Research on the method of dynamic strength evaluation of ceramics by caustics

采用焦散线法，结合超高速摄影、加热炉和动态加载装置，研究了陶瓷材料在不同温度下的动态断裂行为，并对焦散线技术进行了改进。因此，获得以下结果。(1)通过制备具有高度抛光表面的样品和使用特殊布置的光学装置，可以获得清晰的焦散图形。结果表明，焦散线法可用于研究陶瓷材料在高温动态载荷下的断裂。(2)对于锆陶瓷，使用2mW的气体激光光源可以进行高达1200 ℃的实验，对于氮化硅陶瓷，使用35mW的激光器可以获得高达1100 ℃的清晰焦散图案。结果表明，温度和加载速率对锆基陶瓷的断裂行为有较大的影响，而对氮化硅基陶瓷的影响不大。(3)利用焦散线倍增技术，可以得到铝和赛隆陶瓷清晰的焦散线图形。(4)结果表明，在Ⅱ型加载条件下，初始曲线尺寸对K值的影响很小。(5)基于AE波的可视化图案也被获得，并且示出了该图案以瑞利波速度传播。(6)通过引入图像处理技术，可以提高焦散线的精度。此外，还提出了一种简单的测量弹性常数的方法。通过本研究，对实验技术进行了改进，提出了一种评价陶瓷材料高温动载强度的基本方法。

Dynamic fracture behavior of the ceramics at various temperatures is investigated by using the caustic method together with ultra high-speed camera, heating furnace and dynamic loading device, and moreover, some improvements of the technique of caustics are studied. Consequently, the following results are obtained. (1) Clear caustic pattern can be obtained by preparing the specimen with highly polished surface and by using the specially arranged optical setup. It is shown that the caustic method can be applied for studying the fracture of ceramics under dynamic loading at high temperature. (2) For zirconium ceramics, it is possible to perform experiment up to the temperature of 1200ﾟC by using 2mW gas laser light source and for silicon-nitride ceramics, it is possible to obtain a clear caustic pattern up to 1100ﾟC by using 35mW laser. It is revealed that effects of temperature and loading rate on the fracture behavior are considerably large in zirconium ceramics, but those effects are not so large in silicon-nitride ceramics. (3) A clear caustic pattern can be obtained for aluminum and sialon ceramics by employing multiplication technique of caustics. (4) It is shown that the effect of the size of initial curve on K-value is very small under Mode II loading condition. (5) The visualized pattern based on AE-wave is also obtained and it is shown that this pattern propagated at Rayleigh wave velocity. (6) By introducing the image processing technique, it is possible to improve the accuracy of caustics. Moreover, a simple technique for measuring the elastic constants is proposed. Through this study, some improvements of experimental technique are accomplished and a basic technique for evaluating strength of ceramics under dynamic loading at high temperature is proposed.