Experimental Investigations on the Coefficient of Restitution of Single Particles

Particle-based modeling approaches, such as the discrete element method, require the definition of accurate contact (collision) models. An essential parameter within these models is the coefficient of restitution (e), which mathematically defines the ratio of postcollision to precollision relative velocity during the collision of two materials. More generally, the coefficient of restitution provides a way of accounting for the kinetic energy lost during the collision of materials. This becomes important during particle-particle and particle-boundary collisions in both dry granular and multiphase flow models. This work studies e for particle-boundary type collisions through detailed experimental investigations of falling spheres colliding with thin stationary plates over a range of impact velocities. The results of these studies are also examined against analytical formulations for the coefficient of restitution. Experiments are performed on various sphere-plate material combinations, which include several tribologically relevant materials, such as low-carbon steel, tungsten carbide, and NiTiNOL 60. Experimental results for metallic material combinations displayed a decreasing trend in e for increased impact velocities. These metallic combinations also showed the lowest overall e values, whereas collisions involving glass showed the highest e values.