CONDITIONS FOR LOCALIZED COMPACTION OF POROUS GRANULAR MATERIALS

Abstract eng:
Compaction bands are a form of localized deformation found in both field and laboratory specimens of high porosity rock. These bands consist of planar zones of pure compressional deformation that form perpendicular to the direction of maximum compression. Recent experimental results indicate that compaction bands and/or shear bands (angled to the direction of maximum compression) occur in high porosity sandstone during a transitional loading regime where multiple damage mechanisms may be active. Therefore, a two-yield surface constitutive model is employed to examine conditions for localized deformation. The first yield surface corresponds to a dilatant, frictional mechanism, while the second is a yield surface cap, which corresponds to a compactant mechanism. A bifurcation approach to localization is used, revealing that localization conditions are strongly influenced by the choice of constitutive relation. Using a single yield surface constitutive model shear bands, but not the observed compaction bands, are predicted. However, the two-yield surface model predicts both experimentally observed band types for reported values of key material parameters. Additionally, the shear band angles predicted by the two-yield surface model are in general agreement with experimentally observed shear band angles.

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