This thesis presents a modeling and design exploration study of a novel twisting wing whose motion is enabled by a tensegrity mechanism. First, the aerodynamic characteristics of the twisting wing, which does not require control surfaces to modulate its shape, are compared with those of a conventional wing having a control surface. It is shown via computational fluid dynamics analyses that the twisting wing displays higher lift-to-drag ratio than the conventional wing and hence the twisting wing is more aerodynamically efficient. Subsequently,the torsional tensegrity mechanism, composed of multiple tensegrity cylindrical cells forming a column along the wingspan, is described. A finite element model of the wing incorporating this mechanism is developed. Using the model, a full factorial design of experiments study of the influence of the topological parameters of the torsional tensegrity mechanism on the twist angle, mass, and stress in the different components of the wing is performed. A wingspan of 142.24 cm and a chord length of 25.31 cm are assumed, corresponding to those of the Carl Goldberg Falcon 56 Mk II R/C unmanned aerial vehicle. For a wing of such dimensions, the maximum achievable twist angle from root to tip per unit mass without any component exceeding their allowable stress is 5.93◦/kg and delivered 13.5◦of twisting with-out violating any of the material failure stresses. This torsional deformation is sufficiently large to allow for effective modulation of the aerodynamic characteristics of the wing. The torsional tensegrity mechanism for this design consists of eight cylindrical cells and four setsof actuator wires along the circumference of each cell. Subsequently, a design of experiments study performed using the orthogonal array (a.k.a.Taguchi) method is conducted to evaluate the effects of varying design parameters such as the thicknesses of the skin and ribs,the wire diameters, number of cells and wire sets, spar diameter, and material types. The most favorable design with a maximum twist angle to mass ratio of 10.85◦/kg is presented and delivered up to 19.5◦of twisting without violating any of the material failure stresses.Finally, befitting for the actuation of the tensegrity mechanism due to their wire form, shape memory alloy (SMA) wire actuators are explored for the reconfiguration of the wing shape through thermally driven material actuation. The combination of lightweight and compact tensegrity mechanism and SMA wire actuators eliminate the need for bulky components,such as hydraulic and electric actuators, to enhance the flight performance. The torsional morphing capability enabled by SMA actuation is demonstrated experimentally through a tensegrity twisting wing prototype integrated with commercially available SMA wire actuators. An additional orthogonal array design of experiments study is performed on the wing model with incorporated SMA wire actuators, where results analogous to those obtained from artificial strains in the aforementioned studies are obtained. The most favorable design of this DOE delivered a substantial 15.85◦total twist angle without any material failure and had a mass of 2.02 kg. The obtained twist angle was comparable to the twist angle observed from the testing of the tensegrity twisting wing prototype with integrated SMA wire actuators.

Carbon possesses a distinctive ability to form chemical bonds with other carbon atoms and create unique architectures. In the last few decades, we have witnessed the discovery of different carbon systems, including fullerene, nanotubes, and graphene. The versatile and diverse nature of the element can be fully exploited only if different shapes and microstructures can be manufactured, especially at the small length scales, given the potential of carbon in microengineering applications. Two promising miniaturization approaches for small-scale manufacturing of carbon microelectromechanical systems are photolithography and electrospinning. However, these fabrication methods need to be further evolved to have the ability to fabricate complex three-dimensional shapes and to enable tailoring of the carbon microstructure.

The first part of this work integrates photolithography and origami design, where an assisted folding approach and a self-folding approach are devised and demonstrated as three-dimensional carbon microfabrication methods. In the assisted folding method, fabrication of three-dimensional polymer shapes is achieved by adjusting the material properties of photopolymer films along their planform and utilizing the enhanced surface tension effect at small length scales. Complex surface geometries with patterned facets are fabricated by implementing capillary folding on a photo patternable material. For the self-folding method, the photolithography process is tailored such that the developer solution is non-uniformly absorbed throughout the thickness of the fold regions. The solvent is diffused into the foldable regions of low cross-linking density during the development step of the photolithography process. The solvent concentration is non-uniform across the thickness of the folds and causes a strain gradient at these regions when the solvent is removed by heating the films, enabling self-folding. Experiments are performed to calibrate a model that relates the dimensions of the folds and their exhibited fold angle. The model is incorporated into a computational implementation of the unfolding polyhedra method, a versatile approach for origami design that considers smoothly bent folds. This method, enhanced with the experimentally calibrated model, enables the design of planar films programmed to reliably self-fold into target three-dimensional shapes when heated. Polyhedral shapes are fabricated to demonstrate the developed method for origami-based fabrication.

In the second part of this work, the design of carbon microstructure using mechanical and chemical treatments is presented. By applying stress during carbonization, we demonstrate how to retain the alignment of Polyacrylonitrile (PAN) molecular chains achieved through electrospinning to produce a more uniformly graphitized carbon. The resulting carbon exhibits an oriented but fragmented lattice structure and is innately rich in nitrogen heteroatoms. Besides this mechanically induced graphitization, we also report a chemically induced graphitization method on patterned nanowires using a combination of low voltage electromechanical spinning and electrodeposition of nickel. These nickel-coated carbon wire structures are used as templates to deposit multi-layer graphene selectively. This patterning technique offers high throughput for nano writing, which outperforms other existing nanopatterning techniques, making it a potential candidate for large-scale carbon nanomanufacturing.

This thesis presents a modeling, design exploration, and optimization study of novel shape memory alloy (SMA) axial actuators. Shape memory alloys are materials that can generate and recover moderate inelastic strains through temperature modulation and exhibit high actuation energy density compared to other smart material actuators. This characteristic enables SMAs to function as lightweight and compact thermomechanical actuators. The synthesis of SMA actuators for systems with specific requirements on their actuation path (displacement stroke vs. temperature) currently relies on complex and expensive material processing and characterization. First, a geometric approach for synthesizing novel SMA axial actuators, termed as hybrid SMA actuators, whose dimensions and material distribution are modulated to approximate a target actuation path. Through the combination of multiple SMA wire sections in series, the hybrid SMA actuators can exhibit actuation paths not achievable by using single monolithic SMA wires. A reduced-order numerical model for the hybrid SMA actuators that allows for efficient design evaluations is derived and implemented. An approach to incorporate uncertainty in the parameters of the actuators within the design framework is implemented to allow for the determination of robust actuator designs. A machine learning-assisted framework for the surrogate modeling of hybrid SMA actuators is then detailed. This approach allows for the prediction of their actuation path without the use of structural simulations leveraging numerical implementations of constitutive models, allowing for simplified and computationally efficient modeling and circumventing convergence issues. A surrogate model consisting of an ensemble of binary decision trees is trained using data obtained via a design of experiments performed using structural simulations. A validation test using 5000 design samples for hybrid SMA actuators with two sections demonstrates R2 values of 0.99983 and 0.99979 for the actuation displacement during heating and cooling, respectively. The evaluation time for the validation samples using the trained surrogate model is less than 8 minutes, while the evaluation time using structural simulations is 59 minutes. A surrogate-based optimization approach is then demonstrated through the synthesis of hybrid SMA actuators capable of exhibiting prescribed target actuation paths. Lastly, a modeling, experimental prototyping, and computational design exploration study of a morphing wing enabled by a tensegrity mechanism and actuated by shape memory alloy (SMA) wires is investigated. The studied wing design circumvents conventional control surfaces such as hinged flaps and ailerons through the implementation of a smooth wing shape that twists to modulate its flight characteristics. The continuous and smooth wing surface lessens aerodynamic drag to enhance aerodynamic efficiency. The morphing capability of the wing is enabled through an integrated lightweight tensegrity mechanism, which provides twisting motion through elongation/contraction of the SMA wires. Befitting for the actuation of the tensegrity mechanism due to their rod form, SMA wire actuators are incorporated to reconfigure the wing shape through thermally driven material actuation. A finite element model that integrates the wing, tensegrity mechanism, and SMA wire actuators is created to assess the stresses, maximum attainable twist angle, and structural mass of the wing. A design of experiment study is performed to evaluate the influence of the topological and geometrical design parameters on performance responses such as twist angle and mass. The most favorable design demonstrates a maximum twist angle of 15.85◦ and a mass of 2.02 kg without exceeding the material stress limits. The SMA-enabled torsional morphing capability is also demonstrated experimentally through a tensegrity twisting wing prototype equipped with commercially available SMA wire actuators.