bluuebunny/crossref_metadata_2025 huggingface dataset:
A Skin-Like Pressure Sensor Array Based on Silver Nanowires and Conductive Elastomer
Authors: Wang H. P. , Zhou Debao , Cao Jianguo , Lindeke Richard
Published: February 2014

In this research, we developed a skin-like tactile sensor array to measure the contact pressure of curved surfaces. The sensor array is laminated into a thin film with 3mm in thickness and can easily be wrapped around a pencil without damaging its skin-like structure. So far we have achieved the array containing 8×16 sensor elements. Its spatial resolution is 1 element per 9mm2 area and it can measure the pressure up to 360kPa. The sensor-array patch contains three layers. The upper and lower layers are polydimethylsiloxane (PDMS) thin films embedded with conductor strips formed by PDMS-based silver nanowires (AgNWs) networks. The middle layer is formed by the mixing of nickel powder with liquid PDMS for contact force measurement. Experimental tests have demonstrated that conductor strips on the upper layer can maintain their resistances around 23Ω with less than 4Ω increase when the tensile strain is up to 50%. Noted is that conductors made with carbon nanotubes can keep its conductivity unchanged for up to only 40% tensile strain. Through fatigue tests, it is observed that the measured AgNWs/PDMS conductor strip exhibits low and stable resistances. This is one of the desired behaviors of the stretchable interconnects for signal transmission. The integrated sensor system can successfully measure the contact pressure induced by objects of different shapes. It can be applied on curved or non-planar surfaces in robots or medical devices for force detection and feedback.
Seismic Control of Base Isolated Structures Using Novel Magnetorheological Elastomeric Bearings
Authors: Behrooz Majid , Wang Xiaojie , Gordaninejad Faramarz
Published: February 2014

This paper presents the performance of a novel semi-active variable stiffness magnetorheological elastomer (MRE) bearing for seismic mitigation of civil structures. The proposed MRE bearing consists of a traditional steel-rubber vibration absorber, as the passive element, and a MRE with a controllable stiffness behavior. The controllability of the prototype MRE bearing is investigated experimentally under quasi-static and dynamic shear tests. The behavior of the MRE bearings is modeled using a phenomenological method which includes Bouc-Wen hysteresis element. The results show that both the single MRE bearing and an integrated system with four MRE bearings can increase the stiffness, damping, and hysteresis effect with a control input electric current. In addition, to demonstrate the feasibility of utilizing the MRE base isolation for seismic control of structures, a 1:16 scaled, three-story building supported by four MRE bearings, is constructed. A feedback control system is used to validate the effectiveness of the controlled MRE bearing in reducing structural responses. The scaled El-Centro seismic earthquake excitation is applied to the isolated building. The response of the controlled building shows significant reduction in displacement and acceleration compared to those of passive and on-state conditions.
Directional Sensitivity Analysis of a Hydrogel-Supported Artificial Hair Cell
Authors: Sarlo Rodrigo , Leo Donald
Published: February 2014

An artificial hair cell sensor imitates the function of cilia in natural hair cells in order to detect surrounding fluid displacement. Here, a novel structure for creating artificial hair cell sensors uses established methods of creating lipid bilayers at the interfaces of millimeter scale hydrogel shapes. This paper describes the fabrication of the sensor components and the manner in which they are assembled and tested. The hair’s vibration can be detected by monitoring changes in the current produced by mechanical fluctuations in the bilayer. The cross-sectional geometry of the hair can be changed to enable directional sensitivity. Spectral analysis of the sensor current response indicates that frequencies and magnitudes change when a flattened hair is excited in different directions. Finally, the sensor is shown to become more sensitive with applied potential across the bilayer. Results agree with similar studies on this phenomenon.
An Innovative Laser-Processed NiTi Self-Biasing Linear Actuator
Authors: Panton B. , Michael A. , Pequegnat A. , Daly M. , Zhou Y. , Khan M. I.
Published: February 2014

The revolutionary multiple memory material technology allows local modification of shape memory alloy functional properties to create monolithic actuators that exhibit several different thermomechanical characteristics. In this work, high density laser energy was used to process a monolithic piece of NiTi shape memory alloy material to allow synergistic pseudoelastic and shape memory effect behavior. The resulting actuator contains self-biasing properties eliminating the need for a separate biasing mechanism for cyclic actuation. The characteristics of these different local behaviors were analyzed using tensile testing and differential scanning calorimetry. The stress and strain amplitude of the self-biasing linear actuation was characterized with relation to input current control. This work provides proof of concept for local modification of martensitic and austenitic phases; enabling self-biasing linear actuation.
Energy-Efficient MRF-Clutch With Optimized Torque Density
Authors: Güth Dirk , Schamoni Markus , Maas Jürgen
Published: February 2014

The viscous losses at high rotational speeds in idle mode represent a major drawback for an energy-efficient operation of MRF brakes and clutches. In this paper, an innovative concept is presented that allows a complete torque-free idle mode of the mentioned actuators by the use of a MR-fluid control. Using magnetic forces, the MR-fluid control is capable to increase the efficiency and lifetime of MRF based actuators for torque transmission. An approach of designing actuators using the investigated MR-fluid control is applied which considers in detail the required magnetic excitation systems for enabling a MRF movement in the shear gaps. A clutch is presented and simulations of the transient switching behavior are performed. Measurements of a realized clutch underline the functionality and efficiency of those actuators. Additionally, further approaches for a shear gap design are introduced that increase the maximum torque capacity. By the use of a micro-grooved structure for the MR-fluid control, a torque-to-volume ratio can be achieved that is in the order of typical MRF actuators for torque-transmission with completely filled shear gaps.
Operational Model Updating of Low-Order HAWT Models for Structural Health Monitoring Applications
Authors: Velazquez Antonio , Swartz R. Andrew
Published: February 2014

For the past decade, wind turbines have become the largest source of installed renewable-energy capacity in the United States. Economical, maintenance and operation are critical issues when dealing with such large slender structures, particularly when these structures are sited remotely. Because of the chaotic nature of non-stationary rotating-machinery systems such as the horizontal-axis wind turbines (HAWTs), in-operation modeling and computer-aided numerical characterization is typically troublesome, and tends to be imprecise while predicting the real content of the actual aerodynamic loading. Loading environment under operation conditions is usually substantially different from those driven by modal testing or computer-aided model characterization and difficult to measure directly in the field. In addition, rotational machinery such as HAWTs exhibit complex and nonlinear dynamics (i.e., precession and Coriolis effects, torsional coupling, nonlinear geometries, plasticity of composite materials); and are subjected to nonlinear constrained conditions (i.e., aeroelastic interaction). For those reasons, modal-aeroelastic and computer-aided models reproduced under controlled conditions may fail to predict the correct non-stationary loading and resistance patterns of wind turbines in actual operation. Operational techniques for extracting modal properties under actual non-stationary loadings are needed in order to (1) improve computer-aided elasto-aerodynamic models to better characterize the actual behavior of HAWTs in operational scenarios, (2) improve and correlate models, (3) monitor and diagnose the system for integrity and damage through time, or even (4) optimize control systems. For structural health monitoring (SHM) applications, model updating of stochastic aerodynamic problems has gained interest over the past decades. For situations where optimizing objective functions are not differentiable, convex or continuous in nature that is the case of gradient methods such as Modal Assurance Criterion (MAC), global optimization (metaheurstic) methods based on probability principles have emerged. These search engine techniques are promising suitable to cope with non-stationary-stochastic system identification methods for model updating of HAWT systems. A probability theory framework is employed in this study to update the wind turbine model using such a stochastic global optimization approach. Structural identification is addressed under regular wind turbine operation conditions for non-stationary, unmeasured, and uncontrolled excitations by means of the eigensystem realization theory (ERA). This numerical framework is then tied up with an adaptive simulated annealing (ASA) numerical engine for solving the problem of model updating. Numerical results are presented for an experimental deployment of a small HAWT structure. Results are benchmarked and validated with other empirical mode-decomposition and time-domain solutions.
Construction of Bayesian Prediction Intervals for Smart Systems
Authors: Wentworth Mami T. , Smith Ralph C.
Published: February 2014

In this paper, we employ adaptive Metropolis algorithms to construct densities for parameters and quantities of interest for models arising in the analysis of smart material structures. In the first step of the construction, MCMC algorithms are used to quantify the uncertainty in parameters due to measurement errors. We then combine uncertainties from the input parameters and measurement errors, and construct prediction intervals for the quantity of interest by propagating uncertainties through the models.
Controlling the Postbuckling Response of Cylindrical Shells Under Axial Compression for Applications in Smart Structures
Authors: Burgueño Rigoberto , Hu Nan , Lajnef Nizar
Published: February 2014

Elastic instability, long considered mainly as a failure limit state or a safety guard against ultimate failure is gaining increased interest due to the development of active and controllable structures, and the growth in computational power. Mode jumping, or snap-through, during the postbuckling response leads to sudden and high-rate deformations due to generally smaller changes in the controlling load or displacement input to the system. A paradigm shift is thus emerging in using the unstable response range of slender structures for purposes that are rapidly increasing and diversifying, including applications such as energy harvesting, frequency tuning, sensing and actuation. This paper presents a finite element based numerical study on controlling the postbuckling behavior of fiber reinforced polymer cylindrical shells under axial compression. Considered variables in the numerical analyses include: the ply orientation and laminate stacking sequence; the material distribution on the shell surface (stiffness distribution); and the anisotropic coupling effects. Preliminary results suggest that the static and dynamic response of unstable mode branch switching during postbuckling can be fully characterized, and that their number and occurrence can be potentially tailored. Use of the observed behavior for energy harvesting and other sensing and actuation applications will be presented in future studies.
Electronic Damping in Multifunctional Systems
Authors: Wang Ya , Inman Daniel J.
Published: February 2014

As the recent structures seek lighter weight, damping becomes a more critical issue. Decreasing weight increases flexibility causing vibrations to become more prevalent. Damping treatments to reduce unwanted vibrations are usually classified into three categories: passive, semi active and active depending on the degree to which external energy and complexity is needed to achieve the required reduction in vibration. Here we examine the use of a multifunctional structure’s philosophy to introduce and research the concept of “electronic damping” offering an alternative to traditional damping solutions and a capability of providing uniform energy dissipation across a wide range of ambient frequencies and temperatures. The proposed research addresses increasing the range of effectiveness of damping by addressing the temperature and frequency dependence of material damping by using a multifunctional composite system containing an active element. Our approach is to model the mechanics using Lagrange’s formulation for multi-physics systems and to experimentally validate our models using careful experiments. We propose to examine the strength models and properties of the system and to examine the performance by constructing and testing some prototype systems. The focus is on both the electrical integration and the structural integration of the different material systems required to design a completely stand alone multifunctional composite with superior damping properties useful for suppressing vibrations.
Three-Dimensional Numerical Simulation of Thermomechanical Constitutive Model for Shape Memory Polymers With Application to Morphing Wing Skin
Authors: Balogun Olaniyi A. , Mo Changki , Mazher A. K. , Brigham John C.
Published: February 2014

This paper presents three-dimensional numerical simulation of thermomechanical constitutive model for shape memory polymers. Shape memory polymers (SMPs) are a class of smart materials with high potential for application to automotive, aerostructures, and medical devices, which can benefit from its intrinsic shape changing properties. In particular, looking at its application to aerospace substructure such as morphing wings, thermomechanical behavior of the SMPs needs to be well established and predicted.

In order to predict the thermomechanical behavior of SMPs structures, a one-dimensional rheological thermomechanical constitutive model was adopted and a numerical simulation of this model was developed using a commercial finite element analysis package ABAQUS. The particular one-dimensional model was selected due to its potential to represent the key material behaviors of SMP with a relatively low number of required material constants, which is practical for engineering industrial applications. The model was expanded to a three-dimensional isotropic model and then incorporated into the finite element method by means of an ABAQUS user-defined subroutine (UMAT). The methods of three-dimensional expansion and numerical implementation are presented in this work. A time evolution of the analysis was conducted by making use of the backward difference method, which was applied to all quantities within the model including the material properties. A comparison of the numerical simulation results was carried out with the available experimental data.

Numerical simulation results clearly exhibit the thermomechanical properties of the material, which include shape fixity, shape recovery, and recovery stress. Finally, a preliminary set of predictions for an unmanned aerial vehicle (UAV) morphing wing skin are also presented.
Energetic and Dynamic Effects of Operating Fluid on Fluidic Artificial Muscle Actuators
Authors: Meller Michael A. , Bryant Matthew J. , Garcia Ephrahim
Published: February 2014

Pneumatic artificial muscles (PAMs) are a relatively common type of lightweight, fluid power actuation. Some disadvantages of PAMs include the compressibility of the working fluid and low damping. These characteristics result in low efficiencies, poor dynamic response, as well as undesired oscillations of the actuators. This paper presents utilizing hydraulic liquid as the working fluid instead of compressed air. Hydraulic operation resulted in almost triple the efficiency of pneumatic operation. The artificial muscles are experimentally characterized both quasi-statically and dynamically. The quasi-static experiments include the tension-strain relationship as a function of pressure, and an actuator net work efficiency analysis. The dynamic tests consist of a free vibration experiment to determine the change in effective spring constant and damping terms. These experiments are conducted for both PAMs and HAMs (hydraulic artificial muscles), and the results are presented herein.
Swelling Characteristics of 3D-Arbitrary-Geometry of the pH-Sensitive Hydrogels
Authors: Suthar Kamlesh J. , Mancini Derrick C. , Ghantasala Muralidhar K.
Published: February 2014

We present our simulation results of swelling responses of the pH-sensitive, 3D-arbitarary-geometry hydrogel in steady state conditions. The swelling responses of the hydrogels to the changes in environmental stimuli such as solution pH are discussed. The finite element simulation uses three nonlinear partial-differential equations for responsible physical phenomena namely- chemical for ionic transport across the hydrogel, electrical for local electric charge balance within hydrogel, and mechanical for expansion of the hydrogel by the Nernst-Planck, the Poisson’s, and the mechanical field equations respectively. In the case of pH-sensitive hydrogel, material properties such as modulus of elasticity and Poisson’s ratio changes with a change in surrounding environments. Finite element analysis used for present study was carried out by full coupling of above three partial-differential equations with variable material properties. Employing a moving mesh method for 3D geometry, the FEM simulation was performed to account for large-swelling of the pH-sensitive hydrogel. This highly nonlinear and computationally intensive simulation was performed using multicore parallel-processing computer. The simulation results using above mentioned strategy has been validated for 2D geometry and results are in agreement with other published experimental results.
Computational Micromechanics Model to Study the Effective Macroscale Piezoresistivity of Carbon Nanotube-Polymer Nanocomposites for Strain and Damage Sensing
Authors: Chaurasia Adarsh K. , Seidel Gary D. , Ren Xiang
Published: February 2014

The formation/disruption of the electron hopping pathways is considered to be one of the dominant mechanisms affecting macroscale effective piezoresistive response of carbon nanotube (CNT)-polymer nanocomposites. In this study, a computational micromechanics model is developed using finite element techniques to capture the effect of electron hopping induced conductive pathways at the nanoscale which contribute to the macroscale piezoresistive response of the CNT-polymer nanocomposites. In addition, damage is allowed to evolve at the CNT-polymer interface through electromechanical cohesive zones resulting in disruption of electron hopping pathways in the direction of applied strain. The impact of the electron hopping mechanism and nanoscale interfacial damage evolution on the effective piezoresistive response is studied through the macroscale effective material properties and gauge factors evaluated using micromechanics techniques based on electrostatic energy equivalence. It is observed that the interfacial damage at the nanoscale results in lower gauge factors as compared to the perfectly bonded interface.
Development of High-Efficiency Piezoelectric-Based Energy-Harvesting Power Sources Using Motion-Doubling Mechanisms
Authors: Rastegar Jahangir , Murray Richard
Published: February 2014

Piezoelectric-based energy harvesting power sources that employ spring-mass vibrating systems have been employed with great success to harvest energy from various shock loading and/or vibration and oscillatory motions in numerous systems. In these systems, the external stimuli is used to store mechanical energy in the spring of a mass-spring unit which is attached to a piezoelectric element or a magnet and coil generator, and generate electrical energy as the vibrating mass-spring unit undergoes vibration and applies a cyclic load to the piezoelectric element. In this paper, the implementation of such energy harvesting power sources with a novel motion-doubling mechanism is presented. This novel force transmission method has two key advantages. Firstly, it provides the means to amplify the force applied to the piezoelectric element. Secondly, it provides the means of doubling the number of cycles of compressive forces applied to the piezoelectric elements during each cycle of vibration as compared to the direct mass-spring-piezoelectric generators that have been developed to date. The motion doubling and the resulting halving of the required number of cycles of vibration of the mass-spring unit for generating a certain amount of electrical energy has the effect of significantly increasing the mechanical to electrical energy conversion efficiency of the power source by significantly reducing structural damping losses in the spring element and by the increase in the level of force that is applied to the energy harvesting piezoelectric elements. The design and prototype fabrication of such an energy harvesting power sources is discussed.
FEM of Coupled Chemo-Electro-Mechanical Behavior of Human Intervertebral Disc
Authors: Mistri Gayatri K. , Suthar Kamlesh J.
Published: February 2014

This paper describes a fully coupled finite element simulation of the chemo-electro-mechanical effect of the swelling characteristic of a human intervertebral disc. The swelling behavior of human intervertebral disc is strongly influenced by various environmental stimuli such as concentration of the mobile ions, fixed charges on fibrous material, and pH of the surrounding bio-fluid. The swelling behavior can be described by three physical partial differential equations. These equations are-Nernst-Plank for chemical species transport, Poisson’s for the balanced fixed charges inside the vertebral disc, and mechanical field for balanced osmotic pressure and resulting expansion of the disc. The converged solution of the 2D finite element simulation was achieved by full coupling among these equations in moving mesh domain. The effects of several important physical conditions, such as concentration of mobile ions, pH change in surrounding bio-fluid, electrical charge balance, and the expansion/shrinkage of vertebral disc are simulated. The simulation results are discussed in detail.
Experimental Performance Evaluation of Vibration Monitoring Sensor Prototype Driven by Piezocomposite Vibration Energy Harvester Under Low Intensity Excitation Condition
Authors: Adachi Kazuhiko , Sakamoto Tatsuya
Published: February 2014

In this study, we have developed a sensor prototype for vibration acceleration monitoring driven by the authors’ proposed vibration energy harvester. It uses a commercial LTC3588 energy harvesting chip with capacitors and the piezo-bimorph cantilever-type energy harvester consists of the surface bonded two Macro-Fiber Composites. The power consumption of the acceleration sensor was typically 1mW, and the driving current was typically 400 microamperes. For vibration condition monitoring applications of industrial rotating machinery, we assumed that the typical casing or pedestal vibration amplitude of the rotating machinery was 0.71 mm/sec rms according to ISO standard. This low intensity excitation condition was the input for experimental evaluation of the developed sensor prototype. The sensor prototype was able to measure the vibration acceleration of approximately 17 seconds under the vibration input of 0.013G (RMS) at approximately 56Hz every two minutes. Approximately 12% of the input of vibration energy was used for driving the acceleration sensor. Therefore, estimated overall energy transfer efficiency was about 12%. The experimental results indicate the feasibility of the sensor prototype driven by piezocomposite vibration energy harvester.
Demonstration of Combined Shear and Squeeze Strengthening Modes in a Searle-Type Magnetorheometer
Authors: Becnel Andrew C. , Wereley Norman M.
Published: February 2014

This research details a novel method of increasing the shear yield stress of magnetorheological (MR) fluids by combining shear and squeeze modes of operation to manipulate particle chain structures, to achieve so-called compression-assisted aggregation. The contribution of both active gap separation and particle concentration are experimentally measured using a custom-built Searle cell magnetorheometer, which is a model device emulating a rotary Magnetorheological Energy Absorber (MREA). Characterization data from large (1 mm) and small (250 μm) gap geometries are compared to investigate the effect of the gap on yield stress by compression enhancement. Two MR fluids having different particle concentrations (32 vol% and 40 vol%) are also characterized to demonstrate the effect of solids loading on compression-assisted chain aggregation. Details of the experimental setup and method are presented, and a chain microstructure model is used to explain experimental trends. The torque resisted by practical rotary MREAs is directly related to the strength of the MR fluid used, as measured by the shear yield stress. This study demonstrates that it is feasible, utilizing the compression-enhanced shear yield stress, to either (1) design a rotary MREA of a given volume to achieve higher energy absorption density (energy absorbed normalize by device volume), or (2) reduce the volume of a given rotary MREA to achieve the same energy absorption density.
Self-Sensing and Self-Healing of Structural Damage in Fiber Reinforced Composites
Authors: Liu Yingtao , Rajadas Abhishek , Chattopadhyay Aditi
Published: February 2014

Carbon fiber reinforced composites have been used in a wide range of applications in aerospace, mechanical, and civil structures. Due to the nature of material, multiple types of structural damage including micro matrix cracks and delaminations can significant degrade the integrity and safety of composites. It is difficult to detect and repair such damage since they are always barely visible to the naked eye. This paper presents the development of self-sensing and self-healing functions in order to detect damage progression and conduct in-situ damage repair in composite structures. Carbon nanotubes, which are highly conductive materials, are uniformly distributed within epoxy to develop the self-sensing capability. Shape memory polymer is used in the hot spot to obtain the self-healing capability. The developed multi-functional material is applied to carbon fiber reinforced composites for the autonomic detection and heal the matrix cracking. Experimental results showed that the developed composite materials are capable of detecting and healing the matrix cracks and delaminations. The developed self-healing material has the potential to be used as a novel structural material in mechanical, civil, aerospace applications. It can be used to detect and in-situ repair matrix damage induced by low velocity impacts and fatigues.
Cooling Efficiencies of a NiTi-Based Cooling Process
Authors: Schmidt Marvin , Schütze Andreas , Seelecke Stefan
Published: February 2014

Energy saving and environmental protection are topics of growing interest. In the light of these aspects alternative refrigeration principles become increasingly important. Shape memory alloys (SMA), especially NiTi alloys, generate a large amount of latent heat during solid state phase transformations, which can lead to a significant cooling effect in the material. These materials do not only provide the potential for an energy-efficient cooling process, they also minimize the impact on the environment by reducing the need for conventional ozone-depleting refrigerants.

Our paper, presenting first results obtained in a project within the DFG Priority Program SPP 1599 “Ferroic Cooling”, focuses on the thermodynamic analysis of a NiTi-based cooling system. We first introduce a suitable cooling process and subsequently illustrate the underlying mechanisms of the process in comparison with the conventional compression refrigeration system. We further introduce a graphical solution to calculate the energy efficiency ratio of the system. This thermodynamic analysis method shows the necessary work input and the heat absorption of the SMA in stress/strain- or temperature/entropy-diagrams, respectively. The results of the calculations underline the high potential of this solid-state cooling methodology.
Dynamic Model of Dielectric Elastomer Diaphragm Generators for Oscillating Water Column Wave Energy Converters
Authors: Rosati Papini Gastone Pietro , Vertechy Rocco , Fontana Marco
Published: February 2014

Dielectric Elastomers (DEs) are incompressible rubber-like solids whose electrical and structural responses are highly nonlinear and strongly coupled. Thanks to their coupled electro-mechanical response, intrinsic lightness, easy-manufacturability and low-cost, DEs are perfectly suited for the development of novel solid-state polymeric energy conversion units with capacitive nature and high-voltage operation, which are more resilient, lightweight, integrated, economic and disposable than traditional generators based on conventional electromagnetic technology. Inflated Circular Diaphragm DE Generators (ICD-DEGs) are a special embodiment of polymeric transducer which can be used to convert pneumatic energy into usable electricity. Potential application of ICD-DEGs is as Power Take-Off (PTO) system for wave energy converters based on the Oscillating Water Column (OWC) principle. This paper presents a reduced, yet accurate, dynamic model for ICD-DEGs which features one degree of freedom and which accounts for DE visco-elasticity. The model is computationally simple and can be easily integrated into existing wave-to-wire models of OWCs to be used for fast analysis and real-time applications. For demonstration purposes, integration of the considered ICD-DEG model with a lumped-parameter hydrodynamic model of a realistic OWC is also presented along with a simulation case study.
High-Frequency Dynamic Model of a Pre-Loaded Circular Dielectric Electro-Active Polymer Actuator
Authors: Hodgins Micah , Rizzello Gianluca , York Alex , Seelecke Stefan
Published: February 2014

In this work a high-frequency dynamic model of a pre-loaded circular DEAP actuator is developed and experimentally validated. The model is capable of predicting both the static and dynamic response of the actuator. The static response is modeled based on a free energy approach and consists of an Ogden term representing the elastic energy, and a electrical term representing the electrical-mechanical coupling [1]. The addition of viscoelastic elements (spring-dashpot configurations) enables the model to capture the dynamic response. The Ogden coefficients were first identified through a quasi-static force-displacement test of the actuator. A series of validation tests of the actuator at various pre-loads and voltage frequencies showed the model to be in good agreement with the experiments. The model is shown to accurately predict the actuators observed natural frequencies as the pre-deflection and the stiffness of the spring were changed. Future work will include additions to the model to account for relaxation and creep inherent in DEAP material.
Bioinspired Design of IntraVAD Assistive Device for Congestive Heart Failure Patients Using Ionic Polymer Metal Composites and Shape Memory Alloys
Authors: Hosseinipour Milad , Elahinia Mohammad
Published: February 2014

Design and actuation modes of IntraVAD assistive device for end stage congestive heart failure patients are discussed in this paper. Flexibility, biocompatibility and coupled behavior of Ionic Polymer Metal Composites and Shape Memory Alloys allow replicating the motion of natural heart to address the cardiac deficiency. The squeezing motion of the heart is approximated by propulsion mechanism of a jelllyfish, while the rising-twisting motion of the heart is augmented by upward-downward motion of a cone shaped structure. These motion mechanisms may be combined or used separately, in order to create various blood flow regimes and provide different levels of support for each individual. Not only as actuators, but SMAs and IPMCs may be utilized as sensors to provide feedback from instantaneous status of the device to the controller. A device embodiment is introduced and followed by discussion on IPMC and antagonistic two-way SMA actuators in order to explain how actuation modes are delivered.
Miniaturized Pneumatic Artificial Muscles Actuating a Bio-Inspired Robot Hand
Authors: Pillsbury Thomas E. , Robinson Ryan M. , Wereley Norman M.
Published: February 2014

Pneumatic artificial muscles (PAMs) are used in robotics applications for their light-weight design and superior static performance. Additional PAM benefits are high specific work, high force density, simple design, and long fatigue life. Previous use of PAMs in robotics research has focused on using “large,” full-scale PAMs as actuators. Large PAMs work well for applications with large working volumes that require high force and torque outputs, such as robotic arms. However, in the case of a compact robotic hand, a large number of degrees of freedom are required. A human hand has 35 muscles, so for similar functionality, a robot hand needs a similar number of actuators that must fit in a small volume. Therefore, using full scale PAMs to actuate a robot hand requires a large volume which for robotics and prosthetics applications is not feasible, and smaller actuators, such as miniature PAMs, must be used. In order to develop a miniature PAM capable of producing the forces and contractions needed in a robotic hand, different braid and bladder material combinations were characterized to determine the load stroke profiles. Through this characterization, miniature PAMs were shown to have comparably high force density with the benefit of reduced actuator volume when compared to full scale PAMs. Testing also showed that braid-bladder interactions have an important effect at this scale, which cannot be modeled sufficiently using existing methods without resorting to a higher-order constitutive relationship. Due to the model inaccuracies and the limited selection of commercially available materials at this scale, custom molded bladders were created. PAMs created with these thin, soft bladders exhibited greatly improved performance.
Design and Modeling of a Dielectric Elastomer Cylindrical Actuator With Quasi-Constant Available Thrust
Authors: Berselli Giovanni , Scirè Mammano Giovanni , Dragoni Eugenio
Published: February 2014

A novel design for a Dielectric Elastomer (DE) actuator is presented. The actuator is obtained by coupling a cylindrical DE film with a series of slender beams axially loaded beyond their buckling limit. Similarly to previous published solutions, where different actuator geometries were coupled with compliant mechanisms of various topologies, the elastic beams are designed so as to provide a suitable compensating force that allows obtaining a quasi-constant available thrust along the entire actuator stroke. The overall system performance are subsequently evaluated by means finite element analysis, accounting for the large deflection of the buckled-beam springs and for the DE material hyperelasticity. Final results confirm that compact and better behaved constant force cylindrical actuators can be obtained, which potentially outperform similar devices in terms of achievable stroke.
On the Control of a Dielectric Elastomer Artificial Muscle With Variable Impedance
Authors: Palli Gianluca , Berselli Giovanni
Published: February 2014

Artificial Muscles based on Dielectric Elastomers (DE) can potentially enable the realization of bio-inspired actuation systems whose intrinsic compliance and damping can be varied according to the task requirements. Nonetheless, the control of DE-based Variable Impedance Actuators (VIA) is not trivial owing to the non-linear viscoelastic response which characterizes the acrylic dielectrics commonly employed in practical devices.

In this context, the purpose of the present paper is to outline a novel strategy for the control of DE-based VIA. Although the proposed methodology is applicable to generic DE morphologies, the considered system is composed of a couple of conically-shaped DE films in agonistic-antagonistic configuration. Following previously published results, the system dynamic model is firstly recalled. Then, a DE viscoelasticity compensation technique is outlined together with a control law able to shape the DE actuator impedance as desired. The operative limits of the system are explicitly considered and managed in the controller by increasing the operating DE actuator stiffness if required. In addition, the problem of model uncertainties compensation is also addressed. Finally, as a preliminary step towards the realization of a practical DE-based VIA, the proposed control approach is validated by means of simulations.
Frequency Shaped Semi-Active Control for Magnetorheological Fluid-Based Vibration Control Systems
Authors: Choi Young-Tai , Wereley Norman M. , Hiemenz Gregory J.
Published: February 2014

Novel semi-active vibration controllers are developed in this study for magnetorheological (MR) fluid-based vibration control systems, including: (1) a band-pass frequency shaped semi-active control algorithm, (2) a narrow-band frequency shaped semi-active control algorithm. These semi-active vibration control algorithms designed without resorting to the implementation of an active vibration control algorithms upon which is superposed the energy dissipation constraint. These new Frequency Shaped Semi-active Control (FSSC) algorithms require neither an accurate damper (or actuator) model, nor system identification of damper model parameters for determining control current input. In the design procedure for the FSSC algorithms, the semi-active MR damper is not treated as an active force producing actuator, but rather is treated in the design process as a semi-active dissipative device. The control signal from the FSSC algorithms is a control current, and not a control force as is typically done for active controllers. In this study, two FSSC algorithms are formulated and performance of each is assessed via simulation. Performance of the FSSC vibration controllers is evaluated using a single-degree-of-freedom (DOF) MR fluid-based engine mount system. To better understand the control characteristics and advantages of the two FSSC algorithms, the vibration mitigation performance of a semi-active skyhook control algorithm, which is the classical semi-active controller used in base excitation problems, is compared to the two FSSC algorithms.
Linear Two-Port Model of an Active Thermoplastic Composite Structure
Authors: Winkler Anja , Marschner Uwe , Starke Eric , Modler Niels , Fischer Wolf-Joachim , Hufenbach Werner
Published: February 2014

This paper describes new active composite structures based on thermoplastic matrices which contain material homogeneous embedded piezoceramic modules. Starting point is the development of novel thermoplastic compatible piezoceramic modules, so called TPMs. By the utilization of the same matrix material for the composite structure and for the TPM carrier films, these modules afford an opportunity to become directly embedded into the component during its manufacturing process. In this context, the manufacturing technology of the TPMs and of the active composite structure is presented. Furthermore, selected test samples are investigated concerning their modal behavior. Based on the determined characteristics a linear two-port model is used for the reproduction of the experimental results.
An Experimental and Numerical Investigation Into the Effects of Squealer Blade Tip Modifications on Aerodynamic Performance
Authors: Ledezma G. A. , Allen J. , Bunker R. S.
Published: February 2014

Gas turbine blades using the so-called squealer tip configuration represent a majority of the high-pressure first stage blades in service. The squealer tip in its most basic format is simply a two-tooth labyrinth seal projecting from the blade tip towards the stationary shroud or casing. As with all blade tip configurations, the geometry is a compromise between aerodynamics, cooling, mechanical stress, durability, and repair. While many proposed blade tip innovations involve more complex geometries, this study seeks to determine if a simpler geometry, other than a flat tip, can provide equivalent aerodynamic performance with a reasonable chance of satisfying all other design factors. Using an annular sector blade cascade, total pressure loss surveys are measured with three blade tip geometries, the standard squealer tip, a single-sided suction side seal strip, and the single-sided strip with a pressure side winglet added. The same cascade is modeled numerically as a periodic passage for each of the geometries tested. Experiment and simulation both utilize all blade tip cooling flow injection locations and nominal magnitudes, as well as a constant tip clearance above the suction side seal strip. Experimental data show that the removal of the pressure side seal strip reduces the area-averaged total pressure loss slightly, while the addition of a winglet returns the performance to the baseline result. Numerical predictions indicate essentially equal performance for all geometries. The numerical results provide insight into the loss mechanisms of both the tip leakage flows and the coolant injection flows. This study, when combined with literature data on heat transfer and cooling, concludes that the simpler single-sided suction seal strip is better overall than the commonly employed squealer tip.
Blade Tip Carving Effects on the Aero-Thermal Performance of a Transonic Turbine
Authors: De Maesschalck C. , Lavagnoli S. , Paniagua G.
Published: February 2014

Tip leakage flows in unshrouded high speed turbines cause large aerodynamic penalties, induce significant thermal loads and give rise to intense thermal stresses onto the blade tip and casing endwalls. In the pursuit of superior engine reliability and efficiency, the turbine blade tip design is of paramount importance and still poses an exceptional challenge to turbine designers. The ever-increasing rotational speeds and pressure loadings tend to accelerate the tip flow velocities beyond the transonic regime. Overtip supersonic flows are characterized by complex flow patterns, which determine the heat transfer signature. Hence, the physics of the overtip flow structures and the influence of the geometrical parameters on the overtip flow require further understanding to develop innovative tip designs. Conventional blade tip shapes are not adequate for such high speed flows and hence, potential for enhanced performances lays in appropriate tip shaping.

The present research aims to quantify the prospective gain offered by a fully contoured blade tip shape against conventional geometries such as a flat and squealer tip. A detailed numerical study was conducted on a modern transonic turbine rotor blade (Reynolds number is 5.5 × 105, relative exit Mach number is 0.9) by means of three-dimensional Reynolds-Averaged Navier-Stokes calculations. The novel contoured tip geometry was designed based on a 2D tip shape optimization in which only the upper 2% of the blade span was modified. This study yields a deeper insight into the application of blade tip carving in high speed turbines and provides guidelines for future tip designs with enhanced aerothermal performances.
Effects of Blade Degradation on Turbine Performance
Authors: Granovskiy Andrey , Manaev Igor , Vassiliev Vladimir , Kissel Harald
Published: February 2014

The degradation of gas turbine parts due to aging leads to changes in airfoil shape and often causes performance loss. Although the degradation mechanisms and their effects on performance are understood in general (e.g. it is well known that fouling of compressor airfoils reduces mass flow and efficiency), the first quantitative relationships between specific types of part degradation and performance characteristics have only recently been published.

In this paper the degradation of turbine blades with aft-loaded airfoils is considered. The typical deviations of shape were identified based on field experience. The effects of these deviations on turbine performance were assessed using different calculation methods, including 3D Navier-Stokes calculations and methods based on empirical correlations. The effect of blades-length reduction, chord-length reduction, changes in trailing-edge thickness and shape, and variation of stagger angle were analysed. The analysis showed that for aft-loaded airfoils without shrouds, the major influence on turbine performance is the degradation of radial clearances.

A simplified engineering procedure allowing estimation of turbine performance loss due to degradation has been developed. This paper demonstrates how this simplified procedure, can be applied to the estimation of turbine recovery potential during a typical engine overhaul.
Top-down fabrication of large-area GaN micro- and nanopillars
Authors: Debnath Ratan , Ha Jong-Yoon , Wen Baomei , Paramanik Dipak , Motayed Abhishek , King Matthew R. , Davydov Albert V.
Published: February 2014

Large-area gallium nitride (GaN) micro- and nanopillar (NP) arrays were fabricated by plasma etching of lithographically patterned GaN thin-film grown on Si substrate. Deep-ultraviolet lithography, inductively coupled plasma (ICP) etching, and subsequent chemical treatments were effectively utilized to fabricate GaN pillars with diameters ranging from 250 nm to 10 μm. The impact of various plasma etching process parameters and chemical etchants on the morphology, strain, and surface defects of these NPs were studied using scanning-electron microscopy, photoluminescence (PL), and Raman spectroscopy. It was found that the shape of the NPs can be controlled by the substrate temperature during the plasma etch and by using different gas chemistries. Room-temperature PL and Raman spectroscopy measurements revealed significant strain relaxation in 250 nm diameter pillars as compared to 10 μm diameter pillars. PL measurement also indicated that the surface damage from the plasma etch can be removed by etching in KOH-ethylene glycol solution. Post-ICP selective wet chemical etch enabled us to fabricate functional structures such as micro- and nanodisks of GaN, which potentially could be utilized in nitride-based resonators and lasers.