Dipl.-Ing. Robert Wegner

Abstract

This study presents a design workflow for braided 3D branched structures composed of fiber-reinforced polymer (FRP), integrating both, global coarse and local refined stages. The algorithm begins with an iterative coarse-resolution process that optimizes key design parameters -- such as branch valency, node positions, and branch cross-sections -- in response to applied loads. The resulting global data model is transferred to a fine-resolution local domain, where branch and node geometries are refined and reinforced with braided FRP hulls to ensure efficient load transfer. The algorithm determines the optimal number of branches and adjusts their cross-sections to effectively meet structural demands. Node positions are further updated using the Force Density Method. Finally, the geometry of the interconnected nodes and branches is optimized to maximize load-carrying capacity while accommodating the fabrication constraints of the braiding technique. This approach establishes a framework for the design of braided 3D branched systems, paving the way for the next generation of lightweight structures.

Abstract

Climate change necessitates exploring innovative geoengineering solutions to mitigate its effects---one such solution is deploying planetary sunshade satellites at Sun--Earth Lagrange point 1 to regulate solar radiation on Earth directly. However, such long-span space structures present unique technical challenges, particularly structural scalability, on-orbit manufacturing, and in-situ resource utilization. This paper proposes a structural concept for the sunshade's foil support system and derives from that a component-level modular system for long-span fiber composite lightweight trusses using coreless filament winding. Within a laboratory-scale case study, the component scalability, as well as the manufacturing and material impacts, were experimentally investigated by bending deflection testing. Based on these experimental results, FE models of the proposed structural concept were calibrated to estimate the maximum displacement and mass of the foil support structure, while comparing the influences of foil edge length, orbital load case, and material selection.

Abstract

Polymer 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.

Abstract

Mineral cast, also referred to as polymer concrete, is a type of composite material commonly used in the construction of machine tools. It consists of mineral fillers and a thermosetting matrix and is used as an alternative to grey cast iron due to its improved damping properties, lower thermal expansion and density. However, due to its poor tensile and bending properties, it is not suitable for use in load-bearing or moving machine components. In order to open up such components as further application possibilities and to be able to use the advantages of mineral cast, the tensile properties must be improved. In order to achieve the durable bearing of tensile loads, prestressed carbon fibre reinforcements are investigated. The presented research aims to enhance the tensile properties of mineral cast through the integration of pre-stressed carbon fibre reinforcements. The study investigates the suitability of using rovings in contrast to pultruded rods for this application. The adhesion of the reinforcement within the mineral cast is evaluated with pull-out tests, and the impregnation behavior of prestressed rovings in the mineral cast is examined through micrographs. Results from the tests indicate that the pull-out forces of rovings are more than 200 \% higher than those of comparable rods with the same fibre content. However, prior consolidation of the rovings is necessary for complete impregnation.