Application of Asymmetric Notched Semi-Circular Bending Specimen to Evaluate Mixed-Mode I-II Fracture Behaviors of Sandstone
Application of Asymmetric Notched Semi-Circular Bending Specimen to Evaluate Mixed-Mode I-II Fracture Behaviors of Sandstone
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DOI：
10.3390/fractalfract6060336
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发表时间：
2022-06
影响因子：
5.4
通讯作者：
G. Ma;Jiangteng Li;Xiaoping Zhou;Lianying Zhang;Pei-tao Qiu;Yang Yu
中科院分区：
文献类型：
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作者：
G. Ma;Jiangteng Li;Xiaoping Zhou;Lianying Zhang;Pei-tao Qiu;Yang Yu
为了研究混合模式I-II断裂行为，通过调整托辊之间的角度和距离，设计了3种不同的非对称缺口半圆弯曲试件（ANSCB），进行了非对称三点弯曲试验。利用声发射（AE）、数字图像相关（DIC）、裂纹扩展仪（CPG）和扫描电子显微镜（SEM）等辅助技术监测和评估断裂特征。同时，基于重建的数字断裂面，对断裂面进行分形维数评估。结果表明：混合模态ANSCB三点弯曲断裂是一种主裂纹迅速贯通、承载能力急剧下降的脆性破坏；基于DIC方法，将整个断裂过程分为非线性弹性阶段、断裂过程区、裂纹萌生阶段和裂纹扩展阶段。裂纹的起裂主要是由裂纹尖端的拉剪应变集中引起的。在微观尺度上，裂纹扩展路径总是沿晶界扩展，在晶界处，合成应力最弱。通过声发射监测发现，微拉伸裂纹是造成不对称三点弯曲断裂的主要原因。CPG数据表明，亚临界裂纹扩展速率与极限荷载呈正相关。此外，不对称加载导致断裂面更粗，从而导致断裂面的分形维数更高。本研究可以更好地理解岩石的I-II混合模式断裂行为。
In this paper, to investigate mixed-mode I-II fracture behaviors, three different asymmetric notched semi-circular bending specimens (ANSCB) were designed by adjusting the angle and the distance between supporting rollers to conduct asymmetric three-point bending tests. Several aid technologies, including acoustic emission (AE), digital image correlation (DIC), crack propagation gauge (CPG), and scanning electron microscopy (SEM), was utilized to monitor and assess the fracture characteristic. Meanwhile, the fractal dimension of the fracture surface was assessed based on the reconstructed digital fracture surface. The results show that mixed-mode I-II ANSCB three-point bending fracture is a brittle failure with the characteristics of the main crack being rapidly transfixed and the bearing capacity decreasing sharply. Based on the DIC method, the whole fracture process consists of a nonlinear elastic stage, fracture process zone, crack initiation stage and crack propagation stage. The crack initiation is mainly caused by the tension-shear strain concentration at the pre-existing crack tip. At the microscale, the crack propagation path is always along the grain boundary where the resultant stress is weakest. According to the monitoring of the AE, it can be found that micro-tensile cracks are mainly responsible for the asymmetric three-point bending fracture. The data obtained by CPG suggest that the subcritical crack growth rate is positively correlated to the ultimate load. In addition, asymmetric loading leads to a coarser fracture surface, and thus a higher fractal dimension of the fracture surface. The current study can provide a better understanding of the mixed-mode I-II fracture behaviors of rock.