Rate- and strain-dependent brittle deformation of rocks
Rate- and strain-dependent brittle deformation of rocks
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DOI：
10.1002/2013jb010448
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发表时间：
2014-03-01
影响因子：
3.9
通讯作者：
Meredith, P. G.
中科院分区：
文献类型：
--
作者：
Brantut, N.;Heap, M. J.;Meredith, P. G.
我们开发了一个统一的框架来量化率相关的变形在脆性领域，并建立微观尺度的时间依赖性裂纹扩展过程和宏观观察到的率依赖性之间的联系。对三种砂岩进行了恒应变率和恒应力（蠕变）条件下的三轴变形实验。测得的相对演化的P波速度作为非弹性轴向应变的函数是类似的两种类型的测试，尽管高达3个数量级的应变率的差异。这种相似性表明，存在一个直接的，与时间无关的链接之间的微观结构状态（反映在P波速度的变化）和非弹性轴向应变。恒定应变率和蠕变实验之间的施加应力作为非弹性应变的函数的比较表明，蠕变变形需要较少的机械功使样品失效。这种能量亏损对应于应力亏损，这可能与微裂纹的能量释放速率的亏损有关。我们根据经验建立蠕变应变速率由（Δ）除以与exp（Δ Q/σ *）成比例的点给出，其中Δ Q是应力亏损（负），σ * 是活化应力。蠕变应变率与应力赤字之间的经验指数关系类似于速率与状态摩擦定律。我们开发了一种基于断裂力学的微观力学方法，以确定蠕变变形过程中裂纹尖端的有效应力强度因子的演变，并估计负责脆性蠕变的应力腐蚀反应的活化体积。
We develop a unifying framework to quantify rate-dependent deformation in the brittle field and establish links between the microscale time-dependent crack growth processes and the macroscopically observed rate dependency. Triaxial deformation experiments have been performed under both constant strain rate and constant stress (creep) conditions on three types of sandstone. The measured relative evolution of P wave speeds as a function of inelastic axial strain is similar for both types of test, despite differences in strain rate of up to 3 orders of magnitude. This similarity indicates that there exists a direct, time-independent link between the microstructural state (as reflected by the variations in P wave speed) and the inelastic axial strain. Comparison of applied stresses between constant strain rate and creep experiments as a function of inelastic strain indicates that creep deformation requires less mechanical work to bring the sample to failure. This energy deficit corresponds to a stress deficit, which can be related to a deficit in energy release rate of the microcracks. We establish empirically that the creep strain rate is given by (epsilon) over dot proportional to exp(Delta Q/sigma*), where Delta Q is the stress deficit (negative) and sigma* is an activation stress. This empirical exponential relation between creep strain rate and stress deficit is analogous to rate-and-state friction law. We develop a micromechanical approach based on fracture mechanics to determine the evolution of an effective stress intensity factor at crack tips during creep deformation and estimate the activation volume of the stress corrosion reaction responsible for brittle creep.