Relation between subcritical crack growth behavior and crack paths in granite
Relation between subcritical crack growth behavior and crack paths in granite
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DOI：
10.1016/j.ijrmms.2006.03.016
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发表时间：
2006-12
影响因子：
7.2
通讯作者：
Y. Nara;K. Koike;T. Yoneda;K. Kaneko
中科院分区：
文献类型：
--
作者：
Y. Nara;K. Koike;T. Yoneda;K. Kaneko
在断裂力学中，当裂纹尖端的应力强度因子达到断裂韧性时，裂纹就会扩展[1,2]。然而，即使应力强度因子小于断裂韧性，裂纹也可以扩展。这种现象称为亚临界裂纹扩展，其主要机制为应力腐蚀[3,4]。为了确保岩体结构的长期稳定性，如地下发电厂、储存液化石油或天然气的洞穴或地下放射性废物的储存库，有必要了解岩石的时间依赖性行为。因此，研究随时间变化的岩石变形与破裂问题具有十分重要的意义。我们之前研究了岩石中的亚临界裂纹扩展[5-8]。首先，我们展示了如何使用双扭转（DT）试验[9]估计各向同性岩石[7]亚临界裂纹扩展的活化能。然后，为了将该技术扩展到各向异性岩石，特别是花岗岩，我们提出了一种定量方法来估计预先存在的微裂纹的正交弹性常数和密度[8,10]。利用弹性常数和裂纹密度分析了花岗岩的亚临界裂纹扩展行为。考虑微裂纹的影响，估计了亚临界裂纹扩展的活化能。花岗岩的亚临界裂纹扩展依赖于已存在微裂纹的密度，并且裂纹的扩展是通过与裂缝前缘之前的已存在微裂纹连接来实现的。由于裂纹前沿微裂纹的密度与裂纹扩展方向有关，裂纹扩展行为会影响裂纹路径的几何形状。有必要验证上述分析。一些研究人员已经报道了裂纹路径的观察结果，这对于研究岩石组构对裂纹扩展行为的影响是有用的。例如，Swanson[11]在Westerly花岗岩中观察了亚临界裂纹扩展的裂纹路径，并表明石英、斜长石和黑云母中穿晶裂纹的百分比在裂纹扩展速率较高时趋于较高。Kudo et al.[12]观察了Aji花岗岩的裂纹路径，并研究了裂纹路径与矿物颗粒的相互作用。石英颗粒起到了重要的阻碍作用；长石晶粒因其解理面而改变裂纹路径方向；黑云母颗粒在本构比很小的情况下对裂纹路径也有显著影响。然而，这些研究并未明确裂纹扩展行为与裂纹路径几何形状之间的关系。本研究旨在观察DT试验获得的裂纹路径，探讨裂纹扩展行为与裂纹路径几何形状之间的关系。为了估计裂纹路径的几何形状，进行了分形分析并测量了裂纹长度。
In fracture mechanics, crack growth occurs when the stress intensity factor at the crack tip reaches the fracture toughness [1, 2]. However, a crack can propagate even when the stress intensity factor is less than the fracture toughness. This phenomenon is called subcritical crack growth, and the main mechanism is stress corrosion [3, 4]. To ensure the long-term stability of structures in a rock mass, such as an underground power plant, a cavern for storing liquefied petroleum or natural gas (LPG or LNG), or a repository for radioactive wastes in underground, it is necessary to know the time-dependent behavior of the rock. Therefore, it is very important to study the problems of time-dependent rock deformation and fracturing. We previously investigated subcritical crack growth in rock [5–8]. First, we showed how to estimate the activation energy for subcritical crack growth in isotropic rock [7] using double torsion (DT) test [9]. Then, to extend this technique to anisotropic rock, especially granite, we presented a quantitative method for estimating the orthorhombic elastic constants and density of pre-existing microcracks [8, 10]. The elastic constants and crack density were used to analyze the subcritical crack growth behavior in granite. The activation energy for subcritical crack growth was estimated by considering the effect of pre-existing microcracks. Subcritical crack growth in granite was found to be dependent on the density of pre-existing microcracks, and cracks propagated by connecting with pre-existing microcracks ahead of the crack front. Since the density of microcracks ahead of the crack front was dependent on the crack propagation direction, the crack growth behavior could affect the geometry of the crack path. It is necessary to verify the above analysis. Observations of the crack path, which have been reported by several researchers, can be useful for investigating the effect of rock fabrics on crack growth behavior. For example, Swanson [11] observed crack paths for subcritical crack growth in Westerly granite and showed that the percentage of transgranular cracks tended to be higher in quartz, plagioclase, and biotite when the crack growth rate was higher. Kudo et al.[12] observed crack paths in Aji granite and investigated the interaction between the crack paths and mineral grains. The quartz grain played an important role as an obstacle; feldspar grain could change the direction of the crack paths because of its cleavage plane; and biotite grain had a significant effect on the crack paths even when its constitutive ratio was very small. However, the relation between the crack growth behavior and the geometry of the crack path is not clear from these studies. This study aims at observing the crack paths obtained from DT tests and investigating the relationship between the crack growth behavior and the geometry of the crack path. To estimate the geometry of the crack path, fractal analysis was performed and the crack lengths were measured.