Bending vibration of flat plates is controlled using patches of active constrained layer damping (ACLD) treatments. Each ACLD patch consists of a visco-elastic damping layer which is sandwiched between two piezo-electric layers. The first layer is directly bonded to the plate to sense its vibration and the second layer acts as an actuator to actively control the shear deformation of the visco-elastic damping layer according to the plate response. With such active/passive control capabilities the energy dissipation mechanism of the visco-elastic layer is enhanced and the damping characteristics of the plate vibration is improved. A finite element model is developed to analyze the dynamics and control of flat plates which are partially treated with multi-patches of ACLD treatments. The model is validated experimentally using an aluminum plate which is 0.05 cm thick, 25.0 cm long and 12.5 cm wide. The plate is treated with two ACLD patches, each of which is made of SOUNDCOAT (Dyad 606) visco-elastic layer sandwiched between two layers of AMP/polyvinylidene fluoride (PVDF) piezo-electric films. The piezo-electric axes of the patches are set at zero degrees relative to the plate longitudinal axis to control the bending mode. The effect of the gain of a proportional control action on the system performance is presented. Comparison between the theoretical predictions and the experimental results suggest the validity of the developed finite element model. Also, comparisons with the performance of conventional passive constrained layer damping clearly demonstrate the merits of the ACLD as an effective means for suppressing the vibration of flat plates.
A novel concept is proposed: the use of shape memory alloy (SMA) to reduce panel thermal deflection and flutter responses. SMA has a unique ability to recover large pre-strains completely when the alloy is heated above the austenite finish temperature Af. The transformation austenite start temperature As for nitinol can be anywhere between -60 °F (-50 °C) and +340 °F (+170 °C) by varying the nickel content. During the recovery process, a large tensile recovery stress occurs if the SMA is restrained. The shape memory effect phenomenon is attributed to a change in crystal structure known as a reversible austenite to martensite phase transformation. This solid-solid phase transformation also gives a large increase in Young's modulus and yield stress. In this paper, a panel subject to the combined aerodynamic and thermal loading is investigated. A nonlinear finite element model based on the von Karman strain-displacement relation is utilized to study the effectiveness of an SMA-embedded panel on the flutter boundary, critical buckling temperature, post-buckling deflection and free vibration. The study is performed on an isotropic panel with embedded SMA. The aerodynamic model is based on the first-order quasi-steady piston theory. The dynamic pressure effect on the buckling and post-buckling behaviour of the panel is investigated by introducing the aerodynamic stiffness term, which changes the critical buckling temperature. Panels with SMA embedded in either the longer or shorter direction and either fully or partially embedded are investigated for post-buckling behaviour. Similarly, the influence of temperature elevation on the flutter boundary and vibration frequencies is investigated.
The Active Constrained Layer Damping (ACLD) treatment has been used successfully for controlling the vibration of various flexible structures. It provides an effective means for augmenting the simplicity and reliability of passive damping with the low weight and high efficiency of active controls to attain high damping characteristics over broad frequency bands. In this paper, optimal placement strategies of ACLD patches are devised using the modal strain energy (MSE) method. These strategies aim at minimizing the total weight of the damping treatments while satisfying constraints imposed on the modal damping ratios. A finite element model is developed to determine the modal strain energies of plates treated with ACLD. The treatment is then applied to the elements that have highest MSE in order to target specific modes of vibrations. Numerical examples are presented to demonstrate the utility of the devised optimization technique as an effective tool for selecting the optimal locations of the ACLD treatment to achieve desired damping characteristics over a broad frequency band.
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