bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and Control of Semi-Active Railway Vehicle Suspension Featuring MR Damper
Authors: Oh Jong-Seok , Kim Hwan-Choong , Choi Seung-bok
Published: December 2014

In this work, control performance of a semi-active railway vehicle suspension system featuring MR damper is evaluated. Firstly, a mathematical model for railway vehicle which contains car body, bogie frame and wheel-set is derived to represent lateral, yaw and roll motions. From this model, design parameters of MR damper are optimally determined. And then, MR dampers which can generate proper damping force to control the unwanted vibration of the railway vehicle are manufactured and evaluated experimentally. In order to attenuate the vibration of railway vehicle, in this work, skyhook controller is designed and implemented. Control performances of MR damper for railway vehicle including car body lateral motion and acceleration of MR damper are evaluated using test rig composed of a car body and two bogies.
Modeling of Single Crystal Magnetostriction Based on Numerical Energy Relaxation Techniques
Authors: Kiefer Björn , Buckmann Karsten , Bartel Thorsten , Menzel Andreas
Published: December 2014

This paper presents an energy relaxation-based approach for the modeling of single crystalline magnetic shape memory alloy response under general two-dimensional magneto-mechanical loading. It relies on concepts of energy relaxation in the context of non-convex free energy landscapes whose wells define preferred states of straining and magnetization. The constrained theory of magnetoelasticity developed by DeSimone and James [1] forms the basis for the model development. The key features that characterize the extended approach are (i) dissipative effects, accounted for in an incremental variational setting, and (ii) finite magnetocrystalline anisotropy energy. In this manner, important additional response features, e.g. the hysteretic nature, the linear magnetization response in the pre-variant reorientation regime, and the stress dependence of the maximum field induced strain, can be captured, which are prohibited by the inherent assumptions of the constrained theory. The enhanced modeling capabilities of the extended approach are demonstrated by several representative response simulations and comparison to experimental results taken from literature. These examples particularly focus on the response of single crystals under cyclic magnetic field loading at constant stress, and cyclic mechanical loading at constant magnetic field.
A Framework to Find the Upper Bound on Power Output as a Function of Input Vibration Parameters
Authors: Heit John , Roundy Shad
Published: December 2014

This paper outlines a mathematical framework necessary to determine the optimal transducer force for a given vibration input. This relationship, between input vibration parameters and transducer force gives a critical first step in determining the optimal transducer architecture for a given vibration input. This relationship also yields a theoretical maximum energy output for a system with a given proof mass and parasitic mechanical losses, modeled as linear viscous damping.

This relationship is then applied to three specific vibration inputs; a single sinusoid, the sum of two sinusoids, and a single sinusoid with a time dependent frequency (chirp). For the single sinusoidal case, the optimal transducer is found to be a linear spring, resonant with the input frequency, and a linear viscous damper, with matched impedance to the mechanical damping. The resulting transducer force for the input as a sum of two sinusoids is found to be inherently time dependent. This time dependency shows that an active system (not only dependent on the states of the system) can outperform a passive system (dependent only on the states). The final application, for a swept sinusoidal input, results in a transducer of a linear viscous damper, with matched impedance to the mechanical damping, as well as a linear spring with a time dependent coefficient.
Development of Active-Cells for Macroscopically Deformable Structures
Authors: Nawroj Ahsan I. , Swensen John P. , Dollar Aaron M.
Published: December 2014

In this paper we describe extensions and improvements upon prior work on “active cells” — small contractile electromechanical elements used in large numbers to create actuated composite structures. Each element (cell) consists of square fiberglass end-pieces encapsulating a bias spring within two telescoping tubes, actuated using two contractile shape memory coils, and occupying approx. 1cm3 when fully contracted. The end-pieces contain conductive interfaces to nearby cells, thus allowing channeling of power through a connected network of cells to provide actuation far from the source of electrical current. Prior work developed the conceptual structure of such a cell as well as preliminary prototypes. This paper describes the attachment of cells to each other and to rapid-prototyped cell interconnects — as well as improved fabrication techniques for the shape-memory coils — resulting in robust actuation for each cell, and the creation of considerably more complex chained and networked composite structures. A detailed exploration of appropriate interconnect mechanisms, powering schemes to provide network-level structural deformations, and examples of multi-cell structures are presented.
Visualization of Particle-Toughening Mechanism in Transparent Polyurethanes
Authors: Malakooti Mohammad H. , Anderson Patrick L. , Sodano Henry A.
Published: December 2014

Highly cross-linked polyurethanes have a high elastic modulus and creep resistance, but they undergo a brittle fracture below the glass transition temperature. Unfortunately, a large number of glassy polyurethanes are prone to brittle fracture without undergoing large elastic deformations; in particular, brittle failure is common under conditions such as low temperature and high strain rates. While the rigidity in polymers is required for practical applications, the lack of resistance against crack propagation is essential to avoid catastrophic failures. The toughening of polymers is a crucial aspect of improving the strength and ductility at specific temperatures and deformation rates. One method that has shown promise in recent years is the creation of local regions of reduced modulus that absorb strain energy and toughen the polymer. For instance, rubbers are typically added to epoxy which phase separate upon polymerization and create local elastic regions that significantly toughen the polymer.

In this study, a variety of two-phase transparent polyurethanes in the form of single inclusions is designed to study the toughening mechanism of the local regions of reduced modulus with an embedded crack. Synthesized heterogeneous polyurethanes show a transition from brittle to ductile behavior in addition to a drastic increase in the maximum load that the polymer can withstand. Compact tension experiments demonstrate that a small reduction in the inclusion’s Young’s modulus (∼10%) leads to an increase in the toughness by factor of 7 (∼700%). Moreover, digital image correlation is performed to map the strain distribution around the crack in order to visualize possible toughening mechanism. Comparison between the induced strain field in samples with inclusion and samples without inclusion reveals an efficient toughening mechanism of the polymers.
Synthesis and Characterization of a Bio-Compatible Shape Memory Polymer Blend for Biomedical and Clinical Applications
Authors: Song Janice J. , Kowalski Jennifer , Naguib Hani E.
Published: December 2014

Shape memory polymers (SMP) are a class of stimuli-responsive materials that are able to respond to external stimulus such as heat by altering their shape. Bio-compatible SMPs have a number of advantages over existing SMP materials and are being studied extensively for biomedical and clinical applications. Polymer blending has proved to be an effective method to improve the mechanical properties of polymers (such as tensile strength and toughness) as well as shape memory properties. In this study, we investigate the effect of blending two bio compatible polymers, thermoplastic polyurethane (TPU), a polymer with a high toughness and percent elongation, and poly-lactic acid (PLA), a stiff and strong polymer. The thermal, mechanical and thermo-mechanical (shape memory) properties of TPU/PLA blends were characterized in the following weight percent compositions: 80/20, 65/35, and 50/50 TPU/PLA. The TPU/PLA SMP blending was achieved with melt-blending and the tensile samples were fabricated with compression molding. The mechanical properties of each blend were studied at three different temperatures. The following thermo-mechanical (or shape memory) properties were also studied at each temperature: the shape fixity rate (Rf), shape recovery rate (Rr) and the effect of recovery temperature on the shape memory behavior. The microstructure of the polymer blends were investigated with an environmental scanning electron microscope (SEM). The results showed that the glass transition temperatures of the blends were similar to pure PLA. The toughness of the SMP blend increased with increasing TPU concentration and the tensile strength of the blend increased with PLA composition. The shape fixity rate of the TPU/PLA blend increased with increasing TPU content and the shape recovery rate increased with increasing deformation and recovery temperature. The various TPU/PLA SMP blends characterized in this study have the potential to be developed further for specific biomedical and clinical applications.
Design of a Mouse-Type Combined Haptic Device for Cutaneous, Thermal and Kinaesthetic Sensations
Authors: Yang Tae-Heon , Kim Yu-Joon , Park Yon-Kyu , Koo Jeong-Hoi , Kim Sang-Youn
Published: December 2014

To provide a realistic haptic sensation, cutaneous, thermal, and kinaesthetic sensation should be simultaneously conveyed to a user. While many research efforts have been conducted to develop separate haptic modules, it is quite challenging to construct an integrated haptic device which is sufficiently small to be incorporated into a computer mouse interface. In an effort to achieve this goal, this study proposes the new design of a compact combined haptic device with cutaneous, thermal, and kinaesthetic modules. To convey realistic tactile sensations despite the limited size of the interface, the cutaneous module includes a 3 × 3 miniature pin-array display and an amplitude-modulated (AM) vibration generator. The pin-array display is intended to mimic both small-scale shapes and rough surfaces. The AM vibration generator creates a variety of amplitude-modulated vibrations to replicate the continuous texture of a virtual object. To further convey the temperature and thermophysical properties of an object, the thermal module including a peltier element and a cooling jacket is integrated to the cutaneous module. Since the kinaesthetic information is equally important while perceiving objects, two kinaesthetic actuators operated by MR fluids are located on the control circuit board while supporting the cutaneous and thermal modules. The integrated haptic device can be used to enhance the sense of reality with combined haptic feedbacks while users interact with virtual graphic environments.
Structural Health Monitoring of Truss Type Structures Using Statistical Approach
Authors: Saffari Mahdi , Sedaghati Ramin , Stiharu Ion
Published: December 2014

This paper proposes an effective statistical based vibration health monitoring technique using Auto Regressive (AR) parameters and Support Vector Machine (SVM) for truss type structures. The finite element method has been utilized to obtain acceleration response signals of a space truss structure under random excitations. The signals are then processed to extract their AR parameters as the feature vectors in which the AR parameters of the healthy structure are considered to be the reference baseline data. A Damage Index is then defined to be the standard deviation of the feature vectors from the baseline data. The proposed index provides an effective tool to detect the damage in the structure. It is shown that using only one sensor, it is still possible to accurately detect the damage.

To locate the damage, data classification technique based on Support Vector Machine (SVM) has been employed. It is shown that SVM can successfully classify different signals extracted from the structure. Finally extensive sensitivity analysis has been performed to study the effect of different parameter such as crack size, number of sensors and AR parameter numbers on the accuracy of detection and localization processes.
Static Design of a Selective Compliance Morphing Wing Profile Based on Integrated Variable Stiffness Bi-Stable Components
Authors: Kuder Izabela K. , Arrieta Andres F. , Rist Mathias , Ermanni Paolo
Published: December 2014

The realisation of morphing requires an efficient internal structure capable of significant shape adaptations, implying vastly anisotropic stiffness properties. In this context, introducing variable stiffness elements into distributed compliance systems shows great promise. Specifically, bi-stable laminates demonstrate stiffness variability characteristics arising from the markedly different properties of each equilibrium configuration. This paper presents a novel concept of a morphing wing section based on a distributed arrangement of embeddable variable stiffness bi-stable composites. The final configuration emerges from parameter studies into positioning distinct optimised bi-stable elements within a NACA 0012 profile. The structural response of the aerofoil is assessed numerically, with a particular focus on the global stiffness modification potential as well as exploring the snap-through behaviour of the component laminates. Final specimen manufacturing and testing validates the numerical strategy developed, confirming the feasibility of the innovative morphing approach based on variable stiffness bi-stable elements integrated into a selectively compliant system.
Polychromatic Composite Films for Adaptive Camouflage
Authors: Gent Ian O. , Seddon Annela M. , Roberts Nicholas W. , Trask Richard S.
Published: December 2014

Having the correct camouflage for the current surroundings increases the safety of personnel and can provide a tactical advantage. However, theatres of war are rarely homogeneous and this leads to a compromise in order for the pattern to work in different subsets. In this work we take inspiration from the photonic structures found in insects to produce elastomeric composite materials with embedded photonic crystals that suggest a material solution for an adaptive camouflage system. Colour change for these materials is effected through mechanical straining of the produced composite. The procedure used to make these materials is detailed and preliminary results from testing of the mechanical and optical properties that these materials exhibit is presented.
A Multiple-Degree-of-Freedom Velocity-Amplified Vibrational Energy Harvester: Part A — Experimental Analysis
Authors: O’Donoghue Declan , Nico Valeria , Frizzell Ronan , Kelly Gerard , Punch Jeff
Published: December 2014

Vibrational energy harvesters (VEHs) are devices which convert ambient vibrational energy into electrical power, offering an alternative to batteries for powering wireless sensors. Detailed experimental characterisation of a 2-degree-of-freedom (2-Dof) VEH is presented in Part A of this paper, while a theoretical analysis is completed in Part B. This design employs velocity amplification to enhance the power harvested from ambient vibrations, while also seeking to increase the bandwidth over which power can be harvested. Velocity amplification is achieved through sequential collisions between free-moving masses. Electromagnetic induction was chosen as the transduction mechanism as it can be readily implemented in a velocity amplified system, although other transduction mechanisms can also be used.

The VEH prototype was tested experimentally under both sinusoidal excitation and exponentially correlated Gaussian noise, with different VEH geometries. The maximum power generated under a sinusoidal excitation of arms = 0.6 g was 12.95 mW for a resistive load of 13.5 Ω at 12 Hz, while the maximum power under exponentially correlated Gaussian noise with σ = 0.8 grms, autocorrelation time τ = 0.01s and resistive load 13.5 Ω was 5.3 mW. Maximum bandwidths of 54% and 66%, relative to the central frequency, were achieved under sinusoidal and noise excitation, respectively. The device shows resonant peaks at approximately 15 and 30 Hz, while significant power is also generated in the 17–20 Hz range due to non-linear effects. The VEH component dynamics were analysed using a laser Doppler vibrometer (LDV), while Lab VIEW was used to control the electromagnetic shaker, read the LDV signal and record the VEH output voltage. The aim of this investigation is to achieve a more complete understanding of the dynamics of velocity-amplified systems to aid the optimization of velocity amplified VEH designs.
A Multiple Degree-of-Freedom Velocity-Amplified Vibrational Energy Harvester: Part B — Modelling
Authors: Nico Valeria , O’Donoghue Declan , Frizzell Ronan , Kelly Gerard , Punch Jeff
Published: December 2014

Vibrational energy harvesting has become relevant as a power source for the reduced power requirement of electronics used in wireless sensor networks (WSNs). Vibrational energy harvesters (VEHs) are devices that can convert ambient kinetic energy into electrical energy using three principal transduction mechanisms: piezoelectric, electromagnetic and electrostatic.

In this paper, a macroscopic two degree-of-freedom (2Dof) nonlinear energy harvester, which employs velocity amplification to enhance the power scavenged from ambient vibrations, is presented. Velocity amplification is achieved through sequential collisions between free-moving masses, and the final velocity is proportional to the mass ratio and the number of masses. Electromagnetic induction is chosen as the transduction mechanism because it can be readily implemented in a device which uses velocity amplification.

The experimental results are presented in Part A of this paper, while in Part B three theoretical models are presented: (1) a coupled model where the two masses of the non-linear oscillator are considered as a coupled harmonic oscillators system; (2) an uncoupled model where the two masses are not linked and collisions between masses can occur; (3) a model that considers both the previous cases. The first two models act as necessary building blocks for the accurate development of the third model.

This final model is essential for a better understanding of the dynamics of the 2-Dof device because it can represent the real behaviour of the system and captures the velocity amplification effect which is a key requirement of modelling device of interest in this work. Moreover, this model is essential for a future optimization of geometric and magnetic parameters in order to develop a MEMS scale multi-degree-of-freedom device.
Optimization of a Bend-Twist-and-Sweep Compliant Mechanism
Authors: Calogero Joseph , Frecker Mary , Wissa Aimy , Hubbard James E.
Published: December 2014

The overall goal of this research is to develop design optimization methodologies for compliant mechanisms that will provide passive shape change. Our previous work has focused on designing two separate contact-aided compliant elements (CCE): one for bend-and-sweep deflections, called the bend-and-sweep compliant element (BSCE), and another for twist deflection, called the twist compliant element (TCE). In the current paper, all three degrees of freedom, namely bending, twist, and sweep, are achieved simultaneously using a single passive contact-aided compliant mechanism. A new objective function for a contact-aided compliant mechanism is introduced and the results of the optimization procedure are presented. A bend-twist-and-sweep compliant element (BTSCE) can be inserted into the leading edge spar of an ornithopter, which is an avian-scale flapping wing un-manned air vehicle. The multiple objective functions of the optimization problem presented in this paper are: for upstroke, maximize tip bending and sweep deflections, maximize twist angle, and minimize the mass and peak von Mises stress in the BTSCE, and for downstroke, minimize tip bending and sweep deflections, minimize twist angle, and minimize the mass and peak von Mises stress in the BTSCE. This allows a designer to select a CCE from a set of optimal designs to accomplish all three displacement goals. The BTSCE was modeled using a commercial finite element program and optimized using NSGA-II, a genetic algorithm. The results for a single angled compliant joint (ACJ) for quasi-static upstroke loading conditions are presented. Two optimal designs are discussed and compared, one with a moderate peak stress and moderate deflections, the other with a high peak stress and large deflections. The optimization results are then compared to the previous results for the two independent CCEs. A design study showed that the angle of the ACJ needs to be obtuse to achieve a positive twist angle during upstroke, and an acute contact angle reduces peak stress. The deflection objective functions were relatively insensitive to eccentricity for upstroke and downstroke compared to the other parameters, and a high stress penalty was paid for any gains in deflection. The downstroke objective functions were relatively insensitive to all parameters compared to the upstroke objective functions, and were much smaller in magnitude. The optimization showed that under simplified upstroke loading conditions, the BTSCE with a single ACJ allowed bending deflection near 30% of the length of the BTSCE, twist angle near 0.14 radians, and sweep deflection near 5% of the length of the BTSCE.
Induced Strain Actuation for Solid-State Ornithopters: A Parametric Study
Authors: Hauris Francis , Bilgen Onur
Published: December 2014

This numerical study seeks to find a feasible location and orientation for a piezoelectric material to actuate a solid-state ornithopter modelled after the Great Blue Heron. The analysis is first conducted statically and dynamically on a simple rectangular cantilevered plate. A separate simplified model of a plate with Great Blue Heron wing profile is also examined statically and dynamically. The parameters considered are the angles of two piezoelectric Macro-Fiber Composite patches that are adhered to the cantilevered substrate near its base and at mid-span. The orientations of the patches are swept from 0 to 180 degrees as they are actuated at amplitude of 1000 Volts either statically or harmonically. By varying the orientation angles, various bending and twisting deflections are obtained and the responses are analyzed.
Underwater Dynamic Actuation of Macro-Fiber Composite Flaps With Different Aspect Ratios: Electrohydroelastic Modeling, Testing, and Characterization
Authors: Shahab Shima , Erturk Alper
Published: December 2014

Macro-fiber composite (MFC) actuators offer simple and scalable design, robustness, noiseless performance, strong electromechanical coupling, and particularly a balance between the actuation force and deformation capabilities, which is essential to effective and agile biomimetic locomotion. Recent efforts in our lab have shown that MFC bimorphs with polyester electrode sheets can successfully be employed for fish-like aquatic locomotion in both tethered and untethered operation. MFC swimmers can outperform other smart material-based counterparts, such as the compliant ionic polymer-metal composite based swimmers, in terms of swimming speed per body length. Cantilevered flaps made of MFC bimorphs with different aspect ratios can be employed for underwater actuation, sensing, and power generation, among other aquatic applications of direct and converse piezoelectric effects. In an effort to develop linearized electrohydroelastic models for such cantilevers, the present work investigates MFC bimorphs with three different aspect ratios. The MFCs used in this study use the 33-mode of piezoelectricity with interdigitated electrodes. Underwater dynamic actuation frequency response functions (FRFs) of the MFCs are defined as the tip velocity per actuation voltage (tip velocity FRF) and current consumption per actuation voltage (admittance FRF). The tip velocity and admittance FRFs are modeled analytically for in-air actuation and validated experimentally for all aspect ratios. Underwater tip velocity and admittance FRFs are then derived by combining their in-air counterparts with corrected hydrodynamic functions. The corrected hydrodynamic functions are also identified from aluminum cantilevers of similar aspect ratios. Both tip vibration and current consumption per voltage input are explored. The failure of Sader’s hydrodynamic function for low length-to-width aspect ratios is shown. Very good correlation is observed between model simulations and experimental measurements using aspect ratio-dependent, corrected hydrodynamic function.
Development of a Bio-Inspired Tactile Magnetostrictive Whisker Sensor Using Alfenol
Authors: Raghunath Ganesh , Flatau Alison B. , Na Suok-Min , Barkley Brett
Published: December 2014

Alfenol (FexAl100−x) is an alloy similar to Galfenol (Fe-Ga alloys) in crystal lattice structure and magnetostriction trend (peaking at ∼20% composition). Although single-crystal Fe80Al20 exhibits lower magnetostriction (∼184 ppm, about half of Fe80Ga20), its magneto-elastic coupling coefficient is on par with that of Fe-Ga. In addition, characteristics such as machinability and rollability are superior to that of Galfenol, making it possible to achieve textured sheets (thickness∼200 μm) which, while having a high elastic modulus, are very flexible. Furthermore, Aluminum is non toxic, cheap (∼1% the cost of Ga) and is available in abundance. These attributes make Alfenol an ideal candidate for a bio-inspired whisker-like tactile sensor (mimicking mystacial vibrissae of cats, sea lions, etc.).

This work deals with the design and development of an accurate, cost efficient, real-time, and non-invasive sensor prototype that tracks displacements, vibrations and scour on bridge piers with minimal signal conditioning. Making such a sensor is possible thanks to Alfenol’s linear response to strain in the presence of appropriate bias magnets. The change in its magnetic state due to inverse magnetostriction from applied bending stresses will be observed using Hall Effect sensors to derive deflection information.

A protocol to manufacture rolled and textured Alfenol whisker samples will be presented in this research. The effect of bias conditions on sensor performance will be studied empirically and by using multi-physics simulations. Optimization of the sensor by varying the dimensions of the whisker, and its correlation to flux leakage will also be examined followed by an effort to understand the micro-magnetic response of Alfenol to mechanical stimulation. Finally, results from using this biomimetic sensor to measure displacements and vibrations, and its viability to be used as a flow sensor will be discussed.

The robustness of this sensor has been exploited to develop a novel real-life application to provide an early warning system for bridge pier scour due to soil transportation during a weather event. The effectiveness of these sensors for scour detection in riverbeds will subsequently be simulated in a water flume and analyzed.
Mechanotransduction of Multi-Hair Droplet Arrays
Authors: Tamaddoni Nima , Sarles Stephen A.
Published: December 2014

Early embodiments of droplet interface bilayer (DIB)-based hair cell sensors demonstrated the capability of sensing discrete and continuous perturbations, including single flicks and constant airflow, respectively, of a hair structure that is held in close proximity to a single lipid membrane. In those studies, the use of a single bilayer formed between a pair of droplets provided the necessary environment for studying the physical mechanism of mechanotransduction of a membrane-based sensor as well as the sensitivity and directionality of the assembly. More recently, we showed that additional lipid-coated droplets could be connected in series to form multi-bilayer arrays. Measurements of bilayer current through each interface demonstrated that perturbation of the hair creates a vibration that propagates across several droplets, allowing for the additional interfaces to also sense the perturbation. Depending on the location of the hair in the droplet array, these sensing currents can occur in-phase with one another, allowing for a total sensing current to be easily summed. Two important remaining questions about multi-bilayer arrays include: 1) How is signal propagation affected by the configuration of droplets in the array? 2) How does perturbation of multiple hair structures affect signal propagation and sensing currents in a droplet-array? To study these questions, we form linear series and L-shaped arrays of DIBs where each droplet is instrumented with a sensing electrode. Our experiments show that the motion of the perturbed hair can be transduced by up to three membranes away from the hair and that a change in the orientation of successive interfaces does not significantly affect the propagation of vibrational energy. Separately, experiments on serial arrays with multiple hairs indicate that a second, unperturbed hair does not affect bilayer currents generated by the perturbed hair and that hairs of varying length can add frequency selectivity and stimulus localization capability to multi-bilayer sensors.
Shape Memory Alloy Cables for Civil Infrastructure Systems
Authors: Daghash Sherif , Ozbulut Osman E. , Sherif Muhammad M.
Published: December 2014

Shape memory alloys (SMAs) have attracted a great deal of attention as a smart material that can be used in various civil engineering applications due to their favorable mechanical properties such as ability to undergo large deformations, high corrosion and fatigue resistance, good energy dissipating capacity, and excellent re-centering ability. In contrast to the use of SMAs in the biomedical, mechanical and aerospace applications, which requires mostly small diameter of material, the larger size bars are usually needed in a civil engineering application. It is well known that properties of large-section SMA bars are generally poorer than those of wires due to difficulties in material processing. Furthermore, large diameter SMA bars are more expensive than thin SMA wires.

Shape memory alloy cables have been recently developed as an alternative and new structural element. They leverage the superior mechanical characteristics of small diameter SMAs into large-size structural tension elements and possess several advantages over SMA bars. This study explores the performance of NiTi SMA cables and their potential use in civil engineering. The SMA cable, which has a diameter of 8 mm, is composed of 7 strands and each strand has 7 wires with a diameter of 0.885 mm. The uniaxial tensile tests are conducted at various loading rates and strain amplitudes to characterize the superelastic properties of the SMA cable and study the rate-dependent mechanical response of the SMA cable under dynamic loads. An optical digital image correlation measurement system and an infrared thermal imaging camera are employed to obtain the full-field strain and temperature fields. Potential applications of SMA cables in civil infrastructure applications are discussed and illustrated.
Improved Adjusting Capacitor Method for Piezoelectric Frequency Tuning and Maximum Energy Harvesting
Authors: AL Maliki Murtadha A. , Mossi Karla M.
Published: December 2014

Energy harvesting refers to conversion of ambient energy into electrical energy. A typical way to accomplish this conversion is through the use of a piezoelectric harvester. This device produces a maximum power when its natural resonance frequency matches that of the ambient vibration. This property is the main limitation to developing many application. To address this restriction, it has been proposed by several investigators that a capacitor be connected in parallel to a piezoelectric cantilever as a method of electrical tuning. When such passive element is connected, the power decreases from its original value. In this paper an improvement to this approach is proposed. Once the tuning capacitor is connected, an inductor value is chosen such that conjugate impedance matching becomes reasonable and plugging this component can give an improvement for both the voltage and power generated. Capacitors of 0.2 μF to 1.5μF values were connected in parallel to a piezoelectric unimorph Type TH-7R with an inherent capacitance of 166 nF and a 208 Hz resonance frequency to develop a tuning range of four Hz. The harvested power during the tuning was proved to be correlated inversely to the shunt capacitor value. By connecting a 700 mH and 2 H inductors in parallel to the system, a significant improvement in power was obtained. In addition, a correlation between the resonance frequency and optimal load resistance with the shunt capacitor value has been studied. The results show that this innovative method is an efficient method for frequency tuning and maximum power extraction.
Optimal Energy Harvesting From Impulse Trains Using Piezoelectric Transduction
Authors: Kody A. A. , Scruggs J. T.
Published: December 2014

In applications of vibration energy harvesting to embedded wireless sensing, the available power and energy can be very low. This poses interesting challenges for technological feasibility if the parasitic losses in the electronics used to harvest this energy are prohibitive. In this study, we present a theory for the active control of power generation in energy harvesters in a manner which addresses and compensates for parasitic loss. We conduct the analysis in the context of a single-transducer piezoelectric bimorph cantilever beam subjected to a low-frequency impulse train. The power generation of the vibration energy harvester is maximized while considering mechanical losses, electrical losses, and the static power required to activate control intelligence and facilitate power-electronic conversion. It is shown that the optimal harvesting current can be determined through the use of linear quadratic optimal control techniques. The optimal harvesting time over which energy should be generated, following an impulse, is determined concurrently with the optimal feedback law. We show that this optimal harvesting time exhibits bifurcations as a function of the parameters characterizing the losses in the system.
A Novel Tubular Thin-Wall IPMC Sensor Capable of Two-Dimensional Sensing: Fabrication, Characterization and Modeling
Authors: Lei Hong , Tan Xiaobo
Published: December 2014

An ionic polymer-metal composite (IPMC) sensor typically consists of a thin ion-exchange membrane with electrodes on both surfaces. Such IPMC sensors respond to deflections in the beam-bending directions only and thus are considered one-dimensional. In this paper, a novel IPMC sensor capable of two-dimensional sensing is presented. This tubular thin-wall IPMC has one common inner electrode and four outer electrodes, which form four routes of common-ground outputs. The fabrication method is reported along with the sensor package. A custom-designed experimental setup, which provides dynamic tip bending with adjustable orientations and controlled bending amplitude, is used to characterize the sensor response (short-circuit current) to the 2D mechanical stimulus in air. Based on the characterization results, we further model the proposed 2D tubular IPMC sensor by treating pairs of infinitesimal portion of tube wall as one-dimensional IPMC sensors and integrating them around the tube. Experimental results show that the fabricated IPMC sensor responds to omnidirectional stimulus within the cross-section plane and the proposed model captures well the sensor responses, indicating that this tubular IPMC sensor can be potentially used for 2D flow and displacement sensing.
Characterization of Piezoelectric Macrofiber Composite Actuated Winglets
Authors: Guha Tufan Kumar , Oates William , Kumar Rajan
Published: December 2014

Piezoelectric macro-fiber composite (MFC) structures have been used to develop oscillating winglets for active control of wing-tip vortices. A MFC structure was embedded inside a wing-section to oscillate the winglet at its free end. The goal is to weaken the potentially harmful tip vortices by introducing controlled instabilities through both spatial and temporal perturbations produced by an oscillating winglet. In the present study we have characterized MFC actuated winglets under different input excitation and pressure loading conditions. It consisted of bench-top experiments to characterize the structural resonance, with and without point pressure loading and wind tunnel tests involving distributed pressure loading. Surface pressure measurements were carried out at three spanwise locations to measure the effect of oscillating winglet on the pressure distributions on the wing surface. MFC actuated winglets show bimodal resonance behavior and the modes of oscillations are independent of magnitude of input excitation and the pressure loading.
Time Integration and Assessment of a Model for Shape Memory Alloys Considering Multiaxial Nonproportional Loading Cases
Authors: Zaki Wael , Gu Xiaojun , Morin Claire , Moumni Ziad , Zhang Weihong
Published: December 2014

The paper presents a numerical implementation of the ZM model for shape memory alloys that fully accounts for non-proportional loading and its influence on martensite reorientation and phase transformation. Derivation of the time-discrete implicit integration algorithm is provided. The algorithm is used for finite element simulations using Abaqus, in which the model is implemented by means of a user material subroutine. The simulations are shown to agree with experimental and numerical simulation data taken from the literature.
Thermoacoustic Modeling of a Graphene-Based Actuator
Authors: Bin Jonghoon , Oates William S. , Taira Kunihiko
Published: December 2014

A model for two-dimensional graphene-based thermoacoutic membranes is investigated analytically and validated numerically in this study. In one-dimension, the temperature and the pressure variables are analytically determined by decoupling the two variables in the governing equations due to the large disparity between length scales. We further extend the one-dimensional findings to three dimensions. The three-dimensional pressure fluctuation produced by the surface temperature variation is determined with the aid of the acoustic piston model. Through the one and three-dimensional model analysis, the dependence of acoustic pressure as a function of frequency is studied and the acoustic response with respect to the frequency shows different characteristics when assuming Dirichlet (temperature) or Neumann (heat flux) boundary conditions. The general thermoacoustic model is then applied to a graphene-on-paper sound device. Probabilistic Bayesian method coupled with Monte Carlo Markov Chain (MCMC) algorithms is used to optimize model parameters and to analyze model parameter uncertainty. Excellent correlations of thermoacoustic behavior is predicted by the model which provides insight into heat transport mechanisms associated with generating sound from thermally cycling graphene at high frequencies.
Feedback Control Applied to Finite Element Models of Morphing Structures
Authors: Bertagne Christopher , Moghadas Peyman , Malak Richard , Hartl Darren
Published: December 2014

This paper demonstrates a framework for integrating full feedback control with a high-fidelity finite element model in order to simulate control of morphing structures. Most of the previous finite element simulations involving control of morphing structures consider the effects of the controller, but do not incorporate true feedback control. Additionally, when feedback control is considered, numerical models other than finite element analysis are used. Thus, a trade-off must be made between a high-fidelity model and consideration of feedback control. In this work, these aspects are unified to create a tool that can simulate real-time feedback control of a finite element model.

The framework itself consists of two components: the finite element model and the controller. The finite element model must be capable of varying external loads as the solution evolves in time. In this paper, the finite element model is implemented in ABAQUS. The controller component is written in Python. In order to ensure the framework is suitable for a wide range of applications, no assumptions are made regarding the natures of the finite element model or the control architecture. Additionally, the components are designed to be modular. For example, simulating different controller architectures does not require alteration of the finite element model. The result is a highly flexible framework that is particularly well-suited for validating and demonstrating controllers on high-fidelity models.
Design and Evaluation of a Knee Actuator for a Dynamic Knee-Ankle-Foot Orthosis
Authors: Tian Feng , Elahinia Mohammad , Hefzy Mohamed Samir
Published: December 2014

Dynamic KAFOs are developed to recover the normal walking ability during both stance and swing phases. Three types of dynamic KAFOs have been reported in the literature. Various actuation mechanisms including spring, pneumatic and hydraulic systems have been used. These devices can improve walking disability and compensate lower leg muscle deficiency. However, they are bulky, in some cases need complex control systems and do not recreate the normal gait pattern. These shortcomings have limited the application of dynamic KAFOs in daily life. The purpose of this paper is to develop a novel knee actuator for a dynamic KAFO that is actuated easily by employing shape memory materials. Such an actuation system makes the KAFO lightweight and has a greater potential to restore the normal gait. Torsional superelastic alloys are used in this actuator in order to match the stiffness of the knee joint of the KAFO with that of a normal knee joint during the walking gait cycle. There are two distinct parts in the knee actuator, acting independently to mimic the two phases of the gait cycle. One engages only in the stance phase and the other works in the swing phase. Each part is developed by combining a superelastic rod and a stiff rotary spring, in series. According to numerical simulation, such combination reproduces the varying knee stiffness during the whole walking gait. Also mechanical experiments have been conducted to further verify the conceptual design. The simulation and experimental results show that the actuator is able to reproduce the stiffness of the normal knee joint during the gait cycle.
Interval Type-2 Fuzzy Logic Control of NM70 Shape Memory Actuator
Authors: Dominik Ireneusz
Published: December 2014

The main aim of this article is to present the usage of type-2 fuzzy logic controller to control a shape memory actuator. To enhance real-time performance simplified interval fuzzy sets were used. The algorithm was implemented in the ATmega32 microcontroller. The dedicated PC application was also built. The fuzzy logic controller type-2 was tested experimentally by controlling position of the shape memory alloy actuator NM70 which despite its small size distinguishes itself by its strength. The obtained results confirmed that type-2 fuzzy controller performed efficiently with a difficult to control nonlinear plant. The research also proved that interval type-2 controllers, which are a simplified version of the general type-2 controllers, are very efficient. They can handle uncertainties without increasing drastically the computational complexity.

Experimental data comparison of the fuzzy logic controller type-2 with type-1 clearly indicates the superiority of the former, especially in reducing overshooting.
Design and Validation of Acceleration Measurement Using the Martlet Wireless Sensing System
Authors: Dong Xinjun , Zhu Dapeng , Wang Yang , Lynch Jerome P. , Swartz R. Andrew
Published: December 2014

The adoption of wireless sensing technology by the structural health monitoring community has shown advantages over traditional cable-based systems, such as convenient sensor installation and lower system cost in many applications. Recently, a new generation of wireless sensing platform, named Martlet, has been collaboratively developed by researchers at the University of Michigan, Georgia Tech, and Michigan Tech. Martlet adopts a Texas Instruments Piccolo microcontroller running up to 90 MHz clock frequency, which enables Martlet to support high-frequency data acquisition and high-speed onboard computation. The extensible design of the Martlet printed circuit boards allows convenient incorporation of various sensor boards. In order to obtain accurate acceleration data and meanwhile reduce the sensor cost, a new Martlet sensor board, named integrated accelerometer wing, is developed. The integrated accelerometer wing adopts a commercial-off-the-shelf MEMS (microelectromechanical systems) accelerometer and contains an onboard signal conditioner performing three basic functions, including mean shifting, anti-aliasing filtering and signal amplification. One distinct feature of the signal conditioner is the on-the-fly programmable cut-off frequency and amplification gain factor. To validate the performance of Martlet and the integrated accelerometer wing, experiments are carried out on a laboratory four-story aluminum shear-frame structure. The laboratory experiment results demonstrate that the performance of the wireless sensing system is comparable to that of cabled reference sensors. In addition, using data collected by wireless sensors, vibration modal properties of the structure are identified and finite element (FE) model updating is performed.
Experimental Characterization of Strain and Damage Evolution in Carbon Nanotube-Polymer Nanocomposites
Authors: Sengezer Engin Cem , Seidel Gary D.
Published: December 2014

An experimental characterization of nanocomposite strain and damage sensing in support of development of CNT-polymer nanocomposites for structural health monitoring (SHM) applications was conducted. As such, effort here is focused towards examining the piezoresistive behavior of poly(dimethyl-siloxane) (PDMS) and epoxy filled with acid treated single walled carbon nanotubes (COOH-SWNTs) under quasi-static compression and tension. Precision LCR Meter with two terminal method, in conjunction with mechanical testing and data acquisition system were used to measure instantaneous resistance values. Given the emphasis on SHM applications which correlate changes in electrical resistivity to deformation and damage, 0.1 wt% COOH-SWCNTs concentration below the nanocomposite electrical percolation threshold was considered for PDMS and epoxy. Measurements confirmed the onset of damage prior to noticeable effects in the stress-strain response. The resistance measurements were able to both detect strain for PDMS nanocomposites and damage initiation and provide continuous assessment of the damage state between damage initiation events for epoxy nanocomposites. Digital Image Correlation (DIC) System was used to observe the crack propagation on notched epoxy nanocomposite compact tension samples.