Abstract
In this study, the effect of loading rate on shale fracture behaviors was investigated under dynamic and static loading conditions. Cracked straight through Brazilian disc (CSTBD) shale specimens were tested with a split Hopkinson pressure bar (SHPB) setup and INSTRON1346 servo-testing machine under pure mode I loading conditions. During the test, the crack propagation process was recorded by high-speed (HS) camera, and the acoustic emission (AE) signal generated by the fracture was collected by acoustic emission (AE) system. At the same time, crack propagation gauge (CPG) was used to measure the crack propagation velocity of the specimen. The results show that the crack propagation velocity and fracture toughness of shale have a positive correlation with the loading rate. The relationship among the crack propagation velocity, the fracture toughness and the loading rate is established under the static loading condition. In addition, the characteristics of AE signals with different loading rates are analyzed. It is found that the AE signals generated by microcrack growth decrease with the increase of loading rates. Meanwhile, the turning point of cumulative counting moves forward as the loading rate increases, which shows that the AE signal generated by shale fracture at low loading rate mainly comes from the initiation and propagation of microcracks, while at high loading rate it mainly comes from the formation of macro large-scale cracks. The fracture mechanism that causes shale fracture toughness and crack propagation velocity to vary with loading rate is also discussed based on the analysis results of AE signals.
摘要
本研究从动态和静态加载条件下考察了加载速率对页岩断裂行为的影响。在纯I 型加载条件下 采用分离式的SHPB 杆和INSTRON1346 伺服试验机对页岩试样进行了测试。在测试过程中,使用高 速摄影仪和声发射采集系统分别对试样破坏过程和试样破坏产生的声发射信号进行监测,同时,通过 裂纹扩展仪(CPG)测量裂纹扩展速度。结果表明,页岩的断裂韧度和裂纹扩展速度与加载速率呈正相 关。在静态载荷条件下建立了断裂韧度和裂纹扩展速度与加载速率之间的关系。另外,还对不同加载 速率下的声发射信号特征进行了分析。发现随着加载速率的增加,微裂纹扩展产生的声发射信号减小, 同时,声发射累积计数的突变点随着加载速率的增加而向前移动,这表明低加载速率下页岩破裂产生 的声发射信号主要来自微裂纹的萌生和扩展,而高加载速率下则主要来自宏观大尺度裂纹的形成。根 据声发射信号的分析结果,探讨了引起页岩断裂韧度和裂纹扩展速度随加载速率变化的断裂机理。
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XIE Qin is responsible for the experimental part and the paper writing. LI Sheng-xiang is responsible for the data processing and part of the paper writing. LIU Xi-ling is responsible for experimental setup and theoretical analysis. GONG Feng-qiang and LI Xi-bing is responsible for experimental results analysis.
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XIE Qin, LI Sheng-xiang, LIU Xi-ling, GONG Feng-qiang and LI Xi-bing declare that they have no conflict of interest.
Foundation item: Project(41630642) supported by the National Natural Science Foundation of China
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Xie, Q., Li, Sx., Liu, Xl. et al. Effect of loading rate on fracture behaviors of shale under mode I loading. J. Cent. South Univ. Technol. 27, 3118–3132 (2020). https://doi.org/10.1007/s11771-020-4533-5
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DOI: https://doi.org/10.1007/s11771-020-4533-5
Key words
- shale
- loading rate
- cracked straight through Brazilian disc
- fracture toughness
- acoustic emission
- crack propagation velocity