Fatigue damage analysis in asphalt concrete mixtures based upon dissipated energy concepts

Fatigue cracking is the most important structural distress that is used in the design of a pavement and the models used for this design require significant improvement. Current fatigue models are either phenomenological or damage based models. The phenomenological models are easy and simple; therefore, they are widely used. However, the phenomenological fatigue models do not consider damage accumulation. In addition, the traditional fatigue failure (number of load cycles to 50% reduction in the value of the initial stiffness) is an arbitrary definition that was not based on material behavior. The damage/energy based fatigue method is simple and based on sound theoretical background. Dissipated energy was used to model fatigue damage in asphalt concrete mixtures in the past. Unfortunately, these studies assumed all energy dissipated in the fatigue test produced damage. In fact, this is not correct; it is the change in the dissipated energy that is responsible for damage. Based on this concept, a new method to characterize the fatigue test was developed with the energy fatigue curve.; A damage curve that relates to the percentage of dissipated energy producing damage to the material under cyclic loading was obtained based on the concept of change in dissipated energy. Using the damage curve a new failure point was defined based on the damage/energy concepts. The constant value of percentage of dissipated energy that produces damage to the material under cyclic loading was defined as the Plateau Value (PV). It is believed the PV may present a material property. It was found that the PV is highly dependent on the initial loading conditions, stress, strain, and dissipated energy, thus it can be used conveniently in pavement design.; A new energy fatigue relation was developed using the PV and the new failure point. The energy fatigue relation is a consistent relation that appears to unify between two modes of loading, load pulse shapes, and durations.; The number of load cycles to 50% reduction in initial stiffness was found to be highly correlated to the new failure point. Therefore, the new failure point can be predicted using the traditional failure point.; The new dissipated energy approach was used to investigate fatigue limit in asphalt concrete pavements. Preliminary data support the fatigue limit showing now the dissipated energy approach can investigate material behavior compared to traditional fatigue approach.; The results of this study provide a foundation for fatigue analysis based on dissipated energy concepts. Using the dissipated energy concepts in fatigue analysis make it possible to account for damage in a straightforward manner. The energy fatigue relation is easy, simple and based on a theory it is believed it win be the way to go in fatigue analysis in the future.