Application and Improvement of Discrete Finite-Element Method for Mesoscale Fracture Analysis of Asphalt Mixtures

Abstract

The mesoscale structure of asphalt mixture in finite-element (FE) models has been widely used in evaluating crack growth and fatigue performance. However, the present methodology for establishing the mesoscale structure in a FE model depends mainly on images obtained by specimen scanning technology, while computer-aided generation (CAG) is not extensively utilized in FE simulation. It is limited by the lack of professional commercial software support and the difficulty of code programming. In this study, a discrete-element (DE) method was applied in a CAG process using particle flow code (PFC) version 5.0 software. Then cross sections of the CAG DE models were transformed into binary images based on particle coordinates. On this basis, image-based (IB) modeling technology was applied to establish a two-dimensional (2D) FE model for a virtual semicircular bending (SCB) test. At the same time, a series of 2D SCB FE models were generated based on images obtained by computed tomography (CT) scanning. The cracking behavior of cohesive elements in a fine aggregate mixture was defined by a bilinear cohesive zone model (BCZM). By comparing FE simulation results with SCB laboratory test results, the simulation results obtained from DE-FE models and CT-FE models were found to be in good agreement with the laboratory test results and had satisfactory accuracy. To make the crack propagation path more realistic during the simulation process, a new mapped meshing method, called a refined triangular meshing method, is proposed in this article. In the cracking region of the SCB FE model, right triangular meshes were used instead of square meshes. In this way, the mesh density could be increased and the possible crack propagation paths enriched. In addition, the shapes of aggregates in FE models could be more realistic. The simulation results show that the simulation accuracy of the FE model with refined triangular meshes is very similar to that of a square meshed FE model, but it can suppress the zigzag fluctuations of the load-displacement curves and make the simulation results more stable. Also, refined triangular meshes improve the simulation effect of crack morphology and make it closer to the crack propagation path of an actual specimen.