Abstract
The vibroacoustic bending properties of honeycomb sandwich panels with composite faces are studied from the wavenumber modulus to the mechanical impedance, passing through the modal density. Numerical results extracted from finite element software computations are compared with analytical results. In both cases, the homogenization method is used to calculate the global properties of the sandwich panel. Since faces are made of composite material, the classical laminate theory serves as reference. With particular conditions used in the application for symmetric panels, the original orthotropic mechanical properties can be reduced simply to three parameters commonly used in vibroacoustic characterizations. These three parameters are the mass per unit area, the bending rigidity and the out-of-plane shear rigidity. They simultaneously govern the wavenumber modulus, the modal frequencies, the modal density and the mechanical impedance. For all of these vibroacoustic characterizations, a special frequency called the transition frequency separates two domains. In the first domain, below the transition frequency or for low frequencies, the orthotropic sandwich panel has a classical isotropic plate behavior. In the second domain, above the transition frequency or for high frequencies, the out-of-plane shear rigidity is very significant and changes the behavior.However, the results discussed are only valid up to a certain frequency which is determined by the thickness and out-of-plane shear stiffness of the honeycomb core, the thickness and the bending stiffness of the laminated face sheets and then the mass per unit area and bending stiffness of the total sandwich structure. All these parameters influence the final choice of model and simplifications presented.Experimental measurements of the bending wavenumber modulus and modal frequencies for our own application were carried out. In the vibroacoustic domain, the critical frequency is also an important frequency. It again depends on the mass per unit area, the bending rigidity and the out-of-plane shear rigidity. The experimental and numerical results of the article are reasonably in agreement with the analytical formula. They all confirm the changes in frequency through different boundary conditions around the panel.The analytical modal frequencies of rectangular sandwich panels with transverse shear, under simply supported boundary conditions are well known, but under free boundary conditions it is more difficult to predict them. For experiments, however, these latter conditions are the most common. We present, in this paper, an analytical formula that we have developed for the modal frequencies of such a panel under free boundary conditions. All parameters being controlled, it is possible from dynamic measurements and with a special process to identify some honeycomb and composite mechanical properties.
Highlights
Sandwich panels are being increasingly used for various industrial applications
The wavenumber modulus is compared to the experimental and analytical results obtained from a set of rectangular sandwich panels tested in various research projects, and validated with numerical computations performed using a finite element model and several different boundary conditions applied around the plates
The reference transverse shear stiffness S being homogenized on the multilayer, it is analytically expressed with hS and the two equivalent transverse shear moduli: S 1⁄4 hSÀGxzeq U GyzeqÁ1=2: (13)
Summary
Sandwich panels are being increasingly used for various industrial applications. They are composed of a relatively soft and thick core made of honeycomb or foam, or both together, lying between two face sheets, which can either be made of an isotropic material or be a stack of laminated composite plies. The wavenumber modulus is compared to the experimental and analytical results obtained from a set of rectangular sandwich panels tested in various research projects, and validated with numerical computations performed using a finite element model and several different boundary conditions applied around the plates. Blevins coefficients [7], or Warburton coefficients [14] and a particular factor varying with the boundary conditions, called correction factor of transverse shear All of these extensions are applied to our case studied: rectangular symmetric honeycomb sandwich plates with composite faces. This new work is complementary to the developments by Yu and Cleghorn [9] by the extension of their application of a honeycomb sandwich with isotropic face sheets to composite face sheets
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