bluuebunny/crossref_metadata_2025 huggingface dataset:
Fracture Modeling of an Embedded Crack in Self-Healing Polymers
Authors: Malakooti Mohammad H. , Sodano Henry A.
Published: July 2013

The healing process exhibited by biological structures has inspired the creation of engineered materials capable of mimicking this behavior, providing adaption to impeding crack propagation and subsequently healing it. Recently, a new approach to self-healing was devised in which a sensing network was combined with shape memory polymers (SMPs) to allow the controlled response of the material to damage. The system was designed such that in the presence of a crack the polymer locally modified its modulus to toughen the damaged region and arrest crack growth. This process is followed by the shape memory response, closing the crack and healing the system. This paper will study the mechanics of the toughening portion of this self-healing system and specifically develop models to predict the stress intensity factor of a crack tip in a nonhomogeneous inclusion. The models will be formulated using finite element analysis (FEA) and a single inclusion model based on Eshelby’s equivalent theory with the elastic gradient defined by a point source thermal load. It will be shown that as the temperature of the crack tip passes the glass transition temperature of the polymer, the stress intensity factor at crack tip decreases to 95% of the original material stress intensity factor. This is due to the formed elastic gradient and deflection of the stress concentration away from the crack tip into the bulk polymer.
Load Monitoring of Aerospace Structures Using Micro-Electro-Mechanical Systems (MEMS)
Authors: Martinez M. , Rocha B. , Li M. , Shi G. , Beltempo A. , Rutledge R. , Yanishevsky M.
Published: July 2013

The National Research Council of Canada has developed Structural Health Monitoring (SHM) test platforms for load and damage monitoring, sensor system testing and validation. One of the SHM platform consists of two 2.25 meter long, simple cantilever aluminium beams that provide a perfect scenario for evaluating the capability of a load monitoring system to measure bending, torsion and shear loads. In addition to static and quasi-static loading procedures, these structures can be fatigue loaded using a realistic aircraft usage spectrum while SHM and load monitoring systems are assessed for their performance and accuracy. In this study, Micro-Electro-Mechanical Systems (MEMS), consisting of triads of gyroscopes, accelerometers and magnetometers, were used to compute changes in angles at discrete stations along the structure. A Least Squares based algorithm was developed for polynomial fitting of the different data obtained from the MEMS installed in several spatial locations of the structure. The angles obtained from the MEMS sensors were fitted with a second, third and/or fourth order degree polynomial surface, enabling the calculation of displacements at every point. The use of a novel Kalman filter architecture was evaluated for an accurate angle and subsequent displacement estimation. The outputs of the newly developed algorithms were then compared to the displacements obtained from the Linear Variable Displacement Transducers (LVDT) connected to the structures. The determination of the best Least Squares based polynomial fit order enabled the application of derivative operators with enough accuracy to permit the calculation of strains along the structure. The calculated strain values were subsequently compared to the measurements obtained from reference strain gauges installed at different locations on the structure. This new approach for load monitoring was able to provide accurate estimates of applied strains and loads.
Development of Localized, Light-Weight Pressurization Mechanisms: Approach, Feasibility, and Impact
Authors: Sutter Thomas M. , Dickerson Matthew B. , Creasy Terry S. , Baur Jeffery W. , Justice Ryan S.
Published: July 2013

This work presents a novel gas-generation mechanism designed to enable bioinspired actuators. Specifically, the fundamental aspects involved in harnessing the gaseous products from biologically catalyzed reactions and recycling the gases into an actuation pressurization scheme are explored. The capability of having such a self-regulating, self-regenerating system of gas generation could provide the necessary pneumatically-driven force to enable devices that require localized pressurization, such as rubber muscle actuators. This work reports 1) the utilization of biological systems to produce gaseous products that will ultimately affect actuator density in situ, and 2) the construction of a freely moving power rig to monitor rubber muscle actuator performance under pressure generated from biologically powered reactions.
Gyroscopic Effects of Horizontal Axis Wind Turbines Using Stochastic Aeroelasticity via Spinning Finite Elements
Authors: Velazquez Antonio , Swartz R. Andrew
Published: July 2013

Horizontal axis wind turbine (HAWTs) structures, throughout the years, have presumed to be of relatively simple construction, but wind-induced aerodynamic vibrations, wind-field conditions, and power requirements tend to lead to the need for increasingly complicated designs. One phenomenon that requires special attention is the gyroscopic or Coriolis effect. In general, blades design codes are written to optimize for lightness and slenderness, but also to withstand excitations at high frequency. As a result, gyroscopic motion derives as a nonlinear dynamic condition in the out-of-plane direction that is difficult to characterize by means of the well-known vibrational theory that has been established for their design and analysis. The present study develops and presents a probabilistic analysis of the precession — gyroscopic — effects of a wind turbine model developed for tapered-swept cross-sections of nt degree with nonlinear variations of mass and geometry along the body of the blade. A dynamic orthogonal decoupling method is utilized to successfully perform the aeroelastic analysis by decoupling the damped-gyroscopic equations of motion, as a result of the addition of Rayleigh damping — symmetric proportional mass and stiffness — within the linear system in study. Results are valid for yaw-free rotor configurations by means of unknown and random (though bounded) yaw rates. Simultaneously, those results can easily be expanded for yaw-controlled mechanisms. The yaw-free assumption presents a higher risk of potential reliability expectations, given the stochastic impairment of the gyroscopic nature that is present for out-of-plane axis motions, requiring special attention at higher frequencies. This impairment becomes particularly troublesome for blade profiles with tapered-swept cross-section variations. This uncertainty can be minimized by incorporating a mathematical framework capable of characterizing properly the yaw action such that gyroscopic effects can be fully interpreted and diagnosed. In summary, the main goal is to decipher the complexity of gyroscopic patterns of flexible rotor blades with complex shape configurations, but also to provide substantial elements to successfully approach yaw-mechanics of tapered-swept rotor blades.
A Micro Kinetic Energy Harvester Demonstrating Energy Harvesting From 3-D Mechanical Motion and Power Increasing Through Magnetic-Based Frequency Rectification
Authors: Chung Tien-Kan , Wang Chieh-Min , Tseng Chia-Yuan , Liu Tzu-Wei , Yeh Po-Chen
Published: July 2013

In this paper, we report a micro 3-D kinetic energy harvester demonstrating an energy conversion from environmental mechanical-energy (3-D mechanical motion) to electrical energy (voltage output). In addition to energy harvesting/conversion from 3-D motion, we demonstrate a non-contact frequency-up rectification approach which converts an incoming lower vibration frequency to a higher frequency in order to increase the power output of the harvester.
Designing Active Surface Structures to Regulate Heat Transport in Microchannels
Authors: Mills Zachary Grant , Aziz Basat , Alexeev Alexander
Published: July 2013

We used three dimensional computer simulations to examine heat transport in a microchannel that encompasses a periodic array of biomimetic synthetic cilia. We modeled two different configurations of tilted cilia. Both configurations consisted of a grid of evenly spaced cilia with length L and square cross-section 0.1L×0.1L. The cilia were spaced at a distance δx between cilium rows and the inter-cilia spacing in the rows was fixed at δz = 0.25L for one configuration and δz = 0.5L for the other. The channel was filled with a viscous fluid and its top and bottom walls were maintained at different temperatures. The cilia were attached to the bottom channel wall at a specific angle and were actuated by a periodic external force applied vertically to their free ends. The periodical beating of cilia induces fluid mixing inside the fluid that facilitates heat transport. To model this multi-component system, we employed a thermal lattice Boltzmann model coupled with the lattice spring model. In order to investigate how the active cilia affect the heat transfer between the channel walls we varied three parameters in the system. Specifically, we systematically changed the tilt of the cilia, the spacing between cilia and the oscillation frequency of the cilia. Our investigations have allowed us to determine the optimal conditions for using cilia to increase the heat flux from a heated surface. Our findings could be useful for developing new methods for temperature control in microscale devices.
Back-Relaxation of Carbon-Based Ionic Electroactive Polymer Actuators
Authors: Vunder Veiko , Punning Andres , Aabloo Alvo
Published: July 2013

Back-relaxation — a phenomenon, where the ionic electro-active polymer actuator in its excited state decays back towards its initial shape — is commonly associated with the aqueous IPMC and explained with leak of water. Regardless of the absence of the fluent liquid, the dry actuators with electrodes made of carbon and ionic liquid as electrolyte, exhibit similar side effect. We show that by means of their long-term transient spatial actuation, moment of force, and back-relaxation, the behavior of the carbon-based actuators is comparable to the water-based IPMC actuators.
Fabrication of a Dielectric Electro Active Polymer Tube Actuator With Pre-Strain Mechanism
Authors: Alvarado Oscar , Flatau Alison
Published: July 2013

The aim of this paper is to discuss and present our work on the fabrication of a Dielectric Electro Active Polymer (DEAP) actuator with a pre-strain mechanism. In this study the actuator uses commercially available evaluation DEAP film from Danfoss Polypower A/S. The manufacturing process is presented as well blocked force and free displacement data for voltages ranging from 0 to 2500 volts. Challenges encountered during the manufacturing of the actuator are also described and possible solutions discussed.
Investigation of Low Velocity Impact Damage in Aluminum Alloys
Authors: Cooper Benjamin , Zagrai Andrei
Published: July 2013

In structural health monitoring (SHM), impact detection and characterization techniques often focus on identifying parameters of impact such as the location and velocity of an impacting object. A distributed network of sensors is used to passively detect the mechanical wave created by the impact. Various techniques are used to analyze the signals based on time of arrival, amplitude and phase. A simpler architecture could be used to determine whether an impacting event was benign or caused damage and requires further evaluation. This research focuses on detecting attributes of impact-generated elastic wave signals that are indicative of local damage at the impact site. Waveforms deviate insignificantly for undamaged materials, however, when a material is stressed to plastic deformation or damaged the waveform of propagation through the material is noticeably affected. This change in wave speed may be detectable by SHM sensors, and can be used as an indicator of damage. Low velocity impact experiments were conducted on thin aluminum plates instrumented with piezoelectric and magneto-elastic sensors at various locations. The sensors acquired the initial passage of the impact wave signal before reflections off the boundaries became a significant element. By inspecting the signal for deviations induced by damage (such as plastic deformation), a routine for evaluating damage can be inferred. Further work may correlate features of the signal with damage severity providing an extra level of information in determining the next step in evaluating the damage. Using this approach, it may be possible to evaluate impact damage using limited numbers of passive sensors.
Automatic Extraction of Hyperbolic Signatures in Ground Penetrating Radar Images
Authors: Xie Zhenhua , Wei Xiangmin , Zhang Ying
Published: July 2013

Deterioration of concrete structures has become a widespread problem with high repair costs. The corrosion of rebar is one of the major causes. GPR has potential for rebar corrosion detection. But the rapid survey generates a large amount of data, which require an automatic approach for effective data processing and information extraction. This paper proposes an automatic process to effectively extract the rebar reflection in the radargram image and estimate the concrete condition above the rebar. The process uses template matching to locate the hyperbola position, image processing to extract hyperbolic region, and algebraic fitting to rapidly estimate hyperbola parameters. The estimated parameters can be used to calculate the wave propagation velocity and relative permittivity in concrete above the rebar, which can be used to further evaluate the concrete condition. The effectiveness of the proposed method is validated using experiment testing.
An Investigation on the Detectability of Deeper Rebar Layer in Concrete Bridge Decks Using GPR
Authors: Wei Xiangmin , Xie Zhenhua , Zhang Ying
Published: July 2013

Ground penetrating radar (GPR) is one of the most extensively used nondestructive evaluation methods with rapid development in civil engineering in the past few years for its efficiency and high resolution. The evaluation mechanism of concrete materials using GPR is generally based on the reflected signals from the rebar. According to rebar reflections, the corrosion level of the rebar and the material deteriorating condition above the rebar can be deduced. GPR has been successfully applied to shallow subsurface rebar detection in concrete structures. However, very few literatures have addressed the detectability of reflected signal from the deeper layer of rebar. As the result, only a small shallow section of the bridge deck can be evaluated by GPR data so far. In this paper, the detectability of the deeper rebar layer in concrete bridge decks using GPR is investigated with the help of data processing and image processing techniques. The GPR data collected from both a simulation model and a test slab are used to demonstrate the proposed methods and the preliminary results show the reflected signals from the second layer of rebar can be extracted using proposed methods.
Theoretical and Experimental Evaluation of System Energy Balance and Power Generation Efficiency for Piezocomposite Vibration Energy Harvester Under Low Intensity Excitation Condition
Authors: Adachi Kazuhiko , Sakamoto Tatsuya
Published: July 2013

In the authors’ previous study, the vibration energy harvester of the piezoelectric bimorph cantilever type was proposed for vibration condition monitoring applications of industrial rotating machinery. According to an ISO standard, vibration level of newly commissioned class I rotating machinery is under 0.71mm/sec rms in all frequency range. Authors assumed that the typical casing or pedestal vibration amplitude of the rotating machinery was 0.71 mm/sec rms and this low intensity excitation condition was the input for experimental evaluation of the voltage generation performance of the piezocomposit vibration energy harvester. The vibration energy harvester consists of the surface bonded two Macro-Fiber Composites (MFCs). In this study, energy transfer efficiency was derived from the system energy balance during the natural period of the proposed vibration energy harvester. Energy balance equations were successfully obtained from the governing equations of the piezoelectrically coupled electromechanical system. The maximum AC power through 114.3 Kilo-Ohm resistor which includes instrument internal resistances experimentally obtained 242.07 microwatt when subjected to vibration source input magnitude of 0.71 mm/s rms at the resonant frequency of the harvester (29.42 Hz). The impedance matching between MFCs and the electrical resistive load was effective for maximizing AC power transfer of the vibration energy harvester. Estimated energy transfer from mechanical system to electrical system shows the agreement with the experimentally evaluated generating power during the natural period of the vibration energy harvester with about 3% difference. Estimated energy transfer efficiency was about 30% for different excitation magnitudes: 0.71, 0.568 and 0.355 mm/sec rms.
Two Architectures for Bending-Twisting Flapping Using Macro-Fiber Composites
Authors: Samur Algan , Erturk Alper
Published: July 2013

There has been growing interest in the research fields of morphing-wing and flapping-wing aircraft for improved flight efficiency and maneuverability. Recent efforts have focused on the use of smart materials as actuators in biomimetic morphing and flapping. Macro-Fiber Composites (MFCs) are composed of piezoelectric fibers sandwiched between interdigitated electrodes in addition to Kapton and epoxy laminates. The MFC technology offers effective sensing and actuation with its light weight, high flexibility, durability, high performance, and availability in various sizes. Researchers have studied the use of MFCs in structural health monitoring, vibration control, actuation, and energy harvesting. In the last few years, MFCs have been successfully integrated to morphing-wing aircraft by several others. However, there has been limited work on MFC-based flapping wing by dynamic actuation. The flapping-wing flight is more beneficial than conventional flight at relatively small scales due to its high maneuverability. Biological flapping-wing flyers incorporate different wing motions such as dynamic bending, twisting, and folding to create asymmetry for positive lift and thrust resultants. This paper experimentally characterizes the electroelastic dynamics and power consumption of two MFC-based architectures for bio-inspired flapping. The first configuration employs an asymmetric wide bimorph architecture with 0° and 45° piezoelectric fibers to have an actuation authority in bending and twisting. The second configuration uses a double bimorph arrangement made of two narrow bimorphs with 0° fibers with a chord-wise spacing to create both bending and twisting depending on the relative actuation inputs. Both of the bending-twisting architectures considered herein are tested over a wide range dynamic actuation levels and frequencies to characterize the electroelastic response. In addition to measuring the power consumption levels in dynamic bending and twisting, flexible solar films are investigated as the light-weight multifunctional substructure layers that can create both lift surface and electricity toward the concept of self-powered flapping.
Metamaterial Concepts for Structure-Borne Wave Energy Harvesting: Focusing, Funneling, and Localization
Authors: Carrara M. , Cacan M. R. , Toussaint J. , Leamy M. J. , Ruzzene M. , Erturk A.
Published: July 2013

Enhancement of structure-borne wave energy harvesting is investigated by exploiting metamaterial-based and metamaterial-inspired electroelastic systems. The concepts of wave focusing, funneling, and localization are leveraged to establish novel Metamaterial–Energy Harvester (MEH) configurations. The MEH system transforms the incoming structure-borne wave energy into electrical energy by coupling the metamaterial and electroelastic domains. The energy harvesting component of the work employs piezoelectric transduction due to the high power density and ease of application offered by piezoelectric materials. Therefore, in all MEH configurations studied in this work, the metamaterial system is combined with piezoelectric energy harvesting for enhanced electricity generation from waves propagating in elastic structures. Experiments are conducted to validate the dramatic performance enhancement in MEH systems as compared to using the same volume of piezoelectric patch in the absence of the metamaterial component. It is shown that MEH systems can be used for both broadband and tuned wave energy harvesting. Examples include (1) wave guiding using an acoustic funnel, (2) wave focusing using a metamaterial-inspired elliptical acoustic mirror (both for broadband energy harvesting), and (3) energy localization using an imperfection in a 2-D lattice structure (for tuned energy harvesting).
Fish-Like Self Propulsion Using Flexible Piezoelectric Composites
Authors: Cen Lejun , Erturk Alper
Published: July 2013

The capacity of humankind to mimic fish-like locomotion for engineering applications depends mainly on the availability of suitable actuators. Researchers have recently focused on developing robotic fish using smart materials, particularly Ionic Polymer-Metal Composites (IPMCs), as a compliant, noise-free, and scalable alternative to conventional motor-based propulsion systems. In this paper, we investigate fish-like self propulsion using flexible bimorphs made of Macro-Fiber Composite (MFC) piezoelectric laminates. Similar to IPMCs, MFCs also exhibit high efficiency in size, energy consumption, and noise reduction. In addition, MFCs offer large dynamic forces in bending actuation, strong electromechanical coupling as well as both low-frequency and high-frequency performance capabilities. The experimental component of the presented work focuses on the characterization of an MFC bimorph propulsor for thrust generation in a quiescent fluid as well as the development of a preliminary robotic fish prototype incorporating a microcontroller and a printed-circuit-board (PCB) amplifier to generate high actuation voltage for battery-powered free locomotion. From the theoretical standpoint, a reliable modeling framework that couples the actuator dynamics, hydroelasticity, and fish locomotion theory is essential to both design and control of robotic fish. Therefore, a distributed-parameter electroelastic model with fluid effects and actuator dynamics is coupled with the elongated body theory. Both in-air and underwater experiments are performed to verify the incorporation of hydrodynamic effects in the linear actuation regime. For electroelastically nonlinear actuation levels, experimentally obtained underwater vibration response is coupled with the elongated body theory to predict the thrust output. Experiments are conducted to validate the electrohydroelastic modeling approach employed in this work and to characterize the performance of an MFC bimorph propulsor. Finally, a battery-powered preliminary robotic fish prototype is developed and tested in free locomotion.
Comparative Investigation of the Electroelastic Dynamics of Piezoceramics With Interdigitated and Uniform Electrodes
Authors: Cacan Martin , Erturk Alper
Published: July 2013

Piezoelectric systems and structures have been used for decades in a variety of applications ranging from vibration control and sensing to morphing and energy harvesting. Conventional piezoelectric ceramics with uniform electrodes typically employ the 31-mode of piezoelectricity in bending, where the 3- and 1-directions are the directions of poling and strain, respectively. In order to employ the more effective 33-mode of piezoelectricity, Interdigitated Electrodes (IDEs) have been used recently in the design of the Macro-Fiber Composite (MFC). In this paper, an investigation into the two-way electroelastic coupling in bimorph cantilevers (in the sense of direct and converse piezoelectric effects) that employ IDEs for 33-mode operation is conducted. To this end, distributed-parameter electroelastic models are developed for the dynamic scenarios that involve two-way coupling, namely piezoelectric power generation and shunt damping as well as the problem of dynamic actuation. Various interdigitated MFC bimorph cantilevers are tested against the model under dynamic actuation, power generation, and shunt damping to identify their modal electromechanical coupling terms. Detailed investigations are conducted by decoupling the system dynamics to keep the direct and converse effects separately pronounced for parameter identification. Additionally, this work sheds light on the literature comparing the electrical power generation performances of 33-mode (interdigitated electrodes) and 31-mode (uniform electrodes) piezoelectric bimorphs of the same volume based on extensive experiments and distributed-parameter electroelastic modeling.
Optimization of the Charging Process for Dielectric Elastomer Generators
Authors: Graf Christian , Hoffstadt Thorben , Maas Jürgen
Published: July 2013

Energy harvesting using dielectric elastomers is an upcoming possibility to convert ambient energy into electric energy. So far energy harvesting cycles are known and described, in which the charging and discharging of the polymer is realized during a constant stretch phase. In real applications a continuously changing stretch must be assumed, so that the time frames of the charging- and discharging-intervals have a considerable influence on the amount of harvested energy. The contribution of this paper is related to the calculation of the optimal charging- and discharging-intervals to maximize the energy gain. Therefore the physical model of a lossy generator is investigated to derive the converted energy as a function of the timing of the charging- and discharging-interval. Afterwards the optimization is carried out for the most significant harvesting cycles with constant electric field and constant charge. The achievable energy gain of these optimized harvesting cycles are compared to each other and control laws for the realization of harvesting cycles are quoted.
Problems and Solutions for Shape Memory Actuators in Automotive Applications
Authors: Langbein Sven , Czechowicz Alexander
Published: July 2013

The increased automation of technical applications in automobiles requires the use of simple and effective actuator components. The interior of vehicles offer numerous opportunities where mechanical actuators can be or have already been replaced by electrical actuators, e.g. unlocking functions for cup holders or glove boxes. The growing application range of electrical actuators leads to new problems. The growing application range of electrical actuators leads to more weight, sounds and costs. With it the increased automation of technical applications in automobiles requires the use of simple and effective actuator components. Because of the high power density, the simple design and the noiseless actuation of shape memory alloys, they are a solution for this problem. Shape memory alloys are smart materials and have the ability to react to an exterior thermal or electrical stimulus. Besides they can combine sensor and actuator functions in one component. SMAs are rarely used by design engineers although there are numerous possibilities to use them in diverse automotive applications. One reason for this rejection is the effects of functional fatigue in SMA wires. There are no prognosis models or even simulation tools for these effects compared to the many studies on structural fatigue in other materials. After a certain number of cycles, the wire shows an elongation which slowly dislocates its working position. Moreover, with a growing number of cycles, it suffers a loss of effect which results in the reduction of its maximal displacement in technical applications. Another reason is that the transformation temperatures are too low for automotive applications. With it the requirements of a short reactivation time, of a high durability and for an operability in ambient temperatures between −40 and +85°C have been identified as critical for SMA actuators. Therefore, ways to increase these properties by technical means are presented in this study. The idea of “adaptive preload” for example pursues the aim to increase the transformation temperatures and to compensate the existing and inevitable fatigue.
Fluid-Structure Interaction Model of a Synthetic Jet Using Coupled Computational Fluid Dynamics and Finite Elements
Authors: Seeley Charles E. , Weaver Stan , Rush Brian
Published: July 2013

Synthetic jets offer new capabilities for localized active cooling of electronics due to their compact size, low cost and substantial cooling effectiveness. The design of devices to create synthetic jets and optimize active cooling performance is challenging due to the strong, two way, fluid-structure interaction (FSI) between the working fluid and the flexible structure that moves the fluid driven with piezoelectric actuators. Previous modeling efforts relied on lumped parameter approaches or electrical analogs. Although computationally less intensive, these approaches may not be accurate in all regions of the design space of interest and trade off fidelity for ease of use. In this effort, a 3D finite element model of the structure is coupled with a 3D computational fluid dynamics model of the fluid to explore the viability of such an approach. The motion of the structure moves the fluid grid, and the fluid feeds back pressure forces onto the structure that are required to converge at each iteration. Transient response of the deflection, pressure and exit velocity will be presented. Validation of the FSI model with experimental data for the frequency response of these quantities will also be presented.
Design and Fabrication of an SMA Actuated Bat
Authors: Furst Stephen J. , Peele Bryan , Seelecke Stefan
Published: July 2013

Shape memory alloy (SMA) actuator wires provide a natural analog for biological muscles. Additionally, SMA wires are lightweight and have an extremely high energy density, making them desirable for aerospace applications. Therefore, it is natural to consider implementing SMA actuator wires in a flapping flight platform based on the biology of an animal, such as a bat.

This work focuses on the design and fabrication of a bat with SMA-actuated elbow and shoulder joints configured to mimic the flapping pattern of a bat. The joints themselves are made from super-elastic SMA ribbons that can bend through large angles and constrain the rotation of each joint to a single degree of freedom. The design process involves careful consideration of the SMA wire placement and joint geometry such that the desired joint rotation is induced without exposing either the super-elastic joint material or actuator wires to excessive stresses. A simplified bending and force model is used to estimate the bending and stresses, and an optimization algorithm is employed to maximize bending without exceeding stress limits.

Fabrication involves carefully attaching the small, 75 μm diameter, actuator wires such that they can be guided through the natural curves of the bat’s body, and their pre-strain can be tuned after assembly. The heating power input waveforms are shaped by a custom-built power control devise for multi-functional SMA wires such that the flapping motion mimics that of the natural flyer. The prototype has been tested to 100,000 cycles and installed in an exhibit at the Raleigh Museum of Natural Science as an example of how technology often finds inspiration from nature.
Force-Deflection Characteristics of SMA-Based Belleville Springs
Authors: Furgiuele Franco , Maletta Carmine , Sgambitterra Emanuele
Published: July 2013

The thermo-mechanical properties of Nickel-Titanium based Belleville washers have been analyzed by numerical simulations. In fact, these components exhibit unique mechanical and functional features due to the reversible stress-induced and/or thermally-induced phase transition mechanism of NiTi alloys. The numerical simulations have been carried out by using a commercial finite element software code and a special constitutive model for SMAs. The effects of the geometrical configuration of the washers as well as of the operating temperature, under fully austenitic conditions, have been analyzed. The results highlighted a marked hysteretic response, in terms of force-deflection curve, due to the hysteresis in the stress-strain behavior of NiTi alloys. In addition, a marked influence of the geometry, as well as of the temperature, has been observed on the thermo-mechanical response of the washer, i.e. in terms of both mechanical and functional properties.
Towards a Nitinol Actuator for an Active Surgical Needle
Authors: Datla Naresh V. , Honarvar Mohammad , Nguyen Tuan M. , Konh Bardia , Darvish Kurosh , Yu Yan , Dicker Adam P. , Podder Tarun K. , Hutapea Parsaoran
Published: July 2013

Surgical needles, for safe and accurate percutaneaous interventions, need to be navigated accurately through the tissue and placed precisely at the targets. A novel active needle, using Nitinol wires as actuators, has been proposed to navigate the needle within the tissue. In this design, when temperature of Nitinol wire was increased by Joule heating, the material undergoes a phase transformation that produces relatively large actuating forces and strains. Using both experimental and numerical simulations, the force-temperature response of the Nitinol wires were characterized. The results indicate that increasing the applied current decreases the response time to reach maximum force, but increases the maximum temperature reached. Therefore, the chosen applied current should be high enough to produce sufficient actuation force and shorter response time, but not too high such that the lower actuator temperatures are maintained to minimize tissue damage.
Wireless Vibration Sensing Without a Battery
Authors: Huang Haiying , Hew Yayu
Published: July 2013

This paper presents the implementation and characterization of a low power wireless vibration sensor that can be powered by a flash light. The wireless system consists of two components, namely the wireless sensor node and the wireless interrogation unit. The wireless sensor node includes a wireless strain gauge that consumes around 6 mW, a signal modulation circuit, and a light energy harvesting unit. To achieve ultra-low power consumption, the signal modulation circuit was implemented using a voltage-controlled oscillator (VCO) to convert the strain gauge output to an intermediate frequency (IF) signal, which is then used to alter the impedance of the sensor antenna and thus achieves amplitude modulation of the backscattered antenna signal. A generic solar panel with energy harvesting circuit is used to power the strain sensor node continuously. The wireless interrogation unit transmits the interrogation signal and receives the amplitude modulated antenna backscattering, which can be down-converted to recover the IF signal. In order to measure the strains dynamically, a Phase Lock Loop (PLL) circuit was implemented at the interrogator to track the frequency of the IF signal and provide a signal that is directly proportional to the measured strain. The system features ultra-low power consumption, complete wireless sensing, solar powering, and portability. The application of this low power wireless strain system for vibration measurement is demonstrated and characterized.
Small Wind Energy Harvesting From Galloping Using Piezoelectric Materials
Authors: Zhao Liya , Tang Lihua , Yang Yaowen
Published: July 2013

A galloping piezoelectric harvester for small wind energy harvesting usually consists of a cantilever beam clamped at one end and a tip body attached to its free end. The tip body has significant influence on the aeroelastic characteristic of the harvester thus the efficiency of energy harvesting. However, no systematic study on the tip body is available in the literature. This article focuses on the effect of tip body on the performance of the harvester. A prototype device is fabricated with different tip bodies having various cross sections, lengths, and masses. Wind tunnel tests are conducted to determine the influence of these parameters on the power generated. A peak output power of 8.4 mW is achieved at a wind velocity of 8 m/s for the harvester with a tip of square section. An analytical model integrating electromechanical and aerodynamic formulations is established, and the results agree well with the experiments. It is recommended that the tip of square section should be used for galloping energy harvesters.
Novel Dielectric Stack Actuators for Dynamic Applications
Authors: Herold Sven , Kaal William , Melz Tobias
Published: July 2013

In order to realize dielectric elastomer stack actuators suitable for dynamic applications a new actuator design with rigid, perforated electrodes is developed. The low surface resistance of the metal electrodes predestines this concept for dynamic applications where higher currents are present. Detailed numerical analyses are performed to show the potential of this approach, to study the complex material deformation and to optimize the aperture geometry. A multilayer stack actuator is then manufactured and characterized experimentally under various load conditions to gain suitable parameters for a parametrized model. It is subsequently used to attenuate vibrations of a truss structure. By careful adjusting the parameters it functions both as passive absober and as actuator. A comparison of experimental and simulation results proves the high quality of the simulation model. The work shows the great potential of the new design concept for future applications especially in the field of smart structures.
A Study of Actuation Fatigue of Shape Memory Alloy
Authors: Agboola Babatunde O. , Hartl Darren J. , Lagoudas Dimitris C.
Published: July 2013

The use of shape memory alloy (SMA) components as actuators is an attractive option for some aerospace, automotive, and oil and gas exploration applications, especially when installation volume is limited. Fatigue failures constitute a major structural reliability issue confronting industrial entities looking to employ this technology. Knowing and understanding the failure mechanism and resulting fatigue life of SMAs is therefore necessary and useful for design and certification prior to commercial use. An in-house developed experimental set-up based on Joule heating was used to complete a comprehensive set of fatigue tests on SMA actuators composed of a nickel-rich Nickel-Titanium (Ni-Ti) alloy subjected to cyclic thermomechanical loadings. A special forced convective cooling environment has been designed that utilizes compressed air and vortex tubes to maintain the test environment at a temperature well below the martensitic finish temperature. To thermally cycle the specimen, a time controlled scheme developed using LabVIEW was used. The system design allows full thermal cycling of large SMA specimens in approximately 80 seconds. Consequently, each test (comprised of thousands of cycles) takes weeks to be completed. Actuation fatigue life results of a complete test matrix for specimens undergoing full transformation at multiple stress levels are presented. Significant spread was observed in the number of cycles to failure for specimens under same isobaric loading across different choice of applied stress. Post-mortem microscopic observation of failed specimens suggested that failure is linked to cracks initiating within Ni3Ti precipitates. Observations reported further suggest that the failure of the specimen may not be due to plastic strain to failure.
Piezoelectric Two Layer Plate for Position Stabilization
Authors: Krause Martin , Steinert Daniel , Starke Eric , Marschner Uwe , Pfeifer Günther , Fischer Wolf-Joachim
Published: July 2013

Numerous vibrating electromechanical systems miss a rigid connection to the inertial frame. An artificial inertial frame can be generated by a shaker which compensates for vibrations. In this paper we present an encapsulated and perforated unimorph bending plate for this purpose. As basis for system simulation and optimization a new 3-port multi domain network model was derived. An extension of the network allows the simulation of the acoustical behavior inside the capsule. Network parameters are determined using Finite Element simulations. The dynamic behavior of the network model agrees with the Finite Element simulation results up to the first resonance of the system. The network model was verified by measurements on a laboratory setup, too.
Active Distributed Attachment Surfaces: Distributed Latching Technique and Demonstration
Authors: Redmond John A. , Czarnocki Isabel , Luntz Jonathan , Brei Diann , Enke Andrew
Published: July 2013

Latches are essential mechanical elements used to controllably connect multiple bodies throughout industry. Latches conventionally attach bodies at a single point or at a few discrete points, and are designed for multiple operation cycles. Actuator controlled latches, minimize the amount of complexity and costs involved with installation and removal by making the attachment between structures controllable, tool-free and fast. However, the use of multiple single point fasteners carries additional part count, material costs, and labor associated with installation and removal, and can creating load concentrations at attachment sites. Alternatively, surface attachments, such as traditional hook and loop mechanisms, distribute structural connection over an area or across many points reducing stress concentrations, allowing engagement of multiple bodies, maintaining structural connections in nonspecific locations and orientations and reducing labor costs to install and detach bodies. However, performance limitations of conventional surface attachments, such as low retention force, restrict potential applications. An active distributed attachment technique has the potential to increase the performance of conventional distributed attachments, as well as overcome the complexity and operation of conventional point attachments. This paper introduces three active distributed latch approaches (Pegboard, Interlocking Teeth, and Active Velcro) that utilize lightweight, compact SMA actuation. Proof-of-concept prototypes were built, and tested experimentally to investigate the engagement, retention, and release performance. The best performing of the three is demonstrated in a full application scale. The first generation prototypes improved upon the performance of conventional surface attachments and show promise in maintaining the necessary structural attachment for industrial applications.
A Feasibility Investigation on Improving Structural Integrity of Thermoelectric Modules With Varying Geometry
Authors: Erturun Ugur , Mossi Karla
Published: July 2013

This study investigates the feasibility of improving the structural integrity of thermoelectric modules (TEMs) with varying geometry. For this purpose, six different TEM models with various thermoelectric leg geometries were designed and modeled in order to perform a thermal stress FEA using ANSYS Workbench. Temperature dependent material properties were used since some properties such as coefficients of thermal expansion change with temperature. Significant decrease in thermal stresses and leg deformations were observed with some models. Particularly, the cylindrical TE leg geometry model has approximately 54% lower Von Mises stresses (294MPa) and 13% lower TE leg deformations (3.9μm) than those of the typical TE leg geometry model (635MPa and 4.5μm). Power generation analyses of the models were performed to evaluate the effect of new TE leg geometries on the performance. TEM model with cylindrical TE leg geometry has the highest power generation (29.3mW) among all the models.
Analysis of Shape Memory Polymer-Alloy Composites: Modeling and Parametric Studies
Authors: Park Jungkyu , Headings Leon M. , Dapino Marcelo J. , Baur Jeffery W. , Tandon Gyaneshwar P.
Published: July 2013

Shape memory composites (SMCs) based on shape memory alloys (SMAs) and shape memory polymers (SMPs) are interesting due to their controllable temperature-dependent mechanical properties. The complementary characteristics of SMAs and SMPs can be used to create materials or systems with shape recovery created by the SMA and shape fixity provided by the SMP. In this research, three SMC operating regimes are identified and the behavior of SMC structures is analyzed by focusing on composite fixity and interfacial stresses. Analytical models show that certain SMPs can achieve sufficient shape fixing. COMSOL Multi-Physics simulations are in agreement with analytical expressions for shape fixity and interfacial stresses. Analytical models are developed for an end-coupled linear SMP-SMA two-way actuation system.
Optimization of an electron beam lithography instrument for fast, large area writing at 10 kV acceleration voltage
Authors: Greve Martin M. , Holst Bodil
Published: July 2013

Electron beam lithography (EBL) is a maskless lithography technique used in numerous applications for fabrication of ultrahigh-resolution photolithography masks. The main disadvantage of EBL is that it is time-consuming, requiring the pattern to be written in a successive fashion. Various approaches are used to lower the write time. Throughput-oriented EBL instruments used in industrial applications typically apply a very high acceleration voltage (≥50 kV). However, in many research environments, more cost-effective instruments are used. These tools are usually optimized for high-resolution writing and are not very fast. Hence, they are normally not considered very suitable for writing large-scale structures with high pattern densities, even for limited resolution applications. In this paper, the authors show that a carefully considered optimization of the writing parameters in an EBL instrument (Raith e_LiNE) can improve the writing time to more than 40 times faster than commonly used instrument settings. The authors have applied the optimization procedure in the fabrication of high-precision photolithography masks. Chrome photolithography masks, 15 mm in diameter with a write resolution of 200 nm, were routinely produced during overnight exposures (less than 9 h). The write time estimated by the instrument software for most commonly used settings was close to 14 days. A comparison with conventional chrome masks fabricated using a high-resolution (128 000 dpi) photolithography mask printer showed that our pattern definition is significantly better.
Visualizing graphene edges using tip-enhanced Raman spectroscopy
Authors: Su Weitao , Roy Debdulal
Published: July 2013

The edges of a single layer graphene (SLG) flake play important roles in determining the electronic transport properties of graphene devices. Accurate determination of the phase-breaking lengths (Lσ) near the edges remains to be a significant challenge for near field optical measurements. This article presents an image of graphene edges using high resolution tip-enhanced Raman spectroscopy (TERS) of mechanically exfoliated SLG and reports the value of Lσ (4.2 ± 0.5 nm). The current near-field measurements verify the theoretical value of Lσ and highlight the potential of TERS in characterizing graphene at the nanoscale.