Molecular dynamics simulation on friction performance of collision sliding contacts of soft metals in vibration environment

Soft metals are often used for space mechanism lubrication because of their low shear strength. In outer space, the vibration of spatial mechanism will occur when there is a small disturbance due to the effects of microgravity environment. Studies on the friction properties of soft metals in vibration environment could contribute to the application of space lubrication materials. Taking a clearance joint as an example, the relative motion between the shaft and the bearing is simplified to a sliding contact between a cylinder and two smooth contact bodies. A molecular dynamics model of the collision sliding contact between a rigid cylindrical indenter and an elastic substrate is established. The effects of sliding velocity, collision velocity and indenter radius on the friction properties of soft metals are studied. The results show that the Ag substrate and Au substrate present strong adhesion to the Fe indenter. The indenter and the substrate are always in a state of adhesive sliding contact. The larger the initial collision velocity of the indenter, the higher the friction force. The friction force shows great values as the sliding velocity increases. As the increase of indenter radius, the contact area is enlarged, which results in a high friction force. The adhesion of the Cu substrate to the Fe indenter is weak, so the friction force shows a low value, and the friction performance of Cu is the best, while the friction performance of Au is the worst. 软金属因剪切强度低, 具有一定的抗压强度和韧性, 常用于空间机构润滑。空间微重力环境导致运动机构在很小的扰动下发生颤振, 研究颤振环境下软金属的摩擦性能对于空间润滑材料应用有非常重要的意义。以空间间隙铰链为例, 将轴与轴承的相对运动简化为圆柱体与基体的碰撞滑动接触运动, 建立了刚性圆柱压头与弹性基体碰撞滑动接触的分子动力学模型, 研究了滑动速度、碰撞速度和压头半径对软金属摩擦性能的影响。结果表明: Ag基体和Au基体对Fe压头的黏着作用较强; 压头与基体始终处于黏着滑动状态, 压头初始碰撞速度越大, 摩擦力越大; 随着滑动速度的增加, 摩擦力增大; 压头半径增加, 摩擦力增大。Cu基体对Fe压头的黏着作用较小, 摩擦力较小, 且软金属Cu的摩擦性能最优, Au的摩擦性能较差。