Dynamic In Situ Three-Dimensional Imaging and Digital Volume Correlation Analysis to Quantify Strain Localization and Fracture Coalescence in Sandstone
Dynamic In Situ Three-Dimensional Imaging and Digital Volume Correlation Analysis to Quantify Strain Localization and Fracture Coalescence in Sandstone
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DOI：
10.1007/s00024-018-2003-x
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发表时间：
2018-10
影响因子：
2
通讯作者：
François Renard;J. McBeck;B. Cordonnier;Xiaojiao Zheng;Neelima Kandula;Jesus R. Sanchez;M. Kobchenko-M.-Kobchen
中科院分区：
文献类型：
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作者：
François Renard;J. McBeck;B. Cordonnier;Xiaojiao Zheng;Neelima Kandula;Jesus R. Sanchez;M. Kobchenko-M.-Kobchen
在三轴压缩变形装置设计、动态X射线显微层析成像、数据分析技术和数字体积相关分析方面的进展，提供了无与伦比的对岩石内发展应变的原位四维分布的访问。为了展示这些新技术的威力，并获得关于多孔岩石损伤演化、变形和破坏的微观力学的详细信息，我们在X射线透明三轴压缩装置中对低孔隙度丰丹白露砂岩的3厘米尺度圆柱形试件进行了变形，并随着差应力的增加重复记录了试件的三维层析图像，直到宏观破坏发生。实验是在室温下进行的，围压范围为10-20 Mpa。不同的灰度子集，指示密度，使三维断层图像能够分割成完整的岩石基质、孔隙空间和裂缝。对断层图像的数字体积相关分析在整个实验过程中提供了三维增量应变张量场的时间序列。在达到屈服应力后，试件首先通过微裂纹的张开和扩展变形，然后通过颗粒旋转和应变局部化沿断层发生剪切滑动。对于两个样品，损伤和剪胀发生在晶界打开，然后在破坏时颗粒岩石骨架突然坍塌。对于第三个样品，断层在屈服点附近形核，并通过穿晶微裂纹的发展在样品中传播。这些结果证实了以前对同一岩石的实验研究结果，并提供了新的详细量化：(1)样品中剪切应变与扩张应变的比例，(2)断层发展时微裂缝张开与孔洞张开的扩张量，以及(3)当接近破坏时，晶界和孔壁在钉扎微裂缝扩展和减缓损伤累积速度方面的作用。我们的研究展示了如何将高分辨率原位动态X射线显微层析成像和数字体积图像相关分析相结合，为揭示与上地壳相关的应力条件下岩石的脆性破坏过程提供额外的信息。
Advances in triaxial compression deformation apparatus design, dynamic X-ray microtomography imaging, data analysis techniques, and digital volume correlation analysis provide unparalleled access to the in situ four-dimensional distribution of developing strain within rocks. To demonstrate the power of these new techniques and acquire detailed information about the micromechanics of damage evolution, deformation, and failure of porous rocks, we deformed 3-cm-scale cylindrical specimens of low-porosity Fontainebleau sandstone in an X-ray-transparent triaxial compression apparatus, and repeatedly recorded three-dimensional tomograms of the specimens as the differential stress was increased until macroscopic failure occurred. Experiments were performed at room temperature with confining pressure in the range of 10–20 MPa. Distinct grayscale subsets, indicative of density, enabled segmentation of the three-dimensional tomograms into intact rock matrix, pore space, and fractures. Digital volume correlation analysis of pairs of tomograms provided time series of three-dimensional incremental strain tensor fields throughout the experiments. After the yield stress was reached, the samples deformed first by dilatant opening and propagation of microfractures, and then by shear sliding via grain rotation and strain localization along faults. For two samples, damage and dilatancy occurred by grain boundary opening and then a sudden collapse of the granular rock framework at failure. For the third sample, a fault nucleated near the yield point and propagated in the sample through the development of transgranular microfractures. The results confirm findings of previous experimental studies on the same rock and provide new detailed quantifications of: (1) the proportion of shear versus dilatant strain in the sample, (2) the amount of dilatancy due to microfracture opening versus pore opening when a fault develops, and (3) the role of grain boundaries and pore walls in pinning microfracture propagation and slowing down the rate of damage accumulation as failure is approached. Our study demonstrates how the combination of high-resolution in situ dynamic X-ray microtomography imaging and digital volume image correlation analysis can be used to provide additional information to unravel brittle failure processes in rocks under stress conditions relevant to the upper crust.