| The non-ballasted track had been widely used with the development of the high-speed railway in China. But it was evident that non-ballasted track take the crackdamages as main form, especially the influence of rainwater to the damages. Nowadays, domestic and foreign related problems was lack of the systematic research. Aiming at the water-containing crack propagation issue among the typical damages of the CRTS II ballastless track, this paper carried out theoretical and experimental research on crack propagation mechanism of concrete under the action of the high-speed dynamic load of railway and water invasion,and took hydrodynamic pressure tests on cracks of concrete by applying a cyclic dynamic load based on characteristics of dynamic load.The tests studied characteristics of hydrodynamic pressure and cracks propagation,and this paper studied development mechanism and related factors of concrete cracks under the environment of rainwater,based on concrete fracture mechanics and erosion theory.(1) Internal crack water pressure calculation model and parameters under the interaciton between dynamical load and waterFor the force features of water-containing cracks at the CA mortar bottom of CRTS II slab track, the paper established "three dementions calculation models with bi-dimensional transient FSF", based on applied structure dynamics,fulid dynamics and the principle of FSI. The model can be used to simulating calculate water dynamic pressure of cracks when high speed railway pass the non-ballasted track.Train load was one of main parameters, which had the properties of high frequency and large force.Provided loading parameters for relevant theoretical calculations and experimental studies by ensuring loading distribution, size of force and frequency etc.(2) Test of water pressure inside cracks under cyclic loadsA cyclic load was applied on a specimen with cracks in a sink by using hydraulic servo fatigue machine. The water pressure can be measured by using a high sensitive sensor. In this test, the change characteristics of water pressure in different position inside the cracks and the influence of loading frequency and amplitude on water pressure were investigated.The water pressure inside the cracks can be arisen by the driven of water when the cyclic loading stats to act on the specimen. The testing results show that the amplitude and frequency of loads can influence the water pressure. If the testing point is moved to deeper position, the water pressure is gradually increased, until it reaches the maximum pressure at the cracks tips. In addition, the increase of loading frequency can lead to an increase in water pressure when the loading amplitude is constant. Similarly, the increase of loading amplitude can increase water pressure when the loading frequency is constant.The water pressure may lead to model I fracture of the cracks when the stress intensive factor induced by water pressure exceed the fracture toughness of the material.At the same time, theoretical calculation is completed by using above water pressure model for non-ballasted tracks based on the specimen and loading condition. The result is compared with that of experimental result.(3) Acting behavior of water pressure inside cracksBased on bidirectional transient three-dimensional fluid-solid coupling field analysis, water pressure in the cracks containing water in the bottom of mortar is simulated by using commercial software ANSYS Transient Structure-CFX considering different loading frequency and amplitude.The width, depth, opening displacement and the amplitude and frequency of vehicular loads are the main factors that influence the water pressure. The water pressure increases at the points along the depth of cracks. The position of the maximum water pressure is located at the middle point at the same depth. Water pressure reaches the maximum at the crack tip when the opening size is 3 mm. Water pressure is increased with the increasing of depth when opening displacement is constant. Water pressure is increased with the increasing of loading frequency which is influenced by train speed.(4) The investigation of cracks propagation under the action of coupling of high frequency dynamic loads and waterThe cracks propagate when the stress intensity factor caused by external loading is greater than fracture toughness of material. The fracture toughness of material can be determined by tensile tests. Base on the statistical value of water pressure in cracks from previous calculation, stress intensity factors are calculated using commercial software ANSYS/W ORKBENCH-Fracture under different condition. The results show the propagation characteristics of cracks and provide theory knowledge for fixing the material by comparing with the experimental results.The research result shows that the maximum stress intensity factor is located at the point on the crack front line. The width, depth and opening displacement are the main factors which influence the propagation of cracks.Based on the calculation results of stress intensity factor in cracks tip, a patching technical standard in views of depth, width and opening size of cracks is provided in this work.(5) Establishment of a water-cracks erosion model and the analysis of the mechanism of cracks propagation and erosionBased on ANSYS-CFX digital simulation software, the model of macroscopic state of the solid-liquid two-phase flow analysis was established. The properties of particle motion within the crack were taken as the research objects and analyzed the effects of motion track,water flow velocity,width of cracks and the range of diameter distrbution on cracks erosion, when the crack surfaces were not usually punch.Studies show that water flow velocity, width of cracks and the range of diameter distrbution were important factors that influenced the rate of erosion.Erosion rate would increase with the increasing of the water flow velocity, would decrease with the increasing of the width of cracks, and the more little, the more larger average particle diameter. |
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