# Scholarly Works, Center for Intelligent Material Systems and Structures (CIMSS)

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- Self-Healing of Ionomeric Polymers with Carbon Fibers from Medium-Velocity Impact and Resistive HeatingSundaresan, Vishnu Baba; Morgan, Andrew; Castellucci, Matt (Hindawi, 2013-06-20)
Show more Self-healing materials science has seen significant advances in the last decade. Recent efforts have demonstrated healing in polymeric materials through chemical reaction, thermal treatment, and ultraviolet irradiation. The existing technology for healing polymeric materials through the aforementioned mechanisms produces an irreversible change in the material and makes it unsuitable for subsequent healing cycles. To overcome these disadvantages, we demonstrate a new composite self-healing material made from an ionomer (Surlyn) and carbon fiber that can sustain damage from medium-velocity impact and heal from the energy of the impact. Furthermore, the carbon fiber embedded in the polymer matrix results in resistive heating of the polymer matrix locally, melts the ionomer matrix around the damage, and heals the material at the damaged location. This paper presents methods to melt-process Surlyn with carbon fiber and demonstrates healing in the material through medium-velocity impact tests, resistive heating, and imaging through electron and optical microscopy. A new metric for quantifying self-healing in the sample, called width-heal ratio, is developed, and we report that the Surlyn-carbon fiber-based material under an optimal rate of heating and at the correct temperature has a width-heal ratio of >0.9, thereby demonstrating complete recovery from the damage.Show more - Active Vibration Isolation Using an Induced Strain Actuator with Application to Automotive Seat SuspensionsMalowicki, Mark; Leo, Donald J. (Hindawi, 2001-01-01)
Show more Active vibration isolation of automotive seats requires actuators that achieve millimeter-range displacements and forces on the order of 300 N. Recent developments in piezoceramic actuator technology provide a means for achieving these force and displacement levels in a compact device. This work demonstrates that prestressed, curved piezoceramic actuators achieve the force and displacement levels required for active isolation of automotive seats. An estimate of the force and displacement requirements are obtained from numerical simulations on a four-degree-of-freedom car and seat model that utilize representive road accelerations as inputs. An actuator that meets these specifications is designed using piezoceramic materials. Free displacement of 4.4 mm and blocked force greater than 300 N are measured. The actuator is integrated within a dead mass setup that simulates the isolation characteristics of an automotive seat. Control experiments demonstrate that active vibration is achievable with realistic road disturbances. Feedback control is able to eliminate any amplification due to mechanical resonance and reduce the isolation frequency from 9.5 Hz to 2 Hz.Show more - Modeling of Shock Propagation and Attenuation in Viscoelastic ComponentsRusovici, R.; Lesieutre, G.A.; Inman, Daniel J. (Hindawi, 2001-01-01)
Show more Protection from the potentially damaging effects of shock loading is a common design requirement for diverse mechanical structures ranging from shock accelerometers to spacecraft. High damping viscoelastic materials are employed in the design of geometrically complex, impact-absorbent components. Since shock transients are characterized by a broad frequency spectrum, it is imperative to properly model frequency dependence of material behavior over a wide frequency range. The Anelastic Displacement Fields (ADF) method is employed herein to model frequency-dependence within a time-domain finite element framework. Axisymmetric, ADF finite elements are developed and then used to model shock propagation and absorption through viscoelastic structures. The model predictions are verified against longitudinal wave propagation experimental data and theory.Show more - Enhanced Piezoelectric Shunt DesignPark, Chul H.; Inman, Daniel J. (Hindawi, 2003-01-01)
Show more Piezoceramic material connected to an electronic shunt branch circuit has formed a successful vibration reduction device. One drawback of the conventional electronic shunt circuit is the large inductance required when suppressing low frequency vibration modes. Also, the large internal resistance associated with this large inductance exceeds the optimal design resistance needed for low frequency vibration suppression. To solve this problem, a modified and enhanced piezoelectric shunt circuit is designed and analyzed by using mechanical-electrical analogies to present the physical interpretation. The enhanced shunt circuit developed in this paper is proved to significantly reduce the targeted vibration mode of a cantilever beam, theoretically and experimentally.Show more - Use of Response Surface Metamodels for Identification of Stiffness and Damping Coefficients in a Simple Dynamic SystemRutherford, A.C.; Inman, Daniel J.; Park, G.; Hemez, F.M. (Hindawi, 2005-01-01)
Show more Metamodels have been used with success in many areas of engineering for decades but only recently in the field of structural dynamics. A metamodel is a fast running surrogate that is typically used to aid an analyst or test engineer in the fast and efficient exploration of the design space. Response surface metamodels are used in this work to perform parameter identification of a simple five degree of freedom system, motivated by their low training requirements and ease of use. In structural dynamics applications, response surface metamodels have been utilized in a forward sense, for activities such as sensitivity analysis or uncertainty quantification. In this study a polynomial response surface model is developed, relating system parameters to measurable output features. Once this relationship is established, the response surface is used in an inverse sense to identify system parameters from measured output features.A design of experiments is utilized to choose points, representing a fraction of the full design space of interest, for fitting the response surface metamodel. Two parameters commonly used to characterize damage in a structural system, stiffness and damping, are identified. First changes are identified and located with success in a linear 5DOF system. Then parameter identification is attempted with a nonlinear 5DOF system and limited success is achieved. This work will demonstrate that use of response surface metamodels in an inverse sense shows promise for use in system parameter identification for both linear and weakly nonlinear systems and that the method has potential for use in damage identification applications.Show more - Power consumption of piezoelectric actuators driving a simply supported beam considering fluid couplingStein, Steve C.; Liang, Chen; Rogers, Craig A. (Acoustical Society of America, 1994-09-01)
Show more An electromechanical impedance model is applied to the case of a simply supported beam in an infinite rigid baffle with a fluid medium on one side. The effects of the fluid medium are included in the impedance analysis by considering fluid-structure interaction. The use of static and impedance model for structural acoustic analysis is discussed. Various power consumptions of PZT actuator-driven underwater beam structures will be quantified. The analysis discussed in this paper will be used to determine radiated structural acoustic power without using microphones. This work is the first step toward the determination of power requirements for underwater active structural acoustic control.Show more - Active structural acoustic control of broadband disturbancesBaumann, William T.; Ho, Fu-Sheng; Robertshaw, Harry H. (Acoustical Society of America, 1992-09-01)
Show more A control design technique is developed to actively suppress the acoustic power radiated from a structure, with negligible fluid loading, that is persistently excited by narrow-band or broadband disturbances. The problem is constrained by the assumption that the far-field pressure cannot be measured directly. A method for estimating the total radiated power from measurements on the structure is developed. Using this estimate as a cost function and assuming knowledge of the spectrum of the disturbance, a controller is designed using the linear-quadratic-Gaussian (LQG) theory to minimize the cost. Computer simulations of a clamped-clamped beam show that there is a significant difference in the total radiated power between a system with a vibration-suppression controller and a system with an acoustic controller that accounts for the coupling of these vibrations to the surrounding fluid. In some cases, the acoustic controller increases the system vibration in order to minimize the radiated power.Show more - Active vibration and structural acoustic control of shape memory alloy hybrid composites: Experimental resultsRogers, Craig A. (Acoustical Society of America, 1990-12-01)
Show more Shape memory alloy hybrid composites have been shown both by analytical simulations and experiments to be effective adaptive materials for active vibration and structural acoustics control [Rogers and Robertshaw, Engineering Science Preprints 25, ESP25.88027, Society of Engineering Sciences (1988) and ASME Paper 88-WA/DE-9 ( 1988); Rogers et al., in Proceedings of the 30th Structures, Structural Dynamics, and Materials Conference, AIAA Paper 89-1389 (1989)]. Structural acoustics is the study of how elastic structures radiate or receive sound, and in its most fundamental form involves the simultaneous solution of the differential equations describing the structure and fluid media with appropriate boundary conditions between the two, i.e., a "fully" coupled analysis. This paper will review the state-ofthe-art of active control utilizing shape memory alloy hybrid composites and present experimental results showing active dynamic tuning by a method called active strain energy tuning (ASET), active control of sound radiation from a clamped-baffled beam, and transient vibration control of a cantilevered beam.Show more - Dynamic analysis of piezoelectric actuator-driven circular rings using an impedance approachRossi, Anna; Liang, Chen; Rogers, Craig A. (Acoustical Society of America, 1994-09-01)
Show more This paper presents a dynamic model for the response of a circular ring excited by piezoelectric transducer (PZT) actuators bonded on the ring surface. The dynamic response is determined based on the dynamic interaction between the PZT actuators and the structure using an impedance approach. Compared with the conventional static approach, in which a statically determined ''equivalent force'' of the actuator is used as the forcing function in the dynamic analysis, the impedance approach cannot only capture the physics of the actuator/structure interaction, but also accurately predict the structural dynamic response. Experiments have also been conducted to verify the theoretical model. The predicted dynamic response using the impedance approach agrees very well with the experimental results. Comparison of the conventional static approach and the impedance model has also been presented.Show more - Modeling of induced strain actuation of shell structuresChaudhry, Zaffir; Lalande, Frederic; Rogers, Craig A. (Acoustical Society of America, 1995-05-01)
Show more Based on the thin-shell Donnell theory, a model to represent the action of discrete induced strain actuator patches symmetrically bonded to the surface of a circular cylindrical shell has been developed. The model provides estimates of the bending curvatures due to the out-of-phase actuation and the in-plane strains due to the in-phase actuation of the bonded actuator patches. The magnitudes of the induced curvature and the in-plane strain are found to be identical to those of plates; however, due to the strain-displacement relations in cylindrical coordinates, the in-plane and out-of-plane displacements are coupled. Expressions for the equivalent forces and moments that represent the action of the actuator patches have been developed. Due to the curvature of the shell, the representation of the in-phase actuation with an equivalent in-plane line force applied along the edge of the actuator results in the application of erroneous rigid-body transverse forces. To avoid these rigid body forces, a method to represent the in-phase actuation with a system of self-equilibrating forces is proposed. The action of the actuator is then represented by an equivalent in-plane force and a transverse distributed pressure applied in the region of the actuator patch. Finite element verification of the proposed model is presented. The displacements due to the actual actuator actuation are compared with the proposed model, and very good agreement is found. Copyright 1995 Acoustical Society of AmericaShow more - Modeling of distributed piezoelectric actuators integrated with thin cylindrical shellsZhou, Su-Wei; Liang, Chen; Rogers, Craig A. (Acoustical Society of America, 1994-09-01)
Show more The dynamic interaction between induced strain piezoelectric (PZT) actuators and their host structures is often ignored in the modeling of intelligent structures. A more realistic investigation of intelligent material systems must account for the dynamic behaviors of integrated actuator/substrate systems. In this paper, a generic method for the dynamic modeling of distributed PZT actuator-driven thin cylindrical shells has been developed using a mechanical impedance approach. The impedance characteristics of a cylinder corresponding to the excitation of a pair of pure bending moments have been developed, from which the dynamic output moments (or forces) of PZT actuators can be accurately predicted. Direct comparisons have been made between a conventional static modeling approach and the impedance method in order to identify the critical differences between these modeling methods for thin cylindrical structures. The case studies demonstrate that the mechanical impedance matching between PZT actuators and host structures has an impact on the output performance of the actuators. The dynamic essence of integrated PZT/substrate systems has thus been revealed.Show more - Computational analysis of ionic polymer cluster energeticsWeiland, Lisa M.; Leo, Donald J. (American Institute of Physics, 2005-06-01)
Show more In recent years there has been considerable study of the potential mechanisms underlying the electromechanical response of ionic-polymer-metal composites. The most recent models have been based on the response of the ion-containing clusters that are formed when the material is synthesized. Most of these efforts have employed assumptions of uniform ion distribution within spherical cluster shapes. This work investigates the impact of dispensing with these assumptions in order to better understand the parameters that impact cluster shape, size, and ion transport potential. A computational micromechanics model has been developed to predict the equilibrium state of a single cluster of an ionomeric polymer with cluster morphology. No assumptions are made regarding the distribution of charge or the shape of the cluster. For a constant solvated state, the model tracks the position of individual ions within a given cluster in response to ion-ion interaction, mechanical stiffness of the pendant chain, cluster surface energy, and external electric-field loading. Expressions are developed to directly account for forces imposed on ions due to ion-cluster surface interaction. Results suggest that ion pairing is rarely complete; this in turn suggests that the classic assumptions will tend to underpredict electromechanical actuation response. (C) 2005 American Institute of Physics.Show more - Transport modeling in ionomeric polymer transducers and its relationship to electromechanical couplingWallmersperger, Thomas; Leo, Donald J.; Kothera, Curt S. (American Institute of Physics, 2007-01-15)
Show more Ionomeric polymer transducers consist of an ion-conducting membrane sandwiched between two metal electrodes. Application of a low voltage (< 5 V) to the polymer produces relatively large bending deformation (> 2% strain) due to the transport of ionic species within the polymer matrix. A computational model of transport and electromechanical transduction is developed for ionomeric polymer transducers. The transport model is based upon a coupled chemoelectrical multifield formulation and computes the spatiotemporal volumetric charge density profile to an applied potential at the boundaries. The current induced in the polymer is computed using the isothermal transient ionic current associated with surface charge accumulation at the electrodes induced by nonzero volumetric charge density within the polymer. The stress induced in the polymer is assumed to be a summation of linear and quadratic functions of the volumetric charge density. Euler-Bernoulli beam mechanics are used to compute the bending deflection of the transducer to an applied potential. The diffusion coefficient and permittivity of the polymer is identified from the measured current density to a step change in the applied potential. A comparison between the measured data and the predicted response demonstrates that this model accurately predicts the current discharge due to the applied potential at voltages over the range of 50-500 mV. Furthermore, the measured strain response is accurately predicted by determining the two parameters of the mechanics model that relates volumetric charge density to induced stress. The coupled model with parameters identified from the step response analysis is used to predict the harmonic response of the current and the bending strain. Comparisons between measured data and simulations illustrate that the coupled transport-mechanics model accurately predicts the magnitude and trends associated with the current response and strain output. Excellent agreement is obtained at excitation periods above approximately 1 s while good agreement is obtained at longer excitation periods. The transport model highlights the importance of the asymmetry that develops at large applied potentials and long excitation periods in the volumetric charge density due to the fixed anionic species in the polymer. (c) 2007 American Institute of Physics.Show more - Ionic polymer cluster energetics: Computational analysis of pendant chain stiffness and charge imbalanceWeiland, Lisa M.; Leo, Donald J. (American Institute of Physics, 2005-06-15)
Show more In recent years there has been considerable study of the potential mechanisms underlying the electromechanical response of ionic-polymer-metal composites. The most recent models have been based on the response of the ion-containing clusters that are formed when the material is synthesized. Most of these efforts have employed assumptions of uniform ion distribution within spherical cluster shapes. This work investigates the impact of dispensing with these assumptions in order to better understand the parameters that impact cluster shape, size, and ion transport potential. A computational micromechanics model applying Monte Carlo methodology is employed to predict the equilibrium state of a single cluster of a solvated ionomeric polymer. For a constant solvated state, the model tracks the position of individual ions within a given cluster in response to ion-ion interaction, mechanical stiffness of the pendant chain, cluster surface energy, and external electric-field loading. Results suggest that cluster surface effects play a significant role in the equilibrium cluster state, including ion distribution; pendant chain stiffness also plays a role in ion distribution but to a lesser extent. Moreover, ion pairing is rarely complete even in cation-rich clusters; this in turn supports the supposition of the formation of anode and cathode boundary layers. (c) 2005 American Institute of Physics.Show more - High surface area electrodes in ionic polymer transducers: Numerical and experimental investigations of the electro-chemical behaviorAkle, Barbar J.; Habchi, Wassim; Wallmersperger, Thomas; Akle, Etienne J.; Leo, Donald J. (American Institute of Physics, 2011-04-01)
Show more Ionomeric polymer transducer (IPT) is an electroactive polymer that has received considerable attention due to its ability to generate large bending strain (> 5%) and moderate stress at low applied voltages (+/-2 V). Ionic polymer transducers consist of an ionomer, usually Nafion, sandwiched between two electrically conductive electrodes. A novel fabrication technique denoted as the direct assembly process (DAP) enabled controlled electrode architecture in ionic polymer transducers. A DAP built transducer consists of two high surface area electrodes made of electrically conducting particles uniformly distributed in an ionomer matrix sandwiching an ionomer membrane. The purpose of this paper is to investigate and simulate the effect of these high surface area particles on the electro-chemical response of an IPT. Theoretical investigations as well as experimental verifications are performed. The model used consists of a convection-diffusion equation describing the chemical field as well as a Poisson equation describing the electrical field. The two-dimensional model incorporates highly conductive particles randomly distributed in the electrode area. Traditionally, these kinds of electrodes were simulated with boundary conditions representing flat electrodes with a large dielectric permittivity at the polymer boundary. This model enables the design of electrodes with complicated geometrical patterns. In the experimental section, several transducers are fabricated using the DAP process on Nafion 117 membranes. The architecture of the high surface area electrodes in these samples is varied. The concentration of the high surface area RuO2 particles is varied from 30 vol% up to 60 vol% at a fixed thickness of 30 mu m, while the overall thickness of the electrode is varied from 10 mu m up to 40 mu m at a fixed concentration of 45%. The flux and charge accumulation in the materials are measured experimentally and compared to the results of the numerical simulations. Trends of the experimental and numerical investigations are in agreement, while the computational capacity is limiting the ability to add sufficient amount of metal particle to the electrode in order to match the magnitudes. (C) 2011 American Institute of Physics. [ doi:10.1063/1.3556751]Show more - Nonlinear piezoelectricity in electroelastic energy harvesters: Modeling and experimental identificationStanton, Samuel C.; Erturk, Alper; Mann, Brian P.; Inman, Daniel J. (American Institute of Physics, 2010-10-01)
Show more We propose and experimentally validate a first-principles based model for the nonlinear piezoelectric response of an electroelastic energy harvester. The analysis herein highlights the importance of modeling inherent piezoelectric nonlinearities that are not limited to higher order elastic effects but also include nonlinear coupling to a power harvesting circuit. Furthermore, a nonlinear damping mechanism is shown to accurately restrict the amplitude and bandwidth of the frequency response. The linear piezoelectric modeling framework widely accepted for theoretical investigations is demonstrated to be a weak presumption for near-resonant excitation amplitudes as low as 0.5 g in a prefabricated bimorph whose oscillation amplitudes remain geometrically linear for the full range of experimental tests performed (never exceeding 0.25% of the cantilever overhang length). Nonlinear coefficients are identified via a nonlinear least-squares optimization algorithm that utilizes an approximate analytic solution obtained by the method of harmonic balance. For lead zirconate titanate (PZT-5H), we obtained a fourth order elastic tensor component of c(1111)(p)=-3.6673 x 10(17) N/m(2) and a fourth order electroelastic tensor value of e(3111)=1.7212 x 10(8) m/V. (C) 2010 American Institute of Physics. [doi:10.1063/1.3486519]Show more - Modeling the electrical impedance response of ionic polymer transducersFarinholt, Kevin M.; Leo, Donald J. (American Institute of Physics, 2008-07-01)
Show more An analytical study is presented that investigates the electrical impedance response of the ionic polymer transducer. Experimental studies have shown that the electromechanical response of these active materials is highly dependent upon internal parameters such as neutralizing counterion, diluent, electrode treatment, as well as environmental factors such as ambient temperature. Further examination has shown that these variations are introduced predominantly through the polymer's ability to convert voltage into charge migration. This relationship can easily be represented by the polymer's electrical impedance as measured across the outer electrodes of the transducer. In the first half of this study an analytical model is developed which predicts the time and frequency domain characteristics of the electrical response of the ionic polymer transducer. Transport equations serve as the basis for this model, from which a series of relationships are developed to describe internal potential, internal charge density, as well as surface current. In the second half of this study several analytical studies are presented to understand the impact that internal parameters have on the polymer's electrical response, while providing a conceptual validation of the model. In addition to the analytical studies several experimental comparisons are made to further validate the model by examining how well the model predicts changes in temperature, viscosity and pretention within the ionic polymer transducer. (c) 2008 American Institute of Physics.Show more - Power generation and shunt damping performance of a single crystal lead magnesium niobate-lead zirconate titanate unimorph: Analysis and experimentErturk, Alper; Bilgen, O.; Inman, Daniel J. (AIP Publishing, 2008-12-01)
Show more This letter investigates the power generation and shunt damping performance of the single crystal piezoelectric ceramic lead magnesium niobate-lead zirconate titanate (PMN-PZT) analytically and experimentally. PMN-PZT is a recently developed interface for energy harvesting and shunt damping with its large piezoelectric constant (-2252 pm/V) and coupling coefficient (0.95) for the transverse piezoelectric mode. A unimorph PMN-PZT cantilever with an aluminum substrate is tested under base excitation and its electromechanical response is predicted with a coupled distributed parameter model. The power generation performance of the device is 138 mu W/(g(2) cm(3)) at 1744 Hz, causing 84% tip vibration attenuation due to the resistive shunt damping effect.Show more - Resonant manifestation of intrinsic nonlinearity within electroelastic micropower generatorsStanton, Samuel C.; Erturk, Alper; Mann, Brian P.; Inman, Daniel J. (AIP Publishing, 2010-12-01)
Show more This letter investigates the nonlinear response of a bimorph energy harvester comprised of lead zirconate titanate (PZT-5A) laminates. For near resonant excitations, we demonstrate significant intrinsic nonlinear behavior despite geometrically linear motion. Fourth order elastic and electroelastic tensor values for PZT-5A are identified following methods recently published concerning a PZT-5H bimorph. A response trend indicative of a nonlinear dissipative mechanism is discussed as well as the inadequacy of linear modeling. The PZT-5A bimorph exhibits an increased softening frequency response in comparison to PZT-5H. The results contained herein are also applicable to electroelastic sensor and actuator technologies. (C) 2010 American Institute of Physics. [doi:10.1063/1.3530449]Show more - On the energy harvesting potential of piezoaeroelastic systemsErturk, Alper; Vieira, W. G. R.; De Marqui, C.; Inman, Daniel J. (AIP Publishing, 2010-05-01)
Show more This paper investigates the concept of piezoaeroelasticity for energy harvesting. The focus is placed on mathematical modeling and experimental validations of the problem of generating electricity at the flutter boundary of a piezoaeroelastic airfoil. An electrical power output of 10.7 mW is delivered to a 100 k load at the linear flutter speed of 9.30 m/s (which is 5.1% larger than the short-circuit flutter speed). The effect of piezoelectric power generation on the linear flutter speed is also discussed and a useful consequence of having nonlinearities in the system is addressed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3427405]Show more