The aim of this study was to obtain bandgaps that are much better, that is at lower frequencies and in broader frequency ranges. Novel nonuniform metamaterial beams with periodically variable cross ...sections and inertial amplification mechanisms are designed and investigated by numerical and experimental methods. Flexural vibration equations of the nonuniform metamaterial beams are established, and the enhanced bandgap and vibration reduction properties are achieved by combining Bragg scattering and the inertial amplification mechanisms. Numerical results of the bandgaps for the periodic elastic beams with and without the inertial amplification mechanisms are validated by comparing them with the results of vibration experiments. Effects of the amplification mass and angle on the bandgap properties are investigated. Larger amplification mass and angle lead to much enhanced bandgap performances of the nonuniform metamaterial beams in lower to higher frequency ranges.
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NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
Pre-stresses or axial loadings induced by deformations of adjacent structures, edge constraints or mounting inaccuracies and elastic supporting components attached to one side of the sandwich ...structures may affect the aerothermoelastic stability, which is an important subject in the design of supersonic aircraft. Therefore, the nonlinear flutter and thermal buckling behavior of composite lattice sandwich beams with translational springs under axial loading in supersonic airflow is investigated in this paper. In the structural modeling, the von Kármán large-deflection theory is applied to establish the stain–displacement relations. The aerodynamic pressure is evaluated by the supersonic piston theory. The differential equations of motion are obtained by Hamilton’s principle and the assumed mode method. The highlight of this study is that a new approach for limit cycle oscillation (LCO) suppression and thermal buckling elimination without changing the stiffness of the lattice sandwich structure is proposed by utilizing the axial loading and translational springs. The structural natural frequencies are obtained and compared with reference results in the literature. The influences of the axial loading and the translational springs on the nonlinear supersonic flutter and thermal buckling properties of the sandwich beams are analyzed. Numerical results indicate that the present method is effective for nonlinear flutter suppression, and the thermal buckling effect can be completely eliminated by adjusting the axial loading of the sandwich beams.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A hybrid acoustic metamaterial is proposed as a new class of sound absorber, which exhibits superior broadband low-frequency sound absorption as well as excellent mechanical stiffness/strength. Based ...on the honeycomb-corrugation hybrid core (H-C hybrid core), we introduce perforations on both top facesheet and corrugation, forming perforated honeycomb-corrugation hybrid (PHCH) to gain super broadband low-frequency sound absorption. Applying the theory of micro-perforated panel (MPP), we establish a theoretical method to calculate the sound absorption coefficient of this new kind of metamaterial. Perfect sound absorption is found at just a few hundreds hertz with two-octave 0.5 absorption bandwidth. To verify this model, a finite element model is developed to calculate the absorption coefficient and analyze the viscous-thermal energy dissipation. It is found that viscous energy dissipation at perforation regions dominates the total energy consumed. This new kind of acoustic metamaterials show promising engineering applications, which can serve as multiple functional materials with extraordinary low-frequency sound absorption, excellent stiffness/strength and impact energy absorption.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
As the counterpart of electromagnetic and acoustic metamaterials, elastic metamaterials are artificial periodic elastic composite materials offering the possibility to manipulate elastic wave ...propagation in the subwavelength scale through different mechanisms. For the promising superlensing in the medical ultrasonic detection, double-negative metamaterials possessing the negative effective mass density and elastic modulus simultaneously can be utilized as the ideal superlens for breaking the diffraction limit. In this paper, we present a topology optimization scheme to design the two-dimensional (2D) single-phase anisotropic elastic metamaterials with broadband double-negative effective material properties and demonstrate the superlensing effect at the deep-subwavelength scale. We also discuss the impact of several design parameters adopted in the objective function and constraints on the optimized results. Unlike all previously reported mechanisms, the present optimized structures exhibit the novel quadrupolar or multipolar resonances for the negative effective mass density and negative effective elastic modulus. In addition, negative refraction of the transverse waves in a single-phase material is observed. Most optimized structures in this paper can serve as the anisotropic zero-index metamaterials for the longitudinal or transverse waves at a certain frequency. The cloaking effect is demonstrated for both the longitudinal and transverse waves. Moreover, with the particular constraints in the optimization procedure, a super-anisotropic metamaterial exhibiting the double-negative and hyperbolic dispersions in two principal directions within two different frequency ranges is obtained. The developed optimization scheme provides a robust computational tool for negative-index engineering of elastic metamaterials and may guide the design and optimization of other types of metamaterials, including the electromagnetic and acoustic metamaterials. The unusual properties of our optimized structures can inspire new ideas and novel applications including the low-frequency vibration attenuation, flat lens and ultrasonography for elastic waves.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
An investigation of the generalized dynamic intensity factors (GDIFs) of cracked homogeneous and linear magnetoelectroelastic (MEE) solids using the extended finite element method (X-FEM) is ...presented. Stationary straight and curved cracks in two-dimensional (2D) MEE solids with impermeable electromagnetic crack-face boundary conditions under coupled electro-magneto-mechanical impact loads are investigated. The effects of various aspects including mesh sensitivity; combined dynamic impact loads; time-step size; material polarization directions and interaction cracks on the GDIFs are numerically studied. A dynamic X-FEM computer code, integrated with Newmark time integration scheme and the level set method to accurately capture the crack geometry, is developed. The eight-fold enrichment functions particularly suitable for cracks in MEE materials are adopted to appropriately describe the singular fields at the crack-tips. To assess the dynamic stress, electric displacement and magnetic induction intensity factors accurately and efficiently, domain-form of the integration integral taking the inertial effect into account in conjunction with the asymptotic near crack-tip fields in MEE materials is presented. Several numerical examples are shown to confirm the accuracy of the proposed approach, and the numerical results are thus investigated, compared and discussed in detail.
► Advanced generalized dynamic intensity factors of cracked magnetoelectroelasticity are analyzed. ► Interaction integral taking the inertial effect into account for magnetoelectroelastic is presented. ► Effects of polarizations, loadings, mesh sizes, etc. on dynamic intensity factors are investigated. ► Numerical examples with straight and curved cracks in MEE solids are investigated. ► Numerical results show the effects of the coupled fields on the generalized dynamic intensity factors.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This paper is devoted to investigate the nonlinear vibration characteristics and active control of composite lattice sandwich plates using piezoelectric actuator and sensor. Three types of the ...sandwich plates with pyramidal, tetrahedral and Kagome cores are considered. In the structural modeling, the von Kármán large deflection theory is applied to establish the strain–displacement relations. The nonlinear equations of motion of the structures are derived by Hamilton’s principle with the assumed mode method. The nonlinear free and forced vibration responses of the lattice sandwich plates are calculated. The velocity feedback control (VFC) and
H
∞
control methods are applied to design the controller. The nonlinear vibration responses of the sandwich plates with pyramidal, tetrahedral and Kagome cores are compared. The influences of the ply angle of the laminated face sheets, the thicknesses of the lattice core and face sheets and the excitation amplitude on the nonlinear vibration behaviors of the sandwich plates are investigated. The correctness of the
H
∞
control algorithm is verified by comparing with the experiment results reported in the literature. The controlled nonlinear vibration response of the sandwich plate is computed and compared with that of the uncontrolled structural system. Numerical results indicate that the VFC and
H
∞
control methods can effectively suppress the large amplitude vibration of the composite lattice sandwich plates.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
► A dynamic X-FEM model is developed for stationary dynamic cracks in piezoelectricity. ► Interaction integral taking the inertial effect into account for piezoelectric materials is presented. ► ...Generalized dynamic intensity factors are extracted and investigated in details. ► Effects of polarizations, loads, mesh sizes, time-steps, etc. on dynamic intensity factors are investigated.
This work presents a transient dynamic analysis of stationary cracks in two-dimensional, homogeneous and linear piezoelectric solids subjected to coupled electromechanical impact loads using the extended finite element method (X-FEM). To serve this purpose, a dynamic X-FEM computer code using quadrilateral elements in conjunction with the level set method to accurately describe the crack geometry is developed. The sixfold basis enrichment functions particularly suitable for cracks in piezoelectric materials are adopted to fully capture the singular fields at the crack-tips in piezoelectricity. The governing equations are transformed into a weak-form and the time-dependent system of discrete equations is then obtained, which is solved by the unconditionally implicit time integration method at each time-step. To accurately assess the relevant dynamic mechanical stress and electric displacement intensity factors precisely and efficiently, domain-form of the contour integration integral taking the inertial effect into account in conjunction with the asymptotic near crack-tip fields of piezoelectric materials is presented. Four numerical examples for stationary cracks in homogeneous piezoelectric solids with impermeable crack-face boundary condition under impact loads are considered, respectively. Validation of the present method is made by comparing the present results with reference solutions available in the literature, and very good agreements are obtained. The effects of different poling directions and combined electromechanical impact loads are analyzed in details.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A novel active elastic metamaterial plate is proposed, with tunable vibration band-gap characteristics is by using the periodically placed piezoelectric actuator and sensor pairs along one direction ...of the plate. Active control strategies are employed to actively adjust the band-gap properties of the metamaterial plate. Displacement and acceleration feedback control methods are applied to design the controllers so that the positive active stiffness and inertia for the elastic metamaterial plate can be provided. The dynamic responses of the finite plate with periodic piezoelectric actuator/sensor pairs are calculated using the spectral element method (SEM), and the calculation accuracy of the SEM is validated by the finite element method. The present results reveal that zero-frequency band gaps can be generated for the elastic metamaterial plate, and the band-gap characteristics in the medium and high frequency ranges can be significantly enhanced by using the acceleration feedback control. Moreover, very wide band gaps for the elastic metamaterial plate can be obtained by using the active acceleration control, and the starting frequencies of the first band gap under the acceleration control can be reduced by increasing the acceleration control gain. The widths of the zero-frequency and Bragg-type band gaps for the elastic metamaterial plate can be amplified by increasing the displacement feedback control gain. The control voltages to be applied on the actuators for the elastic metamaterial plate are also calculated and discussed.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This paper investigates the axisymmetric thermoelastic contact of a functionally graded material (FGM) coated half-space. A rigid insulated punch rotates on the surface of the FGM coating with a ...constant angular velocity. The frictional heating is generated within the contact region. The thermoelastic properties of the coating vary exponentially along the thickness direction. By using the Hankel integral transform, the problem is reduced to Cauchy singular integral equations, which are solved numerically to obtain the normal contact stress, radial stress and surface temperature. The effects of the friction coefficient, angular velocity, gradient index, coating thickness and punch geometry on the surface thermoelastic contact characteristics are investigated and discussed in detail.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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