<p>A key aspect of color change is altering perceived value or intensity. This dissertation presents a methodology to achieve value change through mechanical means via the deflection of bistable structures. We create the Mechxel, two methods of mechanical pixel-based, reversible color change using 3D printed switchable multistability and bistable switch panels that augment the projected area a viewer perceives which enables the creation of image and character tessellation.</p> <p>Switchable multistability (SMS) arises from the combination of pre-strain and shape memory, allowing us to access multiple elastically programmed shapes at elevated temperatures with fast morphing and low actuation forces, while retaining high stiffness at room temperature. We design and manufacture SMS Mechxels using fused deposition modeling (FDM) 3D printing on the Ultimaker 3D printer in a bilayer layup of polylactic acid (PLA) with a [90/0] print direction while iteratively miniaturizing the physical size to enhance the resolution while also reducing the size of the overall tessellated display. Leveraging SMS properties programmed into each Mechxel, the projected area to a viewer will vary between the unit’s stable states, creating a difference in perceived value of coloration due to changes in area. To ease the tessellation process, we also introduce a tessellation user interface that maps images to their tessellated equivalent to reduce tessellation trial and error. This interface also calculates the number of Mechxels required in their respective states and the final physical size of the display. We then carry out image processing to justify this change in value between stable states and run preliminary optical character recognition.</p> <p>Inspired by mechanical bistable mechanisms, the bistable switch Mechxels utilize changes in a surface’s projected area to a viewer via changes in the angle of a bistable tile using a 5-by-5 grid for character replication and display. Comprising of three main components – two bistable switches, a colored tile and a base, design considerations were made to create an easy to assemble and replaceable 3D printed grid system that could be interacted with by audiences or easily electromechanically actuated. Using pixel-by-pixel comparisons and Sorensen-Dice coefficient, characters using the typeface Silkscreen were documented on these tiled grids yielding high similarity and low error when compared to their digital reference images in various positions and orientations. We also experiment with transitional waves as a promising means of actuation to change the Mechxel between their stable states.</p> <p>The Mechxels considered in this research introduce a new means of purely mechanical color change, character, and image display either leveraging the elastic properties of shape memory polymers (SMPs) or bistable mechanisms. With potential applications in passive morphing architecture, adaptive camouflage, and interactive aesthetic, Mechxels opens the door to limitless design possibilities through a new perspective into color change.</p>

As a new concept for morphing structures, the use of piezoelectric actuators to effect snap-through behavior of simple unsymmetric cross-ply composite laminates is examined. Many unsymmetric laminates have more than one stable room-temperature shape and can be snapped through from one stable shape to another. In this new concept for morphing structures, one or more piezoelectric actuators are bonded to unsymmetric laminates, and are then used to snap the laminate from one shape to another. The actuator would be used to change shape, but would not be required to maintain the shape. Using the Rayleigh-Ritz technique, several models are developed to predict the interaction between the base laminate and the actuator. In particular, the voltage (applied to the actuator) needed to snap the laminate is predicted. The NASA-LaRC Macro-Fiber Composite&174; (MFC&174;) actuator is chosen as the actuator of choice for this work. A laminate is manufactured, an actuator is bonded to the laminate, and experiments are performed. Since the agreement between the initial models and experimental results was not good, the models were revised. Good agreement between the predictions of the revised model and experiment is reached. Suggestions for future research directions are presented. / Ph. D.

4D printing is a rapidly emerging field in which 3D printed stimuli-responsive materials produce morphing and multifunctional structures, with time being the fourth dimension. This approach enables the 3D printing of pre-programmed responsive sheets, which transition into complex curved shapes upon exposure to external stimuli, resulting in a substantial reduction in material consumption and printing time (70 - 90 %). Commonly used materials for 4D printing are polymer composites, such as hydrogels, polydimethylsiloxane (PDMS), liquid crystal elastomers (LCEs), and shape memory polymers (SMPs). However, the low elastic modulus (E) that these materials exhibit during shape change (E range of 10-4 – 10 MPa) limits their scalability, actuation stress, and load bearing. Moreover, these materials exhibit low ultimate stresses, leading to correspondingly low toughness (K) values in the range of 0.08 to 5 MJ m-3. Consequently, this results in structures with low damage tolerance. Therefore, an existing challenge for the field of 4D printing is to develop materials that can maintain their large and predictable morphing mechanism for complex shape transformation, while improving the E and K for high performance applications. Furthermore, many existing approaches rely on passive structures that necessitate the control of global conditions of the surrounding environment (e.g., hot plates, ovens, external magnets, water baths) to provide the stimulus for actuation. In this work, we tackle these challenges by introducing novel materials, ink formulations, and innovative printing techniques for multi-material Direct Ink Writing (DIW). We aim to create electrically controllable 4D printed structures that exhibit exceptional stiffness and toughness, all while preserving a large and predictable morphing mechanism for intricate shape transformations. First, we introduce multiscale heterogeneous polymer composites as a novel category of stiff, electrically controllable thermally responsive 4D printed materials. These composites consist of an epoxy matrix with an adjustable cross-link density and a plurality of isotropic and anisotropic nanoscale and microscale fillers. Leveraging this platform, we generate a set of 37 inks covering a broad range of negative and positive linear coefficients of thermal expansion. This set of inks exhibits an elastic modulus range that is four orders of magnitude greater than that of existing 4D printed materials and offers tunable electrical conductivities for simultaneous Joule heating actuation and self-sensing capabilities. Utilizing electrically controllable bilayers as building blocks, we design and print a flat geometry that changes shape into a 3D self-standing lifting robot, displaying record actuation stress and specific force when compared to other 3D printed actuators. We integrate this lifting robot with a closed-loop control system, achieving autoregulated actuation exhibiting a 4.8 % overshoot and 0.8 % undershoot, while effectively rejecting disturbances of up to 170 times the robot's weight. Furthermore, we employ our ink palette to create and 3D print planar lattice structures that transform into various self-supporting complex 3D surfaces. Ultimately, we achieve a 4D printed electrically controlled crawling robotic lattice structure, highlighting its capacity to transport loads up to 144 times its own weight. Finally, we introduced a printable PDMS adhesive that serves as synthetic fascia to hold our epoxy-based synthetic muscle together, enhancing the K of our 4D printed structures, all while maintaining high stiffness, large, predictable, and addressable actuation mechanism. Through the integration of these soft adhesive materials with high-stiffness thermally responsive epoxies via DIW, we achieved an improvement of about two orders of magnitude in the K of the resulting synthetic muscle composite, all while maintaining high stiffness and morphing mechanism. Utilizing this fabrication method, we printed an electrically controllable bilayer exhibiting damage detection and tolerance, enduring up to 7 fractures while continuing to function effectively. Furthermore, we integrated the synthetic muscle composite into our lifting robot design, setting yet again new records in specific force and actuation stress when compared to other 3D printed actuators. Notably, even after failure, the actuator maintained its operational integrity and high performance. Ultimately, we present a 4D printed lattice structure featuring the incorporation the synthetic muscle composite, showcasing a sensitive electrically responsive surface with fracture detection capabilities. To emphasize this, we subjected one of these 4D printed lattices to extreme conditions, driving a car over it. Notably, the lattice structure detected fractures and exhibited high resilience, enduring external compressive damage equivalent to 331,060 times its own weight. / 2026-05-23T00:00:00Z

International aviation regulations on emissions are becoming more strict. Improvements goals on fuel efficiency demand development of technologies capable of reducing fuel consumption and gas emissions. Morphing structures capability to adapt their aerodynamic shape for optimal condition in flight brings potential for reduction of aircraft drag and operating fuel consumption, minimizing gas emissions and fuel expenses. This study presents an investigation on the impact of a camber morphing winglet on midsize business jet using numerical simulation and wind tunnel experiments. A genetic algorithm was used to optimize the winglet sections camber for different flight conditions. Optimized geometries achieved total drag reduction of up to 0.58% compared to original winglet for single condition optimization, reaching up to 7 % reduction on consumed fuel on a typical mission. This efficiency improvement allows aircraft to carry 900 kg additional load, comprising the morphing system and extra payload. There is an indication of even better results for applications on a bigger commercial jet. Presented methodology is also suitable for new winglet fixed geometry design or incorporating morphing technology. Aerodynamic balance force measurements showed that optimized winglets increased the wing effective aspect ratio (AReff), reducing the lift-induced drag, and maximum lift coefficient (CLmax). However, maximum lift to drag ratio (L/Dmax) was reduced on CL optimization region due to flow differences between optimization and wind tunnel conditions. Aerodynamic efficiency improvement was found for greater lift coefficients (CL). Reductions on wing tip vortex size and intensity due to winglet installation are seen on measured vorticity map, showing liftinduced drag reduction according to Maskells equation. Parabolic drag polar and Maskells equation methods were used for lift-induced drag calculation, using balance force and flowing mapping data for calculations. The presented concept showed considerable aircraft performance improvement, using a feasible device with greater certification ease than other morphing structures concepts, once the failure of this system would not compromise flight safety. Further investigation using computational fluid dynamics (CFD) and wind tunnel experiments is necessary to develop and test a functional camber morphing winglet device. / Regulamentações internacionais sobre emissões estão se tornando mais rigorosas. Metas de melhoria da eficiência de consumo de combustível demandam o desenvolvimento de tecnologias capazes de reduzir o consumo e emissões de gases. Estruturas capazes de adaptar sua forma aerodinâmica para condição ótima em voo trazem potencial de redução do arrasto e consumo de combustível da aeronave, minimizando as emissões de gases e gastos com combustível. Este estudo apresenta uma investigação sobre o impacto de uma winglet de camber variável em um jato executivo da categoria mid size utilizando simulação numérica e experimentos em túnel de vento. Um algoritmo genético foi usado para otimizar o camber das seções para diferentes fases de voo. As geometrias otimizadas reduziram o arrasto total em até 0.58% comparadas a winglet original na otimização de condição única, alcançando até 7% de redução no combustível consumido em missão típica. Essa melhoria de eficiência permite a aeronave carregar 900 kg de carga adicional, composta pelo sistema de adaptação e carga paga extra. Há uma indicação de resultados ainda melhores para aplicação em um jato comercial maior. A metodologia apresentada é apropriada para projeto de uma nova winglet de geometria fixa ou que incorpore a tecnologia de adaptação. Medidas de força com balança aerodinâmica mostraram que as winglets otimizadas aumentaram o alongamento efetivo da asa (AReff), reduzindo o arrasto induzido, e o coeficiente de sustentação máximo (CLmax). No entanto, a máxima razão entre sustentação e arrasto (L/Dmax) foi reduzida dentro do intervalo de CL da otimização devido as diferenças entre as condições do escoamento na otimização e no túnel de vento. Melhoria na eficiência aerodinâmica foi obtida para coeficientes de sustentação (CL) maiores. Reduções no tamanho e intensidade do vórtice de ponta de asa são vistas nos mapas de vorticidade medidos, mostrando redução do arrasto induzido segundo a equação de Maskell. Os métodos da polar de arrasto parabólica e da equação de Maskell foram usados para o cálculo do arrasto induzido, utilizando nos cálculos os dados de força da balança e o mapeamento do escoamento. O conceito apresentado mostrou melhoria considerável no desempenho da aeronave, utilizando um sistema factível e com maior facilidade para certificação que outros conceitos de estruturas adaptáveis, uma vez que a falha desse sistema não comprometeria a segurança do voo. Mais estudos são necessários para desenvolver e testar uma winglet de camber varável funcional.

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