Lecture Johannes Rödel
|05 December 2003||FWN-Building 5118.-158, Nijenborgh 4, 9747 AG, Groningen|
|Speaker:||Dr. Johannes Rödel|
|Affiliation:||Institut für Werkstoffwissenschaft, Technische Universität Dresden, Germany|
|Title:||Micro-mechanical concepts for modeling of ferroelectric ceramics|
|Date:||Fri Dec 5, 2003|
|Host:||E. van der Giessen|
|Telephone:||+31 50 363 8046|
Various methods have been established to describe the behavior of ferroelectric materials on various length scales, ranging from ab initio molecular dynamics to macroscopically phenomenological modeling. Between these extremes, micro-mechanical models describe the material on the length scales ranging from defects to grains.
In the talk, the key elements of micro-mechanical models are introduced, which are mainly:
- laminates to model domain structures and
- inclusions to model individual grains and grain interactions in polycrystals, but also dislocations and disclinations to model effects of microscopic eigenstrain incompatibilities. Using this approach, the interesting nonlinear and hysteresis behavior of ferroelectrics can be desribed by moving discontinuities, like walls or line defects.
On this basis, a micro-electromechanical model is presented, which describes the macroscopic behavior of ferroelectric ceramics under weak signal and unipolar large signal loading conditions. The approach is based on a laminar domain structure and a hierarchical homogenization procedure, which considers grains as spherical inclusions within a homogenized effective medium. The model predicts the extrinsic effects of mobile domain walls, hysteresis at large fields, and ferroelectric fatigue by unipolar cycling.
While the emphasis will be on general concepts, numerical results for barium titanate ceramics will be presented as an example.
|Last modified:||22 October 2012 2.30 p.m.|