不同加载速率Ⅰ型预制裂纹花岗岩断裂特征研究

以CCD相机配合高速相机搭建试验变形观测系统，开展不同加载速率下含Ⅰ型预制裂纹花岗岩试件的三点弯试验。利用数字散斑相关方法对试验过程采集的数字散斑图像进行分析，对不同加载速率作用下含Ⅰ型预制裂纹花岗岩试件裂纹扩展过程中的变形演化特征、裂纹扩展速率、裂纹尖端张开位移、裂纹张开角以及初始断裂应力强度因子进行研究，研究结果表明：（1）花岗岩试件初始裂纹扩展速率随着加载速率的增加总体呈线性增加趋势；最大扩展速率随着加载速率增加呈现先较快增加后缓慢增加的变化趋势。（2）不同加载速率作用下，花岗岩试件预制裂纹尖端张开位移均呈现非线性缓慢增长-迅速增长-线性增长的变形趋势，且线性增长阶段曲线斜率随着加载速率的增加而增大。（3）随着加载速率的增加，花岗岩试件初始裂纹张开角先逐渐减小后稳定在0.1o～0.13o。（4）随着加载速率的增加，花岗岩试件初始断裂应力强度因子呈指数增长。

Fracture characteristics of granite with mode-I pre-crack at different loading rates

The deformation measurement system was built with a CCD camera and a high-speed camera. Experimental tests were conducted on rectangular granite specimens with pre-cracks of mode-I under different loading rates. The speckle images captured in the process of experiments were analysed by the digital speckle correlation method (DSCM). We studied the speed of crack growth, crack-tip opening displacement, crack tip opening angle and crack stress intensity factor (SIF) of granite specimens with pre-cracks of mode-I under different loading rates. The initial speed of the crack growth of granite specimens increases linearly with the loading rate. With the increase of loading rate, the maximum speed crack increased rapidly at first and then slowly. At different loading rates, the crack-tip opening displacement of granite specimens showed three stages of evolution: nonlinear slow growth，rapid growth, and linear growth. In the linear growth stage, the slope of the curve increased with the increase of loading rate. With the increase of loading rate, the initial crack opening angle of granite specimen decreases gradually and then stabilises to 0.1°～0.13°. Before the initial fracture of granite specimens, the SIF value increased exponentially with the increase of loading rate.