Ph.D. Thesis Defense by Lisa D. Mauck
Tuesday, December 3, 2002
(Dr. Chris Lynch, advisor)
"The Role of Rate Dependence and Dissipation in the Constitutive Behavior of Ferroelectric Ceramics for High Power Applications"
In the aerospace industry, structural control such as flap and aileron actuation is achieved through hydraulic actuation systems. Conventional hydraulic systems are large, heavy, require heat exchangers and require hydraulic lines to be run throughout the aircraft. Northrop-Grumman, under the DARPA funded Smart Wing program, funded Georgia Tech to develop a piezohydraulic pump. The piezohydraulic pump allows compact construction; hence, individual pumps may be distributed throughout the aircraft in lieu of hydraulic lines, central pumps, and heat exchangers.
To achieve high output power the piezoelectric in the pump application was driven at high electric field and high frequency. As a result, it was driven into the non-linear irreversible response regime. The resulting hysteresis lead to self-heating and limited pump drive frequency to 60Hz. Constitutive laws are not available to predict the generation of heat, the minor hysteresis loops, and the saturation of the piezoelectric response at high field.
The purpose of the thesis work was to bridge the gap between engineering applications and engineering science in the field of high drive ferroelectric actuation. A piezohydraulic pump capable of large force-large displacement was constructed. This self-heating design problem motivated the development of improved constitutive models. Two computational polycrystalline models have been developed. The first captures high-field and thermal effects; the second captures rate and self-heating effects. Hence, both the details of pump development and performance are presented, as well as details of constitutive modeling of the irreversible, rate dependent behavior driving self-heating.