bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis and Modeling of Vibratable End-Effector Angle of Catheter for Thrombus Dissolution
Authors: Ajoudanian M. , Jiang Z. , Morita M.
Published: April 2011

The cerebral thrombus or blood clot might cause cerebral stroke and even decease if the clot could not be dissolved within several hours after it was formed. By stirring the blood around the thrombus after the infusion of the agent, the quick dissolution can be obtained. To over come of lack design of structure of other micro stirrer like bending type actuators this study addresses this issue and describes an end-effector of catheter which provides high displacement with high power. The catheter is a beam with supported one side and the other side is free. Under Ultrasonic longitudinal wave excited by transducer from support side, traveling through beam and before reach to end-effector of beam amount of them impinges to slanted surface some of the energy of the incident longitudinal wave reflected with orientations different from the length direction. The other energy would be converted to shear waves. Despite the elongation and bending at tip, there is no significant bending across other part of beam. The angle of end-effector was evaluated by vertical tip displacement and density of energy at end-effector by transient analysis using FEM analysis. The obtained results demonstrated that the vertical motion of the stirrer was influenced by the intensity of shear wave which produced by mode conversion for longitudinal waves impinging on skew interface. Due to shear wave that reach to the end-effector, the limitation on the angle is determined.
Effect of Microstructure on Lifetime Performance of Barium Titanate Ceramics Under DC and AC Electric Fields
Authors: Shieh Jay
Published: April 2011

Bulk barium titanate (BaTiO3 ) ceramic specimens with bimodal microstructures are prepared and their dielectric and fatigue strengths are investigated under an alternating current (AC) electric field and a direct current (DC) electric field. It is found that under AC electrical loading, both the dielectric and fatigue strengths decrease with increasing amount of coarse abnormal grains. The scatter of the AC fatigue strength is characterized with the Weibull statistics. The extent of scatter of the AC fatigue strength data correlates strongly with the size distribution of the coarse grains. Such correlation is resulted from the presence of intrinsic defects within the microstructure. For DC electrical loading, the time to failure of the specimens with coarse abnormal grains is significantly shorter than the lifetimes of the specimens with only small normal grains. It is found that under a DC electric field of 6 MVm−1, the BaTiO3 specimens would fail within 200 h when abnormal grains are present in the microstructure. However, the lifetimes of the specimens containing abnormal grains vary significantly from one to another. The Weibull statistical analysis indicates that the amount of abnormal grains has little influence on the lifetime performance of bulk BaTiO3 ceramics under large DC electric fields. In most of the failed BaTiO3 specimens under DC electrical loading, regardless of their lifetimes, large through-thickness round holes with recrystallization features are present. A mixed failure mode consisting of avalanche and thermal breakdowns is proposed for the failed specimens.
Mechanical Properties of Metallic Cellular Materials With Polymer
Authors: Kishimoto Satoshi , Naito Kimiyoshi , Shimizu Toru , Yin Fuxing
Published: April 2011

A metallic cellular materials containing polymer was fabricated by the penetrating polymer into metal foam. The aluminum and stainless steel foams were selected for the metal foam and epoxy resin and polyurethane resin were selected for the penetrated polymer. The mechanical, damping shock absorbing properties of this material were measured. The results of the compressive tests show that this material has different stress-strain curves among the specimens that include different materials in the cells. Also, these results show that this material has high-energy absorption. The internal friction of this material was measured and the result shows that the internal friction of this material is larger than that of pure aluminum closed cellular material without any polymer and change with increasing of temperature. The shock absorbability of this material is larger than that of polymer and smaller than that of metallic cellular material.
Tunable Energy Harvesting From Ambient Vibrations
Authors: Rhimi Mohamed , Lajnef Nizar
Published: April 2011

Most civil structures have a low vibration response frequency range, generally one to two orders of magnitude lower than the operating frequency spectrum of most piezoelectric energy scavenging devices, which is dictated by the device’s design and the used materials. This considerably limits the levels of harvestable power under ambient vibrations. In this paper, the improvement of the energy harvesting characteristics of a bimorph cantilever lead zirconate titanate (PZT) piezoelectric beam through the application of initial pre-stress loading conditions is studied. A generalized model that can take into account all the vibration modes of the beam as well as the back coupling effect is derived using the Hamiltonian principle. The model describes the effect of the pre-stress parameters on the harvestable energy levels. Results showing the variations of the natural frequency, amplitude, and efficiency of the piezoelectric device with varying preload are presented. Vibration recordings from a bridge under ambient loading are used to show variations of the harvested power with different pre-stress conditions. Increases of up to 250% in the output power levels are shown possible through the application of 8N of compressive axial loading for a system with a 15g vibrating mass. Experimental verification of the model is also performed. The time and frequency domain responses of a piezoelectric bimorph are measured and compared to theoretical results.
Modeling of Hysteresis and Backlash Within a Smart Fin With a Piezoelectric Actuator
Authors: Trabia Mohamed B. , Yim Woosoon , Saadeh Mohammad
Published: April 2011

This work presents a dynamic model of a smart fin, which is activated by a piezoelectric bimorph actuator that is made by bonding two Macro Fiber Composites (MFCs). The actuator is completely enclosed within the fin. Earlier research has indicated that the use of a linear model for the fin dynamics does not fully describe the fin. This work presents a more realistic approach to the problem by incorporating additional components into the model. Therefore, a proportional damping matrix is introduced. It was also observed that experimental results exhibit hysteresis and backlash. A Bouc-Wen hysteresis model is combined with two backlash operators to model the observed saturation and the non-symmetry of the response. Hybrid Fuzzy Simplex Genetic Algorithm (HFSGA) is used to identify the optimal set of parameters for the damping matrix constants, the Bouc-Wen model, and the backlash operators. The results show that proposed method can predict the hysteresis of the smart fin–actuator system under various operational conditions.
Numerical Magneto-Mechanics of Embedded Magnetostrictive Composite Sensors
Authors: Rudd Jonathan , Myers Oliver , Spayde Dustin
Published: April 2011

Numerical models are generated for magneto-mechanical analysis of Terfenol-D embedded in a carbon fiber laminate with delaminations. The modeling is broken down into three stages; each having studies to observe the affect of the controlling parameters on the magnetic signature. The first stage, which is presented in this paper, involves modeling the magnetostrictive layer and excitation coil. This stage contains three preliminary studies to observe the affect of the controlling parameters on the magnetic flux density. The modeling geometry and the magneto-mechanical properties of the magnetostrictive particle (MSP) layer, Terfenol-D, were also defined. Study I consisted of models with 1, 15, 30, and 100 subdomains in the Terfenol-D layer to simulate particulate actuation. The results revealed that subdomain refinement has a significant affect, altering the magnetic flux density by at least one order of magnitude. Furthermore, the study revealed that the magnitude of the magnetic flux density converged at 15, 30, and 100 divisions. Study II was conducted to investigate the affect of the alternating current frequency on the magnetic flux density magnitude. The frequency was varied from 100 Hz to 3000 Hz on all the models. The results from the frequency variation study revealed that flux density of the Terfenol-D modeled with the 15, 30, and 100 divisions was not significantly affected by the change in frequency from 100–3000 Hz. Study III uses Ampere’s Law and a magnetostriction equation for the magnetic flux density to analytically validate the numerical results from the flux density plot. The initial results reveal that the numerical results follow the correct trend, but the magnitudes are being validated. A preliminary model for the second stage, which consists of modeling the Terfenol-D layer embedded in a carbon fiber laminate, is shown. Experimental samples were also made to validate the numerical results in the future. These samples are made of unidirectional prepreg carbon fiber embedded with Terfnol-D. They have varying internal delaminations, ply orientations, and number of plies. The results presented in this work are preliminary, and will be used as a foundation for continuing this research.
On Line Health Monitoring for Cracked Simply Supported Fiber Reinforced Composite Structures
Authors: Gaith Mohamed S. , Zaben Ahmad , Bawayah Naeem , Israwi Yazan , Farraj Mosa’ab
Published: April 2011

A crack in structural member introduces local flexibility which is function of crack depth and location. This flexibility changes the dynamic behavior of the system and its stability characteristics. A continuous cracked beam vibration theory is implemented for the lateral vibration of cracked Euler–Bernoulli beams with single-edge open cracks. In this work, the crack identification as on line health monitoring for simply supported graphite/epoxy fiber reinforced composite beams is considered. The effects of crack depth and location, fiber orientation, and fiber volume fraction on the flexibility and consequently on natural frequency and mode shapes for cracked fiber reinforced composite beams are investigated.
Computational Study of Inclusion Burst via the Proton Sponge Hypothesis
Authors: Freeman Eric , Mauck Weiland Lisa , Meng Wilson S.
Published: April 2011

Biological proteins embedded in either a biological or an engineered membrane will actively maintain electrochemical balance across that membrane through transport of fluid and charge. While membrane studies are often planar, in nature they typically take the form of inclusions (∼spherical). Study and ultimately manipulation of the protein transporter types and density, and interior/exterior states of these inclusions lend insight into burst mechanisms appropriate to a broad array of engineering and biological applications, such as intracellular burst release of a vaccine. To explore these phenomena the governing equations of each transporter, as well as the membrane state are established. The result is a model requiring the simultaneous solution of a stiff system of differential equations. Presented is the computational solution of this system of equations for a specific burst scenario — the hypothesis that a proton sponge may be employed to expedite intracellular burst release of a DNA vaccine is explored.
The Chemo-Electro-Mechanical Behavior of the pH Sensitive Hydrogels in Transient Condition
Authors: Suthar Kamlesh J. , Ghantasala Muralidhar K. , Mancini Derrick C.
Published: April 2011

Hydrogels are 3-D network polymeric materials that exhibit a phase-transition due to a change in their environment so that the response causes the hydrogel to swell or shrink. The changes in the solvent pH cause the hydrogel to swell or shrink, which is exploited for designing a drug delivery system. The time taken for drug uptake or delivery is an important aspect in these applications. The development of such systems require thorough understanding of the kinetic behavior of hydrogel swelling. We report the results of our research effort to model the time-dependent behavior using the finite element analysis. The hydrogel response is modeled using three partial differential equations in which two are nonlinear and third equation uses nonlinear material constants. Solving all three nonlinear equations using the finite element method for transient condition is a significant challenge. Our model is implemented using the generic finite element software COMSOL and the method can be used with any software having similar capabilities. We discuss the simulation of phase-transitions in transient conditions emphasizing the response to change in the solvent pH. The simulation was carried out on hydrogels with diameters from 200 μm to 500 μm while varying the solvent pH from 3 to 6. The results are compared with the published experimental data. A major achievement of this work is that the transient analysis is carried out in 2D, while the most reported literature are confined to one-dimensional analysis.
Ionic Polymer Transducer Sensing Response to Shear Deformation
Authors: Zangrilli Ursula T. , Weiland Lisa M.
Published: April 2011

Ionic polymer transducers (IPTs) show promise as both actuators and sensors. However, experiments show that the voltage required to actuate these materials is not symmetric to the voltage in sensing response of these materials. Therefore, the physical mechanism responsible for actuation is different than the mechanism for sensing. It is hypothesized that the physical mechanism responsible for sensing is streaming potential, as this supposition can explain the existence of an IPT response in any mode of deformation. This work will look specifically at developing a model of IPT sensing response to shear deformation. The scale at which the proposed mechanism operates is on the micro level, thus the study explores the implications of IPT phenomena at this length scale, but then volume averages it to the transducer length scale.
Linear and Nonlinear Modeling and Experiments of a Piezoaeroelastic Energy Harvester
Authors: De Marqui Junior Carlos , de Mello Anice´zio Marcela , Vieira Wander G. R. , Trista˜o Saulo F.
Published: April 2011

In this paper a piezoaeroelastically coupled lumped-parameter model for energy harvesting due to flow excitation is presented. A two-dimensional airfoil having two degree of freedom, i.e. pitch and plunge, is investigated. Piezoelectric coupling is considered for the plunge degree of freedom. Therefore an additional electrical degree of freedom is added to the problem. A load resistance is considered in the electrical domain. The unsteady aerodynamic loads are obtained from a time domain lumped vortex model. Two case studies are presented here. First the interaction of piezoelectric energy harvesting and a linear aeroelastic typical section is investigated for a set of electrical load resistances. Time domain responses for pitch and plunge as well as for the electrical outputs (voltage, current and electrical power) are presented. The linear model predictions are compared against experimental results. Later a concentrated nonlinearity (free play) is added to the pitch degree of freedom and the typical section is used to investigate LCO for piezoelectric energy harvesting.
Investgation of Wake Effects in Aeroelastic Flutter Vibration Energy Harvesting
Authors: Bryant Matthew J. , Isenberg Michael E. , Garcia Ephrahim
Published: April 2011

This paper examines a novel energy harvesting device for powering wireless sensors or other low power electronics by extracting energy from an ambient fluid flow. In particular, a simple device driven by aeroelastic flutter vibrations has been designed to extract vibratory energy from the flow and then transduce these vibrations to electrical current via cyclically straining piezoelectric patches. This energy harvester is driven by aeroelastic flutter vibrations of a two degree of freedom structure that grow in amplitude until steady limit cycle oscillation is reached. One application for such as system is using multiple devices simultaneously to create a “wind panel” system that could be used in areas where traditional wind turbines are impractical. Successful design of such a system will require consideration of the downstream wake effects of multiple energy harvesters operating in close proximity. Preliminary wind tunnel studies investigating these effects on the steady state power output of several aeroelastic energy harvesting devices arranged in multiple configurations are presented and analyzed.
Effect of Distribution of Functionalized Magnetic Nanoparticles on Ferrogel Actuation
Authors: Suthar Kamlesh J. , Ghantasala Muralidhar K. , Mancini Derrick C. , Mowat Joseph E. , Ilavsky Jan
Published: April 2011

The ferrogels elongate, contract, and deflect in response to an applied magnetic field. In order to study its response to magnetic fields, ferrogels were prepared using meghamite (Fe304) nanoparticles (size ∼ 10–25 nm) using the hydrogel based on N-isopropylacrylamide (NIPAm). The particle distribution is determined for different cross-linking density of the gel in the range of 2% to 8%. The ferrogels were analyzed using ultra small angle x-ray scattering (USAXS) and the particle distribution were compared with direct imaging of the samples using transmission electron microscopy. The uniformity of the distribution of the particles for different samples prepared was determined using USAXS. Magnetic characteristics of the ferrogel were determined using a direct current superconducting quantum interference device (DC-Squid). The magnetic moments of the polyvinylpyrrolidone (PVP) coated Fe3O4 nanoparticles based ferrogel are reduced from 2.5 – 0.4 emu/g, as the particle concentration is decreased from 8.75 to 1.25%. Subsequently, the deflection and strain also reduced under static magnetic field. These studies showed that a maximum deflection of 20% and strain of 10% to its original value could be achieved by varying the particle size and/or distribution. The crosslinking ratio of the polymer was varied from 1.2 – 8%. The deflection and elongation characteristics were studied using a custom-built electromagnetic set-up with a pole gap of 10 mm with magnetic field strength up to 2500 Gauss. However, the maximum strain reduces as the crosslinking density increases. This study clearly shows the dependence of the deflection and strain on the functionalization material coated on the particle. Details of the results of our experiments are presented in this paper.
Novel Flexible Pivot With Large Angular Range and Small Center Shift to be Integrated Into a Bio-Inspired Robotic Hand
Authors: Martin Javier , Robert Mathieu
Published: April 2011

This paper presents a novel flexible pivot with large angular range and small center shift. It is conceived to provide the inter-phalangeal rotational degrees of freedom of the fingers of a new bio-inspired robotic hand, simultaneously removing friction and backlash from the mechanism. The specifically developed mathematical model shows that the proposed solution meets all design requirements. Preliminary tests carried out on a prototype show an accurate matching between the model and the real behavior. The advantages offered by the new flexible pivot can be extended to any robotic application where frictionless, zero-backlash, compact and easy to manufacture pivots are required for pure rotation over long angular strokes.
Two Tiered Analysis of a CFRP Laminate Imbedded With Magnetostrictive Particles
Authors: Currie George , Spayde Dustin , Myers Oliver
Published: April 2011

The overall purpose of this research is to characterize the affects of imbedding magnetostrictive particles (MSP) in a CFRP laminate for the purpose of nondestructive evaluation. This paper details an investigation using an analytical and experimental approach. At the time of this publication, both the analytical and experimental investigations are in a preliminary stage and the results have not yet converged. The analytical investigation utilizes fundamental equations for the magnetomechanical properties of the MSP and classical laminate theory for the strength and stiffness of the CFRP laminate to obtain a model of the combination. It is assumed that the magnetomechanical relationship of the MSP layer is a function of the prestress acting on the layer. This relationship is nonlinear in nature but is broken down into a number of linear sections to facilitate analysis. This prestress acting on the MSP layer is a result of the CFRP laminate’s stiffness resisting the induced strain of the MSP layer. Classical laminate theory is used to obtain the value of the prestress as a function of this induced strain. As would be expected, this analysis becomes an iterative process. The induced strain is calculated based on a prestress level of zero. This strain is then used to calculate the amount of stress in the CFRP laminate which becomes the prestress value, and the process is repeated until convergence is reached. Unidirectional CFRP laminates are used in this analysis. The experimental approach involved testing a collection of composite beams imbedded with MSP using a scanner that surrounded the beams. The scanner was composed of an excitation coil and a sensing coil. A detailed schematic of the scanner is included in the paper showing the slide along which the scanner apparatus moved, and the sensing coil surrounded by the excitation coil. The samples used in this analysis were constructed from unidirectional prepreg carbon fiber with varying internal delaminations, ply orientations, and number of plies. A program was constructed that allowed the user to control the signal being output to the excitation coil as well as record data from the sensing coil. The results presented in this paper are not final and will be used to create a foundation for continuation of this research.
Characterizing and Modeling the Free Recovery and Constrained Recovery Behavior of a Polyurethane Shape Memory Polymer
Authors: Volk Brent L. , Lagoudas Dimitris C. , Maitland Duncan J.
Published: April 2011

In this work, tensile tests are performed on a polyurethane shape memory polymer for both free recovery (extension recovery at zero load) and constrained recovery (stress recovery at constant extension) conditions. The experimental characterization is conducted on an electromechanical screw driven test frame, and a laser extensometer is used in conjunction with the electromechanical frame to provide a non-contact technique for measuring the deformation of the material. The specimens are deformed, above the glass transition temperature, to 10% extension. The SMP is then cooled, at a constant value of extension, to below the glass transition temperature to ‘lock’ the temporary shape. The extension recovery at zero load as well as the stress recovery at a constant value of extension is measured during the first shape memory cycle as the SMP is heated to above its glass transition temperature. The material is observed to recover 93% of the applied deformation when heated at zero load. In addition, a stress recovery of 1.5 MPa is observed when heated while holding a constant value of deformation (10% extension). After performing the experiments, the Chen and Lagoudas model, implemented in 1-D by Volk, et al., is used to simulate and predict the experimental results. The material properties used in the model — namely the coefficients of thermal expansion, shear moduli, and frozen volume fraction — are calibrated from a single free recovery experiment. The calibrated model is then used to simulate the material response for the free recovery tests as well as predict the response for the constrained recovery condition. The model simulations agree well with the free recovery experimental data but predict a larger compressive stress than what is observed during the constrained recovery experiment.
On the Manifestation and Influence of Material Nonlinearity in Electroelastic Power Generators
Authors: Stanton Samuel C. , Erturk Alper , Mann Brian P. , Inman Daniel J.
Published: April 2011

We investigate and model observed nonlinear piezoelectric response of an electroelastic energy harvester. The model employed is a simplified version of the fully nonlinear model proposed by Stanton and Mann [1] since the mechanical oscillations of the experimental device remain in the geometrically linear regime. However, we include quadratic damping due to the appearance of even superharmonics in experimental data as well as suppressed frequency response. Nonlinear coefficients are identified via a nonlinear least squares optimization algorithm that utilizes an approximate analytic solution obtained by the method of harmonic balance. For PZT-5H, we obtained a fourth order elastic tensor component of cp1111 = −8.2515 × 1015 N/m2 and a fourth order electroelastic tensor value of e3111 = 9.6816 × 107 m/V.
Development of Modeling Techniques for Damping Applications of Nano Structured Composites With High Aspect Ratio Fillers
Authors: Varischetti Joshua A. , Jang Jae-Soon , Suhr Jonghwan
Published: April 2011

Recent advances in the production and wide scale availability of nano scale constituents, coupled with ongoing fundamental research utilizing them as fillers in host matrices for a variety of specific engineering inquiries has led to a notable interest in the use of nano scale fillers for specific commercial applications, specifically in the aerospace industry. Damping is of particular importance in modern composites, having high stiffness and low density, damping becomes a large issue, both for structural integrity as well as noise attenuation. The largest obstacle which must first be overcome in order to incorporate the nano scale constituents in commercial applications is the development of design useful modeling and analysis techniques which allow for calculated design decisions based on constituent properties. Currently, there is a large gap in performance of nano structured composites, where in the current analysis techniques tend to overstate the performance achieved relative to experimental results. This discrepancy has been attributed to a number of factors ranging from non-perfect geometry, to issues at the interface between matrix and filler, however there has not yet been a detailed investigation to the ability to accurately predict composite viscoelastic performance based on constituent properties. On of the most common approaches to modeling high aspect ratio nano fillers, carbon nano tubes and carbon nano fibers, is to assume a perfect cylindrical geometry, even though it is well understood that these fillers can have a significant curvature or waviness to them. This investigation combines modeling work looking at the effect of the waviness and the resulting reinforcement provided, in terms of viscoelastic response, which is then compared to experimental results. Damping is characterized with respect to operating temperatures and frequency range, of specific interest is the low frequency range, which is traditionally more difficult to damp. Experimental investigations utilize dynamic mechanical analysis (DMA) to characterize viscoelastic performance, which is then compared to modeling data where it has been found that trends can be accurately predicted.
Investigation of Soft and Hard Ceramics and Single Crystals for Resonant and Off-Resonant Piezoelectric Energy Harvesting
Authors: Erturk Alper , Lee Ho-Yong , Inman Daniel J.
Published: April 2011

Piezoelectric materials have received the most attention for vibration-to-electricity conversion over the last decade. Harmonic excitation is the most commonly investigated form of excitation in piezoelectric energy harvesting and it can be divided into two subgroups as resonant and off-resonant excitations. Although resonant excitation is preferred for extracting the maximum electrical power output from the device, there are several practical cases where it is not possible to excite the energy harvester at its resonance frequency (e.g. varying frequency excitations or very low frequency excitations where the input frequency is much lower than the fundamental resonance frequency). Several researchers have used soft piezoceramics (e.g. PZT-5A and PZT-5H) for power generation under resonant excitation. Typically, these soft piezoceramics have larger piezoelectric strain constant and larger elastic compliance compared to hard piezoceramics (e.g. PZT-4 and PZT-8). However, it is known that hard piezoceramics can have an order of magnitude larger mechanical quality factor compared to soft piezoceramics. Consequently, hard piezoceramics can generate more power under resonant excitation even though researchers have mostly focused on the soft piezoceramics. On the other hand, soft piezoceramics can generate more power for low frequency excitation below the resonance frequency due to their large effective piezoelectric stress constants. This difference is also the case for soft and hard single crystals (e.g. soft PMN-PZT versus hard PMN-PZT-Mn). In addition, single crystals can generate more power than ceramics at low off-resonant frequencies due to their large dynamic flexibilities (which is related to their large elastic compliances). This work investigates the specific advantages of soft and hard piezoceramics and single crystals for vibration-based energy harvesting. An experimentally validated piezoelectric energy harvester model is used to compare the power generation performances of soft and hard ceramics as well as soft and hard single crystals. The soft and the hard piezoceramics considered in this work are PZT-5H and PZT-8, respectively, while the soft and the hard single crystals considered here are PMN-PZT and PMN-PZT-Mn, respectively.
Broadband and Low Frequency Vibration-Based Energy Harvesting Improvement Through Magnetically Induced Frequency Up-Conversion
Authors: Wickenheiser Adam M.
Published: April 2011

In order to extract as much energy as possible from ambient vibrations, many vibration-based energy harvesters (VEHs) are designed to resonate at a specific base excitation frequency. Unfortunately, many vibration energy sources are low frequency (0.5 Hz–100 Hz), intermittent, and broadband. Thus, resonant VEHs would not be excited continuously and would require a large mass or size to tune to such a low frequency. This work presents the modeling, analysis, and experimental application of a nonlinear, magnetically excited energy harvester that exhibits efficient broadband, frequency-independent performance. This design utilizes a passive auxiliary structure that remains stationary relative to the base motion of the VEH. This device is especially effective for driving frequencies well below its fundamental frequency, thus enabling a more compact design compared to traditional resonant topologies. A mechanical model based on Euler-Bernoulli beam theory is coupled to a linear circuit and a model of the nonlinear, magnetic interaction to produce a distributed parameter magneto-electromechanical system. The results of both harmonic and broadband, stochastic simulations demonstrate multiple-order-of-magnitude power harvesting performance improvement at low driving frequencies and an insensitivity to time-varying base excitation frequency content. Furthermore, the proposed system is shown to enable more practical designs than a resonant energy harvester for the specific example of harvesting energy from walking motion.
Experimental Study of Impact Modulation for Quantifying Loose Bolt Torque in On-Demand Satellites
Authors: Jaques Janette L. , Adams Douglas E. , Doyle Derek , Reynolds Whitney
Published: April 2011

The development of on-demand satellites has created the need for methods that quickly assess the structural integrity of the system. In particular, because of rapid testing and assembly, workmanship errors such as loose bolts within the satellite structure are a concern. Current methods of loose bolt detection, which often rely on baseline data or analytical models, are not practical due to the variable geometry of the satellites and the time constraints on testing. The method of impact modulation is a nonlinear vibration method which is quick to perform and is robust to changes in the geometry of the structure. This paper presents the results of applying impact modulation to a simplified structure used to model a single bolted joint within a satellite. Results show that impact modulation can distinguish changes in torque within the bolted joint. In addition, several examples of how the underlying linear characteristics of the system affect impact modulation results are given.
Magnetic Properties of Ferrogels
Authors: Cooper Kelsey , Faidley LeAnn , Timmons Sarah , Han Yi , Hong Wei
Published: April 2011

This paper presents the magnetic properties of ferrogels subject to cyclic magnetic fields. Ferrogels are compliant materials composed of a nonmagnetic, flexible matrix with a micro- or nano-sized magnetic powder filler. In this paper a poly-vinyl-alcohol matrix is chemically cross-linked with sodium tetraborate and micro-sized particles of carbonyl iron are dispersed randomly in the sample. Ferrogels exhibit active behavior characterized by a deformation, a stiffness increase, and a change of other properties when subjected to a magnetic field making them promising future actuator materials. Furthermore, since the composition of ferrogels can be easily varied the active properties of these materials can be designed over a wide range of possibilities. In order for this to be possible however, a thorough understanding of the active behavior of these materials and its dependence on external factors is necessary. This paper focuses on the magnetic properties of PVA/carbonyl iron ferrogels and how they are dependent on internal and external factors. Magnetization of the ferrogel sample will be measured under a uniform, sinusoidal magnetic field for constrained and unconstrained samples with various iron concentrations and under a range of excitation frequencies. Uniform excitation fields of up to 500 G are created by passing current through a coil that is substantially larger than the sample size. Excitation frequencies of 0.1 Hz to 20 Hz and iron concentrations of 12 wt%, 20 wt% and 27 wt% are investigated. The magnetization is determined by measuring the voltage induced in a pickup coil that surrounds the ferrogel sample. The objective of these tests is to investigate the magnetic properties of a poly-vinylalcohol/carbonyl iron ferrogel to help in the future design of ferrogels for specific applications.
Multi Impact Identification Base Kalman Filter
Authors: Moon Yoo-Sung , Lee Sang-Kwon , Shin Kihong , Lee Young-Sup
Published: April 2011

The aim of this paper is to present the method of identifying the impact location on the plate. This basic research has the purpose to achieve the human-interaction technology based on the signal processing, piezoelectric materials, and wave propagation. The work concerning the location identification of a single impact on the plate has been previously studied by means of the time frequency analysis applied to accelerometer signals. In this paper, a novel approach for the location identification of the discrete impact is presented to investigate the feasibility of applying to a human-interaction system. For the identification of the impact location, the major axisymmetry mode of the Lamb wave on the plate is used for this work and Kalman filter tracking is employed.
Analysis of Shape Memory Alloy Components Using Beam, Shell, and Continuum Finite Elements
Authors: Hartl Darren , Zimmerman Tyler , Dilligan Matthew , Mabe James , Calkins Frederick
Published: April 2011

This work discusses the increased capabilities of a three-dimensional analysis tool for shape memory alloy engineering components. As the number and complexity of proposed SMA applications increases, engineers and designers must seek out or develop more capable predictive methods. Three-dimensional models implemented in a continuum finite element analysis (FEA) framework can be applied to most SMA component geometries. However, such methods may require fine meshes in 3-D space, resulting in many degrees of freedom and potentially long analysis times. On the other hand, constitutive models implemented in one dimension can be simple and fast, but are restricted to a limited class of problems for which such reductions are appropriate (e.g., rods and beams). More recently, engineers have begun investigating more complex SMA bending components for which 2-D shell elements might provide a computationally efficient FEA discretization. Here we consider a single modeling tool (a material subroutine) that combines 1-D, 2-D, and 3-D implementations for use in a general FEA framework. As an example analysis case, we consider an SMA bending element that has been adhesively bonded to a carbon fiber-reinforced polymer (CFRP) laminate and is subjected to thermally-induced actuation. The active SMA and passive composite components are bonded in a pre-stressed configuration such that the elastic laminate provides a variable restoring force to the SMA during transformation, resulting in repeatable actuation cycles. This two-part bonded configuration is analyzed using different types of finite elements (1-D beam, 2-D shell, and full 3-D continuum elements). The constitutive behavior of the shape memory alloy is defined using an established three-dimensional model based on continuum thermodynamics and motivated by the methods of classical plasticity. A user material subroutine (UMAT) in an Abaqus Unified FEA framework is used to implement the model. The methodology for capturing 1-D, 2-D, and 3-D thermomechanical response in a single such UMAT is described. The run times of the various analyses are compared, and the relative accuracies of the results are discussed.
Fatigue Life Monitoring of Metallic Structures by Decentralized Rainflow Counting Embedded in a Wireless Sensor Network
Authors: O’Connor Sean , Kim Junhee , Lynch Jerome P. , Law Kincho H. , Salvino Liming
Published: April 2011

Fatigue is one of the most widespread damage mechanisms found in metallic structures. Fatigue is an accumulated degradation process that occurs under cyclic loading, eventually inducing cracking at stress concentration points. Fatigue-related cracking in operating structures is closely related with statistical loading characteristics, such as the number of load cycles, cycle amplitudes and means. With fatigue cracking a prevalent failure mechanism of many engineered structures including ships, bridges and machines, among others, a reliable method of fatigue life estimation is direly needed for future structural health monitoring systems. In this study, a strategy for fatigue life estimation by a wireless sensor network installed in a structure for autonomous health monitoring is proposed. Specifically, the computational resources available at the sensor node are leveraged to compress raw strain time histories of a structure into a more meaningful and compressed form. Simultaneous strain sensing and on-board rainflow counting are conducted at individual wireless sensors with fatigue life prediction made using extracted amplitudes and means. These parameters are continuously updated during long-term monitoring of the structure. Histograms of strain amplitudes and means stored in the wireless sensor represent a highly compressed form of the original raw data. Communication of the histogram only needs to be done by request, dramatically reducing power consumption in the wireless sensing network. Experimental tests with aluminum specimens in the laboratory are executed for verification of the proposed damage detection strategy.
Performance Assessment and Actuator Design of a Flexible Tail Propulsor in an Artificial Alligator
Authors: Philen Michael , Neu Wayne
Published: April 2011

The overall objective of this research is to develop analysis tools for determining actuator requirements and viable actuator technology for design of a flexible tail propulsor in an artificial alligator. A simple hydrodynamic model that includes both reactive and resistive forces along the tail is proposed and the calculated mean thrust agrees well with conventional estimates of drag. Using the hydrodynamic model forces as an input, studies are performed for a 1.5 m alligator having 5 antagonistic pairs of actuators distributed along the length of the tail. As a result of the large amplitude of the tail motion, large actuator forces and strains are required for an alligator swimming at speeds 0.3 to 1.8 body lengths/s. Several smart materials are considered for the actuation system, and preliminary analysis results indicate that the acrylic electroactive polymer and the flexible matrix composite actuators are potential artificial muscle technologies for the system.
Electro-Mechanical Analysis of a DEAP Actuator Coupled to a Negative-Rate Bias Spring Mechanism
Authors: Hodgins Micah , York Alexander , Seelecke Stefan
Published: April 2011

This paper presents the design and analysis of a Negative-rate Bias Spring (NBS) paired with a Dielectric Electro-Active Polymer (DEAP). A NBS is a bi-stable mechanism with a negative slope region between its two stable configurations. The objective of this work is to demonstrate the increased stroke output of a DEAP actuator when biased by such a bistable mechanism. Possible devices that could use this actuation technology are lightweight, miniature pumps and valves. First, the NBS is mechanically tested and its bi-stable behavior is observed along with the negative slope region between the stable configurations. Then the NBS is coupled with a circular DEAP actuator (to provide the bias force) and is experimentally tested under a variety of loading conditions with a focus on the force and stroke capabilities. The stroke output of the device was approximately 1mm for a range of electrical loading rates (0.1Hz, 1Hz, and 10Hz). The measured force and stroke are then correlated to the force vs. displacement data observed during the mechanical characterization experiments. Additionally, the force vs. displacement behavior of the NBS-DEAP is analytically modeled and showed good comparison with the results.
Evaluation of Robust Covariance Estimation Techniques for Anomaly Detection of Insulated Gate Bipolar Transistors (IGBT)
Authors: Patil Nishad , Menon Sandeep , Das Diganta , Pecht Michael
Published: April 2011

An approach to detect anomalies in IGBTs is to monitor the collector-emitter current and voltage in application. These current and voltage parameters can then be reduced to a univariate distance measure called the Mahalanobis Distance (MD). The MD values with the use of an appropriate threshold enable anomaly detection of these devices. Mahalanobis distances (MD) are weighted Euclidean distances; the distance of each point from the center of the distribution is weighted by the inverse of the sample variance-covariance matrix. The presence of outliers in the monitored data can lead to the overestimation of the covariance matrix that in turn affects the anomaly detection results. This issue can be addressed by the use of robust covariance estimation techniques. In this study, the minimum volume ellipsoid (MVE) estimator, the minimum covariance determinant estimator (MCD) and the nearest neighbor variance estimator (NNVE) were used for anomaly detection of IGBTs. IGBTs were aged under a resistive load until failure. The monitored collector-emitter current and voltage values were used as input parameters for the MD calculation. The three robust covariance estimation techniques were used to compute the MD values and the anomaly detection times were compared to the results obtained by the classical covariance estimation technique.
Diagnostic/Prognostic Experiments for Capacitor Degradation and Health Monitoring in DC-DC Converters
Authors: Kulkarni Chetan S. , Biswas Gautam , Koutsoukos Xenofon , Celaya Jose , Goebel Kai
Published: April 2011

Studying and analyzing the ageing mechanisms of electronic components avionics in systems such as the GPS and INAV are of critical importance. In DC-DC power converter systems electrolytic capacitors and MOSFET’s have higher failure rates among the components. Degradation in the capacitors under varying operating conditions leads to high ripples output voltages and currents affecting downstream components leading to cascading faults. For example, in avionics systems where the power supply drives a GPS unit, ripple currents can cause glitches in the GPS position and velocity output, and this may cause errors in the Inertial Navigation (INAV) system, causing the aircraft to fly off course The work in this paper proposes a detail experimental and systematic study on analyzing the degradation phenomenon is electrolytic capacitors under high stress operating conditions. The output degradation is typically measured by an increase in ESR (Equivalent Series Resistance) and decrease in the capacitance value. We present the details of our accelerated ageing methodology along with analysis and comparison of the results.
Assessment of Current Health of Hard Disk Drives
Authors: Zeid Abe , Kamarthi Sagar
Published: April 2011

Prognostics and health management of computer hard disk drives is beneficial from two different angles: it can help computer users plan for timely replacement of HDDs before they catastrophically fail and cause serious data loss; it can also help product recover facilities reuse hard disks recovered from the end-of-life computers for building refurbished computers. This paper presents a HDD health assessment method using Self-Monitoring, Analysis, and Reporting Technology (SMART) attributes. It also presents the state-of-the art results in monitoring the condition of hard disks and offers future directions for distributed hard disk monitoring.
Damage Tracking Using Smart Sensor Network
Authors: Jalalpour Mohammad , Reda Taha Mahmoud , El-Osery Aly
Published: April 2011

Sensors are frequently used in damage diagnosis for structural health monitoring (SHM) of aerospace structures. This process typically requires a considerably large number of sensors. By increasing the number of sensors, the amount of data collected, though useful, becomes a burden due to the required computational overhead. In this paper, a random correlation cumulative approach is used to track damage intensity and propagation. The relative correlation between any two randomly chosen sensors is recorded and compared over time. The randomness of the process leads to detecting and tracking any arbitrary crack propagation. A case study for damage detection and tracking using 40 sensors in a steel plate is presented and discussed. It is shown that the proposed method can successfully allow damage tracking while limiting the data considered in the sensor network.