In view of the problem of rail squat in the operation of railways,the specific morphological characteristics of rail squat such as squat depth,crack propagation angle,and squat size were summarized.The propagation process of rail squat was discussed.The formation mechanism of rail squat was analyzed systematically.The action mechanisms of wheel-rail contact pressure,stress/strain in the contact zone,and temperature change in the contact zone during squat formation were analyzed from the perspectives of plastic deformation and thermal phase transformation.The main factors affecting the development of rail squat were defined from the aspects of locomotive and vehicle performances,line parameters,track types,and other factors.The different field detection methods of rail squat such as axle box acceleration were investigated,and the applicabilities of various methods in squat detection were compared and analyzed.According to the formation mechanism and influencing factors of the squat,the effective measures and strategies for preventing and controlling the squat were analyzed from the perspectives of vehicle traction/braking control and rail grinding.Test results show that at present,the research on the formation mechanism and development process of rail squat mainly adopts the means of field investigation,sample test simulation,and numerical simulation.The ultimate deformation and thermal phase transformation of rail base metal caused by the large creep and sliding state between wheel and rail are the main reasons for the formation of rail squat.The contact state between wheel and rail will be affected by the factors such as train operation state,horizontal and vertical section parameters of the line,and the type of foundation under the line,thus inducing the formation and development of rail squat.According to the detection modes of rail squat,at present,the axle box acceleration response method,frequency response function method,and eddy current detection method can be mainly used,but the detection accuracies of different methods are different for squat to varying degrees.As for the prevention and control of rail squat,it is more effective to control the wheel and rail adhesion overrun in the process of controlling train traction/braking before the formation of squat.The safety hazards can be reduced by grading grinding or changing rail according to the degree of formed squat.3 tabs,21 figs,105 refs.
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