Thermal Vibration Analysis And Model Updating Of Ceramic Matrix Thermal Protection/insulation Structure

Vibration characteristics of a sandwich structure and a thermal protection system(TPS) composite structure subjected to high temperature and large gradient thermal environment were studied in this paper. The sandwich structure was composed of fiber-reinforced mullite matrix composite face sheets and ceramic foams elastic layer. The TPS composite panel was composed of the ceramic composite sandwich and a metal plate. The natural frequency and damping property of this kind of structures are studied in high temperature and large gradient thermal environment in order to comprehend the mechanism of the natural vibration characteristics influenced by the thermal environment. The target is to get an effectual estimation method of natural vibration characteristics in thermal environment to save the experimental expenses of the corresponding problems. The experimental methods and numerical simulating tools are employed to research the thermal protection/insulation integrated composite structure. The main works are listed below:The vibration experiments of the thermal protection/insulation integrated composite structure were implemented in the thermal environment to get the thermal vibration characteristics. The high temperature and large gradient environment was carried out to simulate the actual flight condition. And the natural frequency impact by the thermal environment was obtained. Different boundary conditions were set up to the experiments because the thermal stress is sensitive to the boundary condition. The situation and the mechanism of the natural frequencies influenced by the thermal environment were given out respectively in the conditions of free boundary and fixed boundary.The damping measurement experiments of composite panels composed of a ceramic composite sandwich and a metal plate were implemented in the thermal environment to get the thermal damping property. Owing to the large discreteness of damping measurements, all the experimental conditions were kept the same and repeated experiments were carried out in order to eliminate the damping measurement error caused by uncertainties.The mechanism of the natural frequencies influenced by the thermal environment was studied according to the experimental results and the theory of thermal structures. The natural frequencies of the TPS composite panels impacted by the thermal environment under different boundary conditions were obtained and the impact on the natural frequencies of the thermal stress was analysis. Finite element method(FEM) models of the TPS composite panels were constructed. Reasonable vibration characteristics were obtained by the modal analysis of the FEM model, which will be the basic of the simulating of complex structures.The impact of the thermal environment on the panel modal damping ratios was investigated by vibratory experiments.63 sets of thermal vibration experiments were carried out. A high temperature modal damping estimation empirical formula for this kind of composite plates under one side heating thermal load is proposed. The empirical formula is verified by the experimental results. Application conditions are discussed. The empirical formula has a wide application condition. Then the modal damping ratios in high temperature environments are estimated by the empirical formula using the finite element method(FEM) results of natural frequencies in the same thermal environment. From the error relevant to the experimental results, it is determined that the modal damping ratios in high temperature environments can be estimated by the proposed empirical formula using the FEM results.The model updating research was implemented for the FEM of the researched panel structures. Firstly, the model updating of the FEM model in the room temperature environment was carried out. And then on this basis, the model updating method for the thermal vibration simulating was investigated. An updating method of the additional stiffness matrix caused by thermal stresses, which are sensitive to the boundary conditions. This model updating method is based on the experimental data and optimization algorithms.Finally, the dynamic responses of the TPS panels were calculated in the high temperature thermal environment. The steady-state dynamic response analysis of the TPS panels in the steady thermal environment was carried out first. The simulating results were validated by experiments. Then the transient dynamic response analysis of the TPS panels in the steady thermal environment was implemented and also validated by experiments. The stiffness change caused by the material property change with temperature elevated and the thermal stress inside the structure were considered in the dynamic analysis process. The damping matrix was constructed by the measured modal damping ratios in the experiments and the estimation results by the empirical formula.In conclusion, the vibration characteristics of ceramic matrix TPS panel were studied by experimental and simulative method, natural frequencies and damping property included. A set of convenient and reliable thermal vibration experimental procedures are constructed. The mechanism of thrmal environments influencing the vibration characteristics was announced. Emperical formulas of damping estimation in thermal environment are proposed. And a dynamic FE model optimization method of which the modificating variables were the additional stiffness caused by thermal stresses are proposed for this kind of TPS panel subjected to high temperature thermal environment.