飞行器超音速飞行时产生的气动加热会使飞行器材料及其结构产生热变形，且飞行器材料的强度和承载能力也会有明显的衰减，这些都将影响热防护结构的完整性和可靠性，从而影响飞行器的气动外形和安全飞行。本项目针对飞行器大面积防热用聚合物基复合材料的热变形及高温力学性能衰减规律开展研究。首先通过组分材料高温响应机理研究，阐述基体材料的热分解特性、热软化过程和纤维材料的高温相变特性。然后考虑温度/扩散/变形之间的耦合作用，建立高温变形的多场耦合模型，并利用非接触式高温变形测量实验验证模型的正确性。最后根据等效夹杂理论和多孔介质弹性力学，提出考虑孔隙压力影响的高温弹性模量预报方法，基于不同温度和加热时间下材料响应机理和破坏机理，建立高温强度模型。课题最终建立一套高温环境下聚合物基防热复合材料热/力学行为的表征方法，为该类型热防护材料及其结构的安全设计和可靠性评价奠定基础。

Aerodynamic heating can cause thermal deformation of the thermal protective materials and its structures, as well as the strength and loading capacity of the vehicle material significantly degrade when the spacecraft is flying at supersonic. This adversely affects the integrity and reliability of thermal protection structures, and thus influences the aerodynamic shape and flight safety of spacecraft. The thermal deformation and degradation in high-temperature mechanical properties of the polymer composites which widely applied in the large-area thermal protection structures of spacecraft were studied in this project. The response mechanisms of component materials under high-temperatures were investigated, firstly. The thermal decomposition behavior, thermal softening effect of matrix materials and phase transition process of fiber materials were determined. And then a multi-physics field coupling analysis model was proposed to predict the high deformation of polymer composites under high temperatures. The coupling actions of temperature, diffusion and deformation were taken into account in the model. The accuracy of the model was evaluated using the non-contact high temperature deformation experiment. Moreover, according to equivalent inclusion theory and elastic mechanics of porous materials, the prediction method of the high-temperature stiffness property which considering the effect of pore pressure on volume modulus was developed. Based on the response and failure mechanisms of materials under different temperatures and heating times, the high-temperature strength model was proposed. The evaluation methods of the thermo-mechanical behavior of polymer composites under high temperatures were established, finally. And this is significant for the structure design, evaluation of integrity and reliability of the thermal protection structures for this kind of composite.