Showing papers on "Constrained-layer damping published in 1994"

Hybrid damping through intelligent constrained layer treatments

Abstract: This paper is to propose a viable hybrid damping design that integrates active and passive dampings through intelligent constrained layer (ICL) treatments. This design consists of a viscoelastic shear layer sandwiched between a piezoelectric constraining cover sheet and the structure to be damped. According to measured vibration response of the structure, a feedback controller regulates axial deformation of the piezoelectric layer to perform active vibration control. In the meantime, the viscoelastic shear layer provides additional passive damping. The active damping component of this design will produce adjustable and significant damping. The passive damping component of this design will increase gain and phase margins, eliminate spillover, reduce power consumption, improve robustness and reliability of the system, and reduce vibration response at high frequency ranges where active damping is difficult to implement. To model the dynamics of ICL, an eighth-order matrix differential equation governing bending and axial vibrations of an elastic beam with the ICL treatment is derived. The observability, controllability, and stability of ICL are discussed qualitatively for several beam structures. ICL may render the system uncontrollable or unobservable or both depending on the boundary conditions of the system. Finally, two examples are illustrated in this paper. The first example illustrates how an ICL damping treatment, which consists of an idealized, distributed sensor and a proportional-plus-derivative feedback controller, can reduce bending vibration of a semi-infinite elastic beam subjected to harmonic excitations. The second example is to apply an ICL damping treatment to a cantilever beam subjected to combined axial and bending vibrations. Numerical results show that ICL will produce significant damping.

Finite element model for active constrained-layer damping

Abstract: Constrained layer damping has been used for many years to increase the damping in engineering structures. Several researchers have suggested the concept of using viscoelastic materials with piezoceramics as the constraining layer. Since the piezoceramics are active materials, this concept can be referred to as active constrained layer damping. The paper presents a finite element model for a sandwich beam consisting of a host layer, a viscoelastic layer, and a piezoelectric layer. Lesieutre's method (Augmenting Thermodynamic Fields) for modeling damping was modified and applied to active constrained layer damping. Previous work on active constrained layer material has used the loss factor approach to modeling the viscoelastic layer. Such approaches are limited to steady state considerations, while the approach taken here is suitable for transient disturbances. Active damping and passive damping are individually of interest, however, here we propose to combine these two types of damping to produce an active constrained layer system with the best of both technologies.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Performance characteristics of active constrained-layer damping

Abstract: Theoretical and experimental performance characteristics of the new class of actively controlled constrained layer damping (ACLD) treatment are presented. The ACLD under consideration consists of a visco-elastic damping layer which is sandwiched between two piezo-electric layers. The three-layer composite ACLD when bonded to a vibrating structure acts as a SMART constraining layer damping treatment with built-in sensing and actuation capabilities. Particular emphasis is placed on studying the performance of ACLD treatments that are provided with sensing layers of different spatial distributions. The effect of the modal weighting characteristics of these sensing layers on the broad band attenuation of the vibration of beams that are fully treated with the ACLD is presented theoretically and experimentally. The equations governing the operation of ACLD treatments with modally shaped sensors are presented. The theoretical predictions of the model are compared with the experimental performance of a computer-controlled beam treated with Dyad 606 visco-elastic layer sandwiched between two layers of polyvinylidene fluoride (PVDF) piezo-electric films. Comparisons with the performance of conventional passive constrained layer damping are also presented.

Initial studies into the use of active constrained-layer damping for controlling resonant vibration

Abstract: The work described in this paper is concerned with controlling the strain of the constraining layer of a composite structure in such a way as to enhance the shear generated in the viscoelastic material and hence improve the overall damping of the composite structure. The results have indicated that this concept of active damping produces very effective levels of vibration suppression. In the case of cantilever beams the first two modes can be almost eliminated when velocity feedback of the beam tip is used. The results show that the addition of active control and passive damping in a single structure combines the advantages of passive damping in the higher modes and active control in the lower modes. In addition active damping as defined in this paper produces a fail safe mechanism in case of instability occurring in the feedback loop since passive damping is always present.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Two-dimensional finite element modeling of constrained-layer damping

Abstract: A new finite element is developed that reduces the modeling required to define the constrained layer damping treatment. The new element emulates the traditional method of modeling constrained layer damping with plate elements on either side of a thin hex element. Trade studies are performed in the application of constrained layer damping treatments to beams and plates. The effects of the thicknesses of the constraining layer and the viscoelastic layer are studied as well as some studies on the location of the damping treatment.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Damping Properties under Flexural Vibration for CFRP/Damping Materials Laminates.

Abstract: New materials, that possess high damping capabilities and high strength properties, have been studied in carbon fiber reinforced plastics (CFRP). These materials are referred to in this article as CFRP/damping-material laminates. The CFRP/damping-material laminates investigated here are composed of a unidirectional carbon/epoxy prepreg sheet and a polyethylene based damping material sheet used as an interleaf. Cantilever beam tests revealed the high damping properties of these laminates. Loss factor values for these composites are 10 to 100 times as large as that for conventional CFRP. These values could be predicted by using the constrained layer damping theory, except for two specimens.

Active damping for the control of flexible structures

Abstract: Active damping can be generated in a number of ways, the most obvious one being applying a force to the structure which is proportional to the velocity at a point on the structure. Another technique is to actively increase the damping of a structure by using a passive damping element i.e. dissipate the energy of vibration by increasing the relative motion of the structure with respect to the passive damping element. A practical way to achieve this is by using constrained layer damping (CLD). It is well known that CLD is effective because of the relative motion of the structure and the constraining layer which produces extra shear in a layer of viscoelastic material. The work described in this paper is concerned with controlling the strain of the constraining layer of a composite structure in such a way as to enhance the shear generated in the viscoelastic material and hence improve the overall damping of the composite structure. If the control law selected forces the constraining layer to move 180 degrees out of phase with the structure then the viscoelastic damping layer undergoes maximum shear and active damping is achieved. The results have indicated that this concept of active damping produces very effective levels of vibration suppression. In the case of cantilever beams the first two modes can be almost eliminated when velocity feedback of the beam tip is used. The results show that the addition of active control and passive damping in a single structure combines the advantages of passive damping in the higher modes and active control in the lower modes. In addition active damping as defined in this paper produces a fail safe mechanism in case of instability occurring in the feedback system since passive damping is always present.

Jitter suppression experiment passive damping design cycle

Abstract: The University of Dayton Research Institute is teamed with McDonnell Douglas Aerospace to develop and fly a NASA IN-STEP experiment entitled Jitter Suppression Experiment (JSX). The JSX will demonstrate a combined active/passive vibration control system on an actual full scale space structure. This paper presents the details of the design of the passive control system to be applied to six graphite/epoxy support tubes for a gimballed telescope assembly (GTA) and the results of concept development laboratory tests. The most promising damping concepts for tubes such as the GTA truss tubes were constrained layer dampers and tuned dampers. The advantages and disadvantages of each of these damping concepts and the reasons for choosing a constrained layer concept are discussed. To verify the effectiveness of the passive damping design and to determine the constrained layer damping system effectiveness for axial modes, a finite element analysis of a single truss tube with the proposed constraining layer design was performed. A laboratory simulation was designed, developed, and evaluated to verify the analysis.

Pole-zero modeling for smart viscoelastic structures

Abstract: Experimental and numerical results are presented which illustrate the use of pole-zero models for design of smart viscoelastic structures. Smart viscoelastic structures are defined here to be those class of structures containing both piezoceramic sensors and actuators as well as constrained layer viscoelastic treatments. Such devices have received recent attention in the literature as having excellent vibration suppression qualities. However, the modeling of viscoelastic elements is not particularly straightforward, leading to difficulties in design predictions for the active constrained layer damping treatments. The work presented here discusses pole-zero modeling results for various configurations of embedded and surface-mounted piezoceramic/viscoelastic layers in laminated beams. The specific arrangement of fiberglass, piezoceramic, and viscoelastic materials are examined in the context of pole-zero modeling approaches for smart viscoelastic structures. In this paper, the pole-zero models of each composite beam configuration lend insight into the preferred design strategy when blending passive elements (constrained layer viscoelastic) with active elements (piezoceramic sensors and actuators) to perform vibration suppression.

Tuning using electromechanical surface damping

Abstract: The electromechanical surface damping (EMSD) technique, for controlling the peak vibration amplitudes of beam-like structures, is modified to extend the effective range of the approach. The technique is a combination of the constrained layer damping and the shunted piezoelectric methods, where the viscoelastic constrained layer attached to the vibrating surface is constrained by a shunted piezoelectric ceramic element. The mathematical model of the modified EMSD element is presented, implemented into a finite element algorithm and applied to demonstrate the ability of the technique to simultaneously and effectively suppress the first three resonant peaks of a generic aluminum cantilever beam.

Structure-property relationships in viscoelastic behavior of interpenetrating polymer networks for constrained-layer damping

Abstract: Interpenetrating polymer networks (IPNs) are materials composed of two or more crosslinked polymers permanently and intimately intertwined on a molecular level. The resulting distribution of microenvironments can result in a material with a high mechanical loss in the glass-rubber relaxation, that is shifted in temperature and broadened over that of either constituent polymer. Several series of polyurethane/epoxy IPNs have been prepared for evaluation as possible broad band damping materials. Dynamic mechanical analysis and differential scanning calorimetry revealed that the temperature of the loss peak could be varied widely with sample formulation. Flexible epoxy components and plasticizers were incorporated. This resulted in materials with relatively low Young's and shear moduli, with losses that were broadened in the temperature regime. Simply supported beam assemblies were used to measure damping of three layer constrained structures. Comparison of measured temperature and frequency dependent viscoelastic behavior in constrained layer structures is analyzed in terms of the Ross-Kerwin-Ungar model for coated beams, and correlated to polymer composition and morphology.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.