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报告1 (Prof. Andreas Ricoeur): Research Activities in the Field of Smart Materials and Structures: An overview on selected topics
The continuum mechanics group of Mechanical Engineering at the University of Kassel has been researching for approximately 15 years in the field of smart materials and structures. The wide range of work comprises theoretical and experimental basic research in coupled electrodynamics–mechanics, constitutive modelling of ferroelectric, ferromagnetic or multiferroic materials bridging different scales, numerical discretization schemes for solving electromechanical or magnetomechanical boundary value problems of smart structures, and theoretical as well as experimental investigations on fracture and damage in piezoelectric ceramics. The talk gives an overview of some selected topics, among others, ferroelectric self-heating in bulk and thin-film specimens, crack growth and deflection in ferroelectrics with electric loading, experimental validation of Maxwell stress models, and an efficient multiscale approach for simulating ferroelectric boundary value problems.
报告2 (Dr. Andreas Warkentin): Smart energy harvesting: from material modeling to process optimization
Ferroelectrics exhibit many interesting effects, both linear and nonlinear, which is why they are widely used in science and technology. Generally, these materials have been employed as energy harvesters, however in this context, they are more famous for their linear effects than their nonlinear ones, not least because the latter are accompanied by energy dissipation, which invariably leads to heat generation and damage. Recently, the utilization of nonlinear effects in the field of energy harvesting has been gaining momentum and is called ferroelectric/ ferroelastic energy harvesting. The latter comprises cyclic processes, wherein the external electromechanical loads are arranged such that at appropriate stages the material is systematically de- and repolarized. Due to the actively induced switching processes, the problem of unintended depolarization and thus functional degradation due to purely mechanical load, as in piezoelectric energy harvesting, is avoided.
报告3 (Dr. Lennart Behlen): Electrostatic Forces on Dielectrics: Insights into a Century of Controversy
This talk gives an overview of the most prevalent Maxwell stress formulations for polarizable matter in conjunction with their corresponding physical interpretations. What is more, careful transformation of the integral formulations for electrostatic force and couple to their localized counterparts reveals hitherto unnoticed manifestations as concentrated loads, which strongly depend on singularities of the Maxwell stress tensor. These singularities arise naturally, among other things, in the context of electromechanical crack problems, where electric field and polarization suffer square root singularities at the tip of a semi- or impermeable crack. While investigations of dielectric fracture in most cases have been restricted to accounting for electrostatic tractions at crack faces, in this work the full effect of Maxwell stress induced loads, covering also body and concentrated line forces, is analyzed at the example of a Griffith crack. In doing so, fundamentally different contributions to crack tip loading and even higher-order stress singularities become apparent.
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Andreas Ricoeur教授，于1988-1994年在德国斯图加特大学机械制造系学习，毕业后留校并在1999年取得博士学位。1998-2009年在德国弗莱贝格工业大学任高级研究员，与Meinhard Kuna教授一起开展各种关于铁电材料损伤破坏分析的工作，包括压电复合材料的失效准则，压电材料中裂缝问题的建模，微电畴偏转下的铁电裂纹扩展等。Ricoeur教授于2007年在弗莱贝格工业大学取得特许任教资格（Habilitation），并从2009年开始在德国卡塞尔大学力学研究所连续介质力学方向任职W3教授（最高级别教授）。自2011年起Ricoeur教授被任命为卡塞尔大学机械制造系教务长。迄今为止，共发表200余篇同行评审论文以及作百余次会议报告。 Ricoeur教授研究团队目前的主要研究方向有： (a) 数值分析，涵盖电、磁、力、热的多场耦合问题。从微观物理和宏观现象角度描述材料的本构行为，并包括非线性的特质，例如电畴翻转和相变。利用有限元分析方法解决耦合材料的边界值问题，并应用在压电材料或磁致伸缩执行器和多铁性复合材料，以及准晶材料的力学性能分析上。 (b) 断裂和损伤力学。数值分析材料在极端条件下裂纹生长并模拟裂纹生长路径。其中包括各向异性、残留应力、不完美界面的交互作用以及复杂加载条件。断裂力学的处理方法同时也被应用到具有耦合本构行为的功能材料上。在损伤力学范畴内，主要预测裂纹的萌生和研究损伤的演化。 (c) 多尺度和均质化的研究。尤其是已知杂质材料有效性质或物理特性的情况下，该杂质可以是微观上的裂纹、缺陷或晶界，也可以是宏观上的聚合物复合材料。 Ricoeur教授作为连续介质力学方向的负责人，组内共有13名全职工作人员，建有两个固体力学实验室，已完成或正在进行多项德国DFG和黑森州文化教育局的科研项目，并承担多项第三方项目，例如与大众汽车、戴姆勒奔驰公司的合作等。
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