Ferro- and piezo-electric materials from low to high rate and temperature
Principal Supervisor: Dr Bill Proud
Materials are piezo electric due to a polar non-symmetrical crystal structure. Charge is given out as the material is strained driven by a potential gradient developed across the sample. Ferroelectricity is a property of certain materials in which they possess a spontaneous electric polarization that can be reversed by the application of an external electric field. Materials such as PZT and PVDF are used as stress sensors and time of arrival sensors - with greater or lesser degrees of characterisation.
Fundamental subject of this PhD - in shock studies the charge output can be measured as a function of strain, stress, velocity and imposed voltage. An advantage of these material types is that this charge output can also be used as a self-diagnostic. This allows insight into the crystal level deformations occurring in these materials as well as the 'bulk' material properties.
It is known that factors such as porosity, temperature and strain rate affect the amount of charge given out. it has been seen that some porous piezo-electric materials are LESS susceptible to temperature and strain rate than pore-free samples. Speculation on why this occurs includes more flow of the material before fracture, however, porous materials generally start to fracture at lower stress; are the pores acting as crack-stoppers?
Also many of these materials are used as micro- or nano-translators enabling the application of a voltage to cause the material to change shape or increase its internal stress state before OR during the impact process - i.e. modify the loading route dynamically. The charge output varies with crystal orientation - so it is possible that these materials be used as longitudinal and lateral stress sensors.