The Fatigue-Creep Coupling Effect of Asphalt-Mixture Damage Model under Different Loading Frequencies

To evaluate the fatigue-creep damage coupling effect of asphalt mixture under different loading frequencies, three tests—tension-compression fatigue, direct tensile fatigue, and static creep—were carried out with haversine cyclic loading at four loading frequencies of 5, 10, 20, and 50 Hz, respectively. In this research, the elastic modulus was selected as a damage variable for evaluation, and the evolution of fatigue damage and creep damage was analyzed by the Chaboche model and the Kachanov model, respectively. Then, based on haversine fatigue stress decomposition, tension-compression fatigue damage, direct tension fatigue damage, and creep damage under four loading frequencies were compared, and the fatigue-creep damage coupling model under those loading frequencies was established. The results indicated that, with the increase in loading frequency, the corresponding damage under the same standardized coordinate decreased, the growth rate of the damage evolution curve decreased, and the damage increased more rapidly when the asphalt mixture was damaged. It was found that the direct tensile fatigue damage of the asphalt mixture under repeated loads was not the direct superposition of pure fatigue and pure creep damage, but a coupling effect of fatigue-creep damage. In the direct tensile fatigue tests, the fatigue-creep damage coupling effect was negative and during the coupling effect the creep effect was more obvious. The model proposed in this result can better characterize the fatigue-creep damage coupling effect and damage evolution process of asphalt mixtures under different loading frequencies.