FINITE-ELEMENT ANALYSIS OF GRAIN-MATRIX MICRO-CRACKING IN SHALE WITHIN THE CONTEXT OF A MULTISCALE MODELING APPROACH FOR FRACTURE

The paper models grain-scale micro-cracking in shale at grain-matrix interfaces, assuming constituents are composed of quart silt grains and compacted clay matrix for a typical shale. The influence of the grain-matrix-grain interaction on micro-crack patterns is investigated. Elasto-plastic pressure-sensitive cohesive-surface models are inserted at grain-matrix interfaces and intra-clay-matrix finite-element facets. A bulk elasto-plasticity model with bifurcation, but currently no post-bifurcation constitutive model, is employed for the clay matrix to compare to the intra-clay-matrix cohesive-surface model. Numerical examples are presented under two-dimensional plane strain condition at small strains.