Modelling And Optimal Design Of Cement-Based Piezoelectric Composites

Cement-based piezoelectric composites fabricated by cement matrix and piezoelectric ceramic phase in different mixing rules and volume fraction are new kinds of materials. Cement-based piezoelectric composites have very sensitive transduction properties as well as good compatibilities with the most popular construction materials (cement and concrete) used in civil engineering. They have received much research attention in the recent decades and have appeared to be a novel kind of electromechanical transducer materials in structural health monitoring (SHM). The studying of overall properties of PZT-cement composites is crucial to the design, optimization and practical engineering application of transducer. In this dissertation, theoretical predicting models of effective properties for PZT-cement composites in different types were focused. Experiments on cement-based composites with different types were carried out to verify theoretical models. After numerical discussions, some considerable suggestions were made on the optimal design of cement-based piezoelectric composites. This dissertation was organized as follows:(1) Based on the fact that the bonding between cement and PZT is not always good, a general spring-type interface model was proposed and the relation between spring-type interface parameters and interphase material was obtained. The Eshelby problem was formulated for a piezoelectric ellipsoidal inclusion embedded in an infinite piezoelectric matrix when the interfacial bonding between them is imperfect. The modified piezoelectric Eshelby tensor was derived via the classical piezoelectric Eshelby tensor. The averaged piezoelectric Eshelby tensor was calculated by using two methods. Numerical results were presented and discussed for a simple spring-type interface model.(2) By incorporating the spring-type imperfect interface model and using the modified Eshelby tensor for piezoelectricity, this dissertation have successfully further developed and extended four micromechanics models such as modified dilute method, modified Mori-Tanaka method, modified differential scheme and modified self-consistence method to predict the effective properties of piezoelectric composites containing imperfect interfaces. By comparing the calculated results with the published experimental data, application scopes of classical methods were discussed.(3) Based on the fact that the effective properties of PZT-cement composites containing particles show size-dependence and the SEM result of cement-based composites, a micromechanics model was adopted to calculate the effective properties of composites. The adopted model can take the imperfect interfaces into account and the theoretically estimated results are in good agreement with the experimental observations. In fact, the results are quite perspicuous on the account of the fact that, there are imperfect interfaces in the composite and its influence on the effective properties increase with the decreasing surface-to-volume ratio of PZT particles. Some suggestions for the design and optimization of0-3type cement-based piezoelectric composites were furthergiven.(4) For the unidirectional periodic characteristic of2-2type cement-based piezoelectric composites, asymptotic homogenization method with macro-and micro-scale was formulated to calculate the effective properties of cement-based piezoelectric composite. Some experiments about2-2type cement-based piezoelectric composites were done to verify this model. It is shown that by manipulating the volume fraction of PZT, hydrostatic piezoelectric constant dhEff of composites can be higher, than dhEff of the constituents.(5) For the characteristic of1-3type cement-based piezoelectric composites with two periodic directions, double homogenization method was adopted to calculate the effective properties of these kinds of periodic structures. Some properties of1-3type cement-based piezoelectric composite were measured. Comparisons between the experimental data and predicted values indicate the correctness of the model. Moreover, numerical discussions and experiments show that one should choose proper volume fraction of constituents to obtain the best performance of the1-3type cement-based piezoelectric, composites.This research focused on the cement-based piezoelectric composites but was not limited to these kinds of composites. Proposed models can be extended to broader range such as polymer based piezoelectric composites, piezomagnetic composites, and so on. This study is useful for the design and engineering application of intelligent composites.