TY - CONF
AB - DC-DC converters for on-board chargers (OBC) of electrical vehicles are usually galvanically isolated allowing modular single-phase PFC front-end solutions, but require transformers which are more bulky, costly and lossy than inductors of non-isolated DC-DCs. Furthermore, for vehicle-to-grid applications, bidirectional converters with transformers are generally more complex and have a higher count on semiconductor switches than transformerless solutions. However, when using non-isolated DC-DC converters within an OBC, the large common-mode (CM) capacitance comprising capacitive parasitics of the traction battery as well as explicit Y-capacitors connecting the high-voltage DC-system (HV-system) within specific HV-loads to ground has to be considered. For the PFC front-end stage, when supplied from the three-phase mains this means that generation of high-frequency and high-amplitude CM voltages, as it is common e.g. with the conventional six-switch full-bridge converter, has to be strictly avoided. For this reason, a modified topology is suggested leading to a different mode of operation and to a very low common-mode noise behaviour: The three-phase four-wire full-bridge PFC with split DC-link, whose midpoint is connected to the mains neutral provides very stable potentials at the DC-link rails and therefore it can be classified as Zero-CM-topology.For dedicated single-phase operation, as required for most OBC, an additional balancing leg may be added to the topology to reduce the required DC-link capacitance and allow non-electrolytic capacitors.The function of the bidirectional Zero-CM three-phase four-wire full-bridge PFC was verified by simulation and on an 11 kW-laboratory sample. The power factor is above 0.999 and an efficiency of 98 % is measured.
AU - Strothmann, Benjamin
AU - Schafmeister, Frank
AU - Böcker, Joachim
ID - 29849
KW - Three-phase four-wire
KW - OBC
KW - Y2G
KW - PFC
KW - CM
KW - EY charger
KW - balancing circuit
T2 - 2021 IEEE Applied Power Electronics Conference and Exposition (APEC)
TI - Common-Mode-Free Bidirectional Three-Phase PFC-Rectifier for Non-Isolated EV Charger
ER -
TY - JOUR
AU - Brosch, Anian
AU - Wallscheid, Oliver
AU - Böcker, Joachim
ID - 29657
JF - IEEE Open Journal of Industry Applications
TI - Model Predictive Control of Permanent Magnet Synchronous Motors in the Overmodulation Region Including Six-Step Operation
VL - 2
ER -
TY - CONF
AU - Gedlu, Emebet Gebeyehu
AU - Wallscheid, Oliver
AU - Böcker, Joachim
ID - 29663
T2 - 2021 IEEE International Electric Machines & Drives Conference (IEMDC)
TI - Temperature estimation of electric machines using a hybrid model of feed-forward neural and low-order lumped-parameter thermal networks
ER -
TY - JOUR
AU - Rehlaender, Philipp
AU - Schafmeister, Frank
AU - Böcker, Joachim
ID - 29892
IS - 9
JF - IEEE Transactions on Power Electronics
KW - Electrical and Electronic Engineering
SN - 0885-8993
TI - Interleaved Single-Stage LLC Converter Design Utilizing Half- and Full-Bridge Configurations for Wide Voltage Transfer Ratio Applications
VL - 36
ER -
TY - CONF
AU - Korthauer, Bastian
AU - Rehlaender, Philipp
AU - Schafmeister, Frank
AU - Böcker, Joachim
ID - 29895
T2 - 2021 IEEE Applied Power Electronics Conference and Exposition (APEC)
TI - Design and Analysis of a Regenerative Snubber for a 2.2 kW Active-Clamp Forward Converter with Low-Voltage Output
ER -
TY - JOUR
AU - Book, Gerrit
AU - Traue, Arne
AU - Balakrishna, Praneeth
AU - Brosch, Anian
AU - Schenke, Maximilian
AU - Hanke, Sören
AU - Kirchgässner, Wilhelm
AU - Wallscheid, Oliver
ID - 22162
JF - IEEE Open Journal of Power Electronics
SN - 2644-1314
TI - Transferring Online Reinforcement Learning for Electric Motor Control From Simulation to Real-World Experiments
ER -
TY - JOUR
AU - Weber, Daniel
AU - Heid, Stefan
AU - Bode, Henrik
AU - Lange, Jarren
AU - Hüllermeier, Eyke
AU - Wallscheid, Oliver
ID - 29653
JF - IEEE Access
TI - Safe Bayesian Optimization for Data-Driven Power Electronics Control Design in Microgrids: From Simulations to Real-World Experiments
VL - 9
ER -
TY - CONF
AB - In electric vehicles (EV) the large common-mode (CM) capacitance comprising capacitive parasitics of the traction battery as well as explicit Y-capacitors connecting within specific loads the high-voltage DC-system (HV-system) to ground, can cause issues when using non-isolated EV Chargers. One solution for a power factor correction (PFC) rectifier that is capable to operate with a non-isolated DC-DC converter, is the three-phase four-wire full-bridge PFC, with split DC-link, whose midpoint is connected to the mains neutral. Therefore, it provides very stable potentials at the DC-link rails and accordingly can be classified as Zero-CM topology, which facilitates a common-mode-free operation. When to be operated at a single-phase supply, which is a common requirement for On-board chargers (OBCs) this topology results in the voltage-doubler PFC (V2-PFC) being characterised by a comparably large DC-link voltage ripple at mains frequency. If the DC-link capacitance shall be minimized, for instance to avoid lifetime-limited electrolytic capacitors, two more circuits in addition to the original V2-PFC are proposed for keeping the common-mode-free operation: A balancing circuit (BC), that balances the voltages over the split capacitors and a ripple port (RP), that buffers the 100 Hz power pulsation of the mains. For both circuits the available two bridge legs of the three-phase topology in single-phase operation may be utilized. A 3.7 kW laboratory sample verifies the functionality of the additional circuits in conjunction with the V2-PFC and achieves an efficiency of 95 %.
AU - Strothmann, Benjamin
AU - Book, Gerrit
AU - Schafmeister, Frank
AU - Böcker, Joachim
ID - 29850
T2 - PCIM Europe digital days 2021; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management
TI - Single-Phase Operation of Common-Mode-Free Bidirectional Three-Phase PFC-Rectifier for Non-Isolated EV Charger with Minimized DC-Link
ER -
TY - CONF
AB - LLC resonant converters typically employ power
MOSFETs in their inverter stage. The generally weak reverse
recovery behaviour of the intrinsic body diodes of those
MOSFETs causes significant turn-on losses when being forced
to hard commutations. Continuous operation in this way will
lead to self-destruction of the transistors. Consequently,
zero-voltage switching (ZVS) is essential in a MOSFET-based
inverter stage. To ensure ZVS, the LLC converter is operated in
the inductive region. On the contrary, IGBTs show dominant
turn-off losses and are therefore conventionally not applied in
LLC converters typically requiring high switching frequencies
to achieve low output voltages. However, if the LLC converter
is intentionally designed for capacitive operation, zero-current
switching (ZCS) is enabled and thus robust and cost-efficient
IGBTs can be applied in the inverter stage. The aim of this work
is to investigate the use IGBTs in the inverter of an LLC
converter. The theory behind the capacitive operated LLC is
derived using a switched simulation model and compared with
the fundamental harmonic approximation (FHA). The results
prove FHA to be useless for practical converter design. Instead,
a stress value analysis based on switched model simulations is
proposed to the design a capacitive operated LLC utilizing ZCS.
A 2 kW prototype for on-board EV applications was built to
verify the theory and design approach. The prototype confirms
the derived theory and thus the deployment of IGBTs in the
inverter stage of LLC resonant converters. Synchronous
rectification turns out to require a specific control solution, but
if given the resulting efficiency in the most critical operation
point exceeds the value of a MOSFET-based (inductive
operated) LLC-design of an identical application. Therefore,
this concept should be further developed.
AU - Urbaneck, Daniel
AU - Rehlaender, Philipp
AU - Böcker, Joachim
AU - Schafmeister, Frank
ID - 29871
T2 - 2021 IEEE Applied Power Electronics Conference and Exposition (APEC)
TI - LLC Converter in Capacitive Operation Utilizing ZCS for IGBTs – Theory, Concept and Verification of a 2 kW DC-DC Converter for EVs
ER -
TY - JOUR
AU - Stender, Marius
AU - Wallscheid, Oliver
AU - Böcker, Joachim
ID - 30030
IS - 11
JF - IEEE Transactions on Power Electronics
KW - Electrical and Electronic Engineering
SN - 0885-8993
TI - Accurate Torque Control for Induction Motors by Utilizing a Globally Optimized Flux Observer
VL - 36
ER -
TY - CONF
AU - Stender, Marius
AU - Wallscheid, Oliver
AU - Böcker, Joachim
ID - 30031
T2 - 2021 IEEE 19th International Power Electronics and Motion Control Conference (PEMC)
TI - Accurate Torque Estimation for Induction Motors by Utilizing a Hybrid Machine Learning Approach
ER -
TY - CONF
AU - Stender, Marius
AU - Wallscheid, Oliver
AU - Böcker, Joachim
ID - 30029
T2 - IECON 2021 – 47th Annual Conference of the IEEE Industrial Electronics Society
TI - Combined Electrical-Thermal Gray-Box Model and Parameter Identification of an Induction Motor
ER -
TY - CONF
AU - Stender, Marius
AU - Wallscheid, Oliver
AU - Böcker, Joachim
ID - 30032
T2 - 2021 IEEE 19th International Power Electronics and Motion Control Conference (PEMC)
TI - Gray-Box Loss Model for Induction Motor Drives
ER -
TY - CONF
AU - Karakaya, Kadiray
AU - Bodden, Eric
ID - 30084
T2 - 2021 IEEE 21st International Working Conference on Source Code Analysis and Manipulation (SCAM)
TI - SootFX: A Static Code Feature Extraction Tool for Java and Android
ER -
TY - CONF
AU - Hanke, Sören
AU - Wallscheid, Oliver
AU - Böcker, Joachim
ID - 29665
TI - Comparison of Artificial Neural Network and Least Squares Prediction Models for Finite-Control-Set Model Predictive Control of a Permanent Magnet Synchronous Motor
ER -
TY - JOUR
AU - Wallscheid, Oliver
ID - 29664
JF - IEEE Open Journal of Industry Applications
TI - Thermal Monitoring of Electric Motors: State-of-the-Art Review and Future Challenges
ER -
TY - JOUR
AU - Kirchgässner, Wilhelm
AU - Wallscheid, Oliver
AU - Böcker, Joachim
ID - 21251
IS - 3
JF - IEEE Transactions on Energy Conversion
SN - 0885-8969
TI - Data-Driven Permanent Magnet Temperature Estimation in Synchronous Motors with Supervised Machine Learning: A Benchmark
VL - 36
ER -
TY - JOUR
AU - Balakrishna, Praneeth
AU - Book, Gerrit
AU - Kirchgässner, Wilhelm
AU - Schenke, Maximilian
AU - Traue, Arne
AU - Wallscheid, Oliver
ID - 21254
JF - Journal of Open Source Software
SN - 2475-9066
TI - gym-electric-motor (GEM): A Python toolbox for the simulation of electric drive systems
ER -
TY - JOUR
AU - Schenke, Maximilian
AU - Wallscheid, Oliver
ID - 25031
JF - IEEE Open Journal of the Industrial Electronics Society
SN - 2644-1284
TI - A Deep Q-Learning Direct Torque Controller for Permanent Magnet Synchronous Motors
ER -
TY - JOUR
AU - Schenke, Maximilian
AU - Wallscheid, Oliver
ID - 29662
JF - arXiv preprint arXiv:2105.08990
TI - Improved Exploring Starts by Kernel Density Estimation-Based State-Space Coverage Acceleration in Reinforcement Learning
ER -
TY - CONF
AU - Gedlu, E. G.
AU - Wallscheid, O.
AU - Böcker, J.
ID - 29995
T2 - The 10th International Conference on Power Electronics, Machines and Drives (PEMD 2020)
TI - PERMANENT MAGNET SYNCHRONOUS MACHINE TEMPERATURE ESTIMATION USING LOW-ORDER LUMPED-PARAMETER THERMAL NETWORK WITH EXTENDED IRON LOSS MODEL
ER -
TY - JOUR
AU - Brosch, Anian
AU - Wallscheid, Oliver
AU - Böcker, Joachim
ID - 21557
JF - IEEE Transactions on Industrial Informatics
SN - 1551-3203
TI - Torque and Inductances Estimation for Finite Model Predictive Control of Highly Utilized Permanent Magnet Synchronous Motors
ER -
TY - JOUR
AU - d’Agostini, Franca
AU - Ficara, Elena
ID - 30099
JF - History and Philosophy of Logic
KW - History and Philosophy of Science
KW - History
SN - 0144-5340
TI - Hegel’s Interpretation of the Liar Paradox
ER -
TY - JOUR
AU - Ficara, Elena
ID - 30097
JF - Fichte-Studien
TI - ‘Transcendental’ in Kant and Fichte. A Conceptual Shift and its Philosophical Meaning
VL - 49
ER -
TY - JOUR
AU - Ficara, Elena
ID - 30098
IS - 3
JF - History and Philosophy of Logic
TI - The Birth of Dialetheism
VL - 42
ER -
TY - GEN
AB - BloKK-Beitrag für das ZeKK, 08.10.2021
AU - Lebock, Sarah
ID - 26010
TI - Blogpost "Von der Dankbarkeit über ein offenes Ohr"
ER -
TY - JOUR
AB - Topological photonic crystals (TPhCs) provide robust manipulation of light with built-in immunity to fabrication tolerances and disorder. Recently, it was shown that TPhCs based on weak topology with a dislocation inherit this robustness and further host topologically protected lower-dimensional localized modes. However, TPhCs with weak topology at optical frequencies have not been demonstrated so far. Here, we use scattering-type scanning near-field optical microscopy to verify mid-bandgap zero-dimensional light localization close to 100 THz in a TPhC with nontrivial Zak phase and an edge dislocation. We show that because of the weak topology, differently extended dislocation centers induce similarly strong light localization. The experimental results are supported by full-field simulations. Along with the underlying fundamental physics, our results lay a foundation for the application of TPhCs based on weak topology in active topological nanophotonics, and nonlinear and quantum optic integrated devices because of their strong and robust light localization.
AU - Lu, Jinlong
AU - Wirth, Konstantin G.
AU - Gao, Wenlong
AU - Heßler, Andreas
AU - Sain, Basudeb
AU - Taubner, Thomas
AU - Zentgraf, Thomas
ID - 28255
IS - 49
JF - Science Advances
SN - 2375-2548
TI - Observing 0D subwavelength-localized modes at ~100 THz protected by weak topology
VL - 7
ER -
TY - CONF
AU - Alshomary, Milad
AU - Gurcke, Timon
AU - Syed, Shahbaz
AU - Heinisch, Philipp
AU - Spliethöver, Maximilian
AU - Cimiano, Philipp
AU - Potthast, Martin
AU - Wachsmuth, Henning
ID - 25297
T2 - Proceedings of the 8th Workshop on Argument Mining
TI - Key Point Analysis via Contrastive Learning and Extractive Argument Summarization
ER -
TY - CONF
AU - Nouri, Zahra
AU - Prakash, Nikhil
AU - Gadiraju, Ujwal
AU - Wachsmuth, Henning
ID - 25294
T2 - Proceedings of the Ninth AAAI Conference on Human Computation and Crowdsourcing, HCOMP 2021
TI - iClarify - A Tool to Help Requesters Iteratively Improve Task Descriptions in Crowdsourcing
ER -
TY - CONF
AU - Coy, Sam
AU - Czumaj, Artur
AU - Feldmann, Michael
AU - Hinnenthal, Kristian
AU - Kuhn, Fabian
AU - Scheideler, Christian
AU - Schneider, Philipp
AU - Struijs, Martijn
ED - Bramas, Quentin
ED - Gramoli, Vincent
ED - Milani, Alessia
ID - 30217
T2 - 25th International Conference on Principles of Distributed Systems, OPODIS 2021, December 13-15, 2021, Strasbourg, France
TI - Near-Shortest Path Routing in Hybrid Communication Networks
VL - 217
ER -
TY - JOUR
AU - Huber-Gedert, Marina
AU - Nowakowski, Michał
AU - Kertmen, Ahmet
AU - Burkhardt, Lukas
AU - Lindner, Natalia
AU - Schoch, Roland
AU - Herbst‐Irmer, Regine
AU - Neuba, Adam
AU - Schmitz, Lennart
AU - Choi, Tae‐Kyu
AU - Kubicki, Jacek
AU - Gawelda, Wojciech
AU - Bauer, Matthias
ID - 30216
IS - 38
JF - Chemistry – A European Journal
KW - Photocatalytic Hydrogen Production
KW - Catalysis
KW - Inorganic Chemistry
SN - 0947-6539
TI - Fundamental Characterization, Photophysics and Photocatalysis of a Base Metal Iron(II)‐Cobalt(III) Dyad
VL - 27
ER -
TY - JOUR
AB -
In this work the solubility of 15 amino acids and 18 peptides in aqueous 2-propanol solutions was successfully modelled using PC-SAFT that used recently determined experimental melting properties as input data.
AU - Do, Hoang Tam AU - Franke, Patrick AU - Volpert, Sophia AU - Klinksiek, Marcel AU - Thome, Max AU - Held, Christoph ID - 30208 IS - 18 JF - Physical Chemistry Chemical Physics KW - Physical and Theoretical Chemistry KW - General Physics and Astronomy SN - 1463-9076 TI - Measurement and modelling solubility of amino acids and peptides in aqueous 2-propanol solutions VL - 23 ER - TY - GEN AU - Bothe, Mike AU - Fedorov, Alexander AU - Frei, Herrmann AU - Kenig, Eugeny ID - 26829 TI - Modeling and investigations of chemical absorption process for prevention of emergencies ER - TY - JOUR AB - The increasing economic and ecological demands on the mobility sector require efforts to reduce resource consumption in both the production and utilization phases. The use of lightweight construction technologies can save material and increase energy efficiency during operation. Multi-material systems consisting of different materials and geometries are used to achieve weight reduction. Since conventional joining processes reach their limits in the connection of these components, new methods and technologies are necessary in order to be able to react versatilely to varying process and disturbance variables. For fundamental investigations of new possibilities in joining technology, numerical investigations are helpful to identify process parameters. To generate valid results, robust and efficient material models are developed which are adapted to the requirements of versatile joining technologies, for instance to the high plastic strains associated with self-piercing riveting. To describe the inherent strain-induced plastic orthotropy of sheet metal an anisotropic Hill-plasticity model is formulated. Tensile tests for different sheet orientations are conducted both experimentally and numerically to adjust the anisotropic material parameters by inverse parameter identification for aluminium EN AW-6014 and steel HCT590X. Then, the layer compression test is used to validate the model and the previously identified parameters. AU - Friedlein, J. AU - Wituschek, S. AU - Lechner, M. AU - Mergheim, J. AU - Steinmann, P. ID - 30647 JF - IOP Conference Series: Materials Science and Engineering TI - Inverse parameter identification of an anisotropic plasticity model for sheet metal VL - 1157 ER - TY - JOUR AB - As a new and innovative processing method for fabrication for fiber-reinforced thermoplastic composites (CFRTs), the feasibility of ultrasonic welding technology was proven in several studies. This method offers potential for the direct manufacturing of CFRT–metal structures via embedded pin structures. Despite the previous studies, a deeper understanding of the process of energy input and whether fibers work as energy directors and consequently can, in combination with chosen processing parameters, influence the consolidation quality of the CFRTs, is still unknown. Consequently, the aim of this work is to establish a deeper process understanding of the ultrasonic direct impregnation of fiber-reinforced thermoplastics with an emphasis on the fiber’s function as energy directors. Based on the generated insights, a better assessment of the feasibility of direct, hybrid part manufacturing is possible. The produced samples were primarily evaluated by optical and mechanical test methods. It is demonstrated that with higher welding time and amplitude, a better consolidation quality can be achieved and that independent of the process parameters chosen in this study, no significant fiber breakage occurs. This is interpreted as a sign of a gentle impregnation process. Furthermore, based on the examination of single roving and 5-layer set-ups, it is shown that the glass fibers function as energy directors and can influence the transformation of sonic energy into thermal energy. In comparison to industrially available CFRT material, the mechanical properties are weaker, but materials and processes offer potential for significant improvement. Based on these findings, proposals for a direct impregnation and joining process are made. AU - Popp, J. AU - Wolf, M. AU - Mattner, T. AU - Drummer, D. ID - 30645 JF - Journal of Composites Science TI - Energy direction in ultrasonic impregnation of continuous fiber-reinforced thermoplastics VL - 5 ER - TY - JOUR AB - The multi-material design and the adaptability of a modern process chain require joining connections with specifically adjustable mechanical, thermal, chemical, or electrical properties. Previous considerations primarily focused on the mechanical properties. The multitude of possible combinations of requirements, materials, and component- and joining-geometry makes an empirical determination of these joining properties for the clinching process impossible. Based on the established and empirical procedure, there is currently no model that takes into account all questions of joinability—i.e., the materials (suitability for joining), design (security of joining), and production (joining possibility)—that allows a calculation of the properties that can be achieved. It is therefore necessary to describe the physical properties of the joint as a function of the three binding mechanisms—form closure, force closure, and material closure—in relation to the application. This approach illustrates the relationships along the causal chain “joint requirement-binding mechanism-joining parameters” and improves the adaptability of the mechanical joining technology. Geometrical properties of clinch connections of the combination of aluminum and steel are compared in a metallographic cross-section. The mechanical stress state of the rotationally symmetrical clinch points is qualified with a torsion test and by measuring the electrical resistance in the base material, in the clinch joint, and during the production cycle (after clinching, before precipitation hardening and after precipitation hardening). AU - Kalich, J. AU - Füssel, U. ID - 30643 JF - Journal of Manufacturing and Materials Processing TI - Influence of the production process on the binding mechanism of clinched aluminum steel mixed compounds VL - 5 ER - TY - JOUR AB - Computational homogenization is a powerful tool allowing to obtain homogenized properties of materials on the macroscale from simulations of the underlying microstructure. The response of the microstructure is, however, strongly affected by variations in the microstructure geometry. In particular, we consider heterogeneous materials with randomly distributed non-overlapping inclusions, which radii are also random. In this work we extend the earlier proposed non-deterministic computational homogenization framework to plastic materials, thereby increasing the model versatility and overall realism. We apply novel soft periodic boundary conditions and estimate their effect in case of non-periodic material microstructures. We study macroscopic plasticity signatures like the macroscopic von-Mises stress and make useful conclusions for further constitutive modeling. Simulations demonstrate the effect of the novel boundary conditions, which significantly differ from the standard periodic boundary conditions, and the large influence of parameter variations and hence the importance of the stochastic modeling. AU - Pivovarov, D. AU - Mergheim, J. AU - Willner, K. AU - Steinmann, P. ID - 30644 JF - Computational Mechanics TI - Stochastic local FEM for computational homogenization of heterogeneous materials exhibiting large plastic deformations ER - TY - JOUR AB - Sheet metal forming as well as mechanical joining demand increasingly accurate and efficient material modelling to capture large deformations, the inherent sheet orthotropy and even process-induced damage, which is expected to be influential. To account for large strains the additive logarithmic strain space is utilised that enables a straightforward incorporation of plastic anisotropy, herein modelled by a Hill48 yield function. A gradient-enhancement is used to equip the ductile damage model with an internal length scale curing the damage-induced localisation. An affine combination of the local and non-local softening variable is derived enabling a more efficient single surface formulation for the regularised plasticity-damage material model. AU - Friedlein, J. AU - Mergheim, J. AU - Steinmann, P. ID - 30642 JF - PAMM TI - Anisotropic plasticity‐damage material model for sheet metal — Regularised single surface formulation VL - 21 ER - TY - CONF AU - Bielak, Christian Roman AU - Böhnke, Max AU - Bobbert, Mathias AU - Meschut, Gerson ID - 20807 TI - Further development of a numerical method for analyzing the load capacity of clinched joints in versatile process chains ER - TY - JOUR AB - Due to increasingly strict emission targets and regulatory requirements, especially for companies in the transport industry, the demand for multi-material-systems is continuously rising in order to lower energy consumption. In this context, mechanical joining processes offer an environmentally friendly and flexible alternative to established joining methods, especially in the field of lightweight design. For example, cold-formed cylindrical pin structures show high potentials in joining multi-material-systems without auxiliary elements. The pin structures are joined either by pressing them directly into the joining partner or by caulking with a pre-punched part. However, to evaluate the strength of the joint and to ensure the joining reliability for versatile processes, such as changing joining partners or batch variations, engineering designers currently have only limited design principles available compared to thermal joining processes. Consequently, the design of an optimal pin joint requires cost- and time-intensive experimental investigations and adjustments to design or process parameters. As a solution, data-driven methods offer procedures for structuring data and identifying dependencies between varying process parameters and resulting pin structure characteristics. Motivated by this, the paper presents an approach for the data-driven analysis of cold-formed pin structures and offers a deeper understanding of how versatile processes affect the pin characteristics. Therefore, the application of an intelligent design of experiment in combination with several machine learning methods enable the setup of a best-fitting meta-model. Resulting, the determination of a mathematical model provides the opportunity to accurately estimate the pin height considering only relevant geometrical and process parameters with a prediction quality of 95 %. AU - Römisch, D. AU - Zirngibl, C. AU - Schleich, B. AU - Wartzack, S. AU - Merklein, M. ID - 30650 JF - IOP Conference Series: Materials Science and Engineering TI - Data-driven analysis of cold-formed pin structure characteristics in the context of versatile joining processes VL - 1157 ER - TY - JOUR AB - In clinching, the combinations of requirements, materials, component dimensions and tools influence the resulting joint geometry and the resulting bonding mechanisms. These in turn affect the property profile of the joint. For example, it is possible to use different tools to flexibly adapt clinching points to the respective required load regime. Clinching points dimensioned in this way can be geometrically similar, but have different mechanical stress states, which leads to different properties in terms of load-bearing behavior. Within the scope of this work, the clinching process with different tools in optimal and compromise design and its effect on the force and form-closure component, is investigated in a torsion test of the clinched connection. Clinched steel sheets with two thicknesses and joining directions are analyzed. Virtual experiments are carried out using finite element analyses (FEA) of the joining process and are followed by a springback simulation. Subsequently, the surface pressure between the two joining partners in the clinching points is calculated on the basis of the results from the FEA and the transmittable moment of the connection, as an indicator for the force-closure component, is determined. Finally, the experimental and simulated data are compared and discussed. AU - Steinfelder, C. AU - Kalich, J. AU - Brosius, A. AU - Füssel, U. ID - 30648 JF - IOP Conference Series: Materials Science and Engineering TI - Numerical and experimental investigation of the transmission moment of clinching points VL - 1157 ER - TY - JOUR AB - Continuous Fiber Reinforced Thermoplastic (CFRT) hybrid parts offer interesting possibilities for lightweight application, which can exceed the capabilities of mono material metal or CFRT parts. In this case, the joining technology oftentimes is the limiting factor. This study investigates a joining operation with metal pin structures which are additively manufactured via powder bed fusion featuring different diameters and tip geometries, which are inserted into the locally infrared heated CFRT part. The resulting fiber rearrangement is assessed using transmitted light microscopy, confocal laser scanning microscopy as well as micro-computer-tomography. It could be shown that for all assessed pin variants a similar distinct fiber displacement can be seen and that the pin diameter has a significant effect on the resulting fiber orientation with smaller pin diameters being advantageous because of gentle fiber displacement and reduced undulation. The tip geometry has only minor effect on the fiber orientation. Especially in the X/Y plane no systematic influence of the tip geometry on the fiber displacement could be observed. Based on the gained insights a three-stage model of the fiber orientation processes is proposed. AU - Popp, J. AU - Kleffel, T. AU - Römisch, D. AU - Papke, T. AU - Merklein, M. AU - Drummer, D. ID - 30653 JF - Applied Composite Materials TI - Fiber Orientation Mechanism of Continuous Fiber Reinforced Thermoplastics Hybrid Parts Joined with Metallic Pins VL - 28 ER - TY - JOUR AB - Clinching continuous fibre reinforced thermoplastic composites and metals is challenging due to the low ductility of the composite material. Therefore, a number of novel clinching technologies has been developed specifically for these material combinations. A systematic overview of these advanced clinching methods is given in the present paper. With a focus on process design, three selected clinching methods suitable for different joining tasks are described in detail. The clinching processes including equipment and tools, observed process phenomena and the resultant material structure are compared. Process phenomena during joining are explained in general and compared using computed tomography and micrograph images for each process. In addition the load bearing behaviour and the corresponding failure mechanisms are investigated by means of single-lap shear tests. Finally, the new joining technologies are discussed regarding application relevant criteria. AU - Gröger, B. AU - Troschitz, J. AU - Vorderbrüggen, J. AU - Vogel, C. AU - Kupfer, R. AU - Meschut, G. AU - Gude, M. ID - 30652 JF - Materials TI - Clinching of Thermoplastic Composites and Metals—A Comparison of Three Novel Joining Technologies VL - 14 ER - TY - JOUR AB - Industrial X-ray computed tomography (XCT) is a tool for non-destructive testing and a volumetric analysis method with the ability to measure dimensions and geometry inside a component without destroying it. However, XCT is a relatively young technology in the field of dimensional metrology and thus faces several challenges. The achievement of a high measurement resolution, which is re-quired to detect small geometrical features, depends on a variety of influencing factors. In this arti-cle, the interface structural resolution (ISR) as one of the key challenges will be investigated. The two-sphere standard called the hourglass standard allows the determination of the structural resolu-tion by evaluation of the surrounding area of an ideal point contact of two spheres after the CT re-construction in form of a neck-shaped transition. Close to the contact point of the two spheres two opposing surfaces exist. Their distances from each other increase as the distance from the contact point of the two spheres increase. The determination of the distances between the spheres’ surface allows a statement about the ISR. A new developed specimen or standard with a variable gap size consisting of calibrated parallel gauge blocks allows statements about the ISR, too. Because of the higher number of probing points of the gauge block standard the results of the determined ISR are more stable compared to the hourglass standard. This paper compares the results of the computed tomography measurements for the designed interface structural resolution standard with those of the hourglass standard. AU - Busch, M. AU - Hausotte, T. ID - 30662 JF - Key Engineering Materials TI - Determination of the Interface Structural Resolution of an Industrial X-Ray Computed Tomograph Using a Spherical Specimen and a Gap Specimen Consisting of Gauge Blocks VL - 883 ER - TY - CONF AB - Several algorithms for finding the best arm in the dueling bandits setting assume the existence of a Condorcet winner (CW), that is, an arm that uniformly dominates all other arms. Yet, by simply relying on this assumption but not verifying it, such algorithms may produce doubtful results in cases where it actually fails to hold. Even worse, the problem may not be noticed, and an alleged CW still be produced. In this paper, we therefore address the problem as a ”testification” task, by which we mean a combination of testing and identification: The online identification of the CW is combined with the statistical testing of the CW assumption. Thus, instead of returning a supposed CW at some point, the learner has the possibility to stop sampling and refuse an answer in case it feels confident that the CW assumption is violated. Analyzing the testification problem formally, we derive lower bounds on the expected sample complexity of any online algorithm solving it. Moreover, a concrete algorithm is proposed, which achieves the optimal sample complexity up to logarithmic terms. AU - Haddenhorst, Björn AU - Bengs, Viktor AU - Brandt, Jasmin AU - Hüllermeier, Eyke ED - de Campos, Cassio ED - Maathuis, Marloes H. ID - 30725 T2 - Proceedings of the Thirty-Seventh Conference on Uncertainty in Artificial Intelligence TI - Testification of Condorcet Winners in dueling bandits VL - 161 ER - TY - JOUR AB - In lightweight design, clinching is a cost-efficient solution as the joint is created through localized cold-forming of the joining parts. A clinch point’s quality is usually assessed using ex-situ destructive testing methods. These, however, are unable to detect phenomena immediately during the joining process. For instance, elastic deformations reverse and cracks close after unloading. In-situ methods such as the force-displacement evaluation are used to control a clinching process, though deviations in the clinch point geometry cannot be derived with this method. To overcome these limitations, the clinching process can be investigated using in-situ computed tomography (in-situ CT). However, a clinching tool made of steel would cause strong artefacts and a high attenuation in the CT measurement, reducing the significance of this method. Additionally, when joining parts of the same material, the sheet-sheet interface is hardly detectable. This work aims at identifying, firstly, tool materials that allow artefact-reduced CT measurements during clinching, and, secondly, radiopaque materials that can be applied between the joining parts to enhance the detectability of the sheet-sheet interface. Therefore, both CT-suitable tool materials and radiopaque materials are selected and experimentally investigated. In the clinching process, two aluminium sheets with radiopaque material in between are clinched in a single-step (rotationally symmetric joint without cut section). It is shown that e.g. silicon nitride is suited as tool material and a tin layer is suitable to enhance the detectability of the sheet-sheet interface. AU - Köhler, D. AU - Kupfer, R. AU - Troschitz, J. AU - Gude, M. ID - 30659 JF - ESAFORM 2021 TI - Clinching in In-situ CT – Experimental Study on Suitable Tool Materials ER - TY - JOUR AB - As lightweight design gains more and more attention, time and cost-efficient joining methods such as clinching are becoming more popular. A clinch point’s quality is usually determined by ex situ destructive analyses such as microsectioning. However, these methods do not yield the detection of phenomena occurring during loading such as elastic deformations and cracks that close after unloading. Alternatively, in situ computed tomography (in situ CT) can be used to investigate the loading process of clinch points. In this paper, a method for in situ CT analysis of a single-lap shear test with clinched metal sheets is presented at the example of a clinched joint with two 2 mm thick aluminum sheets. Furthermore, the potential of this method to validate numerical simulations is shown. Since the sheets’ surfaces are locally in contact with each other, the interface between both aluminum sheets and therefore the exact contour of the joining partners is difficult to identify in CT analyses. To compensate for this, the application of copper varnish between the sheets is investigated. The best in situ CT results are achieved with both sheets treated. It showed that with this treatment, in situ CT is suitable to properly observe the three-dimensional deformation behavior and to identify the failure modes. AU - Köhler, D. AU - Kupfer, R. AU - Troschitz, J. AU - Gude, M. ID - 30661 JF - Materials TI - In Situ Computed Tomography—Analysis of a Single-Lap Shear Test with Clinch Points VL - 14 ER - TY - JOUR AB - Due to increasing demands regarding ecological and economic specifications in vehicle design, the effort required for production is continuously increasing. One trend is the increased use of multi-material systems, which are characterised by the use of different materials such as high-strength steels or aluminium alloys. In addition to the varying mechanical properties of the components, an increased number of variants accompanied by different geometries is leading to increasing challenges on body construction. For the assembly and connection of the individual components, conventional joining methods reach their limitations. Therefore, new joining methods are necessary, which feature properties of versatility and can adapt to process and disturbance variables. One way of achieving tailored joints is to use a tumbling self-piercing riveting process. For the design of the process route, numerical investigations are necessary for which a characterisation of the friction properties is necessary. This paper therefore investigates the contact and friction conditions that occur in a tumbling self-piercing riveting process. The individual contacts between the process components are identified and based on this, suitable processes for the characterisation of the friction factors - and coefficients are selected and performed. AU - Wituschek, S. AU - Lechner, M. ID - 30719 JF - Key Engineering Materials TI - Friction Characterisation for a Tumbling Self-Piercing Riveting Process VL - 883 ER - TY - CONF AU - Haddenhorst, Björn AU - Bengs, Viktor AU - Hüllermeier, Eyke ED - Beygelzimer, A. ED - Dauphin, Y. ED - Liang, P. ED - Vaughan, J. Wortman ID - 30723 T2 - Advances in Neural Information Processing Systems TI - Identification of the Generalized Condorcet Winner in Multi-dueling Bandits ER - TY - GEN AU - Peckhaus, Volker ID - 17751 T2 - Staatslexikon. Recht, Wirtschaft, Gesellschaft, Bd. 5: Schule - Virtuelle Realität TI - Technikphilosophie ER - TY - GEN AB - Information exchange over networks can be affected by various forms of delay. This causes challenges for using the network by a multi-agent system to solve a distributed optimisation problem. Distributed optimisation schemes, however, typically do not assume network models that are representative for real-world communication networks, since communication links are most of the time abstracted as lossless. Our objective is therefore to formulate a representative network model and provide practically verifiable network conditions that ensure convergence of distributed algorithms in the presence of interference and possibly unbounded delay. Our network is modelled by a sequence of directed-graphs, where to each network link we associate a process for the instantaneous signal-to-interference-plus-noise ratio. We then formulate practical conditions that can be verified locally and show that the age of information (AoI) associated with data communicated over the network is in $\mathcal{O}(\sqrt{n})$. Under these conditions we show that a penalty-based gradient descent algorithm can be used to solve a rich class of stochastic, constrained, distributed optimisation problems. The strength of our result lies in the bridge between practical verifiable network conditions and an abstract optimisation theory. We illustrate numerically that our algorithm converges in an extreme scenario where the average AoI diverges. AU - Redder, Adrian AU - Ramaswamy, Arunselvan AU - Karl, Holger ID - 30792 T2 - arXiv:2105.04230 TI - Practical sufficient conditions for convergence of distributed optimisation algorithms over communication networks with interference ER - TY - CONF AB - Graph neural networks (GNNs) have been successfully applied in many structured data domains, with applications ranging from molecular property prediction to the analysis of social networks. Motivated by the broad applicability of GNNs, we propose the family of so-called RankGNNs, a combination of neural Learning to Rank (LtR) methods and GNNs. RankGNNs are trained with a set of pair-wise preferences between graphs, suggesting that one of them is preferred over the other. One practical application of this problem is drug screening, where an expert wants to find the most promising molecules in a large collection of drug candidates. We empirically demonstrate that our proposed pair-wise RankGNN approach either significantly outperforms or at least matches the ranking performance of the naive point-wise baseline approach, in which the LtR problem is solved via GNN-based graph regression. AU - Damke, Clemens AU - Hüllermeier, Eyke ED - Soares, Carlos ED - Torgo, Luis ID - 27381 KW - Graph-structured data KW - Graph neural networks KW - Preference learning KW - Learning to rank SN - 0302-9743 T2 - Proceedings of The 24th International Conference on Discovery Science (DS 2021) TI - Ranking Structured Objects with Graph Neural Networks VL - 12986 ER - TY - GEN AB - Automated machine learning (AutoML) strives for the automatic configuration of machine learning algorithms and their composition into an overall (software) solution - a machine learning pipeline - tailored to the learning task (dataset) at hand. Over the last decade, AutoML has developed into an independent research field with hundreds of contributions. While AutoML offers many prospects, it is also known to be quite resource-intensive, which is one of its major points of criticism. The primary cause for a high resource consumption is that many approaches rely on the (costly) evaluation of many machine learning pipelines while searching for good candidates. This problem is amplified in the context of research on AutoML methods, due to large scale experiments conducted with many datasets and approaches, each of them being run with several repetitions to rule out random effects. In the spirit of recent work on Green AI, this paper is written in an attempt to raise the awareness of AutoML researchers for the problem and to elaborate on possible remedies. To this end, we identify four categories of actions the community may take towards more sustainable research on AutoML, i.e. Green AutoML: design of AutoML systems, benchmarking, transparency and research incentives. AU - Tornede, Tanja AU - Tornede, Alexander AU - Hanselle, Jonas Manuel AU - Wever, Marcel Dominik AU - Mohr, Felix AU - Hüllermeier, Eyke ID - 30866 T2 - arXiv:2111.05850 TI - Towards Green Automated Machine Learning: Status Quo and Future Directions ER - TY - JOUR AU - Schulz, Andreas AU - Wecker, Christian AU - Inguva, Venkatesh AU - Lopatin, Alexey S. AU - Kenig, Eugeny Y. ID - 30864 JF - Chemical Engineering Science KW - Applied Mathematics KW - Industrial and Manufacturing Engineering KW - General Chemical Engineering KW - General Chemistry SN - 0009-2509 TI - A PLIC-based method for species mass transfer at free fluid interfaces VL - 251 ER - TY - JOUR AB -