Constrained-layer damping

About: Constrained-layer damping is a research topic. Over the lifetime, 795 publications have been published within this topic receiving 15758 citations.

Aerospace Structures Technology Damping Design Guide. Volume 1. Technology Review

Abstract: : This volume contains a summary of the current technology used in the application of viscoelastic damping to primarily aerospace structures. The topics covered include the fundamentals of damping, the level of the damping present in metals, composites and aerospace structures made from these materials, and methods for measuring this damping; the fundamentals of viscoelastic damping materials, the test methods used to obtain the damping material data and the method of presenting these data; the basic viscoelastic damping theory for the free and constrained layer damping design and for tuned dampers, and the finite element analysis used in the design of more complex viscoelastic damping applications. A brief review of the classical methods for predicting the vibration response of aircraft type structures is also included together with a discussion of the effect of damping on the noise transmission loss of these types of aircraft structures.

Vibration characteristics analysis of CLD/plate based on the multi-objective optimization

Abstract: The multi-objective optimization configurations of thickness, the locations of constrained layer damping (CLD) patches for plate are investigated and the vibration characteristics of the CLD/plate are analyzed based on the Pareto optimal solutions. The finite element method, in conjunction with the Golla-Hughes-McTavish (GHM) method, is employed to model the plate with CLD treatments to predict its vibration characteristics. A multi-objective optimization model for CLD/plate is formulated based on the dynamical equation. The design objectives are to maximize the mode loss factors, while the design variables include the thicknesses of viscoelastic material (VEM) and constrained layer material (CLM), the locations of CLD treatments on the plate. Aiming to the special real-integer hybrid variables optimization problems, the non-dominated sorting genetic algorithm II (NSGA-II) is employed and improved. Two different optimization strategies are proposed. As the results of the numerical example, the various feasible Pareto optimal solutions are successfully obtained, and effects of the design variables on the vibration characteristics are discussed. The influences of algorithm parameters on the optimization procedure are also investigated. The results show the validity of improved NSGA-II and the optimization strategies. The potential multiple selections of CLD treatments for different vibration control objectives and constrained conditions are also demonstrated.

Constrained-layer damping with gradient polymers for effectiveness over broad temperature ranges

Abstract: The effectiveness of a constrained-layer damping treatment in dissipating energy and thereby augmenting the system damping is contingent on the viscoelastic polymer having a fairly significant value of material loss factor. A monolithic viscoelastic polymer tends to be lossy over a fairly narrow temperature range, corresponding to the material being in the transition state. At temperatures below this range, the viscoelastic polymer displays glassy behavior, whereas for higher temperatures, it displays rubbery behavior. In either case, the material loss factor reduces sharply and the effectiveness of the damping treatment is severely degraded. A gradient viscoelastic polymer layer, for which the properties vary through the thickness of the layer, can increase the temperature range of effectiveness of the damping treatment. This is because different regions through the thickness enter transition at different temperatures, and so the gradient polymer as a whole provides damping augmentation over a broader temperature range. Classical constrained-layer damping treatments with monolithic polymeric damping layers routinely assume a uniform shear strain through the thickness of the damping layer. However, because the shear modulus of the gradient viscoelastic polymer can vary by up to two-three orders of magnitude through the thickness, the shear strain can also be expected to vary substantially through the thickness. Consequently, a new analysis is developed with the gradient viscoelastic polymer modeled as comprising N discrete sublayers, each with its distinct properties and each assigned an independent shear degree of freedom. Simulation results are presented for a gradient polymer comprising N = 2 discrete sublayers. The results of the study are used to understand the underlying physics. It is seen that ideally, the glassy temperature of the two sublayers should be approximately similar. Further, the treatment is most effective if the sublayer that goes into glass transition at higher temperatures has a lower rubbery modulus than the sublayer going into glass transition at lower temperatures.