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。由于在铁电材料中施加电场而产生的应变，使机电执行器受益。在驱动装置中可能会产生许多内部应力源。首先，制造过程会引入残余应力。与执行器封装有关的边界条件是工作压力的另一个来源。在更细的尺度上，由于铁电材料(多晶结构)的非均质性，压电应变通常是不相容的，导致在施加电场时产生内应力。尽管其具有重要的作用，但在执行器的设计中很少考虑内应力与压电应变的相关性，这主要是因为它很难量化或预测。铁电行为的微观-宏观模型的发展为建立铁电材料的完全耦合的机电本构关系提供了途径。这样的本构定律将改进电场诱导应变的定量描述，并允许优化压电驱动器的设计。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加应力和内应力对铁电行为的影响。这将为设计高性能的铁电驱动器提供工具。

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.