Mesh-independent fracture modeling for overlay pavement system under heavy aircraft gear loadings

Flexible overlay systems often fail before reaching their design life due to the occurrence of reflective cracking caused by stress concentrations in the vicinity of joints and cracks in the underlying pavement. In this paper, a two-dimensional finite-element fracture model of a rehabilitated airfield overlay system subjected to mixed-mode loadings was developed to obtain accurate nonarbitrary critical fracture responses in asphalt overlays placed over rigid airfield pavements. A stress-intensity factor (SIF) and J-contour integral approach based on the fracture mechanics theory was selected and implemented to analyze the mechanism of airfield pavement cracking. The predicted SIFs using singular elements were verified by comparison with reference solutions based on the displacement correlation technique. The verified fracture model was applied to investigate a number of complicated environmental effects and critical aircraft gear loading conditions in an airfield overlay system associated with heavy aircraft. The gear configuration and tire pressure of a Boeing 777 aircraft were selected and applied at 12 different loading positions. Temperature-induced Mode-I SIFs were found to be extremely high, and although the magnitude of the responses would be expected to be lower with improved material models and more advanced temperature gradient modeling, the simulations nevertheless emphasized the importance of modeling temperature change in addition to gear loading in climates where daily diurnal temperature cycling is significant. A surprising finding was that aircraft gear loadings placed in the vicinity of the crack tip did not produce the most critical Mode-I stress intensities at the crack tip. Instead, counterflexure produced by gears located 3-4 m from the underlying joint produced higher stress intensities.