Numerical modelling of thermal jet assisted rock cutting with double PDC cutters

Preconditioning of rock for drilling operations is a potential method to facilitate the mechanical breakage and mitigate the tool wear. This paper numerically investigates one such preconditioning technique, namely, the thermal jet assisted rock cutting. For this end, a numerical method for solving the governing thermo-mechanical problem is developed and validated. The continuum approach is chosen to describe the rock failure, being based on a damage-viscoplasticity model with the Drucker-Prager yield surface and the modified Rankine surface as the tensile cut-off. In the damage part, separate scalar damage variables are employed for tension and compression. The cutters are modelled as rigid bodies and their interaction with the rock is modelled by imposing contact constraints by the forward increment Lagrange multiplier method, which is compatible with the chosen explicit time integration scheme. A damage-based erosion criterion is applied to remove the contact nodes surrounded by heavily damaged elements. The thermal jets are modelled with a moving external heat flux boundary condition. The global thermo-mechanical problem is solved with a staggered approach explicitly in time while applying mass scaling to increase the critical time step. The novel 3D numerical simulations involving two cutters demonstrate the capabilities of the method with a special emphasis on cutter-thermal jet configurations. Therefore, the present method provides a potential tool for the bit design in thermal jet assisted drilling.