磨屑对润滑油摩擦性能的影响

通过实验和模拟研究磨粒对润滑油摩擦性能的影响。首先通过微纳米压/划痕试验测量含磨屑润滑油的摩擦因数。同时，建立边界润滑体系模型，采用分子动力学方法模拟含磨屑润滑油膜在不同载荷下沿膜厚方向的压缩率和密度分布；对体系的上下固体壁面施加方向相反的剪切速度，计算出壁面原子的应力、摩擦力、正压力和摩擦因数；分析不同粒径磨屑的动态行为特征；通过减少润滑油分子数量，探究乏油工况下含磨屑润滑体系的摩擦性能。结果表明，润滑体系摩擦因数的模拟值与试验值一致；磨屑的存在会降低油膜的压缩率，同时在高载下磨屑的存在会对油膜的分层产生破坏，影响磨屑附近的密度分布；含小粒径磨屑的润滑体系的摩擦因数比含大粒径磨屑的润滑体系的小，表明磨粒聚集长大现象会恶化润滑油的润滑性能；磨屑在剪切过程中同时存在滚动和滑动，含小粒径磨屑的润滑体系剪切过程中表现出波动幅度更大的角速度；随着载荷的增大，磨屑角速度减小，波动幅度降低；在乏油工况下，磨屑会在剪切过程中出现变形破碎现象。

Effect of Wear Debris on Friction Performance of Lubricating Oil

The effect of abrasive particles on the tribological properties of lubricating oil was studied by experiments and simulation.The friction coefficient of lubricating oil containing abrasive particles was measured by micro-nano indentation/scratch test.At the same time,the boundary lubrication system model was established,and the molecular dynamics (MD) method was used to simulate the density distribution and compression ratio of the lubricating oil films along the film thickness direction under different loads.The shear velocity in opposite directions was applied to the upper and lower solid walls of the system,and the stress,friction force and positive pressure and friction coefficient of the solid surface were calculated.The dynamic behavior characteristics of the wear debris with different particle sizes were analyzed.By reducing the number of lubricating oil molecules,the friction performance of the abrasive lubrication system under the condition of lack of oil was explored.The results show that the MD simulation value of friction coefficient is consistent with the experimental value.The presence of abrasive particles will reduce the compression rate of the oil film,and the presence of abrasive particles under high load will destroy the delamination of the oil film and affect the density distribution near the abrasive particles.The friction coefficient of the lubricating system containing small particle size abrasive particles is smaller than that of the lubricating system containing large particle size abrasive particles,indicating that the phenomenon of abrasive particles gathering and growing will deteriorate the lubricating performance of lubricating oil.There are both rolling and sliding during the shearing process,and the lubrication system with small particle size abrasive particles shows greater angular velocity fluctuation during the shearing process.With the increase of load,the angular velocity of abrasive particles and the fluctuation amplitude decrease.Under the condition of oil shortage,the abrasive particles will deform and break during the extrusion shear process.