Collaborative Research: Experimental and Theoretical Investigation of Compaction and Dilation Bands

Suny At Stony Brook, Stony Brook NY

Investigators

Abstract

Issen/Wong 0106932/0106580 Compaction bands, a recently identified type of localized deformation, form in high porosity sandstone, perpendicular to the direction of maximum compressive stress. They occur for stress states associated with the transition from brittle faulting to distributed cataclastic flow, where microstructural observations show damage partitioned between at least two damage mechanisms: axial microcracks that may grow and coalesce to form a shear fault, and pores that collapse while grains are crushed. Theoretical predictions from recent reassessments of the bifurcation approach to strain localization do not correlate well with the scarce existing experimental data. This proposal suggests that an inadequate constitutive model causes the discrepancy. Thus, a two-yield surface constitutive model, representing both damage mechanisms, will be used with experimentally derived constraints for the important material parameters to enable further theoretical analyses regarding the onset of localization. Experimental and theoretical results will be synthesized to extrapolate a model to predict failure modes and localization development in crustal settings for different stress states and loading paths. Recent theoretical works have also highlighted two potentially important, but previously neglected failure modes: "dilation bands" and "dilating shear bands". A lack of data has hampered the mechanical analysis of analogous structures that structural geologists refer to as "hybrid shear fractures" or "transitional tensile fractures." Theoretical work predicts formation of these bands in low porosity rocks under overall compressive loading. Thus, the proposed work also includes experimental and theoretical investigation of dilation band formation using low porosity rock in triaxial extension tests.