Research On Damage Identification Of Concrete In Ballastless Trackbased On Acoustic Emission Technology

With the rapid development of high-speed railway in our country,no frantic jumble track with its advantages of high stability,comfort has become an important structure in the construction of high-speed railway,and concrete,as the core material without a frantic jumble orbit in the complex environment,such as train load,temperature cycle load under the action of coupling is hard to avoid injuries,for example,the track plate cracking,cracking of support layer of fracturing and support rail,sleeper damage,etc.In the past,scholars in the study of ballastless track damage mostly focused on the cracking position,depth and width of the crack,the number of cracks and other aspects of the component,but the evaluation of the overall damage of concrete members,especially the internal damage evolution in the early stage of the crack formation lack of effective means to identify and study.Based on the acoustic emission technology and the train load,this paper designed the concrete compression failure experiment and the four-point bending and tensile experiment of concrete beam respectively,monitored the cracking and damage process of concrete materials under different stress modes and carried out damage evaluation,and discussed the feasibility of identifying the damage of ballastless track.Acoustic emission crack point localization system was used to identify the evolution process of crack point and the final damage area of specimen.The research contents and conclusions of this paper are as follows:First of all,to identify without a frantic jumble of track structure,especially the key parts of the whole internal structure of wound area and evaluation of health,in this paper,ae non-destructive testing technology,considering the uncertainty of the full scale experiment,so the design cube concrete under uniaxial compression experiment,the arrangement of sensors in pairs around the specimen,the experiment through monitoring.Experiments on damage identification of cube concrete under different loading rates were carried out.Secondly,the acoustic emission signals collected during the whole failure process of the cube specimen at two different rates were analyzed by using parameter analysis method and crack point spatial location theory.The results show that the failure of the specimen under compression can be divided into three stages.The frequency of the signal center during the whole process of fracturing and failure is concentrated around 25 k Hz and 105 k Hz.The loading rate affects the whole damage state of the specimen.Finally,in order to make the concrete test specimens more fit the ballastless track structure,the concrete beam four-point bending test was designed,and two sensor arrangement modes were set to identify the damaged area of the beam from different dimensions.At the same time,the extended finite element method was used to establish the same-size model for crack propagation simulation analysis.The results show that there are three stages in the whole process of beam cracking and failure.In the whole process of beam failure,the concentrated frequency of AE signals is roughly the same as that of specimen failure under compression.The plane location of the crack point can identify the final propagation direction of the crack,and the crack propagation path has been preliminarily identified in the second stage.The crack point spatial location can accurately identify the crack damage area of the beam body,and the crack point density around the crack propagation path increases sharply in the third stage.The crack growth simulated by the extended finite element method is in good agreement with the experimental crack morphology and acoustic emission monitoring results.Therefore,it can be considered to embed it into the ballastless track model and combine it with acoustic emission technology to be used as a damage identification method for ballastless track.