Universität Stuttgart
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Item 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.Item 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.Item 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, LadanThe 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.Item 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.Item 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.Item Open Access Impact of long-term weathering on the properties of a digestate-based biocomposite(2021) Gebhardt, Marion; Milwich, Markus; Gresser, Götz T.; Lemmer, AndreasNatural 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.Item Open Access Validation of the manufacturing Methodology of prestressed fiber-reinforced polymer concrete by the variation of process parameters(2023) Engert, Michelle; Werkle, Kim Torben; Wegner, Robert; Born, Larissa; Gresser, Götz T.; Möhring, Hans-ChristianPolymer concrete has proved to be advantageous in machine building for many years thanks to its excellent damping properties. Until now, its use was limited to machine beds due to its comparatively low tensile strength. Its use in moving structural components has not been possible until now. Recent research results have shown that this challenge can be met by integrating prestressed carbon fibers. Until now, the production of samples out of prestressed fiber-reinforced polymer concrete has been carried out according to fixed specifications. It is not yet clear whether these specifications are suitable to fully exploit the potential of the material. Samples manufactured to these specifications show at least a large scatter in bending stiffness. Within the scope of this paper, the existing manufacturing process is validated by the variation of process steps. Specifically, this involved the use of a shaker, variation of the dwell time in the mold, variation of the resin content, and the procedure for impregnating the fibers. The characterization of the samples showed that the scatter could only be reduced by increasing the dwell time. However, this leads to a decrease in bending stiffness and, thus, is not suitable for further improvement of the novel material.Item Open Access Textile-based coils for inductive wireless power transmission(2021) Micus, Sebastian; Padani, Laura; Haupt, Michael; Gresser, Götz T.We developed and evaluated different textile-based inductive coils for near-field wireless power transmission. The technology uses electromagnetic induction for the contactless transfer of electrical energy. Therefore, we investigated various methods for the attachment of conductive materials on a textile-based material and the production of textile-based coils based on QI standard. Afterwards, the textile-based coils were examined and evaluated due to their specific quality characteristics. This happens by calculating the transmission quality and the maximum efficiency of the system which enables comparison of different coil systems and indicates the transmission efficiency of the systems.Item Open Access Deformation behavior of elastomer-glass fiber-reinforced plastics in dependence of pneumatic actuation(2021) Mühlich, Mona; González, Edith A.; Born, Larissa; Körner, Axel; Schwill, Lena; Gresser, Götz T.; Knippers, JanThis paper aims to define the influencing design criteria for compliant folding mechanisms with pneumatically actuated hinges consisting of fiber-reinforced plastic (FRP). Through simulation and physical testing, the influence of stiffness, hinge width as well as variation of the stiffness, in the flaps without changing the stiffness in the hinge zone, was evaluated. Within a finite element model software, a workflow was developed for simulations, in order to infer mathematical models for the prediction of mechanical properties and the deformation behavior as a function of the aforementioned parameters. In conclusion, the bending angle increases with decreasing material stiffness and with increasing hinge width, while it is not affected by the flap stiffness itself. The defined workflow builds a basis for the development of a predictive model for the deformation behavior of FRPs.Item 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.