bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of Mechanical Behavior of NiTi Shape Memory Alloys Under Complex Loading: Model Formulation and its Performance in Applications
Authors: Sedlák Petr , Frost Miroslav , Kruisová Alena , Šittner Petr , Heller Luděk
Published: December 2014

Actuators in the form of a helical spring made from shape memory alloy are attractive due to light weight, large recoverable deformation, high energy density and manufacturing simplicity. For their optimal design and control detailed information on evolution of phase and stress distribution within the material during operation is advantageous. In this work a constitutive model tailored for non-proportionally loaded shape memory alloys exhibiting R-phase transition, transformation strain anisotropy, tension-compression asymmetry is employed to reveal and interpret relation between macroscopic response of such an actuator and microscopic state within the shape memory material. Numerical simulations confirm good predictive capability of the model and demonstrate that because of naturally non-proportional loading mode, phase and stress distributions within cross-section of the wire may be rather complex and counterintuitive.
Uniaxial, Pure Bending and Buckling Characterization of Superelastic NiTi Rods and Tubes: An Experimental Study
Authors: Watkins Ryan , Reedlunn Benjamin , Shaw John
Published: December 2014

Although the tensile behavior of shape memory alloys (SMAs) is relatively well understood, the effects of other modes of loading on SMA behavior are still unknown. To examine the influence of loading and specimen geometry on structural behavior and phase transformation morphology, this work presents an experimental characterization of commercially-available superelastic NiTi rods and tubes under tensile, compressive, pure bending and column buckling loading. At room temperature and under isothermal loading conditions, the mechanical response for each loading configuration and structural geometry is measured and stereo digital image correlation is used to capture local displacement and strain phenomena (such as strain localization and propagating phase boundaries).

It is found that the length and cross-sectional geometry of NiTi structures affects the nature of stress-induced phase transformation; in particular, transformation induced strain localization. During uniaxial tension, the rod specimens exhibit strain localization and propagating phase transformation fronts along well-defined load plateaus, and phase boundaries manifest as diffuse propagating necks. The tube specimens also exhibit localization/propagation phenomena, but fronts consist of distinct angled finger-like features due to the relatively thin-walled cross-section. During uniaxial compression, both forms exhibit (now well-known) tension-compression asymmetry in their mechanical responses, no propagating fronts are observed, and distinct load plateaus are absent. During pure bending, the moment-curvature responses of both forms exhibit plateaus during localizing forward and reverse transformations. In the case of the rod, high curvature localizes and propagates along the specimen; whereas, finger-like high strain regions develop along the tensile side of the tube. During column buckling, the structures are loaded into the post-buckling regime yet recover their straight forms upon unloading. Localization is observed, but only for high length/diameter aspect ratio tubes and has little affect on the mechanical response. Therefore, due to the varying phase transformation behaviors observed, understanding geometric and material effects on phase transformation, along with the resulting effects on the material response, is necessary to predict SMA beam behavior.
The Influence of Thermo-Oxidative Degradation on the Behavior of Epoxy Shape Memory Polymers
Authors: Dasharathi Kannan , Shaw John A.
Published: December 2014

Results are reported from an ongoing experimental investigation of the effects of thermo-oxidative aging on the mechanical behavior of an epoxy shape memory polymer (SMP). Chemo-rheological degradation due to macromolecular scission and cross-linking is one of the main factors contributing to the chemical aging of thermo-responsive SMPs. This aging may manifest as residual strain or irreversible material property changes, which can affect the performance and limit the useful life of a SMP. A relatively new epoxy SMP based on the diglycidyl ether of bisphenol A is synthesized, and specimens are tested under uni-axial tension using a dynamic mechanical analyzer. Fundamental viscoelastic behavior and thermal expansion coefficients are first characterized, showing a glass transition near 60 °C. Shape memory cycle experiments are performed at shape fixing temperatures of 80, 125, 150 and 175 °C, and the effect of fixing time at each temperature is examined upon subsequent strain recovery at 80 °C. Performance parameters such as recovery ratio, speed of recovery and residual strain are quantified as a function of shape fixing time and temperature. No effect of chemical aging was seen at a fixing temperature of 80 °C, although the recovery ratio decreases initially with increasing fixing time and stabilizes near 92 %. Only minor effects of chemical aging are seen in the mechanical responses for fixing temperatures of 125 and 150 °C, but specimens exhibit progressively more noticeable color changes that indicate oxidation. Significant effects are observed at the highest fixing temperature of 175 °C, where chemical aging at longer fixing times results in a reduction in recovery rate across the rubber-glass transition temperature, progressively larger residual strains, lack of complete strain recovery at 80 °C, and higher temperatures to achieve 90 % strain recovery.
Inverse Design of LCN Films for Origami Applications Using Topology Optimization
Authors: Fuchi Kazuko , Buskohl Philip R. , Ware Taylor , Vaia Richard A. , White Timothy J. , Reich Gregory W. , Joo James J.
Published: December 2014

Liquid crystal polymer networks (LCNs) have unique advantages as potential constituents of origami-based smart materials due to their reversible actuations and availability of fabrication techniques to create complex strain fields. Although identifying functional designs is crucial in making use of this technology, conventional approaches have largely consisted of trial-and-error experimentation. We introduce an inverse design procedure based on a topology optimization method to map out an LCN pattern with a desired spontaneous strain field to achieve prescribed shapes. In this study, we focus on a target deformation of a film to create an improved hinge to be integrated into an origami structure. Our preliminary results indicate the potential of using computational tools to determine what designs yield desired functionalities and how to best pattern LCN films to achieve them.
Effects of Piezoceramic Actuator in Quasistatic Use
Authors: Riemenschneider Johannes , Huxdorf Oliver , Opitz Steffen
Published: December 2014

In the field of smart structures, piezoceramic actuators are wildly used for vibration reduction and acoustic manipulation of structures. Those applications typically run at frequencies between 10 Hz and 10k Hz. Prominent examples are the piezoceramic actuators implemented in helicopter rotor blades to twist them dynamically for higher harmonic control (HHC) or individual blade control (IBC). Once the actuators are implemented it would be a great benefit to also use them to statically change the blade twist (higher twist for take-off and landing — for higher lift; lower twist for high speed forward flight — for reduced drag). Staying with this example it can be found that sensing the twist displacement is not an easy task at all (see [1, 2]), so it would be most desirable, to use open loop control. In order to do that, the transfer function has to be known accurately. Unfortunately measurements show that the amplitudes for such very low frequencies behavior behave strongly non linear. This paper presents experimental results investigating the influence of the frequency on the amplitude — especially going for frequencies in the lower mHz region. A variety of piezoceramic actuators has been investigated: from stacks to patch type, d33 as well as d31 effect actuators.

A second focus of this paper is the reaction of piezoceramic actuators on the application of a constant DC voltage. The drift that occurs has to be taken into consideration.

A third focus of this paper is the dependency of a displacement output of such an actuator at a constant applied DC voltage on the voltages that the actuator had seen before. This topic is of special importance for aerodynamically effective surfaces that are driven by piezoceramic actuators and should be analyzed (generation of polars) in static conditions.
Vehicle Propulsion by Solid State Motion
Authors: Jones Lucas , Spahnie Josh , Lefeave Kevin , Haltom Charles , Underwood Adam , Aber Jacob , Malladi V. V. N. Sriram , Joyce Bryan S. , Tarazaga Pablo A.
Published: December 2014

Traveling waves have shown the potential to transport material and are thus investigated as a propulsion mechanism. Through the use of piezoelectric actuators (PZTs), traveling waves were produced in beams with both free-free and fixed-free boundary conditions. It is shown that traveling waves can be generated by exciting two PZTs at a common frequency with a phase difference between the PZT signals. Experimentation showed the signal that creates the best traveling wave occurs at a driving frequency halfway between adjacent bending resonance frequencies and a phase difference of 90° between both PZTs signals. This has produced traveling waves in fixed-free beams and free-free beams in both air and water as well as for an underwater vehicle. These traveling waves generated useful propulsion in both the fixed-free and free-free beams.
Analysis Driven Design Optimization of SMA-Based Steerable Active Needle
Authors: Konh Bardia , Datla Naresh V. , Hutapea Parsaoran
Published: December 2014

The continuous implementation of shape memory alloys’ (SMAs’) actuation capabilities in various applications from aerospace to biomedical tools has attracted researchers’ interests into design optimization of active systems. Traditional methods of optimization have mostly relied on several iterations of altering and testing different possible design of prototypes seeking the best configuration. This trial and error experimentation method is usually expensive and time consuming. In the recent years the availability of computational analysis has facilitated the optimization process by avoiding the developments of many prototypes in the whole design space. In this work an automated design optimization frameworks is presented especially for the systems including active components. Design exploration of a recently proposed medical device was considered as a case study to elaborate this iterative technique. SMA activated needle is an innovative medical tool to be used in needle-based surgeries aiming the enhancement of the needle tip placement inside the tissue. Different configurations have been assessed by altering the design variables in the assigned domain seeking the maximum needle tip deflection to assure the maximum flexibility of the structure where all the analyses were constrained to the stress level of SMAs to be in the safe range preventing plasticity. A commercially available finite element package was used for the iterative assessments in the optimization approach. The challenging part in any analysis of active components is the incorporation of a suitable material model. For this purpose three experimental setups were developed to get the material properties of SMAs through different responses of the wires. These material properties along with the implementation of Brinson model led to the generation of the isothermal stress strain curves which were defined as material model of the active components in the FE analyses. The FE model was then linked to the iterative engine of direct optimization to iterate through the whole domain and determine the best configuration. The Design of Experiments (DOE) and the Multi-Objective Genetic Algorithm (MOGA) were used for the case study optimization. Both the design optimization and the design sensitivity studies were described. The results showed the length of the needle and the offset between the neutral axis of needle and the actuator were the most sensitive variables. The best five configurations with the maximum tip deflection was also presented.
Travelling Wave Phenomenon Through a Piezoelectric Actuation on a Free-Free Beam
Authors: Malladi V. V. N. Sriram , Avirovik Dragan , Priya Shashank , Tarazaga Pablo A.
Published: December 2014

A mechanical wave is generated as a result of an oscillating body interacting with the well-defined medium and it propagates through that medium transferring energy from one location to another. The ability to generate and control the motion of the mechanical waves through the finite medium opens up the opportunities for creating novel actuation mechanisms. The focus of this study is on understanding the traveling wave generation and propagation by establishing the relationships that illustrate the role of structural and electromechanical parameters. A brass beam with free-free boundary conditions was selected to be the medium through which the wave propagation occurs. Two piezoelectric elements were bonded on the opposite ends of the beam and were used to generate the controlled oscillations. Excitation of the piezoelectrics results in coupled system dynamics that can be translated into generation of the waves with desired characteristics. Theoretical analysis based on the distributed parameter model and experiments were conducted to provide the comprehensive understanding of the wave generation and propagation behavior.
Elastically Bi-Stable Heartbeat Powered Energy Harvester
Authors: Arrieta Andres F. , Ermanni Paolo , Inman Daniel J. , Karami M. Amin
Published: December 2014

We present an MRI-compatible vibration energy harvester for powering implantable medical devices with heartbeat induced vibrations. The state of the art heartbeat-powered energy harvesters are magnetically bi-stable, rendering this devices MRI incompatible. A type of nonlinear harvester exhibiting purely elastic multi-stability based on bi-stable composite laminates is herein proposed for this purpose. The purely elastic nature of the exhibited bi-stability is crucial for powering medical devices as magnetic based multi-stable harvesters are not suitable for implantation. The energy harvester structure based on cantilevered bi-stable laminates used in this paper is inherently nonlinear and is thus MRI compatible. Harmonic frequency sweeps and previously measured signals simulating vibrations produced around the chest area of the human heart are used as vibration inputs to the harvesting device for experimental tests. The results show the capability of harvesting sufficient energy for powering conventional pacemakers with the exact vibration inputs expected during in vivo operation.
Self-Powered Active Control for an Aeroelastic Plate-Like Wing Using Piezoelectric Material
Authors: Silva Tarcisio M. P. , De Marqui Junior Carlos
Published: December 2014

This paper presents the self-powered active control of elastic and aeroelastic oscillations. A plate-like wing with two piezoelectric layers on the bottom surface and one piezoelectric layer on the top surface is modeled along with an electrical circuit. The direct piezoelectric effect of the bottom layer is used for mechanical to electrical energy conversion. The electrical circuit calculates the control voltage to be applied into the top piezoelectric layer that works as an actuator. The required actuation energy is fully supplied by the harvested energy. The control voltage is obtained from a Linear Quadratic Regulator (LQR) control law. Three cases are investigated. In the first one the harmonic base excitation of the cantilevered wing is considered, the suppression of flutter oscillations is investigated in the second case and the atmospheric turbulence induced vibrations problem is presented in the third case. The performance of the self-powered controller is similar to the performance of a conventional active controller with limited control voltage.
Design and Optimization of an SMA-Based Self-Folding Structural Sheet With Sparse Insulating Layers
Authors: Peraza Hernandez Edwin A. , Hartl Darren J. , Kotz Andreas , Malak Richard J.
Published: December 2014

Origami inspired structures possess attractive characteristics such as the potential to be reconfigurable and the capability to be folded into compact forms for storage. Self-folding structures, which are systems able to perform folding operations without external mechanical input, are desirable in certain circumstances such as remote applications (e.g., space applications, underwater robotics). A self-folding structural sheet consisting of two outer layers of shape memory alloy (SMA) orthogonal wire meshes separated by an inner insulating layer is considered in this work. The inner layer consists of ABS plastic columns that connect the SMA wire mesh intersections of the top and bottom layers, which are co-located and co-oriented (denoted sparse middle layer/aligned meshes design). Significant reduction on the heat transfer between the SMA layers is expected in this design compared to previously considered designs with continuous or perforated elastomeric middle layers. The geometric and power input parameters of the sparse middle layer/aligned meshes design are optimized under mechanical and thermal constraints considering finite element and reduced order analytical models. The optimal folding performance of the sparse middle layer/aligned meshes design is compared to that of the previous designs. The results show that the sparse middle layer/aligned meshes design has promising characteristics as a self-folding structural sheet and provides for tighter folds compared to the designs with elastomeric middle layers.
Nonlinear Dissipative Electroelastic Dynamics of an M-Shaped Broadband Piezoelectric Energy Harvester
Authors: Leadenham Stephen , Erturk Alper
Published: December 2014

The use of nonlinear dynamic phenomena for frequency bandwidth enhancement in vibration-based energy harvesting has received growing attention over the last few years. Various designs have been studied to create Duffing oscillators usually by introducing magnetoelastic coupling. In such devices, magnetic forces are typically coupled with elastic beams involving ferromagnetic components to achieve a nonlinear restoring force of the monostable or bistable Duffing type. Other than the increased volume and structural complexity due to additional magnets and discrete components, these magnetoelastic piezoelectric energy harvesters are not suitable to use in various compact applications and in systems that are sensitive to magnetic fields. The M-shaped structural configuration studied in this work overcomes these issues due to the asymmetric stiffness nonlinearity created by a simple structural configuration composed of a bent spring steel beam with piezoelectric patches. The electroelastic dynamics of the M-shaped broadband piezoelectric energy harvester is governed by various interacting nonlinearities, such as the deliberately introduced stiffness nonlinearity of hardening type resulting from the substrate geometry, inherent elastic nonlinearities of softening type as well as hysteretic losses associated with piezoelectric patches, and other dissipative effects due to large velocities experienced in response to base excitation. A recently developed nonlinear non-conservative electroelastic modeling framework for the piezoelectric patches is combined with geometric nonlinearities of the M-shaped energy harvester to establish a nonlinear dissipative model of the electromechanically coupled system. Energy harvesting experiments for a set of resistors and base excitation levels are then performed to experimentally characterize the bandwidth enhancement using the M-shaped broadband piezoelectric energy harvester.
Modeling and Experimentation of Thickness Mode E/M Impedance and Rayleigh Wave Propagation for Piezoelectric Wafer Active Sensors on Thick Plates
Authors: Kamas Tuncay , Giurgiutiu Victor , Lin Bin
Published: December 2014

This paper discusses theoretical and experimental analyses of the standing harmonic waves through the electro-mechanical impedance spectroscopy (EMIS) and guided surface acoustic waves (SAW) through the guided wave propagation (GWP) analyses. Both EMIS and GWP analyses have been carried out by utilizing piezoelectric wafer active sensors (PWAS) for in situ structural inspection. PWAS has recently been extensively employed in many applications such as nuclear-structural as well as aero-structural health monitoring and non-destructive evaluations (NDE). EMIS method is utilized for high frequency local modal sensing to determine the dynamic characteristics of PWAS bonded on nuclear-structural component for in-situ ultrasonics. Rayleigh waves a.k.a., SAW, were generated in relatively thick isotropic elastic plates. Rayleigh waves have the property of propagating close to the plate surface, with rapid attenuation with depth. The polarization of Rayleigh waves lies in a plane perpendicular to the surface so that the effective penetration depth is less than a wavelength. Rayleigh waves are a high frequency approximation of the first symmetric (S0) and anti-symmetric (A0) Lamb wave modes. As the frequency becomes very high the S0 and the A0 wave speeds coalesce, and both have the same value. This value is exactly the Rayleigh wave speed and becomes constant along the frequency.

In the first part of the study, simplified theoretical constrained PWAS-EMIS model is briefly discussed in relatively high frequency range (in MHz order of magnitude) in terms of thickness mode. Analytical predictive thickness mode impedance simulations of PWAS bonded on plate-like host structures are presented in corresponding with the experiments. For the experimental analyses, PWAS transducers are affixed on isotropic elastic plates such as aluminum plate in relatively high thickness and on a rail I-beam. The extent of the agreement between the experimental and analytical EMIS analyses of PWAS in thickness mode is presented. The study is followed with GWP tests through the pitch-catch method. Rayleigh wave signal packets which are generated in the relatively thick plate and a rail I-beam in high frequency region are assessed along with the experimental thickness mode PWAS-EMIS results. The tuning curve of Rayleigh wave is determined to show the tuning effect of the structure thickness on producing a dominant Rayleigh wave mode. The significant usage of the tuned Rayleigh wave mode is essentially discussed for the applications in the in-situ inspection of relatively thick structures such as nuclear power plant structures. The paper ends with summary, conclusions and suggestions for future work.
Carbon Nanotube Strain Measurements via Tensile Testing
Authors: Geier Sebastian M. , Wierach Peter , Mahrholz Thorsten , Sinapius Michael
Published: December 2014

Discovering and characterizing new smart materials is an urgent need to close the performance-gaps of standard active materials. There is still the demand for a material providing high modulus, low density and large strain. Carbon materials catch scientific attention since a while but one sort among these is of special interest, carbon nanotubes (CNTs). Beside excellent material properties another interesting feature was first mentioned 1999 — the active behavior of paper-like mats made of CNTs. The CNT-papers are electrical activated using a double-layer interaction of ions provided by an electrolyte and the charged high surface area of the paper formed by carbon tubes. Until now the mechanism behind the strain generation of CNT-based architectures is unknown. The principle of the mechanism reveals the potential of carbon tubes to be or not to be a resilient smart material in order to use the strong carbon bonds instead of weak van der Waals force as linking between the tubes. This paper presents further investigations about the mechanical composition of CNT-papers as well as vertical aligned CNT-arrays using an actuated tensile test set-up. For better comparison the experiments are conducted in dry, wet and wet/charged conditions. Especially in the case of CNT-arrays it is essential to preload the specimens because their curly CNT-structure superimposes the vertical orientation of the arrays. While the CNT-paper is tested in an one molar sodium chloride solution, the hydrophilic character of CNT-arrays requires an ionic liquid (IL). It is found that the mechanical properties of CNT-papers drop significantly by wetting and further more by charging what indicates an electrostatic dominated effect. In contrast the CNT-arrays show similar results independent of their test-conditions and an active, reversible behavior of tube-elongation by charging. These results indicate strongly a quantum-mechanical effect of the single tubes.
PVDF Based Wearable Joystick Using Gesture Recognition via Neural Networks
Authors: Van Volkinburg Kyle R. , Washington Gregory N.
Published: December 2014

In this study spatially shaded PVDF was incorporated into a compression sleeve and used to create a wearable joystick which was able to identify and classify gestures made by the right hand. A multilayered feedforward neural network was used to discriminate movements of the hand at the wrist. In feedforward operation, the output voltage of the PVDF was collected using a DAQ system and used to populate an updating input vector which was fed into the network for real-time pattern classification. The network was trained using traditional backpropagation methods where the training inputs were an assortment of collected and simulated voltage patterns of three specific hand gestures and the outputs were specified vectors corresponding to said hand gestures. This training, coupled with the networks ability to generalize, allowed the network to correlate an input voltage profile with the gesture that generated it and correctly classify it.
Surface Synthetic Jet Actuators for Flow Control Applications in Internal Combustion Engines
Authors: Gilmore Paul , Sundaresan Vishnu Baba
Published: December 2014

Charge motion in internal combustion engines is controlled by valves located near the engine ports in the intake path. The valve bodies are obstructions in the air-flow path and are a source of inefficiencies in the engine over its entire operating load. In order to achieve charge motion control without the use of valves, this research investigates the use of synthetic jet actuators to perform swirl and tumble of the air mass entering the cylinder. The purpose of this research is to design, test, and characterize a synthetic jet actuator, and determine the feasibility of using synthetic jet actuators in automotive air-intake systems. The accomplished work to date has led to geometrical optimization, fabrication of a prototype, and experimental investigation for determining jet velocities. The geometrical optimization of synthetic jets has led to a device with a thinner profile that allows it to be embedded in structures with thin (< 5mm) cross-sections and hence we refer to our synthetic jets as surface synthetic jets. It is shown here that air exiting the surface synthetic jets achieves sustained peak velocities well above 125 m/s. A variational principles-based approach is used to model the frequency response of the piezoelectric diaphragm, coupled with the lumped-parameter model for the surface synthetic jets and simulated using MATLAB Simulink®. The results of this model are validated with experimental results and extended to design charge motion control devices. From these results, it is anticipated that these surface synthetic jet actuators can achieve charge motion control using a radial array of surface synthetic jet actuators distributed around the intake runner.
Piezo-Optical Active Sensing With PWAS and FBG Sensors for Structural Health Monitoring
Authors: Lin Bin , Giurgiutiu Victor
Published: December 2014

This paper presents the investigation of piezo-optical active sensing methodology for structural health monitoring (SHM). Piezoelectric wafer active sensors (PWAS) have emerged as one of the major structural health monitoring (SHM) technology; with the same installation of PWAS transducers, one can apply a variety of damage detection methods; propagating acousto-ultrasonic waves, standing waves (electromechanical impedance) and phased arrays. In recent years, fiber Bragg gratings (FBG) sensors have been investigated as an alternative to piezoelectric sensors for the detection of ultrasonic waves. FBG have the advantage of being durable, lightweight, and easily embeddable into composite structures as well as being immune to electromagnetic interference and optically multiplexed.

In this paper, the investigation focused on the interaction of PWAS and FBG sensors with structure, and combining multiple monitoring and interrogation methods (AE, pitch-catch, pulse-echo, phased-array, thickness mode, electromechanical impedance). The innovative piezo-optical active sensing system consists of both active and passive sensing. PWAS and FBG sensors are bonded to the surface of the structure, or are integrated into structure by manufacturing process. The optimum PWAS size and excitation frequency for energy transfer was determined. The FBG sensors parameters (size, spectrum, reflectivity, etc.) for ultrasonic guided waves sensing were also evaluated. We focused on the optimum FBG length and design to improve the sensitivity, coverage, and signal to noise ratio. In this research, we built the fundamental understanding of different sensors with optimum placement. Calibration and performance improvements for the optical interrogation system are also discussed. The paper ends with conclusions and suggestions for further work.
Fabrication and Performance of Magneto-Active Elastomer Composite Structures
Authors: von Lockette Paris
Published: December 2014

This works discusses the use of magneto-active elastomer (MAE) as an active material for use in origami engineering and other applications where transformation of a composite structure between target shapes is desired. Magneto-active elastomer, as the name implies, consists of magnetic powders dispersed in an elastomer (polymer) fluid which is subsequently cured in the presence of a magnetic field to produce a net remanent magnetization in the cured solid. Having their own internal magnetization, MAE materials are affected by both magnetic forces, due to gradients in local field, as well as magnetic torques resulting from the cross product of the field and the magnetization. In this fashion, patches of MAE material, distributed throughout a non-magnetic elastomeric structure, act as distributed actuators producing deformed shapes. The use of rare-Earth magnets as the magnetic actuation elements is also investigated. The work highlights experimental efforts to develop structures with integrated MAE patches and rare-Earth magnets of varying magnetization orientations using multi-step casting processes and 3D printing techniques. Initial results show success at generating active structures having locally oriented MAE patches and magnets in accordion, water bomb and and Miru fold patterns.
Dynamic Electromechanical Modeling of a Spring-Biased Dielectric Electroactive Polymer Actuator System
Authors: Rizzello Gianluca , Hodgins Micah , Naso David , York Alexander , Seelecke Stefan
Published: December 2014

This paper presents a dynamic electromechanical model for an actuator system based on a Dielectric Electro-Active Polymer (DEAP) membrane biased with a linear spring. The motion is generated by the deformation of the membrane caused by the electrostatic compressive force between two compliant electrodes applied on the surface of the polymer. A mass and a linear spring are used to pre-load the membrane, allowing stroke in the out-of-plane direction. The development of mathematical models which accurately describe the nonlinear system dynamics is a fundamental step in order to design model-based, high-precision position control algorithms. In particular, knowledge of the nonlinear electrical dynamics of the actuator driving circuit can be exploited during the control system design in order to achieve desirable features, such as self-sensing or control energy minimization. This work proposes an electromechanical physical model of the DEAP actuator system. By means of numerous experiments, it is shown that the model can be used to predict the current by measuring deformation and voltage (electrical dynamics), as well as predicting deformation and current by measuring the voltage (electromechanical dynamics).
Micro-Structural Model of Magneto-Rheological Composites With Magnetically Induced Stress for Harmonic Shear Deformation
Authors: Shibuya Yotsugi , Nasuno Hiroshi , Sunakoda Katsuaki
Published: December 2014

Magneto-rheological composites with magnetic particles are prepared. The magnetic particle is Fe-Si-B-Cr system and the average diameter is 10μm. Matrix of the composite is silicon gel. We characterized dynamic response of the material by shear test in magnetic field where intensities are 0 mT, 105 mT and 211 mT. The stiffness and damping capacity of the composite increase with increasing of the magnetic field. To understand mechanism of behavior of magneto-rheological composites, we make a model of the composite with periodical micro structure. The magneto-rheological composite undergoes magnetically induced internal stress field by applied magnetic field. The analysis model involved effect of the applied magnetic field as initial stress in the material. Particles and the magnetically induced stress make locally large strain field in the gel material. A large deformation analysis with the Ogden model using finite element method is made to demonstrate behavior of magneto-rheological composites. The simulation results are compared with experiment results and verified the effectiveness of the model.
Self-Propelled Swimming Simulations of Self-Assembling Smart Boxes
Authors: Daghooghi Mohsen , Borazjani Iman , Karami M. Amin , Esfahani Ehsan Tarkesh
Published: December 2014

This paper presents self-propelled swimming simulations of a smart foldable structure capable of swimming and self-assembly for rescue or rapid construction missions, e.g., making temporary bridges. The open configuration of the robot is like a wide cross, which undulates like an eel to swim to a given location. Micro Fiber Composites (MFCs) attached to the surface of the foldable robot actuate the surfaces for swimming purpose. Once the robot arrives at the desired locations shape memory alloys will be activated to fold the robot to a box. To optimize the kinematics of the robot to achieve either highest speed or maximize efficiency during locomotion. self-propelled swimming simulations of the robot was carried out by varying two kinematic parameters: the body motion wavelength and the amplitude. The simulations shows that to achieve higher speed, higher wavelengths are more desirable, e.g., wavelength of 0.95L achieved 15% higher swimming speed relative to 0.65L (L is the swimmer’s length). In contrast, to achieve higher efficiency, lower wavelengths (0.65L) and higher undulation amplitude (0.15L) was 14% more efficient than the other swimmer with wavelength 0.95L and amplitude 0.1L.
Investigation of Asymmetrical Configurations for Piezoelectric Energy Harvesting From Fluid Flow
Authors: Deivasigamani Arvind , McCarthy Jesse M. , John Sabu , Watkins Simon , Coman Floreana
Published: December 2014

Energy harvesting from wind-induced flutter using piezoelectric Polyvinyledene Fluoride (PVDF) was investigated. Previous studies suggested that coupled bending-torsion mechanical vibrations were capable of producing about 30% more power output compared to a pure bending case. In this work, asymmetrical configurations, with amplification devices hinged to the PVDF, capable of bending-torsion vibrations were investigated for energy harvesting from fluid flow. Results indicated that asymmetrical configurations, when excited by fluid flow, were more prone to chaotic flapping and hence provided lower power output compared to a symmetrical harvester. Also, asymmetrical configurations were more prone to fatigue due to excessive non-linear strains. A detailed study of the power output, flutter behavior, piezoelectric operating modes and their limitations are provided in this work.
Predictions of MSMA Response Under Bi-Axial Mechanical Loading
Authors: Dikes Jason L. , Feigenbaum Heidi P. , Ciocanel Constantin
Published: December 2014

Magnetic shape memory alloys (MSMAs) are materials commonly used for actuation, sensing, and/or power harvesting applications. To date, these applications have primarily been explored under a magnetic field and/or a compressive stress, with the stress and the field acting along directions perpendicular to each other. However, other applications may be envisioned, and existing applications may be optimized, with alternate load configurations. The alternate load configuration to be explored in this work is the application of bi-axial compressive stresses. This configuration could be used in actuation or power harvesting applications. A constitutive model, proposed by LaMaster et al. [1], is simplified and used to predict the response of the material under bi-axial compressive stresses. Model predictions are compared with experimental data from the literature.
Properties of Cement-Sand Based Piezoelectric Composites
Authors: Zhao Ping , Kim Sunjung , Braden Joel , Abens Conner , Hinderliter Brian
Published: December 2014

A novel cement-sand based piezoelectric smart composite was developed for structural health monitoring (SHM) in civil infrastructures. Most researches have focused on cement-based piezoelectric composites that are unrealistic in their applications due to their incompatibility with reinforced concrete with cement and sand. In this study, sand was applied to fabricate the composite to address the important issue. Two sets of specimens containing 30 vol% and 50 vol% lead zirconate titanate (PZT) were manufactured and their piezoelectric coefficient and dielectric constant were determined. The results showed that the piezoelectric effect and dielectric constant were enhanced with increasing PZT content. In addition, the sensing effect was conducted under compressive tests. The invesitigation demonstrated the feasibility of the new composite in its application to the SHM system.
Analysis of the Wrist-Wearable Energy Harvester With Vibrating Piezoelectric Multiple Bimorph Cantilevers Using FEM and Topology Optimization
Authors: Kim Cheol , Song Young-Geun
Published: December 2014

A small wrist-watch-like wearable electric energy harvester which can extract electricity from swinging motions of people’s arms while walking has been developed newly. The harvester consists of multiple vibrating piezoelectric cantilevered thin beams attached to a round central hub structure radially with tip masses. The cantilevers are made of a polycarbonate substrate beam, PMN-PT piezoelectric material on its both sides, and a high density tungsten tip mass. The swinging of a human arm with the harvester causes the bending deformations in each blade while walking and then produces electricity from strains in two piezoelectric layers. The swinging motion was formulated mathematically and kinematically in terms of swinging angles, angular velocities and accelerations. Finite element analysis was used to model the cantilevered beams and calculate the voltage output. The optimum shape of piezoelectric layers were calculated on the basis of the topology optimization method specialized for piezoelectric materials.
Experimental Validation and Numerical Simulation of Shape Memory Flat Wire Actuators
Authors: Czechowicz Alexander , Langbein Sven
Published: December 2014

Shape memory alloys (SMA) are thermally activated smart materials. Due to their ability to change into a previously imprinted actual shape through the means of thermal activation, they are suitable as actuators for mechatronical systems. Despite of the advantages shape memory alloy actuators provide, these elements are only seldom integrated by engineers into mechatronical systems. Reasons are the complex characteristics, especially at different boundary conditions and the missing simulation- and design tools. Also the lack of knowledge and empirical data are a reason why development projects with shape memory actuators often lead to failures. This paper deals with the dynamic properties of SMA-actuators (Shape Memory Alloy) — characterized by their rate of heating and cooling procedures — that today can only be described insufficiently for different boundary conditions. Based on an analysis of energy fluxes into and out of the actuator, a numerical model of flat-wire used in a bow-like structure, implemented in MATLAB/SIMULINK, is presented. Different actuation parameters, depending on the actuator-geometry and temperature are considered in the simulation in real time. Additionally this publication sums up the needed empirical data (e.g. fatigue behavior) in order to validate the numerical two dimensional model and presents empirical data on SMA flat wire material.
Theoretical and Experimental Analysis of Frequency Up-Conversion Energy Harvesters Under Human-Generated Vibrations
Authors: Olympio Raul B. , Donahue John , Wickenheiser Adam M.
Published: December 2014

Piezoelectric energy harvesters are devices capable of converting the kinetic energy present in vibration-based motion into electrical energy using piezoelectric transducers. This kind of device has its maximum efficiency when the exciting frequency matches its natural frequency. In the past years, some authors have explored the use of human motion as a vibration source, and harvesting energy in this situation is not trivial because the low-frequency characteristics of the motion are not compatible with small, light-weight transducers, which have relatively high natural frequencies. To overcome this problem, a method known as frequency up-conversion is used; it consists of a nonlinear vibration-based, magnetically excited harvester that exhibits frequency-independent performance, allowing the device to be efficient in a wide band of frequencies. In this work, the power output of a piezoelectric energy harvesting with frequency up-conversion submitted to walking and running vibrations is analyzed. Data are collected using an accelerometer located on the front pocket of each subject and then used in simulations. The model used consists of a cantilever beam with a permanent magnetic tip at the free end; this tip interacts with a magnetized structure that adds a nonlinear interaction to the model. A pure resistance matching the device’s impedance at its fundamental frequency is used to account for the output power. To verify the advantages of using the frequency up-conversion method for vibration-based energy harvesters regarding the power output and frequency band, a comparison with the linear cantilever model is analyzed. Also, in order to confirm the simulation results, a prototype of the device is built and submitted to vibration tests using a horizontally oriented motor-driven cart that recreates the motions recorded by the accelerometer; it is tested with and without the magnetic force in order to experimentally determine the nonlinearity’s effects on the power harvesting performance.
Model-Based Optimization and Characterization of DEAP Multilayer Stack-Actuators
Authors: Hoffstadt Thorben , Maas Jürgen
Published: December 2014

Actuators based on dielectric electroactive polymers (DEAP) use the electrostatic pressure to convert electrical into mechanical energy. Stack-actuators are a common approach to realize DEAP-based multilayer actuators. To optimize the stationary generated force and stretch the influences of material and free design parameters are investigated based on a model of a loss-free actuator. For this purpose the stretch-force-behavior depending on the applied electric energy is introduced. Based on this approach, besides the general scalability of the force and stretch, an optimal operating point can be determined at which the ratio of generated mechanical work to the applied electrical energy is maximized. To further consider performance limitations of such actuators the known effect of electromechanical instability is finally investigated depending on the generated force yielding to critical stretches, forces and energies.
Development of Biomechanical Knee Force Model for Evaluation of Piezoelectric Sensors for In-Vivo Monitoring
Authors: Wilson Brooke E. , Anton Steven R. , Meneghini R. Michael
Published: December 2014

Traditional total knee replacement (TKR) implants have two components: a tibial component consisting of a metal tibial tray with a stem inserted into the tibia and a polyethylene bearing surface inserted into the tray, and a metal femoral component attached to the end of the femur. While these components replicate the functionality of the knee, they are passive and offer no ability to provide data on the status of the knee replacement unit. In this work, piezoelectric materials are considered for both sensing and energy harvesting in TKR implants. This paper focuses on the development of a biomechanical force model that can be used to determine the forces exerted by the human body, which must be endured by the piezoelectric harvester/sensor once it has been implanted in the knee. This model has been developed using OpenSim, an open source software that is used for biomechanical modeling of musculoskeletal systems. The forces calculated in this model are applied directly to the piezoelectric material to determine the power generated during a typical step. Simulation results show that 3–35 mW of average power can be harvested depending on the piezoelectric material used in the stack. Compared to typical low power sensors, which operate in the μW – mW range, the generated power is sufficient to power an embedded sensor in the TKR unit.
Self-Powered Event Detection Sensors With Integrated Safety Electronics for Initiation and Switching in Munitions
Authors: Rastegar Jahangir , Feng Dake , Pereira Carlos
Published: December 2014

A new class of self-powered acceleration event detection sensors are presented that are powered by electrical energy harvested during munitions launch by integrated piezoelectric elements. The sensors are provided with a novel safety electronic and logic circuitry that is used to differentiate the firing event from all accidental events such as accidental drops, transportation vibration, and the like. When the launch conditions are detected from the magnitude of the experienced acceleration as well as its duration, the remaining electronics and logics circuitry of the device is enabled. The developed self-powered sensors may also be used in place of G-switches in munitions and other industrial and commercial devices with the advantage of activating not only from the magnitude of the experienced acceleration but also from its duration. The latter capability is essential in many munitions and commercial applications to avoid false switching event. For example in some cases dropping of around over a hard surface may impart higher peak acceleration than actual firing. And in many industrial and commercial devices and equipment, high-G and very short duration shock loadings do not cause damage and G-switches used to deactivate the device may not be desired to trip.

Prototypes of the developed piezoelectric-based self-powered event detection sensors as standalone sensors and as switches for detecting and opening or closing circuitry upon detection of shock or vibration loading with prescribed magnitude and duration thresholds with integrated electronics and logics circuitry have been designed, fabricated and successfully tested for a number of munitions and industrial applications. In this paper the design and operation of such devices and their testing are described.