bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of Shape Memory Alloy Wire Meshes Using Effective Lamina Properties for Improved Analysis Efficiency
Authors: Peraza-Hernandez Edwin , Hartl Darren , Lagoudas Dimitris
Published: February 2014

Shape memory alloy (SMA) wire meshes are being investigated for their potential effectiveness as active layers in self-folding origami laminates. The currently studied meshes consist of two orthogonal sets of equally spaced parallel SMA wires. The modeling of self-folding laminates with SMA wire meshes becomes computationally demanding at full scale due to the expenses of accurately representing the bending segments of the SMA meshes. Modeling the wires as beam, shell, or three-dimensional entities can be used for such purposes; however, those options become difficult to implement due to the small dimensions of the mesh compared to the full scale self-folding system and the algorithmic complexity of considering the application of heating power to discrete wire regions. A solution to this problem is to model the SMA meshes using an equivalent lamina representation. In this work, an effective lamina model for the representation of the SMA wire meshes that accounts for thermoelastic and inelastic phase transformation behavior is developed. A reduced order version of the effective lamina model is implemented and validated against finite element simulations of an SMA wire mesh considering the same underlying 3D constitutive model. The results show that the effective lamina model accurately predicts the behavior of the fully modeled SMA wire mesh. Future work includes the calibration of the full version of the model and its implementation in a finite element framework.
Concurrent Energy Harvesting From Vibratory Base Excitations and Aerodynamic Flows
Authors: Bibo Amin , Daqaq Mohammed F.
Published: February 2014

This paper presents theoretical and experimental investigations into the potential of utilizing a piezoaeroelastic micropower generator to harvest energy from the combination of an external base excitation and an aerodynamic load. In particular, a harvester consisting of a rigid airfoil supported by a flexural piezoelectric beam and a torsional spring is placed in an incompressible air flow and subjected to an external harmonic base excitation in the plunge direction. Electromechanical equations describing the nonlinear system are given along with theoretical simulations. The performance of the piezoaeroelastic generator is studied experimentally below and above the flutter speed and found to exhibit qualitative agreement with the theory. Below the flutter speed, the response of the harvester is observed to be always periodic with the air flow serving to amplify the influence of the base excitation on the response by reducing the effective stiffness of the system, and hence, increasing the RMS output power. Beyond the flutter speed, the harvester’s response and its performance were observed to depend on the nearness of the excitation frequency to the frequency of the self-sustained oscillations induced by the flutter instability and the magnitude of the base excitation. When the base excitation is small and/or the excitation frequency is not close to the frequency of the self-sustained oscillations, the response of the harvester is two-period quasiperiodic with amplitude modulation due to the presence of two incommensurate frequencies. This amplitude modulation reduces the RMS output power. On the other hand, when the frequency of excitation is close to the frequency of the self-sustained oscillations and/or the amplitude of excitation is large enough to quench the quasiperiodic behavior, the response becomes periodic and the output power increases exhibiting little dependence on the base excitation.
Fiber Bragg Gratings for Heat Flux Measurements in Thermal Protection Systems Under a Steady Conductive Thermal Load
Authors: Hackney Drew A. , Peters Kara J. , Black Richard J. , Costa Joannes M. , Moslehi Behzad , Zarnescu Livia
Published: February 2014

This paper examines the performance of fiber Bragg gratings (FBGs) as embedded heat flux sensors for ablative thermal protection systems (TPS). Ablative TPS materials are currently used for reentry spacecraft applications because ablative TPS materials are able to withstand the higher temperatures present in ballistic reentry than non-ablative materials. It is important to measure the through-the-thickness temperature profile in-situ to verify the heat shielding performance. FBG sensors were chosen to monitor the temperature in the TPS primarily because of a good match in the thermal properties of the silica fibers and the TPS material. A TPS specimen was subjected to a conductive and steady thermal load. Two FBG sensor arrays were embedded in the TPS specimen. One array was embedded horizontally in the specimen near the surface where the heat was applied, and the second array was embedded diagonally through the thickness of the specimen. The temperature load was produced using the lower platen of a hot press, and the maximum temperature was below the ablation temperature of the material. After the specimen was heated, it was removed from the hot press and allowed to passively cool on a metal table. The peak wavelength output from each sensor was monitored and recorded during the loading cycle, and the wavelength measurements were converted to temperature data over time. The test was completed three times, and excellent repeatability was present across the three tests and the temperature response of the FBGs was reasonable, even though the test setup was torn down and reassembled between two of the tests. Thermal images of the specimen were also collected during the test with an IR camera. The thermal images were used to provide a temperature map of the specimen which showed good agreement with the FBG data.
Analytical Electromechanical Model of Cantilevered Bi-Stable Composites for Broadband Energy Harvesting
Authors: Arrieta Andres F. , Delpero Tommaso , Ermanni Paolo
Published: February 2014

Vibration based energy harvesting has received extensive attention in the engineering community for the past decade thanks to its potential for autonomous powering small electronic devices. For this purpose, linear electromechanical devices converting mechanical to useful electrical energy have been extensively investigated. Such systems operate optimally when excited close to or at resonance, however, for these lightly damped structures small variations in the ambient vibration frequency results in a rapid reduction of performance. The idea to use nonlinearity to obtain large amplitude response in a wider frequency range, has shown the potential for achieving so called broadband energy harvesting. An interesting type of nonlinear structures exhibiting the desired broadband response characteristics are bi-stable composites. The bi-stable nature of these composites allows for designing several ranges of wide band large amplitude oscillations, from which high power can be harvested. In this paper, an analytical electromechanical model of cantilevered piezoelectric bi-stable composites for broadband harvesting is presented. The model allows to calculate the modal characteristics, such as natural frequencies and mode shapes, providing a tool for the design of bi-stable composites as harvesting devices. The generalised coupling coefficient is used to select the positioning of piezoelectric elements on the composites for maximising the conversion energy. The modal response of a test specimen is obtained and compared to theoretical results showing good agreement, thus validating the model.
Effect of Processing and Loading on Equiatomic NiTi Fatigue Life and Localized Failure Mechanisms
Authors: Wheeler Robert , Santa-Cruz Judy , Hartl Darren , Lagoudas Dimitris
Published: February 2014

Shape Memory Alloys (SMAs) have many promising applications in the aerospace, automotive, and energy industries. However, due to a lack of understanding of their actuation fatigue, applications are sometimes limited to non-structural or non-critical components. This paper addresses the actuation fatigue characteristics of a specific SMA, equiatomic Nickel-Titanium (NiTi), with varying heat treatments, as well as different methods for assessing actuation fatigue response, including improved testing procedures and distributed extension measurement methods. Heat treatments ranged from 350°C to 400°C for one to three hours. Dogbone specimens processed from heat treated NiTi sheets were mechanically loaded on test frames which provided resistive heating and forced convective cooling with dry air via vortex tubes. Two mechanical loading schemes were utilized: constant uniaxial load (initial stress of 200MPa) and a linear or spring load centered at 200MPa (and ranging from approximately 150MPa to 250MPa). Linear loading schemes were introduced in order to better simulate actuation in an aerospace application, such as the morphing of semi-rigid surfaces. Specimens were thermally cycled to full actuation with a time-based control scheme developed in LabVIEW. Fatigue responses varied widely as a result of different heat treatments and loading schemes. Due to the main failure mechanism being high localized extension (necking) for the constant loading schemes, additional hardware and software were developed to visually capture extension distribution over specimen length. By analyzing actuation characteristics (e.g. transformation strain) and fatigue mechanisms, the ideal post-processing for actuator applications was determined. Utilizing the local extension distribution evolution over the fatigue life of NiTi specimens as well as postmortem analysis of the failure surfaces allowed for the failure modes to be determined for each heat treatment.
Piezoelectric Energy Harvesting From Nonlinear Aeroelastic Vibrations
Authors: Vieira Wander Gustavo Rocha , De Marqui Junior Carlos
Published: February 2014

In this paper, the modeling and analysis of a nonlinear rectangular plate-like wing with embedded piezoceramics is presented for aeroelastic energy harvesting. The nonlinear electromechanical finite-element plate model is based on the von Karman plate assumptions while the unsteady aerodynamic model uses the doublet-lattice method (originally in frequency domain). The aerodynamic model is converted to the time domain by using Roger’s approximation. A load resistance is considered in the electrical domain of the problem. The set of nonlinear equations is solved with the iterative Newton-Raphson method and the generalized alpha method is used to numerically integrate the equations. Five different wing configurations with aspect ratios varying from one to five are investigated. The effect of the aspect ratio on the linear aeroelastic behavior is first investigated for the short circuit condition. Later, the nonlinear electroaeroelastic behavior is investigated for a range of load resistances and the different aspect ratios of the linear case. The effects of aspect ratio and load resistance on the cut-in speed of limit cycle oscillations (LCOs), on the range of airflow speeds of LCOs of acceptable amplitudes and also on the mechanical and electrical outputs of the generator are investigated.
Power Density Performance Improvements for High Pressure Ripple Energy Harvesting
Authors: Verma Nalin , Cunefare Kenneth A. , Skow Ellen , Erturk Alper
Published: February 2014

A hydraulic pressure energy harvester (HPEH) device, which utilizes a housing to isolate a piezoelectric stack from the hydraulic fluid via a mechanical interface, generates power by converting the dynamic pressure within the system into electricity. Prior work developed an HPEH device capable of generating 2187 microWatts from an 85 kPa pressure ripple amplitude using a 1387 mm3 stack. A new generation of HPEH produced 157 microWatts at the test conditions of 18 MPa static pressure and 394 kPa root-mean-square pressure amplitude using a 50 mm3 stack, thus increasing the power produced per volume of piezoelectric stack principally due to the higher dynamic pressure input. The stack and housing design implemented on this new prototype device yield a compact, high-pressure hydraulic pressure energy harvester designed to withstand 35 MPa. The device, which is less than a 2.54 cm in length as compared to a 5.3 cm length of a previous HPEH, was statically tested up to 21.9 MPa and dynamically tested up to 19 MPa with 400 kPa root-mean-square dynamic pressure amplitude. An inductor was included in the load circuit in parallel with the stack and the load resistance to increase the power output of the device. A previously developed electromechanical power output model for this device that predicts the power output given the dynamic pressure ripple amplitude is compared to the power results. The power extracted from this device would be sufficient to meet the proposed applications of the device, which is to power sensor nodes in hydraulic systems.
Design and Experimental Validation of a Metacomposite Made of an Array of Piezopatches Shunted on Negative Capacitance Circuits for Vibroacoustic Control
Authors: Tateo F. , Collet M. , Ouisse M. , Ichchou M. N. , Cunefare K. A.
Published: February 2014

In the last few decades, researchers have given a lot of attention to new engineered materials with the purpose of developing new technologies and devices such as mechanical filters, low frequency sound and vibration isolators, and acoustic waveguides. For instance, elastic phononic crystals may come to mind. They are materials with elastic or fluid inclusions inside a matrix made of an elastic solid. The anomalous behavior in phononic crystals arises from interference of waves propagating within an inhomogeneous material. The inclusions inside the matrix cause strong modifications of scattering properties. However, the application of phononic crystals is still limited to sonic frequencies. In fact, band gaps can be generated only when the acoustic wavelength is comparable to the distance between the inclusion. In order to overcome this limitation, a new class of metamaterial has been proposed: meta composite. This new class of material can modify the dynamics of the underlying structure using a bidimensional array of electromechanical transducers, which are composed by piezo patches connected to a synthetic negative capacitance. In this study, an application of the Floquet-Bloch theorem for vibroacoustic power flow optimization will be presented. In the context of periodically distributed, damped 2D mechanical systems, this numerical approach allows one to compute the multimodal waves dispersion curves into the entire first Brillouin zone. This approach also permits optimization of the piezoelectric shunting electrical impedance, which controls energy diffusion into the proposed semiactive distributed set of cells. Experiments performed on the examined structure illustrates the effectiveness of the proposed control method. The experiment requires a rectangular metallic plate equipped with seventyfive piezopatches, controlled independently by electronic circuits. More specifically, the out-of-plane displacements and the averaged kinetic energy of the controlled plate are compared in two different cases (control system on/off). The resulting data clearly show how this proposed technique is able to dampen and selectively reflect the incident waves.
Correlations Between Quantum Mechanics and Continuum Mechanics for Ferroelectric Material Simulations
Authors: Oates William S.
Published: February 2014

Higher order effects in ferroelectric materials are investigated by integrating electron density calculations using quantum mechanics into a homogenized, nonlinear continuum modeling framework. Electrostatic stresses based on the Hellmann-Feynman theorem are used to identify connections with the higher order quadrupole density. These higher order relations are integrated into a nonlinear mechanics free energy function to simulate electromechanical coupling. A specific example is investigated by conducting density functional theory (DFT) calculations on barium titanate and fitting the results to a thermodynamic potential function. Through the use of nonlinear geometric effects, electromechanical coupling is obtained without the use of electrostrictive or piezoelectric coupling coefficients.
Design and Characterization of Piezo-Based Stereocilia
Authors: Vandaele Mathieu , Joyce Bryan S. , Tarazaga Pablo A.
Published: February 2014

The hair cells in the cochlea are responsible for transforming sound-induced vibration into electrical signals. Damage to these hair cells is among the most common forms of hearing loss in the developed world. Researchers have studied various artificial hair cell (AHC) designs for replacing these hair cells. One such method uses piezoelectric beams to mimic the hair cell’s mechanoelectrical transduction. A piezoelectric beam will produce an electric potential from an applied sound pressure. In the literature, the response of the cochlea to sound pressures is often described using tuning curves. Tuning curves plot the sound pressure level at a given frequency which produces a particular displacement, velocity, or neuron firing rate. The work presented here examines using piezoelectric AHC’s to mimic cochlear hair cells by creating tuning curves of constant tip velocity and voltage. A piezoceramic (PZT) beam and a piezo film (PVDF) bending sensor are examined. An output feedback controller based on PID control is developed to vary the sound pressure from a speaker to create tuning curves for the piezoelectric AHC’s. The tuning curves for the piezoelectric beams are compared to measurements obtained from the biological cochlea.
Biaxial Mechanical Characterization of Bat Wing Skin and Development of Biomimetic Constructs
Authors: Skulborstad A. J. , Goulbourne N. C.
Published: February 2014

The highly flexible and extensible wing skin of bats enables various wing shapes and flight modes, which distinguishes it from all other natural flyers making bats an ideal model for micro-aerial vehicles. We propose that an understanding of the relationship between the structure, properties and function of the wing tissue is essential to replicate and utilize the bat’s natural capabilities. In this work, we present the first biaxial mechanical characterization of bat wing skin, identify key mechanisms in its deformation, and employ these concepts to fabricate biomimetic skins. Ten Glossophaga soricina bat specimens were available for experiment obtained from Prof. Swartz or Brown University. Of the 20 excised wing skin samples, 11 were used for establishing testing protocols, 3 tore during preparation, and 6 were tested for the characterization presented in this work. The tissue was shown to be nonlinear, heterogeneous, anisotropic, and viscoelastic. The wrinkled tissue structure and substantial anisotropy promote great spanwise deployment and deformation increasing wing area and aspect ratio enabling greater lift generation. Comparison of the material structural organization with strain field responses demonstrated that the underlying fiber architecture corresponds to observed local strain variations and that the tissue represents a departure from traditional fiber reinforced materials since the mesoscopic elastin fiber architecture appears to be the soft component while the matrix provides the stiffening role. Fabricated skins capture the inherent mismatch in natural configurations of the spanwise elastin fibers and the matrix and exhibit the characteristic wrinkle pattern observed in the in vivo bat wing skin. Future work will include static mechanical testing of the synthetic skins as well as aerodynamic testing to investigate the link between tissue structure, properties and functional flight capabilities.
Self-Powered Sensing System for the Monitoring of Quasi-Static Structural Response
Authors: Lajnef Nizar , Burgueño Rigoberto , Chakrabartty Shantanu , Borchani Wassim
Published: February 2014

Many signals of interest in the assessment of structural systems lie in the quasi-static range (frequency ≪ 1Hz). This poses a significant challenge for the development of self-powered sensors that are required not only to monitor these events but also to harvest the energy for sensing, computation and storage from the signal being monitored. This paper combines the use of mechanically-equivalent frequency modulators and piezo-powered threshold detection modules capable of computation and data storage with a total current less than 10nA. The system is able to achieve events counting for input deformations at frequencies lower than 0.1Hz.

The used mechanically-equivalent frequency modulators allow the transformation of the low-amplitude and low-rate quasi-static deformations into an amplified input to a piezoelectric transducer. The sudden transitions in unstable mode branch switching, during the elastic postbuckling response of slender columns and plates, are used to generate high-rate deformations. Experimental results show that an oscillating semi-crystalline plastic polyvinylidene fluoride (PVDF), attached to the up-converting modules, is able to generate a harvestable energy at levels between 0.8μJ to 2μJ.

In this work, we show that a linear injection response of our combined frequency up-converter / piezo-floating-gate sensing system can be used for self-powered measurement and recording of quasi-static deformations levels. The experimental results demonstrate that a sensor fabricated in a 0.5-μm CMOS technology can count and record the number of quasi-static input events, while operating at a power level significantly lower than 1μW.
Speed of Sound Measurement in Solids Using Polyvinylidene Fluoride (PVDF) Sensors
Authors: Headings Leon M. , Kotian Kunal , Dapino Marcelo J.
Published: February 2014

Piezoelectric film sensors such as polyvinylidene flouride (PVDF) generate an electrical voltage in response to an applied mechanical stress with a remarkably high sensitivity. They provide very fast response times and do not require extensive signal conditioning. This paper presents a straightforward method of measuring the speed of sound in solid materials and structures using commercial PVDF sensors.

PVDF sensors are most commonly used to measure stresses applied in the sensors’ thickness direction. However, this requires that the sensors be located in the load path, which may result in damage to the sensor or affect the response of the system. In this paper, two PVDF sensors are bonded to the side of a structure and a small impact is applied to one end. The sensors are used to measure the time for the impact-induced plane stress wave to travel between the sensors. The observed speed of the propagating stress wave is shown to be in good agreement with the theoretical speed of sound for the material and finite element calculations. In addition, the finite element simulations confirm the validity of the plane wave assumption for non-ideal and non-uniform impact inputs.
Research on Time Delay of MR Buffer System Under Impact Load
Authors: Zheng Jiajia , Li Zhaochun , Wang Jiong , Koo Jeong Hoi
Published: February 2014

The primary purpose of this paper is to provide a comprehensive review on the time delay of impact MR buffer system. The phenomenon of time delay which occurs in most of the MR buffer systems has been given little attentions especially in the applications where little time delay is demanded. Furthermore, the methods of reducing time delay have not been discussed in detail. So, in this study, several efforts have been made to decrease or even eliminate the phenomenon of time delay. Firstly, we analyzed two kinds of power supply sources and coil winding patterns. Next, an advanced correcting circuit was designed and the parameters of transfer function were determined by experimental data. The results show that, compared with the original circuit, it only takes 5ms to achieve 95% of the final state after correction, which increases 75% immediately. Furthermore, to evaluate the effect of compensation control strategy on time delay, the adaptive Smith compensation control was adopted and tested. Using the open on-off control strategy, four operating start times of current were applied, ranging from 0 to 300ms in increments of 100ms. The results show that the original maximum time delay is more than 150ms and it can be reduced to less than 50ms by adaptive smith compensation. Further analysis illustrates that decreasing time delay improves the dynamic performance of MRD in the buffer process, such as decreased overshoot, less fluctuation etc.
The Impact of Boundary Conditions on the Response of NiMnGa Samples in Actuation and Power Harvesting Applications
Authors: Nelson Isaac , Ciocanel Constantin , LaMaster Doug , Feigenbaum Heidi
Published: February 2014

Magnetic shape memory alloys (MSMAs) are materials that can display up to 10% recoverable strain in response to the application of a magnetic field or compressive mechanical stress. The magnetomechanical response of the material makes MSMAs suitable for applications such as actuation, sensing, and power harvesting. While the magnetomechanical response of the material has been extensively investigated to date, there is no report in the literature on the effect of the boundary conditions (BCs) on its response.

The response of MSMAs is primarily driven by the reorientation of internal martensite variants, in conjunction with rotation of magnetization vectors, and domain wall motion. During the reorientation process a change in material’s magnetization occurs. For sensing and power harvesting applications, a pick-up coil may be used to convert this change in magnetization into an electric potential/voltage. To date, it has been confirmed experimentally that, according to Faraday’s law of induction, the magnitude of the output voltage depends on the number of turns of the pick-up coil, the amplitude of the reorientation strain, the magnitude and direction of the biased magnetic field, and the frequency at which the reorientation occurs. However, to our knowledge, no study has been carried out to investigate the effect of the BCs on the voltage output.

This paper examines the effect of the BCs on the material’s magnetomechanical response, as well as on the corresponding voltage output. Three BCs are considered in the performed experiments: i) simply supported, ii) clamped, and iii) mixed (i.e. one end clamped and one end guided). The difference observed in the magnetomechanical response of the material, between the tested BCs, is attributed to the local effects caused by the grips (particularly the clamped and mixed conditions) and by the rotation of the specimen within the grips (in the simply supported condition). The latter is facilitated by the difference between the cross section of the specimen and the cross section of the cavity receiving the sample and by the larger effective length of the specimen in this case.
Functional Characterization of NiTi Shape Memory Elements for Smart Micro-Actuation
Authors: Biffi Carlo Alberto , Bonacina Luca , Nespoli Adelaide , Previtali Barbara , Tuissi Ausonio
Published: February 2014

Shape Memory Alloys (SMAs) are smart and functional materials, which are considered good candidates for the activation of devices for the automotive, aerospace, biomedical and mechanical systems, thanks to the shape memory effect. In this work, a study on the mechanical response of NiTi SMA snake like elements has been proposed. The production route of these elements from thin sheets, was given by laser machining followed by chemical etching. The micro-elements were characterized by means of calorimetric analysis for the definition of the theoretical operating temperatures and by means of thermo-mechanical testing for the evaluation of their functional performances. Mechanical tests has been carried out to assess the tensile behavior of martensite and austenite separately, and to evaluate the thermal hysteresis under different constant loads. Moreover, Finite Element Modeling (FEM) has been also accomplished to study the numerical evaluation of the stress field that origins by the application of the different loads in both the martensitic and austenitic phases.
Fiber Bragg Grating Strains to Obtain Structural Response of a Carbon Composite Wing
Authors: Nicolas Matthew J. , Sullivan Rani W. , Richards W. Lance
Published: February 2014

The objective of this study was to determine the deflected wing shape and the out-of-plane loads of a large-scale carbon-composite wing of an ultralight aerial vehicle using Fiber Bragg Grating (FBG) technology. The composite wing, subjected to concentrated and distributed loads, was instrumented with an optical fiber on its top and bottom surfaces positioned over the main spar, resulting in approximately 780 strain sensors bonded to the wings. The in-plane strains from the FBG sensors were used to obtain the out-of-plane loads as well as the wing shape at various load levels using NASA-developed real-time load and displacement algorithms. The calculated out-of-plane displacements and loads were generally within 4% of the measured data.
Effects of Altitude on Active Structural Health Monitoring
Authors: Cooper Benjamin , Zagrai Andrei , Kessler Seth
Published: February 2014

As the field of Structural Health Monitoring (SHM) expands to spacecraft applications, the understanding of environmental effects on various SHM techniques becomes paramount. In January of 2013, an SHM payload produced by New Mexico Tech was sent on a high altitude balloon flight to a full altitude of 102,000 ft. The payload contained various SHM experiments including impedance measurements, passive detection (acoustic emission), active interrogation (guided waves), and wireless strain/temperature sensing. The focus of this paper is the effect of altitude on the active SHM experiments. The active experiment utilized a commercial SHM product for generation and reception of elastic waves that enabled wavespeed measurements, loose bolt detection, and crack detection through the full profile of the flight. Definite deviations were observed in the data through the stages of the flight which included a ground, ascent, float, and descent phases. Several elements of the high altitude environment can have an effect on the measurement such as temperature and pressure. The flight data was compared against a ground altitude baseline and heavy emphasis is placed on comparing changes in the data with the temperature profile of the flight. Conclusions are drawn on the effect of altitude on wavespeed of elastic waves, crack detection, and the sensing of a loose bolt.
Field-Driven Phase Transformations in Relaxor Ferroelectric Single Crystals
Authors: Gallagher John A. , Lynch Christopher S.
Published: February 2014

Relaxor ferroelectric single crystals such as PMN-PT and PIN-PMN-PT undergo field driven phase transformations when electrically or mechanically loaded in crystallographic directions that provide a positive driving force for the transformation. The observed behavior in certain compositions is a phase transformation distributed over a range of field levels without a distinct forward or reverse coercive field. This work focuses on the material behavior that is observed when the crystals are loaded sufficiently to drive a partial transformation and then unloaded as might occur when driving a transducer to achieve high power levels. A set of experiments was conducted to characterize the minor hysteresis loops that occur with the partial transformations. Distributed transformations have been modeled using a Gaussian distribution of transformation thresholds. In this work the Gaussian model is extended to include the partial transformations that occur when the field is reversed before the transformation is complete. The resulting minor hysteresis loops produced by the model are in good agreement with the experimental results.
On the Dielectric and Mechanical Behavior of Metal Oxide-Modified PVDF-Based Nanocomposites
Authors: Khodaparast Payam , Ounaies Zoubeida
Published: February 2014

Nanoparticle modified polymers have promise as hybrid materials that exhibit properties beyond those predicted by mixing law theories. In the case of metal-oxide nanoparticles in a polymer, it is expected that multifunctional properties of the obtained nanocomposite, including dielectric and mechanical, will be dominated by presence of interface rather than predicted by the inherent properties of individual components. This paper will focus on understanding the role of different types of nanoparticles, namely, titania, silica and alumina and a polymer matrix, Polyvinylidene fluoride (PVDF) in affecting the final dielectric and mechanical properties.
Experimental Investigation of Temperature Effects on Dielectric Electro-Active Polymer Actuators and Sensors
Authors: York Alexander , Seelecke Stefan
Published: February 2014

Dielectric electro-active polymers (DEAP) are an attractive material for use in actuator technologies due to their lightweight, high energy density, high energy efficiency, scalability and low noise features. In real world applications, DEAP actuators and sensors will be subjected to various environmental conditions such as changing temperatures. The effects of these environmental changes need to be understood in order to not only optimize performance, but also document environmental limitations and possibly protect against or compensate for them. This paper presents a systematic experimental investigation of the mechanical and electrical behavior of a silicone based DEAP actuator/sensor under varying controlled temperature conditions. Measurements are performed in a climactic chamber with controlled temperatures from −10 to +60 °C. During these tests, a particular focus was placed on the mechanical hysteresis and viscoelastic effects for actuator performance and on the changes in capacitance for sensor performance. For various constant temperatures, the DEAP was subjected to out of plane displacement loading, while the force and capacitance was measured. The effects of the viscous component of the viscoelastic DEAP material is shown to decrease with increased temperature. The capacitance of the DEAP is also shown to decrease with increased temperature. These results will effect actuator and sensor performance respectively and will be used for DEAP application design considerations and improve future modeling efforts.
Modeling and Closed Loop Control of Contraction in a Pneumatic Artificial Muscle
Authors: Bubert Edward , Kothera Curt S. , Wang Gang , Wereley Norman M.
Published: February 2014

Pneumatic Artificial Muscles (PAMs) are remarkable for their simplicity, light weight, high stroke, and high force. PAMs are used extensively in robotics applications where actuator bandwidth requirements are relatively low (e.g., < 1 Hz) compared to aerospace applications where higher bandwidth is needed (e.g., as high as 30 Hz in rotor vibration control). Because PAMs couple large stroke with high specific actuation force, adapting PAMs to aerospace applications may provide a substantial gain in performance over conventional hydraulic and pneumatic actuators. This study develops a semi-empirical, nonlinear, pneumo-mechanical analysis of the time histories of pressure, force, and displacement, which is validated using experimental response data from a single PAM working against a spring and mass. A linear proportional + integral + derivative (PID) controller was then tuned analytically to achieve command following of sinusoids. Frequency responses are obtained via both simulation and experiment, and the ability to track relatively high frequency control inputs is demonstrated for periodic motions up to 24 Hz.
Model-Based Shape Memory Alloy Wire Ratchet Actuator Design
Authors: Kim Wonhee , Utter Brent , Luntz Jonathan , Brei Diann , Muhammad Hanif , Alexander Paul
Published: February 2014

Shape Memory Alloy (SMA) wire ratchet actuators overcome SMA wire strain limitations by accumulating actuation stroke over multiple cycles. The underlying architecture is effective for producing large strokes from a small package, creating continuous rotation or extended displacement, and precise. It also provides discrete positioning with zero-power hold. While there have been several successful implementations of SMA ratchet actuators, most are designed ad-hoc since limited models exist to predict the stroke and force interaction during actuation cycles. Since the SMA wire actuation is highly dependent on the forces experienced through the ratchet mechanism, a model requires the prediction of the force interaction between the rack and pawl teeth along with friction in the device, and of the external force variation over actuation cycles due to the relative position change between the external system and the SMA wire. This paper presents a model-based systematic design methodology for SMA ratchet actuator which actuates position-dependent external systems. A generalized ratchet mechanism and operation sequence is introduced along with a force balance model for both austenite and martensite equilibrium to address the mechanical coupling changes. Analytical kinematic and kineto-static rack and pawl interaction models are reviewed, which feed into the force balance models. The effective stroke is evaluated by subtracting backlash from the SMA wire stroke, found through equilibrium with the mechanism and external system. This effective stroke accumulates to produce the overall actuator motion. A design methodology is suggested along with visualization methods to aid design decisions. Parametric studies expose the effects of design parameters on the SMA ratchet actuator to gain further design insight. This model-based design foundation and parametric understanding enable the synthesis of SMA wire ratchet actuators.
Effect of Bending and Mushrooming Damages on Heat Transfer Characteristic in Labyrinth Seals
Authors: Yan Xin , Lei Lijie , Li Jun , Feng Zhenping
Published: February 2014

Using conjugate heat transfer calculations, the heat transfer in straight-through labyrinth seals with and without rub damages (bending and mushrooming damages) were numerically investigated. Firstly, the numerical methods were carefully validated on the basis of obtained experimental data. At two different sealing clearances and a range of Reynolds numbers, Nu distributions on the seal rotor and stator surfaces for the original design cases were numerically computed and compared to the experimental data. The temperature fields in the fluid and inside the solid domains were obtained to account for the heat transfers between fluid and adjacent solids. Then, a range of bending angles, wear-off ratios and mushrooming radiuses were selected to investigate the influence of rub damages on heat transfer characteristic in the labyrinth seals, and the numerical results were also compared to that of original design cases. The results show that the calculated Nu distributions are in good agreement with the experimental data at a range of Re numbers and different sealing clearances. The turbulence model has pronounced effect on the heat transfer computations for the labyrinth seal. Among the selected eddy viscosity turbulence models, the low-Re k-ω and SST turbulence models show superior accuracy to the standard k-ε and RNG k-ε turbulence models, which over-predict Nu by about 70%. Bending damage reduces Nu on the labyrinth fin whereas enhances heat transfer on the opposite smooth stator. The effect of bending angle on Nu distribution on the seal stator surface is larger than on the rotor surface. The mushrooming damage has pronounced effect on Nu distributions on both rotor and stator surfaces for the labyrinth seal. It shows that Nu distributions on the rotor and stator surfaces decreases with the increase of mushrooming radius, but increases with the increase of wear-off ratio and Re.
Optimizing the Tip Section Profiles of a Steam Turbine Blading
Authors: Dvořák Rudolf , Šafařík Pavel , Luxa Martin , Šimurda David
Published: February 2014

Though there is not much freedom in shape modification of profiles for tip sections of steam turbines of large output, there is still enough space for optimizing these profiles. The constraints are already in the thermodynamic design of the last stage blading. The layout of the tip cascade indicates that the optimizing strategy should primarily concern the leading edge region and the trailing edge. Proper design can cut down both the front and exit shock wave intensities and the shock wave direct and indirect losses, as well as attenuate the interacting shock waves. This “partial optimization” method has been experimentally verified and is presented in this paper.
Measurement of Blade Tip Heat Transfer and Leakage Flow in a Turbine Cascade With a Multi-Cavity Squealer Tip
Authors: Park Jung Shin , Lee Sang Hoon , Kwak Jae Su , Lee Won Suk , Chung Jin Taek
Published: February 2014

Tip leakage flow induces high heat transfer to the blade tip and causes significant aerodynamic losses. In this paper, we propose a multi-cavity squealer tip with an additional rib in the squealer cavity. Our study investigated the effects of the rib location and shape on the blade tip heat transfer and the total pressure loss. Experiments were performed in a five-bladed linear cascade using a low speed wind tunnel. The blade chord, pitch, and span length were 126mm, 102.7mm, and 160mm, respectively. The Reynolds number, based on the blade chord and cascade exit velocity, was 2.44×105, and a tip clearance of 1.25% of the blade span was considered. The additional rib was installed in the squealer tip cavity near the leading edge, the mid-chord, and the training edge, respectively. The shape of the rib was also varied from rectangular to triangular in order to minimize the rib surface area exposed to the hot gas. The secondary flow and total pressure loss were measured using a seven-hole probe at one-chord downstream of the blade trailing edge, and the heat transfer coefficient distributions were measured by utilizing the hue-detection based transient liquid crystal technique. Flow measurement results indicated that the proposed multi-cavity tip reduced the total pressure loss. The blade tip heat transfer measurement results showed that the proposed multi-cavity tip was able to reduce the maximum heat transfer region near the cavity floor near the leading edge, but the heat transfer on the second cavity floor increased due to the leakage flow reattachment.
Monte Carlo dosimetry for 103Pd, 125I, and 131Cs ocular brachytherapy with various plaque models using an eye phantom
Authors: Lesperance Marielle , Martinov M. , Thomson R. M.
Published: February 2014

Purpose:

To investigate dosimetry for ocular brachytherapy for a range of eye plaque models containing103Pd, 125I, or 131Cs seeds with model‐based dose calculations.

Methods:

Five representative plaque models are developed based on a literature review and are compared to the standardized COMS plaque, including plaques consisting of a stainless steel backing and acrylic insert, and gold alloy backings with: short collimating lips and acrylic insert, no lips and silicone polymer insert, no lips and a thin acrylic layer, and individual collimating slots for each seed within the backing and no insert. Monte Carlo simulations are performed using the EGSnrc user‐code BrachyDose for single and multiple seed configurations for the plaques in water and within an eye model (including nonwater media). Simulations under TG‐43 assumptions are also performed, i.e., with the same seed configurations in water, neglecting interseed and plaque effects. Maximum and average doses to ocular structures as well as isodose contours are compared for simulations of each radionuclide within the plaque models.

Results:

The presence of the plaque affects the dose distribution substantially along the plaque axis for both single seed and multiseed simulations of each plaque design in water. Of all the plaque models, the COMS plaque generally has the largest effect on the dose distribution in water along the plaque axis. Differences between doses for single and multiple seed configurations vary between plaque models and radionuclides. Collimation is most substantial for the plaque with individual collimating slots. For plaques in the full eye model, average dose in the tumor region differs from those for the TG‐43 simulations by up to 10% for125I and 131Cs, and up to 17% for 103Pd, and in the lens region by up to 29% for 125I, 34% for 103Pd, and 28% for 131Cs. For the same prescription dose to the tumor apex, the lowest doses to critical ocular structures are generally delivered with plaques containing 103Pd seeds.

Conclusions:

The combined effects of ocular and plaque media on dose are significant and vary with plaque model and radionuclide, suggesting the importance of model‐based dose calculations employing accurate ocular and plaque media and geometries for eye plaque brachytherapy.
Method of measuring NEQ as a quality control metric for digital mammography
Authors: Bloomquist Aili K. , Mainprize James G. , Mawdsley Gordon E. , Yaffe Martin J.
Published: February 2014

Purpose:

Current quality control protocols for digital mammography rely on subjective assessments of image quality or simple measures that are not comparable between vendor platforms. The noise‐equivalent quanta (NEQ) can be expressed in units of image quanta (fluence) for the spatial frequency range of interest, enabling comparisons between systems and x‐ray spectra. The purpose of this work is to explore use of a simple phantom to measure the components of the noise‐equivalent quanta of digital mammography systems for use in routine quality control.

Methods:

A simple phantom is imaged on six mammography systems from different vendors. The phantom contains uniform regions for measurement of noise power spectrum (NPS), slanted edges for measurement of modulation transfer function (MTF), and objects of various thicknesses for measurement of contrast. Images were acquired at a range of dose levels on each system to examine how measurements scale with dose, and multiple images were taken at a single dose point to examine measurement reproducibility.

Results:

The phantom and measurement methods show good reproducibility, with average coefficient of variation values of less than or equal to 15% on all systems evaluated. Measured MTF and NPS values are comparable to other published results when the increase in scattered radiation generated by placing the phantom on the breast support is accounted for.

Conclusions:

Measurement of the parameters required to calculate NEQ from a single image of a simple phantom is practical, and shows promise as a method of evaluating image quality for routine quality control of digital mammography systems.
Susceptibility to interference by music and speech maskers in middle-aged adults
Authors: Başkent Deniz , van Engelshoven Suzanne , Galvin John J.
Published: February 2014

Older listeners commonly complain about difficulty in understanding speech in noise. Previous studies have shown an age effect for both speech and steady noise maskers, and it is largest for speech maskers. In the present study, speech reception thresholds (SRTs) measured with competing speech, music, and steady noise maskers significantly differed between young (19 to 26 years) and middle-aged (51 to 63 years) adults. SRT differences ranged from 2.1 dB for competing speech, 0.4–1.6 dB for music maskers, and 0.8 dB for steady noise. The data suggest that aging effects are already evident in middle-aged adults without significant hearing impairment.
Learning to detect a tone in unpredictable noise
Authors: Jones Pete R. , Moore David R. , Shub Daniel E. , Amitay Sygal
Published: February 2014

Eight normal-hearing listeners practiced a tone-detection task in which a 1-kHz target was masked by a spectrally unpredictable multitone complex. Consistent learning was observed, with mean masking decreasing by 6.4 dB over five sessions (4500 trials). Reverse-correlation was used to estimate how listeners weighted each spectral region. Weight-vectors approximated the ideal more closely after practice, indicating that listeners were learning to attend selectively to the task relevant information. Once changes in weights were accounted for, no changes in internal noise (psychometric slope) were observed. It is concluded that this task elicits robust learning, which can be understood primarily as improved selective attention.