On June 13, 2022, Jacob L. Mingear became the first student within the MAESTRO Laboratory to complete all necessary requirements to earn his doctoral degree in Materials Science and Engineering, a department in which his Chair Dr. Hartl is an affiliated faculty member. Jacob joined the MAESTRO Laboratory after completing his B.S. in Materials Science and Engineering at University of Florida. He has taken a position at Los Alamos National Laboratory.
The full text of Dr. Mingear’s dissertation abstract is as follows:
“Shape memory alloys (SMAs) are capable of producing some of the highest actuation stresses of any active material, however, large monolithic SMA actuators are currently limited to low cyclic actuation frequencies due to their associated high thermal masses coupled with innate low thermal diffusivities of the material. An increase in the effective thermal diffusivity of an SMA actuator system will result in an increase in actuation frequency, i.e., more cycles over a given time interval. An increase in cyclic actuation frequency alone could position SMA actuators on par or to exceed the highest power density option among all actuators, i.e., hydraulic system, broadening the implementation of SMA actuators to new applications. To achieve this goal, liquid metal (gallium-indium) has been integrated into additively manufactured NiTi actuators to act as a multifunctional induction heating and forced fluid convection cooling system. Though for effective induction capabilities, the liquid metal must be electrically insulated from the surrounding SMA. There is special consideration for the printability of overhanging geometries and internal features; the surfaces produced by laser powder-bed fusion are rough and irregular. The complex internal channels require a chemical procedure that can effectively attack titanium compounds; this has been studied in detail using a relatively safe sodium fluoride solution, allowing for the application of subsequent processes in a controlled manner. A systematic investigation into the anodization of the NiTi SMA for the purpose of electrical insulation has been studied to provide robust and wear resistant insulative coatings based on their tribological, thermomechanical, chemical, and electrical properties. After the implementation of the prior enabling surface modifications, the actuation of internal channel liquid metal SMA actuators are presented. Liquid metal-enabled induction heating and closed loop cooling has been achieved for 12 cycles with tensile bar geometries consisting of a through-hole channel. Such demonstrations indicate that higher actuation frequencies can be achieved.”