Dr.-Ing. Pascal Mindermann

Zusammenfassung

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.

Zusammenfassung

The linear design workflow for structural systems, involving a multitude of iterative loops and specialists, obstructs disruptive innovations. During design iterations, vast amounts of data in different reference systems, origins, and significance are generated. This data is often not directly comparable or is not collected at all, which implies a great unused potential for advancements in the process. In this paper, a novel workflow to process and analyze the data sets in a unified reference frame is proposed. From this, differently sophisticated iteration loops can be derived. The developed methods are presented within a case study using coreless filament winding as an exemplary fabrication process within an architectural context. This additive manufacturing process, using fiber-reinforced plastics, exhibits great potential for efficient structures when its intrinsic parameter variations can be minimized. The presented method aims to make data sets comparable by identifying the steps each data set needs to undergo (acquisition, pre-processing, mapping, post-processing, analysis, and evaluation). These processes are imperative to provide the means to find domain interrelations, which in the future can provide quantitative results that will help to inform the design process, making it more reliable, and allowing for the reduction of safety factors. The results of the case study demonstrate the data set processes, proving the necessity of these methods for the comprehensive inter-domain data comparison.

Zusammenfassung

Despite all current efforts, climate change is the greatest challenge of the 21st century. Since existing measures will fail to prevent critical tipping points from being reached, in addition to terrestrial geoengineering methods, efforts are underway to explore new ways to implement space-based geoengineering methods into the short-term construction of a buffer solution - the International Planetary Sunshade (IPSS). The IPSS system reduces solar irradiation mitigating the global mean temperature rise while offering a sustainable energy supply. The developement of the system poses multifaceted challenges only to be mastered by a collaboration of space agencies and private companies, while supported by society. Therefore, tackling the IPSS within international roadmaps is essential to exploit synergies, shorten development time, and promote international cooperation. An evolutionary concept achieves stepwise Earth independence by utilizing lunar resources. The feasibility of the IPSS also depends on the foil’s supporting structure. Therefore, a lightweight manufacturing technology that meets several criteria, such as scalability, adaptivity, material compatibility, full automation, on-orbit manufacturing, in-situ resource utilization, and digital design including function integration, must be adopted. Hence, coreless filament winding (CFW) may be a suitable technology for realizing the demanded mass savings. The prerequisite for the superiority of CFW structures is an application- and material-compliant component and fiber net design. Previous experience with CFW cannot be directly transferred to the IPSS system due to the changed requirements for space application. This paper will present a systematic design concept for the IPSS, initially exploring a CFW support structure by discussing segmentation and modularity, proposing a new connection system, and implementing function integration.

Zusammenfassung

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.

Zusammenfassung

Digitization and automation are essential tools to increase productivity and close significant added-value deficits in the building industry. Additive manufacturing (AM) is a process that promises to impact all aspects of building construction profoundly. Of special interest in AM is an in-depth understanding of material systems based on their isotropic or anisotropic properties. The presented research focuses on fiber-reinforced polymers, with anisotropic mechanical properties ideally suited for AM applications that include tailored structural reinforcement. This article presents a cyber-physical manufacturing process that enhances existing robotic coreless Filament Winding (FW) methods for glass and carbon fiber-reinforced polymers. Our main contribution is the complete characterization of a feedback-based, sensor-informed application for process monitoring and fabrication data acquisition and analysis. The proposed AM method is verified through the fabrication of a large-scale demonstrator. The main finding is that implementing AM in construction through cyber-physical robotic coreless FW leads to more autonomous prefabrication processes and unlocks upscaling potential. Overall, we conclude that material-system-aware communication and control are essential for the efficient automation and design of fiber-reinforced polymers in future construction.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

Natural structural systems that have developed over millions of years illustrate how large loads can be absorbed with very little material. This is achieved by adapting the structural properties to a predominant load profile. If we succeeded in transferring these principles to structures created by people, it would be possible to significantly reduce the consumption of resources in the construction industry. As a contribution to this, the Rosenstein Pavilion was developed based on bio-inspired optimization strategies in order to demonstrate the potential of resource-efficient building.

Zusammenfassung

Nature creates efficient, complex structures using the smallest possible amount of material. The construction principles employed and the intelligent use of materials regarding their specific properties can be transferred to modern production methods. The objective is to produce functional low-weight building components that consume as few resources as possible. In this chapter we show how this bionic transfer takes place by continuing the development of production methods, such as fiber technology (pultrusion, fiber deposition), 3D printing, the manufacture of concrete components, and a combination of these three methods.

Zusammenfassung

Fiber-reinforced materials offer a large improvement in structural performance if specific load cases can be determined. In aerospace, lightweight structures are crucial because of launcher limitations. For academic purpose CubeSats are a powerful concept to participate in space research on a low-cost-level. Reducing the structural mass, while keeping the mechanical performance, provides a bigger payload mass budget. Additionally, there are several types of payloads that do not fit in common structural components. Inasmuch as CubeSats are mainly used in research, such systems change substantially, so that an easily adaptive method would be beneficial to be no longer restricted by prefabricated structural components. The developed rapid prototyping technology tackles these issues by having an automated 3D deposi- tion method which can produce extremely lightweight as well as geometrical- and load-adaptive primary structures with minimum space requirements. A fiber deposition head for a six-axis robot has been devel- oped to impregnate and wind a single carbon roving on a frame to produce 3D integral components. The geometry of the frame can be adjusted to the required application by introducing holes or attachment points at nearly any position. Its modular layout varies, so that it only can be fabricated economically by fused deposition modeling and removed after resin curing easily. Furthermore, by blending additives into the resin it is possible to create material gradient components. Hence adaptiveness can be generated e.g. in terms of solar energy absorption. Compared with 1U aluminum wall structures available on market a carbon fiber-reinforced plastics (CFRP) winded structure results in a mass saving of 45% for a solid and 76% for a skeletonized wall segment, premised on calculations for two layers of CFRP made of 24K rovings with a fineness of 1600 tex at a fiber-volume-fraction of only 50%. This concludes that maximum potential can only arise with optimized fiber path generation. Costs can be saved in terms of material (no fiber blend), molding (3D printed frame), design of fiber path (sys- tematic guidelines), assembly (integral design) and manufacture (robotic production). The advantages will be demonstrated with a generic non-in-situ-sensory 1U CubeSat because it is easy to compare it to other systems due to the strict design specifications. The paper will include detailed information on the design of the robotic fiber deposition head, the modular and adjustable frame, the winding pattern generation and the mechanical testing.

Zusammenfassung

The goal of the Optical Coatings Ultra Lightweight Robust Spacecraft Structures (OCULUS) project is to develop a high-quality metallization process for surface modification of high precise carbon fiber reinforced plastics (CFRP) structures. As a joint research project between the Institute of Space Systems at Technical University of Braunschweig, Invent GmbH and the Fraunhofer Institute for Surface Engineering and Thin Films (IST) the technology enables the construction of space-suitable, lightweight and cost-effective refractors, which allows a drastic mass reduction of mirrors in the application for space telescopes. The state-of-the-art of conventional telescopes operated on ground as well as in space uses mirror materials with high density, such as metal or ceramics, which are the main contributor to overall system mass. The aperture diameter is proportional to the optical performance of the system and is limited by the launcher. A mass reduction and deployment of mirror segments can increase the performance of such a system. Within the OCULUS project the mirror mass can be reduced by a minimum of 80%. This paper introduces a detailed overview of the demonstrator design with special focus on the mechanism that deploys and aligns the primary and secondary mirror. A design trade-off will be summarized and the dependencies of the mechanical positioning mechanism will be discussed. Followed by a description of the optical system, the internal working process and autonomous control to align the mirror. This leads to the detailed design of the deployment and alignment mechanism with respect to the other satellite subsystems as well as the overall volume-, mass- and energy-budget. The positioning accuracy and resulting optical performance of the space telescope for Earth observation will be estimated. In addition a testing environment to proof the shown concept and assess the optical system and its alignment accuracy is proposed. Concluding a conceptual design to demonstrate the functionality of the deployment mechanism independently of alignment mechanism in microgravity tests is derived.

Zusammenfassung

The favorable properties of carbon fiber reinforced plastics (CFRP) are well-known in aerospace engineering. Strength and stiffness can be optimized due to the use of fiber reinforcements within the com- posite material. Additionally, being very light-weight and featuring a temperature expansion coefficient that is scalable to near zero, CFRP structures enjoy a great popularity and are often the means of choice for future satellite missions. The OCULUS (Optical Coatings Ultra Lightweight Robust Spacecraft Structures) project aims at even widen the use spectrum of the material by developing a coating technology that allows for adjusting the surface properties of CFRPs. While the current focus is on reflectivity, other properties, such as low coefficients of friction, wear resistance, and electric conductivity, are possible. The Oculus- Cube is a CubeSat sized technology demonstrator that will show the scalability of the technology from large main mirrors of space telescopes to small optical apertures on 1U-2U spacecraft.

Zusammenfassung

This paper presents the design and test of a docking mechanism that is based on mushroom-shaped dry adhesives as well as a theoretical assessment of highest achievable adhesion. The presented mechanism is adaptable to different target geometries, reusable, switchable, and robust to loads in any direction with espect to the target surface. The design of the mechanism is based on a detailed trade-off of different concepts to apply the adhesives, supporting the most suitable design for the requirements on which the trade-off is based. Tests have been conducted with an engineering model in a laboratory environment. Preliminary tests have already shown the functionality of the mechanism to attach to a smooth planar object, lift, move, and subsequently release it without applying strong disturbing forces. In additional tests, the influence of curvature, load angle and macroscopic contact splitting on the mechanism’s adhesion has been analyzed.