Onur Bilgen

Solid-State Ornithopter: A Feasibility Study

The broad goal of this research is to demonstrate the feasibility of fully solid-state ornithopter-like flight using only smart materials. To this end, first, a parametric static and dynamic finite element analysis is conducted to understand the behavior of a non-active rectangular composite wing. A one-piece plate-like wing surface was assumed similar to the glide planform of a Great Blue Heron. Several non-active composite wings and one active wing prototypes were fabricated. The flapping and twisting motions of the wing were induced with the use of several distributed surface-bonded piezocomposite actuators. In preliminary experiments, a commercially available microcontroller and a high-voltage converter was used to excite the active piezocomposite wing demonstrating tip deflections in excess of 10 cm. A one degree-of-freedom testing apparatus constrained to the lift direction is used to simulate boundary conditions as experienced during flight. This paper focuses on detailed theoretical and experimental analyses on the fabricated prototypes. Results for halfinactive-wing force-displacement response and full-active-wing voltage-displacementresponse are presented.

Constrained-Energy Cross-Well Actuation of the Duffing-Holmes Oscillator

In this paper, the dynamics of a bistable structure is investigated. The analysis focuses on the minimum required energy to move a bistable structure between stable equilibrium positions of the system. The investigation is done under a limited scenario for energy and force. The nonlinear behavior of bistable structures have been previously proposed as a method to hold shape with no energy consumption in a variety of applications including common electronic devices such as switches, relays, and in small aerial, land, and underwater vehicles as control surfaces. This paper focuses on the wellknown Duffing-Holmes oscillator as a one-degree-of-freedom representative of a bistable structure. The paper identifies several unique features of the response of the nonlinear system subjected to force and energy constraints. The paper also shows how the required energy for cross-well oscillation varies as a function of damping ratio, frequency ratio, and for different values of excitation force amplitudes. The response of the bistable nonlinear system is compared to a mono-stable linear system with the same parameters. For a linear system, it was observed that the energy function is quantized, and the energy function becomes more continuous and less quantized by increasing the force amplitude. For a bistable structure subjected to a harmonic force amplitude less than the static force, the energy function is scattered and divided into several levels. By increasing the force amplitude to the so-called static force or larger values, the ranges of excitation frequency ratios and damping ratios, which are able to achieve cross-well oscillation, increase significantly, and also the energy requirement becomes less quantized.

Fatigue Characterization of Piezo-Active Beams in Bending

This paper presents the fatigue characterization of piezo-active beams in bending with surface bonded Macro-Fiber Composite actuators. Three substrate materials are considered: stainless steel, aluminum, and brass. First, the bending response is quantified theoretically using the classical laminate plate theory. The theoretical bending results indicate that the beam with the steel substrate had the largest curvature, and the specimen with the aluminum had the least. Next, midpoint deflection in a simply supported configuration in response to harmonic quasi-static actuation is experimentally measured. The results from the experiments showed no evidence of degradation of actuation for up to four million cycles at the harmonic excitation amplitude of 500 V; however, the results appeared highly sensitive to temperature.Copyright

Parametric Analysis of a Compliant Hinge Mechanism for a Shape Memory Alloy Actuated Arm

A compliant hinge is proposed to replace conventional revolute joints for a shape memory alloy actuated arm-like mechanism. The arm-like mechanism is designed to replicate the articulation of the elbow joint, linking the humerus and radius, while being able to lift a dead load using a shape memory alloy wire as the biceps muscle. A parametric analysis on hinge geometry and Young’s modulus is performed to determine if a feasible geometric and material solution exists based on the application requirements. The results indicate optimum solutions are logarithmically correlated between modulus of elasticity and width-to-thickness ratio. Overlaying the results of the parametric study onto an Ashby chart indicates that large hinge widths are necessary. These results indicate more complex geometries are needed for arm-like manipulator applications.Copyright

Constrained-Energy Dynamic Cross-Well Motion of Bistable Structures Subjected to Noise Disturbance

Bistable structures have two stable equilibrium positions and can be utilized to maintain a static shape with no energy consumption. This paper focuses on the minimum energy required for performing...

Induced Strain Actuation for Solid-State Ornithopters: A Geometric Configuration Study

This paper investigates geometric parameters and boundary conditions that structurally influence static and dynamic bending and twisting response of a wing-like plate when actuated with a surface-bonded piezoelectric material. A simple parametrized cantilevered plate is examined. The response is analyzed using a finite element model that is validated by comparison with known analytical solutions. A piezocomposite wing prototype is fabricated and actuated harmonically with two Macro-Fiber Composite actuators. The resulting experimental data is then used to further validate the theoretical models. The validated finite-element model is subjected to a parametric analysis. The geometric parameters and boundary conditions of the plate such as: the aspect ratio, actuator position, actuator angle, thickness-ratio of the active piezocomposite to the inactive substrate, and portion of the fixed end of the cantilevered structure that is fixed in the chordwise direction are varied. For harmonically actuated cases, the bending resonant frequency is also examined. Performance metrics for bending, twisting, and composite performance are also developed, and the results are reported. The highest bend, twist, and composite performance configurations are presented.