Research On Crack Propagation Characteristics Of Asphalt Pavement Based On Fracture Mechanics

Asphalt pavement is the main form of highway pavement structure in our country,which has the advantages of high flatness and good wear resistance.However,under the increasingly heavy driving load and the effect of the natural environment,the asphalt pavement often appears small cracks and then cracks expand,which leads to the reduction of pavement performance and service life,and increases the maintenance cost.Therefore,the research on the crack propagation characteristics has practical value.Existing research on cracks in asphalt pavements is based largely on the theory of elastic layered systems.The crack propagation is judged by interlayer tensile stress and shear stress,but the traditional system cannot explain the phenomenon of stress concentration at the crack tip,which is far from the actual situation;while the traditional finite element method based on fracture mechanics is used for modeling,many of the element forms at the crack tip are still conventional elements,although the calculation speed is fast,but the accuracy is not enough;the study of crack propagation under the coupling effect of temperature stress and load less.In view of the above analysis,based on the theory of fracture mechanics,singular element was set in the model to ensure the accuracy requirements,and stress intensity factor was introduced to analyze the stress field at the crack tip.The subroutine was used to simulate the application of moving load and the temperature field of pavement.The factors of crack growth under the load had been analyzed and the temperature sensitive crack had been simulated and analyzed.The main contents of the study are as follows:(1)The finite element model of asphalt pavement with longitudinal cracks on the road surface is established.The moving load is applied,and the influence of driving speed,axle load and elastic modulus of upper layer,middle layer and lower layer on the longitudinal crack propagation are considered.The analysis shows that under the moving load,the longitudinal crack propagation of the road surface is mainly type ?crack propagation,the increase of low speed and axle load will promote the longitudinal crack propagation;And the higher the modulus of the upper layer,the lower the modulus of the middle layer and the lower layer,the more likely type ? cracking and expansion will occur.(2)Based on the theory of heat transfer and winter cold wave climate,a model of asphalt pavement with transverse cracks on the road surface is established.The influence of temperature stress,traffic load and load temperature stress coupling on the transverse crack propagation are considered.The analysis shows that the transverse cracks mainly develop type ? crack propagation at low temperature,and type ? crack propagation mainly occurs under the action of moving load alone The temperature stress has a great influence on the mode ? crack growth,while the temperature stress has a little influence on the mode ? crack growth.(3)Referring to the structural form of semi-rigid asphalt pavement,the finite element model of reflective crack propagation is established,cyclic load is applied,and the influence of surface layer thickness,base module and axial load on reflective crack propagation are considered.The analysis shows that reducing the base modulus,increasing the thickness of the surface layer and the axial load can lead to the propagation of reflection cracks in the surface layer.