Dynamic Propagation Of Reflective Fatigue Crack Based On Modified Paris Law For Asphalt Pavement

Fatigue cracking is one of the common diseases of asphalt pavement.Studying the propagation characteristics of fatigue crack is of great significance for design and maintain of asphalt pavement structure.The existing numerical research on fatigue cracking of asphalt mixture mainly analyzes the crack propagation trend by the magnitude of the crack tip stress intensity factor under static state,which cannot visually describe crack dynamic expansion process.The recently developed Extended Finite Element Method?XFEM?,which doesn't require re-meshing when simulating crack propagation,nor does it need to define the crack propagation path in advance,can automatically simulates the crack propagation process.Based on modified Paris Law characterized in this paper,And a model of fatigue crack dynamically propagating is established by Extended Finite Element Method?XFEM?to analysis the fatigue crack growth process of asphalt mixture.In this model,the fatigue crack propagation is divided into three stages:low speed stable expansion stage I,medium-speed stable expansion stage?,and rapid propagation stage?.Semi-circular bending fatigue tests of AC-13,AC-20,AC-25and AC-13?SBS?with pre-notched specimens are carried out,The N-a curve obtained from the tests are fitted by the second-order exponential growth function,And the parameters c₁,c₂,c₃,and c₄ of the crack propagation stage I and II of four kinds of asphalt mixture are obtained respectively.Among the four kinds of asphalt mixtures,the longer the fatigue life,the larger the parameters of c₁ and c₄,and the smaller the parameters of c₂ and c₃.Extended Finite Element Method is used to simulate semi-circular bending fatigue tests,The results show that the N-a curve obtained from the finite element model is highly consistent with the experimental results,which verifies the feasibility of analysis of asphalt mixture based on modified Paris Law characterized by fracture energy release rate.Based on the fatigue fracture parameters of asphalt mixture obtained from Semi-Circular Bending Test,the dynamic fatigue expansion model of reflective cracks in semi-rigid base asphalt pavement was established by using Extended Finite Element Method.The results show that the upper layer only accounts for 0.2%of the fatigue life of the surface layer,which is almost negligible.This means that once the crack extends to the top of the mid-surface,the ability of the entire surface layer to resist temperature stress disappears.And the surface thickness of semi-rigid base asphalt pavement resisting thermal shrinkage reflection crack propagation mainly concentrates on the middle and lower layers.The influence of pavement structure parameters on the fatigue life of reflective crack of the surface layer were analyzed.The results show that the asphalt mixture with higher ultimate fracture energy and fatigue resistance can increase the fatigue life of the surface layer,and delay the expansion of the reflection crack to the top of the surface layer.The fatigue of the surface layer can increase with the increasing thickness of the surface layer and the reducing elastic modulus of the base layer.The reducing elastic modulus of the base layer can increase the fatigue life per unit depth of the surface layer,and increase the depth of the upper layer against the thermal-shrinking fatigue reflection cracks.