Fracture failure of asphalt binder in mixed mode (Modes I and II) by using phase-field model

Abstract

In the pavement industry, asphalt binder fracture failure is one serious problem that may be caused by excessive loading. In the state-of-the-art research of asphalt cracking, pure single mode cracking, especially Mode I has been studied by many researchers. However, there is a lack of theoretical and experimental research on the mixed-mode cracking, which is more reasonable and realistic. In this paper, a new approach, namely, the phase-field method (PFM) is presented for modelling the mixed mode (Modes I and II) cracking failure in the asphalt binder. The traditional way is to use the Griffith's theory for analysing the initiation and propagation of cracks. Our PFM model describes the whole cracking system using a phase-field variable which assumes a negative one in the void region and a positive one in the solid region. Considering the fact that asphalt is brittle when the temperature is below the glass transition temperature, the fracture toughness is considered as the material property and modelled as the surface energy stored in the diffuse interface between the intact solid and the crack void. The non-conserved Allen–Cahn equation is adopted to evolve the phase-field variable to account for the growth of cracks. The energy-based formulation of the PFM handles the competition between the growth of the surface energy and the release of elastic energy in a natural way: the crack propagation is a result of the energy minimisation in the direction of the steepest descent. Both the linear elasticity and phase-field equation are solved in a unified finite element framework, which is implemented in the commercial software COMSOL. The mixed mode cracking experiment is then performed for validation. It is discovered that PFM can give a good result in predicting the onset of crack propagation.

Keywords:

• mixed mode cracking
• phase field
• self-adaptive meshing
• asphalt binder
• experiment

Acknowledgements

This work was supported by the FHWA under the Asphalt Research Consortium Project. The authors express their sincere gratitude to FHWA for funding, and the project panel for advising.