Simulation On The Tribological Performances Of PTFE-based Composites And The Motion Law Of The Filler Particles During Friction

In this thesis,a software of Particle Flow Code in 2 Dimensions(PFC2D)is employed to established the sliding friction model of PTFE(Polytetrafluoroethylene)composites and 45# steel.The effects of load,relative sliding velocity,filler content and filler particle size on the tribological properties of PTFE composites and the role of mixed fillers in the friction process were systematically studied.In addition,the movement track and motion law of the copper and graphite particles were also studied.Based on the above research results,the main innovative conclusions can be drawn as follows:(1)In the sliding friction process of PTFE composites/45# steel,the particles on the matrix of the composites fall off from the matrix under the action of friction shear force and normal pressure.Under certain conditions,some of the fall-off particles establish new bonds with the 45# steel and form a layer of transfer particles.The transfer particle layer is composed of PTFE particles,copper particles and graphite particles.Its formation and composition are affected by various factors.Among them,load and relative sliding speed can significantly affect the formation of the transfer particle layer,and filler content and particle size will affect the composition of transfer particle layer.(2)The mixed fillers of copper and graphite in PTFE composites have significant effects on the tribological properties.The copper particles in the matrix can enhance the overall structural strength,but at the same time large abrasive particles will be formed at the friction interface and aggravate the wear,the wear results are affected by both of them.The friction coefficient of the composites increases with the increasing number of the copper particles in the transfer particle layer.When copper and graphite are mixed at the same time,the effect of graphite on wear and friction coefficient is not obvious.(3)During the friction process,the filler particles exhibit different movement laws with the different positions of particles.The movement of the filler particles on the friction interface mainly occurs in the quasi fluid layer.The particles in the quasi fluid layer show a certain velocity in the horizontal direction,which keep consistent with the movement direction of the lower sample,and the numerical value is smaller.The particles migrate randomly in the vertical direction.Generally,the tracks of particles in the same region of the quasi fluid layer is similar,which are related to the flow direction of particles in the friction interface.Graphite particles are more likely to become discrete particles than copper particles,which makes it easier to move in the friction interface.