Techn. Universiẗat, Diss., 2006--Darmstadt.

Universiẗat, Diss., 2001--Dortmund.

Zugl.: München, Universiẗat der Bundeswehr, Diss., 2009.

Techn. Universiẗat, Diss., 2003--Darmstadt.

No description available.

Magnetoactive elastomers (MAEs) are polymer composites containing magnetically soft or hard particles incorporated into an elastomer matrix during the crosslinking procedure. In the presence of a magnetic field, the induced magnetic interactions and the corresponding particle rearrangements significantly alter the mechanical properties in dependence on the initial particle distribution and sample shape. In addition, applying magnetic fields also changes the macroscopic shape of an MAE. This thesis investigates the magneto-mechanical coupled behaviour of MAEs by means of analytical and numerical methods. The effects of particle distribution and sample shape have been studied with the help of a physically motivated model of MAEs that considers dipole-dipole interactions between magnetizable particles. The presence of a magnetic field leads to a mechanical anisotropy in MAEs with isotropic particle distribution, and the induced anisotropy is directed along the orientation of the field. Thus, MAEs exhibit direction-dependent mechanical properties with distinct elastic moduli along and perpendicular to the field direction when the MAE sample is subjected to uniaxial deformation. A good agreement is reported between the physically motivated approach and conventional transversely isotropic material models. Furthermore, we investigate the important interplay between the particle distribution and the sample shape of MAEs, where a simple analytical expression is derived based on geometrical arguments to describe the particle distribution inside MAEs. We show that the enhancement of elastic moduli arises not only from the induced dipole-dipole interactions but also considerably from the change in the particle microstructure. Moreover, the magneto-mechanical behaviour of isotropic MAEs under shear deformations is studied. Three principal geometries of shear deformation are investigated with respect to the orientation of the applied magnetic field. We show that the Cauchy stress tensor of MAEs is not always symmetric due to the generation of a magnetic torque acting on an anisometric MAE sample under shear loadings. The theoretical study of magneto-mechanical behaviour of MAEs confirms that the effect of sample shape is quite significant and cannot be neglected. On the other hand, the initial particle distribution and presumed rearrangements due to the magnetic field additionally influence the material response of MAEs. Finally, the physically motivated model of MAEs could be transformed into an invariants-based model enabling its implementation in commercial finite element software. Therefore, we have uncovered a new pathway to model MAEs based on dipole-dipole interactions, leading to a constitutive relation analogous to the macro-scale continuum approach and revealing a synergy between both modelling strategies.

Asymmetrically sandwiched ferromagnetic thin films display a large number of spin-orbit effects, including the Dzyaloschinsii-Moriya interaction (DMI), spin-orbit torques (SOT) and magnetoresistance (MR) effects. Their concurrence promises the implementation of interesting magnetic structures like skyrmions in future memory and logic devices. The complex interplay of various effects originating from the spin-orbit coupling and their dependencies on the microstructural details of the material system mandates a holistic characterization of its properties. In this PhD thesis, a comprehensive study of the spin-orbit effects in a chromium oxide/cobalt/platinum trilayer sample series is presented. The determination of the complete micromagnetic parameter set is based on a developed measurement routine that utilizes quasistatic methods. The unambiguous quantification of all relevant constants is crucial for the modeling of the details of magnetic structures in the system. In this context the necessity of a strict distinction of magnetic objects, that are stabilized by magnetostatics or the DMI, was revealed. Furthermore, a sample layout was developed to allow for the simultaneous quantification of the magnitudes of SOTs and MR effects from nonlinear magnetotransport measurements. In conjunction with a structural characterization, the dominating dependence of the effect magnitudes on microstructural details of the systems is concluded. Precisely characterized systems establish a solid groundwork for further investigations that are needed for viable skyrmion-based devices.

Asymmetrically sandwiched ferromagnetic thin films display a large number of spin-orbit effects, including the Dzyaloschinsii-Moriya interaction (DMI), spin-orbit torques (SOT) and magnetoresistance (MR) effects. Their concurrence promises the implementation of interesting magnetic structures like skyrmions in future memory and logic devices. The complex interplay of various effects originating from the spin-orbit coupling and their dependencies on the microstructural details of the material system mandates a holistic characterization of its properties. In this PhD thesis, a comprehensive study of the spin-orbit effects in a chromium oxide/cobalt/platinum trilayer sample series is presented. The determination of the complete micromagnetic parameter set is based on a developed measurement routine that utilizes quasistatic methods. The unambiguous quantification of all relevant constants is crucial for the modeling of the details of magnetic structures in the system. In this context the necessity of a strict distinction of magnetic objects, that are stabilized by magnetostatics or the DMI, was revealed. Furthermore, a sample layout was developed to allow for the simultaneous quantification of the magnitudes of SOTs and MR effects from nonlinear magnetotransport measurements. In conjunction with a structural characterization, the dominating dependence of the effect magnitudes on microstructural details of the systems is concluded. Precisely characterized systems establish a solid groundwork for further investigations that are needed for viable skyrmion-based devices.:1 Introduction 2 Fundamentals 2.1 Towards new devices 2.2 Spin-orbit effects 2.2.1 Spin-current sources 2.2.2 Magnetoresistanceeffects 2.2.3 Spin-orbit torques 2.2.4 Harmonic analysis 2.3 Micromagnetic model 2.3.1 Dzyaloshinskii-Moriya interaction (DMI) 2.3.2 Consequences of the DMI for magnetic structures 2.3.3 Interface-induced DMI in asymmetrically stacked ferromagnets 2.3.4 Quantification of the interface-induced DMI 2.3.5 Levy-Fert three-site model including roughness 3 The CrOx/Co/Pt sample system 3.1 Experimental techniques 3.2 Structural characterization 4 Complete micromagnetic characterization 4.1 Magnetometry 4.1.1 Static investigation 4.1.2 Ferromagnetic resonance 4.2 DMI quantification 4.2.1 Field-driven domain wall creep motion 4.2.2 Asymmetric domain growth 4.2.3 Winding pair stability 4.3 Determination of the exchange parameter 4.3.1 Generation of circular magnetic objects 4.3.2 Homochiral magnetic bubble domains 4.4 Results 5 Magnetotransport measurements 5.1 Measurement setup 5.2 Magnetoresistance effects 5.3 Spin-orbit torque quantification 5.4 Results 6 Discussion 6.1 Structural predomination of the DMI strength 6.2 Ultra-thin limit exchange parameter reduction 6.3 Magnetotransport properties 6.4 Magneticstructures in //CrOx/Co/Pttrilayers 7 Conclusion and Outlook A Appendix A.1 Calculation of the skyrmion diameter A.2 Micromagnetic simulation of the winding pair stability Bibliography Acknowledgements

As part of the FVA research project 965 I with the topic 'Elastic-plastic design of the press connection between rotor shaft and laminated core of high-speed electric machines to increase power density', the shaft-hub connection (WNV) is being investigated in accordance with the topic. The elastically/plastically joined WNV is intended to prevent slippage of the laminated core even at high speeds (centrifugal speed up to 22,000 rpm) and torque loads up to 3000 Nm. The background to this is the widening of the plate pack, which inevitably leads to a reduction in the joint pressure. The joint of the WNV is composed of three tribological partners. On the one hand, it is the shaft made of 18CrNiMo7-6, and on the other hand, it is the NO20-13 type electrical steel sheet with the baked enamel, which initially makes the tribological system difficult to describe. Many factors, such as the type of sheet cut (stamped or lasered), have an influence on the static friction coefficient in the joint and thus on the torque transmission. In order to better estimate and test the actual load capacity of the joint, this paper describes how the static friction coefficient is determined experimentally at the Institute of Construction and Drive Technology (IKAT) using various devices. On the other hand, a high-speed test rig is presented, which should enable tests close to real components. In particular, the increased requirements on the test rig components with regard to dynamic balancing and centrifugal forces as well as their design solutions are presented.:Introduction Friction coefficent between shaft and hub - model experiments Static experiments Dynamic experiments under high speed / Im Rahmen des FVA-Forschungsprojektes 965 I mit dem Thema 'Elastisch-plastische Auslegung der Pressverbindung zwischen Rotorwelle und Blechpaket von hochdrehenden E-Maschinen zur Steigerung der Leistungsdichte' wird die Welle-Nabe-Verbindung (WNV) gemäß dem Thema untersucht. Mit der elastisch/plastisch gefügten WNV soll ein Durchrutschen des Blechpaketes auch bei großen Drehzahlen (Schleuderdrehzahl bis 22.000U/min) und Drehmomentlasten bis 3000 Nm verhindert werden. Hintergrund ist die Aufweitung des Blechpaketes, die zwangsläufig zu einer Reduktion des Fugendruckes führt. Die Fuge der WNV setzt sich aus drei tribologischen Partnern zusammen. Einerseits ist es die Welle aus 18CrNiMo7-6, andererseits ist es das Elektroblech vom Typ NO20-13 mit dem Backlack, welches das tribologische System zunächst schwer beschreibbar macht. Viele Faktoren, wie beispielsweise die Art des Blechzuschnittes (gestanzt oder gelasert), haben Einfluss auf den Haftreibwert in der Fuge und damit auf die Drehmomentübertragung. Um die tatsächliche Belastbarkeit der Verbindung besser abschätzen und prüfen zu können, wird in dieser Arbeit beschrieben, wie der Haftreibwert experimentell am Institut für Konstruktions- und Antriebstechnik (IKAT) mit Hilfe verschiedener Vorrichtungen ermittelt wird. Andererseits wird ein Hochdrehzahlprüfstand (Abbildung) vorgestellt, der Realbauteilnahe Versuche ermöglichen soll. Insbesondere werden die erhöhten Anforderungen an die Prüfstandkomponenten bezüglich des dynamischen Wuchtens und der Fliehkräfte sowie deren konstruktive Lösungen dargestellt.:Introduction Friction coefficent between shaft and hub - model experiments Static experiments Dynamic experiments under high speed