Shape Effects on Microbody Impacts against a Flat Surface

A general numerical model is developed to simulate the impact of an elongated microbody with a spherical tip against a flat surface. Experimental data of sphere impacts are used to determine the parameters used in the simulations. Two kinds of microbodies are considered: a rod with spherical ends and 2 hemispheres connected by a thin rigid rod. The results show that under the same incident velocity and orientation angle, the impacts are affected by the microbody shape. Angular velocity changes are quite sensitive to the length and orientation of the rod. Rotational energy balance plays an important role for long microbodies. The rebound velocity at the contact tip and the center of mass is different and can lead to secondary impacts. In contrast to spheres, tangential (friction) and normal forces are coupled for elongated microbodies. Because the tangential and normal forces act over the contact area at the end of the rod, a moment about the mass center is produced. The rotation of the rod is driven by this moment, which, in turn, changes the relative velocity and contact forces over the contact area. Thus the coefficient of restitution at the contact tip is also effected by and becomes a function of the geometry and orientation of the microbody. The simulation results support that three-dimensional (3D) microbody impact response is determined not only by the material and incident velocities but also by the geometry and orientation of the principal axis of the microbody.