Studies On The Microstructure Evolution And Its Effects On Ferroelectric Materials With Defects

Ferroelectric materials have attracted attentions from the area of smart structures for its excellent properties of low energy consumption and quick response time.However,the ferroelectric materials are intrinsically brittleness and prone to fracture.Under the external mechanical-electric load,local stress concentration and electric field concentration will cause the domain swtiching,which tend to change the electric field and result in internal stress.And ultimately lead to mechanical-electrical nonlinearity response of ferroelectric materials.Based on phase field method,this thesis focuses on the study of the microstructure evolution and its effects on ferroelectric materials with defects including theoretical deduction and numerical simulation,a single crack model and multiple cracks model simulation by the loading of multi-field coupling.The main work of the paper is as follows:In Chapter 1,the current research status of the microstructure evolution on ferroelectric materials with defects are introduced,and the problems needed to be further studied.From the basic assumptions of thermodynamic principles,the complete derivation process of Ginzburg-Landau equation is given in Chapter 2 based on the microforce equilibrium equation and its physical background.Combined with electric enthalpy of ferroelectrics given by Landau-Devonshire,the ferroelectric constitutive equations are perfected based on the principle of the microforce.Meanwhile,the formulation of the adiabatic temperature change is deduced in the cracked ferroelectric model,and the permissible conditions of the existing adiabatic temperature change equation in ferroelectric materials are given.Considering the interaction between defect and microstructure,the electric properties of the medium inside the crack have to be taken into account in Chapter 3.In this article,domain switching,the hysteresis loop of polarization versus electric field,and the electro-elastic field concentration around the crack tip are investigated by a phase field model under different temperature.In the Chapter 4,Effect of three electric-inclusion models(air,oil,water)on the giant electrocaloric effect induced by temperature is discussed under the applied electric field.The microstructure evolution process have shown the the origin of the large adiabatic temperature change in a cracked ferroelectric model.Form Chaper 5 to Chaper 7,the different temperature-induced nonlinear behavior and electro-elastic field concentration around the crack tips in a conduction crack/multiple conduction cracks / multiple electrodes have been studied based on a phase field approach.Under the different temperature,the stress field concentration can be reduced on the condition of proper electromechanical external load,to provide the theoretical direction for structural safety design and health prediction of ferroelectric components.Chapter 8 makes a summary and the future works on the topic are prospected.The main innovative points of the article are listed as below:(1)From the basic assumptions of thermodynamic principles,the complete derivation process of Ginzburg-Landau equation is given based on the microforce equilibrium equation and its physical background.Combined with electric enthalpy of ferroelectrics given by Landau-Devonshire,the ferroelectric constitutive equations are perfected follow the idea of the microforce.Meanwhile,the formulation of the adiabatic temperature change is deduced in the cracked ferroelectric model,and the applicable range of the adiabatic temperature change is given.(2)Considering the interaction between defect and microstructure,the electric properties of the medium inside the crack have to be considered.In this thesis,we consider the effect of the unusual temperature on domain switching,the hysteresis loop of polarization versus electric field,and the electro-elastic field concentration around the crack tip based on a phase field model.(3)We first discover the effect of three electric inclusion models(air,oil,water)on the giant electrocaloric effect under the applied electric field.The microstructure evolution process have shown the the origin of the large adiabatic temperature change in a cracked ferroelectric model.(4)The different temperature-induced nonlinear behavior and electro-elastic field concentration around the crack tips in a conduction crack/ multiple conduction cracks/ multiple electrodes have been discussed based on a phase field approach.