Laboratory and discrete-based numerical investigation on the collision problem of impactor-block systems with soft-porous and hard-crystalline analog rocks

We investigated experimentally the normal coefficient of restitution (COR) of impactors colliding on the surfaces of two different blocks; a soft-porous block composed of plaster (dry impacts) and a hard-crystalline rock composed of granite (dry and wet impacts). The experiments were performed in a range of low-impact velocities and various particle types were used including perfectly spherical smooth glass beads and ceramic balls, rough glass beads as well as natural rough sand grains. Image processing was carried out to quantify the formed contours of craters caused by the surface damage of the soft blocks due to the impact. The results indicated very low COR values on the plaster block compared with the granite block as the energy was dissipated by means of surface plastic deformations on the plaster, however the contour crater images showed that the collision mechanisms depended on the roughness of the impactor. The behavior of impactor-fluid-block systems was dependent on both surface roughness and global morphology of the impactors. Discrete-based (DEM) numerical simulations were performed to provide further insights into the behavior of the impactor-block systems subjected to collision using the COR values from the experiments as the micro-scale parameters and data from the literature as the macro-scale parameters for the model calibration. The numerical output was used to observe the development of compression and tension force chain networks and how these involved during and after impact on different base blocks.