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Yasmin Ahmed Salem, M.A.
Yasmin Ahmed Salem
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Phone: +49 211 6792 722
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Scientific Events

Scientific Events

Month:

18024 1552645836

International Workshop on Advanced and In-situ Microscopies of Functional Nanomaterials and Devices, IAMNano 2019

The workshop aims to provide a forum for researchers who are interested in applying advanced imaging and spectroscopy methods of electron microscopy, including aberration-corrected, in situ, environmental and low-voltage electron microscopy, to topical issues in materials science and engineering, in nanoscience, in soft matter research, in interface and surface science, and in biomaterials research. As these methods are of fundamental importance in virtually all technological fields, contributions are invited that address the broad spectrum of current materials research. Novel methodological developments will be discussed as well as topical areas of research on thin films, bulk materials, surfaces, materials at the nanoscale and at the interface between the physical and life sciences, for understanding structure‐property relationships of materials, as well as for metrology. Selected topics will be introduced by invited keynote speakers during the plenary sessions. A poster session provides room for the presentation and discussion of current research. [more]

HEA symposium "High entropy and compositionally complex alloys" at DPG Spring Meeting 2019 in Regensburg

4th International Conference on Medium and High Manganese Steels

TEM Studies on Materials with a Negative Poisson’s Ratio

17790 1551084527

TEM Studies on Materials with a Negative Poisson’s Ratio

[more]

MPIE Seminar

17321 1549460332

Computational Modeling of Moving Boundary Problems

The focus of this presentation is on computational methods for moving boundary/interface problems and its applications including fracture, fluid structure interaction, inverse analysis and topology optimization. First, two computational methods for dynamic fracture will be presented, i.e. the cracking particles method (CPM) and dual-horizon peridynamics (DH-PD). These methods do neither require a representation of the crack surface and associated complex crack tracking algorithms nor criteria for crack branching and crack interactions. They also do not need to distinguish between crack nucleation and crack propagation. Complex discrete fracture patterns are the natural outcome of the simulation. The performance of these methods will be demonstrated by several benchmark problems for non-linear quasi-brittle dynamic fracture and adiabatic shear bands. Subsequently, a local partition of unity-enriched meshfree method for non-linear fracture in thin shells -- based on Kirchhoff-Love theory -- exploiting the higher order continuity of the meshfree approximation will be presented. The method does not require rotational degrees of freedom and the discretization of the director field. This also drastically simplifies the enrichment strategy accounting for the crack kinematics. Based on the meshfree thin shell formulation, an immersed particle method (IPM) for modeling fracturing thin-structures due to fluid-structure interaction is proposed. The key feature of this method is that it does not require any modifications when the structure fails and allows fluid to flow through the openings between crack surfaces naturally.The last part of the presentation focuses on inverse analysis and topology optimization with focus on computational materials design of piezoelectric/flexoelectric nanostructures and topological insulators. In the first application of piezo/flexoelectricity, we use isogeometric basis functions (NURBS or RHT-splines) in combination with level sets since C1 continuity is required for the numerical solution of the flexoelectric problem. Hence, only the electric potential and the displacement field is discretized avoiding the need of a complex mixed formulation. The level set method will be used to implicitly describe the topology of the structure. In order to update the level set function, a stabilized Hamilton-Jacobi equation is solved and an adjoint method is employed in order to determine the velocity normal to the interface of the voids/inclusions, which is related to the sensitivity of the objective function to variations in the material properties over the domain. The formulation will be presented for continua though results will also be shown for thin plates. The method will be extended to composites consisting of flexible inclusions with poor flexoelectric constants. Nonetheless, it will be shown that adding these flexible inclusions will result in a drastic increase in the energy conversion factor of the optimized flexoelectric nanostructures. In the second application, we propose a computational methodology to perform inverse design of quantum spin hall effect (QSHE)-based phononic topological insulators. We first obtain two-fold degeneracy, or a Dirac cone, in the bandstructure using a level set- based topology optimization approach. Subsequently, four-fold degeneracy, or a double Dirac cone, is obtained by using zone folding, after breaking of translational symmetry, which mimics the effect of strong spin-orbit coupling and which breaks the four-fold degeneracy resulting in a bandgap, is applied. We use the approach to perform inverse design of hexagonal unit cells of C6 and C3 symmetry. The numerical examples show that a topological domain wall with two variations of the designed metamaterials exhibit topologically protected interfacial wave propagation, and also demonstrate that larger topologically- protected bandgaps may be obtained with unit cells based on C3 symmetry. [more]

17498 1548412926

Nanoscale thermodynamics at complex oxide surfaces and interfaces for application in electronics, sensing, and energy conversion

Perovskite oxides exhibit a plethora of fascinating electronic material properties covering an exceptionally wide range of phenomena in solid state and surface physics. This has led to tremendous efforts to functionalize these materials in applications for energy technology, gas sensing, and electronics. Layered in an atomically defined epitaxial heterostructures and superlattices, diverse properties of perovskites can be combined on the nanoscale level. In such structures, even new functionality can arise at interfaces of layered materials, exhibiting properties that are absent in the bare bulk materials. In our approach, we utilize atomically-defined layer growth to obtain desired material properties. However, on top of that, we employ thermodynamic engineering of crystal defects as a unique approach to functionalize material properties at surfaces and interfaces: Even at material synthesis conditions close to perfection, device properties are often determined by imperfection, hence, by lattice disorder and crystal defects. As we discuss, we can intentionally control defect structure in nanoscale devices, by developing and utilizing thermodynamic routes to trigger surface and interface reactions in confined systems. While historically defects were seen as something to be avoided, a change of paradigm is required in the field of complex oxides today: In these materials, we can promote functionality, such as metallicity in nominally insulating compounds, by atomic defect-management. Therefore, rather than avoiding defect formation, it is an essential necessity to control and to utilize defect formation in oxides on the nanoscale. Here, we discuss fundamental aspects of lattice disorder effects in bulk oxides, and elaborate the special character of defect formation in thin films, surfaces and interfaces. Focusing on SrTiO3 as a perovskite model system, we will crosslink fundamental perspectives on lattice disorder to actual applications, addressing different examples, such as resistive switching memories, high-mobility electron gases and induced magnetism, oxygen sensors, and electro-catalysts. [more]

17511 1548419576

Opportunities for bcc refractory-metal superalloys

Reinforcement with ordered intermetallic precipitates is a potent strategy for the development of strength alongside damage tolerance and is central to the success of fcc nickel-based superalloys. Such a strategy is equally of interest within bcc-based systems for their increased melting point and acceptable cost. However, only limited studies have been made on refractory metal (RM) or titanium based alloys strengthened by ordered-bcc precipitates (e.g. B2 or L21). Are such “bcc superalloys” possible? Do they offer useful properties? In this talk, opportunities for refractory-metal-based superalloys systems will be discussed, including a review of Cr-Ni2AlTi, Mo-NiAl, Ta-(Ti,Zr)2Al(Mo,Nb) and Nb-Pd2HfAl systems together with newly developed alloys. These alloys exploit an extensive two-phase field that exists between A2 (RM,Ti) and B2 TiFe to produce nanoscale precipitate reinforced microstructures that increase strength by over 500 MPa. This work was supported through EUROfusion Researcher Grant & EPSRC Doctoral Prize Fellowships, EPSRC ‘DARE’ (darealloys.org) EP/L025213/1 and Rolls-Royce/EPSRC Strategic Partnership EP/H022309/1 and EP/H500375/1. [more]

 
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