374 Works

Rare event analysis using the Limited Relative Error algorithm for OMNeT++ simulations

Sebastian Lindner, Raphael Elsner, Phuong Nga Tran & Andreas Timm-Giel
The Limited Relative Error algorithm is an alternative statistical method for data evaluation. Through online result analysis it continuously requests more samples until it deems the evaluation confident enough. With this it allows researchers to hand over the control of simulation time to the algorithm, and through a-priori configuration the target result resolution is set so that arbitrarily rare events can be investigated. We provide a new description of the method as well as a...

A cloud-based platform for automated order processing in additive Manufacturing

Jan-Peer Rudolph & Claus Emmelmann
Additive Manufacturing (AM) is increasingly used in the industrial part production. More than almost any other manufacturing technology, AM embodies the fourth industrial revolution (Industry 4.0). Even though AM allows a nearly direct manufacturing of parts out of their CAD data, the order processing still requires a lot of manual work. This paper addresses this issue by presenting a cloud-based platform, which has the intension to integrate and automate the order processing for additively manufactured...

Modeling of fracture in small punch tests for small- and large-scale yielding conditions at various temperatures

Celal Soyarslan, Betül Gülçimen Çakan, Swantje Bargmann & Peter Hähner
We present a systematic numerical study on temperature dependent fracture mode change in small punch tests. Following Needleman and Tvergaard (2000), we model the material as thermo-inelastic, where the ductile fracture mode, by void nucleation, growth and coalescence is accounted for by Gurson's porous metal plasticity (Gurson, 1977). The brittle fracture mode by cleavage is accounted for by Ritchie-Knott-Rice's deterministic maximum principal stress criterion (Ritchie et al., 1973). The well-known problem of mesh dependence associated...

Head taper corrosion causing head bottoming out and consecutive gross stem taper failure in total hip arthroplasty

Michael Morlock, Emilie C. Dickinson, Klaus-Peter Günther, Dennis Bünte & Valerie Polster
Taper corrosion in total hip arthroplasty for bearings with metal heads against polyethylene has developed from an anecdotal observation to a clinical problem. Increased taper wear and even gross taper failure have been reported for one particular design. It is hypothesized that corrosion of the female head taper results in taper widening, allowing the cobalt-chromium head to turn on the stem and wear down the softer titanium alloy by abrasive wear, ultimately causing failure. The...

New biocatalytic approaches for lactonization and lactamization

Lei Huang
Lactone und Lactame sind cyclische Ester bzw. Amide. Sie werden als Monomere für die Synthese von Polyestern und Polyamiden wie Polycaprolacton und Polycaprolactam eingesetzt und finden als vielseitig einsetzbare Polymere Anwendungen im täglichen Leben sowie in der Industrie. Weiterhin werden Lactone und Lactame als Rohstoffe in der pharmazeutischen Industrie, als Aromen und Duftstoffe oder zum Bleichen verwendet. Bei der industriellen Synthese der meisten Lactone und Lactame werden seit langem chemische Synthesemethoden angewendet, die vor Jahrzehnten...

Sediments and the \"system\" : from site-specific to regional-scale research : a story of joy in researching dirt

Wim Salomons & Ulrich Förstner
For both of us, it has been a struggle on how to write a kind of official “Farewell address” to our colleagues. After all, we do it only once in our lifetime. The result is twofold; we will have one editorial with a broad and short (admittedly very biased) history and outlook of our experience, and a second, more scientific editorial, which covers the first 10 years of our Journal of Soils and Sediments.

IR-thermography for quality prediction in selective laser deburring

Mauritz Möller, Christian Conrad, Walter Haimerl & Claus Emmelmann
Selective Laser Deburring (SLD) is an innovative edge-refinement process being developed at the Laser Zentrum Nord (LZN) in Hamburg. It offers a wear-free processing of defined radii and bevels at the edges as well as the possibility to deburr several materials with the same laser source. Sheet metal parts of various applications need to be post-processed to remove sharp edges and burrs remaining from the initial production process. Thus, SLD will provide an extended degree...

Molecular simulations of thermodynamic properties for the system α-cyclodextrin/alcohol in aqueous solution

Daniel Markthaler, Julia Gebhardt, Sven Jakobtorweihen & Niels Hansen
Free-energy calculations based on molecular simulations provide access to a wide range of thermodynamic properties such as the solubility and partitioning of a molecule in and between various phases. It is demonstrated how molecular dynamics free-energy simulations may be used to obtain the solubilities of primary alcohols and n-alkanes in water and binding affinities of primary alcohols to α-cyclodextrin. The equivalence of two distinct routes to calculate binding free energies is shown leading to the...

Numerical simulation of deep vibration compaction in abaqus/CEL and MPM

Alexander Chmelnizkij, Sparsha Sinduri Nagula & Jürgen Grabe
A numerical model is set up to compare CEL and MPM simulating the densification of dry sand using the deep vibration compaction method. This compaction method densifies loose sands by means of shear deformation processes imparted by horizontal vibrations of vibrator probe at the required soil depth. Both methods are capable to simulate large deformation without the drawbacks of mesh distortion. A hypoplastic constitutive model is used to characterize the stress-strain behaviour of the sand....

Analysis of laser ablation of CFRP by ultra-short laser pulses with short wavelength

Claus Emmelmann, Maren Petersen, André Goeke & Marten Canisius
Material processing of carbon fiber-reinforced polymers (CFRP) by means of shape-cutting technologies is state-of-the-art today. These processes still perform in some applications with lack of part quality such as delamination and low processes productivity. Therefore, laser processing by ultra-short laser pulses has a great potential in material ablation of CFRP. Nevertheless laser process parameters have to be adjusted carefully to reduce extension of heat affected zone (HAZ) and its influence on part quality.

Hydrogen bonding and thermoplastic elastomers - a nice couple with temperature-adjustable mechanical properties

Elisabeth Wittenberg, Andreas Meyer, Steffen Eggers & Volker Abetz
Styrene-butadiene copolymers are modified with varying fractions of benzoic acid moieties being able to perform hydrogen bonding. This is done by using a simple synthetic approach which utilizes click hemistry. Temperature-dependent dynamic mechanical properties are studied, and it turns out that even the apparently rather simple ydrogen bonding motif has a marked impact on the material properties due to the fact that it facilitates the formation of a supramolecular polymer network. Besides a glass transition,...

Photonic glass for high contrast structural color

Guoliang Shang, Lukas Maiwald, Hagen Renner, Dirk Jalas, Maksym Dosta, Stefan Heinrich, Alexander Petrov & Manfred Eich
Non-iridescent structural colors based on disordered arrangement of monodisperse spherical particles, also called photonic glass, show low color saturation due to gradual transition in the reflectivity spectrum. No significant improvement is usually expected from particles optimization, as Mie resonances are broad for small dielectric particles with moderate refractive index. Moreover, the short range order of a photonic glass alone is also insufficient to cause sharp spectral features. We show here, that the combination of a...

Elastic behaviour at the nanoscale of innovative composites of nanoporous gold and polymer

Emma Griffiths, Swantje Bargmann & B. D. Reddy
Nanoporous gold is a material with unique properties that make it attractive for use in multiple areas. It has an extremely high compressive strain capability but is very brittle in tension which limits its usage. One means of addressing this limitation is to fill the voids of the nanoporous material with a polymer, resulting in a more ductile and stronger material. In this work, the mechanical properties of a nanocomposite representative sample are studied numerically....

Elastic and plastic poisson’s ratios of nanoporous gold

Lukas Lührs, Celal Soyarslan, Jürgen Markmann, Swantje Bargmann & Jörg Weissmüller
We explore the elastic and plastic Poisson’s ratios, mE and mP, of nanoporous gold, using digital image correlation during compression experiments including load/unload segments. The two coefficients differ significantly, with mE independent of the ligament size, L, and with a trend for mP / L at not too large L. Disorder in the network of ligaments may explain why mE is smaller than predicted by lattice-based models. Finite element simulations, based on the Deshpande–Fleck constitutive...

Nanoporous gold : testing macro-scale samples to probe small-scale mechanical behavior

Nadiia Mameka, Ke Wang, Jürgen Markmann, Erica Lilleodden & Jörg Weissmüller
Nanoporous gold made by dealloying exemplifies how the exciting mechanical properties of nanoscale objects can be exploited in designing materials from which macroscopic things can be formed. The homogeneous microstructure and the possibility of adjusting the ligament size, L, between few and few hundred nm, along with the high deformability and reproducible mechanical behavior predestine the material for model studies of small-scale plasticity using reliable macroscopic testing schemes on mm- or cm-size samples. Such experiments...

Local flow stresses in interpenetrating-phase composites based on nanoporous gold — in situ diffraction

Ke Wang, Christian Hartig, Malte Blankenburg, Martin Müller, Robert Günther & Jörg Weissmüller
We report a synchrotron in situ diffraction experiment exploring stress evolution during compression of interpenetrating-phase nanocomposites based on nanoporous gold and polymer.While previous experiments provided indirect indication of local flow conditions based on macroscopic effective flow stress and micromechanics models such as Gibson-Ashby scaling law, the lattice parameter data of our experiment access the flow stress directly. At small structure size we find excellent agreement with previous reports, supporting thematch between material andmodel of those...

Piezoelectric gold : strong charge-load response in a metal-based hybrid nanomaterial

Charlotte Stenner, Li-Hua Shao, Nadiia Mameka & Jörg Weissmüller
Impregnating the pores of nanoporous gold with aqueous electrolyte yields a hybrid nanomaterial with two separate and interpenetrating charge transport paths, electronic conduction in the metal and ionic conduction in the electrolyte. As the two paths are capacitively connected, space‐charge layers along the internal interfaces are coupled to electric potential differences between the paths and can be controlled or detected thereby. The present experiments show that the space charge couples to mechanical deformation of the...

Surface excess elasticity of gold: ab initio coefficients and impact on the effective elastic response of nanowires

Beatrix A. M. Elsner, Stefan Müller, Swantje Bargmann & Jörg Weissmüller
Predicting the influence of the surface on the effective elastic properties of nanoscale structures and nanomaterials remains a challenge, which we here address on both levels, continuum and atomic. Density Functional Theory (DFT) computation at the atomic level yields the first reliable surface excess elastic parameters for the (111) and (001) surfaces of gold. At the continuum level, we derive closed-form expressions for the effective elastic behavior that can be combined with the DFT-derived excess...

Women withdrawers in engineering studies : identity formation and learning culture as gendered barriers for persistence?

Andrea Wolffram, Wibke Derboven & Gabriele Winker
Scholarship on women in engineering education mainly focuses on the question of how to attract more women to this subject. The topic concerning women in engineering education is here guided by the question of why women leave engineering studies. The paper aims to examine the main conflicts women encounter in engineering education and to derive implications for interventions suited for strengthening institutional bonding forces.

Comparing prediction market mechanisms : an experiment-based and micro validated multi-agent simulation

Frank M. A. Klingert & Matthias Meyer
Prediction markets are a promising instrument for drawing on the “wisdom of the crowds”. For instance, in a corporate context they have been used successfully to forecast sales or project risks by tapping into the heterogeneous information of decentralized actors in and outside of companies. Among the main market mechanisms implemented so far in prediction markets are (1) the continuous double auction and (2) the logarithmic market scoring rule. However, it is not fully understood...

Forwarding strategies for 6LoWPAN-fragmented IPv6 datagrams

Andreas Weigel
Diese Arbiet untersucht verschiedene Implementierungsstrategien für den Weiterleitungsaspekt des 6LoWPAN protocols für „low power and lossy networks“ (LLNs). Die Leistungsfähigkeit in Hinblick auf Latenz und Zuverlässigkeit wird für das LLN-typische Datensammlung- Verkehrsmuster für direkte und reassemblierende Strategien untersucht. Ein neuartiger Ansatz basierend auf Lauschen und dem Aussetzen von Transmissionen wird entwickelt und es wird gezeigt, dass dieser die Ende-zu-Ende-Zuverlässigkeit in einem Großteil der untersuchten Simulationsszenarien und Testnetzwerken signifikant verbessert.

Adaptation in coupled problems

Christos Vokas & Manfred Kasper
The purpose of this paper is to address the formulation, implementation, and adaptation of closely coupled multi-physics problems with h- and p-adaptive finite element methods. A general formulation is chosen allowing for coupled problems of various types. Adaptation algorithms for h- and p-refinement are given.

From open source in the digital to the physical world: a smooth transfer?

Nizar Abdelkafi, Thorsten Blecker & Christina Raasch
The purpose of this paper is to investigate the transferability of the open source principles of product development from the realm of software to the realm of physical products.

Experimental analysis of a bubble wake influenced by a vortex street

Sophie Rüttinger, Marko Hoffmann & Michael Schlüter
Bubble column reactors are ubiquitous in engineering processes. They are used in waste water treatment, as well as in the chemical, pharmaceutical, biological and food industry. Mass transfer and mixing, as well as biochemical or chemical reactions in such reactors are determined by the hydrodynamics of the bubbly flow. The hydrodynamics of bubbly flows is dominated by bubble wake interactions. Despite the fact that bubble wakes have been investigated intensively in the past, there is...

Data aggregation of mobile M2M traffic in relay enhanced LTE-A networks

Safdar Nawaz Khan Marwat, Yasir Mehmood, Carmelita Görg & Andreas Timm-Giel
Machine-to-machine (M2M) communication is becoming an increasingly essential part of mobile traffic and thus also a major focus of the latest 4G and upcoming 5G mobile networks. M2M communication offers various ubiquitous services and is one of the main enablers of the Internet-of-things (IoTs) vision. Nevertheless, the concept of mobile M2M communication has emerged due to the wide range, coverage provisioning, high reliability as well as decreasing costs of future mobile networks. Resultantly, M2M traffic...

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  • 2018

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