A Micromechanics-Based Multiscale Constitutive Model for Brittle to Ductile Behavior of Porous Geomaterial

Brittle to ductile transition with the increase of confining pressure is a common behavior of porous geomaterial. In the present work, a micromechanics-based multiscale constitutive model is constructed to describe the macroscopic mechanical behavior of porous chalk. At the microscopic scale, the Drucker–Prager criterion is adopted to describe the plastic behavior of the solid matrix with dissymmetric responses between tensile and compressive loading. Based on the macroscopic yield criterion derived in Shen et al. (Int J Plast 126:102609, 2020), an effective damage parameter is introduced and then a complete multiscale constitutive model is constructed and implemented with a plastic hardening law and a macroscopic plastic potential to describe the overall mechanical behavior of porous geomaterial. Through the evolution of microstructure of the studied porous materials, the proposed micromechanics-based multiscale model well describes the transition from brittle behavior to ductile one with the increase of confining pressure. The proposed constitutive model is then applied to porous chalk and validated by the comparisons between its numerical predictions and experimental results under different confining pressures. The main features of porous materials are captured by the proposed model which improves significantly the phenomenological ones.