Micromechanics and Strain Localization in Sand in the Ductile Regime
Micromechanics and Strain Localization in Sand in the Ductile Regime
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DOI：
10.1029/2022jb024983
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发表时间：
2022-11
期刊：
影响因子：
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通讯作者：
G. Shahin;R. Hurley
中科院分区：
文献类型：
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作者：
G. Shahin;R. Hurley
包括地震断层、储层划分和井眼破坏在内的关键过程涉及高压力学行为和砂岩等沉积岩的应变局部化。砂常被用作模型材料来研究低岩化砂岩的力学行为。最近的研究探索砂的多尺度力学的特点是脆性，低压状态的行为;然而，有限的工作提供了深入了解延性，高压状态的行为通过原位测量。因此，延性机制的关键特征，包括晶粒破碎、晶粒微观力学和体积应变行为仍处于探索之中。在这里，我们使用一种新的高压三轴仪与原位X射线断层扫描提供新的见解变形条带，颗粒破碎，并在渥太华砂进行三轴压缩围压10和45 MPa之间的颗粒微观力学。我们观察到压力高于15 MPa时的应变硬化和压力低于15 MPa时的应变中性响应。在所有压力下均观察到压实剪切带和颗粒破碎，除不太圆的砂中破碎略有增加外，颗粒尺寸没有显著变化。晶粒破碎出现在应力水平低于假定的屈服阈值和更强烈的破碎与薄的变形带。晶间接触处的接触滑动表现出分叉成双峰分布，变形带内的滑动剧烈，变形带外的滑动减少但不可忽略，这表明带外区域在应变硬化期间保持机械活性。
Critical processes including seismic faulting, reservoir compartmentalization, and borehole failure involve high‐pressure mechanical behavior and strain localization of sedimentary rocks such as sandstone. Sand is often used as a model material to study the mechanical behavior of poorly lithified sandstone. Recent studies exploring the multi‐scale mechanics of sand have characterized the brittle, low‐pressure regime of behavior; however, limited work has provided insights into the ductile, high‐pressure regime of behavior via in‐situ measurements. Critical features of the ductile regime, including grain breakage, grain micromechanics, and volumetric strain behavior therefore remain under‐explored. Here, we use a new high‐pressure triaxial apparatus with in‐situ x‐ray tomography to provide new insights into deformation banding, grain breakage, and grain micromechanics in Ottawa sand subjected to triaxial compression under confining pressures between 10 and 45 MPa. We observed strain‐hardening at pressures above 15 MPa and strain‐neutral responses at pressures below 15 MPa. Compacting shear bands and grain breakage were observed at all pressures with no significant variation due to grain size, except for minor increases in breakage in less‐rounded sands. Grain breakage emerged at stress levels lower than the assumed yield threshold and more intense breakage was associated with thinner deformation bands. Contact sliding at inter‐grain contacts demonstrated a bifurcation into a bimodal distribution, with intense sliding within deformation bands and reduced but non‐negligible sliding outside of deformation bands, suggesting that off‐band zones remain mechanically active during strain hardening.