Study For Crack Parameters And Fatigue Life Of Top-down And Bottom-up Cracks On Semi-rigid Base Asphalt Pavement Based On Williams Element

Bottom-up cracks and Top-down cracks respectively refer to base crack and surface crack in this thesis.Comparing with situations of single base crack or surface crack,coexistence of base crack and surface crack weakens intensity and stiffness of pavements more severely.With external loads,weakening stiffness of the whole structure quickens pavement's cracking.Stress intensity factor is the most important fracture parameter in fracture mechanics analysis.'This thesis,basing on calculation model for coexistence of base crack and surface crack on semi-rigid base asphalt pavement,includes the following contents.Firstly,with the same material parameters of all structure layers in semi-rigid base asphalt pavement,a hypothesizing research sets up Williams element of multi-crack stress intensity factor on a plate.Acquiring all crack tip stress intensity factor needs only to solve GDOFS of each crack tip,which avoids huge workloads and precision loss that are caused by finite element method.Comparison among Williams element solution,singular element solution and precise solution proves that method in this thesis has higher precision and less calculation than that of finite element method.Secondly,considering different materials of structure layers in semi-rigid base asphalt pavement,Williams element for analyzing crack tip stress intensity factor of base crack and surface crack is set up,and connection of ANSYS software and Williams element dissociation model is preliminarily realized.This method,combining advantages like free meshing of ANSYS software,non-complex post-processing and insensitivity for singular area sizes of William element,solves irregular crack problems.With Williams element,examples of the thesis analyze how traffic loads location influences crack tip stress intensity factor on base crack and surface crack.Moreover,by comparing with singular element solution,the examples prove that Williams element has precision and efficiency for analyzing crack tip stress intensity factor on base crack and surface crack of semi-rigid base asphalt pavement with different materials in structure layers.Thirdly,influences on each tip crack stress intensity factor,which are from surface crack location,elasticity modulus and thickness of each structure layer,are analyzed with Williams element.Some anti-crack measures are provided.From the examples,main solutions are as follows.Extension of surface crack can'be controlled or delayed by properly lessening surface elasticity modulus and enlarging thickness of semi-rigid base;extension of base crack can be controlled or delayed by properly enlarging elasticity modulus and thickness of sub-base.Finally,based on GDOFS,fatigue life prediction models of I-II hybrid crack and ? crack are found,which is respectively used for analyzing fatigue life of base crack and surface crack.Traditional PARIS model needs to match functional relation between stress intensity factor and length of crack extension,but method in this thesis needs only to match functional relation between GDOFS and length of crack extension.Therefore,with higher precision and efficiency,model in this thesis avoids complex post-processing calculation on stress intensity factor of traditional PARIS model.