用超小型压力机研究裂纹的稳态与非稳态扩展

本文利用显微镜观察记录了玻璃中预制小裂纹稳态与非稳态扩展的全过程。当对玻璃加载到初始压力P和压缩量u时,停止加载,并观察稳态扩展过程,测量破裂扩展的速度。根据测量结果,发现在预制裂纹稳态扩展时,扩展速度随着时间在增长,而初始压力P和压缩量u却保持不变。但是一旦非稳态扩展出现,初始压力P和压缩量u便突然下降。实验中的应力降和地震中的应力降在数量级上是相同的。最后我们讨论了稳态扩展过程中P和u不变的原因。我们认为:Griffith的破裂准则应用到破裂过程时不是十分完善的,需要作适当的修正。

THE EXPERIMENTAL STUDIES OF STABLE AND UNSTABLE CRACKING BY USING A ULTRASMALL TESTING MACHINE

In this paper, we observed and recorded the whole process of stable and unstable cracking of a small pre-crack by using a microscope.When the load on a piece of glass was up to a presure P or compression to a value u, we stopped loading and observed the stable cracking process and measured the cracking velocity. According to the measurements, we found that the cracking velocity was increasing with time when the pre-crack was developing, and the initial pressure P or compression u did not change during that time. But when the unstable cracking was happening, the pressure P and compression value u dropped down suddenly. The order of the stress drop in the experiment is same as that in the earthquake.Finally, we discuss the reason why the pressure P or compression u is unchanged during stable cracking. It is likely that the Griffith criterion, when applied to the fracture mechanics of glass, needs further improvement.