Crack growth in ferroelectrics driven by cyclic electric loading

前人对非导电裂纹的研究表明，只有在电场垂直于裂纹扩展方向的情况下，铁电材料才会由于电循环而出现裂纹扩展。然而，对于循环电场的先前极化、极性和频率的影响，仍然缺乏一个明确的定量和机理的理解。在本项目的实验部分，将研究在有机械预紧力和无机械预紧力的情况下，PZT中DCB试件中由于电循环而产生的穿透厚度裂纹的扩展。还将进行可切换应变和宏观材料表征。该项目的理论部分将提供90°开关和180°开关的切换区，并将包括压电效应，以便通过评估沿裂纹尖端周围的轮廓积分的牵引力来计算裂纹尖端的应力强度因子。通过对试件几何形状的计算，进一步检验了模型的一致性，在机械和电混合载荷作用下，得到了稳定的裂纹路径。

Prior work from the literature of non-conducting cracks indicates that ferroelectrics can exhibit crack growth due to electrical cycling only with the electrical field perpendicular to the crack propagation direction. A clear quantitative and mechanistic understanding about the influences of prior poling, polarity and frequency of the cyclic electric field, however, is still missing. In the experimental part of this project, crack propagation of through thickness cracks in DCB specimens in PZT due to electrical cycling will be investigated with and without a mechanical preload. Switchable strain and macroscopic material characterization will also be performed. The theoretical part of the project will provide switching zones for 90° switching, for 180° switching and will include the piezoelectric effect in order to compute the stress intensity factor at the crack tip via an evaluation of the tractions along a contour integral around the crack tip. A further consistency check of the model is afforded by calculating the specimen geometries where a stable crack path is obtained under mixed mechanical and cyclic electrical loading.