Investigation of fatigue cracking: Bottom-up or top-down
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Traditionally, HMA pavement designs and modeling methods have historically been based on the fundamental assumption that fatigue cracking generally initiates at the bottom of the HMA layer due to excessive tensile stresses/strains, and then propagates upwards to the surface. However, fatigue cracking can either be bottom-up or top-down initiated depending on the location of the maximum horizontal tensile stresses and strains in the HMA layer. Various factors such as the pavement structure and wheel/tire loading configurations influence the fatigue crack-related tensile strains that are induced in the HMA layer. In this study, the influence of these factors on the tensile strains responses and potential location of fatigue crack initiation in HMA pavements was investigated. To address the non-uniformity distribution of the tire-pavement contact pressure (TPCP), a three-dimensional finite element (3-D FE) program was utilized for the computational simulations and numerical analyses. Specifically, the actual TPCP of different tire types and tread patterns measured under variable load levels and tire inflation pressures were utilized to evaluate and analyze the potential locations of maximum tensile strains in terms of fatigue crack initiation. The results showed that fatigue cracking, bottom-up or top-down, depended on pavement structure, material parameters, and has little relative with the magnitude and distribution of tire-pavement contact pressure. Finally, the potential locations of fatigue crack initiation in asphalt pavements were recommended. 2008 Taylor & Francis Group, London.
