Mr. Sebastian M. Geier Profile

Sebastian M. Geier

Student at Deutsches Zentrum für Luft- und Raumfahrt eV

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Publications (11)

Proceedings Article | 20 April 2016 Presentation + Paper

Experimental and finite element analyses of multifunctional skins for morphing wing applications

Sebastian Geier, Markus Kintscher, Thorsten Mahrholz, Peter Wierach, Hans-Peter Monner, Martin Wiedemann

Proceedings Volume 9803, 980328 (2016) https://doi.org/10.1117/12.2219357

KEYWORDS: Composites, Skin, Nose, Aerodynamics, Manufacturing, Glasses, Carbon, Metals, Kinematics, Integration

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As a consequence of operational eﬃciency because of rising energy costs, future transport systems need to be mission-adaptive. Especially in aircraft design the limits of lightweight construction, reduced aerodynamic drag and optimized propulsion are pushed further and further. The ﬁrst two aspects can be addressed by using a morphing leading edge. Great economic advantages can be expected as a result of gapless surfaces which feature longer areas of laminar ﬂow. Instead of focusing on the kinematics, which are already published in a great number of varieties, this paper emphasizes as major challenge, the qualiﬁcation of a multi-material layup which meets the compromise of needed stiﬀness, ﬂexibility and essential functions to match the ﬂight worthiness requirements, such as erosion shielding, impact safety, lighting protection and de-icing. It is the aim to develop an gapless leading edge device and to prepare the path for higher technology readiness levels resulting in an airborne application. During several national and European projects the DLR developed a gapless smart droop nose concept, which functionality was successfully demonstrated using a two-dimensional 5 m in span prototype in low speed (up to 50 m/s) wind tunnel tests. The basic structure is made of commercially available and certiﬁed glass-ﬁber reinforced plastics (GFRP, Hexcel Hexply 913). This paper presents 4-point bending tests to characterize the composite with its integrated functions. The integrity and aging/fatigue issues of diﬀerent material combinations are analyzed by experiments. It can be demonstrated that only by adding functional layers the mentioned requirements such as erosion-shielding or de-icing can be satisﬁed. The total thickness of the composite skin increases by more than 100 % when required functions are integrated as additional layers. This fact has a tremendous impact on the maximum strain of the outer surface if it features a complete monolithic build-up. Based on experimental results a numerical model can be set up for further structural optimizaton of the multi-functional laminate.

Proceedings Article | 16 April 2016 Presentation + Paper

Actuation mechanisms of carbon nanotube-based architectures

Sebastian Geier, Thorsten Mahrholz, Peter Wierach, Michael Sinapius

Proceedings Volume 9802, 980214 (2016) https://doi.org/10.1117/12.2219341

KEYWORDS: Electrodes, Ions, Carbon nanotubes, Carbon, Scanning electron microscopy, Liquids, Electroactive polymers, Actuators, Smart materials, Ceramics

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State of the art smart materials such as piezo ceramics or electroactive polymers cannot feature both, mechanical stiﬀness and high active strain. Moreover, properties like low density, high mechanical stiﬀness and high strain at the same time driven by low energy play an increasingly important role for their future application. Carbon nanotubes (CNT), show this behavior. Their active behavior was observed 1999 the ﬁrst time using paper-like mats made of CNT. Therefore the CNT-papers are electrical charged within an electrolyte thus forming a double- layer. The measured deﬂection of CNT material is based on the interaction between the charged high surface area formed by carbon nanotubes and ions provided by the electrolyte. Although CNT-papers have been extensively analyzed as well at the macro-scale as nano-scale there is still no generally accepted theory for the actuation mechanism. This paper focuses on investigations of the actuation mechanisms of CNT-papers in comparison to vertically aligned CNT-arrays. One reason of divergent results found in literature might be attributed to diﬀerent types of CNT samples. While CNT-papers represent architectures of short CNTs which need to bridge each other to form the dimensions of the sample, the continuous CNTs of the array feature a length of almost 3 mm, along which the experiments are carried out. Both sample types are tested within an actuated tensile test set-up under diﬀerent conditions. While the CNT-papers are tested in water-based electrolytes with comparably small redox-windows the hydrophobic CNT-arrays are tested in ionic liquids with comparatively larger redox-ranges. Furthermore an in-situ micro tensile test within an SEM is carried out to prove the optimized orientation of the MWCNTs as result of external load. It was found that the performance of CNT-papers strongly depends on the test conditions. However, the CNT-arrays are almost unaﬀected by the conditions showing active response at negative and positive voltages. A micro alignment as result of tensile stress can be proven. A comparison of both results point out that the actuation mechanism strongly depends on the weakest bonds of the architectures: Van-der-Waals-bonds vs. covalent C-bonds.

Proceedings Article | 9 April 2015 Paper

Actuation-mechanisms of CNT-bucky papers and CNT-arrays

Sebastian Geier, Thorsten Mahrholz, Peter Wierach, Michael Sinapius

Proceedings Volume 9432, 94320H (2015) https://doi.org/10.1117/12.2084556

KEYWORDS: Electrodes, Carbon, Scanning electron microscopy, Liquids, Carbon nanotubes, Composites, Smart materials, Ultrasonics, Ions, Sodium

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In the fields of smart materials there is still a demand for a material featuring high modulus, low density and large strain. Carbon materials catch enormous scientific attention not only since carbon fibers were used for highperformance composite structures. But more and more the scientific attention moves from the macroscale to the nanoscale. This paper focuses with a adaptive point of view on one of the carbon allotropes: carbon nanotubes (CNTs). Beside excellent electromechanical properties another interesting feature was first mentioned 1999 - the active behavior of paper-like mats (bucky-papers) made of CNTs. CNT-papers are electrically activated using a double-layer interaction of ions provided by an electrolyte and the charged, high specific surface area of the paper formed by carbon nanotubes. Until now the detailed mechanism behind the strain/force generation of CNT-based architectures is unknown. A clarification of this principle reveals the potential of carbon tubes to be or not to be a resilient smart material in order to use their strong covalent carbon bonds instead of weak van der Waals force as tube-linking. This paper presents further investigations about the composition of CNT-papers and their performance in contrast to vertical aligned CNT-arrays using an actuated tensile test set-up. For better comparison the experiments of both specimen-types are carried out in dry, wet and wet/charged conditions. Especially in the case of CNT-arrays it is essential to preload the specimens because the curly CNT-structure superimposes the vertical orientation. While the CNT-paper is tested in an aqueous solution of one molar sodium chloride, the hydrophobic character of CNT-arrays requires an ionic liquid (IL) as electrolyte. It is found that the mechanical properties of CNT-papers drop significantly by wetting and can be controlled by charging what indicates an electrostatic dominated effect. In contrast the CNT-arrays show identical results regardless of the test conditions and furthermore an active, reversible behavior of tube elongation by charging. These results indicate strongly a quantum mechanical effect as reason of a CNT-array actuation.

Proceedings Article | 10 April 2013 Paper

Characterization of multifunctional skin-material for morphing leading-edge applications

Sebastian Geier, Markus Kintscher, Thorsten Mahrholz, Peter Wierach, Hans-Peter Monner, Martin Wiedemann

Proceedings Volume 8688, 868818 (2013) https://doi.org/10.1117/12.2009865

KEYWORDS: Metals, Adhesives, Skin, Interfaces, Aerodynamics, Glasses, Manufacturing, Failure analysis, Composites, Kinematics

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Proceedings Article | 9 April 2013 Paper

Strain measurements on scattered, highly oriented CNTs

Sebastian Geier, Thorsten Mahrholz, Johannes Riemenschneider, Peter Wierach, Michael Sinapius

Proceedings Volume 8691, 869110 (2013) https://doi.org/10.1117/12.2009855

KEYWORDS: Electrodes, Chemical analysis, Actuators, Liquids, Analytical research, Carbon, Silicon, Thermal effects, Smart materials, Ferroelectric materials

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Since carbon nanotubes (CNTs) have been discovered in 1991, worldwide scientific research reveals excellent properties. Most of the found properties refer to almost defect-free, single-walled carbon nanotubes (SWCNTs) with nano-scale dimensions. However, scientists try to incorporate CNTs into applications to transfer their features in order to push the specific performance. Typically the results are comparably lower than expected because of the varying quality of used CNTs. This paper presents results of research using CNTs as actuators. In contrast to published paper which analyzed architectures of entangled CNTs as active components, like papers or yarns, to measure their bulk-strain this paper focuses on scattered, highly aligned CNTs. This approach promises to clarify the effect of actuation, whether it is a quantum-mechanically, or rather an combined electrostatic volume-transfer effect. Two experimental set-ups are presented. The first experiment is carried out using highly aligned multi-walled CNTs (MWCNT-arrays). Their orientation is investigated intensively in comparison to other analyzed CNT-arrays. Furthermore their substrate consists of electrical conductive carbon. The CNT-array is optically analyzed along the longitudinal geometry of the vertically aligned MWCNTs. The interfaces of the set-up, which may influence the measurement, have been analyzed in order to avoid second-order effects like thermal swelling or chemical degradation. The results reveal comparable high deflections starting at an activation-voltage of ±1.75V. The ionic liquid is tested within a voltage-range of ±2V due to time-staple performance. The second presented results are found by using Raman-spectroscopy to analyze single SWCNTs. This paper presents the first results of the challenging test campaign to analyze single-walled nanotubes within an electrolyte during charging. A shifting of Raman-peaks according to the wavenumber can be directly attributed to a geometry-change. Thus, the two presented experiments uses aligned CNTs a driving actuation mechanism of single CNTs may be identified.

Proceedings Article | 28 March 2012 Paper

Investigation of aligned carbon nanotube architectures to understand the actuation mechanism

Sebastian Geier, Johannes Riemenschneider, Thorsten Mahrholz, Peter Wierach, Michael Sinapius

Proceedings Volume 8342, 83421G (2012) https://doi.org/10.1117/12.915269

KEYWORDS: Liquids, Ultrasonics, Carbon, Particles, Manufacturing, Carbon nanotubes, Actuators, Ions, Silicon, Composites

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Proceedings Article | 28 March 2012 Paper

Material characterization for morphing purposes in order to match flight requirements

Sebastian Geier, Markus Kintscher, Olaf Heintze, Peter Wierach, Hans-Peter Monner, Martin Wiedemann

Proceedings Volume 8341, 834113 (2012) https://doi.org/10.1117/12.915240

KEYWORDS: Composites, Nose, Skin, Metals, Aerodynamics, Manufacturing, Material characterization, Aerospace engineering, Interfaces, Climatology

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Natural laminar flow is one of the challenging aims of the current aerospace research. Main reasons for the aerodynamic transition from laminar into turbulent flow focusing on the airfoil-structure is the aerodynamic shape and the surface roughness. The Institute of Composite Structures and Adaptive Systems at the German Aerospace Center in Braunschweig works on the optimization of the aerodynamic-loaded structure of future aircrafts in order to increase their efficiency. Providing wing structures suited for natural laminar flow is a step towards this goal. Regarding natural laminar flow, the structural design of the leading edge of a wing is of special interest. An approach for a gap-less leading edge was developed to provide a gap- and step-less high quality surface suited for natural laminar flow and to reduce slat noise. In a national project the first generation of the 3D full scale demonstrator was successfully tested in 2010. The prototype consists of several new technologies, opening up the issue of matching the long and challenging list of airworthiness requirements simultaneously. Therefore the developed composite structure was intensively tested for further modifications according to meet requirements for abrasion, impact and deicing basically. The former presented structure consists completely of glass-fiber-prepreg (GFRP-prepreg). New functions required the addition of a new material-mix, which has to fit into the manufacturing-chain of the composite structure. In addition the hybrid composites have to withstand high loadings, high bending-induced strains (1%) and environmentally influenced aging. Moreover hot-wet cycling tests are carried out for the basic GFRP-structure in order to simulate the long term behavior of the material under extrem conditions. The presented paper shows results of four-points-bending-tests of the most critical section of the morphing leading edge device. Different composite-hybrids are built up and processed. An experimental based trend towards an optimized material design will be shown.

Proceedings Article | 28 April 2011 Paper

Fundamental investigations of carbon nanotubes working as actuators

Sebastian Geier, Thea Schnoor, Johannes Riemenschneider, Thorsten Mahrholz, Peter Wierach, Karl Schulte, Michael Sinapius

Proceedings Volume 7978, 79780O (2011) https://doi.org/10.1117/12.879838

KEYWORDS: Actuators, Liquids, Manufacturing, Carbon nanotubes, Ions, Composites, Solids, Analytical research, Scanning electron microscopy, Chemical analysis

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Excellent properties like low density, high mechanical stiffness as well as an outstanding thermal and electrical conductivity make researchers focusing on carbon nanotubes (CNTs) since years. Beside that it is found that structures made of CNTs can be actuated when they are set up like a capacitor. Usually two dimensional (2D) CNT-papers with randomly oriented CNTs, called Bucky-papers, are used. They are charged and divided by an electrically insulating but ionic conductible electrolyte. Experiments demonstrate low voltages for actuation (±1V). Although the mechanism of CNT-actuation is still an open issue theoretical studies suggest a charge and ion induced lengthening of the C-bonds, which predict theoretical strains up to 1%. These characteristics make CNTs a potential candidate for lightweight and powerful actuators of future adaptive aerospace applications. The presented work gives an overview of possible CNT-actuator configurations. Comprehensive analysis tools for 2D mats of randomly oriented CNTs have been developed to guarantee a consistent data base for the comparison of different CNT-configurations. It is focused on the electro-mechanical properties with respect to the processing and configuration of CNT-actuators. For a more efficient use of the mechanical advantages of the CNT-geometry a new aligning manufacturing approach is presented, to get highly oriented 2D CNT-papers. Their properties are compared with randomly oriented CNT-papers. Finally a new test set-up will be introduced, which enables deflection measurements directly on the top of vertically aligned CNTs (CNT-arrays). The buildup and necessary prework are shown, as well as results of the first experiments. The method of measuring along the axis of aligned CNTs qualifies this set-up to get a deeper understanding about the actuation mechanism of CNTs. Vertically aligned CNTs promise to be a more efficient actuator configuration because of their high stiffness in direction of actuation.

Proceedings Article | 27 April 2011 Paper

The preparation of a composite structure for a first large scale ground test of a smart and gapless wing leading edge

Olaf Heintze, Sebastian Geier, Daniel Hartung, Markus Kintscher

Proceedings Volume 7977, 79771K (2011) https://doi.org/10.1117/12.880596

KEYWORDS: Skin, Composites, Nose, Kinematics, Manufacturing, Failure analysis, Glasses, 3D modeling, Interfaces, Actuators

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Proceedings Article | 31 March 2010 Paper

Investigations of the key mechanism of carbon-nanotube actuators and their dependencies

Sebastian Geier, Johannes Riemenschneider, Thorsten Mahrholz, Peter Wierach, Michael Sinapius

Proceedings Volume 7644, 76441G (2010) https://doi.org/10.1117/12.847252

KEYWORDS: Actuators, Solids, Manufacturing, Carbon nanotubes, Ions, Thermal effects, Scanning electron microscopy, Capacitors, Single walled carbon nanotubes, Chemical analysis

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Future adaptable applications require electro-mechanical actuators with a high weight-related energy. Among modern multi-functional materials carbon nanotubes (CNTs) have some special characteristics which give them the potential to solve this demand. On the one hand raw CNTs have excellent mechanical properties like their low density (1330kg/m³) and very high estimated stiffness of about 1TPa. On the other hand CNTs have the ability under presence of ions, wired like a capacitor and activated by a charge injection to perform a dimensionchange (length of C-C bondings). Calculations and experiments present achievable active strains of 1% at low voltage of ±1V what qualifies CNT-based materials for leightweight powerful actuators. In this paper the former work done with actuators using CNT-containing mats and Nafion as solid electrolyte is evaluated by analyzing the two main-components in more detail. On the one hand the CNT-based modelmaterial SWCNT-mats called Bucky-paper (BP) and on the other hand ion donating electrolytes in liquid-phase like a NaCl-solution and its solid equivalent Nafion as thin-foils are tested. Additional methods of fabrication, preparation and characterization of the CNT-powder and the manufactured BPs containing randomly oriented single-walled carbon nanotubes (SWCNTs) are presented which provide a deeper system-understanding. Both materials (BPs and Nafion-foils) are intensively investigated in different deflection-test-rigs due to their structural assembly. This paper presents a method for electro-mechanical measurements of BPs in an in-plain test set-up which avoids sensing secondary effects like thermal expansion or mass-transport and confirm that BP-deflection should only be a capacity-driven effect. Nafion as solid electrolyte will be tested in an out-of-plane facility to measure its possible actuation within the lamellar-direction. With this approach the dependencies of each component and their individual characters on the deflection can be estimated. The active response can be referred to the internal structure of both components as well as of the whole structural assembly. The results give a certain direction to a BP-optimization referring to active strain, density, structural integrity and conductibility. In addition to these facts the active character of BPs using CNTs of different suppliers and Nafion is analyzed. These investigations are of particular importance for detection of global dependencies and using both materials in a hybrid-assembly like solid actuators which are needed for structural applications.

Proceedings Article | 6 April 2009 Paper

Solid electroytes for CNT-based actuators

Johannes Riemenschneider, Sebastian Geier, Thorsten Mahrholz, Jürgen Mosch, Hans Peter Monner, Michael Sinapius

Proceedings Volume 7287, 728713 (2009) https://doi.org/10.1117/12.815451

KEYWORDS: Actuators, Solids, Electrodes, Liquids, Resistance, Carbon nanotubes, Manufacturing, Raw materials, Capacitors, Ions

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Actuators based on carbon nanotubes (CNT) have the potential to generate high forces at very low voltages. The density of the raw material is just 1330 kg/m3, which makes them well applicable for lightweight applications. Moreover, active strains of up to 1% can be achieved - due to the CNTs dimensional changes on charge injection. Therefore the nanotubes have to be arranged and electrically wired like electrodes of a capacitor. In previous works the system's response of the Nanotubes comprising a liquid electrolyte was studied in detail. The major challenge is to repeat such experiments with solid electrolytes, which is a prerequisite for structural integration. In this paper a method is proposed which makes sure the expansion is not based on thermal expansion. This is done by analysing the electrical system response. As thermal expansion is dominated by ohmic resistance the CNT based actuators show a strong capacitive behavior. This behavior is referable to the constitution of the electrochemical double layer around the nanotubes, which causes the tubes to expand. Also a novel test setup is described, which guarantees that the displacement which is measured will not be caused by bending of a bimorph but due to expansion of a single layer of nanotubes. This paper also presents experimental results demonstrating both, the method of electrical characterization of CNT based actuators with implemented solid electrolytes and the novel test setup which is used to measure the needed data. The actuators which were characterized are hybrids of CNT and the solid electrolyte NAFION which is supplying the ions needed to constitute the electrochemical double layer. The manufacturing, processing of these actuators and also some first experimental results are shown. Unfortunately, the results are not as clear as those for liquid electrolytes, which depend on the hybrid character of the analyzed devices. In the liquid electrolyte based case the CNTs are the only source of stiffness, whereas in the solid electrolyte case electrodes and electrolyte contribute to the overall stiffness and damping as well. Since the introduction of solid electrolytes is a major stumbling block in the development of such actuators, this work is of particular importance.

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