Damping Of Composite Structures Research Articles

Free vibration of functionally graded carbon nanotube‐reinforced composite damping structure based on the higher‐order shear deformation theory

AbstractMulti‐phase functionally graded carbon nanotube‐reinforced composite damping structure (FG‐CNTRCDS) excels other composite structures in that it inherits the excellent performance of the functionally graded carbon nanotube‐reinforced composite, and exhibits an improved damping performance due to the added viscoelastic damping films. Despite its superior properties, investigations on dynamic properties of the FG‐CNTRCDS under clamped boundary conditions are still lacking. Aiming at filling this gap and paving the way to accurately design and analyze the FG‐CNTRCDS, a dynamic analytical model, which is based on the higher‐order shear deformation theory to formulate governing equations for predicting free vibration of FG‐CNTRCDS, has been established. The analytical solution that satisfies clamped boundary conditions is obtained using the Rayleigh–Ritz method. The existing analytical results from the literature have been used to verify the correctness of the theoretical model. In addition, effects of various structural parameters (such as volume fraction and core‐to‐skin thickness ratio) on dynamic performance have been investigated. Here, the dynamic performance refers to the first‐order natural frequency and the first‐order loss factor.

Dynamic Performance of Laminated High-Damping and High-Stiffness Composite Structure Composed of Metal Rubber and Silicone Rubber.

In this study, a laminated composite damping structure (LCDS) with metal rubber (MR) as matrix and silicone rubber (SR) as reinforcement has been designed. The embedded interlocking structure formed by the multi-material interface of the LCDS can effectively incorporate the high damping characteristics of traditional polymer damping materials and significantly enhance the adjustable stiffness of the damping structure. Based on the periodic cyclic vibration excitation, dynamic tests on different laminated structures were designed, and the damping performance and fatigue characteristics under periodic vibration excitation of the LCDS, based on MR and SR, were explored in depth. The experimental results exhibited that, compared to single-compound damping structures, the LCDS with SR as reinforcement and MR as matrix has excellent stiffness and damping characteristics. The incorporation of the silicon-based reinforcement can significantly improve the performance of the entire structure under cyclic fatigue vibration. In particular, the effects of material preparation and operating parameters on the composite structure are discussed. The effects of MR matrix density, operating frequency, amplitude, and preload on the stiffness and damping properties of the MR- and SR-based LCDS were investigated by the single factor controlled variable method. The results demonstrated that the vibration frequency has little effect on the LCDS damping performance. By increasing the density of the MR matrix or increasing the structural preload, the energy dissipation characteristics and damping properties of the LCDS can be effectively improved. With the increase in vibration excitation amplitude, the energy consumption of the LCDS increases, and the average dynamic stiffness changes at different rates, resulting in the loss factor decreasing first and then increasing. In this study, a damping structure suitable for narrow areas has been designed, which overcomes the temperature intolerance and low stiffness phenomena of traditional polymer rubber materials, and provides effective guidance for the design of damping materials with controllable high damping and stiffness.

Analysis of failure mechanism of W1-type fastening clip in high speed railway and structure study of damping composite

In this paper, the fastener clip in high-speed railway with the speed of 300–350 km/h is taken as the research object, it studied the relationship among parameters such as high-speed rail wear, dynamic frequency response of clip and dynamic stress of clip, revealed the dynamic failure mechanism of clip damage in high-speed rail caused by high-frequency excitation (580–680 Hz).In order to improve the service life of existing W1-typefastener in high-speed rail on the basis of guaranteeing design requirements and installation interchangeability of clips, taking “keeping away from excitation frequency band and reducing vibration amplitude” as the research objective, the clip geometric parameter optimization based on the correlation theory and the composite damping structure design of clip based on the modal damping theory are mainly promoted. Under the conditions of installation and use of rail clips, high damping clips with different combination of inner and outer diameters are obtained and strength simulation analysis, damping clip samples and dynamic frequency response test of optimized damping clips are carried out. The results show that, (1) with the increase of the equal ratio of outer diameter and damping diameter of high damping clip, the attentive mode frequency of clip increases up to 18.5%;(2) As the ratio of outer diameter and damping diameter of high damping clip increases, the response amplitude of high damping clip significantly decreases, up to 31.6%, (3) As the ratio of outer diameter and damping diameter of high damping clip increases, the overall mass of fastener clip also decreases, up to 9.7%.To a certain extent, the design structure of high damping composite clip is not only far away from the excitation frequency of wheel and rail, but also improves the dynamic fatigue life of clip, saves the cost of fastener system and has more applicability for high-speed railway lines.

The impact of mesoscale textile architecture on the structural damping in composite structures

In this article, a method allowing for prediction of the effective structural damping given the mesoscale architecture of a composite is presented. The method enables a fast and accurate calculation of the loss factor as a function of the direction of the wave propagation and the frequency in any periodic textile composite. The scheme combines two reduction methods, the first being the wave and finite element method that employs periodic structure theory to reduce the size of the problem by allowing for modelling only a unit cell of a periodic structure, while the second reduction approach is a mode-based component mode synthesis that reduces the size of the dynamic stiffness matrix of a unit cell. The exhibited methodology allows for structural damping prediction and optimisation through judicious design of the textile architecture. Numerical examples several complex architectures are exhibited.

Experimental Study on Scheme Optimization of Composite Damping Structure

Experimental study on scheme optimization of composite damping structure was carried out and the effect of environmental temperature on damping characteristic was investigated in the present study. Damping coefficient of three layers composite damping structure is nearly ten times of that of light plate. The scheme of composite damping structure has a significant effect on damping characteristic. Effect of environmental temperature on damping characteristic was analyzed under temperature range from −10 °C to 80 °C. It shows that both of frequency and damping coefficient of composite damping structure are influenced by environmental temperature. There is a minimum frequency value which occurs at nearly 30 °C in the temperature range. Damping coefficient decreases with the increase of environmental temperature. The maximum damping coefficient is more than twice of the minimum one. Environmental temperature needs to be well considered in the practical application of composite damping structure.

Numerical investigation of rub-induced composite fan blade vibrations and abradable coating removals

Composite blade vibrations, removal of abradable coating, and blade stress resulting from blade/casing rubs are investigated. Composite fan blade models with different stacking sequences and a metal blade are created and calculated through a three-dimensional finite element method. Centrifugal stiffness, damping of composite structures, B-spline surfaces, and abradable coating are included in the calculations. The results show that the maximum vibration amplitudes of composite blades at different rotational speeds could be affected by stacking sequences. The responses of metal blade are more sensitive to the natural frequencies of the second to the fifth blade modes than those of the composite blades. Abradable coating removals are highly related to blade vibration amplitudes. Considerably more coatings are removed by the metal blade than by the composite blades at the design speed, particularly in the axial direction. Moreover, according to the stress results, the metal blade is more vulnerable to rub-induced vibrations than the composite blades at the design speed. Larger vibration amplitudes in the composite blades do not necessarily lead to lower failure margins because of the complexity of composite structures. The strategy established can be utilized to aid in the initial designs of state-of-the-art composite blades and reduce potential rub-induced problems.

Study on low-velocity impact of embedded and co-cured composite damping panels with numerical simulation method

According to the designable mechanical characteristics of composite material, the embedded and co-cured composite damping structure (ECCDS) consisting of fiber reinforced resin layers and one (or more) damping layer(s) embedded into composite material component is manufactured. The finite element model and experiment model of ECCDS are established and low velocity impact performances of the composite damping panels are simulated and tested by using the explicit dynamic analysis software LS-DYNA and the Drop-weight Impact equipment, respectively. The structural behaviors under impact of the damping panels are compared with those of the composite panels without the damping layer. The results of numerical simulation and experiment are in good agreement with each other, which demonstrates that the finite element model and simulation method using present study are valid. Finally the impact properties versus the different geometrical parameters of damping layers are investigated also. The simulation model and method can provide an important foundation for the theoretical predict of impact characteristics of ECCDS.

A research on sound insulation characteristics and processing of the embedded and co-cured composite damping structures

According to the designable mechanical characteristics of composite structure, the ingredients of viscoelastic damping material is developed by synthetically considering the vulcanization characteristics of viscoelastic materials and the cure behaviours of epoxy resins, and 5231/EW180B glass cloth prepreg is presented here to manufacture the embedded and co-cured composite damping structure (ECCDS). A secondary vulcanization method of viscoelastic material is investigated to fabricate the experimental specimens of ECCDS. The co-cured processing of the composite material embedding viscoelastic damping membrane is explored according to the glass fabric/epoxy composite cure cycle. By using a standing wave tube method, sound insulation performance of the composite damping structure is firstly studied and compared with the composite material without the damping layer. The conclusion indicates that ECCDS has a very strong potential to insulate sound.

Sound Insulation Characteristics of the Embedded and Co-Cured Composite Damping Structures

Based on the designable mechanical characteristics of composite structure, a secondary vulcanization method of viscoelastic material is developed to manufacture the experimental specimens of embedded and co-cured composite damping structure (ECCDS). The mid-temperature co-cured process of the composite material embedding viscoelastic damping membrane is explored according to the glass fabric/epoxy composite cure cycle. By using a standing wave tube method, sound insulation performance of the composite damping structure is tested and compared with the composite laminates without the damping layer. The conclusion indicates that ECCDS has a very strong potential to insulate sound.

A Research on Loss Factor of Embedded and Co-Cured Composite Damping Structure

In this paper, modal strain energy method is employed to calculate the modal loss factor of embedded and co-cured composite damping structure (ECCDS). To illustrate the validity of modeling and calculating method, the simulation results are compared with the experimental data. The effects of thickness, number and location of damping layers on damping performance of ECCDS have also been studied in detail.

Active vibration damping of composite structures using a nonlinear fuzzy controller

The present paper presents a comprehensive methodology for the structural active vibration damping using a fuzzy logic control. The proposed application setup consists of a cantilever beam equipped with two pairs of collocated piezoceramic (PZT) actuators and sensors. The investigated carbon composite beam is modeled using a shell 2D-model on Abaqus commercial finite element code. The PZT patches are modeled as additional layers with a coupled electromechanical effect. Experimental data corresponding to the controlled and to the uncontrolled systems are also presented considering fixed frequency and pulse force excitation.

Numerical Simulation of Embedded and Co-Cured Composite Damping Structure under Low Velocity Impact

Embedded and co-cured composite damping structure is a novel damping processing structure, which possesses excellent damping properties and mechanical performances. In this paper, explicit dynamic analysis software LS-DYNA is employed to simulate low velocity impact on embedded co-cured composite damping structure panels. To illustrate the validity of modeling and calculation method, the simulation results are compared with the experimental data. And the results show that the impact resistance of embedded co-cured composite damping structure is much better than composite panel without damping material.

Damping Performance of Cocured Composite I-Shaped Beams with Embedded Viscoelastic Layers

Composite I-shaped beams are currently used in aerospace, ocean and civil engineering applications. Increasing the vibration damping of composite structures is a concerned need in those applications. This research is an effort to investigate the damping performance of composite I-shaped beams with cocured viscoelastic damping layers using finite element method and modal testing technique. A hybrid finite element model for a damped composite I-shaped beam was developed. Modal strain energy method was used to estimate the linear viscoelastic modal loss factors of the composite beams. A numerical parametric investigation was conducted to study the effects of various parameters on the dynamic properties of composite beams under free-free end boundary condition. Selective design parameters included inserting location and thickness of damping layers. Natural frequency and modal loss factor were also extracted by experimental modal analysis. Static tests were performed to obtain the loss of static stiffness for inserting soft viscoelastic layers. Experimental and analytical results show the inserting location of cocured damping layers has significant effects on the damping and there exists a critical damping layer thickness for optimal damping with less significant modal frequency decrease. Static tests results demonstrate a little loss of static stiffness for embedding low module damping layers. A careful selection of damping layer location and thickness is needed to optimize the damping benefits desirable and the mechanics stiffness reduction that can be tolerated for intergral damping composite structures.

Clamping effects on the dynamic characteristics of composite machine tool structures

Substituting composite structures for conventional metallic structures has many advantages for structural dynamic characteristics because composite materials have the higher specific stiffness and damping characteristics than conventional materials. However, the dynamic characteristics such as the fundamental natural frequency and damping of composite structures are influenced much by their joints. In this work, the effects of clamping conditions on the dynamic characteristics of cantilever type composite machine tool structures with clamped joint were investigated to increase the natural frequency and damping of structures. In order to improve the shear property of the clamping part of composite machine tool bar, a new method for the clamping part was developed with metal core or sleeve inserted in the composite body at the clamping part. From the finite element and experimental results, suitable clamping conditions for the maximum dynamic stiffness were obtained for the composite structures with clamped joint.

Modeling of vibration damping in composite structures

An improved dynamical model for vibration damping in composite structures is introduced to investigate the stacking sequence and the degree of anisotropy as a function of the vibration modes. Extensive investigation has been carried out from the fitting of modal measurements with lowest residual errors to establish quasi-uniform mass damping models in terms of normal coordinates system. The analysis of the obtained results proves not only the efficiency of the proposed model but also its applicability in any wide range of frequency spectrum of composites.

MODELLING OF VIBRATION DAMPING IN COMPOSITE STRUCTURES

An improved dynamical model for vibration damping in composite structures is introduced to incorporate the code number and the degree of isotropism against the modal parameters. A substantial development has been carried out from the fitting of modal measurements with lowest residual errors to permit an establishment of quasi uniform mass damping models in terms of normal coordinates system. The analysis of the obtained results proves not only the efficiency of the developed model but also its applicability in any wide range of frequency spectrum of composites.

Damping characterization of unidirectional fibre reinforced polymer composites

The main concern of this paper is the modelling of material damping in composite structures. A method is derived to predict the homogenized damping properties analytically. The procedure is based on the micromechanical theory of a representative fibre-matrix cell. Since the dissipative phenomena cannot generally be defined by a unique mathematical model, an equivalent viscous damping model is suggested. On the structural level damping can be analysed by the finite element method. Modal damping is illustrated by numerical applications.

Effects of interply damping layers on the dynamic characteristics ofcomposite plates

Integrated damping mechanics for composite plates with constrained interlaminar layers of polymer damping materials are developed. Discrete layer damping mechanics are presented for composite laminates with damping layers, in connection with a semianalytical method for predicting the modal damping in simply supported specialty composite plates. Correlations between predicted and measured response in graphite/epox y plates illustrate the accuracy of the method. Additional application cases for graphite/epoxy plates of various laminations demonstrate the potential for higher damping than geometrically equivalent aluminum plates. The effects of aspect ratio, damping layer thickness, and fiber volume ratio on static and dynamic characteristics of the composite plate are also investigated. AMPING is a significant dynamic parameter for vibration and sound control, dynamic stability, positioning accu- racy, fatigue endurance, and impact resistance. Many current structural applications (e.g., large space structures, engine blades, and high-speed machinery) require light weight and high dynamic performance. Therefore, candidate sources of passive damping should add minimal parasitic weight and be compatible with the structural configuration. Two potential damping sources satisfying the previous re- quirements are the constrained damping layer approach and the damping capacity of composites. Constrained damping layers in isotropic metallic structures have been widely applied and investigated.1 They provide high damping, but tend to increase the structural weight and offer limited means for damping tailoring. The inherent damping capacity of compos- ite materials also seems promising. Although the damping of composite structures is not very high, it is significantly higher than that for most common metallic structures. Moreover, composites are the materials of preference in many cases, since they readily provide high specific stiffness and strength. More importantly, research on the damping mechanics of composite laminates2'4 and structures5'6 has shown that composite damp- ing is anisotropic, highly tailorable, and depends on an array of micromechanic al, laminate, and structural parameters. It has been further demonstrated that optimal tailoring may significantly improve the damped dynamic performance of composite structures.7 It seems likely that the combination of both approaches (i.e., composite structures with interlaminar damping layers) will offer the advantages of high damping, damping tailoring, good mechanical properties, and low weight addition. In addi- tion, the interlaminar damping concept is highly compatible with the laminated configuration of composite structures and their fabrication techniques. In contrast to isotropic materials, the variations in anisotropy and elastic properties of each

Computational Simulation of Damping in Composite Structures

A computational methodology is developed for the prediction of passive damping in composite structures. The method involves multiple levels of damping model ling by integrating micromechanics, laminate, and structural damping theories. The effects of temperature and moisture on structural damping are included. The simulation of damp ing in the structural level is accomplished with finite-element discretization. Applications are performed on graphite/epoxy composite beams, plates, and shells to illustrate the methodology. Additional parametric studies demonstrate the variation of structural modal damping with respect to ply angles, fiber volume ratio, and temperature.

Loss Factors of Viscoelastic Systems in Terms of Energy Concepts

The definition of loss factor in terms of energy quantities is re-examined, particularly as it applies to composite viscoelastic systems. A restatement of this definition in terms of a corresponding viscoelastic spring is used to show that this definition is extremely useful for massless (ideal viscoelastic spring) systems, but may be applied unambiguously to spring systems with a single attached mass only at resonance. Simple relations are presented which express the loss factors of series-parallel arrays of massless viscoelastic springs in terms of properties of the individual components. Implications of these relations in damping of composite structures are discussed. (This work was supported in part by the Aeronautical Systems Division, U. S. Air Force.)