Cracking and deformation of cuboidal sandstone with a single nonpenetrating flaw under uniaxial compression

To get a good understanding of the cracking mechanism of a nonpenetrating flaw, digital carving technology was employed to pre-cut a nonpenetrating flaw within a rock block. Uniaxial compression tests were conducted on the specimens containing a single nonpenetrating flaw. A strain measuring system was employed to monitor the local microstrain near the flaw tips. Meanwhile, the failure process of specimens was recorded simultaneously using a video camera and the noncontact video gauge. Based on the experimental results, the crack propagation behaviors and the fracture characteristics of the nonpenetrating-flaw sandstone specimens during uniaxial loading were presented. Also, the relationship between peak strength and pre-existing flaw angle was shown. Furthermore, numerical models containing a penetrating or nonpenetrating flaw were developed using 3D particle flow code to investigate the crack propagation mechanisms under uniaxial compression. By comparing the contact force distribution and the principal stress distributions around pre-existing nonpenetrating or penetrating flaw just before crack initiation, the crack initiation and propagation of sandstone specimens containing a single nonpenetrating flaw was explained from the microscopic point. It is found that (a) the average peak strength increases with the growth of nonpenetrating flaw angle and reduced by 21.8% for 0 degrees, 16.0% for 30 degrees, 13.0% for 45 degrees, 4.7% for 60 degrees, and 0.5% for 90 degrees comparing with the peak strength of the intact specimen; (b) the crack first appears at the flaw tip on the front surface and then a new crack appears in the middle of the flaw on the back surface, the tensile stress gradually decreases from the front to the back; (c) the local strain at the front surfaces of the pre-existing flaw tip is greater than that at the same position on the back, the flaw tip of the model front is prone to stress concentration; (d) the final failure pattern relies on the pre-existing flaw angle and as the pre-existing flaw angle increases, the failure mode changes from mixed tension and shear failure to shear failure.

Automated summary

This study investigated the crack propagation behavior and fracture characteristics of nonpenetrating flaws in rock specimens using digital carving technology and experimental testing. By observing the location of crack initiation and analyzing stress distribution, the microscopic mechanism of flaw initiation and propagation was explained. The results showed that increasing the angle of the nonpenetrating flaw led to an increase in peak strength of the specimens. The crack first appeared at the front surface and then extended to the back surface, and the failure mode changed from mixed tension and shear failure to shear failure as the angle of the flaw increased.