3D numerical modelling of bit‐rock fracture mechanisms in percussive drilling with a multiple‐button bit

Abstract

SUMMARY This paper considers numerical modelling of rock fracture induced by dynamic bit–rock interaction in percussive drilling. The work presented here extends the author's earlier research on the topic from the axisymmetric case to 3D case. The numerical method for modelling rock fracture includes a constitutive model for rock and a contact mechanics-based technique to simulate the bit–rock interaction. The constitutive model is based on a combination of the recent viscoplastic consistency model, the isotropic damage concept and a parabolic compression cap. This model is improved here from its earlier state by calibrating the softening laws using fracture energies GIc and GIIc in tension and compression, respectively. Moreover, the viscosity modulus in tension is calibrated based on the dynamic Brazilian disc test. With these enhancements, the developed method is applied to 3D case of the bit–rock interaction problem assuming one symmetry plane. Single impact with single and multiple-button bits is simulated. In the latter case, an initial borehole is modelled in order to simulate the usual in-situ drilling conditions. The different failure types observed in the experiments as well as the interaction between the buttons resulting in chipping are realistically captured in the simulations. Copyright © 2012 John Wiley & Sons, Ltd.