Research On The Influence Of Surface Defect On Rolling Contact Fatigue Damage Of Pre-rolled Wheel Steel

With the development of high-speed and heavy load railway transportation,the problems faced by railway vehicles are increasing and more complex,and the wheel/ rail rolling contact fatigue is one of them.When the railway vehicle is in motion,the wheel tread is inevitably damaged.After the tread was damaged,defect is usually occurred on the wheel surface.If the surface defect is not handled in time,it may aggravate the rolling contact fatigue damage of wheel.However,it is difficult to know the sensitivity of wheel materials to surface defects and the influence of surface defects on the initiation and propagation of rolling contact fatigue cracks in wheel materials during vehicle operation.Therefore,it is necessary to research the rolling contact fatigue damage behavior of wheel steel with surface defects.Considering that the actual wheel surface defects appear after a certain rolling,the influence of surface defects on rolling contact fatigue damage of pre-rolled wheel steel was studied,to determine the critical size of defects that cause rolling contact fatigue damage of the wheel materials and the law of fatigue cracks initiation and propagation at the surface defects of the wheel materials.In this thesis,firstly,in order to research the influence of pre-rolled on surface defects,the defects with depth and diameter of 200 μm were manufactured on the surface of new wheel disk samples with a diameter of 59.82 mm and a width of 5 mm through the drilling equipment,and the interruption test was conducted under the condition of oil lubrication with contact load of 1200 MPa and slip rate of-0.3%.Then,the defects with depth of 200 μm and diameter of100-500 μm were manufactured on the surface of pre-rolled wheel disk samples,and the influence of surface defects on the rolling contact fatigue damage of the pre-rolled wheel steel was studied by rolling contact fatigue test under the same test conditions.Finally,by means of finite element simulation of wheel and rail disc pairs with surface defects,the stress state near the defects is calculated,and the critical distance theory is combined with the multiaxial fatigue model to evaluate the fatigue damage of the dangerous points of the wheel model with surface defects.The results show that the surface resistance to plastic deformation is improved and the surface defect size is difficult to decrease after the new wheel steel sample is pre-rolled.When the new wheel sample is pre-rolled for 60,000 cycles,the surface plastic deformation tends to be stable.The critical defect size of the rolling contact fatigue damage of the sample of prerolled wheel steel is 100-200 μm.The fatigue crack which causes the spalling initiated in the middle of the defect.Combined with finite element simulation,it is found that the stress concentration is severest in the middle of the defect,and with the increase of the defect size from 50 μm to 500 μm,the more serious the stress concentration is,the lower the rolling contact fatigue life of the wheel sample is.Furthermore,it is found that the rolling contact fatigue damage behavior of wheel steel with surface defects can be evaluated well by combining the critical distance theory with the FS multiaxial fatigue model.