Abstract
To deeply understand the influence of crack inclination angle on crack propagation and coalescence in fractured limestone, uniaxial compression tests were carried out on limestone specimens with prefabricated cracks. The strain field evolution diagram of the failure process of the specimens was obtained using 3D digital image correlation technology (3D-DIC technology). This, in combination with the crack propagation diagram, was used to analyze the entire failure process of the limestone specimens. The test results show that the evolution process of the principal strain field agrees well with the process of crack initiation, propagation, and coalescence. The crack development process is the process of the high strain zones consistently propagating and also the process of micro-cracks appearing, developing, and nucleating to form macro-cracks. With the increase in the parallel crack inclination angle, the stress concentration zone of the intermediate crack transfers from both ends of the crack to the middle. Meanwhile, the coalescing crack type between the parallel crack and the intermediate crack changes from a coexisting tensile crack and tensile-shear crack to a single tensile crack. With the increase in the parallel crack inclination angle, the failure of the fractured limestone specimens changes from simple splitting or tensile failure to the coexistence of tensile-shear fracture and splitting. 3D-DIC technology provides an effective method to study crack propagation and coalescence during rock failure.
Highlights
To study the failure process of these defective rocks, scholars from China and other countries have carried out many in-depth studies in the laboratory using high-speed photography, acoustic emission, 3D printing, CT technology, and scanning electron microscopy (SEM)
Technology as the main observation method, uses maximum elongation line strain theory as the criterion to identify crack initiation, and investigates the influence of crack inclination on crack propagation and coalescence in fractured limestone based on the principal strain nephogram and the crack propagation nephogram drawn from real-time images
It is a bold attempt to carry out the research on the crack propagation of rocks with multiple cracks by 3D-DIC technology, which provides a new idea for future research on the crack propagation of rocks with multiple cracks
Summary
As a natural nonhomogeneous material, is widely used in various projects. Due to the influence of natural or man-made factors, various kinds of defects (such as voids and fissures) can form inside or on the surface of rocks, and the consistent propagation and coalescence of these defects are one of the important factors leading to rock failure. Zhao et al [36], Zhu et al [37], and Guo et al [38] obtained the principal strain field of a defective rock’s surface under uniaxial action through digital image correlation technology and analyzed the entire process of crack initiation, propagation, and failure by using the linear strain. Ma et al [39] conducted uniaxial compression tests on slab granite specimens with prefabricated circular holes, and used 3D-DIC technology to observe and calculate the displacement field and strain field on the surface of the specimen during the failure process. This study takes fractured limestone as the main study object, uses 3D-DIC technology as the main observation method, uses maximum elongation line strain theory as the criterion to identify crack initiation, and investigates the influence of crack inclination on crack propagation and coalescence in fractured limestone based on the principal strain nephogram and the crack propagation nephogram drawn from real-time images. It is a bold attempt to carry out the research on the crack propagation of rocks with multiple cracks by 3D-DIC technology, which provides a new idea for future research on the crack propagation of rocks with multiple cracks
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