bluuebunny/crossref_metadata_2025 huggingface dataset:
A Hybrid Master-Slave Genetic Algorithm-Neural Network Approach for Modeling a Piezoelectric Actuator
Authors: Trabia Mohamed B. , Saadeh Mohammad Y.
Published: July 2013

This work presents an approach for developing the model of a smart fin dynamics that is activated by a fully-enclosed piezoelectric (PZT) bimorph actuator, which is created by bonding two Macro Fiber Composites (MFCs). Observing the dynamics of the fin indicates that the use of a linear dynamic model does not adequately describe its behavior. An earlier work proposed incorporating a proportional damping matrix as well as Bouc-Wen hysteresis model and backlash operators to create a more accurate model. However, the number of parameters describing the expanded model is large, which limits its use. Therefore, there is a need for a different approach for developing an alternative model of the fin. In this work, a hybrid master-slave Genetic Algorithm (GA)-Neural Network (NN) model is proposed to identify the optimal set of parameters for the damping matrix constants, the Bouc-Wen hysteresis model and the backlash operators. A total of nine sinusoidal input voltage cases that resemble a grid of three different amplitudes excited at three different frequencies are used to train and validate the model. Three input cases are considered for training the NN architecture, connection weights, bias weights and learning rules using GA. The NN consists of three layers: an input layer that has two nodes for the amplitude and the frequency of the input voltage, an output layer that has seven nodes for the backlash, hysteresis, and damping operators, and a hidden layer that is free to have any number of nodes between two and nine. The GA constantly performs natural selection of chromosomes that propagate best compilation of NN parameters. Simulation results show that the proposed model can predict the damping, hysteresis and backlash of the smart fin–actuator system under various operational conditions.
Energy Harvesting From Hydraulic Pressure Fluctuations
Authors: Cunefare Kenneth A. , Verma Nalin , Erturk Alper , Skow Ellen , Savor Jeremy , Cacan Martin
Published: July 2013

State-of-the-art hydraulic hose and piping systems employ integral sensor nodes for structural health monitoring in order to avoid catastrophic failures. These systems lend themselves to energy harvesting for powering sensor nodes. The foremost reason is that the power intensity of hydraulic systems is orders of magnitude higher than typical energy harvesting sources considered to date, such as wind turbulence, water flow, or vibrations of civil structures. Hydraulic systems inherently have a high energy intensity associated with the mean pressure and flow. Accompanying the mean pressure is what is termed dynamic pressure ripple caused by the action of pumps and actuators. Pressure ripple is conducive to energy harvesting as it is a deterministic source with an almost periodic time domain behavior. Pressure ripple generally increases in magnitude with the mean pressure of the system, which in turn increases the power that can be harvested. The harvested energy in hydraulic systems could enable self-powered wireless sensor nodes for applications such as energy-autonomous structural health monitoring and prognosis. An energy harvester prototype was designed for generating low-power electricity from dynamic pressure ripples. The prototype employed an axially-poled off-the-shelf piezoelectric stack. A housing isolated the stack from the hydraulic fluid while maintaining mechanical coupling to the system to allow for dynamic pressure induced deflection of the stack. The system exhibits an attractive off-resonance energy harvesting problem since the fundamental resonance of the piezoelectric stack is much higher than the frequency content of ripple. Although the energy harvester is not excited at resonance, the high energy intensity of the ripple results in significant electrical power output. The prototype provided a maximum output of 1.2 mW at 120Ω. With these results, it is clear that the energy harvester provides non-negligible power output suitable for powering sensors and other low power components. This work also presents electromechanical model simulations for predicting the piezoelectric power output in terms of the force transmitted from the pressure ripple as well as experimental characterization of the power output as a function of the force from the ripple.
A Design of an Active Tool Holding Device
Authors: Boldering Alexander L. , Raatz Annika
Published: July 2013

The challenge of producing high performance, productive and precise machine tools must be accepted by the machine tool industry. These requirements can be reached by increasing the grinding machine parameters, such as the cut depth or the feed rate. Both will increase the grinding force during the grinding process, and can result in an excitation of the machine structure. Based on this excitation, the machine structure shows an undesired dynamic behavior which can result in machine vibrations. These vibrations can cause chatter marks on the workpiece surface, and if large enough can result in a stop in production. To minimize the chance of this situation, the machine user often chooses machine parameters which will not excite the machine structure. This is a disadvantage, because the machine design allows much more efficiency. To employ the complete efficiency of the design, this paper presents an approach which allows the active reduction of possible vibrations during a grinding process.
Mode I Steady Crack-Growth in Superelastic Shape Memory Alloys
Authors: Baxevanis Theocharis , Lagoudas Dimitris , Landis Chad
Published: July 2013

A numerical analysis of quasi-static, steady state crack growth in superelastic Shape Memory Alloys (SMAs) under small-scale transformation conditions is carried out for plane strain, mode I loading. Crack growth is assumed to proceed at a critical level of the crack-tip energy release rate. Finite-element results concerning the mechanical fields near the advancing crack tip are presented and the ratio of the far-field applied energy release rate to the crack-tip energy release rate is obtained for a range of thermomechanical parameters. A substantial fracture toughening is observed associated with closure stresses placed on the crack tip by the transformed material left behind in the wake of the advancing crack tip.
Electromechanical Behavior of Conductive Polyaniline/Poly (Vinyl Alcohol) Blend Films Under Uniaxial Loading
Authors: Akhilesan S. , Varughese Susy , Lakshmana Rao C.
Published: July 2013

Polyaniline (PANI) an electronically conducting polymer, and its charge transfer complexes are interesting engineering materials due to their unique electronic conductivity, electrochemical behavior, low raw material cost, ease of synthesis and environmental stability in comparison with other conjugated polymers. The main disadvantage of PANI is its limited processability. Blending of conducting polymers with insulating polymers is a good choice to overcome the processability problem. In this study a solution-blend method is adopted to prepare conductive polyaniline/polyvinyl alcohol (PANI/PVA) blend films at various blend ratios. Interest in applications for polyaniline (PANI) has motivated investigators to study its electro mechanical properties, and its use in polymer composites or blends with common polymers. The work described here looks at the uniaxial deformation behavior of the conducting polymer films and the anisotropic dependency of electrical conductivity of the blend films exposed to static and dynamic loading conditions. The relation between mechanical strain, electrical conductivity and film microstructure is investigated on PANI/PVA blend films.
Modeling of Non-Monotonic Hysteresis Behavior in VO2-Coated Microactuators
Authors: Zhang Jun , Merced Emmanuelle , Sepúlveda Nelson , Tan Xiaobo
Published: July 2013

Vanadium dioxide (VO2) undergoes a thermally induced solid-to-solid phase transition. A VO2-coated silicon cantilever demonstrates large change in its bending curvature across its phase transition. Due to phase transition and thermal expansion effects, the curvature – temperature hysteresis in VO2 actuators comes with a non-monotonic hysteretic behavior, introducing new challenges in its modeling. Motivated by the underlying physics, in this paper we present a novel model that combines a monotonic Preisach hysteresis operator with a linear operator. A constrained least square scheme is proposed to estimate the model parameters. For comparison purposes, we also consider a Preisach operator with a signed weighting function, and a hybrid model consisting of a monotonic Preisach operator for the curvature within the transition and linear operators outside the transition. Experimental results confirm the effectiveness of the proposed model.
Homogenized Energy Model and Markov Chain Monte Carlo Simulations for Macro Fiber Composites Operating in Broadband Regimes
Authors: Hu Zhengzheng , Smith Ralph C. , Burch Nathanial , Hays Michael , Oates William S.
Published: July 2013

Macro Fiber Composites (MFCs), comprised of PZT fibers, are being considered for a variety of applications due to their flexibility and relatively low production costs. Like other PZT actuators, MFCs also exhibit hysteresis and constitutive nonlinearities that must be characterized in models and control designs to achieve the full potential. Here we use an Euler-Bernoulli beam model coupled with the homogenized energy strain model to predict the structural/hysteretic response of a thin cantilever beam with an MFC patch attached during a series of frequency sweep experiments. Optimization routines are employed to optimized both MFC parameters and beam parameters using a subset of displacement data. The posterior probability distribution of each model parameter is estimated using Markov Chain Monte Carlo simulations. Finally, we present model predictions with quantified uncertainties.
Adaptive Disturbance Tracking Control With Wind Speed Reduced Order State Estimation for Region II Control of Large Wind Turbines
Authors: Thapa Magar Kaman S. , Balas Mark J. , Frost Susan A.
Published: July 2013

In this paper we introduce an Adaptive Disturbance Tracking Control (ADTC) Theory and make some modifications to implement it to address Region II control problem of large wind turbines. Since ADTC requires measurement of wind speed, a wind speed and partial state estimator based on linearized lower-order model of wind turbine at Region II operating point was developed. The estimated wind speed was then used with the adaptive controller and the states were used for state feedback. The combination of partial state feedback and adaptive disturbance tracking control is implemented in National Renewable Energy Laboratory (NREL)’s 5 MW offshore wind turbine model and simulated in MATLAB/Simulink. The simulation result was then compared with existing fixed gain controller.
Sliding Mode Control for Inverse Compensated Hysteretic Smart Systems
Authors: McMahan Jerry A. , Smith Ralph C.
Published: July 2013

Ferroelectric (e.g., PZT), ferromagnetic (e.g., Terfenol-D) and ferroelastic (e.g., shape memory alloy (SMA)) materials offer unique capabilities for a range of present and emerging control applications. To fully realize the capabilities these materials offer, model-based control designs must account for the nonideal effects (e.g., creep, rate-dependent hysteresis, and constitutive nonlinearities) that the materials exhibit. In this paper, we employ the homogenized energy model (HEM) to characterize rate-dependent hysteresis behavior, construct an approximate inverse algorithm to compensate the material nonlinearities, and combine this with a sliding mode controller to accommodate uncertainties in the model. We illustrate this in the context of an actuator employing the ferroelectric material PZT but note that the general framework is also applicable to magnetic and shape memory alloy transducers. Through numerical examples, we illustrate the effectiveness of the HEM inverse-based sliding mode design for tracking a reference trajectory in the presence of modeling and inversion errors.
A Structural Health Monitoring System for Composite Beams With Coupled Bending-Torsion
Authors: Hasan Zeaid , Atmeh Ghassan
Published: July 2013

Structural health monitoring (SHM) is the process of damage identification in structural systems which have been an area of interest and a well-recognized field of technology in the past decade. Such systems involve the integration of smart materials, sensors and decision-making algorithms into the structure to detect damage, evaluate the structural integrity and predict the remaining life time. These systems have the potential to replace traditional non-destructive evaluation (NDE) of structures.

This study focuses on presenting an automated structural health monitoring (SHM) system based on detecting shifts in natural frequencies of the structure. The damage detection technique is implemented on a cracked composite beam vibrating in coupled bending-torsion where the crack is assumed open. Modal analysis is conducted on the composite beam in order to predict the natural frequency and the associated mode shapes. Based on this analysis, a database of information related to the specific composite beam being analyzed such as layups and natural frequencies are stored. The natural frequency will be measured and compared to that database for damage detection. A finite element model is also presented and compared with the analytical results. It is observed that the variation of natural frequencies in the presence of a crack is affected by the crack ratio, crack location and fiber orientation. In particular, the variation pattern is different as the magnitude of bending-torsion coupling changes due to different fiber angles.

A simple circuit containing a microcontroller is implemented to simulate the automated SHM concept. The microcontroller serves as the data storage device as well as the decision maker based on the instantaneous comparison between the healthy and the damaged structure. The proposed system may be implemented in many structural components such as aircraft frames and bridges. This SHM technology may help replace the current time-based maintenance scheme with a condition-based one. The condition-based maintenance scheme relies on the ability to monitor the condition of the system and supply information of damage detection to allow a corrective action to be taken.
Wireless Strain Sensors Using Electromagnetic Resonators
Authors: Daliri Ali , John Sabu , Wang Chun H. , Galehdar Amir , Rowe Wayne S. T. , Ghorbani Kamran
Published: July 2013

The concept of wireless passive strain sensors has been introduced in the last few years for applications such as structural health monitoring. This study investigates the use of circular microstrip patch antenna (CMPA) sensors for wireless passive measurement of strain. The strain induced in an aluminium plate was measured wirelessly up to 5 cm away from the sensor using a CMPA made from commercial FR4 substrate, and at a distance up to 20 cm using a CMPA made from Rogers® RT/duroid 6010™. These results show the substrate of antennas is one of the factors affecting the interrogation distance. The interrogation distance between the sensor and the patch antenna was improved significantly using the Rogers® substrate.
A Morphing Bi-Stable Composite Laminate Actuated by Electric Heating Method
Authors: Li Hao , Dai Fuhong , Du Shanyi
Published: July 2013

As the “morphing” or “shape adaptive” structural systems are getting considerable attention, a practical realization of a morphing needs substantial effort. This study proposes a concept of morphing bi-stable composite laminate. The morphing bi-stable laminate is locally embedded with electric heating material and has two stable states. The embedded heating material can elevate the temperature and relieve the thermal stress of the region heated by it. With this heating actuation method, an appropriate embedment of heating materials will enable the bi-stable laminate a morphing structure. This morphing bi-stable laminate can transform from one stable state to the other stable state by the heating effect of its heating composition. The FEA of the morphing process of this morphing bi-stable laminate was performed, and the critical temperature of the snap-through phenomenon was predicted. Experiment was conducted to verify the morphing process of this morphing bi-stable laminate, good agreement between the experiment and the FEA results are obtained.
Series Connection of Multiple Piezoelectric Oscillators
Authors: Lin H. C. , Wu P. H. , Lien I. C. , Shu Y. C.
Published: July 2013

This article investigates the electrical response of piezoelectric energy harvesters (PEHs) connected in series. Analytic estimates of harvested power output are proposed for a series PEH array system attached to various energy harvesting circuits, including standard and parallel-/series-SSHI (synchronized switch harvesting on inductor) interfaces. In contrast to the case of parallel connection of multiple oscillators, the results are presented through the matrix formulation of charging on capacitance. Besides, they are validated numerically by standard circuit simulations.
A Fractal-Inspired Multi-Frequency Piezoelectric Energy Converter: Computational and Experimental Characterization
Authors: Castagnetti Davide
Published: July 2013

In order to develop self-powered wireless sensor nodes, many energy harvesting devices, able to convert freely available ambient energy into electrical energy, have been proposed in the literature. A promising technique, in terms of simplicity and high conversion efficiency, is the harvesting of ambient kinetic energy through piezoelectric materials.

The aim of this work is to design and investigate the modal response and the power output of a fractal-inspired, multi-frequency, piezoelectric energy converter, previously presented by the author. Two are the steps of the work. First, a computational modal analysis of the converter is performed. Second, a physical prototype of the converter is built and its eigenfrequencies and power generation under different resistive loads are experimentally examined in the range between 0 and 120 Hz. The converter exhibits three eigenfrequencies and a good power output, in particular at the first eigenfrequency.
A Minimally Invasive Cage for Spinal Fusion Surgery Utilizing Superelastic Hinges
Authors: Anderson Walter , Chapman Cory , Karbaschi Zohreh , Elahinia Mohammad
Published: July 2013

An innovative shape memory alloy actuated cage has been developed for spinal fusion surgery. Spinal fusion surgery is performed on people suffering from low back pain. The viscoelastic spinal disc between the two vertebrae can degenerate in some fashion, such as herniation, and the space needs to be restored to relive the pressure on the nerves within the lower back. There are two main parts to a spinal disc, the annulus fibrosis and the nucleolus. The annulus fibrosis is a cartilaginous structure and is of interest to preserve. Therefore a minimally invasive cage utilizing superelastic elements has been developed. Furthermore, the cage safety and efficacy has been proven and will be presented here. Within this work, the efficacy and longevity of the cage will be presented. To this end, ASTM testing for spinal implants has been conducted on an electromechanical test system capable of inducing simultaneous axial and torsional forces.
On a Physics-Based Model of the Electrical Impedance of Ionic Polymer Metal Composites
Authors: Cha Youngsu , Aureli Matteo , Porfiri Maurizio
Published: July 2013

In this paper, we analyze the chemoelectrical behavior of ionic polymer metal composites (IPMCs) in the small voltage range with a novel hypothesis on the charge dynamics in proximity of the electrodes. Specifically, this paper introduces a so-called composite layer which extends between the polymer membrane and the metal electrode. This homogeneous layer describes the charge distribution at the electrode via two species of charge carriers, that is, electrons and mobile counterions. Charge dynamics is described by adapting the multi-physics formulation based on the Poisson-Nernst-Planck (PNP) equations through the incorporation of the electron transport in the composite layer. Under the hypothesis of small voltage input, we use the linearized PNP model to derive an equivalent IPMC impedance model with lumped elements. The equivalent model is represented as a resistor connected in series with the parallel of a capacitor and a Warburg impedance element. These elements idealize the phenomena of charge build up in the double layer region and the faradaic impedance related to mass transfer, respectively. We validate the equivalent model through measurements on in-house fabricated samples addressing both IPMC step response and impedance.
The Application of Multiwall Carbon Nano-Tubes/Polypyrrole Composite Electrode in Flexible Energy Storage System for Electronic Textile and Wearable Electronics
Authors: Lee Ka Yeung Terence , Naguib Hani , Lian Keryn , Biddiss Elaine
Published: July 2013

A nanocomposite of Multi-walled Carbon nanotubes (MWCNT) and Polypolypyrrole (PPy) is fabricated and characterized for supercapacitor application. PPy is uniformly coated on the MWCNT surface by mean of in-situ chemical polymerization. MWCNT content is varied to control the thickness of deposited Pyrrole layer. Ferric chloride solution (FeCl3.6H2O) is used as oxidant to polymerize Pyrrole. Highly conductive nickel foam is used as a current collector for the electrode. Scanning Electron Microscopy (SEM) and Transmission Electron (TE) imaging were used in characterizing composite surface morphology. Electrochemical behavior is studied by mean of Cyclic Voltammetry (CV) and AC Impedance Spectrometry. The effect of varying monomer to MWCNT weight ratio in composite electrical properties was studied in this paper.
Evaluation of Damage in a Continuum Through a Multi-Objective Optimization Inverse Approach
Authors: Wang Mengyu , Brigham John
Published: July 2013

An approach is presented to incorporate a multi-objective genetic algorithm (GA) optimization strategy for the evaluation of damage within a solid continuum. Through simulated test problems based on the characterization of internal pipe surface geometry (as could potentially be affected by a damage process) from steady-state dynamic measurements of outer surface displacement, the multi-objective GA is shown to provide substantial computational improvement over single-objective strategies. Furthermore, the multi-objective approach consistently traversed the optimization search space to efficiently produce more accurate characterization results and exhibited consistently better tolerance to measurement noise in contrast to the single-objective strategies. In general, the multi-objective approach maintains a high level of diversity in the solution population during the search process, thus being potentially better equipped to avoid local minima during the search process and identify multiple solutions where they exist.
Modeling, Analysis and Experimental Validation of an Electromagnetic Energy Harvesting Unit
Authors: Chen Yan , Salehian Armaghan
Published: July 2013

Vibration energy harvesting devices have been widely used to power many electronic self-sustainable devices. Most traditional linear energy harvesters exploit the phenomenon of resonance to produce electric power. Nonlinear energy harvesters however present more interesting alternatives and have demonstrated capabilities to harvest power over a wider range of frequencies due to characteristics such as bifurcation. The aim of this study is to introduce an alternative design to nonlinear electromagnetic energy harvesting devices to improve the power production of the unit. The configuration presented in the current work has more degrees of freedom compared to some previously designed devices, and has demonstrated higher power efficiency over a wider range of frequencies. The power outputs for both previous and current designs are compared and validated against their experimental values. Finally, the validated numerical model is used to find the optimal design to produce the maximum power.
Experimental Nondestructive Testing Using Magnetostrictive Particles Embedded in Carbon Fiber Reinforced Polymer Beams
Authors: Rudd Jonathan , Spayde Dustin , Myers Oliver
Published: July 2013

In this paper, the experimental sensing results of damage testing using magnetostrictive particulate sensors, embedded in fiber reinforced polymer laminates, are presented. Carbon fiber reinforced polymer (CFRP) laminates (Hexcel AS4/3501-6) are embedded with terfenol-d particles and the ply count is varied to observe the change in the sensing. Sensing is observed using a non-contacting magnetostrictive strain sensor setup. The sensing parameter observed is the voltage induced in the secondary circuit. Two of the three batches presented have laminates that are embedded with .5″×.5″, release agent coated patches that prevent bonding between the terfenol-d and the CFRP layer. The laminate ply count ranges from 2–14 unidirectional plies. Two fabrication methods are used to distribute the particles in the laminate. The experimental results from the three batches reveal that the fabrication technique has a significant effect on the sensing signal. The effect of particle accumulation near the sensor dominates the sensing signal and makes the presence of a delamination difficult to assess. The experiments also show that when the ply count is varied, there is not much variation in the sensing signal.
Evolution of Linear Moduli and Nonlinear Responses of a PZT Wafer Under Electric Field at Room and High Temperatures
Authors: Lee Najae , Ji Dae Won , Kim Sang-joo , Kim Yong Soo
Published: July 2013

A poled PZT wafer is subject to electric field loading of pulse type whose magnitude is increasing and then decreasing during a complete cycle of polarization reversal at four room and high temperatures. The PZT wafer is also subject to pure temperature increase from 20 to 110 Celsius degree at various initial states. During the two experiments, electric displacement and in-plane strain are measured. From the measured data, piezoelectric coefficient, permittivity, pyroelectric coefficient, and thermal expansion coefficient are evaluated and their distribution over remnant polarization and temperature is discussed. The dependency of linear moduli on temperature and remnant polarization is used to calculate reference remnant polarization and reference remnant in-plane strain responses to cyclic electric field loading at four different temperatures.
Nonlinear Vibration Response of a Beam With a Breathing Crack
Authors: Wang Gang
Published: July 2013

In this paper, a single degree of freedom system was used to model a beam with a breathing crack. Then analytical approximate solution approach was employed to solve this nonlinear vibration equation based on the Homotopy Perturbation Method (HPM). Nonlinear free vibration frequencies under different crack depth to thickness ratios were calculated and compared to the results that were predicted by the bilinear oscillator model. Both predictions were validated experimental data. It has been clearly shown that the fundamental frequency of a beam with a breathing crack is lower than the case in which the crack is assumed to be open and remains open. Nonlinear forced vibration responses containing all harmonics were determined analytically. Numerical simulation results were used to validate our analytical approximation solutions. A damage detection scheme was proposed to relate the crack depth to thickness ratio with a damage index, which is derived from the nonlinear forced responses. This damage index is able to accurately assess the breathing crack condition even for a very small crack depth.
An Approach for Measuring Quasi-Static Mechanical Loads Using a Low-Power Piezoelectric Sensor
Authors: Vine John A. , Moss Scott D.
Published: July 2013

The Australian Defence Science and Technology Organisation (DSTO) is developing Structural Health Monitoring (SHM) approaches for use on air vehicles. This work describes a potential method for measuring quasi-static strains by monitoring the mechanical-load induced capacitive changes in a piezoelectric sensor. This approach may be combined with the well-documented capability of piezoelectric material to measure dynamic-strain, and may hence allow piezoelectric transducers to be used as low-power, single-solution strain sensors. DSTO has experimentally confirmed that the electrical impedance of a Macro Fiber Composite (MFC) piezoelectric transducer changes with varying strain. In particular, a sensitivity of 1.7 mΩ per με has been observed. With accurate transducer modelling, these changes could be used as an indication of the quasi-static strain in the underlying vehicular structure.
Miniaturization of QR Code Carriers Based on Shape Memory Polymer
Authors: Fritzsche Nikolaus , Pretsch Thorsten
Published: July 2013

Here we present a suitable tag prototype with phase-segregated poly(ester urethane) (PEU) as base material for effectively switching a quick response (QR) code in its surface from non-readable to readable. In comparison with recently introduced tags (different geometry) we minimized the thickness from plaque (2 mm) to foil size (0.5 mm) and reduced the lateral QR code length from 15 to 5 mm. Subsequent to surface-dyeing by means of guest diffusion, the QR code was laser-engraved. The implementation of thermo-mechanical functionalization via tensile deformation and cooling resulted in the formation of stable shapes, which exceeded the barrier of QR code readability at an elongation of 20%. Once functionalized, tags were switched on demand by heating. As such the recovery of the PEU was accomplished and the QR code could again be read out. QR code carriers based on shape memory polymer can be used in product and brand protection applications.
Durability of QR Code Carriers Based on Shape Memory Polymer
Authors: Ecker Melanie , Pretsch Thorsten
Published: July 2013

The surface of a shape memory poly(ester urethane) (PEU) was either black- or blue-colored to obtain switchable quick response (QR) codes after laser engraving and thermo-mechanical functionalization (programming). The investigation of dye and functional stability against UVA and hydrolytic aging (at 23 and 60 °C) gave that contrast decline due to dye decolorization (in case of UVA aging) or distinct dye diffusion (in case of hydrolytic aging) finally inhibited the QR code readability. By contrast, PEU as marked base material could be adequately fixed and recovered even when the Michelson contrast in the QR code region was falling in course of aging below a crucial value of 0.1, whereupon the QR code was no longer readable. Hence, we concluded that under the given experimental conditions the decisive parameter for tag applicability was the surface contrast.
Feasibility of Structural Health Monitoring of High Strain Rate Events Using Fiber Bragg Grating Sensors
Authors: Ayers James , Weerasooriya Tusit , Ghoshal Anindya , Pecora Collin , Gunnarsson Allan , Sanborn Brett , Turney Peter
Published: July 2013

Strategically located Fiber Bragg Grating (FBG) Sensors have been proposed as an in situ method to increase the signal to noise ratio (SNR) for metallic and composite components. This paper presents a systematic study that investigates the viability of FBG Sensors under high strain rate loading by initially measuring 1D-strains in a compression Hopkinson bar experiment, followed by 2D full-field strain-tensor in impact and blast experiments on plates. Specifically, high strain rates from commercialized FBG Sensors are compared to traditional resistive and semi-conductor based strain gages under various levels of 1D high strain rate loading. In the projectile-plate impact experiments, full-field back-surface strain measured using FBG Sensor arrays are compared with that measured from 3D surface Digital Image Correlation (3D-sDIC) strain measuring technique. Finally, strains in welded steel plates subjected to high explosive discharge are monitored with mounted FBG Sensors on the back surface. From this study, potential improvements in the SNR of FBG Sensors are recommended, and the survivability of these sensors under more complex, dynamic loading is evaluated.
Investigations on the Amplitude-Dependent Damping Behavior of Superelastic Shape Memory Alloys
Authors: Böttcher Jonas , Neubauer Marcus , Wallaschek Jörg
Published: July 2013

The nonlinear, hysteretic stress-strain characteristic of superelastic shape memory alloys (SMA) results in energy dissipation and therefore in high damping capacities. Due to the nonlinearity the damping capacity strongly depends on the amplitude of the applied excitation. In this work, a rheological non-smooth model is used to describe the principle behavior of superelastic SMA undergoing harmonic displacements. The equivalent mechanical model consists of a spring representing the elastic deformation of the superelastic SMA in austenitic and detwinned martensitic state. A friction element represents the stress plateaus for forward and backward transformation between austenitic and martensitic state. A constant force is applied to the system to generate an offset which shifts the hysteresis to positive force values. Two mechanical stops are implemented to describe the end of the stress plateaus and therefore correspond to the strain differences of the stress levels for forward and backward transformation. Thus, the system behavior is highly amplitude-dependent.

A harmonic approximation of the force generated by the superelastic SMA element during one excitation period is calculated by applying the Harmonic Balance Method to the nonlinear force signal of the rheological model. In this context the Fourier coefficients are calculated by performing a piecewise integration of the force signal. The Integrals are being calculated for each steady interval. The equivalent stiffness and damping coefficients are given for this approximation as functions of excitation amplitude and the system parameters. Based on these results, the damping capacity of a superelastic shape memory element undergoing harmonic displacements is presented using an analytical expression for the damping ratio.
Optimal Arrangement of Lead Zirconate Titanate (PZT) Actuators for Buckling Control of Cylindrical Shells
Authors: Sandeep Jose , Lakshmana Rao C. , Tangirala Arun K.
Published: July 2013

Cylindrical shells, very commonly used in aerospace applications, are susceptible to buckling when subjected to static and dynamic or transient loads. Bucking load enhancement with minimum weight addition is an important requirement in space structures. Buckling control of space structures using piezoelectric actuators is an emerging area of research. The earlier work on enhancement of buckling load on columns reported a 3.8 times enhancement theoretically and 123% experimentally [1–2]. The enhancement was (25%) when buckling control was implemented on plates [3] using PZT actuators. Buckling control of cylindrical shells is challenging because of the uncertainties in the location of buckling and the coupling between bending and membrane action. Earlier attempt to improve the buckling load carrying capacity of the cylindrical shell did not result in a considerable increase in the buckling load [4]. This is because the buckling modes of cylindrical shell are very close to each other when compared to structures like column and plate. An optimized actuator location is hence necessary to improve the load carrying capacity of the cylindrical shells. Unlike vibration control problems where the actuators locations are optimized to minimize the structural Volume Displacement (SVD) or to maximize the energy dissipation, buckling control is aimed at controlling the critical modes of buckling and hence improving the load carrying capacity of the shells [5]. Numerical analyses are carried out, comparing different configurations used in buckling control of thin shells. Experiments are performed to support the numerical analysis as the behavior of cylindrical shells under axial compression is highly sensitive to geometric imperfections. Load – Axial shortening graphs are used to compare the performance of cylindrical shell for the various actuator configurations.
Detecting Cracks in Reciprocating Compressor Valves Using Pattern Recognition in Frequency Space
Authors: Pichler Kurt , Lughofer Edwin , Buchegger Thomas , Klement Erich Peter , Huschenbett Matthias
Published: July 2013

This paper presents a novel data-driven approach for detecting cracks in reciprocating compressor valves by analyzing vibration data. The main idea is that the time-frequency representation will show typical patterns, depending on the fault state and other variables. The problem of detecting these patterns reliably is solved by taking a detour via two dimensional autocorrelation. This emphasizes the patterns and reduces noise effects, thus identifying appropriate features becomes easier. The features are then classified using well known pattern recognition approaches. The methods performance is validated by analyzing real world measurement data.
Corrosion Damage Monitoring Using Guided Lamb Waves
Authors: Yoo Byungseok , Purekar Ashish
Published: July 2013

In this paper, a Guided Lamb Wave (GLW) technique using piezoelectric transducers is presented to detect and monitor corrosion damage in an aluminum panel. An electro-chemical etching method was applied to simulate corrosion damage in the test article. A signal processing approach using time-based analysis was demonstrated to measure amplitude change and phase shift of GLW signals captured in the aluminum specimen. Damage Index (DI) for each sensor network was calculated based on the time-domain signal processing method. From the DI information, damage profile maps were produced by using a tomographic algorithm. Corrosion damage location and its size were identified from an integrated damage profile map. The severity of the corrosion damage was examined based on the phase shift of a fundamental anti-symmetric mode (A0) in the GLW signals. The experimental results show the capability of the proposed corrosion monitoring technique based on the GLW approach.
Multimodal Lamb Waves Power and Transfer Function Analysis of Structurally-Bonded PWAS
Authors: Lin Bin , Kamal Ayman , Giurgiutiu Victor , Kamas Tuncay
Published: July 2013

This paper presents an investigation of predictive power and energy modeling of space structures for structural health monitoring (SHM) with piezoelectric wafer active sensors (PWAS). After a review of PWAS principles, the paper developed the multi-physics modeling of pitch-catch PWAS transfer function and discusses and the power and energy transduction between structurally guided Lamb waves and PWAS. The focus is a power and energy transduction analysis between the PWAS and a structure containing multimodal ultrasonic guided Lamb waves. The use of multimodal Lamb waves solution for power modeling is an extension of our previously presented simplified model that considered axial and flexural waves with low frequency approximation. Comparison between the axial and flexural approach and Lamb waves approach was evaluated. Frequency response functions are developed for voltage, current, complex power, active power, etc. The paper ends with summary, conclusion, and suggestion for further work.
Cellular Honeycomb-Like Structures With Internal Inclusions in the Unit-Cell
Authors: Pontecorvo Michael E. , Barbarino Silvestro , Gandhi Farhan S.
Published: July 2013

Cellular structures with hexagonal unit cells show a high degree of flexibility in design. Based on the geometry of the unit cells, highly orthotropic structures, structures with negative Poisson’s ratios, structures with high strain capability in a particular direction, or other desirable characteristics may be designed. Much of the prior work on cellular structures is based on hexagonal honeycomb-like unit cells, without any inclusions. The present paper envisages extending conventional cellular honeycomb-like structures to have inclusions or internal features within the unit cells. Various types of internal features such as contact elements, buckling beams, bi-stable/snap-through elements or viscous dashpots can result in unit cells which display stiffening, softening, negative stiffness, or dissipative behavior. A structure can be assembled using a specific element type, or different types of elements in specific arrangements, to provide desired system level behavior. The ability to so optimally and flexibly design cellular structures could potentially lead to their replacing conventional structures made from bulk materials.

As a first step, this paper presents work on hexagonal unit cells with linear springs as the simplest of inclusions. The hexagonal cell itself is comprised of rigid links and pin-joints. Since such a cell has no stiffness of its own, the behavior of any internal feature is emphasized. However, for kinematic stability purposes, three springs are required, and the significance of these constraints within the cell will be discussed. For different spring arrangements, closed-form analytical expressions are derived for the in-plane modulus and Poisson’s ratio. The analytical expressions are validated using NASTRAN finite element simulations, as well as against experimental tensile/compressive tests of fabricated unit cells with internal springs. When the spring stiffness exceeds certain values, the rigid cell wall assumption is no longer valid, and these bounds are established. The validated analysis is used to conduct design studies on how the cell modulus would vary with geometric parameters such as cell angle and cell wall length ratio.
Intrinsic Spatio-Temporal Resolution Analysis of Nondestructive Impact Diagnostic Force Ensembles and Collocated Accelerations in a Composite Beam Structure
Authors: Georgiou Ioannis T.
Published: July 2013

Several ensembles of sweeping diagnostic impulsive forces were measured in a unidirectional carbon-epoxy composite beam modified locally with a soft viscoelastic patch. The spatial uniformity of the typical ensemble of diagnostic signals is addressed by a systematic spatio-temporal coherence analysis in terms of proper orthogonal decomposition (POD) modes. All samples of spanning ensembles are strongly dominated by the same POD mode characterized by a nearly uniform spatial modulation and a sharp triangular pulse time modulation. The higher POD modes have small amounts of energy. They possess an important statistics property: their spatial modulation mean value is nearly zero with standard deviation nearly identical to the nearly uniform value of the dominant POD mode. The nearly uniform spatial distribution of the dominant POD mode is a fuzzy picture of the ideal or nominal one where the impact-generated diagnostic forces should have a time waveform independent of the site of impact. Despite this energy content deficiency, the ensemble of acceleration signals acquired at a fixed point while the beam is excited by an ensemble of sweeping diagnostic forces has very robust POD modal structure. The POD modes show in a clear manner the presence of a soft viscoelastic patch simulating mass modifications. The POD-based coherence analysis of ensembles of diagnostic forces generated in this practical problem is potentially useful for a real-time verification-inspection of the integrity of networks of embedded and surface-mounted actuators and sensors.
Model-Based Feedforward Control of a Robotic Manipulator With Pneumatic Artificial Muscles
Authors: Robinson Ryan M. , Wereley Norman M. , Kothera Curt S.
Published: July 2013

Pneumatic artificial muscles (PAMs) are lightweight, flexible actuators capable of higher specific work than comparably-sized hydraulic actuators at the same pressure and electric motors. PAMs are composed of an elastomeric bladder surrounded by a helically braided sleeve. Lightweight, compliant actuators are particularly desirable in portable, heavy-lift robotic systems intended for interaction with humans, such as those envisioned for patient assistance in hospitals and battlefield casualty extraction. However, smooth and precise control remains difficult because of nonlinearities in the dynamic response. The objective of this paper is to develop a control algorithm that satisfies accuracy and smooth motion requirements for a two degree-of-freedom manipulator actuated by pneumatic artificial muscles and intended for interaction with humans, such as lifting a human. This control strategy must be capable of responding to large, abrupt variations in payload weight over a high range of motion. In previous work, the authors detailed the design and construction of a proof-of-concept PAM-based manipulator. The present work investigates the feasibility of combining output feedback using proportional-integral-derivative control or fuzzy logic control with model-based feedforward compensation to achieve improved closed-loop performance. The model upon which the controller is based incorporates the internal airflow dynamics, the geometric parameters of the pneumatic actuators, and the arm dynamics. Simulations were performed in order to validate the control algorithm, guide controller design, and predict optimal gains. Using real-time interface software and hardware, the controller was implemented and experimentally tested on the manipulator. Performance was evaluated for several trajectories, and different payload weights. The effect of varying the feedforward gain was also analyzed. Model refinement further improved performance.
Experimental Characterization of Two-Dimensional Tunable Metamaterials
Authors: Delpero Tommaso , Ermanni Paolo , Casadei Filippo , Ruzzene Massimo , Bergamini Andrea
Published: July 2013

A periodic array of shunted piezoelectric patches is used to produce a two-dimensional metamaterial with tunable properties. The proposed configuration exploits the waveguiding capabilities of a phononic crystal plate in conjunction with a periodic arrangement of eight surface-bonded PZT disks. Each piezo transducer is connected to an independent resistive-inductive network, so that the system features an internal resonance that occurs at the tuning frequency of the shunting circuits. The dispersion relations of the resulting metamaterial are experimentally estimated through detailed mappings of the wavefield measured using a scanning laser doppler vibrometer. Experimental results indicate that the coupled system features a band structure behavior induced by the internal resonance of the electrical networks, and suggest the possibility to alter the waveguiding properties of the considered metamaterial without modifying the physical structure of the phononic crystal plate.
A Biomimetic Jellyfish-Inspired Jet Propulsion System Using an Iris Mechanism
Authors: Marut Kenneth , Stewart Colin , Villanueva Alex , Avirovik Dragan , Priya Shashank
Published: July 2013

A bio-inspired jet propulsion mechanism was designed and developed for development of proficient unmanned undersea vehicles (UUVs). The propulsion mechanism mimics that of the Sarsia sp. jellyfish which measures approximately 1 cm in diameter. In order to achieve a biomimetic uniform bell contraction, an electrical motor was used in conjunction with a novel circumferential actuator based upon a mechanical iris diaphragm. This mechanism allows actuation of a deformable cavity. The current prototype was scaled to a diameter 10 times larger than Sarsia measuring 10 cm in diameter. The performance of the propulsion mechanism was analyzed both experimentally theoretically. The prototype was mounted on a test stand which allowed for measurement of thrust and power consumption. Analytical and experimental results were compared to that of the performance of Sarsia. It was found that the overall mechanism created a maximum thrust of 5.1 N with a calculated vehicle efficiency of 0.17% and proficiency of 4.8 s−1.