Friction Property of Impact Sliding Contact under Vacuum and Microgravity

Vacuum and microgravity are two typical environments in space. High friction in the space environment is a challenge to the spacecraft. In vacuum, the adhesion effects are severe to induce a high friction force due to clean contact surfaces. Besides, the microgravity environment results in impact between the contact bodies, which will influence the friction property further. It is difficult to do microgravity friction experiments on the earth, and the chance to do a friction experiment in space is scarce. In this paper, considering adhesion effects in vacuum, a modelling method is developed to investigate the nanoscale impact sliding contact under microgravity. Based on energy conservation principle, the kinematic mechanism of a sliding contact body under microgravity is modeled, and the effects of impact on friction property is studied by comparing with the result of a smooth sliding contact. Considering the kinematic mechanism, the friction properties are investigated for different impact velocity and different tip radius. The kinetic energy of the tip will be converted to the mechanical energy during the impact process, and the friction forces could be underestimated if the impact effects are neglected. Owing to the contribution of impact velocity and the mass of the tip to the kinetic energy, the friction forces are increased as the increase of impact velocity and tip radius. Furthermore, using the principle of tribology, the ploughing component and adhesion component of the friction force are discussed to explain the friction phenomena under vacuum and microgravity environments.