Showing papers on "Constrained-layer damping published in 2004"

Reduction of squeal noise from disc brake systems using constrained layer damping

Abstract: Squeal noise generation during braking is a complicated dynamic problem which automobile manufacturers have confronted for decades. Customer complaints result in significant yearly warranty costs. More importantly, customer dissatisfaction may result in rejection of certain brands of brake systems. In order to produce quality automobiles that can compete in today's marketplace, the occurrence of disc brake squeal noise must be reduced. The addition of a constrained layer material to brake pads is commonly utilized as a means of introducing additional damping to the brake system. Additional damping is one way to reduce vibration at resonance, and hence, squeal noise. The simulation of braking events in dynamometers has typically been the preferred insulator selection process. However, this method is costly, time consuming and often does not provide an insight into the mechanism of squeal noise generation. This work demonstrates the use of modal analysis techniques to select brake dampers for reducing braking squeal. The proposed methodology reduces significantly the insulator selection time and allows an optimized use of the brake dynamometer to validate selected insulators.

Optimal control of thin circular cylindrical laminated composite shells using active constrained layer damping treatment

Abstract: Active control of the vibration of laminated circular cylindrical composite shells has been demonstrated using optimally placed patches of active constrained layer damping (ACLD) treatment. A finite element model has been derived to formulate the dynamics of the composite shells integrated with the patches of ACLD treatment. Optimal placements of the patches are determined by employing a modal controllability criterion to control the first two modes of vibration. The optimal size of the patches located at the optimal places has been determined on the basis of a frequency constraint. The performance of these patches in enhancing the damping of the symmetric cross-ply and angle-ply laminated shells has been illustrated with frequency response functions of the shells.

Constrained Damping Layer Treatments: Finite Element Modeling

Abstract: In this paper we assess the performance of finite element models in modeling structures with sheer damping treatments. We analyze the finite element modeling of constrained layer damping (CLD) and integrated layer damping (ILD) treatments using viscoelastic materials, devoting special attention to the spatial modeling of the treatment and to the characterization of the viscoelastic material properties. In this work, we used a finite element commercial software (MSC.Nastran) to simulate the dynamic response of aluminum plates with both treatment configurations (CLD and ILD). The spatial modeling of the treatment was devel-oped using three different models, all based on a layered assembly of plate/brick conventional finite elements. The dynamic properties of the viscoelastic material were taken into account in the numerical simulation using the complex modulus approach. The numerical results are correlated with experimental data obtained for four treated specimens by direct comparison of the frequency respo...

Novel epoxy compositions for vibration damping applications

Abstract: Three epoxy compositions have been developed by using polyether amine hardeners having varying chain lengths of polyethers. Unlike normal epoxies, the compositions show low glass transition temperatures (0-45°C). Dynamic mechanical analysis and time-temperature superposition of the isotherms indicate that they have broad and high loss factor values over broad frequency and temperature ranges suggesting their application as viscoelastic materials in constrained layer damping of structural vibrations.

Active control of laminated composite beams using a piezoelectric fiber reinforced composite layer

Abstract: The effectiveness of piezoelectric fiber reinforced composite (PFRC) material in the development of new actuators as elements of smart structures has been theoretically investigated. The piezoelectric fibers considered in this study are longitudinally oriented to yield the bending mode of actuation. Micromechanics is used to predict the effective mechanical properties and the effective electromechanical constant of such composites which gives rise to actuation in the fiber direction when subjected to an electric field transverse to the fiber direction. These effective properties are useful for the analysis of smart beams. A micromechanics study reveals that beyond a critical fiber volume fraction, this electromechanical constant is improved over that of the piezoelectric material alone. The performance of this new material used as distributed actuators has been investigated through active constrained layer damping (ACLD) of laminated composite beams in which the constraining layer is made of piezoelectric fiber reinforced composite. A finite element model has been developed to describe the dynamic behavior of a laminated composite beam coupled with active constrained layer damping (ACLD) treatment. The controlled response is illustrated through plots of frequency response functions. The results indicate that these new piezoelectric composites may be superior candidate materials for use in developing lightweight smart structures, as compared with the existing piezoelectric materials alone.

Robust control of plate vibration via active constrained layer damping

Abstract: In this paper, the theoretical modeling of a plate partially treated with active constrained layer damping (ACLD) treatments and its vibration control in an H ∞ approach is discussed. Vibration of the flat plate is controlled with patches of ACLD treatments, each consisting of a viscoelastic damping layer which is sandwiched between the piezo-electric constrained layer and the host plate. The piezo-electric constrained layer acts as an actuator to actively control the shear deformation of the viscoelastic damping layer according to the vibration response of the plate excited by external disturbances. In the first part of this paper, the Mindlin–Reissner plate theory is adopted to express the shear deformation characteristics of the viscoelastic damping layer, meanwhile GHM (Golla–Hughes–McTavish) model of viscoelastic damping material and FEM (finite element model) are incorporated to describe the dynamics of the plate partially treated with ACLD treatment. In the second part, particular emphasis is placed on the vibration control of the first four modes of the treated plate using H ∞ robust control method. For this purpose, an H ∞ robust controller is designed to accommodate uncertainties of the ACLD parameters, particularly those of the viscoelastic damping core which arise from the variation of the operation temperature and frequency. Disturbances and measurement noise are rejected in the closed loop by H ∞ robust controller. In the experimental validation, external disturbances of different types are employed to excite the treated plate. The results of the experimental clearly demonstrate that the proposed modeling method is correct and the ACLD treatments are very effective in fast damping out the structural vibration as compared to the conventional passive constrained layer damping (PCLD).

Lagrangian Formulation of Rotating Beam With Active Constrained Layer Damping in Time Domain Analysis

Abstract: In this paper, Lagrangian formulation of a horizontal rotating beam with active constrained layer damping (ACLD) treatment is presented. The problem is approached by the Rayleigh-Ritz method. By assuming modal functions as the displacement shape functions and using effective damping model of the visco-elastic material (VEM) layer, the number of degrees of freedom of the system is greatly reduced. The damping of the visco-elastic material is characterized by a shear (storage) modulus and a loss factor. Also the dynamic behavior of the rotating ACLD beam is analyzed in the time domain. The effects of control gains, shear modulus and loss factor of the VEM on the dynamic response are also investigated.

Plasma deposition of constrained layer damping coatings

Abstract: Plasma techniques are used to generate constrained layer damping (CLD) coatings on metallic substrates. The process involves the deposition of relatively thick, hard ceramic layers on to soft polymeric damping materials while maintaining the integrity of both layers. Reactive plasma sputter-deposition from an aluminium alloy target is used to deposit alumina layers, with Young's modulus in the range 77-220 GPa and thickness up to 335mm, on top of a silicone film. This methodology is also used to deposit a 40mm alumina layer on a conventional viscoelastic damping film to produce an integral damping coating. Plasma CLD systems are shown to give at least 50 per cent more damping than equivalent metal-foil-based treatments. Numerical methods for rapid prediction of the performance of such coatings are discussed and validated by comparison with experimental results.

Vibration control of an arc type shell using active constrained layer damping

Abstract: Active constrained layer damping (ACLD) combines the simplicity and reliability of passive damping with the low weight and high efficiency of active control to attain high damping characteristics. A cantilevered shell type arc that is made of carbon/epoxy composite material is chosen to investigate the potential of ACLD effectiveness. Using a system identification method, the arc/ACLD system is modelled as an ARMAX (autoregressive moving average exogenous) model and converted into a state space form to design optimal control laws. A linear quadratic regulator (LQR) controller is used to find optimal control gains. The performance of the ACLD system is determined and compared with passive constrained layer damping (PCLD) in order to demonstrate the effectiveness of the ACLD treatment.

Hard ceramic coatings: an experimental study on a novel damping treatment

Abstract: This paper describes a novel damping treatment, namely hard ceramic coatings. These materials can be applied on almost any surface (internal or external) of a component. Their effect is the significant reduction of vibration levels and hence the extension of life expectancy of the component. The damping features of air-plasma-sprayed ceramic coatings (for example amplitude dependence, influence of initial amplitude) are discussed and the experimental procedure employed for testing and characterising such materials is also described. This test procedure is based around a custom-developed rig that allows one to measure the damping (internal friction) of specimens at controlled frequencies, strain amplitudes and, if required, various temperatures. A commonly used Thermal Barrier Coating, Yttria Stabilised Zirconia (8%), is used to demonstrate the above mentioned features. The damping effectiveness of this coating is then compared against two established damping treatments: polymer Free Layer Damping (FLD) and Constrained Layer Damping (CLD). The paper discusses the major issues in characterising ceramic damping coatings and their damping effectiveness when compared against the "traditional" approaches. Finally, the paper concludes with suggestions for further research.

Multi-objective optimization of an active constrained layer damping treatment for shape control of flexible beams

Abstract: This work presents the use of a multi-objective genetic algorithm (MOGA) to solve an integrated optimization problem for the shape control of flexible beams with an active constrained layer damping (ACLD) treatment. The design objectives are to minimize the total weight of the system, the input voltages and the steady-state error between the achieved and desired shapes. Design variables include the thickness of the constraining and viscoelastic layers, the arrangement of the ACLD patches, as well as the control gains. In order to set up an evaluator for the MOGA, the finite element method (FEM), in conjunction with the Golla–Hughes–McTavish (GHM) method, is employed to model a clamped-free beam with ACLD patches to predict the dynamic behaviour of the system. As a result of the optimization, reasonable Pareto solutions are successfully obtained. It is shown that ACLD treatment is suitable for shape control of flexible structures and that the MOGA is applicable to the present integrated optimization problem.

Analytical formulation and finite element modelling of beams with arbitrary active constrained layer damping treatments

Abstract: This paper concerns arbitrary active constrained layer damping (ACLD) treatments applied to beams. In order to suppress vibration, hybrid active-passive treatments composed of piezoelectric and viscoelastic layers are mounted on the substrate beam structure. These treatments combine the high capacity of passive viscoelastic materials to dissipate vibrational energy at high frequencies with the active capacity of piezoelectric materials at low frequencies. The aim of this research is the development of a generic analytical formulation that can describe these hybrid couplings in an accurate and consistent way. The analytical formulation considers a partial layerwise theory, with an arbitrary number of layers, both viscoelastic and piezoelectric, attached to both surfaces of the beam. A fully coupled electro-mechanical theory for modelling the piezoelectric layers is considered. The equations of motion, electric charge equilibrium and boundary conditions are presented. A one-dimensional finite element (FE) model is developed, with the nodal degrees of freedom being the axial and transverse displacements and the rotation of the centreline of the host beam, the rotations of the individual layers and the electric potentials of each piezoelectric layer. The damping behavior of the viscoelastic layers is modeled by the complex modulus approach. Three frequency response functions were measured experimentally and evaluated numerically: acceleration per unit force, acceleration per unit voltage into the piezoelectric actuator and induced voltage per unit force. The numerical results are presented and compared with experimental results to validate the FE model.

Effect of Delamination on Active Constrained Layer Damping of Smart Laminated Composite Beams

Abstract: An ove lw ork demonstrates the effect of delamination in smart laminated composite beams on the performance of active constrained layer damping (ACLD) treatment. A finite element model has been derived to formulate the dynamics of the composite beams integrated with a patch of ACLD treatment and a patch of piezoelectric film acting as a distributed sensor with and without the presence of delamination at different locations. Frequency response functions of the beams have been examined to observe the effect of delamination on the performance of ACLD treatment. It has been observed that the ACLD treatment improves the active damping characteristics of the beams, even in the presence of delamination, and that the responses of the beams are sensitive to the variation of the location of delamination. The responses due to active constrained layer damping presented may provide a useful guide to detect the presence of delamination in smart composite beams by the use of the existing numerical techniques.

Piezoelectric active control for workpiece chatter reduction during milling

Abstract: Regenerative chatter is a form of unstable, self-excited vibration that occurs in machining operations such as milling and turning. In high speed milling of many aircraft components, regenerative chatter is the fundamental factor that limits metal removal rate and consequently productivity. Regenerative chatter is essentially a feedback process: the cutting chip thickness produces a force between the tool and workpiece, and the dynamics of these components results in a change in the cutting chip thickness. An exciting method of avoiding chatter is to actively control the workpiece or tool during cutting. On thin walled workpieces, such as those for aerospace structural components, this can be achieved using piezoelectric devices. A wide range of control regimes could be applicable, such as feed-forward actuation, active constrained layer damping, or active damping, using either non-collocated or collocated sensors and actuators. This study focuses on active damping with collocated sensors and actuators. In this article, an experimental study is described whereby workpiece chatter during milling is reduced by using active vibration control with piezoelectric sensors and actuators.

Constrained layer damping assembly

Abstract: A constrained layer damping assembly for a rigid base member having a substantially planar surface comprises a gas impervious damping layer disposed on the substantially planar surface of the base member, and a load element disposed on the damping layer. The damping layer defines at least one void region extending between the planar surface and the load element, and the load element defines at least one channel for coupling a low pressure to the void region relative to the pressure external to the constrained layer damping assembly to establish a pressure differential between the inside of the void region and the outside of the constrained layer damping assembly. The pressure differential keeps the damping layer under compression and secures the load element and the damping layer onto the base member.

Design and fabrication of optimal constrained layer damping topologies

Abstract: Of the many methods available for achieving effective vibration damping, adding viscoelastic lamina constrained by a stiff elastic materials is an inexpensive, space efficient means for achieving significant damping levels. Recently, the desire to apportion this material in a way that will take the greatest advantage of its dissipative characteristics has led to studies in optimization 1-7 . The aim of this research is to determine the optimal shape of a constrained viscoelastic layer on an elastic beam used for vibration damping by means of topology optimization and to experimentally verify these results. The optimization objective is to maximize the system loss factor for the first resonance frequency of the base beam. All previous optimal design studies on viscoelastic lamina have been size or shape optimization studies assuming a certain topology for the damping treatment (with the exception of Lumsdaine 8 and Lumsdaine and Pai 9 , of which this work is an extension). In this study, this assumption is relaxed, allowing an optimal topology to emerge. The loss factor is computed using the Modified Modal Strain Energy Method 10 in the optimization process. It is observed that a novel topology emerges from the optimized result. From this computational result, a topology is interpreted that can be reasonably manufactured, and this topology is custom fabricated to experimentally validate the computational result. The experimental results show that significant improvement in damping performance, over 300%, is obtained by optimizing the constrained damping layer topology.

Newtonian and Variational Formulations of the Dynamics of Plates with Active Constrained Layer Damping Treatments

Abstract: In this paper we present Newtonian and variational formulations of the dynamics of plates treated fully with active constrained layer damping (ACLD). The governing equations of the plate/ACLD system are derived to describe the interaction between the dynamics of the plates, the viscoelastic damping layer and the active piezoelectric constraining layers. The developed equations of the plate/ACLD system provide analytical models for predicting the dynamics of laminated plates subjected to passive and active vibration damping controls. Numerical solutions of the analytical models are presented for simply-supported plates in order to study the performance of the plate/ACLD system for different control strategies. The developed models present invaluable means for designing and predicting the performance of the smart laminated plates that can be used in many critical engineering applications.

Multi-disciplinary optimization of railway wheels

Abstract: A numerical procedure for multi-disciplinary optimization of railway wheels, based on Design of Experiments (DOE) methodology and automated design, is presented. The target is a wheel design that meets the requirements for fatigue strength, while minimizing the unsprung mass and rolling noise. A 3-level full factorial (3LFF) DOE is used to collect data points required to set up Response Surface Models (RSM) relating design and response variables in the design space. Computationally efficient simulations are thereafter performed using the RSM to identify the solution that best fits the design target. A demonstration example, including four geometric design variables in a parametric finite element (FE) model, is presented. The design variables are wheel radius, web thickness, lateral offset between rim and hub, and radii at the transitions rim/web and hub/web, but more variables (including material properties) can be added if needed. To improve further the performance of the wheel design, a constrained layer damping (CLD) treatment is applied on the web. For a given load case, compared to a reference wheel design without CLD, a combination of wheel shape and damping optimization leads to the conclusion that a reduction in the wheel component of A-weighted rolling noise of 11 dB can be achieved if a simultaneous increase in wheel mass of 14 kg is accepted.