Surface-Contact Mechanics During Oblique Impact of Microspheres with Planar Surfaces

The surface-contact mechanics and impact characteristics of a microsphere with an inclined planar surface are examined by experiments and numerical simulation. The results of base-case experiments are presented in which mono disperse, electrically neutral microspheres obliquely impact a molecular-smooth flat surface under vacuum. Experiments different from the base case delineate the effects of variations in surface material properties and roughness, and microsphere material properties, size, spin and electrical charge. The presence of microsphere spin prior to impact is found to significantly affect the impact response. The nature of the contact mechanics changes and is affected by variations in surface and microsphere material properties. Increased surface roughness alters the microsphereʹs impact response and biases experimental results at shallow incidence angles, at times yielding apparent coefficients of restitution greater than unity. Finally, electrical charge is shown to lower the microsphereʹs rebound velocity most appreciably at normal incidence