Study On Dynamical And Acoustic Characteristics Of Sandwich Composite Structures

Modern composite with the characteristics of large rigidity, high strength, low mass and excellent fatigue and heat resistance has been widely used in space shuttle, vehicle, buildings, mechanical design and manufacture industry in recent years.Sandwich structure first appeared since 1940s and it was widely used after the Second World War. Sandwich structure is a special kind of composite structure mainly made by multilayer panel with single or multiple sandwich core structure. Due to its light weigh, large stiffness, and efficient heat dissipation properties, usually it is used in ships, cars, and the shell structure of the space shuttle. Consequently, the vibration and sound transmission characteristics become a research hotspot. The development and application of composite and the sandwich structure promotes the shipping industry.Based on the classical laminated plate theory and the first-order shear deformation theory, the stiffness matrix, vibration control equations and the natural frequencies of the four-edge simply supported composite laminated plate with special layers were deduced. The relationship between laminated plate length ratio and natural frequency of the structure in any angle was explored as well. The four node quadrilateral element of the laminated plate was deduced based on the first-order shear laminated plate theory. The static and modal analysis were conducted by using four node quadrilateral finite element algorithm compiled in FORTRAN. Besides, the dynamic response characteristics of laminated plates under different excitation frequency were analyzed.In the last chapter, the influences of structure parameters on the sound transmission characteristics of the sandwich cavity structure were analyzed. It is assumed that the upper and lower panels of the structure are identical in structure and sound transmission characteristics. Then the sound transmission model for homogenous plate with air cavity structure was constructed. The sound transmission coefficient expression of the sandwich plate under four-edge simply supported boundary condition with an (?,?) angle incident plane harmonic wave was derived. The effect of acoustic elevation angle and panel thickness on sound transmission characteristics results were studied by using MATLAB algorithms. In addition, a simplified sound transmission model for homogenous plate with air cavity structure under four-edge simply supported boundary condition was constructed by assuming that the cross-ply panels on the top and bottom of the structure were identical. The effect of acoustic elevation angle, panel thickness and the number of layers on sound transmission characteristics results were analyzed by using MATLAB as well. The results show that the structure has better insulation capacity with smaller acoustic elevation angle. The sound transmission loss increases 20 dB with the panel thickness increase twice under low frequency incident sound waves. The number of layers improves the structure insulation capacity with same stack sequence and panel thickness.