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|Title:||Effective piezoelectric properties of composite materials||Authors:||Ho, Chi-hin||Keywords:||Hong Kong Polytechnic University -- Dissertations
|Issue Date:||2007||Publisher:||The Hong Kong Polytechnic University||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.||Description:||[viii], 108 leaves : ill. ; 31 cm.
PolyU Library Call No.: [THS] LG51 .H577M AP 2007 Ho
|URI:||http://hdl.handle.net/10397/3382||Rights:||All rights reserved.|
|Appears in Collections:||Thesis|
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