A STUDY OF CRACK-TIP DEFORMATION AND CRACK GROWTH IN ASPHALT CONCRETE USING FRACTURE MECHANICS

This paper presents findings from a comprehensive experimental/analytical study of crack growth in asphalt concrete using fracture mechanics. The primary objective of this study is to provide critical information that is complementary to the viscoelastoplastic continuum damage model in modeling crack growth using finite element analysis. To simulate mode I fracture, uniaxial monotonic and cyclic tension tests were conducted on prismatic specimens with symmetric double notches. Digital Image Correlation (DIC), a noncontact, full-field displacement/strain measurement technique, was utilized to investigate the size and shape of the fracture process zone (FPZ). Irrespective of the notch size and testing conditions, the FPZ was observed to be similar in size and shape for the mixture. Also, it was found that the strain at the crack tip immediately before crack initiation is a decreasing function of strain rate. The experimental data were analyzed using several fracture mechanics theories, including the cohesive crack model and crack growth rate laws based on the stress intensity factor, K1. The cohesive crack model analysis provides the fracture energy and softening function that describe the post-peak behavior with strain localization. The analysis based on K1 shows that the specimen size has no significant effect on the crack growth rate laws. The effect of temperature is pronounced in the crack growth rate law using temperature-reduced crack speed based on K1. The time-temperature superposition principle, with the shift factor from the linear viscoelastic range, was applied to these crack growth rate laws and successfully collapsed the curves at different temperatures into a single relationship.