Proceedings of the Munich Symposium on Lightweight Design 2020

Engineers have always faced the challenge of solving conflicting objectives such as high stiffness combined with high damping. Structurally optimised components are used, especially by pushing lightweight construction. This design adaptation of component mass and stiffness generally has a negative effect on the dynamic component properties, as both the natural frequencies are shifted and component damping is reduced. In the majority of applications, the resulting vibrations are undesirable and must be reduced by suitable mechanisms. For example, vibrations in the vehicle can lead to a reduction in driving comfort or to a reduced service life.

One approach to solving conflicting objectives is the targeted integration of effects into components through additive manufacturing. In this paper, the effect-engineering on a laser beam melted motorcycle triple clamp is illustrated. The triple clamp is a highly dynamically loaded structural component where unwanted vibrations occur due to road unevenness, leading to critical hand-arm vibrations. This paper focuses on the simulative design of the triple clamp. The triple clamp is topology-optimised and extended by the effect of particle damping, so that the component is optimised in terms of stiffness, damping and mass. The optimisation also makes it possible to achieve a high degree of functional integration by saving 20 components. The effect of particle damping is experimentally evaluated by preliminary studies, which show that component damping can be increased by up to a factor of 20. The laser powder bed fusion (LPBF) makes it possible to store unmelted powder in the interior of the component in a targeted manner and thus produce particle-damped structures inside the triple clamp.

Polygon meshes and particularly triangulated meshes can be used to describe the shape of different types of geometry such as bicycles, bridges, or runways. In engineering, such polygon meshes can be supplied as finite element meshes, resulting from topology optimization or from laser scanning. Especially from topology optimization with low member size settings, frame-like polygon meshes with slender parts are typical and often have to be converted into a CAD (Computer-Aided Design) format, e.g., for further geometrical detailing or performing additional shape optimization. Especially for such frame-like geometries, CAD designs are constructed as beams with cross-sections and beam-lines, whereby the cross-section is extruded along the beam-lines or beam skeleton. In our research, automatic parameterization of polygon meshes into a subdivision surface representation is tried out. For this purpose, the beam-lines are approximated by computation of curved skeletons, which are determined by a homotopic thinning method. These skeleton lines are transformed into a subdivision surface control grid by using the Euclidean distance transformation.

Through continuous topology optimization the design within product development of structural loaded components is enhanced by using maximized lightweight potential. At the same time the product development process is accelerated due to a reduced number of design cycles. Because topology optimization yields an optimized material distribution, the designer is not required anymore to iteratively work out the basical geometric shape. However, optimized material distribution itself neither follows design rules, nor does it provide parametric relations within parts. Instead, a redesign has to be done in order to fulfill manufacturing requirements and to obtain a parametric CADmodel. This takes effort in time and expert knowledge.

For the reason of a consistent development approach under assistance of computer aided methods, a concept is presented, that is demanded to solve the task of redesigning topology optimization results in parametric CAD-models in a semi-automated manner. To achieve this, medial axis skeletons are used for analyzing the geometric data firstly, and, in a second step, for rebuilding CADmodels. They are taken as references for common CAD-functionality whereby a parametric and history-based modeling structure is generated. Though open challenges exist in further automation and consideration of manufacturing techniques, this represents a basical approach on how to use the medial axis for reconstruction.

CHIME (Copernicus Hyperspectral Imaging Mission for the Environment) is part of ESA’s Sentinel Expansion Program for which OHB System AG in Oberpfaffenhofen, Germany has been selected as the instrument prime contractor. In this paper we present the development of the ultra-stable stiffness architecture for the instrument structure. Backed by a trade study of different structural concepts with a focus on the opto-mechanical decoupling, assembly integration and test accessibility, and the demanding optical performance criteria, we derive a robust solution: The main stiffness element is a central monolithic CFRP (Carbon Fiber Reinforced Plastic) torus, on which several sub-elements are mounted for precise positioning of the highly-sensitive optical elements, creating a modular 3D optical bench. We demonstrate the use of topology optimization for design concept finding considering mass and performance criteria. The paper concludes with the results from a breadboard test campaign and an outlook on the next development steps.

Reducing the weight of a system leads to lower forces being exerted, which in turn allows for lower requirements and an even lighter system. This “virtuous circle of lightweight engineering design” can especially be present when designing dynamic systems. Design optimization is a tool to enable and exploit this favorable phenomenon. This work introduces a unified approach to reap the benefits of optimally designed lightweight systems in structural dynamics and multibody dynamics. An efficient gradient-based optimization framework has been implemented and this is explained and demonstrated. The centerpiece of this optimization methodology is the design sensitivity analysis applied to the time integration with a nonlinear solver. A semi-analytical approach is chosen to balance computational effort and implementation effort, where the sensitivities are derived via direct differentiation with numerical differences for the sensitivities of the system parameters. Nomenclature is introduced to simplify these equations for a more lucid description showing the intrinsic equivalence of the solving routines of structural dynamics and multibody dynamics. The method is shown on the practical example for the optimal design of a hydraulic engineering mechanism.

Machining of fiber reinforced composites remains a challenging process at the end of the value chain. Malfunctions of machinery and bad surface quality cause a tremendous loss of value and need to be reduced to increase competitiveness in lightweight applications. Monitoring of machining steps can be carried out by many different techniques and strategies all with their unique benefits and drawbacks. These provide information about machining hours, wear status of the tool, potential malfunctions of the system and can estimate the quality of the machining process. This contribution presents an approach to fuse different sensing systems on the hard- and software side to combine the information of different systems that provide a consolidated basis for the analysis of the machine status, tool status and machining quality. To this end we present results from a sensor fusion approach to measure acoustic information during the machining and the software framework UHU that was developed to provide a blueprint for a real-time capable environment for CNC feedback control and machining quality documentation.

To produce hollow-shaped, lightweight composite structures made out of fiber reinforced polymers (FRP), many manufacturing processes require a shape-giving tooling in form of a core. Additive manufacturing (AM) offers the potential to fabricate such tools and production aids with increased geometric complexity and functionality at reduced costs and lead time. An AM core can remain inside the produced composite part and provide additional functionality such as the integration of metallic inserts. A core can also be removed from the final composite part to reduce the part mass. To enable the removal of a core, a promising approach is to use AM to design and produce a core in form of thinwalled shell that integrates breaking lines. After curing of the composite part, the breaking lines are used to break and disassemble the core into smaller patches, which are removed through an opening of the cured composite part. To stabilize the core shell during composite production, it is filled with a filler material such as salt. Although AM break-out cores offer many benefits, only a limited amount of works exists that study such cores. Therefore, this work contributes novel concepts for the design of AM break-out cores. The focus lies on the use of perforated and continuous breaking lines to enable a controlled fracture of cores. A case study demonstrates their application to produce parts of a motorcycle including the flow intake and tank structure. After the case study, the work discusses possible improvements and outlines future research directions.

Auf dem globalen Automobilmarkt stellen Brennstoffzellenfahrzeuge im Vergleich zu Batterieelektrofahrzeugen immer noch ein Nischenprodukt dar. Neben einem dünnen Tankstellennetz, das sich erst im Aufbau befindet, ist ein hoher Fahrzeugpreis einer der Gründe dafür. Ein großes Potenzial für Kostenreduktion birgt die Nutzung gemeinsamer Fahrzeugarchitekturen für batterieelektrische sowie mit Wasserstoff betriebene Fahrzeuge, um Skaleneffekte in der Entwicklung und Produktion nutzen zu können. Die Nutzung gleicher Bauräume für die Antriebskomponenten und Energiespeicher ist dafür eine Grundvoraussetzung. Für zukünftige Brennstoffzellenfahrzeuge bedeutet dies eine Integration der Wasserstoffdruckbehälter in die flachen Batteriespeicherbauräume im Fahrzeugunterboden. Im Zuge dessen werden Tankkonzepte basierend auf zylindrischen Druckbehältern untersucht. Besondere Herausforderungen stellen dabei das Fertigungsverfahren sowie die Permeation dar. Eine erste Potenzialabschätzung für das Speichervolumen zeigt die Umsetzbarkeit kundenrelevanter Fahrzeugreichweiten. Als alternatives Konzept werden nahezu quaderförmige Druckbehälter mit Zugverstrebung im Inneren untersucht. Ein neuartiges Fertigungsverfahren wurde für die Herstellung entwickelt und anhand eines Baumusters validiert. Eine Potenzialabschätzung für die Speicherkapazität zeigt im Vergleich zur Variante mit zylindrischen Komponenten ein ca. 25% höheres Wasserstoffvolumen. Die Technologie befindet sich allerdings noch im Forschungsstadium.

Im Rahmen der vom Bundeswirtschaftsministerium geförderten BRYSON Projektgruppe (BauRaumeffiziente HYdrogenSpeicher Optimierter Nutzbarkeit) wird an der Hochschule München an einem zugverstreben Wasserstofftank für PKW mit Brennstoffzellenantrieb geforscht, der effizient in die Unterbodenstruktur integriert werden kann. Die Untersuchungen zeigen die grundlegende Machbarkeit eines flachen, kubischen Drucktanks mit innerer Zugverstrebung. Wesentliche Aspekte, wie das Tragverhalten bei hoher Strebenanzahl, Dichtigkeit und Fertigbarkeit konnten untersucht und analysiert werden.

This paper covers new and paradigm changing findings in analysis, optimization, design and manufacturing of endless fiber composites as developed by an international group of experts in research and industry inspired and driven by Prof. em. Stephen Tsai. This was presented at the 2019 Munich Lightweight Symposium and is added to the 2020 proceedings as an introduction of the application as presented by Neuhäusler in this year’s symposium [7]. The fundamental finding used for the new concepts is the normalizing property of the trace of the stiffness matrix of a unidirectional ply as an invariant material property of plies and laminates. This as a basis enables the use of variable ply angles, a so-called Double-Double architecture of sub-laminates and many more. Much simpler stackings, less design rules to follow, increased strength of laminates, thinner minimum gages, simplified optimization and easier and cost-efficient manufacturing can be obtained.

This work includes the application and evaluation of new methods to describe laminate stiffness and strength. Tsai et al. have shown that the trace of laminate stiffness is a rotationally invariant quantity and accurately describes the stiffness potential of a material [1]. In combination with a rotationally invariant strength criterion, the Unit Circle criterion, this allows a simple approach for the dimensioning of fiber composite structures [2]. The use of two biaxial, so called “double-double” [±ϕ/±ψ] sublaminates with the possibility of asymmetrical stacking sequences but homogenization of laminates further simplifies the design and manufacturing process of such structures [3].

The principles mentioned above are applied as an example for the optimization of an aerospace wing box. They are compared with classical optimization algorithms, an Evolutionary Algorithm (EA) and the Adaptive Response Surface Method (ARSM) [4]. The wing box is optimized with respect to stiffness while simultaneously minimizing weight. It is shown that the use of [±ϕ/±ψ] sublaminates instead of the traditional [0/±45/90] sublaminates can lead to a weight reduction of the composite skins of more than 10%. The simplified search algorithm based on the principles of Tsai et al. yields a different sublaminate than the classical optimization methods EA and ARSM. The computational effort though can be significantly reduced with the former.