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深部岩石的动力破坏,是岩石力学研究的一个热点问题。为模拟深部岩石动态断裂情况,选取一种花岗岩制备带10 mm预制裂纹的板状试样,开展含预应力条件下的岩板动态破坏行为研究。试件尺寸为305 mm×305mm×10.5 mm岩板,在静态竖向预压的条件下,使用25 mm杆径的霍普金森压杆进行冲击试验。利用超高速摄影仪记录试样裂纹扩展的全过程,采用数字图像相关(DIC)技术分析试样的位移场及应变场,通过设置虚拟引伸计,获得预应力条件下岩板起裂时刻、裂纹长度、裂纹扩展速度及断裂韧性等动态断裂力学参量。研究结果显示:该岩板试件裂纹扩展速度可达到瑞利波速的0.57倍(~1000 m/s),验证了采用花岗岩岩板测试的优势。在特定预应力条件下,岩板的裂纹扩展速率与动态断裂韧性具有明显的率相关性;特定冲击速度条件下,随着静态预应力的增加,裂纹扩展速度受到抑制,破坏模式由单一裂纹扩展向多条微裂纹扩展等复杂模式转变,甚至出现止裂现象。当气枪冲击气压103.43 kPa、静态预应力30 MPa时,裂纹扩展速度降为452.4 m/s,属于低速裂纹扩展范围。
The dynamic destruction of deep rock is a hot issue in rock mechanics research. In order to simulate the dynamic fracture of deep rock, a kind of granite was used to prepare a plate specimen with 10 mm prefabricated cracks to study the dynamic failure behavior of the rock under prestressed condition. The specimen size was 305 mm × 305 mm × 10.5 mm and subjected to impact test under the condition of static vertical preloading using a Hopkinson pressure bar with a diameter of 25 mm. The whole process of crack propagation was recorded by a super fast camera. The displacement field and strain field of the sample were analyzed by Digital Image Correlation (DIC) technique. By setting the virtual extensometer, the crack initiation time and crack Length, crack growth rate and fracture toughness and other dynamic fracture mechanics parameters. The results show that the crack growth rate can reach 0.57 times the Rayleigh wave velocity (~ 1000 m / s), which verifies the advantage of using granite slab test. Under specific prestressing conditions, the crack growth rate of rock slab has a significant correlation with the dynamic fracture toughness. With the increase of static prestressing force, the crack propagation rate is restrained under the specific impact velocity. The failure mode is characterized by single crack propagation To a number of micro-crack growth and other complex modes of change, or even stop the phenomenon. When the air gun impact pressure is 103.43 kPa and the static prestress is 30 MPa, the crack propagation velocity is reduced to 452.4 m / s, which belongs to the range of low-speed crack propagation.