冲击载荷作用下含孔洞大理岩动态力学破坏特性试验研究

利用一种大理岩试件加工制备含圆形和椭圆形孔洞的板状试样,试样尺寸为60 mm×60 mm×15 mm,使用75 mm杆径的分离式霍普金森压杆(SHPB)进行冲击压缩试验,通过超动态应变仪监测入射杆和透射杆的应变信号,利用高速摄像仪记录试样完整的裂纹萌生、扩展、贯通直至试样破坏的全过程,分析冲击载荷作用下预制孔洞试样的动态抗压强度、破坏模式和裂纹扩展特性。研究发现,孔洞大小、形状和空间位置对岩石的动态抗压强度都有一定影响,孔洞的存在降低了大理岩试样的动态抗压强度。在冲击载荷作用下,预制中心孔洞的大理岩试样在孔洞周边产生平行于轴向加载方向的初始拉伸裂纹和类X型初始剪切裂纹,在试件破坏中起主导作用。圆形孔洞试样中,随着孔径增大,剪切裂纹扩展速度随之增大,而拉伸裂纹扩展速度则减小;椭圆形孔洞的长短轴比、长轴与加载方向的夹角均是影响裂纹扩展速度和动态抗压强度的因素。在30~45 s-1的加载应变率范围内,大理岩孔洞试样的平均裂纹扩展速度为100~450 m/s。

EXPERIMENTAL STUDY OF THE DYNAMIC STRENGTH AND FRACTURING CHARACTERISTICS OF MARBLE SPECIMENS WITH A SINGLE HOLE UNDER IMPACT LOADING

The dynamic compressive tests were carried out with ?75 mm split Hopkinson pressure bar(SHPB) on the plate-shape marble specimens(size of 60 mm×60 mm×15 mm) with a single circular or an elliptical hole in the center of the specimen. The dynamic strain signals in the incident bar and the transmitted bar were monitored with the ultra-dynamic strain indicator. The process of crack initiation，propagation and coalescence in the marble specimens was recorded with a high speed video camera. The dynamic strength，failure mode and crack propagation characteristics of the specimens were analyzed and discussed. It is found that the rock dynamic strength is influenced by the size，the shape and the spatial location of the water jet cut hole. The strength of the holed specimen is obviously smaller than that of the intact marble specimen. Axial tensile cracks parallel to the loading direction and X-type shear cracks surrounding the hole are the dominant factors for the failure of the specimens. With the increase of the diameter of the round hole，the speed of shear crack propagation increases while the speed of tensile crack propagation decreases. For the specimens containing an elliptical hole，the eccentricity and the angle between the loading direction and the long axes influence the cracking behavior and dynamic strength under impact loading. The average speed of dynamic crack propagation of the marble specimens is in the range of 100–450 m/s at the loading rate of 30–45 s－1.