Theoretische und experimentelle Untersuchungen zur zyklischen Thermoviskoplastizität

Im Rahmen dieser Arbeit wurde ein Viskoplastizitätsmodell nach Chaboche mit ausschließlich kinematischer Verfestigung untersucht. Hierbei wurden auch die Auswirkungen eines Temperaturgeschwindigkeitsterms in der kinematischen Verfestigung betrachtet. Am Werkstoff AISI 316L(N) wurden isotherme Versuche zur Bestimmung der Parameter des Modells sowie nichtisotherme Versuche zur Beurteilung der Möglichkeiten des Modells durchgeführt. Die Versuche haben gezeigt, daß sowohl der E - Modul als auch die Fließgrenze mit steigender Temperatur abnehmen. Der Werkstoff zeigt bei monotoner und bei zyklischer Belastung nennenswerte Verfestigung. Der Betrag der Spannungsrelaxation und somit die Viskosität des Werkstoffs bzw. die sich aufbauende Überspannung nimmt mit steigender Temperatur ab. Es zeigte sich, daß der Werkstoff eine der thermischen Zyklierung vorangehende Verformung mit zunehmender Lastspielzahl "vergißt". Die Gegenüberstellung von Versuch und Rechnung macht deutlich, daß die Modellantwort des verwendeten Viskoplastizitätsmodells als gute Näherung einzustufen ist. Dies gilt insbesondere während des ersten Lastwechsels. Zu höheren Lastspielzahlen hin wird die Differenz zwischen Versuch und Rechnung größer, da das Modell nicht in der Lage ist, die bei AISI 316L(N) auftretende zyklische Verfestigung nachzuvollziehen. In Bereichen, in denen der Betrag der Spannung und die Temperatur gleichzeitig zunehmen, kann es aufgrund der Temperaturabhängigkeit der Fließgrenze zu Unterschieden zwischen Versuch und Rechnung kommen

Morphology-Dependent Influences on the Performance of Battery Cells with a Hierarchically Structured Positive Electrode

The rising demand for high-performing batteries requires new technological concepts. To facilitate fast charge and discharge, hierarchically structured electrodes offer short diffusion paths in the active material. However, there are still gaps in understanding the influences on the cell performance of such electrodes. Here, we employed a cell model to demonstrate that the morphology of the hierarchically structured electrode determines which electrochemical processes dictate the cell performance. The potentially limiting processes include electronic conductivity within the porous secondary particles, solid diffusion within the primary particles, and ionic transport in the electrolyte surrounding the secondary particles. Our insights enable a goal-oriented tailoring of hierarchically structured electrodes for high-power applications

Morphology‐Dependent Influences on the Performance of Battery Cells with a Hierarchically Structured Positive Electrode**

The rising demand for high-performing batteries requires new technological concepts. To facilitate fast charge and discharge, hierarchically structured electrodes offer short diffusion paths in the active material. However, there are still gaps in understanding the influences on the cell performance of such electrodes. Here, we employed a cell model to demonstrate that the morphology of the hierarchically structured electrode determines which electrochemical processes dictate the cell performance. The potentially limiting processes include electronic conductivity within the porous secondary particles, solid diffusion within the primary particles, and ionic transport in the electrolyte surrounding the secondary particles. Mitigating these limits requires an electronic conductivity in the active material of at least 10−4 S m−1 and a primary particle radius below 100 nm. Our insights enable a goal-oriented tailoring of hierarchically structured electrodes for high-power applications

Foundations of self-consistent particle-rotor models and of self-consistent cranking models

The Kerman-Klein formulation of the equations of motion for a nuclear shell model and its associated variational principle are reviewed briefly. It is then applied to the derivation of the self-consistent particle-rotor model and of the self-consistent cranking model, for both axially symmetric and triaxial nuclei. Two derivations of the particle-rotor model are given. One of these is of a form that lends itself to an expansion of the result in powers of the ratio of single-particle angular momentum to collective angular momentum, that is essentual to reach the cranking limit. The derivation also requires a distinct, angular-momentum violating, step. The structure of the result implies the possibility of tilted-axis cranking for the axial case and full three-dimensional cranking for the triaxial one. The final equations remain number conserving. In an appendix, the Kerman-Klein method is developed in more detail, and the outlines of several algorithms for obtaining solutions of the associated non-linear formalism are suggested.Comment: 29 page

A re-interpretation of the concept of mass and of the relativistic mass-energy relation

For over a century the definitions of mass and derivations of its relation with energy continue to be elaborated, demonstrating that the concept of mass is still not satisfactorily understood. The aim of this study is to show that, starting from the properties of Minkowski spacetime and from the principle of least action, energy expresses the property of inertia of a body. This implies that inertial mass can only be the object of a definition - the so called mass-energy relation - aimed at measuring energy in different units, more suitable to describe the huge amount of it enclosed in what we call the "rest-energy" of a body. Likewise, the concept of gravitational mass becomes unnecessary, being replaceable by energy, thus making the weak equivalence principle intrinsically verified. In dealing with mass, a new unit of measurement is foretold for it, which relies on the de Broglie frequency of atoms, the value of which can today be measured with an accuracy of a few parts in 10^9