Smart Material Wing Morphing for Unmanned Aerial Vehicles.

Morphing, or geometric adaptation to off-design conditions, has been considered in aircraft design since the Wright Brothers’ first powered flight. Decades later, smooth, bio-mimetic shape variation for control over aerodynamic forces still remains elusive. Unmanned Aerial Vehicles are prime targets for morphing implementation as they must adapt to large changes in flight conditions associated with locally varying wind or large changes in mass associated with payload delivery. The Spanwise Morphing Trailing Edge (SMTE) concept is developed to locally vary the trailing edge camber of a wing or control surface, functioning as a modular replacement for conventional ailerons without altering the wing’s spar box. The SMTE design was realized utilizing alternating active sections of Macro Fiber Composites (MFCs) driving internal elastomeric compliant mechanisms and passive sections of anisotropic, elastomeric skin with tailorable stiffness, produced by additive manufacturing. Experimental investigations of the modular design via a new scaling methodology for reduced-span test articles revealed that increased use of more MFCs within the active section did not increase aerodynamic performance due to asymmetric voltage constraints. The comparative mass and aerodynamic gains for the SMTE concept are evaluated for a representative finite wing as compared with a conventional, articulated flap wing. Informed by a simplistic system model and measured control derivatives, experimental investigations identified a reduction in the adaptive drag penalty up to 20% at off-design conditions. To investigate the potential for augmented aeroelastic performance and actuation range, a hybrid multiple-smart material morphing concept, the Synergistic Smart Morphing Aileron (SSMA), is introduced. The SSMA leverages the properties of two different smart material actuators to achieve performance exceeding that of the constituent materials. Utilizing the relatively higher work density and phase transformation of Shape-Memory Alloys combined with the larger bandwidth and conformal bending of MFCs, the resultant design is demonstrated to achieve the desired goals while providing additional control authority at stall and for unsteady conditions through synergistic use of reflex actuation. These advances highlight and motivate new morphing structures for the growing field of UAVs in which adaptation involves advanced compliance tailoring of complex geometry with synergistic actuation of embedded, smart materials.PhDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111533/1/alexmp_1.pd

Electrospinning of Cellulose and Carbon Nanotube-Cellulose Fibers for Smart Applications

Cellulose is one of the Earth’s most abundant natural polymers and is used as a raw material in various applications. Recently, cellulose based electro-active paper (EAPap) has been investigated for its potential as a smart material. The electrospinning method of fiber production is not a new way of fabrication; however, it has attracted a great deal of attention as a means of producing non-woven membranes of nanofibers due to its simple methodology and the advent of nano applications. Electrospinning occurs when the electrical force on a polymer droplet overcomes its surface tension, and a charged jet is ejected. As the liquid jet is continuously elongated and the solvent is evaporated, the fibers of sub-micron size or nano size are formed, depending on the conditions. In a previous study, a cellulose mat was electro-spun and tested for piezoelectric characteristics. This aligned, electrospun cellulose mat showed a possibility as a promising smart material. Additionally, carbon nanotubes have been considered for the versatile nano-applications due to their superior material properties such as low density and high aspect ratio. Parametric studies were conducted to find optimum conditions for electrospinning. Various ways of reducing surface tension of solutions were investigated including radiative and convective heating of the solution. Pre-examination of solution is very important in consistent, uniform fiber formation. In this study, cellulose and CNT-cellulose composite fibers were prepared via electrospinning. The optimal experimental conditions for fiber generation were found so that the mechanical strength of both the composite and the pure cellulose fibers could be compared in future tests. Eventually, this fiber will be interwoven into the CNT-cellulose mat and be used as an electro-active paper sensor and actuator. The CNT-cellulose electrospun mat will be widely applicable to the fields of sensors, filters and reinforcements in composites because of its intrinsic properties of porosity, light weight, flexibility, and large surface area. To be used in the aforementioned applications, piezoelectric properties of this composite will also be tested in the next step

Synergistic Smart Morphing Aileron

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106472/1/AIAA2013-1512.pd

Stall Recovery of a Morphing Wing via Extended Nonlinear Lifting-Line Theory

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143096/1/1.J055042.pd

Piezoelectric Artificial Kelp: Experimentally Validated Parameter Optimization of a Quasi-Static, Flow-Driven Energy Harvester

Piezoelectric energy harvesting is the process of taking an external mechanical input and converting it directly into electrical energy via the piezoelectric effect. To determine the power created by a piezoelectric energy harvester, a specific application with defined input and design constraints must first be chosen. The following thesis established a concept design of a hydrokinetic energy harvesting system, the piezoelectric artificial kelp (PAK), which uses piezoelectric materials to harvest coastal ocean waves while having a beneficial impact on the surrounding environment. The harvester design mimics the configuration of sea-kelp, a naturally occurring plant that anchors to the ocean floor and extends into the water column. Underwater currents caused by wave-action result in periodic oscillations in the kelp. In order to determine the average power generated by this design concept, predictive tools were devised that allowed for the determination of the optimized average power produced by the piezoelectric energy harvester. For a stiff energy harvester, the linear differential equations were analytically solved to find an equation for the average power generated as a function of design parameters. These equations were used to compare the effect on power output of the design configuration and piezoelectric material choice between a piezopolymer (PVDF) and a piezoceramic (PZT). The homogeneous bimorph was found to have the optimal design configuration and it was shown that a harvester constructed using PVDF would produce approximately 1.6 times as much power as one using PZT. For a flexible energy harvester, an iterative nonlinear solution technique using an assumed polynomial solution for the local curvature of the energy harvester was used to verify and extend the analytic solutions to large deflections. An energy harvester was built using off-the-shelf piezoelectric elements and tested in a wave tank facility to validate experimentally the voltage and average power predicted by the analytical solution. The iterative code showed the PAK harvester to produce volumetric power on the order of other energy harvesting concepts (17.8 micro [mu]W/cm³). Also, a full-scale PAK harvester approximately ten meters long in typical wave conditions was found to produce approximately one watt of power

Synergistic Smart Morphing Aileron: Aero-structural Performance Analysis

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140418/1/6.2014-0924.pd

Synergistic Smart Morphing AIleron: Capabilites Identification

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140590/1/6.2016-1570.pd

Design of Soft Origami Mechanisms with Targeted Symmetries

The integration of soft actuating materials within origami-based mechanisms is a novel method to amplify the actuated motion and tune the compliance of systems for low stiffness applications. Origami structures provide natural flexibility given the extreme geometric difference between thickness and length, and the energetically preferred bending deformation mode can naturally be used as a form of actuation. However, origami fold patterns that are designed for specific actuation motions and mechanical loading scenarios are needed to expand the library of fold-based actuation strategies. In this study, a recently developed optimization framework for maximizing the performance of compliant origami mechanisms is utilized to discover optimal actuating fold patterns. Variant patterns are discovered through exploring different symmetries in the input and output conditions of the optimization problem. Patterns designed for twist (rotational symmetry) yield significantly better performance, in terms of both geometric advantage and energy requirements, than patterns exhibiting vertical reflection symmetries. The mechanical energy requirements for each design are analyzed and compared for both the small and large applied displacement regimes. Utilizing the patterns discovered through optimization, the multistability of the actuating arms is demonstrated empirically with a paper prototype, where the stable configurations are accessed through local vertex pop-through instabilities. Lastly, the coupled mechanics of fold networks in these actuators yield useful macroscopic motions and can achieve stable shape change through accessing the local vertex instabilities. This survey of origami mechanisms, energy comparison, and multistability characterization provides a new set of designs for future integration with soft actuating materials