Development of domain integral and generalized finite element methods for three dimensional analysis of near-surface cracking in flexible pavements

摘要

Layered elastic theories and finite element method are among the most familiar and practiced mechanistic approaches. These approaches succeed to a certain extent in the analysis of classical bottom-up fatigue cracking of relatively thin flexible pavements, where tensile stresses and strains govern the behavior at the asphalt layer. However, elastic theories are incapable of predicting other pavement distresses, including near-surface cracking. Similarly, finite element method, which is equipped with fracture and continuum mechanics theories, also poses a significant challenge to the analysis of the near-surface cracking problem, where crack initiation and propagation planes are not easily predictable. Hence, the main objective of this study is to identify the effect of loading tire contact stresses on developing near-surface cracking potential. A numerical approach is chosen to analyze the problem, taking into account considering nonuniform tire-pavement contact stresses and multi-axial stress states in the proximity of tires.This study highlights the impact of novel computational methods, such as the Generalized Finite Element Method (GFEM), on the discovery and understanding of cracking mechanisms in pavements. GFEM allows for realistic modeling of complex phenomena that control fracture initiation and propagation. In this study, GFEM is adapted to analyze relatively thick flexible pavement structures to predict near-surface cracking. The three-dimensional (3-D) and highly multi-axial nature of the problem is successfully captured by this method, which is ideally designed for 3-D fracture problems for complex geometries and mixed loading conditions.This study proposes a high-order domain integral method for the computation of the crack front parameters such as energy release rate and stress intensity factors (SIFs). The method provides an approximation of the energy release rate function as a linear combination of Legendre polynomials. As a result, extracted functions are smoothly varying, which is crucial to obtain accurate crack propagation paths in 3-D for elastic or inelastic materials. Crack front directionality is captured by the proposed formulations and implementation using an energy release rate-based approach. The study also applies for the first time the domain integral techniques to pavement fracture problems utilizing the asphalt concrete viscoelastic characteristics.The GFEM, equipped with the tools developed in this study, is used as a computational platform to analyze near-surface cracking in relatively thick flexible pavement structures. Three-dimensional models of typical pavement structures are developed to analyze near-surface cracking and make predictions for potential critical locations for crack initiation and growth. Two potential scenarios become evident for crack growth in the vicinity of tires: Shear crack under compression and tensile crack. It is observed from the analysis that shear crack growth is the dominant mode of crack development due to loading in the proximity of tires, while tensile crack growth appears to develop within the pavement.