Study On The Thermal Stress Of Composite Thermal Protection Structure Along The Trajectory Environment

The structure surface is under strong influence of aerodynamic heating when hypersonic aerocraft flies in aerosphere. Thermal protection and thermal expansion are very important to the design of a flight vehicle. Great progress in thermal protection system (TPS) has been made in the past decades to make vehicle flies higher and faster within the allowed range of surface and structure temperature. Many research studies have been carried out to improve the structures and materials in order to improve the performance of aerocraft. Advanced composite materials have some merits, such as high stiffness ratio, high intension ratio, high fatigue resistance, high damp and low thermal expansion, get the extensive applications in aeronautical and space technologies. SR-71"Black Bird"uses a large number of titanium alloy and Wrinkled coating. Newly-developed thermal protective materials are all belong to composite. But the temperature of the composite materials is not well-distributed in working time. The thermal stress problem is severe. If the design of a flight vehicle structure does not consider thermal stress, the thermal stress and thermal distortion may be very high, even the structure may lose its potency.Many research studies have been carried out on normal composite materials. And the research on thermal response of composite material is quite important for the space engineering. Therefore, the thermal response characteristics of composite materials used in heat shield of spacecraft subjected to aerothermal heating need to be investigated thoroughly. In order to understand the regularities of thermal stress distribution, the finite element method, FEM, program is established. The regularities of thermal stress distribution in monolayer and multi-layer structures are studied in this thesis, and the optimization method is discussed based on the results of present studies. This thesis is divided into five chapters as follows:The first chapter is the introduction, in which the background of this paper is reviewed briefly. The relevant research is narrated. And the idea of this thesis is also described in this paper.In the second chapter, the basic FEM formulas about thermal stress are presented. Tetrahedral element, hexahedron element and their interpolating function are described. And the isoparametric elements and their transforming are introduced.In the third chapter, the program using hexahedral structure grid and isoparametric elements method is described in detail based on the FEM formulas. The results of examples are verified with the commercial software ABAQUS, that provides a guarantee to the thermal stress study for the head cap structure of a hypersonic vehicle.The fourth chapter discusses the thermal stresses of monolayer and multi-layer thermal protection structures. The thermal environment and temperature field get from the condition of simulation trajectory. The results show that the thermal stress distribution is under the influence of temperature field. At the same time, the material characteristics make great influence to the multi-layer structure. All the factors need to be considered in study.In chapter five, the optimization about the characteristic of structure materials is investigated based on the regularities of thermal stress distribution. The study emphasis the alteration of material axes. The results show that the optimization is feasible. The optimization method developed will make the structure of flight vehicle more reasonable and high efficiency.The final part is the brief conclusion of this thesis. Our work about thermal stress on nose-cone structure is discussed, and some research work that should be done in future is proposed.