Research On Prediction Method Of The No-powered Wheelset Wheel Rim Crack Growth Of CRH2 Type Emus

Fatigue cracks in wheel rims can cause wheels to collapse and trains to derail.Based on the wheel rim fatigue crack behavior of the non-powered wheelset of CRH2 EMUs and the probabilistic curves of fatigue crack growth rates and test loading conditions,the methods of wheel fatigue crack germination,expansion and safety analysis are explored,and the results show that:(1)The surface size of the rim cracks of various types rarely changes during fatigue;The crack near the base circle produces significant plastic deformation at about 10,000 km of wheelset,and the plastic deformation after 30,000 km covers the cracks and is difficult to identify with the naked eyes.Orthogonal planing of cracks confirms that radial cracks mainly extend in the direction of depth;Oblique cracks spread obliquely along the crack surface and gradually tend to be parallel;Compound cracks have a cross angle between the crack surface and the axle axis,so that the lateral expansion of the crack is hindered,tending to expand deeper.(2)A two-stage nonlinear calculation method for the propagation of wheel rim crack propagation is established.Ansys was used to establish a finite element overall mesh model of wheelset-track without defects,apply the nonlinear cyclic stress-strain relationship of solid materials,and calculate the overall stress-strain distribution of wheelset structure at a certain time in combination with the test loading conditions;In the crack area,the crack driving force calculation submodel is cut,the strain condition on the boundary is used as the constraint of the submodel,and it is used as the inp file of ABAQUS calculation,combined with FRANCC3D and ABAQUS,to realize the submodel calculation,and reasonably determine the stress intensity factor of the crack tip front,which is significantly better than the conventional method.The computational analysis of typical rim radial cracks,oblique cracks and composite cracks,which coincided with the bench test results,revealed the reasons why the size of the tread crack did not change and the crack spread to the deep-to-bevel.(3)The calculation method of the remaining life of rim cracks and the scale of critical safety cracks are established.Combined with the probabilistic fatigue crack propagation curve of ER8 material,the remaining life of the surface semi-elliptical crack with an initial size of 2c-a of 15-3.5 mm and a critical radial depth of 16.37 mm was determined at the level of confidence C of 99%and the survival probability rate P of 0.9999.(4)The calculation reveals the friction effect of the crack surfaces in the fatigue crack propagation:the friction coefficient of the crack surfaces is large,the coefficient of friction per unit is also large,the driving forces K_I and K_III of I and II cracks at the deepest point of the crack tip tend to be zero,the range of equivalent stress intensity factor is reduced(?Keq),and the amplitude expansion tends to be flattened.When the crack-free surface is in contact,the K_I is much less than zero,and the two cracked surfaces produce a penetration phenomenon,which accelerates the increase of K_II and K_III.Therefore,the crack structure should try to increase the friction of the crack surface,thereby reducing the driving force of crack propagation and increasing the remaining life of the cracked structures.This paper is of great significance for exploring the analysis method of structural fatigue crack propagation and promoting the progress of fatigue safety research on wheel structures.