Acoustic techniques for property estimation in green and fired ceramic powder compact components.
A commonly used process for the formation of ceramic wall tile bodies is powder compaction. Variations in density in wall tile bodies introduced by the compaction process can cause rejection at later stages of production. Quality control equipment currently employed does not identify reject bodies in the unfired state. Scope exists to reduce production costs by the timely removal of reject bodies in the unfired state. In this thesis an ultrasonic non-destructive technique is presented which allows the mapping of the density variations found in wall tile bodies in the unfired and fired states to an accuracy of ± 0.5%. An effective medium theory for the propagation of ultrasound in porous media is developed. The significance of the dependence of Young's modulus on density in determining the relationship between compression wave propagation velocity
and density is explored. Using a vibrational resonance technique, it is shown that the evolution of Young's modulus
and Poisson's ratio in the wall tile body material are very sensitive to the conditions used for the firing operation.
The Biot two-phase theory of acoustic propagation in fluid saturated porous media which considers dissipation due to friction between the fluid and porous frame is reviewed, and
the applicability to the wall tile body material assessed. It is shown that this dissipation mechanism is insignificant for this particular material. A modification is made to the
model in an attempt to include dissipation due to the inelasticity and scattering of the porous frame. The results show that the two-phase theory reduces to an effective medium
theory in the limit of the saturating fluid being air.
The thesis concludes that density variations in wall tile bodies can be measured using and ultrasonic technique and that an effective medium theory can be used to describe the
propagation of ultrasound in porous media.