Force prediction in blow-out preventer shearing of drill pipes

An accurate prediction of blow-out preventer (BOP) drill pipe shearing is of critical importance in the applications of offshore drilling equipment. To simulate the shear process, a ductile failure criterion is clearly needed. In this paper, we employ an extended Mohr-Coulomb (EMC) criterion, which makes validated predictions for shear fracture by including the stress triaxiality T and Lode parameter L. This criterion has six parameters to be calibrated either by experimental tests or by numerical simulations. Here, we present a micromechanics model to calibrate the undetermined parameters via a void coalescence mechanism, and predict the forces for pipe shearing by finite element analyses. The shear force profile for the case where the EMC criterion parameters are micromechanically determined agrees with that for the case where the parameters are experimentally determined. This paper demonstrates the predictive capability of a micromechanics-based ductile fracture model in conjunction with the EMC criteria for BOP drill pipe shearing.