Fiber-reinforced Conjugated Polymer Torsional Actuator and Its Nonlinear Elasticity Modeling

Abstract-Reported conjugated polymer actuators have typically been limited to bender or linear extender configurations. In this paper, we present a fiber-reinforced conjugated polymer actuator capable of torsional motion. By incorporating platinum fibers into the material matrix during the electrochemical fabrication process, we create anisotropy in the interaction between the fiber and the material matrix, resulting in torsion and other associated deformations upon actuation. A nonlinear elasticitybased model is utilized to capture the actuator performance for both small and large deformations. The effectiveness of the model is verified through comparison with experimental results

Nonlinear analysis of a fiber-reinforced tubular conducting polymer-based soft actuator

This study presents the analytical modeling of a fiber-reinforced tubular conducting polymer (FTCP) actuator. The FTCP actuator is a low voltage-driven electroactive polymer arranged in an electrochemical cell. The electrochemical model is developed following an electrical circuit analogy that predicts the charge diffused inside the actuator for an applied voltage. An empirical relation is applied to couple the two internal phenomena, viz., diffusion of the ions and mechanical deformation. Further, the finite deformation theory is applied to predict the blocked force and free strain of the FTCP actuator. The developed model is consistent with existing experimental results for an applied voltage. In addition, the effect of various electrical and geometrical parameters on the performance of the actuator is addressed

Thermomechanical Modeling of Polymerica Actuators

In this dissertation, the application of smart polymers as actuators was investigated, with focuses on shape memory polymers and twisted-then-coiled artificial muscles. Thermomechanical models have been developed for various polymeric actuators, so as to facilitate interpretation of the underlying mechanisms and to provide guidance for future design. The classical one-way shape memory effect in amorphous shape memory polymers was first reproduced. The amorphous shape memory polymer was treated as a frozen-phase matrix with active-phase inclusions embedded in it. A phase evolution law was proposed from the physics perspective and the Mori-Tanaka approach was used to predict the effective mechanical properties. Then, a phenomenological constitutive model was developed based on the multiple natural configurations framework for the semi-crystalline two-way shape memory effect. The model elucidated how the programming procedure affect the crystallization behavior and eventually determine the two-way shape memory effect via storage of internal stress. Artificial muscles with hierarchical chiral structure that can offer a hundredfold increase in power over natural muscles of equivalent lengths have recently been demonstrated experimentally. To investigate the physical origin behind the remarkable tensile actuation behavior and, therefore, the correlation between the actuation performance and the intrinsic material parameters, a multi-scale modeling framework from macro-scale helical spring structure top-down to the molecular chain interaction has been developed Then, based on the prediction results of the multi-scale model, a new type of hierarchical chiral structured artificial muscle was fabricated using two-way shape memory polymer fiber. The usual improvement in the axial actuation of the twisted-then-coiled muscles were demonstrated both experimentally and theoretically

Characterizing material properties of drawn monofilament for Twisted Polymer Actuation

The field of smart materials has experienced a significant growth in the past fifteen years in actuation applications due to their smart and adaptive capabilities. However, most of these smart materials share the drawback of high cost, making their development and implementation difficult. This limitation leads us to the study of Twisted Polymer Actuators (TPAs). TPAs are inexpensive drawn monofilaments of polymers, such as fishing line, capable of actuation under thermal loads. The actuation on TPAs is due to the anisotropic thermal expansion responses of the material in the radial and axial directions. The properties of the precursor monofilament can be used to predict the actuation of TPAs. This thesis focuses on characterizing the mechanical and thermal properties of the precursor monofilament necessary as input parameters for actuation models. The properties obtained in this thesis are: axial modulus, shear modulus, radial modulus, Poisson's ratio, axial thermal contraction, and radial thermal expansion. The mechanical properties are presented as a function of temperature under the assumption of linear elasticity, but also as a function of time to characterize the viscoelastic effect at room temperature. The thermal expansion properties are also presented as functions of temperature and time, and it is found that viscous effects on thermal properties can be ignored for rapid actuation periods. Finally, this thesis presents experimental actuation data for different test conditions: free torsional actuation and torsional actuation under an isotonic torsional load. In the latter, actuation is performed for two different configurations: single monofilament and a triple strand in parallel arrangement

Development of Multifunctional Shape Memory Polymer and Shape Memory Polymer Composites

Shape memory polymers (SMPs) are an emerging class of active polymers that can be used on a wide range of reconfigurable structures and actuation devices. The present study comprehensively examines the unconstrained shape recovery abilities of an epoxy-based SMP. In doing so, epoxy based SMP is synthesized and thermo-mechanically characterized. Results show that the present SMP exhibits excellent shape recoveries under unconstraint conditions, for a range of fixing strains and temperatures. Additionally, the stress-strain behavior of the SMP is determined to be nonlinear, finite deformation at all regions. The strain energy based models have been used to capture the complicate stress-strain behavior and shape recovery process of the SMPs. Further SMP based composites are considered to obtain a smart material that is suitable for applications at both above and below the glass transition temperature of the polymer. A smart composite made of SMP and SMA would allow many design possibilities due to their controllable temperature-dependent mechanical properties. In this study, the shape memory composites (SMCs) are created by embedding SMA components (particles and fibers) into SMP matrices, which take advantage of the complementary properties of SMAs and SMPs. The SMA-particle and SMA-fiber reinforced SMP composites are designed through numerical simulations for different weight fractions of the SMA fillers were varied from 0-50%. Addition of SMA fillers significantly increased modulus across the temperature regimes while maintaining the large actuation strain. In addition to the simulations, SMA-Particle + SMP composites are synthesized and tested using DMA in compression. The obtained modulus results from the simulations for SMA-Particle + SMP composite is comparable with the experimentally determined results. However, since SMP matrix is not conductive these composites often require external stimuli such as external heaters which limit their applications. To overcome this limitation, multi-functional Shape memory polymer based composites are thus fabricated in the present study by embedding CNT fibers and Ni particles in SMP matrix that resulted in electrically conductive and thermally stable SMP based composites

Additively Manufactured Dielectric Elastomer Actuators: Development and Performance Enhancement

The recently emerging and actively growing areas of soft robotics and morphing structures promise endless opportunities in a wide range of engineering fields, including biomedical, industrial, and aerospace. Soft actuators and sensors are essential components of any soft robot or morphing structure. Among the utilized materials, dielectric elastomers (DEs) are intrinsically compliant, high energy density polymers with fast and reversible electromechanical response. Additionally, the electrically driven work principle allows DEs to be distributed in a desired fashion and function locally with minimum interference. Thus, a great effort is being made towards utilizing additive manufacturing (AM) technologies to fully realize the potential of DE soft actuators and sensors. While soft sensors have received more attention and development due to their simpler implementation, DE actuators (DEAs) set stricter AM and electrode material requirements. DEAs’ layered structure, compliant nature, and susceptibility to various defects make their manufacturability challenging, especially for non-trivial biomimetic soft robotics geometries. This dissertation comprehensively analyzes DE materials’ transition into a soft actuator using AM to facilitate effective DEA soft actuator fabrication. Closely interrelated fabrication techniques, material properties, and DEA geometries are analyzed to establish a fundamental understanding of how to implement high-quality DEA soft actuators. Furthermore, great attention is paid to enhancing the performance of printed DEAs through developing printable elastomer and electrode materials with improved properties. Lastly, performance enhancement is approached from the design point of view by developing a novel 3D printable DEA configuration that actuates out-of-plane without stiffening elements

A new mixed model based on the enhanced-Refined Zigzag Theory for the analysis of thick multilayered composite plates

The Refined Zigzag Theory (RZT) has been widely used in the numerical analysis of multilayered and sandwich plates in the last decay. It has been demonstrated its high accuracy in predicting global quantities, such as maximum displacement, frequencies and buckling loads, and local quantities such as through-the-thickness distribution of displacements and in-plane stresses [1,2]. Moreover, the C0 continuity conditions make this theory appealing to finite element formulations [3]. The standard RZT, due to the derivation of the zigzag functions, cannot be used to investigate the structural behaviour of angle-ply laminated plates. This drawback has been recently solved by introducing a new set of generalized zigzag functions that allow the coupling effect between the local contribution of the zigzag displacements [4]. The newly developed theory has been named enhanced Refined Zigzag Theory (en- RZT) and has been demonstrated to be very accurate in the prediction of displacements, frequencies, buckling loads and stresses. The predictive capabilities of standard RZT for transverse shear stress distributions can be improved using the Reissner’s Mixed Variational Theorem (RMVT). In the mixed RZT, named RZT(m) [5], the assumed transverse shear stresses are derived from the integration of local three-dimensional equilibrium equations. Following the variational statement described by Auricchio and Sacco [6], the purpose of this work is to implement a mixed variational formulation for the en-RZT, in order to improve the accuracy of the predicted transverse stress distributions. The assumed kinematic field is cubic for the in-plane displacements and parabolic for the transverse one. Using an appropriate procedure enforcing the transverse shear stresses null on both the top and bottom surface, a new set of enhanced piecewise cubic zigzag functions are obtained. The transverse normal stress is assumed as a smeared cubic function along the laminate thickness. The assumed transverse shear stresses profile is derived from the integration of local three-dimensional equilibrium equations. The variational functional is the sum of three contributions: (1) one related to the membrane-bending deformation with a full displacement formulation, (2) the Hellinger-Reissner functional for the transverse normal and shear terms and (3) a penalty functional adopted to enforce the compatibility between the strains coming from the displacement field and new “strain” independent variables. The entire formulation is developed and the governing equations are derived for cases with existing analytical solutions. Finally, to assess the proposed model’s predictive capabilities, results are compared with an exact three-dimensional solution, when available, or high-fidelity finite elements 3D models. References: [1] Tessler A, Di Sciuva M, Gherlone M. Refined Zigzag Theory for Laminated Composite and Sandwich Plates. NASA/TP- 2009-215561 2009:1–53. [2] Iurlaro L, Gherlone M, Di Sciuva M, Tessler A. Assessment of the Refined Zigzag Theory for bending, vibration, and buckling of sandwich plates: a comparative study of different theories. Composite Structures 2013;106:777–92. https://doi.org/10.1016/j.compstruct.2013.07.019. [3] Di Sciuva M, Gherlone M, Iurlaro L, Tessler A. A class of higher-order C0 composite and sandwich beam elements based on the Refined Zigzag Theory. Composite Structures 2015;132:784–803. https://doi.org/10.1016/j.compstruct.2015.06.071. [4] Sorrenti M, Di Sciuva M. An enhancement of the warping shear functions of Refined Zigzag Theory. Journal of Applied Mechanics 2021;88:7. https://doi.org/10.1115/1.4050908. [5] Iurlaro L, Gherlone M, Di Sciuva M, Tessler A. A Multi-scale Refined Zigzag Theory for Multilayered Composite and Sandwich Plates with Improved Transverse Shear Stresses, Ibiza, Spain: 2013. [6] Auricchio F, Sacco E. Refined First-Order Shear Deformation Theory Models for Composite Laminates. J Appl Mech 2003;70:381–90. https://doi.org/10.1115/1.1572901

Micro - and macro - mechanical properties of aerospace composite structures and their dynamic behaviour

The research presented in this thesis focuses on the micro- and macro-mechanical properties of aerospace composite structures, and their buckling, free vibration, and flutter behaviour. The first part of the thesis concentrates on fundamental experimental research into prediction and enrichment of polymers composites with nanoparticles with particular emphasis on polyurethane and polyaniline. To this end, a conducting thermoplastic elastomer is developed and characterised using physiochemical methods for thermo-mechanical properties. Consequently, a sophisticated new polyurethane nanocomposite elastomer with improved mechanical and thermal properties is developed. The second part of the thesis is a development of an accurate dynamic stiffness matrix for a three-layered sandwich beam of asymmetric cross-section using the Timoshenko beam theory, Hamiltonian mechanics and symbolic computation. The resulting dynamic stiffness matrix is used to investigate the free vibration characteristics of a number of sandwich beams examples and their results are validated by experiment. Next, a detailed analysis is carried out to establish the rigidity properties (stiffnesses) of fibre reinforced composite structures with particular emphasis on solid rectangular and thin-walled box section. The effect of ply orientation on rigidity properties and the consequent coupling between various modes of deformation is studied. Buckling analysis is carried out to provide an estimate of the stiffnesses. Free vibration investigations on flat and box carbon fibre-reinforced composite beams are then carried out to gain important insights into the material- geometrical coupling effects, and modal interchange in bending-torsion coupled behaviour. Although the dynamic stiffness method is primarily used in the analyses, some complementary finite element analysis and experimental modal analysis using an Impulse Hammer Kit were performed to confirm the predictable accuracy of the dynamic stiffness method. A few carefully designed composite beams were fabricated for the experimental work. Flutter behaviour of swept and unswept wing is also investigated. The results are discussed with significant conclusions drawn. A scope for further work is outlined

NASA Tech Briefs, December 2007

Topics include: Ka-Band TWT High-Efficiency Power Combiner for High-Rate Data Transmission; Reusable, Extensible High-Level Data-Distribution Concept; Processing Satellite Imagery To Detect Waste Tire Piles; Monitoring by Use of Clusters of Sensor-Data Vectors; Circuit and Method for Communication Over DC Power Line; Switched Band-Pass Filters for Adaptive Transceivers; Noncoherent DTTLs for Symbol Synchronization; High-Voltage Power Supply With Fast Rise and Fall Times; Waveguide Calibrator for Multi-Element Probe Calibration; Four-Way Ka-Band Power Combiner; Loss-of-Control-Inhibitor Systems for Aircraft; Improved Underwater Excitation-Emission Matrix Fluorometer; Metrology Camera System Using Two-Color Interferometry; Design and Fabrication of High-Efficiency CMOS/CCD Imagers; Foam Core Shielding for Spacecraft CHEM-Based Self-Deploying Planetary Storage Tanks Sequestration of Single-Walled Carbon Nanotubes in a Polymer PPC750 Performance Monitor Application-Program-Installer Builder Using Visual Odometry to Estimate Position and Attitude Design and Data Management System Simple, Script-Based Science Processing Archive Automated Rocket Propulsion Test Management Online Remote Sensing Interface Fusing Image Data for Calculating Position of an Object Implementation of a Point Algorithm for Real-Time Convex Optimization Handling Input and Output for COAMPS Modeling and Grid Generation of Iced Airfoils Automated Identification of Nucleotide Sequences Balloon Design Software Rocket Science 101 Interactive Educational Program Creep Forming of Carbon-Reinforced Ceramic-Matrix Composites Dog-Bone Horns for Piezoelectric Ultrasonic/Sonic Actuators Benchtop Detection of Proteins Recombinant Collagenlike Proteins Remote Sensing of Parasitic Nematodes in Plants Direct Coupling From WGM Resonator Disks to Photodetectors Using Digital Radiography To Image Liquid Nitrogen in Voids Multiple-Parameter, Low-False-Alarm Fire-Detection Systems Mosaic-Detector-Based Fluorescence Spectral Imager Plasmoid Thruster for High Specific-Impulse Propulsion Analysis Method for Quantifying Vehicle Design Goals Improved Tracking of Targets by Cameras on a Mars Rover Sample Caching Subsystem Multistage Passive Cooler for Spaceborne Instruments GVIPS Models and Software Stowable Energy-Absorbing Rocker-Bogie Suspension