Experimental and finite element analysis of oblique impacts with different initial spins

When a group of particles collide each other, oblique impacts with different initial spins are inescapable. The behavior of particles during and after an impact depends on different parameters such as size, shape and material properties of particles. In this article, the effects of incidence angle and initial spin on the coefficients of normal and tangential restitution were studied. The results including the coefficients of normal and tangential restitution with different incidence angles and spins were obtained through finite element (FE) simulations. The normal coefficient of restitution (COR) was also measured experimentally. The present results showed a contradiction to some of the studies in the literature such as C. Thornton (2009), in which it was claimed that the only effective parameter on the coefficients of restitution is the ratio of tangential to normal velocities at contact point v(t)/v(n), regardless of the incidence angle (w.r.t. centers of mass). In this work, it was found that the normal COR depends on both vt/vn and the incidence angle. However, the tangential COR was observed to be only a function of v(t)/v(n) based on the FEM results in agreement with the previous research. Different processes of stick, stick-slip and slip-stick-reverse slip could be found while the tangential COR varied with v(t)/v(n). The experimental data points corresponding to different vt/v, and impact angles confirmed the numerical results with maximum difference of 6.6%. (C) 2019 Elsevier Ltd. All rights reserved.