Journal of Intelligent Material Systems and Structures recent issues

Spherical Brake with MR Fluid as Multi Degree of Freedom Actuator for Haptics

Senkal, D., Gurocak, H. — Thu, 12 Nov 2009 03:08:42 PST

This research explored design of a magnetorheological (MR) spherical brake as a multi-DOF actuator. To the best of our knowledge, our design is the first ever multi-DOF spherical brake using MR fluid. The primary goal was to design a compact but powerful brake using the serpentine flux path approach. An optical position measurement system was also designed to eliminate the gimbal mechanisms that are typically used in spherical joints for position measurement. It was found that the braking torque scales up proportionally to the cube of the brake radius. This enables making much more powerful brakes without increasing the overall size significantly. A prototype spherical brake was built with 76.2 mm diameter and 3.7 Nm braking torque. Experiments were conducted to identify the characteristics of the prototype brake and to test it in virtual wall collision, damping and Coulomb friction simulations for haptics. A joystick was built as a haptic device using the MR spherical brake. Virtual wall collision experiments showed crisp reaction force at initial contact and very high rigidity during the contact.

Recursive Memory-based Hysteresis Modeling for Solid-state Smart Actuators

Bashash, S., Jalili, N., Evans, P., Dapino, M. J. — Thu, 12 Nov 2009 03:08:42 PST

This article presents a new modeling approach for the memory-dependent hysteresis phenomenon in a broad class of smart structures and systems. We propose a recursive formulation to relate the minor hysteresis trajectories to their surrounding loops. More specifically, each internal (minor) trajectory targets its previous turning point and converges to its neighboring loop with a tunable exponential rate. By applying the ‘curve alignment’ and the ‘wiping out’ properties at the turning points, we present a new strategy within the context of a memory-based hysteresis modeling framework. A Galfenol-driven micropositioning actuator and a piezoelectrically driven nanopositioning stage are used to experimentally validate the model. Galfenol exhibits large butterfly-type nonlinearity with a small hysteresis effect, while the piezoelectric actuator exhibits wide hysteresis loops. The model is able to precisely predict the major and minor hysteresis loops in both the Galfenol and piezoelectric actuators, and is expected to be effectively and conveniently applicable to general systems exhibiting memory-dependent hysteresis.

Reduction of Structural Acoustic Radiation Via Left and Right Eigenvector Assignment Approach

Wu, T.Y., Wang, K.W. — Thu, 12 Nov 2009 03:08:42 PST

The objective of this research is to investigate the feasibility of utilizing a new left—right eigenvector tailoring method in reducing the acoustical radiations of flexible structures. The structural sound pressure radiation can be expressed in terms of a combination of vibration modes, where its magnitude is also a function of the external disturbance distribution. In other words, the radiated sound pressure level depends on both the right eigenvectors (related to the structural mode shapes) and left eigenvectors (related to the system disturbance rejection ability) of the vibrating structure. The basic idea of the proposed approach is to simultaneously modify the structural modal velocity distribution and the system capability of disturbance rejection through active left—right eigenvector assignment control actions, so that the sound pressure radiated from the vibrating structure can be reduced. Numerical simulations are performed to evaluate the effectiveness of the proposed method on structural noise reduction. Frequency responses of sound pressure at a receiver in the selected frequency range are illustrated. It is shown that with the proposed active control method, one can re-shape the modal velocity distribution and enhance disturbance rejection, and hence can effectively minimize the structural sound pressure radiation.

Finite Deformations of Tubular Dielectric Elastomer Sensors

Son, S., Goulbourne, N.C. — Thu, 12 Nov 2009 03:08:42 PST

This article describes a numerical model validated with experimental results for a large stretch tubular sensor. The sensor is a dielectric elastomer (DE) membrane with electrical properties that can be accurately correlated with mechanical strain, for strains well over 50%. The DE sensor is a passive capacitive sensor. To illustrate the concept, the sensor is attached to the inner surface of a fiber-reinforced elastomer actuator, which serves as the host substrate. Fiber-reinforced elastomers configured for pneumatic operation are employed as actuators in robotic, prosthetic, and morphing applications. An electromechanical model for the two-layer composite consisting of the fiber-reinforced elastomer and the sensor is derived. For several illustrative loading profiles, the model yields a strain output for an input capacitance value. Using identical loading cases, an experimental setup was designed to measure sensor output for two different sensor materials: silicone and polyacrylate. The sensitivity of the DE sensor was also evaluated for varying geometrical parameters and is mainly dependent on the initial thickness. Comparison of experimental data and numerical results is very good with an overall error of 3—6%. This work shows that the model is robust in the large strain range and furthermore predicts non-linear strain behavior.

Unsteady Fluid Flow in Hybrid Hydraulic Actuators

John, S., Chaudhuri, A., Cadou, C., Wereley, N. M. — Thu, 12 Nov 2009 03:08:42 PST

The ability of smart materials like piezoelectrics to deliver large blocking forces in a small package while operating at high frequencies makes them extremely attractive for converting electrical energy to mechanical power. This led to the development of hybrid actuators consisting of co-located smart material actuated pumps and hydraulic cylinders that are connected by a set of fast-acting valves. The overall success of the hybrid concept hinges on the effectiveness of the coupling between the smart material and the fluid. This, in turn, is strongly dependent on the resistance to fluid flow in the device. This article presents results from 3D simulations of unsteady fluid flow in the pumping chamber of a prototype hybrid actuator powered by a piezoelectric stack. The results show that the forces associated with moving the fluid into and out of the pumping chamber exceed 10% of the piezo stack blocked force at relatively low frequencies near 100 Hz and approach 80% of the blocked force at 800 Hz. This reduces the amplitude of the piston motion in such a way that the volume flow rate remains approximately constant above operating frequencies of 600 Hz. As the driving frequency is increased beyond 800 Hz, the flow rate starts to decrease. This study also presents a decomposition of the pressure loss into its Fourier components and identifies the important harmonics.

Temperature Dependence of Magneto-rheological Materials

Sahin, H., Wang, X., Gordaninejad, F. — Thu, 12 Nov 2009 03:08:42 PST

The properties of magneto-rheological (MR) materials are temperature dependent. Compared to MR fluids, MR greases (MRGs) are more sensitive to temperature due to their inherent behavior of carrier materials. In this study, MRGs are studied to examine the temperature effect on their yield stress and apparent viscosity. Experimental data are obtained for magnetic fields ranging from 0.14 T to 0.53 T and temperatures ranging from 10^°C to 70^°C. It is observed that temperature has a significant effect on the field-induced yield stress of MRGs. A new yield stress model, based on an extended Herschel—Bulkley constitutive relation, in which the shear yield stress is a function of magnetic field and temperature, is proposed. Excellent agreement between the theoretical results and experimental data is obtained.

Equivalent Circuit Modeling of Piezoelectric Energy Harvesters

Yang, Y., Tang, L. — Thu, 12 Nov 2009 03:08:42 PST

Last decade has seen growing research interest in vibration energy harvesting using piezoelectric materials. When developing piezoelectric energy harvesting systems, it is advantageous to establish certain analytical or numerical model to predict the system performance. In the last few years, researchers from mechanical engineering established distributed models for energy harvester but simplified the energy harvesting circuit in the analytical derivation. While, researchers from electrical engineering concerned the modeling of practical energy harvesting circuit but tended to simplify the structural and mechanical conditions. The challenges for accurate modeling of such electromechanical coupling systems remain when complicated mechanical conditions and practical energy harvesting circuit are considered in system design. In this article, the aforementioned problem is addressed by employing an equivalent circuit model, which bridges structural modeling and electrical simulation. First, the parameters in the equivalent circuit model are identified from theoretical analysis and finite element analysis for simple and complex structures, respectively. Subsequently, the equivalent circuit model considering multiple modes of the system is established and simulated in the SPICE software. Two validation examples are given to verify the accuracy of the proposed method, and one further example illustrates its capability of dealing with complicated structures and non-linear circuits.

Coil-based Electromagnetic Damper and Actuator for Vibration Suppression of Cantilever Beams

Cheng, T.-H., Oh, I.-K. — Thu, 12 Nov 2009 03:08:42 PST

In this study, both an eddy current coil damper and an electromagnetic actuator were developed for the vibration suppression of a cantilever beam integrated with a copper coil and a permanent magnet. The control system for the vibration suppression of the electro-magneto-mechanically coupled beam that consists of a coil attached to an aluminum beam and a permanent magnet installed below the coil was proposed. Alternatively, the conductive coil can be passively and actively used as a damper and an actuator. The effects of various coil shapes including a cylindrical tube, a square tube and a circular sheet were investigated to determine optimal vibration suppression for the cantilever beam. The frequency response function of a beam with the theoretical model of the magnetic eddy current damping system was predicted and its accuracy was compared to the experimentally measured frequency response. Also, the results of the active control with a positive position feedback method were compared with those of the passive eddy current dampers with open and closed circuits. The experimental data showed that the tube type coils had much higher vibration suppression efficiency than the sheet type coil and the active vibration control strategy can be alternatively used to improve the electromagnetic damper system.

Detecting Water Accumulation in Honeycomb Sandwich Structures by Optical-fiber-based Distributed Temperature Measurement

Minakuchi, S., Tsukamoto, H., Takeda, N. — Thu, 12 Nov 2009 03:08:42 PST

Water accumulation in honeycomb sandwich structures is a perceived problem for aircraft operators since it significantly degrades the structural integrity. The authors developed a fiber-optic-based technique to detect water accumulation in large-scale aircraft honeycomb sandwich structures. An optical-fiber network was formed in the adhesive layer and a Brillouin-based sensing system with high spatial resolution (specifically, pre-pump pulse Brillouin optical time domain analysis (PPP-BOTDA)) was utilized to detect the non-uniform internal temperature distribution during cooling in aircraft ascent. First, the temperature change during the ascent was investigated to evaluate the feasibility of the proposed technique. A verification test was then conducted using a Nomex honeycomb sandwich panel. The non-uniform temperature induced by water accumulation was detected from the peak-frequency distributions and the width of the Brillouin gain spectrum, which is the output of the PPP-BOTDA. The spectrum width, which represents the temperature non-uniformity within the spatial resolution of the PPP-BOTDA, could indicate the presence of smaller water accumulations compared to the peak frequency, which represents the temperature averaged over the spatial resolution, thus confirming the importance of evaluating the spectrum width. The developed system is quite useful for continuously monitoring large-scale aircraft sandwich structures.

Modeling and Experimental Study of Simultaneous Creep and Transformation in Polycrystalline High-Temperature Shape Memory Alloys

Lagoudas, D. C., Chatzigeorgiou, G., Kumar, P. K. — Thu, 12 Nov 2009 03:08:42 PST

The viscoplastic behavior in high-temperature shape memory alloys and its interaction with the transformation behavior is investigated in this work. Standard creep tests and isobaric transformation-induced tests were conducted for a TiPdNi high-temperature shape memory alloy on a uniaxial frame fitted with a custom high-temperature setup. Motivated by the experimental observations indicating simultaneous creep and phase transformation, a 1D constitutive model is presented that aims to capture the coexistence of the rate-independent transformation and the rate-dependent viscoplastic behavior. Based on continuum thermodynamics, the evolution equations for forward and reverse transformation and viscoplasticity are properly chosen. The material parameters needed for the model calibration are identified from the experimental data. The predicted material response by the proposed constitutive model is in good agreement with the experimental results.

Shaped Modal Sensors for Linear Stochastic Beams

Adhikari, S., Friswell, M.I. — Thu, 12 Nov 2009 03:08:42 PST

Modal sensors and actuators using distributed piezoelectric material have a wide range of applications, for example in vibration control and piezoelectric transformers. The design of these transducers usually ignores any uncertainty and variability in the host structure, which can have a significant effect on their performance. This article investigates the design of shaped piezoelectric sensors for beam structures that are robust with respect to uncertainties in the system. The modal transducers are defined using a discrete approximation to the equations of motion for linear stochastic systems and their shapes are represented using the underlying finite element shape functions. The optimal shape design has been coupled with the stochastic finite element method to consider parametric uncertainty described using random fields, using a first-order perturbation-based approach to obtain the second-order covariance of the modal matrix. The numerical results for linear elastic beam structures showed that the shape of the sensors of the stochastic system can differ significantly from the corresponding deterministic system. However, sensors with shapes designed using a smoothness criterion also perform very well for structures with uncertainty.

Strain and Back Cavity of Tunnel Engineering Surveyed by FBG Strain Sensors and Geological Radar

Li, C., Zhao, Y.-G., Liu, H., Wan, Z., Xu, J.-C., Xu, X.-P., Chen, Y. — Thu, 12 Nov 2009 03:08:42 PST

A differential fiber Bragg grating strain sensor is developed, thereinto, the strain of a gage rod is translated into the deflection of the cantilever beam, on which the fiber Bragg gratings suffer the strain and shift their Bragg wavelengths. In this scheme, temperature compensation is achieved by the differential operation between the Bragg wavelength shifts of sensing gratings mounted on the top and bottom surfaces of the beam. The loading experiment indicates that the least-square linearity between the strain of the gage rod and the difference of the Bragg wavelength shifts of the sensing gratings is 0.3% in the range of the strain -1500 to 1500 µ, the maximum error is 20 µ, and the measure precision is 0.007. According to the flaws of the second lining of Shan Xin-Po Tunnel explored by the geological radar, these differential fiber Bragg grating strain sensors are installed on the lining. During the backfill period of 53 days and the operation period of 341 days, the strain survey results that the strains are related to the distribution of back cavity in the backfill period; however, the strains became gradually stable in the operation period.

Development of a Distributed Force Detectable Artificial Skin Using Microbending Optical Fiber Sensors

Heo, J.-S., Kim, K.-Y., Lee, J.-J. — Tue, 03 Nov 2009 09:03:55 PST

This article describes a skin-like tactile sensor system that can detect a distributed force using microbending optical fiber sensors. In this design, optical fibers are used both as actual force elements and as signal-transmission media. The tactile array sensor is formed by appropriately arranging fibers into two overlapping layers, forming a 2D grid of fibers. When force is imparted to a given fiber taxel, small distortions (microbends) appear in the stressed fibers, resulting in decreases in the transmitted light intensity in these fibers. A prototype sensor of this type has been fabricated and tested. Comparison with a conventional tactile sensor reveals that the proposed tactile sensor provides outstanding performance and many advantages such as water resistive characteristics, high durability, and simple wiring.

Semiactive Backstepping Control for Vibration Reduction in a Structure with Magnetorheological Damper Subject to Seismic Motions

Zapateiro, M., Karimi, H. R., Luo, N., Phillips, B. M., Spencer, B. F. — Tue, 03 Nov 2009 09:03:55 PST

The use of magnetorheological (MR) dampers for mitigating vibrations caused by seismic motions in civil engineering structures has attracted much interest in the scientific community because of the advantages of this class of device. It is known that MR dampers can generate high damping forces with low energy requirements and low cost of production. However, the complex dynamics that characterize MR dampers make difficult the control design for achieving the vibration reduction goals in an efficient manner. In this article, a semiactive controller based on the backstepping technique is proposed. The controller was applied to a three-story building with an MR damper at its first floor subjected to seismic motions. The performance of the controller was evaluated experimentally by means of real time hybrid testing.

A FSDT--MITC Piezoelectric Shell Finite Element with Ferroelectric Non-linearity

Zouari, W., Ben Zineb, T., Benjeddou, A. — Tue, 03 Nov 2009 09:03:55 PST

A shell finite element based on the Reissner/Mindlin first-order shear deformation theory and integrating a bi-dimensional phenomenological ferroelectric constitutive law for domain switching effects is proposed. An electric switching function is considered to indicate the onset of domain switching. Only one internal variable (the remanent polarization) is used in the model. An implicit integration technique based on the return-mapping algorithm is adopted. The shell element is implemented into the commercial finite element code Abaqus^® via the subroutine user element. Some linear (piezoelectric) and non-linear (ferroelectric) tests are considered to validate first, the element formulation and second, the implementation of the bi-dimensional ferroelectric model. It is shown by studying a complex example (the spiral actuator) that the Reissner/Mindlin kinematic hypothesis (no variation of the displacement across the thickness or no thickness variation) is not sufficient for some electromechanical applications for which the d₃₃ effect is of major importance.

Performance Evaluation of Multi-tier Energy Harvesters Using Macro-fiber Composite Patches

Song, H. J., Choi, Y.-T., Purekar, A. S., Wereley, N. M. — Tue, 03 Nov 2009 09:03:55 PST

This study presents the performance evaluation of a vibration-based energy harvester using macro-fiber composite (MFC) elements, which can harvest power from environmental or ambient vibration and shock. An innovative multi-tier energy harvester (MTEH), comprised of a small number of vibrating beam elements with same fundamental frequencies, is developed in this study to overcome the harvested power limitations of single-tier energy harvesters (STEHs) with only a single vibrating beam element. First, the governing equations of motion of an MTEH were theoretically obtained for series and parallel connections of pairs of MFC patches on each tier surface. Based on the theoretical model, a vibration-based MTEH, having three tiers with MFC patches adhered to the bottom and top of each tier surface, was designed and fabricated. MTEH performance, which included generated voltage, current, and power, was experimentally and theoretically evaluated in the frequency domain and compared with that of a similar STEH.

Parameter Estimation and its Sensitivity Analysis of the MR Damper Hysteresis Model Using a Modified Genetic Algorithm

Xiaomin, X., Qing, S., Ling, Z., Bin, Z. — Tue, 03 Nov 2009 09:03:55 PST

The recently developed magnetorheological (MR) dampers serve as an ideal candidate for diverse applications including structural vibration suppression, shock absorption, and vibration control in vehicle systems. Previous research indicates that they are characterized with non-linear hysteresis and this was further testified in the present study. Various models have been proposed to interpret the complex characteristic, but they are plagued by certain limitations. In view of this, the present study sets out to propose a more efficient genetic algorithm (GA) and a simplified Bouc—Wen model. And it moves to adopt and improve the GA by some effective methods including effective selection methods, adaptive genetic operators and appropriate termination criteria. Then the simplified Bouc—Wen model is obtained by fixing the values of the insensitive parameters in the original model based on the sensitivity analysis theory. Finally, the experimental data of the MR damper responses verify that the proposed approaches are capable of efficient computations and accurate parameter estimation. Also suggested are the implications of the present study on other novel smart dampers.

On-line Estimation of Effective Bulk Modulus in Fluid Power Systems Using Piezoelectric Transducer Impedance

Kim, G. W., Wang, K.-W. — Tue, 03 Nov 2009 09:03:55 PST

The effective bulk modulus of working fluids plays an important role in the control of hydraulic actuation systems because of its effect on the system response time and performance. Therefore, to ensure good control, monitoring the effective bulk modulus of the working fluids is an important task. Current methods normally require precision test equipment consisting of many complex components. The size of these devices is large and thus makes online measurement impractical. In this research, we develop a new on-line technique to estimate effective bulk modulus of the working fluids based on measurements of the impedance of piezoelectric transducers. The idea is to generate a sensitivity curve characterizing the relationship between the effective bulk modulus and the impedance resonant frequency via either off-line numerical simulation or off-line experimental calibration; the curve can then be used for monitoring the working fluids bulk modulus in an online manner. In this article, a simulation model is utilized to predict the peak resonance frequency of the impedance function and identify its dependency on the variation of the fluid bulk modulus. The new approach is then illustrated and a sensitivity curve is generated through comparing the simulation results with experimental data.

Development, Characterization, and Design Considerations of Ni19.5Ti50.5 Pd25Pt5 High-temperature Shape Memory Alloy Helical Actuators

Stebner, A., Padula, S., Noebe, R., Lerch, B., Quinn, D. — Tue, 03 Nov 2009 09:03:55 PST

Shape memory alloys (SMAs) have been used in various applications since their discovery. However, their use as actuation devices in high-temperature environments has been limited due to the temperature constraints of commercially available materials. Recently, SMAs that produce good work characteristics at elevated temperatures have been developed at NASA’s Glenn Research Center. One such alloy, Ni_19.5Ti_50.5Pd₂₅Pt₅, has shown repeatable strain recovery on the order of 2.5% in the presence of an externally applied stress at temperatures greater than 250°C. Based on these findings, potential applications for this alloy are being explored and further work is being done to assess the use of this alloy in various structural forms. In this article, the characterization of Ni_19.5Ti_50.5Pd₂₅Pt₅ helical actuators is reported, including their mechanical responses and how variations in their responses correlate to changes in geometric parameters and training loads. Finally, implementation of previously published SMA spring design methodology in future SMA helical actuator development is considered through comparison of the observed and predicted responses.

Durability Assessment of Styrene- and Epoxy-based Shape-memory Polymer Resins

Tandon, G.P., Goecke, K., Cable, K., Baur, J. — Tue, 03 Nov 2009 09:03:56 PST

The present study is a baseline assessment of the durability of styrene- and epoxy-based shape memory polymer resin materials being considered for morphing applications when exposed to service environment. The approach for the experimental evaluation is a measurement of the shape memory properties and elastomeric response before and after separate environmental exposure to (i) water at 49^°C for 4 days, (ii) in lube oil at room temperature and at 49°C for 24 h, and (iii) after exposure to xenon arc (63°C, 18 min water and light/102 min light only) and spectral intensity of 0.3—0.4 watts/m² for 125 cycles (250 h exposure time). Parameters being investigated include modulus in the rubbery and glassy state, stored strain, shape fixity, stress recovery ratio, and linear shape recovery. In addition, we monitor changes in specimen color, weight, and dimensions along with onset of damage due to conditioning and subsequent thermomechanical cycling.

A Smart Steel Strand for the Evaluation of Prestress Loss Distribution in Post-tensioned Concrete Structures

Zhou, Z., He, J., Chen, G., Ou, J. — Wed, 21 Oct 2009 07:43:50 PDT

Prestress loss adversely affects the behavior of in-service post-tensioned structures in terms of deflection/camber, cracking, and ultimate capacity. It is thus important to determine the level of prestressing force at various loading stages from the initial prestressing force transfer to the structure, through different in-service loads, to the ultimate load of the structure. Prestress loss is difficult to evaluate due to several intertwined factors such as creep, shrinkage, relaxation, geometric configuration, distributed friction, and slippage of post-tensioned strands. Till date, there is no cost-effective and reliable sensor and installation technique for the long-term monitoring and evaluation of prestress loss. In this study, a smart fiber-reinforced polymer (FRP) rebar with an embedded novel optical fiber (OF) is developed for the distributed strain of post-tensioned strands. The new OF is an integrated global and local monitoring technology developed by combining the Brillouin optical time domain analysis/refectory sensor and the optical fiber Bragg grating into one single fiber. The FRP rebar and six steel wires were bundled together to form a seven-wire steel strand for the post-tensioning and monitoring of concrete structures. The performances of the smart rebar and strand were validated with static tests of a prestressed steel frame structure and a post-tensioned concrete beam. The smart steel strand can accurately measure the prestress loss at each loading stage, which agrees well with that measured by a pressure loading cell and predicted by a design code.

Modeling and Characterization of a Linear Piezomotor

Arafa, M., Aldraihem, O., Baz, A. — Wed, 21 Oct 2009 07:47:08 PDT

This article presents the modeling and characterization of a new class of piezoelectric linear motor. The motor relies in its operation on a set of piezoelectric bimorphs which are sequentially activated to linearly move a drive rod along spring loaded rollers. Emphasis in this article is placed on studying the dynamic behavior of this class of piezoelectric motors, both theoretically and experimentally, in an effort to predict the piezomotor response to various loads and excitation schemes. To this end, a numerical model has been developed to simulate the dynamics of the piezoelectric bimorphs comprising the piezomotor. Friction between the bimorph elements and the drive rod are handled using an appropriate friction model. Experimental testing of the motor is carried out to validate the predictions of the theoretical model.

Design of Piezoelectric Energy Harvesting Systems: A Topology Optimization Approach Based on Multilayer Plates and Shells

Rupp, C. J., Evgrafov, A., Maute, K., Dunn, M. L. — Wed, 21 Oct 2009 20:16:59 PDT

We develop a computational approach to analyze and design piezoelectric energy harvesting systems composed of layered plates and shells connected to an electrical circuit. The finite element method is used to model the coupled electromechanics of the piezoelectric harvesting structure and a lumped parameter model for the dynamics of the electrical circuit. We assume the harvester is subjected to a prescribed harmonic base excitation and that the structural and electrical responses are linear. We use topology optimization to design the layout of a multilayer structure consisting of structural, piezoelectric, and electrode layers, as well as the electrical circuit. The flexibility of our formalism admits the definition of specific system-level objectives, e.g., maximize the power harvested, in an algebraic fashion. After describing our analysis and design approaches, we present examples that demonstrate the versatility of our approach and show how it can be used to explore general behavior and develop overarching design principles for piezoelectric energy harvesting devices. For the objective of maximizing the power harvested, we investigate: (i) optimal designs for various piezoelectric to substrate thickness ratios, (ii) the effect of mass loading on optimal design, and (iii) the sensitivity of designs to shape variations.

Finite Element Modeling of a Slewing Non-linear Flexible Beam for Active Vibration Control with Arrays of Sensors and Actuators

Gilardi, G., Buckham, B.J., Park, E.J. — Wed, 21 Oct 2009 20:16:59 PDT

In this article, a new finite element model (FEM) of an Euler—Bernoulli beam, developed through an absolute nodal coordinate formulation (ANCF), is presented for simulation and analysis of the performance of surface-bonded piezoelectric actuators in suppressing non-linear transverse vibrations that are induced by very fast slewing. The elastic deformations experienced are an order of magnitude larger than cases considered to date, and the model employs a unique cubic spline approximation to the beam’s deformed elastic line that is in terms of node positions and curvatures. To ensure relevant commentary on the vibration suppression properties of the distributed piezoelectric actuators, a material damping model was introduced in the continuum equations to capture the non-linear damping of the very slender beam that is observed in experiments. Following the ANCF methodology, the constitutive damping moment is formulated in terms of the absolute nodal coordinates with care taken to ensure the calculation is singularity free. Galerkin’s method of weighted residuals is applied to discretize the revised equations of motion derived for the beam continuum. The FE beam model exploits a synergy between the twisted spline geometry and the lumped mass approximation to halve the size of the matrix equations that must be solved on each time step. However, this condensation of the matrix equations requires the use of interelement boundaries at the edges of the surface-bonded piezos. Using a single-link flexible manipulator as an example, a number of static and dynamic simulation examples that illustrate the validity of our FEM are presented, including comparisons to theoretical and other existing numerical solutions in literature. In addition, active vibration control examples are presented using proportional- and derivative-based hub motion and piezoelectric actuator controls in suppressing dramatic vibrations induced by fast slewing.

The Effect of Non-linear Piezoelectric Coupling on Vibration-based Energy Harvesting

Triplett, A., Quinn, D. D. — Wed, 21 Oct 2009 20:16:59 PDT

Advances in electronic and consumer technology are increasing the need for smaller, more efficient energy sources. Thus vibration-based energy harvesting, the scavenging of energy from existing ambient vibration sources and its conversion to useful electrical power, is becoming an increasingly attractive alternative to traditional power sources such as batteries. Energy harvesting devices have been developed based on a number of electromechanical coupling mechanisms and their design must be optimized to produce the maximum output for given environmental conditions. While the role of non-linearities in the components has been shown to be significant in terms of the overall device efficiency, few studies have systematically investigated their influence on the system performance. In this work the role of a non-linear piezoelectric relationship is considered on the performance of a vibration-based energy harvester. Using a Poincaré-Lindstedt perturbation analysis the response of the harvesting system is approximated, including mechanical damping, stiffness non-linearities, and the above mentioned non-linear piezoelectric constitutive relationship. The predicted behavior is then compared against numerical simulations of the original system, focusing on the relationship between the power generated by the device, the ambient vibration characteristics, and the non-linearities in the system.

Flexible Skin Development for Morphing Aircraft Applications via Topology Optimization

Joo, J. J., Reich, G. W., Westfall, J. T. — Wed, 21 Oct 2009 20:16:59 PDT

This article describes the development of engineered composite skins for morphing aircraft applications. Some of these applications suggest that materials with low in-plane stiffness and relatively high out-of-plane stiffness may be required. To this end, a two-step design process has been developed in order to synthesize skins to meet these requirements. The first step in the process is to determine bulk material properties for the skin and the layout of attachments between the skin and underlying substructure. This results in a distribution of bulk properties across the skin. The second step utilizes these property values as constraints to match the found bulk property in a multi-phase material optimization in order to determine the layout of a set of microscopic multi-phase material unit cells. As a first attempt, a 2D engineered skin design using a proposed two-step process is demonstrated in this article, and material fabrication process using a rapid prototyping (RP) technique and test result are discussed.

A High-voltage and High-power Amplifier for Driving Piezoelectric Stack Actuators

Wang, D.H., Zhu, W., Yang, Q., Ding, W.M. — Wed, 21 Oct 2009 20:16:59 PDT

Aiming at the strong capacitive impedance of piezoelectric stack actuators, the principle to improve the dynamic performance of piezoelectric stack actuators through increasing the peak values of the output current and output power of power amplifiers are explored. Based on the error-amplified principle, the method that enlarges the output voltage of the dynamic power amplifiers through using a high-voltage operational amplifier in series with the power booster section, as well as the method that improves the peak values of the output current and output power through paralleling multiple power booster units utilizing the class AB quasi-complementary symmetry power amplifier circuits, are proposed and analyzed. Utilizing the proposed principle and method, a high-voltage and high-power amplifier for driving piezoelectric stack actuators is developed, simulated, and tested. The research results indicate that the developed power amplifier not only can break through the limit that each single power booster unit can only achieve the power output <125 W, but also can disperse the current and power averagely among the power booster units in parallel, which are beneficial to realizing the high power output with good static and dynamic performance and enhancing the reliability of the power amplifier.

On the Reduced-order Modeling of Energy Harvesters

Seuaciuc-Osorio, T., Daqaq, M. F. — Wed, 21 Oct 2009 20:16:59 PDT

This work addresses the accuracy and convergence of reduced-order models (ROMs) of energy harvesters. Two types of energy harvesters are considered, a magnetostrictive rod in axial vibrations and a piezoelectric cantilever beam in traverse oscillations. Using generalized Hamilton’s principle, the partial differential equations (PDEs) and associated boundary conditions governing the motion of these harvesters are obtained. The eigenvalue problem is then solved for the exact eigenvalues and modeshapes. Furthermore, an exact expression for the steady-sate output power is attained by direct solution of the PDEs. Subsequently, the results are compared to a ROM attained following the common Rayleigh—Ritz procedure. It is observed that the eigenvalues and output power near the first resonance frequency are more accurate and has a much faster convergence to the exact solution for the piezoelectric cantilever-type harvester. In addition, it is shown that the convergence is governed by two dimensionless constants, one that is related to the electromechanical coupling and the other to the ratio between the time constant of the mechanical oscillator and the harvesting circuit. Using these results, some interesting conclusions are drawn in regards to the design values for which the common single-mode ROM is accurate. It is also shown that the number of modes necessary for convergence should be obtained at maximum electric loading for the piezoelectric harvester and at minimum electric loading in the magnetostrictive case.

The Flutter Response of a Piezoelectrically Damped Cantilever Pipe

Elvin, N. G., Elvin, A. A. — Wed, 21 Oct 2009 20:16:59 PDT

The investigation of passively damped piezoelectric structures within fluid flows is important for two reasons: (a) to increase the critical flutter speed and (b) conversely to generate electrical energy to power small scale electronic systems. In this article, a cantilever pipe with resistive piezoelectric damping is chosen as the model structure to demonstrate behavior over a range of fluid/structure mass ratios. The effects of piezoelectric coupling on the critical flutter velocity, capacitance, load resistance, and piezoelectric location are investigated. The modeling shows that depending on the piezoelectric parameters chosen and the attached electrical load resistance, the addition of a passive piezoelectric element can either increase or decrease stability of the system (i.e., the critical flutter speed of the cantilever pipe can be altered and hence controlled).

Preface: Design Modeling and Experiments of Adaptive Structures and Smart Systems II

Wallmersperger, T., Polit, O. — Mon, 28 Sep 2009 09:14:36 PDT

Refined 2D Models for the Analysis of Functionally Graded Piezoelectric Plates

Brischetto, S., Carrera, E. — Mon, 28 Sep 2009 09:14:36 PDT

This article investigates the static analysis of a single-layered functionally graded piezoelectric plate, in both sensor and actuator configurations. Refined theories (order of expansion in the thickness direction from linear to fourth order) are compared with classical ones, such as the first order shear deformation theory, to demonstrate the effectiveness of these theories in the case of functionally graded piezoelectric materials (FGPMs). Both elastic and electrical properties in FGPMs are described via opportune thickness functions, which are a combination of Legendre polynomials, with an order of expansion in thickness direction equal to 10. Such types of functions permit any functional variation of the FGPM properties to be described efficiently in the thickness direction.

Thermomechanical Modeling of Functionally Graded Plates

Leetsch, R., Wallmersperger, T., Kroplin, B. — Mon, 28 Sep 2009 09:14:36 PDT

In this contribution, the 3D thermomechanical behavior of functionally graded plates subjected to transverse thermal loads is investigated by means of a series of 2D finite plate elements. In the framework of the Unified Formulation developed by Carrera (2003), the governing equations for both the heat conduction problem and the resulting thermomechanical bending problem are derived within the principle of virtual work. The order of the axiomatically assumed thickness functions is explicitly chosen independently for the thermal and the mechanical problem, respectively. Upon introduction of the thickness functions, the problem is reduced to 2D and solved by means of the finite element method. The locally varying, effective material properties are approximated by mean field estimates, e.g., the Mori—Tanaka scheme. A numerical assessment of the developed models is given. In particular, the influence of the order of the assumed thickness functions is analyzed. It will be shown that higher order assumptions are mandatory for accurate results in comparison with 3D solutions available in the literature.

Sensitivity Analysis of Thickness Assumptions for Piezoelectric Plate Models

D'Ottavio, M., Polit, O. — Mon, 28 Sep 2009 09:14:36 PDT

This article compares different axiomatic 2D theories for linear homogeneous piezoelectric plates. Simple actuator and sensor configurations are considered of thin and thick piezoelectric ceramics working either in transverse extension (31 mode) or in shear mode (15 mode). By generalizing a previously established unified formulation, a large number of different through-thickness approximations for the in-plane displacement, the transverse displacement and the electrostatic potential are introduced. Additionally, either full 3D constitutive law or reduced constitutive equations accounting for a vanishing transverse normal stress are employed in these plate theories. By referring to an analytical Naviertype closed-form solution, a systematic assessment of various 2D models is performed. The proposed sensitivity analysis of plate theories with respect to their electromechanical response can serve as a useful guide for choosing appropriate models depending on the piezoelectric polarization scheme, the use as sensor or actuator, and the plate thickness.

Aspects of Modeling Piezoelectric Active Thin-walled Structures

Marinkovic, D., Koppe, H., Gabbert, U. — Mon, 28 Sep 2009 09:14:36 PDT

The objective of this article is to reconsider some important aspects of modeling piezoelectric active thin-walled structures. Hence, it is dealt here with thin-walled laminated structures involving piezoelectric patches. A recently developed shell type finite element is used for the purpose. The first aspect is adequate modeling of electric field within the piezoelectric patches polarized in the thickness direction. The influence of higher order functions for the electric field on the accuracy of the model is discussed. The second aspect is related to modeling geometrical non-linearities in the behavior of the considered structures and their significance on the accuracy of the predicted behavior. Both aspects are considered with respect to static and dynamic cases.

Use of Classical Plate Finite Elements for the Analysis of Electroactive Composite Plates: Theoretical Aspects

Osmont, D., Pablo, F. — Mon, 28 Sep 2009 09:14:36 PDT

Smart structures including piezoelectric materials have been under interest for many years. As a consequence many piezoelectric finite elements have been developed to simulate the behavior of such structures. The present article is focused on the development of an original plate theory based upon a priori assumptions for active vibration control applications. The main result of this theory lies in the removal of electrical variables from the problem unknowns, according to the electric boundary conditions. The electromechanical effects are then taken into account via elastic coefficient modifications and external electric loads.

Use of Classical Plate Finite Elements for the Analysis of Electroactive Composite Plates. Numerical Validations

Pablo, F., Bruant, I., Polit, O. — Mon, 28 Sep 2009 09:14:36 PDT

An original piezoelectric plate theory has been presented in the companion paper (Osmont and Pablo, 2008). The particularity of the ‘piezoelectric’, finite element stemming from this theory lies in the fact that no electric degree of freedom is needed to take into account the electromechanical coupling. This article is focused on the validation of this theory through various benchmarks issued from literature. It will be proved that results are in quite agreement with static and dynamic reference solutions of laminated composite plates equipped with piezoelectric patches.

Strain-type Sensor Networks for Structural Monitoring of Beam-type Structures

Krommer, M., Zellhofer, M., Heilbrunner, K.-H. — Mon, 28 Sep 2009 09:14:36 PDT

In our previous work, we have shown that distributed strain-type sensors can be used to measure desired structural entities. A distributed strain-type sensor, whose distribution coincides with any statically admissible stress distribution due to quasi-static auxiliary forces, measures the work of these forces done on the original structural entities. Hence, a proper choice of the auxiliary forces results in the measurement of desired structural entities. In this article, we focus on the approximation of distributed sensors by sensor networks composed of sensor patches with constant intensity. The question is where to locate and how to assign weights to the patches such that the combined output of the network approximates the output of the distributed sensor. Our method is based on an integral statement characterizing the output of the distributed sensor and an integral statement for the output of the sensor network. As we cannot ensure the identity of the kernels of the integral statements, we develop methods ensuring the identity of the integral statements themselves. We develop the method for beam-type structures in detail. As a case study, we discuss a one-story frame structure and we seek to design sensor networks to measure desired structural entities; e.g., deflections or slopes.

Integrated Motion Measurement for Flexible Structures using a Modal and Krylov Subspace Model Reduction Approach

Ortel, T., Wagner, J. F. — Mon, 28 Sep 2009 09:14:36 PDT

Integrated navigation for vehicle guidance is a well-known application of integrated motion measurement systems. For this, the vehicle is modeled as a single rigid body with six degrees of freedom to be determined. Stability problems with these systems occur, but can be avoided by distributing sensors over the vehicle structure. However, in this case the rigid body assumption has to be replaced to take the distributed sensors and the flexibility of the structure into account. By means of a modal approach and Krylov subspaces, appropriate models for the example of a flexible beam have been developed and tested based on simulated data.