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.

Numerical simulation of percussive drilling

“…(ii) This law is rate‐independent; that is, it does not significantly depend on the penetration velocity of the indenter in the range of velocities spanned in percussive drilling . (iii) The law can be approximated by a bilinear model that is characterized by two stiffness parameters , one for the loading phase and one for the unloading phase, K R and γ K R , respectively. See the experimental and numerical examples reported in Figure .…”

“…The combination of a finite element discretization in space with an event‐driven time integration strategy is proposed to solve the piecewise partial differential equations that govern the process model. The versatility of this approach, developed by the authors in the case of unilateral elastic constraints , makes it possible to relax some of the present model simplifications in future work, for example, the replacement of the pressure law by a thermodynamical model or the explicit modeling of the bit/rock interaction rather than the simple force/penetration relationship we have assumed. The proposed model and simulation procedure are thus expected to serve as a stepping stone toward a more integrated analysis of percussive drilling.…”

Experimental and numerical study of drill bit drop tests on Kuru granite

“…with several buttons [13]. As far as the numerical simulations are concerned, the substantial influence of (i) the presence and position of the cap and (ii) the strain rate and viscous effects, on the predicted (iii) stress distribution under the buttons and (iv) force versus displacement curve resulting from the bit-rock interaction (BRI) were enlightened [14]. Moreover, it was observed that the nature of the energy transfer will influence the efficiency of penetration [15].…”

Effects of surface cracks and strain rate on the tensile behavior of Balmoral Red granite

“…Saksala et al [6] studied the fracture behavior of Kuru granite by analyzing the Brazilian Disc tests with numerical and experimental approaches. In a separate study, Saksala et al [7] extended the modeling approach to 3D and studied the bit-rock interactions and rock fracture in percussive drilling. Tang et al [8,9] carried out numerical simulations to study the influence of microstructure on rock failure in uniaxial compression.…”