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

Issen/Wong 0106932/0106580压实带是最近发现的一种局部变形类型，形成于高孔隙度砂岩中，垂直于最大压应力方向。 它们发生的应力状态与过渡从脆性断层分布catacerstic流，微观结构的观察显示至少有两种损伤机制之间的损害分区：轴向微裂纹，可能会增长和合并，形成剪切断层，和孔，崩溃，而颗粒被压碎。 从最近的重新评估的分叉的方法，应变局部化的理论预测不相关，以及与现有的实验数据稀缺。 这一建议表明，一个不适当的本构模型的差异。 因此，一个双屈服面本构模型，代表两种损伤机制，将使用实验推导的重要材料参数的约束，使进一步的理论分析关于发病的本地化。 将综合实验和理论结果，外推一个模型，以预测不同应力状态和加载路径下地壳环境中的破坏模式和局部化发展。 最近的理论工作也强调了两个潜在的重要，但以前被忽视的破坏模式：“膨胀带”和“膨胀剪切带”。 由于缺乏数据，阻碍了对类似结构的力学分析，结构地质学家称之为“混合剪切断裂”或“过渡拉伸断裂”。“理论工作预测了在整体压缩载荷下低孔隙度岩石中这些带的形成。 因此，建议的工作还包括实验和理论研究的膨胀带形成低孔隙度岩石在三轴拉伸试验。

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.