Finite Element Prediction of Damping in Structures with Constrained Viscoelastic Layers
01 Sep 1982-AIAA Journal (American Institute of Aeronautics and Astronautics (AIAA))-Vol. 20, Iss: 9, pp 1284-1290
TL;DR: In this article, an efficient method for finite element modeling of three-layer laminates containing a viscoelastic layer is described, and modal damping ratios are estimated from undamped normal mode results by means of the modal strain energy method.
Abstract: An efficient method is described for finite element modelling of three-layer laminates containing a viscoelastic layer. Modal damping ratios are estimated from undamped normal mode results by means of the modal strain energy method. Comparisons are given between results obtained by the MSE method implemented in NASTRAN, by various exact solutions for approximate governing differential equations, and by experiment. Results are in terms of frequencies, modal damping ratios, and mechanical admittances for simple beams, plates, and rings. Application of the finite element -- MSE method in design of integrally damped structures is discussed.
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TL;DR: In this article, a review of the available literature on damping in composite materials is presented, where a chronological review of test methods for damping estimation is presented in order to describe the time-line of theoretical knowledge development in this field.
Abstract: The present review aims at gathering the available literature on damping in composite materials. A chronological review of test methods for damping estimation is presented in order to describe the time-line of the theoretical knowledge development in this field. In the last years many new material configurations have emerged that deserve investigation, such as nano-composites, hybrid laminates and sandwich materials. Damping models specifically meant for non-homogeneous materials are reported to provide a background for understanding this problem. Although not widely exploited yet, fibre reinforced polymers has the potential to be tailored for damping by acting on constituents, geometry and boundary conditions. Nano-composites, for instance, are shown to possess a high potential for damping purposes. New hybrid and sandwich-type structures are emerging as noise and vibration control solutions in lightweight applications. The effort devoted to mathematical and numerical model in view of Finite Element integration of damping properties is also addressed. Finally, the conclusions summarise the ideas of the authors on needed steps to advance the state-of-the-art in each of the described topic.
240 citations
TL;DR: A comprehensive review of the various research methods and theory calculation models that are employed in engineering to study the static and dynamic vibration characteristics of viscoelastic damping material (VDM) formed structures is presented in this article.
204 citations
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28 Feb 2013TL;DR: In this paper, the authors present a case study of a horizontal machining center at the Lawrence Livermore National Laboratory (LLNL), where they used a generalized modeling approach developed through the course of creating several unique designs.
Abstract: This thesis is written to advance the reader's knowledge of precision-engineering principles and their application to designing machines that achieve both sufficient precision and minimum cost. It provides the concepts and tools necessary for the engineer to create new precision machine designs. Four case studies demonstrate the principles and showcase approaches and solutions to specific problems that generally have wider applications. These come from projects at the Lawrence Livermore National Laboratory in which the author participated: the Large Optics Diamond Turning Machine, Accuracy Enhancement of High- Productivity Machine Tools, the National Ignition Facility, and Extreme Ultraviolet Lithography. Although broad in scope, the topics go into sufficient depth to be useful to practicing precision engineers and often fulfill more academic ambitions. The thesis begins with a chapter that presents significant principles and fundamental knowledge from the Precision Engineering literature. Following this is a chapter that presents engineering design techniques that are general and not specific to precision machines. All subsequent chapters cover specific aspects of precision machine design. The first of these is Structural Design, guidelines and analysis techniques for achieving independently stiff machine structures. The next chapter addresses dynamic stiffness by presenting several techniques for Deterministic Damping, damping designs that can be analyzed and optimized with predictive results. Several chapters present a main thrust of the thesis, Exact-Constraint Design. A main contribution is a generalized modeling approach developed through the course of creating several unique designs. The final chapter is the primary case study of the thesis, the Conceptual Design of a Horizontal Machining Center.
201 citations
Cites methods from "Finite Element Prediction of Dampin..."
...More complex structures generally require finite element analysis (FEA) to model, and the approach developed by [Johnson and Kienholz, 1982] using modal strain energy is both accurate and simple....
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TL;DR: In this article, the optimal placement of active and passive members in complex truss structures was studied using the simulated annealing technique, where the authors adopted the maximization of the cumulative energy dissipated over a finite time interval as the measure of optimality.
Abstract: Active structural members with built-in sensing, feedback control, and actuation functions are used herein, along with passively damped members, to augment the inherent damping in truss structures. The effective use of such members makes it desirable to distribute them optimally throughout the structure. For simple structural systems, it is possible to place these members with some degree of optimality on the basis of engineering judgment. However, for more complex systems, the number of possible choices is so large that one may have to rely on a more formal optimization technique. This paper deals with the optimal placement of active and passive members in complex truss structures. The problem falls in the class of combinatorial optimization, for which the solution becomes exceedingly intractable as the problem size increases. This difficulty is overcome herein by use of the simulated annealing technique. We adopt the maximization of the cumulative energy dissipated over a finite time interval as the measure of optimality. The selection of nearly optimal locations for both passive and active members is consistently treated through the use of the finite-time energy dissipation criterion within the framework of the simulated annealing algorithm. Numerical examples are used to illustrate the effectiveness of this methodology.
147 citations
TL;DR: In this paper, the authors describe the results of an extensive study on the seismic behavior of a viscoelastically damped structure under mild and strong earthquake ground motions, and the results show that the VE dampers are effective in attenuating seismic structural response.
Abstract: This paper describes the results of an extensive study on the seismic behavior of a viscoelastically damped structure under mild and strong earthquake ground motions. Shaking-table studies were conducted on a 2/5-scale five-story steel model with added viscoelastic (VE) dampers under various ambient temperatures, damper-placement cases, and earthquake intensities. Three types of VE dampers distinguished by dimensions and viscoelastic materials designed to provide the structure with similar damping ratios at room temperature were used. Analytical studies were carried out to predict the equivalent damping ratios and seismic response of the viscoelastically damped structure. Experimental results show that the VE dampers are effective in attenuating seismic structural response under mild and strong earthquake ground motions. Numerical results show that the structural damping and structural response with added VE dampers can be easily and accurately calculated by the proposed analytical methods. The methods are readily available to practical applications.
141 citations
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TL;DR: In this article, the authors discussed the nature of damping mechanisms and how the damping depends on the amplitude and frequency of the cyclic motion of the system. But they did not consider the effect of the frequency and amplitude on damping.
384 citations
TL;DR: In this article, a complete set of equations of motion and boundary conditions governing the vibration of sandwich beams are derived by using the energy approach, and they are solved exactly for important boundary conditions.
Abstract: A complete set of equations of motion and boundary conditions governing the vibration of sandwich beams are derived by using the energy approach. They are solved exactly for important boundary conditions. The computational difficulties that were encountered in previous attempts at the exact solution of these equations have been overcome by careful programming. These exact results are presented in the form of design graphs and formulae, and their usage is illustrated by examples.
326 citations
265 citations
TL;DR: In this paper, a free and forced-vibration analysis of a three-layer laminated ring consisting of an inner and outer elastic layer with a core capable of transmitting only shear is made.
Abstract: A free‐ and forced‐vibration analysis is made of a three‐layer laminated ring consisting of an inner and outer elastic layer with a core capable of transmitting only shear. The Variational Method is used to obtain the equations of motion. Analytical expressions are obtained for the response and the natural frequencies of the laminated ring having an elastic core material. Curves are obtained which demonstrate the variation of the natural frequencies of the laminated ring for specific values of the core thickness and shear parameters with a change in the elastic thickness parameter for the first four circumferential bending modes. The resonance response is investigated and analytical expressions are obtained for the system having a viscoelastic core. Curves are obtained relating the resonant‐frequency parameter and the composite‐loss factor to the geometrical and physical properties of the ring vibrating in the fundamental circumferential bending mode.
26 citations
TL;DR: In this article, experimental and theoretical results of the radial driving point mechanical impedance of three-layered sandwich rings are presented and discussed and compared with the theoretical predictions over a wide frequency range of interest.
Abstract: Experimental and theoretical results of the radial driving point mechanical impedance of three-layered sandwich rings are presented and discussed. The composite sandwich rings, subjected to a time-harmonic radially-concentrated load, are made up of two thin elastic layers with a thin viscoelastic damping core between them. The effects of the operational temperature and frequency ranges concerned on the viscoelastic material properties are taken into account. Experimental data are compared well with the theoretical predictions over a wide frequency range of interest. Resonant conditions for lobar bending modes are also given.
22 citations