bluuebunny/crossref_metadata_2025 huggingface dataset:
Fundamental Understanding of Wave Propagation in a Beam Using PZT Actuators and Sensors
Authors: Venugopal Vishnu Prasad , Wang Gang
Published: February 2014

Embedded smart actuators/sensors, such as piezoelectric types, have been used to conduct wave transmission and reception, pulse-echo, pitch-catch, and phased array functions in order to achieve in-situ nondestructive evaluation for different structures. By comparing to baseline signatures, the damage location, amount, and type can be determined. Typically, this methodology does not require analytical structural models and interrogation algorithm is carefully designed with little wave propagation knowledge of the structure. However, the wave excitation frequency, waveform, and other signal characteristics must be comprehensively considered to effectively conduct diagnosis of incipient forms of damage. Accurate prediction of high frequency wave response requires a prohibitively large number of conventional finite elements in the structural model. A new high fidelity approach is needed to capture high frequency wave propagations in a structure.

In this paper, a spectral finite element method (SFEM) is proposed to characterize wave propagations in a beam structure under piezoelectric material (i.e., PZT) actuation/sensing. Mathematical models are developed to account for both Uni-morph and bi-morph configurations, in which PZT layers are modeled as either an actuator or a sensor. The Timoshenko beam theory is adopted to accommodate high frequency wave propagations, i.e., 20–200 KHz. The PZT layer is modeled as a Timoshenko beam as well. Corresponding displacement compatibility conditions are applied at interfaces. Finally, a set of fully coupled governing equations and associated boundary conditions are obtained when applying the Hamilton’s principle. These electro-mechanical coupled equations are solved in the frequency domain. Then, analytical solutions are used to formulate the spectral finite element model. Very few spectral finite elements are required to accurately capture the wave propagation in the beam because the shape functions are duplicated from exact solutions. Both symmetric and antisymmetric mode of lamb waves can be generated using bimorph or uni-morph actuation. Comprehensive simulations are conducted to determine the beam wave propagation responses. It is shown that the PZT sensor can pick up the reflected waves from beam boundaries and damages. Parametric studies are conducted as well to determine the optimal actuation frequency and sensor sensitivity. Such information helps us to fundamentally understand wave propagations in a beam structure under PZT actuation and sensing. Our SFEM predictions are validated by the results in the literature.
Nonlinear Dynamics of the Hybrid Rotary-Translational Energy Harvester
Authors: Karami M. Amin , Inman Daniel J.
Published: February 2014

The analytical modeling and experimental investigation of a nonlinear electromagnetic rotational energy harvester, which can harvest power from rotary and translational excitations, are presented. Some application of energy harvesting such as energy harvesting for tire pressure sensing require an energy harvester which is efficient in generating power from rotational ambient vibrations. The majority of literature on vibration energy harvesting assumes that the ambient excitations are along a single axis. The vibrations from human motion or rotary machines have two components of translational motion as well as a strong rotary motion. The energy harvesting device studied in this paper is a pendulum like device. The base excitations result in rotations of a pendulum. The pendulum is connected to a direct current micro generator. The rotational vibrations of the pendulum generates electricity through the DC generator. Since the energy harvester is responsive to both translational and rotational base excitations, it is called Hybrid Rotary-Translational (HRT) generator.

In this paper a small size HRT harvester is introduced and modeled. The model is used to investigate the relation between the frequency and the amplitude of base vibrations on the vibrations and power generation characteristics of the HRT system. For each frequency and amplitude of vibrations the coexistence of multiple solutions and their basin of attractions are investigated. Three types of ambient excitations are studied: rotational, translational along the direction of gravity, and translational normal to the direction of the gravity.
Analysis of the Experimental Torque Characteristic of a Magnetorheological Clutch Using Neural Networks
Authors: Bucchi Francesco , Forte Paola , Frendo Francesco
Published: February 2014

In this paper the dependence of the torque characteristic of a magnetorheological clutch on several working parameters is analysed by means of a feedforward neural network. The clutch was envisaged to have the possibility to disengage the vacuum pump in diesel engine vehicles, in order to increase the overall vehicle efficiency.

A large set of test was carried out following different protocols in order to obtain a detailed characterization of the clutch. Results showed how, due to the characteristics of MR fluids and to the complex mechanism of torque transmission, the torque characteristics (both the yield torque and the torque-slip behaviour) is function of the relative speed between the primary and secondary clutch groups and also function of the dissipated energy during the clutch slip and of the rest time between consecutive slippages. The data acquired during all tests were used to train a neural network with five input elements and one output element.

The developed neural network was proved to satisfactorily reproduce the actual clutch properties and can be used in the future in an engine-vehicle simulator in order to model the torque characteristic of the clutch subjected to different operating cycles.
Bat Noseleaves as an Inspiration for Smart Emission Baffle Structures
Authors: Gupta Anupam K. , Fu Yanqing , Webster Dane , Müller Rolf
Published: February 2014

Baffle shapes are commonly used in engineered devices to interface sound sources with the free field. Examples are acoustic horns seen in megaphones and horn-loaded loudspeakers. Typical for these devices are simple, static shapes that serve primarily an impedance-matching function. Diffracting baffles linked to a sound source are also common in the biosonar system of bats. In particular in bat groups that emit their ultrasonic pulses nasally, the nostrils are always surrounded by some baffle shape. This is the case across several large and diverse bat families such as horseshoe bats (Rhinolophidae), Old World leaf-nosed bats (Hipposideridae), and New World leaf-nosed bats (Phyllostomidae). However, biosonar baffles differ from their technical counterparts in two important ways: They typically have a much greater geometrical complexity and they are capable of non-rigid shape changes over time. Although simple horn shapes can be found in the noseleaves of many bat species, they are rarely as plain and regular as in megaphones and other technical applications of acoustical horns. Instead, the baffles are broken up into several parts that are frequently augmented with intricate local shape features such as ridges, furrows, and spikes. Furthermore, we have observed that in species belonging to the horseshoe bats and the related Old World leaf-nosed bats these local shape features are often not static, but can undergo displacements as well as non-rigid deformations. At least some of these dynamic effects are not passive byproducts of e.g., sound production or exhalation, but due to specific muscular actuation that can be controlled by the animals. To study these intricate, dynamic baffles as inspirations for smart structures, we have recreated the degrees of freedoms that Old World leaf-nosed bats have in deforming their noseleaves in a digital model using computer animation techniques. In its current form, our model has 6 degrees of freedom that can be used to test interactions between different motions using actuation patterns that occur in life as well as patterns that have not been observed, but could aid understanding. Because of the high-dimensional parameter space spanned by the different degrees of freedom, a high-performance computing platform has been used to characterize the acoustic behavior across a larger number of deformed no seleaf shapes. A physical test bed is currently under construction for implementing baffle motions that have been found to result in interesting changes of the acoustic device characteristics and could hence be of use to engineering applications.
Underwater Energy Harvesting From Base Excitation of Ionic Polymer Metal Composites Undergoing Torsional Vibrations
Authors: Cha Youngsu , Shen Linfeng , Porfiri Maurizio
Published: February 2014

In this study, we investigate underwater energy harvesting from torsional vibration of a patterned ionic polymer metal composite (IPMC). The IPMC design consists of a rectangular polymer strip with patterned electrodes to split the top and bottom surfaces in two equal pairs. We focus on harmonic base excitation of an IPMC, which is modeled as a slender beam with thin cross section vibrating in a viscous fluid. Torsional vibrations with large–amplitude are described using a complex hydrodynamic function considering nonlinear hydrodynamic damping from the surrounding fluid. Along with the theoretical beam model, an electromechanical model is utilized to predict the IPMC electrical response from the torsional deformation of the beam. The integration of both models allows to predict the output voltage of the IPMC from the knowledge of the frequency and amplitude of base excitation. The theoretical predictions are validated against experiments.
Modeling of Conductive Shape Memory Polymer Nanocomposites Based Structure From a Control Perspective
Authors: Shen He , Xu Yunjun , Liang Fei , Gou Jihua , Mabbott Bob
Published: February 2014

Shape memory polymers (SMPs) can recover their original shape under external stimulus such as light, heat, pH, humidity, and electric power. However, the applications of SMPs are limited by the number of shapes they can memorize and whether or not these shapes can be precisely and repeatedly controlled. Although a vision based PID controller has been shown by the authors to be capable of controlling the deflection angle of a SMP structure, the repeatability and precision are still low. In order to enhance the robustness and repeatability of the SMP shape control system, in this paper, the macro-scale behavior model of the SMP structure from the control perspective is proposed and the unknown parameters are identified using real-time vision, temperature, and resistance signals.
Understanding Micro-Droplet Interface Bilayers for Developing Bioinspired Sensors
Authors: Venkatesan Guru , Sarles Andy
Published: February 2014

Droplet-based biomolecular arrays form the basis for a new class of bioinspired material system, whereby decreasing the sizes of the droplets and increasing the number of droplets can lead to higher functional density for the array. In this paper, we report on a non-microfluidic approach to form and connect nanoliter-to-femtoliter, lipid-coated aqueous droplets in oil to form micro-droplet interface bilayers (μDIBs). Two different modes of operation are reported for dispensing a wide range of droplet sizes (2–200μm radius). Due to the high surface-area-to-volume ratios of microdroplets at these length scales, droplet shrinking is prominent, which affects the stability and lifetime of the bilayer. To better quantify these effects, we measure the shrinkage rates for 8 different water droplet/oil compositions and study the effect of lipid placement and lipid type on morphological changes to μDIBs.
Harvesting of Bending Waves in One-Dimensional Infinite Beams Using Resistive-Reactive Circuits
Authors: Tol Serife , Degertekin F. Levent , Erturk Alper
Published: February 2014

Vibration-to-electricity conversion has been heavily researched over the last decade with the ultimate goal of enabling self-powered small electronic components to use in wireless applications ranging from medical implants to structural health monitoring sensors. Regardless of the transduction mechanism used in transforming vibrational energy into electricity, the existing research efforts have mostly focused on deterministic or stochastic harvesting of direct vibrational energy available at a fixed location in space. Such an approach is convenient to design and employ linear and nonlinear vibration-based energy harvesters, such as base-excited cantilevers with piezoelectric laminates. Although the harvesting of local vibrations using linear and nonlinear devices has been well studied, there has been little effort to investigate power extraction from elastic waves propagating in host structures to gain a fundamental understanding of power flow and to best exploit not only standing but also traveling wave energy. This paper explores the problem of piezoelectric energy harvesting from one-dimensional bending waves involving propagating and evanescent components with a focus on infinitely long thin beams. A pair of electroded piezoelectric patches is implemented as the energy harvesting interface connected to a complex electrical load. An analytical modeling framework is given in order to relate the harvested power to incoming wave in the presence of a generalized resistive-reactive circuit. Effects of energy harvesting on the global wave dynamics as well as individual propagating and evanescent wave components are investigated with an emphasis on the wavelength matching concept. The electrical loading conditions for maximum power and efficiency are identified for several special cases in the low frequency range.
Characterizing the Sources of Current Generated by a Membrane-Based Hair Cell Sensor
Authors: Tamaddoni Nima , Sarles Andy
Published: February 2014

Recently, researchers have developed a method to construct a membrane-based hair cell sensor that generates a measurable current in response to physical disturbance of the hair. Representing the cell membrane, a phospholipid bilayer is formed at the interface of two lipid-encased hydrophilic volumes and a hair is located in a center of one of the volumes act a shaking element. In this work, we study the current generated by free vibration of the hair in a revised hair cell embodiment that uses a hair that is physically supported by the surrounding substrate. The current generated by the sensor is measured by a patch clamp amplifier, and the net charge displaced across the membrane during motion of the hair is computed. Experiments performed with a complete hair cell sensor and various control cases that lack a bilayer indicate that the current measured at 0mV applied across the membrane is due to vibration of the positive electrode that changes the local electromagnetic field. Experiments conducted with both geland liquid-supported membranes indicate that gel-supported membranes have a higher sensitivity of (0.066 pC/mV) than liquid-supported membranes (0.015 pC/mV) as the applied voltage increases. Lastly, the motion of the tip of the hair is imaged using a high-speed camera. This test shows that the hair oscillates at the same frequency observed in the measured current traces, which indicates that transverse bending of the bilayer is the cause for the time rate of change in capacitance in the membrane that produces a voltage-dependent current.
Application of SMA Wire for an Active Steerable Cannula
Authors: Konh Bardia , Honarvar Mohammad , Hutapea Parsaoran
Published: February 2014

In this article we present the feasibility of using the shape memory alloy (SMA) wires, namely Nitinol, as an actuator for a steerable surgical cannula. A 3D finite element (FE) model of the actuated steerable cannula was then developed in ANSYS to show deflection of the surgical cannula under the actuation force. The behavior of SMAs was simulated by defining the isothermal stress-strain curves using the multi-elasticity capability of ANSYS. The transformation temperatures of the Nitinol wire at different levels of stress were gathered to form the transformation diagram. Using the one-dimensional Brinson model, the isothermal stress-strain response of the wire was obtained. The thermomechanical characteristics of SMAs were also studied completely by a series of experiments performed on the wires. Birth and death method was used in the solution procedure to have the prestrain condition on Nitinol wire prior to the actuation step. A prototype of the actuated steerable cannula was also developed to validate the numerical simulation. Finally a study was done on design parameters affecting the deflection such as Young’s modulus of cannula, SMA diameter and its offset from the neutral axis of the cannula which can be useful in design optimization.
Active-Cells for the Construction of Redundant and Configurable Articulated Structures
Authors: Swensen John P. , Dollar Aaron M.
Published: February 2014

This paper describes preliminary design and analysis of “active cells” used for the construction of homogeneous actuated electromechanical composite structures made from many of these electromechanical active cells. Each cell consists of a simple rapid-prototyped outer shell containing both a contractile Nitinol element and a return spring, such that these tiny, self-contained contractile engineered cells can serve as the building blocks for larger articulated structures. Each cell occupies approximately 3.0 cm3 in volume. Design considerations are explored that will affect the packing of a number of cells in a mold with a highly elastic binding agent to constrain them. The structures made from these cells can be easily fabricated in a nearly arbitrary shape — by producing an appropriate mold to contain the cells — and can be highly redundant and robust to localized cell failures. The composite structure is actuated via the application of an electrical potential across each of the individual cells, causing the cells to activate through resistive heating. The material properties of the ensemble structure can be varied by changing the properties of the binding material and the return springs of the cells, thus enabling the design of a wide range of stiffness and damping properties.
Design of a Bulk Conductive Polymer Using Embedded Macroscopic Copper Cells
Authors: Nawroj Ahsan I. , Swensen John P. , Dollar Aaron M.
Published: February 2014

This paper introduces a technique of inducing bulk conductivity in a polymer. The technique uses coiled copper ‘cells’ embedded into a polymer during fabrication which can subsequently create highly redundant series-parallel networks. The preceding body of work aimed to improve the conductivity of non-conducting polymers by embedding particulates (of metal, carbon, etc.) into the polymer, or by altering the polymerization chemistry to incorporate conductive elements. The technique described here keeps the process independent of the specific polymer chosen by not relying on the polymerization chemistry to aid in the incorporation of the cells. The embedding drastically lowers the resistivity of the polymer, from 1012 Ω -cm (approx.) for pure silicone rubber to less than 50 Ω -cm for the composite at room temperature: a drop of 12 orders of magnitude. A secondary consideration of this paper is the mechanical stiffness changes brought about by the embedding of metal inside a flexible polymer. Although the connected network of copper cells allows the rubber to be highly conductive in bulk, the cells are themselves compliant and thus have minimal effect on the stiffness of the cured silicone rubber.
A Systematic Approach to Corrosion-Powered Sensor Network Design
Authors: Ouellette Scott , Todd Michael
Published: February 2014

Energy harvesting systems for structural health monitoring applications may be described by three stages: ambient energy transduction, electrical power conditioning, and data acquisition and transmission. Recent developments in low-power CMOS devices have allowed for expanded energy harvesting techniques by reducing the total power demand of sensor nodes.

This paper investigates the system-level interaction between a corrosion-based energy harvester and the low-power sensor node to which it is supplying power. An equivalent circuit model of the energy harvester is developed and the matched parameters (source voltage and equivalent series resistance) are used in the design of the power conditioning and wireless transmitter circuitry. Analysis of the power demand from the sensor node is used to determine the optimum data sampling parameters in terms of available supplied power for long-term in-situ sensing operations on a marine structure.
Control of Snap-Through Transitions in the Response of Mechanically-Equivalent Frequency Modulators
Authors: Borchani Wassim , Lajnef Nizar , Burgueño Rigoberto
Published: February 2014

Converted energy from ambient loading in civil and mechanical structures is typically used as a viable alternative. Although, piezoelectric vibration harvesters have been widely used given their energy conversion ability, these elements exhibit a narrow natural frequency response range, thus considerably limiting the levels of harvestable power.

Recently our group has introduced the concept of using mechanically-equivalent frequency modulators that can transform the low-amplitude and low-rate service and ambient deformations into an amplified input to the piezoelectric transducer. The introduced methods allow energy generation and conversion within the unexplored quasi-static frequency range (≪ 1 Hz). The post-buckling behavior of bilaterally constrained columns was used for frequency up-conversion, and piezoelectric cantilever beams, attached to the columns, were used for energy conversion.

The introduced concept was experimentally validated and finite element simulations were developed to evaluate the effect of system parameters (stiffness, thickness, and walls gap) on the position of the snap-through transition events and the levels of force-displacement at the multiple-equilibrium configurations. It was shown that the considered system parameters can determine the absolute levels of force and displacement, but they offer limited control on the number and the relative spacing between the energy-drop events. This paper shows that the combination of multiple slender elastic columns modulators, in parallel configurations, allows for the tailoring of the number and magnitude of the mode branch switching during the postbuckling response of the complete system. Experimental and numerical results are presented to validate the proposed concept.
Modeling of the Effective Actuation Response of SMA-MAX Phase Composites With Partially Transforming NiTi
Authors: Lester Brian T. , Lagoudas Dimitris C.
Published: February 2014

Shape Memory Alloy (SMA) composites are being increasingly investigated to address a variety of engineering problems. An application of growing interest is an SMA-MAX phase ceramic composite for use in extreme environments. By joining these two constituents, it is intended that the martensitic transformation of the SMA phase may be used with the unique kinking behavior of the MAX phases to improve the composite response. One particular intended outcome of this utilization is the development of residual stress states in the composite. These residual stress states are generated due to the formation of irrecoverable strains resulting from the interaction of the inelastic mechanisms in the system. By tailoring this stress state, the improved mechanical response of the ceramic phase under compression may be taken advantage of. These residual stress states and their effect on the effective thermomechanical response of the composite are explored in this work. To this end, a finite element model of the composite is development. Specifically, a recent 3D phenomenological constitutive model of the SMA phase is incorporated to describe the effects of martensitic transformation and a constitutive assumption for the MAX phase response associated with kink band formation is introduced. An additional non-transforming NiTi phase is noted and the role of its constitutive response is considered. This model is used to study the micromechanics of the associated composite residual stress states. The influence of these residual stresses on the effective actuation response is then investigated and the on the associated composite behavior determined. Specifically, it is shown that the variation in inactive NiTi leads to an altered actuation response.
Dimensionally Stable Optical Metering Structures With NiTi Composites Fabricated Through Ultrasonic Additive Manufacturing
Authors: Evans Phillip , Dapino Marcelo , Hahnlen Ryan , Pritchard Joshua
Published: February 2014

High performance optical metering structures in airborne and space applications need to exhibit dimensional stability in demanding thermal and mechanical environments. Materials for this application should have a low coefficient of thermal expansion, high thermal diffusivity, high specific stiffness and exhibit good ductility. Current materials are limited in one or more of these properties. Common choices are invar, carbonfiber composite, and silicon-carbide. The former has low specific stiffness and thermal diffusivity and the latter choices are brittle materials that require special care and have slow manufacturing processes. In this work, the development of a thermally invariant metal matrix composite will be described along with its incorporation into a high performance optical metering structure. The material is a composite of super-elastic NiTi ribbons and aluminum, where the ribbons are embedded using ultrasonic additive manufacturing. Measurements and modeling of the thermo-elastic response will be presented followed by the design and manufacture of a metering structure. The metering structure design eases integration with an optical bench and lens bezels while leveraging the advantageous properties of this new metal matrix composite.
Characterization of Electrochemical Capacity of a Biotemplated Polypyrrole Membrane
Authors: Northcutt Robert G. , Sundaresan Vishnu-Baba
Published: February 2014

Recent studies of polypyrrole (PPy) electrodes have been increasing the interfacial surface area in order to increase electrochemical performance. We present a novel method of electropolymerizing PPy doped with dodecylbenzenesulfonate (DBS) referred to as biotemplating. A biotemplated conducting polymer utilizes phospholipid vesicles in order to form a three dimensional structure with a sponge-like shape. The vesicles, measuring 1–2 μm in diameter, are added in situ with the polymerization solution. They become enveloped while maintaining their structure during electropolymerization of PPy(DBS). The result of this structure is a significant increase in surface area compared to current techniques. There are several advantages in using biotemplated conducting polymers as battery electrodes. Compared to a planar PPy(DBS) membrane, biotemplated PPy(DBS) membranes have a roughly 50% increased storage capacity. There is an expected reduction in volumetric expansion during ion ingress/egress into the polymer backbone. This reduction would result in decreased fatigue loading and improving cyclability. Further, biotemplated PPy(DBS) membranes can be fabricated into thin structures with increased flexibility, allowing them to be rolled into various packaging sizes. In this article, the charge density of a biotemplated PPy(DBS) membrane as a function of charging and discharging currents is compared to a planar PPy(DBS) membrane. The structural enhancement offers systemic advantages by providing higher volumetric energy density and decreased fatigue loading for applications involving conducting polymer electrodes.
A Chemo-Mechanical Constitutive Model for Conducting Polymers
Authors: Venugopal Vinithra , Zhang Hao , Sundaresan Vishnu-Baba
Published: February 2014

Conducting polymers undergo volumetric expansion through redox-mediated ion exchange with its electrolytic environment. The ion transport processes resulting from an applied electrical field controls the conformational relaxation in conducting polymer and regulates the generated stress and strain. In the last two decades, significant contributions from various groups have resulted in methods to fabricate, model and characterize the mechanical response of conducting polymer actuators in bending mode. An alternating electrical field applied to the polymer electrolyte interface produces the mechanical response in the polymer. The electrical energy applied to the polymer is used by the electrochemical reaction in the polymer backbone, for ion transport at the electrolyte-polymer interface and for conformational changes to the polymer. Due to the advances in polymer synthesis, there are multitudes of polymer-dopant combinations used to design an actuator. Over the last decade, polypyrrole (PPy) has evolved to be the most common conducting polymer actuator. Thin sheets of polymer are electrodeposited on to a substrate, doped with dodecylbezenesulfonate (DBS-) and microfabricated into a hermetic, air operated cantilever actuator. The electrical energy applied across the thickness of the polymer is expended by the electrochemical interactions at the polymer-electrolyte interface, ion transport and electrostatic interactions of the backbone. The widely adopted model for designing actuators is the electrochemically stimulated conformational relaxation (ESCR) model. Despite these advances, there have been very few investigations into the development of a constitutive model for conducting polymers that represent the input-output relation for chemoelectromechanical energy conversion. On one hand, dynamic models of conducting polymers use multiphysics-based non-linear models that are computationally intensive and not scalable for complicated geometries. On the other, empirical models that represent the chemomechanical coupling in conducting polymers present an over-simplified approach and lack the scientific rigor in predicting the mechanical response. In order to address these limitations and to develop a constitutive model for conducting polymers, its coupled chemomechanical response and material degradation with time, we have developed a constitutive model for polypyrrole-based conducting polymer actuator. The constitutive model is applied to a micron-scale conducting polymer actuator and coupling coefficients are expressed using a mechanistic representation of coupling in polypyrrole (dodecylbenzenesulfonate) [PPy(DBS)].
Folding Actuation and Locomotion of Novel Magneto-Active Elastomer (MAE) Composites
Authors: von Lockette Paris , Sheridan Robert
Published: February 2014

Magneto-active elastomers (also called magnetorheological elastomers) are most often used in vibration attenuation application due to their ability to increase in shear modulus under a magnetic field. These shear-stiffening materials are generally comprised of soft-magnetic iron particles embedded in a rubbery elastomer matrix. More recently researchers have begun fabricating MAEs using hard-magnetic particles such as barium ferrite. Under the influence of uniform magnetic fields these hard-magnetic MAEs have shown large deformation bending behaviors resulting from magnetic torques acting on the distributed particles and consequently highlight their ability for use as remotely powered actuators.

Using the magnetic-torque-driven hard-magnetic MAE materials and an unfilled silicone elastomer, this work develops novel composite geometries for actuation and locomotion. MAE materials are fabricated using 30% v/v 325 mesh barium ferrite particles in Dow Corning HS II silicone elastomers. MAE materials are cured in a 2T magnetic field to create magnetically aligned (anisotropic) materials as confirmed by vibrating sample magnetometry (VSM). Gelest optical encapsulant is used as the uniflled elastomer material.

Mechanical actuation tests of cantilevers in bending and of accordion folding structures highlight the ability of the material to perform work in moderate, uniform fields of μ0H = 150 mT. Computational simulations are developed for comparison. Folding structures are also investigated as a means to produce untethered locomotion across a flat surface when subjected to an alternating field similar to scratch drive actuators; geometries investigated show promising results.
Non-Contact Torque Measurement Using Magnetostrictive Galfenol
Authors: Raghunath Ganesh , Flatau Alison B. , Purekar Ashish , Yoo Jin-Hyeong
Published: February 2014

This work deals with the development of a non-contact torque sensor system prototype made from rolled and textured Galfenol, a magnetostrictive alloy of Iron and Gallium. It is already known that this smart material exhibits a linear response to strain in the presence of appropriate biasing magnets. The response of a sensor system built from it follows commercially available strain gages. In this research, the magnetic change in Galfenol due to shear strain experienced by the shaft in torque will be monitored using Hall effect sensors to derive the torque information. Factors affecting the performance of this Wireless Magneto-Elastic Torque Sensor System (WIMETs) such as annealing, rolling process and strain transfer of adhesives shall be explored.

The ability to provide real-time measurements with minimal signal conditioning requirements make a well-designed torque system attractive for applications such as condition based maintenance. Factors such as being non-contact and passive to the shaft, compact and easy to install, accurate, sensitive and cost effective are highly desired for any torque measurement system. A rate-of-change torque sensor that demonstrates both a sensitivity and time resolution high enough to not only recognize failing machinery, but to specifically identify the failing part is also a critical feature. These characteristics have been incorporated in the current design of WIMETs.

A mathematical model for the magneto-elastic coupling along with simulations from COMSOL shall be presented. Results from static tests for various torques and dynamic tests for various torques at different RPMs will be discussed. It will be shown that the WiMET sensor system setup in a clamshell is reliable and exhibits sensitivity of up to 10mV/in-lb. over a wide range of torque (0–150 lb.-in). Its performance will be compared with a commercial torque sensor and results for detection of eccentric loads on the shaft will also be furnished.
Adaptive and Robust Control of an Unmanned Surface Vessel
Authors: Lee Dongbin
Published: February 2014

This paper presents an adaptive sliding mode control structure of underactuated unmanned surface vessel systems under parametric uncertainty. The primary motivation in this research is to compensate for disturbances related to the added hydrodynamic forces and moment in the nonlinear control of a three degree-of-freedom marine vessel. The novelty of this work is the tracking robustness and the compensation for uncertainties common to surface vessels. The first work is to divide the dynamic model of the system into the ship rigid-body terms and added terms induced by hydrodynamics. A sliding-mode controller is designed to force the error trajectory into the sliding surface, which produces a robust tracking result in a finite time. For the parametric uncertainties in the dynamic model, an adaptive controller is designed to compensate using a projection-based adaptation law. After combining these two control schemes, a closed-loop controller designed by a Lyapunov-based control approach over feedback linearization is appropriately designed to yield the nonlinear tracking system bounded in the presence of uncertainties. The mathematical proof shows that a stable tracking result in the sense of Lyapunov-type stability is achieved. Numerical simulation results are shown to demonstrate the validity of these proposed controllers.
An Adjoint Based Approach for Optimal Design of Morphing SMP
Authors: Wang Shuang , Brigham John C.
Published: February 2014

This work presents a strategy to identify the optimal localized activation and actuation for a morphing thermally activated SMP structure or structural component to obtain a targeted shape change or set of shape features, subject to design objectives such as minimal total required energy and time. This strategy combines numerical representations of the SMP structure’s thermo-mechanical behavior subject to activation and actuation with gradient-based nonlinear optimization methods to solve the morphing inverse problem that includes minimizing cost functions which address thermal and mechanical energy, morphing time, and damage. In particular, the optimization strategy utilizes the adjoint method to efficiently compute the gradient of the objective functional(s) with respect to the design parameters for this coupled thermo-mechanical problem.
Efficient Dynamic Modeling and Simulation of Smart Structures With (Equivalent) Circuits
Authors: Marschner Uwe , Starke Eric , Pfeifer Günther
Published: February 2014

The modeling and simulation of smart structures and systems involves coupled field calculations which cause currently high computational costs. Especially time and frequency analyses of sensor or actuator constructions described by equation systems with 10,000 to several 100,000 degrees of freedom demand efficient design methods. A successful approach to solve this problem is to increase the abstraction in a model hierarchy by switching to macro models. In this paper the merits of multi-physics network models applied as macro models are discussed. The main advantage is the significant reduction of the degree of freedom and the transition from PDEs to ODEs. Steady state problems can be efficiently solved with algebraic equations in the complex domain. Another important aspect appreciated by design engineers is the structural graphical system representation offered by networks. Particularly, feedback mechanisms, e.g. from an acoustic subsystem into the mechanical subsystem, can be overviewed. Moreover, linear time-invariant (LTI) multi-physics networks allow the transformation of network elements from one physical domain into another domain. As a consequence transducers can be eliminated and thus the network be simplified. Besides this, passive LTI systems are reversible. This property is the basis of precise measurement techniques.
Damage Detection in Composite Structures With Wavenumber Array Data Processing
Authors: Tian Zhenhua , Leckey Cara , Yu Lingyu
Published: February 2014

Guided ultrasonic waves (GUW) have the potential to be an efficient and cost-effective method for rapid damage detection and quantification of large structures. Attractive features include sensitivity to a variety of damage types and the capability of traveling relatively long distances. They have proven to be an efficient approach for crack detection and localization in isotropic materials. However, techniques must be pushed beyond isotropic materials in order to be valid for composite aircraft components.

This paper presents our study on GUW propagation and interaction with delamination damage in composite structures using wavenumber array data processing, together with advanced wave propagation simulations. Parallel elastodynamic finite integration technique (EFIT) is used for the example simulations. Multi-dimensional Fourier transform is used to convert time-space wavefield data into frequency-wavenumber domain. Wave propagation in the wavenumber-frequency domain shows clear distinction among the guided wave modes that are present. This allows for extracting a guided wave mode through filtering and reconstruction techniques. Presence of delamination causes spectral change accordingly. Results from 3D CFRP guided wave simulations with delamination damage in flat-plate specimens are used for wave interaction with structural defect study.
Analytical Evaluation of Adaptive Seat Energy Absorber for Rotorcraft Semi-Active Crash Safety Seat Development
Authors: Murugan Muthuvel , Yoo JinHyeong , Hiemenz Gregory , Wereley Norman
Published: February 2014

This research study focuses on the analytical evaluation of magneto-rheological (MR) dampers for enhanced occupant protection during vertical crash landings of a helicopter. The current state-of-the-art helicopter crew seat has passive safety mechanisms that are highly limited in their capability to optimally adapt to each type of crash scenario due to variations in both occupant weight and crash severity level. While passive crash energy absorbers work well for a single design condition (50th percentile male occupant and fixed crash severity level), they do not offer adequate protection across a broad spectrum of crash conditions by minimizing the load transmitted to the occupant. This study reports the development of a lumped-parameter human body model including lower leg in a seated posture for rotorcraft crash injury simulation. A physical model of lumped-parameter human body restrained on a crew seat was implemented in multi-body dynamics simulation software. For implementing control, a control algorithm was made to work with the multi-body dynamic model by running co-simulation. The injury criteria and tolerance levels for the biomechanical effects are discussed for each of the identified vulnerable body regions, such as the thoracic lumbar loads for different sized adults. The desired objective of this analytical model development is to develop a tool to study the performance of adaptive semi-active magnetorheological seat suspensions for rotorcraft occupant protection.
Evaluation of the Damage Detection Characteristics of Electrical Impedance Tomography
Authors: Loyola Bryan R. , Arronche Luciana , LaFord Marianne , La Saponara Valeria , Loh Kenneth J.
Published: February 2014

In the United States, many civil, aerospace, and military aircraft are nearing the end of their service life. Many of these service life predictions were determined by models that were created at the time of the design of the structure, possibly decades ago. As a precaution, these structures are inspected on a regular basis with techniques that tend to be expensive and laborious, such as tear-down inspections of aircraft. To complicate matters, new complex materials have been incorporated in recent structures to take advantage of their desirable properties, but these materials sustain damage in a manner that is different from that of past monolithic materials. One example is fiber-reinforced polymer (FRP) composites, which are heterogeneous, direction-dependent, and tend to manifest damage internal to their laminate structure, thus making the detection of this damage nearly impossible. For these reasons, numerous groups have focused on developing sensors that can be applied to or embedded within these structures to detect this damage. Some of the most promising of these approaches include using piezoelectric materials as passive or active ultrasonic sensors and actuators, fiber optic-based sensors to measure strain and detect cracking, and carbon nanotube-based sensors that can detect strain and cracking. These are mostly point-based sensors that are accurate at the location of application but require interpolative methods to ascertain the structural health elsewhere on the structure. To conduct direct damage detection across a structure, we have coupled the ability to deposit a carbon nanotube thin film across large substrates with a spatially distributed electrical conductivity measurement methodology called electrical impedance tomography. As indicated by previous research on carbon nanotube thin films, the electrical conductivity of these films changes when subjected to strain or become damaged. Our structural health monitoring strategy involves monitoring for changes in electrical conductivity across an applied CNT thin film, which would indicate damage. In this work, we demonstrate the ability of the Electrical Impedance Tomography (EIT) methodology to detect, locate, size, and determine severity of damage from impact events subjected to glass fiber-reinforced polymer composites. This will demonstrate the value and effectiveness of this next-generation structural health monitoring approach.
Characteristics of Experimental MSMA-Based Pneumatic Valves
Authors: Flaga Stanislaw , Sioma Andrzej
Published: February 2014

In the course of work on a linear actuator based on a magnetic shape memory alloy (MSMA), a research workstation was constructed enabling the examination of pneumatic valves featuring an electromechanical transducer created with MSMA technology. In this article, the general construction of the research workstation is presented, together with an initial study of a demonstrator of a pneumatic, one-stage, one-way throttle valve. In the presented demonstrator, a simple replacement of a electromechanical transducer into a transducer created with MSMA technology was performed. In addition, the study also describes the problems appearing in such structures along with potential troubleshooting methods.
Origami-Inspired Folding and Unfolding of Structures: Fundamental Investigations of Dielectric Elastomer-Based Active Materials
Authors: Ahmed Saad , McGough Kevin , Ounaies Zoubeida , Frecker Mary
Published: February 2014

We are investigating the use of dielectric elastomers (DE) to realize origami-inspired folding and unfolding of structures. DEs are compliant materials where the coupled electro-mechanical actuation takes advantage of the low modulus and high breakdown strength of the elastomer. Until recently, pre-straining of relatively thick DE materials was necessary in order to achieve the high electric fields required to trigger electrostatic actuation. However, the current availability of thinner DE materials (ex: VHB 9469PC-130μm, VHB 9473 PC −260 μm) has enabled their actuation at achievable electric fields without the need to pre-strain. In this work, an exhaustive study on the fundamentals of DE actuation is done by exploring thickness actuation mechanism and studying the change in dielectric permittivity; we also take advantage of the thin DEs to build actuators with very large bending angles. In particular, we relate the electrostatically-induced thickness contraction in a DE monomorph to the resulting bending once an inactive substrate is added. Both statically and dynamically induced electromechanical thickness strains are measured, and the experimental data is used as an input to a bender model to predict and optimize bending response; variables such as type of inactive material, number of DE layers, and type of electrodes are examined. We will also experimentally track the changes in the dielectric constant as a function of strain, electrode type, and applied electric field; the measured behavior will be used to model thickness and bending actuation. These fundamental studies are necessary to determine ability and limitation of DE materials in a bender configuration. Finally, bending of the DE actuator is transformed into folding by a novel geometric approach, where different shaped notches are introduced in the inactive substrate. The folding configuration is a step towards realizing active origami structure.