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.

Testing and characterization of highly damped structural materials

Abstract: Wavy composite is a new form of constrained layer damping that uses opposing sinusoidal waveforms in composite constraining layers to greatly enhance damping. Damping measurements as high as 26%, with the stiffness of aluminum and titanium are shown. This research is focused on evaluating a test system capable of determining the stiffness and damping of structural materials with high inherent damping. Time-temperature superposition can be applied to create a master curve from 1 Hz to 10,000 Hz that completely describes material performance as a function of frequency and temperature. This paper reveals how the accuracy of the low frequency portion of the nomograph is affected by very small errors in the test data that translate to large errors in the Arrhenius frequency shift constants. Detailed sensitivity analyses confirm the accuracy of test results, especially the magnitude of the damping and stiffness results. However, this paper shows how the frequency at which a given value of damping and stiffness occur is subject to increasing error when extrapolated to lower frequencies. Arrhenius time-temperature superposition constants are determined experimentally. Error associated with extrapolating to very low frequencies is discussed.

Restriant layer structure damping plate material

Abstract: The utility model discloses a constrained layer damping plate, comprising an upper plate (1) and a lower plate (2). It is characterized in that a damping layer (3) is arranged between the upper plate (1) and the lower plate (2). With simple structure and excellent acoustic performance, such damping plate is widely used.

Passive Damping in Stiffened Structures Using Viscoelastic Polymers

Abstract: Noise and vibration suppression is an important aspect in the design process of structures and machines. Undesirable vibrations can cause fatigue in a structure and are, therefore, a risk to the safety of a structure. One of the most effective and widely used methods of mitigating these unwanted vibrations from a system is passive damping, by using a viscoelastic material. This dissertation will primarily focus on constrained layer passive damping treatments in structures and the investigation of associated complex modes. The key idea behind constrained damping treatment is to increase damping as affected by the presence of a highly damped core layer vibrating mainly in shear. Our main goal was to incorporate viscoelastic material in a thick stiffened panel with plate-strip stiffeners, to enhance the damping characteristics of the structure. First, we investigated complex damped modes in beams in the presence of a viscoelastic layer sandwiched between two elastic layers. The problem was solved using two approaches, (1) Rayleigh beam theory and analyzed using the principle of virtual work, and (2) by using 2D plane stress elasticity based finite-element method. The damping in the viscoelastic material was modeled using the complex modulus approach. We used FEM without any kinematic assumptions for the transverse shear in both the core and elastic layers. Moreover, numerical examples were studied, by including complex modulus in the base and constraining layers. The loss factor was calculated by modal strain energy method, and by solving a complex eigenvalue problem. The efficiency of the modal strain energy method was tested for different loss factors in the core layer. Complex mode shapes of the beam were also examined in the study, and a comparison was made between viscoelastically damped and non-proportionally damped structures. Secondly, we studied the free vibration response of an integrally stiffened and/or stepped plate. The stiffeners used here were plate-strip stiffeners, unlike the rib stiffeners often investigated by researchers. Both plate and stiffeners were analyzed using the first-order shear deformation theory. The deflections and rotations were assumed as a product of Timoshenko beam functions, chosen appropriately according to the given boundary conditions. Unlike Navier and Levy solution techniques, the approach used here can also be applied to fully clamped, free and cantilever supported stiffened plates. The governing differential equations were solved using the Rayleigh-Ritz method. The development of the stiffness and the mass matrices in the Ritz analysis was found to consume a huge amount of CPU time due to the recursive integration of Timoshenko beam functions. An approach is suggested to greatly decrease this amount of CPU time, by replacing the recursive integration in a loop structure in the computer program, with the analytical integration of the integrand in the loop. The numerical results were compared with the exact solutions available in the literature and the commercially available finite-element software ABAQUS R ©. Some parametric studies were carried out to show the influence of certain important parameters on the overall natural frequencies of the stiffened plate. Finally, we investigated the damped response of an adhesively bonded plate employing plate-strip stiffeners, using FSDT for both the plate and stiffeners. The problem was analyzed using the principle of virtual work. At first, we did not consider damping in the adhesive in order to validate our code, by comparing our results with those available in the literature as well as with the results obtained using ABAQUS R © 3D model. The results were found to be highly satisfactory. We also considered the effect of changing the stiffness of the adhesive layer on the vibration of the bonded system. As a second step, we included damping in the stiffened structure using complex modulus approach, a widely used technique to represent the rheology of the viscoelastic material. We observed an overall increase in the natural frequencies of the system, due to the damping provided by the viscoelastic material. Moreover, it was noticed that when the thickness of the adhesive layer is increased, the natural frequencies and loss factor of the stiffened structure decrease. A viscoelastic material with high loss factor and small thickness will be a perfect design variable to obtain overall high damping in the structure. Passive Damping in Stiffened Structures Using Viscoelastic Polymers

Effectiveness of Partial Coverage for Constrained‐Layer‐Damping Treatments

Abstract: A new approach to the analysis of constrained‐layer‐damping treatments has been developed in order to consider the behavior of partial‐coverage configurations. The basic damping expressions, which are derived using strain‐energy principles, are applicable to one‐dimensional deformation of plates that are partially covered by constrained viscoelastic treatments. When specialized to the full coverage cases investigated by earlier authors, the present expressions are found to be in agreement. Considerable attention is given to the effect of symmetric, partial‐coverage treatments on the damping of the fundamental mode of simply supported and clamped‐ended configurations. Curves which present the damping, for thin treatment applications, as a function of the percent coverage and the shear parameter are included. These curves reveal the unexpected and significant characteristic that, for some values of shear parameter, damping increases rather than decreases as the coverage is reduced. This phenomenon provides verification and increases understanding of some earlier experimental results which showed that, under certain circumstances, cutting the constraining layer at regular intervals improved the performance of constrained‐damping treatments.