高超声速飞行器具有很高的军事和民用价值，是未来进入空间并控制空间、 保证控制优势的关键支柱，同时也是对空间进行大规模开发的载体，是一种具有 广阔开发前景的飞行器。我国在十四五规划纲要中明确提出要瞄准包含空天科技 的前沿领域实施一批具有前瞻性、战略性的国家重大科技项目，强化国家战略科 技力量。航天飞行器在飞行过程中会受到外部高速来流的气动加热和发动机燃烧 室高温燃气的加热，随着航天飞行器飞行速度与时间的提高，飞行器驻点、翼前 缘、发动机热端等位置将承受越来越剧烈的热震载荷，在这种极端或苛刻的热震 环境下，结构内部将会瞬间产生巨大热应力，使结构发生损伤或断裂而失效。在 这种情况下，选择优秀的耐热材料对先进航天飞行器的研制至关重要。

陶瓷材料由于具有优异的高温力学性能，并且耐磨损、耐腐蚀，广泛的应用 于各工业部门，特别是像近空间高超声速飞行器的热防护系统（ZrB2-SiC 等）， 高速飞行器红外窗口（ZnS 等）和燃气轮机内壁（3Y-ZrO2 等）等极端高温高技 术工业领域。但陶瓷材料在烧结、熔覆、喷涂等制备过程中或多或少的会含有气 孔和微裂纹，陶瓷材料固有的脆性使得他们在加工和服役过程中更容易产生缺陷 的同时又对缺陷的存在十分敏感。在受到极端的热震载荷后，陶瓷内部往往会从 这些大小形状各异的缺陷处开始萌生出裂纹，许多微小的裂纹逐渐彼此链接起来 形成了宏观上的裂纹最终导致材料的损伤与结构的失效。因此亟需对陶瓷材料在 热震载荷下的缺陷效应进行机理研究。另外，随着热震损伤机理研究的深入，确 定材料热震下裂纹的发生发展过程变得越来越重要，迫切需要一种方法来观测材 料热震开裂的完整过程。但由于快速热震过程中包含复杂的物理和化学反应，目 前少有对陶瓷材料热震开裂过程的现场动态观测的报道。在上述背景下，我们做 了以下工作：

（1） 水淬热震下预制缺陷对陶瓷裂纹扩展的影响

以半透明氧化铝陶瓷为例，实验研究了在水淬过程中预制缺陷对陶瓷片热震 裂纹扩展的影响。实验结果表明，热震裂纹在与预制缺陷相交前，扩展速度不受 预制缺陷影响。热震裂纹扩展到预制缺陷后，在预制缺陷的下端会出现二次裂纹， 二次裂纹的扩展速度与其他热震裂纹相似，但其垂直方向的最终裂纹长度比其他 热震裂纹短。并且随着预制缺陷角度的增大，二次裂纹的长度以及出现的概率逐 渐增大。另外我们引入了一个带有预制缺陷的细观损伤力学有限元模型来模拟陶 瓷片的水淬实验，数值模拟结果与实验结果基本一致，说明以细观损伤力学为基 础的模拟计算可以较好地预测陶瓷材料水淬实验的结果。

（2） 陶瓷材料火焰热震开裂的实时观测

以半透明氧化铝陶瓷为例，研究了试样尺寸和火焰热流密度对火焰热震下陶 瓷热震裂纹扩展的影响。我们提出了一种利用氧乙炔火焰和高速成像实时观测陶 瓷热震开裂的实验方法。通过这种方法，捕捉了裂纹扩展过程，计算了裂纹扩展 速度。另外为了定性地确定试样尺寸对裂纹扩展速度的影响，我们还通过有限元 方法模拟计算了不同尺寸陶瓷的裂纹尖端瞬态热应力强度因子。结果表明，火焰 热冲击下，裂纹会从陶瓷内部出现，向两侧扩展，最终形成贯通裂纹，导致灾难 性破坏。热震裂纹的扩展速度最初较快，接近瑞利波速，然后逐渐减小。热流密 度和试样尺寸的增加会导致裂纹扩展过程中出现不稳定的裂纹分叉。此外，试样 尺寸的增加也会增加热震裂纹的初始扩展速度。这些现象与水淬热震下的裂纹扩 展模式有很大的不同。

（3） 火焰热震下含预制缺陷陶瓷的热震开裂实时观测

采用实时观测方法研究了含有预制缺陷的半透明氧化铝陶瓷在火焰热震下 的扩展规律。实验结果表明，在火焰热冲击下，预制缺陷的两端均会产生翼状裂 纹，且试样的完全破坏是一个高速过程，裂纹的扩展速度先快后慢。距离受热面 较近的预制缺陷尖端（上尖端）的热震裂纹最大扩展速度随预制缺陷与受热边界 之间距离的增加而增大，距离受热面较远的预制缺陷尖端（下尖端）的最大扩展 速度随预制缺陷与受热边界之间距离的增加而减小。此外，我们使用基于动态断 裂力学的经典有限元法数值模拟再现了含有预制缺陷陶瓷材料的整个热冲击热 震开裂过程。为此，通过实验和数值模拟相结合，确定了 100~2600m/s 速度范围 内动态应力强度因子与裂纹扩展速度的关系。模拟结果和上述关系与实验观测结 果一致。热冲击裂纹的演化过程由于裂纹的速度较快，在实验中很难观察到，而 该数值模型则能够较好地再现热冲击裂纹的演化过程。

（4） 数字图像相关方法测量陶瓷材料的水淬开裂过程

以氧化铝和氧化锆为例，结合数字图像相关（DIC）方法对非透明陶瓷的水 淬热震开裂过程进行了实时观测。实验结果表明，数字图像相关方法计算所得两 种陶瓷的裂纹形貌与染色法所得试样裂纹形貌非常接近。数字图像相关方法计算 所得的氧化铝在水淬过程中的热震裂纹扩展与之前的半透明氧化铝的水淬热震 裂纹扩展一致，可以认为，这一部分的内容提出了一种不透明陶瓷水淬热震裂纹 萌生和扩展的原位测量方法。由于材料性质不同，氧化铝的热冲击裂纹扩展速度 比氧化锆快。

Hypersonic vehicle has high military and civilian value which is the key pillar to enter and control space in the future and to ensure the advantage of control. At the same time, it is also the carrier of large-scale development of space, which is a kind of aircraft with broad development prospects. In the Outline of the 14th Five-Year Plan, it is clearly stated that a number of forward-looking and strategic major national science and technology projects should be carried out in frontier fields, including space science and technology, to strengthen the national strategic scientific and technological strength. Aerospace vehicles will be subjected to aerodynamic heating from external high-speed flow and high temperature gas heating from engine combustion chamber during flight. With the increase of flight speed and time of aerospace vehicles, aircraft stationary point, wing leading edge, engine hot end and other positions will be subjected to more intense thermal shock load. In such extreme and harsh thermal shock environment, Huge thermal stress will be generated instantly inside the structure, which will lead to failure of the structure because of the materials’ damage or fracture. In this case, the selection of excellent heat-resistant materials is very important for the development of advanced space vehicles.

Ceramic materials are widely used in various industrial sectors for their excellent high temperature mechanical properties, wear resistance and corrosion resistance, especially in extreme high temperature and high-tech industrial fields such as the thermal protection system of near-space hypersonic aircraft (ZrB2-SiC, etc.), infrared window of high-speed aircraft (ZnS, etc.) and gas turbine inner wall (3Y-ZrO2, etc.). However, ceramic materials contain pores and micro-cracks inevitably in the preparation process of sintering, cladding, spraying, etc. The inherent brittleness of ceramic materials not only makes them more likely to produce defects in the process of processing and service, but also very sensitive to the existence of defects. After being subjected to extreme thermal shock, cracks often start to sprout from these defects of different sizes and shapes in ceramics. Many tiny cracks gradually link with each other to form macroscopic cracks, which eventually lead to material damage and structural failure. Therefore, it is urgent to study the mechanism of defect effect of ceramic materials under thermal shock. In addition, with the further study of thermal shock damage mechanism, it becomes more important to determine the occurrence and development process of cracks in materials under thermal shock, and a method is urgently needed to observe the complete process of thermal shock. However, due to the complex physical and chemical reactions involved in the rapid thermal shock process, there are few reports on the dynamic observation of the thermal shock cracking process of ceramic materials. Against the above background, we have done the following:

(1) Effect of prefabricated defects on the crack propagation of ceramics during water quenching

Taking semi-transparent alumina ceramics as an example, the effect of prefabricated defects on the thermal shock crack propagation during water quenching was studied experimentally. The experimental results show that the propagation velocity of thermal shock crack is not affected by the prefabricated defect before it intersects with the prefabricated flaw. After the thermal shock crack extends to the prefabricated defect, a secondary crack will appear at the lower end of the prefabricated defect. The propagation speed of the secondary crack is similar to that of other thermal shock cracks, but the final crack length in the vertical direction is shorter than that of other thermal shock cracks. The length and occurrence probability of secondary crack will increase gradually with the increases of the angle of prefabricated defects. In addition, we introduced a finite element model with prefabricated defects based on meso-damage mechanics to simulate the water quenching process of ceramic sheets. The numerical simulation results are basically consistent with the experimental results, indicating that the simulation calculation based on meso-damage mechanics can predict the results of the water quenching experiment of ceramic materials well.

(2) Real-time observation of flame thermal shock cracking of ceramics

Taking translucent alumina ceramics as an example, the effects of sample size and flame heat flux on the thermal shock crack propagation of ceramics under flame shock were studied. An experimental method for real-time observation of ceramic’s thermal shock cracking by oxyacetylene flame and high speed imaging is presented. By this method, the crack growth process is captured and the crack growth velocity is calculated. In addition, in order to qualitatively determine the effect of sample size on crack propagation velocity, the transient thermal stress intensity factors of ceramics with different sizes are simulated by finite element method. The results show that cracks appear from inside the ceramic and spread to both sides, and finally form through cracks, leading to catastrophic failure. The propagation speed of thermal shock crack is fast at first, close to Rayleigh wave velocity, and then gradually decreases. The increase of heat flux and sample size will lead to unstable crack bifurcation in the process of crack propagation. In addition, the increase of sample size also increases the initial propagation speed of thermal shock crack. These phenomena are quite different from the crack propagation mode during water quenching.

(3) Real-time observation of thermal shock cracking of ceramics with prefabricated defects under flame thermal shock

The cracks’ propagation of semi-transparent alumina ceramics with prefabricated defects under flame thermal shock was studied by real-time observation method. The experimental results show that wing cracks occur at both ends of the prefabricateddefects, and the sample were rapidly and completely destroyed. The crack propagation is fast at the beginning and then slow down. The maximum propagation velocity of thermal shock crack at the prefabricated defect tip closer to the heating surface increases with the increase of the distance between the prefabricated defects and the heating boundary, while the maximum propagation velocity at the prefabricated defect tip further away from the heating surface decreases with the increase of the distance between the prefabricated defect and the heating boundary. In addition, we use the classical finite element method based on dynamic fracture mechanics to simulate the entire thermal shock cracking process of ceramic materials with prefabricated defects. Therefore, the relationship between dynamic stress intensity factor and crack growth velocity in the range of 100~2600m/s was determined by both experiment and numerical simulation. The simulation results and the above relationship are in agreement with the experimental observation results. The evolution process of thermal impact crack is difficult to be observed in experiments due to the high speed of crack, but the numerical model can reproduce the evolution process of thermal impact crack well.

(4) Measurement of ceramics cracking during water quenching by the digital image correlation method

Taking alumina and zirconia as examples, the hot shock cracking process of non-transparent ceramics was observed in real time by digital image correlation method. The experimental results show that the crack morphologies of the two ceramics calculated by digital image correlation method are very close to those of the samples obtained by dyeing method. The thermal shock crack propagation of alumina during water quenching calculated by digital image correlation method is consistent with the thermal shock crack propagation of translucent alumina during water quenching before. It can be considered that this part proposes an in situ measurement method for thermal shock crack initiation and propagation of opaque ceramics during water quenching. The thermal shock crack propagation rate of alumina is faster than that of zirconia due to different material properties.