Studies On Impact Sliding Contact Of Textured Surface Under Vacuum And Microgravity Environment

With the development of aerospace engineering,the mechanical devices on spacecraft are becoming more and more complex,and the friction between the components has become one of the most important limiting factors of spacecraft reliability.In vacuum,the atoms of contact surface are clean,and the adhesive effects induce a high adhesion component of a friction force.Under the microgravity,an irregular impact between contact bodies results in a high plowing component of a friction force.These two components are the main components of a friction force,so the vacuum and microgravity in space environment result in high friction forces.The surface morphology of mechanical components shows an important influence on the friction behavior,and the textured surface is an effective approach to improve friction behaviors.Therefore,it is necessary to study the textured surface applied in the vacuum and microgravity environment,which has an important theoretical significance and engineering value for the friction reduction of the space mechanism.In this paper,the impact sliding contact mechanism is studied based on the motion characteristics of the components under the vacuum and microgravity environments.The influence of various parameters of textured surfaces on friction behaviors are investigated,and the textured surface suitable for vacuum and microgravity environments is designed,which provides a certain theoretical basis for the surface design of spacecraft materials.The main content and results of this paper are as follows:(1)Taking a crank slider mechanism with clearance joint as an example,the mechanical system dynamics model is developed using ADAMS software,and the motion of the crank slider mechanism with clearance at high,medium and low speed is analyzed.The influence of gravity on kinematics and dynamic characteristics of the mechanism with clearance joint is studied by comparing the motion trajectory,impact force and acceleration of the journal under gravity and microgravity environments.(2)Based on the characteristics of the significant adhesion in the vacuum environment,and considering the model scale and CPU cost,using LAMMPS software,a coarse-grained molecular dynamic(CGMD)model of sliding contact problem is established.The results of sliding contact problem by the CGMD model and the whole atom model under a constant load are compared and analyzed,and the effectiveness of the CGMD model is verified.The effects of the sliding speed and normal load on the friction force in sliding process are also studied by using CGMD model.(3)A simplified CGMD model of the clearance joint is developed to investigate the impact sliding contact problem.The single impact sliding process is analyzed in detail and the effects of initial impact velocity and sliding velocity on the impact sliding process are studied.Then,the impact velocity,impact force and friction force in the continuous impact sliding process are studied.The friction forces in the impact sliding process and in the suspension sliding process are compared,which indicates that the impact effect cannot be ignored in the vacuum and microgravity environments.(4)Different textured surfaces are designed to improve the friction behaviors,and the influence of the texture depth,width,direction and shape parameters on the friction behaviors in the impact sliding process is discussed.The results could provide some theoretical basis for exploring the textured surface which can improve the friction behaviors in the vacuum and microgravity environments.Finally,some comments and conclusions are given and the futher research works are pointed out.