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.

Damping in composite materials: Properties and models

Research and applications of viscoelastic vibration damping materials: A review

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.

Principles and Techniques for Designing Precision Machines

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.

Optimal placement of active/passive members in truss structures using simulated annealing

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.

Seismic behavior of steel frame with added viscoelastic dampers

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.

Finite Element Prediction of Damping in Structures with Constrained Viscoelastic Layers

Finite element prediction of damping in structures with constrained viscoelastic layers

: This report presents three design-oriented methods for the dynamic analysis of sandwich plates, i.e., laminated plates incorporating a core layer of viscoelastic material for vibration damping. The methods are complementary in that each represents a different trade-off between generality, accuracy, and cost of use. This work was performed by the Aerospace Structures Information and Analysis Center, which is operated for the Flight Dynamics Laboratory by Anamet Laboratories, Inc., under Contract F33615-81-C-3201. The work was performed in support of the Advanced Radiation Technology (ART) Program Office at the Air Force Weapons Laboratory.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA363361&Location=U2&doc=GetTRDoc.pdf

Conor D. Johnson

Papers

Finite Element Prediction of Damping in Structures with Constrained Viscoelastic Layers

Finite element prediction of damping in structures with constrained viscoelastic layers

Analysis of Damped Plates