Study On Crashworthiness And Stability Of Coupler And Draft Gear With Gas-Hydraulic Buffer And Expansion Tube

Rail Transit is the most important medium and long-distance transport mode worldwide.Although safety problems have made great progress,collision accidents are still inevitable,resulting in serious casualties and property losses.A train is mainly connected by coupler and draft gear.Its crashworthiness determines the collision behavior and attitude of vehicles.If the capacity of a coupler is insufficient,it will become rigid and jack up or tilt the vehicle.Moreover,some components fail if the impact load exceeds the limit.The coupler and draft gear of EMU adopts a high-capacity gas-hydraulic buffer and expansion tube.The strong nonlinearity and stability problems are significant challenges in the design and analysis process.Therefore,this paper studies the crashworthiness and stability of the coupler,and the research results can provide a reference for designing couplers with large compression strokes.The research contents are as follows:(1)Explore the high nonlinearity of the mechanical characteristics of the gas-hydraulic buffer.The structural characteristics and working principle are introduced,and a finite element model for the flow field is established and explores the effect of pressure flow and shear flow on pressure loss.The effect of structural deformation caused by high-pressure fluid on resistance force and compression stroke is analyzed.A theoretical prediction model for the compression resistance is established to explore the nonlinear mechanical response.Further,the effects of collision speed on the buffer’s compression speed and resistance are investigated,and the resistance reaches 1500 k N(the expansion tube’s action force)in advance is explored.(2)Analyze the effect of the contact state on the deformation and mechanical properties of expansion tubes.The deformation and mechanical characteristics of expansion tubes are analyzed by the finite element method.The stress distribution,curvature distribution,and expansion rate in the deformation process are investigated.The contact mode is studied and divided into line contact mode and surface contact mode,and the critical condition is discussed.A theoretical prediction model for the compression resistance is established and verified by quasistatic experiments.The influence of structural parameters on crashworthiness is explored through the experimental design method.(3)Analyze the axial mechanical characteristics and behavior of the combined structure of the gas-hydraulic buffer and expansion tubes.The coupler and draft gear are large-scale and high resistance.Thus,two-test cars in the coupled state and rigid wall collision tests are carried out under various impact speeds and stiffness to examine the couplers.Dynamics Model is established based on the tests and investigates the effect of impact speeds and stiffness on the crashworthiness and the expansion tube’s triggering condition.(4)Analyze the deformation and impact stability of the coupler under oblique loading.The impact stability of the coupler and draft gear is examined by the two-test cars and rigid wall collision tests.The instability mechanism and deformation characteristics of the expansion tube are analyzed,and a theoretical analysis model is established.The influence of the conical die’s initial defects is explored,and the critical conditions for instability are calculated.The Influence factors and improvement direction are investigated.A finite element model of the two-test cars and rigid wall collision test is established and study the influence of the coupler’s stability problems on the deformation mode and mechanical response.(5)Explore the scheme for improving the impact stability of the coupler.The improvement scheme in structural respects of the expansion tube is studied.A square-die expansion tube is proposed with a considerable contact length.A finite element model of the square-die expansion tube is established to analyze the influence of structural parameters on the deformation and crashworthiness and compared with the original expansion tube.A theoretical prediction model of the compressing steady force is proposed.Through the validation by the finite element simulation of the two-test cars and rigid wall collision,the square-die expansion tube significantly improves the mechanical characteristics and stability of the coupler and draft gear.