Viscoelastic Sandwich Research Articles

Active Vibration Control and Parameter Optimization of Genetic Algorithm for Partially Damped Composites Beams.

The paper partially covered Active Constrained Layer Damping (ACLD) cantilever beams' dynamic modeling, active vibration control, and parameter optimization techniques as the main topic of this research. The dynamic model of the viscoelastic sandwich beam is created by merging the finite element approach with the Golla Hughes McTavish (GHM) model. The governing equation is constructed based on Hamilton's principle. After the joint reduction of physical space and state space, the model is modified to comply with the demands of active control. The control parameters are optimized based on the Kalman filter and genetic algorithm. The effect of various ACLD coverage architectures and excitation signals on the system's vibration is investigated. According to the research, the genetic algorithm's optimization iteration can quickly find the best solution while achieving accurate model tracking, increasing the effectiveness and precision of active control. The Kalman filter can effectively suppress the impact of vibration and noise exposure to random excitation on the system.

Global sensitivity analysis of damped sandwich plates using sparse polynomial chaos expansions

The present article aims at performing a global sensitivity analysis of modal properties of a frequency dependent viscoelastic sandwich plate. The latter are evaluated using a finite element model relying on Kirchhoff theory for the elastic faces and the Mindlin-Reissner approach for the viscoelastic layer. The plate’s characteristics are considered as random variables following log normal laws. Sparse polynomial chaos expansions are employed to evaluate Sobol’s indices. For high damping, the resonant frequencies and loss factors turn to be sensitive to the elastic face properties, while in the weak damping case they are mostly affected by the viscoelastic model parameters.

Nonlinear dynamic response and damping performance of the viscoelastic composite core-based sandwich plates subjected to blast load

Nonlinear dynamic response and damping performance of the viscoelastic composite core-based sandwich plates subjected to blast load

High strength and high damping CFRP composites with co‐curing viscoelastic sandwich film

AbstractThe high temperature co‐curing damping composite was investigated by co‐curing technology to improve the mechanical property and damping performance of the traditional fiber reinforced resin matrix composite. Fluororubber with stable chemical properties and high‐temperature resistance was used as the core layer of novel carbon fiber reinforced bismaleimide resin matrix High‐temperature Co‐curing Damping Sandwich Composites (HCDSC). The curing temperature and curing time of fluororubber were consistent with that of bismaleimide resin by adjusting the formula. The viscoelastic damping properties and thermal stability of zinc methacrylate reinforced fluororubber were investigated in detail. Static mechanical tests, modal tests and interfacial shear tests prove that HCDSC display excellent mechanical and damping properties. The interfacial microscopic analysis reveals that viscoelastic sandwich materials are closely bonded with the composites. The dynamic characteristics of damping sandwich composite plate with fixed support on four sides is analyzed theoretically, and the vibration equilibrium equation of composite plate is derived by combining first‐order shear deformation theory, variational principle, and Hamilton principle. The damping performance of the composite plate are discussed through modal tests to verify the accuracy of theoretical derivation. This research is of great significance to solve the problem of structural dynamics, and provides a new idea for the design of structural and functional composite materials.Highlights A viscoelastic damping material with large damping and high strength was prepared. The dynamic performance of co‐curing sandwich composite structures was studied. The free vibration of composite structures was explored via experiment and theory.

A new guided mode so-called minimum group velocity in viscoelastic sandwich plates: A parametric numerical study

Zero-Group-Velocity (ZGV) guided mode has recently received particular attention because of its highly sensitive to structural changes, such as defects. Parallel to ZGV, in the present work, we introduce a new guided mode so-called Minimum-Group-Velocity (MGV) that is a remarkable phenomenon in defect detection applications. Strictly speaking, when any two phase-velocity dispersion curves of Lamb modes approach each other without overlapping, we observe this new mode in group-velocity dispersion curves. It is worth noting that this MGV mode has never been addressed in literature. We compute the Lamb-like modes in asymmetric viscoelastic sandwich plates using the Stiffness Matrix Method (SMM). We show that the change in properties of this sandwich can dramatically affect frequency ranges associated with ZGV and MGV modes. However, a linear correlation between phase velocities and this change on viscoelastic properties is discussed, where we observed an interconnection phenomenon in the dispersion curves. This interconnection happens between specific points on the dispersion curves, each corresponding to a ZGV- or MGV-mode. On the other hand, we verify that the detection of changes in level of viscoelastic properties or variations in the thickness of the buffer viscoelastic layer is possible within a limited segment of the damped mode curve.

Nonlinear damping and forced vibration investigation of three-layered viscoelastic sandwich beams on nonlinear elastic foundation with interlaminar continuous shear stress Zig–Zag theories

Nonlinear damping and forced vibration investigation of three-layered viscoelastic sandwich beams on nonlinear elastic foundation with interlaminar continuous shear stress Zig–Zag theories

Vibration analysis of a smart viscoelastic porous sandwich micro-shell with magnetorheological fluid core using the modified couple stress theory

In the current study, for the first time, the size-dependent vibration of a functionally graded (FG) porous sandwich cylindrical microshell with magnetorheological fluid core is investigated using modified couple stress theory (MCST) and the first-order shear deformation theory (FSDT). The microshell is made of FG porous material and for investigating the material properties, two types of porous distributions are considered. Based on FSDT and the MCST, the governing equations are derived using Hamilton’s principle regarding the energy dissipation due to the shear deformation of the magnetorheological core layer and the interaction between all layers. Different assumptions, based on the continuity in transverse shear stresses and slope of in-plane displacements, are considered in the theoretical formulation. The natural frequency and loss factor of the microshell with sliding simply supported boundary conditions are determined using Navier’s solution method. Finally, the influence of some parameters such as material length scale(l/h: 0-1), types of porous distributions (symmetric-asymmetric), porosity volume fraction (e0: 0-1), magnetic field intensity (B: 0-800) and aspect ratio (L/R: 1-8, R/h: 10-100) on the vibration damping characteristics of microshell, is investigated and validity of the results is studied.

Creep instability analysis of viscoelastic sandwich shell panels

Creep instability analysis of viscoelastic sandwich shell panels

Topology optimization of damping layer in frequency-dependent viscoelastic sandwich panels considering steady-state free vibration

Attaching viscoelastic materials (VEMs) to structures has been widely used to improve structural dynamic properties. Nevertheless, the adhesion of VEMs inevitably leads to the increase in overall structural mass. Topology optimization is one of the most effective methods to tackle this contradiction. In the traditional topology optimization, VEMs damping cores in constrain layer damping (CLD) sandwich structures are often simplified into linear elastic materials with constant parameters, usually ignoring their frequency-dependent and temperature-dependent dynamic characteristics, which will cause the distortion of the optimization results. Therefore, we propose a topology optimization method for CLD sandwich panels with a frequency-dependent VEM damping core considering steady-state free vibration in this study, where the anelastic displacement fields (ADF) model is adopted to combine the derived frequency-dependent complex constitutive relationship with the layerwise finite element (LFE) model, and the iterative modal strain energy (IMSE) method is used to determine the modal parameters of the CLD sandwich panels. The results of numerical examples show that the proposed method in this study not only has the advantages of simple and intuitive model, high calculation efficiency, and accuracy but also can achieve relatively good dynamic properties of the CLD sandwich structures.

FINITE ELEMENT ANALYSIS FOR DYNAMIC RESPONSE OF VISCOELASTIC SANDWICHED STRUCTURES INTEGRATED WITH ALUMINUM SHEETS

Passive vibration attenuation of modern mechanical structures is one of the most essential technologies applied to the arsenal of modern mechanical structures. In this work, dynamics analysis is performed on viscoelastic (VE) sandwich beam and plate by using finite element method. The proposed structure is composed of a VE core and aluminum face sheets as substrate layers on both sides of the structure. Small-strain VE material is modeled based on complex constant moduli model and numerical method is used to develop the finite element (FE) shear model based on first-order shear deformation theory (FSDT) and Hamilton principle. In modal analysis, model-effective mass analysis is performed to investigate its dominant mode shape and sweet spot at resonance using C3D20 and CPS8 elements. The former is indicated as a 3-D element with 20 nodes while the latter is indicated as a 2-D plane strain element with eight nodes. In harmonic analysis, resonance frequency is obtained based on mode superposition method to evaluate the steady-state response of VE sandwich beam via maximum deformation. Thereafter, the results are compared against analytical solutions from the literature. Moreover, a parametric study shows that the natural frequency of the beam did not change with the increase in core thickness. However, normalized loss factor of VE sandwich beam is directly proportional to VE damping factor and the thickness of VE core layer. Based on frequency response function, the results of resonance frequencies for VE beam are in the range of modal natural frequency.

Layerwise models for supersonic flutter analysis of viscoelastic sandwich panels with curvilinear fibre composite skins

In this work, an assessment of layerwise finite element models for supersonic flutter analysis of soft core viscoelastic sandwich panels is presented, making use of various kinematic descriptions involving shear deformation theories and Lagrange z-expansions with thickness stretching, progressively refined to render numerically accurate and computationally efficient solutions. Numerical applications of sandwich panels include either viscoelastic or purely elastic core with skins of metal or laminated composite, using unidirectional or curvilinear fibres, considering thin and moderately thick panels, with core thickness ratios ranging from narrow to wide cores. A comprehensive assessment of the models predictive capabilities in free vibration analysis is carried out by comparison with three-dimensional exact solutions and numerical methods available in the literature. Even though it is concluded that layerwise first-order modelling, with no thickness stretching, ensures a fair compromise between numerical accuracy and computational efficiency in the aeroelastic flutter analysis of thin sandwich panels, layerwise high-order theories accounting for thickness stretching are rather necessary for the proper modelling of moderately thick sandwich panels, with either viscoelastic or purely elastic core.

Modelling and predicting the dynamic response of an axially graded viscoelastic core sandwich beam

The present study explored the influence of axial gradation of viscoelastic materials on the dynamic response of the sandwich beam for structural applications. The finite element (FE) formulations are used to model and investigate dynamic response of the sandwich beam. The classical beam theory is used to develop the FE formulations and Lagrange's approach is considered to obtain the equations of motion (EOM). FE code is developed and validated with the existing literature and also conducted the convergence study for the developed FE method. Further, the influence of different viscoelastic materials and boundary conditions on the dynamic response of the sandwich beam is investigated. Four different axial gradation configurations of viscoelastic materials are considered for the present work to explore the influence on natural frequency, loss factor and frequency response of the sandwich beam. The modeled axial gradation of viscoelastic material has displayed a considerable impact on the peak vibrational amplitude response of the sandwich beam for all the boundary conditions and these configurations improved the damping capabilities at different configurations for the structural applications.

A Novel Method to the Aging Feature Extraction of Viscoelastic Sandwich Structures

The viscoelastic sandwich structure exhibits highly nonlinear dynamic characteristics, and minimal changes in signal caused by aging state alterations, thus posing a challenge for extracting its aging characteristics. A method is proposed for extracting aging features from viscoelastic sandwich structures using variational mode decomposition (VMD) and permutation entropy (PE). First, the original dynamic response signal is decomposed by VMD to acquire several intrinsic mode functions (IMF). Then the permutation entropy characteristics of each IMF are calculated. The research results show that there are obvious differences in the distribution of permutation entropy corresponding to each IMF component, which indicates that the permutation entropy feature extracted based on the variational modal decomposition is more susceptive to the change of the aging state of the structure, thus verifying the availability of this method for feature extraction.

A generalized finite element formulation for nonlinear frequency response analysis of viscoelastic sandwich beams using harmonic balance method

A generalized finite element formulation for nonlinear frequency response analysis of viscoelastic sandwich beams using harmonic balance method

Modified couple stress theory for wave propagation in viscoelastic sandwich microplates with FG-GPLRC core and piezoelectric face sheets as sensor and actuator

In the present investigation, wave propagation of the viscoelastic sandwich microplates with functionally graded graphene nanoplatelets’ reinforced composite (FG-GPLRC) core and piezoelectric face sheets as sensor and actuator has been analyzed by the refined zigzag theory (RZT). Electromagnetic field is exposed to core and piezoelectric layers. Young's modulus, mass density, and Poisson's ratio are calculated based on the modified Halpin–Tsai model and rule of mixtures because FG-GPLs are arranged as uniform, parabolic, and linear patterns along the thickness of core. In addition, viscoelastic properties of the structure are simulated by the Kelvin–Voigt model. The system is located on an orthotropic visco Pasternak medium. The modified couple stress theory (MCST) is applied to simulate the microscale effects of the structure. Hamilton's principle is utilized for deriving the motion equations. Phase velocity, cut-off, and escape frequencies are computed with an analytical solution. The influence of valuable parameters, such as geometrical dimensions of the system, magnetic field, external voltage, small scale parameter, viscoelastic structural damping coefficient, various foundation types, weight fraction, and different distributions of GPLs on phase velocity, will be studied. The results of this study have a significant effect on the design and fabrication of sandwich micro-structures used in various industrial equipment.

Modal performance degradation of naturally aged NBR

Damping is often an invisible requirement for a good mechanical design. To render the long-term service of viscoelastic dampers, it is essential for design engineers to estimate the degradation of the damping characteristics with age. Nitrile butadiene rubber (NBR) is a widely used damping and sealing material. Viscoelastic sandwich beam configurations have been used to mount electronic components for various automobile and aerospace applications. The present work emphasizes the estimation of modal parameter degradation of NBR with age in an oxidative environment. NBR is assumed to be homogeneous and isotropic and is allowed to age naturally with no load under ambient conditions. Fourier-transform infrared spectroscopy (FTIR) was used to detect age-related changes in the functional groups of the NBR material with age. Dynamic mechanical analysis (DMA) tests were performed to relate the complex properties of naturally aged materials to those of virgin materials in the frequency and temperature domains. Mechanical tests were performed to determine the hardness, elongation break, and failure stress of the virgin NBR and naturally aged NBR. The damping ability of the NBR was investigated using an unconstrained sandwich cantilever beam with aluminum as the base material. For sinusoidal sweep excitation, the influence of viscoelasticity on structural damping was investigated. Based on the experimental results, the damping ability of the NBR has been observed to degrade with age. As the age increased, the damping ability of the NBR decreased by 8% at the first resonance frequency and by 34% at the third resonance frequency.

Stability analysis of a spinning soft-core sandwich beam with CNTs reinforced metal matrix nanocomposite skins subjected to residual stress

The stability of a soft-cored spinning viscoelastic sandwich beam and carbon nanotubes (CNTs) reinforced metal matrix nanocomposites (MMNCs) skin subjected to residual stress have been investigated. The metal matrix nanocomposites (MMNCs) skins are symmetrical and isotropic. In addition, these skins reinforced with uniform and functionally graded (FG) distributions of carbon nanotubes (CNTs) are considered. The soft-core of the sandwich beam is deemed to be elastomeric and has internal damping of viscoelastic type. The skin layers of the sandwich beam are subject to residual stresses caused by the production process. Also, the effective material properties of skins are obtained using the rule of mixture (ROM) and Halpin-Tsai (H-T) micromechanics models. First, the governing equations of motion of a spinning viscoelastic sandwich beam are obtained using the Hamilton principle. Then, the sandwich beam's natural frequencies are calculated using the differential quadrature method (DQM). The effects of CNTs distribution, nanotube volume fraction, spinning speed, critical loading, the thickness of the core, axial force, and residual stress on the sandwich beam's natural frequency and stability regions are investigated. According to the results of this study, based on the sandwich beam's different spinning speeds, it is possible to estimate the optimal amount of core thickness to prevent instability, which can be very important in the design of spinning sandwich structures.

Energy absorption and vibration of smart auxetic FG porous curved conical panels resting on the frictional viscoelastic torsional substrate

In recent years, the utilization of various methods to absorb vibration in widely-used structures has gained significant attention to control and reduce the destructive effect of the resonance phenomenon. The increased useful lifetime and reduced maintenance and repair costs are the advantages of vibration absorption. Besides, utilization of energy absorbers is one of the most effective strategies for reducing energy supply costs for different parts of the structure, such as sensors. In this regard, a numerical study is performed in this research to evaluate the energy absorption by vibrations' absorption in a conical three-layered panel located on a viscoelastic substrate. This three-layered panel is composed of three parts: piezoelectric upper layer reinforced with Graphene nanoplatelets (GPLs), auxetic core, and functionally graded material (FGM) porous lower layer. The substrate includes spring element, shear, torsion, and substrate-structure friction factor. Hamilton's principle and energy method have been used to extract the governing equations to model the first-order shear deformation theory (FSDT) for the presented structure. The Differential Cubature Method (DCM) and the Newmark method have been used to solve the governing equations. Results show that by applying the negative voltage to the sandwich conical panel, the in-plane compression forces and natural frequency are increased, while the maximum dynamic deflection is decreased. Furthermore, increasing the inherent damping coefficient increases the damping decrement. Meanwhile, the nonlinear scattering and increased dispersion concentration of GPLs near the upper and lower surfaces of the piezoelectric layer will increase the frequency and energy absorption. Besides, the increased friction factor of the viscoelastic substrate and sandwich cone leads to more absorption energy.

Thermal buckling and free vibration of viscoelastic functionally graded sandwich shells with tunable auxetic honeycomb core

In this paper, thermal buckling and free vibration of viscoelastic functionally graded sandwich shell with tunable auxetic honeycomb core is investigated. The sandwich shell has functionally graded material (FGM) skins at top and bottom and tunable auxetic honeycomb core at the middle. The viscoelastic behavior of the skins and core are modeled according to complex modulus approach in combination with the elastic–viscoelastic correspondence principle. Poisson's ratio of the auxetic honeycomb core is tunable. It has positive or negative value, which depends on an angle parameter of the unit cell of the auxetic honeycomb core. The equations of motion for the viscoelastic FGM sandwich shell with tunable auxetic honeycomb core are derived using Hamilton's principle. Analytical solution for simply supported shell is obtained using Navier's solution procedure. The effects of the geometry parameters, temperature rise, parameters of the tunable auxetic honeycomb core are studied.

Dynamics of viscoelastic material sandwich beam

ABSTRACT In this study, the non-linear dynamics of a horizontal motioned hub-beam system with passive constrained layer damping treatment are presented. The beam is constructed with three layers, viz., the host layer and the constrained layer with isotropic material, and the core layer of viscoelastic material. The system is non-linear due to coupling between the rigid motion of hub and flexible motion of the beam and also due to consideration of the beam curvature effect of bending. The equations of motion are derived using Hamilton’s principle based on expressing the kinetic energy and potential energy of the manipulator system in terms of generalised coordinates. The problem is approached by the finite element method, and the Newmark’s beta time integration scheme is adopted. Numerical simulations show that the viscoelastic material not only reduces the amplitude of elastic deflection but also quickly attenuates the vibration to zero. The results are evaluated for different values of thickness of the constrained layer, viscoelastic layer, payloads, and elastic modulus of each layers. It is observed that the vibration amplitude could be controlled through the use of the passive layer of damping.