Comparative analysis on dynamic tensile mechanical properties of three kinds of rocks

Red sandstone,gray sandstone and granite are three kinds of rocks that are common in rock engineering and have large differences in wave impedance. The dynamic splitting tensile test of three kinds of Brazilian disc specimens at different impact velocities was carried out by using the split Hopkinson pressure bar (SHPB) test system to study the difference of dynamic tensile mechanical properties of different lithologic rocks. At the same time,the ultra-high speed digital image correlation (DIC) test system was used to observe the strain field change process and the dynamic tensile failure process of rock samples. The tensile strain field and shear strain field of three kinds of rocks were studied comparatively. The dynamic tensile strength,tensile sensitivity and failure morphology of rock samples under different impact velocities and different loading rates were compared and the effects of wave impedance on dynamic mechanical properties of rock were studied. The results show that:① The difference of failure modes of three kinds of rocks is mainly reflected in the wedge-shaped local shear fracture zone,and the area of the fracture zone is affected by the impact velocity. ② The dynamic tensile strength of three kinds of rocks increases linearly with the increase of impact velocity and loading rate. At the same impact velocity,the loading rate and dynamic tensile strength of granite are the largest,followed by gray sandstone and red sandstone. ③ The tensile strength of red sandstone is the most sensitive to loading rate,granite is the second and gray sandstone is the weakest. With the increase of impact velocity and loading rate,the tension sensitivity coefficients of three kinds of rocks increase linearly. ④ Under the same stress wave,the stress wave propagation process,loading history and dynamic tensile properties of rock are affected by wave impedance of rock,and there is a progressive relationship between them.