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In this paper, the influence of carbon nanotubes on vibrational properties of laminated composite plates is studied theoretically and experimentally. The plates are made of glass/epoxy composite. Multi walled and single walled carbon nanotubes in different weight percentages are added to these composites. At first, carbon nanotubes are dispersed in the epoxy resin via ultrasonic procedure. Then the composite plates are made by hand layup and vacuum bagging methods in a mould manufactured for this research. Mechanical properties of the fiber composite reinforced by carbon nanotubes calculated using modified Halphin-Tsai equations. Next composite plates are modeled in ABAQUS software and frequency analysis is done. Also vibrational properties of structure are obtained by experimental modal analysis in fixed boundary condition. Experimental results showed 210% increase in damping for samples which have 0.5 weight percent of single walled carbon nanotubes (in comparison with plane glass/epoxy composite plates). Also a good agreement was observed between obtained natural frequencies from finite element analyses and experimental tests.

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In this paper, the sound behavior of a double walled composite with an intermediate porous layer has been conducted using the classical laminated plate theory (CLPT). The main objective of the paper is devoted to considering the analytical study of various boundaries on porous layers as well as parameter study on power transmission through the structure. Thus, viscous and inertia coupling in a dynamic equation, as well as stress transfer, thermal and elastic coupling of porous material are considered based on Biot theory. In addition, the equation of wave propagation are extracted according to vibration equation of composite layers. Then, with applying the various boundaries on the structures along with solving these equations simultaneously, the Transmission Loss (TL) is calculated. The analytical results are compared with both numerical ones obtained from Statistical energy Analysis (SEA) as well as empirical results and an excellent agreement is observed. The parametric studies are presented to investigate the effects of boundary conditions on TL. The results indicate that the interface of porous-composite layers as well as stacking sequences of the composite layers would play an important role in reduction of power transmission through the structure.