花岗岩动态断裂能各向异性试验研究

Experimental study of dynamic fracture energy anisotropy of granitic rocks

由于微裂纹的存在以及长期构造应力下矿物晶粒排列所造成的自然各向异性,岩石的力学性质大多表现出各向异性的特点。研究选取Barre花岗岩和Standstead花岗岩,利用改装的分离式霍普金森压杆系统和国际岩石力学学会推荐的直切槽半圆盘弯曲试样,进行了花岗岩动态断裂能各向异性的试验。试验中根据纵波波速所确定的主方向制备岩石试样,每种岩石制备三组试样。试验采用波形整形技术实现动态力平衡,并利用激光测量裂缝表面张开位移。利用这些测量结果并结合能量分析,确定2种岩石样品的动态断裂能。研究结果表明,加载率在0~200 GPa·m1/2/s范围,2种岩石三个方向的动态断裂能均随着加载率的增加而增加。在相同的加载率下,2种岩石的动态断裂参数具有明显的各向异性。2种岩石X方向(波速最小)的动态断裂能最小,Z方向(波速最大)的动态断裂能最大。此外,随着加载率的提高,2种岩石动态断裂能的各向异性差异越来越明显,这主要是由于高加载率下扩展过程中损伤区域的增大造成的。

Due to pre-existing micro-cracks induced by the long-term tectonic loading,rock exhibits strong anisotropy. Using a split Hopkinson pressure bar（SHPB） system with International Society of Rock Mechanics（ISRM） suggested method for dynamic fracture test and the notched semi-circular bend（NSCB） specimen,the anisotropy of dynamic fracture energy of Barre granite and Standstead granite are investigated. The P-wave velocities of two rocks are measured to determine the three principal directions. The notches of the NSCB specimen are made along these three principal directions. Thus for each rock,three groups of NSCB specimens are fabricated. The pulse shaping technique was used to achieve dynamic force balance and a laser gap gauge was utilized to measure the crack surface opening distance（CSOD）. Using these methods,the fracture energy for the specimen is determined using energy analysis. For samples in the same orientation group,the dynamic fracture energy of two rocks shows clear loading rate dependence,i.e. the fracture energy increases with the loading rate. The dynamic fracture energy is anisotropic for SG and BG. At the similar loading rate,the dynamic fracture energy for SG and BG along X direction is minimum and the fracture energy along Z direction is maximum. In addition,the fracture energy anisotropy of SG and BG increases with the loading rate. This is attributed to the increase of damage zone around the fracture path under higher loading rates.