Thermal vibration characteristics of fiber-reinforced mullite sandwich structure with ceramic foams core

This paper researched a sandwich structure composed of fiber-reinforced mullite matrix composite face sheets and ceramic foams elastic layer subjected to high temperature and large gradient thermal environment. The vibration characteristics of the hybrid structure with free-free boundary condition were investigated in room and high temperature thermal environment by both experimental means and finite element method (FEM). Finite element models were established to estimate the vibration characteristics of the hybrid sandwich structure. Modal tests by hammer impulse method and exciter were carried out in room temperature environment to get the natural frequencies and corresponding modal shapes and damping loss factors. Then the exciter experiment was performed with the same setups as room temperature test to get the temp-varying vibration characteristics under high temperature thermal loads. The numerical simulation results agree well with the experimental results. The natural frequencies and damping loss factors of the hybrid sandwich structure show steady state with the temperature increased up to 800 °C and so large gradient. Correspondently, the structural stiffnesses and damping characteristics of such composite structures keep excellent performance in thermal environment.