Brittle-ductile failure transition in geomaterials modeled by a modified phase-field method with a varying damage-driving energy coefficient

摘要

With elevated confining pressure and low temperatures, geomaterials may exhibit brittle-to ductile failure transition due to increased cataclastic flow. In this work, we propose a modified phase-field damage model to capture this transition, wherein a portion chi(f) of the plastic work that contributes to the fracture driving force, is assumed. In particular, we propose to compute chi(f) based on a specific normalized stress parameter based on Byerlee's rule, which ranges from brittle tension fracture to cataclastic flow. In the former case, all the stored plastic free energy is assumed to contribute to fracture. However, in all other cases, the brittle fracture process at the macroscale is gradually suppressed with the increase of pressure, rendering a smaller value of chi(f). The proposed model includes eight material parameters, all of which can be calibrated from standard laboratory tests, i.e., conventional triaxial compressive experiments. To validate the performance of the proposed model, three pre-cracked specimens are constructed under plane strain conditions. Numerical simulations show that the predicted failure patterns agree with the experimental testing, which highlights the predictive capability of the model to capture brittle and ductile failure mechanisms. In addition, the proposed model can describe the brittle-ductile failure transition behavior in the homogeneous case and can predict the realistic failure process at the structural level.