Study On Friction And Wear Mechanism Of PTFE/Carbon Fiber Composites Based On Multi-scale Simulation

Polymer composites are usually subjected to the comprehensive effects of tensile,compressive and shear stress when they work under the complex friction conditions.These stresses tend to cause damage in polymer composites,thereby affecting their service lifespan.Therefore,it is essential to investigate the damage mechanisms of polymer composites during friction.In this paper,molecular dynamics method and first principles are used to calculate the mechanical parameters required for the constitutive model of polymer composites.Based on the finite element simulation method,under the premise of considering the damage of matrix phase,reinforcement phase,interface phase and the deletion of failure elements,taking polytetrafluoroethylene(PTFE)/carbon fiber(CF)composite as an example,to analyze the effects of the friction-induced structural changes of CFs on the tribological properties of composites on the mesoscopic scales.To construct a finite element friction model of PTFE/CF composite materials containing matrix phase,reinforcement phase,and interface phase,this paper first established molecular models of PTFE,three types of CF microstructures,and interfaces.Moreover,the tensile and shear simulation of the above molecular model is carried out to obtain their mechanical properties parameters,such as elastic modulus and shear modulus and so on based on the molecular dynamics and the first principles.The results show that the elastic modulus of PTFE is 935.5 MPa;The maximum tensile stress at the interface is717.295 MPa.Then,the CF finite element model was established based on the parameters obtained from molecular simulation,and the correctness of the CF model containing three microstructures was verified by combining molecular dynamics and finite element methods.Finally,the tension compression and shear strength of CF structures are calculated by using the finite element method.The friction model of GCr15-PTFE/CF composite was built based on the finite element method.The mechanical parameters and damage parameters of the composite obtained from molecular simulation and finite element simulation are brought into the friction model of composite.The damage of each component of composite during friction and their impacts on the tribological properties were analyzed.It was found that the damage of each component of the composite is the main factor in the change of friction coefficient,and PTFE failure occurred around GCr15 upper specimen.CF damage is related to its own strength and distribution position in PTFE,that is,the lower the strength,the closer to GCr15 upper specimen,the more serious the damage.PTFE-CF interface has little effect on friction coefficient.Based on the test method,the correctness of the finite element friction results of PTFE/CF composite is verified.In addition,the effects of different speeds,loads and CF content on the friction of PTFE/CF composites were studied,and finally the optimal performance of friction and wear of PTFE/CF composites under various factors was found.