Study On The Mechanical Behavior And Evolution Of Ballastless Track Interface Damage Under High Speed Vehicle And Environmental Load

The interface damage of hige-speed ballastless track structure during the long-term service process is common and increasingly prominent,which is mainly shown as concrete cracking,motar cracking,interface seperation and interlayer voiding.The damage of the bongding interface between layers of ballastless track not only increases the track maintenance cost,but also poses a threat to the safety of train operation.Therefore,it is one of the urgent researches to investigate the generation mechanism of the interlayer interface damage of ballastless track concrete structure and propose maintenance and repair strategies.Funded by the National Key Basic Research and Development Plan(973 plan)project "basic research of high-speed railway infrastructure dynamic performance evolution and service safety(2013CB036200)" and the National Natural Science Foundation of China Major Project " dynamic performance evolution,damage mechanism and control strategy of high-speed rail transit infrastructure(11790283)”,and with the support of the organization of the investigation group and related research units,the research method combining the laboratory testing and theoretical analysis has been used to carry out research on the generation of interlayer interface damage in ballastless tracks and study on its evolution mechanism.The main research work of this paper is as follows:(1)The damage state of typical ballastless track of Chinese high-speed railway during the long-term service is investigated on the spot,the common forms and main characteristics of concrete interface damage in multi-type ballastless track structures are summarized.And the major factors causing interface damage of ballastless track are analyzed.The advantages and disadvantages of fracture mechanics theory and damage mechanics theory in the current interface damage research are summarized.The current research status about the mechanical constitutive model,the basic mechanical performance test and damage numerical simulation of the interface of ballasless track are discussed.(2)The concrete composite specimens of CRTS I double-block ballastless track,CRTS II and CRTS III slab ballastless track are manufactured,and the basic mechanical properties and dynamic mechanical properties test methods of the interlayer interface of ballastless track are designed.The ballastless track interface bonding strength test,freeze-thaw cycle test and high-speed dynamic impact test are carried out.The key mechanical parameters of the interface normal and tangential direction of three typical ballastless track are determined,and the complete interface mechanics constitutive relationship curve is extracted;Based on digital image correlation technology and acoustic emission technology,the whole evolution process of the interface normal and tangential failure that from damage initiation to fully debond are captured.The evolution law of the interface strength of the specimen with the freeze-thaw cycles is revealed,and the interface failure mode under high-speed load impact is proved,and the dynamic damage and cracking evolution process of the interface is captured.The number of freeze-thaw cycles and the change of air pressure under impact load are analyzed,and the reasons for the difference in mechanical properties of the interface between different ballastless tracks are analyzed.(3)A full-scale model test of interface degradation of high-speed railway ballastless track under fatigue load is carried out.The test is based on a multi-functional test platform of full-scale high-speed railway track-subgrade system,and the accelerated test method is used to impose a cyclic load on the ballastless track.It is proved that the interface damage area of CRTS I double-block ballastless track shows a trend of increasing first and then tends to be stable with the increase of cyclic loading times.(4)A variety of interface damage constitutive models of ballastless track are constructed.The validity of the interface damage constitutive models is verified by experimental results and numerical simulation;Through secondary development,the interface damage constitutive interaction is embedded into the cohesive element,and the finite element model is established to simulate the interlayer interface damage of ballastless track,the advantages and inferiorities of different interface damage constitutive models in the interlayer damage analysis of ballastless track are analyzed;The results show that the exponential cohesive model has the highest conformity with the interface normal mechanics,followed by the bilinear model,and the polynomial model is the worst.However,those three cohesive constitutive models are insufficient in describing the tangential mechanical behavior of the interface of ballastless track.The interface damage analysis of ballastless track under the action of negative temperature gradient is carried out,and the stress state,opening displacement and damage degree distribution of the bonding interface of typical ballastless track under different temperature gradients condition are obtained,the ability of typical ballastless track bonding interface to resist cracking under extreme temperature condition is revealed.The critical limit of temperature gradient for predicting the damage of ballastless track interface is proposed.(5)The low-cycle fatigue damage constitutive model and the high-cycle fatigue damage constitutive model of the ballastless track interface are proposed,which broke through the limitation that the existing fatigue model could not analyze the cracking and damage evolution of the interface under mixed-mode condition,the converge problem of low-cycle fatigue interface damage constitutive model is solved and the deficiency that the load ratio could not be considered in existing interface high-cycle fatigue analysis is made up.Based on the vehicle-track coupled dynamics simulation model,the wheel-rail force is solved,and the dynamic response characteristics of the bongding interface under different train operating conditions are invetigated.Based on the thermal stress coupling method and damage mechanics theory and fluid-structure coupling theory,the fatigue damage analysis model of CRTS III ballastless track interface under cyclic temperature field is established,and the interface damage analysis model of ballastless track under the combined action of water pressure and train dynamic load is modeled repectively.The low-cycle fatigue damage analysis of ballastless track bonding interface is carried out to reveal the evolution process of low-cycle fatigue damage,failure mechanism and evolution of interface failure mode of ballastless track under the combined action of cyclic temperature gradient and train load-hydrodynamic pressure.The results show that the mixed failure mode occurs at the bonding interface of ballastless track under the action of cyclic temperature gradient.The interface damage of the ballastless track is mixed-mode failure form under the action of the cyclic temperature gradient,and the failure mode changes continuously with the increase of loading cycles,the interface gradually evolves from the normal-dominant failure mode of the initial damage to the tangential-dominant failure mode.Based on the interface fatigue damage model with load ratio is considered,the effects of different load ratios on the high cycle fatigue crack growth rate of the ballastless track interface is studied.