A Research On Viscoelastic Fatigue Damage Model Of Asphalt Mixture

Fatigue cracking is a main destroy form of asphalt pavements, and the damage always evolves with fatigue developing. Analyzing fatigue cracking problems of highway engineering with fatigue damage theory is becoming focus. However, it is not adapt to analyse fatigue damage evolvement of asphalt pavements with tradition fatigue damage models, because asphalt mixture is one of viscoelastic materials, as well the influence of temperature and time for damage evaluation can not be denoted by tradition fatigue damage models.Firstly, the stress response law of asphalt pavements under cycle vehicle loading is qualitatively analyzed and numeric calculated, which indicates that it is feasible on the assumption that the stress response law of asphalt pavements under cycle vehicle loading approximates to half sine wave and the frequency of stress cycle equales to the frequency of loading cycle. This approximate way is the fundation of viscoelastic fatigue damage model and viscoelastic fatigue damage life analysis in this study.Secondly, a viscoelastic fatigue damage model based on cycle stress law is deduced with energy dissipation concept, which starts from the viscoelastic constitutive relation. The influnce of temperature, loading frequency and stress to damage evolvement is denoted in this model. This model can be applied to analyse fatigue carcking initiation life of asphalt pavements. A new comprehensible method to judge fatigue damage cumulation law is deduced directly from damage evolvement law. The "damage equivalent state" is proved theoretically, and the reasons for "damage equivalent state" being not found by testing is discussed.Thirdly, the parameters of viscoelastic material and viscoelastic fatigue damage model is obtained by testing which includes stress relaxation tests and fatigue tests. It is discussed whether or not tradition fatigue testing methods can be applied to obtain parameters of viscoelastic fatigue damage model. A new method is put forwared to test viscoelastic fatigue damage parameters.Fourthly, for viscoelastic fatigue damage calculating, the calculating time is so long that viscoelastic fatigue damage calculating can not becompleted at present. The main problem of tradition fatigue damage calculating methods is discussed, and a new fatigue damage calculating method is put forward. Comparing with tradition fatigue damage calculating methods, the calculating time of the new method can be greatly reduced, which makes viscoelastic fatigue damage calculating be possible.Lastly, the fatigue life of asphalt pavements is forecasted by analyzing fatigue damage evolvement with the viscoelastic fatigue damage model and the viscoelastic fatigue damage calculating method developed in this study. The results indicate that the new model and the new calculating method developed in this study is feasible.