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

Issen/Wong 0106932/0106580压实带是新近发现的一种局部化变形类型，形成于垂直于最大压应力方向的高孔隙度砂岩中。它们发生在与从脆性断层到分布式碎裂流的转变相关的应力状态下，在这种状态下，微观结构观察显示，损伤至少在两种损伤机制之间分配：轴向微裂纹可能增长并合并形成剪切断层，以及孔隙在颗粒被粉碎时坍塌。从最近对应变局部化的分叉方法的重新评估得出的理论预测与现有的稀缺实验数据不能很好地关联。这一建议表明，不充分的本构模型导致了这种差异。因此，代表两种损伤机制的双屈服面本构模型将与重要材料参数的实验导出约束一起使用，以便能够进一步从理论上分析局部化的开始。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种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”。缺乏数据阻碍了对类似结构的力学分析，结构地质学家将其称为“混合剪切裂缝”或“过渡性拉伸裂缝”。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，这项工作还包括在三轴拉伸试验中利用低孔隙度岩石形成膨胀带的实验和理论研究。

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.