Peridynamic simulation of deep rock fragmentation subjected to cutter impact with Johnson-Cook model

Abstract

The low penetration rate is one of the limitations of ultra-deep well drilling, which usually results from the high strength of formation rock with high in-situ stress. The shock-assisted-drilling technique has been proven to be effective in improving the penetration rate of deep rock; however, the fragmentation mechanism is still not clear. Benefiting from the advantages of Peridynamics in simulating crack-involved problems, this paper first introduces the concepts of ordinary state-based Peridynamics and the nonlocal plastic deformation. Then, the nonlocal strain rate effect is reconstructed by reformulating the Peridynamic constitutive relations with the Johnson-Cook model, and the numerical algorithm is developed subsequently. The strain rate effect of yield strength is then validated by solving a benchmark example of uniaxial loading; the stress-strain relation subjected to different load rates is generated. To further investigate the fragmentation under different load rates, the crack propagation of the Brazilian Disk subjected to the Split Hopkinson test is simulated. The crack propagation simulation of BD with/without a slot is consistent with the experiment results. Furthermore, the research systematically reveals the coupling influence of cutter impact and in-situ stress on rock damage evolution and plastic deformation. The numerical simulation demonstrates the stress regulation and damage suppression effects of cutter impact under different in-situ stresses. The dynamic behavior of the rock exhibits a strain-rate-strengthening characteristic and shows a positive correlation between yield strength and strain rate. These findings elucidated the damage evolution mechanism of deep formation rock under impact loads.