Analysis of fracture process zone of coral reef limestone under dynamic impact

Abstract

The cohesive zone model is an important model for describing the fracture process zone (FPZ) of brittle materials, with a constitutive relationship corresponding to the force–displacement behavior in the non-elastic deformation zone, providing clear physical significance. Coral reef limestone (CRL), a heterogeneous sedimentary rock, has complex pore structure that significantly affects its fracture behavior. Given this, dynamic impact tests were conducted on CRL notched semi-circular bending (CRL-NSCB) specimens using a modified Split Hopkinson Pressure Bar. The study comparatively analyzed the differences in calculations of dynamic fracture toughness using different methods, such as the empirical formula recommended by the International Society for Rock Mechanics and Rock Engineering, the J-integral method, and method of linear elastic fracture mechanics. Additionally, a high-speed camera was adopted to capture the dynamic fracture process of the specimens, and the FPZ length of CRL was accurately measured based on the digital image correlation method. A numerical model of the CRL-NSCB specimen was also established, and a numerical case was conducted by hybrid finite-discrete element method to explore the effect of pore structure on the fracture process. The results indicate that the J-integral method accounts for energy release in the FPZ, allowing for a more accurate consideration of the heterogeneity effects. Loading rate primarily influences the crack propagation mode. At low loading rates, large pores near the expected crack path induce deviation from the expected crack path. Additionally, FPZ parameters exhibit a clear rate effect. These research conclusions provide new insights into the fracture process of porous CRL.