Surface Damping Treatments Research Articles

Comparative study on damping performance of different shape memory polymers

Vibration analysis using an unconstrained layer damping for surface damping treatment is presented in the paper. The layer made of viscoelstic material is applied over the structure on single side known as an unsymmetrical unconstrained layer damping treatment is discussed along with the same material is glued on two sides of the surface called as symmetrical unconstrained layer damping treatment. In the present investigation, based on UTM and DMA tests, different analytical studies were carried out using shape memory polymers such as polyurethane, silicone, and butyl rubbers as damping materials for symmetrical and unsymmetrical configurations with damping layer thicknesses of 10 mm to evaluate the damping performance of unconstrained layer damped specimens. The feasibility studies of all the selected shape memory polymers revealed that the structure layered with butyl rubber gives better results than others in reducing vibration amplitude when the possibility of rectangular and cylindrical cavities in the layer are considered and discussed. The extensional damped samples were modeled using the modeling software tool, i.e. Solid Works, and modal analysis was carried out on the ANSYS workbench. Finally, the whole structure’s damping is predicted using RKU (Ross-Kerwin-Ungar) analysis, and the optimum values of system’s loss factor are obtained using Python programming.

A finite element formulation for the transient response of free layer damping plates including fractional derivatives

This paper presents a finite element formulation specifically developed for the transient dynamic analysis of free layer damping plates, in which the viscoelastic behaviour of damping layers is modelled by means of fractional derivatives. This formulation is based on the homogenisation of thin multi-layered plates, adapted to consider fractional derivatives. Then, a fractional matrix equation system is reached, and the time response is solved by means of the implicit Newmark method in conjunction with the Grünwald-Letnikov discretisation of the fractional derivatives. The validation of the method is carried out by comparing the results of three different numerical applications with the ones provided by a finite element model built with hexahedral elements. As conclusion, it can be pointed out that the proposed finite element formulation based on the homogenisation of multi-layer plates reproduces accurately the time response of plates with surface damping treatments. In addition, this method allows conventional plate mass and stiffness matrices to be used to model each individual layer, without requiring specific formulations.

Dynamic response of fractionally damped two-layered viscoelastic plate

The vibration response of the plates attached with the free viscoelastic damping layer is investigated to predict the performance of free surface damping treatment. The frequency-dependent dynamic properties of the viscoelastic layer are expressed by fractional Kelvin-Voigt model. A simple and efficient identification approach based on the gradient-based optimization principle is employed to evaluate the viscoelastic model parameters from the experimental data. Both classical and fractional Kelvin-Voigt models are employed to describe the viscoelasticity, and the corresponding model parameters are identified. Further, the application of these identified parameters in the modeling and analyzing of real viscoelastic composite structures is demonstrated through quantitative examples. Step load-induced transient responses of the viscoelastic structures modeled using the classical and fractional model parameters are investigated and compared, to demonstrate the consequences of unknowingly using the classical Kelvin-Voigt model. The effects of the viscoelastic layer thickness on the transient response of the two-layered plate are also studied.

Effect of Carbon Black on the Performance of Nitrile Rubber For Analyzing Free Layered Surface Damping Treatment

Abstract The Mechanical and damping properties of Nitrile rubber of 40, 50 and 60 shore A hardness were performed with tensile and DMA tests on specimens for the purpose of improving structural damping. The Nitrile rubber of 60 shore A material showed better static and dynamic characteristics than those of the 40 and 50 shore A hardness because of high carbon black content. The results obtained from vibration test carried with free layered surface damping treated samples are agreed with the modal analysis of two-layered damping system in the frequency domain under vibrational excitation using ANSYS Workbench 14.0 software.

Characterization of Brake Shims Using Analytical Constrained Layer Damping Theories

AbstractShims in automotive brake systems are applied to suppress brake squeal resulting from self‐excited vibrations. These composite structures consist of thin metal plates and elastomer layers having high damping potential. The characterization and subsequent selection of shims is mainly based on a wide range of experimental investigations so far. To reduce measuring efforts significantly a systematic modeling of shims is focused. Therefore, approaches from literature describing surface damping treatments analytically are considered. The damping effect is mainly based on the shearing of the viscoelastic core which is taken into account by the applied theory. The dissipation potential is characterized by the complex shear modulus of the elastomer layer. Hence, sandwich beam theories enable the prediction of natural frequencies and in particular loss factors of bending mode shapes. In this contribution shims bonded on rectangular steel plates are examined. The main focus is on the determination of rheological influencing variables as well as the impact of boundary conditions in detail. Moreover, the impact of the shim length on the damping behavior is investigated experimentally.

Investigation of Weight Reduction of Automotive Body Structures with the Use of Sandwich Materials

The use of sandwich materials in automobile body panels is investigated in this study. In the first part, floor, luggage, firewall and rear wheel panels of a car body-in-white are replaced with panels made of sandwich materials in order to reduce the weight. Final sandwich material configurations are obtained through a trial and error based optimization approach where weights of the panels are minimized while keeping bending stiffness performances of the panels same. In the second part, the use of sandwich materials in laminated steel form as light weight alternatives to free layer surface damping treatments attached to floor panels is investigated. Free layer damping treatments are applied to body panels to decrease primarily the structure-borne noise inside the cabin. This effect is achieved by increasing structural damping in the panel structures. It has been demonstrated that, same level of vibration damping increase in a floor panel can be achieved using a sandwich material in laminated steel form with a lesser amount of weight addition to the original sheet metal floor panel compared to a free layer surface damping treatment.

Lightweight damping of composite sandwich beams: Experimental analysis

The purpose of this article is to experimentally study the damping of composite sandwich beams with lightweight honeycomb core. The top and bottom facesheets are made of carbon/epoxy layers with partial interleaved viscoelastic layers. A new damping approach consisting of selectively targeting the inflection points of the bending mode shapes is proposed. At the nodes, the shearing deformation in the beam is maximal, and so is the strain in the viscoelastic layers. The experimental investigation of damping is made by means of standard impact tests using an instrumented hammer performed on beam specimens. The nodes are determined experimentally by moving a small accelerometer along the beam axis and by measuring the amplitude of the acceleration at each point. This novel damping approach keeps the damping ratio as high as the ratio obtained with standard (full coverage) surface damping treatment while reducing the added mass by almost 50%. A comparison of the results obtained in this study with experimental and numerical results found in the literature leads to the conclusion that the most efficient way of damping this type of sandwich structure is to modify and/or improve the viscoelastic properties of the core.

Surface damping effect of anchored constrained viscoelastic layers on the flexural response of simply supported structures

Viscoelastic (VE) materials are commonly used to control vibration-induced fatigue in airframes and to suppress general vibration in various structures. This study investigates the effects of anchored constrained VE layers on the flexural response of simply supported Euler beams or plate strips under base excitations. Emphasis is placed on the development of two surface damping treatments: one VE layer anchored at one end, and two VE layers anchored at their different ends. Each anchorage is realized with a thin stiff layer in tension, such as a fiber reinforced polymer sheet, bonded to the surface of a VE layer and anchored to one end of the beam for maximum shear deformation in the constrained VE layer. Non-uniform shear deformation in VE layers is taken into account in the new solution formulation. Sensitivity analyses are performed to understand and quantify the effects of various parameters on flexural responses of the structures. The minimum thickness of VE layers is mainly bounded by the relative stiffness between the VE layers and the constraining face layer. The performances of various configurations are compared and the two-end anchored configuration is found most effective in vibration suppression.

A statistical characterization method for damping material properties and its application to structural-acoustic system design

The performance of surface damping treatments may vary once the surface is exposed to a wide range of temperatures, because the performance of viscoelastic damping material is highly dependent on operational temperature. In addition, experimental data for dynamic responses of viscoelastic material are inherently random, which makes it difficult to design a robust damping layout. In this paper a statistical modeling procedure with a statistical calibration method is suggested for the variability characterization of viscoelastic damping material in constrained-layer damping structures. First, the viscoelastic material property is decomposed into two sources: (i) a random complex modulus due to operational temperature variability, and (ii) experimental/model errors in the complex modulus. Next, the variability in the damping material property is obtained using the statistical calibration method by solving an unconstrained optimization problem with a likelihood function metric. Two case studies are considered to show the influence of the material variability on the acoustic performances in the structural-acoustic systems. It is shown that the variability of the damping material is propagated to that of the acoustic performances in the systems. Finally, robust and reliable damping layout designs of the two case studies are obtained through the reliability-based design optimization (RBDO) amidst severe variability in operational temperature and the damping material.

Modeling and validation of the response of ribbed panels using numerical methods and experimental data.

Rib-reinforced panels are widely used by the aeronautical industry. This kind of structure is typical on the fuselage of airplanes. Under flight conditions, the fuselage suffers several dynamic loads, which may be localized or distributed. Consequently, the vibration response will produce noise inside the cabin. On the other hand, the passive control based on surface damping treatments by the addition of viscoelastic material can reduce the levels of structural vibration and the noise generated. In this paper results of experimental data and numerical models in finite element method about the vibration response in aeronautical panels are introduced by comparison of the response itself whether considered a viscoelastic material or not.

Application of Cork Compounds in Sandwich Structures for Vibration Damping

The remarkable damping over a broad temperature range and thermal insulation properties of cork make it a suitable material to be applied on integrated and surface damping treatments in sandwich structures, improving its dynamic behavior. Experimental analysis and numerical modeling of sandwich structures with cork compound layers is therefore essential for a better understanding of the cork compound influence on the dynamic properties of a layered structure. In this article, an evaluation study on the dynamic properties of a set of sandwich plates with cork compound cores inside two aluminium faces is performed. For this purpose, three test samples were assembled following the described configuration, using cork compounds with different properties (density, granulometry and thickness). To numerically simulate these layered plates, a partial layerwise plate finite element (FE), with a multilayer configuration, was developed and integrated in a MATLAB FE code. The constitutive relation of the cork compounds is included in the FE model by using the material complex modulus in a direct frequency analysis procedure. For the different cork compounds hereby considered, the extensional complex modulus was previously identified by using a specific experimental methodology which simulates a semidefinite two degrees of freedom system, where the cork compound test sample represents the complex stiffness. From the complex modulus data, both extensional storage modulus and loss factor of the cork compound were obtained. The experimental evaluation of the dynamic properties of the sandwich plates was performed carrying out an experimental modal analysis on each test specimen, being measured a set of frequency response functions (FRFs). Additionally, the developed layerwise plate element was validated through the comparison between the measured driving point FRFs and the FE method predicted ones.

Vibration Analyses of Cylindrical Hybrid Panel with Viscoelastic Layer Based on Layerwise Finite Elements

Based on full layerwise displacement shell theory, the vibration and damping characteristics of cylindrical sandwiched panels with viscoelastic layers are investigated. The transverse shear deformation and the normal strain of the cylindrical hybrid panels are fully taken into account for the structural damping modeling. The layerwise finite element model is formulated by using Hamilton’s virtual work principle and the cylindrical curvature of hybrid panels is exactly modeled. Modal loss factor and frequency response functions are analyzed for various structural parameters of cylindrical sandwich panels. Present results show that the full layerwise finite element method can accurately predict the vibration and damping characteristics of the cylindrical hybrid panels with surface damping treatments and constrained layer damping.

층별변위 유한요소법에 기초한 점탄성층을 갖는 원통형 복합적층 패널의 진동해석

Based on a full layerwise displacement shell theory, the nitration and damping characteristics of cylindrical sandwiched panels with viscoelastic layers are investigated. The transverse shear deformation and the normal strain of the cylindrical hybrid panels are fully taken into account for the structural damping modelling. The present finite element model Is formulated by using Hamilton's virtual work principle and the cylindrical curvature of hybrid panels is exactly modeled. Modal loss factors and frequency response functions are analyzed for various structural parameters of cylindrical sandwich panels. Present results show that the full layerwise finite element method can accurately predict the vibration and damping characteristics of the cylindrical hybrid panels with surface damping treatments and constrained layer damping.

Use of Microcellular Foam Materials in Constrained Layer Damping Treatments

Constrained layer damping (CLD) treatment is a widely used surface damping treatment for vibration and noise control. In this paper, two feasibility studies were conducted using microcellular foam in CLD applications. The first study explores the feasibility of using modified polyethylene teraphthalate (PETG) microcellular foam as a damping material. Two foam configurations were tested: uncompressed (regular) and compressed foam. The second feasibility study evaluated damping performance of CLD with microcellular foam as a standoff layer. Results of the feasibility studies show that the loss factor of PETG foam with densities from 42 kg/m3 to 240 kg/m3 is in the range of 2% to 8%. In addition, there is no significant difference in loss factor between the uncompressed and compressed foams. Also, use of microcellular foam as standoff layer can reduce vibration amplitude up to 80% with only a 2% to 3% weight penalty.

Performance Characteristics of the Magnetic Constrained Layer Damping

A new class of surface damping treatment is proposed to provide effective means for attenuating undesirable structural vibrations. The proposed treatment relies in its operation on the use of smart damping treatments which consist of integrated arrays of constrained visco‐elastic damping layers that are controlled passively by a specially arranged network of permanent magnets. The interaction between the magnets and the visco‐elastic layers aims at enhancing the energy dissipation characteristics of the damping treatments. In this manner, it would be possible to manufacture structures that are light in weight which are also capable of meeting strict constraints on structural vibration when subjected to unavoidable disturbances.Emphasis is placed here on introducing the concept and the basic performance characteristics of this new class of smart Magnetic Constrained Layer Damping (MCLD) treatments. Comparisons are also presented with conventional Passive Constrained Layer Damping (PCLD) in order to determine the merits and limitation of the MCLD treatments.

The influence of damping on waves and vibrations

Summary This paper provides a unified approach for conventional and generalised linear models of viscoelastic constitutive behaviour. Creep, relaxation and hysteresis effects of materials and structures are described consistently. Advantages of the fractional derivative concept are outlined. Mathematical consequences resulting from operator non-locality in time domain and uniqueness questions arising in frequency domain are addressed. The elastic-viscoelastic correspondence principle serves as a tool to obtain as well analytical and numerical BEM and FEM solutions of wave propagation and vibration problems by transform methods. Characteristics of viscoelastic waves and vibrations are discussed. The paper focusses on material damping but includes aspects of radiation damping description by discretisation methods as well. Important aspects of damping description are beyond the scope of selected topics of this survey paper. This is why additional reading is recommended on the following subjects: Thermo-viscoelasticity and non-linear viscoelasticity [3, 4, 21], determination of mechanical properties by experimental methods [2, 4, 38, 43], damping devices and surface damping treatment [31, 38, 43], material damping data [3, 31] and structural damping [45] including the nonlinear dissipation in mechanical joints such as bolted or riveted connections [46–48]. A list which is by far not complete.

MODAL PROPORTIES OF BEAMS AND PLATES ON RESILIENT SUPPORTS WITH ROTATIONAL AND TRANSLATIONAL COMPLEX STIFFNESS

For beam and plate vibrations, energy dissipation may be mostly attributed to internal damping inside the structure and external damping at the supports. Surface damping treatment is one of the most effective tools to control vibrations of beam and plate in general. Sometimes it is not always desirable, however, to apply this damping treatment, for practical reasons. In such cases, one must rely on the damping treatment at the supports. In this presentation, the effects of damped compliant boundary conditions on modal parameters are investigated for two types of continuous systems; an elastic beam and a circular plate. The impedances at the boundaries to translational and rotational motions are given by springs with complex stiffness. The governing equations are solved numerically to obtain the natural frequencies and modal loss factors. Numerical results are represented in dimensionless terms, based on which a procedure of selecting the support parameters is illustrated to obtain desirable modal properties.

Structure-borne noise control for propeller aircraft

A laboratory test apparatus was developed which would allow the study and development of propeller wake/vortex-induced structure-borne interior noise control measures. Various methods of wing structural modification, including blocking masses, surface damping treatments, and tuned mechanical absorbers, were evaluated relative to reduced interior noise levels. Inboard wing fuel was found to act as an effective blocking mass. Wing panel add-on damping treatment in the form of a single, constrained layer was not an effective control measure, except in the area of the propeller wake. However, highly damped, tuned mechanical absorbers were found to be the most efficient structure-borne noise (SBN) control measure.

Acoustic transmission loss of pipes excited by internally propagating plane waves

A control valve constitutes a source of mechanical vibration, nearfield imcompressible pressure fluctuations and radiated acoustic waves. An ideal mechanical vibration filter placed several wavelengths from the source will remove the influence of the first two excitations from the response of the downstream pipe. The internal propagation of acoustic energy, however, is unaffected and so the transmission loss of pipes to these propagating waves is of concern. In the plane-wave region, Morfey, Heckl, and others have measured acoustic radiation far greater than their estimates. This work has been directed towards explaining these differences. Experiments with plane acoustic excitation of steel and P.V.C. pipes were performed. Different gases were used inside the P. V. C. pipe, for which the wall response was forced, to investigate the radiation from subsonic and supersonic axisymmetric wave motion. Close agreement was found, in contrast to the case of steel pipes, where a strong resonant response occurred. This theoretically unpredicted resonant response (which was about 45 dB above the forced estimate) contained all resonant modes but was dominanted by the modes with the highest circumferential mode order. The acoustic radiation, however, was greater than the forced estimate by only 25 dB, since it is determined by the most efficient radiators—the n=1 “bending” modes. Only these latter modes are damped by the pipe supports; the measured Q of these modes was about 100. Similarly these modes are most strongly coupled to the excitation, and consequently the n=1 modes control the radiation. It was found that the application of surface damping treatments caused reductions of 10 to 20 dB in response, but only 2–5 dB in power radiated. This is because surface damping treatments are particularly effective on higher-order circumferential modes and much less effective on the n=1 modes, in which there are no changes in circumferential radius of curvature. It is concluded that a significant reduction in power radiated requires damping procedures directed specifically at the n=1 modes. Experiments in progress suggest that for the pipes studied, a Q less than 20 for n=1 modes is required to achieve the lower bound power radiated corresponding to a forced response.