Experimental investigation and micromechanics-based constitutive modeling of the transition from brittle to ductile behavior in saturated low-porosity rocks

This paper presents a unified experimental and numerical investigation on the transition from brittle to ductile behavior in a low-porosity sandstone under drained conditions. The experimental results demonstrate a transition in the mechanical behavior from brittle faulting to dilatant ductile flow at room temperature with an increase in effective confining pressure, suggesting that microcracking-controlled local friction is the underlying plastic deformation mechanism. For constitutive modeling, the sandstone is considered as a heterogeneous medium composed of a pores-weakened elastic solid matrix and distributed microcracks. By following a two-step homogenization procedure and irreversible thermodynamics framework, a micromechanics-based elastoplastic damage model incorporating a non-associated local plastic flow rule is formulated, in which the coupling between plasticity, damage and pore pressure is taken into account. In this context, a non-associated macroscopic effective strength criterion as an inherent part of the corresponding model is derived. Originally, a theoretical linear relation between critical state of damage at peak strength and effective confining pressure is established, which is efficient in describing post-peak softening behavior. Comparisons of numerical simulations with experimental data demonstrate that the proposed model effectively reproduces the main features of the sandstone with a brittle-ductile transition.

Automated summary

This paper presents a study on the transition from brittle to ductile behavior in a low-porosity sandstone under drained conditions. Experimental results show that the mechanical behavior changes from brittle faulting to dilatant ductile flow with increasing effective confining pressure. A micromechanics-based elastoplastic damage model is formulated to simulate this behavior, taking into account the coupling between plasticity, damage, and pore pressure. The model effectively reproduces the main features of the sandstone with a brittle-ductile transition, as shown by the comparison with experimental data.