Abstract
Deformation and fracture of brittle materials, especially crack propagation, have drawn wide attention in recent years. But dynamic crack propagation under impact loading was not well understood. In this paper, we experimentally tested Brazilian disk (BD) fine sandstone specimens containing pre-cracks under cyclic impact loading by theΦ74 mm diameter split Hopkinson pressure bar (SHPB) test device. The pre-cracked specimens were named central straight through crack flattened Brazilian disk (CSCFBD). By using the low air-pressure loading conditions (0.1 MPa, equal to the impact velocity of 3.76 m/s), a series of dynamic impact tests were detected successfully, and the effects of pre-cracks on dynamic properties were analyzed. Experimental results show that the multiple cracks mostly initiate at/or near the pre-crack tips and then propagate in different paths and directions varying by inclination angles, leading to the ultimate failure. Compared to static or quasi-static loading, dynamic crack propagation and fracture behavior are obviously different. Furthermore, we characterized the crack propagation paths, directions, and fracture patterns and discussed the influences of the pre-cracks during the breakage process. We concluded that the results obtained are significant in investigating the failure mechanism and mechanical properties of brittle materials under impact loading.
Highlights
Dynamic deformation and fracture of brittle materials are complex processes
Crack growth and catastrophic failures initiated from pre-existing defects subjected to multiaxial loads are the main concerns for geotechnical engineers and designers of underground structures. e defects in rock can promote the initiation of new defects, which in turn may propagate and coalesce with other defects, and can further decrease the strength of the rock mass [5,6,7,8]. e presence of pre-cracks may obviously reduce the fracture toughness, dynamic uniaxial compressive strength, and dynamic tensile strength and lead to fragmentation and multiple crack interactions, branching, and coalescence [9]
Al-Shayea [24] studied crack propagation paths in pre-cracked limestone central straight though crack Brazilian disk (CSCBD) specimens loaded with diametrical compression, and they investigated the possibility of using outcrop specimens to estimate the fracture toughness behavior of the reservoir rock at in-situ conditions of temperature and confining pressure
Summary
Dynamic deformation and fracture of brittle materials are complex processes. Mining, tunnel excavation, and natural disasters such as landslides and earthquakes are all involved in the problems of dynamic damage. e failure of brittle materials is usually associated with crack propagation initiated from natural or artificial pre-existing defects. In previous studies, the fracture behavior and crack propagation of brittle materials were mainly investigated under static/quasi-static loading or used in intact specimens. Al-Shayea [24] studied crack propagation paths in pre-cracked limestone central straight though crack Brazilian disk (CSCBD) specimens loaded with diametrical compression, and they investigated the possibility of using outcrop specimens to estimate the fracture toughness behavior of the reservoir rock at in-situ conditions of temperature and confining pressure. E motivation for this work will focus on the following two points: (1) investigating the dynamic fracture patterns, multiple crack propagation paths, and directions in pre-cracked specimens; (2) characterizing and analyzing the crack types initiated from pre-cracks under cyclic impact loading.
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