GPGPU-parallelised hybrid finite-discrete element modelling of rock chipping and fragmentation process in mechanical cutting

Abstract

Mechanical cutting provides one of the most flexible and environmentally friendly excavation methods. It has attracted numerous efforts to model the rock chipping and fragmentation process, especially using the explicit finite element method (FEM) and bonded particle model (BPM), in order to improve cutting efficiency. This study investigates the application of a general-purpose graphic-processing-unit parallelised hybrid finite-discrete element method (FDEM) which enjoys the advantages of both explicit FEM and BPM, in modelling the rock chipping and fragmentation process in the rock scratch test of mechanical rock cutting. The input parameters of FDEM are determined through a calibration procedure of modelling conventional Brazilian tensile and uniaxial compressive tests of limestone. A series of scratch tests with various cutting velocities, cutter rake angles and cutting depths is then modelled using FDEM with calibrated input parameters. A few cycles of cutter/rock interactions, including their engagement and detachment process, are modelled for each case, which is conducted for the first time to the best knowledge of the authors, thanks to the general purpose graphic processing units (GPGPU) parallelisation. The failure mechanism, cutting force, chipping morphology and effect of various factors on them are discussed on the basis of the modelled results. Finally, it is concluded that GPGPU-parallelised FDEM provides a powerful tool to further study rock cutting and improve cutting efficiencies since it can explicitly capture different fracture mechanisms contributing to the rock chipping as well as chip formation and the separation process in mechanical cutting. Moreover, it is concluded that chipping is mostly owed to the mix-mode I-II fracture in all cases although mode II cracks and mode I cracks are the dominant failures in rock cutting with shallow and deep cutting depths, respectively. The chip morphology is found to be a function of cutter velocity, cutting depth and cutter rake angle.