Effective piezoelectric properties of composite materials

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Effective piezoelectric properties of composite materials


Author: Ho, Chi-hin
Title: Effective piezoelectric properties of composite materials
Degree: M.Phil.
Year: 2007
Subject: Hong Kong Polytechnic University -- Dissertations.
Composite materials.
Department: Dept. of Applied Physics
Pages: [viii], 108 leaves : ill. ; 31 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2094032
URI: http://theses.lib.polyu.edu.hk/handle/200/38
Abstract: The Poon and Shin approach of finding an explicit formula for the effective dielectric constant of 0-3 composites was extended to obtain two explicit expressions for the prediction of the elastic properties (bulk modulus and shear modulus) of isotropic 0-3 composites. Predictions using these two expressions were compared with experimental data for elastic properties of a glass/epoxy composite. Good agreements, even for high volume fractions of the glass fibers were resulted. These two expressions were then combined with Poon and Shin's explicit effective dielectric formula into the calculation scheme of Wong et al. As a result, two explicit formulas for the prediction of d31 and d33 values for binary 0-3 piezoelectric composites were obtained. Comparisons of the predictions made by these explicit formulas, Wong et. al.'s scheme and the published experimental data of d31 of PZT/PVDF and d33 of PbTiO3/P(VDF/TeFE) were presented. Another pair of explicit formulae for the effective piezoelectric coefficients (d31 and d33) of 0-3 composite of ferroelectric spheres embedded in a ferroelectric matrix taking into account the piezoelectric properties were also derived based on Poon and Shin approach, By assuming that both phases were dielectrically and elastically isotropic even they were polarized, we were able to express the effective piezoelectric coefficients directly in terms of the properties of the constituents. Predictions made were then compared with published experimental data of the d31 of a PZT/PVDF composite (in which only the ceramic phase was polarized), the d33 of a PZT/P(VDF-TrFE) composites (with both phases polarized in the same direction) and d31 , d33 of a PZT/P(VDF-TrFE) composite (with the two phases polarized in opposite directions). Fairly good agreements were demonstrated. For the first two cases, results showed that both our model and Wong et. al.'s scheme had comparable performance. However, for the last case, our model gave more favourable predictions. Effective piezoelectric coefficients of 1-3 piezoelectric fibre composites were also considered. Two explicit formulae for the effective piezoelectric stress coefficients (e31 and e33) were derived based on an effective medium theory (EMT) method, under the assumptions that both phases were transversely isotropic and the electric field strengths inside the constituents were equal to the applied electric field. The results obtained were then combined with Chen model to evaluate the longitudinal piezoelectric strain coefficient d33. Apart from the analytical EMT method, the effective piezoelectric coefficients of 1-3 composite were also calculated by a numerical EMT scheme. Results from both schemes were compared with the published experimental data of d33 of a 1-3 PZT/epoxy composite and the numerical values of e31 and e33 estimated by a finite element method of a 1-3 PZT/polymer composite.

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