力电脉冲作用下压电陶瓷疲劳裂纹扩展模拟与实验验证

Piezoceramics are susceptible to cracking during the poling process or in service because of their low strength and fracture toughness. The fatigue fracture is their most fatal failure mode. Unlike the ideal alternating loadings such as sinusoidal wave or rectangular wave, the real loadings on piezoelectric devices usually take the form of pulse shape. As known to us, the mechanical pulses will excite the considerable inertial effects and lead to heavily dynamic overshooting on the crack-tip fracture parameters. Meanwhile, the electric pulses always behave the extremely high amplitude in a short moment which do deadly harm to any electronic devices. However, most of the current studies are focused on the electrically induced fatigue cracking under alternating electric field using experimental tests.The corresponding theoretical models and the simulation methods are lacking. To this end, this project will set up a univeral BEM software platform on the basis of the existing experimental results about fatigue crack propagation under various cycle loadings. A multi-scale fatigue model is proposed on the basis of the existing macroscopic and mesoscopic models. The macroscopic phenomenological model considers the inertial effects induced by dynamic loading and electrically induced domain wall motion. At the same time, the mesoscopic damage mechanism takes account of the crack-tip local domain switch and plastic yielding. Further, we develop the corresponding BEM program module. The numerical results are combined with the experimental data to determine the intrinsically governing fracture parameters of the fatigue crack propagation, propose a multi-parameter crack growth formula, and then build a growth model for the fatigue crack. Finally, we develop a high efficient and stable BEM universal software to simulate the propagating process of the fatigue crack and evaluate the rest life of piezoelectric devices under any electromechanical loadings. Then we apply this software platform to the special loading of the electromechanical pulse. The corresponding experimental tests are also carried out to reveal the fatigue crack growth law and varify the numerical results. The solutions to this problem are of great significance for the piezoceramics fatigue theories and their engineering applications for reliability design.

压电陶瓷的强度与断裂韧度低，在极化与服役中极易产生缺陷，疲劳断裂是其最危险的失效形式。与静态载荷不同，压电器件的实际载荷往往是脉冲形式。机械脉冲会引起不可忽视的惯性效应；电脉冲持续时间极短、峰值高，对电子器件的危害性极大。而现阶段研究侧重于对交变电场所致疲劳断裂的实验研究，缺乏有效的理论模型与数值模拟手段。因此，本项目首先根据文献中各种交变载荷下压电陶瓷的疲劳试验与理论分析结果，宏细观相结合建立多尺度疲劳模型。宏观唯象模型考虑动载的惯性效应与电致畴壁运动，细观损伤机制考虑裂尖小范围畴变与塑性屈服。分析确定疲劳裂纹扩展的控制参量与准则，并提出多参数扩展公式；进而开发高效稳定的通用边界元软件平台，实现疲劳裂纹扩展的数值模拟与寿命预测。针对典型力电脉冲情况，应用此数值软件进行实例模拟，与实验对比逐步完善模型与软件。研究成果对于压电陶瓷的疲劳断裂理论与可靠性设计都具有十分重要的科学意义和实用价值。

压电陶瓷由于强度与断裂韧度低，在极化与服役中极易产生缺陷，疲劳断裂是其最危险的失效形式。与静态载荷不同，压电器件的实际载荷往往是脉冲形式。而现阶段研究侧重于对交变电场所致疲劳断裂的实验研究，缺乏有效的理论模型与数值模拟手段。因此，本项目基于压电陶瓷的疲劳试验与理论研究现状，研究的主要内容包括断裂参数的高效精确计算方法、有效的裂纹模型、压电裂纹扩展的断裂准则、不同载荷条件下的疲劳裂纹扩展公式等。课题主要创新性成果有：率先将相互作用积分法引入对压电裂纹的边界元分析中；提出磁电介质界面裂纹断裂参数计算公式；提出一种新的断裂参数——周向机械应变能释放率，实现了对压电裂纹扩展方向的快捷计算，并考虑断裂韧度的各向异性提出修正的最大周向机械应变能释放率准则，成功对压电裂纹扩展路径的准确模拟；对机械循环载荷下考虑裂尖小范围畴变与塑性屈服，对电致疲劳考虑裂尖电屈服的条状饱和区模型，对压电裂纹疲劳扩展公式中的控制参量进行了合理选择。最终，课题组开发了高效稳定的通用边界元软件平台，实现了对压电裂纹准静态扩展以及疲劳裂纹扩展的数值模拟与寿命预测。研究成果对于压电陶瓷的疲劳断裂理论与可靠性设计都具有十分重要的科学意义和实用价值。