cooling performance can be simulated. This enables the simulation of cooling performance for various application scenarios and facilitates comparisons between transparent, semi-transparent, and opaque textile materials.
Open Access
Insights into the processing of recycled carbon fibers via injection molding compounding
(2020) Wellekötter, Jochen; Resch, Julia; Baz, Stephan; Gresser, Götz Theo; Bonten, Christian
Although fiber-reinforced plastics combine high strength and stiffness with being lightweight, major difficulties arise with high volume production and the return of manufactured parts back into the cycle of materials at the end of their lifecycles. In a novel approach, structural parts were produced from recycled material while utilizing the so-called injection molding compounding process. Recycled fibers and recycled polyamide matrix material were used by blending carbon and matrix fibers into a sliver before processing. Injection molding was then used to produce long fiber-reinforced parts through a direct fiber feed system. Recycled matrix granules were incorporated into the injection molding process by means of an injection molding compounder to investigate their influences on the mechanical properties of the parts. The findings show that the recycled fibers and matrix perform well in standardized tests, although fiber length and fiber content vary significantly and remain below expectations.
Open Access
Integrating electronics to textiles by ultrasonic welding for cable-driven applications for smart textiles
(2021) Micus, Sebastian; Rostami, Sahar Golmohammadi; Haupt, Michael; Gresser, Götz T.; Meghrazi, Milad Alizadeh; Eskandarian, Ladan
The connection between flexible textiles and stiff electronic components has always been structurally weak and a limiting factor in the establishment of smart textiles in our everyday life. This paper focuses on the formation of reliable connections between conductive textiles and conventional litz wires using ultrasonic welding. The paper offers a promising approach to solving this problem. The electrical and mechanical performance of the samples were investigated after 15 and 30 wash-and-dry cycles in a laundry machine. Here the contact resistances and their peeling strength were measured. Furthermore, their connection properties were analysed in microsections. The resistance of the joints increased more than 300%, because the silver-coated wires suffered under the laundry cycles. Meanwhile, the mechanical strength during the peeling test decreased by only about 20% after 15 cycles and remained the same after 30 cycles. The good results obtained in this study suggest that ultrasonic welding offers a useful approach to the connection of textile electronics to conductive wires and to the manufacture of smart textiles.
Open Access
Investigation of the fabrication suitability, structural performance, and sustainability of natural fibers in coreless filament winding
(2022) Mindermann, Pascal; Gil Pérez, Marta; Knippers, Jan; Gresser, Götz T.
Coreless filament winding is an emerging fabrication technology in the field of building construction with the potential to significantly decrease construction material consumption, while being fully automatable. Therefore, this technology could offer a solution to the increasing worldwide demand for building floor space in the next decades by optimizing and reducing the material usage. Current research focuses mainly on the design and engineering aspects while using carbon and glass fibers with epoxy resin; however, in order to move towards more sustainable structures, other fiber and resin material systems should also be assessed. This study integrates a selection of potential alternative fibers into the coreless filament winding process by adapting the fabrication equipment and process. A bio-based epoxy resin was introduced and compared to a conventional petroleum-based one. Generic coreless wound components were created for evaluating the fabrication suitability of selected alternative fibers. Four-point bending tests were performed for assessing the structural performance in relation to the sustainability of twelve alternative fibers and two resins. In this study, embodied energy and global warming potential from the literature were used as life-cycle assessment indexes to compare the material systems. Among the investigated fibers, flax showed the highest potential while bio-based resins are advisable at low fiber volume ratios.
Open Access
Material monitoring of a composite dome pavilion made by robotic coreless filament winding
(2021) Mindermann, Pascal; Rongen, Bas; Gubetini, Drilon; Knippers, Jan; Gresser, Götz T.
A hemispherical research demonstration pavilion was presented to the public from April to October 2019. It was the first large-scale lightweight dome with a supporting roof structure primarily made of carbon- and glass-fiber-reinforced composites, fabricated by robotic coreless filament winding. We conducted monitoring to ascertain the sturdiness of the fiber composite material of the supporting structure over the course of 130 days. This paper presents the methods and results of on-site monitoring as well as laboratory inspections. The thermal behavior of the pavilion was characterized, the color change of the matrix was quantified, and the inner composition of the coreless wound structures was investigated. This validated the structural design and revealed that the surface temperatures of the carbon fibers do not exceed the guideline values of flat, black façades and that UV absorbers need to be improved for such applications.
Open Access
New flexible protective coating for printed smart textiles
(2021) Bartsch, Valérie; Arnim, Volkmar von; Kuijpens, Sven; Haupt, Michael; Stegmaier, Thomas; Gresser, Götz T.
In the field of food packaging, the addition of exfoliated layered silicates in polymers has been established to improve the polymers’ gas barrier properties. Using these polymers as coatings to protect smart textiles from oxidation and corrosion while maintaining their textile properties should significantly extend their lifetime and promote their market penetration. The aim of this study was to print new polymer dispersions containing layered silicates to protect screen-printed conductive structures, and to test the resulting samples. For this, appropriate printing parameters were determined by statistical design of experiments. According to these results, conductive structures were printed and protected with the selected coating. The abrasion resistance and the continuity of the protective layer of the printed samples were then measured. A continuous protective coating of approximately 70–80 µm thickness was applied on a conductive structure. The printed samples showed a very high resistance to abrasion (unchanged by 85,000 abrasion cycles) while remaining flexible and presenting a lower water vapor permeability (<2.5 g/m² d) than the coatings commonly used in the textile field.