| Self-lubricating radial spherical plain bearings are widely used in aerospace and other high-tech areas,and the accurate prediction of their service lives has great significance on the safe use of the equipments.At present,when predict the bearings'service lives,most manufacturers only consider swivel motion,but neglect tilt motion and combined swivel and tilt motion(combined motion)which lack detailed research,and only INA company merely put forward the calculation methods of equivalent oscillation angles under different oscillation modes.Because the considered influence factors are different,for the same size bearings,there are considerable differences among their lives obtained by different formulas.The failure mechanisms of this kind of bearing in different oscillation modes also lack research in current literatures.In this disseration,self-lubricating radial spherical plain bearings with friction pair of steel/PTFE fabric liner were taken as the research object,and the failure mechanisms of the self-lubricating radial spherical plain bearings under different motion conditions were further discussed,and the life evaluation methods for the bearings were studied.The researches have important theoretical guiding significance on the understanding of the bearings'failure mechanisms,accurate estimation of the bearing service lives,and prolonging the service lives.The main researches and achievements are listed as follows:(1)With ABAQUS software,3D simplified models for finite element analysis(FEA)were established for a self-lubricating radial spherical plain bearing,which can simulate different motions of the inner ring including swivel motion,tilt motion and combined motion.FEA results show that even under constant radial loads,zigzag contact pressures can appear periodically on the liner contact surface.Under different oscillation modes,contact pressure distributions and pressure amplitudes are different.Motion directions,friction forces and wear depths can cause offset distributions of higher contact pressures zone and higher deformations zone of the liner on the liner's boundary zones for tilt motion and combined motion;but for swivel motion higher contact pressures zone and higher deformations zone offset along peripheral direction.The amplitudes and offset directions of higher contact pressures and deformation change periodically during the motions.Combined with the test results,different fatigue damage mechanisms of the liner such as sweep deformation and fracture of the liner fibers,surface fatigue wear,and impact damage effects were analyzed,and the characteristics of the fatigue failure behaviors of the liner were revealed.(2)Based on the weave microstructure of the self-lubricating liner of the bearing,two physical wear models for PTFE/Kevlar fabric woven liners with different adhesive contents were established.Based on mesomechanics and mechanics of composite materials,calculation methods for elastic constants of the liners during the wear process were provided,and elastic constants for the liners in main directions and in off-axis directions during wear process were obtained.With FEA model established for the radial spherical plain bearing,effects of elastic constants and wear depth of the liner on the surface contact pressures were studied,respectively.FEA results show that increase of wear depth can lead to bigger contact pressures and has bigger influence on the contact pressures between the liner and inner ring compared with the changed elastic constants.Under swivel motion,accelerated life tests for two radial spherical plain bearings with different liners in which adhesive contents were different were carried out,and test results verified the reliability of the physical wear models of the liners,and the failure mechanisms of the liners can be well revealed by the wear models and FEA results,and the adhesive content of the liner has larger effect on the tribological performances of the beraings.(3)Based on the combined abrasion wear theory,under combined motion condition,via movement analysis,force analysis and wear loss analysis for the radial spherical plain bearing,new analytical formulas for such bearing's service live evaluation were derived,and the calculation methods were put forward,with which the wear lives respectively for swivel motion,tilt motion,and combined motion can be obtained,.Assume that work condition parameter K was the same,and pressure index m and speed index n meet the assumption that m=n=1.Through the calculation of the numerical examples under different oscillation motions,the life ratios of the radial spherical plain bearings change with oscillation angles and oscillation friquencies were studied,and the results were close to the results obtained from exsited theories.Under different oscillation motions,wear rates features change with different friction coefficients were emphasisly contrasted and investigated,and the calculation formulas of the wear rates hereby were simplified.(4)With combined motion life test machine for radial spherical plian beraings,under the work condition that the constant radial load was P=22 kN and the oscillation angles were?=?=±6~o,took the oscillation frequency as the acceration stress,fixed number terminated accelerated life tests without substitution for a certain type of self-lubricating radial spherical plain bearings were carried out.Under the assumptions that services life comply with Weibull distribution and the accelerated life equations comply with inverse power law life model,the best linear unbiased estimation method(BLUE)was used to deduce the accelerated life equations about the oscillation frequency.Bearings'lives distribution regularities and Weibull distribution reliability under different oscillation motions were investigated.Results show that under the same applied load and oscillation frequency,the highest life occurred under swivel motion,followed by tilt motion,and the shortest life occurred under combined motion.Results also show that big differences exist between theoretical results and experimental results.In addition,under the assumptions that the bearings'service lives comply with Weibull distribution,Maximum likelihood estimation algorithm were investigated to estimate the life distribution parameters.(5)Combined with the calculation method of equivalent oscillation angles put forward by INA company,effect laws of the motion frequency,radial load and motion angle on the estimation of the bearing service lives under different motions calculated separately by SKF model and JB/T 8565-2010 model were compared and investigated.It was found that the life results and their change regularities obtained from two models have big differences with the test results.Take pv value as the comprehensive function variables,and according to life test data as well as BLUE method,inverse power type accelerated life models under different oscillation modes were deduced,and the equations were verified and corrected via experiments.For the service life equations,load factor correction method for the swivel motion and oscillation angle correction method for the combined motion were proposed.The revised life equations for combined motion can also be applied to estimate the bearing's service life under swivel motion and tilt motion,and the calculated results agree well with the exprrimental results.Based on the accelerated life equations,important evaluation parameters in the wear rate functions in the analytic life models of the bearing under different oscillation modes were deduced and so the analytic life models were improved.Based on the improved analytical life models,influences of the bearing's structure parameters on the bearing service life were investigated,and results show that effects of structural parameters on the service lives of different radial spherical plain bearings are close. |
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