| Laser quenching treatment technology is a new surface treatment technology,which can effectively improve the wear resistance of rail materials.However,the effect of laser quenching on the rolling contact fatigue(RCF)damage of rail has not been fully studied.Peridynamics(PD)as a novel non-local theory,has obvious advantages in simulating material damage evolution across scales.Therefore,the study on RCF performance of laser quenched rail based on PD theory has important significance for improving the service safety of rail.In this paper,the initiation and propagation behaviors of rail fatigue cracks during the wheel/rail rolling contact process were simulated through establishing a PD model of RCF of laser quenched rail.Then,the effect of laser quenching on RCF damage performance of rail under different cycles was studied using the MJP-30A rolling wear and contact fatigue apparatus.The RCF mechanism of laser quenched rail was revealed based on the combination analysis of simulation and experimental results.The main conclusions of are as follows:(1)During the wheel/rail rolling contact,the tangential stress on the rail material was mainly concentrated on both sides of the contact area,and the stress on the side with the same rolling direction as the wheel was greater.The normal stress was symmetrically distributed on both sides of the contact area,and reached the maximum value at the center.Rail fatigue cracks first initiated at the edge of the quenching region.During the transition from the pure rolling state to the pure sliding state of the wheel,the crack initiation position transferred from 0.2 mm beneath the surface to the surface and gradually approached the edge of the quenched region,and the crack initiation life was reduced from 2.34×10~4times to0.58×10~4times.(2)During the wheel/rail rolling contact,the crack in quenching region would experience the dynamic evolution process of“opening-closing-reopening-reclosing”.The fatigue crack grew from the quenching region to the transition region and then to the substrate region.During the growth process in the quenching region,transition region and the substrate region,the crack propagation mode changed.The crack propagation mode was mainly open type(mode-I)in the quenching region,sliding type(mode-II)in the transition region and the substrate region.The increase of pre-crack length and load would aggravate the propagation of mode-I and mode-II cracks,and the wheel rolling speed and slip had little effect on the transient behavior of crack propagation.(3)The microstructure of the rail has undergone significant transformation after the laser quenching treatment,the quenching region and the substrate region were composed of martensite and pearlite structures,respectively,and the surface hardness was increased by about 189%.In the wheel-rail RCF damage tests,the surface damage of the rail material became more serious with the increase in the number of cycles,and gradually expanded from the boundary to the center of the quenching region.The crack length,crack depth and the average number of cracks inside the quenching region increased with the increase in the number of cycles.(4)Comparing the simulation and experiment results,it was found that the RCF crack propagation path of laser quenched rail material was divided into four stages:(I)cracks initiation at the edge of quenching region on the same side as the rolling direction of the rail;(II)cracks propagation at a large angle in the quenching region;(III)the direction of cracks propagation changed after reaching the transition region,the branch cracks began to appear and expand along the boundary of the transition region;(IV)cracks broke through the transition region to reach the substrate region,and expanded around in the substrate region,eventually the spalling or fracture occurred in the rail.The crack growth rate showed a trend of increasing first and then decreasing,and the crack growth rate reached the maximum in the transition region. |
PDF Full Text Request