Effects of irregular holes defect on the entire dynamic progressive fracture process of SCT limestone in split Hopkinson pressure bar tests: laboratory experiments and FEM modeling

Investigating the impact of irregular hole defects on the dynamic mechanical properties and fracture behavior of natural rocks is crucial for tunnel construction support, rock engineering stability evaluation, and rock burst prevention. In this study, we used a split Hopkinson pressure bar (SHPB) system and LS-DYNA numerical simulation to examine the dynamic fracture behavior of limestone specimens featuring single cleavage triangle (SCT) and different hole defects, subjected to impact load. We further analyzed the dynamic compressive strength, deformation modulus, failure mode, and crack expansion behavior of the SCT limestone specimens with double-hole defects under impact load. We used an image processing method for this analysis, supplementing it by employing the digital image correlation (DIC) method. This method enabled us to observe the evolution characteristics of the tensile strain field at the crack tip and the shear strain field surrounding the defect. Our findings revealed that specimens with asymmetric hole spacing were prone to premature compression deformation failure due to uneven force distribution. Specimens with asymmetrically distributed, wide-spaced hole defects resulted in fewer final cracks, which helped minimize rock chip flaking on the rock surface. Notably, the lower part hole defects significantly influenced the crack's propagation path, altering the initial tensile crack extension direction. There was strong agreement between the experimental and numerical simulation results, which highlighted the hole defects’a role in causing a non-uniform stress field distribution. This non-uniformity affected the strain field around the crack propagation direction, resulting in irregular sample deformation. Beyond the main prefabricated cracks and the cracks originating on the hole surface, we also identified secondary shear and tensile failure zones. These insights provide a theoretical reference for understanding the initiation and propagation mechanisms of cracks in the surrounding rock of tunnels and mine roadways.