Analysis And Prediction Method Of Cracks In CRTSⅢ Track Slab Of High Speed Railway

In recent 10 years,with the rapid development of China’s high-speed railway industry,slab track,as the main structure of high-speed railway,has been widely used.Among them,the CRTSⅢ slab track independently developed by China is the main form of slab track in the future.The field investigation shows that the overall service condition of CRTSⅢ slab track is good.With the passage of time,the possibility of damage and deterioration of slab track increases.At this stage,it is necessary to carry out the research on damage and deterioration of CRTSⅢ slab track in advance.In reality,due to the material problems,transportation problems,construction problems and other factors,there may be initial cracks and initial damage of slab track at the initial stage of service.If the initial damage happens to be in the area of high stress level of slab track and bears the repeated load for a long time,the damage may accumulate to a certain extent in the later service period of slab track,which will cause the deterioration of the whole track structure and endanger the traffic safety.Most of the existing studies use damage mechanics theory to analyze the damage process of slab track,while the research on macro cracks of track slab is relatively less,and the research on cracks of CRTSⅢ track slab is less.Therefore,it is necessary to carry out the research on the analysis and prediction method of cracks in CRTSⅢ slab of high-speed railway,improve the service condition of CRTSⅢ slab track,and improve the maintenance level of track structure.In this paper,following the strategy of strengthening transportation in the new era,the space model of crtsiii slab track based on fracture mechanics is established,and the analysis method of crack propagation process of track slab is proposed.The possible initial displacement and crack propagation of track slab in the later service period under various load forms are analyzed The propagation path and the change of the stress intensity factor at the crack tip during the propagation process.The fatigue growth rate of the crack is calculated by Paris formula,and the corresponding crack growth rate formula is put forward.The fatigue growth life of some cracks with critical growth length is calculated.The main research results and conclusions are as follows(1)The damage and deterioration status of CRTSⅢ track slab was investigated,and the crack of CRTSⅢ track slab was determined as the research object.The space model of CRTSⅢ slab slab track based on fracture mechanics is established.Based on the application of extended finite element method in ABAQUS,an analysis method is proposed to simulate the crack cracking and propagation process of track slab by combining the two functions of extended finite element method,and the law of possible surface crack generation and development in the later stage of track slab is revealed.The results show that the negative temperature gradient load is the main reason for the surface macro cracks in the later service period of track slab under the condition that the tensile strength of some track slabs may be greatly reduced;Under global cooling load and negative temperature gradient load,the stress intensity factor of surface crack tip increases monotonously with the increase of crack length;It is difficult for the whole cooling load to cause the instability propagation of the track slab surface crack,and generally there is no instability propagation length;When the crack depth increases from0.05 m to 0.1m,the corresponding propagation length decreases from 1.4m to 0.16 m.(2)In view of the existence of vertical cracks on the side of some track slabs,the research on the generation and development process of cracks on the side of track slabs is realized by combining the crack propagation function of extended finite element and the stress intensity factor solution function.The generation and development of vertical cracks on the side of type Ⅲ track slab are revealed.In the later stage of track slab service,the positive temperature gradient load is the main cause of side cracks;Under the positive temperature gradient load and train load,the stress intensity factor at the vertical tip of the crack first increases and then decreases with the increase of vertical depth,and finally tends to be stable.The stress intensity factor at the crack tip is less than the fracture toughness of the track slab under both loads,and there is no risk of instability propagation of the crack.(3)Based on the analysis method of crack propagation process of track slab,the crack around the lifting hole of track slab is studied.The generation and development of vertical cracks around the lifting hole of type Ⅲ track slab are revealed.The stress level of the lower part of the lifting hole is lower than that of the surrounding track with the same height;The lifting hole has a certain deflection effect on the propagation path of the vertical crack around,which makes the crack propagation direction tend to the bottom of the lifting hole.The deflection of the crack is particularly obvious under the positive temperature gradient,but the lifting hole has a certain inhibition effect on the propagation of the vertical crack,and slows down the propagation trend of the vertical crack around the lifting hole of the track plate.(4)Based on the theory of fatigue crack growth,Paris formula is used to analyze the fatigue growth rate and fatigue growth life of track slab crack,and the propagation law of various cracks under the action of temperature and train load is explored.The results show that the negative temperature gradient is the main factor of the surface crack fatigue growth of the track slab at the later stage.The crack depth has a certain influence on the fatigue growth rate;The results show that the fatigue growth rate of side cracks of track slab under positive temperature gradient load and train load increases at first and then decreases with the increase of vertical crack depth.When the vertical crack depth reaches0.04 m to 0.05 m,the fatigue growth rate reaches the maximum;At a negative temperature gradient of 45°C/m,when the initial crack length is 0.02 m and the depth is 0.05 m,the fatigue growth life of the surface crack is about 580000 times.If the temperature gradient is cycled once a day,it will take 1589 years,which is far beyond the service life of the track plate.When the crack depth increases to 0.1m,the fatigue growth life of the crack with the same initial length is about 96000 times.If the temperature gradient is cycled once a day,it will take 263 years,which is also far beyond the service life of the track plate.However,with the increase of the depth,the fatigue life of the surface crack of the track plate decreases greatly.There are 115 figures,39 tables and 120 references in this manuscript.