EXAMINING STRESS DISTRIBUTION AND ITS EFFECT ON SHEAR LOCALIZATION IN POLYCRYSTAL MODELS

Shear localization is common in deforming rocks and can be used as an indicator to determine the applied stress direction. For example, shear zones form 45° to compression. What is unclear about shear localization is how stress affects the spacing of deformation patterns. By modeling the compression of a polycrystalline rock, precise analysis of the stress distribution and the resulting strain distribution can be acquired. Previous finite element modeling of heterogeneous, polycrystalline material by Burnley [Nature Communications, DOI: 10.1038/ncommons3117 (2013)] has shown that the spacing of shear bands is closer when there is a higher density of patterning in the stress distribution. The stress patterning resembled force chains, linear, high-stress features that form parallel to compression. Force chains have been studied and linked to shear localization in granular materials using photoelastic bead experiments and compressional simulations. Polycrystalline materials have not been examined within the paradigm of force chains and might yield new insights into shear localization.

Adapting techniques from granular materials, I will examine the existence and role of force chains on strain distribution. Granular studies represented their experiments/simulations as a contact network and stress-weighted network for analyses. A contact network defines grains as nodes and grain contacts as edges. A stress-weighted contact network weighs edges based on the stress between the nodes. Granular studies employ clustering techniques on a stress-weighted contact network, which groups high-stress grains in contact. The results are force chains that are then quantified using metrics such as the length of the force chain; how much stress the force chain carries; and how linear the force chains are. These force chain metrics can all be compared to the strain distribution of the material and assessed for correlations. Using clustering on finite element models of polycrystalline materials, I will explore the existence and role of force chains in polycrystalline materials.