Fatigue Damage Evolution Behavior Of Slab Track Based On Damage-Finite Element Coupled Method

The deterioration of CA mortar layer/self-compacting concrete layer(adjustment layer)and the crack of track slab are the main diseases of slab track in actual operation line.Because the train load has the characteristics of high frequency,low amplitude and high number of action,the deterioration effect on the material is manifested as high cycle fatigue.Therefore,fatigue damage is the core scientific and technological problem that the slab track with 60 years service life cannot be avoided.The continuum damage theory provides a theoretical basis for analyzing the whole process of material fatigue deterioration and reflecting the evolution rules of mechanical indexes or internal variables,and undoubtedly provides an opportunity for the refined development of slab track.Considering the fatigue damage evolution is bound to a certain extent,cause structure of internal stress redistribution,and yet there are no existing fatigue damage constitutive subroutine of slab track,makes it difficult to damage and structural stress field coupling analysis,so it is necessary to introduce new technical method to more scientificly and reasonably describe fatigue damage behavior of key components for slab track.Chapter 2 first systematically introduces the damage-coupled finite element method and its advantage.The establishment of the evolution of material constitutive relation and material user subroutine embedded development is the core technology problems and key techniques respectively.Then we combed the user material subroutine of the development process and the framework of continuum damage mechanics.Combined with the bearing characteristics of different structural components,the modified high cycle fatigue damage constitutive model based on Palmgren-Miner fatigue damage criterion and the high cycle fatigue damage constitutive model based on tension and compression anisotropy of track slab were proposed respectively in the theoretical framework of damage mechanics.Chapter 3 Based on Palmgren-Miner fatigue damage constitutive relationship in Chapter 2,the damage-finite element coupled method is used to develop the material subroutine of high-cycle fatigue damage constitutive relationship of CA mortar and selfcompacting concrete,and the finite element coupled calculation method of embedded damage constitutive relation is established.The effects of train load,initial deterioration of materials,and the combination of these factors on the evolution of fatigue damage and the evolution of damage-stress distribution of the adjustment layer are analyzed.It is found from the calculation results that the void of CA mortar layer and the debonding of selfcompacting concrete layer are the main factors to accelerate the damage accumulation of the adjustment layer,and the concrete process of the stress field redistribution due to the damage of the structure is described in detail.It can be seen that the damage-finite element coupled method can reveal the coupling relationship between fatigue damage and structural stress,which makes up the limitation of the traditional decoupling method that the structural stress does not change with the accumulation of damage,and reveals the fatigue damage law of the adjustment layer of slab track more reasonably to a certain extent.In Chapter 4,Palmgren-Miner’s damage accumulation criterion is not applicable to the track slab,which is different from the adjustment layer,due to its thickness and direct bearing of rail supporting force impact,resulting in complex loading form.In addition,the existing tests do not consider the characteristics of train high frequency and low amplitude load,so it is necessary to determine the fatigue damage behavior of slab concrete under train load through tests.It is found that the stress level has a significant effect on the damage development,while the loading frequency has a limited effect.In Chapter 5,the loading test data at the loading frequency of 15 Hz and the stress level of 0.3 and 0.5 were selected as the basis for determining the evolution parameters of concrete anisotropic fatigue damage.In addition,VIC-3D technology was used to measure the whole strain of concrete and reveal the development of deformation capacity of concrete specimens after loading with the increase of historical stress level.In Chapter 5,fatigue damage constitutive equation of the concrete track slab is deduced as incremental form,and the damage rate function parameter selection was determined through the existing literature and test conducted in Chapter 4.Meanwhile,parameters analysis was carried out to clear the influence of various parameters on the different stage of damage sensitivity and the influence law.Then,a calculation model was established to reveal the fatigue damage behavior of the track slab respectively under train load conditions,reinforcement and prestressed system,and debonding of CA mortar at slab end.The cumulative rule of the damage time history at the maximum damage position was described with emphasis.The diffusion,propagation and transfer of damage field or stress field of track slab are analyzed,and the change process of constitutive relation of local material under train fatigue load is traced.Finally,a feasible calculation and analysis method for fatigue damage behavior of key components of slab track is proposed.