岩石偏心圆孔单裂纹平台圆盘的动态裂纹扩展与止裂

针对平台圆环构型的优点, 提出偏心圆孔单裂纹平台圆盘(cracked eccentrically holed flattened disc, CEHFD), 该试样具有更长的断裂路径。利用霍普金森压杆加载系统, 径向冲击CEHFD试样, 完成Ⅰ型动态断裂实验。砂岩试样表面粘贴应变片和裂纹扩展计, 用于监测裂纹动态起裂、扩展和止裂的全过程。实验表明, 在整个断裂过程中, 裂纹非匀速扩展, 裂纹扩展速度在裂纹起裂后加速上升, 在裂纹止裂前有明显的减速, 与地震时断层的动态破裂全过程完全吻合。采用实验-数值-解析法得到动态应力强度因子, 其时间历程呈现先增大后减小的趋势。根据断裂过程不同时刻, 得到相应的动态起裂韧度、扩展韧度及止裂韧度。在动态断裂全过程中, 动态扩展韧度为速度的函数, 变化趋势与速度一致, 随着时间先增大后减小; 动态起裂韧度大于动态止裂韧度, 止裂韧度随着裂纹最大扩展速度的增大而降低, 并且有较大的离散性。

Dynamic crack propagation and arrest investigated with a cracked eccentrically-holed flattened disc of rock

Expanding the advantages of flattened ring geometry, a new test specimen geometry with a longer fracture path was advised to investigate the complete dynamic fracture process.This geometry was cracked eccentrically holed flattened disc (CEHFD) which was more conducive to study the unstable dynamic crack propagation and dynamic crack arrest.In order to study the mode Ⅰ (opening mode) dynamic fracture process of a rock, CEHFD specimens with strain gauges and crack propagation gauge glued on the specimen's surface were diametrically impacted by a split Hopkinson pressure bar.The experiment investigated crack initiation, rapid crack propagation, and crack arrest, all in one specimen.In a single complete fracture event, the crack accelerated after initiating and decelerated before arresting.The process monitored by the laboratory is completely consistent with the whole process of the dynamic rupture of faults in earthquake.A hybrid experimental-numerical-analytical method was used to determine the dynamic stress intensity factor that increased with increasing time.The dynamic fracture toughness was obtained with the fracture time information.Crack propagation velocity was first increased and then decreased with the time, and the dynamic propagation toughness had the same variation tendency with time as it was the function of velocity.The dynamic arrest toughness was smaller than the dynamic initiation toughness, and decreased when the maximum crack propagation speed increased.