Numerical investigation of dynamic fracture in rock specimens containing a pre-existing surface flaw with different dip angles
Numerical investigation of dynamic fracture in rock specimens containing a pre-existing surface flaw with different dip angles
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含有不同倾角的预先存在的表面缺陷的岩石样本动态断裂的数值研究
DOI：
10.1016/j.engfracmech.2019.106675
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发表时间：
2020-01-01
影响因子：
5.4
通讯作者：
Wang, Kai
中科院分区：
文献类型：
--
作者：
Qian, Xi Kun;Liang, Zheng Zhao;Wang, Kai
通过有限元分析，具有三维预先存在的表面缺陷的数值模拟样本会受到应力波的影响，直至失效。再现了不同类型的裂纹，包括翼状裂纹、反翼状裂纹、贝壳状裂纹和剥落断裂。分析了动载条件下不同缺陷倾角对翼状裂纹、反翼状裂纹和壳状裂纹萌生和扩展的影响。数值模拟结果表明，缺陷倾角对动态加载下缺陷试件的裂纹行为和破坏模式起着重要作用。当预存缺陷倾角小于60°时，试件表面会出现翼状裂纹和反翼状裂纹，并呈现相似的裂纹扩展模式。相比之下，缺陷倾角为 75 度和 90 度的试样仅出现翼形裂纹。除裂纹倾角为 90 度的试样外，在所有情况下，试样内部都会再现贝壳状裂纹。此外，壳状裂纹在翼裂纹和反翼裂纹停止扩展后继续扩展。同时，数值模拟还确定了试件的声发射（AE）计数和能量，它们与动态破坏过程中的缺陷倾角密切相关。缺陷倾角对试件的动态强度有轻微影响。此外，基于数值研究，比较了动态和静态加载条件下具有单个预先存在缺陷的样本的开裂模式。动态载荷会产生更多裂纹并导致更复杂的开裂行为。此外，加载速率可以显着影响岩石样本的裂纹扩展模式和声发射特性。在高负载率下，样品的破碎效率更高。此外，对于承受高加载速率的试件，发生的剪切断裂越多，累积AE能量越大，AE计数越少。最后，非均匀性对于材料中微裂纹的分布和裂纹扩展模式也起着重要作用。裂纹分支发生在相对异质的岩石中，影响早期产生的裂纹的进一步扩展。应力集中区不是唯一的决定因素，可以用不均匀程度来代替来决定裂纹的萌生和扩展。该研究结果可为异质脆性材料在动载作用下的破坏过程研究提供有价值的参考。
Numerically simulated specimens with a three-dimensional pre-existing surface flaw are subjected to stress waves until failure via finite element analysis. Different types of cracks are reproduced, including wing cracks, anti-wing cracks, shell-like cracks and spalling fractures. The effects of different flaw dip angles on the initiation and propagation of wing cracks, anti-wing cracks and shell-like cracks are analysed under dynamic loading conditions. The numerical simulation results indicate that the dip angle of the flaw plays an important role in the crack behaviour and failure patterns of flawed specimens under dynamic loading. Wing cracks and anti-wing cracks emerge and present similar crack propagation patterns on the surface of the specimen when the pre-existing flaw dip angle is less than 60 degrees. In contrast, only wing cracks appear in specimens with flaw dip angles of 75 degrees and 90 degrees. Shell-like cracks are reproduced inside of the specimens in all cases except the specimen with a flaw dip angle of 90 degrees. In addition, the further propagation of shell-like cracks proceeds after the wing and anti-wing cracks stop propagating. Meanwhile, the numerical simulation also identifies the acoustic emission (AE) counts and energy of the specimen, which are closely related to the flaw dip angle during the dynamic failure process. The flaw dip angle has a slight effect on the dynamic strength of the specimens. Furthermore, the cracking patterns of specimens with a single pre-existing flaw under dynamic and static loading conditions are compared based on numerical investigations. Dynamic loading can produce more cracks and lead to more complex cracking behaviour. Moreover, loading rates can significantly influence crack propagation patterns and AE characteristics of rock specimens. Under high loading rates, the specimens fragment more efficiently. In addition, for specimens subjected to high loading rates, the more shear fractures occur, the greater the cumulative AE energy and the fewer the AE counts. Finally, heterogeneity also plays an important role in the distribution of micro-cracks in the material and the crack propagation patterns. Crack branching occurs in relatively heterogeneous rocks, which affects the further propagation of cracks initiated early. The stress concentration zone is not the only decisive factor and may be replaced by the degree of heterogeneity to determine the crack initiation and propagation. The results of this study can provide a valuable reference for studies on the failure process of heterogeneous brittle materials under dynamic loading.