@article{58492, abstract = {{A coupled finite plasticity ductile damage and failure model is proposed for the finite element simulation of clinch joining, which incorporates stress-state dependency and regularisation by gradient-enhancement of the damage variable. Ductile damage is determined based on a failure indicator governed by a failure surface in stress space. The latter is exemplary chosen as a combination of the Hosford–Coulomb and Cockcroft–Latham–Oh failure criteria for the high and low stress triaxiality range, respectively, to cover the wide stress range encountered in forming. Damage is coupled to elasto-plasticity to capture the damage-induced degradation of the stiffness and flow stress. This affects the material behaviour up to failure, thereby realistically altering the stress state. Consequently, especially for highly ductile materials, where substantial necking and localisation precede material fracture, the failure prediction is enhanced. The resulting stress softening is regularised by gradient-enhancement to obtain mesh-objective results. The analysis of a modified punch test experiment emphasises how the damage-induced softening effect can strongly alter the actual stress state towards failure. Moreover, the impact of successful regularisation is shown, and the applicability of the damage and failure model to clinch joining is proven.}}, author = {{Friedlein, Johannes and Mergheim, Julia and Steinmann, Paul}}, issn = {{0022-5096}}, journal = {{Journal of the Mechanics and Physics of Solids}}, keywords = {{Finite plasticity, Ductile damage, Gradient-enhancement, Stress-state dependency, Failure}}, publisher = {{Elsevier BV}}, title = {{{Modelling of stress-state-dependent ductile damage with gradient-enhancement exemplified for clinch joining}}}, doi = {{10.1016/j.jmps.2025.106026}}, volume = {{196}}, year = {{2025}}, } @inproceedings{62079, abstract = {{This paper investigates two modeling approaches for the simulation of the deformation and decomposition behavior of preconsolidated rovings above the thermoplastic matrix{\textquoteright} melting temperature. This is crucial for capturing the local material structure after processes introducing highly localized deformation such as mechanical joining processes between metal and fiber reinforced thermoplastics (FRTP). A generic finite element (FE) model is developed, incorporating interfaces discretized through either cohesive zone (CZ) elements or Coulomb friction-based contacts. The material parameters for the FE elements are derived from the initial stiffness of a statistical volume element (SVE) at micro scale modelled with an Arbitrary-Lagrange-Eulerian method for three load cases. The CZ properties calculated are based on the shear viscosity of the composite. The CZ and contact modelling approaches are evaluated using three load cases of the SVE, comparing force-displacement curves. Under simple loading conditions, such as normal pressure tension and bending, both methods produce similar results; however, in complex load cases, the CZ approach shows clear advantages in handling interface interactions and shows robust simulations. The CZ approach thus presents a promising method for simulating roving decomposition in FRTP-metal joining applications above the matrix{\textquoteright} melting temperature.}}, author = {{Gröger, Benjamin and Gerritzen, Johannes and Hornig, Andreas and Gude, Maik}}, booktitle = {{Sheet Metal 2025}}, editor = {{Meschut, G. and Bobbert, M. and Duflou, J. and Fratini, L. and Hagenah, H. and Martins, P. and Merklein, M. and Micari, F.}}, isbn = {{978-1-64490-354-4}}, keywords = {{Finite Element Method (FEM), Process, Thermoplastic Fiber Reinforced Plastic}}, pages = {{268–275}}, publisher = {{Materials Research Forum LLC, Materials Research Foundations}}, title = {{{Modeling approaches for the decomposition behavior of preconsolidated rovings throughout local deformation processes}}}, doi = {{10.21741/9781644903551-33}}, year = {{2025}}, } @inproceedings{54807, abstract = {{This paper considers the shape formation problem within the 3D hybrid model, where a single agent with a strictly limited viewing range and the computational capacity of a deterministic finite automaton manipulates passive tiles through pick-up, movement, and placement actions. The goal is to reconfigure a set of tiles into a specific shape termed an icicle. The icicle, identified as a dense, hole-free structure, is strategically chosen to function as an intermediate shape for more intricate shape formation tasks. It is designed for easy exploration by a finite state agent, enabling the identification of tiles that can be lifted without breaking connectivity. Compared to the line shape, the icicle presents distinct advantages, including a reduced diameter and the presence of multiple removable tiles. We propose an algorithm that transforms an arbitrary initially connected tile structure into an icicle in 𝒪(n³) steps, matching the runtime of the line formation algorithm from prior work. Our theoretical contribution is accompanied by an extensive experimental analysis, indicating that our algorithm decreases the diameter of tile structures on average.}}, author = {{Hinnenthal, Kristian and Liedtke, David Jan and Scheideler, Christian}}, booktitle = {{3rd Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2024)}}, editor = {{Casteigts, Arnaud and Kuhn, Fabian}}, isbn = {{978-3-95977-315-7}}, issn = {{1868-8969}}, keywords = {{Programmable Matter, Shape Formation, 3D Model, Finite Automaton}}, pages = {{15:1–15:20}}, publisher = {{Schloss Dagstuhl – Leibniz-Zentrum für Informatik}}, title = {{{Efficient Shape Formation by 3D Hybrid Programmable Matter: An Algorithm for Low Diameter Intermediate Structures}}}, doi = {{10.4230/LIPIcs.SAND.2024.15}}, volume = {{292}}, year = {{2024}}, } @inbook{54802, abstract = {{Motivated by the prospect of nano-robots that assist human physiological functions at the nanoscale, we investigate the coating problem in the three-dimensional model for hybrid programmable matter. In this model, a single agent with strictly limited viewing range and the computational capability of a deterministic finite automaton can act on passive tiles by picking up a tile, moving, and placing it at some spot. The goal of the coating problem is to fill each node of some surface graph of size n with a tile. We first solve the problem on a restricted class of graphs with a single tile type, and then use constantly many tile types to encode this graph in certain surface graphs capturing the surface of 3D objects. Our algorithm requires O(n^2) steps, which is worst-case optimal compared to an agent with global knowledge and no memory restrictions.}}, author = {{Kostitsyna, Irina and Liedtke, David Jan and Scheideler, Christian}}, booktitle = {{Structural Information and Communication Complexity}}, editor = {{Emek, Yuval}}, isbn = {{9783031606021}}, issn = {{0302-9743}}, keywords = {{Programmable Matter, Coating, Finite Automaton, 3D}}, publisher = {{Springer Nature Switzerland}}, title = {{{Universal Coating by 3D Hybrid Programmable Matter}}}, doi = {{10.1007/978-3-031-60603-8_21}}, year = {{2024}}, } @article{54847, abstract = {{The widespread adoption of ultra-high strength steels, due to their high bulk resistivity, intensifies expulsion issues in resistance spot welding (RSW), deteriorating both the spot weld and surface quality. This study presents a novel approach to prevent expulsion by employing a preheating current. Through characteristic analysis of joint formation under critical welding current, the importance of plastic material encapsulation around the weld nugget (plastic shell) at high temperatures in preventing expulsion is highlighted. To evaluate the effect of preheating on the plastic shell and understand its mechanism in expulsion prevention, a two-dimensional welding simulation model for dissimilar ultra-high strength steel joints was established. The results showed that optimal preheating enhances the thickness of the plastic shell, improving its ability to encapsulate the weld nugget during the primary welding phase, thereby diminishing expulsion risks. Experimental validation confirmed that by employing the optimal preheating current, the maximum nugget diameter was enhanced to 9.42 mm, marking an increase of 13.4 % and extending the weldable current range by 27.5 %. Under quasi-static cross-tensile loading, joints with preheating demonstrated a 7.9 % enhancement in maximum load-bearing capacity compared to joints without preheating, showing a reproducible and complete pull-out failure mode within the heat-affected zone. This study offers a prevention method based on underlying mechanisms, providing a new perspective for future research on welding parameter optimization with the aim of expulsion prevention.}}, author = {{Yang, Keke and El-Sari, Bassel and Olfert, Viktoria and Wang, Zhuoqun and Biegler, Max and Rethmeier, Michael and Meschut, Gerson}}, issn = {{1526-6125}}, journal = {{Journal of Manufacturing Processes}}, keywords = {{Expulsion Resistance spot welding Finite element modelling Preheating Weldable current range Ultra-high strength steel}}, pages = {{489--502}}, publisher = {{Elsevier BV}}, title = {{{Expulsion prevention in resistance spot welding of dissimilar joints with ultra-high strength steel: An analysis of the mechanism and effect of preheating current}}}, doi = {{10.1016/j.jmapro.2024.06.034}}, volume = {{124}}, year = {{2024}}, } @article{55519, abstract = {{Im Folgenden wird ein wellenleiterbasierter Ansatz zur Bestimmung von viskoelastischen Materialparametern für eine numerische Simulation der Schallausbreitung in transversal isotropen Polymeren vorgestellt. Ein hierfür entwickeltes Puls-Echo-Messverfahren liefert Messsignale, welche anschließend zur Schätzung der Materialparameter von absorbierenden, zylindrischen Polymerproben genutzt werden. Darüber hinaus kommen in dem Messaufbau Schallwandler zum Einsatz, die eine segmentierte ringförmige Anregung der Probe verursachen und die Sensitivität gegenüber Scherbewegungen erhöhen. Mithilfe einer ersten strahlentheoretischen Startwertschätzung werden eine multimodale, semianalytische Simulation der Schallausbreitung im Wellenleiter realisiert und schließlich die Materialparameter im inversen Ansatz geschätzt.}}, author = {{Dreiling, Dmitrij and Itner, Dominik and Gravenkamp, Hauke and Birk, Carolin and Henning, Bernd}}, isbn = {{2196-7113}}, journal = {{tm - Technisches Messen}}, keywords = {{Materialcharakterisierung, Puls-Echo Methode, inverse Verfahren}}, number = {{s1}}, pages = {{26--31}}, publisher = {{De Gruyter}}, title = {{{Die Bestimmung viskoelastischer Materialparameter von Polymeren mittels eines Puls-Echo-Messverfahrens}}}, doi = {{10.1515/teme-2024-0045}}, volume = {{91}}, year = {{2024}}, } @phdthesis{56654, abstract = {{Residual stresses in directly joined laminates made of steel and carbon fiber reinforced epoxy resin reduce the interface and bond strength and thus have to be taken into account for the strength analysis of structural components. For a holistic description of residual stresses, a thermo-chemo-mechanical constitutive model is introduced in the present work and presented for the multi-scale analysis of residual stress patterns. In this context, the analysis of representative unit cells with regular and stochastic distribution of fibers gives information about the associated deformation and stress fields. Dehomogenization at macroscopically highly stressed regions, characterized by local stress peaks, reveals the effect of gradient deformation in the microstructure. Another aspect of this work is the development of FFT-based Galerkin methods, which allows an evaluation of the effect of defect densities, heterogeneities and morphologies on the applicability of the incremental hole drilling method. It could be demonstrated that the incremental hole drilling method is particularly sensitive to defects running along the surface.}}, author = {{Tinkloh, Steffen Rainer}}, isbn = {{9783757887650}}, keywords = {{Hybride Werkstoffverbunde, Eigenspanungen, FFT-basierte Galerkin-Methode, Mikromechanik, Finite-Elemente-Methode}}, pages = {{168}}, publisher = {{BoD - Books on Demand}}, title = {{{Mikromechanische Analyse von Eigenspannungen in direktgefügten kohlenstofffaserverstärkten Kunststoff-Stahl-Schichtverbunden}}}, year = {{2024}}, } @techreport{52127, abstract = {{This report documents the program and the outcomes of Dagstuhl Seminar 23161 "Pushing the Limits of Computational Combinatorial Constructions". In this Dagstuhl Seminar, we focused on computational methods for challenging problems in combinatorial construction. This includes algorithms for construction of combinatorial objects with prescribed symmetry, for isomorph-free exhaustive generation, and for combinatorial search. Examples of specific algorithmic techniques are tactical decomposition, the Kramer-Mesner method, algebraic methods, graph isomorphism software, isomorph-free generation, clique-finding methods, heuristic search, SAT solvers, and combinatorial optimization. There was an emphasis on problems involving graphs, designs and codes, also including topics in related fields such as finite geometry, graph decomposition, Hadamard matrices, Latin squares, and q-analogs of designs and codes.}}, author = {{Moura, Lucia and Nakic, Anamari and Östergård, Patric and Wassermann, Alfred and Weiß, Charlene}}, keywords = {{automorphism groups, combinatorial algorithms, finite geometries, subspace designs}}, pages = {{40--57}}, publisher = {{Schloss Dagstuhl - Leibniz-Zentrum für Informatik}}, title = {{{Pushing the Limits of Computational Combinatorial Constructions (Dagstuhl Seminar 23161)}}}, doi = {{10.4230/DagRep.13.4.40}}, volume = {{13, Issue 4}}, year = {{2023}}, } @article{56097, abstract = {{We contrast different gradient-enhancements for plasticity-damage material models in the logarithmic strain space and compare them to reference models based on multiplicative plasticity. The models being compared include plasticity - gradient-damage, where the gradient-enhancement is applied on the local damage variable, and gradient-plasticity - damage with a gradient-enhanced plastic hardening variable. Thereby, gradient-plasticity proved to be able to simultaneously regularise plastic and ductile (plasticity-driven) damage localisation as confirmed by numerical localisation analyses. This appears to be especially advantageous for logarithmic strain space plasticity-damage, because of the observed plastic localisation even for the case of plasticity with hardening. Even though gradient-plasticity appears to be numerically more demanding, two numerical examples indicate a good robustness and mesh objectivity in the softening regime. Moreover, the internal length for plasticity is able to adjust the damage zone width, similarly to gradient-damage, however ensuring a priori that damage takes place exclusively inside the plastic zone.}}, author = {{Friedlein, Johannes and Mergheim, Julia and Steinmann, Paul}}, issn = {{0997-7538}}, journal = {{European Journal of Mechanics - A/Solids}}, keywords = {{Finite plasticity, Logarithmic strain space, Ductile damage, Gradient-enhancement, Gradient-plasticity, Gradient-damage, Loss of ellipticity}}, publisher = {{Elsevier BV}}, title = {{{Efficient gradient enhancements for plasticity with ductile damage in the logarithmic strain space}}}, doi = {{10.1016/j.euromechsol.2023.104946}}, volume = {{99}}, year = {{2023}}, } @article{35643, abstract = {{Immer mehr Kinder besuchen täglich pädagogische Einrichtungen und verbringen dort zunehmend mehr Zeit; dies führt dazu, dass sie auch vermehrt in pädagogischen Einrichtungen essen. Als Qualitätsmerkmal von Kindertageseinrichtungen wird dabei zunehmend das Thema Essen als gesunde Ernährung zentral. Gleichzeitig liegen bislang erst wenige Studien vor, die auch die Beteiligungs- und Selbstbestimmungsmöglichkeiten von Kindern beim Essen im Alltag der Kindertageseinrichtung betrachten. Auf der empirischen Basis der Frankfurter Kinderbefragung 2018 fragt der vorliegende Beitrag danach, mit welchen kollektiven Orientierungsmustern pädagogische Fachkräfte in Kindertageseinrichtungen die Mahlzeiten gestalten und welche Rolle sie den beteiligten Akteur*innen darin zuweisen. Während in den Gruppendiskussionen einerseits disparate Orientierungen an Ernährungserziehung und Ernährungsbildung sichtbar werden, eint sie andererseits, dass den Kindern selbst kaum substanzielle Einflussmöglichkeiten auf die soziale Gestaltung der Mahlzeit eröffnet werden.}}, author = {{Klein, Alexandra and Landhäußer, Sandra}}, journal = {{Soziale Passagen}}, keywords = {{Ernährung Mahlzeiten Gruppendiskussion Dokumentarische Methode Beteiligung}}, number = {{14}}, pages = {{pages 307–320}}, publisher = {{Springer}}, title = {{{Essen in Kindertageseinrichtungen. Orientierungsmuster von Fachkräften zwischen Anpassung und Ermöglichung}}}, doi = {{doi.org/10.1007/s12592-022-00438-0}}, year = {{2022}}, } @misc{25126, abstract = {{Motivated by the prospect of computing agents that explore unknown environments and construct convex hulls on the nanoscale, we investigate the capabilities and limitations of a single deterministic finite automaton robot in the three-dimensional hybrid model for programmable matter. In this model, active robots move on a set of passive tiles, called configuration, with the geometric shape of rhombic dodecahedra on the adjacency graph of the face-centered cubic sphere-packing. We show that the exploration problem is equally hard in the hybrid model and in three-dimensional mazes, in which tiles have the shape of cubes and are positioned at the vertices of $\mathbb{Z}^3$. Thereby, a single robot with a constant number of pebbles cannot solve this problem in the hybrid model on arbitrary configurations. We provide algorithms for a robot with two pebbles that solve the exploration problem in the subclass of compact configurations of size $n$ in $\O(n^3)$ rounds. Further, we investigate the robot's capabilities of detection and hull construction in terms of restricted orientation convexity. We show that a robot without any pebble can detect strong $\O$-convexity in $\O(n)$ rounds, but cannot detect weak $\O$-convexity, not even if provided with a single pebble. Assuming that a robot can construct tiles from scratch and deconstruct previously constructed tiles, we show that the strong $\O$-hull of any given configuration of size $n$ can be constructed in $\O(n^4)$ rounds, even if the robot cannot distinguish constructed from native tiles.}}, author = {{Liedtke, David Jan}}, keywords = {{Robot Exploration, Finite Automaton, Hybrid Model for Programmable Matter, Convex Hull}}, title = {{{Exploration and Convex Hull Construction in the Three-Dimensional Hybrid Model}}}, year = {{2021}}, } @article{45785, abstract = {{In this paper, we implement the multidomain compact finite difference method to numerically study high dimensional chaos by considering the nine-dimensional Lorenz system. Most of the existing numerical methods converge slowly for this kind of problems and this results in inaccurate approximations. Though highly accurate, the compact finite difference method becomes less accurate for problems characterized by chaotic solutions, even with an increase in the number of grid points. As a result, in this work, we adopt the multidomain approach. This approach remarkably improves the results as well as the efficiency of the method.}}, author = {{Kouagou, N.J. and Dlamini, P.G. and Simelane, S.M.}}, issn = {{1110-0168}}, journal = {{Alexandria Engineering Journal}}, keywords = {{Multidomain, Compact finite difference, 9D Lorenz system}}, number = {{4}}, pages = {{2617--2625}}, title = {{{On the multi-domain compact finite difference relaxation method for high dimensional chaos: The nine-dimensional Lorenz system}}}, doi = {{https://doi.org/10.1016/j.aej.2020.04.025}}, volume = {{59}}, year = {{2020}}, } @inproceedings{9969, abstract = {{Zuverlässigkeit, Sicherheit und Verfügbarkeit gewinnen bei der Anwendung von technischen Systemen eine immer größere Bedeutung. Aus diesem Grund hat sich Condition Monitoring, die Zustandsüberwachung eines technischen Produkts, in verschiedenen Industriebranchen etabliert. Die sensorbasierte Überwachung eines Produkts während seiner Betriebsdauer in Kombination mit Condition Monitoring Methoden ermöglichen die Bestimmung des aktuellen Zustands des Produkts und somit eine Diagnose, ob das Produkt seine ihm zugeschriebene Funktion zum aktuellen Zeitpunkt erfüllt. Neben Diagnosen bietet Condition Monitoring auch die Möglichkeit Prognosen aufzustellen, dabei wird die restliche Nutzungsdauer des Produkts aufbauend auf geeigneten Sensordaten geschätzt. So kann eine intelligente Wartungsplanung umgesetzt werden, die im Gegensatz zu klassischen Ansätzen keine festen Wartungsintervalle benötigt und die Nachteile einer rein reaktiven Wartung kompensiert. Stattdessen ist es möglich ein Element bis vor das Ende seiner Lebensdauer zu nutzen und erst dann zu warten, um eine optimale Nutzung zu gewährleisten. Durch eine Bestimmung der verbleibenden Restlebensdauer während des Betriebs ist eine optimale Wartungsplanung möglich, wodurch die Verfügbarkeit und die Auslastung der überwachten Produkte signifikant gesteigert werden kann. In dieser Arbeit soll ein produktspezifisches Condition Monitoring System für Gummi-Metall-Elemente entwickelt werden. Diese Elemente werden zur Federung, Geräusch- und/oder Schwingungsisolation in vielen verschiedenen Anwendungen eingesetzt, wie bspw. in Nutz- und Schienenfahrzeugen oder Windenergieanlagen. In Industrie und Forschung werden bereits Zustandsüberwachungen von Systemen mit integrierten Gummi-Metall-Elementen eingesetzt, allerdings noch keine Condition Monitoring Systeme zur alleinigen Zustandsüberwachung dieser Elemente. Aktuell ist es üblich die Lebensdauer dieser Elemente aufbauend auf beschleunigten Lebensdauerversuchen und Erfahrungswerten abzuschätzen. Mit dem Ziel die Lebensdauer des fokussierten Produkts präziser vorherzusagen und damit eine intelligente Wartungsplanung zu ermöglichen, wird die Entwicklung eines Condition Monitoring Systems für Gummi-Metall-Elemente angestrebt und in dieser Arbeit erläutert.}}, author = {{Bender, Amelie and Kaul, Thorben and Sextro, Walter}}, booktitle = {{Verlagsschriftenreihe des Heinz Nixdorf Instituts Band 369, Paderborn, 2017}}, keywords = {{Zustandsüberwachung, Condition Monitoring, Prognose, Gummi-Metall-Elemente, Restlebensdauerschätzung}}, pages = {{347--358}}, title = {{{Entwicklung eines Condition Monitoring Systems für Gummi-Metall-Elemente}}}, year = {{2017}}, } @article{9972, abstract = {{The transportation of dry fine powders is an emerging technologic task, as in biotechnology, pharmaceu-tical and coatings industry the particle sizes of processed powders get smaller and smaller. Fine powdersare primarily defined by the fact that adhesive and cohesive forces outweigh the weight forces, leadingto mostly unwanted agglomeration (clumping) and adhesion to surfaces. Thereby it gets more difficult touse conventional conveyor systems (e.g. pneumatic or vibratory conveyors) for transport. A rather newmethod for transporting these fine powders is based on ultrasonic vibrations, which are used to reducefriction between powder and substrate. Within this contribution an experimental set-up consisting of apipe, a solenoid actuator for axial vibration and an annular piezoelectric actuator for the high frequencyradial vibration of the pipe is described. Since amplitudes of the radial pipe vibration should be as large aspossible to get high effects of friction reduction, the pipe is excited to vibrate in resonance. To determinethe optimum excitation frequency and actuator position the vibration modes and resonance frequenciesof the pipe are calculated and measured. Results are in good accordance.}}, author = {{Dunst, Paul and Hemsel, Tobias and Sextro, Walter}}, journal = {{elsevier}}, keywords = {{Powder transport Piezoelectrics Ultrasonics Pipe vibration Finite element simulation Fine powder}}, pages = {{733--736}}, title = {{{Analysis of pipe vibration in an ultrasonic powder transportationsystem}}}, volume = {{Sensors and Actuators A 263}}, year = {{2017}}, } @inproceedings{9955, abstract = {{Wire bonding has been an established packaging technology for decades. When introducing copper as wire material for high power applications, adaptations to the bonding process and to machines became necessary. Here, challenges occur due to the stiffer wire material and changing oxide layers on the contact partners. To achieve sufficient process stability, a clean bond area is required, which can only be achieved with high shear stresses in the contact partners surfaces. These necessitate high normal forces to plastically deform the wire and substrate. To achieve such high stresses in the contact area, the bonding tool needs to be able to transmit the needed tangential forces to the top side of the wire. The wire itself performs a shear movement and transmits the force into the contact area to clean the contaminant and oxide layers and to level the desired bond surfaces. The main function of the tool is to transmit these forces. If the bond tool can only transmit low forces in the direction of excitation, the parameter space for a stable bond process is severely restricted. Here, a modeling approach to estimate how well different tool shapes meet the demand of transmitting high tangential forces is presented. The model depends on wire deformation and thus on the ultrasonic softening effect.}}, author = {{Althoff, Simon and Meyer, Tobias and Unger, Andreas and Sextro, Walter and Eacock, Florian}}, booktitle = {{IEEE 66th Electronic Components and Technology Conference}}, keywords = {{finite element simulation, wire bonding, tool geometry}}, pages = {{2103--2110}}, title = {{{Shape-Dependent Transmittable Tangential Force of Wire Bond Tools}}}, doi = {{10.1109/ECTC.2016.234}}, year = {{2016}}, } @phdthesis{24751, abstract = {{Das Thema der vorliegenden Dissertation ist die "Prozessqualifizierung zur verlässlichen Herstellung von Produkten im Polymer Lasersinterverfahren". Über eine definierte Qualitätsprozesskette werden sämtliche, auf die Produktqualität relevanten Einflussparameter, bestimmt und berücksichtigt. Unterschiedliche Methoden zur Materialcharakterisierung des pulverförmigen Ausgangsmaterials werden analysiert und bewertet. Rheologische sowie chemische Eigenschaften, aber auch die Partikelgrößenverteilung oder die Schüttdichte werden hinsichtlich Relevanz, Einfluss und Anwenderfreundlichkeit untersucht. Das Ziel ist eine sinnvolle Bestimmung des Ausgangszustandes des Pulvers anhand definierter, relevanter Materialeigenschaften, um reproduzierbare technische Bauteileigenschaften zu gewährleisten. Dazu werden mechanische, dynamisch-mechanische, physikalische, elektrische, thermische sowie chemische Untersuchungen durchgeführt und hinsichtlich wichtiger Einflussparameter evaluiert. Die Bestimmung erfolgt über entwickelte Referenzjobs, in denen die hauptsächlichen Einflussfaktoren auf das Polymer-Lasersinterverfahren entlang der Qualitätsprozesskette berücksichtigt werden. Die charakterisierten Daten dienen zur Auslegung eines fiktiven Produktes aus der Luftfahrtindustrie. Mit Hilfe dieser Methoden lassen sich Materialkennwerte für diverse Simulationstools eindeutig bestimmen um eine realitätsnahe Berechnung zu gewährleisten. }}, author = {{Rüsenberg, Stefan}}, keywords = {{Additive Fertigung, Polymere, Lasersintern, Methode, Qualität, Konstruktion, Eigenschaften, Material, Charakterisierung, Qualifizierung}}, pages = {{242}}, publisher = {{Shaker Verlag GmbH}}, title = {{{Prozessqualifizierung zur verlässlichen Herstellung von Produkten im Polymer Lasersinterverfahren}}}, volume = {{Band, 2}}, year = {{2015}}, } @article{13893, abstract = {{In this contribution, we present an efficient approach for the transient and time-causal modeling of guided waves in viscoelastic cylindrical waveguides in the context of ultrasonic material characterization. We use the scaled boundary finite element method (SBFEM) for efficient computation of the phase velocity dispersion. Regarding the viscoelastic behavior of the materials under consideration, we propose a decomposition approach that considers the real-valued frequency dependence of the (visco-)elastic moduli and, separately, of their attenuation. The modal expansion approach is utilized to take the transmitting and receiving transducers into account and to propagate the excited waveguide modes through a waveguide of finite length. The effectiveness of the proposed simulation model is shown by comparison with a standard transient FEM simulation as well as simulation results based on the exact solution of the complex-valued viscoelastic guided wave problem. Two material models are discussed, namely the fractional Zener model and the anti-Zener model; we re-interpret the latter in terms of the Rayleigh damping model. Measurements are taken on a polypropylene sample and the proposed transient simulation model is used for inverse material characterization. The extracted material properties may then be used in computer-aided design of ultrasonic systems.}}, author = {{Bause, Fabian and Gravenkamp, Hauke and Rautenberg, Jens and Henning, Bernd}}, issn = {{0957-0233}}, journal = {{Measurement Science and Technology}}, keywords = {{viscoelasticity, ultrasonics, guided waves, inverse problem, scaled boundary finite element method}}, number = {{095602 (17pp)}}, title = {{{Transient modeling of ultrasonic guided waves in circular viscoelastic waveguides for inverse material characterization}}}, doi = {{10.1088/0957-0233/26/9/095602}}, volume = {{26}}, year = {{2015}}, } @inproceedings{9868, abstract = {{In order to increase mechanical strength, heat dissipation and ampacity and to decrease failure through fatigue fracture, wedge copper wire bonding is being introduced as a standard interconnection method for mass production. To achieve the same process stability when using copper wire instead of aluminum wire a profound understanding of the bonding process is needed. Due to the higher hardness of copper compared to aluminum wire it is more difficult to approach the surfaces of wire and substrate to a level where van der Waals forces are able to arise between atoms. Also, enough friction energy referred to the total contact area has to be generated to activate the surfaces. Therefore, a friction model is used to simulate the joining process. This model calculates the resulting energy of partial areas in the contact surface and provides information about the adhesion process of each area. The focus here is on the arising of micro joints in the contact area depending on the location in the contact and time. To validate the model, different touchdown forces are used to vary the initial contact areas of wire and substrate. Additionally, a piezoelectric tri-axial force sensor is built up to identify the known phases of pre-deforming, cleaning, adhering and diffusing for the real bonding process to map with the model. Test substrates as DBC and copper plate are used to show the different formations of a wedge bond connection due to hardness and reaction propensity. The experiments were done by using 500 $\mu$m copper wire and a standard V-groove tool.}}, author = {{Althoff, Simon and Neuhaus, Jan and Hemsel, Tobias and Sextro, Walter}}, booktitle = {{Electronic Components and Technology Conference (ECTC), 2014 IEEE 64th}}, keywords = {{adhesion, circuit reliability, deformation, diffusion, fatigue cracks, friction, interconnections, lead bonding, van der Waals forces, Cu, adhering process, adhesion process, ampacity improvement, bond quality improvement, cleaning process, diffusing process, fatigue fracture failure, friction energy, friction model, heat dissipation, mechanical strength, piezoelectric triaxial force sensor, predeforming process, size 500 mum, total contact area, van der Waals forces, wedge copper wire bonding, Bonding, Copper, Finite element analysis, Force, Friction, Substrates, Wires}}, pages = {{1549--1555}}, title = {{{Improving the bond quality of copper wire bonds using a friction model approach}}}, doi = {{10.1109/ECTC.2014.6897500}}, year = {{2014}}, } @inproceedings{9895, abstract = {{Power semiconductor modules are used to control and switch high electrical currents and voltages. Within the power module package wire bonding is used as an interconnection technology. In recent years, aluminum wire has been used preferably, but an ever-growing market of powerful and efficient power modules requires a material with better mechanical and electrical properties. For this reason, a technology change from aluminum to copper is indispensable. However, the copper wire bonding process reacts more sensitive to parameter changes. This makes manufacturing reliable copper bond connections a challenging task. The aim of the BMBF funded project Itsowl-InCuB is the development of self-optimizing techniques to enable the reliable production of copper bond connections under varying conditions. A model of the process is essential to achieve this aim. This model needs to include the dynamic elasto-plastic deformation, the ultrasonic softening effect and the proceeding adhesion between wire and substrate. This paper focusses on the pre-deformation process. In the touchdown phase, the wire is pressed into the V-groove of the tool and a small initial contact area between wire and substrate arise. The local characteristics of the material change abruptly because of the cold forming. Consequently, the pre-deformation has a strong effect on the joining process. In [1], a pre-cleaning effect during the touchdown process of aluminum wires by cracking of oxide layers was presented. These interactions of the process parameters are still largely unknown for copper. In a first step, this paper validates the importance of modeling the pre-deformation by showing its impact on the wire deformation characteristic experimentally. Creating cross-section views of pre-deformed copper wires has shown a low deformation degree compared to aluminum. By using a digital microscope and a scanning confocal microscope an analysis about the contact areas and penetration depths after touchdown has been made. Additionally, it has to be taken into account that the dynamical touchdown force depends on the touchdown speed and the touchdown force set in the bonding machine. In order to measure the overshoot in the force signals, a strain gauge sensor has been used. Subsequently, the affecting factors have been interpreted independently Furthermore, the material properties of copper wire have been investigated with tensile tests and hardness measurements. In a second step, the paper presents finite element models of the touchdown process for source and destination bonds. These models take the measured overshoot in the touchdown forces into account. A multi-linear, isotropic material model has been selected to map the material properties of the copper. A validation of the model with the experimental determined contact areas, normal pressures and penetration depths reveals the high model quality. Thus, the simulation is able to calculate and visualize the three dimensional pre-deformation with an integrated material parameter of the wire if the touchdown parameters of the bonding machine are known. Based on the calculated deformation degrees of wire and substrate, it is probably possible to investigate the effect of the pre-deformation on the pre-cleaning phase in the copper wire bonding.}}, author = {{Unger, Andreas and Sextro, Walter and Althoff, Simon and Eichwald, Paul and Meyer, Tobias and Eacock, Florian and Brökelmann, Michael}}, booktitle = {{Proceedings of the 47th International Symposium on Microelectronics (IMAPS)}}, keywords = {{pre-deformation, copper wire bonding, finite element model}}, pages = {{289--294}}, title = {{{Experimental and Numerical Simulation Study of Pre-Deformed Heavy Copper Wire Wedge Bonds}}}, year = {{2014}}, } @article{34442, abstract = {{Radial shaft seals are used in a variety of applications, where rotating shafts in steady housings have to be sealed. Typical examples are crankshafts, camshafts, differential gear or hydraulic pumps. In the operating state the elastomeric seal ring and the shaft are separated by a lubrication film of just a few micrometers. Due to shear strain and fluid friction the contact area is subject to a higher temperature than the rest of the seal ring. The stiffness of the elastomeric material is intensely influenced by this temperature and thus contact pressure, friction and wear also strongly depend on the contact temperature. In order to simulate the contact behavior of elastomer seal rings it is essential to use a comprehensive approach which takes into consideration the interaction of temperature, friction and wear. Based on this idea a macroscopic simulation model has been developed at the MEGT. It combines a finite element approach for the simulation of contact pressure at different wear states, a semi-analytical approach for the calculation of contact temperature and an empirical approach for the calculation of friction. In this paper the model setup is presented, as well as simulation and experimental results.}}, author = {{Frölich, D. and Magyar, Balázs and Sauer, B.}}, issn = {{0043-1648}}, journal = {{Wear}}, keywords = {{Radial shaft seal ring, Contact temperature, Wear, Friction torque, Finite element simulation}}, number = {{1}}, pages = {{71--80}}, title = {{{A comprehensive model of wear, friction and contact temperature in radial shaft seals}}}, doi = {{https://doi.org/10.1016/j.wear.2013.12.030}}, volume = {{311}}, year = {{2014}}, }