Damage Analysis Of Cement Asphalt Mortar Layers Interface For CRTSâ…¡Ballastless Slab Track

The ballastless slab track has a very simple multilayer structure, but as for the situation is extremely complex. Under the influence of the external environment, the track structure frequently occures damages like the seam of mortar layer. The damage deteriorates the mechanical characteristics of the track, and shortens the service life. Based on the existed research, the damage behavior of mortar layer interface under temperature gradient in the CRTS Ⅱ ballastless slab track is studied for theoretically supporting the maintenance.After a brief literature review of the relative researches on the development of ballastless slab track, this thesis describes and analyses the current situation of interlaminar damage between slab and mortar layer, also introducing the control index of seam, additionally the theory and method in damage of double materials. Several models of ballastless track are displayed, and the finite element method was applied to establish numerical models of CRTS Ⅱ ballsteless track, including cohesion elements model to simulate the mechanical behavior of the interface.Based on the research results in different fields, the distribution and the development of the damage in the interface of the mortar layer are calculated under a temperature gradient, the damage zone and the interface stress are analyzed, in addition to the damage factor of the corner of the interface. Numerical results show that the damage factor of the corner of the interface increases rapidly with the increase of the temperature gradient; a temperature gradient greater than 90℃/m or less than -45℃/m can lead to a complete damage of the interface; the seam has a little effect on the vertical deformation and is mainly caused by the interface stress.Then, the ranges of the elastic modulus and the thermal expansion coefficient of track structure, the adhesive strength representing the degradation of the track, the percent of the seam area and the temperature gradient of initial damage, the influence of the degradation of the track on the interface damage under temperature gradient are analyzed. Results indicate that the percent of the seam area has a positive effect on the elastic modulus and thermal expansion coefficient of track structure, and a negative one to the adhesive strength; the temperature gradient of the initial damage is negative for the elastic modulus and the thermal expansion coefficient of track structure and the adhesive strength. Combining the percent of seam area and the temperature gradient of the initial damage, the elastic modulus and thermal expansion coefficient of track structure and the adhesive strength should be controlled within a reasonable range.Finally, based on the research results, the cumulative damage characteristics of the interface under temperature gradient in different adhesive strength are analyzed to simulate the interface characteristics under daily temperature range. The results show that after 20 cycles of the temperature gradient, the corner and lateral edges of the highly adhesive strength interface produce a damage zone but don’t influence the seam. The damage zone is closer to the center in an annular shape and influence the seam. With the increasing cycles of temperature gradient, the development of the different position changes and the reason causing the damage of the different position in different stages also changes. The reason of the damage on lateral edges is the longitudinal shear stress; the reason of the damage in most longitudinal edges is the lateral shear stress over the adhesive strength.