Mechanisms of Anisotropy in Salt Rock Upon Microcrack Propagation
Mechanisms of Anisotropy in Salt Rock Upon Microcrack Propagation
复制标题
DOI：
10.1007/s00603-020-02096-1
复制
发表时间：
2020-04
影响因子：
6.2
通讯作者：
Xianda Shen;C. Arson;Ji-hui Ding;F. Chester;J. Chester
中科院分区：
文献类型：
--
作者：
Xianda Shen;C. Arson;Ji-hui Ding;F. Chester;J. Chester
盐岩是一种多晶材料，由于其低渗透性和在有利的应力和温度条件下通过压力溶解而自愈的潜力，因此对地质储存感兴趣。通常假设微裂纹扩展和愈合导致各向同性刚度变化。本研究的目的是检查这一假设，并获得控制损伤和不可逆变形的积累的机制的基本理解。对热固结合成盐岩进行了围压为1 MPa的循环轴向载荷试验。应力-应变曲线和显微组织的图像在关键阶段的周期揭示了一个复杂的系统的滑动和翼微裂纹，其方向是负载依赖的形成。我们解释的机制，控制耦合演化的裂纹族的离散翼裂纹弹塑性损伤（DWCPD）模型。裂纹扩展由模式I和模式II断裂力学标准控制。滑动的“主”裂纹增长，如果一个内聚摩擦标准得到满足，而翼裂纹扩展在拉伸。裂纹面处的位移跃变与岩石代表单元体的变形有关。DWCPD模型能够反映加载过程中的非线性应力应变关系和刚度退化。模拟结果表明，微裂纹的产生经历了两个阶段：（1）翼裂纹萌生，主裂纹不扩展;（2）翼裂纹和主裂纹同时扩展。裂纹面处的较高摩擦导致较高强度。黏聚力越大，盐岩强度越高，损伤发展越慢，表现为粘滑演化。在高约束条件下，翼裂纹的萌生被推迟，从而导致强度的提高。在压缩前受损的试件中，损伤率高于未受损的试件。建议DWCPD模型可以扩展到任何多晶半脆性材料，并可以应用于了解地质存储设施中的裂纹模式的形成。
Salt rock is a polycrystalline material of interest for geostorage because of its low permeability and potential to self-heal by pressure solution at favorable stress and temperature conditions. It is often assumed that microcrack propagation and healing lead to isotropic stiffness changes. The goal of this study is to check this assumption and to gain a fundamental understanding of the mechanisms that control the accumulation of damage and irreversible deformation. Cyclic axial loading tests are performed under a confining pressure of 1 MPa on synthetic salt rock generated by thermal consolidation. The stress–strain curves and the microstructure images taken at key stages of the cycles reveal the formation of a complex system of sliding and wing microcracks, the orientation of which is loading dependent. We interpret the mechanisms that control the coupled evolution of crack families by a discrete wing crack elastoplastic damage (DWCPD) model. Crack propagation is controlled by Mode I and Mode II fracture mechanics criteria. Sliding “main” cracks grow if a cohesive frictional criterion is met, while the wing cracks propagate in tension. Displacement jumps at crack faces are related to the deformation of the rock representative elementary volume (REV). The DWCPD model can capture the nonlinear stress–strain relationship and the degradation of stiffness during the loading cycles. Simulations show that microcracks occur following two stages: (1) wing cracks initiate and main cracks do not propagate; (2) wing cracks and main cracks then propagate simultaneously. Higher friction at the crack faces leads to higher strength. With a larger cohesion, salt rock strength increases, damage development is delayed and exhibits a stick-slip evolution. At higher confinement, the initiation of wing cracks is delayed, which results in an increase of strength. The damage rate is higher in specimens that are damaged prior to compression than in the ones that are not. The proposed DWCPD model can be extended to any polycrystalline semi-brittle material, and can be applied to understand the formation of crack patterns in geostorage facilities.