A Research On Vibro-acoustic Properties Of Sandwich Panels With Foam And Honeycomb Cores

Significantly improving the sound insulation performance of the vehicle body without increasing its weight is an important issue in the design of high-speed rail vehicles.Sandwich panels with foam and honeycomb cores have excellent properties of light weight,high static stiffness,and are widely used in the bodies of transportation tools such as aerospace and high-speed trains.However,the sound transmission loss(TL)of this type of lightweight structure is usually very poor.In this paper,the TL of sandwich panels with foam and honeycomb cores under the excitation of the diffuse sound field is systematically investigated with the application background of vibration noise control of high-speed train car body.An efficient method for calculating the TL of sandwich panels based on the prediction of apparent bending stiffness of beams is proposed in this paper.Based on this,the influence law of parameters of sandwich panels with excellent static performance and broadband high sound insulation performance is revealed,and a design criterion and implementation method based on the apparent bending stiffness are given,which solves the problem of lack of key parameters in the acoustic design of complex sandwich panels.In addition,a method for determining the complex shear modulus of the viscoelastic core layer is proposed.The main research contents and innovation points of this paper are as follows.(1)A method for calculating the TL of sandwich panels based on the prediction of apparent bending stiffness of beams is proposed.That is,the apparent bending stiffness of the corresponding sandwich panel is calculated by the analysis of the natural frequencies of the sandwich beam by the finite element method.With the obtained apparent bending stiffness,the vibration of a sandwich plate can be described by a simplified fourth-order governing equation,and subsequently,the TL can be easily calculated by the modal superposition method.Compared with existing commercial software,this method has the advantages of clear physical concepts,high computational accuracy,and faster computational speed.The sandwich panels can be multi-layered,the thickness and material of the face sheets can be different,and the boundary conditions can also be different.The influences of core shear modulus on the TL and coincidence region are investigated.The relationship between the weighted sound reduction index and the shear modulus is illustrated,which provides important theoretical guidance for the design of sandwich panels with excellent acoustic properties.(2)The concept and calculation method of critical apparent bending stiffness are proposed.The critical apparent bending stiffness is defined as the apparent bending stiffness when the TL of a sandwich panel reaches the mass law,which is used as the design criterion for sandwich panels with high sound insulation performance.Based on the obtained critical apparent bending stiffness,it can directly guide the design of complex sandwich structures with ‘high static and low dynamic’ characteristics,to achieve broadband high sound insulation performance while having sufficient loadbearing stiffness.Theoretical and experimental results show that the introduced low specific modulus viscoelastic layer reduces the dynamic bending stiffness of the sandwich panel while maintaining high static bending stiffness,which significantly improves the broadband sound insulation performance of the sandwich panel and achieves the mass law of homogeneous panels in a wide range of frequencies.(3)An analytical method to calculate the dynamic bending stiffness and TL of sandwich panels with perforated honeycomb structure cores is proposed,and the static bending stiffness and compressive stiffness of these structures are analyzed based on the finite element method.The effects of honeycomb shape,shape and number of perforations,and wall thickness on the vibroacoustic and mechanical properties of sandwich panels were investigated.In addition,based on space harmonic expansion and modal expansion method,a calculation method for predicting the TL of one-way stiffened sandwich panels is proposed.The influences of key parameters such as the shear modulus of the core,loss factor of stiffened sandwich panel,and the space between stiffeners on the TL of stiffened sandwich panel are analyzed.This study provides a feasible calculation idea for predicting the TL of stiffened sandwich panels.(4)An estimation of the frequency-dependent complex shear modulus of the viscoelastic core material is presented by fitting the analytical solution of the beam transfer function of a constrained viscoelastic material layer under free-free boundary conditions to the measured results using a genetic algorithm.By varying the length of the constrained beam,it is possible to characterize the complex parameters of the viscoelastic material over a wide range of frequency.Finally,the frequency-dependent complex shear modulus of the characterized viscoelastic layer is introduced into the finite element model to calculate the complex natural frequency of the sandwich beam,and the comparison between the calculated and measured results shows that the error is within 2.33% for the real part and within 3.31% for the imaginary part.This study provides the necessary technical support for the research of improving the acoustic vibration characteristics of sandwich panels by introducing viscoelastic materials.