超高温陶瓷复合材料动态本构模型及破坏机理研究

In order to ensure the safety and reliability, the spacecraft requires materials to possess good shock resistance under drastic dynamic loads causing by extreme environments of high temperature and high speed. The researches on dynamic mechanical behavior and fracture mechanisms of ultra high temperature ceramic composites which widely used in the thermal protection materials of spacecraft were developed in this study. The effects of strain rate on mechanical properties were declared to obtain strain rate reinforcement factors using the experimental measure, firstly. And then on the basis of microstructure and fracture modes under different strain rates, dynamic fracture mechanisms were revealed to further present the dynamic criteria for crack propagation. Moreover, the damage evolution equation was provided taking into account the relationship between macroscopic damage variable and damage mechanisms. The dynamic constitutive model was established finally, which can be applied to predict dynamic failure strength and damage tolerance of ultra high temperature ceramic composites by the finite element method. It is believed that this study can lay the foundation for shock resistance evaluation and reliability analysis of ultra high temperature ceramic composites and their structures.

高温高速的极端使用环境使飞行器结构承受急剧的强动荷载，这就要求飞行器材料具有良好的抗冲击能力来保障结构的安全可靠。本项目针对飞行器防热用超高温陶瓷复合材料的动态力学行为及破坏机理开展研究。首先通过动态力学性能测试，阐明应变率对材料力学性能的影响规律，获得应变率强化因子。然后考虑材料微结构与不同应变率下材料破坏模式，揭示动态破坏机理，建立率相关的裂纹扩展破坏准则。最后结合宏观损伤变量与损伤机制的关系，提出损伤演化方程，建立率相关的动态本构模型，实现超高温陶瓷复合材料动态失效强度与损伤容限的有限元预报，为该类材料及其结构的抗冲击性能评价与可靠性分析奠定基础。

高温高速的极端使用环境使飞行器结构承受急剧的强动荷载，这就要求飞行器材料具有良好的抗冲击能力来保障结构的安全可靠。本项目针对飞行器防热用ZrB2-SiC超高温陶瓷复合材料的动态力学行为及破坏机理展开研究。首先开展了ZrB2-SiC材料的动态力学性能测试，包括动态劈拉、压缩与断裂韧性，阐明了应变率或加载速率对该材料力学性能的影响规律，获得了率强化因子。试验结果表明ZrB2-SiC材料的动态劈拉强度、动态压缩强度与动态断裂韧性具有明显的率效应，随着应变率或加载速率的增加，强度与断裂韧性近似呈线性增长；另外，通过材料微结构与材料动态破坏模式分析，揭示了应变率或加载速率对动态破坏机理的影响，加载速率越大，试件破坏后的碎片尺寸越小，碎片数量越多；并以强度为指标，建立了率相关的动态强度失效准则；并将动态强度失效准则引入到JH-2动态本构模型中，建立了改进的率相关的动态本构模型，结合损伤演化方程，实现了超高温陶瓷复合材料动态失效强度与破坏过程的有限元预报，结果表明本项目建立的动态本构模型可以较好地预报ZrB2-SiC超高温陶瓷复合材料动态力学行为，动态劈拉与动态压缩的数值预报结果与试验结果吻合较好，可以应用该模型预报更高应变率下该类材料及其结构的动态力学行为，为强动荷载作用下该类材料的抗冲击性能评价与可靠性分析奠定了基础。