TY - JOUR
AU - Mirhosseini, Hossein
AU - Tahmasbi, Hossein
AU - Kuchana, Sai Ram
AU - Ghasemi, Alireza
AU - Kühne, Thomas
ID - 33657
JF - Computational Materials Science
KW - Computational Mathematics
KW - General Physics and Astronomy
KW - Mechanics of Materials
KW - General Materials Science
KW - General Chemistry
KW - General Computer Science
SN - 0927-0256
TI - An automated approach for developing neural network interatomic potentials with FLAME
VL - 197
ER -
TY - CONF
AU - Balos, Vasileios
AU - Elgabarty, Hossam
AU - Wolf, Martin
AU - Kühne, Thomas
AU - Netz, Roland
AU - Bonthuis, Douwe Jan
AU - Kaliannan, Naveen
AU - Loche, Philip
AU - Kampfrath, Tobias
AU - Sajadi, Mohsen
ED - Razeghi, Manijeh
ED - Baranov, Alexei N.
ID - 33654
T2 - Terahertz Emitters, Receivers, and Applications XII
TI - Ultrafast solvent-to-solvent and solvent-to-solute energy transfer driven by single-cycle THz electric fields
ER -
TY - JOUR
AU - Wang, Mengying
AU - Ranjbar, Ahmad
AU - Kühne, Thomas
AU - Belosludov, Rodion V.
AU - Kawazoe, Yoshiyuki
AU - Liang, Yunye
ID - 33656
JF - Carbon
KW - General Chemistry
KW - General Materials Science
SN - 0008-6223
TI - A theoretical investigation of topological phase modulation in carbide MXenes: Role of image potential states
VL - 181
ER -
TY - JOUR
AB - Abstract
We performed a virtual materials screening to identify promising topological materials for photocatalytic water splitting under visible light irradiation. Topological compounds were screened based on band gap, band edge energy, and thermodynamics stability criteria. In addition, topological types for our final candidates were computed based on electronic structures calculated usingthe hybrid density functional theory including exact Hartree–Fock exchange. Our final list contains materials which have band gaps between 1.0 and 2.7 eV in addition to band edge energies suitable for water oxidation and reduction. However, the topological types of these compounds calculated with the hybrid functional differ from those reported previously. To that end, we discuss the importance of computational methods for the calculation of atomic and electronic structures in materials screening processes.
AU - Ranjbar, Ahmad
AU - Mirhosseini, Hossein
AU - Kühne, Thomas
ID - 33659
IS - 1
JF - Journal of Physics: Materials
KW - Condensed Matter Physics
KW - General Materials Science
KW - Atomic and Molecular Physics
KW - and Optics
SN - 2515-7639
TI - On topological materials as photocatalysts for water splitting by visible light
VL - 5
ER -
TY - JOUR
AB - AbstractVaccinations, lockdowns and testing strategies are three potential elements of an effective anti-coronavirus, and in particular Covid-19, health policy. The following analysis considers - within a simple model - the potentially crucial role of a Corona testing approach in combination with a quarantine approach which is shown herein to be a substitute for broad lockdown measures. The cost of lockdowns/shutdowns are rather high so that – beyond progress in terms of a broad vaccination program – a rational testing strategy should also be carefully considered. Testing has to be organized on the basis of an adequate testing infrastructure which could largely be implemented in firms, schools, universities and public administration settings. As regards the cost of a systematic broad Covid-19 testing strategy, these could come close to 0.5% of national income if there are no vaccinations. The Testing & Quarantine approach suggested here – with tests for symptomatic as well as asymptomatic people - is based on a random sampling and would require rather broad and frequent testing; possibly one test per person every 7–10 days. At the same time, one should consider that the cost of further lockdowns/shutdowns of a duration of 1 month could be very high, such that a standard cost benefit analysis supports the testing approach suggested herein. Also, an optimal policy mix could be designed where both vaccinations and testing play a crucial role. As of late January 2021, no further lockdowns in Germany and other OECD countries would be necessary if a broad testing infrastructure can be established rather quickly. This in turn will reinforce economic optimism and help to jumpstart economic growth in Europe, the US and Asia in a solid way. The basic logic of the testing approach pointed out here for industrialized countries could also be applied in developing countries. The approach presented is complementary to the IMF analysis of Cherif/Hasanov.
AU - Gries, Thomas
AU - Welfens, Paul J. J.
ID - 33668
IS - 1
JF - International Economics and Economic Policy
KW - Economics and Econometrics
SN - 1612-4804
TI - Testing as an approach to control the Corona epidemic dynamics and avoid lockdowns
VL - 18
ER -
TY - JOUR
AB - AbstractIn light of the COVID-19 pandemic, we scrutinize what has been established in the literature on whether entrepreneurship can cause and resolve extreme events, the immediate and long-run impacts of extreme events on entrepreneurship, and whether extreme events can positively impact (some) entrepreneurship and innovation. Based on this, we utilize a partial equilibrium model to provide several conjectures on the impact of COVID-19 on entrepreneurship, and to derive policy recommendations for recovery. We illustrate that while entrepreneurship recovery will benefit from measures such as direct subsidies for start-ups, firms’ revenue losses, and loan liabilities, it will also benefit from aggregate demand-side support and income redistribution measures, as well as from measures that facilitate the innovation-response to the Keynesian supply-shock caused by the pandemic, such as access to online retail and well-functioning global transportation and logistics.
AU - Gries, Thomas
AU - Naudé, Wim
ID - 33667
IS - 3
JF - Economics of Disasters and Climate Change
KW - General Medicine
SN - 2511-1280
TI - Extreme Events, Entrepreneurial Start-Ups, and Innovation: Theoretical Conjectures
VL - 5
ER -
TY - JOUR
AU - da Silva, Marcos A.R.
AU - Silva, Ingrid F.
AU - Xue, Qi
AU - Lo, Benedict T.W.
AU - Tarakina, Nadezda V.
AU - Nunes, Barbara N.
AU - Adler, Peter
AU - Sahoo, Sudhir K.
AU - Bahnemann, Detlef W.
AU - López-Salas, Nieves
AU - Savateev, Aleksandr
AU - Ribeiro, Caue
AU - Kühne, Thomas
AU - Antonietti, Markus
AU - Teixeira, Ivo F.
ID - 33681
JF - Applied Catalysis B: Environmental
KW - Process Chemistry and Technology
KW - General Environmental Science
KW - Catalysis
SN - 0926-3373
TI - Sustainable oxidation catalysis supported by light: Fe-poly (heptazine imide) as a heterogeneous single-atom photocatalyst
VL - 304
ER -
TY - JOUR
AB - The influence of different polymer side chains on the vapor phase infiltration with TMA is investigated and supported by DFT-calculations.
AU - Mai, Lukas
AU - Maniar, Dina
AU - Zysk, Frederik
AU - Schöbel, Judith
AU - Kühne, Thomas
AU - Loos, Katja
AU - Devi, Anjana
ID - 33675
IS - 4
JF - Dalton Transactions
KW - Inorganic Chemistry
SN - 1477-9226
TI - Influence of different ester side groups in polymers on the vapor phase infiltration with trimethyl aluminum
VL - 51
ER -
TY - GEN
AU - Wiecher, Carsten
AU - Fischbach, Jannik
AU - Greenyer, Joel
AU - Vogelsang, Andreas
AU - Wolff, Carsten
AU - Dumitrescu, Roman
ID - 27058
T2 - arXiv preprint
TI - Integrated and Iterative Requirements Analysis and Test Specification: A Case Study at Kostal
ER -
TY - CONF
AU - Zahera, Hamada Mohamed Abdelsamee
AU - Heindorf, Stefan
AU - Ngonga Ngomo, Axel-Cyrille
ID - 29291
T2 - Proceedings of the 11th on Knowledge Capture Conference
TI - ASSET: A Semi-supervised Approach for Entity Typing in Knowledge Graphs
ER -
TY - CHAP
AU - Feldhans, Robert
AU - Wilke, Adrian
AU - Heindorf, Stefan
AU - Shaker, Mohammad Hossein
AU - Hammer, Barbara
AU - Ngonga Ngomo, Axel-Cyrille
AU - Hüllermeier, Eyke
ID - 29292
SN - 0302-9743
T2 - Intelligent Data Engineering and Automated Learning – IDEAL 2021
TI - Drift Detection in Text Data with Document Embeddings
ER -
TY - CONF
AB - Knowledge graph embedding research has mainly focused on the two smallest
normed division algebras, $\mathbb{R}$ and $\mathbb{C}$. Recent results suggest
that trilinear products of quaternion-valued embeddings can be a more effective
means to tackle link prediction. In addition, models based on convolutions on
real-valued embeddings often yield state-of-the-art results for link
prediction. In this paper, we investigate a composition of convolution
operations with hypercomplex multiplications. We propose the four approaches
QMult, OMult, ConvQ and ConvO to tackle the link prediction problem. QMult and
OMult can be considered as quaternion and octonion extensions of previous
state-of-the-art approaches, including DistMult and ComplEx. ConvQ and ConvO
build upon QMult and OMult by including convolution operations in a way
inspired by the residual learning framework. We evaluated our approaches on
seven link prediction datasets including WN18RR, FB15K-237 and YAGO3-10.
Experimental results suggest that the benefits of learning hypercomplex-valued
vector representations become more apparent as the size and complexity of the
knowledge graph grows. ConvO outperforms state-of-the-art approaches on
FB15K-237 in MRR, Hit@1 and Hit@3, while QMult, OMult, ConvQ and ConvO
outperform state-of-the-approaches on YAGO3-10 in all metrics. Results also
suggest that link prediction performances can be further improved via
prediction averaging. To foster reproducible research, we provide an
open-source implementation of approaches, including training and evaluation
scripts as well as pretrained models.
AU - Demir, Caglar
AU - Moussallem, Diego
AU - Heindorf, Stefan
AU - Ngonga Ngomo, Axel-Cyrille
ID - 29287
T2 - The 13th Asian Conference on Machine Learning, ACML 2021
TI - Convolutional Hypercomplex Embeddings for Link Prediction
ER -
TY - CONF
AU - Nickchen, Tobias
AU - Heindorf, Stefan
AU - Engels, Gregor
ID - 29294
T2 - 2021 IEEE Winter Conference on Applications of Computer Vision (WACV)
TI - Generating Physically Sound Training Data for Image Recognition of Additively Manufactured Parts
ER -
TY - GEN
AU - Heindorf, Stefan
ID - 33733
TI - Automatically generating instructions from tutorials for search and user navigation
ER -
TY - CONF
AU - Piskachev, Goran
AU - Krishnamurthy, Ranjith
AU - Bodden, Eric
ID - 26407
T2 - 2021 IEEE 21st International Working Conference on Source Code Analysis and Manipulation (SCAM)
TI - SecuCheck: Engineering configurable taint analysis for software developers
ER -
TY - CONF
AU - Luo, Linghui
AU - Schäf, Martin
AU - Sanchez, Daniel
AU - Bodden, Eric
ID - 22463
T2 - Proceedings of the 29th ACM Joint Meeting on European Software Engineering Conference and Symposium on the Foundations of Software Engineering
TI - IDE Support for Cloud-Based Static Analyses
ER -
TY - CONF
AU - Karakaya, Kadiray
AU - Bodden, Eric
ID - 33840
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 - JOUR
AB - We demonstrate the integration of amorphous tungsten silicide superconducting nanowire single-photon detectors on titanium in-diffused lithium niobate waveguides. We show proof-of-principle detection of evanescently coupled photons of 1550 nm wavelength using bidirectional waveguide coupling for two orthogonal polarization directions. We investigate the internal detection efficiency as well as detector absorption using coupling-independent characterization measurements. Furthermore, we describe strategies to improve the yield and efficiency of these devices.
AU - Höpker, Jan Philipp
AU - Verma, Varun B
AU - Protte, Maximilian
AU - Ricken, Raimund
AU - Quiring, Viktor
AU - Eigner, Christof
AU - Ebers, Lena
AU - Hammer, Manfred
AU - Förstner, Jens
AU - Silberhorn, Christine
AU - Mirin, Richard P
AU - Woo Nam, Sae
AU - Bartley, Tim
ID - 23728
JF - Journal of Physics: Photonics
SN - 2515-7647
TI - Integrated superconducting nanowire single-photon detectors on titanium in-diffused lithium niobate waveguides
VL - 3
ER -
TY - GEN
AU - Müller, Stefanie Jutta Marianne
AU - Kundisch, Dennis
ID - 21509
TI - Gesellschaftliche Transformationen durch die Steigerung (popmusik)kultureller Teil-habe mittels innovativer Preiskonzepte – ein interdisziplinärer Literaturüberblick
ER -
TY - JOUR
AB - Heat-assisted forming processes are becoming increasingly important in the manufacturing of sheet metal parts for body-in-white applications. However, the non-isothermal nature of these processes leads to challenges in evaluating the forming limits, since established methods such as Forming Limit Curves (FLCs) only allow the assessment of critical forming strains for steady temperatures. For this reason, a temperature-dependent extension of the well-established GISSMO (Generalized Incremental Stress State Dependent Damage Model) fracture indicator framework is developed by the authors to predict forming failures under non-isothermal conditions. In this paper, a general approach to combine several isothermal FLCs within the temperature-extended GISSMO model into a temperature-dependent forming limit surface is investigated. The general capabilities of the model are tested in a coupled thermo-mechanical FEA using the example of warm forming of an AA5182-O sheet metal cross-die cup. The obtained results are then compared with state of the art of evaluation methods. By taking the strain and temperature path into account, GISSMO predicts greater drawing depths by up to 20% than established methods. In this way the forming and so the lightweight potential of sheet metal parts can by fully exploited. Moreover, the risk and locus of failure can be evaluated directly on the part geometry by a contour plot. An additional advantage of the GISSMO model is the applicability for low triaxialities as well as the possibility to predict the materials behavior beyond necking up to ductile fracture.
AU - Camberg, Alan Adam
AU - Erhart, Tobias
AU - Tröster, Thomas
ID - 33895
IS - 17
JF - Materials
KW - General Materials Science
SN - 1996-1944
TI - A Generalized Stress State and Temperature Dependent Damage Indicator Framework for Ductile Failure Prediction in Heat-Assisted Forming Operations
VL - 14
ER -
TY - BOOK
ED - Famula, Marta
ED - Otto Eke, Norbert
ID - 33894
TI - Ästhetik im Vormärz. Jahrbuch Forum Vormärz Forschung 2020
ER -
TY - CHAP
AU - Famula, Marta
ED - Röskau-Ryde, Isabel
ED - Kubacki, Artur
ID - 33905
T2 - Literatur und Kultur zwischen West und Ost. Imagination, Kommunikation und Wahrnehmung in regionalen Kulturräumen. Festschrift für Paul Martin Langner zum 65. Geburtstag
TI - Die Landstraße jenseits der Bedeutung. Peter Handkes spätes Drama Die Unschuldigen, ich und die Unbekannte am Rand der Landstraße
ER -
TY - CHAP
AU - Famula, Marta
ED - Otto Eke, Norbert
ED - Famula, Marta
ID - 33904
T2 - Ästhetik im Vormärz. Jahrbuch Forum Vormärz Forschung
TI - Von der auf den Kopf gestellten Schönheit oder die Verneinung der Negation im Hässlichen. Zur dialektischen Funktion des Erhabenen und des Hässlichen bei Christian Hermann Weiße
ER -
TY - JOUR
AU - Famula, Marta
ID - 33902
JF - Kosmos Dürrenmatt. Eine Annäherung an den Denker, Dichter und Maler. Berner Zeitschrift für Geschichte, H. 3. Sonderdruck Spiezer Tagung, in: Annelise Hüssy, Stefanie Leuenberger (Hgg.)
TI - Vom Entschluss, die Welt zu bestehen. Dürrenmatts Ethik des ‚à la bande‘
ER -
TY - CHAP
AU - Famula, Marta
AU - Otto Eke, Norbert
ED - Otto Eke, Norbert
ED - Famula, Marta
ID - 33903
T2 - Ästhetik im Vormärz. Jahrbuch Forum Vormärz Forschung 2020
TI - Ästhetik im Vormärz – Zur Einführung
ER -
TY - GEN
AU - Famula, Marta
ID - 33939
T2 - Jahrbuch für internationale Germanistik, Jahrgang LIII – Heft 1 (2021)
TI - Lukas Bärfuss: Malinois. Erzählungen. Wallstein: Göttingen 2019
ER -
TY - JOUR
AU - Meer, Philipp
AU - Hartmann, Johanna
AU - Rumlich, Dominik
ID - 21914
IS - 2
JF - European Journal of Applied Linguistics
SN - 2192-9521
TI - Folklinguistic perceptions of Global Englishes among German learners of English
VL - 9
ER -
TY - CHAP
AU - Famula, Marta
ED - Langner, Paul Martin
ED - Majkiewicz, Anna
ED - Mirecka, Agata
ID - 33906
T2 - Wiederholung im Theater. Zur deutschsprachigen Gegenwartsdramatik und ihrer Inszenierung, (= Gesellschaftskritische Literatur – Texte Autoren – Debatten 9)
TI - Das Unveränderliche und die Wiederholung. Die Rolle der Kontingenz in Max Frischs letztem Drama Triptychon
ER -
TY - BOOK
ED - Famula, Marta
ED - Mirecka, Agata
ED - Langner, Paul Martin
ID - 33899
TI - Drama zwischen Text und Bühne (Schriftenreihe seit 2021)
ER -
TY - JOUR
AB - While increasing digitalization enables multiple advantages for a reliable operation of technical systems, a remaining challenge in the context of condition monitoring is seen in suitable consideration of uncertainties affecting the monitored system. Therefore, a suitable prognostic approach to predict the remaining useful lifetime of complex technical systems is required. To handle different kinds of uncertainties, a novel Multi-Model-Particle Filtering-based prognostic approach is developed and evaluated by the use case of rubber-metal-elements. These elements are maintained preventively due to the strong influence of uncertainties on their behavior. In this paper, two measurement quantities are compared concerning their ability to establish a prediction of the remaining useful lifetime of the monitored elements and the influence of present uncertainties. Based on three performance indices, the results are evaluated. A comparison with predictions of a classical Particle Filter underlines the superiority of the developed Multi-Model-Particle Filter. Finally, the value of the developed method for enabling condition monitoring of technical systems related to uncertainties is given exemplary by a comparison between the preventive and the predictive maintenance strategy for the use case.
AU - Bender, Amelie
ID - 25046
IS - 10
JF - Machines
KW - prognostics
KW - RUL predictions
KW - particle filter
KW - uncertainty consideration
KW - Multi-Model-Particle Filter
KW - model-based approach
KW - rubber-metal-elements
KW - predictive maintenance
SN - 2075-1702
TI - A Multi-Model-Particle Filtering-Based Prognostic Approach to Consider Uncertainties in RUL Predictions
VL - 9
ER -
TY - JOUR
AU - Gröger, B.
AU - Köhler, D.
AU - Vorderbrüggen, J.
AU - Troschitz, J.
AU - Kupfer, R.
AU - Meschut, G.
AU - Gude, M.
ID - 30698
JF - Production Engineering
TI - Computed tomography investigation of the material structure in clinch joints in aluminium fibre-reinforced thermoplastic sheets
ER -
TY - JOUR
AU - Weiß, D.
AU - Schramm, B.
AU - Kullmer, G.
ID - 30699
JF - Production Engineering
TI - Holistic investigation chain for the experimental determination of fracture mechanical material parameters with special specimens
ER -
TY - JOUR
AU - Zirngibl, C.
AU - Schleich, B.
AU - Wartzack, S.
ID - 30696
JF - Proceedings of the Design Society
TI - Approach for the automated and data-based design of mechanical joints
VL - 1
ER -
TY - JOUR
AU - Zirngibl, C.
AU - Dworschak, F.
AU - Schleich, B.
AU - Wartzack, S.
ID - 30700
JF - Production Engineering
TI - Application of reinforcement learning for the optimization of clinch joint characteristics
ER -
TY - JOUR
AU - Römisch, D.
AU - Popp, J.
AU - Drummer, D.
AU - Merklein, M.
ID - 30701
JF - Production Engineering
TI - Joining of CFRT-steel hybrid parts via hole-forming and subsequent pin caulking
ER -
TY - JOUR
AU - Lafarge, R.
AU - Wolf, A.
AU - Guilleaume, C.
AU - Brosius, A.
ID - 30697
JF - Minerals, Metals and Materials Series
TI - A New Non-destructive Testing Method Applied to Clinching
ER -
TY - JOUR
AB - Due to stricter emission targets in the mobility sector and the resulting trend towards lightweight construction in order to reduce weight and consequently emissions, multi-material systems that allow a material to be placed in the right quantity and in the right place are becoming increasingly important. One major challenge that is holding back the rapid and widespread use of multi-material systems is the lack of adequate joining processes that are suitable for joining dissimilar materials. Joining processes without auxiliary elements have the advantage of a reduced assembly effort and no additional added weight. Conventional joining processes without auxiliary elements, such as welding, clinching, or the use of adhesives, reach their limits due to different mechanical properties and chemical incompatibilities. A process with potential in the field of joining dissimilar materials is joining without an auxiliary element using pin structures. However, current pin manufacturing processes are mostly time-consuming or can only be integrated barely into existing industrial manufacturing processes due to their specific properties. For this reason, the present work investigates the production of single- and multi-pin structures from high-strength dual-phase steel HCT590X + Z (DP600, t0 = 1.5 mm) by cold extrusion directly out of the sheet metal. These structures are subsequently joined with an aluminium sheet (EN AW-6014-T4, t0 = 1.5 mm) by direct pin pressing. For a quantitative evaluation of the joint quality, tensile shear tests are carried out and the influence of different pin heights, pin number, and pin arrangements, as well as different joining strategies on the joint strength is experimentally evaluated. It is proven that a single pin structure with a diameter of 1.5 mm and an average height of 1.86 mm achieves a maximum tensile shear force of 1025 N. The results reveal that the formation of a form-fit during direct pin pressing is essential for the joint strength. By increasing the number of pins, a linear increase in force could be demonstrated, which is independent of the arrangement of the pin structures.
AU - Römisch, D.
AU - Kraus, M.
AU - Merklein, M.
ID - 30684
JF - Journal of Manufacturing and Materials Processing
TI - Experimental study on joining by forming of hct590x + z and en-aw 6014 sheets using cold extruded pin structures
VL - 5
ER -
TY - JOUR
AB - Lightweight constructions become more and more important, especially in the mobility sector. In this industry, the increasingly strict regulations regarding the emissions of carbon dioxide can be achieved to a certain extent by reducing the vehicle weight. Thus, multi-material systems are used. Conventional joining techniques reach their limits when joining different materials due to different thermal expansion, unequal stiffness or chemical incompatibilities. This is why additional joining elements or adhesives are used. These must be viewed critically regarding a lightweight and resource-efficient production, since they add weight or complicate the recycling process of these components. Consequently, there is a great and growing need for new versatile joining technologies in order to overcome these challenges and to be able to react to changing process parameters and boundary conditions. Joining without an auxiliary element using pin structures formed directly from the sheet metal plane is one approach to meet these challenges. These pin structures are then joined by direct pressing into the joining partner. This is possible with a variety of material combinations, but is advantageous with regard to continuous fibre-reinforced thermoplastic composites (CFRTP), as the fibres do not have to be cut when joining CFRTP using pin structures. In this paper, the formability of pin structures made of a dual-phase steel DP600 (HCT590X + Z) is investigated. The extruded pin structures are joined by direct pin pressing with an EN AW-6014 to form tensile shear specimens. Different joining strategies are investigated to compare their influence on the joint strength. The results have shown that it is feasible to form suitable pins from a DP600 dual-phase steel to produce reliable connections with an aluminium sheet joined by direct pin pressing.
AU - Römisch, D.
AU - Kraus, M.
AU - Merklein, M.
ID - 30682
JF - Key Engineering Materials
TI - Investigation of Different Joining by Forming Strategies when Connecting Different Metals without Auxiliary Elements
VL - 883
ER -
TY - JOUR
AB - The growing demands of resource-saving processes and products are leading to increasing importance of lightweight construction for the automotive industry. One approach is multi-material design, which uses high-strength steels and aluminium alloys in the production of vehicle bodies. Therefore, reliable processes for joining components with different mechanical properties and geometries are necessary. As conventional joining processes reach their limits, new versatile processes and methods are required which can adapt to different process conditions and disturbance variables. A widely used joining process to join different materials is self-piercing riveting as a joining by forming method, however it is characterised as inflexible to changing process conditions due to a linear process kinematic and rigid dies. An approach to extend the process limits is the application of a tumbling kinematic for the punch. Thus, an adapted tumbling strategy can be used to influence the joining process and to achieve a controlled material flow in order to manufacture tailored joints. For the fundamental investigation of the process, numerical investigations are necessary. In order to achieve high model quality a precise material modelling is crucial. Therefore, a characterisation of the materials HCT590X+Z and EN AW-6014 as typical materials of multi-material mixes and the rivet material 38B2 is performed. Due to the different stress conditions during tumbling self-piercing riveting suitable characterisation methods are selected and carried out.
AU - Wituschek, S.
AU - Lechner, M.
ID - 30718
JF - ESAFORM 2021
TI - Material characterisation methods for a tumbling self-piercing riveting process
ER -
TY - JOUR
AB - When joining lightweight parts of various materials, clinching is a cost efficient solution. In a production line, the quality of a clinch point is primarily controlled by measurement of dimensions, which are accessible from outside. However, methods such as visual testing and measuring the bottom thickness as well as the outer diameter are not able to deliver any information about the most significant geometrical characteristic of the clinch point, neck thickness and undercut. Furthermore, ex-situ destructive methods such as microsectioning cannot detect elastic deformations and cracks that close after unloading. In order to exceed the current limits, a new non-destructive in-situ testing method for the clinching process is necessary. This work proposes a concept to characterize clinch points in-situ by combining two complementary non-destructive methods, namely, computed tomography (CT) and ultrasonic testing. Firstly, clinch points with different geometrical characteristics are analysed experimentally using ex-situ CT to get a highly spatially resolved 3D-image of the object. In this context, highly X-ray attenuating materials enhancing the visibility of the sheet-sheet interface are investigated. Secondly, the test specimens are modelled using finite element method (FEM) and a transient dynamic analysis (TDA) is conducted to study the effect of the geometrical differences on the deformation energy and to qualify the TDA as a fast in-situ non-destructive method for characterizing clinch points at high temporal resolution.
AU - Köhler, D.
AU - Sadeghian, B.
AU - Kupfer, R.
AU - Troschitz, J.
AU - Gude, M.
AU - Brosius, A.
ID - 30683
JF - Key Engineering Materials
TI - A Method for Characterization of Geometric Deviations in Clinch Points with Computed Tomography and Transient Dynamic Analysis
VL - 883
ER -
TY - JOUR
AB - The use of clinch joints, e.g. vehicle structures, is determined by the reliability of the joint and its strength properties - in particular the fatigue strength. Clinch connections offer the advantage over form-closure and force-closure processes that they can also be used for hybrid material combinations. In order to be able to evaluate the influence of the geometry parameters such as e.g. undercut, neck thickness or also base thickness on the fatigue behavior, three clinch connections (in optimum and compromise design) with different tool parameters were designed and examined using the example of a joining task with aluminum sheet material. For this purpose, fatigue curves (F-N curves) in the range of high to very high numbers of load cycles (N = 105 to 107) were determined. In this load cycle range, a so-called "neck fracture" is mainly to be expected as the type of failure, whereas for quasi-static tests, a “buckling” is more likely to occur. The tests were carried out on single-cut overlapping shear tensile specimens. Metallographic and scanning electron microscopic examinations of the joints and the fracture surfaces served to identify the crack initiation site and to clarify the respective type of failure. Significant differences in the damage behaviour of the three clinching variants could be shown. This observation enables one step into the direction of fully understanding the relationship along the causal chain "joint requirements - joining process - fatigue strength". Thus the adaptability of the clinching process can be improved.
AU - Ewenz, L.
AU - Kalich, J.
AU - Zimmermann, M.
AU - Füssel, U.
ID - 30663
JF - Key Engineering Materials
TI - Effect of Different Tool Geometries on the Mechanical Properties of Al-Al Clinch Joints
VL - 883
ER -
TY - JOUR
AB - Thermally supported clinching (Hotclinch) is a novel promising process to join dissimilar materials. Here, metal and fibre-reinforced thermoplastics (FRTP) are used within this single step joining process and without the usage of auxiliary parts like screws or rivets. For this purpose, heat is applied to improve the formability of the reinforced thermoplastic. This enables joining of the materials using conventional clinching-tools. Focus of this work is the modelling on mesoscopic scale for the numerical simulation of this process. The FTRP-model takes the material behaviour both of matrix and the fabric reinforced organo-sheet under process temperatures into account. For describing the experimentally observed phenomena such as large deformations, fibre failure and the interactions between matrix and fibres as well as between fibres themselves, the usage of conventional, purely Lagrangian based FEM methods is limited. Therefore, the combination of contact-models with advanced modelling approaches like Arbitrary-Lagrangian-Eulerian (ALE), Coupled-Eulerian-Lagrangian (CEL) and Smooth-ParticleHydrodynamics (SPH) for the numerical simulation of the clinching process are employed. The different approaches are compared with regard to simulation feasibility, robustness and results accuracy. It is shown, that the CEL approach represents the most promising approach to describe the clinching process.
AU - Gröger, B.
AU - Hornig, A.
AU - Hoog, A.
AU - Gude, M.
ID - 30688
JF - ESAFORM 2021 - 24th International Conference on Material Forming
TI - Modelling of thermally supported clinching of fibre-reinforced thermoplastics: Approaches on mesoscale considering large deformations and fibre failure
ER -
TY - JOUR
AB - Joints are an essential part of modern (lightweight) structures in a broad variety of applications. The reason for this is the rapidly increasing number of different material combinations needing to be joined in application areas like the automotive industry. It is currently common to use numerous auxiliary or standardized elements instead of individually adapted joining elements. This leads to a large number of different joining elements per product and thus to high costs. An innovative approach to overcoming this issue is the design, manufacture and setting of joint-specific joining elements. A good candidate for the manufacture of adapted joining elements of this type is the so-called friction spinning process. The joining elements formed in this way can be specifically adapted to the application in question in terms of both shape and mechanical properties. The part geometry required for the properties of a given joint is formed using a universal forming tool. This makes it possible to form a wide variety of sub geometries for the auxiliary joining part as a function of the prevailing joint condition, using a single forming tool and starting from the same semi-finished bar material. By applying different process strategies for the rotational speed and feed rate during the forming operation, the same part geometry can even be given different local mechanical properties. The following contribution presents the results of ongoing research work and includes the process concept, process properties, tooling and the results of experimental investigations into the joining of two sheet metal parts with help of this new joining process.
AU - Wiens, E.
AU - Wischer, C.
AU - Homberg, W.
ID - 30685
JF - ESAFORM
TI - Development of a novel adaptive joining technology employing friction-spun joint connectors (FSJC)
ER -
TY - JOUR
AB - Corrosion is a major cause for the failure of metallic components in various branches of the industry. Depending on the corrosion severity, the time until failure of the component varies. On the contrary, a study has shown that certain riveted metal joints, exposed to a short period of mechanical loading and corrosion, have greater fatigue limits. This study gives rise to the question how different corrosion exposure times affect joint metallic components. In the present research, a theoretical approach is developed in order to evaluate the influence of galvanic corrosion on joint integrity of clinched metal joints. At first, the framework for modeling galvanic corrosion is introduced. Furthermore, a simulative investigation of a clinching point is carried out based on the assumption that corrosion leads to a reduction of the contact area which leads to a local increase in contact pressure. For this purpose, the stiffness values of individual elements in a finite element model are reduced locally in the contact area of the undercut and the contact stress along a path is evaluated. Summarizing, a modeling approach is introduced to investigate corrosion effects on load-bearing behavior of clinched joints.
AU - Harzheim, S.
AU - Steinfelder, C.
AU - Wallmersperger, T.
AU - Brosius, A.
ID - 30664
JF - Key Engineering Materials
TI - A First Approach for the Treatment of Galvanic Corrosion and of Load-Bearing Capacity of Clinched Joints
VL - 883
ER -
TY - JOUR
AB - In recent years, clinching has gathered popularity to join sheets of different materials in industrial applications. The manufacturing process has some advantages, as reduced joining time, reduced costs, and the joints show good fatigue properties. To ensure the joint strength, reliable simulations of the material behaviour accounting for process-induced damage are expected to be beneficial to obtain credible values for the ultimate joint strength and its fatigue limit. A finite plasticity gradient-damage material model is outlined to describe the plastic and damage evolutions during the forming of sheet metals, later applied to clinching. The utilised gradient-enhancement cures the damage-induced localisation by introducing a global damage variable as an additional finite element field. Both, plasticity and damage are strongly coupled, but can, due to a dual-surface approach, evolve independently. The ability of the material model to predict damage in strongly deformed sheets, its flexibility and its regularization properties are illustrated by numerical examples.
AU - Friedlein, J.
AU - Mergheim, J.
AU - Steinmann, P.
ID - 30694
JF - Key Engineering Materials
TI - A finite plasticity gradient-damage model for sheet metals during forming and clinching
VL - 883 KEM
ER -
TY - JOUR
AB - Joining and local forming processes for fibre-reinforced thermoplastics (FRTP) like hole-forming or variations of the clinching process require an in-depth understanding of the process induced effects on meso-scale. For numerical modelling with a geometrical description of a woven fabric, adequate material models for a representative unit cell are identified. Model calibration is achieved employing a mesoscopic finite-element-approach using the embedded element method based on tensile tests of the consolidated organo-sheets and a phenomenological evaluation of photomicrographs. The model takes temperature dependent stiffness and fibre tension failure into account.
AU - Gröger, B.
AU - Hornig, A.
AU - Hoog, A.
AU - Gude, M.
ID - 30689
JF - Key Engineering Materials
TI - Temperature dependent modelling of fibre-reinforced thermoplastic organo-sheet material for forming and joining process simulations
VL - 883 KEM
ER -
TY - JOUR
AB - Predicting the durability of components under mechanical loading combined with environmental conditions leading to corrosion is one of the most challenging tasks in mechanical engineering. Precise predictions are neccesary for lightweight design in transportation due to environmental protection. During corrosion often hydrogen is produced by electrochemical reactions. Hydrogen embrittlement is one of the most feared damage mechanisms for metal constructions leading to early and unexpected failure. Until now predictions are mostly done through costly experiments. In the present research, a first simple simulation model based on the fundamentals of electrochemistry and continuum damage mechanics is developed to couple the damage induced by the mechanical stress with the hydrogen embrittlement. Results of the durability are presented for the case of uniaxial cyclic loading for varying testing frequency.
AU - Hofmann, M.
AU - Shi, Y.
AU - Wallmersperger, T.
ID - 30720
JF - PAMM
TI - A first Model of Fatigue Corrosion of a Metal through Hydrogen Embrittlement
VL - 20
ER -
TY - JOUR
AB - Due to their cost-efficiency and environmental friendliness, the demand of mechanical joining processes is constantly rising. However, the dimensioning and design of joints and suitable processes are mainly based on expert knowledge and few experimental data. Therefore, the performance of numerical and experimental studies enables the generation of optimized joining geometries. However, the manual evaluation of the results of such studies is often highly time-consuming. As a novel solution, image segmentation and machine learning algorithm provide methods to automate the analysis process. Motivated by this, the paper presents an approach for the automated analysis of geometrical characteristics using clinching as an example.
AU - Zirngibl, C.
AU - Schleich, B.
ID - 30695
JF - Key Engineering Materials
TI - Approach for the automated analysis of geometrical clinch joint characteristics
VL - 883 KEM
ER -
TY - CONF
AB - Computational homogenization is a powerful tool which allows to obtain homogenized properties of materials on the macroscale from the simulation of the underlying microstructure. The response of the microstructure is, however, strongly affected by variations in the microstructure geometry. The effect of geometry variations is even stronger in cases when the material exhibits plastic deformations. In this work we study a model of a steel alloy with arbitrary distributed elliptic voids. We model one single unit cell of the material containing one single void. The geometry of the void is not precisely known and is modeled as a variable orientation of an ellipse. Large deformations applied to the unit cell necessitate a finite elasto-plastic material model. Since the geometry variation is parameterized, we can utilize the method recently developed for stochastic problems but also applicable to all types of parametric problems — the isoparametric stochastic local FEM (SL-FEM). It is an ideal tool for problems with only a few parameters but strongly nonlinear dependency of the displacement fields on parameters. Simulations demonstrate a strong effect of parameter variation on the plastic strains and, thus, substantiate the use of the parametric computational homogenization approach.
AU - Pivovarov, Dmytro
AU - Mergheim, Julia
AU - Willner, Kai
AU - Steinmann, Paul
ID - 34208
IS - 1
SN - 1617-7061
T2 - PAMM
TI - Parametric FEM for computational homogenization of heterogeneous materials with random voids
VL - 20
ER -
TY - JOUR
AU - Knust, Steffen
AU - Ruhm, Lukas
AU - Kuhlmann, Andreas
AU - Meinderink, Dennis
AU - Bürger, Julius
AU - Lindner, Jörg
AU - de los Arcos de Pedro, Maria Teresa
AU - Grundmeier, Guido
ID - 34087
IS - 7
JF - Journal of Raman Spectroscopy
KW - Spectroscopy
KW - General Materials Science
SN - 0377-0486
TI - In situ backside Raman spectroscopy of zinc oxide nanorods in an atmospheric‐pressure dielectric barrier discharge plasma
VL - 52
ER -