Cohesive zone modeling of I-II mixed mode fracture behaviors of hot mix asphalt based on the semi-circular bending test

Low temperature cracking is a major distress form of asphalt pavement. In this study, I-II mixed mode fracture test was conducted using cohesive zone modeling technique under-10 degrees C. Laboratory tests and virtual finite element modeling (FEM) tests were both conducted on semi-circular bending (SCB) specimens with the notch angle varying from 0 to 75 degrees to yield the mixed fracture behaviors. Different loading rates, including 5 mm/min, 10 mm/min, 20 mm/min and 30 mm/min, were applied to investigate the influence of loading rate on the fracture resistance. Results indicated that the peak load increased with the increase of notch angle, which was caused by the increased alignment cracking area. Mode I critical stress intensity factor (KIC) decreased, while mode II critical stress intensity factor (KIIC) increased firstly and decreased subsequently from 1.25 MPa center dot m(1/2) to 0.35 MPa center dot m(1/2) with the increase of notch angle. Compared to KIC tested under the loading rate of 5 mm/min, KIC obtained at 30 mm/min increased by 12.6 %, 8.5 %, 8.4 %, 7.3 %, 7.4 % and 10.4 % for specimens with the notch angles of 0, 15 degrees, 30 degrees, 45 degrees, 60 degrees and 75 degrees, respectively. For KIIC, the increments were 8.5 %, 8.4 %, 7.3 %, 7.4 % and 10.4 %, respectively. The mixity parameter, Me, was adopted to characterize the contribution of each fracture mode on the overall fracture behaviors. It was found that with the increase of notch angle, the mode II contribution on the overall fracture increased. However, the influence of loading rate on Me was very slight, indicating the loading rate could not play any impact on the respective contributions of mode I and II fracture on the overall fracture resistance. Moreover, a linear relationship was found between Me and the notch angle.