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Yasmin Ahmed Salem
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Scientific Events

Scientific Events

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Linking Microstructural Evolution and Tribology in Metallic Contacts

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Linking Microstructural Evolution and Tribology in Metallic Contacts

The tribology community presently relies on phenomenological models to describe the various seemingly disjointed steady-state regimes of metal wear. Pure metals such as gold -- frequently used in electrical contacts - exhibit high friction and wear. In contrast, nanocrystalline metals, such as hard gold, often show much lower friction and correspondingly low wear. The engineering community has generally used a phenomenological connection between hardness and friction/wear to explain this macroscale response, and thus to guide designs. We present results of recent simulations and experiments that demonstrate a general framework for connecting materials properties (i.e. microstructural evolution) to tribological response. We present evidence that the competition between grain refinement (from cold working), grain coarsening (from stress-induced grain growth), and wear (delamination and plowing) can be used to describe transient and steady state tribological behavior of metals, alloys and composites. We will explore the seemingly disjointed steady-state friction regimes of metals and alloys, with a goal of elucidating the structure-property relationships, allowing for the engineering of tribological materials and contacts based on the kinetics of grain boundary motion. [more]

Symposium "Tribology across length-scales: Experiments and simulations" at the MSE (Materials Science Engineering)

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Symposium "Tribology across length-scales: Experiments and simulations" at the MSE (Materials Science Engineering)

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High-throughput with Particle Technology

High-throughput screening is a well-established method for scientific experimentation in chemistry and biology. Examples are heterogeneous catalysts, drug developments and nanoparticle toxicology. These methods involve the synthesis of small sample volumes often in form of particles that are quickly tested. These tests are designed to quickly obtain easily accessible data (called descriptors) that are related with a predictor function to the desired properties. The descriptor-predictor-relation is found through mathematical modelling and calibration. One particle based high-throughput concept for the evaluation of potential toxicological hazards will be presented in more detail. Furthermore, a new concept is presented which transfers high-throughput screening to the exploration of new structural metals. The method comprises the synthesis of many small alloy samples in form of particles. These samples obtain a defined microstructure by fast or parallel thermal and mechanical treatments and are subsequently subjected to novel fast descriptor tests while a mathematical algorithm develops the predictor function. The method presented here is a collaborative approach among many researchers and also involves sample routing and automation considerations as well as process modelling. [more]

5th International Symposium on Computational Mechanics of Polycrystals, CMCn 2016 and first DAMASK User Meeting

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5th International Symposium on Computational Mechanics of Polycrystals, CMCn 2016 and first DAMASK User Meeting

The Max-Planck-Institut für Eisenforschung in Düsseldorf is organizing the 5th International Symposium on Computational Mechanics of Polycrystals and we would like to invite you and your research colleagues to participate in this event. This symposium is part of a biannual series of symposia that originated from the first joint research group established between the Max Planck Society and the Fraunhofer Society on the Computational Mechanics of Polycrystals. This year the symposium is combined with the first DAMASK User Meeting. DAMASK is the multi-physics simulation software developed at MPIE. If you and your colleagues would like to attend this event, then please register online before July 1st 2016. We emphasize that registration is mandatory and that there are limited places only. Many thanks and hope to see you in Düsseldorf! [more]

MPIE-Colloquium: Tuning Materials Properties Through Extreme Chemical Complexity

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MPIE-Colloquium: Tuning Materials Properties Through Extreme Chemical Complexity

The development of metallic alloys is arguably one of the oldest of sciences, dating back at least 3,000 years. It is therefore very surprising when a new class of metallic alloys is discovered. High Entropy Alloys (HEA) appear to be such a class furthermore, one that is receiving a great deal of attention in terms of the underlying physics responsible for their formation as well as unusual physical,mechanical and radiation resistance properties that make them candidates for technological applications. The term HEA typically refers to alloys that are comprised of 5, 6, 7… elements, each in in equal proportion, that condense onto simple underlying crystalline lattices but where the different atomic species are distributed randomly on the different sites -face centered cubic (fcc) Cr0.2Mn0.2Fe0.2Co0.2Ni0.2 and body-centered-cubic (bcc) V0.2Nb0.2Mo0.2Ta0.2W0.2 being textbook examples. The naming of these alloys originates from an early conjecture that these unusual systems are stabilized as disordered solid solutions alloys by the high entropy of mixing associated with the large number of components  - a conjecture that has since proved insufficient. In the first part of the presentation I will describe a model that allows us to predict which combinations of N elements taken from the periodic table are most likely to yield a HEA that is based on the results of modern high-throughput ab initio electronic structure computations. In the second part I will broaden the discussion to a wider class of equiatomic fcc concentrated solid solution alloys that is based on the 3d- and 4d-transition metal elements Cr, Mn, Fe, Co, Ni, Pd that range from simple binary alloys, such as Ni0.5Co0.5 and Ni0.5Fe0.5, to the quinary high entropy alloys Cr0.2Mn0.2Fe0.2Co0.2Ni0.2 and Cr0.2Pd0.2Fe0.2Co0.2Ni0.2 themselves. Here I will discuss the role that increasing chemical complexity and disorder has on the underlying electronic structure and the magnetic and transport properties. Finally, I will argue that the manipulation of chemical complexity may offer a new design principle for more radiation tolerant structural materials for energy applications. [more]

A pull-to-bend testing technique for testing Single crystal Silicon

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A pull-to-bend testing technique for testing Single crystal Silicon

[more]

Magnetic Material Modeling for Numerical Simulation of Electrical Machines

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MagneticMaterial Modeling for Numerical Simulation of Electrical Machines

The development of energy efficient electrical machines requires accurate knowledge of the magnetic material behavior, i.e., iron loss components  and magnetizability, already in the design stage. In addition, knowledge on the magnetic property deterioration due to induced  residual  stresses occurring during the manufacturing as well as due to applied mechanical  stresses during the operation of the electrical machine is indispensable for the contemporary machine-design.In general, the modeling can be approached at different length scales, i.e., from quantum mechanics at the atomic level and micromagnetics at the sub-micrometer length scale to continuum modeling at the ultra-millimeter scale. The difficulty to apply micromag- netic approaches in the numerical simulation of electrical machines is given both, by the tremendous  need of computational effort as well as the difficulty to consider the inter- action with effects present at the macroscale such as, e.g., residual  stresses or non-local eddy currents.A more modern view of such aspects is to regard materials  as multilevel structures, where structural features at all length scales play a significant role. Multiscale modeling is the field of solving such problems that have important features at multiple spatial and/or temporal scales.  It allows calculating material properties on one level using information or models from other levels. In the light of this, this presentation will give an overview on the current modeling  approaches applied at the Institute of Electrical Machines (IEM) for soft magnetic materials in the simulation of rotating electrical machines.  Particular attention will be paid to the effect of residual  as well as applied  mechanical stress on the magnetic behavior occurring at the various steps of machine manufacturing and during machine operation.Selected References[1] N. Leuning, S. Steentjes, M. Schulte, W. Bleck, and K. Hameyer, ”Effect of elastic and plastic tensile mechanical loading on the magnetic properties of NGO elec- trical steel,” Journal of Magnetism and Magnetic Materials, vol.  417, pp.  42-48, November 2016.[2] S. Elfgen,  S. Steentjes, S. B¨ohmer, D. Franck, and K. Hameyer, ”Continuous Local Material Model for Cut Edge Effects in Soft Magnetic Materials,” IEEE Transac- tions on Magnetics, vol. 52, no. 5, pp. 1-4, May 2016.[3] N. Leuning, S. Steentjes, M. Schulte, W. Bleck, and K. Hameyer, ”Effect of Mate- rial Processing and Imposed Mechanical  Stress on the Magnetic, Mechanical, and Microstructural Properties of High-Silicon Electrical Steel,” steel research interna-tional, to appear, 2016.  [more]

 
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