Influence of external load on friction coefficient of Fe-polytetrafluoroethylene

A coarse-grained molecular dynamics simulation model was developed in this study to investigate the friction process occurring between Fe and polytetrafluoroethylene(PTFE).We investigated the effect of an external load on the friction coefficient of Fe–PTFE using the molecular dynamics simulations and experimental methods.The simulation results show that the friction coefficient decreases with the external load increasing,which is in a good agreement with the experimental results.The high external load could result in a larger contact area between the Fe and PTFE layers,severer springback as a consequence of the deformed PTFE molecules,and faster motion of the PTFE molecules,thereby affecting the friction force and normal force during friction and consequently varying the friction coefficient.     

速度对聚四氟乙烯摩擦系数影响的分子动力学模拟

基于分子动力学方法建立了双层聚四氟乙烯(polytetrafluoroethylene,PTFE)摩擦模型,研究了不同速度下PTFE的摩擦过程.通过分析不同速度下接触区内下层PTFE分子键长、键角、分子形状的变化及接触过程中摩擦力和正压力的变化,从微观角度研究了速度对PTFE摩擦系数的影响.研究结果表明:随着速度的增加,接触区内PTFE粒子间的键长变短,键角变小,分子链沿x;方向的变形量增加.变形后的PTFE分子产生的回弹力导致上、下层PTFE分子间相互作用力增加,从而增加了摩擦力.当速度进一步增大时,接触区内下层PTFE粒子间的键长和键角多处于平衡位置,分子链沿x方向的变形量减小.这很可能是由于接触区内下层PTFE分子沿速度方向倾斜,使上、下层PTFE分子趋于平行滑动,从而降低了摩擦力.不同速度下正压力几乎保持不变.因此,当上层PTFE所受外载荷固定时,摩擦系数随着速度的增加先增大后减小,临界速度为1.2 m/s,这与实验研究结果一致.