Viscoelastic Damping Treatment Research Articles

Simulation on dynamic passive control of structures using corrugated viscoelastic damping treatments

Passive damping treatments using viscoelastic materials (VEMs) are widely applied as addon solutions to control the dynamic response of light structures. These surface treatments are simple, reliable, and can be optimized by using proper design rules and simulation tools. In this work, a new treatment configuration is proposed, simulated, and assessed, being compared with the most effective configuration currently used. The novelty resides in the VEM layer’s geometry, which in the proposed configuration assumes a waved shape. This waved shape is imposed to the viscoelastic layer due to indentations created in the inner faces of the host structure and the constraining layer. The results demonstrate that the wavy configuration, designated as corrugated viscoelastic layer (CVL), outperforms the typical damping treatments for relatively thick host structures and when using thick VEM layers. In addition, this new configuration reduces the stiffness decoupling effect due to the soft VEM layer, restoring the flexural stiffness of the original undamped structure.

Influence of the Poisson's ratio on the efficiency of viscoelastic damping treatments

An efficient way of mitigating noise and vibration is to embed viscoelastic patches into the host structure. Viscoelastic properties are of significant importance in determining the performance of the passive damping treatment. The behaviour of homogeneous isotropic materials is described by two elastic constants (generally the Young modulus and the Poisson ratio, or the shear and bulk moduli), which are frequency- and temperature-dependent in the case of viscoelastic materials. In practice, the Poisson's ratio is often considered as independent of temperature and frequency. One goal of this work is to numerically evaluate the validity of this assumption and its limitations (frequency range, thickness of the viscoelastic layer). To this end, a thermo-mechanical characterization of a viscoelastic material is carried out by dynamic measurements of the complex shear and bulk moduli, allowing the indirect measurement of the frequency- and temperature-dependent Poisson's ratio. Moreover, the measurements of the Poisson's ratio (direct or indirect) can lead to considerable uncertainties. For instance, large discrepancies have been observed when characterizing the Poisson's ratio of polymer foams. Another goal of this work is to investigate the influence of those uncertainties on the dynamic response of a damped structure.

Impact of viscoelastic damping properties on vibration response of scale models

There are many industries that utilized scale models to test the behavior of systems before building full-size structures, such as aircraft, spacecraft, and marine vehicle design. While vibration and acoustic response may not be the only quantities of interest when testing scale models, scale models can be utilized to predict full-scale acoustic behavior. When damping treatments are to be applied to full-scale systems, there will also be a need to apply these treatments to the scale models. Typically, these damping treatments use viscoelastic materials due to their high loss factor. However, since the stiffness and loss factor of viscoelastic materials change significantly with frequency, viscoelastic damping treatments will not behave consistently between model- and full-scale. This work shows the impact of using the same viscoelastic damping treatment on scale models as designed for full-scale systems. As a test case, a model of a thin vibrating plate will have a constrained layer damper applied on one surface. The total surface velocity response of a full-scale and model-scale finite element plate with a viscoelastic constrained layer damper is compared. Methods of designing viscoelastic materials for scale-models will also be presented. There are many industries that utilized scale models to test the behavior of systems before building full-size structures, such as aircraft, spacecraft, and marine vehicle design. While vibration and acoustic response may not be the only quantities of interest when testing scale models, scale models can be utilized to predict full-scale acoustic behavior. When damping treatments are to be applied to full-scale systems, there will also be a need to apply these treatments to the scale models. Typically, these damping treatments use viscoelastic materials due to their high loss factor. However, since the stiffness and loss factor of viscoelastic materials change significantly with frequency, viscoelastic damping treatments will not behave consistently between model- and full-scale. This work shows the impact of using the same viscoelastic damping treatment on scale models as designed for full-scale systems. As a test case, a model of a thin vibrating plate will have a constrained layer damper applied on one...

Topology optimization of frequency dependent viscoelastic structures via a level-set method

Viscoelastic materials follow a liquid-like elastic behavior whose characteristics depend on the excitation frequency. Nowadays, this type of materials represent a high opportunity for vibration damping treatments in the automotive and aeronautic industries, for instance. This work is devoted to the application of the level-set method for topology optimization of viscoelastic structures. We look for the best distribution of viscoelastic material within a reference domain for the design of purely viscoelastic 3D damping structures and 2D viscoelastic damping treatments. In both cases one desires to maximize the structure capacity to dissipate energy measured here by the modal loss factor of the first vibration mode.

A sustainable approach of damping treatment for aluminium honeycomb sandwich structures

The damping plays a vital role in structural dynamic and acoustic performance of aluminium honeycomb sandwich structures. The viscoelastic damping treatment of skins is most common. An alternative, the use of sustainable cork inserts to improve the damping of cores and the whole assembly is investigated in this study. Structures with different filling degrees are analysed, as well as the optimum location for inserts is determined. The structural dynamic as well as the vibro-acoustic performance is estimated numerically. Average squared displacement amplitude reduction efficiency [Formula: see text] is defined as the target parameter for structural dynamic performance, whereas average transmission loss effectiveness [Formula: see text] is designed for vibro-acoustic performance. The structural dynamic models are validated by experimental vibration analysis, whereas the vibro-acoustic models are validated against published data. Different ways of bonding the inserts to the host structure are analysed in order to maximise damping. The highest improvement is obtained with a filling degree of 64% honeycomb voids and 9.76% increase in mass, for which an average squared displacement amplitude reduction of 35.25% and an average increase in transmission loss of 1.5 dB is achieved. The transmission loss increase in relation to the added mass is much higher than that achieved by doubling of mass in the mass law region. The introduction of cork inserts spreads the energy in local modes to a larger space, effectively decreasing the resonance amplitudes. Interestingly, damping does not increase with the number of inserts in a monotonic way and the improvement depends on the spatial distribution of inserts.

Complex-valued Modal Loss Factor Maximization for an Unconstrained Damping Layout with Topology Optimization

An unconstrained viscoelastic damping treatment is an effective way to control vibration in structures. With a fully-covered damping treatment, the mass of structure is heavy and the damping effect is not significantly increasing. Thus, a well-distributed partial damping treatment is an effective method in terms of a less weight with high damping effects. To determine the placement of damping material, topology optimization technique is used. The objective function is the modal loss factor at a specific mode and the constraint is a fixed mass of viscoelastic damping material. In order to accurately estimate the modal loss factor, complex-valued eigenvalues are considered. The modal strain energy method has been found to over-predict the modal loss factors where the dissipative elements have a high material loss factor. This research shows that significant beneficial damping effects can be achieved by using topology optimization with high accuracy of modal loss factors.

Wavenumber transform analysis for acoustic black hole design.

Acoustic black holes (ABHs) are effective, passive, lightweight vibration absorbers that have been developed and shown to effectively reduce the structural vibration and radiated sound of beam and plate structures. ABHs employ a local thickness change that reduces the speed of bending waves and increases the transverse vibration amplitude. The vibrational energy can then be effectively focused and dissipated by material losses or through conventional viscoelastic damping treatments. In this work, the measured vibratory response of embedded ABH plates was transformed into the wavenumber domain in order to investigate the use of wavenumber analysis for characterizing, designing, and optimizing practical ABH systems. The results showed that wavenumber transform analysis can be used to simultaneously visualize multiple aspects of ABH performance including changes in bending wave speed, transverse vibration amplitude, and energy dissipation. The analysis was also used to investigate the structural acoustic coupling of the ABH system and determine the radiation efficiency of the embedded ABH plates compared to a uniform plate. The results demonstrated that the ABH effect results in acoustic decoupling as well as vibration reduction. The wavenumber transform based methods and results will be useful for implementing ABHs into real world structures.

Flutter suppression of plates subjected to supersonic flow using passive constrained viscoelastic layers and Golla–Hughes–McTavish method

The present study involves the application of surface viscoelastic damping treatments to remedy panel flutter problems in existing aircraft components in which active control strategies cannot be easily performed. The rationale for such study is the fact that as the viscoelastic materials are often used to solve a variety of resonant noise and vibration problems in aerospace industry, it becomes important to quantify the increase of aeroelastic stability that can be obtained by the inclusion of viscoelastic treatments. The flutter boundaries of the aeroviscoelastic system accounting for the frequency- and temperature-dependent behavior of the viscoelastic material are computed by adopting the so-named Golla–Hughes–McTavish model. Since the inclusion of internal variables in the viscoelastic model leads to an augmented coupled system of equations of motion, a numerical pre-processing is found to be necessary prior to the resolution of the complex eigenvalue problem for the purposes of flutter analysis. After the theoretical foundations, the stability analysis of a three-layer sandwich plate under supersonic flow is addressed. The results show that it is possible to increase the critical flutter speeds of flat panels using surface viscoelastic damping treatments. However, the temperature and the thicknesses of the layers have significant effect on the flutter boundary.

Optimum design of grain sieve losses monitoring sensor utilizing partial constrained viscoelastic layer damping (PCLD) treatment

Grain sieve losses has been an important dominant factor for automatic adjustment of the major working parameters of combine harvesters such as cylinder speed, concave clearance, fan speed and vehicle forward speed. To monitor grain sieve losses real-timely in the working processing of combine harvester, a grain sieve losses monitoring sensor, which utilizing YT-5 type piezoelectric ceramic as sensing material developed. To accelerate grain sieve losses monitoring sensor's detecting speed, theoretical analysis was performed from view of structural vibration and a partial constrained viscoelastic layer damping (PCLD) treatment was carried out on the surface of the grain sieve losses monitoring sensor. On the basis of analyzing the mechanical relationships among each layer of the sandwich in depth, an optimal position to past the viscoelastic layer was found. Grain collision experiment results found that grain collision signal attenuate time was shortened to about 2–3ms after treated with PCLD in places with relative larger modal deformation, namely, the developed sensor could identify more than 300–500 grains within 1s in theory, which verified that the sensor's detecting speed was significantly improved. To test the performance of the developed sensor, calibration experiments carried out in the laboratory, and analysed the influence of moisture content (MC), sensor mounts height and angle on measurement accuracy. At last, installed grain sieve losses monitoring sensor on a combine harvester field experiments took place; experimental results showed that the largest measurement relative error was 4.48% when harvesting rice.

Vibration and Damping Analysis of Composite Fiber Reinforced Wind Blade with Viscoelastic Damping Control

Composite materials are increasingly used in wind blade because of their superior mechanical properties such as high strength-to-weight and stiffness-to-weight ratio. This paper presents vibration and damping analysis of fiberreinforced composite wind turbine blade with viscoelastic damping treatment. The finite element method based on full layerwise displacement theory was employed to analyze the damping, natural frequency, and modal loss factor of composite shell structure. The lamination angle was considered in mathematical modeling. The curved geometry, transverse shear, and normal strains were exactly considered in present layerwise shell model, which can depict the zig-zag in-plane and out-of-plane displacements. The frequency response functions of curved composite shell structure and wind blade were calculated. The results show that the damping ratio of viscoelastic layer is found to be very sensitive to determination of magnitude of composite structures. The frequency response functions with variety of thickness of damping layer were investigated. Moreover, the natural frequency, modal loss factor, and mode shapes of composite fiber reinforced wind blade with viscoelastic damping control were calculated.

A novel viscoelastic damping treatment for honeycomb sandwich structures

Constrained layer dampers (CLD) are in widespread use for passive vibration damping, in applications including aerospace structures which are often lightweight. The location and dimensions of CLD devices on structures has been the target of several optimisation studies using a variety of techniques such as genetic algorithms, cellular automata, and gradient techniques. The recently developed double shear lap-joint (DSLJ) damper is an alternative method for vibration damping, and can be placed internally within structures. The performance of the DSLJ damper is compared in a parametric study with that of CLD dampers on beam and plate structures under both cantilever and simply supported boundary conditions, using finite element analysis. The objective was to determine which damper and in which configuration produced the highest modal loss factor and amplitude reduction for least added mass, as would be important for lightweight applications. The DSLJ tend to be more mass efficient in terms of loss factor and amplitude reduction for cantilevered beam and plate structure, and are competitive with CLD dampers in simply supported beam and plate structures. The DSLJ works well because it has the potential to magnify global flexural deformation into shear deformation in the viscoelastic more effectively than traditional CLD dampers.

Vibration and Damping Analysis of Carbon Fiber Wind Turbine Blade with Viscoelastic Damping Treatment

The paper have described the vibration and damping analysis of carbon fiber wind turbine blade with viscoelastic damping treatment using commercial ANSYS program. The wind turbine system including a carbon fiber layer and a viscoelastic damping layer was attached on inside of carbon layer. Firstly, the natural frequencies and mode shape of pure carbon fiber turbine blade were compared with viscoelastic damping treated turbine blade using modal analysis. There were 1mm, 2mm, 3mm thickness damping layer finite element model to be constructed. The results show the little changes in lower first mode but getting smaller with higher modes. Finally, the frequency response functions of damped and undamped turbine blade were calculated for investigating the damping effect of viscoelastic damping layer. As shown in the results, the viscoelastic damping layer has good damping effect for vibration control of carbon fiber wind turbine blade.

Experimental approach in studying temperature effects on composite material structures realized with viscoelastic damping treatments

This paper presents a study aimed at evaluating how viscoelastic materials embedded in composite plates affect structural damping during the flight of a civil aircraft. The vibro-acoustic responses of composite fuselage structures realized with embedded viscoelastic damping treatments have been experimentally characterized at different temperature conditions. The real influence of viscoelastic materials on composite structures has been investigated, focusing the investigations on aspects still unknown, related mostly to temperature effects. In order to simulate the temperature level of commercial transport aircraft in cruise flight conditions, tests were performed using a climatic room where temperature and humidity were controlled. Vibrational tests were performed on two composite fuselage skin coupons: one treated with embedded viscoelastic damping treatments and the other one untreated. The tests were performed at temperatures of for the untreated composite fuselage structure, and and for the treated composite fuselage structure. The damping values were carried out by the impulse response decay method and the loss factor was obtained as an average of many repeated acquisitions. In order to maximize the damping effect, the best temperature interval for the treated composite fuselage skin coupon was evaluated, and the behavior for both composite fuselage structures (treated and untreated) was characterized. Thanks to the high number of tests, a statistical analysis was performed in order to validate the approach used.

Vibration Analysis of Cylindrical Sandwich Aluminum Shell with Viscoelastic Damping Treatment

This paper has applied the constrained viscoelastic layer damping treatments to a cylindrical aluminum shell using layerwise displacement theory. The transverse shear, the normal strains, and the curved geometry are exactly taken into account in the present layerwise shell model, which can depict the zig-zag in-plane and out-of-plane displacements. The damped natural frequencies, modal loss factors, and frequency response functions of cylindrical viscoelastic aluminum shells are compared with those of the base thick aluminum panel without a viscoelastic layer. The thickness and damping ratio of the viscoelastic damping layer, the curvature of proposed cylindrical aluminum structure, and placement of damping layer of the aluminum panel were investigated using frequency response function. The presented results show that the sandwiched viscoelastic damping layer can effectively suppress vibration of cylindrical aluminum structure.

Dimensionless analysis of constrained damping treatments

One of the most effective ways of controlling vibrations in plate or beam structures is by means of constrained viscoelastic damping treatments. Contrary to the unconstrained configuration, the design of constrained and integrated layer damping treatments is multifaceted because the thickness of the viscoelastic layer acts distinctly on the two main counterparts of the strain energy – the volume of viscoelastic material and the shear strain field. In this work, a parametric study is performed exploring the effect that the design parameters, namely the thickness/length ratio, constraining layer thickness, material modulus, natural mode and boundary conditions have on these two counterparts and subsequently, on the treatment efficiency. This paper presents five parametric studies, namely, the thickness/length ratio, the constraining layer thickness, material properties, natural mode and boundary conditions. The results obtained evidence an interesting effect when dealing with very thin viscoelastic layers that contradicts the standard treatment efficiency vs. layer thickness relation; hence, the potential optimisation of constrained and integrated viscoelastic treatments through the use of properly designed thin multilayer configurations is justified. This work presents a dimensionless analysis and provides useful general guidelines for the efficient design of constrained and integrated damping treatments based on single or multi-layer configurations.

Vibration Analysis of a Multiple-Layered Viscoelastic Structure Using the Biot Damping Model

The viscoelastic damping treatment is a very popular method for attenuating vibration and noise problems. It provides the designer much flexibility in adjusting the system damping to eliminate resonances in the structures. A survey of the previous research on material damping models found inadequacies in developing the numerical models of multiple-layer constrained layers and the introduction of the combination of different viscoelastic damping materials through advanced frequency domain damping models. In this paper, a detailed numerical analysis and design of a multiple-layer constrained damping structure using the Biot damping model are presented to investigate the vibration performance. The nonlinear curve fitting of the complex shear modulus and the transient response solution of the numerical viscoelastic damping structure are also discussed. By the proposed approach, the simple beam problem that is presented can be easily extended to the industrial problem with arbitrary geometries and boundary conditions. The validation of this numerical approach is proven by comparison with the previous closed-form results.

Thermal post-buckled behaviors of cylindrical composite shells with viscoelastic damping treatments

The finite element method for the vibration and damping analyses of the thermal post-buckled cylindrical composite shells with damping treatments was developed adopting the layerwise displacement field theory. The arc-length method was used to trace the nonlinear post-buckling behavior of the composite shell induced by the thermal load, and the complex modulus was adopted to consider the effects of the structural damping. The verification of the present results was performed in comparison with previous results, and the dynamic characteristics of several composite shells with damping treatments were investigated. The results show that the viscoelastic damping treatments could significantly affect the thermal post-buckling behaviors and the dynamic characteristics of the composite shells.

Effects of partial constrained viscoelastic layer damping parameters on the initial transient response of impacted cantilever beams: Experimental and numerical results

The effects of partial constrained viscoelastic layer damping on the first milliseconds of the transient vibration of an impacted beam is studied using an analytical model. The viscoelastic properties of the core are frequency dependent and the shear modulus is modelled using a Prony Series. The equations of motion of the system are obtained using Lagrange's equations. The equations of motion are converted in the frequency domain using a Fourier Transform and they are solved for frequency displacements using the assumed modes method. They are then converted back in the time domain using an inverse Fourier Transform. The technique is validated for transient responses using experimental impact force signals. The numerical results are in good agreement with experimental data. Four partial constrained viscoelastic layer damping parameters are studied: the length, the placement, the viscoelastic layer thickness and the constraining layer thickness. It turns out that the length of the partial constrained viscoelastic layer damping has the most important effect on the initial transient displacement while the viscoelastic layer thickness has little effect. Noncausal effects in the model are discussed and are mainly induced when the partial constrained viscoelastic layer damping treatment is poorly effective.

PARTIAL CONSTRAINED VISCOELASTIC DAMPING TREATMENT OF STRUCTURES: A MODAL STRAIN ENERGY APPROACH

The constrained viscoelastic layer damping treatment is an effective means for the passive vibration control of plate and beam-kind structures. In order to reduce the treatment cost, while minimizing structural modifications, particularly the increase in mass, constrained viscoelastic treatments can be successfully applied in a partial and localized manner. The effectiveness of these treatments depends on their extension and relative location with respect to the target mode shape, which is not usually expeditiously established. In order to minimize the cost of the numerical optimization of the partial treatments, an efficient numerical methodology based on the ratio between the modal strain energy of the treated area and that of the structure is hereby proposed. This method is used in the analysis of the location and extension effects of partial constrained viscoelastic treatments on the modal damping of thin plates. The numerical results are verified through an experimental study on specimens with partial constrained viscoelastic layer damping treatments.

Aeroelastic characteristics of cylindrical hybrid composite panels with viscoelastic damping treatments

Supersonic flutter analysis of cylindrical composite panels with structural damping treatments has been performed using the finite element method based on the zig-zag layerwise shell theory. The natural frequencies and loss factors of cylindrical viscoelastic composites are computed considering the effects of transverse shear deformation. And Kumhaar's modified piston theory is applied for the calculation of aerodynamic forces. The flutter of cylindrical composite panels is analyzed considering structural damping effect. With respect to aeroelastic stabilities, various damping characteristics of unconstrained layer, constrained layer, and symmetrically co-cured sandwich laminates are compared with those of an original base panel.