Catastrophic failure: how and when? Insights from 4D in-situ x-ray micro-tomography
Catastrophic failure: how and when? Insights from 4D in-situ x-ray micro-tomography
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灾难性失败：如何以及何时？
DOI：
10.1002/essoar.10503361.1
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Cartwright-Taylor A
中科院分区：
文献类型：
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作者：
Cartwright-Taylor A
脆性岩石的灾难性破坏对于管理与系统规模材料破坏相关的风险非常重要。这种失效是由微裂纹的成核、生长和合并引起的，这些微裂纹在压应力下沿着局部损伤区域自发地自组织。在这里，我们提出了 X 射线显微断层扫描观察结果，阐明了从同步加速器中进行的新型三轴压缩实验获得的原位微米级过程。我们研究了起始材料（Ailsa Craig 微花岗岩；以几乎无裂纹而闻名）的微观结构异质性对裂纹网络演化和定位的影响。为了控制异质性，我们通过热应力在一个样品中引入随机纳米级裂纹网络，留下第二个样品。通过评估裂纹尺寸和空间分布的时间相关统计数据，我们检验了以下假设：起始异质性程度影响完整状态和失效状态之间相变的顺序和可预测性。我们证明，在系统规模上确实是这样。最初更异质（热处理）的样品显示出二阶转变的明确证据：相关长度的逆幂律加速与接近失效的明确定义的奇点以及缩放指数的明显变化。更均匀（未经处理）的样品显示出一阶转变的证据：与分布式损伤和突然失效之前不稳定裂纹成核相关的相关长度呈指数增加。在这两种情况下，初始孔隙度的各向异性决定了断层方向，当相关长度接近晶粒尺寸时，就会发生系统尺寸的故障。这些结果对于不同材料灾难性失效的可预测性具有重要意义。
Catastrophic failure of brittle rocks is important in managing risk associated with system‐sized material failure. Such failure is caused by nucleation, growth, and coalescence of microcracks that spontaneously self‐organize along localized damage zones under compressive stress. Here we present X‐ray microtomography observations that elucidate the in situ micron‐scale processes, obtained from novel tri‐axial compression experiments conducted in a synchrotron. We examine the effect of microstructural heterogeneity in the starting material (Ailsa Craig microgranite; known for being virtually crack‐free) on crack network evolution and localization. To control for heterogeneity, we introduced a random nanoscale crack network into one sample by thermal stressing, leaving a second sample as‐received. By assessing the time‐dependent statistics of crack size and spatial distribution, we test the hypothesis that the degree of starting heterogeneity influences the order and predictability of the phase transition between intact and failed states. We show that this is indeed the case at the system‐scale. The initially more heterogeneous (heat‐treated) sample showed clear evidence for a second‐order transition: inverse power law acceleration in correlation length with a well‐defined singularity near failure and distinct changes in the scaling exponents. The more homogeneous (untreated) sample showed evidence for a first‐order transition: exponential increase in correlation length associated with distributed damage and unstable crack nucleation ahead of abrupt failure. In both cases, anisotropy in the initial porosity dictated the fault orientation, and system‐sized failure occurred when the correlation length approached the grain size. These results have significant implications for the predictability of catastrophic failure in different materials.