Numerical Simulation Of The Effect Of Mixed Fillers On Tribological Properties Of PTFE Composites

When the polymer composites slide in the metal surface,a layer of transfer film will be formed in the coupled metal surface,whose quality is of great significance to improve the tribological properties of the composites.It has been found that the formation of the transfer film is a dynamic process with partial fragmentation and renovation,which is crucial to the study of the formation mechanism of the transfer film and its effect of the tribological properties.However,due to the limitations of the general experimental conditions,it is difficult to observe the dynamic formation process of the transfer film,which also restricts the study of the tribological properties of polymer materials to a certain extent.In view of this,two dimensional Particle Flow Code(PFC2D)based on the DEM was used to establish the sliding friction model of PTFE and 45#steel friction pair system,and reproduced the dynamic friction process between PTFE and 45# steel.Based on this model,the effect of mixed fillers of copper and graphite added to PTFE composites on the wear resistance,transfer performance,bond strength of transfer film,friction coefficient and mechanical properties(compressive and shear properties)of PTFE composites were studied.Then the correlation between the wear properties and friction coefficient of PTFE composites and the bond strength of transfer film,compressive strength and shear strength of the composite were studied by statistical correlation analysis.Based on the above research,the main conclusions are as follows:(1)In the process of sliding friction between PTFE and 45# steel,the rough surface of 45# steel would produce shear compression effect on PTFE,which caused the PTFE on the contact surface to be dragged down to form a PTFE fragment.And part of the dragged PTFE fragment adhered to the surface of the coupled part to form a transfer film.With the development of friction process,the transfer film tended to be stable,which could effectively reduce friction and wear of the PTFE composite.The formation of the transfer film was not a static process,but a dynamic process with the transfer of particles falling off and renovating.(2)Mixed fillers of copper and graphite added to PTFE composites had a significant effect on the tribological properties of the composites.The number of transferred particles increased with the increase of copper content in the filler.The addition of graphite also increased the number of transfer particles to a certain extent.The mixed filler has a similar effect on the bond strength of the transfer film.Theaddition of mixed fillers can effectively improve the wear resistance of PTFE.The wear rate decreased with the increase of copper content,but the effect of graphite enhancement is sensitive to the load.The friction coefficient of the composites increased with the increase of copper content,but graphite could effectively reduce the friction coefficient.(3)Mixed fillers of copper and graphite added to PTFE composites had a significant effect on the compression and shear properties of the composites.Both of the properties were enhanced with the increase of the copper content.The addition of graphite could improve the compressive properties of the composites to some extent,but the enhancement effect decreased with the increase of copper content in the mixture.The effect of graphite on the shear properties of composites was complex.With the increase of the content of copper in the mixture,the effect of graphite on shear properties increased firstly and then decreased.(4)Based on the analysis of the tribological properties and mechanical properties of composites,it was found that the wear resistance of the material had a strong correlation with the strength of the transfer film and the compressive strength of the material,and there is a significant correlation between the friction coefficient and the shear strength of the material.