Pore-scale modeling of deformation and shear band bifurcation in porous crystalline rocks

We develop a computational framework that captures the microfracture processes leading to shear band bifurcation in porous crystalline rocks. The framework consists of computational homogenization on a representative elementary volume that upscales the pore-scale microfracture processes to the continuum scale. The assumed enhanced strain finite element approach is used to capture the discontinuous displacement field generated by the microfractures. Homogenization at the continuum scale results in incrementally nonlinear material response, in which the overall constitutive tangent tensor varies with the stress state and with the loading direction. Continuum bifurcation detects the formation of a shear band on the representative elementary volume level; multi-dimensional strain probes, necessitated by the incremental nonlinearity of the overall constitutive response, determine the most critical orientation of shear band bifurcation. Numerical simulations focus on microfracturing at the pore scale with either predominant interface separation or predominant interface contact modes. Results suggest a non-associative overall plastic flow and shear band bifurcation that depends on the microfracture length and the characteristic sliding distance related to slip weakening. Copyright (C) 2016 John Wiley & Sons, Ltd.