In this paper dynamic damping properties of a nominated flexible Structural adhesive have been identified using an extended-direct modal based joint identification method. It has been revealed that damping characteristics of adhesive are correlated to both frequency and mode shape. Young’s and shear moduli increase with frequency but damping on the other hand, decrease. The results showed that mode shape has an important role on the dynamic mechanical properties of adhesive. Modes that dominantly create normal stress on the adhesion surface represent higher stiffness and lower loss factor compared to shear modes. The different level of loss factors between bending modes and shear modes are notable, but damping property of bending modes and shear modes on the other hand, is in the same order and decreases with frequency. It has been shown that the effective, viscoelastic, mechanical properties of the adhesive can be identified successfully, using the suggested method of identification.

This paper investigates the effect of Structural damping on the chaotic behavior of nonlinear panels in supersonic flow. The nonlinear governing equations, based on Von Karman’s large deflection of isotropic flat plates, are considered with Structural damping. A first order piston theory is utilized for aerodynamic panel loadings. The governing equation includes the effect of constant axial loading in the panel middle surface plus a static pressure differential. The Galerkin approach is used to transform the nonlinear governing equations into a set of nonlinear ordinary differential equations. The resulting system of equations is solved through a numerical integration scheme. Static and dynamic bifurcation boundaries as well as panel limit cycles are determined for various Structural damping coefficients. Chaotic analysis is performed using several criteria, results indicate that Structural damping highly influences the panel stability boundary and limit cycle amplitude as well as the domain of the chaotic region.

In this study, strongly nonlinear free vibration behavior of a microbeam considering the Structural damping effect is investigated analytically on the basis of modified couple stress theory. Employing Von Karman’s strain-displacement relations and implementing the Galerkin method, the governing nonlinear partial differential equation is reduced to a nonlinear ordinary differential equation which is related to the size effect of the beam. Because of large coefficient of nonlinear term and due to existence of the damping effect, none of the traditional perturbation methods leads to a valid solution. Also, there are many difficulties encountered in applying homotopy techniques when the damping effect is taken in to account in the strongly nonlinear damped system. To overcome these limitations, here, a new analytical method is presented which is based on classical perturbation methods and fundamentals of Fourier expansion with an embedding nondimensional parameter. To solve the equation, the nonlinear frequency is assumed to be time dependent. The comparison between time responses of the system obtained by the presented approach and numerical method indicates the high accuracy of the new method. To validate the results of the presented method with those available in the literatures which are obtained for a special case of an undamped system, the damping coefficient is set to zero. The comparison shows a good agreement between the results for a wide range of vibration amplitudes.

The main objective of this study is to modify the blend formulation of a Chlorobutyl rubber compound to improve its damping properties for Structural applications. A new rubber composite was created by adding Acrylonitrile Butadiene Rubber (NBR) and Chlorinated Polyethylene (CPE) to Chlorobutyl rubber. The viscoelastic parameters of the cured original CIIR (control sample) and modified CIIR (i.e., CIIR/NBR/CPE) compounds were determined by Dynamic Mechanical Thermal Analysis (DMTA) in tension mode. Subsequently, cyclic shear tests were performed at room temperature and loading frequencies of 0.5, 0.75, 1 and 3 Hz on prototype viscoelastic damper devices fabricated from the rubber blends. The shear force-deformation hysteresis loops of the prototype dampers at shear strains of 0.5, 1.0 and 1.5 revealed that the viscoelastic properties (i.e., shear storage and loss moduli as well as loss factor) of the modified CIIR significantly improved as compared to the original CIIR. The test results demonstrated an increase exceeding 100% and 160% in the shear storage and loss moduli, respectively, of the modified CIIR compared to the reference CIIR.

This paper discusses static and dynamic response of nanoplate resting on an orthotropic visco-Pasternak foundation based on Eringen’ s nonlocal theory. Graphene sheet modeled as nanoplate which is assumed to be orthotropic and viscoelastic. By considering the Mindlin plate theory and viscoelastic Kelvin-Voigt model, equations of motion are derived using Hamilton’ s principle which are then solved analytically by means of Fourier series-Laplace transform method. The parametric study is thoroughly accomplished, concentrating on the influences of size effect, elastic foundation type, Structural damping, orthotropy directions and damping coefficient of the foundation, modulus ratio, length to thickness ratio and aspect ratio. Results depict that the Structural and foundation damping coefficients are effective parameters on the dynamic response, particularly for large damping coefficients, where response of nanoplate is damped rapidly.