Research On The Dynamic Response And Damage Law Of Frog Core Under Track Stiffness Irregularity

The frog is an important part of the train line crossing,which has the characteristics of complex structure,harsh force condition,easily damaged and short life.In recent years,with the increasing of transportation volume of coal and other resources in China,the heavy-duty truck is gradually improved in terms of speed,load capacity and running density,which not only lead to frequent wear and tear,strip off blocks and fracture of the frog components with harsh force,but also greatly reduce their working life and seriously increase the maintenance cost of railway equipment.In this trend,the influence of track stiffness irregularity on the working life of the frog components is gradually exposed.Therefore,in order to further improve the operation efficiency of the truck,it is particularly important that the relationship between track stiffness irregularity in the frog area and the dynamic interaction of the wheel-rail system is studied,and the ways which can prolong the working life of the frog components are found on the basis of ensuring the safe operation of the truck.In order to reduce the damage and improve the working life of frog core in the crossing area of bridge-subgrade transition section of the Datong-Qinhuangdao Railway,the No.12 straight fixed frog of 75 kg/m rail is taken as the research object,and the coupling dynamics model of heavy-duty truck-flexible frog is jointly established by using the SIMPACK-ABAQUS.The effect of track stiffness irregularity in the frog area on the dynamic performance of the wheel-rail system is analyzed and the fatigue damage of the frog core is simulated numerically.Firstly,the effect of different working conditions on the dynamic performance of the wheel-rail system at the frog core is analyzed by using the coupling dynamics model of heavy-duty truck-flexible frog from the perspectives of under-rail support,under-sleeper support,ballast bed loosening or hardening,and the location of the wheel-rail impact point on the frog core surface is determined.Then,the wheel-frog core local contact model is established by using ABAQUS.The quasi-static contact stress analysis is carried out on the impact point location,and the crack sprouting life of the dangerous point(the point with the maximum contact stress)in the frog core is predicted under different working conditions;Finally,the dangerous point on the surface of the frog core is taken as the crack sprouting point.The crack extension path of the two-dimensional(XZ plane)frog core is simulated,the fatigue life and damage law of the frog core are analyzed under different working conditions.The main jobs are as follows:(1)The research background and current situation of vehicle-track coupling dynamics,track stiffness irregularity and frog damage are summarized.In view of the frequent damage and fracture of the frog core in the frog area of the transition section of the Da-Qin Line,the general idea of the dynamic performance of the wheel-rail system under various types of working conditions is obtained by using SIMPACK-ABAQUS joint simulation,the analysis of quasi-static and fatigue damage is simulated by using the wheel-frog core local contact model is proposed.(2)Based on the 75 kg/m rail surface,the structural dimensions of No.12 frog and the measured characteristic section data of the frog area,the flexible frog model is established by using ABAQUS.Combined with the heavy-duty truck vehicle parameters and the under-rail support parameters in the frog area of the Da-Qin Line,the coupled dynamic model of the heavy-duty truck-flexible frog is established by using SIMPACK.The truck is simulated to pass through the flexible frog at a speed of 60 km/h,then the results of wheel-rail interaction force under the corresponding rail support condition are derived and compared with the existing research and literature data to verify the correctness of the model.which lays the foundation for the later analysis of the dynamic performance of the wheel-rail system.(3)Based on the simulation of SIMPACK,the dynamic performance of the wheel-rail system under various types of track stiffness irregularity conditions is obtained.The derailment coefficient of the wheels on the frog core side,the wheel weight reduction rate,the overall vehicle overturning coefficient,the body vibration acceleration and the interaction between the wheels and the frog core are used as evaluation indexes.The impact of track stiffness irregularity on the safe and smooth operation of trucks is illustrated by comparing and analyzing the index data under different working conditions,The impact force between the wheels and the frog core is used as a data source to analyze the damage pattern of the frog core surface.(4)The three-dimensional model of wheel-frog core local contact is established by using ABAQUS,the quasi-static analysis based on the simulation results of the dynamics model is carried out.The location of the frog core surface dangerous point(the point with the maximum contact stress)and the contact stress value are determined by changing the under-rail support working conditions.The results of the stress analysis under different working conditions are compared and combined with the strain-life(E-N)curve of the frog core material,then fatigue sprouting life analysis is carried out on the frog core surface danger point.(5)The XZ cross-section is extracted from the 3D model of wheel-frog core local contact according to the location of the frog core surface danger point,the extracted 2D model of wheel-frog core local contact is divided into cracked and non-cracked areas,and the initial crack is prefabricated at the danger point.The effect of track stiffness irregularity on crack extension life and damage type are analyzed according to the Paris formula and the maximum circumferential positive normal stress criterion.