Visiting Researcher Grant - Multiscale modelling of ferroelectric materials for actuator design

压电陶瓷越来越多地被用作控制、医疗、电子和微电子机械（MEMS）应用的机电传感器和执行器的基础。机电致动器利用电场在铁电材料中的作用所产生的应变。在致动装置中可能产生许多内应力源。首先，制造过程会引入残余应力。与致动器封装有关的边界条件是操作应力的另一个来源。在更小的尺度上，由于铁电材料（多晶结构）的非均质性，压电应变通常不相容，在施加电场时产生内应力。尽管压电应变对内应力的影响很大，但在执行器的设计中很少考虑到内应力对压电应变的依赖关系，主要是因为它难以量化或预测。铁电行为微观-宏观模型的发展为建立铁电材料的完全耦合电-力本构规律提供了途径。这样的本构律将改善电场感应应变的定量描述，并允许压电致动器的优化设计。因此，通过开发多尺度工具，本项目的目标是以定量的方式描述外应力和内应力对铁电行为的影响。这将为设计高性能铁电执行器提供工具。

Piezoelectric ceramics are becoming used increasingly as the basis for electromechanical sensors and actuators for control, medical, electronic and microelectronic machine (MEMS) applications. Electromechanical actuators take benefit from the strain resulting from the application of an electric field in ferroelectric materials. Many sources of internal stress can arise in actuation devices. First the manufacturing process can introduce residual stresses. The boundary conditions related to the actuator packaging is another source of operating stress. At a finer scale still, due to the heterogeneity of ferroelectric materials (polycrystalline structure), the piezoelectric strain is usually not compatible, resulting in internal stresses when an electric field is applied. Despite its significant role, the dependence of the internal stress on the piezoelectric strain is rarely accounted for in the design of actuators, mainly because it is difficult to quantify or predict. The development of micro-macro models of ferroelectric behaviour provides a pathway to establish fully coupled electro-mechanical constitutive laws for ferroelectric materials. Such constitutive laws will improve the quantitative description of electric field induced strains, and allow the optimisation of piezoelectric actuator design.Consequently, through the development of multiscale tools the objective of this project is to describe in a quantitative way the effect of applied and internal stress on ferroelectric behaviour. This will provide the tools to design high performance ferroelectric actuators.