陶瓷材料因其在高温下具有稳定的化学和力学性能，被广泛应用在航空航天的高温构件中。但是，由于陶瓷材料固有的脆性，当环境温度急剧升高或降低（热震）时容易在结构内部或表面产生裂纹，降低结构的性能，还可能导致结构直接失效而造成巨大的损失，严重制约了陶瓷材料在高温领域的应用。

另外，陶瓷材料在制备和加工过程中或多或少地会产生一些缺陷（微气孔、微裂纹等），热震过程中缺陷处因应力集中而容易产生裂纹扩展，进而影响材料的抗热震性能和使用寿命。因此，研究缺陷对陶瓷材料热震裂纹萌生和扩展的影响对提高其抗热震性能具有重要的科学意义。本文通过实验和数值模拟研究了预制裂纹氧化铝陶瓷在火焰热冲击下的裂纹扩展过程，分析了预制裂纹的角度和位置对裂纹形貌和裂纹扩展速度的影响。

实验上，实现了火焰热冲击下含不同角度和位置预制裂纹氧化铝陶瓷裂纹扩展过程的实时观测。实验结果表明，不同角度和位置预制裂纹的两个尖端都出现了翼形裂纹，裂纹快速扩展并最终贯穿试样，试样的完全破坏是一个高速过程；预制裂纹尖端的裂纹扩展速度开始很快，然后逐渐减慢。另外，随着预制裂纹角度的增加，近火焰裂纹尖端和远火焰裂纹尖端的最大扩展速度都呈现出增加的趋势；近火焰裂纹尖端的最大扩展速度随着预制裂纹到加热表面的距离增加而增加，而远火焰裂纹尖端则观察到相反的趋势。大部分实验结果表明，近火焰裂纹尖端在火焰热冲击下会率先扩展，然后远火焰裂纹尖端才开始扩展。

本文基于动态断裂力学建立了火焰热冲击过程的数值模型，以期重现热冲击下裂纹扩展的过程。通过部分实验和数值模拟相结合的方式，确定了100m/s~2600m/s范围内临界动态应力强度因子与裂纹扩展速度的关系。将该关系用于模拟其它实验的裂纹扩展过程，最终模拟的结果与实际观察的结果一致。数值模型可以如实地再现含预制裂纹氧化铝陶瓷在火焰热冲击下的裂纹演化过程。

Ceramic materials are widely used in high-temperature components of aerospace because of their stable chemical and mechanical properties at high temperatures. However, due to the inherent brittleness of ceramic materials, when the ambient temperature sharply increases or decreases (thermal shock), it is easy to produce cracks in the interior or surface of the structure, reducing the performance of the structure, and may also lead to direct failure of the structure and cause huge losses, which seriously restricts the application of ceramic materials in high-temperature fields.

In addition, some defects (micro-pores, micro-cracks, etc.) will occur more or less during the preparation and processing of ceramic materials. During the thermal shock process, the defects are prone to crack propagation due to stress concentration, which will affect the thermal shock resistance and service life of the material.

Therefore, it is of great scientific significance to study the effect of defects on the initiation and propagation of thermal shock cracks in ceramic materials to improve their thermal shock resistance. In this paper, the crack propagation process of prefabricated crack alumina ceramics under flame thermal shock was studied through experiments and numerical simulations, and the effects of prefabricated crack angle and position on the crack morphology and crack propagation speed were analyzed.

Experimentally, real-time observation of crack propagation process of alumina ceramics with prefabricated cracks at different angles and positions under flame thermal shock was realized. The experimental results show that wing cracks are generated from both tips of prefabricated cracks with different angles and positions. The cracks propagation rapidly and finally penetrates the specimen. The complete failure of the specimen is a high-speed process; The crack propagation speed at the prefabricated crack tip begins fast and then gradually slows down. In addition, with the increase of prefabricated crack angle, the maximum propagation speed of near flame crack tip and far flame crack tip shows an increasing trend; The maximum propagation speed at the near flame crack tip increases with the increase of the distance from the prefabricated crack to the heating surface, while the opposite trend is observed at the far flame crack tip. Most of the experimental results show that the near flame crack tip will propagates first under flame thermal shock, and then the far flame crack tip will begin to propagate.

Based on the of dynamic fracture mechanics, a numerical model of flame thermal shock process is established to reproduce the process of thermal shock crack propagation. The relationship between the critical dynamic stress intensity factor and crack propagation speed in the speed range of 100m/s~2600m/s was identified by combining some experiments and numerical simulation. The relationship is used to simulate the crack propagation process of other experiments, and finally the simulated results are consistent with the actual observation results. The numerical model can faithfully reproduce the crack evolution process of alumina ceramics with prefabricated cracks under flame thermal shock.