Study On Fatigue Propagation Of Reflective Cracks In Asphalt Pavement Under Multi-field Coupling Based On XFEM

Asphalt pavement will produce diseases under the action of external factors.Most of the diseases are cracks.Cracks are divided into surface cracks and reflection cracks.Because this thesis adopts the pavement structure of Jingxiong Expressway,its structure is composed of semi-rigid base layer.The stiffness of this base layer is large and the temperature shrinkage is obvious.Therefore,most of the diseases are reflected cracks.The reflection cracks,after appearing,are continually influenced by traffic,temperature,and water;the stress concentration at the crack tip is unmistakable.The reflection cracks are easy to penetrate the base layer and extend to the surface layer.XFEM(extended finite element method)can simulate the development of cracks well,and does not need to subdivide the grid many times in the development,and does not need to set the development route of cracks in advance,so it is very suitable for the numerical simulation of cracks.Based on the improved Paris formula,this thesis divides the process into three stages : slow expansion,medium-speed stable expansion and rapid expansion.In this thesis,the fracture energy release rate of different crack tips is compared to describe the stage of crack propagation and the propagation process of reflective fatigue cracks.Based on the extended finite element method and the improved Paris formula,this thesis uses the XFEM module in ABAQUS to simulate the fatigue propagation of reflective cracks in asphalt pavement.Firstly,the fatigue propagation law of reflective cracks in asphalt pavement under driving load is analyzed,and the fatigue propagation of reflective cracks in asphalt pavement is realized.The relationship between the number of driving load cycles and the fatigue propagation of reflective cracks is obtained,and the effects of changing the four factors of tire ground pressure,surface thickness,base modulus and base thickness on the propagation of load-type reflective cracks are studied.The results show that increasing the thickness of the base layer,the modulus of the base layer,the thickness of the surface layer and reducing the grounding pressure of the driving load are helpful to suppress the expansion of the reflection crack.Secondly,the expansion process of temperature-shrinkage reflective cracks caused by the repeated action of temperature-shrinkage stress in the base layer is analyzed,and the relationship between the number of temperature-shrinkage stress cycles and the expansion of reflective cracks is obtained.The relationship between the four factors of different asphalt pavement base elastic modulus,base thickness,base crack spacing and surface thickness and the expansion of temperature-shrinkage reflective cracks is studied.The results show that increasing the thickness of the surface layer,the thickness of the base layer,and reducing the crack spacing of the base layer and the elastic modulus of the base layer are all helpful to suppress the expansion of reflective cracks.The process of fatigue characteristic expansion of reflective cracks under multi-field action of driving load-temperature-seepage is explored,and the relationship between the evaluation indexes of fatigue expansion of reflective cracks under multi-field repeated action is obtained.The results show that the fatigue life is the smallest under multi-field coupling.The addition of water reduces the fatigue life but the reduction is smaller than that of temperature shrinkage.The temperature shrinkage stress is the main reason for the fatigue expansion of reflective cracks.At the end of this thesis,the grey correlation method is used to explore the correlation degree between the thickness of the surface layer,the grounding pressure,the thickness of the base layer and the modulus of the base layer and the load-type reflective cracks,the correlation degree between the thickness of the surface layer,the thickness of the base layer,the modulus of the base layer and the crack spacing of the base layer and the temperature-shrinking reflective cracks,and the correlation degree between the load,temperature and seepage and the evaluation index of the fatigue expansion of the reflective cracks.The results show that the thickness of the surface layer has the greatest correlation with the evaluation index of load-type and temperature-shrinkage reflective cracks,and the temperature has the greatest correlation with the evaluation index of reflective cracks.The effect of temperature increases the energy release rate of the reflective crack tip and reduces the number of fatigue propagation of reflective cracks.