Journal of Intelligent Material Systems and Structures

The article presents the analytical model of a linear/rotary solid-state actuator formed by a shape memory wire wound over a cylindrical drum. The model assumes a bilinear stress-strain behavior of the wire in the martensitic state (low temperature) and a linear elastic response in the austenitic state (high temperature). Based on simple equilibrium conditions, the model calculates the stress and strain distributions in the wire when subjected to a constant external backup force and undergoing frictional sliding forces at the contact with the drum. Closed-form expressions are supplied for the stroke produced by whatever actuator geometry and are validated numerically against finite element results. For a particular actuator configuration, the analytical forecasts are also checked experimentally on a proof-of-concept prototype. The analytical model shows that large strokes (up to one-half of the drum’s diameter) are achieved if the frictional coefficient is kept below 0.01. Rolling-contact architectures or sonic-pulse excitations of the drum are discussed as technical solutions to obtain such low friction values.

The effects of transverse strain on the wavelength shifts of surface-mounted fiber Bragg grating (FBG) sensors are investigated. A new FBG model including the concept of strain transmissibility coefficients along the longitudinal and transverse directions of the sensors is proposed. The finite element method is applied to obtain the strain transmissibility coefficients between the FBG sensor and surface of the base structure. The wavelength shifts of each FBG sensor are calculated with respect to the assumed thermal strain condition of the base structures; the estimated strains by the proposed FBG model are compared with the results from conventional FBG model. The numerical results show that the surface strains of the composite structure can be predicted well using the proposed FBG model, while the conventional FBG model results in a larger error when the transverse strain of the base structure is much larger than longitudinal strain of the base structure, as in composite structures under thermal loadings.

A coupled electromechanical finite element formulation for active control of geometrically non-linear transient response of laminated composite plate is studied. First-order shear deformation theory and von Karman type non-linear strain displacements are used. The plate is discritized using eight-noded quadratic isoparametric elements with five mechanical degrees of freedom and one electrical degree of freedom per node. Newton-Raphson iterative method in association with Newmark time integration method is used to solve the non-linear finite element equilibrium equation. Negative velocity feedback control algorithm is used to control the dynamic response of the smart laminated composite plate. AFC layer poled in fiber direction acting as distributed actuator and PVDF layer poled in thickness direction acting as sensor are considered. This study involves two types of actuator sensor arrangements: (1) the substrate is sandwiched between AFC actuator and PVDF sensor, called non-collocated arrangement and (2) AFC actuator and PVDF sensor are placed on top of the substrate, called collocated arrangement. The effect of piezoelectric fiber orientation in actuator layer on vibration control for both cross-ply and angle-ply laminates are examined.

This work presents a dynamic model of a smart fin that is activated by a piezoelectric bimorph actuator, which is made by bonding two MFCs. The actuator is completely enclosed within the fin. Earlier research has indicated that the use of a linear model for the fin dynamics does not fully describe the fin. This work presents a more realistic approach to this problem by incorporating additional components into the model. Therefore, a proportional damping matrix is introduced. It is also observed that experimental results exhibit hysteresis and backlash. A Bouc-Wen hysteresis model, combined with four backlash operators, is proposed. These backlash operators are used to model the observed saturation and the non-symmetry of the response. HFSGA is used to identify the optimal set of parameters for the damping matrix constants, the Bouc-Wen model, and the backlash operators. One input case is considered for training the genetic algorithm. The results show that proposed model can predict the hysteresis of the smart fin-actuator system under various operational conditions.

The use of both shunted piezoelectric elements and periodic arrays have been investigated independently as well as used in conjunction to modify the vibration of a system. Piezoelectric patches bonded to a cantilever beam which is shunted with an active circuit, specifically a negative capacitance shunt, can control broadband flexural vibrations of a structure. Also, periodic arrays integrated into a structure allow for modification of propagating waves through the mechanical ‘‘stop-bands’’. The performance of a combined shunted periodic piezoelectric patch array will be analyzed in this study by investigating the velocity amplitude of the beam upstream and downstream of the array section and the number of control elements in the array. The negative capacitance shunts caused a global spatial average velocity reduction of 5 dB at the modal peaks from 500 to 5000 Hz. The reduction is shown to be greater in the downstream section of the beam. Also, by increasing the number of patches in the array, the attenuation of the resonances increased non-linearly. The results show that a negative capacitance periodic control array is an effective global vibration reduction system and has the ability to localize energy near the forcing of a structure.

The focus of this study is on sensor placement for damage detection. In particular, novel sensor placement techniques are presented to detect the length of a crack in ground vehicles. These techniques are designed to provide vibration characteristics for structures that have both cracks and structural variability. Such techniques are needed because structural variability affects the mode shapes of a structure, and thus the optimal sensor locations for detecting cracks are affected. Two key approaches are developed and used: (1) PROMs, and (2) BMA. Based on PROMs and BMA, a novel sensor placement is proposed to determine the optimal sensor locations for complex structures with cracks and structural variability. The information from the sensors can be used to determine variations in the mode shapes of the structure for different crack lengths. The variation in mode shapes can then be used to identify the crack length. Numerical results are presented for a ground vehicle frame. The sensor placement method is applied first to find the optimal sensor locations in the presence of parameter variability, and then to identify the length of a crack.

As large arrays of actuators become increasingly common in adaptive structures, many systems do not have enough power supplies to control each actuator individually due to design, weight, or cost constraints. This issue can be addressed by grouping multiple actuators together and powering each group with a single power supply. As this is done, it is important to determine which actuators to group together, that is, optimize the groupings for best performance. Currently, GAs and other heuristic algorithms are used to determine this grouping, where a global optimum or even acceptable solution is not always guaranteed. In order to effectively group the actuators and insure that the global optimum is found, a new method is developed in this research - the EME technique. This is an efficient algorithm that will locate the global optimum without having to examine every possible grouping combination. In this article, a detailed explanation of the EME algorithm is given and the efficacy of this method demonstrated. An example consisting of a beam with static deformation, multiple actuators, and different constraints on the number of power supplies is used to illustrate the concept. Utilizing an instrumented beam test stand, experimental investigation, and validation of the proposed method are performed.

In much of the vibration-based energy harvesting literature, resonant energy harvesters are designed around a single base excitation frequency, whereas many applications comprise broadband, time-varying vibrations. Since many naturally occurring vibrations are low frequency, a relatively large mass or beam length is required to resonate at the driving frequencies. This article presents a modeling and optimization procedure for designing vibration energy harvesters for maximizing power generated by vibrations recreated from real-world sources at low frequencies. It is shown that the device coupling coefficient, a significant parameter in determining the energy transduction performance, can be decoupled into terms related to the stiffness and mass distribution of the device, each of which can be optimized independently. To demonstrate the use of this design optimization procedure, measured accelerations are used to provide time-varying, broadband inputs to the energy-harvesting system. Under various size and mass constraints, optimal linear resonant harvesters are presented for human walking and automobile driving scenarios. The frequency response functions are presented alongside time histories of the power harvested using the experimental base acceleration signals. Finally, these results are compared to a non-linear device that utilizes spatially periodic magnetic excitation, a feature that is particularly suited to low-frequency, time-varying excitation.

This article is concerned with the analysis of actuation requirements for dynamic shape control of a piezoelectric structure. A general procedure is given for determining the distributed actuation input required to satisfy a partially specified displacement field for a generic piezoelectric shell structure. It is shown that under certain conditions, a servoconstraint that defines a finite number algebraic relations on the motion of the material points of the structure can be satisfied in steady state by an equivalent number of independent actuators. Application examples are developed to demonstrate application of the theory and its potential usefulness in the analysis and design of advanced engineering structures.

Torsional shape memory and superelastic NiTi elements provide low-profile, effective solutions for many biomedical applications such as orthopedic and orthotic devices. In this article, two different modeling approaches are used to model the torsional behavior of these alloys. For thin-walled tubes, a 1D model is adapted, while for thicker elements, a 3D model is chosen. Both of these models are implemented in the form of FE solutions. Experiments are conducted to find the modeling parameters, verify models, and compare the performance of these two modeling methods. These models are further used to for geometric and parametric studies of NiTi elements in torsion.

There are two different ways of using shape memory alloy (SMA) wire as an actuator for shape control of flexible structures: it can be either embedded within the composite laminate or externally attached to the structure. As the actuator can be placed at different offset distances from the beam, external actuators produce more bending moment and, consequently, considerabnle shape changes with the same magnitude of actuation force compared with the embedded type. Such a configuration also provides faster heat transfer rate owing to convection, which is very important in shape control applications that require a highfrequency response of SMA actuators.

Although combination and physics-based modeling of externally attached SMA actuator wires and strips have been considered by many researchers, these studies have some drawbacks, which, if neglected, result in a number of errors in the theoretical results compared with experimental results. These shortcomings are considering the linear Euler-Bernoulli beam theory, not deriving the actuation force of the SMA from the constitutive equations, and taking into account the effect of only one SMA wire actuation force on, for example, the structure. These assumptions may lead to erroneous theoretical modeling results compared with experimental results.

In this study, the aforementioned difficulties of attaching SMA actuators to the smart structures have been addressed. In other words, instead of linear beam theory, nonlinear beam theory is used in system modeling and, therefore, the proposed method and results are valid in large deflection and rotation behavior of beam. Also, in comparison to many other analyses that the effect of only one SMA wire is investigated, in the present research the effect of all active and inactive SMA wires is considered. Accordingly, the result of this paper can easily be generalized to the structure with several SMA wire actuations. Moreover, with the purpose of having practical applications in modeling and control, the heat transfer equations of all SMA wires are considered in the analysis and, as a result, the control inputs of the presented model are SMA wire electric currents rather than SMA temperatures.

First, a flexible beam actuated by two active SMA actuators is modeled. Then, the Brinson constitutive equations and thermoelectric equations for SMA materials are coupled with the nonlinear beam behavior, and the coupled system of equations is numerically solved for some particular practical cases. Finally, the numerical results of the model simulation are verified against the experimental results using a test setup to validate the proposed model prediction. The implemented method used in this paper can be easily extended to the more complex smart structure with numerous externally attached SMA wires.

This article presents a novel haptic interface for rehabilitation purposes using MR-dampers. In the rehabilitation, patients are required to do certain exercises to train damaged muscles. Specialized devices are required to ensure patients will do the exercise accurately. Typical devices that are used for this application are difficult to program and may cause damage by applying excessive force to human body. The haptic device that is designed in this article will address the issues by employing MR-dampers and a user-friendly programming methodology. The concept of Resistive-Map generation is introduced as main strategy for activating MR-dampers and restricting the motion to the regions determined by the therapist. To simulate the performance of the system, an accurate model of MR-damper is obtained and validated experimentally. To test the performance of the proposed MR-based haptic device, the resistance-maps are first generated. MR-dampers are activated according to the positions of the MR-dampers in the resistance-map. The system is also simulated in MATLAB ^®/ SimMechanics. The experimental and simulation results are in good agreement. The promising results of the proposed haptic interface make it a potential candidate for rehabilitation applications. Patients will be able to take the device home and the physiotherapists can online programme the exercises and monitor the performance of patients.