Bedding effect and macro-micro mechanism of graphite ore dynamic mechanical properties under impact loads

To reveal the influence law of graphite ore with different bedding angles under impact load, impact experiments on graphite ore samples with different bedding angles (0°, 45° and 90°) were conducted by using a 50 mm diameter split Hopkinson pressure bar (SHPB) device, with the combined use of high-speed photography and electron microscopy scan. The dynamic mechanical properties and impact failure modes were investigated during the dynamic fracture process. The results show that most of the minerals in graphite ore are arranged in an allotriomorphic granular orientation within an irregular contact boundary. There is a high content of muscovite and quartz, associated with graphite and enriched along the bedding planes. The bedding angles have a deterioration effect on samples, and the 45° bedding angle has the strongest deterioration effect. The energy dissipation characteristics show a U-shaped trend with the increase of bedding angle, similar to the strength characteristics. At the same strain rate, the average particle size of the broken samples is strongly correlated with the energy dissipation density. The average particle size of 0° bedding angle is the smallest, with the largest energy dissipation density. On the contrary, the average particle size is the largest when the bedding angle is 45°, with the smallest energy dissipation density. When graphite flakes are subjected to external forces, they will not only break from the inside but also be torn by associated minerals. The destruction form can be summarized as the evolution of tensile failure-shear failure-tensile splitting failure. The relevant characteristic results obtained from the experiments show that the damage degree of the graphite flakes is mainly controlled by the magnitude and direction of the impact load. Tensile failure can reduce the internal fracture of graphite flakes, and a low strain rate can reduce the production of rock powder. Therefore, the destructive effect of blasting impact load on graphite flakes can be reduced by adjusting the propagation direction of the shock wave, reducing the peak stress, and increasing the failure area of ore tensile stress. © 2023 Explosion and Shock Waves. All rights reserved.