Study on the Thermal Shock Fracture Mechanism of Ceramics Based on the Dynamic Characterization of Thermal Stress and Microfracture Process

高温下使用的陶瓷材料通常会因热冲击断裂而受到损坏。最流行的热冲击试验之一是水淬火试验，其中临界温度差，其中样品受到严重损坏，被用作抗热冲击性的量度。然而，热冲击下的微断裂过程的表征以及瞬态热应力场是必不可少的，因为热冲击断裂是由微观损伤的积累，如热应力下的微裂纹。本计画提出一种新的热震断裂实验技术--盘-棒试验。测量了试件内部的温度场，并计算了二维热应力场。此外，微断裂过程进行了表征AE测量。在本项目中，已完成以下工作：1.研制了盘-棒试验系统。通过数字摄像机对热冲击下裂纹的萌生和扩展行为进行了现场观察。此外，通过引入全版本有限元程序（ANSYS），实现了热应力的三维分析.动态表征了热冲击下的裂纹扩展行为。定量地了解了裂纹稳定性对预裂纹长度的依赖关系，这与Hasselman统一理论的理论预测吻合较好。此外，还成功地表征了增韧陶瓷复合材料的裂纹扩展行为.陶瓷材料在机械载荷作用下的微断裂过程的无损评价技术得到了迅速发展并应用于生物陶瓷。发展了陶瓷材料长期可靠性的评估技术，并将其应用于热冲击断裂。

Ceramic materials used at elevated temperatures are usually subjected to damage due to thermal shock fracture. One of the most popular thermal shock tests is the water quench test, in which the critical temperature difference, where samples are subjected to severe damage, is used as a measure of the thermal shock resistance. However the characterization of microfracture process under thermal shock as well as transient thermal stress field is indispensable, since thermal shock fracture is caused by the accumulation of microscopic damages such as microcrackings under thermal stress. In this project, a new experimental technique for the investigation of thermal shock fracture behavior, Disc-on-Rod test, is proposed. The temperature fields in the specimen were measured and used to calculate the 2 dimensional thermal stress field. Furthermore, microfracture process was characterized by AE measurement. In the present project, followings have been achieved.1. Experimental system of Disc-on-Rod test was significantly developed. The in-situ observation of crack initiation and propagation behavior under thermal shock was enabled by digital video camera unit. Furthermore, the 3D-analysis of thermal stress was enabled by introducing full-version FEM code (ANSYS).2. The crack propagation behavior under thermal shock was characterized dynamically. The dependence of crack stability on the length of pre-crack was understood quantitatively, which showed good agreement of theoretical prediction by Hasselman's unified theory. In addition, the crack growth behavior of toughened ceramic composites was characterized successfully.3. Non-destructive evaluation technique of microfracture process in ceramics under mechanical loading was drastically developed and applied to bioceramics. The assessment technique of long-term reliability of ceramics was developed and will be applied to thermal shock fracture.