Abstract
Dynamic properties of rocks are extremely important in a variety of rock mechanics and rock engineering problems. The split Hopkinson tensile bar (SHTB) system is used in this paper to measure the mechanical properties of sandstone specimens under dynamic direct tension, and the full stress-strain curves of the specimens at different strain rates is obtained. The experimental results indicate that the tensile strength, the tensile modulus and the peak strain of the specimen increase almost linearly with the strain rate. The increases in the tensile strength, the tensile modulus and the peak strain reach 125 %, 37 % and 98 % respectively as the strain rate increases by 252 %. The microscopic structure characteristics of the fracture surfaces after the tensile failure of the specimens are investigated by three-dimensional scanning. The results suggest that the fracture surface roughness of the sandstone under direct tension is significantly sensitive to the strain rate. Both the roughness coefficient and the fractal dimension of the specimen increase with the strain rate. The fracture surface of the specimen changes from a relatively flat two-dimensional state to a three-dimensional state, and its relative area gradually increases. Finally, it is manifested from the aspect of energy consumption that both the energy consumed in the fracture process and the dynamic direct tensile strength enhance with the fracture surface roughness. It is believed that the investigation results can provide an important reference for the research on dynamic properties of rocks involved in experimental research and engineering practice.
Highlights
The accurate determination of rock dynamic properties has always been an important issue for rock engineering and mining engineering [1]
STRESS-STRAIN CURVES OF SANDSTONE SPECIMENS UNDER DYNAMIC DIRECT TENSION Based on the propagation theory of one-dimensional elastic wave [9], the stress, strain and average strain rate can be calculated by equation (1), equation (2) and equation (3), respectively
The results show that the fracture surface roughness of the rock material under dynamic direct tension is notably sensitive to the strain rate
Summary
The accurate determination of rock dynamic properties has always been an important issue for rock engineering and mining engineering [1]. Its applications include rock mass excavation, the prediction of rock bursts and earthquakes, drilling and blasting, projectile penetrations, etc [2]. Rocks are brittle materials and have tensile strength much lower than their compressive strength [3]. Tensile failure normally occurs in rocks under external loading, and the failure process is highly sensitive to the strain rate of the external loading [4], [5]. It is of great significance to understand. The associate editor coordinating the review of this manuscript and approving it for publication was Laurence T.
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