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IN THIS VOLUME


Aerospace

2002;():3-12. doi:10.1115/IMECE2002-39028.

Ongoing research is presented on processing of NiTi-based shape memory alloy (SMA) foams. The aim is to demonstrate a new class of materials that combine the advantages of light-weight metallic foams with the strain recovery and energy-dissipation capability of SMAs. There are a number of potential novel structural and biomedical applications that could be enabled by the unusual passive and active properties of such a material. This paper presents initial results on our attempt to fabricate functional prototype specimens using a polymeric foam precursor and a powder metallurgy process to produce NiTi foams with user-selected topology and relative density. It is shown that open-cell NiTi foams with relative density less than 5% can be produced with this technique. While definite martensitic transformational behavior has been achieved in the prototypes, the quality of the foams are found to be sensitive to the sintering temperature, the binder system employed, and the levels of interstitial contamination. Further work is needed before good superelastic and shape-memory properties can be demonstrated. Nevertheless, the current technique appears promising, since the method is capable of producing NiTi foam with a more regular structure and at a relative density nearly an order of magnitude less than other techniques currently used to produce porous NiTi.

Commentary by Dr. Valentin Fuster
2002;():13-26. doi:10.1115/IMECE2002-39034.

In this work, the effect of pseudoelastic response of shape memory alloys (SMAs) on damping and passive vibration isolation will be presented. This study has been conducted by developing and utilizing a shape memory alloy (SMA) model (a physically based SMA model) to perform extensive parametric studies on a non-linear hysteretic dynamic system, representing an actual SMA damping and passive vibration isolation prototype device. The prototype device consists of SMA tubes undergoing pseudoelastic transformations under transverse loading. To accurately model the non-linear hysteretic response of SMA tubes present in the prototype device, a Preisach model (an empirical model based on system identification) has also been modified to simulate the response of the prototype device. Both the simplified SMA model and the Preisach model have been utilized to perform experimental correlations with the results obtained from actual testing of the prototype device. The investigations show that variable damping and tunable isolation response are major benefits of SMA pseudoelasticity. Correlation of numerical simulations and experimental results has shown that large amplitude displacements causing phase transformations of SMA components are necessary for an SMA based vibration isolation device to be effective in reducing the transmissibility of a dynamic system. It has also been shown that SMA based devices can overcome performance trade-offs inherent in a typical softening spring-damper vibration isolation system. In terms of modeling, the Preisach model gave relatively accurate results due to close proximity in predicting actual SMA component behavior. However, for a generic parametric study, the simplified SMA model has been found to be more useful as it is motivated from the constitutive response of SMAs and hence, could easily incorporate different changes in system conditions.

Commentary by Dr. Valentin Fuster
2002;():27-35. doi:10.1115/IMECE2002-39003.

Ionic Polymer-Metal Composite (IPMC) is a new class of polymeric material exhibiting large strain with inherent soft actuation. The observed motion characteristics of an IPMC subjected to an electric field is highly non-linear. This is believed to be due primarily to the particle electrodes on the IPMC surface, which is inherently both capacitive and resistive due to particle separation and density. Knowing that the value of resistivity and capacity can be manipulated by the number of metal platings applied to the IPMC, the force response of an IPMC when subjected to an imposed electric field is due to the interaction of an array of capacitors and resistors along with ionic migration. In this effort we attempt to incorporate a capacitive and resistive model into the previously developed linear irreversible thermodynamic model. The advantages of using such a model are i) the possible dynamic predictability of the material itself; and ii) the realization of capacitive and resistive effect arising from the particle electrodes and the base polymer, respectively. The behavior of the proposed model can explain typical experimentally obtained values well. Also, an experimental effort to improve the properties of the base polymer was carried out by a novel nanocomposite technique. The experiment results on the current/voltage (I/V) curves indicate that the starting material of ionic polymer-metal composites (IPMCs) can be optimized to create effective polymer actuators.

Commentary by Dr. Valentin Fuster
2002;():37-46. doi:10.1115/IMECE2002-39007.

A co-reduction process is developed for plating ionic polymer materials with precious and non-precious metal electrodes. The purpose is to develop a process that reduces the use of expensive precious metals such as platinum and gold in the development of ionic polymer transducers. Previous results by Bennett and Leo (1) have demonstrated that oxidation is the key issue associated with the use of non-precious metal electrodes. The present work overcomes this problem through the use of a co-reduction process in which an alloy of platinum and copper is deposited in an impregnation/reduction process. A thin (~50 nm) layer of gold is then deposited to increase the surface conductivity of the electrode. Actuators developed using this process are tested for longevity for approximately 250,000 cycles. The results demonstrate the stability of the electrode, although multiple tests reveal that variations in the process produce variations in the electrode stability.

Commentary by Dr. Valentin Fuster
2002;():47-57. doi:10.1115/IMECE2002-39008.

A coupled, linear electromechanical model is developed for ionic polymer transducers. The model is based on the linear equations for a piezoelectric material. Integrating the equations over the geometry of the transducer produces a model of the electromechanical coupling of the polymer transducers as a function of fundamental material parameters and geometry. Explicit modeling of electromechanical coupling produces a model that is useful for analyzing sensing or actuation using ionic polymer transducers. Experiments on polymer samples verify the scaling of the model parameters as a function of sample length and width. The results also demonstrate the reciprocity of the electromechanical coupling. The symmetric model is expressed as a linear transformer which can be incorporated into system-level models for design of devices that utilize ionic polymer materials. The model is limited to linear operation at low-voltage with constant levels of material hydration.

Topics: Modeling , Polymers
Commentary by Dr. Valentin Fuster
2002;():59-63. doi:10.1115/IMECE2002-39037.

Ionic polymer metal composites (IPMC’s) exhibit spectacular coupling between electrical and mechanical domains. Sensing and actuation properties of these materials and the force and displacement characteristics have been investigated as a means of determining the electromechanical coupling coefficients of the material. An electric field applied across the thickness of the polymer causes electrophoretic ionic migration within the material. Electro-osmotic drag induces solvent migration in addition to the ion motion, and a stress is generated within the material causing the material to deform. This phenomenon is also reversible, making it possible to use ionic polymer materials as sensors, transducers and power generators. The salient feature of ionic polymeric materials, as compared to other electromechanical transducers such as piezoelectrics, is the large deformations that are achievable with low electric fields. Cantilever samples of ionic polymer material exhibit tip displacements on the order of their length with applied electric fields of the order of 10 volts per mm. Recent measurements of the motion of cantilever samples of ionic polymers have demonstrated a controllable, repeatable deformation in which the zero force position of the ionic polymer changes depending on the amplitude of the applied electric field. This effect appears to be controllable in the sense that the change in the zero force position of the polymer is a function of the amplitude of the applied electric field. It is also reversible to a degree because a step change in the voltage with the opposite polarity will change the shape of the ionic polymer strip back to a position that is close to the original position before cycling of the material. Thus, there is a potential to use this effect as a deformation memory mechanism within the polymer material. These observations and subsequent interpretations are reported in this presentation.

Commentary by Dr. Valentin Fuster
2002;():65-70. doi:10.1115/IMECE2002-33998.

This paper describes the effect of particulate crystallographic orientation on the dynamic magnetomechanical properties of Terfenol-D/epoxy 1–3 magnetostrictive particulate composites. Two different types of composites with approximately 50% Terfenol-D volume fraction were fabricated for comparison with [112]-textured monolithic Terfenol-D. In the first type, needle-shaped, [112]-oriented particles cut from the monolithic Terfenol-D were used and in the second type, irregular-shaped, randomly oriented particles ball-milled from the monolithic material were employed. Elastic moduli (E33 H and E33 B ), dynamic strain coefficient (d33 ), and magnetomechanical coupling coefficient (k33 ) were investigated as a function of bias field. Both composites demonstrate similar property trends with the negativeE, d33 , and k33 values maximizing near 30 kA/m. The maximum values achieved in the oriented type are up to 67% larger than the non-oriented type and approaches 65% of the monolithic Terfenol-D. The property improvement in the oriented type is shown to be attributed to [112] preferential particulate orientation.

Commentary by Dr. Valentin Fuster
2002;():71-78. doi:10.1115/IMECE2002-39004.

This paper aims at presenting the structural vibration-suppression capability of the recently developed Macro-Fiber Composite (MFC) actuator as a passive piezoelectric absorber using an inductive resonant shunt circuit. The resistance and inductance of the series RL shunt circuit are designed by the analogy with the single-degree-of-freedom mechanical damped vibration absorber and by using the maximum power transfer theorem of the electric network. Experimental test of a simple cantilevered beam demonstrates that the MFC actuator has excellent capability of improving the dynamic response of the beam as a piezoelectric damping system. The damping enhancement performance of the MFC actuator is superior to that of the conventional monolithic PZT actuator.

Commentary by Dr. Valentin Fuster
2002;():79-89. doi:10.1115/IMECE2002-39005.

The use of piezoelectric ceramic materials for structural actuation is a fairly well developed practice that has found use in a wide variety of applications. However, just as advanced composites offer many benefits over traditional engineering materials for structural design, actuators that utilize the active properties of piezoelectric fibers can improve upon many of the limitations encountered with monolithic piezoceramic devices used to control structural dynamics. This paper discusses the Macro Fiber Composite (MFC) actuator, which utilizes piezoceramic fibers, for example, lead zirconate titanate (PZT), embedded in an epoxy matrix for structural actuation. An overview of the MFC assembly process is presented, followed by a cure kinetics model that describes the behavior of the thermosetting matrix. This empirical model is seen to agree closely with the experimental data. Lastly, a hybrid classical lamination theory is developed to predict the linear elastic properties of the MFC package as a function of the PZT fiber lamination angle.

Commentary by Dr. Valentin Fuster
2002;():91-96. doi:10.1115/IMECE2002-33995.

Rhombohedral relaxor single crystals are a class of materials that includes PZN-PT and PMN-PT in a certain range of compositions. This work presents an approach to predicting the physical properties of relaxor single crystals with an engineered domain state. A model based on properties of crystal variants and volume averaging indicates large piezoelectric coefficient d31 (690 pC/N) and d32 (−1670 pC/N) for the <110> cuts and a value over 4000 pC/N for d15 and the existence of d16 with a value as large as −2300 pC/N in <111> orientation cuts. The predictive capability of the approach results in a computational tool for the design of engineered domain states with properties optimized for specific applications. This has resulted in the identification of a crystal cut optimized for actuator and sensor applications that utilizes the transverse mode piezoelectric coupling coefficients (d31 and d32 ).

Commentary by Dr. Valentin Fuster
2002;():97-102. doi:10.1115/IMECE2002-33996.

To date, much of the work done on ferroelectric fracture assumes the material is elastically isotropic, yet there can be considerable polarization induced anisotropy. More sophisticated solutions of the fracture problem incorporate anisotropy through the Stroh formalism generalized to the piezoelectric material. This gives equations for the stress singularity, but the characteristic equation involves solving a sixth order polynomial. In general this must be accomplished numerically for each composition. In this work it is shown that a closed form solution can be obtained using orthotropy rescaling. This technique involves rescaling the coordinate system based on certain ratios of the elastic, dielectric, and piezoelectric coefficients. The result is that the governing equations can be reduced to the biharmonic equation and solutions for the isotropic material utilized to obtain solutions for the anisotropic material. This leads to closed form solutions for the stress singularity in terms of ratios of the elastic, dielectric, and piezoelectric coefficients. The results of the two approaches are compared and the contribution of anisotropy to the stress intensity factor discussed.

Commentary by Dr. Valentin Fuster
2002;():103-109. doi:10.1115/IMECE2002-39009.

This article describes remarkable similarities in the nonlinear mechanical response of different active/smart materials despite fundamental differences in the underlying mechanisms associated with each material. Active/smart materials (i.e., piezoelectric (PZT-5H), magnetostrictive (Terfenol-D), and shape memory alloys (NiTi)) exhibit strong non-linear mechanical behavior produced by changing non-mechanical internal states such as polarization, magnetization, and phase/twin configuration. In active/smart materials the initial deformation proceeds linearly followed by a jump in strain associated with the transformation of an internal non-mechanical state. After the transformation, the mechanical response returns to linear elastic. Upon unloading, a residual strain is observed which can be recovered with the application of a corresponding external field (i.e., electric, magnetic, or thermal). Due to coupling between applied fields and non-mechanical internal states, mechanical deformation is also a function of applied external fields. At a critical applied field, the residual strain is eliminated, providing repeatable cyclic characteristics that can be used in passive damping applications. Even though different intrinsic processes (i.e., polarization, magnetization, and phase/twin variant composition) govern the deformation of each material, their macroscopic behavior is explained using a unified volume fraction concept. That is, the deformation of piezoelectric material is described in terms of the volume fraction of ferroelectric domains with polarization parallel or orthogonal to the applied load; the deformation of magnetostrictive materials is described in terms of the volume fraction of magnetic domains with magnetization parallel or orthogonal to the applied load; and the deformation of shape memory material is described in terms of the volume fraction of twin variants that are oriented favorably to the applied load. Although the qualitative behavior of each material is similar, the average magnitude of stress required to induce non-linearity varies from ~10 MPa for Terfenol-D to ~65 MPa for PZT-5H to ~300 MPa for NiTi shape memory alloy. It is hypothesized that a composite material made of these materials connected in series would exhibit passive damping over a wide range of applied stress.

Topics: Deformation
Commentary by Dr. Valentin Fuster
2002;():111-123. doi:10.1115/IMECE2002-39013.

The electric field induced strain in piezoelectric materials subjected to an electron flux is examined in this paper. An analysis using quantum mechanics indicates that stable and controllable strains with very low current draw should be achievable over a range of positive and negative control potentials. The model also predicts an instability in the internal electric field at larger negative potentials. The model was evaluated by observing the strain output of PZT5h plates subjected to an electron flux on one face and voltage inputs from a single electrode on the opposite face. The strain response and current flow were measured as a function of electrode potential and electron energy. All of the significant predictions of the model were verified by the experimental results. Further experiments were performed to examine the time response of the strain induced in the plate. It was found that the location and potential of the electron collector dramatically influences the dynamic response of the system.

Commentary by Dr. Valentin Fuster
2002;():125-132. doi:10.1115/IMECE2002-33980.

The finite element method, in conjunction with the Golla-Hughes-McTavish (GHM) viscoelastic model, is employed to model a clamped-free beam partially treated with active constrained layer damping (ACLD) elements. The governing equations of motion are converted to a state-space form for control system design. Prior to this, since the resultant finite element model has too many degrees of freedom due to the addition of dissipative coordinates, a model reduction is performed to revert the system back to its original size. Finally, optimal output feedback gains are designed based on the reduced models. Numerical simulations are performed to study the effect of different element configurations, with various spacing and locations, on the vibration control performance of a “smart” flexible ACLD treated beam. Results are presented for the damping ratios of the first two modes of vibration. It is found that improvement on the second mode damping can be achieved by splitting a single ACLD element into two and placing them at appropriate positions of the beam.

Commentary by Dr. Valentin Fuster
2002;():133-141. doi:10.1115/IMECE2002-33981.

In this paper, the vibration behavior and control of a clamped-free rotating flexible cantilever arm with fully covered Active Constrained Layer Damping (ACLD) treatment is investigated. The arm is rotating in a horizontal plane in which the gravitational effect and rotary inertia are neglected. The stress-strain relationship for the viscoelastic material (VEM) is described by a complex shear modulus while the shear deformations in the two piezoelectric layers are neglected. Hamilton’s principle in conjunction with finite element method (FEM) is used to derive the nonlinear coupled differential equations of motion and the associated boundary conditions that describe the rigid hub angle rotation, the arm transverse displacement and the axial deformations of the three-layer composite. This refined model takes into account the effects of centrifugal stiffening due to the rotation of the beam and the potential energies of the VEM due to extension and bending. Active controllers are designed with PD for the piezo-sensor and actuator. The vibration frequencies and damping factors of the closed-loop beam/ACLD system are obtained after solving the characteristic complex eigenvalue problem numerically. The effects of different rotating speed, thickness ratio and loss factor of the VEM as well as different controller gain on the damped frequency and damping ratio are presented. The results of this study will be useful in the design of adaptive and smart structures for vibration suppression and control in rotating structures such as rotorcraft blades or robotic arms.

Commentary by Dr. Valentin Fuster
2002;():143-148. doi:10.1115/IMECE2002-33987.

This paper describes an INertially STabilized Rifle where a Recurve actuator, constructed from piezoelectric material, is used to internially stabilize the barrel assembly of a tactical rifle to compensate for the small user-induced disturbances. The requirements of this system are discussed and the actuator requirements are derived. A prototype Recurve actuator is described and the test results reported. Similarly, the power electronics needed for INSTAR are discussed. Test results for an prototype circuit are given.

Topics: Actuators
Commentary by Dr. Valentin Fuster
2002;():149-156. doi:10.1115/IMECE2002-39021.

The aim of this research is to determine the optimal shape of a constrained viscoelastic damping layer on an elastic beam by means of topology optimization. The optimization objective is to maximize the system loss factor for the first resonance frequency of the base beam. All previous optimal design studies on viscoelastic lamina have been size or shape optimization studies, assuming a certain topology for the damping treatment. In this study, this assumption is relaxed, allowing an optimal topology to emerge. The loss factor is computed using the Modal Strain Energy method in the optimization process. Loss factor results are validated by using the half-power bandwidth method, which requires obtaining the forced response of the structure. The ABAQUS finite element code is used to model the structure with two-dimensional continuum elements. The optimization code uses a Sequential Quadratic Programming algorithm. Results show that significant improvements in damping performance, on the order of 100% to 300%, are obtained by optimizing the constrained damping layer topology. A novel topology for the constraining layer emerges through the optimization process.

Commentary by Dr. Valentin Fuster
2002;():157-165. doi:10.1115/IMECE2002-33940.

Conventional sensors, such as proximeters and accelerometers, are add-on devices usually adding additional weights to structures and machines. Health monitoring of flexible structures by electroactive smart materials has been investigated over the years. Thin-film piezoelectric material, e.g., polyvinylidene fluoride (PVDF) polymeric material, is a lightweight and dynamic sensitive material appearing to be a perfect candidate in monitoring structure’s dynamic state and health status of flexible shell structures with complex geometries. The complexity of shell structures has thwarted the progress in studying the distributed sensing of shell structures. Linear distributed sensing of various structures have been studied, like beam, plate, cylindrical shell, conical shell, spherical shell, paraboloidal shell and toroidal shell. However, distributed sensing control of nonlinear shell structures has not been carried out rigorously. This study is to present the microscopic signals, modal voltages and distributed micro-sensing components of truncated nonlinear conical shells laminated with distributed infinitesimal piezoelectric neurons. Signal generation of distributed neuron sensors laminated on conical shells is defined first. The dynamic signal of truncated nonlinear conical shell consists of microscopic linear and nonlinear membrane strain components and linear bending strain component based on the von Karman geometric nonlinearity. Micro-signals, modal voltages and distributed sensing components of two different truncated nonlinear conical shells are investigated and their sensitivities discussed.

Topics: Shells , Signals
Commentary by Dr. Valentin Fuster
2002;():167-175. doi:10.1115/IMECE2002-33976.

Inflated space-based structures have become popular over the past three decades due to their minimal launch-mass and launch-volume. Once inflated, these space structures are subject to vibrations induced by guidance systems and space debris as well as from variable amounts of direct sunlight. Understanding the dynamic behavior of space-based structures is critical to ensuring their desired performance. Inflated materials, however, pose special problems when testing and trying to control their vibrations because of their lightweight, flexibility, and high damping. Traditional modal testing techniques, based on single-input, single-output (SISO) methods, are limited for a variety of reasons when compared to their multiple counterparts. More specifically, SISO modal testing techniques are unable to reliably distinguish between pairs of modes that are inherent to axi-symmetric structures (such as an inflated torus, a critical component of a gossamer spacecraft). Furthermore, it is questionable as to whether a single actuator could reliably excite the global modes of a true gossamer craft, such as a 25 m diameter torus. In this study, we demonstrate the feasibility of using a multiple-input multiple-output (MIMO) modal testing technique on an inflated torus. In particular, the refined modal testing methodology focuses on using Macro-Fiber Composite (MFC® ) patches (from NASA Langley Research Center) as both actuators and sensors. MFC® patches can be integrated in an unobtrusive way into the skin of the torus, and can be used to find a gossamer structure’s modal parameters. Furthermore, MFC® excitation produces less interference with suspension modes of the free-free torus than excitations from a conventional shaker. The use of multiple actuators is shown to properly excite the global modes of the structure and distinguish between pairs of modes at nearly identical resonant frequencies. Formulation of the MIMO test as well as the required postprocessing techniques are explained and successfully applied to an inflated Kapton® torus.

Topics: Testing
Commentary by Dr. Valentin Fuster
2002;():177-183. doi:10.1115/IMECE2002-33977.

Structures and industrial equipment often operate in environments where temperature variations take place. Although thermal effects may be negligible in some cases, they have caused the unexpected failure of mechanical systems many times. Whether or not temperature has significant effects on the dynamical behavior of such machines and structures depends upon several aspects, amongst which are geometry, material properties and boundary conditions. In this paper we investigate the dynamical behavior of a clamped beam under the influence of a uniform, quasi-statically varying temperature field. An analytical model was used, based on Euler-Bernoulli’s beam theory with the introduction of the proper boundary conditions. Temperature effects are included in terms of an axial force that shows up when the beam tends to thermally expand, but this expansion is restrained by the clamping. Preliminary results do not agree with experimental data, since perfect clamping is difficult to achieve in practice. Finally the model is updated with the inclusion of axial and torsional springs connecting the beam to the support. The spring constants were calculated through optimization procedure to minimize the differences between the natural frequencies obtained from the analytical model and the corresponding experimental ones. Agreement with experimental results is reasonable up to the 4th mode of the beam. In the future, this analytical model is to be used for design and simulation of an active controller that accounts for temperature changes in the structure.

Commentary by Dr. Valentin Fuster
2002;():185-189. doi:10.1115/IMECE2002-39010.

Oscillations of micro-electromechanical resonators constructed from clamped-clamped beam structures are studied in this effort. Piezoelectric actuation is used to excite these structures on the input side and piezoelectric sensing is carried out on the output side. Although axial loads in clamped-clamped beam based on micro-electromechanical systems (MEMS) have been considered before, the relevance of buckling to this problem has not studied before in such “small” scale systems. In this work, possibilities for buckling are examined, and it is shown that for resonance excitations, consideration of buckling may help explain associated experimentally observed spatial patterns as a nonlinear phenomenon.

Topics: Buckling
Commentary by Dr. Valentin Fuster
2002;():191-196. doi:10.1115/IMECE2002-39012.

The property of magnetorheological fluids to change their yield stress depending on applied magnetic fields can be employed to develop many controllable devices one of them being MR fluid based clutches. One major problem however with MR fluid based clutches is that at high rotational speeds, the iron/ferrous particles in the MR fluid centrifuge due to very high centrifugal forces. Thus the particles move outward as the speed increases thereby making the fluid non-homogeneous. Many times however the initial analysis assumes fluid homogeneity, which is really not the case. In this paper this problem is addressed by assuming various volume fraction profiles describing the fluid particle orientation. Two cases, one with a linear profile and the other with an exponential profile are discussed. Expressions for the torque transmitted are derived at for both disc shaped and cylindrical shaped clutches. In addition, the use of a MR sponge based clutch that may indeed reduce the effect of centrifugal forces significantly is described. The design methodology and configuration for the sponge clutch are also discussed. An experimental set up used to test the clutch is also described.

Commentary by Dr. Valentin Fuster
2002;():197-204. doi:10.1115/IMECE2002-33982.

As mechanisms approach the micro scale, manufacture and assembly of linear coil springs becomes nearly impossible. For this reason, compliant functionally binary pinned-pinned segments are frequently used in place of them. A new pseudo-rigid-body model (PRBM) is presented for circular functionally binary pinned-pinned (FBPP) segments that undergo large, nonlinear deflections for both tension and compression. A new method of evaluating the maximum moment in the beam is presented, called the focal moment method, which significantly increases the accuracy of the force for a given displacement. This paper also shows how some FBPP segments can be modeled as simple linear tension/compression springs. The deflection limits for a given maximum error can be determined analytically, thereby making it possible to use optimization algorithms in the design of these springs. The effect of the size of the rigid pin joints is also discussed.

Commentary by Dr. Valentin Fuster
2002;():205-216. doi:10.1115/IMECE2002-33993.

A topology optimization method is developed to design a piezoelectric ceramic actuator together with a compliant mechanism coupling structure for dynamic applications. The objective is to maximize the mechanical efficiency with a constraint on the capacitance of the piezoceramic actuator. Examples are presented to demonstrate the effect of considering dynamic behavior compared to static behavior, and the effect of sizing the piezoceramic actuator on the optimal topology and the capacitance of the actuator element. Comparison studies are also presented to illustrate the effect of damping, external spring stiffness, and driving frequency. The optimal topology of the compliant mechanism is shown to be dependent on the driving frequency, the external spring stiffness, and if the piezoelectric actuator element is considered as design or non-design. At high driving frequencies, it was found that the dynamically optimized structure is very near resonance.

Commentary by Dr. Valentin Fuster
2002;():217-233. doi:10.1115/IMECE2002-39000.

This paper introduces a new configuration of a Continuously Variable Transmission (CVT) that is self-adjusting and designed as a compliant mechanism. This new configuration is called the Pivot-Arm CVT. The criteria for classification as a Pivot-Arm CVT is discussed. An analytical model describing the performance of the Pivot-Arm CVT is developed. Special design considerations which may be useful in implementing Pivot-Arm CVTs are introduced and explained. The Pivot-Arm CVT model is validated through controlled testing of two Pivot-Arm CVT prototypes.

Commentary by Dr. Valentin Fuster
2002;():235-242. doi:10.1115/IMECE2002-33990.

Micro-electro-mechanical (MEM) translational tabs are introduced for active lift control on aircraft. These tabs are mounted near the trailing edge of lifting surfaces such as aircraft wings and tails, deploy approximately normal to the surface, and have a maximum deployment height on the order of one percent of the section chord. Deployment of the tab effectively changes the sectional camber, thereby changing the aerodynamic characteristics of a lifting surface. Tabs with said deployment height generate a change in the section lift coefficient of approximately ±0.3. The microtab design and the techniques used to fabricate and test the tabs are presented.

Commentary by Dr. Valentin Fuster
2002;():243-247. doi:10.1115/IMECE2002-33992.

Self-actuating aircraft wings for in-flight deicing with minimal power requirements are proposed. Lightweight piezoelectric actuators are utilized to excite the wing structure to its natural frequencies to induce shear stresses on the surface of the wing. The shears are generated in such a way that they are sufficient to break the weak bond between the ice layer and the wing surface. A laminated composite cantilever plate is used for the modeling and analysis. Analytical model is developed to predict the natural frequencies and shear stresses on the surface of the plate and finite element modal analysis is carried out to verify the results. In addition, finite element model involving the ice deposited on the underlying structure is built. The dynamic responses of the structure to harmonic excitation to its first five natural frequencies are investigated. It is observed that significant amount of ice de-bonding from the substrate occurs in the third mode, or the second symmetric mode. Moreover, the energy requirements of the piezoelectric actuators to actuate an adaptive composite structure with given weight are evaluated.

Commentary by Dr. Valentin Fuster
2002;():249-259. doi:10.1115/IMECE2002-39030.

An optimization method has been developed for the design of a smart conformable rotor airfoil with distributed piezoelectric actuators. A conformable airfoil is proposed as a substitute for trailing edge flaps used for helicopter vibration reduction by achieving high frequency camber variations. A topology optimization approach is used where the objective is to maximize trailing edge deflection while minimizing airfoil deformations due to aerodynamic loads. Solutions of the design problem are obtained using Sequential Linear Programming coupled with a Finite Element Analysis procedure. Results show good algorithm convergence and satisfactory airfoil deformations. A study of the effects of different active material resources, skin thickness and aerodynamic loads is performed. Changes in lift coefficient are found to be lower than those obtained for an equivalent flap at similar deflection angles, suggesting that larger deflections might be required for vibration reduction purposes.

Topics: Design , Rotors , Airfoils
Commentary by Dr. Valentin Fuster
2002;():261-268. doi:10.1115/IMECE2002-39032.

Adaptive or intelligent structures which have the capability for sensing and responding to their environment promise a novel approach to satisfying the stringent performance requirements of future space missions. This paper introduces an intelligent modified Stewart platform as an adaptive thruster mount structure with precision positioning and active vibration suppression capabilities for use in space satellites as an intelligent thruster vector control platform. The intelligent thruster mount would utilize piezoelectric sensors and actuators for precision positioning and active vibration suppression to provide fine-tuning of position tolerance for thruster alignment and low transmissibility of vibration to the satellite structure. Similar intelligent platform, introduced here, may be used for sensitive equipment aboard of the spacecraft to suppress the vibration that resonates throughout the spacecraft structure during a thruster firing, solar panel boom opening/reorientation, etc. This vibration renders sensitive optical or measurement equipment non-operational until the disturbance has dissipated. This intelligent system approach would greatly enhance mission performance by fine tuning attitude control, potentially eliminating the non-operational period as well as minimizing fuel consumption utilized for position correction. The configuration of the intelligent thruster mount system is that of a modified Stewart platform. This system is an intelligent tripod with two in-plane rotational degrees of freedom (2-DOF) for the top device-plate. Precision positioning of this structure is achieved using active members that extend or contract to tilt the upper device-plate where the thruster is mounted. An inverse analysis of a modified Stewart platform is employed to determine the required axial displacement of the active struts for the desired angular tilt of the upper device-plate. The active struts can participate in precision positioning as well as vibration suppression of the upper device-plate where the thruster, i.e., the source of the unwanted vibrations and misalignment, is mounted. The proposed Thruster Vector Control (TVC) intelligent platform offers a promising method for achieving fine tuning of positioning tolerances of a thruster as well as minimizing the effects of the disturbances generated during thruster firing in spacecraft such as a satellite.

Topics: Space vehicles
Commentary by Dr. Valentin Fuster
2002;():269-277. doi:10.1115/IMECE2002-33941.

Piezoelectric thin films incorporating poly(sodium 4-styrenesolfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDDA) were synthesized using the electrostatic self-assembly (ESA) process. The ESA-processed PSS/PDDA film is a layer-by-layer laminated structure, which exhibits piezoelectric response directly, with a piezoelectric coefficient d33 = 6.0 pC/N and without poling treatment. It is assumed that the self-assembly process may play a very important role in molecular alignment resulting in net polarization in the layer-by-layer structured ultrathin film, a process quite different from that used to form conventional piezoelectric films. Further study concerning the principles governing the novel ESA processing of piezoelectric films and self-assembled materials, sensors and actuators is on-going.

Commentary by Dr. Valentin Fuster
2002;():279-283. doi:10.1115/IMECE2002-33984.

Small scale probes implementing shape memory alloy (SMA) actuation show great promise in applications requiring remote and minimally invasive access to small environments. Such environments include physiological spaces like those located in human and animal bodies as well as cavities within mechanical systems. Probes examined here are generally snake like in appearance composed of one or multiple independent segments, which in turn are made up of one or multiple SMA actuators performing work against an elastic spine. As the actuator(s) of a given segment are activated, the spine bends causing the probe to bend in the area of that segment. When the actuator(s) are deactivated, the force generated in the bending of the spine returns the segment to its neutral position. Activation and deactivation of actuators is accomplished by heating and cooling respectively, enacting the solid phase changes that are characteristic to the shape memory effect. The gage of control over probe shape depends on the number of independent segments that are available per unit length and the degree of control an operator has over each of the segments. The work presented here discusses the constraints imposed on the design of SMA actuated probes, and how those constraints become more critical and limiting with reduced physical scale and refinement of motion control. Numerical and finite element models have been developed showing the interrelationship between mechanical design, the thermal and phase states of the SMA actuator(s), and the mechanical performance of the total system. Performance concerns examined include probe shape control and the limits of shape change as a function of physical scale. Comparative data is presented between behavior predicted by the models developed and performance observed during the testing of prototypes. It is concluded that segment length, linked to refinement of probe control, is limited by its thermal boundary conditions.

Commentary by Dr. Valentin Fuster
2002;():285-288. doi:10.1115/IMECE2002-33988.

Obstacle avoidance and object identification are important tasks for robots in unstructured environments. This paper develops an actuated whisker that determines contacted object profiles using a hub load cell. The shape calculation algorithm numerically integrates the elastica equations from the measured hub angle, displacement, forces, and torque until the bending moment vanishes, indicating the contact point. Sweeping the whisker across the object generates a locus of contact points that can be used for object identification. Experimental results demonstrate the ability to identify and differentiate square and curved objects at various orientations.

Commentary by Dr. Valentin Fuster
2002;():289-294. doi:10.1115/IMECE2002-33989.

Piezoelectric Fiber Composite with Interdigitated Electrodes (PFCIDE) was previously introduced as an alternative to monolithic wafers with conventional electrodes for applications of structural actuation. This paper is an investigation into the performance improvement of piezoelectric fiber composite actuators by optimizing the stacking sequence and changing the matrix material. This paper presents the numerical optimization of a piezoelectric fiber/piezoelectric matrix composite actuator with IDE (PFPMIDE). Various concepts from different backgrounds, including three-dimensional linear elastic and dielectric theories, have been incorporated into the present linear piezoelectric model. To see the structural responses of the actuator integrated with the PFPMIDE, three-dimensional finite element formulations were derived. Numerical analysis shows larger center displacement of the curved actuator with the PFPMIDE due to optimization of the piezoelectric fiber angles. This paper presents the concept of a curved actuator that occurs naturally via thermal residual stress during the curing process, as well as the optimization of the maximum curved actuator displacement, which is accomplished using the Davidon-Fletcher-Powell (DFP) method.

Commentary by Dr. Valentin Fuster
2002;():295-299. doi:10.1115/IMECE2002-33943.

The EM method is a valuable tool for Civil Engineering for estimation of the real stress in the prestressing tendons, quality control during construction period, calculating the stress loss due to friction and relaxation, long-time monitoring of stress changes due to concrete creep, temperature changes, traffic load etc. Overview of EM technique with practical applications in the Civil Engineering is presented. The new generation of EM measuring devices is based on more than 15 years experience, including health monitoring systems for the nuclear power plant and a large span cable stayed and suspension bridges. Examples of laboratory and field tests are presented, including uncertainty of stress measurement, long-time stability, resolution and reliability.

Topics: Steel , Cables
Commentary by Dr. Valentin Fuster
2002;():301-313. doi:10.1115/IMECE2002-33946.

A general-order perturbation method involving multiple perturbation parameters is developed for eigenvalue problems with changes in the stiffness parameters. The perturbation solutions and eigenparameter sensitivities of all orders are derived explicitly. The perturbation method is used iteratively in conjunction with an optimization method in a robust damage detection algorithm. The generalized inverse method is used efficiently with the first order perturbations, and the gradient and quasi-Newton methods are used with the higher-order perturbations. Numerical simulations demonstrated the effectiveness of the algorithm in detecting the locations and extents of small to large levels of damage.

Commentary by Dr. Valentin Fuster
2002;():315-323. doi:10.1115/IMECE2002-33947.

This paper presents an efficient technique to uniquely identify damage through the creation of a multi-scale map of material deformations and behavior within a representative volume element (RVE) of the host structure. Optimally distributed, embedded fiber optic sensors provide strain, strain gradient, and integrated strain fields throughout the RVE. As a demonstration, an isotropic, homogeneous RVE is modeled instrumented with an evenly spaced grid of sensing elements. The multi-scale damage identification technique and an equivalent single-scale method are evaluated on the basis of damage detection and identification. A large number of induced, stochastic damage cases are analyzed, generated by introducing a crack defined by three random variables: center location, length, and orientation angle. The multi-scale sensing capability is shown to provide a higher quality strain map of the RVE from the distributed sensors, resulting in significantly improved damage identification.

Commentary by Dr. Valentin Fuster
2002;():325-331. doi:10.1115/IMECE2002-33978.

A technique for a non-destructive detection, location and severity determination of structural defects by means of a time domain technique is presented. Since damage in a structure causes changes in the physical coefficients of elastic modulus and damping parameters, the response of an undamaged and a damaged structure to the same input excitation is different, and this can be used in a damage identification strategy. The present work uses a continuous damage model to describe the current integrity state of a structure. In order to determine this state of structural damage the minimization of an error function is desired, such a function is basically the difference between the time response of the structural model and the real structure one to the same input excitation. The effectiveness of the proposed technique is assessed on a beam like structure, where displacements, accelerations or strains may considered as being measured at a subset of the system degrees of freedom. In order to furnish realism to performed simulations, the corrupting effects of signal filtering and sampling are considered. The analysis of the results for different levels of signal-to-noise ratio is also carried on.

Commentary by Dr. Valentin Fuster
2002;():333-340. doi:10.1115/IMECE2002-39017.

Embedded-Ultrasonics Structural Radar (EUSR) is a new concept and methodology for in-situ nondestructive evaluation (NDE) of thin-wall structures. EUSR utilizes (a) a Piezo Wafer Active Sensors (PWAS) array embedded onto the structure; and (b) electronic modules for signal transmission/reception, processing, and interpretation. The EUSR methodology is developed as an extension of our previous work on the Lamb wave propagation NDE. Based on the study of the Lamb wave characteristic, the excitation signal is optimized to obtain good signal to noise ratio. Lamb wave speed-frequency curve is plotted to obtain the wave speed of the excitation signal. This wave speed is then used to map the EUSR data from time domain to distance domain, thus the locations of the reflectors can be visually displayed. The EUSR algorithm is adopted from the beamforming process currently used in phased-array radar applications. Each element in the PWAS array plays the role of both transmitter and receiver. A circuit is designed to change the role of the PWAS in a round robin fashion. The responses of the structure to all the excitation signals are collected. By applying the EUSR algorithm, an appropriate delay is applied to each signal in the data set to make them all focus on a direction denoted by angle φ. When this angle φ is changed from 0 to 180 degrees, a virtual scanning beam is formed and a large area of the structure can be interrogated. The EUSR algorithm is explained in this paper. Experimental results from a proof-of-concept EUSR system are also presented.

Commentary by Dr. Valentin Fuster
2002;():341-350. doi:10.1115/IMECE2002-33936.

This paper presents an analytical approach for modeling the mechanical-electrical response of annular plate components of space structures containing distributed piezoelectric under static as well as dynamic mechanical or electrical loadings. The analytical approach used in this paper is based on the Kirchhoff plate model. The equations governing the dynamics of the plate, relating the strains in the piezoelectric elements to the strain induced in the system, are derived for annular plate using the partial differential equation. The natural frequencies and mode shapes of the structures were determined by modal analysis. In addition, the harmonic analysis is performed for analyzing the steady-state behavior of the structures subjected to cyclic sinusoidal loads. Numerical simulation results are obtained using finite element approach. Experiments using a thin circular aluminum plate structure with distributed piezoelectric actuators were also conducted to verify the analysis and the computer simulations. Relatively good agreements between the results of these three approaches are observed. Finally, the results show that the model can predict natural frequencies and modes shapes of the plate very accurately.

Commentary by Dr. Valentin Fuster
2002;():351-359. doi:10.1115/IMECE2002-33938.

Piezoelectric sensors and actuators are widely used in smart structures, mechatronic and structronic systems, etc. This paper is to investigate the dynamics and control of nonlinear laminated piezothermoelastic shell structures subjected to the combined mechanical, electrical, and thermal excitations by the finite element method. Governing relations of nonlinear strain-displacement, electric field-electric potential, and temperature gradient-temperature field for a piezothermoelastic shell are presented in a curvilinear coordinate system. Based on the layerwise constant shear angle theory, a generic curved triangular laminated piezothermoelastic shell element is developed. Generic nonlinear finite element formulations for vibration sensing and control analysis of laminated piezoelectric shell structures are derived based on the virtual work principle. Dynamic system equations, equations of electric potential output, and feedback control force are derived and discussed. The modified Newton-Raphson method is used for efficient nonlinear dynamic analysis of complex nonlinear piezoelectric/elastic/control structural systems. For vibration sensing and control, various control algorithms are implemented. The developed nonlinear piezothermoelastic shell element and finite element code are validated and applied to analysis of nonlinear flexible structronic systems. Vibration sensing and control of constant/non-constant curvature piezoelectric shell structures are studied. Thermal effect to static deflection, dynamic response, and control is investigated.

Commentary by Dr. Valentin Fuster
2002;():361-368. doi:10.1115/IMECE2002-33979.

Shallow paraboloidal shells of revolution are common components for reflectors, mirrors, etc. This study is to investigate the micro-control actions and distributed control effectiveness of precision paraboloidal shell structures laminated with segmented actuator patches. Mathematical models and governing equations of the paraboloidal shells laminated with distributed actuator layers segmented into patches are presented first, followed by formulations of distributed control forces and micro-control actions including meridional/circumferential membrane and bending control components based on an assumed mode shape function and the Taylor series expansion. Distributed control forces, patch sizes, actuator locations, micro-control actions, and normalized control authorities of a shallow paraboloidal shell are then analyzed in a case study. Analysis indicates that 1) the control forces and membrane/bending components are mode and location dependent, 2) the meridional/circumferential membrane control actions dominate the overall control effect, 3) there are optimal actuator locations resulting in the maximal control effects at the minimal control cost for each natural mode. The analytical results provide generic design guidelines for actuator placement on precision shallow paraboloidal shell structures.

Commentary by Dr. Valentin Fuster
2002;():369-377. doi:10.1115/IMECE2002-33991.

Scientists have used internal variables to model time-dependent material behavior for many years. Since the 1980s they have been employed to predict transient response of structures that include viscoelastic materials. The potentially large number of extra states introduced by the internal variables can be problematic when designing control systems, so the purpose of this paper is to explore how internal variables affect control system design. Practical designs are based on output feedback of a limited number of the physical states, but this brings up the question of whether it is advantageous to recreate the full state vector (including internal states) using a standard observer. Internal variables based on Maxwell models are used to address observability and controllability as well as full- and partial-state feedback on a single-degree-of-freedom system. Comparisons are also made between complex-modulus and internal-variable representations of viscoelastic behavior.

Commentary by Dr. Valentin Fuster
2002;():379-387. doi:10.1115/IMECE2002-39001.

A substantial amount of research exists concerning shape and vibration control of structures with attached piezoelectric ceramic sheet actuators. Researchers have investigated the optimal placement, size, and electrode pattern of these piezoceramic actuators to maximize the performance of the system. In many situations, the performance could be further improved with tailoring of the electromechanical properties of the actuator. For example, it was found that to avoid exciting higher order modes, the ideal actuator would be one that only actuates in one direction when controlling certain modes in a two-dimensional plate structure [1]. As known, the 31 and 32 electromechanical coupling values of a piezoelectric ceramic patch poled in the 3 direction is equal. Therefore to achieve decoupling of the actuator action in the 31 and 32 directions, a mechanism is required. In this paper, an active stiffener concept is proposed to realize such an effect where a stiffener is inserted between a host structure and the piezoelectric ceramic actuator patch. Using a solid finite element model, an analysis of a single active stiffener attached to a rigid and a flexible host structure is presented. In the analysis, the effects of various material and system parameters on the transmitted force to the structure are presented. It is seen that the active stiffener can significantly reduce the transmitted force in the selected direction. The performance of the active stiffener concept with multiple actuators is presented for controlling the shape of a large flexible circular plate structure.

Topics: Shapes
Commentary by Dr. Valentin Fuster
2002;():389-398. doi:10.1115/IMECE2002-39011.

The last decade has seen the advent of active aperture antennas and other large distributed parameter systems. These antennas have the capability to change their shape to resemble a desired radiation pattern. In this study a method to simultaneously achieve active shape and vibration control of distributed parameter systems is presented. The optimal actuator location is computed for a desired profile using non-linear optimal programming techniques. For most shape control applications the actuator and sensor dynamics are much faster than the structural dynamics and slow shape changes are sufficient, thus quasi-static analysis is sufficient. The quasi-static actuation forces for the desired profile are then calculated by using independent modal space control (IMSC) principles. Quasi-static shape control is then implemented in a closed loop control using a 3-D photogrammetry sensing system. A sliding mode controller is designed for each dominant mode such that it drives the error between the required and actual modal contribution to zero. Conventional sliding mode controllers are discontinuous in nature and they might cause “control spillover”. This is avoided by using an “observer-based” solution.

Commentary by Dr. Valentin Fuster
2002;():399-405. doi:10.1115/IMECE2002-39026.

Positive position feedback (PPF) control is widely used in active vibration control of flexible structures. To ensure the vibration is quickly suppressed, a large PPF scalar gain is often applied in a PPF controller. However, PPF control with a large scalar gain causes initial overshoot, which is undesirable in many situations. In this paper, a fuzzy gain tuner is proposed to tune the gain in the positive position feedback control to reduce the initial overshoot while still maintaining a quick vibration suppression. The fuzzy system is trained by the desired input-output data sets by batch least squares algorithm so that the trained fuzzy system can behave like the training data. A 3.35 meter long I-beam with piezoceramic patch sensors and actuators is used as the experimental object. The experiments include the standard PPF control, standard PPF control with traditional fuzzy gain tuning, and PPF control with batch least squares fuzzy gain tuning. Experimental results clearly demonstrate that PPF control with batch least squares fuzzy gain tuner behaves much better than the other two in terms of successfully reducing the initial overshoot and quickly suppressing vibration.

Commentary by Dr. Valentin Fuster
2002;():407-413. doi:10.1115/IMECE2002-39027.

This paper concerns active vibration control of a 3.35 meter long composite I-beam that is used in civil structures in a cantilevered configuration by using peizoceramics materials, in particular the PZT (Lead Zirconate Titanate), in the form of patches. These PZT patches are surface-bonded on the I-beam and perform as actuators and sensors. A real-time data acquisition and control system is used to record the experimental data and to implement controllers. To assist control system design, open loop testing and system identification are conducted. A Pole Placement controller is designed and is simulated using the identified model. Simulations show the dramatic increase in damping of the beams which when implemented experimentally corroborates the simulation results. Experimental results verify the simulated results and demonstrate the effectiveness of active control of a civil structure using smart materials.

Commentary by Dr. Valentin Fuster

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