Constrained Layer Damping Structure Research Articles

Preparation and properties of silica fume@polyure-thane urea cement composites

In this study, a new material was synthesized by compounding silica fume and polyurethane urea, which is used to evaculate the vibration reduction performance of concrete. The mechanical and damping properties of silica fume@ polyurethane urea (SF@PUU) reinforced cement paste were investigated. Also, FT-IR, XRD, TG analysis, and SEM are included. The results indicated that SF@PUU leads to the production of high damping ratio cement pastes. The damping capacities of SF@PUU cement composites, where the damping mechanism included internal, external, and multiphase friction within the cement matrix. Additionally, SF@PUU created a constrained-layer damping structure in cement paste to improve the damping properties. The review confirmed that SF@PUU subjected to proper treatments can be as the replacement to cement in concrete or as a damping filler. However, more investigation is required into the dimensional stability and durability of SF@PUU-based concrete.

Finite element dynamic modeling and vibration reduction analysis of the double-lap bolted thin plate with partially attached constrained layer damping

The double-lap bolted thin plate is widely used, but it is easy to produce vibration. In this paper, the method of attaching H-shaped constrained layer damping (CLD) is adopted to reduce vibration, and the finite element dynamic model of the double-lap bolted thin plate with H-shaped CLD is investigated. The innovations of the modeling method are described as follows. A composite element with four nodes and 28 degrees of freedom (DOFs) is produced by taking into account the interlaminar shear deformation of the CLD structure and employing complex modulus to quantify the damping characteristics of the viscoelastic layer. A series of transition elements are constructed to conduct the assembly of elements with inconsistent dimensions. Complex stiffness spring components and mass elements are presented to simulate the stiffness, damping, and mass characteristics of the double-lap bolt joint based on the crock-shaped stress distribution in the double-lap bolt joint and taking the bolt effect region into account. Finally, a case study is carried out, and the rationality of the finite element model of the bolted structure in solving the natural characteristics and vibration response parameters is verified by the established experimental tests. At the same time, the test and modeling results show that the H-shaped CLD reduces vibration on the double-lap bolted thin plate. Furthermore, based on the established finite element model, the influence of the attaching position of the H-shaped CLD, thicknesses of the viscoelastic layer, and the constraining layer on the vibration characteristics of the bolted structure are analyzed.

Comparative theoretical and experimental analysis of vibration damping performance in multilayer constrained layer damping structures: Aluminium versus glass fiber reinforced polymer

This study investigates the dynamic behavior of multilayer Constrained Layer Damping (CLD) structures, specifically focusing on constraining layers made of aluminum and Glass Fiber Reinforced Polymer (GRP). Numerical simulations are compared with experimental results using the finite element method (FEM) and the widely used Ross–Kerwin–Ungar (RKU) model to achieve this. Experimental modal analysis is conducted on a vibration shaker to validate the FEA findings. The research reveals valuable insights into the damping performance of aluminum and GRP as constraining layers. Notably, aluminum demonstrates superior damping properties, particularly in the higher frequency range (ultimate loss factor 0.2), while GRP exhibits better-damping characteristics in the lower frequency range (ultimate loss factor 0.13). These results underscore the significance of considering the frequency-dependent behavior of materials when selecting appropriate constraining layers. By shedding light on the dynamic behavior and damping performance of multilayer CLD structures with different constraining layers, this study contributes to the effective mitigation of vibrations in various engineering applications. This endeavor will enhance the understanding and application of constraining layer materials for effective structural vibration control, paving the way for improved engineering solutions.

Viscoelastic damping design – A novel approach for shape optimization of Constrained Layer Damping treatments at different ambient temperatures

Passive damping plays an important role in the vibration mitigation of aeronautic structures. In contrast to active systems, passive damping systems do not require any energy supply. Thus, their readiness is independent, which reduces the failure probability compared to active systems. Constrained Layer Damping (CLD) has become an established treatment for damping bending vibrations. Unlike other passive systems such as shock-mounts, CLD can be compactly integrated into an existing structure as an add-on solution. However, the design scope is limited by mass constraints and the optimal design for maximum damping must be found by optimization. For this purpose, a novel optimization approach is presented. The layer widths of the core and face layers of a CLD structure are treated as design parameters. Compared to the strategy of placing CLD patches on vibration antinodes, the proposed approach provides up to 52 % higher damping. The optimal design of a generic beam structure is determined considering different modes, viscoelastic material stiffnesses and ambient temperatures. Furthermore, the simulated damping is experimentally verified for a shape-optimized beam. The analyses show that the optimal design depends significantly on the viscoelastic material stiffness and is therefore temperature dependent. As a consequence, a generalized design guideline for CLD treatments cannot be derived.

Analysis and Optimization of Damping Properties of Constrained Layer Damping Structures with Multilayers

Constrained layer damping (CLD) structures, which are one of the composite structures with a softer viscoelastic material (VEM) layer sandwiched between a elastic base layer and a relatively stiffer constraining layer, are widely used in engineering applications for reducing vibration and noise radiation. To accurately predict and effectively control vibration and properly and quickly determine the design parameters, optimal designs for the CLD structures are necessary. The optimal designs depend on thoroughly understanding the damping characteristics of the CLD structures. In addition, for some cases, CLD structures with multi-constrained VEM layers are needed to suppress vibration more effectively. In this paper, an effective modeling method to accurately describe the damping properties and a quick optimization design method using COMSOL were proposed for CLD structures with multilayers in detail. The effects of nondimensional thickness ratios of the VEM and constraining layer to the base layer on the damping properties of CLD structures were analyzed. For CLD structures with different configurations, different constraints were selected to obtain the maximized damping in the optimization design. The conclusions from this research provide an insight into the effects of thicknesses of VEM and constraining layers on the damping properties of CLD structures regardless of its size. The modeling and optimal methods using COMSOL in this paper are not limited to CLD structures and can be used by other structures also.

Topology optimization of constrained layer damping plates with frequency- and temperature-dependent viscoelastic core via parametric level set method

Frequency- and temperature-dependent properties of viscoelastic materials have a significant effect on vibration characteristics of constrained layer damping (CLD) structures. In this article, parametrized level set method (PLSM) is extended to solve the topology optimization problem of CLD plates, in which the viscoelastic material with frequency- and temperature-dependent characteristics is employed as damping core. The single/weighted modal loss factors, which are solved by an iterative method, are defined as objective functions, and topology optimization problem is formulated based on the finite element model for CLD plates which are described by combining parametric level set (PLS) functions. The sensitivities of objective functions with respect to expansion coefficients in PLS are calculated by the use of adjoint vector method. As the optimized results with complex constant shear modulus for viscoelastic core indicates, the proposed method is effective for topology optimization of CLD structures and insensitive to initial design. Numerical examples with the consideration of frequency- and temperature-dependent characteristics for “soft” and “hard” viscoelastic core are implemented. Through comparing the optimal results with different models for viscoelastic core, the influences of frequency- and temperature-dependent characteristics for viscoelastic core on natural frequencies, modal loss factors and optimized layouts are analyzed. Similarity indices are defined for distinguishing the difference among optimized layouts and initial design induced by modal strain energy contour. The optimal design dependence on layer thicknesses is further discussed with additional mass of CLD materials unchanged.

Parameter Identification of Brake Pad Shims for Complex Eigenvalue Analysis

AbstractComposite structures called shims are bonded to brake pad backplates to increase the damping in brake systems. The aim of this measure is to avoid squeal which is a high‐frequency audible brake vibration disturbing customers and the environment. This NVH problem originates from self‐excited vibrations resulting from the friction contact between pad and disk. Multi‐layer shim compounds consisting of steel and elastomer layers use the shear deformation of the viscoelastic core obtaining a high energy dissipation potential.In this contribution parameter identification for Finite Element brake simulations, so called complex eigenvalue analyses is focused. Therefore dynamic mechanical analyses on constrained layer damping structures are carried out receiving loss factors for a broad temperature and therefore frequency band. The results are compared with experimental modal analyses and possible differences between the two procedures are pointed out. The main goal is to identify input parameters for a subsequent implementation of damping characteristics for complex eigenvalue analysis.

Sound Radiation Analysis of Constrained Layer Damping Structures Based on Two-Level Optimization.

Constrained layer damping (CLD) is an effective method for suppressing the vibration and sound radiation of lightweight structures. In this article, a two-level optimization approach is presented as a systematic methodology to design position layouts and thickness configurations of CLD materials for suppressing the sound power of vibrating structures. A two-level optimization model for the CLD structure is developed, considering sound radiation power as the objective function and different additional mass fractions as constraints. The proposed approach applies a modified bi-directional evolutionary structural optimization (BESO) method to obtain several optimal position layouts of CLD materials pasted on the base structure, and sound power sensitivity analysis is formulated based on sound radiation modes for the position optimization of CLD materials. Two strategies based on the distributions of average normalized elemental kinetic energy and strain energy of the base plate are proposed to divide optimal position layouts of CLD materials into several subareas, and a genetic algorithm (GA) is employed to optimally reconfigure the thicknesses of CLD materials in the subareas. Numerical examples are provided to illustrate the validity and efficiency of this approach. The sound radiation power radiated from the vibrating plate, which is treated with multiple position layouts and thickness reconfigurations of CLD materials, is emphatically discussed.

Evaluation of mechanic damping properties of montmorillonite/organo-modified montmorillonite-reinforced cement paste

In this study, the mechanical and damping properties of montmorillonite (MMT)/organo-modified montmorillonite (OMMT) reinforced cement paste were investigated. The damping properties were measured by dynamic mechanical analysis (DMA). The compressive strength of cement composites was decreased by a high dosage of MMT or OMMT. The damping capacities of OMMT-reinforced cement paste was superior to that of MMT-reinforced cement, in which the damping mechanism comprised the internal friction, external friction, and multiphase friction within the cement matrix. Moreover, a constrained-layer damping structure was produced in cement paste by the organic modification of MMT and was beneficial to the damping properties of cement paste.

Analysis and implementation of chatter frequency dependent constrained layer damping tool holder for stability improvement in turning process

The machining stability is closely affected by dynamics behavior of the tool holder in turning operation. In this paper, the constrained layer damping (CLD) tool holder with chatter frequency dependent dynamics is analyzed to further improve machining stability. The dynamics behavior of CLD tool holder is first considered to be influenced by the chatter frequency due to the viscoelastic material. The mechanical properties of viscoelastic materials are determined by the testing frequency. Analytical models are built to calculate the modal parameters such as damping ratio. The chatter frequency dependence further increases the critical depth of cuts in stability lobes. Then, dimensions of the CLD structure are simulated and selected to increase damping where the chatter frequency is assumed to approximate the natural frequency, after that the developed CLD tool holder is manufactured. Lastly, modal tests and cutting experiments are performed for verification. The damping ratio of developed CLD tool holder are increased by 99% compared to that of conventional steel tool holder. It has been proved that the developed CLD tool holder can further improve machining stability with better damping performance especially when the chatter frequency is farther from the natural frequency.

Dynamic Optimization of Constrained Layer Damping Structure for the Headstock of Machine Tools with Modal Strain Energy Method

Dynamic stiffness and damping of the headstock, which is a critical component of precision horizontal machining center, are two main factors that influence machining accuracy and surface finish quality. Constrained Layer Damping (CLD) structure is proved to be effective in raising damping capacity for the thin plate and shell structures. In this paper, one kind of high damping material is utilized on the headstock to improve damping capacity. The dynamic characteristic of the hybrid headstock is investigated analytically and experimentally. The results demonstrate that the resonant response amplitudes of the headstock with damping material can decrease significantly compared to original cast structure. To obtain the optimal configuration of damping material, a topology optimization method based on the Evolutionary Structural Optimization (ESO) is implemented. Modal Strain Energy (MSE) method is employed to analyze the damping and to derive the sensitivity of the modal loss factor. The optimization results indicate that the added weight of damping material decreases by 50%; meanwhile the first two orders of modal loss factor decrease by less than 23.5% compared to the original structure.

Experimental Investigation of Damping Performance of Viscoelastic Material Using Constrained Layer Damping Treatment

The purpose of this paper is to determine the performance of damping provided by different viscoelastic materials (VEM). The damping performance of the viscoelastic material is investigated using constrained layer damping (CLD) treatment. Using the viscoelastic material as the core layer in the CLD structures, significant amount of damping can be obtained with minimum impact on the total mass of the structure. Viscoelastic polymeric materials have been used to damp vibrations for many years. Energy is dissipated through relaxation processes in the long chain molecular networks when a polymeric material is subjected to vibrations.In the current study, experimental investigation of the different viscoelastic materials is performed using Oberst beam test specimens and an impulse technique as per ASTM Standard E 756(05). The amount of damping of structure is measured by half- power bandwidth method.

A Mechanics Model and Active Control for Smart Constrained Layer Damping Structure

The active vibration control of beam is researched by using piezoelectric constrained damping structure. The energy characteristic of each layer for the piezoelectric smart constrained damping beam is completely expressed based on the finite element method and the damping layer shearing movement relationship is described by ADF model. Then the structure mechanics model for dynamic parameters is established. Applying displacement error signal, an adaptive filter controller is designed. Under the different outside disturbance, structure vibration responses with active control are analyzed. It shows that the piezoelectric smart constrained damping structure can have good control performance for the active and it has a good engineering prospects.

Development of a new finite element and parametric study for plates with compressible constrained layer damping

Constrained layer damping (CLD) is widely used in many structures for vibration reduction. It is necessary to model CLD structures precisely. Most existing research studies have modeled the structures as beams, which in many cases is not a sufficient approach. These existing models are based on the assumption that shear deformation in the core layer is the only source of damping in the structure. However, previous research has shown that other types of deformation in the core layer, such as deformations from longitudinal extension and transverse compression, can also be important. To more accurately model CLD, a new plate finite element is developed in this study by assuming that there is shear as well as longitudinal and transverse deformations in the damping layer. This model can be used to better predict the structure’s dynamic characteristics, such as resonant frequencies and modal loss factors. By comparing the new model to experimental results from the open literature, this newly developed plate finite element model is validated. With all three types of damping included in this new approach, it becomes possible to study the impact of various design parameters, such as the damping layer’s thickness. To that end, a parametric study is also conducted using the newly developed finite element for various design parameters.

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.

Characterisation and modelling of viscoelastically damped sandwich structures

A passive damping technique with viscoelastic materials is analysed in the present work. Concretely, the constrained layer damping (CLD) configuration, also known as viscoelastically damped sandwich structure, is considered. For an efficient dynamical analysis of viscoelastically damped structures, an accurate material characterisation and suitable mathematical models are necessary for reproducing the real material behaviour. With this aim, a CLD structure has been characterised in the frequency domain by means of experimental tests, considering both homogenised and multilayered approaches. The material-parameter extraction procedure is presented, and mathematical models are reviewed. For the homogenised characterisation, a mathematical model based on the Ross et al. model has been proposed, whereas for the multilayered characterisation, the constraining layers have been considered as linear elastic, and the viscoelastic core has been represented by a four-parameter fractional derivative model. Both material models have been considered for defining both homogenised and layered multimaterial numerical models by the finite element method. The numerical models have been validated by correlating the numerical and the experimentally measured dynamic responses. Both numerical models have reproduced the experimental dynamic response accurately for the bandwidth considered herein.

Optimal Design of Constrained-Layer Damping Structures Considering Material and Operational Condition Variability

of a surface treatment is highly sensitive to the variability in operational temperature. This paper proposes a statistical approachto modelthe variabilityof viscoelastic damping material in aconstrained-layer dampinglayout, to predict variability in the dynamic responses of viscoelastic damping material, and to obtain an optimal robust layout that accounts for severe variability in operational temperature. The viscoelastic damping material property can be modeled as a sum of 1) a random complex modulus due to operational temperature variability and 2) experiment/model errors in the complex modulus. The eigenvector dimension reduction method is used in probability analysis to predict the variability in the dynamic responses of the viscoelastic damping material. It is concluded that temperature variability is strongly propagated to that in the dynamic responses of the damping material. This study also performs reliability-based design optimization for an optimal robust design of the constrained-layer damping structure. It is shown that reliability-based design optimization gives a more robust and reliable damping layout design amidst severe variability in operational temperature.

Development of a single-layer finite element and a simplified finite element modeling approach for constrained layer damped structures

A new finite element (FE) is formulated based on an extension of previous FE models for studying constrained layer damping (CLD) in beams. Most existing CLD FE models are based on the assumption that the shear deformation in the core layer is the only source of damping in the structure. However, previous research has shown that other types of deformation in the core layer, such as deformations from longitudinal extension, and transverse compression, can also be important. In the finite element formulated here, shear, extension, and compression deformations are all included. As presented, there are 14 degrees of freedom in this element. However, this new element can be extended to cases in which the CLD structure has more than three layers. The numerical study shows that this finite element can be used to predict the dynamic characteristics accurately. However, there is a limitation when the core layer has a high stiffness, as the new element tends to predict loss factors and natural frequencies that are too high. As a result, this element can be accepted as a general computation model to study the CLD mechanism when the core layer is soft. Because the element includes all three types of damping, the computational cost can be very high for large scale models. Based on this consideration, a simplified finite modeling approach is presented. This approach is based on an existing experimental approach for extracting equivalent properties for a CLD structure. Numerical examples show that the use of these extracted properties with commercially available FE models can lead to sufficiently accurate results with a lower computational expense.