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采用压缩单裂纹圆孔板确定岩石动态起裂、扩展和止裂韧度

DETERMINATION OF DYNAMIC FRACTURE INITIATION, PROPAGATION, AND ARREST TOUGHNESS OF ROCK USING SCDC SPECIMEN

  • 摘要: 爆炸、冲击、地震等人为或自然灾害不可避免,经常造成大量土木工程设施的破坏,因此岩石在动态载荷作用下的行为受到特别关注.岩石动态断裂韧度是评价岩石抵抗裂纹动态起裂、扩展和止裂性能的材料参数,开展岩石动态断裂韧度测试方法的研究对相关理论基础和实验技术的要求较高.岩石动态断裂韧度分为动态起裂、动态扩展、动态止裂三种,虽然关于动态起裂和动态扩展的研究已有一些成果,对岩石动态止裂的研究仍是一个难题,至今几乎无人问津.研究表明,在分离式霍普金森压杆撞击压缩单裂纹圆孔板岩石试样的I型动态断裂试验中,动态起裂、扩展、止裂的全过程可以由黏贴在压缩单裂纹圆孔板试样上的裂纹扩展计监测,岩石的动态起裂、扩展、止裂韧度可以用实验-数值-解析法确定.特别值得一提的是首次测出了岩石的动态止裂韧度.裂纹扩展计信号还显示,压缩单裂纹圆孔板在止裂后,停止的裂纹还会再次动态起裂、扩展并超出裂纹扩展计的检测范围.从能量的角度分析了动态止裂的过程,指出测试动态止裂韧度时要注意的一些问题.结果显示,岩石动态起裂韧度和动态扩展韧度分别随动态加载率和裂纹扩展速度的增大而增大,岩石动态起裂韧度略大于动态止裂韧度.

     

    Abstract: Inevitable man-made or natural disasters, such as explosion, impact, earthquake, etc, often cause the failure of a large number of civil engineering facilities, and hence rock behavior under dynamic loading has become the focus of special attention. Dynamic fracture toughness of rock is the material parameter for characterizing its resistance to dynamic crack initiation, propagation and arrest. Rock dynamic fracture toughness is then classified into three kinds: dynamic initiation, dynamic propagation and dynamic arrest. Although there were some achievements for studying rock dynamic initiation and propagation, the study on rock dynamic arrest, being a puzzling problem, has been so far almost ignored. In the present research, the single cleavage drilled compression (SCDC) specimen of rock was impacted by split Hopkinson pressure bar in the model-I dynamic fracture test, where a crack propagation gauge (CPG) was glued on the SCDC specimen to monitor the whole fracture process, including dynamic initiation, propagation, and arrest. An experimental-numerical-analytical approach was adopted to determine the dynamic initiation, propagation, and arrest toughness of rock material. The CPG signal indicated that after the arrest of the crack in the SCDC, the stopped crack will be reinitiated, and propagated out of the CPG monitoring range. This dynamic arrest process is analyzed from an energy perspective, and some required attentions in determining the dynamic arrest toughness are pointed out. The results show that the rock dynamic initiation toughness and propagation toughness increase with the increasing dynamic loading rate and crack propagation velocity, respectively, and the dynamic initiation toughness is larger than the arrest toughness.

     

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