含预制裂隙大理岩SHPB动态力学破坏特性试验研究

为了研究端部裂隙形态对岩石动态力学特性以及裂纹扩展的影响,利用50 mm×50 mm圆柱形大理岩加工含不同裂隙倾角的试样,在50 mm杆径分离式霍普金森压杆(SHPB)试验平台上进行冲击加载试验,并使用高速摄影仪实时记录裂纹扩展以及动态破坏全过程。研究表明,大理岩的动态抗压强度、峰值应变、动态弹性模量等力学参数随预制裂隙倾角增大整体呈先减小后增大的趋势;裂纹大多是从裂隙尖端或附近起裂,起裂裂纹为II型剪切裂纹或I–II型复合裂纹(拉剪复合裂纹),起裂角和起裂应力随着预制裂隙角度的增大分别呈M和W型变化,完整和90°裂隙试样最终呈劈裂拉伸破坏,45°裂隙试样呈拉剪复合型破坏,30°和60°裂隙试样呈剪切破坏,存在一个临界角度,临界角两侧裂纹扩展特性表现出较好的对称性;随着预制裂隙角度的增大,岩石的能量吸收率先增大后减小,当端部裂隙与端面成适当角度,会使能量吸收率最大,可以有效提高破岩效率。

Characteristics of dynamic failure of marble with artificial flaws under split Hopkinson pressure bar tests

In order to study the effect of the angle of flaws at the end surface on the dynamic properties of and crack propagation in rock，cylindrical marble specimens of 50 mm×50 mm were manufactured with flaws of different angles. A series of impact loading tests were carried out with a system of split Hopkinson pressure bar(SHPB) with the diameter of 50 mm. The crack propagation and dynamic failure processes were recorded real-timely by a high speed camera. The results show that the dynamic parameters of the marble including the dynamic compressive strength，peak strain and dynamic elastic modulus，decrease first and then increase with the increasing of angles of prefabricated flaw. The cracks initiate almost from or near the tip of flaw and the initiation cracks belong to type II or combined type I-II. The crack initiation angle shows an M-shaped tendency and the crack initiation stress shows a W-shaped tendency with the increase of the flaw angle. The splitting tensile failure is usually observed in the marble specimen intact or with flaw having angle of 90°. The combined tensile-shear failure occurred mainly in the specimen with flaw angle of 45° and the shear failure in specimens with flaw angles of 30° and 60°. The crack propagation characteristics on both sides of the critical angle are rather symmetric. The energy absorption ratio increases first and then decreases with the increasing of the flaw angle. When the end flaw has an appropriate angle to the loading surface，the energy absorption ratio is the largest，indicating that the efficiency of rock breaking can be improved effectively by setting an appropriate flaw angle at the end surface.