报告一：Lifetime prediction and modeling the constitutive behavior of tetragonal ferroelectrics under electromechanical loading
 

报告内容摘要

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Ferroelectric materials are widely used in smart structures and devices as actuators, sensors etc. In this work, a condensed model for ferroelectric solids with tetragonal unit cells is presented. The approach is microelectromechanically and physically motivated, considering discrete switching processes on the level of unit cells and quasi-continuous evolution of inelastic fields on the domain wall level. Hysteresis loops are simulated for a pure electric and an electromechanical loading to demonstrate the influence of a compression preload on the poling and stress-strain behavior. Further, residual stresses are calculated as a result of switching processes and interaction between crystallits. To study the high cycle fatigue damage and to predict lifetime of ferroelectric devices, an accumulation model is proposed based on the growth of microcracks. Here, the Paris law is applied to calculate fatigue crack growth rates. The lifetime is calculated considering different parameters, e.g. initial crack length, material parameters, loading cases etc. The simulations agree with experimental findings, where actuation efficiency and structural integrity come out to be opposing properties.

报告人简介

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Prof. Andreas Ricoeur

10/88 - 09/94                            Studies in Mechanical Engineering at the University of Stuttgart

03/95 - 03/98                            Doctoral candidate at the Robert Bosch GmbH, Department of Applied Physics, and PhD student at the University of Stuttgart

04/98 - 06/2000                         Postdoctoral research fellow at the Institute of Mechanics and Machine Components, Technical University Bergakademie Freiberg

07/00 - 08/09                            Scientific associate at the Institute of Mechanics and Fluid Dynamics (IMFD), TU Bergakademie Freiberg

since 09/2009                           Full Professor for Engineering Mechanics/Continuum Mechanics at University of Kassel

since 04/1011                            Dean of Students of the Department of Mechanical Engineering

since 05/2012                Head of the Institute of Mechanics of the University of Kassel

Dipl.-Ing. Stephan Lange

Since 2012        Research assistant (Ph.D.), Institute of Mechanics, Engineering Mechanics / Continuum Mechanics, Department of Mechanical Engineering, University of Kassel

2007 – 2012   Dual studies (StiP) – Diploma in Mechanical Engineering & Vocational training to Industrial Mechanic, University of Kassel & Rheinmetall AG

 

报告二：Modeling of ferroelectric and ferromagnetic behavior and prediction of magnetoelectric coupling in multiferroic composites

 

报告内容摘要

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The coupling of magnetic and electric fields due to the constitutive behavior of a material is commonly denoted as magnetoelectric (ME) effect. In this work, the theoretical background of nonlinear constitutive multifield behavior as well as the Finite Element (FE) implementation are presented. Nonlinear material models describing the magneto-ferroelectric or electro-ferromagnetic behaviors are presented. Both physically and phenomenologically motivated constitutive models have been developed for the numerical calculation of the nonlinear magnetostrictive and ferroelectric behaviors. On this basis, the polarization in the ferroelectric and magnetization in the ferromagnetic respectively magnetostrictive phases are simulated and the resulting effects analyzed. Numerical simulations focus on the prediction of local domain orientations and residual stress going along with the poling process, thus supplying information on favorable electric-magnetic loading sequences. Goals are to improve the efficiency of ME coupling and to reduce damage associated with the poling process. Further, the developed tools enable the prediction of the electromagnetomechanical properties of smart multiferroic composites and supply useful means for their optimization. The resulting final state of a poling simulation can be implemented as a starting condition for approximate linear simulations and multifield homogenization procedures.

报告人简介

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Dipl.-Ind.-Eng. A. Avakian, M.Sc.

Since 2012        Research assistant (Ph.D.), Institute of Mechanics, Engineering Mechanics / Continuum Mechanics, Department of Mechanical Engineering, University of Kassel

2010 – 2011      Studies of Master of Science – Industrial Engineering (Mechanical Engineering), University of Kassel

2007 – 2010     Dual studies (StiP) – Diploma in Industrial Engineering (Mechanical Engineering) & Vocational training to Industrial Mechanic, University of Kassel & Volkswagen AG

 

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