Journal of Intelligent Material Systems and Structures

The objective of this research is to demonstrate the effect of Active Constrained Layer segmentation on the enhancement of low frequency vibrations damping in flexible beams. The Active Constrained Layer Damping treatment, under consideration, consists of a viscoelastic layer sandwiched between two piezoelectric layers. The shear deformation of the viscoelastic layer causes loss of energy and thus the damping of vibration.

This paper focuses on the effects of constraining layer segmentation. Experimental results obtained for slender beams partially treated with segmented and unsegmented Active Constrained Layer Damping treatments are presented. Tested specimens have low natural frequencies typical. e.g., for long span floors, moment frames, or flexible robotic manipulator arms. The performance of segmented and unsegmented treatments, as well as active and passive treatments are compared. The presented results demonstrate that significant improvement in Active Constrained Layer Damping treatment performance can be achieved by an appropriate segmentation of the constraining layer.

This paper deals with adaptive shape control of laminated composite beams with integrated piezoelectric actuators. The mathematical model is based on a higher order shear deformation theory and accounts for lateral strains. A constrained optimization algorithm has been implemented to calculate the optimal open loop actuator voltages which minimize the error function. A closed loop feedback system is developed to maintain the desired shape even in the presence of quasistatically varying unknown loads. A computationally efficient finite element code is developed for performing the numerical calculations. The effect of stacking sequence and boundary conditions on the actuator voltages for both open loop and closed loop systems is examined. It is observed that the adapted shape achieved by using a full sensor feedback and partial sensor feedback are nearly the same. Thus position sensors at all locations are not required for closed loop shape control.

The controllable rheological behaviour of Electro-Rheological Fluids (ERF) is useful in engineering systems where variable performance is required. In particular the ERF have properties which are changed by an imposed electric field. In this paper a generalised Reynolds equation is solved using finite element techniques in order to simulate the behaviour of misaligned journal bearings lubricated with ERF. The Bingham plastic model is used to described the behaviour of the ERF, when the fluid is in flow mode. It is found that the applied electric field has a substantial influence on the load carrying capacity and the misaligned attitude of the journal bearings. It is concluded that the electric field imposed on the electro-rheological lubricant tends to align the journal in the bearing, making thus the misalignment angle smaller. Thus by changing the electric field it is possible to control the dynamic behaviour of rotor-bearing systems.

In this study, a new discrete-time sliding mode controller is proposed and applied to active vibration control of a flexible smart structure featuring a piezofilm actuator. After deriving the governing equation of motion for the smart structure, a discrete-time control model with system uncertainties is constructed in a state space. A stable sliding surface is then designed followed by the formulations of a discrete-time sliding mode controller which consists of a discontinuous part and an equivalent part. For the design of the discontinuous part, a time-varying control gain is adopted to increase system robustness to the uncertainties. In the design of the equivalent part, a so called equivalent controller separation method is employed to achieve faster reaching to the sliding surface without extension of the sliding region in which undesirable vibration chattering may be arisen. Controlled responses of transient and forced vibrations are evaluated through computer simulation and experimental realization.

In this paper, the governing equations and boundary conditions of laminated beamlike components of smart structures are reviewed. Sensor and actuator layers are included in the beam so as to facilitate vibration suppression. Two mathematical models, namely the shear-deformable (Timoshenko) model and the shear-indeformable (Euler-Bernoulli) model, are presented. The differential equations of the continuous system are approximated by utilizing finite element techniques for both models. A cantilever laminated beam with and without a tip mass is investigated to assess the validity and the accuracy of the two models when used for vibration suppression. Comparison between the two models is presented to show the advantages and the limitations of each of the models. Since the Timoshenko beam theory is higher order than the Euler Bernoulli theory, it is known to be superior in predicting the transient response of the beam. The superiority of the Timoshenko model is more pronounced for beams with a low aspect ratio. It is shown that use of an Euler-Bernoulli based controller to suppress beam vibration can lead to instability caused by the inadvertent excitation of unmodelled modes.

Since an intelligent variable geometry truss (IVGT) is usually equipped with large numbers of redundant actuators for the sake of providing adaptivity, a distributed control is considered a promising approach to dealing with its motion control. In this case, a modeling approach and an integrated model is a key to constructing distributed control systems from both hardware and software. To this end, this paper proposes an object-oriented modeling approach. Through decomposing the control problem domain underlying VGTs into objects, an object model can be obtained to represent various object abstractions and the relationships among these objects. It is shown in this paper that an object model of VGTs is exactly the integrated model for their knowledge organizations as well as the control architectures. Two control schemes resulting from the object models-a hierarchical distributed control and an autonomous distributed control-are discussed in particular. To verify the concepts addressed in this paper, an experimental prototype of IVGTs was manufactured, with a two-level hierarchical distributed control system equipped. With this prototype, an experiment is carried out, simulating a self-construction of space structures with IVGTs in a null gravity space.

Two methods for fabricating high aspect ratio (depth/width) microstructures were developed and compared. The first method is a modified deep X-ray lithography process with thick negative resist. For preventing pattern collapse caused by surface tension while the rinse liquid is evaporated, some post-rinse drying processes were investigated. The second method is a directional etching of polyimide by 02 reactive ion etching (RIE). The advantage of the latter method is that the surface tension of liquids does not affect the microstructure in a dry atmosphere. In both methods, aspect ratio of 10 was achieved in polymer molds for electroplating at pattern width of 5,um without collapse.

Zinc and copper are two elements which mutually interfere with each other in stripping analysis. The cause is the formation of a Zn-Cu intermetallic compound in the mercury film, which affects both Cu and Zn analyses. A backward error propagation artificial neural network has been applied in a novel approach for the determination of zinc in the presence of copper using potentiometric stripping analysis. This performed well in determining the correct zinc concentration in the sample when provided with the stripping times of zinc and copper and the copper concentration (determined by shifting the plating potential to a lower value to prevent the zinc being plated onto the mercury film electrode). The unknown zinc concentration was determined following an initial period of network exposure to a set of experimental data, which were used as examples of the required input/output data mapping.

This paper describes a sensor employing a gel formed from an interpenetrating polymer network of poly(vinyl alcohol) and a copolymer of N-isopropylacrylamide and acrylic acid. This gel exhibits a continuous volume-phase transition that is strongly dependent on the presence of polyvalent metal ions in the gel solvent. A sensor apparatus has been constructed that estimates, in real time, the transition temperature of a gel. When this sensor is loaded with a gel sensitive to metal ions, it could be used to detect the presence and identity of metal ions in a solution.