13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- beam. Accurate failure predictions can only be obtained if microstructural damage is taken into account in the fracture modelling. This requirement has led to the development of the so-called local or continuum approaches to fracture, in which fracture is regarded as the ultimate consequence of the material degradation process. This paper employ the user defined material technique in FEM directly, a constitute equations of damage model which cover the all potential failure area are developed. The damage model allows damage assessments at every point of a structure for any geometry or loading, as long as the damage mechanisms and stress-strain curve are known. This paper is an attempt to advance our understanding of relationship between crack path and microstructure features as they apply to damage evolution in three point bending asphalt bending beam. The objective of this paper is to propose a fracture criteria based on damage model for investing cracking behaviors of the three point bending test of asphalt concrete beam. The proposed damage model is implemented in the commercial finite element analysis software Ansys via the user defined subroutine UPFs .The numerical simulation compared with the experimental results to validate our present criterion. The results show that the proposed criterion reasonably predicts the crack growth initiation in different pre-crack locations and aggregate distributions. 2. Random heterogeneous modeling for asphalt concrete 2.1. Brittle damage model for asphalt mastic For the case of isotropic damage evolution，continuum damage mechanics（CDM）introduces a field variable to represent the damage in a continuum sense. In this paper, this concept has later been used to model the initiation and growth of cracks. By assuming homogeneous distribution of micro voids and the hypothesis of strain equivalence, which states that the strain behavior of a damaged material is represented by constitutive equations of the virgin material (without damage) in the potential of which the stress is simply replaced by the effective stress 1 σ σ= − % D (1) where σ is the stress tensor for the undamaged material. And the corresponding scalar damage variable 0 1 / D D E E = − , in which DE is the effective elastic modulus of the damaged materials, 0E is the elastic constant of the virgin material and D has a range from 0 to 1, D=0 means that material is intact ,while D=1 means that material is damaged completely. The another form of the effective stress can be given by 0(1 ) σ ε = − E D (2) Extended the model to three-dimensional form, such that: (1 ) 3 ρρ σ ε δ ε = − + ij ijkl kl ij kl kl D E D E (3) Written it to the form of matrix, the constitute law is D σ= ε% (4) where D% is elastic damage stiffness matrix which is relative to the elastic modulus E, poisson ratio v and scalar damage variable D which is expressed as
RkJQdWJsaXNoZXIy MjM0NDE=