Coupled static-dynamic tests were carried out on notched semi-circular bend (NSCB) granitic specimens using a modified split Hopkinson pressure bar (SHPB) device, to investigate the effects of axial pre-force and loading rate on dynamic fracture behavior of rocks. Digital image correlation (DIC) method was adopted to obtain the deformation field and fracturing process. The results indicate that the pre-force (up to 50% static peak force) enhances the fracture parameters overall, including fracture initiation toughness, fracture energy, crack propagation velocity (CPV) and fracture propagation toughness, but the effect of loading rate is more significant than that of the pre-force. Digital images show that the increase in pre-force would cause the dominant crack to symmetrically bifurcate since the pre-force strengthened a fan-shaped area for the specimen near the incident bar. The loading rate larger than 124 GPa·m^1/2/s could lead to the secondly fracture of the specimen and thereby more fragments. Compared with previous studies, the present investigation deepens the understanding of fracture characteristics of rocks under coupled static and dynamic loads by further reducing the pre-force interval (0.25 kN). In addition, a new method based on the DIC technique is proposed to calculate crack opening distance (COD) and CPV, which can improve the efficiency and accuracy compared to the strain gauge method. Moreover, fracture propagation toughness is also emphasized apart from the initiation toughness. The findings can provide some enlightenments for rock fracture dynamics and crack propagation of highly stressed rocks.

采用改进的分体式霍普金森压力杆（SHPB）装置对缺口半圆弯（NSCB）花岗岩试样进行静-动力耦合试验，研究轴向预力和加载速率对岩石动态断裂行为的影响。采用数字图像相关（DIC）方法获取变形场和压裂过程。结果表明，预力（高达 50% 静态峰值力）提高了整体断裂参数，包括断裂起始韧性、断裂能、裂纹扩展速度（CPV）和断裂扩展韧性，但加载速率的影响比预力的影响更显着。数字图像显示，预力的增加会导致主要裂纹对称地分叉，因为预力加强了入射杆附近试样的扇形区域。大于124 GPa·m ^1/2 /s的加载速率会导致试样二次断裂，从而产生更多的碎片。与以往的研究相比，本研究加深了对断裂特征的认识通过进一步减少预力间隔（0.25 kN），在耦合静态和动态载荷下的岩石。此外，提出了一种基于DIC技术的裂纹张开距离（COD）和CPV计算新方法，与应变片法相比，该方法可以提高效率和精度。此外，除了起始韧性外，还强调了断裂扩展韧性。研究结果可为岩石断裂动力学和高应力岩石裂纹扩展提供一些启示。