Research On The Effect Of Rolling And Sliding Conditions On The Wear And Contact Fatigue Performance Of High Speed Wheel Steel

With the rapid development of high-speed railways,wheel damage problems mainly due to wear and rolling contact fatigue has become increasingly prominent.Under actual operating conditions,the operating speed,starting and braking as well as rainy and snowy weather will affect the wear and contact fatigue performance of wheel surface.Therefore,carry out rolling contact tests with different rotational speeds and slip ratios under the condition of water lubrication,deeply analyze rolling contact fatigue crack initiation mechanism and propagation law,which is the great significant for guiding engineering practice.In this thesis,double-disk rolling contact tests of ER8 high-speed wheel steel and high-speed rail steel samples with the diameter about 60 mm were carried out at four rotational speeds(250 r/min,500 r/min,750 r/min and 1000 r/min)and two slip ratios(0.6%and 1%)under water lubrication condition and using microcomputer controlled rolling contact material fatigue testing machine.The effects of rotational speed and slip ratio on wheel material wear and rolling contact fatigue damage behavior were analysed from the experimental results of material friction coefficient,spalling life,wear rate,oxidation,surface morphology,plastic flow and crack propagation.It can be concluded that the fatigue life of the wheel material gradually reduces from 68×10~4cycles to 34×10~4 cycles as the rotational speed increases from250 r/min to 1000 r/min.The wear rate of the wheel material decreases at first and then gradually increases as the increase of the rotational speed.Besides,the fatigue life of wheel material increases as the slip ratio increases from 0.6%to 1%.At high rotational speed(750r/min or higher),the wear rate increases as the slip ratio increases.On the contrary,the wear rate decreases as the slip ratio increases when the rotational speed is lower than 750 r/min.In order to further clarify the effect of interaction of rotational speed and slip ratio on the wheel steel wear and rolling contact fatigue performance,a simulation model of crack initiation considering wheel steel cyclic plasticity was established in this thesis.From the aspects of uniaxial tension,residual deformation and simulated life,the simulation results and experimental results are compared to verify the effectiveness of the simulation model.On this basis,the effects of rotational speed and slip ratio on the contact stress distribution in the contact patch were analyzed using the method of dynamic simulation,and the influence of the rotational speed and slip ratio on the crack initiation life and crack initiation angle is calculated by using the model above.It’s found that the crack initiation life decreases from 65.91×10~4cycles to 27.97×10~4cycles,and the crack initiation angle decreases from 29.19°to 19.82°as the rotational speed increases from 250 r/min to 1000 r/min.In addition,when the slip ratio is smaller than 0.6%,the crack initiation life decreases with the increase of slip ratio.However,when the slip ratio is greater than 0.6%,the crack initiation life increases with the increase of slip ratio.Besides,the crack initiation angle decreases from 12.07°to 24.34°as the slip ratio increases from 0.2%to 1%.Under water-lubricated condition,the crack of wheel materials tends to propagate further after its initiation.In order to reveal the influence of slip ratio and rotational speed on its propagation law,this thesis uses linear elastic fracture theory to simulate the effect of rolling slip conditions on crack propagation law under water lubrication.It can be concluded that the higher or lower rotational speed is not a favorable condition for rolling contact fatigue cracks to propagate.As the slip ratio increases,cracks of the wheel material are more likely to propagate along the depth direction and surface direction.Since the experimental and simulation studies carried out in this thesis correspond to the small samples used in the rolling contact material fatigue testing machine,the research results of this thesis can provide some reference information for researchers to develop new wheel materials and to carry out 1:1 large-scale wheel-rail structure rolling contact fatigue experimental research.