Showing papers on "Constrained-layer damping published in 1993"

Modeling of linear viscoelastic space structures

Abstract: The GHM Method provides viscoelastic finite elements derived from the commonly used elastic finite elements. Moreover, these GHM elements are used directly and conveniently in second-order structural models jut like their elastic counterparts. The forms of the GHM element matrices preserve the definiteness properties usually associated with finite element matrices—namely, the mass matrix is positive definite, the stiffness matrix is nonnegative definite, and the damping matrix is positive semi-definite. In the Laplace domain, material properties are modeled phenomenologically as a sum of second-order rational functions dubbed mini-oscillator terms. Developed originally as a tool for the analysis of damping in large flexible space structures, the GHM method is applicable to any structure which incorporates viscoelastic materials.

Method and device for active constrained layer damping for vibration and sound control

Abstract: A new method and device for actively-controlled constrained layer (ACLD) treatment which can be used as an effective means for damping out vibrations and sounds from flexible structures are described. The ACLD treatment consists of a visco-elastic damping layer which is sandwiched between two piezo-electric layers. The three-layer composite ACLD, when bonded to a surface which is subject to vibrational and/or sound disturbances, acts as a smart constraining layer damping treatment with built-in sensing and actuation capabilities. The sensing capability is provided by the piezo-electric layer bonded to the surface of the flexible structure, whereas the actuation or control capability is generated by the other piezo-electric layer which acts as an active constraining layer.

Mechanical properties for CFRP/damping-material laminates

Abstract: New materials that possess high damping capabilities and have 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 5 to 50 times as large as that for conventional CFRP. These values could be predicted by using the analysis constrained layer damping treantment, except for two specimens. Also, the interleaving effect on tensile and compression strength are discussed here

Electromechanical surface damping using constrained layer and shunted piezoelectric

Abstract: An electromechanical surface damping (EMSD) technique is proposed. The technique is a combination of the constrained layer damping and the shunted piezoelectric methods, where the viscoelastic layer attached to the surface of the vibrating substructure is constrained by a shunted piezoelectric ceramic element. A mathematical model of the dynamic behavior of the coupled piezoelectric/constrained layer/substructure (EMSD element) is developed, implemented into a finite element algorithm, and used to investigate the effect of some of the system parameters on the dynamic characteristics (the first three natural frequencies and modal loss factors) of a generic cantilever beam. The effect of the following system parameters is considered: storage modulus ratios, material loss factors, thickness ratios, and the axial location of the EMSD element. The algorithm is also used to demonstrate the effectiveness of the proposed EMSD technique in controlling the peak vibration amplitudes at the first two natural frequencies of the cantilever beam.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Passive damping of large space structures

Abstract: The complex stiffness matrix and the mass matrix of a uniaxial bar subjected to constrained layer damping over its entire length are derived exactly by solving the differential equations of motion of the three-layered structure. The stiffness and mass matrices of a bar with segmented damping treatments are obtained by assembling the corresponding matrices for each segment and eliminating the internal nodes using a reduction procedure similar to static condensation. The natural frequencies, mode shapes, and loss factor of a pinconnected truss containing several damped members are computed by three different methods: truss finite element (TFE) method (exact), equivalent beam element (EBE) method, and scaled beam element (SEE) method, each method being more efficient than the preceding one. A 10-bay plane truss is considered as an example to illustrate each method. The EBE method yields very good results, but the savings in computation is not significant. The SBE method reduces the computational effort drastically and gives reasonably approximate results. I. Introduction T HE space structures of future space stations and other such facilities would be typically latticed, lightweight, and flexible. During regular operation of these space stations, they would be subjected to excitation, causing undesirable low-frequency vibrations. The control of these vibrations is vital for the successful operation of the space structure. In addition to active controls, passive damping techniques can be employed to minimize the mass of components of the active control systems. Constrained layer damping is one of the efficient passive vibration control techniques.1 In this paper we have developed a series of analytical and numerical techniques for the analysis of a large space structure (pin-connected truss) subjected to constrained layer damping. Actually, these techniques are equally applicable to any type of passive damping treatment. Figure 1 depicts the hierarchy of models that can be used in analyzing a passively damped large space structure. First, a closed-form expression is derived for computing the complex stiffness matrix and mass matrix of a uniaxial bar subjected to damping treatment along the entire length (Fig. la). The problem of segmented treatment on a uniaxial bar is solved by considering the bar as an assemblage of fully treated bars (Fig. Ib). The stiffness and mass matrices of the various uniaxial members are assembled to form the global stiffness and mass matrices of the truss structure (Fig. Ic). The loss factor can be computed using the modal strain energy method.2 If the truss has a large number of members—which is typical of large space structures—then an equivalent beam or plate model can be derived. There are several approaches for deriving the equivalent continuum model for an undamped space structure, e.g., Sun et al., 3 Noor et al.,4 and Lee.5 All of these methods are based on the assumption that the large space structure has a repeating unit cell. In this paper we have modified the method described by Lee5 to derive the complex stiffness and mass matrix of an equivalent beam element, which can then be used in the analysis of large structures. Two models, equivalent beam element (EBE) method (Fig. Id) and scaled beam element (SBE)

Combined tuned and constrained layer damping of a Type 13 magnetic recording head suspension

Abstract: The effect of a typical constrained layer damping (CLD) patch on the resonant behavior of a standard Type 13 magnetic recording head suspension is determined and compared with that of a specially designed tuned-CLD patch, using both numerical and experimental techniques. In particular, attention is focused on damping the first in-plane bending mode, or sway mode, of the load beam. In addition, a specification for the real modulus of a damping gel is given which, if realized in a suitable material, would enable the application of the tuned-CLD approach to magnetic head suspensions. >

A formulation for the vibro-acoustic behavior of a rectangular plate with constrained-layer damping

Abstract: The authors develop a rapid but rigorous tool to help acoustics engineers understand and predict the vibro-acoustic behavior of a constrained-layer damping of a plate. A rectangular four layered simply supported baffled plate is considered. In addition, the plate is assumed to be semi-complex in the sense that it can support added masses, stiffeners and several types of excitation (i.e. point, line, surface forces and moment). The problem is formulated using a variational approach and solved by the Rayleigh-Ritz method. The modeling of the stiffeners is based on an equivalent orthotropic layer. Since the plate is assumed to radiate in air, added mass due to fluid loading is ignored. However, possible cross modal coupling due to stiffening or the type of the excitation is accounted for. This is done using a novel method for evaluating the radiation impedance matrix based on multipoles expansions of Green's kernel. The numerical evaluation of the radiated power is done easily from the radiation impedance matrix