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Abstract
The motivation of this research is to build systems that precisely control displacement in the presence of external load (both linear and rotation force). To achieve this, two experimental platforms have been created. Those instruments incorporate actuation stages, rotary apparatus, and rotary encoder and displacement sensors. During experiments the temperature of the stage and the environment are recorded. Characterization of these processes necessarily requires generation and monitoring of forces and measurements of displacement, rotation, and environmental temperature. The actuator methods include thermal expansion and piezoelectrical actuation, and the displacement sensing includes optical knife-edge and capacitive gage sensors. A thermally actuated, single-axis, bidirectional translation stage is designed and constructed. To increase the temperature of the thermal actuator, induction heating is used while air-water-mist cooling is used to decrease the temperature. An automated control strategy comprising PID closed-loop control (for heating) and On/Off switching between air and mist control (for cooling) is described. Future work on thermal actuators includes an investigation of the feasibility of manufacturing and implementation of a compact system that can be integrated into systems scaled between MEMS devices and devices smaller than 25 mm. With a decrease in the overall dimensions of the actuator, it is expected that the dynamic properties will improve while continuing to support loads in excess of 1000 N for displacement control. A second study seeks to determine whether there exist torsional forces during indentation measurements. To precisely measure torsional forces produced by rotations within the indent region, an air bearing is employed since there is little rotational resistance other than inertia of the bearing itself. The general design combines an air bearing and an indentation system. The air bearing system is mounted on the x/y moving table of a Moore measuring machine while the indentation apparatus is mounted on the vertical carriage in place of the spindle stage. A coarse and fine adjustment mechanism is assembled onto the air bearing spindle to align the tip of the nano-indenter to within 1 μm of its axis of rotation. The indentation system consists of an alignment sensor that will provide feedback for the indenter adjustment. Two flexure structures with two capacitance gauges, and a PZT (Lead-Zirconate-Titanate) linear actuator are built for the actuation and load-cell stages. The specimen is glued on the bottom of the load-cell stage. Rotation is measured using an A-B quadrature encoder affixed to the spindle of the air bearing and capable of resolving rotation to 0.0002 µrads. The indentation depth control and data capture are completed using a National Instruments myRIO Data Acquisition device. The actuation stage has a displacement range of 16 μm and this is used to generate a penetration force between a sample and an indenter tip and this force pass through, and is measured by the load-cell stage. Numeric experiments have been performed with penetration depths from 200 nm to 2000 nm and with penetration forces between 20 mN to 200 mN. After indentation, rotations were not detected for this research for Si (hardness ~ 12.5 GPa), Fe, large grain sized Fe, NiP, Cu, large grain sized Cu, Al, and Carbon Fiber Reinforced Polymer (CFRP) (hardness ~ 0.1 GPa).