Simulation Analysis Of Wheel-rail Rolling Contact Fatigue Crack Propagation Behaviour Based On LAMMPS

With the development of high speed and heavy haul railways,the fatigue problem caused by rolling contact has become a major problem threatening the safety of railway operation.Therefore,studying the contact fatigue damage of railway wheel and rail,and proposing corresponding preventive measures have important engineering value.In this paper,based on a novel non-local theory of Peridynamics(PD),a discrete model of rolling contact was established.And the crack propagation of rail in rolling contact under different conditions was studied.Firstly,the Peridynamics model was established by LAMMPS software.The change of stress distribution during rolling was analyzed.Secondly,the shape changes of the vertical prefabricated surface crack during whole dynamic process were calculated without considering the contact between the crack faces,the state of the tip of the crack was predicted,and the Crack-Tip Open Displacement(CTOD)and the Crack-Tip Slip Displacement(CTSD)of the predicted crack tip were obtained.The effects of different initial crack angle,length,load,running speed and slip ratio on transient crack propagation behavior were studied.Finally,the crack propagation was simulated considering the contact of the crack surface,and the crack propagation path was obtained by applying the moving Hertz load,and the influence of different factors on the crack propagation path was compared.The main conclusions of this paper are as follows:(1)The maximum contact stress located at the edge of both sides of the contact zone.In the case of dynamic rolling,the maximum stress values formed on both sides of the contact pattern were different,and the stress value on the same side to the running direction was larger.For vertical cracks,severe compression occurred at around the quarter of the crack near the tip,which was a stress concentration point.During the whole rolling process,the vertical crack experienced two "opening-closing" processes.(2)The propagation mode of the surface crack was mainly affected by the geometry of the crack itself.As the crack angle increased,the propagation mode changed from mode-I to mode-II,and the 45 o crack was the most likely to propagate deep into material.The increase in crack length could increase the leading role of mode-II.Longer cracks were more likely to extend deeper into the material.The increase in load could significantly aggravated the mode-I and mode-II crack propagation.When the speed was less than 100 m/s,CTSD decreased with increasing speed,but when speed was greater than 100 m/s,CTSD would increase.The reciprocating operation of the train could aggravate the crack propagation,and make the crack with small angle easier to turn to the surface and form spalling of material.Parallel cracks could inhibit crack propagation.For the subsurface cracks,the propagation behaviors at the two ends were different.One end extended to the surface and the other extended to the deep.(3)The crack propagation path was affected by various factors.For surface cracks,cracks with small angle turned towards the surface,while cracks with larger initial angle continued to grow downwards into the rail.The propagation results of crack with initial lengths of 1.5 mm and 3 mm were very similar.Specifically,the initial crack length had a small effect on crack propagation path.For cases with a lower coefficient of friction(?=0.1),the cracks turned towards surface earlier.The subsurface crack propagated toward the wheel-rail contact surface on the opposite side of the rolling direction,and on the other side it expanded toward the inside of the rail.Horizontal subsurface cracks of wheel were more likely to propagate on the same side to the rolling direction.Horizontal subsurface cracks of rail were more easily to grow on the opposite side to the rolling direction.Shallow cracks were easier to propagate than deep cracks.