Dynamic fracture behavior of limestone specimens containing double holes and crack under impact loading

Abstract

In-depth understanding of the influence of different hole defect structures on the dynamic mechanical properties and fracture behavior of rocks is an important theoretical guidance for the design of roadway support, rock engineering stability evaluation and mine pressure bump dynamic disaster prevention. The dynamic fracture behavior of limestone specimens containing different hole defects under impact loading was investigated. The fracture characteristics of the limestone specimens containing double-hole and crack were tested under impact conditions by using a split Hopkinson pressure bar (SHPB) impact loading system. The whole process of dynamic crack initiation, propagation and penetration was recorded by the high-speed camera. The dynamic compressive strength, dynamic deformation modulus, failure mode and crack extension behaviour of the double-hole limestone under impact loading were further analyzed by combining image processing method. The results show that the peak strain of specimen varies from 0.00297 to 0.00493 when the double-hole defects appear asymmetric. This is due to uneven stresses prone to earlier compression damage. The asymmetric growth of the hole spacing has a greater weakening effect on the peak strength of limestone specimens. The larger the spacing of the asymmetric hole defects, the higher the degree of weakening of the peak strength of the specimens. The shape, spacing and asymmetry of the double hole defects in the limestone specimens all have the significant effect on dynamic compressive strength. The hole defects in the lower part of the limestone specimen have a significant effect on the propagation of the primary crack. This deflects the direction of initial tensile crack extension, resulting in the main mode of damage being a shear-tensile composite fracture. Among the damage modes of the limestone specimens, far-field tensile and shear cracks of types V and VI are more common. In addition, the cracking velocity considering the extension path fractal effect is 1.01−1.17 times of the apparent crack extension velocity. When the hole defects are asymmetrically distributed and widely spaced, the final number of cracks formed is smaller, the crack expansion velocity is reduced, and it is more favorable to suppress the rock chip flaking phenomenon on the rock surface.

Keywords

• hole defect
• limestone
• split hopkinson pressure bar
• crack propagation
• dynamic property