21 results
Search Results
Now showing 1 - 10 of 21
- ItemSteps towards a Dislocation Ontology for Crystalline Materials(Aachen, Germany : RWTH Aachen, 2021) Ihsan, Ahmad Zainul; Dessì, Danilo; Alam, Mehwish; Sack, Harald; Sandfeld, Stefan; GarcÃa-Castro, Raúl; Davies, John; Antoniou, Grigoris; Fortuna, CarolinaThe field of Materials Science is concerned with, e.g., properties and performance of materials. An important class of materials are crystalline materials that usually contain “dislocations" - a line-like defect type. Dislocation decisively determine many important materials properties. Over the past decades, significant effort was put into understanding dislocation behavior across different length scales both with experimental characterization techniques as well as with simulations. However, for describing such dislocation structures there is still a lack of a common standard to represent and to connect dislocation domain knowledge across different but related communities. An ontology offers a common foundation to enable knowledge representation and data interoperability, which are important components to establish a “digital twin". This paper outlines the first steps towards the design of an ontology in the dislocation domain and shows a connection with the already existing ontologies in the materials science and engineering domain.
- ItemLaser Embossing of Micro-and Submicrometer Surface Structures in Copper(Amsterdam [u.a.] : Elsevier, 2012) Ehrhardt, M.; Lorenz, P.; Frost, F.; Zimmer, K.Micro- and submicrometer structures have been transferred from nickel foils into solid copper surfaces by laser microembossing. The developed arrangement for laser microembossing allows a large-area replication using multi- pulse laser scanning scheme, guaranties a low contamination of the embossed surface and enables the utilization of thick workpieces. In the micrometer range the replicated patterns feature a high accuracy regarding the shape. A significant difference between the master and the replication pattern could be observed for the laser embossing of submicrometer patterns. In conclusion, the results show that the proposed laser embossing process is a promising method with a number of applications in microengineering.
- ItemSupramolecular assemblies of block copolymers as templates for fabrication of nanomaterials(New York, NY [u.a.] : Elsevier, 2011) Nandan, B.; Kuila, B.K.; Stamm, M.Self-assembled polymeric systems have played an important role as templates for nanofabrication; they offer nanotemplates with different morphologies and tunable sizes, are easily removed after reactions, and could be further modified with different functional groups to enhance the interactions. Among the various self-assembled polymeric systems, block copolymer supramolecular assemblies have received considerable attention because of the inherent processing advantages. These supramolecular assemblies are formed by the non-covalent interactions of one of the blocks of the block copolymer with a low molar-mass additive. Selective extraction of the additive leads to porous membranes or nano-objects which could then be used as templates for nanofabrication leading to a variety of ordered organic/inorganic nanostructures. In this feature article, we present an over-view of the recent developments in this area with a special focus on some examples from our group.
- ItemOrigami-Inspired Shape Memory Folding Microactuator(Basel : MDPI, 2020) Seigner, Lena; Bezsmertna, Olha; Fähler, Sebastian; Tshikwand, Georgino; Wendler, Frank; Kohl, ManfredThis paper presents the design, fabrication and performance of origami-based folding microactuators based on a cold-rolled NiTi foil of 20 µm thickness showing the one-way shape memory effect. Origami refers to a variety of techniques of transforming planar sheets into three-dimensional (3D) structures by folding, which has been introduced in science and engineering for, e.g., assembly and robotics. Here, NiTi microactuators are interconnected to rigid sections (tiles) forming an initial planar system that self-folds into a set of predetermined 3D shapes upon heating. While this concept has been demonstrated at the macro scale, we intend to transfer this concept into microtechnology by combining state-of-the art methods of micromachining. NiTi foils are micromachined by laser cutting or photolithography to achieve double-beam structures allowing for direct Joule heating with an electrical current. A thermo-mechanical treatment is used for shape setting of as-received specimens to reach a maximum folding angle of 180°. The bending moments, bending radii and load-dependent folding angles upon Joule heating are evaluated. The shape setting process is particularly effective for small bending radii, which, however generates residual plastic strain. After shape setting, unloaded beam structures show recoverable bending deflection between 0° and 140° for a maximum heating power of 900 mW. By introducing additional loads to account for the effect of the tiles, the smooth folding characteristic evolves into a sharp transition, whereby full deflection up to 180° is reached. The achieved results are an important step towards the development of cooperative multistable microactuator systems for 3D self-assembly.
- ItemEvaluation of Expert Reports to Quantify the Exploration Risk for Geothermal Projects in Germany(Amsterdam [u.a.] : Elsevier, 2015) Ganz, Britta; Ask, Maria; Hangx, Suzanne; Bruckman, Viktor; Kühn, MichaelThe development of deep geothermal energy sources in Germany still faces many uncertainties and high upfront investment costs. Methodical approaches to assess the exploration risk are thus of major importance for geothermal project development. Since 2002, expert reports to quantify the exploration risk for geothermal projects in Germany were carried out. These reports served as a basis for insurance contracts covering the exploration risk. Using data from wells drilled in the meantime, the reports were evaluated and the stated probabilities compared with values actually reached.
- ItemModelling the Surface Heat Flow Distribution in the Area of Brandenburg (Northern Germany)(Amsterdam [u.a.] : Elsevier, 2013) Cacace, Mauro; Scheck-Wenderoth, Magdalena; Noack, Vera; Cherubini, Yvonne; Schellschmidt, Rüdiger; Kühn, Michael; Juhlin, Christopher; Held, Hermann; Bruckman, Viktor; Tambach, Tim; Kempka, ThomasA lithosphere scale geological model has been used to determine the surface heat flow component due to conductive heat transport for the area of Brandenburg. The modelling results have been constrained by a direct comparison with available heat flow measurements. The calculated heat flow captures the regional trend in the surface heat flow distribution which can be related to existing thermal conductivity variations between the different sedimentary units. An additional advective component due to topography induced regional flow and focused flow within major fault zones should be considered to explain the spatial variation observed in the surface heat flow.
- ItemSearching for order in atmospheric pressure plasma jets(Bristol : IOP Publ., 2017-11-10) Schäfer, Jan; Sigeneger, Florian; Å perka, JirÌŒÃ; Rodenburg, Cornelia; Foest, RüdigerThe self-organized discharge behaviour occurring in a non-thermal radio-frequency plasma jet in rare gases at atmospheric pressure was investigated. The frequency of the azimuthal rotation of filaments in the active plasma volume and their inclination were measured along with the gas temperature under varying discharge conditions. The gas flow and heating were described theoretically by a three-dimensional hydrodynamic model. The rotation frequencies obtained by both methods qualitatively agree. The results demonstrate that the plasma filaments forming an inclination angle α with the axial gas velocity uz are forced to a transversal movement with the velocity uφ=tan(α)*uz, which is oriented in the inclination direction. Variations of ${u}_{\phi }$ in the model reveal that the observed dynamics minimizes the energy loss due to convective heat transfer by the gas flow. The control of the self-organization regime motivates the application of the plasma jet for precise and reproducible material processing.
- ItemRadio Frequency CMOS Chem-bio Viscosity Sensors based on Dielectric Spectroscopy([Setúbal] : SCITEPRESS - Science and Technology Publications, Lda., 2017) Guha, Subhajit; Wenger, Christian; Peixoto, Nathalia; Fred, Ana; Gamboa, Hugo; Vaz, MárioThis paper presents a CMOS Radio frequency dielectric sensor platform for the detection of relative viscosity changes in a fluid sample. The operating frequency of the sensor is 12.28 GHz. This frequency range has been chosen for high signal to noise ratio and also to avoid other low frequency dispersion mechanisms for future lab on chip applications. The sensor chip has been fabricated in 250 nm BiCMOS technology of IHP. The measurements conducted to show the relative viscosity variation detection capability of the sensor chip, were based on mixtures of glycerol and water as well as glycerol and organic alcohol. The detection limit of viscosity is dependent on the permittivity contrast of the sample constituent. Therefore, it is also shown the choice of frequency inherently aids in the permittivity contrast of the sample constituents.
- ItemPattern transfer of sub-micrometre-scaled structures into solid copper by laser embossing(Amsterdam [u.a.] : Elsevier, 2014) Ehrhardt, M.; Lorenz, P.; Lotnyk, A.; Romanus, H.; Thelander, E.; Zimmer, K.Laser embossing allows the micron and submicron patterning of metal substrates that is of great interest in a wide range of applications. This replication process enables low-cost patterning of metallic materials by non-thermal, high-speed forming which is driven by laser-induced shock waves. In this study the surface topography characteristics as well as the material structure at laser embossing of sub-micrometre gratings into solid copper is presented. The topography of the laser-embossed copper pattern is analysed with atomic force microscopy (AFM) in comparison to the master surface. The height of the embossed structures and the replicated pattern fidelity increases up to a laser fluence of F ∼ 10 J/cm2. For higher laser fluences the height of the embossed structures saturates at 75% of the master pattern height and the shape is adequate to the master. Structural modifications in the copper mono crystals after the laser embossing process were investigated with transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). Almost no modifications were detected. The residual stress after laser embossing of 32 MPa (F = 30 J/cm2) has only a limited influence on the surface pattern formation.
- ItemOptimization of the energy deposition in glasses with temporally-shaped femtosecond laser pulses(Amsterdam [u.a.] : Elsevier, 2011) Mauclair, C.; Mishchik, K.; Mermillod-Blondin, A.; Rosenfeld, A.; Hertel, I.V.; Audouard, E.; Stoian, R.Bulk machining of glasses with femtosecond laser pulses enables the fabrication of embedded optical functions. Due to the nonlinear character of the laser-matter interaction, structural modifications can occur within the focal region. To reach a full control of the process, ways of controlling the deposition of the laser energy inside the material have to be unveiled. From static and time-resolved pictures of bulk-excitation of a-SiO2 and borosilicate glass, we show that particular laser temporal shapes such as picosecond sequences can better confine the energy deposition than the femtosecond sequence by reducing the propagation artifacts.