13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- （b） Figure. 1 Two 2D numerical specimens of asphalt concrete 2.3. The finite analysis using damage mechanics for asphalt concrete The asphalt mastic is assigned to obey an elastic damage constitute law which implemented into the FEM software. A USERMAT subroutine defining the damage elastic material property is coded using the FORTRAN language. Then it is compiled and integrated into the main program by a user defined variable can save the value of damage. A series of 2D asphalt concrete samples with the dimensions of 150mm×50mm and coarse aggregate gradation shown in Table 2 are modeled. The element we used is 8-node plane183 and the asphalt concretes are treated as composite materials in which component of coarse aggregates which is assigned to elastic material property and asphalt mastic which is assumed to be elastic damage material. The aggregate generation and packing algorithm is used to create its micromechanical asphalt concrete with coarse aggregate, the rest region is modeled as the asphalt mastic. Three point bending experiments are virtually performed. The material properties of coarse aggregate and asphalt mastic are needed to assign independent material parameters. In general, aggregates are linearly elastic, but asphalt mastic is effected by the temperature. In the current paper the asphalt mastic is assumed to be elastic and brittle damaged since temperature is enough low [12], although viscoelasticity in the matrix has been considered in higher temperature. Therefore the detailed parameters of asphalt mastic and coarse aggregates are listed in the Table 3. Table 3. List of material parameters at T=5℃ Elastic damage model for asphalt mastic ( ) E GPa ν εf εu 0.612 0.35 0.002 0.07 Elastic model for coarse aggregate ( ) E GPa ν 40 0.15
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