Thermal Contact Coupling Analysis Of Wheel-rail With Internal Cracks

With the high-quality development of China ’s economy,higher requirements have been put forward for the railway transportation system and transportation capacity.In order to improve the transportation capacity,heavy freight and high-speed passenger transportation will be the inevitable trend.The continuous improvement of train speed and load will inevitably cause huge thermal damage in the process of sliding and braking,which will cause fatigue damage such as wheel-rail wear,cracking and peeling,affecting the integrity of wheel-rail.It not only directly threatens the safety of train operation,but also increases the maintenance and operation cost of railway.Therefore,studying the stress field and temperature field of wheel-rail thermal contact coupling contact has practical engineering significance for wheel-rail thermal damage mechanism,wheel-rail material selection and railway design and maintenance.This paper focuses on the wheel-rail contact relationship,taking JM wheel and 60 kg / m rail as the research object.Based on the wheel-rail contact theory,heat transfer theory,fracture mechanics theory,elastoplastic mechanics theory and material stability theory,a complete wheel-rail contact model with internal cracks is established by using finite element software.The distribution law of wheel-rail stress field and temperature field under pure mechanical condition and thermal contact coupling condition is studied.The main work is as follows:In this paper,the finite element method is used to analyze the transient thermal contact coupling of wheel and rail.Firstly,the transient contact analysis of complete wheel and rail is carried out.The stress difference between wheel and rail is compared from the two working conditions of pure mechanical load and thermal contact coupling.The temperature rise characteristics of wheel and rail under thermal load are compared to obtain the contribution range of thermal load to the stress field in the wheel under normal wheel and rail conditions,which provides reference and comparison results for the later research content.Then,the finite element analysis models of various types of defective wheels with cracks are established.A total of 65 finite element models are established,and the pure mechanical load,thermal contact coupling and stress intensity factor are calculated respectively,a total of130 working conditions.The wheel-rail transient three-dimensional elastic-plastic thermal contact coupling calculation model is established by using the finite element method.From a practical point of view,the influence of the stress field and temperature field at the internal crack of the wheel with different angle crack parameters under the high thermal condition generated by the train braking is analyzed.In this paper,two types of cracks are established.The length and depth of straight and oblique cracks are 10 ～ 18 mm and 2 ～ 10 mm respectively(the length-depth ratio is fixed to 5),and the crack angle is 25 ° ～ 90 °.The calculation results under thermal load conditions show that the enhancement effect of thermal stress on the stress field at the crack tip cannot be ignored,and the contribution rate of thermal stress to the synthetic stress can reach 24.8% under some conditions.Under various working conditions,the stress field at the crack tip of the straight crack is generally higher than that of the oblique crack,indicating that this type of crack is more dangerous and easier to expand.The closer the crack position is to the wheel surface,the higher the crack tip stress is,the easier it is to expand and develop to the surface layer,which in turn causes the wheel tread to peel off the block.The maximum value of the amplitude of the equivalent stress intensity factor often occurs when the oblique crack angle is about 60 °,indicating that when there is a fatigue crack of about 60 ° inside the wheel,the growth rate is the fastest,and the vertical crack will rapidly expand to the inside and may form serious fracture.The crack depth has a great influence on the stress field at the crack tip.With the increase of the crack depth,the crack at the same angle has a greater stress increment at the crack tip,which is more likely to make the stability of the material in the ratchet zone,and then cause the secondary expansion of the existing crack of the wheel,which directly affects the safe operation of the train.