Strain Rate Effect on the Mechanical Properties and Fracture Surface Roughness of Sandstone Subjected to Dynamic Direct Tension

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.