Developments in Ceramic Materials Research

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Dena Rosslere
room is rather poor. Their effectiveness is restricted mainly to the low frequency region. A
selective amplification of sound in the near field of resonators was observed as well as a small
attenuation in the reverberant part of the field in the resonant frequency and near a higher
overtone. A remarkable increase of Clarity and Definition at resonant frequency was also
observed. A computer simulation program, based on energy coupling method between the
pots and the room, showed that the number of pots per unit volume is the most important
parameter that affects the sound quality.
Chapter 6 - Modelling and analysis of a unique geometrically representative Unit Cell has
been shown here as the key to predicting the macro thermal transport behaviour of
composites, which otherwise requires the employment of a vast experimental infrastructure.
Sophisticated materials, such as woven Ceramic Matrix Composites (CMCs), have very
complex and expensive manufacturing routes, used by just a few research organizations. This
broadens the scope of a modelling strategy to be adopted for the characterization of all
possible material designs with various possible constituent volume fractions by using a
commercial FE code such as ABAQUS. The variation of material constituents can be
incorporated in the Unit Cell model geometry with subtle manipulation of key parameters
dictated by quantitative SEM morphological data. Two CMC material systems have been
modeled in the present study. The first material has been analysed with a focus on the
homogenization of microscopic constituent material properties into the macroscopic thermal
transport character. The actual set of property data used for the Unit Cell of this material is
obtained from the cumulative property degradation results extracted from the analyses of
three sub-models based on the material’s unique porosity data. After validating the modeling
methodology through a comparison with the experimental data, a geometrically more
challenging CMC is modelled with a detailed incorporation of its morphological complexity
in order to predict its macroscopic thermal transport behavior. Finally, it is shown how these
models can be more efficiently analysed in a multi-processing parallel environment.
Chapter 7 - Synthesis, characterization, device fabrication, modeling and underwater
evaluation of porous piezoceramics used in the form of 3-3 piezocomposites are discussed in
detail. Piezocomposites have drawn considerable attention in recent years due to their
potential application in medical ultrasonic and underwater transducers. Piezocomposites with
3-3 connectivity are produced from porous piezoceramics by filling the pores with suitable
polymer materials. In this two-phase material, the PZT and the polymer are self-connected in
three dimensions. Synthesis of porous PZT structure by two techniques, namely, BURnout
Plastic Spheres (BURPS) and foam reticulation techniques used to obtain wide range of
porosity are described. Samples with ceramic volume fraction ranging from 10% to 100% are
synthesised and are characterized in terms of their microstructure, piezoelectric charge (d33,
d31) and voltage (g33,g31) coefficients, the hydrostatic coefficients (dH and gH) and hydrostatic
Figure-of-Merit. Variations in dielectric, mechanical and piezoelectric properties as a function
of ceramic volume fraction/ porosity are discussed. The experimental results are compared
with that of a simple analytical model. Finite element modeling (FEM) studies are carried out
on hydrophones constructed from porous and dense PZT discs. An axisymmetric model is
proposed for dense PZT hydrophone and is validated by an analytical model. A 3-dimensional
model is proposed for porous PZT hydrophones. The FEM results agree well with that of the
experiments. Details of the hydrophones fabricated with PZT-air and PZT-polymer
composites with different configurations are presented. The acoustic performance of the
transducers is evaluated underwater. The receiving sensitivity, the electrical impedance