Journal of Intelligent Material Systems and Structures current issue

Biaxial Constrained Recovery in Shape Memory Alloy Rings

Videnic, T., Kosel, F., Sajn, V., Brojan, M. — 2008-07-25

In this article biaxial constrained recovery in a thick-walled shape memory alloy (SMA) ring with a rectangular cross-section is modeled using the theory of generalized plasticity, which is developed by Jacob Lubliner and Ferdinando Auricchio. As a mechanical obstacle that delays free recovery in a SMA ring, a steel ring is used. The result of constrained recovery is the generation of high stresses in both the rings. All equations are written in a closed form in terms of infinite series. Theoretical results are compared with experimental findings and good agreement is found when SMA rings are in the domain of recoverable strains.

FE Modeling of an Innovative Vibration Control Shunt Technique

Ciminello, M., Ameduri, S., Concilio, A. — 2008-07-25

The possibility of simulating and predicting the dynamic behavior of controlled structural systems is a challenging goal because of the complexity of the related architectures. As a matter of fact, obtaining accurate information on system response in pre-design and design phases may reduce both computational and experimental efforts. In this study, the numerical simulation of a specific family of semi-active vibration control devices is taken into account: piezoelectric acting in the synchronized switched shunt architecture (SSSA). Different from the classic shunt inductive architecture, the SSSA is characterized by a switch component adaptively synchronized with the structural response to be controlled, whatever it is. The ability of controlling low range frequencies without large limitations in terms of inductive components represents, together with the adaptive skill, the main advantage of this technique. The reference structure is represented by an isotropic plate, clamped on the edges; the active system is made of an isolated PZT patch, located at the center. A dedicated simulation tool has been realized and implemented to predict piezo effectiveness for the considered configuration. Related matrices have been suitably integrated within the complete model. The switching state of the electrical circuit causes the matrices elements to be time-variant; the related problems have been dealt with in a Newmark-Beta-based integration solver. The integrated structural system has been fully and simultaneously simulated, considering at the same time the structural dynamics, the nonlinear behavior of the electrical device, and the piezoelectric electromechanical response. Results have been presented in terms of time response. The innovative contribution reported in this study concerns the application of the FE approach to the design of a SSSA integrated within MDOF structural systems. A characteristic of the approach is the ability of interacting with commercial FE codes, like MSC-Nastran, in designing and simulating the SSSA control action. References reported in this study face the SSSA control problem applied to single DOF systems (not directly applicable to complex systems, but through modal analysis reduction operations) or deal with FE simulation of classical inductive shunt (not switched). The details of this statement are fully reported in the Introduction.

Integrated Optimization of Material Layout and Control Voltage for Piezoelectric Laminated Plates

Zhan Kang, , Liyong Tong, — 2008-07-25

Topology optimization techniques have recently been successfully applied to the design of piezoelectric smart structures. However, in previous formulations, the material layout is optimized under the condition of given electric actuation voltages. This imposes a restriction to the design problem and may consequently limit application of these approaches, particularly in complex shape control problems. The present article investigates the integrated optimization of structural topology and control voltage of piezoelectric laminated plates. The finite element analysis formulation of laminated plates with surface bonded piezoelectric layers is introduced first. The optimal design problem is then formulated based on an artificial material model with penalization for both mechanical and piezoelectric properties. In the formulated problem, the topologies of both host and actuation layers are optimized simultaneously with spatial distribution of control voltage. Several special cases of the proposed design problem are considered, and numerical techniques for sensitivity analysis and optimal solutions are proposed. Numerical examples are presented to demonstrate the validity and applicability of the proposed methods.

Single-Walled Carbon Nanotubes -- Ionic Polymer Electroactive Hybrid Transducers

Akle, B. J., Leo, D. J. — 2008-07-25

Ionic electroactive polymers, sometimes referred to as artificial muscles, have the ability to generate large bending strain and moderate stress at low applied voltages. Typical types of ionic electroactive polymer transducers include ionic polymers, conducting polymers, and carbon nanotubes. Preliminary research combining multiple types of materials proved to enhance certain transduction properties. Bennett and Leo (Materials Research Society Symposium Proceedings, vol. 785, 2003b) showed that the speed of response, maximum strain, and quasi-static actuation are improved by adding a layer of conducting polymer on an ionic polymer transducer. In this work, a recently developed fabrication method called the direct assembly process (DAP) plating is used to build SWNT/RuO₂ hybrid transducers. The DAP consists of mixing a conducting powder with an ionomer solution. This technique has demonstrated improved response time and strain output as compared to previous methods. Electrodes applied using this new technique of mixing RuO₂ (surface area 45—65 m²/g) particles and Nafion^TMdispersion provided 5x the displacement and 10x the force compared to a transducer made with conventional methods. Furthermore, previous studies demonstrated that the response speed of the transducer is optimized by varying the composition of metal in the electrode (Akle, B.J., Bennett, M.D., Leo, D.J., Wiles, K.B. and McGrath, J.E. 2007. "Direct Assembly Process: A Novel Fabrication Technique for Large Strain Ionic Polymer Transducers,'' Journal of Mat. Sci., 42:7031—7041). For RuO₂, the optimal loading was approximately 45vol%, while carbon nanotubes electrodes have an optimal performance at 30vol%. Due to low percolation threshold, carbon nanotubes actuators perform better at a lower loading compared to other conducting powders. The addition of single-walled carbon nanotubes (SWNT) to the electrode increases both the strain rate and the maximum strain of the hybrid actuator. The strain rate of the transducer increased proportional to the ratio of SWNT to RuO₂ in the electrode. A maximum peak-to-peak strain of 10.6% (±2V) is attained in a 15vol% SWNT/30 vol% RuO₂ hybrid transducer. The maximum strain rate of 2.7%/s is generated by a 20vol% SWNT/25 vol% RuO₂ hybrid transducer.

Finite Element Charts and Active Vibration Suppression Schemes for Smart Structures Design

Ghasemi-Nejhad, M. N., Russ, R., Kougen Ma, — 2008-07-25

This article employs a finite element method to introduce Displacement-Load-Sensor voltage-Actuator voltage (DLSA) Design Charts and associated vibration suppression schemes; namely, Constant Voltage (CV), Optimum Voltage (OV), Corresponding Voltage (COV), and Truncated Corresponding Voltage (TCOV), to develop actuator control voltages with amplitude and phase information for the design of smart structures with piezoelectric sensors and actuators for active vibration suppression. These techniques can be used to (a) design the location, size, and number of actuators without resorting to complex control strategies or formal optimization techniques, (b) investigate the actuation effectiveness of surface-mounted versus embedded piezoelectric patches in similar composite structures, and (c) determine actuator control voltages analogous to a feedforward open-loop control technique. Guidelines are presented for the development of DLSA Design Charts. In addition, closed form analytical equations that can replace DLSA Design Charts, are developed and presented due to their ease of use. An Active Composite Panel (ACP) with a surface-mounted piezoelectric patch actuator for lateral vibration suppression and an Active Composite Strut (ACS) with a piezoelectric stack actuator for axial vibration suppression are considered. The ACP and ACS are employed to demonstrate the applications of the introduced DLSA Design Charts and the vibration suppression schemes for vibration suppression and actuator placement optimization. The vibration suppression of both ACP and ACS is significant over a frequency range encompassing several resonances, and is indicated by the Suppressed Vibration Energy (SVE) index. This investigation shows that the optimum location of the actuator depends on the structural mode shape, based on the criteria of maximum SVE and minimum actuator power. In general, the actuator should be placed on the panel on a sub-area, where the sum of normal strains is maximum. However, a preferred location can be determined over a range of frequencies that encompass more than one natural frequency.

Modal Analysis on Macro-strain Measurements from Distributed Long-gage Fiber Optic Sensors

Suzhen Li, , Zhishen Wu, — 2008-07-25

In a recent study by the authors, an advanced structural health monitoring (SHM) strategy based on distributed fiber optic sensing techniques has been proposed to utilize the strain responses throughout the full or some partial areas of structures to detect the arbitrary and unforeseen damages. As one of the essential components, a two-level scheme based on modal parameters from distributed dynamic macro-strain responses has been developed for damage locating and quantifying. This work further investigates the superiority and some concerns of using distributed long-gage fiber optic sensing technique for vibration based SHM through a theoretical modal analysis on the dynamic macro-strain distribution. Modal testing is also carried out to verify the performance of macro-strain frequency response function (FRF) and identify the modal parameters including resonant frequency, damping ratio, and modal macro-strain vector (MMSV). From the SHM point of view, their applications are summarized finally.

Vibration Control of Smart Composite Laminated Spherical Shell using Neural Network

Kumar, R., Mishra, B., Jain, S. — 2008-07-25

This study presents a neural network approach for the identification and control of a smart composite laminated spherical shell. The spherical shell is in the form of a layered composite shell having a sensor and an actuator layer. The vibratory response of the shell is modeled using FEM. A degenerate shell element is implemented to model composite laminated spherical shell. Modeling is based on the first-order shear deformation theory and linear piezoelectricity theory. The mode superposition method has been used to transform the coupled finite element equations of motion in the physical coordinates into a set of reduced uncoupled equations in the modal coordinates. The reduced uncoupled equations are transformed into discrete state space form. An identifier neural network has been trained using the results of the FEM program to predict the future response of the structure from the immediate history of the system's response. Then a controller neural network has been trained with the aid of the identifier neural network so that the overall behavior of the controlled system can be described by a prescribed reference model. Numerical results have been presented for the vibratory response of the laminated composite spherical shell. The controlled response of the shell is found to exactly follow the reference model.

A Unifying Perspective on the Quasi-steady Analysis of Magnetorheological Dampers

Hong, S.-R., John, S., Wereley, N. M., Choi, Y.-T., Choi, S.-B. — 2008-07-25

A magnetorheological (MR) fluid, modeled as a Bingham plastic (BP) material, is characterized by a field dependent yield stress, and a (nearly constant) postyield plastic viscosity. Based on viscometric measurements, such a BP model is an idealization to physical MR behavior, albeit a useful one. A better approximation involves modifying both the preyield and postyield constitutive behavior as follows: (1) assume a high viscosity preyield behavior when the shear stress is less than the transition stress, and (2) assume a power law fluid (i.e., strain rate dependent viscosity) when the shear stress is greater than the transition stress. Assuming a power law fluid in postyield allows the model to account for shear thinning behavior exhibited by MR fluids at higher strain rates. Such an idealization for MR fluid constitutive behavior is called an viscous-power law model, or a Herschel—Bulkley (HB) model with preyield viscosity. This study develops a quasi-steady analysis for such a constitutive MR fluid behavior applied to an MR flow mode damper. Closed form solutions are developed for the fluid velocity, as well as key performance metrics, such as damping capacity and dynamic range (ratio of field-on to field-off force). For the given fluid properties and flow mode damper geometry, the fluid velocity profile and gradient, and the relationship of the damper force and piston velocity are analyzed. In addition, specializations to existing models, such as the HB, biviscous, and BP models, are shown to be easily captured by this model when physical constraints (idealizations) are placed on the rheological behavior of the MR fluid.

Damping Behavior of Semi-passive Vibration Control using Shunted Piezoelectric Materials

Guyomar, D., Richard, C., Mohammadi, S. — 2008-07-25

Piezoelectric transducers in conjunction with appropriate electric networks can be used as mechanical energy dissipation devices. Semi-passive vibration control devices using nonlinear methods have experienced significant development in recent years, due to their performance and advantages compared with passive and active techniques. More precisely, synchronized switch damping (SSD) and derived techniques, which have been developed in the field of piezoelectric damping, lead to a very good trade-off between simplicity, required power supply, and performance. This technique consists of nonlinear processing of the piezoelement voltage which induces an increase in electromechanical energy conversion. The control law consists of triggering the inverting switch on each extremum of voltage (or displacement). The purpose of this study is the experimental observation of piezoelement damping sensitivity to variations of amplitude and frequency of excitation force. In addition, the effect of the size of piezoelement area on the vibration damping in high and low values of these parameters has been studied using SSDI method. The proposed method for switching sequence is based on statistical evaluation of the structural deflection.