Stress Intensity Factors at the Tip of a Surface Initiated Crack Caused by Different Contact Pressure Distributions

Abstract

Current practice in pavement design is to use a uniformly distributed load over a circular contact patch. However, this is not the reality; tyre-pavement contact stress distributions are very complex. There are vertical, longitudinal and transverse stress components that affect the response of the pavement. The formation of surface initiated cracks is known to be caused by a number of factors, but primarily by the traffic loading, these cracks propagate from the surface into the pavement. The study investigated the Stress Intensity Factors (SIF) of mode one and mode two cracking at the tip of a short crack and as such their influence on the continued propagation further into the pavement. The CAPA-3D finite element software was used to model the two scenarios of uniformly distributed loading and uniformly distributed loading with symmetrical inward shear. This analysis was performed for two different subbase moduli. The analysis was 2D and used plane strain conditions. The loading was moved to a number of different positions relative to the crack for both load cases. The study showed that the SIF for both KI (stress intensity factor for mode one cracking) and KII (stress intensity factor for mode two cracking) was dependant on the load type and also on its location relative to the crack tip. It also showed the increase in the ratio of asphalt modulus to subbase modulus increases the SIF values at all locations. It was shown that the shearing force only had a noticeable impact on the SIF values when the distance from the crack tip was small or zero.