Multi-criteria validation of hi-fidelity numerical model of impact breakage: towards next generation percussion drill simulation

With the extensive application of numerical simulations in engineering fields such as mining, tunnelling, and petroleum, enhancing the accuracy of simulation tools to ensure their reliability has become a widely discussed issue. Using basic rock mechanics experiments to validate numerical models often encounters problems when these models are applied to more complex tests, resulting in distorted simulation results. To address this issue, this study uses single impact tests indicative of percussive drilling as an example, focusing on two crucial aspects during the bit-rock interaction: bit energy loss and the breakage morphology, including metrics for the extent of rock cracking. Seven criteria related to these two aspects were selected to validate the accuracy of the FDEM model. The simulation results were validated against two types of hard sedimentary rocks: St Anne limestone and Rhune sandstone. The numerical simulation results at different impact energies agreed well with experimental results across these seven criteria. The FDEM simulation results accurately reproduced the experimental observations, capturing the different crack morphologies and their evolution as observed in experimental CT scans and high-speed video recordings. The presence of median cracks in limestone and absence in sandstone, as observed in experiments, was reproduced by the simulations. Notably, the simulation results reveal that the generation of side cracks is not necessarily caused by the closure of median cracks because median cracks do not always initiate, as postulated in the literature. Instead, FDEM simulation results indicate that the propagation of side cracks is primarily caused by the tearing induced by the elastic recovery of the rock.