Sliding Contact Behavior And Life Prediction Method Of Silver Matrix Self-lubricating Composites

With the proposal of China’s"14th Five-Year Aerospace Industry Development Plan",as the core material of high-orbit spacecraft electrical power and electrical signal rotation transmission and other key mechanisms,the friction stability and service life of silver matrix self-lubricating composite have attracted much attention.In this paper,the sliding contact behavior characteristics and evolution law of the Single-phase lubricating silver matrix composite and the Two-phase lubricating silver matrix composite were investigated.In view of the lack of quantitative discrimination methods in the running-in process of composite materials,the fractal theory of contact was introduced.The modeling and calculation method for the real contact area realize the quantitative characterization of the running-in process of silver matrix self-lubricating composite;finally,through the analysis of the energy dissipation and thermodynamic state of the friction and wear process of the material,a comprehensive degradation model of the friction system is constructed,and the service life evaluation method of the composite.The main research results of the paper are as follows:（1）The sliding contact behavior of the Single-phase lubricating silver matrix composite was elucidated.The effects of normal load and sliding speed on the tribological performance and running-in behavior of the Single-phase lubricating silver matrix composite are investigated,and the results show that the electrical noise of the Single-phase lubricating silver matrix composite remains stable with a mean value of 3.89 mΩand a standard deviation of 0.40 mΩ,and the lowest mean friction coefficient and wear rate of 0.163 and 4.5×10^-15 m³/（N·m）.With the development of China’s aerospace industry,higher requirements for the long life and stable service of space sliding electrical contact materials have been put forward.（2）The transfer film composition of duplex lubricated the Two-phase lubricating silver matrix composite and their friction and wear reduction mechanisms were revealed.The study found that the average friction coefficient of the Two-phase lubricating silver matrix composite was reduced from 0.163 to 0.122,and the wear rate was reduced from 4.5×10^-15 m³/（N·m）to 2.1×10^-15 m³/（N·m）,the electrical noise is reduced from3.89 mΩto 2.41 mΩ.The discrete element method discretizes the contact medium,and has unique advantages in dealing with fracture,deformation and accumulated damage in the process of friction and wear of materials.The simulation results show that the composite transfer film formed by the Two-phase lubricating silver matrix composite is uniform and stable.It can effectively inhibit the initiation of subsurface cracks in the Two-phase lubricating silver matrix composite caused by cyclic stress,and significantly enhance the antifriction and wear resistance of the materials.（3）The friction and wear mechanism maps of the Two-phase lubricating silver matrix composite was constructed.In order to make up for the lack of local and accurate fitting of discrete data in traditional methods,the modified Shepard method was used to form a map with normal load and sliding velocity as independent variables,which can accurately express the quantitative relationship between friction and wear and wear mechanism.The results show that for the Two-phase lubricating silver matrix composite,when the normal load and sliding speed are low,the material mainly suffers from ploughing wear,which is conducive to the formation of the transfer film at the sliding contact interface;while the high normal load and sliding speed It is easy to cause delamination and wear,which reduces the service stability of the material.The generation of this map effectively solves the problem of lack of design basis for the sliding contact stability of the Two-phase lubricating silver matrix composite.（4）A quantitative analysis method for the running-in behavior of materials was constructed.Aiming at the problem that the friction coefficient curve and the wear rate curve are mostly used for qualitative judgment during the material running-in process,the point cloud data of the sliding contact surface is collected by the profilometer,and the actual contact area calculation model based on the fractal theory is used to form the dimensionless real contact area value and evolution.At the same time,with the analysis of the evolution process of the adhesion component and the ploughing component of the friction coefficient,a quantitative analysis method for the material running-in process is formed.The research shows that according to the traditional judgment method of the running-in process,the sliding distances of the the Two-phase lubricating silver matrix composite during the running-in period are about 200 m（surface roughness）,150 m（friction coefficient）and 50 m（wear rate）,respectively;the research shows that when the sliding distance of the friction pair is 100m,the dimensionless real contact area has an extreme point,and the adhesion component and the ploughing component of the friction factor also have an inflection point.Based on this,it is determined that the end mileage of the running-in process of the material is 100 m.（5）A life prediction method for silver matrix self-lubricating composites based on the energy dissipation and comprehensive degradation model of the friction system is proposed.The temperature distribution of the contact interface is obtained through energy dissipation analysis,and the change law of the entropy value of the friction system is deduced based on the principle of entropy increase,and then combined with the wear rate and friction coefficient,the comprehensive degradation coefficient of the friction system is calculated to quantitatively characterize the wear of the friction pair.The results show that the degradation coefficient of the Two-phase lubricating silver matrix composite decreases from 1.23×10^-7 to 0.64×10^-7 in the running-in stage,while the average degradation coefficient in the steady state stage is as low as 4.45×10^-8;according to the obtained the wear coefficient predicts the life.According to the experimental results,the predicted wear volume of the Two-phase lubricating silver matrix composite when the sliding friction is 100000 m is 1.13×10^-9 m³,and the experimentally measured wear volume is 1.28×10^-9 m³ at this time,and the predicted error rate is 11.7%.Based on this,it is predicted that the service life of the material with high stability can reach 320921 m.Figures 103,tables 6,formulas 153,references 241...