冲击载荷下水泥基压电复合材料的力电耦合失效行为研究

The failure behaviors of cement-based piezoelectric composites under impact loading include 1) Mechanical failure: damage or destruction caused by the propagation of innate cracks；2) Electrical failure: highly concentrated electric field nearly the tip of cracks will result in 90° domain switching of local domain, overall domain switching will lead to the vanishing of piezoelectric properties. The damage evolution and mechatronic domain switching will change the electrical properties and mechanical behaviors of the cement-based piezoelectric composites. In theory, the project employs the damage and switching strain as internal variables, characterizing the switching strain as orientation distribution function, setting up function of Gibbs free energy, analyzing the damage evolution, constructing a model of mechatronic domain switching and a constitutive relation affected by the coupling of loading rate and mechatronic switching effect. In experiment, the project aims to measure the curves of load-time, strain-time, electric potential-time and the hysteresis loop by means of static and dynamic compression experiment with different loading rates and experiment in different electrical fields. All the experiments are carried out before or after poling of the materials. Observing the deformation of materials, distribution of cracks, average size of crack and microstructure of domain boundary and domain switching before and after experiment, estimating the volume fraction of the domain switching zone. The project is to determine the relevant parameters and then set up a constitutive relation affected by the coupling of loading rate and mechatronic domain switching effect and a mechatronic domain switching criteria by means of the finite element method.

冲击载荷下水泥基压电复合材料的失效行为，一是力学失效：先天裂纹扩展引起的损伤破坏；二是电学失效：材料缺陷尖端附近产生高度集中电场，导致小区域内电畴的90°畴变，整体电畴畴变导致压电性能消失。损伤演化和力电畴变效应改变了材料的电学性能和力学行为。本项目理论上以损伤和畴变应变为内变量，用取向分布函数表征畴变应变，构造Gibbs自由能函数，研究损伤演化，在热力学框架下构建材料加载率和力电畴变效应耦合的本构模型和力电畴变模型。实验方面，通过材料在未极化、极化后放电短路、放电加载情况下不同速度的准静态、冲击动态压缩和不同场强作用的实验，测定载荷-时间曲线、应变-时间曲线、电势-时间曲线和电滞回线；观测实验前后材料变形、裂纹分布、裂纹和电畴及畴壁细微结构的平均尺度，估算畴变带的体积分数。通过数值模拟确定相关参数，建立水泥基压电复合材加载率效应和力电畴变效应耦合的本构关系和力电畴变准则。

随着社会经济的不断发展，采用智能传感监测系统的在线健康检测，已在重要混凝土建筑工程中广泛采用。水泥基压电复合材料的出现，有望解决在线检测中传感智能材料与混凝土之间的相容性问题。本项目开展冲击载荷作用下水泥基压电复合材料的力电响应特性、损伤演化规律和力电畴变效应的研究，探索水泥基压电复合材料传感器制作与埋设测量技术。主要内容包括：(1)对混凝土基体材料和压电功能体材料的力学性能研究（撰写相关论文6篇，培养研究生1名）。（2）对1-3型和2-2型水泥基压电复合材料力电响应、畴变规律及损伤演化规律的研究（撰写相关论文4篇，培养研究生4名）。（3）开展相关试验技术装置研究（申请获批实用新型专利3项，申报待批发明专利和实用新型专利各1项）。.对大量试样的准静态单轴压缩试验，循环加载试验，单次冲击和重复冲击压缩试验研究表明：水泥基体、PZT5压电陶瓷和1-3型与2-2型水泥基压电复合材料都是应变率敏感材料；用三种方法对PZT5压电功能体的电畴翻转现象进行研究和互证，确认电畴翻转现象有应力门槛值。当载荷超过一定值后，随着加载应变率和加载次数的增加，电畴翻转现象明显，材料损伤累积，电位移幅值和残余电位移幅值均逐步减小，压电性能下降；在循环载荷作用下，PZT5压电陶瓷和1-3型与2-2型水泥基压电复合材料的应力-输出电位移响应一一对应。不管是静态载荷还是动态冲击载荷，均看到力电响应的灵敏度存在一门槛值。当载荷小于门槛值时，输出电位移与施加载荷间存在较好的线性关系，且重复性好。当载荷大于门槛值时，由于发生了电畴翻转，力电响应线性度下降，而且随着冲击加载次数的增加，试样的输出电位移呈递减变化，力电响应功能衰弱，材料已不适用于制作传感器。模拟计算结果与实验结果相一致。.本项目按照研究目标开展的大量实验研究、理论分析和数值模拟工作及制作探索，对水泥基压电复合材料的工程应用和传感器制作具有指导意义。