Theoretical and experimental investigations of fatigue crack growth in ferroelectrics under cyclic electromechanical loading

疲劳裂纹行为是评估智能结构可靠性和耐久性的重要依据。本研究的目的是定性解释和定量描述铁电和压电陶瓷材料的疲劳裂纹扩展机制。为此，计划的方法，结合实验研究，理论建模和数值模拟。主要的重点是断裂过程区，畴切换现象诱导的非线性效应和控制的故障机制。因此，微观力学和唯象本构模型将被开发，实施到有限元代码和应用于模拟机械，电气和组合载荷下的疲劳裂纹行为。实验将进行调查域切换的非线性效应，并测量断裂韧性和疲劳裂纹扩展速率。将提出合适的断裂准则和疲劳裂纹扩展规律，并通过实验加以验证。研究结果将为智能铁电结构的构件设计和在机电循环载荷作用下的可靠性评估提供指导。

Fatigue crack behaviour is of most importance for the assessment of reliability and durability of smart structures in engineering practice. The aim of the present research proposal is the qualitative explanation and the quantitative description of fatigue crack growth mechanisms in ferroelectric and piezoelectric ceramic materials. For this purpose an approach is planned, combining experimental investigations, theoretical modelling and numerical simulations. The main emphasis is on the fracture process zone, where domain switching phenomena induce nonlinear effects and control the failure mechanisms. Therefore, micromechanical and phenomenological constitutive models will be developed, implemented into FEM-codes and applied to simulate the fatigue crack behaviour under mechanical, electrical and combined loading. Experiments will be undertaken to investigate the nonlinear effect of domain switching and to measure fracture toughening and fatigue crack growth rates. Suitable fracture criteria and fatigue crack growth laws will be proposed and verified by experiments. The results will provide guidelines for component design and reliability evaluation of smart ferroelectric structures under cyclic electromechanical loading.