Additive Manufactured Structures for the 12U Nanosatellite ERNST

One of the emerging technologies in recent years is additive manufacturing. It promises unprecedented design freedom in both modeling and rapid manufacturing. We are reaping the benefits of additive manufacturing for our 12U nanosatellite ERNST by printing the optical bench that supports the spacecraft payloads. We design the structures by using a finite-element numerical approach for optimizing the topology with respect to 1) available design space, 2) payload interfaces, 3) mechanical launch loads, and 4) thermal loads generated by the cryocooler of the MWIR main payload. We cope with the latter by integrating a pyramidal structured radiator surface in the optical bench as a functional element. Making use of the selective laser melting technique, we manufactured the first version of the optical bench for the engineering model of the ERNST spacecraft from AlSi10Mg alloy. Vibrational testing proved the suitability of our multidisciplinary design approach and the production quality. We are currently implementing the next version of the ERNST optical bench including spacecraft design changes and using Scalmalloy®, a material developed for additive manufacturing that provides high tensile strength and low thermal expansion. This marks a next step on the way to the application of additive manufactured components in space

The macroscopic behavior of pantographic sheets depends mainly on their microstructure: experimental evidence and qualitative analysis of damage in metallic specimens

Recently the exotic properties of pantographic metamaterials have been investigated, and various mathematical models (both discrete and continuous) have been introduced. However, the experimental evidence available up to now concerns only polyamide specimens. In this paper, we use specimens printed using metallic powder. We prove experimentally that the main qualitative and quantitative features of pantographic sheets in planar deformation are independent of the constituting materials, at least when they can be regarded as homogeneous and isotropic at micro-level. Of course, the absolute value of Young’s modulus of constituent material affects the overall reaction force needed to the hard device to impose a given displacement: A first investigation on this effect is also attempted

Towards flight qualification of an additively manufactured nanosatellite component: Paper presented at 69th International Astronautical Congress, Bremen, Germany, October 1-5, 2018

Fraunhofer EMI is currently designing a 12U nanosatellite. The mission is called ERNST (Experimental Spacecraft based on Nanosatellite Technology) and its main goal is to evaluate the utility of a nanosatellite mission for scientific and military purposes. As spacecraft developments demand the adaption of different subsystems for every mission, Fraunhofer EMI decided to use Additive Manufacturing (AM) in the construction of secondary satellite structures in order to achieve a highly adjusted structure which serves the exact required purpose of each individual mission. The significant advantage of using AM lies in the design freedom as it has almost no design restrictions as compared to conventional manufacturing methods. Given this, the design freedom can be used to implement a numerical optimization process, using topology optimization algorithms. During the optimization process, material is only placed at necessary areas. A Multidisciplinary Design Optimization for the optical mounting structure (optical bench) of the satellite was established, considering vibrational boundary conditions during the launch period and thermal boundary conditions during the operational phase. This paper presents the latest updates towards flight qualification of the optical bench in terms of design, optimization model and post-process concepts

Micro- and macrostructural investigations of AlSiMg produced by laser beam melting

In Laser Beam Melting (LBM), alloys like AlSi10Mg are locally melted by an intense laser beam. Specifically Designed Materials can be realized by locally varying the exposure parameters and applying diverse exposure strategies. By this approach, different micro- and macrostructures can be obtained that lead to individual mechanical properties within one part. A well-established understanding of the correlation between manufacturing parameters, generated micro- and macrostructure and resulting material properties enables the creation of complex microstructural material compositions meaning specifically Designed Materials. The interdependency of manufacturing parameters on the micro- and macrostructure was studied for different exposure strategies in LBM processing of AlSi10Mg using a 1 kW laser source and building layers of 90 μm. The investigations focus on the analysis of data obtained by imaging techniques like light and scanning electron microscopy. In particular, melt pool boundaries and crystal grains are examined

Nachhaltigkeit der Additiven Fertigung: Vergleichende ökonomische und ökologische Bewertung von additiven und konventionellen Fertigungstechnologien

Additive Fertigungsverfahren (Additive Manufacturing, AM) bieten aufgrund der schichtweisen Generierung von Strukturen eine einzigartige Designfreiheit. Auch die Flexibilität, die Möglichkeit der Funktionsintegration, die Individualisierungsmöglichkeit sowie beschleunigte Innovationszeiten machen die AM zu einer Schlüsseltechnologie der Industrie 4.0. In der vorgestellten Studie geht es um die künftige Anwendung von AM, insbesondere hinsichtlich der Energie- und Ressourceneffizienz sowie der Wirtschaftlichkeit dieser Technologie

The D-MEN sampling device - extracting and collecting asteroid material for sample return: Paper presented at the 68th International Astronautical Congress, IAC 2017, Adelaide, Australia, 25-29 September 2017

We report about the development and the characteristics of a Device for Material Extraction from Near earth objects (D-MEN). The D-MEN sampling device was developed as part of the NEOShield-2 project and is optimized to collect at least 100 grams of asteroid material including up to 4 cm sized particles. The design drivers are a short static landing scenario and the required capability to not only collect loose particles, but also to extract material from solid surfaces having compressive strengths of up to 50 MPa. This performance is achieved by a combination of fluidizing loose regolith material and extracting solid material by pyrotechnically driven bolt actuators. The D-MEN is a highly integrated system including two bolt actuators, two self-closing material compartments and a pressure pipe system. 3D metal printing technologies have been applied to implement the system in a cylindrical volume of 150 mm diameter by 130 mm high. The performance of the system is demonstrated here by comprehensive tests on different target configurations

Design Concepts and Performance Characterization of Heat Pipe Wick Structures by LPBF Additive Manufacturing

Additive manufacturing offers a wide range of possibilities for the design and optimization of lightweight and application-tailored structures. The great design freedom of the Laser Powder Bed Fusion (LPBF) manufacturing process enables new design and production concepts for heat pipes and their internal wick structures, using various metallic materials. This allows an increase in heat pipe performance and a direct integration into complex load-bearing structures. An important influencing factor on the heat pipe performance is the internal wick structures. The complex and filigree geometry of such structures is challenging in regards to providing high manufacturing quality at a small scale and varying orientations during the printing process. In this work, new wick concepts have been developed, where the design was either determined by the geometrical parameters, the process parameters, or their combination. The wick samples were additively manufactured with LPBF technology using the lightweight aluminum alloy Scalmalloy®. The influence of the process parameters, geometrical design, and printing direction was investigated by optical microscopy, and the characteristic wick performance parameters were determined by porosimetry and rate-of-rise measurements. They showed promising results for various novel wick concepts and indicated that additive manufacturing could be a powerful manufacturing method to further increase the performance and flexibility of heat pipes

A parametric mesostructural approach for robust design of additive manufacturing parts

Additive Manufacturing (AM) allows for production of potentially complex design solutions and motivates the use of Structural Optimization tools in product development to chase the structural limit of a design problem and its solution concept. Scratching on the limits of the material strength, design solutions can lack robustness concerning simplifications in model assumptions and uncertainties. However, the design freedom with AM can also actively be used to enhance robustness and reliability of solutions. To this end, an approach is presented that introduces Parametric Mesostructures into selective areas of the Additive Design. Structural members and coherent mechanical characteristics of these mesostructures can significantly reduce local stress peaks and can account for uncertainties, e.g. direction of load application. Their design is motivated by Structural Optimization and analysis results. Implementation of the approach is demonstrated and discussed on the example of a structural aircraft component

2D Numerical Simulation of Auxetic Metamaterials Based on Force and Deformation Consistency

International audienceThis work showcases a novel phenomenological method to create predictive simulations of metallic lattice structures. The samples were manufactured via laser powder bed fusion (LPBF). Simulating LPBF-manufactured metamaterials accurately presents a challenge. The printed geometry is different from the CAD geometry the lattice is based on. The reasons are intrinsic limitations of the printing process, which cause defects such as pores or rough surfaces. These differences result in material behavior that depends on the surface/volume ratio. To create predictive simulations, this work introduces an approach to setup a calibrated simulation based on a combination of experimental force data and local displacements obtained via global Digital Image Correlation (DIC). The displacement fields are measured via Finite Element based DIC and yield the true local deformation of the structure. By exploiting symmetries of the geometry, a simplified parametrized simulation model is created. The simulation is calibrated via Response Surface Methodology based on nodal displacements from FE-DIC combined with the experimental force/displacement data. This method is used to create a simulation of an anti-tetrachiral, auxetic structure. The transferability and accuracy are discussed, as well as the possible extension into 3D space